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

Abstract

Provided are a ferrite particle represented by a specific formula, an electrophotographic developer carrier for an electrophotographic developer including the ferrite particle and a resin coating layer covering the surface of the ferrite particle, an electrophotographic developer including the electrophotographic developer carrier for an electrophotographic developer and toner, and a method for manufacturing the ferrite particle, which have a spinel crystal structure belonging to space group Fd-3m.

Description

Technical Field

[0001] This invention relates to ferrite particles, a carrier for electrophotographic developing agents, an electrophotographic developing agent, and a method for manufacturing ferrite particles. Background Technology

[0002] Electrophotographic developing methods refer to the development of an electrostatic latent image by attaching toner in a developer onto a photoreceptor. The developers used in this method are classified as: two-component developers, which consist of toner and a carrier; and single-component developers, which use only toner. While cascade methods were previously used for developing with two-component developers, the magnetic brush method using magnetic rollers is now the mainstream approach.

[0003] In the magnetic brush method, toner and carrier are agitated and mixed in a developing cartridge filled with developer, thus imparting an electrical charge to the toner. Then, the carrier is conveyed to the surface of the photoreceptor via a magnetically controlled developing roller. At this point, the charged toner is transferred to the photoreceptor surface through the carrier. After the toner image forms on the photoreceptor due to electrostatic attraction, the carrier remaining on the developing roller is recycled back into the developing cartridge, agitated and mixed with new toner, and reused repeatedly for a certain period.

[0004] Unlike single-component developers, two-component developers allow for the separate design of the carrier's magnetic or electrical properties from the toner, resulting in better controllability during developer design. Therefore, two-component developers are suitable for full-color developing devices requiring high image quality and for high-speed printing in copiers or multifunction printers (hereinafter referred to as image forming devices) requiring reliable and durable image retention.

[0005] However, the continuous image forming speed of a typical home-use image forming device is approximately 5 to 15 pages per minute for A4 size prints, while the continuous image forming speed of a professional image forming device is approximately 15 to 50 pages per minute. Thus, professional image forming devices generally have a faster continuous image forming speed than home-use devices, and their start-up speeds, such as warm-up time and first copy time, are also faster. When their printing speeds differ, the required characteristics of the carrier core material also differ.

[0006] When printing speed increases, the carrier and toner are agitated and mixed at high speed within the developing chamber, making it easier for cracks and defects to form in the carrier core material. These cracks and defects can also cause carrier scattering. Therefore, for image forming apparatuses used in high-speed printing, a carrier core material with high magnetization and resistance to cracking and defects during agitation and mixing is required. Thus, as a carrier core material suitable for use in image forming apparatuses for high-speed printing, for example, ferrite particles are proposed in Patent Document 1, which are composed of components with the formula (M... X Fe 3－X The ferrite particles are characterized by a material whose main component is represented by O4 (where M is at least one metallic element selected from the group consisting of Fe, Mg, Mn, Ti, Cu, Zn, Sr, and Ni, and 0 ≤ X < 1), containing Ca and P elements. The Ca content, relative to the P content, ranges from 0.45 to 1.0 by weight. The ferrite particles described in Patent Document 1 aim to improve charge while preventing a decrease in strength, thereby suppressing cracks and defects in the carrier core material.

[0007] Prior technology documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2012-144401 Summary of the Invention

[0010] The technical problem that the invention aims to solve

[0011] In recent years, image forming apparatuses achieving continuous image forming speeds of 100 frames per minute or more have also been known. To achieve such high-speed continuous image forming, the rotational speeds of the photoreceptor and developing roller need to be increased. When the rotational speed of the developing roller increases, the centrifugal force acting on the carrier also increases. When the magnetic attraction between the developing roller and the carrier is relatively small compared to the centrifugal force acting on the carrier, the carrier will scatter from the surface of the developing roller. This results in carrier adhesion to the surface of the photoreceptor, or toner adhesion to unintended locations on the photoreceptor, leading to carrier adhesion or toner scattering. Therefore, to achieve high-speed continuous image forming, it is necessary that the core material, when viewed as a whole, is highly magnetized and, compared to other particles, does not contain low-magnetized particles.

[0012] However, the crystal structure of ferrite particles varies complexly depending on the type and amount of trace components, firing conditions, and other factors. Therefore, even when expressed with the same compositional formula, different crystal structures result in variations in magnetic properties. In the invention described in Patent Document 1, crystal growth is controlled by achieving a balance between the contents of Ca and P elements. However, for example, in ferrite particles with a spinel-type crystal structure, magnetic properties vary depending on the type and valence of the element occupying the B sites. In the method described in Patent Document 1, it is difficult to control the type and valence of the element occupying the B sites, and compared to other particles, there is a higher probability of including particles with low magnetization. Therefore, during high-speed printing, there is a risk that carrier adhesion and toner scattering cannot be adequately suppressed.

[0013] Therefore, the purpose of this invention is to provide ferrite particles, a carrier for an electrophotographic developer, a carrier for an electrophotographic developer, an electrophotographic developer, and a method for manufacturing ferrite particles, which are suitable for carrier core materials of an electrophotographic developer having magnetic properties suitable for high-speed printing and good image properties even during high-speed printing.

[0014] means of solving technical problems

[0015] The present invention includes the following solutions. [1]

[0017] A ferrite particle having a spinel-type crystal structure belonging to space group Fd-3m;

[0018] The ferrite composition is represented by the following formula (1).

[0019] (Fe 3+ u, Mn 2+ v, Mg 2+ w)(Mn 3+ x, Fe 2+ y, Fe 3+ z)2O4···(1)

[0020] in,

[0021] u+v+w=1

[0022] x + y + z = 1

[0023] 0.870 ≤ v < 1.000

[0024] 0.001 ≤ w < 0.070

[0025] 0.000≤x≤0.075 [2]

[0027] As described in [1], ferrite particles, wherein,

[0028] The w in equation (1) satisfies the following condition.

[0029] 0.003≤w≤0.060 [3]

[0031] Ferrite particles as described in [1] or [2], wherein,

[0032] When the total amount of Fe, Mn, and Mg contained in the ferrite particle is recorded as 100 mol, unlike these ferrite constituent elements, it contains more than 0.4 mol and less than 1.2 mol of Sr element. [4]

[0034] Ferrite particles as described in any one of [1] to [3], wherein,

[0035] The internal porosity is below 4.0%. [5]

[0037] Ferrite particles as described in any one of [1] to [4], wherein,

[0038] The saturation magnetization, measured by B-H, is 70 Am when a magnetic field of 3 K·1000 / 4π·A / m is applied. 2 / kg or above, 90Am 2 / kg or less. [6]

[0040] Ferrite particles as described in any one of [1] to [5], wherein,

[0041] The apparent density is 2.10 g / cm³. 3 Above, 2.40 g / cm 3 the following. [7]

[0043] A carrier for an electrophotographic developer includes: ferrite particles as described in any one of [1] to [6], and a resin coating layer covering the surface of the ferrite particles. [8]

[0045] An electrophotographic developer comprising a carrier and toner as described in [7]. [9]

[0047] As described in [8], the electrophotographic developer, wherein,

[0048] This electrophotographic developer is used as a replenishing developer.

[10]

[0050] A method for manufacturing ferrite particles, which is used to manufacture ferrite particles as described in any one of [1] to [6];

[0051] In the manufacturing method of these ferrite particles,

[0052] The raw materials Fe, Mn and Mg are blended in such a way that the following formula (2) is satisfied, and the calcined material is produced.

[0053] Ferrite particles are produced by containing the material to be fired in a refractory container with a porosity of 20% to 35% and firing it.

[0054] 2.00≤n Fe / (n Mn +n Mg )≤3.00···(2)

[0055] in,

[0056] n Fe The amount of Fe element in the Fe raw material (mol%)

[0057] n Mn The amount of Mn element in the Mn raw material (mol%)

[0058] n Mg The amount of Mg element in the Mg raw material (mol%)

[11]

[0060] The method for manufacturing ferrite particles as described in

[10] , wherein,

[0061] The object to be fired is fired in a closed atmosphere heat treatment furnace under pressure in a range where the pressure inside the furnace is 2 Pa higher than the atmospheric pressure outside the furnace but less than 100 Pa higher.

[0062] The effects of the invention

[0063] According to this invention, it is possible to provide ferrite particles, a carrier core material for an electrophotographic developer that has magnetic properties suitable for high-speed printing and can achieve good image characteristics even during high-speed printing, an electrophotographic developer carrier, an electrophotographic developer, and a method for manufacturing ferrite particles. Detailed Implementation

[0064] The following describes embodiments of the ferrite particles, the carrier core material for electrophotographic developers, the carrier for electrophotographic developers, and the electrophotographic developers of this invention. First, 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.

[0065] Furthermore, the following description explains the use of the ferrite particles of this embodiment as a carrier core material for electrophotographic developers. However, the ferrite particles of this invention can be used for various functional fillers such as magnetic inks, magnetic fluids, magnetic fillers, fillers for bonding magnets and fillers for electromagnetic wave shielding materials, as well as electronic component materials. The use of these ferrite particles is not limited to carrier core materials for electrophotographic developers.

[0066] 1. Ferrite particles

[0067] First, the ferrite particles will be described. These ferrite particles are characterized by having a spinel-type crystal structure belonging to the space group Fd-3m, and their ferrite composition is represented by the following formula (1).

[0068] (Fe 3+ u, Mn 2+ v, Mg 2+ w)(Mn 3+ x, Fe 2+ y, Fe 3+ z)2O4···(1)

[0069] in,

[0070] u+v+w=1

[0071] x + y + z = 1

[0072] 0.870 ≤ v < 1.000

[0073] 0.001 ≤ w < 0.070

[0074] 0.000≤x≤0.075

[0075] Spinel-type crystals belonging to space group Fd-3m belong to the cubic crystal system. When the composition of ferrites with this spinel-type crystal structure is represented by the general formula AB₂O₄, its unit lattice is represented by 8(AB₂O₄). The 32 oxygen atoms constituting the unit lattice of the spinel-type crystal form a densest cubic lattice. In the unit lattice, there are two types of lattice points where metal ions are disposed: the central position of a tetrahedron formed by 4 oxygen atoms, i.e., the 8b position (A site), and the central position of a hexahedron formed by 6 oxygen atoms, i.e., the 16c position (B site). In the case of Mn-Mg ferrites, Mg is disposed at the A site as a divalent metal ion.

[0076] On the other hand, Fe and Mn are transition metal elements, and therefore they are positioned as divalent or trivalent metal ions at sites A or B. In the case of Mn-Mg ferrites, Fe is positioned at site A. 3+ “Mn” 2+ “Mg” 2+ At site B, "Mn" is configured. 3+ "Fe" 2+ "and "Fe 3+ The occupancy of these ions at the B site is believed to vary depending on manufacturing conditions, etc. Therefore, the electron spin state at the B site has a significant impact on the magnetic properties of ferrite particles.

[0077] Therefore, the inventors conducted in-depth research and discovered that by making "Mn" at site B... 3+ The occupancy of “Mn” becomes extremely small. Specifically, when the ferrite composition of the ferrite particle is expressed in the above formula (1), “Mn” representing the B site is used. 3+ The "x" value of the occupancy rate of "Mn" is suppressed to below 0.075, thus exhibiting magnetic properties that are highly magnetized when considered as a whole ferrite particle, with virtually no low-magnetized particles, and suitable for high-speed printing of 100 frames per minute or more, and even 120 frames per minute or more. It suppresses carrier adhesion and toner scattering caused by low-magnetized particles, achieving good image characteristics even at high-speed printing. However, in conventional manufacturing methods, "Mn" 3+ "Occupying more than the value of 'x' at site B, the 'Mn' at site B..." 3+ The deviation in the occupancy rate of "" is also relatively large. Therefore, when observed as a whole (powder) of ferrite particles, this is the reason why the magnetization of individual particles, including those with low magnetization, can deviate even when the magnetization is high. Therefore, the inventors of this invention conducted in-depth research and came up with the manufacturing method described later. In the above formula (1), the value of "x" is 0.075 or less, indicating that "Mn" at the B site is " 3+We can manufacture spinel-type ferrite particles with extremely low occupancy and high precision. The details are explained below.

[0078] (1) Ferrite components

[0079] i)(Mn 3+ x, Fe 2+ y、Fe 3+ z)

[0080] In the above formula (1), "(Mn 3+ x, Fe 2+ y, Fe 3+ "z)" is equivalent to "B" in the general formula above. As mentioned above, "x + y + z = 1, 0.000 ≤ x ≤ 0.075". "x", "y", and "z" respectively represent "Mn" at site B. 3+ "Fe" 2+ "Fe" 3+ The percentage of "0.000≤x≤0.075" in the ferrite particles of this invention, where "0.000≤x≤0.075" and the B sites are basically composed of "Fe". 2+ "or "Fe 3+ "Possession. As shown in this example, 'Mn' at site B is inhibited." 3+ In ferrite particles with an intrusive spinel-type crystal structure, the proportion of low-magnetization particles becomes extremely small. That is, it is possible to obtain ferrite particles that are highly magnetized when viewed as a whole, and essentially free of low-magnetization particles, resulting in a small deviation in magnetic properties from individual ferrite particles. Furthermore, the smaller the value of "x", the better; preferably, the upper limit is 0.075, more preferably 0.040, and even more preferably 0.020.

[0081] However, in this specification, when the preferred upper and lower limits for numerical ranges are expressed as "inequality signs" in the formula, it is preferable to replace them with "inequality signs with equal signs," or vice versa. Furthermore, regarding the preferred upper and lower limits, "above" can be replaced with "greater than," and "below" can be replaced with "less than," or vice versa.

[0082] ii)(Fe 3+ u、Mn 2+ v、Mg 2+ w)

[0083] On the other hand, in the above formula (1), "(Fe 3+ u、Mn 2+ v、Mg 2+"w)" is equivalent to "A" in the general formula above. As mentioned above, "0.870≤v<1.000, 0.001≤w<0.070". "u", "v", and "w" respectively represent "Fe" at site A. 3+ “Mn” 2 + “Mg” 2+ "The market share of "

[0084] "Mn" at site B 3+ The occupancy rate of “” is within the range of “x” mentioned above. Furthermore, it is possible to achieve this by using “Mn” at site A. 2 + The occupancy rate of “v” is set within the range of the above “v”, thereby obtaining ferrite particles with magnetic properties suitable for high-speed printing.

[0085] To achieve this effect, it is more preferable that the upper limit of "v" is less than 1.000, and even more preferably, less than 0.998. Furthermore, it is more preferable that the lower limit of "v" is 0.870, even more preferably, 0.900, and even more preferably, 0.960.

[0086] Furthermore, by setting the ferrite composition to include Mn within the range of "2x+v", the magnetization on the low magnetic field side can be increased. Moreover, by setting the ferrite composition to include Mn, re-oxidation of the ferrite during the final firing process can be prevented. Therefore, it is easy to adjust to a good resistance value and to obtain charging characteristics suitable for high-speed printing.

[0087] In addition, when "Mg" at site A 2+ When the percentage of "w" is within the aforementioned range, it is easier to obtain ferrite particles with high magnetization and high resistance. However, when using magnesium hydroxide as the Mg raw material, if the firing temperature during the manufacture of the ferrite particles is low, hydroxyl groups may sometimes remain in the ferrite particles. Therefore, by adjusting the Mg raw material to have a "w" value of less than 0.070, the amount of residual hydroxyl groups due to the raw material can be reduced. Thus, by retaining hydroxyl groups, the variation in electrical properties of the ferrite particles, such as charge or resistance, caused by atmospheric humidity can be suppressed, and the environmental dependence of the electrical properties of the ferrite particles can be improved.

[0088] To achieve this effect, it is more preferable that the upper limit value of "w" is 0.060, more preferably 0.030, and even more preferably 0.020. Furthermore, it is more preferable that the lower limit value of "w" is 0.001, and even more preferably 0.003.

[0089] Furthermore, as a preferred option, it is preferable that 0.003 ≤ w ≤ 0.060.

[0090] (2) Sr content

[0091] When the total amount of Fe, Mn, and Mg contained in the ferrite particles is considered to be 100 mol, it is preferable to contain 0.4 mol to 1.2 mol of Sr, unlike these ferrite constituent elements. By including Sr within this range, the surface roughness of the ferrite particles can be appropriately sized, and deviations in roughness can be suppressed, as well as the peeling of the resin film when the carriers collide with each other. Furthermore, the appropriate surface roughness of the ferrite particles prevents excessively high resistivity when the surface is covered with resin and used as a carrier. On the other hand, when the Sr content exceeds the above range, chlorine released from the Fe raw materials during firing can adsorb 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, there is a risk that the surface resistivity of the ferrite particles will decrease, and the charge will also decrease. In addition, the statement that "in addition to the constituent elements of ferrite, it also contains Sr element" means that Sr element is not an element that constitutes this spinel-type crystal structure, nor is it an element that constitutes ferrite with other crystal structures like Sr ferrite, but rather exists within the particles.

[0092] To achieve this effect, it is preferred that the lower limit of the "Sr" content is 0.5 mol, more preferably 0.6 mol. Furthermore, it is preferred that the upper limit is 1.1 mol, more preferably 1.0 mol.

[0093] (3) Component analysis

[0094] In the above formula (1), “x” and “y+z” are values ​​obtained by Ritwald analysis of X-ray diffraction patterns, and “u”, “v” and “w” are values ​​obtained by the following method: quantitative analysis of the elements contained in ferrite particles by ICP luminescence analysis.

[0095] Furthermore, the Sr content can be obtained in the same order as "u", "v", and "w".

[0096] The following section explains the specific analytical order for each.

[0097] i)x、y+z

[0098] First, the invented ferrite particles were calcined in a rotary drying furnace at 650°C under atmospheric conditions to decompose them into "Fe2O3" and "Mn2O3", thereby preparing a sample. Using this sample, powder X-ray diffraction was performed under the measurement conditions described later to obtain a powder X-ray diffraction pattern.

[0099] Next, Rietwald analysis was performed on the obtained powder X-ray diffraction pattern to determine the composition ratios of "MnFe2O4", "Fe2O3", and "Mn2O3". Based on the obtained composition ratios, the content (mol%) of "Mn2O3" when "Fe2O3" and "Mn2O3" were set to 100 mol% was calculated. The content of "Mn2O3" represents the content of "Mn" at site B. 3+ The percentage of Mn2O3 is given. Therefore, x can be calculated based on the percentage of Mn2O3. Specifically, when the percentage of Mn2O3 is a (mol%), x can be calculated by x = a × 1 / 100.

[0100] If the value of "x" is obtained, then based on the value of "x", the value representing "Fe" at site B can be calculated. 3+ "and "Fe 2+ The total market share of “y+z”.

[0101] The value of “y+z” in the above formula (1) is “x+y+z=1”, so it can be obtained by “y+z”=“1-x”.

[0102] The determination conditions for powder X-ray diffraction and the analytical conditions for Rietveld analysis are as follows.

[0103] (Powder X-ray diffraction)

[0104] As the X-ray diffraction apparatus, the "X'Pert PROM PD" 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 "X'Celarator" can be used. The measurement conditions are set as follows.

[0105] Scanning speed: 0.08° / second

[0106] Diverging slit: 1.0°

[0107] Scattering slit: 1.0°

[0108] Light-receiving slit: 0.15mm

[0109] Voltage and current values ​​of the encapsulated tube: 40kV / 40mA

[0110] Measurement range: 2θ = 15°~90°

[0111] Total number of times: 5

[0112] (Qualitative analysis of crystal phases)

[0113] Based on the above measurement results (powder X-ray diffraction pattern), and according to the structure disclosed by the National Research Agency for Materials Science and Engineering (AtomWorks), available at http: / / crystdb.nims.go.jp / >, the crystal structure is assumed to be as follows. At this point, using the following three phases (phase 1 to phase 3) as the crystal structure model, the Mn at site B is determined based on the composition ratio of each phase in the sample. 3+ The market share "x".

[0114] Phase 1: MnFe2O4 (spinel type crystal phase)

[0115] Crystal structure: Space group Fd-3m (No.227-2)

[0116] Atomic coordinates: Mn 2+ (Position 8b (3 / 8, 3 / 8, 3 / 8))

[0117] Fe 3+ (16c position (0, 0, 0))

[0118] O 2－ (32e position (x, x, x))

[0119] Phase 2: Fe2O3

[0120] Crystal structure: Space group R-3c (No. 167-1)

[0121] Atomic coordinates: Fe 3+ (12c position (0, 0, z))

[0122] O 2－ (18e position (x, 0, 1 / 4))

[0123] Phase 3: Mn2O3

[0124] Crystal structure: Space group Ia-3 (No. 206-1)

[0125] Atomic coordinates: Mn 2+ (24d position (x, 0, 1 / 4))

[0126] Mn 2+ (8a position (0, 0, 0))

[0127] O 2－ (48e position (x, y, z))

[0128] After assuming a crystal structure as described above, the following parameter optimization was performed using the analysis software "RIETAN-FPu2.83". Asymmetry was achieved using the Thompson, Cox, and Hasting quasi-Voigt functions with distribution functions, employing Howard's method. Furthermore, the parameters were refined to represent the accuracy of the fit, with Rwp values ​​below 2% and S values ​​below 1.5.

[0129] (Parameters for refinement)

[0130] • Offset factor

[0131] · Scale factor

[0132] Background parameters

[0133] Gaussian functions U, V, W

[0134] Lorentz functions X, Y

[0135] • Asymmetric parameter As

[0136] • Lattice constant, oxygen atom coordinates

[0137] ii) u, v, w

[0138] The contents of "Fe", "Mn", "Mg" and "Sr" in the ferrite particles used as samples were determined under the test conditions described below, and the values ​​were calculated as follows.

[0139] First, calculate the proportion of Mg (mol%) based on the total amount of Fe, Mn, and Mg, and then determine the value of w. Based on this value of w and the value of x obtained above, calculate u and v using the following formulas.

[0140] u = (1 - w) × (1 - x)

[0141] v = 1 - u - w

[0142] (ICP)

[0143] The specific determination method based on ICP luminescence analysis for the content of "Fe", "Mn" and "Mg" is as follows.

[0144] First, weigh out 0.2 g of ferrite particles to be tested. Then, add 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid to 60 ml of pure water, heat the solution, and add the ferrite particles to prepare an aqueous solution that dissolves the ferrite particles. Using this aqueous solution as a sample, the contents of Fe, Mn, and Mg can be determined using an ICP-based luminescence analyzer (Shimadzu ICPS-1000IV).

[0145] (iii) Sr content

[0146] The Sr content is calculated in the same way as u, v, and w. Specifically, when the ferrite particles contain Sr, Sr dissolves in the aqueous solution prepared for ICP luminescence analysis. When determining the contents of Fe, Mn, and Mg using this aqueous solution as described above, the Sr content is also determined simultaneously. The amount of Sr (mol) when the total amount of substance (mol) of Fe, Mn, and Mg is 100 is calculated, and this value is taken as the Sr content (mol).

[0147] (4) Internal porosity

[0148] Preferably, the internal porosity of the ferrite particles is 4.0% or less. Here, internal porosity refers to a value measured in the following manner.

[0149] Ferrite particles, the subjects of the test, were resin-embedded and cross-sections were fabricated using ion milling to prepare cross-sectional specimens for testing. Ion milling was performed using a Hitachi High-technologies IM4000PLUS microscope with the ion beam accelerating voltage set to 6.0 kV under an argon atmosphere. Furthermore, reflected electron images of the cross-sectional specimens were captured using a scanning electron microscope (Hitachi High-technologies SU8020) at an accelerating voltage of 1 kV and magnified 700 times, and analyzed using image analysis software (Image-ProPlus, Media Cybernetics).

[0150] Here, the internal porosity is calculated as the average of 30 particles. The volume average particle size of the ferrite particles (powder) containing the particles to be measured is denoted as D. 50 When measuring ferrite particles (powder), the maximum diameter Dx is set at D. 50 ×0.8≤Dx≤D 50The particles were measured in a range of ×1.2. Then, for each particle, the area (A) of the enveloping particle formed by the lines enveloping its surface was measured. Next, the cross-sectional area of ​​the particles contained in the particle image was measured as the core material area (B). Then, the sum of the enveloping particle areas (A) measured for each of the 30 particles and the sum of the core material areas (B), calculated using the following formula, was taken as the internal porosity as described in this invention.

[0151] Internal porosity (%)

[0152] = (Area of ​​envelope particles (A) - Area of ​​core material (B)) / Area of ​​envelope particles (A) × 100 where,

[0153] Envelope particle area (A): The area of ​​the region enclosed by the concave and convex lines (envelope lines) of the cross-section of the envelope particle.

[0154] Core area (B): The area of ​​the core material portion

[0155] The internal porosity defined by the above formula is relative to the envelope area, representing the ratio of the continuous porosity area on the surface of the measured particle to the sum of the porosity areas existing independently within the core material in the particle cross-section.

[0156] Ferrite particles with an internal porosity of 4.0% or less, as determined by the above method, indicate a small amount of internal porosity, minimal surface unevenness, and a uniformly shaped aggregate of particles. Furthermore, because of the small internal porosity, these ferrite particles exhibit characteristics such as reduced inclusion of low-magnetization particles compared to other particles, and smaller deviations in the magnetic properties of each particle. Additionally, by reducing the internal porosity, the presence of particles with low strength can be suppressed. Therefore, it is easier to suppress carrier scattering caused by low-magnetization or low-strength particles, and to suppress image defects such as carrier adhesion and toner scattering caused by carrier scattering. Moreover, deviations in image development caused by the presence of low-magnetization particles can be suppressed.

[0157] To achieve this effect, it is preferable that the upper limit of the internal porosity is 3.5%, more preferably 3.0%, more preferably 2.5%, and even more preferably 2.0%.

[0158] (5)Magnetic properties

[0159] Next, the magnetic properties of the ferrite particles will be explained. Preferably, the saturation magnetization of the ferrite particles, measured based on B-H, is 70 Am when a magnetic field of 3 K·1000 / 4π·A / m is applied. 2 / kg or above, 90Am 2 / kg or less. When the saturation magnetization of the ferrite particles is within this range, for example, when the continuous copying speed is increased to 100 sheets / min or more, or 120 sheets / min or more, a magnetic brush can be formed rapidly. In addition, the magnetic attraction between the developing roller and the carrier is strong, and even with the rotation of the developing roller, a greater centrifugal force acts on the carrier than at low-speed printing, which can suppress the following: carrier detachment from the magnetic brush, carrier scattering, carrier adhesion, and toner scattering.

[0160] In this regard, when the saturation magnetization is less than 70 Am 2 At a rate of / kg, when printing at high continuous copying speeds of 100 sheets / min or more, the magnetic force of the carrier may sometimes be weaker relative to the centrifugal force acting on it, posing the following risks: insufficient brush stand-up, or the carrier easily scattering from the developing roller due to low magnetization. Furthermore, when the saturation magnetization exceeds 90 Am... 2 At a magnetization rate of / kg, excessively high saturation magnetization poses the following risks: uneven brush height, potentially leading to image development deviations. Furthermore, there is a trade-off between saturation magnetization and resistance; as the saturation magnetization of the ferrite particles increases, their resistance decreases. Therefore, when the saturation magnetization of the ferrite particles exceeds 95 Am... 2 At a resistance of 85 Am / kg, the resistivity of the ferrite particles decreases, posing a risk of carrier dispersion due to low resistance. To suppress this decrease in resistivity, a higher upper limit for the saturation magnetization is preferred. 2 / kg, and more preferably, 80Am 2 / kg.

[0161] The 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. Between the electromagnets of this device, an H coil for measuring the magnetic field and a 4πI coil for measuring magnetization are arranged. The outputs of the H coil and the 4πI coil, which change the magnetic field H due to the change in current to the electromagnets, are integrated. The H output is plotted on the X-axis, the 4πI coil output on the Y-axis, and the hysteresis loop is plotted on recording paper. From this hysteresis curve, the magnetization when an applied magnetic field of 3 K·1000 / 4π·A / m is determined as the saturation magnetization. The measurement conditions are as follows.

[0162] Sample filling amount: approximately 1g

[0163] Sample filling unit: inner diameter Height 10mm ± 0.1mm

[0164] 4πI coil: 30 turns

[0165] (6) Apparent density (AD)

[0166] Preferably, the apparent density (AD) of the ferrite particles is 2.10 g / cm³. 3 Above, 2.40 g / cm 3 The apparent density referred to here means the value measured in accordance with JIS Z 2504:2012. When the apparent density of the ferrite particles is within this range, it can meet the flowability required for high-speed printing. When the ferrite particles are used as a carrier core material for electrophotographic developers, the degradation of the charge properties caused by stirring pressure can be suppressed even when the carrier and toner are stirred at high speed in the developing chamber.

[0167] In this regard, when the apparent density (AD) of the ferrite particles is less than 2.10 g / cm³ 3 At high printing speeds exceeding 100 sheets per minute, the carrier has low fluidity, making proper mixing with toner within the developing tank difficult. Furthermore, the number of particles with lower magnetization than required by the ferrite particles increases, posing a risk of carrier adhesion due to low magnetization. On the other hand, when the apparent density (AD) of the ferrite particles exceeds 2.40 g / cm³... 3 At this time, due to the high-speed stirring pressure inside the developing chamber, and due to the peeling of the resin coating (described later), the charge-carrying properties may sometimes deteriorate.

[0168] To achieve these effects, it is even more preferable that the apparent density of the ferrite particles is 2.15 g / cm³. 3 That's all. Furthermore, more preferably, the apparent density of the ferrite particles is 2.35 g / cm³. 3 The following is a further preferred value: 2.30 g / cm³ 3 the following.

[0169] Apparent density can be determined using a powder apparent density meter as follows. The powder apparent density meter uses a device consisting 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 measurement is performed in the following order, and the value calculated as follows is taken as the apparent density mentioned herein.

[0170] i) Measurement method

[0171] (a) The sample should be at least 150g.

[0172] (b) The sample is injected into a funnel with a throttling orifice of 2.5 + 0.2 / - 0 mm in diameter. The sample that flows out becomes a cup and flows until it overflows.

[0173] (c) When overflow begins, immediately stop the flow of the sample and use a scraper to smooth the sample that has risen onto the cup along the top of the cup to prevent vibration.

[0174] (d) Gently tap the side of the cup to make the sample sink, remove the sample attached to the outside of the cup, and weigh the sample inside the cup with an accuracy of 0.05g.

[0175] ii) Calculation

[0176] According to JIS-Z8401 (rounding method for numerical values), the measured value obtained in (d) above, multiplied by 0.04, is rounded to two decimal places and is used as "g / cm". 3 "The apparent density per unit".

[0177] (7) Average volumetric particle size (D) 50 )

[0178] Preferably, the average volumetric particle size (D) of the ferrite particles is... 50 The particle size is above 20 μm and below 80 μm. When the volume average particle size (D) of ferrite particles... 50 Within this range, ferrite particles suitable for various applications can be made.

[0179] Furthermore, when using the ferrite particles as a carrier core material for electrophotographic developers, it is preferable that the volume average particle size (D) of the ferrite particles is [missing information]. 50 The thickness is between 25 μm and 50 μm. By setting it within this range, carrier adhesion can be suppressed and image development deviations can be prevented.

[0180] The average volumetric particle size (D) mentioned here 50 The value refers to the value determined by laser diffraction and scattering methods in accordance with JIS Z8825:2013. Specifically, it can be measured using a Microtrac particle size analyzer (Model 9320-X100) manufactured by Nikkiso Co., Ltd., as follows: First, using ferrite particles 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. The sample is dispersed for 20 seconds using an ultrasonic homogenizer (SMT.Co.LTD. UH-150 type) set to output level 4. The sample is prepared by removing bubbles formed on the surface of the beaker. The volume average particle size of the sample, measured using the Microtrac particle size analyzer described above, is taken as the sample's average volume particle size (D). 50 ).

[0181] 2. Carrier for electrophotographic developing agents

[0182] Next, the carrier for electrophotographic developers of this invention will be described. The carrier for electrophotographic developers of this invention includes the aforementioned ferrite particles and a resin coating layer covering the surface of the ferrite particles. That is, the aforementioned ferrite particles are used as the core material of the carrier for electrophotographic developers. As described above, the resin coating layer will be the primary focus of the description here regarding the ferrite particles serving as the core material of the carrier for electrophotographic developers.

[0183] (1) Types of coating resins

[0184] The type of resin constituting the resin coating layer (coating resin) is not particularly limited. For example, fluoropolymers, acrylic resins, epoxy resins, polyamide resins, polyamide-imide resins, polyester resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, phenolic resins, fluoroacrylic resins, acrylic-styrene resins, silicone resins, etc., can be used. Alternatively, modified silicone resins can be used, which are obtained by modifying silicone resins with various resins such as acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamide-imide resins, alkyd resins, polyurethane resins, and fluoropolymers. For example, from the viewpoint of suppressing resin peeling caused by mechanical pressure during mixing with toner, a thermosetting resin is preferred for the coating resin. Suitable thermosetting resins for this coating resin include epoxy resins, phenolic resins, silicone resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, and resins containing them. However, as mentioned above, the type of coating resin is not particularly limited, and the appropriate type can be selected according to the type of toner being combined and the usage environment.

[0185] Furthermore, the resin coating layer can be constructed using either a single type of resin or two or more types of resin. When using two or more types of resin, a single resin coating layer can be formed by mixing the two or more types of resin, or multiple resin coating layers can be formed. For example, it is also preferable to provide a first resin coating layer with good adhesion to the ferrite particles on the surface of the ferrite particles, and to provide a second resin coating layer on the surface of the first resin coating layer for imparting the desired charge-imparting properties to the carrier.

[0186] (2) Resin coating amount

[0187] Preferably, the amount of resin covering the surface of the ferrite particles (resin film content) is 0.1% to 10% by mass relative to the ferrite particles used as the core material. When the resin coverage is less than 0.1% by mass, it may be difficult to adequately cover the surface of the ferrite particles with resin, making it difficult to obtain the desired charge-imparting ability. Furthermore, when the resin coverage exceeds 10% by mass, the carrier particles may aggregate during manufacturing, leading to the risk of reduced productivity, such as decreased yield, and changes in developer properties, such as developer flowability or charge-imparting properties to toner.

[0188] (3) Additives

[0189] Alternatively, the resin coating layer may contain additives designed 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 conductive carbon, oxides such as titanium dioxide or tin oxide, or various organic conductive agents. However, because conductive agents have low resistance, excessive amounts can easily cause charge leakage. Therefore, it is preferable that the content of the conductive agent relative to the solid content of the coating resin is 0.25% by mass or more and 20.0% by mass or less, more preferably 0.5% by mass or more and 15.0% by mass or less, and even more preferably 1.0% by mass or more and 10.0% by mass or less.

[0190] Examples of charge control agents include various charge control agents or silane coupling agents commonly used in toners. The types of these charge control agents or coupling agents are not particularly limited, but aniline black dyes, quaternary ammonium salts, organometallic complexes, metal-containing monoazo dyes, or aminosilane coupling agents or fluorosilane coupling agents are preferred. The content of the charge control agent relative to the solid content of the covering resin is preferably 0.25% by mass or more and 20.0% by mass or less, more preferably 0.5% by mass or more and 15.0% by mass or less, and even more preferably 1.0% by mass or more and 10.0% by mass or less.

[0191] 3. Electrophotographic developing agent

[0192] Next, embodiments of the electrophotographic developer of this invention will be described. This electrophotographic developer comprises the aforementioned carrier for electrophotographic development and toner.

[0193] As the toner constituting the electrophotographic developer, for example, either polymerized toner manufactured by polymerization or pulverized toner manufactured by pulverization is preferred. These toners may also contain various additives, as long as they can be combined with the aforementioned carrier for use as an electrophotographic developer; any type is acceptable.

[0194] Preferably, the volume average particle size (D) of the toner is... 50 The particle size of the toner is 2 μm or larger and 15 μm or smaller, more preferably 3 μm or larger and 10 μm or smaller. 50 When the value is within this range, an electrophotographic developer capable of high-quality electrophotographic printing can be obtained.

[0195] Preferably, the mixing ratio of carrier to toner is between 3% and 15% by mass. Electrophotographic developers containing toner at this concentration readily achieve the desired image density and can more effectively suppress fogging or toner scattering.

[0196] The electrophotographic developer of this invention can also be used as a replenishing developer.

[0197] When this electrophotographic developer is used as a replenishing developer, the preferred mixing ratio of carrier to toner is 2 to 50 parts by mass relative to 1 part by mass of carrier.

[0198] This electrophotographic developer is well-suited for use in various electrophotographic developing apparatuses employing the magnetic brush developing method. This method uses magnetic force to attract and attach a carrier to a magnetic drum or similar object, forming a brush shape. Toner is transported, and while a bias electric field is applied, the toner adheres to an electrostatic latent image formed on a photoreceptor, creating a visible image. When applying the bias electric field, this electrophotographic developer can be used not only in electrophotographic developing apparatuses using a DC bias electric field but also in electrophotographic developing apparatuses using an alternating bias electric field, which is obtained by superimposing an AC bias electric field onto a DC bias electric field.

[0199] 4. Manufacturing method

[0200] The following describes the ferrite particles, carrier core material for electrophotographic developers, carrier for electrophotographic developers, and manufacturing method of the electrophotographic developer of this invention.

[0201] 4-1. Ferrite particles and carrier core materials for electrophotographic developers

[0202] The ferrite particles and carrier core material for electrophotographic developers of this invention, except for the raw material mixing process and formal firing process described later, can be manufactured using a general method for ferrite particles used in applications such as electrophotographic developer carrier core materials.

[0203] Furthermore, the method for manufacturing ferrite particles in this invention is a method for manufacturing ferrite particles used to manufacture the aforementioned ferrite particles, and

[0204] The Fe, Mn, and Mg raw materials are blended in proportions that satisfy equation (2) described later to produce the calcined material.

[0205] Ferrite particles are produced by firing the material in a refractory container with a porosity of 20% to 35%.

[0206] The following explanation follows the order of raw material mixing, pre-firing process, firing process, and post-firing process. The pre-firing process refers to the steps performed after the raw material mixing process and before obtaining the granules (precursors to ferrite particles). Furthermore, the post-firing process refers to processes performed after the firing process, such as degranulation, grading, and surface oxidation treatment.

[0207] 4-1-1. Raw material mixing process

[0208] In the raw material mixing process, in order to obtain ferrite particles represented by the above formula (1), the Fe raw material, Mn raw material and Mg raw material are weighed and mixed in a manner that satisfies the following formula (2).

[0209] 2.00≤n Fe / (n Mn +n Mg )≤3.00···(2)

[0210] in,

[0211] n Fe The amount of Fe element in the Fe raw material (mol%)

[0212] n Mn The amount of Mn element in the Mn raw material (mol%)

[0213] n Mg The amount of Mg element in the Mg raw material (mol%)

[0214] By weighing and mixing Fe, Mn, and Mg raw materials in a manner that satisfies condition (2), ferrite particles that satisfy the above formula (1) can be obtained with high precision. At this time, ferrite particles that satisfy the above formula (1) can be obtained with high precision by performing a formal firing process as follows.

[0215] Here, iron oxides such as Fe2O3 can be used as Fe raw materials. Mn raw materials such as MnO2, Mn2O3, Mn3O4, and MnCO3 can be used. Mg raw materials such as MgO, Mg(OH)2, and MgCO3 can be used. Furthermore, in the case of obtaining ferrite particles containing Sr, Sr oxides or carbonates can be used as raw materials. After weighing these raw materials to a predetermined amount, they are pulverized and mixed using a wet or dry mill, such as a ball mill, sand mill, or vibratory mill, for at least 1 hour, preferably 1 to 20 hours.

[0216] 4-1-2. Pre-firing procedures

[0217] Next, water is added to the mixture obtained by pulverizing and mixing the raw materials as described above, 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 the medium. To ensure uniform dispersion of the raw materials, it is preferable to use beads with microparticles having a particle size of 1 mm or less as the medium. Furthermore, to ensure uniform dispersion of the raw materials, it is preferable to use beads with a volume average particle size (D) of the pulverized material. 50 The particle size is pulverized to a size of 2.5 μm or less, and more preferably, to a size of 2.0 μm or less. Furthermore, to suppress abnormal particle growth, it is preferable to pulverize the particle size (D) on the loose side of the particle size distribution. 90 The slurry is pulverized to a particle size of 3.5 μm or less. Preferably, a dispersant, binder, etc., is added to the slurry obtained in this manner as needed to adjust its viscosity to 2 poise or more and 4 poise or less. In this case, polyvinyl alcohol or polyvinylpyrrolidone can be used as the binder.

[0218] The slurry prepared as described above is sprayed with a spray dryer to dry it, thereby obtaining granules.

[0219] 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.

[0220] However, in the manufacturing process of ferrite particles, a pre-firing process is generally performed before preparing the slurry, where 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, for manufacturing the ferrite particles of the present invention, it is preferable to omit the pre-firing and debinding processes. When these heat treatment processes are performed before the formal firing process, the mixture of raw materials is heated, thereby partially initiating the ferrite formation reaction. Therefore, the granules contain seed crystals that have crystallized into the spinel structure. When such granules are formally fired, the seed crystals become the starting point for crystal growth, thus easily generating internal pores in the ferrite particles obtained after formal firing. This easily leads to a decrease in the magnetization of the ferrite particles. Furthermore, in this case, it is difficult to control the crystal growth of each particle in a uniform manner during the formal firing process, and deviations in the size of internal pores in each particle are easily introduced. Therefore, in order to obtain ferrite particles suitable for high-speed printing carrier core materials with low internal porosity and no low magnetization particles compared with other particles, it is preferable that, under the condition that the ferrite reaction can be carried out before the formal firing process, the raw material mixture powder or granules are not subjected to heat treatment such as pre-firing process or debinding process.

[0221] 4-1-3. Formal firing process

[0222] In order to obtain ferrite particles that satisfy the above formula (1), it is preferable to carry out the formal firing process as follows.

[0223] (1) Firing furnace

[0224] During the formal firing process, compared to a firing furnace where the granules are flowed through a hot section while being fired in a rotary kiln, it is preferable to use a firing furnace with a hot section, such as a tunnel kiln or a lift furnace, in which the granules are placed in a refractory container like a sagger and allowed to pass through in a stationary state. When granules are fired in a firing furnace with the granules placed in a refractory container and allowed to pass through the hot section in a stationary state, the interior of the granules can be fully sintered, thus easily yielding ferrite particles with high magnetization and high resistivity, and where the spinel-type crystal phase is fully formed.

[0225] Furthermore, by using a closed-atmosphere firing furnace with controllable furnace atmosphere, the furnace atmosphere can be adjusted to a preferred firing atmosphere to produce ferrite particles that satisfy formula (1), and it is easy to adjust the firing atmosphere of each particle in the refractory container to be the same. In addition, the preferred firing atmosphere for producing ferrite particles that satisfy formula (1) will be described later.

[0226] For these reasons, it is preferable to use a closed-atmosphere firing furnace such as a tunnel kiln or a lifting furnace when carrying out the formal firing process.

[0227] (2) Refractory containers

[0228] As a refractory container, for example, a generally rectangular container made of a material mainly composed of alumina (Al2O3) can be used. Containers generally referred to as saggers or the like can be used. In order to manufacture ferrite particles that satisfy the above formula (1), it is preferable to use a refractory container with a porosity of 20% or more and 35% or less.

[0229] Here, the porosity of a refractory container refers to the porosity of open pores that exist in the pores of refractory materials and are connected to the surface, and is set as the value obtained by measuring the porosity according to the method specified in "JISR 1634:1998 Determination of density and open porosity of sintered body of fine ceramics".

[0230] When granules are filled into a refractory container, the firing atmosphere, such as the oxygen concentration, inside the refractory container can sometimes become uneven. Therefore, by using a refractory container with a porosity within the aforementioned range, the air permeability of the refractory container's exterior and interior can be ensured, and the occurrence of uneven oxygen concentration in the firing atmosphere inside the refractory container can be suppressed. Thus, the situation where granules are fired under locally different firing atmospheres (e.g., oxygen-free atmosphere) inside the refractory container can be suppressed, and the ferrite formation reaction of each granule can be carried out homogeneously. As a result, ferrite particles that satisfy the above formula (1) can be manufactured with high precision, and ferrite particles with small deviations in the magnetic properties, etc., of each particle can be obtained.

[0231] In this regard, when the porosity is less than 20%, the atmosphere inside the refractory container is inconsistent with the firing atmosphere in the furnace. Even near the inner wall of the refractory container, where the firing atmosphere is the same as in the furnace, the possibility of different atmospheric conditions increases when the atmosphere is closer to the center of the refractory container. Therefore, even when the same refractory container is contained in the same furnace and fired, the firing atmosphere will vary depending on the location of the fired granules, thus causing deviations in the ferrite formation reaction. Therefore, the "Mn" at the B site... 3+ "The occupancy rate is relatively high compared to other particles, which poses a risk of generating particles with low magnetization. On the other hand, when the porosity exceeds 35%, the durability of the refractory container decreases, so it is not preferred."

[0232] To achieve the aforementioned effects, it is more preferable that the lower limit of the porosity of the refractory container is 22%, and even more preferably, it is 25%. Furthermore, it is more preferable that the upper limit of the porosity of the refractory container is 33%, and even more preferably, it is 30%.

[0233] (3) Firing atmosphere

[0234] i) Oxygen concentration

[0235] For the manufacture of the ferrite particles of the present invention, it is preferable that the oxygen concentration in the firing atmosphere is 0.1 vol% (1000 ppm) or more and 4.0 vol% (40000 ppm) or less. When firing is carried out in an oxygen-free atmosphere (oxygen concentration 0.0 vol%), Mn 3+ It will easily invade the B site and make it difficult to manufacture ferrite particles that satisfy formula (1). In order to manufacture ferrite particles that satisfy formula (1), it is more preferable that the atmospheric oxygen concentration is 2.0 vol% (20000 ppm) or less, and even more preferably 1.0 vol% (10000 ppm) or less.

[0236] ii) Furnace pressure

[0237] To manufacture the ferrite particles of this invention, it is preferable to fire the material to be fired in a closed atmosphere heat treatment furnace under pressure where the furnace pressure is 2 Pa higher than or equal to 100 Pa higher than the external atmosphere pressure. By firing under such pressure, which is higher than the external atmosphere pressure, good atmosphere replacement within the refractory container can be achieved, and the atmosphere within the refractory container can be made consistent with the conditioning atmosphere within the furnace. As a result, it is possible to suppress firing under locally different firing atmospheres (e.g., oxygen-free atmosphere) within the refractory container, and to adjust the firing atmosphere of each particle to be uniform.

[0238] A closed-atmosphere firing furnace is not in a sealed state where the external atmosphere and the furnace interior (firing chamber) are completely isolated. It has an air inlet and an exhaust outlet. Atmosphere-conditioning gases such as nitrogen are supplied to the furnace through the air inlet, and air from the furnace is discharged through the exhaust outlet, thereby adjusting the oxygen concentration and other conditions within the furnace to predetermined conditions. During the firing and granulation of the material, air supply and exhaust are continuously performed to maintain the furnace atmosphere at predetermined conditions. Therefore, air supply and exhaust are performed in such a way that the oxygen concentration and other conditions of the furnace atmosphere are maintained at predetermined conditions, and the furnace pressure is adjusted as described above to be within a range of 2 Pa to 100 Pa higher than the external atmosphere pressure. That is, preferably, the exhaust volume is maintained at or above the same level as in the case where the furnace is not pressurized, and the air supply is performed to maintain the oxygen concentration and other conditions of the furnace atmosphere at predetermined conditions.

[0239] (4) Formal firing temperature, etc.

[0240] The formal firing temperature and formal firing time can be selected from the conditions preferred for producing ferrite particles of the desired ferrite composition. For example, it is preferable that the formal firing is performed by holding at a temperature of 850°C or higher for 4 hours to 24 hours. In this case, it is preferable to hold at a temperature suitable for the formation of ferrite particles with a spinel-type crystal structure for 3 hours or more. However, the formal firing temperature and holding time are not particularly limited as long as ferrite particles with a spinel-type crystal structure can be obtained.

[0241] 4-1-4. Post-firing procedures

[0242] After formal firing, the fired material is broken down and classified. Existing classification methods such as wind classification, sieve filtration, and sedimentation are used to adjust the particle size to the desired range. In the case of dry recovery, cyclone separators can also be used. When adjusting the particle size, two or more of the aforementioned classification methods can be selected, or conditions can be modified within a single classification method to remove both coarse and fine particles.

[0243] Furthermore, for ferrite particles after formal firing or grading, surface oxidation treatment can be performed by low-temperature heating of their surface as needed, thereby adjusting the surface resistivity. Surface oxidation treatment can be performed using a rotary furnace, batch furnace, or similar equipment in an oxygen-containing atmosphere such as air, at temperatures between 400°C and 730°C, preferably between 450°C and 680°C. When the heating temperature during surface oxidation treatment is below 400°C, the surface of the ferrite particles cannot be sufficiently oxidized, and sometimes the desired surface resistivity characteristics cannot be obtained. On the other hand, when the heating temperature is higher than 730°C, oxidation may be excessive, risking a decrease in the saturation magnetization of the ferrite particles. To uniformly form an oxide film on the surface of the ferrite particles, a rotary furnace is preferred. However, this surface oxidation treatment is an arbitrary process.

[0244] 4-2. Carriers for Electrophotographic Developers

[0245] The carrier for the electrophotographic developer of this invention uses the aforementioned ferrite particles as the core material, and a resin coating layer is provided on the surface of the ferrite particles. The resin constituting the resin coating layer is as described above. When forming the resin coating layer on the surface of the ferrite particles, known methods can be used, such as brush coating, fluidized bed-based spray drying, rotary drying, and liquid immersion drying based on a universal mixer. To increase the ratio of the resin coating area to the surface area of ​​the ferrite particles (resin coating rate), it is preferable to use a fluidized bed-based spray drying method. Even when using any method, it is possible to perform one or more resin coating treatments on the ferrite particles. It is also possible to include the aforementioned additives in the resin coating solution used when forming the resin coating layer. Furthermore, since the amount of resin coating on the surface of the ferrite particles is as described above, the description is omitted here.

[0246] Alternatively, after coating the ferrite particles with a resin coating solution, sintering can be performed using either external or internal heating methods, as needed. For external heating, stationary or mobile electric furnaces, rotary furnaces, or combustion furnaces can be used. For internal heating, a microwave oven can be used. When using a UV-curable resin as the coating resin, a UV heater is used. 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 a temperature at which the curing of these resins will be fully achieved.

[0247] 4-3. Electrophotographic developing agent

[0248] Next, the method for manufacturing the electrophotographic developer of the present invention will be described.

[0249] The electrophotographic developer of the present invention comprises the carrier for the above-described electrophotographic developer and toner. As described above, the toner can preferably be either polymerized toner or pulverized toner.

[0250] Polymerized toner can be manufactured using known methods such as suspension polymerization, emulsion polymerization, emulsion agglomeration, ester extension polymerization, and phase inversion emulsification. For example, in a color dispersion using a surfactant to disperse the colorant in water, polymerizable monomers, surfactants, and polymerization initiators are mixed and stirred in a water-soluble medium, causing the polymerizable monomers to emulsify and disperse in the water-soluble medium. Polymerization is carried out while stirring and mixing, and then a salting-out agent is added, causing the polymer particles to salt out. The particles obtained through salting-out are filtered, washed, and dried to obtain polymerized toner. External additives can then be added to the dried toner particles as needed.

[0251] Furthermore, in manufacturing these polymerized toner particles, a toner component comprising a polymerizable monomer, a surfactant, a polymerization initiator, and a colorant is used. Fixing modifiers and charge control agents can be formulated into this toner component.

[0252] Toner powder can be pulverized by, for example, thoroughly mixing binder resin, colorant, and charge control agent in a mixer such as a Henschel mixer, then melt-blending it using a twin-screw extruder to uniformly disperse it, cooling it, micronizing it using a jet mill, and then classifying it using a classifier such as an air classifier to obtain toner powder of the desired particle size. Alternatively, it can contain wax, magnetic powder, viscosity modifier, and other additives as needed. Furthermore, additives can be added after classification.

[0253] Example

[0254] Next, embodiments and comparative examples will be shown to specifically describe the invention. However, the invention is not limited to the following embodiments.

[0255] [Example 1]

[0256] (1) Ferrite particles

[0257] In Example 1, MnO, MgO, Fe2O3, and SrO raw materials were weighed out in the following proportions: MnO: 46.0 mol%, MgO: 3.0 mol%, Fe2O3: 51.0 mol%, and SrO: 0.8 mol%. Here, manganese tetroxide was used as the MnO raw material, magnesium hydroxide was used as the MgO raw material, iron oxide was used as the Fe2O3 raw material, and strontium carbonate was used as the SrO raw material. Furthermore, regarding the above formula (2), n... Fe =51.0 × 2 = 102.0, n Mn =46.0, n Mg =3.0, n Fe / (n Mn +n Mg = 2.08.

[0258] Next, the weighed raw materials were pulverized for 5 hours using a dry media mill (vibratory mill, 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 and added to the solid portion (the amount of raw material in the slurry), with 0.2% by mass of PVA added. As a dispersant, a polycarboxylic acid dispersant was added, and the viscosity of the slurry was prepared to 2 poise. Then, granulation and drying were performed using a spray dryer.

[0259] Then, the granules were formally fired in a tunnel furnace, which served as a closed-atmosphere heat treatment furnace, at a firing temperature (holding temperature) of 1230°C and an oxygen concentration of 0.8% by volume for 5 hours. The heating rate was set to 150°C / hour, and the cooling rate to 110°C / hour. Furthermore, the granules were fired in a sagger with a porosity of 20%.

[0260] Furthermore, atmospheric gas was introduced from the outlet side of the tunnel furnace to seal the furnace interior, and the internal pressure was increased to 100.0 Pa higher than the external atmospheric pressure. The resulting calcined material was crushed using a hammer crusher (actually an impact crusher), then classified using a rotary screen employing an intermittent screening method and a turbine classifier with a rotary airflow classifier to adjust the particle size. Low-magnetic-strength particles were separated by magnetic separation to produce the ferrite particles of Example 1. Additionally, no pre-calcination or debinding process was performed before or after the formal calcination process.

[0261] (2) Using the above-mentioned ferrite particles as the core material for the carrier of electrophotographic developer, a resin coating layer is formed on the surface of the ferrite particles as follows, thereby obtaining the carrier of Example 1.

[0262] 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 as the solid portion of the silicone resin, since a resin solution concentration of 20% by mass was used, diluent: toluene) and 100 parts by mass of the aforementioned ferrite particles were mixed in a universal mixer, allowing the toluene to evaporate while 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 oven at 250°C for 2 hours. Then, after cooling to room temperature, the resin-cured ferrite particles were removed, and particle agglomeration was de-gained using a vibrating screen with a 200-mesh sieve. Non-magnetic materials were removed using a magnetic separator. Then, coarse particles were removed again using a vibrating screen with a 200-mesh sieve, resulting in the carrier for an electrophotographic developer of Example 1, with ferrite particles as the core material and a resin coating on its surface.

[0263] [Example 2]

[0264] The raw materials were weighed out in the following proportions: MnO: 40.0 mol%, MgO: 2.0 mol%, Fe2O3: 58.0 mol%, and SrO: 1.2 mol%. The firing temperature was set to 1270°C, the oxygen concentration in the firing atmosphere was set to 1.5% by volume, the furnace pressure was increased by 10.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 35%. Otherwise, similar to Example 1, after manufacturing the ferrite particles, a surface oxidation treatment was performed at 450°C to manufacture the ferrite particles of Example 2. In addition, the value of the above formula (2) is "2.76". Furthermore, except for the use of these ferrite particles, the process was carried out in the same manner as in Example 1 to obtain the carrier for the electrophotographic developer of Example 2.

[0265] [Example 3]

[0266] The raw materials were weighed out in the following proportions: MnO: 43.0 mol%, MgO: 0.5 mol%, Fe2O3: 56.6 mol%, and SrO: 0.8 mol%. The firing temperature was set to 1280°C, the oxygen concentration in the firing atmosphere was set to 0.5% by volume, the furnace pressure was increased by 5.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 35%. Otherwise, the ferrite particles of Example 3 were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "2.60". Furthermore, except for the use of these ferrite particles, the carrier for the electrophotographic developer of Example 3 was obtained in the same manner as in Example 1.

[0267] [Example 4]

[0268] The raw materials were weighed out in the following proportions: MnO: 40.5 mol%, MgO: 9.0 mol%, Fe2O3: 50.5 mol%, and SrO: 1.0 mol%. The firing temperature was set to 1250 °C, the oxygen concentration in the firing atmosphere was set to 0.2% by volume, the furnace pressure was increased by 20.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 30%. Otherwise, the ferrite particles of Example 4 were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "2.04". Furthermore, except for the use of these ferrite particles, the carrier for the electrophotographic developer of Example 4 was obtained in the same manner as in Example 1.

[0269] [Example 5]

[0270] The raw materials were weighed out in the following proportions: MnO: 45.0 mol%, MgO: 3.0 mol%, Fe2O3: 52.0 mol%, and SrO: 0.4 mol%. The ferrite particles of Example 5 were manufactured in the same manner as in Example 1, except that the firing temperature was set to 1180°C, the oxygen concentration in the firing atmosphere was set to 1.2% by volume, the furnace pressure was increased by 50.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 30%. Furthermore, the value of the above formula (2) was "2.17". And, except for the use of these ferrite particles, the process was carried out in the same manner as in Example 1, and the carrier for the electrophotographic developer of Example 5 was obtained.

[0271] [Example 6]

[0272] The raw materials were weighed out in the following proportions: MnO: 38.0 mol%, MgO: 2.0 mol%, Fe2O3: 60.0 mol%, and SrO: 0.8 mol%. The firing temperature was set to 1260°C, the oxygen concentration in the firing atmosphere was set to 0.3% by volume, the furnace pressure was increased by 2.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 35%. Otherwise, ferrite particles were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "3.00". Furthermore, except for the use of these ferrite particles, the process was carried out in the same manner as in Example 1, and the carrier for the electrophotographic developer of Example 6 was obtained.

[0273] [Comparative Example 1]

[0274] The raw materials were weighed out in the following proportions: MnO: 52.0 mol%, MgO: 3.0 mol%, Fe2O3: 45.0 mol%, and SrO: 0.3 mol%. The firing temperature was set to 1170°C, the oxygen concentration in the firing atmosphere was set to 0.3% by volume, the furnace pressure was increased to 190.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 5%. Otherwise, ferrite particles of Comparative Example 1 were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "1.64". Furthermore, except for the use of these ferrite particles, the same procedure as in Example 1 was followed to obtain the carrier for the electrophotographic developer of Comparative Example 1.

[0275] [Comparative Example 2]

[0276] The raw materials were weighed out in the following proportions: MnO: 49.0 mol%, MgO: 2.5 mol%, Fe2O3: 48.5 mol%, and SrO: 0.8 mol%. The firing temperature was set to 1200 °C, the oxygen concentration in the firing atmosphere was set to 0.2% by volume, the furnace pressure was increased by 180.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 15%. Otherwise, ferrite particles of Comparative Example 2 were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "1.88". Furthermore, except for the use of these ferrite particles, the same procedure as in Example 1 was followed to obtain the carrier for the electrophotographic developer of Comparative Example 2.

[0277] [Comparative Example 3]

[0278] The raw materials were weighed out in the following proportions: MnO: 51.0 mol%, MgO: 1.9 mol%, Fe2O3: 47.1 mol%, and SrO: 1.2 mol%. The firing temperature was set to 1220°C, the oxygen concentration in the firing atmosphere was set to 0.1% by volume, the furnace pressure was increased by 160.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 15%. Otherwise, ferrite particles of Comparative Example 3 were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "1.78". Furthermore, except for the use of these ferrite particles, the same procedure as in Example 1 was followed to obtain the carrier for the electron photographic developer of Comparative Example 3.

[0279] [Comparative Example 4]

[0280] The raw materials were weighed out in the following proportions: MnO: 55.0 mol%, MgO: 0.4 mol%, Fe2O3: 44.6 mol%, and SrO: 1.3 mol%. The firing temperature was set to 1230°C, the oxygen concentration in the firing atmosphere was set to 0.3% by volume, the furnace pressure was increased by 150.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 15%. Otherwise, similar to Example 1, after manufacturing the ferrite particles, a surface oxidation treatment was performed at 450°C to manufacture the ferrite particles of Comparative Example 4. In addition, the value of the above formula (2) is "1.61". Furthermore, except for the use of these ferrite particles, the same procedure as in Example 1 was followed to obtain the carrier for the electrophotographic developer of Comparative Example 4.

[0281] [Comparative Example 5]

[0282] The raw materials were weighed out in the following proportions: MnO: 41.0 mol%, MgO: 10.2 mol%, Fe2O3: 48.8 mol%, and SrO: 0.6 mol%. The firing temperature was set to 1170°C, the oxygen concentration in the firing atmosphere was set to 0.4% by volume, the furnace pressure was increased by 200.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 10%. Otherwise, ferrite particles of Comparative Example 5 were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "1.91". Furthermore, except for the use of these ferrite particles, the same procedure as in Example 1 was followed to obtain the carrier for the electrophotographic developer of Comparative Example 5.

[0283] [Comparative Example 6]

[0284] The raw materials were weighed out in the following proportions: MnO: 49.0 mol%, MgO: 5.0 mol%, Fe2O3: 46.0 mol%, and SrO: 0.2 mol%. The firing temperature was set to 1220°C, the oxygen concentration in the firing atmosphere was set to 0.5% by volume, the furnace pressure was increased by 105.0 Pa relative to the external atmosphere pressure, and the porosity of the sagger was set to 18%. Otherwise, ferrite particles of Comparative Example 6 were manufactured in the same manner as in Example 1. In addition, the value of the above formula (2) is "1.70". Furthermore, except for the use of these ferrite particles, the same procedure as in Example 1 was followed to obtain the carrier for the electrophotographic developer of Comparative Example 6.

[0285] Table 1 shows the manufacturing conditions of the ferrite particles in each embodiment and comparative example.

[0286] [evaluate]

[0287] 1. Evaluation Methods

[0288] (1) Component analysis

[0289] For the ferrite particles of the above embodiments and comparative examples, XRD diffraction, Rietwald analysis, and ICP luminescence analysis were performed using the methods described above, and component analysis was conducted to determine the values ​​of "u", "v", "w", "x", and "y+z". The Sr content was also determined as described above.

[0290] (2) Basic characteristics

[0291] For the ferrite particles of the above embodiments and comparative examples, the saturation magnetization, apparent density (AD), and internal porosity were measured using the methods described above.

[0292] (3) Image quality characteristics

[0293] Electrophotographic developers were prepared using the carriers for electrophotographic developers manufactured in the various embodiments and comparative examples, and the results were evaluated for (a) image density reproducibility, (b) image density unevenness, (c) carrier adhesion, and (d) toner scattering.

[0294] Electrophotographic developer is prepared in the following manner.

[0295] Using a ball mill, 18.6 g of the carrier for the electrophotographic developer produced in each example and comparative example was stirred and mixed with 1.4 g of toner 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 (cyan toner, manufactured by Fuji Xerox Co., Ltd. for DocuPrint C3530; average volume particle size (D50) of approximately 5.8 μm) used in full-color printers.

[0296] (a) Image density reproducibility

[0297] Using the electrophotographic developer prepared in the above manner as a sample, the image density reproducibility was determined by a charge measurement device according to the following criteria.

[0298] As a charge measurement device, a magnetic roller was configured. Inside a cylindrical aluminum tube (hereinafter referred to as the sleeve) with a diameter of 31 mm and a length of 76 mm, magnets with a total of 8 poles (magnetic flux density 0.1 T) were alternately arranged, consisting of N and S poles. Furthermore, a cylindrical electrode with a 5.0 mm gap to the sleeve was positioned on the outer periphery of the sleeve. After uniformly attaching 0.5 g of electrophotographic developer (as a sample) to the sleeve, the outer aluminum tube was fixed in place. While rotating the inner magnetic roller at 2000 rpm, a DC voltage of 2500 V was applied between the outer electrode and the sleeve for 60 seconds, causing the toner to move to the outer cylindrical electrode. The mass of toner that moved to the outer electrode (the amount of toner moved) was measured. An electrometer (KEITHLEY insulation resistance meter model 6517A) was used as the outer cylindrical electrode. The image reproduction rate was then calculated using the following formula. The measurement was repeated 10 times, and the average value was calculated.

[0299] Image reproduction rate (%) = (Toner migration amount / Toner mass in 0.5g developer) × 100

[0300] Based on the average image reproduction rate calculated for each sample, evaluations from A to D were conducted using the following criteria.

[0301] A: More than 97%

[0302] B: Above 95%, less than 97%

[0303] C: Above 85%, less than 95%

[0304] D: Less than 85%

[0305] (b) Uneven image density

[0306] Similar to the evaluation of image reproducibility, toner movement was measured. Based on the maximum toner movement, minimum toner movement, and average value from 10 measurements, an evaluation value was generated using the following formula to assess the image density uniformity for each sample. Furthermore, a lower evaluation value indicates less image density uniformity.

[0307] Image density unevenness evaluation value =

[0308] (Maximum toner movement - Minimum toner movement) / Average toner movement × 100 (%)

[0309] Based on the evaluation values ​​obtained for each sample, evaluations of A to D were conducted according to the following criteria.

[0310] A: Less than 0.5%

[0311] B: Above 0.5%, less than 1.5%

[0312] C: Above 1.5%, less than 2.5%

[0313] D: 2.5% or more

[0314] (c) Carrier attachment

[0315] Using an electrophotographic developer prepared as described above as a sample, the carrier adhesion was evaluated in the following manner.

[0316] Using the same charge measurement apparatus as used for evaluating image reproducibility, 1g of the aforementioned electrophotographic developer was uniformly applied to the sleeve. With the outer aluminum tube fixed in place, a DC voltage of 2500V was applied between the outer electrode and the sleeve for 90 seconds while the inner magnetic roller rotated at 2000 rpm, causing the toner to move to the outer electrode. After 90 seconds, the applied voltage was cut off, and after the rotation of the magnetic roller stopped, the outer electrode was removed. The number of carrier particles attached along with the toner that moved to the electrode was measured. Based on the measured number of carrier particles, an evaluation of A to D was performed according to the following criteria.

[0317] A: The number of attached carrier particles is less than 20.

[0318] B: The number of attached carrier particles is more than 20 and less than 40.

[0319] C: The number of attached carrier particles is more than 40 and less than 50.

[0320] D: The number of attached carrier particles is more than 50.

[0321] (d) Toner scattering

[0322] A toner scattering measurement device was constructed by using a magnetic roller with eight magnets (magnetic flux density 0.1T) alternately arranged with N and S poles, and a cutting plate placed 1.0 mm away from the magnetic roller. A particle counter was installed 50 mm away from the cutting plate, which is in contact with the developer, to measure toner scattering. To suppress variations in the measured value due to toner scattering caused by external atmospheric influences, the toner scattering measurement was performed in a cleanroom of Class 1000 (20±5℃, 50±5%). Furthermore, the toner scattering measurement involved counting particles with a diameter of 5 μm that adhered to the cutting plate while the magnetic roller rotated at 2000 rpm for 10 minutes. The number of particles per minute (defined as the number of particles per 1 L volume) was calculated based on the cumulative particle count, and an evaluation from A to D was performed according to the following criteria.

[0323] A: Less than 500 cells / L

[0324] B: Above 500 cells / L, less than 1000 cells / L

[0325] C: Above 1000 cells / L, less than 1600 cells / L

[0326] D: 1600 cells / L or more

[0327] Compared to actual machine evaluation, which assesses image reproducibility, image density uniformity, carrier adhesion, and toner scattering using a real machine (image forming apparatus), the above evaluation method provides a more realistic assessment based on the electrophotographic developer, closely reflecting the actual image quality characteristics. In recent years, the performance of both the machine and the electrophotographic developer has improved; for example, in actual machines with continuous copying speeds of around 50 frames per minute, printing on the machine sometimes yields virtually no noticeable difference. Furthermore, evaluation results can sometimes be biased due to factors such as the type of machine used in the test or the machine's own long-term deterioration. On the other hand, as described above, the alternative evaluation based on a charge measurement device allows for stricter control of the measurement conditions, expanding the evaluation band width by one unit compared to actual machine evaluation. Moreover, in the aforementioned alternative evaluation, the magnetic roller rotation speed is set to an extremely high speed of 2000 rpm. Therefore, a more precise evaluation of the image quality characteristics of the electrophotographic developer during printing on an actual machine with a high continuous copying speed of 120 frames per minute or more can be achieved.

[0328] 2. Evaluation Results

[0329] Table 2 shows the component analysis results for each embodiment and comparative example. Furthermore, Table 3 shows the basic characteristics and image quality characteristics of each embodiment and comparative example.

[0330] (1) Components

[0331] Based on the results shown in Table 2, it was confirmed that the proportions of Fe, Mn, and Mg raw materials for the ferrite particles in each embodiment were as described in formula (2)(n). Fe / (n Mn +n Mg The raw materials are blended in a manner where the value of )) is above 2.00 and below 3.00 to produce granules. These granules are then contained in a refractory container with a porosity of 20% to 35% and fired. This process produces a spinel-type crystal structure belonging to space group Fd-3m, whose ferrite composition satisfies the above formula (1)((Fe)). 3+ u, Mn 2+ v, Mg 2+ w)(Mn 3+ x, Fe 2+ y, Fe 3+ Ferrite particles with the following properties: z)2O4, u+v+w=1, x+y+z=1, 0.870≤v<1.000, 0.001≤w<0.070, 0.000≤x≤0.075.

[0332] On the other hand, the "x" values ​​of the ferrite particles in the comparative examples all exceeded 0.075, and the ferrite particles of the present invention could not be obtained under the manufacturing conditions of each comparative example. The value of "x" as described above represents the "Mn" value at the B site. 3+ The percentage of MnO in Comparative Example 5 was 41.0 mol%, which was lower than that of the other comparative examples. However, in Example 6 (MnO: 38 mol%), where the MnO percentage was smaller than that of Comparative Example 5, the value of "x" was "0.013", unlike in Comparative Example 5 where the value of "x" was a large "0.170". Furthermore, it was confirmed that even when observed only in the comparative examples, the values ​​of "x" in Comparative Examples 2, 3, 4, and 6, which had a larger MnO percentage than Comparative Example 5, were smaller than those in Comparative Example 5. Therefore, it was confirmed that simply reducing the Mn percentage could not produce ferrite particles with the ferrite composition represented by Formula (1).

[0333] However, the ferrite particles of the present invention have Mn at site A. 2+The value of "v" representing the percentage of Mn is in the range of "0.870 ≤ v < 1.000". To obtain ferrite particles with a "v" value within this range, the amount of Mn needs to be "2x + v" when determining the blending ratio of Mn raw materials during ferrite particle manufacturing. Except for Comparative Example 5, the blending ratio of MnO in the other comparative examples is larger than that in the embodiments. However, the value of "v" in each comparative example is smaller than the range specified in this invention. Therefore, it is confirmed that by determining the blending ratio of Mn raw materials solely in a manner where "v" is within the range specified in this invention, the value of "x" will not be within the range of this invention; moreover, Mn... 3+ It will invade the B site, and as a result, it is difficult to set the value of "v" within the scope of this invention.

[0334] That is, the inventors conducted a dedicated study and found that by mixing the Fe, Mn, and Mg raw materials in a manner that satisfies Equation (2), and by using a sagger (refractory container) used during sintering and granulation with a porosity within the aforementioned range, it is possible to suppress Mn during the preparation of the spinel crystal phase. 3+ This method targets the invasion of B sites and obtains ferrite particles with high precision whose "x" and "v" values ​​are within the range specified in this invention. It can suppress Mn... 3+ The rationale for targeting site B is considered as follows.

[0335] First, during the production of granules, the proportions of Mn, Fe, and Mg are determined to satisfy Equation (2). This results in a higher proportion of Fe compared to the proportion of Mn in the granules. In other words, the raw materials are formulated to be Fe-rich. Furthermore, by firing the granules composed of the Fe-rich mixture, it becomes easier for Fe to pass through during the ferrite formation reaction. 2+ or Fe 3+ Preferentially occupying B sites and inhibiting Mn 3+ Regarding the invasion of site B. In particular, it was confirmed that the values ​​of Equation (2) in Examples 2, 3 and 6, which have values ​​of “2.76”, “2.60” and “3.00”, are larger than those in other examples. By using the formulation of raw materials as a Fe-rich condition, it is easier to obtain ferrite particles with smaller “x” values.

[0336] Furthermore, during the firing of granules, by using a sagger with a porosity within a predetermined range, the air permeability of the sagger's exterior and interior can be ensured, and the occurrence of uneven oxygen concentration in the firing atmosphere within the sagger can be suppressed. Therefore, it is easier to make the entire area within the sagger a firing atmosphere suitable for manufacturing ferrite particles that satisfy the above formula (1). That is, it is possible to suppress the following firing conditions: within the sagger, the firing atmosphere locally varies, Mn3+ It is easy to penetrate the B site. Furthermore, the granules can be fired in a state where the firing atmosphere inside the sagger is uniform, so that the ferrite reaction of each granule can be carried out homogeneously. Therefore, it is believed that ferrite particles that satisfy the above formula (1) can be manufactured with high precision, and ferrite particles with small deviations in magnetic properties of each particle can be obtained. At this time, the higher the porosity of the sagger is within the above range, the better. In Examples 1 to 6, it was also confirmed that the sagger with higher porosity is more likely to produce ferrite particles with smaller "x" values.

[0337] Furthermore, by pressurizing the furnace pressure relative to the external atmosphere pressure, it is easier to make the atmosphere inside the sagger the same as the atmosphere inside the furnace, thereby enabling the high-precision production of ferrite particles that satisfy the above formula (1). However, it has been confirmed that a larger difference between the furnace pressure and the external atmosphere pressure is not necessarily better. Preferably, as shown in the embodiments, a slight pressurization is applied within the range specified in this invention (2 Pa or more, 100 Pa or less), using a sagger with a high porosity, and the pressurization level is preferably set to 50.0 Pa or less, more preferably 20.0 Pa or less, and even more preferably 10.0 Pa or less. That is, it is believed that by maintaining the gas supply to the furnace and the exhaust gas from the furnace in a way that the atmosphere pressure inside the furnace does not become too high, it is easier to make the firing atmosphere of each granule in the sagger the same, and to suppress the generation of particles with locally different values ​​of "x".

[0338] Furthermore, no peaks indicating Sr ferrite were observed in the powder X-ray diffraction patterns. Therefore, it is confirmed that Sr is not present as a ferrite constituent element in the ferrite particles of the various embodiments and comparative examples.

[0339] (2) Basic characteristics

[0340] Next, the basic characteristics of each embodiment and comparative example were compared according to Table 3. The ferrite particles of Embodiments 1 to 6 of the present invention were confirmed to have a high saturation magnetization of 70 Am. 2 / kg~86Am 2 / kg, apparent density is 2.14 g / cm³ 3 ~2.31g / cm 3 The internal porosity ranges from 1.3% to 4.0%. On the other hand, the saturation magnetization of the ferrite particles in Comparative Examples 1 to 6 is 60 Am. 2 / kg~72Am 2 / kg, apparent density is 1.91g / cm³ 3 ~2.24g / cm 3 The internal porosity ranges from 2.9% to 5.8%.

[0341] In the ferrite particles of the embodiments, there are also values ​​that are equivalent to those in the comparative examples. However, overall, it can be said that the ferrite particles of the embodiments tend to have high magnetization, higher apparent density, and lower internal porosity. The relationship between the value of "x" and their physical properties is examined as follows. First, in the above formula (1), even if the content ratio of each element in the ferrite particles is the same, when the value of "x", that is, Mn at the B site, is... 3+ When the occupancy rate of "x" is different, the electron spin state at the B site is also different, which, as mentioned above, has a significant impact on magnetic properties. The smaller the value of "x", the easier it is to obtain ferrite particles with high magnetization. Therefore, it is believed that the ferrite particles of the embodiment with a smaller value of "x" have a higher saturation magnetization than the ferrite particles of the comparative example.

[0342] Furthermore, in the above formula (1), even if the proportions of each element in the ferrite particles are the same, the values ​​of "y+z", "u", and "v" are different when the value of "x" is different, and therefore the growth rate of each grain is also different. For example, when sintering spherical granulated powder, when the growth rate of each grain is different, the spherical shape cannot be maintained, and the particle shape may sometimes be deformed. In addition, when the grain grows abnormally, it may become a part that protrudes, or when there is a part that grows slower than others, that part may become flat, etc., resulting in particles with irregular shapes. When particles with different shapes are included, the interparticle voids in the powder will increase. Therefore, the apparent density will decrease. In addition, when the grain grows abnormally, internal voids are easily generated, and the internal porosity will also increase. When the firing atmosphere changes locally in the sagger during firing, it is believed that particles with different values ​​of "x" will be generated, and the apparent density will decrease and the internal porosity will increase. In that case, it is assumed that the value of the saturation magnetization will be lower than the value assumed solely based on the value of "x".

[0343] Therefore, when observing the embodiments and comparative examples, in the embodiments, the porosity and atmosphere pressure of the sagger were appropriately controlled, so it is believed that the correlation between the value of "x" and "saturation magnetization" also becomes higher.

[0344] On the other hand, in the comparative examples, these controls were insufficient. Therefore, it was considered that, based on the fact that "x" and "v" deviated from the range specified in this invention, due to major factors such as the decrease in apparent density and the increase in internal porosity, the correlation between the value of "x" and "saturation magnetization" would also become lower. For example, in Comparative Example 6, although the value of "x" showed a lower value relative to "0.108" and other comparative examples, the saturation magnetization showed a low value of 64 Am. 2 The value per kg.

[0345] (3) Image characteristics

[0346] According to Table 3, when using the electrophotographic developer with ferrite particles as the carrier core material of this embodiment, in the above alternative evaluation assuming a high continuous copying speed of 120 frames / min or more, "image density reproducibility," "image density unevenness," "carrier adhesion," and "toner scattering" received high ratings of "A" or "B." In particular, it was confirmed that the ferrite particles of Example 3 received an "A" rating in all items, making them an extremely suitable carrier core material for electrophotographic developers suitable for high-speed printing. On the other hand, when observing the comparative examples, for the two items "image density reproducibility" and "image density unevenness," if Comparative Example 4 is excluded, the same as the embodiments of the present invention, an evaluation of "A" or "B" was obtained. However, for "carrier adhesion" and "toner scattering," both received low ratings of "C" or "D."

[0347] Therefore, the particularly significant difference in carrier adhesion is considered to be due to the following reasons. The ferrite particles in this embodiment are highly magnetized, and when observing each particle individually, the proportion of particles containing low magnetization is considered extremely small. On the other hand, the ferrite particles in the comparative examples have higher "x" values, and compared to the ferrite particles in this embodiment, they are considered to be low magnetized when observing the ferrite particles as a whole, and when observing each particle individually, the proportion of particles containing low magnetization is higher. As a result, regarding "image density reproducibility" and "image density unevenness," although the same evaluation as in this embodiment is obtained even when high-speed printing is performed, it is considered that in the above alternative evaluation, when the rotation speed of the magnetic roller is set to an extremely high speed of 2000 rpm, and when the ferrite particles of the comparative examples are used as the carrier core material, the magnetic force acting between the magnetic roller and the ferrite particles is smaller relative to the centrifugal force acting on each particle, resulting in more particles detaching from the magnetic roller.

[0348] Toner scattering occurs due to low magnetization of the carrier core material or insufficient charge on the toner. When the carrier core material is low-magnetized, sometimes the toner scatters along with the carrier as it scatters from the magnetic roller. Furthermore, when the toner is insufficiently charged, the electrostatic restraint between the toner and the carrier is weak, and sometimes only the toner scatters as the magnetic roller rotates. Compared to the ferrite particles of the embodiment, the ferrite particles of the comparative example are low-magnetized; therefore, as mentioned above, the carrier is more prone to scattering from the magnetic roller, and thus the amount of toner scattering is greater. Furthermore, it can be said that the ferrite particles with a larger "x" value are a mixed powder composed of multiple types of ferrite particles with different "x" values. Compared to particles of the same type with the same crystal structure rubbing against each other, particles of different types with different crystal structures rubbing against each other are less charged. Compared to the ferrite particles of the embodiment, the ferrite particles of the comparative example have a larger "x" value. Therefore, the comparative example ferrite particles had a greater chance of contact with ferrite particles with smaller "x" values ​​than those with larger "x" values. During the mixing and stirring of the carrier and toner, it was believed that some toner was undercharged, and toner scattering also occurred due to only toner scattering from the magnetic roller. On the other hand, it was believed that the ferrite particles in the example were highly magnetized, which could suppress localized undercharge; therefore, the evaluation of toner scattering amount received either "A" or "B".

[0349] Table 1

[0350]

[0351] Table 2

[0352]

[0353] Table 3

[0354]

[0355] Industrial availability

[0356] According to this invention, it is possible to provide ferrite particles, carriers for electrophotographic developers, and an electrophotographic developer that have magnetic properties suitable for high-speed printing and good image properties during high-speed printing.

[0357] Although the invention has been described in detail with reference to specific embodiments, it will be clear to those skilled in the art that various changes or modifications can be made without departing from the spirit and scope of the invention.

[0358] This application is based on Japanese Patent Application No. 2021-089755, filed on May 28, 2021, the contents of which are incorporated herein by reference.

Claims

1. A ferrite particle having a spinel-type crystal structure belonging to space group Fd-3m; The ferrite composition is represented by the following formula (1). (Fe 3＋ u, Mn 2＋ v, Mg 2＋ w)(Mn 3＋ x, Fe 2＋ y, Fe 3＋ z)2O4 ••• (1) Wherein, u + v + w = ​​1 x + y + z = 1 0.870≤v＜1.000 0.001≤w＜0.070 0.000≤x≤0.075。 2. The ferrite particles as described in claim 1, wherein, The w in the above equation (1) satisfies the following condition: 0.003≤w≤0.

060.

3. The ferrite particles as described in claim 1 or 2, wherein, When the total amount of Fe, Mn, and Mg contained in the ferrite particle is recorded as 100 mol, it contains more than 0.4 mol and less than 1.2 mol of Sr element, which is different from the constituent elements of these ferrites.

4. The ferrite particles as described in claim 1 or 2, wherein, The internal porosity is below 4.0%.

5. The ferrite particles as described in claim 1 or 2, wherein, The saturation magnetization, measured by B-H, is 70 Am when a magnetic field of 3 K•1000 / 4π•A / m is applied. 2 / kg or more, 90Am 2 / kg or less.

6. The ferrite particles as described in claim 1 or 2, wherein, The apparent density is 2.10 g / cm³. 3 Above, 2.40 g / cm 3 the following.

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

8. An electrophotographic developer comprising a carrier and toner as described in claim 7.

9. The electrophotographic developer of claim 8, wherein the electrophotographic developer is used as a replenishing developer.

10. A method for manufacturing ferrite particles, used to manufacture ferrite particles as described in any one of claims 1 to 6; In the manufacturing method of these ferrite particles, The raw materials Fe, Mn and Mg are blended in such a way that the following formula (2) is satisfied, and the calcined material is prepared. Ferrite particles are produced by containing the material to be fired in a refractory container with a porosity of 20% to 35% and firing it. 2.00≤n Fe / (n Mn +n Mg )≤3.00•••(2) in, When the total blending ratio (mol%) of Fe, Mn, and Mg raw materials is set to 100 mol%, n Fe The amount of Fe element in the Fe raw material (mol) n Mn The amount of Mn element in the Mn raw material (mol) n Mg The amount of Mg element in the Mg raw material (mol).

11. The method for manufacturing ferrite particles as described in claim 10, wherein, In a closed-atmosphere heat treatment furnace, the object to be fired is pressurized such that the pressure inside the furnace is 2 Pa higher than or 100 Pa higher than the atmospheric pressure outside the furnace.

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