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

Abstract

To provide a carrier core material having low apparent density and high particle strength.SOLUTION: A carrier core material constituted of ferrite particles includes CaSiO3 and has a true density of 3.5 g / cm3 or more and 4.5 g / cm3 or less. A particle strength index calculated from the following formula (1) is preferably 1.5 vol.% or less. The particle strength index=V2-V1......(1) (where, V1:the cumulative value (vol.%) of a particle size of 22 μm or less in the integrated particle size distribution of the carrier core material before a crushing test, and V2:a cumulative value (vol.%) of a particle size of 22 μm or less in the integrated particle size distribution of the carrier core material after the crushing test), and the crushing test conditions: crushing the carrier core material of 30 g for 60 seconds at a rotation frequency of 14000 rpm using a sample mill.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, proposals have been made to reduce power consumption by reducing the stirring power in developing devices, and to stabilize image quality by suppressing "toner spent," which occurs when components that make up the toner fuse to the surface of the carrier, by creating voids inside the carrier core material and even by filling the internal voids with resin to reduce the mass of the carrier core material (see, for example, Patent Documents 1 and 2).

[0005] However, carrier core materials with internal voids have a lower apparent density but a lower core strength. Therefore, when the carrier core material is subjected to long-term stress during prolonged use, cracks and chips can occur in the carrier core material. When cracks and chips occur in the carrier core material, insulation breakdown can occur at the exposed cross section of the carrier core material, which has poor insulation properties, resulting in defects such as white spots in the image transferred to paper (white spots in the image).

[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.

[0007] However, since SiO2 easily absorbs moisture, practical problems are expected, such as a decrease in the charging characteristics of the carrier core material in a high-temperature, high-humidity environment. [Prior art documents] [Patent documents]

[0008] [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]

[0009] The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a carrier core material that is less likely to cause toner spent and has high particle strength. [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, contains CaSiO3 (calcium silicate), and has a true density of 3.5 g / cm 3 More than 4.5g / cm 3 It is characterized by the following ranges:

[0011] In the carrier core material, it is preferable that the particle strength index calculated from the following formula (1) is 1.5% by volume or less. Particle strength index=V2-V1 (1) (wherein V1 is the cumulative value (volume %) of particles with a particle size of 22 μm or less in the cumulative particle size distribution of the carrier core material before the crushing test, and V2 is the cumulative value (volume %) of particles with a particle size of 22 μm or less in the cumulative particle size distribution of the carrier core material after the crushing test) Crushing test conditions: 30g of carrier core material was crushed using a sample mill at a rotation speed of 14,000 rpm for 60 seconds.

[0012] In the carrier core material, the apparent density of the ferrite particles is 1.7 g / cm 3 More than 2.1g / cm 3 The following ranges are preferred: Specific measurement methods and conditions will be shown in the examples below.

[0013] In the carrier core material, the saturation magnetization of the ferrite particles is 40 Am 2 / kg or more 72Am 2 The specific measurement method and conditions are shown in the examples below.

[0014] In the carrier core material, the residual magnetization of the ferrite particles is 2.5 Am 2 / kg or less, and the coercive force is 30 oersted (30 x 10 3 / (4π)A / m) or less. Specific measurement methods and conditions will be described in the examples below.

[0015] In the carrier core material, the CaSiO3 content in the ferrite particles is preferably in the range of 10% by mass to 50% by mass.

[0016] In the carrier core material, the ferrite particles have a composition formula (Mn X Fe 3-X )O4 (where 0≦X<3), the Ca content is preferably in the range of 3.4 mass% or more and 15.8 mass% or less, and the Si content is preferably in the range of 3.0 mass% or more and 11.4 mass% or less.

[0017] According to the present invention, there is also provided a carrier for electrophotographic development, characterized in that the surface of any one of the carrier core materials described above is coated with a resin.

[0018] Furthermore, according to the present invention, there is provided an electrophotographic developer containing the above-described electrophotographic development carrier and a toner.

[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 is less likely to crack or chip even after long-term use.

[0021] According to the electrophotographic development carrier and electrophotographic developer of the present invention, the occurrence of white spots in an image 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] 1 is a cross-sectional SEM photograph of a carrier core material of Example 1. [Figure 2] This is EDS element (Fe) mapping of the cross-sectional SEM photograph of Figure 1. [Figure 3] This is EDS element (Mn) mapping of the cross-sectional SEM photograph of Figure 1. [Figure 4] This is EDS element (Ca) mapping of the cross-sectional SEM photograph of Figure 1. [Figure 5] This is EDS element (Si) mapping of the cross-sectional SEM photograph of Figure 1. [Figure 6] 1 shows the results of XRD measurement of the carrier core material of Example 1. [Figure 7]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 according to the present invention is that the carrier core material contains CaSiO3. As mentioned above, in the past, in order to reduce the apparent density of the carrier core material, ferrite (true density: about 5 g / cm3), 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 because SiO2 easily absorbs moisture, there are problems such as a decrease in the charging characteristics of the carrier core material in high-temperature, high-humidity environments. Therefore, the inventors of the present invention have conducted extensive research to find a substance that can replace SiO2, which is less susceptible to the effects of the usage environment, such as humidity, and does not significantly affect the charging characteristics of the carrier core material, which has a lower true density than ferrite. As a result, they have found CaSiO3 (true density: approximately 2.9 g / cm 3 ) satisfies the above conditions, and this invention was made based on this finding.

[0024] It is preferable that CaSiO3 is added as a raw material component. The CaSiO3 added as a raw material component remains in the ferrite particles without reacting even during the manufacturing process of the ferrite particles. Note that, although it is possible to add and mix the Ca raw material component and the Si raw material component together with the raw material components of the ferrite particles, so that CaSiO3 is synthesized in the firing process and contained in the ferrite particles, it is preferable that CaSiO3 is added from the beginning as a raw material component of the ferrite particles.

[0025] There is no particular limitation on the content of CaSiO3, and the true density of the carrier core material is within the range described below (3.5 g / cm 3 ~4.5g / cm 3 The content of CaSiO3 is usually preferably in the range of 10% by mass to 50% by mass relative to the carrier core material (ferrite particles), and more preferably in the range of 15% by mass to 35% by mass.

[0026] There is no particular limitation on the CaSiO3 used in the present invention, and commercially available powdered CaSiO3 can be suitably used.

[0027] Another major feature of the carrier core material according to the present invention is that the true density of the carrier core material is 3.5 g / cm 3 More than 4.5g / cm 3 The true density of the carrier core material is in the range below. By having the true density of the carrier core material in this range, which is lower than that of conventional carrier core materials, stress on the developer containing the carrier due to stirring in the developing device is reduced, and cracking and chipping of the toner spent and the carrier (carrier core material) are suppressed even after long-term use. A more preferable true density of the carrier core material is 3.8 g / cm 3 More than 4.5g / cm 3 In the following range

[0028] The true density of the carrier core material can be adjusted mainly by the CaSiO3 content, and also by the ferrite composition that constitutes the carrier core material.

[0029] The composition of the ferrite particles constituting the carrier core material according to the present invention is represented by the formula Mn X Fe 3-X Preferably, the alloy contains 04 (where 0≦X<3). Preferably, the alloy contains 3.4 mass % or more and 15.8 mass % or less of Ca, and 3.0 mass % or more and 11.4 mass % or less of Si.

[0030] The particle strength index of the carrier core material of the present invention, calculated from the above formula (1), is preferably 1.5% by volume or less. If the particle strength index of the carrier core material exceeds 1.5% by volume, the carrier (carrier core material) is likely to crack or chip due to stirring in the developing device, etc. As a result, insulation breakdown may occur from the exposed cross section of the carrier core material, which has low insulation, causing white spots in the image. A more preferred particle strength index of the carrier core material is 1.0% by volume or less.

[0031] The apparent density of the carrier core material of the present invention is 1.7 g / cm 3More than 2.1g / cm 3 The following range is preferable: A more preferable apparent density of the carrier core material is 1.8 g / cm 3 More than 2.0g / cm 3 The range is as follows:

[0032] Saturation magnetization σ of the carrier core material of the present invention s is 40Am 2 / kg or more 72Am 2 / kg or less. s is 40Am 2 If the saturation magnetization is less than σ / kg, the magnetization per particle becomes small, which may cause problems such as part of the carrier adhering to the non-image area (background area) of the photosensitive member (carrier adhesion to background area) or white spots in the image. s 72Am 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 53Am 2 / kg or more67Am 2 / kg or less is more preferable.

[0033] Also, the residual magnetization σ r is 2.5Am 2 / kg or less. r is 2.5Am 2 If the residual magnetization exceeds σ / kg, it may be difficult to separate the carrier from the developing roller. r is 2.2Am 2 / kg or less.

[0034] In addition, the coercive force H c is 30 oersteds (30 x 10 3 / (4π)A / m) or less. c If the coercive force H exceeds 30 oersted, the fluidity and charge imparting ability of the carrier may deteriorate, and toner scattering may occur more easily. c is in the range of 26 oersteds or less.

[0035] The volume average particle diameter (hereinafter sometimes referred to as "average particle diameter") D of the carrier core material of the present invention measured by a laser diffraction particle size distribution measuring device 50 The particle size is preferably in the range of 30 μm to 50 μm, more preferably 30 μm to 40 μm. The cumulative value of particles with a particle size of 22 μm or less in the volume-based cumulative particle size distribution is preferably 1.0% or less. If the cumulative value of particles with a particle size of 22 μm or less exceeds 1.0%, carrier adhesion to background areas may occur.

[0036] The particle shape factor (ISO circularity) of the carrier core material in the present invention is 0.88 or more and 0.98 or less. CaSiO3 and ferrite are heterogeneous materials with different crystal structures, but they can maintain a good spherical shape even when affected by thermal shrinkage during sintering. The measurement method will be described later.

[0037] (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.

[0038] First, the ferrite raw materials, CaSiO3, and, if necessary, conventionally known additives are weighed out. Examples of ferrite raw materials include Fe raw materials and Mn raw materials. Examples of Fe raw materials include Fe2O3. Examples of Mn raw materials include MnCO3 and Mn3O4. The ratios of Fe, Mn, Ca, and Si in the raw materials are almost directly reflected in the composition ratios of each element in the carrier core material. Therefore, the amounts of the Fe raw material, Mn raw material, and CaSiO3 added can be adjusted to achieve the desired composition ratio in the carrier core material. The particle size and shape of the CaSiO3 are not particularly limited, but the average particle size of the CaSiO3 is preferably 15 μm or less to suppress variations in magnetic force within the carrier core material particles, and the average aspect ratio is preferably 2 or more.

[0039] Next, the ferrite raw material components, CaSiO3, and, if necessary, conventional additives are added to the dispersion medium to prepare a slurry. CaSiO3 may be added to the dispersion medium at this stage, or it may be mixed with the slurry after wet milling, as described below. Water is the preferred dispersion medium used in the present invention. If necessary, a binder, dispersant, etc. may be blended into the dispersion medium. 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-based 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 in the range of 50% to 90% by mass, and 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.

[0040] Alternatively, weighed ferrite component raw materials, CaSiO3, and optional additives 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, temperatures below 1540°C allow CaSiO3 to maintain its crystal structure without melting or decomposing. Air is also preferred for the atmosphere during calcination.

[0041] 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.

[0042] CaSiO3 may not be added when preparing the slurry, but may be added to the slurry after wet milling.

[0043] 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.

[0044] 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 large amount of CaSiO3, 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%.

[0045] 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 particle size of the ferrite particles is preferably 30 μm or more and less than 50 μm.

[0046] 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.

[0047] (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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] (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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] (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. 7 shows a schematic diagram of an example of a developing device that performs magnetic brush development. The developing device shown in Fig. 7 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 in parallel 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] In the embodiment shown in Figure 7, 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]

[0063] 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.

[0064] Example 1 The raw materials were 4.9 kg of Fe2O3 (average particle size: 0.6 μm), 1.9 kg of Mn3O4 (average particle size: 3.4 μm), and 3.1 kg of CaSiO3 (average particle size: 5 μm, average aspect ratio: 3), dispersed in 3.2 kg of pure water, and 81.7 g of ammonium polycarboxylate dispersant and 6.2 g of ammonia water (25 wt% aqueous solution) were added as dispersants 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 heated to 1170°C over 4.5 hours at a heating rate of 180°C / h in the temperature range from 500°C to 1170°C. It was then sintered by holding at 1170°C for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired material was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain carrier core particles having an average particle size of 36.0 μm and sufficient sphericity for a carrier core particle. The powder characteristics, shape characteristics, magnetic 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. A cross-sectional SEM photograph of the obtained carrier core material is shown in Fig. 1. EDS element mapping of Fe, Mn, Ca, and Si in the cross-sectional SEM photograph shown in Fig. 1 is shown in Fig. 2 to Fig. 5. Furthermore, the XRD measurement results of the carrier core material of Example 1 are shown in Fig. 6.

[0065] 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.

[0066] The obtained carrier and toner with an average particle size of approximately 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 evaluated using an actual machine, as described below. The following Examples and Comparative Examples were also evaluated using an actual machine in the same manner. The evaluation results are shown in Table 2.

[0067] Example 2 The carrier core material of Example 1 was subjected to oxidation treatment (resistance-increasing treatment) by holding it in an air atmosphere at a temperature of 400°C for 1.5 hours, thereby obtaining a carrier core material with an average particle diameter of 36.0 μm and sufficient sphericity as a carrier core material. The powder characteristics, shape characteristics, magnetic 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.

[0068] Example 3 Carrier core particles having a mean particle diameter of 37.7 μm and sufficient sphericity for carrier core particles were obtained in the same manner as in Example 2, except that the oxidation treatment (resistance-increasing treatment) temperature was 430° C. The powder characteristics, shape characteristics, magnetic 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.

[0069] Example 4 Carrier core particles having a mean particle size of 37.7 μm and sufficient sphericity for carrier core particles were obtained in the same manner as in Example 2, except that the oxidation treatment (resistance increasing treatment) temperature was 460° C. The powder characteristics, shape characteristics, magnetic 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] Example 5 The raw materials were 5.7 kg of Fe2O3 (average particle size: 0.6 μm), 2.2 kg of Mn3O4 (average particle size: 3.4 μm), and 2.1 kg of CaSiO3 (average particle size: 5 μm, average aspect ratio: 3), dispersed in 3.2 kg of pure water, and 81.7 g of ammonium polycarboxylate dispersant and 6.2 g of ammonia water (25 wt% aqueous solution) were added as dispersants 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 heated to 1170°C over 4.5 hours at a heating rate of 180°C / h in the temperature range from 500°C to 1170°C. It was then sintered by holding at 1170°C for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired material was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain carrier core particles having an average particle size of 35.7 μm and sufficient sphericity for a carrier core particle. The powder characteristics, shape characteristics, magnetic 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.

[0071] Example 6 The carrier core material of Example 5 was subjected to oxidation treatment (resistance-increasing treatment) by holding it in an air atmosphere at a temperature of 400°C for 1.5 hours, thereby obtaining a carrier core material with an average particle diameter of 35.7 μm and sufficient sphericity as a carrier core material. The powder characteristics, shape characteristics, magnetic 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.

[0072] Example 7 Carrier core particles having a mean particle size of 35.7 μm and sufficient sphericity for carrier core particles were obtained in the same manner as in Example 6, except that the oxidation treatment (resistance-increasing treatment) temperature was 430° C. The powder characteristics, shape characteristics, magnetic 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 8 Carrier core particles having a mean particle size of 35.7 μm and sufficient sphericity for carrier core particles were obtained in the same manner as in Example 6, except that the oxidation treatment (resistance-increasing treatment) temperature was 460° C. The powder characteristics, shape characteristics, magnetic 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 9 The raw materials were 5.6 kg of Fe2O3 (average particle size: 0.6 μm), 2.2 kg of Mn3O4 (average particle size: 3.4 μm), and 2.2 kg of CaSiO3 (average particle size: 5 μm, average aspect ratio: 3), dispersed in 3.2 kg of pure water, and 81.7 g of ammonium polycarboxylate dispersant and 6.2 g of ammonia water (25 wt% aqueous solution) were added as dispersants 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 heated to 1170°C over 4.5 hours at a heating rate of 180°C / h in the temperature range from 500°C to 1170°C. It was then sintered by holding at 1170°C for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired material was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain carrier core particles having an average particle size of 35.8 μm and sufficient sphericity for a carrier core particle. The powder characteristics, shape characteristics, magnetic 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 10 The carrier core material of Example 9 was subjected to oxidation treatment (resistance-increasing treatment) by holding it in an air atmosphere at a temperature of 400°C for 1.5 hours, thereby obtaining a carrier core material with an average particle diameter of 35.8 μm and sufficient sphericity as a carrier core material. The powder characteristics, shape characteristics, magnetic 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 11 Carrier core particles having a mean particle size of 35.4 μm and sufficient sphericity for carrier core particles were obtained in the same manner as in Example 9, except that the firing temperature in the electric furnace was 1145° C. The powder characteristics, shape characteristics, magnetic 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 12 The carrier core material of Example 11 was subjected to oxidation treatment (resistance-increasing treatment) by holding it in an air atmosphere at a temperature of 400°C for 1.5 hours, thereby obtaining a carrier core material with an average particle diameter of 35.4 μm and sufficient sphericity as a carrier core material. The powder characteristics, shape characteristics, magnetic 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.

[0078] (Comparative Example 1) As raw materials, 7.2 kg of Fe2O3 (average particle size: 0.6 μm) and 2.8 kg of Mn3O4 (average particle size: 3.4 μm) were dispersed in 2.4 kg of pure water, and 48.0 g of carbon black as a reducing agent, 60.4 g of a polycarboxylate ammonium dispersant as a dispersant, and 6.2 g of ammonia water (25 wt% aqueous solution) were added 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 heated to 1035°C over 4.5 hours, after which it was fired by being held at 1035°C for 3 hours. The oxygen concentration in the electric furnace was adjusted to 500 ppm. The resulting fired product was disintegrated using a hammer mill and then classified using a vibrating sieve to obtain a fired product with an average particle size of 34.6 μm. The powder characteristics, shape characteristics, magnetic 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] (Comparative Example 2) As raw materials, 7.2 kg of Fe2O3 (average particle size: 0.6 μm) and 2.8 kg of Mn3O4 (average particle size: 3.4 μm) were dispersed in 2.4 kg of pure water, and 21.8 g of carbon black as a reducing agent, 62.2 g of a polycarboxylate ammonium dispersant as a dispersant, and 6.2 g of ammonia water (25 wt% aqueous solution) were added 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 heated to 1200°C over 4.5 hours. It was then fired by holding at 1200°C for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired material was degranulated using a hammer mill and then classified using a vibrating sieve. The classified fired material was then subjected to an oxidation treatment (resistance-increasing treatment) by being held at 400°C in an air atmosphere for 1.5 hours, thereby obtaining a carrier core material with an average particle diameter of 34.4 μm. The powder characteristics, shape characteristics, magnetic 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] (Comparative Example 3) The raw materials were 6.5 kg of Fe2O3 (average particle size: 0.6 μm), 2.5 kg of Mn3O4 (average particle size: 3.4 μm), and 1.0 kg of CaSiO3 (average particle size: 5 μm, average aspect ratio: 3), dispersed in 3.2 kg of pure water, and 81.7 g of ammonium polycarboxylate dispersant and 6.2 g of ammonia water (25 wt% aqueous solution) were added as dispersants 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 heated to 1170°C over 4.5 hours at a heating rate of 180°C / h in the temperature range from 500°C to 1170°C. It was then sintered by holding at 1170°C for 3 hours. The oxygen concentration in the electric furnace was adjusted to 3000 ppm. The obtained fired material was disintegrated with a hammer mill and then classified with a vibrating sieve to obtain carrier core particles having an average particle size of 35.8 μm and sufficient sphericity for a carrier core particle. The powder characteristics, shape characteristics, magnetic 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] (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. (Calculation of CaSiO3 content) The CaSiO3 content was calculated from the amount of Ca in the carrier core material using the following calculation formula. CaSiO3 content (mass%) = (Ca content (mass%) in carrier core material) × (CaSiO3 molecular weight: 116.17 g / mol) / (Ca atomic weight: 40.08 g / mol)

[0082] (apparent density AD) The apparent density of the carrier core material was measured in accordance with JIS Z 2504.

[0083] (Flow rate FR) The fluidity of the carrier core material was measured in accordance with JIS Z 2502.

[0084] (Average particle diameter D 50 and the proportion of particles with a particle size of 22 μm or less) The volume-based cumulative particle size distribution of the carrier core material was measured using a laser diffraction particle size distribution analyzer (Nikkiso Co., Ltd.'s "Microtrac Model 9320-X100"), and the average particle diameter D 50 The cumulative value of particles with a particle size of 22 μm or less was calculated.

[0085] (pore volume) The pore volume of the carrier core material was measured as follows. The evaluation device used was a POREMASTER-60GT manufactured by Quantachrome. The specific measurement conditions were: Cell Stem Volume: 0.5 ml, Head pressure: 20 PSIA, Surface tension of mercury: 485.00 erg / cm 2 , mercury contact angle: 130.00 degrees, high pressure measurement mode: Fixed Rate, motor speed: 1, high pressure measurement range: 20.00 to 10000.00 PSI, weigh out 1.200 g of sample and measure 0.5 ml (cm 3 The pore volume was calculated by subtracting the volume A (ml / g) at 100 PSI from the volume B (ml / g) at 10,000.00 PSI.

[0086] (BET specific surface area) The evaluation was carried out using a BET single-point specific surface area measuring device (Macsorb HM model-1208, manufactured by Mountec Co., Ltd.) Specifically, 10,000 g of the sample 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.

[0087] (true density) The true density of the carrier core material was measured using "ULTRA PYCNOMETER 1000" manufactured by Quantachrome.

[0088] (Particle shape factor: ISO Circularity) Measurement was carried out using the following measuring device and under the following conditions. Measuring device: Injection type image analysis particle size distribution meter “IF-3200” manufactured by JASCO Analysis software: PIA-Pro 14.18 Sample preparation conditions: 0.07 g of sample is dissolved in 9 cm of polyethylene glycol 400. 3 The screw cap bottle (capacity 9cm) 3 ) and then measured. Measurement conditions: Telecentric zoom lens, 2x magnification Front lens: 2x magnification Calibration value 0.417μm / pixel Spacer thickness 150μm Sampling 20% Analysis type: Relative measurement Measurement amount 0.95cm 3 Analysis Dark Detection Threshold 166 (fill in holes) O-Roughness Filter 0.5 Measurement filter conditions: ISO Area Diameter: Min 1, Max 150, Inner Range Analysis filter criteria: ISO Area Diameter: Min 10, Max 55, Inner Range ISO Solidity: Min 0.97, Max 1, Inner range ISO Circularity: Ratio of the diameter of an equivalent circle to the diameter of an equivalent ellipse ISO Circularity calculation formula: π×Area Diameter (equivalent diameter of a circle) / Perimeter (perimeter)

[0089] (particle strength index) 30 g of carrier core material was placed in a sample mill (Kyoritsu Riko Co., Ltd., "SK-M10") and subjected to a crushing test at 14,000 rpm for 60 seconds. The difference in cumulative value (volume %) of particle sizes of 22 μm or less in the cumulative particle size distribution of the carrier core material before and after the crushing test was determined and used as an index of particle strength for the carrier core material. The cumulative particle size distribution of the carrier core material was measured using a laser diffraction particle size distribution analyzer (Nikkiso Co., Ltd., "Microtrac Model 9320-X100"). The unit is volume %.

[0090] (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.

[0091] (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 1000V DC voltage 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 2mm and the cross-sectional area was 240mm. 2 The electrical resistance of the carrier core material was calculated from the above.

[0092] (Cross-sectional SEM photograph, EDS element mapping) The carrier core material was dispersed in resin and subjected to vacuum degassing to fill the resin within the carrier core material. The resin was then applied to a support plate and heat-treated at 200°C for 20 minutes to harden the resin. The carrier core material was then cut using a cross-section polisher (SM-09010, manufactured by JEOL Ltd.). The cross-section of the carrier core material was then photographed using a scanning electron microscope (JSM-6510LA, manufactured by JEOL Ltd.). Mapping images of the elements Fe, Mn, Ca, and Si were obtained using EDS.

[0093] (Powder X-ray diffraction (XRD) measurement) Powder X-ray diffraction measurements of the carrier core material were performed using an "Ultima IV" manufactured by Rigaku Corporation. A Cu tube (Kα) was used as the X-ray source, and X-rays were generated under 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 0.15 mm, and the scan range was 15°≦2θ≦95°. The product phase was identified from the obtained X-ray diffraction pattern. If a CaSiO3 peak can be confirmed in the obtained X-ray diffraction pattern, it can be determined that the carrier core material contains CaSiO3.

[0094] (Toner Spent Evaluation) The two-component developer thus prepared was placed in a developing device having the structure shown in Figure 7 (peripheral speed of developing roller v1: 406 mm / sec, peripheral speed of photosensitive drum v2: 205 mm / sec, distance between photosensitive drum and developing roller: 0.3 mm), and the developer was stirred for 36 hours. 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 the surface 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.

[0095] (Evaluation of white spots in an image) The two-component developer thus prepared was placed in a developing device having the structure shown in Figure 7 (peripheral speed of developing roller v1: 406 mm / sec, peripheral speed of photosensitive drum v2: 205 mm / sec, distance between photosensitive drum and developing roller: 0.3 mm), and 10 black solid images were developed and printed initially and after 100,000 copies were printed. The degree of whiteout in the black solid areas was visually evaluated according to the following criteria. "◎": No white spots were observed and the image was in good condition. "○": Less than 5 white spots "△": 5 to 10 white spots "X": More than 10 clear white spots are present.

[0096] [Table 1]

[0097] [Table 2]

[0098] The cross-sectional SEM photograph of the carrier core material in Figure 1 reveals that there are almost no voids inside the carrier core material. Furthermore, EDS elemental mapping of Fe, Mn, Ca, and Si in the cross-sectional SEM photographs shown in Figures 2 to 5 reveals that Fe and Mn exist in a common region, and Ca and Si also exist in a common region, and these two regions do not overlap. Furthermore, the XRD analysis results in Figure 6 reveal that the carrier core material in Figure 1 contains both MnFe2O4 and CaSiO3. From these findings, it can be said that the carrier core material of Example 1 is nearly solid, with CaSiO3 dispersed within MnFe2O4. The cross-sectional SEM photographs, EDS elemental mapping, and XRD analysis yielded similar results in Examples 2 to 12.

[0099] As is clear from Tables 1 and 2, the composition contains 27.8 mass% of CaSiO3 and has a true density of 4.0 g / cm 3In the developers using the carrier core materials of Examples 1 to 4, where the toner was fused, the percentage of carrier particles with fused toner was less than 0.5%. Furthermore, in the developers using the carrier core materials of Examples 2 to 4, which had been subjected to high-resistance treatment, no white spots were observed in the image either initially or after 100,000 sheets were printed, and good images were obtained. Furthermore, in the developer using the carrier core material of Example 1, which had not been subjected to high-resistance treatment, the number of white spots in the image was less than 5 either initially or after 100,000 sheets, which was at a level that would not pose a problem in practical use. In Table 2, "BD" stands for breakdown.

[0100] It also contains 19.1 mass% of CaSiO3 and has a true density of 4.2 g / cm 3 or 4.3 g / cm 3 In the developers using the carrier core materials of Examples 5 to 8, which had a high resistance treatment, the percentage of carrier particles to which the toner had fused was less than 1.0%, which was a good result. Furthermore, in the developers using the carrier core materials of Examples 6 to 8, which had been subjected to high-resistance treatment, no white spots were observed in the image either initially or after 100,000 sheets were printed, and good images were obtained. Furthermore, in the developer using the carrier core material of Example 5, which had not been subjected to high-resistance treatment, the number of white spots in the image was less than 5 either initially or after 100,000 sheets, which was a level that would not pose a problem in practical use.

[0101] It contains 20.7 mass% of CaSiO3 and has a true density of 4.2 g / cm 3 or 4.3 g / cm 3 In the developers using the carrier core materials of Examples 9 to 12, which had a high resistance, the percentage of carrier particles to which the toner had fused was less than 1.0%, which was a good result. Furthermore, in the developers using the carrier core materials of Examples 10 and 12, which had been subjected to high-resistance treatment, no white spots were observed in the image either initially or after 100,000 sheets were printed, and good images were obtained. Furthermore, in the developers using the carrier core materials of Examples 9 and 11, which had not been subjected to high-resistance treatment, the number of white spots in the image was less than 5 either initially or after 100,000 sheets, which was a level that would not pose a problem in practical use.

[0102] In contrast, the true density of 4.9 g / cm3 is 4.9 g / cm3, which does not contain CaSiO3.3 and 4.8 g / cm 3 In the developers using the carrier core materials of Comparative Examples 1 and 2, which had high sintering temperatures, the particle strength index was 2.7% by volume and 2.3% by volume, respectively, which was significantly lower than that of the Examples. As a result, 5 to 10 white spots occurred in the image after printing 100,000 sheets. In addition, the carrier core material of Comparative Example 2, which had a high baking temperature of 1200°C, had an apparent density AD of 2.42 g / cm. 3 The ratio of the number of carrier particles to which the toner had fused was 5.0% or more, which was a problematic level for practical use.

[0103] Contains 8.3 mass% CaSiO3 and has a true density of 4.6 g / cm 3 In the developer using the carrier core material of Comparative Example 3, which has a high toner fusion rate, the percentage of carrier particles fused to the toner was 1.0% or more and less than 5.0%, which was a problematic level for practical use. Furthermore, the particle strength index was 2.2% by volume, which was significantly lower than that of the Examples. Therefore, 5 to 10 blank areas occurred in the image after printing 100,000 sheets. [Industrial Applicability]

[0104] According to the carrier core material of the present invention, toner spent is suppressed, and the carrier core material is less likely to crack or chip even after long-term use. [Explanation of symbols]

[0105] 3 Developing roller 5 Photosensitive drum

Claims

1. A carrier core material made of ferrite particles, CaSiO ３ Contains True density is 3.5 g / cm ３ 4.5g / cm or more ３ The range is as follows: The carrier core material is characterized in that the content of CaSiO 3 in the ferrite particles is in the range of 10% by mass to 50% by mass.

2. 2. The carrier core material according to claim 1, wherein the particle strength index calculated from the following formula (1) is 1.5% by volume or less. Particle strength index = V2-V1 (1) (wherein V1 is the cumulative value (volume %) of particles with particle diameters of 22 μm or less in the cumulative particle size distribution of the carrier core material before the crushing test, and V2 is the cumulative value (volume %) of particles with particle diameters of 22 μm or less in the cumulative particle size distribution of the carrier core material after the crushing test) Crushing test conditions: 30 g of carrier core material was crushed using a sample mill at a rotation speed of 14,000 rpm for 60 seconds.

3. The apparent density of the ferrite particles is 1.7 g / cm ３ 2.1g / cm or more ３ 3. The carrier core material according to claim 1, wherein the carrier core material has a molecular weight in the range of:

4. The saturation magnetization of the ferrite particles is 40 Am ２ / kg or more 72Am ２ 3. The carrier core material according to claim 1, wherein the carrier core material has a particle size of 1 / kg or less.

5. The residual magnetization of the ferrite particles is 2.5 Am ２ / kg or less, Coercive force is 30 oersted or less The carrier core material according to claim 1 or 2.

6. The ferrite particles have a composition formula (Mn Ｘ Fe ３－Ｘ ) O ４ (wherein 0≦X<3) The Ca content is in the range of 3.4 mass% or more and 15.8 mass% or less, The Si content is in the range of 3.0 mass % to 11.4 mass %. The carrier core material according to claim 1 or 2.

7. 3. A carrier for electrophotographic development, wherein the surface of the carrier core material according to claim 1 or 2 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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