JP2013137455A - Ferrite carrier core material for electrophotographic developer, ferrite carrier, production 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 which has high strength, significantly suppresses generation of cracks or chips of particles even under influences of agitation stresses for a long time, and has superior strength, a little scattering amount and good fluidity, and also provide a ferrite carrier and an electrophotographic developer using the ferrite carrier.SOLUTION: The ferrite carrier core material for an electrophotographic developer comprises ferrite particles containing Sr and having a shape factor SF-1 (circularity) of 100 to 107 and a shape factor SF-2 (circularity/roundness) of 100 to 113. Nonmagnetic fine particles are adhering to a surface and/or inner surfaces of vacancies of the ferrite particle; the amount of metal elements present in the nonmagnetic fine particles is 500 to 5000 ppm with respect to the ferrite particle; and the amount of Sr present is 1 to 500 ppm with respect to the ferrite particle. A ferrite carrier, production methods of the core material and the ferrite carrier, and an electrophotographic developer using the ferrite carrier are also disclosed.

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, as shown in Patent Document 1 (Japanese Unexamined Patent Publication No. Hei 8-22150), a predetermined amount of a ferrite carrier material is mixed, calcined, pulverized, and calcined after granulation. This is generally performed, and calcination may be omitted depending on conditions.

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 adapted to environmental regulations has been demanded. Accordingly, the ferrite composition used as the carrier core material has shifted from Cu—Zn ferrite and Ni—Zn ferrite to Mn ferrite using Mn, Mn—Mg—Sr ferrite and the like. In Patent Document 1 (JP-A-8-22150), a ferrite carrier in which a part of each oxide having a composition represented by the general formula (MnO) x (MgO) y (Fe ₂ O ₃ ) z is substituted with SrO is disclosed. It is described that the variation in magnetization between particles can be reduced.

  Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-271663) describes a ferrite carrier for an electrophotographic developer having a compression fracture strength and a compression change rate of a certain level or more and a shape factor SF-1 of 100 to 125, It is said that when used as a developer, it has excellent strength against breakage due to stress received in the developing device and has moderate brittleness.

Patent Document 3 (Japanese Patent Application Laid-Open No. 9-6052) discloses a unitary ferrite containing a monovalent metal such as lithium or a composite ferrite obtained by substituting a part thereof with Mn, and V ₂ O ₅ And a ferrite carrier for electrophotography comprising spherical particles containing Bi ₂ O ₃ are described, and abnormal crystal grain growth is suppressed by such a composition.

  In these Patent Documents 2 and 3, it is proposed that ferrite particles that are not destroyed as much as possible even when subjected to stirring stress are used as carriers. These increase the mechanical strength of the ferrite particles themselves, but are not sufficient to maintain the strength over time when used as a developer.

  On the other hand, in Patent Document 4 (Japanese Patent Application Laid-Open No. 2008-250414), a carrier core material is manufactured by dispersing a fired product made of manganese ferrite or magnetite in a combustion flame using a carrier gas and performing a heat treatment. Have been described. According to Patent Document 4, the carrier for an electronic developer obtained by coating the carrier core material with a resin does not cause particle cracking or chipping even under the influence of stirring stress over a long period of time, and has good fluidity. It is described that there is.

  However, since the carrier core material obtained by the firing method described in Patent Document 4 is mechanically stressed, there are no voids that radiate force in one particle at high density, and the energy acts at once. The carrier core material was cracked and its strength was not sufficient.

  Furthermore, Patent Document 5 (Japanese Patent Application Laid-Open No. 2008-96975) describes ferrite core material particles that suppress the generation of large voids, and describes a thermal spray flame method as one of the manufacturing methods. According to an example, it is described that a calcined product is pulverized, melted and spheroidized in a gas phase, and then calcined to be ferrite.

  In Patent Document 5, the ferrite carrier having a resin coating layer on the surface of the ferrite core particle has good image uniformity, little carrier film peeling, good charging stability with time, and toner spent. However, no consideration is given to the strength of the core particles themselves.

  In Patent Document 6 (Japanese Patent Publication No. 6-7272), a compound composed of a metal oxide, which is a raw material for forming ferrite, is passed through a flame formed by a high-temperature combustible gas and oxygen gas to form a ferrite. A method for manufacturing a ferrite carrier is described.

  The manufacturing method described in Patent Document 6 promotes uniform electrostatic properties or uniform mechanical strength in each part of the particles by improving surface non-uniformity, and is more fluid than conventional products. Although it is said that the triboelectric chargeability and mechanical strength are imparted to the ferrite carrier, it does not prevent cracking or chipping of particles under the influence of stirring stress over a long period of time.

  Patent Document 7 (Japanese Patent Laid-Open No. 2010-181524) describes a carrier core material made of a specific ferrite composition containing strontium, and strontium moves to the surface of the carrier core material by primary firing and main firing. The strontium is segregated on the surface of the carrier core material, but is not present independently from the carrier core material.

  As described above, no proposal has been made to effectively prevent cracking or chipping of particles under the influence of stirring stress over time.

JP-A-8-22150 JP 2007-271663 A Japanese Patent Laid-Open No. 9-6052 JP 2008-250214 A JP 2008-96975 A Japanese Patent Publication No. 6-7272 JP 2010-181524 A

  Therefore, the object of the present invention is high strength, and even under the influence of stirring stress for a long time, the occurrence of cracking and chipping of particles is greatly suppressed, and the strength is excellent, the amount of scattering is small, and the fluidity is also good. An object is to provide a good ferrite carrier core material for an electrophotographic developer, a ferrite carrier, and an electrophotographic developer using the ferrite carrier.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that Sr is contained, the circularity and the roundness are in a certain range, and the metal present in the nonmagnetic particles existing on the surface thereof. A ferrite carrier core material composed of ferrite particles having an element amount and a Sr amount within a certain range solves the above-mentioned problems, and such a ferrite carrier core material mixes a ferrite raw material containing Sr together with a specific amount of polyvinyl alcohol as a binder. After that, it was found that it can be obtained by granulation, preliminary firing, thermal spraying in the air, and rapid solidification.

  That is, the present invention comprises ferrite particles containing Sr, having a shape factor SF-1 (circularity) of 100 to 107 and a shape factor SF-2 (roundness) of 100 to 113, and the surface of the ferrite particles. And / or nonmagnetic fine particles adhere to the inner surface of the pores, the amount of metal in the nonmagnetic fine particles is 500 to 5000 ppm with respect to the ferrite particles, and the amount of Sr is 1 to 500 ppm with respect to the ferrite particles. 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, the composition of the ferrite particles is represented by the following formula (1), and a part of (MnO) and / or (MgO) in the following formula (1). Is preferably substituted with SrO.

  In the ferrite carrier core material for an electrophotographic developer according to the present invention, the substitution amount of the SrO is desirably 0.1 to 2.5 mol%.

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

  In the present invention, a ferrite raw material containing Sr is mixed with a binder and then granulated, and the resulting granulated product is pre-fired at 650 to 1250 ° C., then sprayed in the air, and further rapidly cooled and solidified. A method for producing a ferrite carrier core material for an agent, wherein the binder is polyvinyl alcohol, and is contained in an amount of 0.5 to 3.5% by weight in terms of solid content with respect to the granulated product. A method for producing a ferrite carrier core material for a developer is provided.

  The present invention 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.

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

  The present invention also provides an electrophotographic developer comprising a ferrite carrier obtained by the above production method and a toner.

  The ferrite carrier core material for an electrophotographic developer according to the present invention has a certain degree of circularity and roundness, and since there are a certain amount of nonmagnetic fine particles and Sr compound on the surface, it has excellent strength due to its buffering effect, In addition, it has excellent strength, a small amount of scattering, and good fluidity. An electrophotographic developer comprising a ferrite carrier and a toner obtained by coating a resin on the carrier core material greatly suppresses the generation of cracks and chipping of ferrite particles even under the influence of stirring stress over a long period of time. be able to. In addition, the ferrite carrier core material and the ferrite carrier can be stably produced on an industrial scale by the production method of the present invention.

FIG. 1 is a schematic view showing an example of a ferrite carrier core material for an electrophotographic developer according to the present invention.

1 Ferrite carrier core material (ferrite particles)
2 pores 3 nonmagnetic fine particles adhering to the surface of the ferrite carrier core and / or the inner surface of the pores

  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 ferrite carrier core material for an electrophotographic developer according to the present invention contains Sr in its composition. Although the composition is not particularly limited, it is preferably represented by the following formula (1) and part of (MnO) and / or (MgO) in the following formula (1) is substituted with SrO.

  Ferrite particles having such a specific composition are preferably used as a ferrite carrier core material because of high magnetization, good uniformity of magnetization, and little variation.

In the above specific composition, the substitution amount of SrO is desirably 0.1 to 2.5 mol%. When the substitution amount of SrO is less than 0.1 mol%, magnetoplumbite type ferrite (SrO) · 6 (Fe ₂ O ₃ ) and Sr _a Fe _b O _c (provided that a ≧ 2, a + b ≦ c ≦ a + 1.5b), and a small amount of a precursor of strontium ferrite having a perovskite type crystal structure represented by cubic crystal is represented, and as a result, low magnetic particles are generated. When the substitution amount of SrO is larger than 2.5 mol%, the residual magnetization and the coercive force are increased, and the fluidity when used as a carrier is deteriorated, so that the miscibility with the toner is deteriorated.

  The ferrite carrier core material for an electrophotographic developer according to the present invention has a shape factor SF-1 (circularity) of 100 to 107. When the shape factor SF-1 is in this range, the fluidity is good and the stirring stress is not easily received. When the shape factor SF-1 exceeds 107, it means that there is a distorted shape deformed from a spherical shape, and fluidity is impaired. Due to the continuous stirring, particles having a large shape factor SF-1 are locally present in the developing machine, and when the carrier is formed, there is a problem that the toner concentration is not given with respect to the amount of charged toner.

  The shape factor SF-1 is JSM-6060A manufactured by JEOL Ltd., the acceleration voltage is 20 kV, and the ferrite particles are photographed with a SEM at a 450 × field of view so that the ferrite particles do not overlap. Information is introduced into the image analysis software (Image-Pro PLUS) manufactured by Media Cybernetics through the interface, analysis is performed, Area (area) and ferret diameter (maximum) are obtained, and the value obtained from the following formula It is. The closer the shape of the ferrite particle shape factor SF-2 is to a spherical shape, the closer to 100, and the larger the value, the more indefinite. The shape index SF-1 was calculated for each particle, and the average value of 100 particles was defined as the shape index SF-1 of the ferrite carrier core material (ferrite particles).

  The ferrite carrier core material for an electrophotographic developer according to the present invention has a shape factor SF-2 (roundness) of 100 to 113. When the shape factor SF-2 is in this range, there are few surface irregularities, the fluidity is good, and it is difficult to receive a stirring stress. When the shape factor SF-2 exceeds 113, it means that the unevenness of the surface is large, and the unevenness is caught between particles having a large SF-2, so that the fluidity is impaired. Due to the continuous stirring, particles having a large shape factor SF-2 locally exist in the developing machine, and when the carrier is formed, there is a problem that the toner concentration is not given to the charged toner amount.

The shape factor SF-2 is obtained by observing 3000 ferrite particles using a particle size / shape distribution measuring instrument PITA-1 manufactured by Seishin Enterprise Co., Ltd., and using software Image Analysis provided with the apparatus, S (projection area) and L (projection periphery). This is a value calculated from the following formula. As the shape of the ferrite particle is closer to a sphere, the value becomes closer to 100.
As the sample liquid, a xanthan gum aqueous solution having a viscosity of 0.5 Pa · s was prepared as a dispersion medium, and 0.1 g of ferrite 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 maintain the state in which the ferrite particles are dispersed in the dispersion medium, and the measurement can be performed 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.

  As shown in FIG. 1, a ferrite particle (ferrite carrier core material) 1 according to the present invention is non-magnetic attached to the surface of a ferrite carrier core material or the surface of pores 2 (hereinafter collectively referred to as a surface). Fine particles 3 are present. In the present invention, the abundance of the metal element in the nonmagnetic fine particles 3 adhering to the surface is 500 to 5000 ppm with respect to the ferrite particles. By attaching non-magnetic fine particles with metal atoms in the above range to the surface of the ferrite particles (ferrite carrier core material), the non-magnetic fine particles function as a buffer material, even under the influence of stirring stress over a long period of time. It is possible to prevent the ferrite particles from cracking or chipping. When the abundance of metal atoms in the non-magnetic fine particles is less than 500 ppm, since the absolute amount of the ferrite carrier core is present on the surface is small, it cannot act as a buffer material when mechanical stress is applied, and ferrite Many cracks or chipping of particles occur. If the abundance of metal atoms in the non-magnetic particles is more than 5000 ppm, the absolute amount present on the surface of the ferrite carrier core material and / or the inner surface of the pores increases, so the magnetic force of the core material becomes relatively small, and the magnet It becomes impossible to withstand the magnetic force on the roller or the centrifugal force accompanying stirring, and the amount of scattering increases.

  Nonmagnetic fine particles present on the surface of these ferrite carrier core materials include oxides and composite oxides of metal atoms that form the ferrite composition of ferrite particles, and the metal elements include Fe, Mn, Mg, Sr. Etc.

  The amount of Sr present in the nonmagnetic fine particles is 1 to 500 ppm with respect to the ferrite particles. Within this range, the composition of the ferrite particles indicates that the stoichiometric ratio is uniformly maintained, and there is very little composition variation within one particle, and ideal ferrite characteristics can be obtained. If the amount of Sr present is less than 1 ppm, it is in the range of inevitable impurities and is not intentionally present. If the amount of Sr present is more than 500 ppm, the ferrite carrier core material after thermal spray firing is rapidly cooled and ferritized with very little composition variation in one particle, but the surface of the ferrite carrier core material having a large contact with the outside air Therefore, the movement of the specific metal element, that is, strontium, from the surface portion of the ferrite carrier core material is slightly generated. Therefore, composition fluctuations that impair ferrite properties such as magnetization or resistance cannot occur, but because the composition variation on the surface of the ferrite carrier core appears, impact stress cannot be alleviated throughout the particle, and particle cracking occurs. Or chipping occurs. In addition, strontium components with relatively low Mohs hardness are locally scattered on the surface of the ferrite carrier core, causing impact stress to the particles to act at once, causing cracking or chipping of the particles It also becomes.

(Measurement of metal element amount and Sr amount in non-magnetic fine particles)
The amount of metal element and the amount of Sr present on the surface of these ferrite carrier core materials are measured as follows.
That is, 10 g of ferrite particles are added to 100 ml of methanol in a 200 ml beaker, subjected to ultrasonic treatment for 120 seconds, and then allowed to stand for 15 seconds. An anisotropic ferrite magnet (surface magnetic flux density 725 gauss, size (mm): diameter 50 × height 10. The supernatant was separated using a magnet weight (g): 96). The solvent of the supernatant was distilled off, and the resulting residue was dried for 24 hours in a desiccator containing silica gel, and the weight of the residue was weighed. By dividing the weighed residue weight by 10 g of ferrite particles, the metal element amount (% by weight) of the nonmagnetic fine particles adhering to the surface of the ferrite carrier core material (ferrite particles) and / or the inner surface of the pores was calculated.
In addition, EDS measurement is performed while observing the SEM image of the residue, and the amount of strontium when the total amount of residue is 100% is measured and multiplied by the amount of metal element (% by weight). The amount (% by weight) of strontium was calculated.

The processing apparatus and processing conditions in the above measurement are as follows.
1. Ultrasonic treatment Ultrasonic treatment equipment name: ULTRASONIC HOMOGENIZER (UH-150 model), manufactured by SMT Co., Ltd. Vibrator connection parts: Standard horn (HO-12) and tip (ST-12) Assemble the vibrator perpendicular to the base.
Processing conditions: Power monitor meter value during processing: 0.2, pulsar volume: steady, power controller: 4, timer setting switch: 120 sec
2. 2. SEM image measurement SEM image apparatus; JSM-6060A, manufactured by JEOL Co., Ltd. Measurement conditions; SEM analysis at an acceleration voltage of 20 KV and a magnification of 100. EDS measurement EDS measurement apparatus; EX-23000BU, manufactured by JEOL Co., Ltd. Measurement conditions: Necessary element mapping (for example, iron, manganese, magnesium, strontium) on the sample surface was collected to obtain an X-ray spectrum. From the obtained spectrum peak, the metal element amount (mass percentage) was measured and determined.

  The ferrite carrier core material for an electrophotographic developer according to the present invention preferably has a strength of 6.0 or less, and more preferably 4.0 or less. When the strength is 6.0 or less, it indicates that the strength is high, and there are few cracks / chips due to stirring stress. When the strength exceeds 6.0, the presence of metal elements and the amount of Sr in the non-magnetic fine particles is small, so that the strength is insufficient, and cracks and chips due to stirring stress are very large. Further, when the carrier is formed, the core material surface of the uncoated portion is exposed from the crack / chip portion generated by the stirring stress due to the printing durability, and there is a possibility that the carrier adheres due to the applied voltage. This strength is measured by:

(Strength)
A sample mill SAM (manufactured by Nara Machinery Co., Ltd.) was charged with 100 g of sample, and crushing was performed for 10 seconds using a standard rotor under the setting of 16000 rpm. 400 mg each of the crushing-unprocessed sample and the crushing-processed sample were prepared, and the quantity which passed the 795 Mesh net | network by blow-off was measured using blow-off powder charge amount apparatus TB-200 (made by Toshiba Chemical Corporation). At this time, the blow-off conditions were a blow pressure (N 2 gas) of 0.5 kg / cm ² and a blow time of 30 seconds. After completion of the measurement, the amount of fine powder not crushed and the amount of fine powder after crushed were calculated from the following formulas.

  The value obtained by subtracting the fine powder amount of the sample before the crushing treatment from the fine powder amount of the sample after the crushing treatment obtained as described above is defined as the strength.

  The ferrite carrier core material for an electrophotographic developer according to the present invention preferably has a fluidity of 38 sec / 50 g or less, and more preferably 35 sec / 50 g or less. When the fluidity is 38 sec / 50 g or less, the fluidity is very high. Even if it is converted into a carrier, the fluidity is maintained and the mixing property with the toner is good. Even if new toner is additionally supplied due to printing durability, the toner concentration in the developer container is always stable regardless of the location because the toner is highly miscible and the replenishment toner is charged in a relatively short period of time. Kept constant. When the fluidity exceeds 38 sec / 50 g, it indicates that the fluidity is insufficient. Even if it is made into a carrier, it is poorly mixed with toner. When toner is newly supplied due to printing durability, the toner density is not good because the toner is not well mixed and the replenishment toner cannot be charged, and the uncharged toner is driven to the walls and corners in the developer container. As a result, the toner density cannot be obtained in accordance with the charged toner amount. This fluidity is measured by:

(Fluidity)
This is carried out in accordance with JIS Z 2502 “Testing method for fluidity of metal powder”, and 50 g of a sample (ferrite carrier core material) is poured into a funnel having an orifice hole diameter of 2.63 mm, and the flow time (seconds) is measured.

  The ferrite carrier core material for an electrophotographic developer according to the present invention preferably has an average particle size measured by a laser diffraction particle size distribution analyzer of 15 to 120 μm, more preferably 15 to 80 μm, and most preferably 15 to 60 μm. is there. If the volume average particle size is less than 15 μm, carrier adhesion tends to occur, which is not preferable. If the volume average particle diameter exceeds 120 μm, the image quality tends to deteriorate, which is not preferable. This volume average particle size is measured by:

(Volume average particle size)
As a device, a Nikkiso Co., Ltd. Microtrac particle size analyzer (Model 9320-X100) was used. Water was used as the dispersion medium.

  The ferrite carrier core material for an electrophotographic developer according to the present invention preferably has a scattering amount of 1.0 mg or less, and more preferably 0.5 mg or less. When the scattering amount is 1.0 mg or less, even when the carrier is formed, the carrier adhesion on the image is small. When the amount of scattering exceeds 1.0 mg, carrier adhesion on the image increases even when the carrier is formed. The amount of scattering is measured as follows.

(Scattering amount)
Here, the scattering amount of the carrier core material is that the carrier core material obtained in Examples and Comparative Examples is filled in a magnetic drum having a diameter of 50 mm and a surface magnetic force of 1000 Gauss and rotated at 270 rpm for 30 minutes. Thereafter, the scattered particles were collected and the weight thereof was measured.

The apparent density of the ferrite carrier core material obtained by the present invention is preferably less than 2.80 g / cm ³ , more preferably 2.30 to 2.80 g / cm 3. If the apparent density exceeds 2.80 g / cm ³ , it is practically impossible to produce. If it is less than 2.30 g / cm ³ , the sphericity is insufficient, or it is considered that there is a problem in the core material strength due to the denseness inside the core material, which is not preferable. The apparent density here is measured by the following method.

[Apparent density]
It measured based on JISZ2504. Details are as follows.
1. Apparatus The powder apparent density meter is composed of a funnel, a cup, a funnel support, a support bar and a support base. A balance with a weighing of 200 mg and a weighing of 50 mg is used.
2. Measuring method (1) The sample shall be at least 150 g or more.
(2) The sample is poured into a funnel having an orifice with a hole diameter of 2.5 + 0.2 / −0 mm, and poured until the sample that has flowed out fills the glass and overflows.
(3) Stop the inflow of the sample as soon as it begins to overflow, and scrape the sample raised on the cup flatly with a spatula along the top edge of the cup so as not to give vibration.
(4) Tap the side surface of the cup to sink the sample and remove the sample attached to the outside of the cup, and weigh the sample in the cup with an accuracy of 0.05 g.
3. Calculation The numerical value obtained by multiplying the measured value obtained in 2- (4) above by 0.04 is rounded to the second decimal place by JIS-Z8401 (how to round the numerical value), and the unit of “g / cm ³ ” appears. Density.

  The ferrite carrier core material for an electrophotographic developer according to the present invention is oxidized on the surface as necessary. The thickness of the oxidized film formed by this surface oxidation treatment is preferably 0.1 nm to 5 μm. If the thickness is less than 0.1 nm, the effect of the oxide film layer is small, and if it exceeds 5 μm, the magnetization is lowered or the resistance becomes too high, so that problems such as a reduction in developing ability tend to occur. Moreover, you may reduce | restore before an oxidation process as needed. The thickness of the oxide film can be measured from a high-magnification SEM photograph that can confirm that the oxide film is formed. The oxide film may be uniformly formed on the surface of the ferrite carrier core material or may be partially formed with an oxide film.

  In the ferrite carrier for an electrophotographic developer according to the present invention, the surface of the ferrite carrier core material is coated with a resin.

  The ferrite carrier for an electrophotographic developer according to the present invention desirably has a resin coating amount of 0.1 to 10% by weight with respect to the ferrite carrier core material. When the coating amount is less than 0.01% by weight, it is difficult to form a uniform coating layer on the carrier surface. When the coating amount exceeds 10% by weight, the carriers are aggregated together with a decrease in productivity such as a decrease in yield. This causes fluctuations in developer characteristics such as fluidity or charge amount in the actual machine.

  The coating 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.

  A conductive agent can be added to the coating resin for the purpose of controlling the electrical resistance, charge amount, and charging speed of the carrier. Since the conductive agent itself has a low electric resistance, an excessive amount of the conductive agent tends to cause a rapid charge leak. Accordingly, the addition amount 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 coating resin. It is. Examples of the conductive agent include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents.

  Further, the coating 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 exposed area is controlled to be relatively small by forming a coating layer, the charge imparting ability may be reduced, but it can be controlled by adding various charge control agents and silane coupling agents. This is because it can. 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.

  In the method for producing a ferrite carrier core material for an electrophotographic developer according to the present invention, a ferrite raw material containing Sr is mixed with a binder and then granulated, and the obtained granulated material is pre-baked at 650 to 1250 ° C., Next, thermal spraying is performed in the atmosphere, followed by rapid solidification.

  The method of preparing a granulated product by pulverizing, mixing, and mixing the ferrite raw material with a binder is not particularly limited, and a conventionally known method can be adopted, and a wet method can be used even if a dry method is used. It may be used. For example, an iron compound, a Mn compound, an Mg compound, and an Sr compound are mixed as raw materials, and a binder and, if necessary, carbon black or the like are further added and granulated to prepare a granulated product.

  In the production method of the present invention, polyvinyl alcohol is used as a binder, and is contained in an amount of 0.5 to 3.5% by weight in terms of solid content with respect to the prepared granulated product. A binder such as polyvinyl alcohol originally functions as a binder for maintaining the shape of the granulated product. In the electric furnace firing, the binder is sufficient as a binder if it is about 0.3% by weight. In the above-mentioned Patent Document 6, it is said that vacancies move from the outside to the inside of the ferrite carrier core material in rapid cooling after thermal spray firing, but excessively contain polyvinyl alcohol that acts remarkably as a reducing agent that promotes ferrite formation. By doing so, the movement of the holes can be prevented. That is, by including excess polyvinyl alcohol in the granulated product, the density is already high because ferritization is promoted in the preliminary firing described later, and high density and high fluidity can be obtained even after thermal spraying. Since there are no vacancies suddenly generated by thermal spraying and particle variation is suppressed, re-firing after thermal spraying as described in Patent Document 6 is not necessary. In addition, since polyvinyl alcohol remains inside the particles after pre-firing and decomposition gas is released from the inside to the outside during spraying, the movement of pores from the outside to inside of the ferrite carrier core material as in Patent Document 6 is also suppressed. Is done.

  If the content of polyvinyl alcohol in the granulated product is less than 0.5% by weight, sufficient ferrite formation is not promoted in the pre-firing stage, and as a result, pores remain after thermal spraying and the density and fluidity are insufficient. Further, in the thermal spraying treatment, the binding strength of the granulated product is brittle, particle breakage occurs, and a desired particle size cannot be obtained. Further, when the content of polyvinyl alcohol is 3.5% by weight or more, the polyvinyl alcohol remaining after pre-baking is too much and bumps at the time of thermal spray baking. Moreover, the polyvinyl alcohol not involved in bumping remains in the fired product without being vaporized or decomposed. Furthermore, since the gas boiling at the time of thermal spraying forms a hollow portion, a desired particle density cannot be obtained. In some cases, the gas forming the hollow portion becomes excessive and the hollow portion becomes too large. As a result, the particles are broken, and the desired particle size or shape cannot be obtained.

  In the production method of the present invention, the obtained granulated product is pre-fired. Pre-baking is performed at 650 to 1250 ° C., and ferrite formation proceeds in this temperature range, and generation of fine powder is appropriately adjusted. If the pre-baking temperature is less than 650 ° C., it means that ferritization has not progressed and the ferrite raw material is soft or has a lot of voids, so that the mechanical strength of the raw material supply equipment or the flame jet power is reduced before spraying into the atmosphere. Since it cannot be tolerated and cracked, the desired particle size distribution cannot be obtained, and a large amount of fine powder is present on the surface of the ferrite carrier core material. If the pre-baking temperature is higher than 1250 ° C, most of the ferrite raw material is ferritized and the raw material is hard, so fine powder is generated due to the mechanical strength of the raw material supply equipment or the flame jet power before spraying into the atmosphere. It is difficult and there is no cushioning material. As a result, the ferrite particles are cracked or chipped.

  Next, the fired product obtained by preliminary firing is sprayed in the air and rapidly solidified to obtain a ferrite carrier core material.

Combustion gas and oxygen are used for thermal spraying as a combustible gas combustion flame, and the volume ratio of combustion gas and oxygen is 1: 3.5 to 6.0. When the ratio of oxygen to the combustion gas is less than 3.5, the melting is not sufficient, and when the ratio of oxygen to the combustion gas exceeds 6.0, it becomes difficult to form a ferrite. For example used in a proportion of oxygen gas 35~65Nm ³ / hr against the combustion gases 10 Nm ³ / hr.

  Propane gas, propylene gas, acetylene gas or the like is used as the combustion gas used for the thermal spraying, and propane gas is particularly preferably used. The granule flow rate is preferably 20 to 60 m / sec. Here, it is desirable that the flame temperature of the burner used for thermal spraying is 2000 to 3500 ° C. and the flame passage time is within 10 seconds.

  While the conventional firing temperature for ferritization is 1000 to 1500 ° C., the spraying temperature reaches 2000 to 3500 ° C. Thermal spray firing is a high-temperature and instantaneous process, in which the ferritization reaction easily proceeds uniformly, and segregation in ferrite particles or evaporation and separation of specific metal components is small. Therefore, even if fine powder is generated during firing, the specific metal component does not increase in the fine powder, so that the original composition ratio is maintained. Moreover, in order to reduce stirring stress, it is desirable to have high fluidity, but by adjusting the amount of metallic elements and Sr in the nonmagnetic fine particles on the surface, the force acting on the particles is relaxed, Even under the influence of agitation stress over a long period of time, no cracking or chipping of particles occurs. Since the ferrite particles obtained by thermal spray firing have a very good shape factor SF-1, the flowability is good.

  The particles obtained by spraying in this way are put into the air or water and rapidly solidified. Thereafter, collection, drying and classification are performed to obtain a ferrite carrier core material. 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.

  Thereafter, if necessary, the surface can be heated at a low temperature to perform an oxide film treatment to adjust electric resistance. For the oxide film treatment, a general rotary electric furnace, batch electric furnace or the like is used, and for example, heat treatment is performed at 300 to 800 ° C. In order to uniformly form the oxide film on the core particles, it is preferable to use a rotary electric furnace.

  In the manufacturing method according to the present invention, a ferrite carrier coated with a resin is obtained by coating the surface of the ferrite carrier core material with a resin. Carrier characteristics, particularly electrical characteristics such as charge amount, are often influenced by materials and properties existing on the carrier surface. Therefore, the desired carrier characteristics can be accurately adjusted by coating the surface with an appropriate resin. As a coating method, the coating can be performed by a known method such as a brush coating method, a dry 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. In the case of baking after resin coating, either an external heating method or an internal heating method may be used. For example, a stationary or fluid electric furnace, a rotary electric furnace, a burner furnace, or microwave baking 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 mixing ratio of the carrier and the toner, that is, the toner concentration is preferably set to 100 to 3000% 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]
The MnO 39.6 mol%, the MgO 9.6 mol%, the _Fe 2 _{O 3} were weighed ferrite carrier raw material to be 50 mol% and SrO in 0.8 mol%, water and a polycarboxylic acid type dispersing Agent, polyether antifoaming agent and polyvinyl alcohol (10% solution) as a binder were added and pulverized for 6 hours using a wet media mill (horizontal bead mill, 1 mm diameter zirconia beads). A granulated product was prepared with a spray dryer so that the volume average particle size after thermal spray firing was 33 to 37 μm. The binder content in the granulated product was 1.2% by weight in terms of solid content, the C content of the obtained granulated product was 1.33 wt%, and the apparent density was 1.21 g / cm ³ .

The resulting granulated product was pre-fired by maintaining at a set temperature of 1100 ° C. for 1 hour while adjusting the furnace pressure to 5 to 10 Pa in a reducing atmosphere in a reducing atmosphere, and partly ferritized. A knocker (striking from the outside of the furnace) was used as the mechanism of the deposit in the furnace. Moreover, the reducing atmosphere utilized the thermal decomposition gas of the dispersing agent and binder which were added when granulating with a spray dryer. The obtained pre-fired product had a C content of 0.12 wt% and an apparent density of 1.65 g / cm ³ .

The obtained pre-fired product was passed through a frame supplied with propane 8 Nm ³ / hr and oxygen 32 Nm ³ / hr respectively at a supply rate of 60 kg / hr, and then rapidly cooled in the atmosphere to obtain a thermal spray fired product. . The pre-fired product was supplied to the frame by air flow using oxygen gas, and the oxygen gas supply rate was 10 Nm ³ / hr. The obtained thermally sprayed fired product was classified and subjected to magnetic separation to obtain a ferrite carrier core material composed of ferrite particles.

[Example 2]
A ferrite carrier core material composed of ferrite particles was obtained in the same manner as in Example 1 except that the pre-baking temperature was 650 ° C.

[Example 3]
A ferrite carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that the pre-baking temperature was 1250 ° C.

[Example 4]
A ferrite carrier core material composed of ferrite particles was obtained in the same manner as in Example 1 except that SrO was changed to 0.1 mol%.

[Example 5]
A ferrite carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that SrO was changed to 2.5 mol%.

[Example 6]
In spraying conditions, except that propane 5.5 Nm ³ / hr, and oxygen 22 Nm ³ / hr was obtained ferrite carrier core material made of ferrite particles in the same manner as in Example 1.

[Example 7]
In spraying conditions, except that propane 11 Nm ³ / hr, and oxygen 44 nm ³ / hr was obtained ferrite carrier core material made of ferrite particles in the same manner as in Example 1.

[Example 8]
A ferrite carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that the binder content in the granulated product was 0.8% by weight in terms of solid content.

[Example 9]
A ferrite carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that the binder content in the granulated product was 3.0% by weight in terms of solid content.

[Comparative Example 1]
A ferrite carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that SrO was changed to 0.05 mol%.

[Comparative Example 2]
A ferrite carrier core material composed of ferrite particles was obtained in the same manner as in Example 1 except that SrO was changed to 3.0 mol%.

[Comparative Example 3]
A ferrite carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that the pre-baking temperature was 500 ° C.

[Comparative Example 4]
A ferrite carrier core material composed of ferrite particles was obtained in the same manner as in Example 1 except that the pre-baking temperature was 1300 ° C.

[Comparative Example 5]
A ferrite carrier core material composed of ferrite particles was obtained in the same manner as in Example 1 except that the binder content in the granulated product was 0.3% by weight in terms of solid content.

[Comparative Example 6]
A ferrite carrier core material made of ferrite particles was obtained in the same manner as in Example 1 except that the binder content in the granulated product was 5.0% by weight in terms of solid content.

  For Examples 1 to 9 and Comparative Examples 1 to 6, Table 1 shows the ferrite carrier core material production conditions (Sr substitution amount, amount of polyvinyl alcohol in the granulated product, characteristics of the granulated product, pre-calcining temperature, pre-calcined product Table 2 shows the amount of metal elements and Sr in the nonmagnetic fine particles, shape factor SF-1, shape factor SF-2, strength, C amount, apparent density, fluidity, and volume average particle size. And the amount of scattering. The measuring method of C amount and apparent density is as follows, and the other measuring methods are as described above. Moreover, the schematic diagram of the ferrite carrier core material obtained in Example 1 is shown in FIG.

  In Tables 1 and 2, the C content and apparent density of the granulated product, pre-fired product, and ferrite core material were shown. This was confirmed by the apparent density in the process of promoting ferrite formation by the polyvinyl alcohol component during the manufacturing process. It is shown to do. Decreasing the amount of C indicates decomposition of the polyvinyl alcohol component, and at the same time promotes ferrite formation of the pre-fired product and the core material, and increases the apparent density.

  From the amount of C, the polyvinyl alcohol component is insufficient at the pre-baked product stage, the decomposition gas is not released from the inside to the outside during spraying, there are voids inside the core material, and the polyvinyl alcohol component is present at the ferrite core material stage. It can be confirmed whether it is excessive and does not inhibit the intended ferrite characteristics.

  Moreover, in order to produce nonmagnetic fine particles necessary for obtaining high strength, it is possible to evaluate from the apparent density whether or not the ferrite formation to the pre-fired product is promoted to an appropriate level.

[C amount]
Carbon amount was measured using LECO carbon analyzer C-200 type (oxygen gas pressure: 2.5 kg / cm ² , nitrogen gas pressure: 2.8 kg / cm ² ).

As is clear from the results shown in Table 2, the ferrite carrier core materials shown in Examples 1 to 9 have a suitable amount of metal element and Sr in the nonmagnetic fine particles, and thus 6.0. The following high strength is obtained. In Examples 1 to 9, it can be seen from the amount of C in the ferrite carrier core that the polyvinyl alcohol component is completely used because non-magnetic fine particles necessary for obtaining high strength are generated. Since the apparent density of the ferrite carrier core material is as high as 2.30 g / cm ³ or more, it can be seen that particles having high sphericity and high core material strength are obtained. Moreover, since the nonmagnetic fine particles are not generated in a large amount and the amount of Sr in the core material composition is not too small, the amount of scattering is kept low at 1.0 mg or less. Also, as shown in FIG. 1, the ferrite carrier core material of Example 1 has nonmagnetic fine particles attached to the surface thereof.

  Furthermore, since the shape factors SF-1 and SF-2 have an appropriate range by thermal spray firing, a high fluidity of 38.0 or less is obtained, and the fluidity is excellent.

  On the other hand, in Comparative Example 1, since the amount of Sr in the ferrite carrier core material composition is too small, the abundance of the metal element in the nonmagnetic fine particles is small and the strength is inferior. Further, since the amount of Sr in the ferrite carrier core material composition is small, low magnetic particles of the ferrite carrier core material are likely to be generated, and the amount of scattering is larger than that in the examples.

  In Comparative Example 2, the amount of Sr in the nonmagnetic fine particles is increased due to the excessive amount of Sr in the ferrite carrier core material composition, and the strength is inferior. Moreover, since the amount of Sr in the ferrite carrier core material composition is too large, the shape factors SF-1 and SF-2 are also high, the fluidity is high, and the fluidity is inferior.

  In Comparative Example 3, since the pre-baking temperature is low, the abundance of the metal element in the nonmagnetic fine particles is excessive and the amount of scattering is large. Also, the pre-baking strength is low. Since it is difficult to withstand thermal spray firing, the average particle size is smaller than a predetermined value.

  In Comparative Example 4, since the pre-baking temperature is high, the abundance of the metal element in the non-magnetic fine particles after thermal spray firing is small, and the strength of the ferrite carrier core material is extremely deteriorated.

  In Comparative Example 5, since the amount of polyvinyl alcohol in the granulated product is small, ferritization is not promoted in the preliminary firing stage, voids remain, and the apparent density after thermal spraying is greatly reduced. Moreover, particle destruction has occurred in the thermal spraying process, and the average particle diameter is smaller than a predetermined value. Therefore, since the original spherical shape is not maintained, not only the shape factors SF-1 and SF-2 are increased, but also the fluidity is extremely deteriorated and the fluidity is inferior. Furthermore, since the abundance of the metal element in the nonmagnetic fine particles is not properly maintained, the strength is also lowered.

  In Comparative Example 6, since the amount of the polyvinyl alcohol in the granulated product is excessive, it is indicated that the polyvinyl alcohol remains because the amount of carbon is large even after the pre-firing, and bumping occurs during thermal spray firing, A large decrease in density and particle destruction occur due to residual pores, and the average particle size is smaller than a predetermined value. Therefore, since the original spherical shape is not maintained and the shape factors SF-1 and SF-2 are high, the fluidity is extremely deteriorated and the fluidity is inferior. Furthermore, due to bumping during thermal spray firing, there are non-ferritized particles that partially depart from thermal spray firing, so the amount of metal elements present in the non-magnetic fine particles is excessive, and even the amount of scattering is carried out. A large amount compared to the example.

[Example 10]
100 parts by weight of the ferrite particles (ferrite carrier core material) obtained in Example 1 and a condensation-crosslinked silicone resin (weight average molecular weight: about 8000) containing T units and D units as main components were prepared. 5 parts by weight of the solution (since the resin solution concentration is 20%, the solid content is 1 part by weight, diluent solvent: toluene), and the aminosilane coupling agent (3-aminopropyltrimethoxysilane) as the amine compound is added to the resin solid content. It added so that it might become 10 weight%, and it mixed and stirred with the universal mixing stirrer, and coat | covered resin on the ferrite core material surface, volatilizing toluene. After confirming that the toluene was sufficiently volatilized, the stirring was continued for another 5 minutes, and the toluene was almost completely removed. Then, the toluene was taken out from the apparatus, put into a container, placed in a hot air heating oven, and heated at 220 ° C. for 2 hours. Heat treatment was performed.

  Then, it cooled to room temperature, the ferrite particle | grains by which resin was hardened were taken out, the aggregation of particle | grains was released with the vibration sieve of 200M opening, and the nonmagnetic substance was removed using the magnetic separator. Thereafter, coarse particles were again removed with a vibrating sieve to obtain a ferrite carrier coated with a resin.

[Comparative Example 7]
A resin-coated ferrite carrier was obtained in the same manner as in Example 10 except that the ferrite particles (ferrite carrier core material) obtained in Comparative Example 2 were used.

[Comparative Example 8]
A resin-coated ferrite carrier was obtained in the same manner as in Example 10 except that the ferrite particles (ferrite carrier core material) obtained in Comparative Example 3 were used.

  For the ferrite carriers obtained in Example 10 and Comparative Examples 7 to 8, strength, fluidity, carrier adhesion on image (1k printing and 80k printing) and toner concentration (1k printing T / D, 80k printing) Table 3 shows T / D and fluctuation rate. Carrier adhesion and toner concentration were measured as follows. Other evaluations are as described above.

(Amount of carrier adhesion on image)
Printing development was performed under appropriate exposure conditions, and the number of white spots due to carrier adhesion on images after 1 k and after 80 k was visually counted.

(Toner density)
Under an environment of 25 ° C. and 55% RH, the sample (ferrite carrier) and a commercially available magenta toner of imgioMPC2500 manufactured by Ricoh are weighed so that the developer amount is 1 kg with a toner concentration of 7.2% by weight. After being exposed to the above conditions for 12 hours, the mixture was stirred for 30 minutes with a stirrer T2C type T2C type (stirring speed: 96 rpm) manufactured by Turbler Co. to obtain an initial developer. The initial developer was mounted on an Imagio MPC 2500 manufactured by Ricoh, and a printing durability test of 1 to 80 k sheets was performed. Samples developer at 1k and 80k, measured with Epping q / m-meter, PES-Laboratorium suction type charge measurement device (mesh: 635 mesh, suction pressure: 105 ± 10 mbar, suction time: 90 seconds) I asked. Moreover, the fluctuation rate was measured by the following.

  As is clear from the results shown in Table 3, the ferrite carrier shown in Example 10 maintains high strength even when it is converted into a carrier. Since the strength is good, there are few cracks and chippings of the particles even after repeated printing, there is almost no leakage of applied voltage from the core part exposed from the cracks and chipping parts, and the magnet roller is held by the applied voltage. Is less likely to adhere to the image of the carrier. Further, since the flowability of the ferrite carrier is good, the toner concentration in the developer container can be kept stable and constant even when printing is performed.

  On the other hand, Comparative Example 7 using the ferrite carrier core material of Comparative Example 2 results in a significant decrease in strength when converted to a carrier. Since the strength is low, there are many cracks / chips in the particles due to printing, and leakage of the applied voltage from the core material part exposed from the cracked / cracked part causes the carrier to be held on the magnet roller by the applied voltage. The adhesion on the image is increasing. In addition, due to poor printing, the carrier fluidity is poor on the walls and corners in the developer container, so the added uncharged toner accumulates and the toner concentration is not kept constant and is lower than the set concentration. Value.

  In Comparative Example 8 using the ferrite carrier core material of Comparative Example 3, the strength and fluidity of the ferrite carrier core material are high and the fluidity is good, so that the strength and fluidity are maintained even when the carrier is formed, and the toner concentration varies. Is a small result. However, since the amount of the metal oxide in the nonmagnetic fine particles is large, the amount of scattering of the ferrite carrier core material is large. Therefore, when printing is performed after forming a carrier, the carrier on the image from the initial stage (at the time of printing 1k sheets) The result is much adhesion.

  The ferrite carrier core material for an electrophotographic developer according to the present invention has a certain degree of circularity and roundness, and since there are a certain amount of nonmagnetic fine particles and Sr compound on the surface, it has excellent strength due to its buffering effect, The amount of scattering is small and the fluidity is good. An electrophotographic developer composed of a ferrite carrier and a toner obtained by coating a resin on the ferrite carrier core material is suitable for image cracking or chipping of ferrite particles even under the influence of stirring stress over a long period of time. Carrier adhesion to the substrate can be greatly suppressed. In addition, the ferrite carrier core material and the ferrite carrier can be stably produced on an industrial scale 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 (8)

It is composed of ferrite particles containing Sr and having a shape factor SF-1 (circularity) of 100 to 107 and a shape factor SF-2 (roundness) of 100 to 113, and the surface of the ferrite particles and / or in the pores Nonmagnetic fine particles adhere to the surface, the abundance of metal elements in the nonmagnetic fine particles is 500 to 5000 ppm with respect to the ferrite particles, and the abundance of Sr is 1 to 500 ppm with respect to the ferrite particles. A ferrite carrier core material for an electrophotographic developer characterized by the above. The composition of the said ferrite particle is represented by following formula (1), and a part of (MnO) and / or (MgO) in following formula (1) is substituted by SrO. Ferrite carrier core material for developer.

The ferrite carrier core material for an electrophotographic developer according to claim 2, wherein the substitution amount of SrO is 0.1 to 2.5 mol%. 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 carrier for an electrophotographic developer in which a ferrite raw material containing Sr is mixed with a binder and then granulated, and the resulting granulated product is pre-fired at 650 to 1250 ° C., then sprayed in the air, and further rapidly cooled and solidified. A ferrite material for electrophotographic developer, comprising: a core material, wherein the binder is polyvinyl alcohol and is contained in an amount of 0.5 to 3.5% by weight in terms of solid content with respect to the granulated product. Manufacturing method of carrier core material. A method for producing a ferrite carrier for an electrophotographic developer, wherein the ferrite carrier core material obtained by the production method according to claim 5 is coated with a resin. An electrophotographic developer comprising the ferrite carrier according to claim 4 and a toner. An electrophotographic developer comprising a ferrite carrier obtained by the production method according to claim 6 and a toner.

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