Carrier core material, and electrophotographic development carrier and electrophotographic developer using the same

Abstract

To provide a carrier core having low apparent density and capable of preventing career scattering from being caused.SOLUTION: A carrier core material constituted of ferrite particles includes a composite oxide of a Ca element of 1.7 mass% or more and 6.5 mass% or less and an Si element of 1.4 mass% or more and 5.2 mass% or less. A magnetization σ1k of the ferrite particles when applying a magnetic field of 79.58×103 A / m (1000 oersteds) is 58Am2 / kg or more and 75Am2 / kg or less; an apparent density is 1.90 g / cm3 or more and 2.20 g / cm3 or less; and a pore volume is less than 0.010 mL / g.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carrier core material, and an electrophotographic development carrier and an electrophotographic developer using the same. [Background technology]

[0002] For example, in image forming devices using electrophotography, such as facsimiles, printers, and copiers, a toner is attached to an electrostatic latent image formed on the surface of a photoreceptor to make it visible, and this visible image is then transferred to paper or the like, and fixed by applying heat and pressure.From the viewpoint of achieving high image quality and colorization, so-called two-component developers containing a carrier and a toner are widely used as developers.

[0003] In a development method using a two-component developer, carrier and toner are mixed and stirred in a developing device, and the toner is charged to a predetermined amount by friction. The developer is then supplied to a rotating developing roller, forming a magnetic brush on the developing roller. The toner is then electrically transferred to the photosensitive member via the magnetic brush, thereby visualizing the electrostatic latent image on the photosensitive member. After the toner transfers, the carrier is peeled off the developing roller and mixed with the toner again in the developing device.

[0004] In recent years, in order to save energy by reducing the stirring power in the developing device and to stabilize image quality by suppressing "toner spent," which is the fusion of components that make up the toner to the surface of the carrier, it has been proposed to create voids inside the carrier core material and even to reduce the weight of the carrier core material by filling the internal voids with resin (Patent Documents 1 and 2, etc.).

[0005] However, although carrier core particles with internal voids have a lower apparent density, it is difficult to control the amount of coating resin that penetrates into the internal voids of the carrier core particles when the surface of the carrier core particles is coated with resin, which can result in variations in the amount of coating resin on the surface of the carrier core particles.Variations in the amount of coating resin can lead to variations in carrier properties and problems such as carrier scattering.

[0006] Another method for reducing the apparent density of the carrier core material and improving particle strength is to add SiO2 (silicon dioxide), which has a lower true density than ferrite, the main component of the carrier core material, as a raw material component of the carrier core material. However, because SiO2 easily absorbs moisture, there are concerns about practical issues, such as a decrease in the charging characteristics of the carrier core material in high-temperature, high-humidity environments. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-170224 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-086093 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, the present invention has been made in consideration of these conventional problems, and its purpose is to provide a carrier core material that is less likely to cause toner spent, has a consistent amount of coating resin on the surface of the carrier core material, and is less likely to cause carrier scattering.

[0009] Another object of the present invention is to provide a carrier and a developer that provide excellent stability in image quality. [Means for solving the problem]

[0010] The carrier core material according to the present invention, which achieves the above object, is a carrier core material made of ferrite particles, and contains a composite oxide of Ca and Si elements (hereinafter, may be referred to as "CaSi composite oxide"), and contains 1.7 mass % or more and 6.5 mass % or less of Ca element and 1.4 mass % or more and 5.2 mass % or less of Si element, and has a magnetic field of 79.58 × 10 3 Magnetization σ of the ferrite particles when A / m (1000 Oersted) is applied 1k 58Am 2 / kg or more 75Am 2in the range of less than / kg, and the apparent density is 1.90 g / cm 3 or more and 2.20 g / cm 3 or less, and the pore volume is less than 0.010 mL / g.

[0011] In the carrier core material having the above structure, the true density of the ferrite particles is 4.00 g / cm 3 or more and 4.75 g / cm 3 or less, which is preferable.

[0012] Also, in the carrier core material having the above structure, the saturation magnetization σ of the ferrite particles S is 67 Am 2 / kg or more and 90 Am 2 / kg, which is preferable.

[0013] Also, in the carrier core material having the above structure, the residual magnetization σ of the ferrite particles r is 2.0 Am 2 / kg or less, and the coercive force H c is 20 oersted or less, which is preferable.

[0014] Also, in the carrier core material having the above structure, the ferrite particles have a composition mainly represented by the general formula (Mn X Fe 3-X )O4 (where 0 < X < 3), preferably contains 2.0 mass% or more and 4.0 mass% or less of Ca element, and 2.0 mass% or more and 4.0 mass% or less of Si element.

[0015] Also, in the carrier core material having the above structure, the mass ratio of Ca element to Si element, Ca / Si, is preferably 0.5 or more and 2.0 or less.

[0016] Further, according to the present invention, there is provided an electrophotographic developer carrier characterized in that the surface of the carrier core material described above is coated with a resin.

[0017] Furthermore, according to the present invention, there is provided an electrophotographic developer containing the electrophotographic developer carrier described above and toner.

[0018] In addition, magnetization σ 1k , apparent density, pore volume, true density, saturation magnetization σ S , residual magnetization σ r , coercive force H c is a value measured by the measurement method in the examples described later.

[0019] In this specification, the terms "ferrite particles," "carrier core material," "electrophotographic development carrier," and "toner" each refer to an aggregate (powder) of individual particles. Unless otherwise specified, the symbol "to" used in this specification means that the numerical values ​​before and after the symbol "to" are included as the lower and upper limits. [Effects of the Invention]

[0020] The carrier core material of the present invention suppresses toner spent, and also prevents carrier scattering because the amount of resin coated on the surface of the carrier core material is consistent.

[0021] According to the electrophotographic development carrier and electrophotographic developer of the present invention, occurrence of carrier scattering and the like is suppressed, and images of good quality can be obtained stably over a long period of time. [Brief explanation of the drawings]

[0022] [Figure 1] 10 shows the results of XRD measurement of the carrier core material of Example 7. [Figure 2] 13 shows the results of XRD measurement of the carrier core material of Example 13. [Figure 3] 1 shows the results of XRD measurement of the carrier core material of Comparative Example 1. [Figure 4] 10 shows the results of XRD measurement of the carrier core material of Comparative Example 12. [Figure 5] 10 shows the results of XRD measurement of the carrier core material of Comparative Example 14. [Figure 6] FIG. 1 is a schematic diagram illustrating an example of a developing device using a carrier according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] One of the major features of the carrier core material of the present invention is that it is a carrier core material composed of ferrite particles, and contains a CaSi composite oxide, containing 1.7 mass% or more and 6.5 mass% or less of Ca element and 1.4 mass% or more and 5.2 mass% or less of Si element. As mentioned above, in the past, in order to reduce the apparent density of the carrier core material, ferrite (true density: about 5 g / cm), which is the main component of the carrier core material, was used. 3 ) has a smaller true density than SiO2 (true density: approx. 2.2 g / cm 3 It has been proposed to add SiO2 as a raw material component of the carrier core material, but this has caused problems such as a decrease in the charging characteristics of the carrier core material in high-temperature, high-humidity environments because SiO2 easily absorbs moisture. Therefore, the inventors of the present invention have conducted extensive research to find a substitute for SiO2 that is less susceptible to the influence of the usage environment, such as humidity, and has a smaller true density than ferrite, and does not significantly affect the charging characteristics of the carrier core material. As a result, they have found CaSiO3 (true density: approximately 2.9 g / cm 3 The present invention was made based on the finding that CaSi composite oxides such as SiO 2 , SiO 3 , and SiO 4 satisfy the above conditions.

[0024] In this specification, the CaSi composite oxide includes not only composite oxides in the narrow sense composed of Ca (calcium), Si (silicon), and O (oxygen), such as CaSiO3, but also composite oxides in which metal elements constituting ferrite, such as Fe (iron) and Mn (manganese), are dissolved in the composite oxides in the narrow sense.

[0025] The presence of CaSi composite oxide in the carrier core material can be confirmed by, for example, powder X-ray diffraction (XRD) measurement and component analysis. Specifically, this can be confirmed by the presence of a diffraction intensity peak in the incident angle 2θ range of 26.60° to 27.30° in the measured X-ray diffraction pattern, and by component analysis (described below) that shows that the carrier core material contains Ca and Si elements.

[0026] In the case of a composite oxide in the narrow sense, a diffraction intensity peak exists at an incident angle 2θ of 26.84°. Furthermore, in the case of a composite oxide in the narrow sense, for example, an oxide in which Fe is dissolved, a diffraction intensity peak exists at an incident angle 2θ of 27.13°. In the X-ray diffraction pattern of the carrier core material of Example 13 shown in Figure 2, a diffraction intensity peak originating from the composite oxide in the narrow sense (CaSiO3) and a diffraction intensity peak originating from an oxide in which Fe is dissolved ((Ca,Fe)SiO3) in the narrow sense appear in the range of incident angle 2θ of 26.60° or more and 27.30° or less.

[0027] The XRD measurement is carried out as follows. (Powder X-ray diffraction (XRD) measurement) Powder X-ray diffraction measurements of the carrier core material were performed using a Rigaku "Ultima IV." A Cu tube (Kα) was used as the X-ray source, and X-rays were generated under the conditions of an acceleration voltage of 40 kV and a current of 20 mA. The divergence slit opening angle was 1°, the scattering slit opening angle was 1°, the receiving slit width was 0.3 mm, the scanning mode was FT, the step width was 0.0100°, the counting time was 10 seconds, the number of integrations was 1, and the scanning range was 26.0≦2θ≦27.5.

[0028] The CaSi composite oxide is preferably CaSiO3 or a CaSiO3 containing a ferrite-constituting metal element such as Fe or Mn as a solid solution. The CaSi composite oxide is preferably added initially together with the raw material components of ferrite. However, even if CaSiO3 is added initially, a reaction in the manufacturing process may cause some or all of the CaSiO3 to be converted into a composite oxide (e.g., (Ca,Fe)SiO3) containing a ferrite-constituting metal element (e.g., Fe) as a solid solution. The effects of the present invention can be achieved even with such a composite oxide containing Fe as a solid solution. It is also possible to add and mix the Ca raw material component and the Si raw material component together with the raw material components of ferrite, and synthesize CaSiO3 in the firing process and incorporate it into the ferrite particles. However, it is preferable that CaSiO3 be added initially together with the raw material components of ferrite.

[0029] The content of Ca element in the carrier core material of the present invention is in the range of 1.7% by mass to 6.5% by mass. If the content of Ca element is less than 1.7% by mass, the apparent density increases and toner spent tends to occur. On the other hand, if the content of Ca element is more than 6.5% by mass, the magnetization σ 1k The Ca content is more preferably in the range of 2.0% by mass to 4.0% by mass.

[0030] The content of Si element in the carrier core material of the present invention is in the range of 1.4% by mass to 5.2% by mass. If the content of Si element is less than 1.4% by mass, the apparent density increases and toner spent tends to occur. On the other hand, if the content of Si element is more than 5.2% by mass, the magnetization σ 1k The Si content is more preferably in the range of 2.0% by mass to 4.0% by mass.

[0031] Magnetization σ of the carrier core material of the present invention 1k is 58Am 2 / kg or more 75Am 2 / kg or less. Magnetization σ 1k 58Am 2 If the magnetization is lower than σ / kg, the carrier is likely to scatter. 1k is 75Am 2 If the density is higher than 1 / kg, the magnetic brush formed on the outer periphery of the developing roller becomes hard, the density of the magnetic brush becomes low, and the amount of developer transported to the developing area may become insufficient.

[0032] The apparent density of the carrier core material of the present invention is 1.90 g / cm 3 More than 2.20g / cm 3 The following range is preferable: A more preferable apparent density of the carrier core material is 1.97 g / cm 3 More than 2.19g / cm 3 The range is as follows:

[0033] The pore volume of the carrier core material of the present invention is less than 0.010 mL / g. If the pore volume is 0.010 mL / g or more, the amount of resin coating the carrier core material will vary, making carrier scattering more likely. A more preferred pore volume of the carrier core material is in the range of 0.005 mL / g or more and 0.008 mL / g or less.

[0034] The true density of the carrier core material of the present invention is 4.00 g / cm 3 More than 4.75g / cm 3 The following ranges are preferred: the true density of the carrier core material is 4.00 g / cm 3 If the density is lower than 4.75 g / cm, the proportion of CaSi composite oxide will be too high, which may reduce the magnetization per particle and cause carrier scattering. 3 If the density is higher than 4.56 g / cm, toner spent may occur. 3 More than 4.69g / cm 3 The true density of the carrier core material can be adjusted mainly by the content of CaSi composite oxide, and also by the composition of ferrite that constitutes the carrier core material.

[0035] Saturation magnetization σ of the carrier core material of the present invention s is 67Am 2 / kg or more 90Am 2 / kg or less. s 67Am 2 If the saturation magnetization is less than σ / kg, the magnetization per particle becomes small, which may cause carrier scattering. s is 90Am 2 If the saturation magnetization exceeds σ / kg, the magnetic brush formed on the outer periphery of the developing roller becomes hard, the density of the magnetic brush becomes low, and the amount of developer transported to the development area may become insufficient. s is 70Am 2 / kg or more 80Am 2 / kg or less is more preferable.

[0036] Furthermore, the residual magnetization σ of the carrier core material of the present invention r is 2.0Am2 is preferably in the range of 1.5 Am / kg or less. The residual magnetization σ r exceeds 2.0 Am 2 / kg, there is a risk that it becomes difficult to peel off the carrier from the developing roller. A more preferable residual magnetization σ r is in the range of 1.5 Am 2 / kg or less.

[0037] Also, the coercive force H of the carrier core material of the present invention c is preferably in the range of 20 Oersted (20×10 3 / (4π) A / m) or less. When the coercive force H c exceeds 20 Oersted, the fluidity and charge imparting ability of the carrier deteriorate, and toner scattering is likely to occur. A more preferable coercive force H c is in the range of 15 Oersted or less.

[0038] The composition of the ferrite particles constituting the carrier core material according to the present invention is preferably represented by the composition formula Mn X Fe 3-X O4 (where 0 < X < 3). And it is preferable that Ca is contained in the range of 2.0 mass% or more and 4.0 mass% or less, and Si is contained in the range of 2.0 mass% or more and 4.0 mass% or less.

[0039] Here, the mass ratio Ca / Si of the Ca element and the Si element is preferably in the range of 0.5 or more and 2.0 or less.

[0040] The volume average particle diameter (hereinafter sometimes referred to as "average particle diameter") D measured by the laser diffraction type particle size distribution measuring device of the carrier core material of the present invention 50 is preferably in the range of 30 μm or more and 50 μm or less, more preferably in the range of 30 μm or more and 40 μm or less. Also, the cumulative value of the particle diameter of 22 μm or less in the volume-based integrated particle size distribution is preferably 1.5% or less. If the cumulative value of the particle diameter of 22 μm or less exceeds 1.5%, there is a risk of carrier scattering.

[0041] (Manufacturing method) Although there is no particular limitation on the method for producing the carrier core material of the present invention, the production method described below is preferred.

[0042] First, the ferrite raw material components, CaSi composite oxide such as CaSiO3, and conventionally known additives are weighed out, as necessary. Ferrite raw material components include Fe raw material and Mn raw material. Fe2O3 and the like are preferably used as the Fe raw material. MnCO3, Mn3O4 and the like are used as the Mn raw material. The amount ratio of Fe, Mn, Ca, and Si in the raw materials is almost directly reflected in the composition ratio of each element in the carrier core material, so the amounts of the Fe raw material, Mn raw material, and CaSi composite oxide charged can be adjusted to achieve the target composition ratio in the carrier core material.

[0043] Next, the raw materials are added to a dispersion medium to prepare a slurry. The CaSi composite oxide may be added to the dispersion medium at this stage, or may be mixed with the slurry after wet grinding, as described below. Water is a suitable dispersion medium for use in the present invention. In addition to the calcined raw materials, the dispersion medium may also contain a binder, dispersant, etc., as needed. Polyvinyl alcohol, for example, is a suitable binder. The binder content in the slurry is preferably about 0.1% to 2% by mass. Furthermore, ammonium polycarboxylate and methacrylic acid polymers are suitable dispersants. The dispersant content in the slurry is preferably about 0.1% to 2% by mass. Other additives that may be added include a reducing agent such as carbon black, a pH adjuster such as ammonia, a lubricant, and a sintering accelerator. The solids concentration of the slurry is preferably 50% to 90% by mass, more preferably 60% to 80% by mass. If the content is 60% by mass or more, the number of pores within the particles in the granulated product is small, and insufficient sintering during firing can be prevented.

[0044] Alternatively, the weighed raw materials may be mixed, calcined, and deagglomerated, and then added to a dispersion medium to produce a slurry. The calcination temperature is preferably between 750°C and 1000°C. Temperatures above 750°C are preferred because partial ferritization occurs during calcination, gas generation during calcination is minimal, and solid-state reactions proceed sufficiently. On the other hand, temperatures below 1000°C are preferred because sintering during calcination is weak, allowing the raw materials to be sufficiently pulverized in the subsequent slurry milling process. Generally, at temperatures below 1540°C, CaSiO3 can maintain its crystal structure without melting or decomposing. Furthermore, air is preferred as the atmosphere during calcination.

[0045] Next, the slurry prepared as described above is wet-pulverized. For example, wet-pulverization is performed for a predetermined time using a ball mill or a vibration mill. The average particle size of the raw material after pulverization is preferably 5 μm or less, more preferably 2 μm or less. It is preferable to incorporate media of a predetermined particle size into the vibration mill or ball mill. Examples of media materials include iron-based chromium steel and oxide-based zirconia, titania, and alumina. The pulverization process may be either continuous or batchwise. The particle size of the pulverized product is adjusted by the pulverization time, rotation speed, and the material and particle size of the media used.

[0046] By controlling the particle size of the CaSi composite oxide, the residual magnetization σ of the carrier core material can be reduced. r It is also possible to control the level of σ. After subjecting a slurry containing a dispersion medium and ferrite component raw materials to wet grinding treatment, a slurry containing a CaSi composite oxide with an average particle size of 12 μm is obtained, and by further performing the spray drying and subsequent operations described below, the level of σ can be reduced compared to when a CaSi composite oxide with an average particle size of less than 12 μm is mixed. r In this way, by controlling the particle size of the CaSi composite oxide, the σ of the carrier core material can be reduced. rAlthough the mechanism by which this can be controlled is currently unknown, the inventors speculate that if the average particle size of the CaSi composite oxide present inside the carrier core material is small, the number of CaSi composite oxide particles in each carrier core material particle increases, increasing the number of grain boundaries, thereby inhibiting magnetic spin return and increasing remanent magnetization. The upper limit of the average particle size of the CaSi composite oxide is preferably 50% or less of the average particle size of the carrier core material, as this would cause variations in magnetic force within the particles. More preferably, the average particle size of the CaSi composite oxide is 40% or less of the average particle size of the carrier core material.

[0047] The pulverized slurry is then spray-dried to form granules. Specifically, the slurry is introduced into a spray dryer or other spray dryer and sprayed into the atmosphere to form spherical granules. The atmospheric temperature during spray drying is preferably in the range of 100°C to 300°C. This results in spherical granules with a particle size of 10 μm to 200 μm. Next, if necessary, the resulting granules are classified using a vibrating sieve to produce granules with a predetermined particle size range.

[0048] Next, the granulated material is placed in a furnace heated to a predetermined temperature and fired using a conventional method for synthesizing ferrite particles to produce ferrite particles. The firing temperature is preferably in the range of 1050°C to 1350°C, more preferably in the range of 1100°C to 1250°C. If the firing temperature is below 1050°C, phase transformation and sintering are difficult to occur. Furthermore, if the firing temperature exceeds 1350°C, excessive sintering may result in the generation of excessively large grains. Since the ferrite particles of the present invention contain a CaSi composite oxide, if the heating rate is too high, the spherical shape may not be maintained due to the influence of differences in shrinkage rate during firing. In particular, the heating rate from 500°C to the firing temperature is preferably in the range of 100°C / h to 500°C / h. The holding time at the firing temperature is preferably 2 hours or longer. The oxygen concentration during heating, firing, and cooling is preferably controlled in the range of 0.05% to 21%.

[0049] The calcined product thus obtained is disintegrated as necessary. Specifically, the calcined product is disintegrated, for example, using a hammer mill or the like. The disintegration process may be either continuous or batchwise. After the disintegration process, classification may be performed, if necessary, to adjust the particle size to within a predetermined range. As a classification method, conventionally known methods such as air classification or sieve classification can be used. Furthermore, after primary classification using an air classifier, the particle size may be adjusted to within a predetermined range using a vibrating sieve or ultrasonic sieve. Furthermore, after the classification process, non-magnetic particles may be removed using a magnetic separator. The volume average particle size of the ferrite particles is preferably 30 μm or more and less than 50 μm.

[0050] Thereafter, if necessary, the classified ferrite particles may be heated in an oxidizing atmosphere to form an oxide film on the particle surface and increase the resistance of the ferrite particles (resistance-increasing treatment). The oxidizing atmosphere may be either air or a mixed atmosphere of oxygen and nitrogen. The heating temperature is preferably in the range of 200°C to 800°C, more preferably in the range of 360°C to 550°C. The heating time is preferably in the range of 0.5 hours to 5 hours. A low heating temperature is desirable from the viewpoint of homogenizing the surface and interior of the ferrite particles. The spinel-type ferrite particles prepared as described above are used as the carrier core material of the present invention.

[0051] (Electrophotographic developing carrier) The electrophotographic development carrier according to the present invention is obtained by coating the surface of the carrier core material prepared as described above with a resin.

[0052] The resin that coats the surface of the carrier core material may be any conventionally known resin, such as polyethylene, polypropylene, polyvinyl chloride, poly-4-methylpentene-1, polyvinylidene chloride, ABS (acrylonitrile-butadiene-styrene) resin, polystyrene, (meth)acrylic resin, polyvinyl alcohol resin, as well as thermoplastic elastomers such as polyvinyl chloride, polyurethane, polyester, polyamide, and polybutadiene, and fluorosilicone resin.

[0053] To coat the surface of a carrier core with a resin, a resin solution or dispersion can be applied to the carrier core. Examples of solvents that can be used for the coating solution include aromatic hydrocarbon solvents such as toluene and xylene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; cyclic ether solvents such as tetrahydrofuran and dioxane; alcohol solvents such as ethanol, propanol, and butanol; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; and amide solvents such as dimethylformamide and dimethylacetamide. The resin component concentration in the coating solution is generally between 0.001% and 30% by weight, and preferably between 0.001% and 2% by weight.

[0054] Examples of methods that can be used to coat the carrier core material with resin include spray drying, fluidized bed methods, spray drying using a fluidized bed, and immersion methods. Among these, the fluidized bed method is particularly preferred because it allows efficient application with a small amount of resin. In the case of the fluidized bed method, for example, the amount of resin coating can be adjusted by the amount of resin solution sprayed and the spraying time.

[0055] The particle size of the carrier is generally in the range of 30 μm to 50 μm, particularly preferably 30 μm to 40 μm, in terms of volume average particle size.

[0056] (Electrophotographic developer) The electrophotographic developer according to the present invention is obtained by mixing the carrier and toner prepared as described above. There are no particular limitations on the mixture ratio of the carrier and toner, and it may be determined appropriately based on the development conditions of the developing device to be used. In general, the toner concentration in the developer is preferably in the range of 1% by mass or more and 15% by mass or less. If the toner concentration is less than 1% by mass, the image density will be too low, while if the toner concentration is more than 15% by mass, toner scattering may occur within the developing device, causing problems such as contamination inside the device or toner adhesion to background areas such as transfer paper. A more preferred toner concentration is in the range of 3% by mass or more and 10% by mass or less.

[0057] The toner may be produced by a conventional method such as polymerization, pulverization classification, melt granulation, spray granulation, etc. Specifically, a toner containing a colorant, a release agent, a charge control agent, etc., in a binder resin mainly composed of a thermoplastic resin can be suitably used.

[0058] Generally, the particle size of the toner is preferably in the range of 5 μm to 15 μm, more preferably in the range of 7 μm to 12 μm, in terms of the volume average particle size measured by a Coulter counter.

[0059] If necessary, a modifier may be added to the toner surface. Examples of modifiers include silica, alumina, zinc oxide, titanium oxide, magnesium oxide, polymethyl methacrylate, etc. These may be used alone or in combination of two or more.

[0060] The carrier and toner can be mixed using a conventionally known mixing device, such as a Henschel mixer, a V-type mixer, a tumbler mixer, or a hybridizer.

[0061] (developing device) Although there are no particular limitations on the developing method using the developer of the present invention, magnetic brush development is preferred. Fig. 6 is a schematic diagram showing an example of a developing device that performs magnetic brush development. The developing device shown in Fig. 6 includes a rotatable developing roller 3 incorporating multiple magnetic poles, a regulating blade 6 that regulates the amount of developer on the developing roller 3 that is transported to the development section, two screws 1 and 2 that are arranged horizontally parallel to each other and stir and transport the developer in opposite directions, and a partition plate 4 formed between the two screws 1 and 2 that allows the developer to move from one screw to the other at both ends of the screws and prevents the developer from moving anywhere other than at both ends.

[0062] The two screws 1 and 2 have spiral blades 13 and 23 formed on shafts 11 and 21 at the same inclination angle, and are rotated in the same direction by a drive mechanism (not shown), transporting developer in opposite directions. Developer moves from one screw to the other at both ends of the screws 1 and 2. This allows the developer, consisting of toner and carrier, to constantly circulate and agitate within the device.

[0063] Meanwhile, the developing roller 3 is a metal cylindrical body with a surface roughness of several μm, and contains a fixed magnet as a magnetic pole generating means, with five magnetic poles arranged in this order: a developing magnetic pole N1, a transporting magnetic pole S1, a peeling magnetic pole N2, a drawing-up magnetic pole N3, and a blade magnetic pole S2. When the cylindrical body of the developing roller 3 rotates in the direction of the arrow, the magnetic force of the drawing-up magnetic pole N3 draws the developer from the screw 1 onto the developing roller 3. The developer carried on the surface of the developing roller 3 is regulated by a regulating blade 6 to form a layer, and then transported to the development zone.

[0064] In the development area, a bias voltage, which is a DC voltage superimposed with an AC voltage, is applied to the development roller 3 from the transfer voltage power supply 8. The DC voltage component of the bias voltage is set to a potential between the background potential and the image potential on the surface of the photosensitive drum 5. The background potential and the image potential are set to a potential between the maximum and minimum values ​​of the bias voltage. The peak-to-peak voltage of the bias voltage is preferably in the range of 0.5 kV to 5 kV, and the frequency is preferably in the range of 1 kHz to 10 kHz. The waveform of the bias voltage may be any of a square wave, a sine wave, a triangular wave, or the like. This vibrates the toner and carrier in the development area, causing the toner to adhere to the electrostatic latent image on the photosensitive drum 5 and develop the image.

[0065] The developer on the developing roller 3 is then transported into the device by the transport magnetic pole S1, peeled off from the developing roller 3 by the peeling electrode N2, and circulated again within the device by the screws 1 and 2, where it is mixed and stirred with the developer that has not been used for development. Then, new developer is supplied from the screw 1 to the developing roller 3 by the pumping pole N3.

[0066] In the embodiment shown in Figure 6, the developing roller 3 has five magnetic poles built in, but it is of course possible to increase the number of magnetic poles to eight, ten, or twelve in order to further increase the amount of developer movement in the development area or to further improve the pumping performance, etc. [Example]

[0067] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0068] Example 1 As raw materials, 22.13 kg of Fe2O3 (average particle size: 0.6 μm), 8.60 kg of Mn3O4 (average particle size: 3.4 μm), and 3.42 kg of CaSiO3 (average particle size: 12 μm) were dispersed in 11.40 kg of pure water, and 279.3 g of ammonium polycarboxylate dispersant was added as a dispersant to form a mixture. This mixture was pulverized in a wet ball mill (media diameter 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 140°C using a spray dryer to obtain dried granules with particle sizes of 10 to 75 µm, from which fine particles with particle sizes of 25 µm or less were removed using a sieve. The granulated material was placed in an electric furnace and fired by maintaining the temperature at 1145° C. for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired product was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain a carrier core material having an average particle size of 35.9 μm.

[0069] The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0070] Next, the surface of the carrier core material thus obtained was coated with a resin to prepare a carrier. Specifically, 450 parts by mass of silicone resin and 9 parts by mass of (2-aminoethyl)aminopropyltrimethoxysilane were dissolved in 450 parts by mass of toluene as a solvent to prepare a coating solution. This coating solution was applied to 50,000 parts by mass of carrier core material using a fluidized bed coating device and heated in an electric furnace at a temperature of 300°C to obtain a carrier. Carriers for the following examples and comparative examples were also obtained in the same manner.

[0071] The obtained carrier and toner having an average particle diameter of about 5.0 μm were mixed for a predetermined time using a pot mill to obtain a two-component electrophotographic developer. In this case, the carrier and toner were adjusted so that the mass of the toner / (mass of the toner and carrier) was 5 / 100. Developers were obtained in the same manner for all of the following Examples and Comparative Examples. The obtained developers were subjected to the below-described actual machine evaluation. The evaluation results are shown in Tables 1 and 2. The following Examples and Comparative Examples were also subjected to the same actual machine evaluation. The evaluation results are shown in Table 2.

[0072] Example 2 A carrier core material having an average particle size of 36.0 μm was obtained in the same manner as in Example 1, except that the electric furnace temperature in the firing step was changed to 1170° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0073] Example 3 Carrier core particles having an average particle size of 35.6 μm were obtained in the same manner as in Example 1, except that the electric furnace temperature in the firing step was changed to 1200° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0074] Example 4 The carrier core material of Example 3 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 420° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0075] Example 5 A carrier core material having an average particle size of 35.7 μm was obtained in the same manner as in Example 1, except that 3.42 kg of CaSiO 3 (average particle size: 5 μm) having a different average particle size was used as a raw material. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0076] Example 6 A carrier core material having an average particle size of 35.8 μm was obtained in the same manner as in Example 5, except that the electric furnace temperature in the firing step was changed to 1170° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0077] Example 7 The carrier core material of Example 6 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 420° C. for 1.5 hours in an air atmosphere. The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. Also, an XRD measurement diagram of the carrier core material of Example 7 is shown in FIG.

[0078] Example 8 A carrier core material having an average particle size of 34.9 μm was obtained in the same manner as in Example 5, except that the electric furnace temperature in the firing step was changed to 1200° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0079] Example 9 The carrier core material of Example 8 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 400° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0080] Example 10 As raw materials, 22.13 kg of Fe2O3 (average particle size: 0.6 μm) and 8.64 kg of Mn3O4 (average particle size: 3.4 μm) were dispersed in 11.40 kg of pure water, and 279.3 g of ammonium polycarboxylate dispersant was added as a dispersant to form a mixture. This mixture was pulverized in a wet ball mill (media diameter: 2 mm), and 3.42 kg of CaSiO3 (average particle size: 12 μm) was added to form a mixed slurry. Carrier core materials with an average particle size of 35.2 μm were obtained in the same manner as in Example 1. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0081] Example 11 The carrier core material of Example 10 was subjected to an oxidation treatment (resistance increasing treatment) by being kept at a temperature of 420° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0082] Example 12 A carrier core material having an average particle size of 35.9 μm was obtained in the same manner as in Example 10, except that the electric furnace temperature in the firing step was changed to 1170° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0083] Example 13 The carrier core material of Example 12 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 400° C. for 1.5 hours in an air atmosphere. The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. In addition, an XRD measurement diagram of the carrier core material of Example 13 is shown in FIG.

[0084] Example 14 A carrier core material having an average particle size of 34.3 μm was obtained in the same manner as in Example 10, except that 3.42 kg of CaSiO 3 (average particle size: 5 μm) having a different average particle size was used as a raw material. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0085] Example 15 A carrier core material having an average particle size of 35.6 μm was obtained in the same manner as in Example 14, except that the electric furnace temperature in the firing step was changed to 1170° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0086] Example 16 A carrier core material having an average particle size of 35.1 μm was obtained in the same manner as in Example 14, except that the electric furnace temperature in the firing step was changed to 1200° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0087] Example 17 The carrier core material of Example 16 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 400° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0088] (Comparative Example 1) As raw materials, 24.59 kg of Fe2O3 (average particle size: 0.6 μm) and 9.60 kg of Mn3O4 (average particle size: 3.4 μm) were dispersed in 11.40 kg of pure water, and 279.3 g of polycarboxylate ammonium dispersant was added as a dispersant to form a mixture. This mixture was pulverized in a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 140°C using a spray dryer to obtain dried granules with particle sizes of 10 to 75 µm, from which fine particles with particle sizes of 25 µm or less were removed using a sieve. The granulated material was placed in an electric furnace and fired by holding it at 1110° C. for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired product was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain a carrier core material having an average particle size of 35.9 μm. The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. In addition, an XRD measurement diagram of the carrier core material of Comparative Example 1 is shown in FIG.

[0089] (Comparative Example 2) Carrier core particles having an average particle size of 35.9 μm were obtained in the same manner as in Comparative Example 1, except that the electric furnace temperature in the firing step was changed to 1200° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0090] (Comparative Example 3) A carrier core material having an average particle size of 35.7 μm was obtained in the same manner as in Example 1, except that the electric furnace temperature in the firing step was changed to 1110° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0091] Comparative Example 4 A carrier core material having an average particle size of 35.3 μm was obtained in the same manner as in Example 5, except that the electric furnace temperature in the firing step was changed to 1110° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0092] (Comparative Example 5) A carrier core material having an average particle size of 35.8 μm was obtained in the same manner as in Example 10, except that the electric furnace temperature in the firing step was changed to 1110° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0093] (Comparative Example 6) A carrier core material having an average particle size of 35.3 μm was obtained in the same manner as in Example 14, except that the electric furnace temperature in the firing step was changed to 1110° C. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0094] (Comparative Example 7) The carrier core material of Example 1 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 400° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0095] (Comparative Example 8) The carrier core material of Example 1 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 420° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0096] (Comparative Example 9) The carrier core material of Example 14 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 400° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0097] (Comparative Example 10) The carrier core material of Example 5 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 440° C. for 1.5 hours in an air atmosphere. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0098] (Comparative Example 11) As raw materials, 34.20 kg of Fe2O3 (average particle size: 0.6 μm), 13.35 kg of Mn3O4 (average particle size: 3.4 μm), and 2.45 kg of CaSiO3 (average particle size: 5 μm) were dispersed in 16.70 kg of pure water, and 408.0 g of polycarboxylate ammonium dispersant was added as a dispersant to form a mixture. This mixture was pulverized in a wet ball mill (media diameter 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 140°C using a spray dryer to obtain dried granules with particle sizes of 10 to 75 µm, from which fine particles with particle sizes of 25 µm or less were removed using a sieve. The granulated material was placed in an electric furnace and fired by holding it at 1145° C. for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired product was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain a carrier core material having an average particle size of 35.0 μm. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0099] (Comparative Example 12) The carrier core material of Comparative Example 11 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 400° C. for 1.5 hours in an air atmosphere. The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. In addition, an XRD measurement diagram of the carrier core material of Comparative Example 12 is shown in FIG.

[0100] (Comparative Example 13) As raw materials, 28.09 kg of Fe2O3 (average particle size: 0.6 μm), 10.96 kg of Mn3O4 (average particle size: 3.4 μm), and 10.95 kg of CaSiO3 (average particle size: 5 μm) were dispersed in 16.70 kg of pure water, and 408.0 g of polycarboxylate ammonium dispersant was added as a dispersant to form a mixture. This mixture was pulverized in a wet ball mill (media diameter 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 140°C using a spray dryer to obtain dried granules with particle sizes of 10 to 75 µm, from which fine particles with particle sizes of 25 µm or less were removed using a sieve. The granulated material was placed in an electric furnace and fired by holding it at 1170° C. for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired product was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain a carrier core material having an average particle size of 35.8 μm. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0101] (Comparative Example 14) The carrier core material of Comparative Example 13 was subjected to an oxidation treatment (resistance increasing treatment) by being held at a temperature of 400° C. for 1.5 hours in an air atmosphere. The powder properties, magnetic properties, electrical properties, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2. In addition, an XRD measurement diagram of the carrier core material of Comparative Example 14 is shown in FIG.

[0102] (Comparative Example 15) The raw materials were a mixture of 14.43 kg of Fe2O3 (average particle size: 0.6 μm), 4.62 kg of Mn3O4 (average particle size: 2 μm), and 1.04 kg of MgO. This mixture was pelletized using a roller compactor. The resulting pellets were pre-fired in a rotary furnace at 850°C under atmospheric conditions. The pellets were then pulverized in a dry bead mill for 6 hours to obtain a pre-fired raw material. The pre-fired powder was dispersed in 7.12 kg of water, to which 149.5 g of CaCO3 and 219.7 g of an aqueous solution containing 21% methacrylic acid polymer were added. The mixture was then pulverized in a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 130°C using a spray dryer to obtain dried granulated powder. At this time, granulated powders other than those having the desired particle size distribution were removed using a sieve. This granulated powder was placed in an electric sintering furnace and sintered at 1110°C for 3 hours. It was then cooled for 6 hours at an oxygen concentration of 7500 ppm. The sintered product was degranulated and classified using a sieve to obtain a carrier core material with an average particle size of 36.2 μm and a ratio of particles with a particle size of 22 μm or less of 0.9%. The powder characteristics, magnetic characteristics, electrical characteristics, etc. of the obtained carrier core material were measured by the methods described below. The measurement results are shown in Tables 1 and 2.

[0103] (composition analysis) (Fe analysis) The carrier core material containing iron element was weighed and dissolved in a mixed acid solution of hydrochloric acid and nitric acid. After evaporating this solution to dryness, sulfuric acid solution was added to redissolve the carrier core material and volatilize the excess hydrochloric acid and nitric acid. Solid Al was added to this solution to remove the Fe in the liquid. 3+ All Fe 2+ Then, the Fe in this solution is reduced to 2+ The amount of ions was quantitatively analyzed by potentiometric titration with potassium permanganate solution, and Fe(Fe 2+ ) was determined. (Mn analysis) The Mn content of the carrier core material was quantitatively analyzed in accordance with the ferromanganese analysis method (potentiometric titration method) described in JIS G1311-1987. The Mn content of the carrier core material described in this specification is the amount of Mn obtained by quantitative analysis using this ferromanganese analysis method (potentiometric titration method). (Ca analysis) The Ca content of the carrier core material was analyzed by the following method. The carrier core material according to the present invention was dissolved in an acid solution and quantitatively analyzed by ICP. The Ca content of the carrier core material described in the present invention is the amount of Ca obtained by this quantitative analysis using ICP. (Si analysis) The Si content of the carrier core material was quantitatively analyzed in accordance with the silicon dioxide gravimetric method described in JIS M8214-1995.

[0104] (apparent density AD) The apparent density of the carrier core material was measured in accordance with JIS Z 2504.

[0105] (Flow rate FR) The fluidity of the carrier core material was measured in accordance with JIS Z 2502.

[0106] (Average particle diameter D 50 and the proportion of particles with a particle size of 22 μm or less) Average particle diameter D of carrier core material 50 The volume fraction of particles with a particle size of 22 μm or less was measured using a laser diffraction particle size distribution analyzer (Microtrac Model 9320-X100 manufactured by Nikkiso Co., Ltd.).

[0107] (pore volume) The evaluation device used was a POREMASTER-60GT manufactured by Quantachrome. The specific measurement conditions were: Cell Stem Volume: 0.5cm 3 Head pressure: 20PSIA Surface tension of mercury: 485.00 erg / cm 2 Contact angle of mercury: 130.00 degrees High pressure measurement mode: Fixed Rate Motor Speed: 1 High pressure measurement range: 20.00 to 10,000.00 PSI 1,500 g of sample was weighed and measured to 0.5 cm 3 The volume B (cm) at 10,000 PSI was measured. 3 / g) to volume A (cm at 60 PSI 3 The value obtained by subtracting the pore volume (1 / g) was taken as the pore volume.

[0108] (BET specific surface area) Examples 1 to 17, Comparative Examples 1 to 12, and Comparative Example 15 were evaluated using a BET single-point specific surface area measuring device (Macsorb HM model-1208, manufactured by Mountec Co., Ltd.) Specifically, 10,000 g of sample (note that for the carrier core materials of Comparative Examples 13 and 14, 8,000 g was used because 10,000 g could not be filled into the cell) was weighed and filled into a cell with a diameter of 15 mm, and the sample was degassed at 200°C for 30 minutes before measurement.

[0109] (true density) The true density of the carrier core material was measured using "ULTRA PYCNOMETER 1000" manufactured by Quantachrome.

[0110] (magnetic properties) Using a room-temperature dedicated vibrating sample magnetometer (VSM) ("VSM-P7" manufactured by Toei Kogyo Co., Ltd.), the external magnetic field was adjusted to 0 to 79.58 × 10 4 A / m (10,000 Oersted) was applied for one cycle continuously, resulting in a magnetic field of 79.58 × 10 3 Magnetization σ when A / m (1000 Oersted) is applied 1k , saturation magnetization σ s , residual magnetization σ r , coercive force H c was measured.

[0111] (static electrical resistance) Two 2mm thick brass plates with electrolytically polished surfaces were used as electrodes, arranged with a distance of 2mm between the electrodes. 200mg of carrier core material was placed in the gap between the two electrode plates, and then a 240mm diameter piece of PET was placed behind each electrode plate. 2 A magnet was placed between the electrodes to form a bridge of the powder to be measured, and a DC voltage of 100V, 500V, or 1000V was applied between the electrodes, and the current flowing through the carrier core material was measured using the four-terminal method. The current value and the distance between the electrodes was 2 mm and the cross-sectional area was 240 mm. 2 The electrical resistance of the carrier core material was calculated from the above.

[0112] (Toner Spent Evaluation) The two-component developer thus prepared was placed in a developing device (peripheral speed v1 of the developing roller: 259 mm / sec, peripheral speed v2 of the photosensitive drum: 131 mm / sec, distance between the photosensitive drum and the developing roller: 0.3 mm) with the structure shown in Figure 6, and the developing device was operated for a time equivalent to the time required to print 100,000 sheets of A4 landscape paper (time equivalent to printing 100,000 sheets). After that, the carrier was extracted from the developer and observed with a scanning electron microscope (JSM-6510LA, manufactured by JEOL Ltd.), and the percentage of carrier particles with toner fused to their surfaces was measured. "Excellent": The percentage of carrier particles to which the toner was fused was less than 0.5%. "Good": The percentage of carrier particles to which the toner was fused was 0.5% or more and less than 1.0%. "B": The ratio of the number of carrier particles to which the toner was fused was 1.0% or more and less than 5.0%. "X": The proportion of carrier particles to which the toner was fused was 5.0% or more.

[0113] (Evaluation of carrier scattering) The prepared two-component developer was placed in a developing device with the structure shown in Figure 6 (circumferential speed of developing roller v1: 259 mm / sec, peripheral speed of photosensitive drum v2: 131 mm / sec, distance between photosensitive drum and developing roller: 0.3 mm), and the developing device was operated for a time equivalent to the time required to print 100,000 sheets of A4 landscape paper (time equivalent to printing 100,000 sheets).The number of black dots found in the image area after this was defined as α, and the number of black dots found in the background area was defined as β, and carrier scattering was evaluated according to the following criteria. "○": 0≦α+β≦6 pieces "×": 7 pieces ≦ α + β

[0114] [Table 1]

[0115] [Table 2]

[0116] According to the XRD measurement results in Figure 1, the carrier core material of Example 7, to which CaSiO3 having an average particle size of 5 μm was initially added, had a diffraction intensity peak between the diffraction intensity peak position of CaSiO3 and the diffraction intensity peak position of (Ca,Fe)SiO3. This is thought to be because Fe dissolved in a part (surface layer) of CaSiO3 during the manufacturing process, such as firing the carrier core material, to form (Ca,Fe)SiO3, and the diffraction intensity peak position shifted to the higher angle side. 2, the carrier core material of Example 13, which initially contained CaSiO3 (average particle size 12 μm), a particle size larger than that used in Example 7, had two diffraction intensity peaks between the peak position of the diffraction intensity of CaSiO3 and the peak position of the diffraction intensity of (Ca,Fe)SiO3. This is thought to be because, like the carrier core material of Example 7, Fe was dissolved in part of the CaSiO3 (surface layer), but because the average particle size of the CaSiO3 was large, CaSiO3 remained inside the particles, resulting in two diffraction intensity peaks derived from CaSiO3 and (Ca,Fe)SiO3.

[0117] The XRD measurement results show that the carrier core materials of Examples 7 and 13 contain CaSi composite oxides such as CaSiO3 and (Ca,Fe)SiO3. The XRD measurement results of the carrier core materials of Examples other than Examples 7 and 13 were similar.

[0118] On the other hand, according to the XRD measurement results shown in Fig. 3, the carrier core material of Comparative Example 1, in which neither Ca nor Si raw materials were added as raw materials, did not exhibit a diffraction intensity peak in the incident angle 2θ range of 26.60° to 27.30°. In other words, the absence of a diffraction intensity peak in the incident angle 2θ range of 26.60° to 27.30° indicates that the carrier core material does not contain CaSi composite oxide.

[0119] According to the XRD measurement results shown in Figure 4, the carrier core material of Comparative Example 12, which contains a small amount of CaSiO3 as a raw material component, has a diffraction intensity peak in the incident angle 2θ range of 26.60° to 27.30°, but the peak intensity value is low and the peak position is shifted toward the peak position of (Ca,Fe)SiO3. Also, according to the XRD measurement results shown in Figure 5, the carrier core material of Comparative Example 14, which contains a large amount of CaSiO3 as a raw material component, has a diffraction intensity peak in the incident angle 2θ range of 26.60° to 27.30°, and the peak intensity value is high.

[0120] As is clear from Tables 1 and 2, the carrier core materials of Examples 1 to 17 having the configuration of the present invention showed that in the toner spent evaluation, the percentage of carrier particles to which the toner had fused was less than 5.0%, which was not a problem in practical use, and in the carrier scattering evaluation, the number of black dots found in the image and background areas was 6 or less, which was not a problem in practical use.

[0121] In contrast, the carrier core materials of Comparative Examples 1 and 2, which did not contain CaSi composite oxide, had an apparent density of 2.39 g / cm 3 The toner consumption was high and a lot of toner was spent.

[0122] The carrier core particles of Comparative Examples 3 to 6, which were fired at a low temperature of 1100° C., had a large pore volume and varied in the amount of resin coating the surface of the carrier core particle, causing carrier scattering.

[0123] The carrier core materials of Comparative Examples 7 to 10, which were subjected to the high resistance treatment, had high apparent densities and toner-spent occurred. 1k The temperature was low and carrier scattering also occurred.

[0124] The carrier core materials of Comparative Examples 11 and 12, which contained a small amount of CaSi composite oxide, had a high apparent density and generated a large amount of toner spent. On the other hand, the carrier core materials of Comparative Examples 13 and 14, which contained a large amount of CaSi composite oxide, had a high apparent density and generated a large amount of toner spent. 1k The temperature was low and carrier scattering occurred.

[0125] In the carrier core material of Comparative Example 15, in which the composition of the carrier core material was MnMg ferrite and did not contain CaSi composite oxide, the pore volume was large and the magnetization σ 1k The temperature was low and carrier scattering occurred. [Industrial Applicability]

[0126] The carrier core material of the present invention suppresses toner spent and carrier scattering. [Explanation of symbols]

[0127] 3 Developing roller 5 Photosensitive drum

Claims

1. A carrier core material made of ferrite particles, Contains a composite oxide of Ca and Si elements, Contains 1.7% by mass or more and 6.5% by mass or less of Ca element, Contains 1.4 mass% or more and 5.2 mass% or less of Si element, Magnetic field 79.58×10 ３ Magnetization σ of the ferrite particles when a current of 1000 oersted (A / m) is applied １ｋ is 58Am ２ / kg or more 75Am ２ / kg or less, Apparent density is 1.90 g / cm ３ 2.20g / cm or more ３ The range is as follows: Pore ​​volume is less than 0.010 mL / g A carrier core material characterized by:

2. The true density of the ferrite particles is 4.00 g / cm ３ 4.75g / cm or more ３ The carrier core material according to claim 1, wherein the carrier core material has a molecular weight in the range of:

3. The saturation magnetization σ of the ferrite particles Ｓ is 67 Am ２ / kg or more 90Am ２ 3. The carrier core material according to claim 1, wherein the carrier core material has a particle size of 1 / kg or less.

4. The remanent magnetization σ of the ferrite particles ｒ is 2.0 Am ２ / kg or less, Coercive force H ｃ 4. The carrier core material according to claim 1, wherein the viscosity is 20 oersted or less.

5. The ferrite particles are represented by the general formula (Mn Ｘ Fe ３－Ｘ ) O ４ (wherein 0<X<3) as a main component, Contains 2.0% by mass or more and 4.0% by mass or less of Ca element, Contains 2.0 mass % or more and 4.0 mass % or less of Si element The carrier core material according to any one of claims 1 to 4.

6. The mass ratio of Ca element to Si element is Ca / Si, which is 0.5 or more and 2.0 or less. The carrier core material according to any one of claims 1 to 5.

7. 7. A carrier for electrophotographic development, comprising the carrier core material according to claim 1, the surface of which is coated with a resin.

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

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