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

Abstract

[Problem] To provide: ferrite particles that have high environment stability of charging characteristics, and good charge rise properties; a carrier core material for an electrophotographic developer; a carrier for an electrophotographic developer; and an electrophotographic developer. [Solution] The present invention is characterized by containing a crystal phase component including a perovskite crystal represented by composition formula RZrO3 (where R represents an alkaline-earth metal element), and by containing Mg in an amount of 0.45 mass% or less. In addition, the ferrite particles are used as a carrier core material for an electrophotographic developer. In addition, by using same, a carrier for an electrophotographic developer 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. Along with this trend, the particle size of carriers has also been reduced in order to impart a charge to the toner. If the carrier's charging ability is insufficient, fog due to low-charge toner and a reduced amount of toner transported to the development area are likely to occur, resulting in image artifacts.

[0006] For this reason, various studies have been conducted on carriers with high charging ability. For example, Patent Documents 1 and 2 state that a carrier with high charging ability to toner and high environmental stability can be obtained by adding Ti or Sr and using ferrite particles with appropriately controlled surface irregularities as a carrier core material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2016-106262 [Patent Document 2] Patent No. 5886336 Summary of the Invention [Problem to be solved by the invention]

[0008] However, carriers using the above-mentioned conventional ferrite particles (Patent Documents 1 and 2) as a carrier core material have insufficient charging ability and environmental stability. In general, unavoidable impurities such as Cl resulting from the Fe raw material and the like are present on the surface of ferrite particles. These unavoidable impurities are easily ionized by moisture in the atmosphere. Therefore, when a large amount of such unavoidable impurities are present on the surface of ferrite particles, the resistance value is likely to decrease in a high-temperature, high-humidity environment, and the environmental characteristics of the charging characteristics are likely to fluctuate.

[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, which have high charging ability and environmental stability. [Means for solving the problem]

[0010] In order to solve the above problems, The ferrite particles according to the present invention are It contains a crystalline phase component consisting of a perovskite-type crystal represented by the composition formula RZrO3 (where R is an alkaline earth metal element), (MnO)a(MgO)b(Fe 2O 3 )c (wherein a+b+c=100 (mol%), a≠0, 0≦b, c≠0), wherein the ferrite particles contain 90 mass% or more of a spinel-type crystal phase component, When the Mn content in the ferrite particles is x (mass%) and the Fe content is y (mass%), the following formula is satisfied: 0.30y≦x≦0.60y The magnesium content is 0.45 mass % or less.

[0011] 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.

[0012] 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.

[0013] In the ferrite particles according to the present invention, the Cl concentration measured by an elution method is preferably 30 ppm or less.

[0015] The ferrite particles according to the present invention preferably contain substantially no Ti.

[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 a carrier for electrophotographic developer and a 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 having high charging ability and environmental stability, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer. [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 contain a crystalline phase component (hereinafter referred to as "perovskite-type crystalline phase component") consisting of perovskite-type crystals represented by the composition formula RZrO3 (where R is an alkaline earth metal element).

[0024] 1-1. Perovskite-type crystalline phase components First, the perovskite-type crystal phase component represented by the composition formula RZrO3 (where R is an alkaline earth metal element) will be described.

[0025] Two-component electrophotographic developer carriers suitable for the magnetic brush method use resin-coated carriers, which have magnetic particles as core materials and whose surfaces are coated with resin. Ferrite particles, a magnetic oxide containing ferric oxide (Fe2O3), are commonly used as core magnetic particles. To improve the environmental stability of the carrier's charging characteristics, it is important to suppress charge leakage from the carrier surface. Furthermore, to obtain carriers with good charge buildup, it is important to increase the frequency and strength of contact between the carrier and toner. In this specification and elsewhere, environmental stability of charging characteristics refers to little change between the charge amount under normal temperature and humidity conditions and that under high temperature and humidity conditions, or little change between the charge buildup under normal temperature and humidity conditions and that under high temperature and humidity conditions.

[0026] First, we will discuss the environmental stability of charging characteristics. 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 or metal hydroxides containing the desired metal elements 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 ferrites, 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 Na, K, and Cl. 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 generally highly resistive because they are made of metal oxides. However, the resistance decreases when moisture adheres to the surface. Furthermore, unavoidable impurities contained in the raw materials, such as Na, K, and Cl, 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, making them more susceptible to charge leakage. Furthermore, as the amount of unavoidable impurities increases, charge leakage becomes more likely when the ambient humidity becomes high, leading to a deterioration in the environmental stability of the charging characteristics.

[0030] For these reasons, in order to obtain ferrite particles with good charging properties and little environmental dependency of the charging properties, it is necessary to reduce the amount of unavoidable impurities in the ferrite particles. However, as described above, it is practically difficult to completely remove the unavoidable impurities.

[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 environmental stability in charging properties, it is important to include a perovskite-type crystalline phase component represented by the composition formula RZrO3 (where R is an alkaline earth metal element).

[0032] The present inventors speculate as follows about the reason why the above problems can be solved by including a perovskite-type crystalline phase component represented by the composition formula RZrO3 (where R is an alkaline earth metal element).

[0033] The grain boundaries of ferrite particles contain components that are not solid-soluble with 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. For ferrite particles of the same size, larger crystal grains constituting the ferrite particles result in smaller grain boundary volumes than smaller crystal grains. As a result, unavoidable impurities such as Na, K, and Cl are extruded from the grain boundaries and tend to segregate on the surface of the ferrite particles. These substances have a high affinity for moisture in the air and are easily ionized, as described above. The presence of such moisture-sensitive substances on the surface of ferrite particles can easily cause charge leakage, resulting in poor charge buildup and a reduced charge-imparting ability of the carrier. Furthermore, ferrite particles with this structure are likely to exhibit significant environmental fluctuations in charging characteristics due to changes in atmospheric humidity. However, as mentioned above, it is difficult to completely remove unreacted raw materials and unavoidable impurities from ferrite particles.

[0034] On the other hand, perovskite-type crystals represented by the composition formula RZrO3 (where R is an alkaline earth metal element) do not form solid solutions with other crystalline phases with different crystalline structures, such as spinel-type crystals, and therefore the perovskite-type 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 substances, are present at the grain boundaries. In the ferrite particles according to the present invention, grain boundaries are distributed in a complex manner within the particles, and insulating substances such as the unavoidable impurities and the crystalline phase components are distributed discontinuously within the grain boundaries, thereby suppressing the segregation of substances with a high affinity for moisture on the ferrite particle surface. Therefore, it is believed that the ferrite particles according to the present invention can provide good charge build-up and high environmental stability.

[0035] Furthermore, the perovskite-type crystalline phase component 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 and suppress charge leakage. 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. This can also suppress the occurrence of structural defects, resulting in ferrite particles with relatively good charging properties.

[0036] For these reasons, it is presumed that by using ferrite particles containing a perovskite-type crystalline phase component represented by the composition formula RZrO3 (where R is an alkaline earth metal element), it is possible to improve the environmental stability of the charging characteristics for the reasons mentioned above.

[0037] In addition, in the ferrite particles, the phrase "containing a perovskite-type crystalline phase component represented by the composition formula RZrO3 (where R is an alkaline earth metal element)" means that the crystalline phase component is contained at least inside the ferrite particles, and 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 of the ferrite particles.

[0038] 1-2.Mg content (mass%) The ferrite particles exhibit the above-described properties by including the perovskite-type crystalline phase component. Furthermore, by adjusting the Mg content in the ferrite particles to 0.45% by mass or less, the following properties are obtained. Note that the Mg content in the present invention refers to a value determined based on the value measured by ICP elemental analysis, which will be described later. After extensive research, the present inventors have discovered that by adjusting the Mg content in the ferrite particles to within the above range, a ferrite core material with higher charging ability and better environmental stability can be obtained compared to when the Mg content is greater than 0.45% by mass. The present inventors speculate that the reason for this is as follows: Charging occurs due to the transfer of charges. When comparing single-component ferrite with multi-component ferrite, it is believed that charge transfer within the multi-component ferrite is less likely to occur. Therefore, it is believed that by setting the Mg content in the ferrite particles to 0.45% by mass or less and relatively reducing the Mg content in the ferrite composition, the ferrite particles become closer to or become a unitary ferrite, facilitating charge migration and improving charging ability. Here, the lower limit of the Mg content is 0.00% by mass, but the Mg content may be more than 0.00% by mass, and is preferably 0.05% by mass or more.

[0039] 1-3. Spinel-type ferrite particles and spinel-type crystal phase components The ferrite particles contain the perovskite crystal phase and may be spinel ferrite particles, magnetoplumbite ferrite particles, garnet ferrite particles, or the like, except for the Mg content. However, from the viewpoint of obtaining suitable resistance and magnetization as a core material for a carrier in a two-component electrophotographic developer, the ferrite particles are preferably spinel ferrite particles, and particularly preferably spinel ferrite particles containing Mn. Note that spinel ferrite particles containing Mn can be expressed, for example, as (MnO)a(MgO)b(Fe2O3)c (where a+b+c=100 (mol%), a≠0, 0≦b, c≠0). In such spinel ferrite particles containing Mn, if the Mg content is within the above range, the ferrite particles are close to or essentially Mn ferrite as a single element ferrite, which is thought to improve the charging ability as described above.

[0040] Furthermore, by using spinel-type ferrite particles containing Mn, the magnetization on the low magnetic field side can be increased. Furthermore, reoxidation of the ferrite can be prevented when the ferrite is removed from the furnace after sintering. Furthermore, by using spinel-type ferrite particles containing Mg as well as Mn, it becomes easy to adjust the magnetization and resistance of the ferrite particles. However, even if Mg is not contained, the magnetization and resistance can be adjusted by strictly controlling the manufacturing conditions, such as the oxygen concentration during sintering.

[0041] In order to obtain the above effects, it is preferable that the ferrite particles satisfy the following formula, where x (mass %) is the Mn content and y (mass %) is the Fe content. 0.30y≦x≦0.60y (1)

[0042] In the spinel-type crystal phase component represented by the above composition formula, when the values ​​of "x" and "y" change, the magnetic and electrical properties change. When the ferrite particles are spinel-type ferrite particles represented by the above composition formula, if the value of "x" becomes smaller relative to the value of "y," the content ratio of magnetite, which has low resistance, increases, and the resistance value of the ferrite particles as a whole also changes. Therefore, by appropriately adjusting the content ratios of "x" and "y" within a range that satisfies the above formula (1), the balance between magnetization and resistance can be improved, making it easier to obtain the effects described above.

[0043] For example, if the value is below the lower limit of the above formula (1), the content ratio of "MnO" relative to "Fe2O3" in the ferrite particles will be small, and as mentioned above, the content ratio of low-resistance magnetite will increase relatively. In this case, charge will be more likely to leak from the particle surface, which may make it difficult to adjust the resistance value to a value suitable for the carrier core material of a two-component electrophotographic developer. The above formula (1) If the upper limit of the resistance is exceeded, the content ratio of "MnO" to "Fe2O3" in the ferrite particles becomes large, and the resistance value may become too high beyond the appropriate range. In such a case, image defects such as white spots may occur due to the high resistance value, and it may become difficult to adjust the resistance value to a value suitable for the carrier core material of a two-component electrophotographic developer.

[0044] By satisfying the above formula (1), for example, even if the content ratio of "MnO" relative to "Fe2O3" in the ferrite particles is low, as shown in the following formula (2), the above effect can be obtained by adjusting the Mg content and the firing conditions during production of the ferrite particles (for example, the firing temperature and the atmospheric oxygen concentration during firing). 0.30y≦x≦0.36y (2)

[0045] Furthermore, in order to obtain the above-mentioned effect, by increasing the content ratio of "MnO" relative to "Fe2O3" within the range of the above formula (1), for example, as represented by the following formula (3), it is possible to obtain ferrite particles that are highly magnetized, have a resistance value within an appropriate range for the carrier core material of an electrophotographic developer, have higher charging ability, and have better environmental stability of charging characteristics. 0.44y≦x≦0.60y (3)

[0046] In order to obtain the above-mentioned effects, it is also preferable that "x" and "y" are within the following ranges. By appropriately adjusting "x" and "y" within the following ranges, the same effects as those described above can be obtained. 17.0≦x≦27.5, 44.5≦y≦54.5 In the above formulas and the formulas shown below, the inequality signs with equality signs may be converted to inequality signs, and the preferable upper limit values ​​and the preferable lower limit values ​​may be appropriately combined.

[0047] 1-4. 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 ferrite particles preferably contain 0.05 mass % or more and 4.00 mass % or less of the perovskite-type crystalline phase component represented by the above-mentioned composition formula RZrO3.

[0048] When the content of the perovskite-type crystalline phase component represented by the composition formula RZrO3 is within the above range, the crystalline phase component can be easily dispersed uniformly inside the ferrite particles, making it easier to suppress the occurrence of structural defects and to improve the environmental stability of the charging characteristics.

[0049] 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, and preferably 3.50% by mass or less of the crystalline phase component, more preferably 3.00% by mass or less.

[0050] The ferrite particles are preferably spinel-type ferrite particles containing Mn. In this case, the ferrite particles preferably contain 90% by mass or more, preferably 93% by mass or more, and more preferably 95% by mass or more of a spinel-type crystalline phase component. That is, the ferrite particles are preferably spinel-type ferrite particles composed of the perovskite-type crystalline phase component and a spinel-type crystalline phase component, excluding unavoidable impurities or unreacted raw materials. The content of the spinel-type crystalline phase component can be determined by the ratio of metal elements in the raw material blend. Generally, spinel-type ferrite is produced by a solid-state reaction. In the ferritization reaction that occurs during the firing process, a solid solution (spinel-type crystalline phase) begins to form at approximately 850°C and is completed at approximately 1250°C. The spinel-type crystalline phase can be selectively produced by appropriately adjusting the firing temperature, firing time, firing atmosphere, and cooling time during the firing process, thereby determining the content of the spinel-type crystalline phase in the ferrite particles.

[0051] 1-5. Constituent elements and composition 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 perovskite-type crystalline phase component having the composition formula of RZrO3 will be described.

[0052] (1) Zirconium content The ferrite particles preferably contain zirconium in an amount of 0.04% by mass or more and 3.00% by mass or less. By containing zirconium within this range, the content of the perovskite-type crystalline phase component represented by the composition formula RZrO3 is generally within the above range, and ferrite particles having high environmental stability in charging characteristics and a good charge amount rise can be obtained. The content of zirconium in the ferrite particles is more preferably 0.08% by mass or more. Furthermore, the content of zirconium in the ferrite particles is 2.60 It is more preferable that the content is % by mass or less, 2.25It is more preferable that the zirconium content is 100% by mass or less. The zirconium content can be determined by ICP elemental analysis in the same manner as for Mg.

[0053] (2) R (alkaline earth metal elements) 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 content of the alkaline earth metal element (R) is more preferably 0.04% by mass or more and 3.15% by mass or less. By including the alkaline earth metal element (R) within this range, the content of the perovskite-type crystalline phase component represented by the composition formula RZrO3 is approximately within the above range, thereby enabling the production of ferrite particles with high environmental stability of charging characteristics and a good charge build-up. The content of the alkaline earth metal element (R) in the ferrite particles is more preferably 0.16% by mass or more. Furthermore, the content of the alkaline earth metal element (R) in the ferrite particles is more preferably 2.75% by mass or less, and even more preferably 2.35% by mass or less. The alkaline earth metal element content can be quantified by ICP elemental analysis, as with Mg.

[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 zirconate perovskite compounds derived from the zirconium raw material. When a spinel-type crystal phase component is the main component, if a minor component with a crystal structure different from the spinel-type crystal structure is present inside the particle, the main component grows in the direction of the particle surface, where it is relatively easy to grow, resulting in appropriate irregularities on the particle surface. Furthermore, by uniformly incorporating these minor components inside the particle, the irregularities on the particle surface can be controlled to a uniform state.

[0056] (3) Other Known compounds having a perovskite crystal structure include, for example, barium titanate and strontium titanate. The ferrite particles according to the present invention are substantially free of Ti and substantially free of a perovskite crystal phase containing Ti. "Substantially free of Ti" means that when the ferrite particles are produced, Ti or a titanium-containing compound such as TiO2 is not used as a raw material, and Ti is not intentionally added. In other words, Ti is not contained except in the case where Ti is contained within the range of unavoidable impurities inevitably accompanying the following raw materials used when producing the ferrite particles:

[0057] 1-6. Amount of eluted chlorine The ferrite particles according to the present invention preferably have an amount of chlorine dissolved therefrom of 30 ppm or less as measured by a dissolution method. The procedure for measuring the amount of chlorine dissolved therefrom by a dissolution method will be described in the Examples section. By setting the amount of chlorine dissolved therefrom to 30 ppm or less, the ferrite particles can be obtained with little environmental change in charging characteristics.

[0058] As mentioned above, when unavoidable impurities such as Na, K, and Cl are present on the surface of ferrite particles, they easily ionize, allowing moisture in the atmosphere to adsorb to the ferrite particle surface. Increased amounts of these unavoidable impurities on the ferrite particle surface, for example, significantly decrease resistance in high-temperature and high-humidity environments and increase environmental variations in charging characteristics. For example, iron oxide, a by-product of the hydrochloric acid pickling process during steel production, is commonly used as the raw material for iron. Therefore, the Fe raw material contains Cl as an unavoidable impurity. Na and K are often found in the Fe raw material, Mn raw material, and Mg raw material, and their amounts increase when seawater or sodium hydroxide is used in the manufacturing process. Compared to Na, K, and other impurities, the total amount of Cl contained in the raw material as an unavoidable impurity is higher. Therefore, a low amount of dissolved chlorine measured by the leaching method tends to indicate a low amount of other unavoidable impurities. Furthermore, the amount of dissolved chlorine measured by the leaching method represents the amount of chlorine attached to the surface of ferrite particles. Therefore, as described above, when the amount of chlorine dissolved measured by the elution method is 30 ppm or less, the amount of unavoidable impurities such as Na, K, and Cl adhering to the surface of the ferrite particles is small, and even if the ambient humidity changes, the change in the amount of moisture adhering to the surface of the ferrite particles is small, which reduces the fluctuation in resistance value and the environmental fluctuation of charging characteristics.

[0059] The amount of unavoidable impurities can be reduced by using high-purity raw materials. Furthermore, by performing heat treatment at a high temperature (e.g., a temperature similar to that suitable for growing a perovskite crystal phase) in the main firing step, etc., described below, most of the unavoidable impurities can be removed. Because the ferrite particles according to the present invention contain a perovskite crystal phase component, as described above, the crystal grains are relatively small and the grain boundary volume is relatively large. Therefore, even if the content of unavoidable impurities such as Cl is the same, these unavoidable impurities can be precipitated inside the ferrite particles, preventing their segregation on the surface of the ferrite particles. Therefore, compared to when the perovskite crystal phase component is not included, the amount of chlorine eluted by the elution method can be reduced, and environmental fluctuations in charging characteristics can be reduced.

[0060] In order to obtain the above-mentioned effect, the amount of chlorine eluted is more preferably 25 ppm or less, even more preferably 20 ppm or less, even more preferably 15 ppm or less, and still more preferably 10 ppm or less. Note that, although the amount of chlorine eluted can be reduced by carrying out a surface oxidation treatment after the sintering step described later, even if the ferrite particles according to the present invention are not subjected to a surface oxidation treatment after the sintering step, the amount of chlorine eluted by the elution method can be reduced to 30 ppm or less by containing a spinel-type crystal phase component and a perovskite-type crystal phase component as described above.

[0061] 1-7.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 50 emu / g or more and 70 emu / g or less. A saturation magnetization of 50 emu / g or more 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, if the saturation magnetization of the ferrite particles is within this range, a good balance between the two can be achieved, resulting in an electrophotographic developer that can effectively perform high-quality electrophotographic printing. Furthermore, if the resistance is low despite high magnetization, carrier scattering due to low resistance can occur. By maintaining a saturation magnetization of 70 emu / g or less, carrier scattering due to low resistance can also be effectively suppressed.

[0062] 1-8.Electrical characteristics Next, the electrical properties of the ferrite particles will be described. When measured at an electrode distance of 6.5 mm and an applied voltage of 1000 V, the resistance M under normal temperature and humidity conditions (23°C, 55% relative humidity) is 1.0 x 10 6 (Ω) or more 1.0×10 9.5When the resistance value of the ferrite particles is within this range, when the ferrite particles are used as a core material and a resin coating layer is provided on the surface to form a carrier, the resin coating layer peels off during mixing with the toner, exposing the core material, and carrier scattering due to charge injection can be suppressed.

[0063] 1-9.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.

[0064] 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. 50 If 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.

[0065] On the other hand, the volume average particle size (D 50When 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.

[0066] From the above viewpoint, the volume average particle size (D 50 The lower limit of the volume average particle diameter (D 50 The upper limit of the thickness is preferably 38 μm, and more preferably 36 μm.

[0067] (2) BET specific surface area The BET specific surface area of ​​the ferrite particles is preferably within the range represented by the following formula. 0.08≦ X ≦ 0.550 In the above formula, X is the BET specific surface area (m 2 / g).

[0068] The BET specific surface area referred to here can be a value measured using, for example, a specific surface area measuring device (Macsorb HM model-1208 (manufactured by Mountec Co., Ltd.)). When the BET specific surface area of ​​the ferrite particles is within the range expressed by the above formula, the surface irregularities of the ferrite particles are within an appropriate range relative to the particle size. Therefore, when the ferrite particles are used as a core material, the surface can be well coated with a resin. Furthermore, because the difference in surface irregularities relative to the particle size is small, concentration of load on the protrusions when mechanical stress is applied to the surface can be suppressed, preventing cracking and chipping. Therefore, when the ferrite particles are used as a core material, peeling of the resin from the surface can be suppressed during mixing and stirring with the toner, preventing cracking and chipping of the carrier and carrier scattering, etc.

[0069] In order to obtain the above effects, the lower limit of the above formula is more preferably 0.100, and even more preferably 0.120, and the upper limit of the above formula is more preferably 0.400.

[0070] (3) Apparent density The apparent density of the ferrite particles is preferably within the range represented by the following formula. 1.90≦ Y ≦ 2.50 In the above formula, Y is the apparent density of the ferrite particles (g / cm 3 )

[0071] The apparent density referred to here is a value measured by the funnel method in accordance with JIS Z 2504: 2012. When the apparent density of the ferrite particles is within the range represented by the above formula, the fluidity is good and the weight is heavy, which allows the frequency and strength of contact with the toner to be increased.

[0072] To obtain the above effects, the lower limit of the above formula is more preferably 1.95, even more preferably 2.00, and even more preferably 2.15, and the upper limit of the above formula is more preferably 2.45.

[0073] 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.

[0074] (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.

[0075] 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.

[0076] (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.

[0077] (3) Additives The resin coating layer may contain additives such as conductive agents and charge control agents for the purpose of controlling the electrical resistance, charge amount, and charging speed of the carrier. Examples of conductive agents include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents. However, since the electrical resistance of conductive agents is low, if the amount of conductive agent added is too large, charge leakage is likely to occur. Therefore, the content of the conductive agent should be 0.25% by mass or more based on the solid content of the coating resin. 20.0% by mass or less It is preferably 0.5% by mass or more and 15.0% by mass or less, more preferably 1.0% by mass or more and 10.0% by mass or less.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] For example, to produce spinel ferrite particles of a desired composition in (MnO)a(MgO)b(Fe2O3)c (where a+b+c=100 (mol%), a≠0, 0≦b, c≠0), the raw materials are weighed and pulverized and mixed so that a, b, and c have the desired values. As the raw materials, for example, it is preferable to use Fe2O3, Mg(OH)2 and / or MgCO3, and one or more manganese compounds selected from the group consisting of MnO2, Mn2O3, Mn3O4, and MnCO3.

[0089] The ferrite particles according to the present invention contain a perovskite-type crystalline phase component 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.

[0090] Here, when producing ferrite particles containing 0.05% by mass or more and 4.00% by mass or less of the perovskite-type crystalline phase component (however, this is 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), the molar ratio of ZrO2 to 100 of the main component raw material is preferably 0.05 to 4.0, and more preferably 0.1 to 3.0. Furthermore, the molar ratio of the oxide of an alkaline earth metal element (R) to 100 of the main component raw material is preferably 0.1 to 4.0, Oxides of alkaline earth metal elements (R) It is more preferable that the ratio be 0.2 or more and 3.0 or less. The perovskite-type crystalline phase component is generated by a solid-phase reaction between an oxide of an alkaline earth metal element (R) and ZrO2. Therefore, by appropriately changing the amounts and ratios of the oxide of an alkaline earth metal element (R) and ZrO2 added within the above-mentioned preferred ranges, the amount of the perovskite-type crystalline phase component generated can be adjusted.

[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 It is preferable to pulverize the powder so that the particle size (D) is 2.5 μm or less, and more preferably 2.0 μm or less. In order to suppress abnormal grain growth, the particle size (D) on the coarse side of the particle size distribution is 90 ) is preferably pulverized to 3.5 μm or less. By adjusting these factors, the perovskite crystal phase components can be dispersed more uniformly from the surface to the interior of the particles, thereby achieving the various effects described above.

[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 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 perovskite-type crystalline phase components 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, the perovskite-type crystalline phase components can be uniformly dispersed within the particles, and the amount of unavoidable impurities such as Na, K, and Cl on the particle surface can be reduced. In addition, the BET specific surface area can be adjusted within an appropriate range, and cracks and chips can be suppressed at the interface between different crystalline phases that are not solid-soluble with each other even when mechanical stress is applied, thereby improving the strength of the ferrite 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 set to, for example, 750°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 efficiently remove organic matter and perform ferrite reaction, the primary firing temperature is more preferably 800°C or higher, and even more preferably 850°C or higher. Furthermore, in order to suppress abnormal grain growth, the primary firing temperature is more preferably 1000°C or lower, and even more preferably 980°C or lower.

[0100] The sintering is preferably carried out in an inert atmosphere or a weakly oxidizing atmosphere at a temperature of 850°C or higher for 1.5 to 24 hours. However, the sintering temperature is not particularly limited as long as the ferrite particles according to the present invention can be obtained. Here, an inert atmosphere or 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 0.1% by volume (1000 ppm) to 3.5% by volume (35,000 ppm), and even more preferably 0.1% by volume (1000 ppm) to 2.5% by volume (25,000 ppm).

[0101] For example, the ferrite particles can be obtained by holding the ferrite particles at a temperature suitable for generating a spinel-type crystal phase (850°C to 1150°C) for at least three hours, followed by holding the ferrite particles at a temperature suitable for generating a perovskite-type crystal phase (e.g., strontium zirconate, RZrO3, or the like) for at least one hour. This allows for sufficient generation of the spinel-type crystal phase while maintaining the zirconium component well dispersed at the grain boundaries. Furthermore, by appropriately controlling the ferrite particles' sintering temperature, sintering time, and atmospheric oxygen concentration during sintering depending on the type of alkaline earth metal element (R) and the amount of ZrO2, the BET specific surface area, resistivity M, apparent density, and magnetization can be within the ranges of the present invention. Holding the ferrite particles at a temperature of 1200°C or higher for at least two hours can further reduce the amount of chlorine dissolved.

[0102] For example, in the case of strontium zirconate (SrZrO3), in order to sufficiently generate perovskite-type crystalline phase components while keeping the apparent density within the range of the present invention, it is preferable to maintain the firing temperature at a temperature of preferably 1170°C or higher and 1400°C or lower, more preferably 1180°C or higher and 1350°C or lower, and even more preferably 1200°C or higher and 1330°C or lower for one hour or longer. 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 calcinate at a predetermined temperature. To generate the perovskite-type crystalline phase components of calcium zirconate (CaZrO) or barium zirconate (BaZrO), calcination 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, these perovskite-type crystalline phase components can be generated even at temperatures below 1500°C. Thus, the ferrite particles of the present invention can be obtained by maintaining the temperature appropriate for generating the perovskite-type crystalline phase components 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 perovskite-type crystalline phase component 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 the perovskite-type crystalline phase component represented by the composition formula RZrO3 is sufficiently 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] Thereafter, if necessary, the surface of the ferrite particles can be subjected to a surface oxidation treatment by low-temperature heating, thereby adjusting the surface resistance of the ferrite particles. The surface oxidation treatment can be performed by subjecting the ferrite particles to heat treatment at 400°C to 730°C, preferably 450°C to 650°C, in an oxygen-containing atmosphere such as air using a rotary electric furnace, a batch electric furnace, or the like. If the heating temperature during the surface oxidation treatment is lower than 400°C, the surface of the ferrite particles may not be sufficiently oxidized, and the desired surface resistance characteristics may not be obtained. On the other hand, if the heating temperature is higher than 730°C, in the case of manganese-containing ferrite, excessive oxidation of manganese occurs, which is undesirable, resulting in a decrease in the magnetization of the ferrite particles. To form a uniform oxide film on the surface of the ferrite particles, it is preferable to use a rotary electric furnace. However, the surface oxidation treatment is an optional step.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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 fixability improver and a charge control agent.

[0113] 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 melting and kneading the mixture in a twin-screw extruder or the like to uniformly disperse the mixture, and after cooling, pulverizing the mixture in a jet mill or the like. 、 For example, a toner having a desired particle size can be obtained by classifying the toner using an air classifier or the like. If necessary, wax, magnetic powder, viscosity modifier, and other additives may be added. Furthermore, external additives may be added after classification.

[0114] 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]

[0115] (1) Ferrite particles In Example 1, ferrite particles containing a perovskite-type crystalline phase component represented by the composition formula SrZrO (R = Sr) and having a Mg content of 0.45 mass% or less were produced as follows. The ferrite particles of Example 1 were spinel-type ferrite particles mainly composed of a spinel-type crystalline phase component. As the main component raw materials, Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out so that the molar ratio was Fe2O3:50.0, MnO equivalent:49.5, and MgO equivalent:0.5. Furthermore, to obtain the perovskite-type crystalline phase component, SrO raw material was weighed out so that the molar ratio was 100 main component raw material to SrO:0.8. 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.

[0116] 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.

[0117] The resulting crushed material was mixed with water and a ZrO2 raw material with a BET specific surface area of ​​30 m2 to obtain the perovskite crystal phase component. 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 ZrO2:0.30. 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 3.3 μm.

[0118] 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 (rotary kiln) at 950°C for 2 hours in an air atmosphere for primary firing.

[0119] The granulated material was then fired in a tunnel electric furnace at a firing temperature (holding temperature) of 1225°C in an atmosphere with an oxygen concentration of 0.5% by volume for 3 hours. The heating rate was 100°C / hour and the cooling rate was 110°C / hour. The fired material was crushed using a hammer crusher, and then classified using a gyrosifter (vibrating sieve) and a turbo classifier (air classifier) ​​to adjust the particle size. Low-magnetic-force 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.

[0120] (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.

[0121] 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. [Example]

[0122] In this example, the Fe2O3 raw material and the MnO raw material were weighed out as the main component raw materials so that the molar ratio of Fe2O3:50.0 (MnO equivalent:50.0), and the main component was a spinel composition not containing MgO. The ferrite particles of Example 2 were produced in the same manner as in Example 1, except that the main component was a spinel composition not containing MgO. 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 the core material. [Example]

[0123] In this example, the ferrite particles of Example 3 were produced in the same manner as in Example 1, except that the Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out as the main component raw materials so that the molar ratios were Fe2O3:50.0, MnO equivalent:48.0, and MgO equivalent:2.0. 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. [Example]

[0124] In this example, the ferrite particles of Example 4 were produced in the same manner as in Example 1, except that the Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out as the main component raw materials so that the molar ratio was Fe2O3:59.5, MnO equivalent: 40.0, and MgO equivalent: 0.5, and that the firing temperature (holding temperature) during main firing was set to 1213°C. 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. [Example]

[0125] In this example, the ferrite particles of Example 5 were produced in the same manner as in Example 1, except that the Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out so that the molar ratios were Fe2O3:45.0, MnO equivalent: 54.5, and MgO equivalent: 0.5, and that the firing temperature (retention temperature) during main firing was set to 1218°C. 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.

[0126] [Reference example] As a reference example, ferrite particles having a Mg content of more than 0.45% by mass were produced as follows. The ferrite particles of this reference example were also spinel-type ferrite particles mainly composed of a spinel-type crystal phase component, and 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 38.3 in MnO equivalent, 10.4 in MgO equivalent, and 51.3 in Fe2O3. In addition, SrO raw material was weighed out so that the molar ratio was 100 in the main component raw material and 0.8 in SrO. The same raw materials as those used in Example 1 were used.

[0127] 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.

[0128] Water and zirconium dioxide as a ZrO2 raw material were added to the obtained pulverized material, and the mixture was pulverized for 6 hours using a wet media mill (horizontal bead mill, zirconia beads with a diameter of 1 mm). At this time, zirconium dioxide was added to the pulverized material so that the molar ratio of the main component raw material to ZrO2 was 1.0:100. The particle size (primary particle size of the pulverized material) of the obtained slurry was measured using a laser diffraction particle size distribution analyzer (LA-950, Horiba, Ltd.). 50 is about 2 μm, D 90 was 3.2 μm.

[0129] 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). The mixture was then granulated and dried 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 800°C for 2 hours in an air atmosphere to remove organic components such as the dispersant and binder.

[0130] The granules were then fired in a tunnel electric furnace at a firing temperature (holding temperature) of 1250°C in an atmosphere with an oxygen concentration of 0% by volume for 3 hours. The heating rate was 100°C / hour and the cooling rate was 110°C / hour. The fired product was crushed using a hammer crusher and further classified using a gyrosifter (vibrating sieve) and a turbo classifier (air classifier) ​​to adjust the particle size. Low magnetic particles were then separated using magnetic separation to obtain ferrite particles.

[0131] The obtained ferrite particles were subjected to a surface oxidation treatment in a rotary electric furnace equipped with a hot section and a cooling section following the hot section, and then cooled to obtain surface-oxidized ferrite particles. In the surface oxidation treatment, an oxide film was formed on the surface of the ferrite particles in the hot section at 540°C in an air atmosphere. The ferrite particles produced in this way were used as a carrier core material and resin-coated using the same procedure as in Example 1 above, to obtain a carrier for an electrophotographic developer. Comparative Example

[0132] [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 Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out so that the molar ratios were 50.0 Fe2O3, 40.0 MnO equivalent, and 10.0 MgO equivalent, and that the firing temperature (retention temperature) during main firing was set to 1230°C. The main production conditions for 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.

[0133] 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 Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out so that the molar ratios were Fe2O3:50.0, MnO equivalent:47.0, and MgO equivalent:3.0. 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.

[0134] Comparative Example 3 In this comparative example, the ferrite particles of Comparative Example 3 were produced in the same manner as in Example 1, except that the Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out so that the molar ratios were Fe2O3:65.0, MnO equivalent:35.0, and MgO equivalent:3.0, and that the firing temperature (retention temperature) during main firing was set to 1210°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.

[0135] Comparative Example 4 In this comparative example, ferrite particles of comparative example 4 were produced in the same manner as in example 1, except that SrO was not used as a raw material and the firing temperature (retention temperature) during main firing was set to 1200°C. The main production conditions for comparative example 4 are shown in Table 1. In addition, 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.

[0136] Comparative Example 5 In this comparative example, the Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out so that the molar ratios were Fe2O3:50.0, MnO equivalent: 49.5, and MgO equivalent: 0.5, and the ferrite particles of Comparative Example 5 were produced in the same manner as in Example 1, except that ZrO2 was not used as a raw material and the firing temperature (retention temperature) during main firing was set to 1195°C. The main production conditions for Comparative 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.

[0137] Comparative Example 6 In this comparative example, the ferrite particles of Comparative Example 6 were produced in the same manner as in Example 1, except that the Fe2O3 raw material, MnO raw material, and MgO raw material were weighed out so that the molar ratios were Fe2O3:50.0, MnO equivalent:47.0, and MgO equivalent:3.0, and that the firing temperature (retention temperature) during main firing was set to 1135°C. The main production conditions for Comparative 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.

[0138] [Reference comparison example] In this Reference Comparative Example, for comparison with the above Reference Example, ferrite particles of the Reference Comparative Example were produced in the same manner as the above Reference Example, except that a TiO2 raw material was used instead of a ZrO2 raw material, the TiO2 raw material was weighed out so that the molar ratio of TiO2 to the main component raw material was 100 mol to 0.80 mol, and the firing temperature (retention temperature) during main firing was set to 1200° C. Furthermore, except for using the ferrite particles as a core material, a carrier for an electrophotographic developer was produced in the same manner as the above Reference Example, and an electrophotographic developer was produced using the carrier for an electrophotographic developer.

[0139] <evaluation> The ferrite particles of each Example and Comparative Example obtained as described above were measured for (1) perovskite-type crystalline phase component content, (2) spinel-type crystalline phase content and elemental composition, (3) Zr element dispersion degree, (4) volume average particle size, (5) saturation magnetization, (6) resistivity, (7) BET specific surface area, (8) apparent density, and (9) amount of eluted chlorine. In addition, electrophotographic developers were prepared using the carriers for electrophotographic development of each Example and Comparative Example obtained as described above, and (10) charging characteristics were evaluated. The evaluation methods / measurement methods and evaluation results are described below.

[0140] 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 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.

[0141] The X-ray diffraction device used was the "X'PertPRO MPD" manufactured by PANalytical. A Co bulb (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

[0142] 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: Manganese ferrite (spinel-type crystal phase) Crystal structure: space group F d -3 m (No. 227) Phase B: Perovskite-type crystalline phase 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.

[0143] 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 the pseudo-Voigt function of Thompson, Cox, and Hasting, and was asymmetrized by Howard's method. The Rwp and S values, which indicate the accuracy of the fitting, were 2% or less and 1.5 or less, respectively, and after confirming that the main peaks of phases B and C were fitted at 2θ = 35 to 37°, each parameter was optimized.

[0144] Based on the results of the Rietveld analysis of the X-ray diffraction pattern obtained as described above, the content (mass%) of the perovskite-type crystalline phase component (phase B) was determined when a phase composition analysis of the crystalline phase constituting the ferrite particles was performed.

[0145] (2) Spinel-type crystal phase component content (mass%) and elemental composition (mass%) The results of the X-ray diffraction measurements of phases A, B, and C obtained above were analyzed by adding Fe2O3 (phase D), Mn2O3 (phase E), and strontium ferrite (phase F), and the spinel-type crystal phase component content (mass%) in each ferrite particle was determined.

[0146] The elemental composition of each ferrite particle was determined by ICP analysis as follows: First, 0.2 g of each ferrite particle was weighed, and 60 ml of pure water, 20 ml of 1N hydrochloric acid, and 20 ml of 1N nitric acid were added to the weighed ferrite particle, and the mixture was heated to prepare an aqueous solution in which the ferrite particles were completely dissolved. The contents (wt%) of Fe, Mn, and Mg were measured using an ICP analyzer (Shimadzu ICPS-1000IV).

[0147] (3) 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

[0148] 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.

[0149] 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.

[0150] 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.

[0151] (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.

[0152] (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.

[0153] (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)."

[0154] 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.

[0155] 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.

[0156] Here, when there are multiple line segments Dx that are the maximum diameter for one ferrite particle, the line segment Dy (line segment QQ') is considered to have a length of 0.5 or more relative to the line segment Dx. Dx , Dy. The ferrite particles produced in each example are approximately spherical. Therefore, if the length of the line segment Dy (line segment QQ') relative to the line segment Dx is less than 0.5, there is a high probability that such particles are 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.

[0157] (4) 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.

[0158] (5) 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.

[0159] (6) Resistance The ferrite particles produced in each example and comparative example were used as samples, and the resistance value M (Ω) was measured under a room temperature and humidity environment (23°C, 55% relative humidity) according to the following procedure. First, non-magnetic parallel plate electrodes (10 mm x 40 mm) were placed facing each other with an inter-electrode distance of 6.5 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, magnet area in contact with the electrode: 10 mm x 30 mm) attached to the parallel plate electrodes. A voltage of 1000 V was then applied between the opposing parallel plate electrodes, and the resistance was measured using an electrometer (KEITHLEY, insulation resistance meter model 16517A). The resistance value M was measured under a room temperature and humidity environment (23°C, 55% relative humidity) after exposing the sample for 12 hours or more in a constant temperature and humidity chamber where the ambient temperature and humidity were adjusted according to the method, and then measured under the environment according to the above procedure.

[0160] (7) BET specific surface area The ferrite particles produced in each example and comparative example were used as samples, and the BET specific surface area was determined using a specific surface area measurement device (Macsorb HM model-1208, Mountec Co., Ltd.) according to the following procedure. First, approximately 20 g of sample was placed in a glass petri dish and degassed to -0.1 MPa using a vacuum dryer. After degassing and confirming that the degree of vacuum in the glass petri dish had reached -0.1 MPa or less, the dish was heated at 200°C for 2 hours. Approximately 5 to 7 g of the pretreated sample was placed in a standard sample cell designed specifically for the specific surface area measurement device. The mass of the sample placed in the standard sample cell was accurately weighed using a precision balance. The standard sample cell containing the sample was then placed in the measurement port, and the BET specific surface area was measured using the one-point method at temperatures of 10°C to 30°C and relative humidity of 20% to 80%. At the end of the measurement, the mass of the sample was entered, and the calculated value was used as the measured BET specific surface area.

[0161] (8) Apparent density The apparent density was measured in accordance with JIS Z2504:2012 (Metal Powder Apparent Density Test Method).

[0162] (9) Amount of chlorine dissolved First, the sample was accurately weighed to within 50.000g + 0.0002g and placed in a 150ml glass bottle. Next, 50ml of phthalate (pH 4.01) was added to the bottle. Then, 1ml of ionic strength adjuster was added to the bottle and the lid was closed. The sample in the glass bottle was stirred for 10 minutes using a paint shaker. After that, a magnet was placed on the bottom of the 150ml glass bottle, and the sample was filtered into a 50ml polypropylene container using No. 5B filter paper, taking care not to drop the carrier. The voltage of the resulting supernatant was measured using a pH meter. Similarly, solutions with different chlorine concentrations (pure water, 1ppm, 10ppm, 100ppm, and 1000ppm) prepared for the calibration curve were measured, and the amount of chlorine dissolved from the sample was calculated from these values.

[0163] (10) Charging characteristics Using the carrier for electrophotographic developer produced in each of the Examples and Comparative Examples, an electrophotographic developer was prepared by the following method, and the charge amount was determined.

[0164] The electrophotographic developer carrier and toner produced in each example and comparative example were mixed in a Turbula mixer to obtain 50 g of developer (toner concentration 8.0 wt %). The toner used was a commercially available negative toner (average particle size approximately 5.8 μm) used in full-color printers. The developer was exposed to the various environments described below for 12 hours or more. The developer was then placed in a 50 cc glass bottle and stirred at 100 rpm. 30 minutes after the start of stirring, the developer was removed and used as a sample for measuring the charge amount.

[0165] The charge amount measuring device consisted of a magnet roll with a total of eight magnets (magnetic flux density 0.1 T) arranged with alternating north and south poles inside a cylindrical aluminum tube (hereinafter referred to as sleeve) with a diameter of 31 mm and a length of 76 mm, and a cylindrical electrode with a 5.0 mm gap between it and the sleeve and placed on the outer periphery of the sleeve.

[0166] After uniformly attaching 0.5 g of the sample to the sleeve, a DC voltage of 2000 V was applied between the outer electrode and the sleeve for 60 seconds while the inner magnet roll was rotated at 100 rpm with the outer aluminum tube fixed, causing the toner in the developer to transfer to the outer electrode. At this time, an electrometer (KEITHLEY insulation resistance meter model 6517A) was connected to the cylindrical electrode to measure the charge of the transferred toner. After 60 seconds had elapsed, the applied voltage was turned off, the rotation of the magnet roll was stopped, the outer electrode was removed, and the weight of the toner that had transferred to the electrode was measured. The charge amount was calculated from the measured charge amount and the weight of the transferred toner.

[0167] In measuring the charge amount, the following environmental conditions were adopted. Normal temperature and humidity environment (NN environment): Temperature 20°C to 25°C, relative humidity 50% to 60% high temperature high humidity Environment (HH environment): Temperature 30℃~35℃, relative humidity 80%~85% Here, the charge amount measured in a normal temperature and humidity environment is referred to as the NN charge amount, and the charge amount measured in a high temperature and high humidity environment is referred to as the HH charge amount.

[0168] The charge amount measured for the sample with a stirring time of 30 minutes was defined as the "30-minute value," and the charge amount and environmental variation in charge amount under a normal temperature and normal humidity environment and a high temperature and high humidity environment were calculated based on the following calculation formula.

[0169] Charge amount = 30 min value Environmental fluctuation = HH charge amount (30 min value) - NN charge amount (30 min value)

[0170] 2. Evaluation Results The measurement results for each of the above evaluation items are shown in Table 2. 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. The resistivity value M is shown as its logarithmic value logM.

[0171] (1) Spinel-type crystal phase component content and elemental composition The spinel crystal phase component contents in the ferrite particles of each Example and Comparative Example are as shown in Table 2, and it was confirmed that all of them were spinel ferrite particles containing 90 mass % or more of the spinel crystal phase component. Furthermore, when the composition ratio of the spinel crystal phase component was determined based on the measured values ​​of ICP elemental analysis, it was confirmed that the composition ratio was approximately the same as the charged molar ratio, but that there was a slight deviation from the charged molar ratio.

[0172] The results of ICP elemental analysis confirmed that the ferrite particles of Example 2 had a Mg content of 0% by mass, and that the ferrite particles of each Example other than Example 2 had a Mg content of 0.10% by mass to 0.42% by mass. On the other hand, the ferrite particles of Comparative Examples 1 to 3 and 6 had a Mg content of 0.56% by mass to 2.14% by mass, which is higher than the ferrite particles of the Examples according to the present invention. Furthermore, the ferrite particles of Comparative Examples 4 and 5 had Mg contents of 0.11% by mass and 0.10% by mass, respectively, which was confirmed to be similar to that of Examples 1 and 5. Furthermore, when producing the ferrite particles of each Example, Ti or compounds containing Ti, such as TiO2, were not used as raw materials, and these ferrite particles did not substantially contain Ti.

[0173] (2) 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 5 were obtained by using an oxide containing an alkaline earth metal element (R) and zirconium dioxide as raw materials, and thus contained 0.27% to 0.35% by mass of the perovskite-type crystalline phase component represented by the composition formula RZrO3. Furthermore, the degree of dispersion of Zr in the ferrite particles of Examples 1 to 5 was 1.0, confirming that the perovskite-type crystalline phase component was well dispersed within the ferrite particles. In addition, the ferrite particles of the Reference Example contained 0.95% by mass of the perovskite-type crystalline phase component, and the degree of dispersion of Zr was also 1.0. Thus, it was confirmed that ferrite particles containing the perovskite-type crystalline phase component represented by the composition formula RZrO3 could be obtained even when the Mg content was higher than the range specified in the present invention.

[0174] In Comparative Examples 1 to 3, ferrite particles containing the perovskite-type crystalline phase component in an amount of 0.27% by mass to 0.35% by mass and having a Zr dispersion degree of 1.0 were obtained. On the other hand, in Comparative Examples 4 to 6, ferrite particles containing the perovskite-type crystalline phase component were not obtained. In Comparative Example 4, "SrO" was not used as a raw material, and in Comparative Example 5, "ZrO2" was not used as a raw material, so the perovskite-type crystalline phase component (SrZrO2) was not obtained. In Comparative Example 6, "SrO" and "ZrO2" were used in the same amounts as in Examples 1 to 5 and Comparative Examples 1 to 3, but the sintering temperature was low at 1135°C, so it is believed that the perovskite-type crystalline phase was not generated. In the Reference Comparative Example, "TiO2" was used as a raw material instead of "ZrO2", so ferrite particles containing the perovskite-type crystalline phase component represented by the composition formula RZrO3 were not obtained.

[0175] (3) Amount of chlorine dissolved The ferrite particles of Examples 1 to 5 were fired within a suitable firing temperature range to obtain perovskite-type crystalline phase components. Because the firing temperatures in these Examples were high, it is believed that the chlorine compounds decomposed during firing, resulting in low chlorine elution amounts of 4 ppm or less. Among Examples 1 to 5, Example 4, which contained a large amount of Fe2O3, had a relatively large amount of eluted chlorine, while Example 5, which contained a small amount of Fe2O3, had a relatively small amount of eluted chlorine.

[0176] The ferrite particles of Comparative Example 1 and Comparative Example 2 were also fired at firing temperatures similar to those of Examples 1 to 5, but the amount of chlorine eluted was small because the Fe2O3 content was higher than that of each Example. The ferrite particles of Comparative Example 3 had a higher Fe2O3 content than that of each Example, and therefore contained a larger amount of chlorine due to the Fe raw material, which is thought to have resulted in a larger amount of chlorine eluted. The ferrite particles of Comparative Examples 4 and 5 have MgO contents comparable to those of the Examples, and also have relatively high MnO contents relative to Fe2O3. Furthermore, the firing temperature in the firing step is also relatively high. For these reasons, it is believed that the amount of chlorine released was kept low, although it was slightly higher than that of the Examples. On the other hand, the ferrite particles of Comparative Example 6 were fired at a low temperature of 1135°C, which prevented unavoidable impurities such as chlorine in the raw materials from being sufficiently decomposed and removed in the firing step. As a result, the amount of chlorine released was 32 ppm, which is higher than that of the Examples and the other Comparative Examples.

[0177] (4) Saturation magnetization and resistance The saturation magnetization of the ferrite particles of Examples 1 to 4 was confirmed to be high at 60 emu / g. The saturation magnetization of the ferrite particles of Example 5 was 54 emu / g, which is thought to be due to the higher content of Fe2O3, a highly magnetizable component, compared to the other Examples. On the other hand, in terms of resistance, the logarithm (logM) of the resistance M of Examples 1 to 5 was in the range of 6.5 to 7.4, which was within the suitable range for a carrier core material in an electrophotographic developer.

[0178] Compared with Examples 1 to 4, Comparative Example 3 also had a high content of Fe2O3, a highly magnetizable component, and exhibited a high saturation magnetization of 75 emu / g. The logarithm of the resistance value M (logM) of the ferrite particles of Comparative Example 3 was below the measurement limit (BD). The ferrite particles of Comparative Example 3 have extremely low resistance, making them difficult to use as a carrier core material for an electrophotographic developer. It was confirmed that Comparative Examples 1, 2, and 4 to 6 have resistance values ​​within a range suitable for use as a carrier core material for an electrophotographic developer under normal temperature and humidity conditions.

[0179] (5) Other The volume average particle size (D 50 ), BET specific surface area, and apparent density are shown in Table 2.

[0180] (6) Charging characteristics Next, the charging characteristics will be described with reference to Table 3. The NN charge amount (30 min value) of the electrophotographic developer of each Example was 65 μC / g or more, which was a higher value compared to the comparative examples. Also, the HH charge amount (30 min value) of the electrophotographic developer of each Example was 56 μC / g or more, which was a higher value compared to the comparative examples (except for comparative example 2). Furthermore, looking at the environmental variation in charge amount, each Example showed a -10 Within From these results, it was confirmed that by using the ferrite particles of each Example as a carrier core material for an electrophotographic developer, electrophotographic printing is possible even in a high-temperature, high-humidity environment without significant deterioration in charging characteristics from a normal-temperature, normal-humidity environment.

[0181] On the other hand, the NN charge amount (30 min value) of the electrophotographic developer of Comparative Example 2 was 62.5 μC / g and the HH charge amount (30 min value) was 56.3 μC / g, which were values ​​close to those of the Examples, but the NN charge amount (30 min value) of the electrophotographic developers of the other Comparative Examples was less than 60 μC / g and the HH charge amount (30 min value) was less than 50 μC / g, which indicated inferior charging characteristics compared to those of the Examples. Furthermore, it was confirmed that the charge amount of the electrophotographic developers of Comparative Examples 3, 5 and 6 varied greatly depending on the environment, and the environmental stability of the charging characteristics was low.

[0182] [Table 1]

[0183] [Table 2]

[0184] [Table 3] [Industrial Applicability]

[0185] According to the present invention, it is possible to provide ferrite particles having high environmental stability in charging characteristics and good charge build-up properties, a carrier core material for an electrophotographic developer, a carrier for an electrophotographic developer, and an electrophotographic developer.

Claims

1. RZrO ３ (wherein R is an alkaline earth metal element), and contains 90 mass % or more of a spinel-type crystal phase component represented by (MnO)a(MgO)b(Fe2O3)c (wherein a+b+c=100 (mol %), a≠0, 0≦b, c≠0), When the Mn content in the ferrite particles is x (mass%) and the Fe content is y (mass%), the following formula is satisfied: 0.30y≦x≦0.60y Ferrite particles having a Mg content of 0.45 mass% or less.

2. 2. 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.

3. 3. The ferrite particles according to claim 1, 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.

4. The ferrite particles according to any one of claims 1 to 3, wherein the Cl concentration measured by an elution method is 30 ppm or less.

5. The ferrite particles according to any one of claims 1 to 4, wherein the ferrite particles are substantially free of Ti.

6. A carrier core material for an electrophotographic developer, comprising the ferrite particles according to any one of claims 1 to 5.

7. A carrier for electrophotographic developer, comprising: the ferrite particles according to any one of claims 1 to 5; and a resin coating layer provided on the surface of the ferrite particles.

8. An electrophotographic developer comprising the carrier for electrophotographic developer according to claim 7 and a toner.

9. The electrophotographic developer according to claim 8, which is used as a replenishment developer.

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