JP5629958B2 - Resin-filled ferrite carrier core material for electrophotographic developer, ferrite carrier, and electrophotographic developer using the ferrite carrier - Google Patents

Description

  The present invention relates to a resin-filled ferrite carrier core material and a ferrite carrier used in a two-component electrophotographic developer used in a copying machine, a printer, and the like, and more specifically, while maintaining the advantages of a resin-filled carrier. The present invention relates to a resin-filled ferrite carrier core material for an electrophotographic developer capable of obtaining high-quality image quality, high particle strength, excellent durability, and reducing image defects, a ferrite carrier, and an electrophotographic developer using the ferrite 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 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, since such iron powder carrier has a heavy true specific gravity of about 7.8, the toner component is fused to the surface of the iron powder carrier by the stirring and mixing with the toner particles in the developing box, so-called toner spent. It tends 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. Further, since the magnetization is too high, the magnetic brush of the developer becomes hard, and as a result, scratches and roughness occur, so that it is difficult to obtain a high-quality developed 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, in place of an iron powder carrier, a resin coated ferrite carrier having a light true specific gravity of about 5.0 and having a low magnetization and using a low-magnetization ferrite as a carrier or a resin coated on the surface has been widely used. As a result, the developer life and the developed image were dramatically improved.

  However, recently, due to the development of computers and multimedia, further high-definition full-color images are demanded in a wide range of fields from offices to homes. In addition, it has begun to be used in the field of light printing (print-on-demand applications that allow high-mix low-volume printing from document editing to copying and bookbinding) that require higher image stability and high image quality. Higher image quality, higher image quality, and higher reliability have begun to be required for developers. In addition, the networking of the office has evolved from the single-function copying machine to the multifunctional machine, and the service system has been changed from a system in which contracted service personnel regularly maintain and replace developers, etc. However, there has been a shift to the era of maintenance-free systems, and the demand for further extending the life of the developer is increasing further from the market.

  Under such circumstances, as disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 5-40367), for the purpose of reducing the weight and reducing the magnetic force of the carrier particles and aiming for a longer life and higher image quality, Many magnetic powder-dispersed carriers in which magnetic fine particles are dispersed in a resin have been proposed.

  Such a magnetic powder-dispersed carrier has a low true specific gravity and is advantageous for prolonging the service life. However, it tends to be high resistance and it is difficult to easily obtain an image density. Further, since magnetization control is performed with the amount of magnetic powder to be dispersed, it is difficult to maintain a balance between true specific gravity (lifetime index) and other physical properties (image characteristic control).

  In addition, the magnetic powder-dispersed carrier is obtained by solidifying magnetic fine particles with a binder resin. The magnetic fine particles are detached due to agitation stress or impact in a developing machine, or the conventional iron powder carrier or ferrite carrier is used. In some cases, the mechanical strength may be inferior, or the carrier particles may be broken. The detached magnetic fine particles and broken carrier particles may adhere to the photoreceptor and cause image defects.

  Furthermore, since the magnetic powder-dispersed carrier uses fine magnetic fine particles, there are disadvantages that the residual magnetization and the coercive force are increased and the fluidity of the developer is deteriorated. In particular, when a magnetic brush is formed on a magnet roll, since the residual magnetization and coercive force are high, the ears of the magnetic brush become hard and it is difficult to obtain high image quality. In addition, even when the magnet roll is separated, the magnetic aggregation of the carrier is not loosened and the toner is not quickly mixed with the replenished toner, so that the charge amount rises poorly and causes image defects such as toner scattering and fogging. was there.

  As an alternative to the magnetic powder-dispersed carrier, a resin-filled carrier in which a void in a porous carrier core material is filled with a resin has been proposed. Resin-filled carriers suppress crystal growth by controlling the composition and sintering (firing) conditions, form extremely porous core particles, and fill them with arbitrary resin to reduce the true specific gravity. Thus, it is possible to achieve a long life. In addition, the resin filling reduces the magnetization per particle, and the magnetic brush ear does not become stiff, so that a high-quality image excellent in fine line reproducibility and the like can be obtained.

  For example, Patent Document 2 (Japanese Patent Laid-Open No. 2006-337579) discloses a resin-filled carrier obtained by filling a ferrite core material having a porosity of 10 to 60% with a resin. 57943) proposes a resin-filled carrier having a three-dimensional laminated structure.

  In these porous magnetic powders described in Patent Documents 2 and 3, the pore volume of the core material is evaluated by the BET specific surface area and the oil absorption. However, the BET specific surface area is only a surface area, and the actual porosity is not known from the value. In addition, the oil absorption amount reflects the pore volume to some extent, but considering the measurement principle, the gap between particles is also measured and is not the actual pore volume. In general, the void volume between the particles is larger than the actual void volume in the particle, and the index when attempting to fill the resin without excessive excess or deficiency is not accurate. It was. Furthermore, in these Patent Documents 2 and 3, there is no description about the diameter of the pores existing on the ferrite surface filled with the resin and no description about the distribution of the pore diameters. The resin particle-to-particle variation and the resin filling uniformity are lacking. For this reason, the particles with insufficient resin filling are inferior in strength, so that when used on an actual machine, cracks and fine particles of carrier particles are generated, causing image defects.

  Therefore, Patent Document 4 (Japanese Patent Laid-Open No. 2009-175666) and Patent Document 5 (Japanese Patent Laid-Open No. 2009-244837) specify the pore volume, pore diameter, pore diameter distribution, etc. of the porous ferrite core material particles. Has been. In other words, by defining the pore volume, which is the space filled with the resin, and the diameter and distribution of the pores present on the ferrite surface, variation in the degree of resin filling between particles and within individual particles can be suppressed. Aggregation of particles after filling is also prevented. As a result, it is described that the carrier particles have improved fracture strength and a carrier having excellent durability characteristics can be realized.

  In the resin-filled type carrier, since the ferrite core material is located at the center of the particle, the particle strength greatly affects not only the degree of resin filling and the state of filling, but also the strength of the core material itself. Although these Patent Documents 4 and 5 certainly define the porosity of the ferrite core material, regarding the composition of the core material itself, “the porous ferrite core material is Mn, Mg, Li, Ca”. It is only shown a wide range of elements that it is desirable to include at least one selected from the group consisting of Sr, Cu and Zn.

  On the other hand, in order to meet the high definition, high image quality, and high reliability required for developers in the light printing field in recent years, a carrier with further improved particle strength and excellent durability is required. ing. Therefore, since only the methods described in Patent Documents 4 and 5 are not related to the strength of the core material itself, it is difficult to realize a carrier that satisfies the above characteristics.

Patent Document 6 (Japanese Patent Laid-Open No. 8-22150) describes that ferrite particles having a Mn—Mg—Sr composition are used as a carrier core material of a resin-coated carrier. The specific composition, in _{(MnO) x (MgO) y} (Fe 2 O 3) z, x = 35~45mol%, y = 5~15mol%, a composition of z = 45~55mol%, MnO, It is a composition in which a part of MgO and Fe ₂ O ₃ is substituted by 0.35 to 5.0 mol% with SrO, and is a non-porous ferrite particle.

  If the ferrite particles having such a composition are made porous and used as a carrier core material, it is possible to achieve the porosity defined in Patent Documents 4 and 5, but the strength of the core material itself There are limits to further improvements. This is assumed to be as follows.

  That is, as in the composition described in Patent Document 6, when the composition ratio of Mn is increased, the sinterability is likely to proceed. Therefore, in order to obtain the target porosity, it is necessary to set the firing temperature to the low temperature side. There is. As a result, the strength of the porous ferrite core material itself tends to decrease, and it is difficult to achieve a certain level of strength improvement.

  In addition, the resin-filled type carrier certainly reduces the magnetization per particle depending on the amount of resin, but if the magnetization of the porous ferrite core material used is high, the filling resin necessary for softening the ears of the magnetic brush The amount increases. An increase in the amount of resin can simultaneously achieve a reduction in specific gravity and a reduction in weight, but an excessive reduction in weight does not provide sufficient stress with the toner, resulting in a decrease in saturation charge and a slow rise in charge. This may cause toner scattering. Therefore, in order to achieve higher definition and higher image quality, a low-magnetization ferrite core material is required as a porous ferrite core material to be used.

As a low-magnetization ferrite core material, for example, Patent Document 7 (Japanese Patent Laid-Open No. 11-202559) discloses Mn—Mg—Sn ferrite. Specifically, in _{(MnO) x (MgO) y} (Fe 2 O 3) z, x = 5~35mol%, y = 10~45mol%, a composition of z = 45~55mol%, MnO, MgO and It is said that 0.5 to 5.0 mol% of Fe ₂ O ₃ can be substituted with SnO ₂ and the saturation magnetization can be 20 to 43 mol%. By using such a ferrite core material, low saturation magnetization carriers can be obtained stably, there is little variation in magnetization between carrier particles, and carrier surface properties (degree of growth of grain boundaries) can be made uniform. It is disclosed that it is possible.

  However, Patent Document 7 aims to stabilize the characteristics after resin coating by reducing the inter-particle variation of the resin coating by making the carrier surface properties (grain boundary growth degree) uniform. In Examples 7 to 12 and Comparative Example 6, the resin coating amount is 0.3% by weight and 1.3% by weight, as can be seen from this patent document 7, This is related to a carrier carrier coated with a ferrite resin that has been used from the beginning, and is completely different from a resin-filled carrier obtained by positively making particles porous and filling the resulting pores with a resin. Therefore, even if ferrite having a composition as described in Patent Document 7 suppresses crystal growth by sintering (firing) conditions and forms extremely porous core material particles, a particularly desired porous property ( Pore volume, pore diameter, pore distribution) cannot be obtained, and it is difficult to realize a carrier having high particle strength and excellent durability.

JP-A-5-40367 JP 2006-337579 A JP 2007-57943 A JP 2009-175666 A JP 2009-244837 A JP-A-8-22150 JP-A-11-202559

  As described above, a resin-filled ferrite carrier for an electrophotographic developer capable of obtaining high-quality image quality, high particle strength, excellent durability, and reducing image defects while retaining the advantages of the resin-filled carrier described above. Was demanded.

  Accordingly, an object of the present invention is to provide a resin-filled mold for an electrophotographic developer that can provide high-quality image quality, high particle strength, excellent durability, and reduce image defects while retaining the advantages of a resin-filled carrier. It is an object to provide a ferrite carrier core material, a ferrite carrier, and an electrophotographic developer using the ferrite carrier.

As a result of intensive studies to solve the problems as described above, the present inventors have partially substituted Mn—Mg-based ferrite having a specific composition as a carrier core material with Sr and containing a certain amount of SiO _2. The present inventors have found that the above-mentioned problems can be solved by using porous ferrite particles that have been made, and have reached the present invention.

That is, the present invention comprises porous ferrite particles, and the composition of the porous ferrite particles is represented by the following formula (1), and (MnO) (MgO) and / or (Fe ₂ O) in the following formula (1). ₃ ) A resin-filled ferrite for an electrophotographic developer , wherein a portion of ₃ ) is substituted with 0.3 to 4.0 wt% of SrO , and the porous ferrite particles contain ₂₀₀ to 2800 ppm of SiO ₂ A carrier core material is provided.

In the resin-filled ferrite carrier core material for an electrophotographic developer according to the present invention, the porous ferrite particles have a pore volume of 40 to 160 mm ³ / g, a peak pore diameter of 0.5 to 2.0 μm, and a pore diameter. It is desirable that the variation dv of the pore diameter represented by the following formula (2) in the distribution is 1.5 or less.

The resin-filled ferrite carrier core material for an electrophotographic developer according to the present invention preferably has a saturation magnetization of 40 to 60 Am ² / kg.

  The present invention also provides a resin-filled ferrite carrier for an electrophotographic developer, wherein the resin is filled in the pores of the ferrite carrier core material comprising the porous ferrite particles.

  In the resin-filled ferrite carrier for an electrophotographic developer according to the present invention, the resin is preferably a silicone resin.

  In the resin-filled ferrite carrier for an electrophotographic developer according to the present invention, the amount of the resin filled in the porous ferrite particles is 6 to 20 parts by weight with respect to 100 parts by weight of the porous ferrite particles. desirable.

  The resin-filled ferrite carrier for an electrophotographic developer according to the present invention desirably has a resin coated on the surface.

The resin-filled ferrite carrier for an electrophotographic developer according to the present invention has a volume average particle size of 20 to 70 μm, a saturation magnetization of 30 to 55 Am ² / kg, a particle density of 2.8 to 4.3 g / cm ³ , It is desirable that the apparent density is 1.0 to 2.2 g / cm ³ .

  The present invention also provides an electrophotographic developer comprising the resin-filled ferrite carrier and a toner.

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

  The resin-filled ferrite carrier core material for an electrophotographic developer according to the present invention and the ferrite carrier filled with resin in the gap can be reduced in weight and weight, so that it has excellent durability and can achieve a long life, and can be magnetic. Compared to powder-dispersed carriers, it has higher strength and does not crack, deform or melt due to heat or impact. In addition, since the magnetic brush is soft and high-quality image quality is obtained due to low magnetization, it has a specific composition, so that the breaking strength is strong and charging fluctuation during printing can be prevented.

Hereinafter, modes for carrying out the present invention will be described.
<Resin-filled ferrite carrier core material for electrophotographic developer according to the present invention, ferrite carrier>
The resin-filled ferrite carrier core material for an electrophotographic developer according to the present invention is composed of porous ferrite particles, and a high-quality image can be obtained by substituting part of the Mn-Mg ferrite with a specific composition with SrO. As a result, the particle strength is high, and charging fluctuation during printing can be prevented.

The composition of the porous ferrite particles is represented by the following formula (1), and a part of (MnO) (MgO) and / or (Fe ₂ O ₃ ) in the following formula (1) is 0.3 to 0.3 in SrO. 4.0% by weight substituted.

  In the above formula (1), x is 10 to 25 mol%, preferably 10 to 21 mol%, particularly preferably 12 to 19 mol%. Further, y is 25 to 40 mol%, desirably 30 to 40 mol%, most desirably 32 to 37 mol%. Furthermore, z is 45 to 55 mol%, preferably 48 to 54 mol%, particularly preferably 49 to 53 mol%.

  In the composition of the porous ferrite particles according to the present invention, when x is less than 10 mol% and y is more than 40 mol%, the magnetization is too low, and carrier adhesion occurs in actual use, causing image defects. It is not preferable. If x is more than 25 mol and y is less than 25 mol, the magnetization becomes high, and the magnetic brush of the developer becomes hard, and as a result, it is difficult to obtain a high-quality image. Furthermore, this generally indicates that the ratio of Mn increases and the ratio of Mg decreases, but as a result, the strength of the porous ferrite core material decreases, and thus the carrier strength after filling with the resin also increases. Since it falls, it is not preferable. This is presumed as follows. In other words, Mn-based ferrite is easy to sinter, and it is necessary to lower the firing temperature in order to obtain the target porosity. However, Mg-based ferrite maintains its porosity even when the firing temperature is increased. It's easy to do. Therefore, when the ratio of Mn in the porous ferrite composition is increased, the firing temperature must be lowered to obtain the target porosity, and as a result, the strength of the porous ferrite core material is lowered.

In the porous ferrite particles according to the present invention, a part of (MnO) x (MgO) y (Fe ₂ O ₃ ) z in the above formula (1) is substituted with SrO. By containing SrO in the porous ferrite particles, the variation in magnetization between particles can be reduced. Further, when firing is performed at a lower firing temperature in order to obtain porosity, there is an effect of suppressing a decrease in magnetization. That is, when SrO is not contained or less than the desired range, the sinterability is likely to proceed, so that it is difficult to obtain a porous material. The substitution amount of SrO is desirably 0.3 to 4.0% by weight of the porous ferrite particles, and most desirably 0.4 to 2.5% by weight. If the SrO substitution amount is less than 0.3% by weight, the SrO substitution effect described above cannot be obtained, and if it exceeds 4.0% by weight, the remanent magnetization and the coercive force increase. However, aggregation due to magnetic force occurs, and the mixing property with the toner is remarkably deteriorated.

A porous ferrite particles used in the present _invention, that have a SiO 2 containing 200～2800Ppm. By containing SiO ₂ which is a nonmagnetic phase, the strength of the porous ferrite particles can be improved. The content of SiO ₂ is desirably 400 to 1500 ppm, and most desirably 400 to 900 ppm of the porous ferrite particles. If the content of SiO ₂ is less than 200 ppm, the above-described effects cannot be obtained, and if it exceeds 1500 ppm, the sinterability is likely to proceed, so that it is difficult to obtain a porous material. In addition, since the ratio of the nonmagnetic phase increases, variation in magnetization between particles occurs, resulting in generation of low-magnetization particles, which causes carrier adhesion in an actual machine, which is not preferable.

[SiO ₂ content analysis of porous ferrite particles]
The SiO ₂ content of the porous ferrite particles is measured according to JIS-G1212 (silicon dioxide weight method).

  The porous ferrite particles used in the present invention do not contain Cu, Zn or Ni more than inevitable impurities or accompanying impurities. These contents are desirably suppressed to 2.0% by weight or less as a total amount of each of the above elements, more desirably 1.5% by weight or less, and most desirably 1.0% by weight or less.

The pore volume of the porous ferrite particles is desirably 40 to 160 mm ³ / g, more desirably 40 to 100 mm ³ / g, and most desirably 50 to 80 mm ³ / g. If the pore volume of the porous ferrite particles is less than 40 mm ³ / g, it is impossible to reduce the weight because a sufficient amount of resin cannot be filled. On the other hand, if the pore volume of the porous ferrite particles exceeds 160 mm ³ / g, the strength of the carrier cannot be maintained even if the resin is filled.

  The peak pore diameter of the porous ferrite particles is desirably 0.5 to 2.0 μm, more desirably 0.6 to 1.8 μm, and most desirably 0.7 to 1.5 μm. If the peak pore diameter of the porous ferrite particles is 0.5 μm or more, the irregularities on the surface of the core material will be an appropriate size, so the contact area of the toner will increase, and frictional charging with the toner will be performed efficiently. Therefore, the rising characteristics of charging are improved while the specific gravity is low. If the peak pore diameter of the porous ferrite particles is less than 0.5 μm, such an effect cannot be obtained, and the surface of the carrier after filling becomes smooth, so that a carrier having a low specific gravity has sufficient stress with the toner. It is not given, and the rising of charging is deteriorated. In addition, when the peak pore diameter of the porous ferrite particles exceeds 2.0 μm, the area where the resin is present increases with respect to the surface area of the particles, and therefore, when the resin is filled, aggregation between particles is likely to occur. In the carrier particles after the resin is filled, there are many aggregated particles and irregular shaped particles. For this reason, the agglomerated particles are released by the stress in printing durability, which causes charging fluctuation. Furthermore, the carrier core material using porous ferrite particles having a peak pore diameter exceeding 2.0 μm represents large irregularities on the surface of the carrier core material, which means that the shape of the particles themselves is bad. In addition, since the strength is inferior, the carrier particles themselves are cracked due to stress during printing, which causes charging fluctuations.

  Thus, when the pore volume and the peak pore diameter are in the above ranges, it is possible to obtain a resin-filled carrier that does not have the above-described problems and is appropriately reduced in weight.

[Pore diameter and pore volume of porous ferrite particles]
The measurement of the pore diameter and pore volume of the porous ferrite particles is performed as follows. That is, it measured using mercury porosimeter Pascal140 and Pascal240 (ThermoFisher Scientific company make). CD3P (for powder) was used as the dilatometer, and the sample was put in a commercially available gelatin capsule having a plurality of holes and placed in the dilatometer. After degassing with Pascal 140, it was filled with mercury and the low pressure region (0 to 400 Kpa) was measured to obtain 1st Run. Next, deaeration and measurement of the low pressure region (0 to 400 Kpa) were performed again to obtain 2nd Run. After 2nd Run, the combined weight of the dilatometer, mercury, capsule and sample was measured. Next, the high pressure region (0.1 Mpa to 200 Mpa) was measured with Pascal240. After the measurement, the pore volume, pore size distribution, and peak pore size of the porous ferrite particles were determined from data (pressure, mercury intrusion amount) where the pore size converted from pressure was 3 μm or less. Further, when determining the pore diameter, the control / analysis combined use software PASCAL 140/240/440 attached to the apparatus was used, and the surface tension of mercury was calculated to be 480 dyn / cm and the contact angle was 141.3 °. For the peak pore diameter, dV / dlogd was calculated on the same software, and the value of most freq. Was adopted. In the calculation of dV / dlogd, Number of point to average was 6 and Smooth Dumping factor was 0.95.

In the pore size distribution of the porous ferrite particles, the pore size variation dv is desirably 1.5 or less, more desirably 0.9 or less, and most desirably less than 0.8. Here, assuming that the total mercury intrusion amount in the high pressure region is 100%, the pore diameter calculated from the pressure applied to mercury when the indentation amount reaches 84% is d ₈₄ , and the mercury when the indentation amount reaches 16%. the pore size calculated from the pressure applied to that the d _16. The dv value was calculated by the following formula (2).

  When the variation dv of the pore diameter of the porous ferrite particles exceeds 1.5, it means that the unevenness between the particles and the variation of the core material shape become large. Therefore, if the dv value exceeds the desired range, the particle shape and aggregation due to packing are likely to cause inter-particle variations, resulting in poor charge start-up and increased charge fluctuation. Become.

The saturation magnetization of the porous ferrite particles used in the present invention is desirably 40 to 60 Am ² / kg, more desirably 44 to 57 Am ² / kg, and most desirably 46 to 54 Am ² / kg. If the saturation magnetization is less than 40 Am ² / kg, it is not desirable because it causes carrier adhesion. When the saturation magnetization exceeds 60 Am ² / kg, the ears of the magnetic brush become hard, and it is difficult to obtain good image quality.

[Magnetic properties]
Here, the saturation magnetization was measured using an integral BH tracer BHU-60 type (manufactured 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.

  The resin-filled carrier for an electrophotographic developer according to the present invention fills porous ferrite particles (carrier core material) with a resin. The filling amount of the resin is preferably 6 to 20 parts by weight, more preferably 7 to 15 parts by weight, and most preferably 7 to 12 parts by weight with respect to 100 parts by weight of the porous ferrite particles. If the filling amount of the resin is less than 6 parts by weight, sufficient weight reduction cannot be achieved. On the other hand, when the filling amount of the resin exceeds 20 parts by weight, agglomerated particles are likely to be generated at the time of filling, resulting in charging fluctuation.

  The resin to be filled is not particularly limited and can be appropriately selected depending on the toner to be combined, the environment in which it is used, and the like. 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, acrylic-styrene resin, silicone resin, Alternatively, modified silicone resins modified with resins such as acrylic resin, polyester resin, epoxy resin, polyamide resin, polyamideimide resin, alkyd resin, urethane resin, and fluororesin can be used. In view of the detachment of the resin due to mechanical stress during use, a thermosetting resin is preferably used. Specific examples of thermosetting resins include epoxy resins, phenol resins, silicone resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, and resins containing them.

  Among these resins, silicone resins are desirable, and examples of silicone resins include methyl silicone resins, phenyl silicone resins, and methylphenyl silicone resins.

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

  In addition, the charge 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 a large amount of resin is filled, the charge imparting ability may be lowered, but it can be controlled by adding various charge control agents and silane coupling agents. 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 resin-filled carrier for an electrophotographic developer according to the present invention is preferably surface-coated with a coating resin. Carrier characteristics, particularly electrical characteristics such as charging characteristics, are often affected by materials and properties existing on the carrier surface. Therefore, the desired carrier characteristics can be adjusted with high accuracy by coating the surface with an appropriate resin.

  The coating resin is not particularly limited, and may be the same as or different from the above filling resin. 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, acrylic-styrene resin, silicone resin, Alternatively, modified silicone resins modified with resins such as acrylic resin, polyester resin, epoxy resin, polyamide resin, polyamideimide resin, alkyd resin, urethane resin, and fluororesin can be used. In view of the detachment of the resin due to mechanical stress during use, a thermosetting resin is preferably used. Specific examples of thermosetting resins include epoxy resins, phenol resins, silicone resins, unsaturated polyester resins, urea resins, melamine resins, alkyd resins, and resins containing them. The coating amount of the resin is preferably 0.5 to 5.0 parts by weight with respect to 100 parts by weight of the filling type carrier (before resin coating).

  These coating resins can also contain a conductive agent and a charge control agent for the same purpose as described above. The kind and content of the conductive agent and the charge control agent are the same as in the case of the above filling resin.

  The volume average particle size of the resin-filled carrier for an electrophotographic developer according to the present invention is desirably 20 to 70 μm, more desirably 30 to 60 μm, and most desirably 30 to 55 μm. Within this range, carrier adhesion is prevented and good image quality can be obtained.

[Volume average particle size (Microtrack)]
This volume average particle diameter is measured as follows. That is, it is measured using a Nikkiso Co., Ltd. Microtrac particle size analyzer (Model 9320-X100). Water was used as the dispersion medium. Place 10 g of sample and 80 ml of water in a 100 ml beaker and add 2-3 drops of dispersant (sodium hexametaphosphate). Subsequently, using an ultrasonic homogenizer (UH-150 type manufactured by SMT Co Ltd), the output level was set to 4 and dispersion was performed for 20 seconds. Thereafter, bubbles formed on the beaker surface were removed, and the sample was put into the apparatus. The volume% of particles less than 24 μm described later was also measured and calculated in the same manner.

The saturation magnetization of the resin-filled carrier for an electrophotographic developer according to the present invention is preferably 30 to 55 Am ² / kg, more preferably 35 to 53 Am ² / kg, and most preferably 38 to 50 Am ² / kg. If the saturation magnetization is less than 30 Am ² / kg, it is not desirable because it causes carrier adhesion. When the saturation magnetization exceeds 55 Am ² / kg, the ears of the magnetic brush become hard, and it is difficult to obtain good image quality. The method for measuring the saturation magnetization is as described above.

Particle density of the resin-filled carrier for an electrophotographic developer according to the present invention is preferably a 2.8~4.3g / cm ^3, more desirably 3.5~3.9g / cm ^3. If the particle density is less than 2.8 g / cm ³ , the charge imparting ability tends to decrease because the carrier is too light. On the other hand, if the particle density exceeds 4.3 g / cm ³ , the carrier is not sufficiently light and the durability is poor.

[Particle density]
The particle density was measured as follows. That is, it measured using the pycnometer based on JISR9301-2-1. Here, methanol was used as a solvent, and measurement was performed at a temperature of 25 ° C.

The apparent density of the resin-filled carrier for an electrophotographic developer according to the present invention is preferably 1.0 to 2.2 g / cm ³ , more preferably 1.5 to 2.2 g / cm ³ , most preferably 1.7-2.0 g / cm ³ . If the apparent density is less than 1.0 g / cm ³ , the carrier is too light and the charge imparting ability tends to be lowered. When the apparent density exceeds 2.2 g / cm ³ , the weight of the carrier is not sufficient and the durability is inferior.

[Apparent density]
The apparent density is measured in accordance with JIS-Z2504 (Apparent density test method for metal powder).

<Resin-filled ferrite carrier core material for electrophotographic developer according to the present invention and method for producing ferrite carrier>
Next, a resin-filled ferrite carrier core material for an electrophotographic developer and a method for producing a ferrite carrier according to the present invention will be described.

  In order to produce the resin-filled ferrite carrier core material (porous ferrite particles) for an electrophotographic developer according to the present invention, first, an appropriate amount of raw materials are weighed and then 0.5 hours or longer with a ball mill or a vibration mill. The mixture is pulverized and mixed preferably for 1 to 20 hours. The raw material is not particularly limited, but is preferably selected so as to have a composition containing the above-described elements.

  The pulverized material thus obtained is pelletized using a pressure molding machine or the like, and then pre-baked at a temperature of 600 to 1200 ° C. You may grind | pulverize without using a pressure molding machine, add water to make a slurry, and granulate using a spray dryer. After calcination, the mixture is further pulverized with a ball mill or a vibration mill, and then water and, if necessary, a dispersant and a binder are added. After adjusting the viscosity, the mixture is granulated with a spray dryer and granulated. When pulverizing after calcination, water may be added and pulverized by a wet ball mill, a wet vibration mill or the like.

  The preliminary firing is not necessarily performed. In the case of non-porous ferrite particles used in general electrophotographic developer carriers, if pre-baked, independent pores are likely to be generated inside without being continuous from the surface, and particles with magnetization and particle density It is not preferable because it is easy to cause variation in the interval.

  However, in the case of the porous ferrite particles used in the present invention, it is characterized by firing at a low temperature in order to obtain a porous property and positively forming pores. Hateful.

  The pulverizer such as the ball mill or the vibration mill is not particularly limited. However, in order to disperse the raw materials effectively and uniformly, it is preferable to use fine beads having a particle diameter of 1 mm or less for the medium to be used. Further, the degree of grinding can be controlled by adjusting the diameter, composition and grinding time of the beads used.

  Then, the obtained granulated material is heated at a temperature of about 400 to 800 ° C. to remove organic components such as added dispersant and binder. If firing is performed with the dispersant and binder remaining, the oxygen concentration in the firing device is likely to fluctuate due to decomposition and oxidation of the organic components, greatly affecting the magnetic properties, making it difficult to produce stably. It is. Moreover, these organic components cause the control of the porosity, that is, the fluctuation of the crystal growth of the ferrite.

  Thereafter, the obtained granulated product is held at a temperature of 800 to 1500 ° C. for 1 to 24 hours in an atmosphere in which the oxygen concentration is controlled to perform main firing. At that time, using a rotary electric furnace, a batch electric furnace or a continuous electric furnace, the atmosphere at the time of firing also introduces an inert gas such as nitrogen or a reducing gas such as hydrogen or carbon monoxide, The oxygen concentration may be controlled.

  The fired product thus obtained is pulverized and classified. 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.

  Then, if necessary, the surface can be heated at a low temperature to perform an oxide film treatment to adjust the electric resistance. The oxide film treatment can be performed by heat treatment at, for example, 300 to 700 ° C. using a general rotary electric furnace, batch electric furnace or the like. The thickness of the oxide film formed by this 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 it is difficult to obtain desired characteristics. Moreover, you may reduce | restore before an oxide film process as needed. In this way, porous ferrite particles having a pore volume and a peak pore diameter in a specific range are prepared.

  As a method for controlling the pore volume, peak pore diameter and pore diameter variation of the porous ferrite particles (ferrite carrier core material) as described above, the raw material type to be blended, the degree of pulverization of the raw material, the presence or absence of calcination, Calcination temperature, calcination time, binder amount during granulation with spray dryer, calcination method, calcination temperature, calcination time, calcination atmosphere (reduction with nitrogen gas, hydrogen gas, carbon monoxide gas, etc., oxidation with oxygen, etc.) It can be done in various ways. These control methods are not particularly limited, but an example is shown below.

  That is, as a raw material species to be blended, the use of hydroxide or carbonate tends to increase the pore volume as compared with the case of using an oxide, and no calcining or calcining is performed. The pore volume tends to be larger when the temperature is lower, or the firing temperature is lower and the firing time is shorter.

  In addition, if the intermediate baking is performed between the main baking and the temporary baking, the pore volume and the peak pore diameter can be changed because the rate of crystal growth changes.

  Furthermore, the pore volume and pore diameter distribution can be changed by changing the heating rate and cooling rate in the main firing. If the heating rate is fast, the pore volume tends to increase, and if the cooling rate is slow, the crystal The pore size distribution tends to be narrow, probably because of uniform growth.

  As for the peak pore diameter, the degree of pulverization of the raw material to be used, particularly the raw material after calcination, is strengthened, and the smaller the primary particle diameter of the pulverization tends to be smaller. Further, it is possible to reduce the peak pore diameter by introducing a reducing gas such as hydrogen or carbon monoxide rather than using an inert gas such as nitrogen during the main firing.

  Furthermore, with regard to the variation in pore diameter, the variation in pore diameter can be reduced by increasing the degree of pulverization of the raw material used, particularly the raw material after calcination, and sharpening the pulverized particle size distribution.

  By using these control methods singly or in combination, porous ferrite particles having a desired pore volume, peak pore diameter, and variation in pore diameter can be obtained.

  The resin-filled ferrite carrier for an electrophotographic developer according to the present invention can be obtained by filling a carrier core material (porous ferrite particles) with a resin. Various methods can be used as the filling method. Examples of the method include a dry method, a spray drying method using a fluidized bed, a rotary drying method, an immersion drying method using a universal stirrer, and the like. The resin used here is as described above.

  In the step of filling the resin, it is preferable to fill the pores of the porous ferrite particles with the resin while mixing and stirring the porous ferrite particles and the filling resin under reduced pressure. By filling the resin under reduced pressure in this way, it is possible to efficiently fill the hole portion with the resin. The degree of decompression is preferably 1.3 to 93 kPa (about 10 to 700 mmHg). If it exceeds 93 kPa (about 700 mmHg), there is no effect of reducing the pressure, and if it is less than 1.3 kPa (about 10 mmHg), the resin solution tends to boil during the filling step, so that efficient filling cannot be performed.

  The step of filling the resin can be performed in a plurality of times, but it is possible to fill the resin in a single filling step. There is no need to divide it multiple times. However, depending on the type of resin, when a large amount of resin is filled at once, particle aggregation may occur. When aggregation occurs, when it is used as a carrier in a developing machine, the aggregation may be released due to agitation stress of the developing device. The interface of the aggregated particles is not preferable because the charging characteristics are greatly different, and charging fluctuation occurs over time. In such a case, the filling can be performed without being excessive or deficient by preventing the agglomeration by filling in a plurality of times.

  After filling the resin, the resin is heated by various methods as necessary, and the filled resin is brought into close contact with the core material. The heating method may be either an external heating method or an internal heating method, and may be, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or a microwave baking. The temperature varies depending on the resin to be filled, but a temperature higher than the melting point or glass transition point is necessary. With a thermosetting resin or a condensation-crosslinking resin, etc., it is resistant to impact by raising the temperature to a point where the curing proceeds sufficiently. A resin-filled carrier can be obtained.

  As described above, it is desirable to coat the surface with a resin after filling the porous ferrite particles with the resin. Carrier characteristics, particularly electrical characteristics such as charging characteristics, are often affected by materials and properties existing on the carrier surface. Therefore, the desired carrier characteristics can be adjusted with high accuracy 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 resin-filled ferrite 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 (colorant), 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 is added to the dried toner particles.

  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. The amount of such a surfactant used affects the dispersion stability of the monomer and also affects the environmental dependency of the obtained polymerized toner particles. It is preferably used in an amount within the above range that is ensured and does not exert an excessive influence on the environment 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 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 fog and toner scattering are liable to occur, 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.

Mn ₃ O ₄ : 102 parts by weight, Mg (OH) ₂ : 183 parts by weight, Fe ₂ O ₃ : 715 parts by weight, SrCO ₃ : 10 parts by weight, respectively, and 400 ppm after firing SiO ₂ for these. An appropriate amount was added so as to obtain a content of, and pulverized in a dry media mill (vibration mill, 1/8 inch diameter stainless steel beads) for 5 hours. Next, the obtained pulverized material was formed into pellets of about 1 mm square using a roller compactor. After removing the coarse powder with a vibrating sieve having a mesh opening of 3 mm and then removing the fine powder with a vibrating sieve having a mesh opening of 0.5 mm, the pellets are heated in a rotary electric furnace at 1050 ° C. for 3 hours and pre-baked. Went. Next, after crushing to an average particle size of about 3 μm using a dry media mill (vibration mill, 1/8 inch diameter stainless steel beads), water was added, and a wet media mill (vertical bead mill, 1/16) was added. Inch stainless steel beads) for 2 hours. In order to add an appropriate amount of a dispersant to this slurry and obtain an appropriate pore volume, 0.4% by weight of PVA (20% solution) as a binder is added to the solid content, and then granulated and dried by a spray dryer. Then, the particle size of the obtained particles (granulated product) was adjusted, and then heated in a rotary electric furnace at 700 ° C. for 2 hours to remove organic components such as a dispersant and a binder.

  Then, it was held for 5 hours in a tunneling electric furnace under a firing temperature of 1150 ° C. and a nitrogen gas atmosphere. At this time, the heating rate was 150 ° C./hour and the cooling rate was 110 ° C./hour. Thereafter, the mixture was crushed, further classified to adjust the particle size, and the low-magnetic force product was separated and removed by magnetic separation to obtain porous ferrite particles (ferrite carrier core material).

In the above composition, in the ferrite composition (MnO) x (MgO) y (Fe ₂ O ₃ ) z, x = 15 mol%, y = 35 mol%, z = 50 mol%, and a part thereof is 0 in SrO. .7% by weight substituted. Further, SiO ₂ content analysis after baking was 428Ppm.

  Next, as a resin filling the voids of the porous ferrite, the phenyl / methyl molar ratio is 0.63, the differential molecular weight curve has peaks at 630 and 2400, the number average molecular weight is 1704, the weight average molecular weight is 5510, A methylphenyl silicone having a Z average molecular weight of 16190 and a number average molecular weight / weight average molecular weight ratio of 3.234 was prepared. An aminosilane coupling agent (γ-aminopropyltrimethoxysilane) was added to 45 parts by weight of this silicone resin solution (9 parts by weight as the solid content because the resin solution concentration was 20% by weight, dilution solvent: toluene) with respect to the resin solid content. 10% by weight was added to obtain a resin solution. Furthermore, 100 parts by weight of the porous ferrite particles described above and the resin solution were mixed and stirred at 60 ° C. under a reduced pressure of 6.7 kPa (about 50 mmHg), and the resin penetrated into the voids of the porous ferrite particles while volatilizing toluene. Filled.

  After returning the inside of the container to normal pressure and confirming that toluene was sufficiently volatilized, the inside of the stirrer was visually observed, and it was in a state of very good fluidity without feeling damp. While continuing, the heating medium temperature of the stirrer was increased to 220 ° C. at a rate of temperature increase of 2 ° C./min. The resin was cured by heating and stirring at this temperature for 2 hours.

  Then, it cooled to room temperature, took out the ferrite particle with which resin was filled and hardened | cured, the aggregation of particle | grains was lifted with the vibration sieve of 200M opening, and the nonmagnetic thing was removed using the magnetic separator. After that, coarse particles were removed again with a vibrating sieve to obtain resin-filled ferrite particles (resin-filled ferrite carrier) filled with resin.

  Next, a silicone resin having a solid content of 20% by weight (product name: SR-2411, manufactured by Toray Dow Corning) was prepared, and 5 parts by weight of the silicone resin (1 part by weight in terms of solid content) and 5 parts by weight of toluene were used. Aminosilane coupling agent (γ-aminopropyltrimethoxysilane) weighed to 10% by weight with respect to the resin solid content was mixed to prepare a resin solution.

  100 parts by weight of the obtained resin-filled ferrite particles were put into a universal mixing stirrer, and the resin solution was further added, and resin coating was performed by immersion drying.

  Thereafter, the temperature was raised to 210 ° C. and stirred for 2 hours to cure the resin. The ferrite particles coated and cured with the resin were taken out, the particles were agglomerated with a 200M mesh vibrating sieve, and the nonmagnetic material was removed using a magnetic separator. Thereafter, coarse particles were removed again with a vibration sieve to obtain a resin-filled ferrite carrier whose surface was coated with a resin.

A resin-filled ferrite carrier whose surface is coated with a resin is obtained in the same manner as in Example 1 except that the basic composition is MnO = 11 mol%, MgO = 40 mol%, and Fe ₂ O ₃ = 49 mol%. It was.

A resin-filled ferrite carrier whose surface is coated with a resin is obtained in the same manner as in Example 1 except that the basic composition is MnO = 25 mol%, MgO = 26 mol%, and Fe ₂ O ₃ = 49 mol%. It was.

  A resin-filled ferrite carrier whose surface was coated with a resin was obtained in the same manner as in Example 1 except that the substitution amount of SrO was 0.3% by weight.

  A resin-filled ferrite carrier whose surface was coated with a resin was obtained in the same manner as in Example 1 except that the substitution amount of SrO was 3.5% by weight.

A resin-filled ferrite carrier whose surface was coated with a resin was obtained in the same manner as in Example 1 except that an appropriate amount of SiO ₂ was added so as to have a content of 2800 ppm after firing. Incidentally, SiO ₂ content analysis after baking was 2781Ppm.

A resin-filled ferrite carrier whose surface was coated with a resin was obtained in the same manner as in Example 1 except that an appropriate amount of SiO ₂ was added so as to have a content of 200 ppm after firing. Incidentally, SiO ₂ content analysis after firing was 214 ppm.

Comparative example

[Comparative Example 1]
As the basic composition, MnO = 37 mol%, MgO = 13 mol%, Fe ₂ O ₃ = 50 mol%, SrO is not added, and SiO ₂ is added in an appropriate amount so as to have a content of 3500 ppm after firing. A resin-filled ferrite carrier whose surface was coated with a resin was obtained in the same manner as in Example 1 except that the main firing temperature was 1100 ° C. The analysis result of the SiO ₂ content after firing was 3423 ppm.

[Comparative Example 2]
The basic composition is MnO = 7 mol%, MgO = 42 mol%, Fe ₂ O ₃ = 50 mol%, the substitution amount of SrO is 4.5% by weight, and SiO ₂ has a content of 150 ppm after firing. A resin-filled ferrite carrier whose surface was coated with a resin was obtained in the same manner as in Comparative Example 1 except that an appropriate amount was added. Incidentally, SiO ₂ content analysis after firing was 153 ppm.

[Comparative Example 3]
A resin-filled ferrite carrier whose surface was coated with a resin was obtained in the same manner as in Comparative Example 2 except that the main firing temperature was 1150 ° C. Incidentally, SiO ₂ content analysis after firing was 162 ppm.

Table 1 shows the basic composition, SrO substitution amount, and SiO ₂ content of the porous ferrite particles (ferrite carrier core materials) of Examples 1 to 7 and Comparative Examples 1 to 3. Table 1 also shows the characteristics (peak pore diameter, dv value, saturation magnetization, residual magnetization, coercive force, pore volume) of the porous ferrite particles of Examples 1 to 7 and Comparative Examples 1 to 3. The method for measuring the characteristics of the porous ferrite particles is as described above.

  Resin filling amount, resin coating amount and carrier properties used in Examples 1 to 7 and Comparative Examples 1 to 3 (saturation magnetization, volume average particle diameter, apparent density, particle density, carrier strength, charge amount, charge after forced stirring Table 2 shows the amount and the charge amount change rate after forced stirring. The measurement methods of carrier strength, charge amount, and forced stirring test are as follows, and the measurement methods of other characteristics are as described above.

[Carrier strength]
20 g of the carrier was placed in a 50 cc glass bottle, and the glass bottle was stirred for 10 hours with a paint shaker. When the carrier particles are cracked, scraped, or fine particles are generated by the stress due to stirring, the average particle size of the carrier after stirring becomes small. As the carrier is weaker, scraping and fine particles are generated and the average particle size becomes smaller. Therefore, the change rate of the average particle size before and after stirring was used as an index of carrier strength. The average particle diameter is the volume average particle diameter measured using the aforementioned Nikkiso Co., Ltd. Microtrac particle size analyzer (Model 9320-X100), and the rate of change in particle diameter and the criteria for determining the strength are as follows.

[Charge amount]
The charge amount was determined by measuring a mixture of carrier and toner with a suction charge amount measuring device (Epping q / m-meter, manufactured by PES-Laboratorium). The toner used is a commercially available negative polarity toner (cyan toner, for DocuPrint C3530 manufactured by Fuji Xerox Co., Ltd .; average particle size of about 5.8 μm) used in a full-color printer, with a developer amount of 10 g and a toner concentration of 10% by weight. It was adjusted. The adjusted developer is put in a 50 cc glass bottle, and the glass bottle is stored and fixed in a cylindrical holder having a diameter of 130 mm and a height of 200 mm, and stirred for 30 minutes with a tumbler mixer manufactured by Shinmaru Enterprise Co., Ltd., 635M The amount of electrification was measured using the net.

[Forced stirring test]
Using the same commercially available negative-polarity toner as the above-mentioned toner (cyan toner, for DocuPrint C3530 manufactured by Fuji Xerox Co., Ltd .; average particle size of about 5.8 μm), the developer amount is adjusted to 20 g, the toner concentration is adjusted to 10 wt%, The glass bottle was stirred for 10 hours with a paint shaker manufactured by Asada Tekko. After the stirring, the developer was taken out, the toner was sucked using a 635M net, and only the carrier was taken out. The charge amount of the obtained carrier was measured by the above-described charge amount measurement method to obtain the charge amount after forced stirring.
Then, the rate of change in charge amount was calculated according to the following formula to obtain charge fluctuation characteristics.

  Based on the measurement results, magnetic characteristics (saturation magnetization), weight reduction (particle density), carrier strength characteristics, and charging characteristics were evaluated. This evaluation was performed in four stages: ◎: Excellent, ○: Good, Δ: Acceptable, ×: Impossible. The results are shown in Table 3.

[Evaluation criteria for magnetic properties (saturation magnetization)]
^◎: 40Am 2 / kg~50Am less than ^{2 / kg ○: 30Am 2 /} kg~40Am less than ² / kg or 50Am ² / kg~55Am less than ^{2 / kg △: 25Am 2 /} kg~30Am 2 / kg or less than 55Am ² / Kg to less than 60 Am ² / kg ×: less than 25 Am ² / kg or 60 Am ² / kg or more

[Evaluation criteria for weight reduction (particle density)]
^◎: less than ^{3.50g / cm 3 ~3.90g / cm 3} ○: 2.80g / cm 3 less than ~3.5g / cm ³ or 3.90g ^/ cm 3 ~4.30g ^/ cm less than ³ △: 2 .50g ^/ cm ³ ~2.80g ^/ cm 3 or less than 4.30g ^/ cm ³ ~4.50g ^/ cm 3 less ×: 2.50g / cm ³ or less than 4.50 g / cm ³ or more

[Evaluation criteria for carrier strength characteristics]
◎: Less than 0.5% ○: 0.5% to less than 1.0% △: 1.0% to less than 5.0% ×: More than 5.0%

[Evaluation criteria for charge fluctuation characteristics]
◎: 95% or more ○: 90% to less than 95% △: 80% to less than 90% ×: less than 80%

  As is clear from Tables 2 and 3, the resin-filled ferrite carriers of Examples 1 to 7 using the porous ferrite particles according to the present invention can realize the magnetization in a desired range, so that they are actually used. Can expect high-definition and high-quality images. In addition, because the desired range of particle density and strength is maintained, the weight can be reduced, and the charge fluctuation after forced stirring is small. It is easily assumed that good image quality without image defects such as fogging, fogging, and carrier adhesion can be stably obtained.

  On the other hand, the resin-filled ferrite carriers shown in Comparative Examples 1 to 3 are inferior in evaluation regarding magnetic properties, weight reduction, carrier strength and charging fluctuation because the composition, blending ratio and silicon content are not in an appropriate range. there were.

  As described above, when the resin-filled ferrite carriers obtained in Comparative Examples 1 to 3 were actually used, not only high image quality was not obtained, but also the carrier strength was weak, so that charging fluctuations occurred over time, It is easily assumed that image defects such as toner scattering, fogging, and carrier adhesion are promoted and good image quality cannot be stably maintained.

  Since the resin-filled ferrite carrier core material and ferrite carrier for an electrophotographic developer according to the present invention are resin-filled, the weight can be reduced with a low specific gravity, so that the durability is excellent and a long life can be achieved. Compared to powder-dispersed carriers, it has higher strength and does not crack, deform or melt due to heat or impact. Further, because of the low magnetization, the magnetic brush is soft and high-quality image quality is obtained. Furthermore, since it has a specific composition, it has a high breaking strength and can prevent fluctuations in charging during printing.

  Therefore, the resin-filled carrier for an electrophotographic developer according to the present invention can be widely used in fields such as a full-color machine requiring high image quality and a high-speed machine requiring image maintenance reliability and durability.

Claims (10)

It consists of porous ferrite particles, the composition of the porous ferrite particles is represented by the following formula (1), and a part of (MnO) (MgO) and / or (Fe ₂ O ₃ ) in the following formula (1) A resin-filled ferrite carrier core material for an electrophotographic developer, which is substituted by 0.3 to 4.0% by weight with SrO and contains ₂₀₀ to 2800 ppm of SiO ₂ in the porous ferrite particles .

The pore volume of the porous ferrite particles is 40 to 160 mm ³ / g, the peak pore diameter is 0.5 to 2.0 μm, and the pore diameter variation dv represented by the following formula (2) in the pore diameter distribution is 1. The resin-filled ferrite carrier core material for an electrophotographic developer according to claim 1, which is 5 or less.

The resin-filled ferrite carrier core material for an electrophotographic developer according to claim 1 or ² , wherein the saturation magnetization of the porous ferrite particles is 40 to 60 Am ² / kg. A resin-filled ferrite carrier for an electrophotographic developer, wherein a resin is filled in the pores of the ferrite carrier core material comprising the porous ferrite particles according to any one of claims 1 to 3 . The resin-filled ferrite carrier for an electrophotographic developer according to claim 4 , wherein the resin is a silicone resin. The amount of resin to be filled in the porous ferrite particles, the porous electrophotographic developer The resin-filled ferrite according to claim 4 or claim 5 6-20 parts by weight with respect to the ferrite particles 100 parts by weight Career. The resin-filled ferrite carrier for an electrophotographic developer according to any one of claims 4 to 6 , wherein the surface is coated with a resin. The volume average particle size is 20 to 70 μm, the saturation magnetization is 30 to 55 Am ² / kg, the particle density is 2.8 to 4.3 g / cm ³ , and the apparent density is 1.0 to 2.2 g / cm ^3. The resin-filled ferrite carrier for an electrophotographic developer according to any one of claims 4 to 7 . An electrophotographic developer comprising the resin-filled ferrite carrier according to any one of claims 4 to 8 and a toner.   The electrophotographic developer according to claim 9, which is used as a replenishment developer.