JP2013178414A - Ferrite carrier core material for electrophotographic developer, ferrite carrier and manufacturing method of the same, 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 without causing image defects such as carrier adhesion or thin line reproducibility when used for an electrophotographic developer because of high particle resistance and small variation among particles in spite of having a small particle diameter, ferrite carriers and a method for manufacturing the same, and an electrophotographic developer using the ferrite carrier.SOLUTION: There are provided a ferrite carrier core material for an electrophotographic developer, which contains 15 to 22 wt.% of Mn, 0.5 to 3.0 wt.% of Mg, 45 to 55 wt.% of Fe and 0.1 to 3.0 wt.% of Sr, has a lattice constant of 8.430 to 8.475 and in which a surface oxide film is formed, ferrite carriers and a method for manufacturing the same, and an electrophotographic developer using the ferrite carrier.

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 with a true specific gravity of about 5.0, which is light and has a low magnetization, or a resin-coated ferrite carrier whose surface is coated with a resin has been widely used. Lifespan has increased dramatically.

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

  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 achieve both a uniform surface property with moderate unevenness and high charge imparting ability. If the firing temperature is increased, the surface property becomes smoother and more uneven, which not only increases the resistance and charge distribution after coating the resin, but also reduces the strength against agitation stress. . When the firing temperature is lowered, the surface is apparently wrinkled and uniform, but the BET specific surface area increases, resulting in low chargeability and large environmental differences. Further, since the resistance is low, carrier adhesion and fine line reproducibility are not satisfactory.

  As an alternative to the carrier core material using manganese, a carrier core material using magnesium and having a high resistance by surface oxidation treatment has been proposed. For example, Patent Document 2 (Japanese Patent Laid-Open No. 2010-39368) describes a carrier core material that contains magnesium, titanium, and iron at a certain ratio and has a BET specific surface area in a specific range. With this carrier core material, a desired resistance such as a medium resistance or a high resistance is obtained while being highly magnetized, and it has excellent charging characteristics, and has a uniform shape with a surface property having appropriate irregularities.

  Since the carrier core material described in Patent Document 2 has a low content of manganese and titanium, it basically exhibits the characteristics of magnetite and lowers the magnetization on the low magnetic field side. Is concerned about the occurrence of carrier adhesion.

  In addition, although it has unevenness, the depth of the recess is not so large, the BET specific surface area is small, and when the resin coating amount is increased as the particle size is reduced, the resin can be sufficiently retained on the core surface. Therefore, there is a possibility that the resin coating amount is locally different and the life cannot be extended.

  Moreover, there exists patent document 3 (Unexamined-Japanese-Patent No. 2012-13865) as what performed the surface oxidation process by adding titanium to a manganese-magnesium composition.

  Although the carrier of Patent Document 3 contains a certain amount of manganese, the magnetization on the low magnetic field side is sufficient, but since it contains titanium, the specific surface area becomes small, and the distribution of resistance and charge after resin coating becomes wide. In addition to this, the strength against stirring stress also decreases.

  Patent Document 4 (Japanese Patent Laid-Open No. 2011-209475) pays attention to the crystal structure of the carrier core material, but the lattice constant largely depends on the composition. Is different. Further, since it does not contain manganese, it is considered that the magnetization on the low magnetic field side is low.

  In addition, there are Patent Document 5 (Japanese Patent Laid-Open No. 2011-075918) and Patent Document 6 (Japanese Patent Laid-Open No. 2011-086339) that focus on the lattice constant. The former contains Al and the latter contains Si. Therefore, the composition is different. Moreover, it is thought that the dispersion | variation in resistance between particle | grains is also large, and malfunctions, such as carrier adhesion, are anticipated.

  Further, Patent Document 7 (Japanese Patent Laid-Open No. 2008-261955) and Patent Document 8 (Japanese Patent Laid-Open No. 2008-241742) are focused on the half-value width of the carrier core material, but the half-value width largely depends on the composition. Even if the full width at half maximum is the same, the characteristics are naturally different if the composition is different.

JP-A-8-22150 JP 2010-39368 A JP 2012-13865 A JP 2011-209475 A Japanese Patent Application Laid-Open No. 2011-075918 JP 2009-086339 A JP 2008-261955 A JP 2008-241742 A

  Therefore, the object of the present invention is to reduce image defects such as carrier adhesion and fine line reproducibility when used in an electrophotographic developer because of high particle resistance and small variation between particles despite the small particle size. An object of the present invention is to provide a ferrite carrier core material for an electrophotographic developer, a ferrite carrier, a production method thereof, and an electrophotographic image agent using the ferrite carrier.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a ferrite carrier core material in which manganese, magnesium, and strontium are in a specific range and a lattice constant is in a certain range, and this surface is coated with a resin. The ferrite carrier achieves the above-mentioned purpose, and such a ferrite carrier core material has at least a ferrite raw material pulverization, mixing step, main granulation step, main firing step, and surface oxidation treatment step, and a subsequent step of the surface oxidation treatment step. The present inventors have found that it can be produced by a production method having a cooling step, and have reached the present invention.

  That is, the present invention contains 15 to 22% by weight of Mn, 0.5 to 3.0% by weight of Mg, 45 to 55% by weight of Fe, and 0.1 to 3.0% by weight of Sr. Is a ferrite carrier core material for an electrophotographic developer characterized by comprising ferrite particles having a surface oxide film formed thereon.

  In the ferrite carrier core material for an electrophotographic developer according to the present invention, the half width of the (311) plane of the ferrite particles is preferably 0.15 to 0.20.

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 volume average particle size of the ferrite particles measured by a laser diffraction particle size distribution measuring device is preferably 20 to 40 μm.

In the ferrite carrier core material for an electrophotographic developer according to the present invention, the resistance of the ferrite particles at 1,000 V of 6.5 mmGap is 1 × 10 ^{8 to} 3 × 10 ⁹ Ω.

In the ferrite carrier core material for an electrophotographic developer according to the present invention, the ferrite particles preferably have a magnetization of 57 to 67 Am ² / kg when a magnetic field of 3K · 1000 / 4π · A / m is applied.

  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.

Further, the present invention provides a ferrite raw material comprising Mn compound, Mg compound, Sr compound and Fe compound as ferrite raw material, and at least including ferrite powder pulverization, mixing step, main granulation step, main firing step, and surface oxidation treatment step. A method for producing a ferrite carrier core material for an electrophotographic developer comprising:
The ferrite carrier core for an electrophotographic developer, wherein the surface oxidation treatment step is performed in the atmosphere at 600 to 730 ° C., and a cooling step for rapidly cooling to 200 ° C. or less is provided after the surface oxidation treatment step. The manufacturing method of a material is provided.

  In the method for producing a ferrite carrier core material for an electrophotographic developer according to the present invention, it is preferable that the rapid cooling rate is 20 ° C./min or more.

  In the method for producing a ferrite carrier core material for an electrophotographic developer according to the present invention, a pre-baking step, re-pulverization, and mixing step may be provided after the pulverization and mixing steps.

  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.

  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 toner.

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

  Although the ferrite carrier core material for an electrophotographic developer according to the present invention has a small particle size, the particle resistance is high and the variation between particles is small, so that the carrier adheres when used in an electrophotographic developer. And image defects such as fine line reproducibility do not occur. The electrophotographic developer comprising a ferrite carrier and 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>
Ferrite particles used as a ferrite carrier core material for an electrophotographic developer according to the present invention include 15 to 22% by weight of Mn, 0.5 to 3.0% by weight of Mg, 45 to 55% by weight of Fe, and Sr. Contains 0.1 to 3.0% by weight. The Mn content is preferably 17 to 22% by weight, more preferably 18 to 21% by weight, and the Mg content is preferably 0.5 to 2.5% by weight, more preferably 0.5 to 2% by weight. is there. The content of Fe is preferably 47 to 55% by weight, more preferably 48 to 55% by weight. Further, the Sr content is preferably 0.3 to 2.0% by weight, more preferably 0.5 to 1.0% by weight. The balance is O (oxygen) and accompanying impurities. The accompanying impurities are contained in the raw material or mixed in the manufacturing process, and the total amount is 0.5% by weight or less.

By containing manganese, the magnetization on the low magnetic field side can be increased, and the effect of preventing reoxidation at the time of exit from the furnace in the main firing can be expected. The form of manganese when added is not particularly limited, but MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ and MnCO ₃ are preferable because they are easily available for industrial use. When the Mn content is less than 15% by weight, the Fe content is relatively increased. As a result, there are many magnetite components and the magnetization on the low magnetic field side is low, so that not only carrier adhesion occurs, but also the resistance is low, so that the image quality deteriorates, such as generation of fog and deterioration of gradation. If the Mn content exceeds 22% by weight, the resistance becomes high and the edge becomes too effective, and image defects such as white spots may occur or the toner consumption may increase.

  By containing magnesium, it is possible to obtain a developer having a good rise in charge composed of a ferrite carrier and a full-color toner. Also, the resistance can be increased. When the Mg content is less than 0.5% by weight, a sufficient addition effect cannot be obtained, and when the manganese content is relatively low and the Fe content is high, the resistance becomes low and fogging occurs. And the image quality deteriorates, such as deterioration of gradation. When the content of manganese is relatively high and the content of Fe is low, the magnetization becomes too high, so that the ears of the magnetic brush become hard and cause image defects such as scissors. On the other hand, when the Mg content exceeds 3.0% by weight, not only carrier scattering occurs due to a decrease in magnetization, but when the firing temperature is low, the amount of moisture adsorbed is affected by the hydroxyl group caused by magnesium. It becomes large and causes the environmental dependence of electrical characteristics such as charge amount and resistance to deteriorate.

  If the Fe content is less than 45% by weight, if the magnesium content is relatively increased, it means that the low magnetization component increases, and the desired magnetic properties cannot be obtained. When the manganese content is relatively increased, the magnetization becomes too high and the magnetic brush ears become stiff, causing image defects such as scissors, and the edges are increased due to increased resistance. It may be too effective, causing image defects such as white spots and excessive toner consumption. If the Fe content exceeds 55% by weight, the Mg and / or Mn content effect cannot be obtained, and the ferrite carrier core material is substantially equivalent to magnetite.

  Sr contributes to the adjustment of resistance and surface properties, and not only has the effect of maintaining high magnetization during surface oxidation, but also contains the effect of increasing the charging ability of the core material when contained. When the Sr content is less than 0.1% by weight, the Sr content effect cannot be obtained. In particular, when printing is continuously performed at a high printing rate such as a photograph, there is a possibility that a decrease in charge occurs, causing problems such as toner scattering and an increase in toner consumption. If the Sr content exceeds 3.0% by weight, the magnetization of the core material particles decreases and carrier scattering occurs, or the residual magnetization and coercive force increase. When used as a developer, image defects such as streaks are observed. Occurs and the image quality deteriorates.

(Contents 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).

  The ferrite particles used as the ferrite carrier core material for an electrophotographic developer according to the present invention have a surface oxide film formed thereon. The thickness of the surface oxide film is preferably 0.1 nm to 5 μm. If the thickness of the surface oxide film is less than 0.1 nm, the effect of the surface oxide film layer is small, and if the thickness of the surface oxide film exceeds 5 μm, the magnetization is clearly lowered or the resistance becomes too high. Inconveniences such as a decrease in developing ability are likely to occur. Further, if necessary, reduction may be performed before the surface oxidation treatment. The presence or absence of the surface oxide film can be determined from the change in peak and / or integrated intensity associated with the valence change from divalent to trivalent and / or tetravalent manganese by X-ray photoelectron spectroscopy (XPS). The presence or absence of the surface oxide film can also be indirectly known from the change in resistance before and after the surface oxidation treatment. The surface oxide film may be formed uniformly on the ferrite particle surface, or the surface oxide film may be partially formed.

  By forming an oxidation-treated film on the surface of the ferrite particles, the stress (strain of the crystal lattice) generated inside the ferrite particles can be relaxed, and the strength of the ferrite particles can be expected to be improved. Ferrite carrier for electrophotographic developer using ferrite particles with large stress may break the ferrite carrier during stirring in the developer unit when mixed with toner and used as developer, carrier scattering, drum scratches, etc. Cause.

  The lattice constant of the ferrite particles used as the ferrite carrier core material for an electrophotographic developer according to the present invention is 8.430 to 8.475. The value of the lattice constant is preferably 8.430 to 8.470, more preferably 8.430 to 8.465. When the lattice constant of the ferrite particles is within this range, the resistance is increased, and when used in an electrophotographic developer, carrier adhesion is prevented and the fine line reproducibility is excellent. When the lattice constant of the ferrite particles is less than 8.430, it is predicted that the Mn content is low, the Mg content is high, or the surface oxidation treatment temperature is high, which causes carrier scattering. If it exceeds 8.475, it is predicted that the Fe content is low or the surface oxidation treatment temperature is low, which causes the fine line reproducibility to deteriorate.

  The ferrite particles used as the ferrite carrier core material for an electrophotographic developer according to the present invention desirably have a half width of (511) plane, which is a spinel structure main peak, of 0.15 to 0.20. The half width value is more preferably 0.17 to 0.20, and most preferably 0.18 to 0.20. When the half-value width of the ferrite particles is within this range, the resistance becomes high as described above, and when used in an electrophotographic developer, carrier adhesion is prevented, and fine line reproducibility is excellent. If the half-value width of the ferrite particles is less than 0.15, the surface oxidation is insufficient and the resistance is low, and if it exceeds 0.20, there is a large amount of hematite and maghemite, resulting in low magnetization and non-uniform characteristics. Arise.

  The lattice constant of these ferrite particles and the half width of the (311) plane are measured by X-ray diffraction.

(Measurement of crystal structure: X-ray diffraction measurement)
“X′PertPRO MPD” manufactured by Panalical Co., Ltd. was used as a measuring apparatus. Measurement was performed by continuous scanning at 0.2 ° / sec using a Co tube (CoKα ray) as an X-ray source and a concentrated optical system and a high-speed detector “X'Celarator” as an optical system. The measurement results were processed using data for analysis “X'Pert HighScore” in the same manner as in the crystal structure analysis of ordinary powders, and the crystal structure was identified. In identifying the crystal structure, Fe and O are essential elements, and Mn, Mg, and Sr are elements that may be contained. In addition, the X-ray source can be measured without problems even with a Cu tube, but in the case of a sample containing a large amount of Fe, the background becomes larger than the peak to be measured, so it is better to use a Co tube. preferable. In addition, the optical system may obtain the same result even when the parallel method is used, but measurement with a concentrated optical system is preferable because the X-ray intensity is low and measurement takes time. Further, the speed of continuous scanning is not particularly limited, but in order to obtain a sufficient S / N ratio when analyzing the crystal structure, the peak intensity of the (311) plane of the spinel structure is set to about 50000 cps, The measurement was performed by setting the carrier core material in the sample cell so that there was no orientation in a specific preferred direction.

The BET specific surface area of the ferrite particles used as the 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, the resin anchor effect may not be sufficiently obtained even if the resin coating is performed, and the ferrite particles may be aggregated by the uncoated resin. . 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

Ferrite particles for use in electrophotographic developer 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 40 [mu] m, preferably 22～35Myuemu.

  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 the above range. When the volume average particle size is larger than the above range, a high toner concentration cannot be realized when the developer is produced, and a high-quality printed matter cannot be obtained, or when the toner concentration is increased, the developer rapidly The charge amount decreases or the charge amount distribution widens, 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 ferrite particles used in the ferrite carrier core material for an electrophotographic developer according to the present invention preferably have a resistance of 1 × 10 ^{8 to} 3 × 10 ⁹ Ω at a voltage of 6.5 mm Gap applied.

When the resistance at an applied voltage of 6.5 mm Gap is less than 1 × 10 ⁸ Ω, the resistance is too low and white spots may occur or carriers may be scattered when used as a ferrite carrier. When it is higher than 3 × 10 ⁹ Ω, an image with an excessively effective edge when used as a ferrite carrier may be formed, and the toner consumption may increase.

(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.

The ferrite particles used in the porous ferrite core material for an electrophotographic developer according to the present invention have a magnetization of 57 to 67 Am ² / kg measured by BH when a magnetic field of 3K · 1000 / 4π · A / m is applied. It is. When the magnetization of the ferrite particles is less than 57 Am ² / g, carrier scattering occurs. On the other hand, if the magnetization of the ferrite particles exceeds 67 Am ² / g, the thin wire reproducibility is insufficient due to low resistance. This magnetic property (magnetization) is measured as follows.

(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 is placed 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.

  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 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.

<Carrier Core Material for Electrophotographic Developer According to the Present Invention and Carrier Manufacturing Method>
Next, the carrier core material for an electrophotographic developer and the method for producing the carrier according to the present invention will be described.

  The method for producing a carrier core material for an electrophotographic developer according to the present invention comprises using a Mn compound, Mg compound, Sr compound and Fe compound as a ferrite raw material, a pulverizing and mixing step of the ferrite raw material, a main granulation step, a main firing step, This is a method for producing a ferrite carrier core material for an electrophotographic developer comprising ferrite particles having at least a surface oxidation treatment step.

There are no particular restrictions on the production steps of these ferrite raw materials, such as pulverization, mixing step, main granulation step, main firing step, and surface oxidation treatment step. Conventionally known methods can be employed, and dry methods are used. Alternatively, a wet method may be used. Moreover, you may provide a temporary baking process, a regrind, and a mixing process after a grinding | pulverization and a 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, mixing step), and temporarily fired in the atmosphere (temporary baking step). After calcination, 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-pulverization, mixing step), the viscosity is adjusted, and then sprayed Granulate and granulate with a dryer (this 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, 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. Further, the main calcination is performed in an inert atmosphere or a weakly oxidizing atmosphere, for example, an oxygen concentration of 0.1 volume% (1000 ppm) to 5 volume% (50000 ppm), more preferably 0.1 volume% (1000 ppm) to 3.5 volume. % (35000 ppm), most preferably 0.1 vol% (1000 ppm) to 2.5 vol% (25000 ppm) of a mixed gas atmosphere of nitrogen and oxygen at 1090 to 1210 ° C.

  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, even if the BET specific surface area is about the same as the range defined in the present invention, even if the surface of the core particle is sufficiently sintered, the sintering inside the particle does not proceed, and the ferrite particle is used as the carrier core material for the electrophotographic developer. May not have sufficient strength. Therefore, it is desirable to use a tunnel kiln, an elevator kiln, or the like that allows a hot part to pass through the raw material before firing as much as possible in a koji bowl or the like.

  Thereafter, the fired product is crushed and classified to obtain ferrite particles. 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 classification methods described above may be selected and implemented, or the coarse powder side particles and the fine powder side particles may be removed by changing the conditions using one classification method.

  Thereafter, the surface is subjected to surface oxidation treatment by heating at a low temperature, a surface oxide film is formed on the surface of the ferrite particles, and electric resistance adjustment is performed (surface oxidation treatment step). In the surface oxidation treatment, heat treatment is performed at 600 to 730 ° C., preferably 630 to 700 ° C., using a general rotary electric furnace, batch electric furnace, or the like in an oxygen-containing atmosphere such as air. When the heating temperature is lower than 600 ° C., the oxidation of the core 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, 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 rapid cooling condition needs to be 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.

  In the ferrite carrier for an electrophotographic developer of the present invention, the above resin is coated on the surface of the ferrite carrier core material (ferrite particles on which a surface oxide film is formed) 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 fluidized bed method is preferred.

  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.

  The pulverized slurry thus obtained was granulated and dried with a spray dryer, and subjected to primary firing 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. Thereafter, the particles were pulverized and classified to obtain ferrite particles.

  Further, the obtained ferrite particles were subjected to a surface oxidation treatment at 650 ° C. under an atmospheric condition in the hot part using a rotary electric furnace having a cooling part after the hot part. Subsequently, the carrier core material subjected to the oxidation treatment was cooled to 150 ° C. in the cooling section, and surface-oxidized ferrite particles (carrier core material) were obtained. At this time, it passed through the cooling section in 10 minutes, and the rapid cooling rate was 50 ° C./minute.

[Example 2]
Except that the surface oxidation treatment was performed at 600 ° C., ferrite particles (carrier core material) that had been subjected to the surface oxidation treatment were obtained in the same manner as in Example 1.

[Example 3]
Except that the surface oxidation treatment was 630 ° C., ferrite particles (carrier core material) that had been subjected to the surface oxidation treatment were obtained in the same manner as in Example 1.

[Example 4]
Except that the surface oxidation treatment was 680 ° C., ferrite particles (carrier core material) that had been subjected to the surface oxidation treatment were obtained in the same manner as in Example 1.

[Example 5]
Except that the surface oxidation treatment was set to 700 ° C., ferrite particles (carrier core material) subjected to the surface oxidation treatment were obtained in the same manner as in Example 1.

[Example 6]
A surface-treated ferrite particle (carrier core material) was obtained in the same manner as in Example 1 except that the volume average particle size was adjusted to 30.7 μm.

[Example 7]
A surface-oxidized ferrite particle (carrier core material) was obtained in the same manner as in Example 1 except that the volume average particle size was adjusted to 37.4 μm.

[Example 8]
Ferrite particles (carrier core material) that had been subjected to surface oxidation treatment were obtained in the same manner as in Example 1 except that the rapid cooling rate after the surface oxidation treatment was performed at 30 ° C./min for 15 minutes and the rapid cooling was performed at 200 ° C.

[Example 9]
The surface oxidation treatment was performed in a batch-type electric furnace, and after the surface oxidation treatment, it was cooled from 650 ° C. to 150 ° C. in 10 minutes by liquid nitrogen implantation (quenching rate 50 ° C./minute). Ferrite particles (carrier core material) subjected to surface oxidation treatment were obtained.

[Example 10]
A surface-oxidized ferrite particle (carrier core material) was obtained in the same manner as in Example 1 except that the firing temperature was 1170 ° C.

[Comparative Example 1]
Ferrite particles (carrier core material) that had been subjected to surface oxidation treatment were obtained in the same manner as in Example 1 except that surface oxidation treatment and rapid cooling were not performed.

[Comparative Example 2]
Except that the surface oxidation treatment was 540 ° C., ferrite particles (carrier core material) that had been subjected to the surface oxidation treatment were obtained in the same manner as in Example 1.

[Comparative Example 3]
Except that the surface oxidation treatment was 750 ° C., ferrite particles (carrier core material) that had been subjected to the surface oxidation treatment were obtained in the same manner as in Example 1.

[Comparative Example 4]
Surface-treated ferrite particles (carrier core material) were obtained in the same manner as in Example 1 except that 50 mol of Fe ₂ O ₃ and 50 mol of MgCO ₃ were used as ferrite raw materials.

[Comparative Example 5]
After the surface oxidation treatment, ferrite particles (carrier core material) subjected to the surface oxidation treatment were obtained in the same manner as in Example 1 except that the cooling part was not passed and the quenching was not performed.

[Comparative Example 6]
A surface-oxidized ferrite particle (carrier core material) was obtained in the same manner as in Example 1 except that the rapid cooling rate after the surface oxidation treatment was performed at 15 ° C./min for 28 minutes and the rapid cooling was performed at 230 ° C.

  Mixing ratio (number of raw materials charged) of Examples 1 to 10 and Comparative Examples 1 to 6, provisional firing conditions (temperature and atmosphere), pulverized slurry / main granulation conditions (slurry particle size, solid content), primary firing conditions ( Table 1 shows the temperature and atmosphere) and the main firing conditions (temperature and atmosphere). Moreover, the powder characteristics (volume average particle diameter, BET specific surface area), chemical analysis, magnetic characteristics (magnetization), and X-ray diffraction (lattice constant and half of the surface oxidation treatment of Examples 1 to 10 and Comparative Examples 1 to 6 The value range is shown in Table 2. Furthermore, the surface oxidation treatment conditions (temperature and atmosphere) of Examples 1 to 10 and Comparative Examples 1 to 6, rapid cooling conditions (presence / absence and rapid cooling temperature), and powder characteristics after volume oxidation treatment (volume average particle diameter, BET specific surface area) ), Chemical analysis, magnetic properties (magnetization), X-ray diffraction (lattice constant and half width) and resistance are shown in Table 3.

  As shown in Table 3, although Examples 1 to 10 have a small particle diameter, the particle resistance is high, and the specific surface area and magnetization are also in a desired range. In addition, since the surface treatment is uniform, the full width at half maximum is small, the variation between the particles is small, and the resistance is high even though the crystal structure of the particle surface and the inside of the particle is different due to the surface oxidation treatment. Since the surface property is uniform, the properties after coating can be expected.

  On the other hand, Comparative Example 1 is an example in which the surface oxidation treatment is not performed, and since the BET specific surface area is too large and the lattice constant is also large, it is predicted that a desired resistance and charge amount cannot be obtained, and fine line reproduction is performed. It becomes inferior. Comparative Example 2 is an example in which the surface oxidation treatment is performed at a low temperature. However, since the lattice constant is large, the thin line reproducibility is inferior. Comparative Example 3 is an example in which the surface oxidation treatment is performed at a high temperature. However, the lattice constant is small, the BET specific surface area is too small, and the magnetization and resistance are low.

  On the other hand, Comparative Example 4 is an example in which magnesium ferrite particles are used as the ferrite carrier core material, but the lattice constant is too small, the magnetization is too low, and the resistance is too high. Comparative Example 5 is an example in which rapid cooling is not performed after the surface oxidation treatment, and Comparative Example 6 is an example in which rapid cooling is performed slowly. It is considered that the surface property is not uniform and the variation in coating is large.

[Example 11]
An acrylic modified silicone resin (manufactured by Shin-Etsu Silicone Co., Ltd., KR-9706) was applied as a coating resin to the ferrite particles (carrier core material) subjected to the surface oxidation treatment of Example 1 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 carrier core material, and toluene and MEK are 3: 1 by weight so that the resin solid content is 20 wt%. What added the solvent mixed in this 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 12]
Silicone resin (Toray Dow Corning, SR-2411) and aluminum catalyst (Toray Dow Corning, CAT-AC) were applied to the ferrite particles (carrier core material) subjected to the surface oxidation treatment of Example 1. The coating resin was applied with a universal mixing stirrer. At this time, the resin solution was weighed so that the solid content of the resin with respect to the 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 13]
Acrylic resin (Mitsubishi Rayon Co., Ltd., Dianar LR-269) was applied to the ferrite particles (carrier core material) subjected to the surface oxidation treatment of Example 1 as a coating resin by 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 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.

  Table 4 shows the measurement results of the charge amount of Examples 11 to 13 in each environment (N / N and H / H) of the resin-coated ferrite carrier. The method for measuring the charge amount is as follows.

(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 for 12 hours or more under each environment. 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 apparent from the results of Table 4, all of Examples 11 to 13 in which various resins are coated on the ferrite carrier core material according to the present invention have sufficient charging characteristics in a sufficient N / N environment and a H / H environment. It became a ferrite carrier for an electrophotographic developer having

  Although the ferrite carrier core material for an electrophotographic developer according to the present invention has a small particle size, the particle resistance is high and the variation between particles is small, so that the carrier adheres when used in an electrophotographic developer. And image defects such as 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 (14)

  15 to 22% by weight of Mn, 0.5 to 3.0% by weight of Mg, 45 to 55% by weight of Fe, 0.1 to 3.0% by weight of Sr, and a lattice constant of 8.430 to 8% A ferrite carrier core material for an electrophotographic developer, which is made of ferrite particles having a surface oxidation film of .475.   2. The ferrite carrier core material for an electrophotographic developer according to claim 1, wherein the half width of the (311) plane of the ferrite particles is 0.15 to 0.20. 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 the ferrite particles have a volume average particle size of 20 to 40 µm as measured by a laser diffraction particle size distribution analyzer. The ferrite carrier core material for an electrophotographic developer according to any one of claims 1 to 4, wherein the resistance of the ferrite particles at 1,000 V of 6.5 mmGap is 1 x 10 ^{8 to} 3 x 10 ⁹ Ω. The ferrite carrier core material for an electrophotographic developer according to claim 1, wherein the ferrite particles have a magnetization of 57 to 67 Am ² / kg when a magnetic field of 3K · 1000 / 4π · A / m is applied. .   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 ferrite for an electrophotographic developer comprising a ferrite particle having a Mn compound, a Mg compound, an Sr compound and an Fe compound as ferrite raw materials, and having at least a pulverization and mixing step, a main granulation step, a main firing step, and a surface oxidation treatment step of the ferrite raw material A manufacturing method of a carrier core material,
The ferrite carrier core for an electrophotographic developer, wherein the surface oxidation treatment step is performed in the atmosphere at 600 to 730 ° C., and a cooling step for rapidly cooling to 200 ° C. or less is provided after the surface oxidation treatment step. A method of manufacturing the material.   The method for producing a ferrite carrier core material for an electrophotographic developer according to claim 8, wherein the rapid cooling rate is 20 ° C./min or more.   The method for producing a ferrite carrier core material for an electrophotographic developer according to any one of claims 8 and 9, wherein a provisional firing step, re-pulverization, and a mixing step are provided after the pulverization and mixing step.   The method for producing a ferrite carrier core material for an electrophotographic developer according to any one of claims 8 to 10, wherein a primary firing step is provided before the main firing step.   A method for producing a ferrite carrier for an electrophotographic developer, wherein the surface of the ferrite carrier core material obtained by the production method according to claim 8 is coated with a resin.   An electrophotographic developer comprising the ferrite carrier according to claim 7 and a toner.   The electrophotographic developer according to claim 13, which is used as a replenishment developer.