Ferrite particles, carrier for electrophotographic developer, electrophotographic developer, and method for producing ferrite particles

Abstract

Provided are a ferrite particle, a carrier for electrophotographic developers, and the like, which have: a ferrite particle main body having a spinel crystal structure belonging to space group Fd-3m, the spinel component being represented by a specific formula (1); and a coating layer having a spinel crystal structure belonging to space group Fd-3m, covering the surface of the ferrite particle main body; the coating layer being a layer obtained by heat treating a ferrite represented by the specific formula (1), the content ratio of the coating layer in the ferrite particle being 5 mass% or more and 35 mass% or less, as determined by Rietveld analysis of a powder X-ray diffraction pattern, and satisfying a specific formula (2).

Description

Technical Field

[0001] This invention relates to ferrite particles, carriers for electrophotographic developers, electrophotographic developers, and methods for manufacturing ferrite particles. Background Technology

[0002] Electrophotographic developing methods refer to the development of an electrostatic latent image formed on a photoreceptor by having the toner in the developing agent adhere to it. The developing agents used in this method are divided into two-component developing agents consisting of a toner and a carrier, and single-component developing agents using only a toner. While cascade methods and other techniques have been used in the past for developing with two-component developing agents, the magnetic brush method using magnetic rollers is currently the mainstream approach.

[0003] In the magnetic brush method, toner and carrier are stirred and mixed in a developing cartridge filled with developer, and the toner is charged. A developing roller holding a magnet then transports the carrier to the surface of the photoreceptor. At this point, the charged toner is transferred to the surface of the photoreceptor via the carrier. After a toner image is formed on the photoreceptor through electrostatic interaction, the carrier remaining on the developing roller is recycled back into the developing cartridge, stirred and mixed with new toner, and reused for a certain period.

[0004] In recent years, efforts have been made to reduce the particle size of toners in order to achieve high-resolution electrostatic latent images. Along with the reduction in toner particle size, the carrier particle size is also decreasing. By reducing the carrier particle size, the mechanical stress during the stirring and mixing of the carrier and toner can be reduced, and toner consumption can be suppressed, thus extending the developer life compared to the past. However, reducing the carrier particle size can easily lead to carrier dispersion and image defects such as white spots.

[0005] For example, Patent Document 1 discloses a carrier core material containing 15-22% by weight Mn, 0.5-3.0% by weight Mg, 45-55% by weight Fe, and 0.1-3.0% by weight Sr, with a lattice constant of 8.430-8.475, and forming a surface oxide coating. According to the carrier core material disclosed in Patent Document 1, by setting the surface oxide coating, even with small particle sizes, the particle resistivity can be increased, reducing the resistivity imbalance between particles. Therefore, if this carrier core material is used in an electrophotographic developer to suppress carrier adhesion, excellent printed matter with superior fine line reproducibility can be obtained.

[0006] Furthermore, Patent Document 2 discloses a carrier core material, which is composed of M X Fe 3－XO4 (where M is at least one metal selected from the group consisting of Mn, Mg, Ca, Sr, Ti, Cu, Zn, and Ni, 0 < X ​​≦ 1) represents a support core material. The full width at half maximum (FWHM) calculated from the peak value of the surface index (311) in the powder X-ray diffraction pattern is greater than 0.15° and less than 0.20°. After the support core material is pulverized, the difference in lattice constant calculated from the peak value of the surface index (311) in the powder X-ray diffraction pattern before and after pulverization is expressed in absolute value as follows: The following describes how the carrier core material is oxidized not only on the particle surface but also inside the particle, and how it achieves high resistivity. If this carrier core material is used in an electrophotographic developer, the adhesion of the carrier to photosensitive materials, etc., can be suppressed.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-178414

[0010] Patent Document 2: Japanese Patent Application Publication No. 2017-21195 Summary of the Invention

[0011] The technical problem that the invention aims to solve

[0012] Manufacturing conditions are precisely controlled based on the characteristics of developing devices using electrophotographic developers in two-component developers, or the characteristics of toners, so that the magnetization or resistance of the carrier core material is set to a predetermined initial value. However, conventional carrier core materials typically exhibit resistance values ​​that vary depending on factors such as humidity in the atmosphere. That is, the resistance value shows environmental dependence. These existing carrier core materials are composed of particles with small, uneven resistance. Therefore, the resistance change of the powder exhibits behavior approximately the same as the resistance change of each individual particle. Thus, under predetermined atmospheric conditions, images can be printed with extremely high image quality. However, if there are drastic environmental changes such as changes in atmospheric temperature or humidity, the resistance value or the charge of the toner changes, resulting in poor stirring and mixing of the toner and carrier. In such cases, charge growth slows down, and uneven concentration due to uneven charge of the toner sometimes occurs in the early stages of printing.

[0013] Furthermore, in the carrier core material described in Patent Documents 1 and 2, if there are insufficiently oxidized portions when the surface of the ferrite particles is oxidized, the resistance of the carrier core material changes over time due to the oxidation of these portions over time.

[0014] Furthermore, the toner concentration is controlled by detecting the image density of the printed material in the developing device to ensure the toner charge is at an appropriate value. Here, the toner charge tends to increase in low-temperature, low-humidity environments and decrease in high-temperature, high-humidity environments. Moreover, in a two-component developer containing toner and carrier, the toner charge tends to decrease if the toner concentration is high and increase if the toner concentration is low. Therefore, if images are printed in low-temperature, low-humidity environments, the toner charge tends to increase, resulting in lower image density. Therefore, to reduce the toner charge in the developing device, control is implemented by replenishing toner in the developer cartridge, thus increasing the toner concentration. On the other hand, if images are printed in high-temperature, high-humidity environments, as mentioned above, the toner charge tends to decrease, resulting in higher image density. Therefore, in the developing device, control is implemented by stopping toner replenishment until the toner charge is within an appropriate range.

[0015] However, there are also situations where, during a prolonged period of non-use of the developing device under conditions of low temperature and low humidity with increased toner concentration, the atmosphere changes from a low-temperature, low-humidity environment to a high-temperature, high-humidity environment when printing is scheduled. In this case, there is a significant change in the toner's charge, which can hinder proper mixing and agitation of the toner and carrier. As a result, the rate of increase in toner charge may slow down, leading to uneven toner charge distribution and resulting in image defects with inconsistent concentrations in the printed material.

[0016] Furthermore, it is conceivable that the carrier core material disclosed in Patent Documents 1 and 2 is a powder composed of particles with relatively small magnetization unevenness and the same degree of magnetization. During the long-term non-use of the developing device, the carrier particles sometimes agglomerate due to magnetic force. Therefore, when printing after a long period of non-use, it is necessary to break up the agglomeration of the carrier particles during the initial stirring and mixing of the toner and carrier. In particular, the narrower the magnetization distribution and the higher the magnetization, the easier it is for the carrier particles to agglomerate, and the stronger the magnetic bonding force between the particles. For example, in high-speed printing developing devices capable of continuous image formation speeds of 100 frames per minute or more, the stirring and mixing speeds of the toner and carrier are fast, and the torque required to break up the magnetic bonding between the particles is small. However, in medium- and low-speed developing devices with continuous image formation speeds of 40 frames per minute or less, the stirring and mixing speeds are slower, and the torque required to break up the magnetic bonding between the particles is large, making it difficult to mix the toner and carrier well. Therefore, it is difficult to achieve sufficient image density in the initial stage of printing.

[0017] Therefore, the purpose of this invention is to provide ferrite particles preferred for carrier core materials of electrophotographic developers, which have excellent agitation and mixing properties with toners and carriers and can suppress image defects in the early stages of printing even when the environment changes. It also includes carriers for electrophotographic developers, electrophotographic developers, and a method for manufacturing ferrite particles.

[0018] Methods for solving technical problems

[0019] The present invention includes the following solutions. [1]

[0021] A ferrite particle, comprising:

[0022] The ferrite particles have a spinel-type crystal structure belonging to space group Fd-3m, and the spinel composition is represented by the following formula (1).

[0023] The coating layer has a spinel-type crystal structure belonging to space group Fd-3m and covers the surface of the ferrite particle body;

[0024] The coating layer is obtained by heat treatment of ferrite represented by the following formula (1), and the content of the coating layer in the ferrite particles is 5% by mass or more and 35% by mass or less, as determined by Rietwald analysis of the powder X-ray diffraction pattern.

[0025] Satisfy the following equation (2),

[0026] Mg x Mn (1－x) Fe2O4···(1),

[0027]

[0028] in,

[0029] In equation (1), 0.001 ≦ x < 0.300,

[0030] In equation (2), D LC = (lattice constant of the ferrite particle body) - (lattice constant of the coating layer). [2]

[0032] Ferrite particles as described in [1],

[0033] The full width at half maximum (FWHM) of the (311) plane in the powder X-ray diffraction pattern of the ferrite particle is above 0.25° and below 0.35°. [3]

[0035] Ferrite particles as described in [1] or [2],

[0036] When the total amount of Fe, Mn, and Mg contained in the ferrite particles is set to 100 mol, unlike the elements in these spinel-type crystal structures, it contains Sr element at a concentration of more than 0.4 mol and less than 1.2 mol. [4]

[0038] Ferrite particles as described in any of [1] to [3]

[0039] The saturation magnetization, determined by B-H measurements under a magnetic field of 3 K·1000 / 4π·A / m, is 50 Am. 2 / kg or more 75Am 2 / kg or less. [5]

[0041] Ferrite particles as described in any of [1] to [4]

[0042] The apparent density is 2.23 g / cm³. 3 The above 2.35g / cm 3 The surface roughness Rz is above 2.5μm and below 3.5μm. [6]

[0044] Ferrite particles as described in any one of [1] to [5],

[0045] The specific surface area of ​​BET is 0.070 m². 2 / g or more 0.150m 2 / g or less. [7]

[0047] A carrier for an electrophotographic developer, comprising:

[0048] Ferrite particles as described in any of [1] to [6], and a resin coating layer covering the surface of the ferrite particles. [8]

[0050] An electrophotographic developer,

[0051] Includes carriers and toners for electrophotographic developing agents as described in [7]. [9]

[0053] As described in [8], the electrophotographic developer,

[0054] It is used as a supplementary developer.

[10]

[0056] A method for manufacturing ferrite particles, comprising:

[0057] The process of mixing Fe raw materials containing Fe, Mn raw materials containing Mn, and Mg raw materials containing Mg in a predetermined amount to obtain a mixture;

[0058] The process of obtaining granules using the mixture;

[0059] The process involves using a closed-atmosphere heat treatment furnace, which has a closed heat treatment chamber capable of controlling the firing atmosphere and a cooling chamber capable of controlling the cooling atmosphere to be different from the firing atmosphere, to fire the granules in the closed heat treatment chamber to obtain the fired product.

[0060] A cooling process in which the fired product is cooled to below 250°C in a cooling chamber where the oxygen concentration is controlled to be less than 0.3% by volume, without exposing the product to outside air; and

[0061] A process of performing surface heat treatment on the fired product after the cooling process.

[11]

[0063] The method for manufacturing ferrite particles as described in

[10]

[0064] The surface heat treatment is performed using a rotary furnace.

[0065] When the inner diameter of the rotary combustion chamber of the rotary furnace is set to L (m), the rotation speed is set to X (rpm), and the surface heat treatment time is set to t (min), the following equation (3) is satisfied.

[0066] 20≦LπXt≦60···(3).

[12]

[0068] Methods for manufacturing ferrite particles as described in

[10] or

[11] ,

[0069] The formulation ratio of the Fe raw material, the Mn raw material and the Mg raw material in the mixture satisfies the following formula (4).

[0070] 0.80≦n Fe / (n Mn +n Mg )<2.00···(4)

[0071] in,

[0072] n Fe The amount of Fe element in the Fe raw material (mol%)

[0073] n Mn The amount of Mn element in the Mn raw material (mol%)

[0074] n MgThe amount of Mg element in the Mg raw material (mol%)

[0075] Invention Effects

[0076] According to the invention of this case, ferrite particles, a carrier core material for an electrophotographic developer with a magnetic distribution suitable for medium and low speed printing and capable of achieving good image characteristics, an electrophotographic developer carrier, an electrophotographic developer, and a method for manufacturing ferrite particles are provided. Detailed Implementation

[0077] The embodiments of the ferrite particles, the carrier core material for electrophotographic developers, the carrier for electrophotographic developers, and the electrophotographic developers of this invention will be described below. First, the embodiments of the ferrite particles and the carrier core material for electrophotographic developers will be described. Furthermore, in this specification, unless otherwise specified, ferrite particles, the carrier core material for electrophotographic developers, the carrier for electrophotographic developers, and the electrophotographic developers refer to aggregates of individual particles, i.e., powders.

[0078] Furthermore, in the following description, the ferrite particles of this embodiment are used as particles for carrier core materials for electrophotographic developers. However, the ferrite particles of this invention can also be used in various functional fillers such as magnetic inks, magnetic fluids, magnetic fillers, fillers for bonding magnets and fillers for electromagnetic wave shielding materials, electronic component materials, etc. The use of these ferrite particles is not limited to carrier core materials for electrophotographic developers.

[0079] 1. Ferrite particles

[0080] First, the ferrite particles will be described. These ferrite particles are characterized by having: a ferrite particle body having a spinel-type crystal structure belonging to space group Fd-3m, the spinel component being represented by the following formula (1); and a coating layer having a spinel-type crystal structure belonging to space group Fd-3m, covering the surface of the ferrite particle body; the coating layer is a layer obtained by heat treatment of the ferrite represented by the following formula (1), and the content of the coating layer in the ferrite particle, determined by Rietwald analysis of the powder X-ray diffraction pattern, is 5% by mass or more and 35% by mass or less, satisfying the following formula (2).

[0081] Mg x Mn (1－x) Fe2O4···(1),

[0082]

[0083] in,

[0084] In equation (1), 0.001 ≦ x < 0.300,

[0085] In equation (2), D LC = (lattice constant of the ferrite particle body) - (lattice constant of the coating layer).

[0086] The spinel-type crystal structure belonging to space group Fd-3m belongs to the cubic crystal system, and its unit lattice is represented by 8(AB2O4). Here, "A" in "AB2O4" represents the element (metal ion) located at the center of the tetrahedron composed of four oxygen atoms, i.e., the 8b position (A site), and "B" represents the element located at the center of the hexahedron composed of six oxygen atoms, i.e., the 16c position (B site).

[0087] In a ferrite having a spinel composition represented by formula (1), Mg, Mn, and Fe are disposed as divalent or trivalent ions at each lattice site, respectively, and Fe at each lattice site 3+ The higher the Mn occupancy rate, the stronger the magnetization. On the other hand, the higher the Mn occupancy rate at each lattice point, the stronger the Fe occupancy rate at each lattice point. 3+ The portion corresponding to the decrease in occupancy becomes low magnetization. Furthermore, when the lattice constant is determined using the methods described later, it indicates that Fe... 3+ The higher the occupancy rate, the smaller the lattice constant. When the occupancy rate of Mn at each lattice point increases, it indicates that the lattice constant is a larger value.

[0088] In manufacturing ferrite represented by the general formula "AB2O4", when mixing raw materials in a state where the amount of A-site atoms (hereinafter, A-site raw materials) is greater than the stoichiometric amount corresponding to the composition formula, i.e., when the A-site raw materials are prepared in a state that is more abundant than the stoichiometric amount, a ferrite with a high occupancy of A-site atoms at each lattice point is obtained. For example, in this invention, when the raw materials are mixed in a manner that satisfies the A-site atoms, i.e., Mn, as described later in formula (4), a ferrite rich in Mn is obtained with a greater amount of Mn raw materials than the stoichiometric amount corresponding to the composition formula represented by formula (1). At this time, the Mn occupancy at each lattice point is increased, and the Fe at each lattice point is increased. 3+ The reduced occupancy corresponds to the portion of ferrite. The lattice constant of the ferrite produced by this method is approximately... Therefore, in this specification, the value of the lattice constant having a spinel composition expressed by formula (1) is given. The above-mentioned ferrites are conveniently referred to as A-rich ferrites. Furthermore, ferrites having a spinel composition expressed as formula (1) and a lattice constant less than [missing information] are also considered. The ferrite is conveniently referred to as B-rich ferrite. Furthermore, B-rich ferrite is obtained by manufacturing ferrite in a manner where the amount of Fe raw material is relatively high relative to the stoichiometry corresponding to the above formula (1), i.e., the value of formula (4) described later is 2.00 or higher. Furthermore, formula (4) is as described below.

[0089] When a ferrite having a spinel composition represented by formula (1) is subjected to heat treatment, the following reaction is expected to occur.

[0090] 3(Mg x Mn (1－x) Fe2O4→

[0091] (1-x)Mn3O4+3xMgFe2O4+2(1-x)Fe3O4

[0092] Here, the lattice constants of the compounds in the stated reaction are shown below. The lattice constants shown below are values ​​recorded in various literatures.

[0093] MnFe2O4:

[0094] (Source: Phys. Status Solidi A, 1993, 139, K109-K112, Latha K., Ravinder D.)

[0095] MgFe2O4:

[0096] (Source: J. Magn. Magn. Mater., 1992, 110, 147-150, Patil SH, Patil S.I., Kadam SM, Chougule BK)

[0097] Mn3O4:

[0098] (Source: Russ. J. Inorg. Chem., 1990, 35, 877-881, Zinovik MA)

[0099] Fe3O4:

[0100] (Source: J.Phys.Soc.Jpn., 1995, 64, 3484-3495, Okamura A., Nakamura S., Tanaka M., Siratori K.)

[0101] If we assume the coating layer is a composite of Mn3O4, MgFe2O4, and Fe3O4, then, for example, when x = 0.001, the lattice constant of the coating layer is: about.

[0102] Therefore, in A-rich ferrites, the change in lattice constant before and after heat treatment during decomposition is greater. On the other hand, in B-rich ferrites, even if a decomposition reaction occurs through heat treatment, the amount of Mn3O4 formed decreases or almost does not form, while the amount of Fe3O4 formed increases. Since the difference between the lattice constant of the ferrite before heat treatment and the lattice constant of the Fe3O4 formed by heat treatment is small, the change in lattice constant before and after heat treatment is smaller in B-rich ferrites.

[0103] Therefore, when the ferrite particle bulk is an A-rich ferrite, the value of equation (2) becomes an indicator of the degree of surface heat treatment. That is, the difference D between the lattice constants of the ferrite particle bulk and the coating layer. LC When it is within the range of the formula (2), it means that the ferrite particles are covered by a complex of Mn3O4, MgFe2O4 and Fe3O4 and are in a state of being fully heat-treated on the surface.

[0104] On the other hand, when the ferrite particle bulk is a boron-rich ferrite, the change in lattice constant before and after heat treatment is small. Therefore, the value of equation (2) cannot be used as an indicator of whether or not heat treatment is performed on the surface or the degree of heat treatment. In addition, when the ferrite particle bulk is a boron-rich ferrite, even if the surface is decomposed as described above after sufficient heat treatment, it is difficult to satisfy equation (2) because the difference in lattice constant between the ferrite particle bulk and the coating layer is small.

[0105] According to the above, if equation (2) is satisfied, it means that the ferrite particle body is an A-rich ferrite, the surface is fully heat-treated, and a coating layer of uniform thickness is provided.

[0106] Furthermore, when the content of the coating layer in the ferrite particles satisfying formulas (1) and (2) is 5% by mass or more and 35% by mass or less, as determined by Rietwald analysis of the powder X-ray diffraction pattern, the following effect is obtained.

[0107] First, when the ferrite particle bulk is an A-rich ferrite, as mentioned above, the Mn occupancy of each lattice point is relatively high, resulting in a ferrite with low magnetization tendency. Therefore, compared to a ferrite particle bulk composed of B-rich ferrite, i.e., Fe at each lattice point... 3+Compared to ferrites with a higher occupancy, the excessive magnetization of ferrite particles can be suppressed when the powder is formed. Therefore, the ferrite particles according to the present invention exhibit good magnetism when used as a carrier core material for electrophotographic developers used in medium- and low-speed imaging devices. Furthermore, in the case of ferrites rich in A, compared to ferrites rich in B, the occupancy state of each grid point changes, resulting in uneven magnetization of the particles constituting the powder. Therefore, the possibility of magnetic bonding between particles with different magnetizations is higher than the possibility of magnetic bonding between particles with the same degree of magnetization within the powder. It is easier to break the magnetic bonding between particles with different magnetizations than to break the magnetic bonding between particles with the same degree of magnetization. As a result, by using these ferrite particles as a carrier core material, it becomes easy to break the magnetic bonding between carriers, and the toner and carrier can be mixed and stirred quickly to obtain a carrier with high image adaptability, such as sufficient image density, even in the early stages of printing.

[0108] Furthermore, when the content of the coating layer in the ferrite particles, as determined by Rietwald analysis of the powder X-ray diffraction pattern, is 5% to 35% by mass, the surface of the ferrite particle body is fully covered by the coating layer with sufficient thickness. When spinel-type ferrite (AB₂O₄) is formed by firing, an oxygen-deficient spinel-type crystal structure (AB₂O₄-α) may be generated under a low-oxygen atmosphere. When the oxygen-deficient spinel-type crystal is generated, the ferrite oxidizes over time upon contact with atmospheric oxygen, and the surface resistivity increases over time. If the content of the coating layer in the ferrite particles is within the aforementioned range, the surface of the ferrite particle body is sufficiently covered by the coating layer, thus suppressing the exposure of the ferrite particle body. Therefore, even in a state where the surface of the ferrite particle body is prone to oxidation, the coating layer suppresses the contact between the ferrite particle body and atmospheric oxygen, preventing oxidation of the ferrite particle body. Therefore, changes in surface resistivity over time can be prevented.

[0109] The ferrite particles of the present invention will now be described in detail.

[0110] (1) Lattice constant difference (D) LC )

[0111] The lattice constant difference (D) between the ferrite particle bulk and the coating layer LC As described above. Here, each lattice constant is set to a value determined by Rietwald analysis of the powder X-ray diffraction pattern obtained by powder X-ray diffraction as follows.

[0112] (Powder X-ray diffraction)

[0113] As the X-ray diffraction apparatus, the "X'Pert PRO MPD" manufactured by Panaco can be used. As the X-ray source, a Co-tube sphere (CoKα line) can be used. As the optical system, a concentrated optical system and a high-speed detector, the "X'Celarator," can be used. The measurement conditions are as follows.

[0114] Scanning speed: 0.08° / second

[0115] Diffusion slit: 1.0°

[0116] Scattering slit: 1.0°

[0117] Light-receiving slit: 0.15mm

[0118] Voltage and current values ​​for the sealed tube: 40kV / 40mA

[0119] Measurement range: 2θ = 15°~90°

[0120] Total number of times: 5

[0121] (Crystal structure analysis and qualitative assessment)

[0122] Based on the powder X-ray diffraction pattern obtained as described, and the structures disclosed by the National Agency for Materials Science and Engineering, AtomWorks, and the Internet <URL: http: / / crystdb.nims.go.jp / >, the following crystal structures are assumed, and the lattice constants are determined for each crystal structure.

[0123] Ferrite particle bulk: a crystal phase composed of manganese ferrite (spinel-type crystal).

[0124] Crystal structure: Space group Fd-3m (No. 227)

[0125] <Atomic Coordinates>

[0126] Mn: 8b 3 / 8 3 / 8 3 / 8

[0127] Fe: 16c 0 0 0

[0128] O:32e xxx

[0129] Coating layer: a crystalline phase composed of manganese ferrite (spinel-type crystal).

[0130] Crystal structure: Space group Fd-3m (No. 227)

[0131] <Atomic Coordinates>

[0132] Mn: 8b 3 / 8 3 / 8 3 / 8

[0133] Fe: 16c 0 0 0

[0134] O:32e xxx

[0135] After assuming the crystal structure of the ferrite particle bulk and coating layer as described above, the following parameters were optimized using the analytical software "RIETAN-FP u2.83". The distribution function was asymmetric using the Thompson, Cox, and Hastings quasi-Voigt functions, derived from Howard's method. Furthermore, the parameters were refined using Rwp values ​​and S values, representing the correctness of the fit, with Rwp ≤ 2% and S ≤ 1.5 respectively.

[0136] (Refined parameters)

[0137] • Offset factor

[0138] · Scale factor

[0139] Background parameters

[0140] Gaussian functions U, V, W

[0141] Lorentz functions X, Y

[0142] • Asymmetric function As

[0143] • Lattice constant • Oxygen atom coordinates

[0144] The lattice constant difference (D) calculated from the lattice constants of the ferrite particle bulk and the coating layer obtained in the above manner LC When the lattice constant difference (D) is within the specified range, the aforementioned effect is obtained. Based on obtaining this effect, the lattice constant difference (D) LC The upper limit of ) is preferably less than Preferred Preferred option More preferably

[0145] (2) Content of the coating layer (Ritterwald analysis)

[0146] The powder X-ray diffraction pattern obtained as described was subjected to Ritwald analysis in the same manner as described above. Based on the presence ratio of each crystal phase converted by mass, the proportion of compounds with lattice constants different from those of the ferrite particle bulk was set as the content ratio of the coating layer.

[0147] If the content ratio of the coating layer obtained as described is within the specified range, then, as described, when the ferrite particles are used as the carrier core material of an electrophotographic developer, the annual change in the surface resistivity of the carrier can be suppressed. Based on this effect, the lower limit of the content ratio of the coating layer is preferably 10% by mass. Furthermore, the upper limit is preferably less than 35% by mass, more preferably 30% by mass, more preferably 25% by mass, and even more preferably 20% by mass.

[0148] (3) Full width at half peak

[0149] Preferably, the full width at half maximum (FWHM) of the (311) plane of the ferrite particle is between 0.25° and 0.35°. Here, the FWHM is set as the full width at half maximum (FWHM) caused by the diffraction of the Kα1 line in the (311) plane, as described above, by performing Rietwald analysis on the powder X-ray diffraction pattern obtained as described above (**.lst). Conventionally, ferrite particles used as carrier core materials have a uniform crystal structure, and ferrite particles with narrow magnetization distribution are desired. However, as described above, using A-rich ferrite and ferrite particles with uneven crystal structures as carrier core materials results in uneven magnetization of each particle, thus achieving the aforementioned effect. Preferably, the FWHM is within the aforementioned range while achieving an electrophotographic developer with high image density adaptability.

[0150] Based on this effect, the lower limit of the full width at half maximum (FWHM) is preferably greater than 0.25°, more preferably 0.27°, and even more preferably 0.29°. Furthermore, the upper limit of the FWHM is preferably less than 0.35°, more preferably 0.33°, and even more preferably 0.31°.

[0151] (4)x

[0152] In equation (1), “x” is a value obtained by quantifying the elements contained in the ferrite particles using ICP luminescence analysis. The value of “x” is obtained in the following manner.

[0153] (ICP)

[0154] First, weigh 0.2 g of the ferrite particles to be measured. Then, add 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid to 60 ml of pure water and heat. Add the ferrite particles to the solution to prepare an aqueous solution that dissolves the ferrite particles. Use this aqueous solution as a sample and determine the contents of Fe, Mn, and Mg using an ICP luminescence analyzer (ICPS-1000IV manufactured by Shimadzu Corporation). The value of “x” in formula (1) can be obtained from these values.

[0155] Here, as mentioned above, the value is 0.001 ≤ x < 0.300. The lower limit of "x" is preferably 0.050. Furthermore, the upper limit of "x" is more preferably 0.200.

[0156] (5) Sr content

[0157] When the total amount of Fe, Mn, and Mg contained in the ferrite particles is set to 100 mol, it is preferable that the Sr element is present at a concentration of 0.4 mol to 1.2 mol, which is different from the elements in these spinel-type crystal structures. The Sr content can be determined using the same method as the "x" value.

[0158] Specifically, the determination is performed as follows: Sr is dissolved in the aqueous solution prepared when the value of "x" is determined using the ICP luminescence analysis method. Therefore, when using this aqueous solution to determine the contents of Fe, Mn, and Mg, the content of Sr is also determined simultaneously. The amount of "Sr" (mol) when the total amount of "Fe", "Mn", and "Mg" (mol) is set to 100 is obtained, and this value is taken as the content of Sr (mol).

[0159] By including Sr within this range, the surface roughness of the ferrite particles can be determined to be of an appropriate size, and unevenness can be suppressed, thus preventing the resin coating layer from peeling off when the carriers collide with each other. Furthermore, with the surface roughness of the ferrite particles being of an appropriate size, excessively high resistance can be prevented when the surface is covered with resin to form a carrier. On the other hand, when the Sr content increases beyond the aforementioned range, chlorine gas released from Fe raw materials during firing is adsorbed onto the Sr compounds precipitated on the core material surface, making the charge characteristics of the ferrite particles susceptible to atmospheric humidity. Therefore, in high-temperature and high-humidity environments, the surface resistance of the ferrite particles decreases, and their charge may also decrease. Furthermore, the phrase "containing Sr element, unlike spinel-type crystal structure elements" indicates that Sr element is not an element constituting the spinel-type crystal structure, nor is it an element constituting ferrites with other crystal structures like Sr ferrite, and is present within the particles.

[0160] Based on achieving this effect, the lower limit of the "Sr" content is preferably greater than 0.4 mol, more preferably 0.5 mol, and even more preferably 0.6 mol. Furthermore, the upper limit is preferably less than 1.2 mol, more preferably 1.1 mol, and even more preferably 1.0 mol.

[0161] (6)Magnetic properties

[0162] Next, the magnetic properties of the ferrite particle will be explained. The ferrite particle is preferably characterized by a saturation magnetization of 50 Am in B-H measurements when a magnetic field of 3 K·1000 / 4π·A / m is applied. 2 / kg or more 75Am 2 / kg or less. When the saturation magnetization of the ferrite particles is within this range, for example, even in low-to-medium speed imaging devices with an image forming speed of 40 frames per minute or less, it becomes easy to break the magnetic bond between the particles. In cases of long-term non-use, regardless of changes in ambient temperature or humidity, the toner and carrier can be stirred well, and the toner charge can be increased more quickly.

[0163] For this, the saturation magnetization is less than 50 Am. 2 At a magnetization level of / kg, insufficient magnetization can lead to inadequate brush erection or carrier scattering from the developing roller due to low magnetization, potentially causing image defects. Furthermore, saturation magnetization exceeding 75Am... 2 At a concentration of / kg, the magnetic bonding between particles is enhanced, and the fluidity is reduced. Therefore, in such low-to-medium speed imaging devices, it is difficult to effectively stir the toner and carrier, and the increase in the charge of the toner is slower.

[0164] From this perspective, the lower limit of saturation magnetization is preferably greater than 50 Am. 2 / kg, preferably 55Am 2 / kg, more preferably 60Am 2 / kg.

[0165] Saturation magnetization can be measured using an integrating B-H tracer, type BHU-60 (manufactured by Riken Electronics Co., Ltd.). Specifically, the sample is placed in a 4πI coil, and an H coil for measuring the magnetic field and a 4πI coil for measuring magnetization are placed between the electromagnets of the apparatus. The outputs of the H coil and the 4πI coil, which change the current of the electromagnets and the magnetic field H respectively, are integrated. The output of H is used as the X-axis, and the output of the 4πI coil is used as the Y-axis. A hysteresis loop is plotted on recording paper. From this hysteresis loop, the magnetization when an applied magnetic field of 3 K·1000 / 4π·A / m is obtained and defined as saturation magnetization. Furthermore, the measurement conditions are as follows.

[0166] Sample filling amount: approximately 1g

[0167] Sample filling cell: inner diameter Height 10mm ± 0.1mm

[0168] 4πI coil: 30 turns

[0169] (7) Apparent density (AD)

[0170] The apparent density (AD) of the ferrite particles is preferably 2.23 g / cm³. 3 The above 2.35g / cm 3 The apparent density referred to here is the value measured according to JIS Z 2504:2012. When the apparent density of the ferrite particles is within this range, it can meet the flowability requirements for medium and low speed printing. When the ferrite particles are used as a carrier core material for electrophotographic developers, they can effectively agitate the carrier and toner in the developing chamber, and can stably obtain good image density.

[0171] In this regard, if the apparent density (AD) of the ferrite particle is less than 2.23 g / cm³ 3 This could become a cause of carrier adhesion. On the other hand, the apparent density (AD) of these ferrite particles exceeds 2.35 g / cm³. 3 At that time, the stirring stress inside the developing chamber and the peeling of the resin coating layer (described later) cause the charge characteristics to deteriorate, resulting in a decrease in the stability of image density.

[0172] Based on these effects, the upper limit of the apparent density of the ferrite particles is preferably less than 2.35 g / cm³. 3 The preferred value is 2.32 g / cm³. 3 Further preferred value is 2.30 g / cm³. 3 .

[0173] Apparent density can be determined using a powder apparent density meter as follows. The powder apparent density meter consists of a funnel, a cup, a funnel support, a support rod, and a support platform. A balance with a capacity of 200g and a sensitivity of 50mg is used. The determination is performed in the following order, and the value calculated as follows is taken as the apparent density referred to herein.

[0174] i) Measurement method

[0175] (a) The sample must be at least 150g.

[0176] (b) The sample is injected into a funnel with a throttling orifice with a diameter of 2.5 + 0.2 / - 0 mm. The sample flows out and fills the cup to the brim, stopping when it overflows.

[0177] (c) Stop the flow of the sample immediately when it begins to overflow, and scrape the sample off the raised part of the cup with a scraper without applying vibration.

[0178] (d) Gently tap the side of the cup to allow the sample to settle, remove the sample adhering to the outside of the cup, and weigh the sample inside the cup with an accuracy of 0.05g.

[0179] ii) Calculation

[0180] The value obtained by multiplying the measured value obtained in (d) by 0.04 is rounded to two decimal places according to JIS-Z8401 (rounding method for numerical values), and is used as "g / cm". 3 The apparent density of the unit.

[0181] (8) Surface roughness Rz

[0182] The surface roughness Rz of the ferrite particles is preferably 2.5 μm or more and 3.5 μm or less. When the surface roughness Rz of the ferrite particles is within this range, the surface unevenness of the ferrite particles as carrier core material for electrophotographic developers is moderate, which can ensure an effective charged area that helps the toner to be charged and can stably obtain good image density.

[0183] From this perspective, the lower limit of surface roughness Rz is preferably greater than 2.5 μm, more preferably 2.7 μm, and even more preferably 3.0 μm.

[0184] The surface roughness Rz was measured using an OPTELICS laser microscope manufactured by Lasertec Co., Ltd., as follows: First, the measurement conditions were: lens magnification of 100x, optical zoom of 3.0x, measurement spacing of 0.02 μm, cutoff filter λs = 2.5 μm, and λf = 0.08 mm. Under these conditions, the surface roughness of the ferrite particles was measured. Then, using the obtained surface shape data of the ferrite particles, a 10 μm square range was specified, and the ferrite particles were considered spherical. After correcting for a planar surface using spherical data, the value calculated according to JIS B 0601-2001 was taken as the surface roughness Rz.

[0185] Furthermore, the ferrite particles preferably have an apparent density of 2.23 g / cm³. 3 The above 2.35g / cm 3 The surface roughness Rz is above 2.5μm and below 3.5μm.

[0186] (9) BET specific surface area

[0187] The preferred BET specific surface area of ​​the ferrite particles is 0.070 m². 2 / g or more 0.150m 2 When the BET specific surface area is within this range, using these ferrite particles as a carrier core material for electrophotographic developers ensures an effective charged area for the charged carrier that contributes to the toner, resulting in stable and good image density.

[0188] Based on these effects, the lower limit of the BET specific surface area of ​​the ferrite particles is preferably greater than 0.070 m².2 / g, preferably 0.080m 2 / g. Furthermore, the upper limit is preferably less than 0.150m. 2 / g, more preferably 0.130m 2 / g, further preferably 0.120m 2 / g.

[0189] The BET specific surface area can be obtained using the "Automatic Specific Surface Area Measuring Apparatus GEMINI 2360" (manufactured by Shimadzu Corporation), by measuring the amount of N2 adsorbed by the carrier particles used to adsorb N2 as the adsorbed gas. Here, the measuring tube used to measure this N2 adsorption amount is preheated under reduced pressure at 50°C for 2 hours before measurement. Furthermore, 5g of carrier particles are filled into the measuring tube, pretreated under reduced pressure at 30°C for 2 hours, and then allowed to adsorb N2 gas at 25°C, and the adsorption amount is measured. These adsorption amounts are calculated using the BET formula by plotting adsorption isotherms.

[0190] (10) Average volumetric particle size (D) 50 )

[0191] The average volumetric particle size (D) of the ferrite particles 50 The preferred particle size is 20 μm or larger and 80 μm or smaller. The volume average particle size (D) of the ferrite particles is... 50 If within this range, ferrite particles suitable for various applications can be produced.

[0192] Furthermore, when this ferrite particle is used as a carrier core material for an electrophotographic developer, the volume average particle size (D) of the ferrite particle is... 50 The preferred size is 25μm or more and 50μm or less. By setting it within this range, carrier adhesion can be suppressed and uneven image development can be prevented.

[0193] The average volumetric particle size (D) mentioned here 50The value refers to the value determined by laser diffraction and scattering according to JIS Z 8825:2013. Specifically, it can be determined using a microtrac particle size analyzer (Model 9320-X100) manufactured by Nikkiso Co., Ltd., as follows: First, the ferrite particles to be measured are used as the sample. 10g of the sample and 80ml of water are placed in a 100ml beaker, and 2-3 drops of dispersant (sodium hexametaphosphate) are added. Using an ultrasonic homogenizer (UH-150 type manufactured by SMT.Co.LTD.), the output level is set to 4, and dispersion is performed for 20 seconds. By removing the bubbles that have accumulated on the surface of the beaker, the sample is prepared. Using this sample, the volume average particle size of the sample measured by the microtrac particle size analyzer is taken as the average volume particle size (D) of the sample. 50 ).

[0194] 2. Carrier for electrophotographic developing agents

[0195] Next, the carrier for electrophotographic developer of this invention will be described. The carrier for electrophotographic developer of this invention includes the ferrite particles and a resin coating layer covering the surface of the ferrite particles. That is, the ferrite particles are used as the core material of the carrier for electrophotographic developer. Since the ferrite particles used as the core material of the carrier for electrophotographic developer are as described above, the description here will mainly focus on the resin coating layer.

[0196] (1) Types of coating resins

[0197] The type of resin constituting the resin coating layer (coating resin) is not particularly limited. For example, fluoropolymers, acrylic resins, epoxy resins, polyimide resins, polyamide-imide resins, polyester resins, unsaturated polyester resins, urea resins, melamine resins, acid-alcohol resins, phenolic resins, fluoroacrylic resins, acrylic-styrene resins, and silicone resins can be used. Furthermore, modified silicone resins, such as silicone resins modified with various resins including acrylic resins, polyester resins, epoxy resins, polyimide resins, polyamide-imide resins, acid-alcohol resins, polyurethane resins, and fluoropolymers, can also be used. For example, from the viewpoint of suppressing resin peeling caused by mechanical stress during mixing with a colorant, a thermosetting resin is preferred for the coating resin. Examples of thermosetting resins suitable for this coating resin include epoxy resins, phenolic resins, silicone resins, unsaturated polyester resins, urea resins, melamine resins, acid-alcohol resins, and resins containing these. As mentioned above, the type of coating resin is not particularly limited, and an appropriate resin can be selected based on the type of toner used in the combination or the environment of use.

[0198] Furthermore, a single resin can be used to form the resin coating layer, or two or more resins can be used. When using two or more resins, they can be mixed to form a single resin coating layer, or multiple resin coating layers can be formed. For example, a first resin coating layer with good adhesion to the ferrite particles is provided on the surface of the ferrite particles, and a second resin coating layer for imparting desired charge-imparting properties to the carrier is preferably also provided on the surface of the first resin coating layer.

[0199] (2) Resin coating amount

[0200] The amount of resin coating the surface of the ferrite particles (resin coating amount) is preferably 0.1% to 10% by mass relative to the ferrite particles used as the core material. When the resin coating amount is less than 0.1% by mass, it is difficult to adequately coat the surface of the ferrite particles with resin, and it may be difficult to obtain the desired charge-imparting ability. Furthermore, when the resin coating amount exceeds 10% by mass, the carrier particles agglomerate during manufacturing, resulting in reduced productivity such as lower yield, and the developer properties, such as the flowability of the developer in the machine or the charge-imparting properties of the toner, may change.

[0201] (3) Additives

[0202] The resin coating layer may also contain additives intended to control the resistance, charge, or charging speed of the carrier, such as a conductive agent or charge control agent. Examples of conductive agents include oxides of conductive carbon, titanium dioxide, or tin oxide, or various organic conductive agents. Since conductive agents have low resistance, excessive addition can easily cause charge leakage. Therefore, the content of the conductive agent relative to the solid content of the coating resin is preferably 0.25% by mass to 20.0% by mass, more preferably 0.5% by mass to 15.0% by mass, and even more preferably 1.0% by mass to 10.0% by mass.

[0203] Examples of charge control agents include various charge control agents or silane coupling agents commonly used as toners. The types of these charge control agents or coupling agents are not particularly limited, but aniline black dyes, quaternary ammonium salts, organometallic compounds, charge control agents containing metal monoazo dyes, amino-silane coupling agents, or fluorinated silane coupling agents are preferably used. The content of the charge control agent relative to the solid content of the coating resin is preferably 0.25% by mass to 20.0% by mass, more preferably 0.5% by mass to 15.0% by mass, and even more preferably 1.0% by mass to 10.0% by mass.

[0204] 3. Electrophotographic developer

[0205] Next, an embodiment of the electrophotographic developer of this invention will be described. This electrophotographic developer includes a carrier and a toner.

[0206] As a toner constituting the electrophotographic developer, either a polymeric toner manufactured by polymerization or a pulverized toner manufactured by pulverization can preferably be used. These toners contain various additives and can be any toner as long as they can be combined with the carrier for use as an electrophotographic developer.

[0207] The volume average particle size (D) of the toner 50 The preferred particle size is 2μm or larger and 15μm or smaller, more preferably 3μm or larger and 10μm or smaller. The volume average particle size (D) of the toner is... 50 Within this range, an electrophotographic developer capable of producing high-quality electronic photographs can be obtained.

[0208] The mixing 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. Electrophotographic developers containing toner at this concentration can easily achieve the desired image density and better suppress fogging or toner scattering.

[0209] The electrophotographic developer invented in this case can be used as a replenishing developer.

[0210] When the electrophotographic developer is used as a replenishing developer, the mixing ratio of the carrier to the toner is preferably 2 to 50 parts by mass of the toner relative to 1 part by mass of the carrier.

[0211] This electrophotographic developer is applicable to various electrophotographic developing devices using the magnetic brush developing method, which uses magnetic force to attract and attach a carrier to a magnetic drum, forming a brush shape, transferring toner, and simultaneously applying a bias electric field to allow the toner to adhere to a photoreceptor, thus creating a visible image of an electrostatic latent image. This electrophotographic developer can be used not only in electrophotographic developing devices that use a DC bias electric field when applying the bias electric field, but also in electrophotographic developing devices that use an AC bias electric field superimposed on a DC bias electric field.

[0212] 4. Manufacturing method

[0213] The following describes the ferrite particles, carrier core material for electrophotographic developers, carrier for electrophotographic developers, and manufacturing method of electrophotographic developers of this invention.

[0214] 4-1. Ferrite particles and carrier core materials for electrophotographic developers

[0215] The ferrite particles and carrier core material for electrophotographic developers of this invention, except for the firing and cooling processes described later, can be manufactured using the general manufacturing method for ferrite particles used in applications such as electrophotographic developer carrier core materials. Furthermore, it is preferable to perform the raw material mixing process and surface heat treatment process as described later.

[0216] Furthermore, the method for manufacturing ferrite particles according to the present invention is a method for manufacturing ferrite particles for manufacturing the aforementioned ferrite particles, comprising:

[0217] The process of mixing Fe raw materials containing Fe, Mn raw materials containing Mn, and Mg raw materials containing Mg in a predetermined amount to obtain a mixture;

[0218] The process of obtaining granules using the mixture;

[0219] The process involves using a closed-atmosphere heat treatment furnace, which has a closed heat treatment chamber capable of controlling the firing atmosphere and a cooling chamber capable of controlling the cooling atmosphere to be different from the firing atmosphere, to fire the granules in the closed heat treatment chamber to obtain the fired product.

[0220] A cooling process in which the fired product is cooled to below 250°C in a cooling chamber where the oxygen concentration is controlled to be less than 0.3% by volume, without exposing the product to outside air; and

[0221] A process of performing surface heat treatment on the fired product after the cooling process.

[0222] The following sections will describe the raw material mixing process, granulation process, firing process, cooling process, post-cooling process, and surface heat treatment process in sequence.

[0223] 4-1-1. Raw material mixing process

[0224] In the raw material mixing process, Fe raw material, Mn raw material, and Mg raw material are weighed and mixed in such a way that the ferrite particle body represented by the formula (1) is obtained and the spinel component after calcination becomes the desired component. As the Fe raw material, iron oxide such as Fe2O3 can be used. As the Mn raw material, MnO2, Mn2O3, Mn3O4, MnCO3, etc. can be used. As the Mg raw material, MgO, Mg(OH)2, MgCO3, etc. can be used. Furthermore, in the case of obtaining ferrite particles containing Sr, Sr oxides or carbonates can be used as raw materials.

[0225] Here, based on obtaining the ferrite particles of the present invention, it is preferred that the raw material configuration ratio satisfies the following formula (4).

[0226] 0.80≦n Fe / (nMn +n Mg )<2.00···(4)

[0227] in,

[0228] n Fe The amount of Fe element in the Fe raw material (mol%)

[0229] n Mn The amount of Mn element in the Mn raw material (mol%)

[0230] n Mg The amount of Mg element in the Mg raw material (mol%)

[0231] In the above equation (4), “(n Mn +n Mg ")" indicates the amount of raw material at site A in the general formula "AB2O4", and "n" represents the amount of raw material at site A. Fe "" indicates the amount of raw material at site B. By combining the raw materials in a manner that satisfies the above formula (4), and with the stoichiometry corresponding to the above formula (1) as described above, mixing the raw materials with a larger amount of raw material at site A, the lattice constant of the ferrite produced is approximately That is, an A-rich ferrite as defined above is manufactured. Therefore, ferrite particles of the present invention that satisfy formulas (1) and (2) can be manufactured well. When the value of formula (4) below is 2.00 or higher, for the stoichiometry corresponding to formula (1), if the raw materials are mixed in an equal or greater amount of Fe raw material, the lattice constant of the manufactured ferrite may be less than 2.00. That is, it is possible to manufacture B-rich ferrites as defined above. Therefore, there are cases where it is difficult to obtain ferrite particles that satisfy equations (1) and (2). On the other hand, if the value of equation (4) below is less than 0.80, the Fe raw material becomes too little, and the desired saturation magnetization cannot be obtained, making it easy for carrier adhesion to occur.

[0232] Furthermore, after weighing the raw materials in a predetermined amount, they are pulverized and mixed using a ball mill, sand mill, or vibratory mill, either wet or dry, for at least 1 hour, preferably 1 to 20 hours.

[0233] 4-1-2. Granulation Process

[0234] Next, water is added to the mixture of raw materials that have been pulverized and mixed, and the mixture is then finely pulverized using a bead mill or similar device to obtain a slurry. The degree of pulverization can be controlled by adjusting the diameter, composition, and pulverization time of the beads used as a medium. While ensuring uniform dispersion of the raw materials, beads with a particle size of 1 mm or less are preferably used as the medium. Furthermore, while ensuring uniform dispersion of the raw materials, it is preferable to use the volume average particle size (D) of the pulverized material. 50 The particle size should be pulverized to a size of 2.5 μm or less, preferably 2.0 μm or less. Furthermore, to suppress abnormal grain growth, it is preferable to pulverize the particle size (D) on the rough side of the particle size distribution. 90 The slurry is pulverized to a particle size of 3.5 μm or less. Preferably, the resulting slurry is further pulverized by adding dispersants, binders, etc., as needed, to adjust the viscosity to 2 poise or more and 4 poise or less. In this case, polyvinyl alcohol or polyvinylpyrrolidone can be used as the binder.

[0235] The slurry prepared as described is sprayed using a spray dryer, and granules are obtained by drying it.

[0236] Next, before firing the granules, they are classified to remove fine particles, which is preferable in order to obtain ferrite particles with uniform particle size. The granules can be classified using known air classifiers or sieves.

[0237] However, in the manufacturing process of ferrite particles, a pre-firing process is usually performed before preparing the slurry, in which the mixture of raw materials is pre-fired. Furthermore, after obtaining the granules, a so-called debinding process is often performed to remove organic components such as dispersants or binders from the granules. However, in manufacturing the ferrite particles of the present invention, it is preferable not to perform the pre-firing process or the debinding process. Before the main firing process, a heat treatment process is performed, in which the ferrite formation reaction is partially carried out by heating the mixture of raw materials. Therefore, the granules contain seed crystals that form a crystalline portion of the spinel structure. After the main firing of such granules, the seed crystals become the starting point for crystal growth, and internal pores are easily generated in the ferrite particles obtained after the main firing. Therefore, the magnetization of the ferrite particles is easily reduced. Furthermore, at this time, it is difficult to control the crystal growth of each particle to be equal during the main firing process, and the size of the internal pores in each particle is easily uneven. Therefore, based on obtaining ferrite particles suitable for high-speed printing carrier core materials with low internal porosity and no low magnetization particles compared to other particles, it is not preferable to perform heat treatment such as pre-firing process or debinding process on the raw material mixture powder or granules before the main firing process, provided that the ferrite reaction can be carried out.

[0238] 4-1-3. Firing process

[0239] Based on obtaining ferrite particles that satisfy the above formulas (1) and (2), the sintering process is carried out as follows.

[0240] (1) Firing furnace

[0241] During firing, a closed-atmosphere heat treatment furnace is used, which has a closed heat treatment chamber capable of controlling the firing atmosphere and a cooling chamber capable of controlling the cooling atmosphere to be different from the firing atmosphere. Examples of such closed-atmosphere heat treatment furnaces include tunnel furnaces and elevator furnaces. Furthermore, in such a continuous furnace, the granules are placed in a refractory container such as a sagger and passed through the heating section while stationary, thereby enabling thorough sintering of the granules' interior, resulting in a fired product with high magnetization and high resistivity, which easily produces a spinel-type crystal phase. Furthermore, this fired product becomes the main body of ferrite particles.

[0242] Furthermore, by using a closed-atmosphere firing furnace capable of controlling the furnace atmosphere, the firing atmosphere within the closed heat treatment chamber can be adjusted to a firing atmosphere preferred for manufacturing ferrite particles satisfying formulas (1) and (2), making it easy to adjust the firing atmosphere of each particle within the refractory container to be identical. Moreover, the preferred firing atmosphere for manufacturing ferrite particles satisfying formulas (1) and (2) will be described later.

[0243] (2) Firing atmosphere

[0244] Based on the manufacture of the ferrite particles of the present invention, it is preferable to use an oxygen-free atmosphere in the firing atmosphere with an oxygen concentration of less than 0.1 vol% (1000 ppm). By setting the firing atmosphere to such an oxygen-free atmosphere, a ferrite particle body that satisfies the above formulas (1) and (2) can be obtained.

[0245] (3) Firing temperature, etc.

[0246] The firing temperature and firing time can be selected from the preferred conditions for producing spinel-based ferrite particles (ferrite particle body). For example, it is preferable to hold the firing at a temperature of 850°C or higher for 4 to 24 hours. In this case, it is preferable to hold the firing at a temperature suitable for the formation of ferrite particles with a spinel-type crystal structure for 3 hours or more. However, the firing temperature or holding time is not particularly limited as long as ferrite particles satisfying formulas (1) and (2) can be obtained.

[0247] 4-1-4. Cooling process

[0248] After obtaining the sintered product by firing the granules in a closed heat treatment chamber in the manner described above, the sintered product is not exposed to outside air and is cooled to below 250°C in a cooling chamber where the oxygen concentration is controlled to be less than 0.3% by volume. After firing, the surface temperature of the sintered product is high, and the surface of the sintered product becomes highly reactive. Ferrites fired in a low-oxygen atmosphere are believed to form an oxygen-deficient spinel-type crystal structure. Therefore, as described above, if the sintered product comes into contact with oxygen in the atmosphere, the surface of the sintered product oxidizes, forming an oxide film and becoming highly resistive. Therefore, in this invention, after obtaining the sintered product, it is not exposed to outside air, and the sintered product is cooled in a cooling chamber with controlled atmosphere as described above, thereby enabling the sintered product to be removed from the furnace in a state where the surface activity of the sintered product is reduced.

[0249] The firing and cooling processes are configured to use a closed heat treatment furnace having a closed heat treatment chamber that can control the firing atmosphere as described above, and a cooling chamber that can control the cooling atmosphere to be different from the firing atmosphere.

[0250] When the oxygen concentration in the cooling chamber is 0.3% by volume or higher, the sintered material is transported into the cooling chamber in a state of high surface activity. Thus, although it does not come into contact with the outside air, it reacts with the oxygen in the cooling chamber, forming an oxide film on the surface of the sintered material as described above. Therefore, in subsequent surface heat treatment processes, it is difficult to form a coating layer with a lattice constant that satisfies the relationship between the lattice constant of the ferrite particle matrix and Equation (2), which is therefore not preferred.

[0251] From the above perspective, the atmospheric oxygen concentration in the cooling chamber is preferably below 0.2% by volume, and more preferably below 0.1% by volume.

[0252] 4-1-5. Surface heat treatment process

[0253] The cooled calcined material, as described above, is used as the object for surface heat treatment, and the calcined material is subjected to surface heat treatment. A rotary furnace is used for surface heat treatment. At this time, when the inner diameter of the rotary combustion chamber of the rotary furnace is set to L (m), the rotation speed is set to X (rpm), and the surface heat treatment time is set to t (min), the following formula (3) is preferably satisfied.

[0254] 20≦LπXt≦60···(3)

[0255] As such a rotary furnace, a rotary continuous furnace, such as a rotary drying furnace, is preferred. The rotary drying furnace includes a rotary combustion chamber, an inlet for feeding the surface heat-treated material (heat-treated material) into the rotary combustion chamber, and an outlet for discharging the surface heat-treated material from the rotary combustion chamber. It is capable of continuously feeding the surface heat-treated material into the rotary combustion chamber from the inlet at a predetermined feed rate. The rotary combustion chamber is typically roughly cylindrical in shape and has a gently descending slope from the inlet towards the outlet. The surface heat-treated material fed into the inlet rotates within the rotary combustion chamber while moving towards the outlet. The surface heat treatment time (t) is the time it takes for the surface heat-treated material to be discharged from the rotary combustion chamber via the outlet after being fed into the inlet; it represents the time during which the surface heat-treated material (each particle) rotates and passes through the rotary combustion chamber in t hours.

[0256] When the surface of the sinter is heat-treated using such a rotary furnace, the surface of the sinter undergoes thermal decomposition. The surface portion of the sinter, as described, becomes 3(Mgx, Mn(1-x))Fe2O4 → (1-x)Mn3O4 + 3xMgFe2O4 + 2(1-x)Fe3O4, forming a coating layer composed of a complex containing Mn3O4, Fe3O4, and MgFe2O4, with the ferrite particle body inside. When the surface of the sinter is heat-treated with the value of Equation (3) within the aforementioned range, the surface of the sinter undergoes sufficient thermal decomposition. As a result, a coating layer of uniform thickness is formed on the surface of the ferrite particle body, and ferrite particles satisfying Equations (1) and (2) can be obtained.

[0257] In this regard, when the value of Equation (3) is less than 20, the surface of the fired object cannot be sufficiently heat-treated, and a coating layer of uniform thickness may not be formed on the surface of the fired object. In this case, the coating layer is formed locally on the surface of the ferrite particle body represented by Equation (1), or the thickness becomes thinner, and the value of Equation (2) may be less than the lower limit. On the other hand, when the value of Equation (3) is greater than 60, excessive thermal decomposition of the surface occurs, the amount of Mn3O4 generated increases, and as a result, the value of Equation (2) may exceed the upper limit.

[0258] Based on these points of view, the lower limit of equation (3) is preferably greater than 20. Furthermore, the upper limit is preferably less than 60, more preferably 50, and even more preferably 40.

[0259] Furthermore, this surface heat treatment is preferably performed in an oxygen-containing atmosphere such as air at a temperature of 350°C to 600°C, more preferably 400°C to 550°C. By performing surface heat treatment on the surface of the object to be heat treated under such conditions, ferrite particles satisfying formulas (1) and (2) can be manufactured more appropriately.

[0260] On the other hand, when the surface heat treatment temperature is less than 350°C, the surface of the fired object cannot be sufficiently heated, and sometimes a coating layer of uniform thickness cannot be formed on the surface of the fired object. On the other hand, when the surface heat treatment temperature is higher than 600°C, oxidation reactions of Fe2O3 and Mn3O4 produced by thermal decomposition may occur. Specifically, reactions such as 2Fe3O4 + 1 / 2O2 → 3Fe2O3 and 2Mn3O4 + 1 / 2O2 → 3Mn2O3 occur, and the value of equation (2) may exceed the upper limit. In addition, at this time, the saturation magnetization of the ferrite particles may decrease.

[0261] 4-1-6. Crushing and Grading Process

[0262] The fired product or the fired product after the cooling process and / or surface heat treatment process is crushed and classified. As a classification method, existing methods such as air classification, screen filtration, and sedimentation can be used to adjust the particle size to the desired size. In the case of dry recovery, recovery can also be achieved using hydrocyclones or similar methods. When adjusting the particle size, two or more of the aforementioned classification methods can be selected and implemented, or the conditions of one classification method can be changed to remove coarse and fine particles. Especially preferred is the surface heat treatment process performed after the cooling process, crushing, and classification, which allows for uniform surface heat treatment of the fired product.

[0263] 4-2. Carriers for Electrophotographic Developers

[0264] The carrier for the electrophotographic developer of this invention uses ferrite particles as the core material and forms a resin coating layer on the surface of the ferrite particles. The resin constituting the resin coating layer is as described above. Known methods can be used to form the resin coating layer on the surface of the ferrite particles, such as brush coating, spray drying using a fluidized bed, rotary drying, and immersion drying using a universal mixer. To increase the proportion of resin coverage area (resin coating rate) on the surface of the ferrite particles, spray drying using a fluidized bed is preferred. Even when using any of these methods, the ferrite particles can be resin coated once or multiple times. The resin coating solution used to form the resin coating layer may also contain the aforementioned additive. Furthermore, since the amount of resin coating on the surface of the ferrite particles is as described above, further details are omitted here.

[0265] After coating the ferrite particles with a resin coating solution, sintering can be performed using either external or internal heating methods, depending on the requirements. External heating methods can utilize stationary or mobile electric furnaces, rotary electric furnaces, combustion furnaces, etc. Internal heating methods can utilize microwave ovens. If a UV-curable resin is used for the coating, a UV heater is employed. Sintering must be performed at a temperature above the melting point or glass transition point of the coating resin. When using thermosetting resins or condensation-crosslinking resins as the coating resin, sintering must be performed at the temperature at which these resins have fully developed their curing properties.

[0266] 4-3. Electrophotographic developing agent

[0267] Next, the method for manufacturing the electrophotographic developer of the present invention will be described.

[0268] The electrophotographic developer of the present invention includes a carrier for the electrophotographic developer and a toner. As described above, the toner can preferably be either a polymerized toner or a pulverized toner.

[0269] Polymer toners can be manufactured using known methods such as suspension polymerization, emulsion polymerization, emulsion agglomeration, ester elongation polymerization, and phase inversion emulsification. For example, a coloring dispersion obtained by dispersing a colorant in water using a surfactant, a polymerizable monomer, a surfactant, and a polymerization initiator are mixed and stirred in an aqueous medium. This emulsifies and disperses the polymerizable monomer in the aqueous medium, and polymerization occurs simultaneously with stirring and mixing. A salting-out agent is then added to cause the polymer particles to salt out. The salted-out particles are filtered, washed, and dried to obtain the polymer toner. Additives can then be added to the dried toner particles as needed.

[0270] Furthermore, when manufacturing the polymeric toner particles, a toner composition comprising polymerizable monomers, surfactants, polymerization initiators, colorants, etc., is used. This toner composition can be combined with a fixation modifier and a charge control agent.

[0271] Toner powdering involves thoroughly mixing adhesive resins, colorants, charge control agents, etc., using a mixer such as a Henschel mixer, followed by melt kneading using a twin-screw extruder, cooling, and then micronizing by a jet mill or similar method. After classification, such as by an air classifier, toner powders of the desired particle size can be obtained. Depending on the requirements, it may contain wax, magnetic powder, viscosity modifiers, and other additives. Additives can also be added after classification.

[0272] Example

[0273] Next, embodiments and comparative examples will be shown to specifically illustrate the invention. However, the invention is not limited to the embodiments described below.

[0274] [Example 1]

[0275] (1) Ferrite particles

[0276] In Example 1, MnO, MgO, Fe2O3, and SrO raw materials were weighed in proportions of 50.0 mol%, 4.0 mol%, 46.0 mol%, and 0.8 mol%, respectively. Here, manganese tetroxide was used as the MnO raw material, magnesium hydroxide as the MgO raw material, ferrous oxide as the Fe2O3 raw material, and strontium carbonate as the SrO raw material. Furthermore, regarding formula (4), n... Fe =46.0 × 2 = 92.0, n Mn =50.0, n Mg =4.0, n Fe / (n Mn +n Mg =1.70.

[0277] Next, the weighed raw materials were pulverized for 5 hours using a dry media mill (vibratory mill with 1 / 8-inch diameter stainless steel beads), and a slurry binder and dispersant were added. As a binder, PVA (polyvinyl alcohol, 20% by mass solution) was used, with 0.2% by mass of PVA added relative to the solid content (amount of raw materials in the slurry). As a dispersant, a polycarboxylic acid dispersant was added to adjust the slurry viscosity to 2 poise. Then, the slurry was granulated and dried using a spray dryer.

[0278] Subsequently, the granules were fired in a tunnel furnace, which serves as a closed-atmosphere heat treatment furnace, for 5 hours inside the closed heat treatment chamber at a firing temperature (holding temperature) of 1250°C and an oxygen concentration of 0.0% by volume. At this time, the heating rate was set to 150°C / hour.

[0279] The resulting fired object is kept away from external air and cooled in a cooling chamber with an oxygen concentration controlled at 0.0% by volume until it reaches 100°C. The temperature that the fired object should reach during the subsequent cooling process is called the cooling temperature.

[0280] Furthermore, the tunnel furnace used in this embodiment is continuously equipped with a sealed heat treatment chamber and a cooling chamber, which allows the sintered material contained in the sagger to be transported to the cooling chamber via a belt conveyor without contact with outside air. Moreover, since the sealed heat treatment chamber and the cooling chamber are independent, the cooling chamber can be controlled to have a different atmosphere than the sealed heat treatment chamber.

[0281] The calcined material, which has reached the specified cooling temperature (100°C), is crushed using an impact crusher, i.e., a hammer crusher. It is then further classified using a rotary converter that employs an intermittent old classification method and a turbine classifier that is classified as an airflow classification chamber rotary type to adjust the particle size. Low magnetic products are then separated by magnetic separation.

[0282] Then, the inner diameter L (m) of the rotary incineration chamber is adjusted by using a rotary drying furnace to make the value of the formula (3) (LπXt) 60, the rotation speed X (rpm) and the surface heat treatment time t (min) are adjusted, and the surface of the calcined product cooled at 450°C is subjected to heat treatment.

[0283] The ferrite particles of Example 1 are obtained through the above process.

[0284] (2) Carrier for electrophotographic developing agents

[0285] Using the ferrite particles as the core material, a resin coating layer is formed on the surface of the ferrite particles in the following manner to obtain the carrier of Example 1.

[0286] First, a condensation-crosslinked silicone resin (weight average molecular weight: approximately 8000) with T units and D units as the main components was prepared. 2.5 parts by mass of this silicone resin solution (0.5 parts by mass of the solid component of the silicone resin, diluted with toluene, since a 20% by mass solution was used) and 100 parts by mass of the ferrite particles were mixed and stirred using a universal mixer, allowing the toluene to evaporate while simultaneously coating the surface of the ferrite particles with silicone resin. After confirming that the toluene had fully evaporated, the mixture was removed from the apparatus and placed in a container, where it was heated in a hot air-heated oven at 250°C for two hours. Afterward, it was cooled to room temperature, and the resin-cured ferrite particles were removed. The particles were then loosened using a vibrating screen with a 200-mesh opening, and non-magnetic materials were removed using a magnetic separator. Subsequently, coarse particles were again removed using a vibrating screen with a 200-mesh opening, and the ferrite particles were used as the core material to obtain the carrier for the electrophotographic developer of Example 1, which has a resin coating layer on its surface.

[0287] [Example 2]

[0288] The raw materials were weighed in the following proportions: MnO: 58.0 mol%, MgO: 0.2 mol%, Fe2O3: 41.8 mol%, and SrO: 1.2 mol%. The firing temperature was set to 1270°C, the cooling temperature to be reached in the cooling process was set to 250°C, and the surface heat treatment temperature was set to 370°C. During the surface heat treatment, the value of formula (3) was set to "20". Ferrite particles were manufactured in the same manner as in Example 1, and ferrite particles of Example 2 were manufactured. In addition, the value of formula (4) was "1.44". Then, in addition to removing the ferrite particles, the carrier for the electron photographic developer of Example 2 was obtained in the same manner as in Example 1.

[0289] [Example 3]

[0290] The raw materials were weighed in the following proportions: MnO: 50.0 mol%, MgO: 0.1 mol%, Fe2O3: 49.9 mol%, and SrO: 0.8 mol%. The ferrite particles of Example 3 were manufactured in the same manner as in Example 1, with the firing temperature set to 1270°C and the surface heat treatment temperature set to 490°C, and the value of formula (3) during surface heat treatment being "40". Furthermore, the value of formula (4) was "1.99". Then, except for the use of the ferrite particles, the carrier for the electron photographic developer of Example 3 was obtained in the same manner as in Example 1.

[0291] [Example 4]

[0292] The raw materials were weighed in the following proportions: MnO: 58.0 mol%, MgO: 5.0 mol%, Fe2O3: 37.0 mol%, and SrO: 0.8 mol%. The firing temperature was set to 1230°C, the surface heat treatment temperature was set to 510°C, and the value of formula (3) during surface heat treatment was set to "60". Ferrite particles were manufactured in the same manner as in Example 1, resulting in ferrite particles of Example 4. Furthermore, the value of formula (4) was "1.17". Moreover, except for the use of these ferrite particles, the carrier for the electron photographic developer of Example 4 was obtained in the same manner as in Example 1.

[0293] [Example 5]

[0294] The raw materials were weighed in the following proportions: MnO: 55.0 mol%, MgO: 6.5 mol%, Fe2O3: 38.5 mol%, and SrO: 0.4 mol%. The firing temperature was set to 1240°C, and the surface heat treatment temperature was set to 500°C. The value of formula (3) during surface heat treatment was set to "40". Ferrite particles were manufactured in the same manner as in Example 1, thus producing ferrite particles for Example 5. Furthermore, the value of formula (4) was "1.25". Then, except for the use of these ferrite particles, the carrier for the electron photographic developer of Example 5 was obtained in the same manner as in Example 1.

[0295] [Example 6]

[0296] The raw materials were weighed in the following proportions: MnO: 71.3 mol%, MgO: 0.1 mol%, Fe2O3: 28.6 mol%, and SrO: 1.0 mol%. The firing temperature was set to 1260°C, the cooling temperature to be reached in the cooling process was set to 50°C, and the surface heat treatment temperature was set to 450°C. The value of formula (3) during surface heat treatment was set to "45". Ferrite particles were manufactured in the same manner as in Example 1, and ferrite particles of Example 6 were manufactured. In addition, the value of formula (4) was set to "0.80". Then, except for the use of these ferrite particles, the carrier for the electron photographic developer of Example 6 was obtained in the same manner as in Example 1.

[0297] [Comparative Example 1]

[0298] The raw materials were weighed in the following proportions: MnO: 40.4 mol%, MgO: 9.0 mol%, Fe2O3: 50.6 mol%, and SrO: 0.3 mol%. The firing temperature was set to 1180°C, the oxygen concentration in the firing atmosphere was 0.7 vol%, the cooling temperature to be reached in the cooling process was set to 300°C, the oxygen concentration in the cooling atmosphere was set to 0.6 vol%, the surface heat treatment temperature was set to 350°C, and the value of formula (3) during surface heat treatment was set to "15". Ferrite particles were manufactured in the same manner as in Example 1, and ferrite particles of Comparative Example 1 were manufactured. In addition, the value of formula (4) was "2.05". Then, except for the use of these ferrite particles, the carrier for the electron photographic developer of Comparative Example 1 was obtained in the same manner as in Example 1.

[0299] [Comparative Example 2]

[0300] The raw materials were weighed in the following proportions: MnO: 45.0 mol%, MgO: 2.0 mol%, Fe2O3: 53.0 mol%, and SrO: 0.8 mol%. The firing temperature was set to 1200°C, and the oxygen concentration in the firing atmosphere was 0.0 vol%. The cooling temperature to be reached in the cooling process was set to 250°C, and the oxygen concentration in the cooling atmosphere was set to 0.2 vol%. Ferrite particles were manufactured in the same manner as in Example 1, except that no surface heat treatment process was performed. The ferrite particles of Comparative Example 2 were thus manufactured. Furthermore, the value of formula (4) was "2.26". Then, except for the use of these ferrite particles, the carrier for the electrophotographic developer of Comparative Example 2 was obtained in the same manner as in Example 1.

[0301] [Comparative Example 3]

[0302] The raw materials were weighed in the following proportions: MnO: 46.0 mol%, MgO: 2.5 mol%, Fe2O3: 51.5 mol%, and SrO: 0.8 mol%. The firing temperature was set to 1200°C, the oxygen concentration in the firing atmosphere was 1.0 vol%, the cooling temperature to be achieved in the cooling process was set to 300°C, the oxygen concentration in the cooling atmosphere was set to 0.0 vol%, and the surface heat treatment temperature was set to 350°C. The value of formula (3) during surface heat treatment was set to "10". Ferrite particles were manufactured in the same manner as in Example 1 to produce ferrite particles for Comparative Example 3. Furthermore, the value of formula (4) was set to "2.12". Then, excluding the aspect of using the ferrite particles, the carrier for the electron photographic developer of Comparative Example 3 was obtained in the same manner as in Example 1.

[0303] [Comparative Example 4]

[0304] The raw materials were weighed in the following proportions: MnO: 35.0 mol%, MgO: 6.0 mol%, Fe2O3: 59.0 mol%, and SrO: 1.3 mol%. The firing temperature was set to 1150°C, the oxygen concentration in the firing atmosphere was 0.0 vol%, the cooling temperature to be reached by the fired product in the cooling process was set to 250°C, the oxygen concentration in the cooling atmosphere was set to 0.5 vol%, and the surface heat treatment temperature was set to 520°C. The value of formula (3) during surface heat treatment was "62". Except for this, ferrite particles were manufactured in the same manner as in Example 1 to produce the ferrite particles of Comparative Example 4. In addition, the value of formula (4) was "2.88". Then, excluding the aspect using these ferrite particles, the carrier for the electron photographic developer of Comparative Example 4 was obtained in the same manner as in Example 1.

[0305] [Comparative Example 5]

[0306] The raw materials were weighed in the following proportions: MnO: 50.0 mol%, MgO: 1.0 mol%, Fe2O3: 49.0 mol%, and SrO: 1.0 mol%. The firing temperature was set to 1230°C, the oxygen concentration in the firing atmosphere was set to 0.7 vol%, the cooling temperature to be reached in the cooling process was set to 200°C, and the oxygen concentration in the cooling atmosphere was set to 0.0 vol%. Ferrite particles were manufactured in the same manner as in Example 1, except that no surface heat treatment process was performed. The ferrite particles of Comparative Example 1 were manufactured. In addition, the value of the above formula (4) is "1.92". Then, except for the use of these ferrite particles, the carrier for the electron photographic developer of Comparative Example 5 was obtained in the same manner as in Example 1.

[0307] [Comparative Example 6]

[0308] The raw materials were weighed in the following proportions: MnO: 36.0 mol%, MgO: 2.0 mol%, Fe2O3: 62.0 mol%, and SrO: 0.8 mol%. The firing temperature was set to 1200°C, and the oxygen concentration in the firing atmosphere was set to 1.1 vol%. The cooling temperature to be reached by the fired product in the cooling process was set to 300°C, and the oxygen concentration in the cooling atmosphere was set to 0.4 vol%. The surface heat treatment temperature was set to 520°C, and the value of formula (3) during surface heat treatment was set to "70". Except for this, ferrite particles were manufactured in the same manner as in Example 1, and ferrite particles of Comparative Example 1 were manufactured. In addition, the value of formula (4) was "3.26". Then, except for the use of the ferrite particles, the carrier for the electron photographic developer of Comparative Example 6 was obtained in the same manner as in Example 1.

[0309] Table 1 shows the manufacturing conditions of the ferrite particles in each embodiment and comparative example.

[0310] [evaluate]

[0311] 1. Evaluation Methods

[0312] (1) Crystal structure

[0313] For the ferrite particles in the various embodiments and comparative examples, the full width at half maximum (FWHM) of the (311) plane in the powder X-ray diffraction pattern, (b) the lattice constants of the ferrite particle bulk and the coating layer were determined by the method described above, and (c) the difference in lattice constant D between the ferrite particle bulk and the coating layer was calculated. LC .

[0314] (2) The value of “x” and the “Sr content”

[0315] ICP luminescence analysis was performed using the method described above to obtain the value of “x” and “Sr content” in equation (1).

[0316] (3) Basic characteristics

[0317] For the ferrite particles of the various embodiments and comparative examples, the following parameters were measured by the method: (a) saturation magnetization, (b) surface roughness Rz, (c) apparent density (AD), and (d) BET specific surface area.

[0318] (4) Image quality characteristics

[0319] Using the carriers for electrophotographic developers manufactured in the various embodiments and comparative examples, electrophotographic developers were modulated in the following manner, and the following were evaluated: (a) image density adaptability, (b) rate of change of charge over time, (c) image density stability, (d) carrier adhesion amount, and (e) toner scattering amount.

[0320] Electrophotographic developer is prepared in the following manner.

[0321] 18.6 g of carrier and 1.4 g of toner, prepared in each embodiment and comparative example, were mixed by stirring in a ball mill for 10 minutes to produce an electrophotographic developer with a toner concentration of 7.0% by mass. The toner used was a commercially available negative polarity toner (cyanide toner, for DocuPrint C3530 manufactured by Fuji Xerox Corporation) used in full-color printers; the average volume particle size (D...)... 50 (Approximately 5.8 μm).

[0322] (a) Image density adaptability

[0323] Using the electrophotographic developer as described as a sample, the image density suitability was determined using a charge measurement device according to the following criteria.

[0324] As a charge measurement device, a magnetic roller with a total of 8 magnets (magnetic flux density 0.1T) alternating between N and S poles is disposed inside a cylindrical aluminum tube (bottom, sleeve) with a diameter of 31 mm and a length of 76 mm. A cylindrical electrode with a 5.0 mm gap to the sleeve is disposed on the outer periphery of the sleeve. Then, after uniformly attaching 0.5 g of electrophotographic developer (as a sample) to the sleeve, with the outer aluminum tube fixed, the inner magnetic roller is rotated at 80 rpm while a DC voltage of 2000 V is applied between the outer electrode and the sleeve for 60 seconds, causing the toner to migrate to the outer cylindrical electrode. The mass of toner migrated to the outer electrode (toner migration amount) is measured. Similarly, the toner migration amount is also measured when a DC voltage of 2500 V is applied between the outer electrode and the sleeve for 60 seconds. An electrometer (KEITHLEY model 6517A insulation resistance meter) was used as the outer cylindrical electrode. Then, the toner migration amount when the applied voltage was 2000V was set as T2K, and the toner migration amount when the applied voltage was 2500V was set as T2.5K. The reproducibility of the image density when the applied voltage changed according to the following formula was evaluated as the image density adaptability.

[0325] Image density adaptability (%) = (T2.5K - T2K) / T2.5K × 100

[0326] Based on the image concentration adaptability values ​​obtained for each sample, evaluations from A to D are performed using the following criteria.

[0327] A: Less than 5%

[0328] B: 5% or more but less than 10%

[0329] C: 10% or more but less than 15%

[0330] D: 15% or more

[0331] (b) Rate of change of charge over time

[0332] The charge was measured as follows. Using the electrophotographic developer prepared as described, the sample was exposed to an atmosphere of 20±5°C and 50±5% relative humidity for one day. Then, using the same charge measuring apparatus as used to evaluate image density adaptability, a DC voltage of 2500V was applied for 60 seconds, causing the toner to move 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 toner that had moved to the outer electrode. The charge was calculated based on the measured charge and the mass of the toner that had moved. This charge was set as the charge before stirring.

[0333] Furthermore, the electrophotographic developer prepared as described was placed in a 50ml glass bottle and stirred for 10 hours at 150rpm using a paint mixer manufactured by Asada Iron Works Co., Ltd. The developer was then removed, and a DC voltage of 2500V was applied for 60 seconds using the same charge measuring device used to evaluate image density adaptability, causing the toner to move to the outer electrode. At this time, an electrometer (KEITHLEY insulation resistance meter model6517A) was connected to the cylindrical electrode to measure the charge of the toner that had moved to the outer electrode. The charge was calculated based on the measured charge and the mass of the toner that had moved. This was taken as the charge after forced stirring (charge after stirring).

[0334] Then, the rate of change of charge over time is calculated according to the following formula, and evaluated according to the following criteria.

[0335] The rate of change of charge over time (%) =

[0336] |(charge after stirring) - (charge before stirring)| / (charge before stirring) × 100

[0337] A: Less than 1.5%

[0338] B: 1.5% or more but less than 3.0%

[0339] C: 3.0% or more but less than 5.0%

[0340] D: 5.0% or more

[0341] (c) Image density stability

[0342] Using the electrophotographic developer as described, the charge on the carrier after exposing the sample to an atmosphere of 60°C and 80% relative humidity for one day was measured in the same manner as the determination of the "rate of change of charge over time," and this was taken as the charge C1. Similarly, the charge on the carrier after exposing the sample to an atmosphere of 60°C and 80% relative humidity for 15 days was measured, and this was taken as the charge C15.

[0343] Then, the rate of change of charge is calculated according to the following formula, and the image concentration stability is evaluated based on the following benchmarks according to the rate of change of charge.

[0344] Rate of change of charge (%) = |C1 - C15| / C1 × 100

[0345] A: Less than 5%

[0346] B: 5% or more but less than 10%

[0347] C: 10% or more but less than 15%

[0348] D: 15% or more

[0349] (d) Carrier adhesion amount

[0350] Using the electrophotographic developer as described, carrier adhesion was evaluated in the following manner.

[0351] Using the same charge measurement apparatus as used for evaluating image density adaptability, after uniformly attaching 1g of the electrophotographic developer to the sleeve, with the outer aluminum tube fixed, the inner magnetic roller rotates at 80 rpm while a DC voltage of 2500V is applied between the outer electrode and the sleeve for 90 seconds, causing the toner to move to the outer electrode. After 90 seconds, the applied voltage is cut off, the rotation of the magnetic roller is stopped, the outer electrode is removed, and the number of carrier particles attached along with the toner that has moved to the electrode is measured. Based on the measured number of carrier particles, an evaluation of A to D is performed according to the following criteria.

[0352] A: The number of attached carrier particles is less than 20.

[0353] B: The number of attached carrier particles is more than 20 but less than 40.

[0354] C: The number of attached carrier particles is more than 40 but less than 50.

[0355] D: The number of attached carrier particles is more than 50.

[0356] (e) Toner dispersion

[0357] A magnetic roller with a total of 8 magnets (magnetic flux density 0.1T) alternating between N and S poles is installed, along with a scraper mounted on the magnetic roller via a 1.0mm groove. A particle counter measuring unit is positioned 50mm away from the scraper in contact with the developer, serving as a toner dispersion measurement device. To suppress toner dispersion and measurement value fluctuations caused by external air influences, the toner dispersion measurement is performed in a cleanroom with a cleanliness level of 20±5℃ and 50±5% (Class 1000). Furthermore, the toner dispersion measurement involves rotating the magnetic roller at 80 rpm for 10 minutes, counting particles with a diameter of 5μm on the scraper, and calculating the particle count per minute (wherein, the number of particles per 1L volume) from the accumulated particle count. An evaluation from A to D is then performed according to the following criteria.

[0358] A: Less than 500 cells / L

[0359] B: 500 cells / L or more, less than 1000 cells / L

[0360] C: Above 1000 cells / L but less than 1600 cells / L

[0361] D: 1600 cells / L or more

[0362] Compared to actual machine evaluations (evaluating image density adaptability, charge change rate over time, image density stability, carrier adhesion, and toner dispersion using an actual machine (image forming apparatus), the evaluation method described above provides a more accurate assessment of the actual image quality characteristics of electrophotographic developers. In recent years, there have been instances where the performance of actual machines or electrophotographic developers has improved, resulting in almost no difference between actual machine performance and actual printing. Furthermore, there are also instances where the type of actual machine used in the experiment or the aging of the machine itself can cause deviations in the evaluation results. On the other hand, the alternative evaluation based on a charge measurement device, as described above, allows for precise control of the measurement conditions and expands the evaluation range compared to actual machine evaluations. Moreover, in the alternative evaluation, the rotation speed of each magnetic roller is set to an extremely low speed of 80 rpm. Therefore, the image quality characteristics of electrophotographic developers during printing on an actual machine with a medium-low continuous copying speed of 40 sheets / min or less can be evaluated more precisely.

[0363] 2. Evaluation Results

[0364] Table 2 shows various data related to the crystal structure obtained in each embodiment and comparative example. Table 3 shows the evaluation results of the basic properties of the ferrite particles for each embodiment and comparative example. Table 4 shows the evaluation results of the image quality properties of the electrophotographic developer using the ferrite particles of each embodiment and comparative example as the carrier core material.

[0365] (1) Crystal structure

[0366] As shown in Table 2, the ferrite particles in each embodiment are formulated according to the proportions of Fe, Mn, and Mg raw materials as described in formula (4)(n). Fe / (n Mn +n Mg The value of ()) is 0.80 or higher and less than 2.00. Various raw materials are combined to manufacture granules. When the surface heat treatment is set, the value of formula (3) (LπXt) is 20 or higher and less than 60. Thus, the difference between the lattice constant of the ferrite particle body and the lattice constant of the coating layer (D) LC )for The lattice constant of the ferrite particle bulk is The A-rich ferrite as defined above was obtained. Furthermore, ICP emission analysis confirmed that the value of "x" in formula (1) was 0.001 to 0.106. Therefore, formulas (1) and (2), and the ferrite particles of the present invention, were confirmed. Furthermore, the full width at half maximum (FWHM) of the (311) plane in the X-ray diffraction pattern of the ferrite particles of each embodiment was 0.26° to 0.33°, which is larger than that of the comparative example ferrite particles. It is estimated that the magnetic distribution of the ferrite particles of each embodiment is wider than that of the comparative example ferrite particles.

[0367] (2) Basic characteristics

[0368] Next, the basic characteristics of each embodiment and comparative example are compared according to Table 3. The ferrite particles of Embodiments 1 to 6 of the present invention have a saturation magnetization of 51 Am. 2 / kg~75Am 2 / kg, the ferrite particles of Comparative Examples 1 to 6, had a saturation magnetization of 69 Am. 2 / kg~86Am 2 / kg. The ferrite particles of each embodiment and the ferrite particles of each comparative example show the same saturation magnetization value. However, the Mn content ratio in the ferrite particles of the embodiments is higher than that in the ferrite particles of the comparative examples. Therefore, the ferrite particles of the embodiments can be considered to have low magnetization from an overall perspective.

[0369] Furthermore, the apparent density of the ferrite particles in the example is 2.26 g / cm³. 3 ~2.35g / cm 3 In contrast, the ferrite particles in the comparative example had a particle size of 1.91 g / cm³. 3 ~2.20g / cm 3 Under overall application, the apparent density of the ferrite particles in the embodiments tends to be higher. Regarding surface roughness Rz, the ferrite particles in the embodiments have a roughness of 2.5 μm to 3.5 μm, while the ferrite particles in the comparative examples have a roughness of 2.0 μm to 2.1 μm. From an overall perspective, the surface roughness Rz of the ferrite particles in the embodiments shows a larger value. Regarding BET specific surface area, the ferrite particles in the embodiments have a specific surface area of ​​0.050 m². 2 / g~0.128m 2 / g, for which the ferrite particles in the comparative example are 0.152 m 2 / g~0.173m 2 / g, the ferrite particles of the embodiment show a smaller BET specific surface area. Based on this, compared with the ferrite particles of the comparative example, the ferrite particles of the embodiment have a larger surface roughness. Therefore, when this ferrite particle is used as the core material and a resin coating layer is formed on its surface to create a carrier, the ferrite particles of the embodiment have a larger exposed core material, promoting low resistivity of the carrier and suppressing the formation of image memory defects.

[0370] (3) Image quality characteristics

[0371] According to Table 4, when using the ferrite particles of this embodiment as the carrier core material in the electrophotographic developer, high ratings of "Image density adaptability," "rate of change of charge over time," "Image density stability," "Carrier adhesion," and "Toner scattering" were obtained, receiving "A" or "B." In particular, it was confirmed that the ferrite particles of Example 1 received an "A" rating in all items, making them a very suitable carrier core material for electrophotographic developers used in low- to medium-speed printing. On the other hand, observing the comparative examples, regarding "Toner scattering," an "A" rating was obtained except for Comparative Example 1. However, regarding "Image density adaptability" and "Image density stability," both received low ratings of "C" or "D," and regarding "rate of change of charge over time," except for Comparative Examples 4 and 6, both received low ratings of "C" or "D."

[0372] The reason for this result is believed to be as follows.

[0373] First, regarding the amount of toner scattering, considering the influence of the surface properties of the particles, Comparative Example 1 largely deviated from the range of Sr content of 0.4 mol to 1.2 mol when the total amount of Fe, Mn, and Mg was set to 100 mol. Apart from Comparative Example 1, it was confirmed that an electrophotographic developer with a small amount of toner scattering was obtained.

[0374] Next, regarding the rate of change of charge over time, the influence of the coating content ratio was considered. As described, if the coating layer is only locally disposed on the surface of the ferrite particle body, the ferrite particle body oxidizes at the exposed location, and the surface resistance of the core material changes over time. In this embodiment, the ferrite particles have a coating content ratio in the range of 5% to 35% by mass, which is considered to result in an electron photographic developer with a low rate of change of charge. The ferrite particles of Comparative Examples 4 and 6 have a coating content ratio exceeding 35% by mass. If the coating content ratio exceeds 35% by mass by a large margin, excessive surface thermal decomposition of the ferrite particles occurs, eventually resulting in reactions such as 2Fe3O4 + 1 / 2O2 → 3Fe2O3 and 2Mn3O4 + 1 / 2O2 → 3Mn2O3, without further oxidation, thus, as shown in Comparative Examples 4 and 6, the rate of change of charge over time is smaller.

[0375] Regarding image density adaptability and image density stability, the following considerations are made. The ferrite particles in each embodiment, satisfying equations (1) and (2), are, as mentioned above, A-rich ferrites with increased Mn occupancy at each lattice point, and Fe at each lattice point... 3+ Compared to B-rich ferrites with increased occupancy, excessive magnetization can be suppressed. Furthermore, the full width at half maximum (FWHM) of the (311) plane in the X-ray diffraction pattern of the ferrite particles in each embodiment is larger than that of the ferrite particles in the comparative examples. As mentioned above, in the case of A-rich ferrites, the magnetic force distribution tends to be wider. Based on this, the ferrite particles in each embodiment, compared to B-rich ferrites, namely Comparative Examples 1-4 and Comparative Example 6, are easier to break the magnetic bonds between particles, exhibiting excellent agitation and mixing properties. Therefore, the collision frequency between particles per unit time is higher, allowing the toner to be charged to saturation charge rapidly. As a result, in the image density adaptability evaluation test, when the applied voltage changes from 2000V to 2500V, the same level of image density can be maintained regardless of the applied voltage, resulting in an electrophotographic developer with high image density adaptability. Furthermore, in the ferrite particles of each embodiment, the coating layer ratio is 5% to 35%, and it is considered that the coating layer covers the entire surface of the ferrite particle body. Therefore, the coating layer can suppress the oxidation of ferrite particles due to contact with atmospheric oxygen, and can suppress the time-dependent increase in the surface resistivity of the carrier core material. Comparative Example 5 is an A-rich ferrite, but it is considered to have low evaluations in image density adaptability and image density stability due to the lack of a coating layer.

[0376] [Table 1]

[0377]

[0378] [Table 2]

[0379]

[0380] [Table 3]

[0381]

[0382] [Table 4]

[0383]

[0384] Industrial availability

[0385] According to the invention, there is an electrophotographic developer carrier core material, an electrophotographic developer carrier, and an electrophotographic developer that provide excellent agitation and mixing properties of the toner and carrier, and can suppress image defects in the early stages of printing even when the environment changes.

[0386] The present invention has been described in detail or with reference to specific embodiments, but it will be apparent to those skilled in the art that various changes or modifications can be made without departing from the spirit and scope of the invention.

[0387] This application is based on Japanese Patent Application No. 2021-089756, filed on May 28, 2021, the contents of which are incorporated herein by reference.

Claims

1. A ferrite particle, comprising: The ferrite particles have a spinel-type crystal structure belonging to space group Fd-3m, and the spinel composition is represented by the following formula (1); and The coating layer, having a spinel-type crystal structure belonging to space group Fd-3m, covers the surface of the ferrite particle matrix. The coating layer is obtained by heat treatment of ferrite represented by the following formula (1), and the content of the coating layer in the ferrite particles is 5% by mass or more and 35% by mass or less, as determined by Rietwald analysis of the powder X-ray diffraction pattern. It satisfies the following equation (2). Mg x Mn （1－x） Fe2O4•••(1), 0.040Å≦D LC ≦0.070Å•••(2), in, In equation (1), 0.001 ≦ x < 0.300, In the above equation (2), D LC = (lattice constant of the ferrite particle body) - (lattice constant of the coating layer).

2. The ferrite particles according to claim 1, The full width at half maximum (FWHM) of the (311) plane in the powder X-ray diffraction pattern of the ferrite particle is above 0.25° and below 0.35°.

3. The ferrite particles according to claim 1 or claim 2, When the total amount of Fe, Mn, and Mg contained in the ferrite particles is set to 100 mol, unlike the elements in these spinel-type crystal structures, it contains Sr element at a concentration of more than 0.4 mol and less than 1.2 mol.

4. The ferrite particles according to claim 1 or claim 2, The saturation magnetization, determined by B-H measurements under a magnetic field of 3 K•1000 / 4π•A / m, is 50 Am. 2 / kg or more 75Am 2 / kg or less.

5. The ferrite particles according to claim 1 or claim 2, The apparent density is 2.23 g / cm³. 3 The above 2.35g / cm 3 The surface roughness Rz is above 2.5μm and below 3.5μm.

6. The ferrite particles according to claim 1 or claim 2, The specific surface area of ​​BET is 0.070 m². 2 / g or more 0.150m 2 / g or less.

7. A carrier for an electrophotographic developer, The ferrite particles as described in any one of claims 1 to 6, and a resin coating layer covering the surface of the ferrite particles.

8. An electrophotographic developer, Includes the carrier and toner for electrophotographic developing agent as described in claim 7.

9. The electrophotographic developer according to claim 8, Used as a supplementary developer.

10. A method for manufacturing ferrite particles, comprising: The process of mixing Fe raw materials containing Fe, Mn raw materials containing Mn, and Mg raw materials containing Mg in a predetermined amount to obtain a mixture; The process of obtaining granules using the mixture; The process involves using a closed-atmosphere heat treatment furnace, which has a closed-atmosphere heat treatment chamber capable of controlling the firing atmosphere and a cooling chamber capable of controlling the cooling atmosphere to be different from the firing atmosphere, to fire the granules in the closed-atmosphere heat treatment chamber to obtain the fired product. A cooling process in which the fired product is cooled to below 250°C in a cooling chamber where the oxygen concentration is controlled to be less than 0.3% by volume, without allowing the product to come into contact with outside air; and The fired product after the cooling process undergoes a surface heat treatment process. The surface heat treatment is performed using a rotary furnace. Let the inner diameter of the rotary combustion chamber of the rotary furnace be L, the unit be m, the rotation speed be X, the unit be rpm, and the surface heat treatment time be t, the unit be min. At this time, the following equation (3) is satisfied. 20≦LπXt≦60•••(3) The proportions of the Fe raw material, the Mn raw material and the Mg raw material in the mixture satisfy the following formula (4). 0.80≦n Fe / (n Mn +n Mg )<2.00•••(4) in, n Fe The amount of Fe element in the Fe raw material, expressed in mol%. n Mn The preceding text refers to the amount of Mn element in the Mn raw material, expressed in mol%. n Mg The preceding text refers to the amount of Mg element in the Mg raw material, expressed in mol.

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