JP2013205774A - Ferrite carrier core material for electrophotographic developer, ferrite carrier, methods for producing them and electrophotographic developer using the ferrite carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferrite carrier core material for an electrophotographic developer which is free from image defects such as carrier adhesion and fine-line reproducibility when used for an electrophotographic developer since the ferrite carrier core material has a small particle size, excellent electric resistance and small particle size distribution and variation of surface properties between particles, and also provide a ferrite carrier, methods for producing them, and the electrophotographic developer using the ferrite carrier.SOLUTION: A ferrite carrier core material for an electrophotographic developer is made of a ferrite particle and has a volume average particle diameter of 20 to 30 μm. When a circle equivalent particle diameter measured by an image analyzer is divided into units of 1 μm, the frequency of the divided particles in the most frequent region is 8 number% or more. The ferrite carrier, methods for producing the ferrite carrier core material for the electrophotographic developer and the ferrite carrier, and the electrophotographic developer using the ferrite carrier are also provided.

Description

  The present invention relates to a ferrite carrier core material for an electrophotographic developer used in a two-component electrophotographic developer used in a copying machine, a printer, and the like, a ferrite carrier, a production method thereof, and an electrophotography using the ferrite carrier. It relates to a developer.

  The electrophotographic development method is a method in which toner particles in a developer are attached to an electrostatic latent image formed on a photoreceptor and developed, and the developer used in this method is composed of toner particles and carrier particles. The two-component developer and the one-component developer using only toner particles.

  Among these developers, as a developing method using a two-component developer composed of toner particles and carrier particles, the cascade method has been used in the past, but at present, the magnetic brush method using a magnet roll is the mainstream. It is.

  In the two-component developer, the carrier particles are agitated together with the toner particles in the developing box filled with the developer, thereby imparting a desired charge to the toner particles, and thus being charged. A carrier material for transporting toner particles to the surface of the photoreceptor to form a toner image on the photoreceptor. The carrier particles remaining on the developing roll holding the magnet are returned to the developing box from the developing roll, mixed and stirred with new toner particles, and used repeatedly for a certain period.

  Unlike the one-component developer, the two-component developer has the function of mixing and stirring the carrier particles with the toner particles, charging the toner particles, and further transporting the toner particles. Good controllability. Therefore, the two-component developer is suitable for a full-color developing device that requires high image quality and a device that performs high-speed printing that requires image maintenance reliability and durability.

  In the two-component developer used in this manner, image characteristics such as image density, fog, vitiligo, gradation, and resolving power show predetermined values from the initial stage, and these characteristics are in the printing life period. It needs to be kept stable without fluctuating inside. In order to maintain these characteristics stably, it is necessary that the characteristics of the carrier particles contained in the two-component developer are stable.

  Conventionally, iron powder carriers such as iron powder whose surface is covered with an oxide film or iron powder whose surface is coated with a resin have been used as carrier particles for forming a two-component developer. Since such an iron powder carrier has high magnetization and high conductivity, there is an advantage that an image with a good reproducibility of the solid portion can be easily obtained.

  However, such an iron powder carrier has a heavy true specific gravity of about 7.8 and is too high in magnetization, so that the toner constituent components on the surface of the iron powder carrier are mixed by stirring and mixing with toner particles in the developing box. Fusing, so-called toner spent, is likely to occur. The generation of such toner spent reduces the effective carrier surface area and tends to reduce the triboelectric charging ability with the toner particles.

  Moreover, in the resin-coated iron powder carrier, the resin on the surface peels off due to stress during durability, and the core material (iron powder) with high conductivity and low dielectric breakdown voltage is exposed, which may cause charge leakage. . Due to such charge leakage, the electrostatic latent image formed on the photoconductor is destroyed, and a crack or the like is generated in the solid portion, so that it is difficult to obtain a uniform image. For these reasons, iron powder carriers such as oxide-coated iron powder and resin-coated iron powder are no longer used.

  In recent years, instead of iron powder carriers, ferrite particles, which are light as true specific gravity of about 5.0 and have low magnetization, are used as carriers, and resin coated ferrite carriers in which resin is coated on the surface of ferrite particles are often used. As a result, the developer life has been dramatically increased.

  As a method for producing such a ferrite carrier, a predetermined amount of ferrite raw materials are mixed, calcined, pulverized, and generally fired after granulation. Depending on conditions, calcining may be omitted. .

  Recently, environmental regulations have become stricter, and the use of metals such as Ni, Cu, and Zn has been avoided, and the use of metals suitable for environmental regulations has been demanded, and it is used as a carrier core material. The ferrite composition has shifted from Cu-Zn ferrite, Ni-Zn ferrite to manganese ferrite using manganese, Mn-Mg-Sr ferrite, and the like.

  Patent Document 1 (Japanese Patent Laid-Open No. 8-22150) describes a ferrite carrier in which a part of manganese-magnesium ferrite is replaced with SrO. By reducing the variation in magnetization between particles by using this ferrite carrier, it is said that when used as a developer together with toner, it has excellent image quality and durability, is friendly to the environment, has a long life, and is excellent in environmental stability. However, the ferrite carrier described in Patent Document 1 cannot be said to have stable carrier particle characteristics and has a wide range of characteristic values such as particle size distribution and surface properties. The distribution of the image becomes wider and the characteristics such as image density and fine line reproducibility cannot be satisfied.

  In order to stabilize the carrier characteristics, those focusing on the particle size distribution have been known for a long time. For example, Patent Document 2 (Japanese Patent Laid-Open No. 51-3238) mentions a rough particle size distribution, but all the carriers in the examples are about 250 wt. Since it is 60 micrometers or more, it cannot be said that it corresponds to the various characteristics requested | required of the present carrier.

  There have been many proposals focusing on particle size distribution in recent years. For example, Patent Document 3 (Japanese Patent Laid-Open No. 2-281280) defines the abundance of fine powder and coarse powder.

  Further, in Patent Document 4 (Japanese Patent Laid-Open No. 7-98521), a fine particle size distribution is defined by setting the content of carrier particles smaller than 22 μm and 16 μm and the content of carrier particles larger than 62 μm and 88 μm. Yes.

  However, although these patents prescribe the particle size distribution, the distribution width is wide, and it cannot be said that the characteristic value is sufficiently stabilized.

  Patent Document 5 (Japanese Patent Laid-Open No. 2005-195728) and Patent Document 6 (Japanese Patent Laid-Open No. 2005-250424) are examples of narrow particle size distributions. Patent Document 5 strictly defines the particle size distribution, and Patent Document 6 defines the particle size distribution by reducing the ratio between the volume distribution and the number distribution. However, since the measurement is performed using a laser scattering type device, not only the particles are assumed to be spherical, but also the detection of the particle size is based on analog, and it is said that it represents the actual state of the particle size distribution. It ’s hard.

  In Patent Document 7 (Japanese Patent Application Laid-Open No. 2011-186210), a coefficient of variation of the number distribution is defined, and the apparatus using the Coulter method is also used for particle size measurement. However, it cannot be said that it represents the actual size distribution.

JP-A-8-22150 Japanese Patent Laid-Open No. 51-3238 Japanese Patent Laid-Open No. 2-281280 JP-A-7-98521 JP 2005-195728 A Japanese Patent Laid-Open No. 2005-250424 JP 2011-186210 A

  Accordingly, the object of the present invention is to have a small particle size, good electrical resistance, sharp particle size distribution, small surface-to-particle variation, and carrier adhesion and fine line reproduction when used in an electrophotographic developer. An object of the present invention is to provide a ferrite carrier core material for an electrophotographic developer free from image defects such as deterioration of properties, a ferrite carrier, a method for producing them, and an electrophotographic image agent using the ferrite carrier.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention classify the circle-equivalent particle diameter in units of 1 μm with the volume average particle diameter being in a specific range and the ferrite particles measured by the image analyzer. The ferrite carrier core material in which the frequency of the most frequent region of the classified particles is a certain level or more and the ferrite carrier coated with a resin on the surface achieve the above-mentioned purpose, and such a ferrite carrier core material has the purpose. After adjusting the granulation step so that the volume average particle size is 15 μm or more larger than the volume average particle size to be obtained, and after sorting, removing particles having an average particle size 9 μm or more larger than the target volume average particle size The present inventors have found that the remaining particles that have not been sorted and removed can be classified by a production method for obtaining ferrite particles having a target volume average particle diameter, and the present invention has been achieved.

That is, the present invention is a ferrite carrier core material for an electrophotographic developer comprising ferrite particles,
Ferrite particles having a volume average particle diameter of 20 to 30 μm and a frequency of the most frequent region of the divided particles of 8% by number or more when the equivalent circle particle diameter measured by the image analysis apparatus is divided in units of 1 μm A ferrite carrier core material for an electrophotographic developer is provided.

  In the ferrite carrier core material for an electrophotographic developer according to the present invention, it is desirable that the average value of the equivalent circle particle diameter measured by the ferrite particle image analysis apparatus is 25 to 35 μm.

In the ferrite carrier core material for an electrophotographic developer according to the present invention, the ferrite particles preferably have a BET specific surface area of 0.10 to 0.18 m ² / g.

  In the ferrite carrier core material for an electrophotographic developer according to the present invention, the ferrite particles preferably have a surface oxide film.

  The present invention also provides a ferrite carrier for an electrophotographic developer in which the surface of the ferrite carrier core material is coated with a resin.

The present invention also includes a method for producing a ferrite carrier core material for an electrophotographic developer, which has at least a ferrite raw material pulverization and mixing step, a main granulation step, and a main firing step to obtain ferrite particles having a volume average particle size of 20 to 30 μm. Because
In the main granulation step, granulation is performed by adjusting the granulation volume average particle size to be 15 μm or more larger than the target volume average particle size, and after the main firing step, A fractionation step of separating and removing particles having a volume particle size larger than 9 μm, and a particle size adjustment step of obtaining the ferrite particles having the target volume average particle size by classifying the remaining particles that have not been separated and removed. The present invention provides a method for producing a ferrite carrier core material for an electrophotographic developer.

  In the method for producing a ferrite carrier core material for an electrophotographic developer of the present invention, a pre-baking step and a regrinding and mixing step may be provided before the main granulation step.

  In the method for producing a ferrite carrier core material for an electrophotographic developer according to the present invention, a primary firing step may be provided before the main firing step.

  In the method for producing a ferrite carrier core material for an electrophotographic developer according to the present invention, a surface oxidation treatment step may be provided after the particle size adjustment step.

  The present invention also provides a method for producing a ferrite carrier for an electrophotographic developer, wherein the ferrite carrier core material obtained by the above production method is coated with a resin.

  Furthermore, the present invention provides an electrophotographic developer comprising the above ferrite carrier and a toner.

  The electrophotographic developer according to the present invention is also used as a replenishment developer.

  The ferrite carrier core material for an electrophotographic developer according to the present invention has a small particle size, good electrical resistance, a sharp particle size distribution, and small surface-to-particle variation. When used, image defects such as carrier adhesion and thin line reproducibility do not occur. The electrophotographic developer comprising a ferrite carrier and a toner obtained by coating a resin on the ferrite carrier core material prevents carrier scattering in the actual machine, and a printed matter with good fine line reproducibility can be obtained continuously. In addition, the ferrite carrier core material and the ferrite carrier can be stably obtained with productivity by the production method of the present invention.

Hereinafter, modes for carrying out the present invention will be described.
<Ferrite carrier core material and ferrite carrier for electrophotographic developer according to the present invention>

  The composition of the ferrite particles used as the ferrite carrier core material for an electrophotographic developer according to the present invention is not particularly limited, but Mn ferrite and Mn—Mg—Sr ferrite are preferably used. For example, the Mn-Mg-Sr ferrite contains 15 to 22% by weight of Mn, 0.5 to 3% by weight of Mg, 45 to 55% by weight of Fe, and 0.1 to 3.0% by weight of Sr. Is mentioned. Ferrite particles having such a specific composition are desirably used because they have high magnetization and good magnetization uniformity (small variation in magnetization). Considering the recent trend of reducing environmental burdens including waste regulations, it is preferable not to include heavy metals such as Cu, Zn, and Ni beyond the range of inevitable impurities (accompanying impurities). In the present invention, the term “ferrite particles” means an aggregate of individual ferrite particles unless otherwise specified, and the term simply refers to individual ferrite particles.

Ferrite particles for use in electrophotographic developer ferrite carrier core material according to the present invention preferably has a volume average particle size D ₅₀ by the measurement of a laser diffraction particle size distribution measuring apparatus 20 to 30 [mu] m, preferably 22～28Myuemu.

  When the volume average particle size is smaller than the above range, since the magnetic force per ferrite particle is small, carrier scattering cannot be prevented even if the BET specific surface area is within a desirable range. If the volume average particle size is larger than the above range, a high toner concentration cannot be realized when an electrophotographic developer is prepared, and a high-quality printed matter cannot be obtained, or if a high toner concentration is used, electrons are rapidly emitted. The charge amount of the photographic developer is lowered or the charge amount distribution is widened, which causes toner scattering.

(Volume average particle size)
This volume average particle diameter was measured by a laser diffraction scattering method. As a device, a Nikkiso Co., Ltd. Microtrac particle size analyzer (Model 9320-X100) was used. The refractive index was 2.42, and the measurement was performed in an environment of 25 ± 5 ° C. and humidity 55 ± 15%. The average particle diameter (median diameter) referred to here is the cumulative 50% particle diameter in the volume distribution mode and under the sieve display.
The sample (ferrite particles) was dispersed using a 0.2% sodium hexametaphosphate aqueous solution as a dispersion, and subjected to ultrasonic treatment for 1 minute using an Ultrasonic Homogenizer (UH-3C) manufactured by Ultrasonic Industries.
In this microtrack particle size analyzer, the volume-based average particle diameter is measured, and the number average particle diameter is automatically calculated from the measured value. In general, the relationship between the volume average particle size and the number average particle size is as follows.

  The ferrite particles used in the ferrite carrier core material for an electrophotographic developer according to the present invention have a frequency of the most frequent region of the classified particles when the equivalent circle particle diameter measured by the image analyzer is divided in units of 1 μm. Must be 8% by number or more. To divide the circle-equivalent particle diameter in units of 1 μm, 3000 circle-equivalent particle diameters are measured by the method described later, and the number of each μm unit is counted. For example, if the number of the 25 μm range (25.0 μm to less than 26.0 μm) is 330, the frequency of the 25 μm range is (330/3000) × 100 = 11 number%.

  When the frequency of the most frequent region of the classified particles is less than 8% by number, a sharp particle size distribution cannot be obtained, and the surface property variation between particles is large. The reproducibility is inferior. In addition, when the ferrite particles are coated with a resin to form a ferrite carrier, the electrical resistance decreases.

  The ferrite particles used in the ferrite carrier core material for an electrophotographic developer according to the present invention have an average circle equivalent particle diameter of 25 to 35 μm, preferably 27 to 33 μm, as measured by an image analyzer.

  When the average value of the equivalent circle particle diameter is smaller than the above range, the magnetic force per particle is small, so that carrier scattering cannot be prevented even if the BET specific surface area is within a desirable range. If the average value of the equivalent circle particle diameter is larger than the above range, a high toner concentration cannot be realized when an electrophotographic developer is prepared, and a high-quality printed matter cannot be obtained or a high toner concentration is used. The charge amount of the developer rapidly decreases or the charge amount distribution widens, which causes toner scattering.

(Equivalent particle diameter)
3000 particles were observed using a particle size / shape distribution measuring instrument PITA-1 manufactured by Seishin Enterprise Co., Ltd., and an equivalent circle particle diameter of each particle was determined using software Image Analysis included with the apparatus. The average value is an average value of 3000 particles.
The sample solution was prepared by preparing a xanthan gum aqueous solution having a viscosity of 0.5 Pa · s as a dispersion medium, in which 0.1 g of particles were dispersed in 30 cc of the xanthan gum aqueous solution. Thus, by appropriately giving the viscosity of the dispersion medium, it is possible to keep the particles dispersed in the dispersion medium, and to perform measurement smoothly. Furthermore, the measurement conditions are (objective) lens magnification of 10 times, filter is ND4 × 2, carrier liquid 1 and carrier liquid 2 are xanthan gum aqueous solutions having a viscosity of 0.5 Pa · s, and the flow rate is 10 μl / sec. The sample liquid flow rate was 0.08 μl / sec.

The BET specific surface area of the ferrite particles used as the ferrite carrier core material for an electrophotographic developer according to the present invention is preferably 0.10 to 0.18 m ² / g, more preferably 0.12 to 0.17 m ² / g. Most preferably, it is 0.13-0.16 m < ² > / g.

  When the BET specific surface area is smaller than the above range, not only can the resin anchor effect not be sufficiently obtained even if the resin coating is applied to the ferrite carrier core material (ferrite particles), but also the ferrite particles can be formed by the uncoated resin. They may aggregate together. For this reason, the amount of the coating resin is substantially reduced, the life as a carrier is shortened, or the aggregated ferrite particles are unraveled in the developing device, so that the surface of the ferrite particles is greatly exposed and the resistance is reduced to reduce carrier scattering. Cause the occurrence. When the BET specific surface area is larger than the above range, the coating resin does not stay on the ferrite particle surface and soaks too much, so that a desired resistance and charge amount as a carrier may not be obtained. When measuring the BET specific surface area, the measurement results are strongly influenced by the moisture on the ferrite particle surface, which is the measurement sample, so perform pretreatment to remove the moisture adhering to the sample surface as much as possible. Is preferred. Specifically, the moisture is removed by heating to a temperature range in which ferrite particles at 120 ° C. or higher, more preferably 150 ° C. or higher, do not cause alteration or the like while reducing pressure. In a state where moisture remains in the vicinity of the surface of the ferrite particles, the value of the BET specific surface area becomes about 1.2 to 2 times larger than that when the pretreatment is performed, and does not become a correct value.

The BET specific surface area was measured using a specific surface area measuring device (model: Macsorb HM model-1208 (manufactured by Mountec)). About 5 to 7 g of the measurement sample (ferrite particles) was put in a standard sample cell dedicated to a specific surface area measurement device, accurately weighed with a precision balance, the sample was set in a measurement port, and measurement was started. The measurement is performed by a one-point method, and the BET specific surface area is automatically calculated when the weight of the sample is input at the end of the measurement. As a pretreatment before measurement, after about 20 g of the measurement sample was placed in a glass petri dish, it was deaerated to −0.1 MPa with a vacuum dryer, and the degree of vacuum had reached −0.1 MPa or less. After confirmation, it was heated at 200 ° C. for 2 hours.
Environment: temperature; 10-30 ° C, humidity; 20-80% relative humidity, non-condensing

  In the ferrite carrier for an electrophotographic developer according to the present invention, the surface of the ferrite carrier core material (ferrite particles) is coated with a resin. The number of times of resin coating may be only once, or two or more times of resin coating may be performed, and the number of times of coating can be determined according to desired characteristics. Further, the composition of the coating resin, the coating amount, and the apparatus used for resin coating may be changed or may not be changed when the number of times of coating is two times or more.

  The ferrite carrier for an electrophotographic developer according to the present invention desirably has a total resin coating amount of 0.1 to 10% by weight with respect to the ferrite carrier core material. When the total coating amount is less than 0.1% by weight, it is difficult to form a uniform coating layer on the carrier surface. When the total coating amount exceeds 10% by weight, the carriers are aggregated, resulting in a decrease in productivity such as a decrease in yield. At the same time, it may cause fluctuations in developer characteristics such as fluidity or charge amount in the actual machine.

  The film-forming resin used here can be appropriately selected depending on the toner to be combined, the environment in which it is used, and the like. The type is not particularly limited, for example, fluorine resin, acrylic resin, epoxy resin, polyamide resin, polyamideimide resin, polyester resin, unsaturated polyester resin, urea resin, melamine resin, alkyd resin, phenol resin, fluorine acrylic resin, Examples thereof include acrylic-styrene resins, silicone resins, or modified silicone resins modified with resins such as acrylic resins, polyester resins, epoxy resins, polyamide resins, polyamideimide resins, alkyd resins, urethane resins, and fluororesins. In the present invention, acrylic resin, silicone resin or modified silicone resin is most preferably used.

  In addition, a conductive agent can be contained in the film forming resin for the purpose of controlling the electric resistance, charge amount, and charging speed of the carrier. Since the conductive agent has a low electric resistance, if the content is too large, it is likely to cause a rapid charge leak. Accordingly, the content is 0.25 to 20.0% by weight, preferably 0.5 to 15.0% by weight, particularly preferably 1.0 to 10.0% by weight, based on the solid content of the film-forming resin. %. Examples of the conductive agent include conductive carbon, carbon nanotubes having metallic properties, carbon nanotubes having semiconductor properties, oxides such as titanium oxide and tin oxide, and various organic conductive agents.

  In addition, the film forming resin can contain a charge control agent. Examples of the charge control agent include various charge control agents generally used for toners and various silane coupling agents. This is because, when the core material exposed area is controlled to be relatively small by film formation, the charge imparting ability may decrease, but it can be controlled by adding various charge control agents and silane coupling agents. It is. The types of charge control agents and coupling agents that can be used are not particularly limited, but charge control agents such as nigrosine dyes, quaternary ammonium salts, organometallic complexes, and metal-containing monoazo dyes, aminosilane coupling agents, and fluorine-based silane couplings. An agent or the like is preferable.

<Ferrite carrier core material for electrophotographic developer and method for producing ferrite carrier according to the present invention>
Next, the ferrite carrier core material for electrophotographic developer and the method for producing the ferrite carrier according to the present invention will be described.

  The method for producing a ferrite carrier core material for an electrophotographic developer according to the present invention includes at least a ferrite raw material pulverization and mixing step, a main granulation step, and a main firing step, and obtains ferrite particles having a volume average particle size of 20 to 30 μm. This is a method for producing a ferrite carrier core material for an electrophotographic developer.

There are no particular restrictions on the production steps of these ferrite raw materials, such as the pulverization and mixing step, the main granulation step, and the main firing step, and a conventionally known method can be employed. It may be used. Moreover, you may provide a temporary baking process and a regrind mixing process after a grinding | pulverization mixing process. For example, Fe ₂ O ₃ and Mg (OH) ₂ and / or MgCO ₃ and MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , and MnCO ₃ as raw materials and SrO and / or SrCO ₃ is pulverized and mixed (ferrite raw material pulverization and mixing step), and pre-baked in the atmosphere (pre-firing step). After calcining, the obtained calcined product is further pulverized with a ball mill or a vibration mill, and then water and, if necessary, a dispersant, a binder, etc. are added (re-grinding and mixing step), and after adjusting the viscosity, a spray dryer Granulate and granulate (main granulation step). When pulverizing after calcination, water may be added and pulverized by a wet ball mill, a wet vibration mill or the like. In addition, it is preferable to use polyvinyl alcohol or polyvinylpyrrolidone as a binder.

  In the production method of the present invention, in the main granulation step, it is necessary to adjust the granulation so that the granulation volume average particle size is 15 μm or more, preferably 15 to 25 μm larger than the target volume average particle size. It is. That is, when the target volume average particle size of the obtained ferrite particles is 26 μm, the granulated volume average particle size is 41 μm or more, preferably 41 to 51 μm. By granulating in this way, finally ferrite particles having a sharp particle size distribution can be obtained.

  In the production method of the present invention, the obtained granulated product is subjected to primary firing (primary firing step) and then main firing (main firing step) as necessary. Here, primary baking is performed at 600-800 degreeC. Moreover, this baking is performed at 1090-1210 degreeC by inert atmosphere or weakly oxidizing atmosphere.

  When performing the main firing, a firing furnace of a type that passes through the hot part while flowing inside the furnace like a rotary kiln tends to adhere to the furnace when the oxygen concentration of the firing atmosphere is low, and the fluidity A good fired product is discharged outside the furnace before it is fired sufficiently. Therefore, the BET specific surface area is about the same as the preferred range specified in the present invention, and even if the surface of the ferrite particle is sufficiently sintered, the inside of the particle does not progress, and the ferrite particle as a ferrite carrier core material for an electrophotographic developer May not have sufficient strength. Therefore, it is desirable to use a tunnel kiln, an elevator kiln or the like that allows the hot part to pass in a state where the granulated product before firing is placed in a koji bowl or the like as much as possible.

  In the present invention, after the ferrite particles obtained by the main firing are crushed, a fractionation step of fractionating and removing particles having a volume particle size of 9 μm or more, preferably 9 to 15 μm larger than the target volume average particle size is performed. Have. That is, assuming that the intended volume average particle size of the obtained ferrite particles is 26 μm, particles having a volume particle size of 35 μm or more, preferably 35 to 41 μm are fractionated and removed. By performing such a fractionation step, finally ferrite particles having a sharp particle size distribution can be obtained.

  Next, in the present invention, the remaining particles that have not been separated and removed, that is, the particles that have been separated and removed from the ferrite particles on the finer powder side in the previous sorting step have a volume particle size of a certain level or more. There is a particle size adjusting step for classifying and obtaining ferrite particles having a target volume average particle size. By this classification, ferrite particles having a sharp particle size distribution and small surface-to-particle variation can be obtained. As a classification method, the particle size is adjusted to a desired particle size using an existing air classification, mesh filtration method, sedimentation method, or the like. When dry collection is performed, it can also be collected with a cyclone or the like. When adjusting the particle size, two or more of the above classification methods may be selected and implemented, or the conditions may be changed by one type of classification method to remove the coarse particles and fine particles.

  The ferrite particles obtained in this way may be used directly as a ferrite carrier core material, but surface oxidation treatment is performed by heating the surface at a low temperature to form a surface oxide film on the surface of the ferrite particles, thereby adjusting the electric resistance. It is desirable to perform (surface oxidation treatment step). In the surface oxidation treatment, a general rotary electric furnace, batch type electric furnace, or the like is used in an oxygen-containing atmosphere such as air, and the heat treatment is preferably performed at 500 to 730 ° C, more preferably 600 to 700 ° C. When the heating temperature is lower than 500 ° C., oxidation of the ferrite particle surface does not proceed sufficiently, so that desired resistance characteristics cannot be obtained. When the heating temperature is higher than 730 ° C., manganese is excessively oxidized, and the low resistance of the ferrite particles due to the deterioration of the crystallinity of the spinel structure is not preferable. In order to form the surface oxide film uniformly on the ferrite particles, it is preferable to use a rotary electric furnace.

  Oxidation of the ferrite particle surface by mechanical impact such as agitation stress does not generate enough heat to restructure the crystal structure even if the temperature rises instantaneously, so stress (distortion of the crystal lattice) However, the strength of ferrite particles cannot be improved.

  Next, it is desirable that the ferrite particles on which the surface oxide film is formed by the surface oxidation treatment are rapidly cooled to 200 ° C. or lower. As the rapid cooling means, a rotary electric furnace having a rapid cooling part subsequent to the hot part is preferably used. The quenching condition is preferably a quenching condition of 20 ° C./min or more. Thus, by performing surface oxidation treatment at a constant temperature and then performing rapid cooling, variation in the amount of heat due to heat storage can be suppressed, and the crystal structure can be made uniform.

  The ferrite carrier for an electrophotographic developer of the present invention coats the above-mentioned resin on the surface of the ferrite carrier core material (classified ferrite particles or ferrite particles having a surface oxide film formed after classification) to form a resin film. . As a coating method, it can be coated by a known method such as a brush coating method, a spray drying method using a fluidized bed, a rotary drying method, an immersion drying method using a universal stirrer, or the like. In order to improve the coverage, a spray drying method using a fluidized bed is preferable.

  When the resin is coated on the ferrite carrier core and then baked, either an external heating method or an internal heating method may be used, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or a microwave oven Baking by may be used. When a UV curable resin is used, a UV heater is used. Although the baking temperature varies depending on the resin to be used, a temperature equal to or higher than the melting point or the glass transition point is necessary. For a thermosetting resin or a condensation-crosslinking resin, it is necessary to raise the temperature to a point where the curing proceeds sufficiently.

<Electrophotographic developer according to the present invention>
Next, the electrophotographic developer according to the present invention will be described.
The electrophotographic developer according to the present invention comprises the above-described ferrite carrier for electrophotographic developer and toner.

  The toner particles constituting the electrophotographic developer of the present invention include pulverized toner particles produced by a pulverization method and polymerized toner particles produced by a polymerization method. In the present invention, toner particles obtained by any method can be used.

  The pulverized toner particles are, for example, a binder resin, a charge control agent, and a colorant are sufficiently mixed with a mixer such as a Henschel mixer, then melt-kneaded with a twin screw extruder or the like, cooled, pulverized, classified, After adding the external additive, it can be obtained by mixing with a mixer or the like.

  The binder resin constituting the pulverized toner particles is not particularly limited, but polystyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, Furthermore, rosin modified maleic acid resin, epoxy resin, polyester resin, polyurethane resin and the like can be mentioned. These may be used alone or in combination.

  Any charge control agent can be used. For example, nigrosine dyes and quaternary ammonium salts can be used for positively charged toners, and metal-containing monoazo dyes can be used for negatively charged toners.

  As the colorant (coloring material), conventionally known dyes and pigments can be used. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, etc. can be used. In addition, external additives such as silica powder and titania for improving the fluidity and aggregation resistance of the toner can be added according to the toner particles.

  The polymerized toner particles are toner particles produced by a known method such as a suspension polymerization method, an emulsion polymerization method, an emulsion aggregation method, an ester elongation polymerization method, or a phase inversion emulsification method. Such polymerized toner particles are prepared by, for example, mixing and stirring a colored dispersion in which a colorant is dispersed in water using a surfactant, a polymerizable monomer, a surfactant, and a polymerization initiator in an aqueous medium. Then, the polymerizable monomer is emulsified and dispersed in an aqueous medium, polymerized while stirring and mixing, and then a salting-out agent is added to salt out the polymer particles. Polymerized toner particles can be obtained by filtering, washing and drying the particles obtained by salting out. Thereafter, if necessary, an external additive may be added to the dried toner particles to provide a function.

  Further, in the production of the polymerized toner particles, in addition to the polymerizable monomer, the surfactant, the polymerization initiator, and the colorant, a fixability improving agent and a charge control agent can be blended and obtained. Various characteristics of the polymerized toner particles can be controlled and improved. A chain transfer agent can be used to improve the dispersibility of the polymerizable monomer in the aqueous medium and adjust the molecular weight of the resulting polymer.

  The polymerizable monomer used for the production of the polymerized toner particles is not particularly limited. For example, styrene and its derivatives, ethylene unsaturated monoolefins such as ethylene and propylene, vinyl halides such as vinyl chloride, Α-methylene aliphatic monocarboxylic acids such as vinyl esters such as vinyl acetate, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate, dimethylamino acrylate and diethylaminoester methacrylate Examples include esters.

  Conventionally known dyes and pigments can be used as the colorant (coloring material) used in the preparation of the polymerized toner particles. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, and the like can be used. Moreover, the surface of these colorants may be modified using a silane coupling agent, a titanium coupling agent, or the like.

  As the surfactant used in the production of the polymerized toner particles, an anionic surfactant, a cationic surfactant, an amphoteric surfactant and a nonionic surfactant can be used.

  Here, examples of the anionic surfactant include fatty acid salts such as sodium oleate and castor oil, alkyl sulfates such as sodium lauryl sulfate and ammonium lauryl sulfate, alkyl benzene sulfonates such as sodium dodecyl benzene sulfonate, and alkyl naphthalene sulfonic acids. Salt, alkyl phosphate ester salt, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl sulfate ester salt and the like. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin, fatty acid ester, and oxyethylene-oxypropylene block polymer. . Furthermore, examples of the cationic surfactant include alkylamine salts such as laurylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride. Examples of amphoteric surfactants include aminocarboxylates and alkylamino acids.

  The surfactant as described above can be used usually in an amount in the range of 0.01 to 10% by weight with respect to the polymerizable monomer. Such a surfactant affects the dispersion stability of the monomer and also affects the environmental dependency of the obtained polymerized toner particles. Use in an amount within the above range is preferable from the viewpoint of ensuring the dispersion stability of the monomer and reducing the environmental dependency of the polymerized toner particles.

  For the production of polymerized toner particles, a polymerization initiator is usually used. The polymerization initiator includes a water-soluble polymerization initiator and an oil-soluble polymerization initiator, and any of them can be used in the present invention. Examples of the water-soluble polymerization initiator that can be used in the present invention include persulfates such as potassium persulfate and ammonium persulfate, water-soluble peroxide compounds, and oil-soluble polymerization initiators. Examples thereof include azo compounds such as azobisisobutyronitrile and oil-soluble peroxide compounds.

  When a chain transfer agent is used in the present invention, examples of the chain transfer agent include mercaptans such as octyl mercaptan, dodecyl mercaptan, tert-dodecyl mercaptan, carbon tetrabromide, and the like.

  Further, when the polymerized toner particles used in the present invention contain a fixability improver, a natural wax such as carnauba wax, an olefin wax such as polypropylene or polyethylene can be used as the fixability improver. .

  Further, when the polymerized toner particles used in the present invention contain a charge control agent, the charge control agent to be used is not particularly limited, and nigrosine dyes, quaternary ammonium salts, organometallic complexes, metal-containing monoazo dyes, etc. Can be used.

  Examples of the external additive used for improving the fluidity of polymerized toner particles include silica, titanium oxide, barium titanate, fluororesin fine particles, and acrylic resin fine particles. Can be used in combination.

  Furthermore, examples of the salting-out agent used for separating the polymer particles from the aqueous medium include metal salts such as magnesium sulfate, aluminum sulfate, barium chloride, magnesium chloride, calcium chloride, and sodium chloride.

  The volume average particle size of the toner particles produced as described above is in the range of 2 to 15 μm, preferably 3 to 10 μm, and the polymerized toner particles have higher particle uniformity than the pulverized toner particles. . If the toner particles are smaller than 2 μm, the charging ability is lowered, and it is easy to cause fogging and toner scattering, and if it exceeds 15 μm, the image quality is deteriorated.

  An electrophotographic developer can be obtained by mixing the carrier and toner manufactured as described above. The mixing ratio of the carrier and the toner, that is, the toner concentration is preferably set to 3 to 15% by weight. If it is less than 3% by weight, it is difficult to obtain a desired image density. If it exceeds 15% by weight, toner scattering and fogging are likely to occur.

  The electrophotographic developer according to the present invention can also be used as a replenishment developer. At this time, the weight ratio of the toner in the developer, that is, the toner concentration is preferably set to 75 to 99.9% by weight.

  The electrophotographic developer according to the present invention prepared as described above uses an electrostatic latent image formed on a latent image holding member having an organic photoconductor layer, while applying a bias electric field to the toner and the carrier. The present invention can be used in digital copiers, printers, fax machines, printers, and the like that use a developing method in which reversal development is performed using a two-component developer magnetic brush. Further, the present invention can also be applied to a full color machine using an alternating electric field, which is a method of superimposing an AC bias on a DC bias when a developing bias is applied from the magnetic brush to the electrostatic latent image side.

  Hereinafter, the present invention will be specifically described based on examples and the like.

[Example 1]
Fe ₂ O ₃ was weighed to 50.5 mol, MnO ₂ to 37.5 mol, MgCO ₃ to 12.5 mol and SrCO ₃ to 0.25 mol, and pelletized with a roller compactor. The obtained pellets were calcined in a rotary calciner at 970 ° C. under atmospheric conditions.

After coarsely pulverizing this with a dry bead mill, water is added and pulverized with a wet bead mill for 6 hours, and PVA is added as a binder component so as to be 3.2% by weight based on the slurry solid content. A pulverized slurry was prepared by adding a system dispersant such that the slurry had a viscosity of 2 to 3 poise. At this time, the solid content of the slurry was 55% by weight, and the D ₅₀ of the slurry particle size was 1.66 μm.

After thus granulated average particle size D ₅₀ by a spray drier ground slurry obtained was granulated so as to 49 .mu.m (volume average particle diameter of about 26μm of the ferrite particles of interest), dried, air Primary firing was performed at 700 ° C. in the air using a rotary under atmospheric conditions. Next, using an electric furnace, the main calcination was performed by holding at 1150 ° C. for 4 hours under an oxygen concentration of 0.25% by volume. Then, after pulverizing and separating and removing particles with a volume particle diameter D ₅₀ of 38 μm or more as much as possible, the remaining particles that were not separated and removed were classified to obtain ferrite particles.

  Further, the obtained ferrite particles are subjected to a surface oxidation treatment at 650 ° C. under the atmospheric condition in the hot part using a rotary electric furnace having a cooling part after the hot part to form a surface oxide film. Ferrite particles (ferrite carrier core material) were obtained.

[Example 2]
Ferrite particles (ferrite carrier core material) were obtained in the same manner as in Example 1 except that the surface oxidation treatment was not performed.

[Example 3]
After separating and removing particles having a volume particle diameter D ₅₀ of 38 μm or more, the remaining particles that were not separated and removed were classified to a volume average particle diameter of about 27.5 μm, and then surfaced at 550 ° C. Except for the oxidation treatment, ferrite particles (carrier core material) subjected to surface oxidation treatment were obtained in the same manner as in Example 1.

[Example 4]
50 mol of Fe ₂ O ₃ and 50 mol of MnCO ₃ are used as ferrite raw materials, the granulated volume average particle size is 50 μm (the volume average particle size of the intended ferrite particles is about 27 μm), the preliminary firing temperature is 940 ° C. After the particles having a volume particle diameter D ₅₀ of 37 μm or more were separated and removed, the remaining particles that were not separated and classified were classified and surfaced at 530 ° C. A surface-oxidized ferrite particle (ferrite carrier core material) was obtained in the same manner as in Example 1 except that the oxidation treatment was performed.

[Comparative Example 1]
The surface oxidation treatment was performed in the same manner as in Example 1 except that the granulated volume average particle size was 32 μm (volume average particle size of target ferrite particles was about 26 μm), and the fractionation step after firing was not performed. Ferrite particles (ferrite carrier core material) were obtained.

[Comparative Example 2]
The same procedure as in Example 1 except that the granulated volume average particle size was 32 μm (the volume average particle size of the target ferrite particles was about 27 μm), and the particles having a volume particle size D ₅₀ of 29 μm or more were collected and removed. Thus, ferrite particles (ferrite carrier core material) subjected to surface oxidation treatment were obtained.

[Comparative Example 3]
Example 1 Except that particles having a volume particle diameter D ₅₀ of 38 μm or more were collected and removed, and the remaining particles that were not collected and removed were classified to a volume average particle diameter of about 30.5 μm. In the same manner, ferrite particles (carrier core material) that had been subjected to surface oxidation treatment were obtained.

  Mixing ratio (number of raw materials charged) of Examples 1 to 4 and Comparative Examples 1 to 3, temporary firing conditions (temporary firing temperature and atmosphere), pulverized slurry / main granulation conditions (slurry particle size, solid content), primary firing Table 1 shows conditions (granulated volume average particle diameter, firing temperature and atmosphere), main firing conditions (firing temperature and atmosphere), and fractionation conditions (presence / absence of fractionation and fractional particle diameter). In addition, powder characteristics (volume average particle diameter, BET specific surface area), chemical analysis, magnetic characteristics (magnetization) and surface oxidation treatment conditions (oxidation treatment temperature) before the surface oxidation treatment of Examples 1 to 4 and Comparative Examples 1 to 3 And oxidation atmosphere) are shown in Table 2. Furthermore, powder characteristics after the surface oxidation treatment of Examples 1 to 4 and Comparative Examples 1 to 3 (volume average particle diameter, number average particle diameter, average value of equivalent circle particle diameter, most frequent region of equivalent circle particle diameter, Table 3 shows the peak frequency and BET specific surface area), magnetic properties (magnetization), and electrical resistance.

  In Tables 2 and 3, chemical analysis, magnetization, and electrical resistance were obtained as follows. The other characteristics evaluation methods are as described above.

(Chemical analysis: content of Fe, Mn, Mg and Sr)
The contents of Fe, Mn, Mg and Sr described above are measured as follows.
Weigh 0.2 g of ferrite carrier core material (ferrite particles) and heat 60 ml of pure water plus 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid to prepare an aqueous solution in which the ferrite carrier core material is completely dissolved, The contents of Fe, Mn, Mg and Sr were measured using an ICP analyzer (ICPS-1000IV manufactured by Shimadzu Corporation).

(Magnetic properties)
It measured using the integral type BH tracer BHU-60 type (made by Riken Denshi Co., Ltd.). A magnetic field measuring H coil and a magnetization measuring 4πI coil are placed between the electromagnets. In this case, the sample (ferrite particles) is put in a 4πI coil. The outputs of the H coil and the 4πI coil whose magnetic field H is changed by changing the current of the electromagnet are respectively integrated, and the H output is drawn on the X axis, the output of the 4πI coil is drawn on the Y axis, and a hysteresis loop is drawn on the recording paper. As measurement conditions, sample filling amount: about 1 g, sample filling cell: inner diameter 7 mmφ ± 0.02 mm, height 10 mm ± 0.1 mm, 4πI coil: measured with 30 turns.

(Electrical resistance)
This resistance is measured as follows. That is, a non-magnetic parallel plate electrode (10 mm × 40 mm) is opposed with an inter-electrode spacing of 6.5 mm, and 200 mg of the sample (ferrite particles) is weighed and filled between them. A sample is held between the electrodes by attaching a magnet (surface magnetic flux density: 1500 Gauss, area of the magnet in contact with the electrode: 10 mm × 30 mm) to the parallel plate electrodes, and resistance at an applied voltage of 1000 V is measured by an insulation resistance meter (SM-8210, Measured with Toa Decay Co., Ltd.

  As shown in Tables 2 and 3, the ferrite carrier core materials (ferrite particles) of Examples 1 to 4 have good magnetization and electrical resistance at a predetermined particle size, and the peak frequency of the equivalent circle particle size. Is also good.

  In contrast, the ferrite carrier core materials (ferrite particles) of Comparative Examples 1 to 3 have a small difference between the granulated particle size and the volume average particle size of the target ferrite particles, and the value of the peak frequency of the equivalent circle particle size. Therefore, it is expected that sharp particle size distribution cannot be obtained, surface-to-particle variation is large, and carrier adhesion and fine line reproducibility are inferior when used in an electrophotographic developer.

  In addition, although the ferrite carrier core material of Comparative Example 1 shows constant values of magnetization and electrical resistance, as described later, the electrical resistance when the ferrite carrier core material is coated with a resin to form a ferrite carrier is as follows. It will be inferior. The ferrite carrier core material of Comparative Example 2 is also considered to be the same as Comparative Example 1. Although the ferrite carrier core material of Comparative Example 3 can obtain good magnetization and electric resistance, the volume average particle diameter exceeds 30 μm, and thus a predetermined ferrite carrier core material cannot be obtained. When an electrophotographic developer is produced using such a ferrite carrier core material, a high toner concentration cannot be realized, and a high-quality printed matter cannot be obtained, or if a high toner concentration is used, it is rapidly achieved. The charge amount of the electrophotographic developer is lowered or the charge amount distribution is widened, which causes toner scattering.

[Example 5]
An acrylic modified silicone resin (manufactured by Shin-Etsu Silicone Co., Ltd., KR-9706) was applied to the ferrite particles (ferrite carrier core material) subjected to the surface oxidation treatment of Example 1 as a coating resin by a universal mixing stirrer. At this time, the resin solution is weighed so that the resin solid content is 2.5 wt% with respect to the ferrite carrier core material, and toluene and MEK are in a weight ratio of 3: 3 so that the resin solid content is 20 wt%. What added the solvent mixed in 1 was used as a resin solution. After the resin was applied, it was dried with stirring for 3 hours with a heat exchange type stirring and heating apparatus set at 200 ° C. in order to completely eliminate volatile matter. Thereafter, the aggregated particles were crushed to obtain a resin-coated ferrite carrier.

[Example 6]
For the ferrite particles (ferrite carrier core material) subjected to the surface oxidation treatment of Example 1, silicone resin (manufactured by Toray Dow Corning, SR-2441), aluminum-based catalyst (manufactured by Toray Dow Corning, CAT-AC) Was applied as a coating resin by a universal mixing stirrer. At this time, the resin solution was weighed so that the solid content of the resin with respect to the ferrite carrier core was 2.5 wt%, and 2 wt% of the aluminum catalyst was added to the solid content of the resin. Furthermore, what added toluene so that solid content of resin might be 20 weight% was used as a resin solution. After applying the resin, it was dried for 3 hours with a hot air dryer set at 250 ° C. in order to completely eliminate the volatile matter. Thereafter, the aggregated particles were crushed to obtain a resin-coated ferrite carrier.

[Example 7]
The ferrite particles (ferrite carrier core material) subjected to the surface oxidation treatment of Example 1 were coated with acrylic resin (manufactured by Mitsubishi Rayon Co., Ltd., Dianar LR-269) using a universal mixing stirrer. At this time, a resin solution was used in which the resin was weighed so that the solid content of the resin with respect to the ferrite carrier core was 1.5 wt%, and toluene was added so that the solid content of the resin would be 10 wt%. Since the resin is a powder, the resin solution was bathed in water so that the temperature was 50 ° C., and the resin powder was completely dissolved. After the resin was applied, in order to completely eliminate the volatile matter, the resin-coated ferrite carrier was obtained by drying with stirring in a heat exchange type stirring and heating apparatus set at 145 ° C for 3 hours.

[Comparative Example 4]
The surface of the ferrite particles (ferrite carrier core material) subjected to the surface oxidation treatment of Comparative Example 1 was coated with a resin in the same manner as in Example 7 to obtain a resin-coated ferrite carrier.

  For Examples 5 to 7 and Comparative Example 4, the amount of charge in each environment (N / N and H / H) of the resin-coated ferrite carrier was measured and the electrical resistance was measured, and the results are shown in Table 4. The method for measuring the charge amount is as follows, and the method for measuring the electrical resistance is as described above.

(Charge amount)
A sample (ferrite carrier) and a commercially available negative-polarity toner used in full-color printers having an average particle diameter of about 6 μm and a toner concentration of 8% by weight (toner weight = 1.6 g, carrier weight = 18.4 g) ). The weighed carrier and toner were exposed in each environment for 12 hours or more. Thereafter, the ferrite carrier and the toner were put in a 50 cc glass bottle and stirred at a rotation speed of 100 rpm for 30 minutes.
As a charge quantity measuring device, magnets with a total of 8 poles (flux density 0.1T) are arranged alternately in the N and S poles inside a cylindrical aluminum tube (hereinafter referred to as a sleeve) having a diameter of 31 mm and a length of 76 mm. The magnet roll, the sleeve, and a cylindrical electrode having a gap of 5.0 mm were disposed on the outer periphery of the sleeve.
After 0.5 g of developer is uniformly deposited on the sleeve, a DC voltage of 2000 V is applied between the outer electrode and the sleeve while rotating the inner magnet roll at 100 rpm while fixing the outer aluminum tube. Was applied for 60 seconds to transfer the toner to the outer electrode. At this time, an electrometer (insulation resistance meter model 6517A manufactured by KEITHLEY) was connected to the cylindrical electrode, and the charge amount of the transferred toner was measured.
After the elapse of 60 seconds, the applied voltage was turned off, the rotation of the magnet roll was stopped, the outer electrode was removed, and the weight of the toner transferred to the electrode was measured.
The charge amount was calculated from the measured charge amount and the transferred toner weight.

  Each environment is a normal temperature and normal humidity (N / N) environment and a high temperature and high humidity (H / H) environment, and the temperature and humidity conditions are as follows.

(Temperature and humidity conditions)
Normal temperature and humidity (N / N) environment = temperature 20-25 ° C, relative humidity 50-60%
High temperature and high humidity (H / H) environment = temperature 30-35 ° C, relative humidity 80-85%

  As is clear from the results in Table 4, Examples 5 to 7 in which the ferrite carrier core material of Example 1 is coated with various resins all have sufficient charging characteristics under N / N environment and H / H environment. It became a ferrite carrier for electrophotographic developer. Further, this ferrite carrier for electrophotographic developer had good electric resistance.

  On the other hand, the ferrite carrier for electrophotographic developer of Comparative Example 4 in which the ferrite carrier core material of Comparative Example 1 is coated with resin has sufficient charging characteristics under N / N environment and H / H environment, The electrical resistance was inferior.

  The ferrite carrier core material for an electrophotographic developer according to the present invention has a good electrical resistance, a sharp particle size distribution, and a small variation in surface property particles despite having a small particle size. When used in an electrophotographic developer, image defects such as carrier adhesion and reduced fine line reproducibility do not occur. The electrophotographic developer comprising a ferrite carrier and a toner obtained by coating a resin on the ferrite carrier core material prevents carrier scattering in the actual machine, and a printed matter with good fine line reproducibility can be obtained continuously. In addition, the ferrite carrier core material and the ferrite carrier can be stably obtained with productivity by the production method of the present invention.

  Therefore, the present invention can be widely used in the field of full-color machines that particularly require high image quality and high-speed machines that require image maintenance reliability and durability.

Claims (12)

A ferrite carrier core material for an electrophotographic developer comprising ferrite particles,
Ferrite particles having a volume average particle diameter of 20 to 30 μm and a frequency of the most frequent region of the divided particles of 8% by number or more when the equivalent circle particle diameter measured by the image analysis apparatus is divided in units of 1 μm A ferrite carrier core material for an electrophotographic developer, comprising:   2. The ferrite carrier core material for an electrophotographic developer according to claim 1, wherein an average value of equivalent-circle particle diameters measured by the ferrite particle image analyzer is 25 to 35 μm. The ferrite carrier core material for an electrophotographic developer according to claim 1, wherein the ferrite particles have a BET specific surface area of 0.10 to 0.18 m ² / g.   The ferrite carrier core material for an electrophotographic developer according to any one of claims 1 to 3, wherein a surface oxide film is formed on the ferrite particles.   A ferrite carrier for an electrophotographic developer, wherein the surface of the ferrite carrier core material according to claim 1 is coated with a resin. A method for producing a ferrite carrier core material for an electrophotographic developer having at least a ferrite raw material pulverization and mixing step, a main granulation step, and a main firing step, and obtaining ferrite particles having a volume average particle size of 20 to 30 μm,
In the main granulation step, granulation is performed by adjusting the granulation volume average particle size to be 15 μm or more larger than the target volume average particle size, and after the main firing step, A fractionation step of separating and removing particles having a volume particle size larger than 9 μm, and a particle size adjustment step of obtaining the ferrite particles having the target volume average particle size by classifying the remaining particles that have not been separated and removed. A method for producing a ferrite carrier core material for an electrophotographic developer, comprising:   The method for producing a ferrite carrier core material for an electrophotographic developer according to claim 6, wherein a preliminary firing step and a regrinding and mixing step are provided before the main granulation step.   The method for producing a ferrite carrier core material for an electrophotographic developer according to claim 6 or 7, wherein a primary firing step is provided before the main firing step.   The method for producing a ferrite carrier core material for an electrophotographic developer according to any one of claims 6 to 8, wherein a surface oxidation treatment step is provided after the particle size adjustment step.   A method for producing a ferrite carrier for an electrophotographic developer, wherein the ferrite carrier core material obtained by the production method according to any one of claims 6 to 9 is coated with a resin.   An electrophotographic developer comprising the ferrite carrier according to claim 5 and a toner.   The electrophotographic developer according to claim 11, which is used as a replenishment developer.