JP5382522B2 - Carrier core material for electrophotographic developer, carrier, production method thereof, and electrophotographic developer using the carrier - Google Patents

Description

  The present invention relates to a 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 carrier, a production method thereof, and an electrophotographic developer using the carrier. .

  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 reliability and durability of image maintenance.

  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.

  In such a ferrite carrier, magnetization and resistance are important characteristics, and a balance between magnetization and resistance is required.

  In order to balance magnetization and resistance, a heavy metal such as Cu, Zn, Ni, or a ferrite carrier using Mn has been used.

  Recently, environmental regulations have become stricter, and the use of heavy metals such as Ni, Cu, and Zn has been avoided, and the use of metals adapted to environmental regulations has been demanded. For this reason, the ferrite composition used as the carrier core material has shifted from Cu-Zn ferrite and Ni-Zn ferrite to ferrite containing a large amount of Mn such as manganese ferrite and Mn-Mg-Sr ferrite.

  However, even in ferrite containing a large amount of Mn, it is becoming subject to various laws and regulations from the viewpoint of environmental regulations. In addition to not containing the various heavy metals, ferrite with a Mn content as small as possible is added. There is a demand for a carrier core material.

  For this reason, it has been proposed to use ferrite containing Mg, Si or the like as a carrier core material. Patent Document 1 (Japanese Patent Laid-Open No. 2006-317620) proposes using Mg-based ferrite containing no Mn as a carrier core material, but the desired resistance cannot be obtained because the surface is smooth. Is the actual situation.

Patent Document 2 (Japanese Patent Laid-Open No. 2008-65106) includes a magnetic part having a composition represented by MO · Fe ₂ O ₃ (M is a divalent metal element such as Mn, Mg, Fe) and SiO ₂ . A carrier core material having a non-magnetic part is disclosed. However, in Patent Document 2, since the apparent density is 2.0 g / cm ³ or less, the possibility of carrier scattering is high. Furthermore, the content of SiO ₂ is preferably 4 to 20% by weight. With such a content, the magnetization is lowered, and the sintering proceeds too much, so that aggregated particles are likely to be generated.

Patent Document 3 (Japanese Patent Application Laid-Open No. 2008-249899) includes a general formula (MO) x (Fe ₂ O ₃ ) y (where M is one or more elements selected from divalent metals, Electrodevelopment having a soft ferrite composition represented by 0 <5x ≦ 0.5, y = 1−x) and containing 0.1 to 10% by mass of Al and 0.1 to 10% by mass of Si An agent carrier core material is described. However, since the content of Si is large, the magnetization decreases and the sintering proceeds too much. Moreover, since Al is also contained, the fall of magnetization becomes more remarkable.

Patent Document 4 (JP 2009-80348), a carrier core material which is composed of particles comprising a soft ferrite and SiO _2, and SiO ₂ is formed a three-dimensional network structure, SiO ₂ It is disclosed that the ratio (I ₁ / I ₂ ) between the peak intensity (I ₁ ) of quartz crystal and the peak intensity (I ₂ ) of cristobalite crystal of SiO ₂ is not less than a specific range. The amount of Si is preferably 15% by weight or less, but in the examples, it is 4.2% by weight or more. Since the amount of Si is large, the magnetization is lowered and the sintering proceeds too much, so that aggregated particles are likely to be generated.

Patent Document 5 (Japanese Patent Laid-Open No. 2009-86339) discloses a magnetic carrier core for an electrophotographic developer represented by a composition formula: Mn _x Fe _3-x O ₄ (where 0 ≦ x ≦ 1.0). In the powder XRD pattern, MnFe ₂ O ₄ phase and SiO ₂ phase are observed, the SiO ₂ content is 4 to 15 wt% in terms of Si, and the lattice constant is 8.483 to 8.492 Å. Is described. In Patent Document 5, since Si is a large amount of 4 to 15 wt% as described above, magnetization is reduced and sintering proceeds too much, so aggregated particles are likely to be generated.

  In Patent Document 6 (Japanese Patent No. 3997291), in an electrophotographic developing carrier mainly composed of ferrite or magnetite particles, 0.001 to 0.1% by weight of B (boron) and 0.01% in the particles are disclosed. It is shown to contain ~ 0.5 wt% Si. Although Patent Document 6 shows that a small amount of Si is contained, a carrier core material having high resistance and little aggregation cannot be obtained simply by containing a small amount of Si.

Attempts have also been made to improve carrier characteristics, focusing on the carrier shape factor (SF-1). For example, in Patent Document 7 (Japanese Patent No. 3850059), the carrier core material (nuclear body) particles are ferrite powder, the saturation magnetization is 50 to 70 emu / g, the average particle size is 30 to 40 μm, and the particle size is The weight ratio of 22 μm or less is 2.0 to 17.0% by weight, and the shape factor (SF ₁ ) of particles having an average particle size or less is larger than the shape factor (SF ₂ ) of particles exceeding the average particle size, and SF ₁ In the range of 1.15 to 1.35, and the difference between SF ₁ and SF ₂ is in the range of 0.1 to 0.5. This Patent Document 7 prevents gradation boundary white spot phenomenon and image blur phenomenon, does not consider aggregated particles, and there is a high possibility that aggregated particles exist. Therefore, when the particles of Patent Document 7 are used as the core material for an electrophotographic carrier, the aggregated particles are broken in the developing device to generate a large number of fine particles, which may cause damage to the photoreceptor and cause image defects.

  Patent Document 8 (Japanese Patent Laid-Open No. 2009-103782) discloses a carrier for developing an electrostatic latent image in which the shape factor SF-1 of the carrier core is 100 to 110 and the variation coefficient of SF-1 is 15% or less. Is disclosed. This Patent Document 8 is intended to improve fluidity, does not consider aggregated particles, and there is a high possibility that aggregated particles exist. Therefore, when the particles of Patent Document 8 are used as the core material for an electrophotographic carrier, the aggregated particles are broken in the developing device to generate a large number of fine particles, which may damage the photoreceptor and cause image defects.

  As shown in these conventional techniques, a carrier core material for an electrophotographic developer that does not use heavy metals, reduces Mn content as much as possible, obtains high resistance while being highly magnetized, and has few agglomerated particles. A carrier whose surface is coated with a resin has not been obtained.

JP 2006-317620 A JP 2008-65106 A JP 2008-249899 A JP 2009-80348 A JP 2009-86339 A Japanese Patent No. 3997291 Japanese Patent No. 3850059 JP 2009-103782 A

  Accordingly, an object of the present invention is to use a carrier core material for an electrophotographic developer without using heavy metals, reducing the Mn content as much as possible, obtaining high resistance while being highly magnetized, and having few aggregated particles, a carrier, and An object of the present invention is to provide an electrophotographic developer which can achieve a long life using these production methods, has a high charge amount, and has excellent charge stability.

  As a result of intensive studies to solve the above problems, the inventors of the present invention contain a certain amount of Mg, Ti, Fe, Sr, Mn, and Si, and the elution amount of Sr with a pH 4 standard solution is within a certain range. And it was discovered that a carrier core material having a shape factor SF-1 (circularity) of 135 or more in a specific range or less and a carrier coated with a resin on the carrier core material can achieve the above object, and the present invention has been achieved. .

  That is, according to the present invention, Mg is 0.8 to 3 wt%, Ti is 0.5 to 2.4 wt%, Fe is 60 to 70 wt%, Sr is 0.3 to 2 wt%, and Mn is 0.8. 001-4 weight and Si 50-1000 ppm, Sr elution with pH 4 standard solution is 50-1000 ppm, and shape factor SF-1 (circularity) contains not less than 12 number% of particles having 135 or more. The carrier core material for an electrophotographic developer is provided.

  The carrier core material for an electrophotographic developer of the present invention preferably contains an oxide crystal structure containing at least two elements selected from Fe, Ti and Sr in addition to the Mg-containing spinel structure. .

  The carrier core material for an electrophotographic developer according to the present invention preferably has a shape factor SF-2 (roundness) of 100 to 120.

  The carrier core material for an electrophotographic developer according to the present invention preferably has an average particle size of 15 to 120 μm as measured by a laser diffraction particle size distribution analyzer.

  The carrier core material for an electrophotographic developer of the present invention preferably has a surface coating formed by surface oxidation treatment.

In the carrier core material for an electrophotographic developer of the present invention, the Fe ₂ O ₃ component is desirably increased after the surface oxidation treatment.

The carrier core material for an electrophotographic developer of the present invention and the BET specific surface area after the surface oxidation treatment are preferably 0.08 to 0.25 m ² / g.

The carrier core material for an electrophotographic developer according to the present invention preferably has a resistance of 5 × 10 ^{7 to} 5.5 × 10 ⁹ Ω at a 2 mm Gap applied voltage of 250 V after the surface oxidation treatment.

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

  In the electrophotographic developer carrier of the present invention, the resin is preferably an acrylic resin, a silicone resin, or a modified silicone resin.

  In addition, the present invention pulverizes, mixes, and calcines each compound of Fe, Ti, Mg, and Sr, and then re-grinds, mixes, granulates, and the obtained granulated product is subjected to primary firing, main firing, A method for producing a carrier core material for an electrophotographic developer that is subjected to crushing, classification, and surface oxidation treatment, wherein a Si compound is added during the re-pulverization and mixing, and the main baking is performed at an oxygen concentration of 5% by volume or less. The present invention provides a method for producing the carrier core material for an electrophotographic developer.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, the average particle size of the primary particles of the Si compound is preferably 5 to 100 nm.

  In the method for producing a carrier core material for an electrophotographic developer according to the present invention, it is desirable to add a Mn compound in addition to the Fe, Ti, Mg and Sr compounds, and pulverize and mix them.

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

  The present invention also provides an electrophotographic developer comprising the carrier and toner.

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

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

  The carrier core material for an electrophotographic developer according to the present invention does not use each heavy metal, reduces the Mn content as much as possible, obtains high resistance while having high magnetization, and has few aggregated particles. An electrophotographic developer comprising a carrier and a toner obtained by coating the carrier core material with a resin has a long life, has a high charge amount, and is excellent in charging stability. Moreover, the carrier core material and the carrier can be stably produced on an industrial scale by the production method of the present invention.

  Hereinafter, modes for carrying out the present invention will be described.

<Carrier Core Material and Carrier for Electrophotographic Developer According to the Present Invention>
In the carrier core material for an electrophotographic developer according to the present invention, Mg is 0.8 to 3% by weight, preferably 1 to 3% by weight, more preferably 1 to 2.5% by weight, and Ti is 0.5 to 2%. 0.4 wt%, preferably 0.7-2.4 wt%, more preferably 0.7-2.2 wt%, Fe 60-70 wt%, preferably 60-68.5 wt%, more preferably Contains from 60 to 67% by weight and Sr from 0.3 to 2% by weight, preferably from 0.35 to 2% by weight, more preferably from 0.35 to 1.5% by weight. Within the above composition range, high resistance is obtained while being highly magnetized, and charging characteristics are stable and good when used as a carrier for an electrophotographic developer.

  Mg has an excellent electronegativity of MgO on the positive side, so it has a very good compatibility with negative toners, and a developer having a good rise in charge composed of a magnesium ferrite carrier containing MgO and a full color toner can be obtained. I can do it.

Since Ti is TiO ₂ and its electronegativity is slightly biased to the minus side, the compatibility with minus toner is not good originally. However, the compound (oxide) of Fe and Ti is less than 2.4% by weight. As a negative toner carrier, the influence on the charging property can be minimized.

If the Fe content is less than 60% by weight, it means that the nonmagnetic component and / or low magnetization component increases due to the relative increase in the addition amount of Mg and / or Ti, and the desired magnetic properties cannot be obtained. However, if it exceeds 70% by weight, the effect of adding Mg and / or Ti cannot be obtained, and the carrier core material is substantially equivalent to Fe ₃ O ₄ . The content of Mg is most preferably in the vicinity of Mg: divalent Fe = 1: 1 to 1: 4. If the Mg content is less than 0.8% by weight, the amount of magnesium ferrite phase produced in the carrier core material is small, and the amount of Fe ₃ O ₄ phase produced is relatively increased, so that the coercive force is increased and the desired magnetism is increased. The characteristics may not be obtained, and if the Mg content exceeds 3% by weight, the amount of magnesium ferrite produced in the carrier core material may increase and the desired magnetic characteristics may not be obtained. If the Ti content is less than 0.5% by weight, the effect of lowering the firing temperature due to the Ti content may not be obtained, and core particles having a desired surface property may not be obtained. The influence of the nonmagnetic phase due to the composite oxide of Fe and Ti increases, so that the magnetization becomes too low and desired magnetic characteristics may not be obtained. The amount of divalent Fe can be determined by crystal structure analysis by powder X-ray diffraction or by redox titration with potassium permanganate or dichromate when Mn content is low and redox titration is possible. I can do it.

As described above, the carrier core material for an electrophotographic developer according to the present invention contains 0.3 to 2.0% by weight of Sr. When Sr is less than 0.3% by weight, the effect of containing Sr is not obtained, and the decrease in magnetization due to the generation of Fe ₂ O ₃ accompanying the change in oxygen concentration during the main firing tends to increase, which is not preferable. Furthermore, since the effect of moving Sr to the surface of the core particle during the primary firing and the main firing cannot be obtained, the effect of increasing the resistance and the charge amount of the core material cannot be expected. When the content of Sr exceeds 2.0% by weight, it becomes hard ferrite and the fluidity of the developer on the magnetic brush may be abruptly deteriorated.

The crystal structure of the oxide containing Sr and Fe includes strontium ferrite expressed as SrO.6Fe ₂ O ₃ or SrFe ₁₂ O ₁₉ and is contained in the carrier core material for electrophotographic development according to the present invention. May be.

The carrier core material for an electrophotographic developer according to the present invention contains a small amount of Mn. The Mn content is 0.001 to 4% by weight, preferably 0.01 to 3.8% by weight, more preferably 0.01 to 1.5% by weight. Mn may be intentionally added in order to improve the balance between resistance and magnetization depending on the application. In this case, in particular, an effect of preventing reoxidation at the time of exit from the furnace in the main firing can be expected. In the case where it is not intentionally added, there is no problem with the inclusion of a trace amount of Mn as an impurity derived from the raw material. The form of Mn 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.

  The carrier core material for an electrophotographic developer according to the present invention contains Si, and the content thereof is 50 to 1000 ppm, preferably 50 to 800 ppm. By containing Si, it becomes possible to fire at a low temperature, and no agglomerated particles are generated. Moreover, since the sintering proceeds moderately due to the inclusion of Si, the target high magnetization can be obtained by the relatively low temperature main firing without containing much Mn.

(Contents of Fe, Mg, Ti, Sr, Mn and Si)
The contents of these Fe, Mg, Ti, Sr, Mn and Si are measured by the following.
0.2 g of carrier core material is weighed, 60 ml of pure water plus 20 ml of 1N hydrochloric acid and 20 ml of 1N nitric acid is heated to prepare an aqueous solution in which the carrier core material is completely dissolved, and an ICP analyzer (Shimadzu Corporation) The content of Fe, Mg, Ti, Sr, Mn and Si was measured using ICPS-1000IV).

  The carrier core material for an electrophotographic developer according to the present invention is required to have an elution with Sr pH 4 standard solution of 50 to 1000 ppm. Preferably it is 50-900 ppm, More preferably, it is 50-800 ppm.

  When the elution by Sr pH 4 standard solution is lower than 50 ppm, it means that Sr is not contained, which means that the effect of containing Sr cannot be expected. If the amount is more than 1000 ppm, the amount of Sr present on the surface of the core material is too high, so that the core material becomes too high in resistance and causes carrier scattering and image defects due to high resistance when it is turned into a carrier. The elution amount of Sr with pH 4 standard solution is measured as follows.

(Sr elution amount)
50 g of carrier core material and 50 ml of pH 4 standard solution for pH meter calibration were placed in a 100 ml glass bottle and stirred for 10 minutes with a paint shaker. After completion of stirring, 2 ml of the supernatant was sampled, a solution diluted with pure water to 100 ml was measured with ICP, and the obtained measured value was multiplied by 50 to obtain the Sr elution value. The pH 4 standard solution used was specified in the pH measurement method of JIS Z 8802.

  The carrier core material for an electrophotographic developer according to the present invention contains 12% by number or less, preferably 10% by number of particles having a shape factor SF-1 (circularity) of 135 or more. As described above, when the number of particles having a shape factor SF-1 (circularity) of 135 or more is 12% by number or less, a carrier core material free from many agglomerated particles can be obtained. This shape factor SF-1 (circularity) is measured by the following.

(Shape factor SF-1 (circularity))
Observe 3000 core particles using a particle size / shape distribution measuring instrument PITA-1 manufactured by Seishin Enterprise Co., Ltd., and determine the Area (projected area) and ferret diameter (maximum) using the software Image Analysis provided with the device. It is a value obtained by the expression 1 shown. The closer the carrier shape is to a spherical shape, the closer to 100. 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 carrier.

  The sample liquid was prepared by preparing a xanthan gum aqueous solution having a viscosity of 0.5 Pa · s as a dispersion medium, in which 0.1 g of core material particles were dispersed in 30 cc of the xanthan gum aqueous solution. Thus, by appropriately giving the viscosity of the dispersion medium, the core particles can be kept 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.

(Shape factor SF-2 (roundness))
The carrier core material for an electrophotographic developer according to the present invention preferably has a shape factor SF-2 (roundness) of 100 to 120. The shape factor SF-2 is a value obtained by dividing the value obtained by squaring the carrier projection perimeter length by the value obtained by dividing the value by the carrier projection area by 4π, and multiplying it by 100. The shape of the carrier is close to a sphere. The value becomes closer to 100. If the shape factor SF-2 of the carrier core material exceeds 120, it means that the surface of the core material has large irregularities, and the resin is likely to penetrate, so that desired characteristics as an electrophotographic carrier may not be obtained. The shape factor SF-2 (roundness) is calculated by the following formula 2.

  The carrier core material for an electrophotographic developer according to the present invention contains a crystal structure of an oxide containing at least Fe, Ti and Sr in addition to the spinel structure containing Mg. By adding Ti and Sr to Fe-excess magnesium-based ferrite, a composite oxide containing Fe, Ti, and Sr with relatively low magnetization is required in addition to a compound having a spinel crystal structure constituting ordinary ferrite. It is possible to control only the resistance without greatly changing the magnetization by oxidizing the composite oxide containing Fe, Ti and Sr preferentially over the spinel phase during the surface oxidation treatment. It becomes. That is, the resistance is adjusted by changing the valence of Fe contained in the composite oxide containing Fe, Ti, and Sr. The crystal structure is measured by the following.

(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 are processed with data using analysis software “X'Pert HighScore” in the same way as the crystal structure analysis of ordinary powders, the crystal structure is identified, and the obtained crystal structure is refined so that the weight conversion The abundance ratio was calculated. When calculating the abundance ratio, it was difficult to separate the peaks of magnesium ferrite and Fe ₃ O ₄ , so that it was treated as a spinel phase, and the abundance ratios of the other crystal structures were calculated. In identifying the crystal structure, Fe and O are essential elements, and Mn, Mg, Ti, 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 (113) plane of the spinel structure is set to 50000 cps or more, 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.

MgFe ₂ O ₄ is a typical spinel structure that constitutes magnesium ferrite, but as can be seen from the composition ratio of the elements, Fe is excessive, so that part of Mg is replaced with Fe and formally Mg _x Fe. _{y-x O 4, (Mg} x Fe 1-x) (Mg x 'Fe 1-x') 2 O 4 crystal structure and a part thereof is expressed by the like Mn, 1 or more of Ti and Sr All elements substituted with elements are also included, and those in which lattice defects are periodically included in the spinel structure by firing in a non-oxidizing atmosphere are also included.

In addition to magnesium ferrite, Fe ₃ O ₄ may be measured as a spinel structure. In the present invention, Fe ₃ O ₄ is not only Fe ₃ O ₄ but also Fe: O ratio is 2.5: 4 to 3: 4, and including all that part of Fe is replaced with one or more elements of Mg, Mn, Ti and Sr, and fired in a non-oxidizing atmosphere It also includes those in which lattice defects are periodically included in the spinel structure.

As the crystal structure of the oxide containing Fe and Ti, Fe ₂ TiO ₄ is typical in the spinel structure, and FeTiO ₃ and Fe ₂ TiO ₅ are typical in other than the spinel structure. Many as Fe is the amount present overwhelmingly as compared with _Ti, in addition to _{Fe x TiO y (FeTiO 3)} x (Fe 2 O 3) y, Fe (Fe x Ti y) O 4, (Fe x Ti 1- _{x) (Fe x 'Ti 1} -x') which O ₄ crystal structure and a part thereof is expressed by the like is substituted with Mn and / or Sr, periodically by being calcined in a non-oxidizing atmosphere In addition, the crystal structure includes a lattice defect. In addition to the above crystal structure, a part of Sr _a Fe _b O _c which is _a precursor of strontium ferrite is substituted with Ti and / or Mn, Sr _a Fe _b Ti _c O _d , Sr _a Fe _b Mn _c Ti _d O _e All oxides represented by the above and the like are also included, and include those in which lattice defects are periodically included in the crystal structure by firing in a non-oxidizing atmosphere.

  The 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 measuring device of 15 to 120 μm, more preferably 15 to 80 μm, and most preferably 15 to 60 μm. . 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 carrier core material for an electrophotographic developer according to the present invention has a surface coating formed by surface oxidation treatment. 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. If the thickness exceeds 5 μm, the magnetization is clearly 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, an optical microscope, and a laser microscope that can confirm that the oxide film is formed. The oxide film may be formed uniformly on the surface of the core material, or the oxide film may be partially formed.

The carrier core material for an electrophotographic developer according to the present invention preferably has an increased Fe ₂ O ₃ component after the surface oxidation treatment. The resistance can be increased by generating a highly insulating Fe ₂ O ₃ component in the vicinity of the surface of the core material. In general, since Fe ₂ O ₃ has almost no magnetization, generation of Fe ₂ O ₃ by oxidation of Fe ₃ O ₄ cannot satisfy both high magnetization and high resistance at the same time. If the Fe ₂ O ₃ in the firing by the case and atmosphere control the Fe ₂ O ₃ to an internal wood are present are present, can not be obtained core material of a high magnetization. On the other hand, the increase in the Fe ₂ O ₃ component in the vicinity of the surface by the surface oxidation treatment can increase the resistance while minimizing the decrease in magnetization.

  The term “FeO” as used in the present invention includes not only FeO but also Fe: O ratio of 0.8: 1 to 1: 1, and further includes all of which Fe is partially substituted with Mn. Shall be. The crystal structure measurement method will be described later.

The carrier core material for an electrophotographic developer according to the present invention preferably has a BET specific surface area of 0.08 to 0.25 m ² / g after the surface oxidation treatment. When the BET specific surface area is less than 0.08 m ² / g, since the core surface has few irregularities, the anchor effect of the resin after resin coating cannot be obtained, and the life as an electrophotographic carrier may be shortened. If the surface area exceeds 0.25 m ² / g, the irregularities on the surface of the core material are so large that the resin can easily penetrate, so that desired characteristics as an electrophotographic carrier may not be obtained. This BET specific surface area is measured by the following.

(BET specific surface area)
Using an automatic specific surface area measuring apparatus GEMINI 2360 (manufactured by Shimadzu Corp.), it can be determined from the N ₂ adsorption amount of carrier particles measured by adsorbing N ₂ as an adsorption gas. Here, the measurement tube used for measuring the N ₂ adsorption amount was baked for 2 hours at 50 ° C. in a reduced pressure state before the measurement. Further, 5 g of carrier particles were filled in this measuring tube, and after pretreatment at a temperature of 30 ° C. for 2 hours under reduced pressure, N ₂ gas was adsorbed at 25 ° C., and the amount of adsorption was measured. These adsorption amounts are values calculated from the BET equation by drawing an adsorption isotherm.

The carrier core material for an electrophotographic developer according to the present invention desirably has a resistance of 5 × 10 ^{7 to} 5.5 × 10 ⁹ Ω at a 2 mm Gap applied voltage of 250 V after the surface oxidation treatment. If the electric resistance is less than 5 × 10 ⁷ Ω, the resistance is too low, which causes a decrease in charge when used as a carrier. When the electric resistance exceeds 5.5 × 10 ⁹ Ω, the resistance becomes too high, and there is a fear that the movement of electric charge accompanying triboelectric charging is hindered. This electrical resistance is measured by:

(Electrical resistance)
A non-magnetic parallel plate electrode (10 mm × 40 mm) is made to oppose with a distance between electrodes of 2.0 mm, and 200 mg of a sample is weighed and filled between them. A sample is held between electrodes by attaching a magnet (surface magnetic flux density: 1500 Gauss, area of magnet in contact with electrode: 10 mm × 30 mm) to parallel plate electrodes, a voltage of 250 V is applied, and resistance at an applied voltage of 250 V is insulated. The resistance was measured with a resistance meter (SM-8210, manufactured by Toa Decay Corporation). Note that the measurement was performed in a constant temperature and humidity room controlled at a room temperature of 23 ° C. and a humidity of 55%.

In the carrier core material for an electrophotographic developer according to the present invention, the increase amount of Fe ₂ O ₃ is desirably 0 to 7% after the surface oxidation treatment. If it exceeds 7%, the magnetization starts to decrease greatly, so that there is a high possibility that the desired magnetization cannot be obtained. The increased amount of Fe ₂ O ₃ can be known from the change in the composition ratio of the crystal structure obtained by X-ray diffraction measurement of the core material before and after the surface oxidation treatment, and the measurement method is as described above.

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

  The resin-coated 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 carrier core material. When the coating amount is less than 0.1% 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 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.

  A conductive agent can be added to the film-forming 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 an abrupt charge leak. Accordingly, the addition amount is 0.1 to 20.0% by weight, preferably 0.25 to 15.0% by weight, particularly preferably 0.5 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, 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. The method for measuring the charge amount is as described above.

<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 is obtained by pulverizing, mixing, and calcining each compound of Fe, Ti, Mg, and Sr, and then re-pulverizing, mixing, and granulating the resulting product. The granules are subjected to primary firing, main firing, and further pulverization, classification, and surface oxidation treatment.

The method of preparing a granulated product by pulverizing, mixing, and calcining each compound of Fe, Ti, Mg, and Sr, and then re-pulverizing, mixing, and granulating is not particularly limited. It is possible to employ a dry method or a wet method. At this time, a Mn compound may be added. Mixing Fe ₂ O ₃ and TiO ₂ and Mg (OH) ₂ and / or MgCO ₃ and SrCO ₃ as raw materials, adding carbon black and / or binder, and pre-baking in non-oxidizing atmosphere or weak reducing atmosphere It is preferable to generate a ferrite precursor state in which a spinel phase containing at least divalent Fe and a composite oxide phase containing Fe, Ti, and Sr are present, and FeO is generated in this preliminary firing. You may do it. The calcined material obtained after the calcining is pulverized, mixed and granulated again. At the time of pulverization and mixing again, one or more compounds selected from Fe compounds, Mg compounds, Ti compounds, Sr compounds, and Mn compounds may be added as additional raw materials as necessary. The form of the compound of each element when added is not particularly limited, but in the case of Fe compound, Fe ₂ O ₃ , Fe ₃ O ₄ , FeO, in the case of Mg compound, MgO, Mg (OH) ₂ , MgCO ₃ , In the case of Ti compound, TiO ₂ , FeTiO ₃ , Fe ₂ TiO ₅ , in the case of Sr compound, SrO, SrCO ₃ , SrTiO ₃ , in the case of Mn compound, MnO ₂ , Mn ₂ O ₃ , Mn ₃ O ₄ , MnCO ₃ It is preferable because it is easily available for industrial use. In the conventional manufacturing method, since a spinel phase is generated from Fe ₂ O ₃ at the time of main firing, considerable energy is required to change the crystal structure, but Fe ₂ O ₃ , TiO ₂ , Mg (OH) ₂ and / or When MgCO ₃ and SrCO ₃ are mixed and carbon black and / or a binder are added and pre-baking is performed, ferriteization is completed with only a necessary change in the crystal structure in the main baking, so low-temperature baking is performed. It becomes possible. In addition, it is preferable to use polyvinyl alcohol or polyvinylpyrrolidone as a binder.

In the above manufacturing method, the Si compound is added with SiO ₂ or the like at the time of re-pulverization and mixing, and is contained in a final composition of 50 to 1000 ppm. By adding the Si compound in this way, firing is possible at a low temperature, and no agglomerated particles are generated.

  In the production method of the present invention, the obtained granulated product is subjected to primary firing and main firing. The primary firing is performed at 500 to 1100 ° C. in a non-oxidizing atmosphere.

  Next, the main calcination is performed at 1220 ° C. or less, preferably 1100 to 1200 ° C. The main firing has a more solid crystal structure, and an effect of preventing a decrease in magnetization due to surface oxidation can be expected. By performing the primary firing, it can be fired at a lower temperature than in the case where the primary firing is not performed in the main firing, so that not only the core material particles with unevenness are easily formed but also high sphericity can be secured. .

In the production method of the present invention, as described above, not only the crystal structure derived from the raw material but also the spinel phase containing at least divalent Fe and Fe and Ti in advance at the time of granulation of the core material particles before the main firing. And a composite oxide phase containing Sr, and further, by performing primary firing at 500 to 1100 ° C. in a non-oxidizing atmosphere, ferritization can be promoted without passing through Fe ₂ O ₃ , Even in the main baking, low-temperature baking at 1220 ° C. or lower is possible.

  In the production method of the present invention, the main baking is performed in an atmosphere having an oxygen concentration of 5% by volume or less. When the oxygen concentration exceeds 5% by volume, the magnetization of the fired product becomes too low, which causes carrier scattering, which is not preferable. In order to obtain a highly magnetized carrier core material, the oxygen concentration is preferably 3% by volume or less, more preferably 1% by volume or less.

  Thereafter, it is collected, dried and classified to obtain a 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. When dry collection is performed, it can also be collected with a cyclone 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., preferably 450 to 700 ° C. In order to uniformly form the oxide film on the core particles, it is preferable to use a rotary electric furnace.

  In the carrier for an electrophotographic developer of the present invention, the surface of the carrier core material is coated with the above resin 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 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 by microwave It can be burned. 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 carrier for an electrophotographic developer and a 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, Vinyl esters such as vinyl acetate, α-methylene aliphatic monocarboxylic acids such as 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.

Fe ₂ O ₃ , Mg (OH) ₂ , TiO ₂ , so that Fe is 7.72 mol, Mg is 0.415 mol, Ti is 0.15 mol, Sr is 0.04 mol and Mn is 0.1 mol. SrCO ₃ and Mn ₃ O ₄ were weighed and pelletized with a roller compactor. At this time, 1.0 wt% of activated carbon was added for the purpose of promoting firing and to reduce trivalent Fe, and the resulting pellet was temporarily fired in a rotary firing furnace at 1000 ° C. in an atmosphere with an oxygen concentration of 2 vol%. In addition, the ferritization was advanced while removing organic substances and gas components, and at the same time a part of the iron oxide was reduced.

The obtained calcined product was pulverized with a bead mill. Further, during the pulverization, 100 cc of SiO ₂ having an average particle diameter of 12 nm of primary particles dispersed by using a homogenizer T65D ULTRA-TURRAX manufactured by IKA at a ratio of solid content of 20% by weight with respect to water, and PVA as a binder component Was added so that the viscosity of the slurry was 2 to 3 poise, and the D _{50 of} the slurry particle size was 2 μm. The obtained pulverized slurry is granulated again with a spray dryer, and subjected to primary firing in a rotary firing furnace at 900 ° C. in a non-oxidizing atmosphere. Part was reduced.

  After the primary firing, coarse particles were removed using an 80-mesh sieve, and fired in a non-oxidizing atmosphere at 1165 ° C. for 16 hours to obtain a fired product. The obtained fired product was crushed, classified, and magnetically separated to obtain carrier core particles.

  Further, the obtained carrier core material particles were subjected to surface oxidation treatment in a rotary electric furnace under the conditions of a surface oxidation treatment temperature of 530 ° C. and an air atmosphere to obtain surface oxidized carrier core particles.

As shown in Table 2, carrier core particles were obtained in the same manner as in Example 1 except that the addition amount of SiO ₂ was 50 cc.

As shown in Table 2, carrier core particles were obtained in the same manner as in Example 1 except that the amount of SiO ₂ added was 300 cc.

  As shown in Table 3, carrier core particles were obtained in the same manner as in Example 1 except that the main firing temperature was 1110 ° C.

  As shown in Table 3, carrier core particles were obtained in the same manner as in Example 1 except that the main firing temperature was 1195 ° C.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Mg raw material was 0.34 mol.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Mg raw material was 0.6 mol.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Ti raw material was changed to 0.09 mol.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Ti raw material was changed to 0.24 mol.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Sr raw material was 0.03 mol.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Sr raw material was 0.1 mol.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Mn raw material was changed to 0 mol.

  As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Mn raw material was changed to 0.4 mol.

  As shown in Table 4, carrier core particles were obtained in the same manner as in Example 1 except that the surface oxidation treatment temperature was 680 ° C.

  As shown in Table 4, carrier core particles were obtained in the same manner as in Example 1 except that the surface oxidation treatment temperature was 480 ° C.

  As shown in Table 2, carrier core particles were obtained in the same manner as in Example 1 except that the primary firing temperature was 1000 ° C.

  As shown in Table 2, carrier core particles were obtained in the same manner as in Example 1 except that the primary firing temperature was 650 ° C.

  As shown in Table 1, Example 1 except that the Sr raw material was 0.1 mol, the Mn raw material was 0.4 mol, and the addition amount of the reducing agent was 800 cc as shown in Table 2. Similarly, carrier core particles were obtained.

Comparative example

[Comparative Example 1]
As shown in Table 2, carrier core particles were obtained in the same manner as in Example 1 except that the addition amount of SiO ₂ was 0 cc.

[Comparative Example 2]
As shown in Table 2, carrier core particles were obtained in the same manner as in Example 1 except that the addition amount of SiO ₂ was 500 cc.

[Comparative Example 3]
As shown in Table 3, carrier core particles were obtained in the same manner as in Example 1 except that the main firing temperature was 1250 ° C.

[Comparative Example 4]
As shown in Table 3, carrier core particles were obtained in the same manner as in Example 1 except that the main firing temperature was 1090 ° C.

[Comparative Example 5]
As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Mg raw material was changed to 0 mol.

[Comparative Example 6]
As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Mg raw material was changed to 0.83 mol.

[Comparative Example 7]
As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Ti raw material was changed to 0 mol.

[Comparative Example 8]
As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Ti raw material was changed to 0.3 mol.

[Comparative Example 9]
As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Sr raw material was changed to 0 mol.

[Comparative Example 10]
As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the Sr raw material was changed to 0.14 mol.

[Comparative Example 11]
As shown in Table 1, carrier core particles were obtained in the same manner as in Example 1 except that the amount of Mn raw material was 1 mol.

  Regarding Examples 1 to 18 and Comparative Examples 1 to 11, Table 1 shows provisional granulation conditions of the carrier core material, calcination conditions and crystal structure after calcination, Table 2 shows main granulation conditions and pulverization conditions of the carrier core material. , Primary firing, characteristic values (apparent density and magnetization) and crystal structure after primary firing, Table 3 shows main firing conditions, crystal structure after main firing, various properties (number of SF-1 is 1.33 or less / 3000) , SF-2, volume average particle diameter, apparent density), Sr elution amount and chemical analysis value, Table 4 shows surface oxidation treatment conditions, magnetization, resistance and BET specific surface area. A method for measuring the apparent density and the magnetization is shown below. Other measurement methods are as described above.

(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 pore 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.

(Magnetic characteristics: magnetization)
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.

  As is clear from the results in Tables 1 to 4, in Examples 1 to 18, core particles having good shape were obtained with little aggregation between the core materials. Furthermore, even after the surface oxidation treatment, surface properties suitable for resin coating were obtained, and resistance and magnetization were sufficient as a carrier core material. On the other hand, Comparative Examples 1, 4 and 10 all had a large amount of Sr elution, and the resistance was high after the surface oxidation treatment, making it unsuitable as a carrier core material. In Comparative Examples 2, 3, 6, 7, 9, and 11, the number of SF-1 was 135 or more, and the particles were agglomerated so that they were not suitable as carrier core particles. Comparative Example 5 had a small BET specific surface area after the surface oxidation treatment and was not suitable for resin coating. In Comparative Example 8, the amount of Ti added was large, and the resistance after the surface oxidation treatment was too high to be suitable as a carrier core material.

  Carrier core material particles having an average particle size of 59.17 μm were prepared in the same manner as in Example 1, and applied with a fluidized bed coating apparatus using acrylic modified silicone resin KR-9706 manufactured by Shin-Etsu Silicone Co., Ltd. as a coating resin. At this time, the resin solution is weighed so that the resin solid content with respect to the carrier core is 1% by weight, and toluene and MEK are mixed at a weight ratio of 3: 1 so that the resin solid content is 10% by weight. What added the solvent was used. After applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying with stirring in a heat exchange type stirring and heating apparatus set at 200 ° C. for 3 hours.

  Carrier core particles having an average particle size of 59.17 μm were prepared in the same manner as in Example 1, and the silicone resin KR-350 manufactured by Shin-Etsu Silicone, the aluminum-based catalyst CAT-AC manufactured by Toray Dow Corning, manufactured by Shin-Etsu Silicone Aminosilane coupling agent KBM-603 and Lion Ketjen Black EC600JD were applied as a coating resin by a fluidized bed coating apparatus. At this time, the resin solution is weighed so that the resin solid content with respect to the carrier core is 1.5% by weight, the aluminum catalyst CAT-AC is 2% by weight with respect to the resin solid content, and the aminosilane coupling agent. 10% by weight of KBM-603 and 15% by weight of Ketjen Black EC600JD were added. Further, toluene is added so that the solid content of the resin becomes 10% by weight, and after pre-dispersing for 3 minutes with a homogenizer T65D ULTRA-TURRAX made by IKA, a resin solution obtained by dispersing for 5 minutes in a vertical bead mill is used. Used as. After applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying with a hot air dryer set at 250 ° C. for 3 hours.

  Carrier core material particles having an average particle diameter of 59.17 μm were prepared in the same manner as in Example 1, and applied with an acrylic resin Dianal BR-80 manufactured by Mitsubishi Rayon Co., Ltd. as a coating resin using a universal mixing stirrer. At this time, a resin solution was used in which the resin was weighed so that the solid content of the resin with respect to the carrier core was 0.5 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 applying the resin, in order to completely eliminate the volatile matter, the resin-coated carrier was obtained by drying with a hot air dryer set at 145 ° C. for 2 hours.

  For Examples 19 to 21, 47.5 g of carrier and 2.5 g of toner were weighed, placed in a 50 cc glass bottle, stirred and mixed for 30 minutes in a ball mill with a rotation speed of 100 rpm, and a developer for measuring the charge amount with a toner concentration of 5% by weight. Obtained. The charge amount of the obtained developer was measured with a charge amount measuring device q / m-meter manufactured by Epping. The results are shown in Table 5.

  As is clear from the results in Table 5, any of the obtained resin-coated carriers has sufficient charging characteristics and can be sufficiently used as an electrophotographic carrier.

  The carrier core material for an electrophotographic developer according to the present invention does not use each heavy metal, reduces the Mn content as much as possible, obtains high resistance while having high magnetization, and has few aggregated particles. An electrophotographic developer comprising a carrier and a toner obtained by coating the carrier core material with a resin has a long life, has a high charge amount, and is excellent in charging stability. Moreover, the carrier core material and the 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 (17)

  0.8 to 3 wt% Mg, 0.5 to 2.4 wt% Ti, 60 to 70 wt% Fe, 0.3 to 2 wt% Sr, 0.001 to 4 wt% Mn and Si Electrophotographic development characterized by containing 12 to 10% by number of particles having a shape factor SF-1 (circularity) of 135 or more with a dissolution factor of 50 to 1000 ppm and an elution with a pH 4 standard solution of Sr of 50 to 1000 ppm Carrier core material.   The carrier core material for an electrophotographic developer according to claim 1, further comprising an oxide crystal structure containing at least two elements selected from Fe, Ti and Sr in addition to the Mg-containing spinel structure.   The carrier core material for an electrophotographic developer according to claim 1 or 2, wherein the shape factor SF-2 (roundness) is 100 to 120.   The carrier core material for an electrophotographic developer according to any one of claims 1 to 3, wherein an average particle size measured by a laser diffraction particle size distribution analyzer is 15 to 120 µm.   The carrier core material for an electrophotographic developer according to any one of claims 1 to 4, wherein a surface coating is formed by surface oxidation treatment. The carrier core material for an electrophotographic developer according to claim 5, wherein the Fe ₂ O ₃ component is increased after the surface oxidation treatment. The carrier core material for an electrophotographic developer according to claim 5 or 6, wherein the BET specific surface area after the surface oxidation treatment is 0.08 to 0.25 m ² / g. The carrier core material for an electrophotographic developer according to any one of claims 5 to 7, wherein, in the surface oxidation treatment, the resistance at a 2 mm Gap applied voltage of 250 V is 5 x 10 ^{7 to} 5.5 x 10 ⁹ Ω.   A carrier for an electrophotographic developer, wherein the surface of the carrier core material according to any one of claims 1 to 8 is coated with a resin.   The carrier for an electrophotographic developer according to claim 9, wherein the resin is an acrylic resin, a silicone resin, or a modified silicone resin.   After each compound of Fe, Ti, Mg and Sr is pulverized, mixed, calcined, re-pulverized, mixed, granulated, and the resulting granulated product is subjected to primary firing, main firing, further pulverization, classification, surface A method for producing a carrier core material for an electrophotographic developer to be oxidized, wherein the Si compound is added at the time of re-grinding and mixing, and the main firing is performed at an oxygen concentration of 5% by volume or less. A method for producing a carrier core material for an electrophotographic developer according to any one of claims 1 to 8.   The method for producing a carrier core material for an electrophotographic developer according to claim 11, wherein the average particle size of the primary particles of the Si compound is 5 to 100 nm.   The method for producing a carrier core material for an electrophotographic developer according to claim 11 or 12, wherein a Mn compound is added to the Fe, Ti, Mg and Sr compounds, and the mixture is pulverized and mixed.   A method for producing a carrier for an electrophotographic developer, wherein the surface of the carrier core obtained by the production method according to any one of claims 11 to 13 is coated with a resin.   An electrophotographic developer comprising the carrier according to claim 9 and a toner.   An electrophotographic developer comprising a carrier and a toner obtained by the production method according to claim 14.   The electrophotographic developer according to claim 15 or 16, which is used as a replenishing developer.