JP6503645B2 - Carrier for electrostatic image development, developer for electrostatic image development, developer cartridge, process cartridge, and image forming apparatus - Google Patents

Description

  The present invention relates to a carrier for electrostatic charge image development, a developer for electrostatic charge image development, a developer cartridge, a process cartridge, and an image forming apparatus.

  Electrophotographic methods for visualizing image information through electrostatic latent images (electrostatic latent images) are currently used in various fields. In electrophotography, an electrostatic charge image is formed on an image carrier such as a photosensitive member or an electrostatic recording material using various means, and a developer for electrostatic charge image development (hereinafter simply referred to as "electrostatic charge image") is used as the electrostatic charge image. To develop and visualize an electrostatic charge image by attaching electroelectrolytic particles called toner for developing an electrostatic charge image (hereinafter sometimes referred to simply as “toner”) contained in “the developer”. The method is commonly used. The developer used here is a two-component developer that frictionally charges both the holding particles and the toner called a carrier each other to impart an appropriate amount of positive or negative charge to the toner, a magnetic toner, etc. It is roughly divided into one-component developer used by toner alone. In particular, the two-component developer is widely used at present because the carrier itself has functions such as stirring, transport, charging, etc., and the functions required for the developer can be separated, so that the design is easy. ing.

  Carriers are generally classified roughly into resin-coated carriers having a resin coating layer on the surface of magnetic core particles (carrier core particles) and non-coated carriers having no coating layer on the surface. When the developer life and the like are taken into consideration, various types of resin-coated carriers have been developed and put into practical use because resin-coated carriers are superior.

  In recent years, with the reduction in particle size of toner, reduction in particle size has also been studied in carriers, and various studies have been made, such as changing the composition of the carrier core material and the resin composition of the carrier resin coating layer.

In Patent Document 1, in a two-component developer comprising a toner and a carrier, the toner has at least a binder resin and a colorant, and has a median particle diameter (D ₅₀ ) in a specific range, and the carrier Has a resin coating layer in the form of ferrite particles, has a number average particle diameter in a specific range, and has a specific ratio of fluorescent X-ray intensity of iron element to fluorescent X-ray intensity of calcium element by fluorescent X-ray analysis. Two-component developers in the range are described.

  Patent Document 2 discloses a carrier core material for an electrophotographic developing material using soft ferrite containing one or more elements selected from Mn and Mg in iron oxide and further containing a Ca compound, and the carrier core A carrier powder for electrophotographic development is described in which the material is resin coated.

JP, 2006-276354, A JP, 2006-259294, A

  An object of the present invention is a carrier for developing an electrostatic charge image in which image defects caused by a decrease in carrier resistance are suppressed while securing high image quality stably even after long-term image formation under high temperature and high humidity. It is an object of the present invention to provide a developer for developing an electrostatic charge image, a developer cartridge, a process cartridge and an image forming apparatus.

The invention according to claim 1 contains calcium of 0.08% by mass or more and 1.0% by mass or less, and the ratio b / a of the calcium content ratio (b) of the surface part to the internal calcium content ratio (a) is 5 The surface portion after the magnetic core material particle which is the above and the resin coating layer which covers the surface of the magnetic core material particle and which is covered with the resin coating layer to the calcium content ratio (b) An electrostatic charge image in which the ratio c / b of the calcium content ratio (c) is 0.1 or more and 0.5 or less, and the exposure ratio of the magnetic core particles on the surface of the carrier is 4.0% or more and 32% or less It is a carrier for development.

  The invention according to claim 2 is the carrier for developing an electrostatic charge image, wherein the exposure ratio of the magnetic core particles on the surface of the carrier is 5.0% or more and 30% or less.

  In the invention according to claim 3, an average interval Sm of irregularities on the surface of the magnetic core particle is 1.0 μm ≦ Sm ≦ 5.0 μm, and a maximum height Ry of the surface of the magnetic core particle is 0.5 μm. The carrier for developing an electrostatic charge image, wherein Ry ≦ 3.0 μm.

  The invention according to claim 4 is an electrostatic charge image developing developer containing the carrier for electrostatic charge image development and the toner for electrostatic charge image development.

  The invention according to claim 5 is a developer cartridge containing the developer for electrostatic charge image development.

  The invention according to claim 6 is a developing method for containing the developer for electrostatic charge image development and for developing an electrostatic charge image formed on the surface of the image carrier with the developer for electrostatic charge image development to form a toner image A process cartridge which is detachably mounted to the image forming apparatus.

  The invention according to claim 7 is an image carrier, an electrostatic charge image forming means for forming an electrostatic charge image on the surface of the image carrier, and development of the electrostatic charge image using the developer for electrostatic charge image development. An image forming apparatus comprising: developing means for forming a toner image; and transfer means for transferring the developed toner image to a transfer target.

According to the invention of claim 1, the magnetic core particles contain calcium in an amount of 0.08% by mass to 1.0% by mass, and the calcium content ratio in the magnetic core particles (a) The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particle to the core is 5 or more, and further, the carrier surface portion after being coated with the resin coating layer to the calcium content ratio (b) The ratio c / b of the calcium content ratio (c) is 0.1 or more and 0.5 or less, and in addition, the exposure ratio of the magnetic core particles on the surface of the carrier is 4.0% or more and 32% or less An electrostatic charge image in which image defects caused by a decrease in carrier resistance are suppressed while stably maintaining high image quality even after long-term image formation under high temperature and high humidity as compared with the case where it is not A carrier for development is provided.

  According to the invention as set forth in claim 2, compared with the case where the exposure ratio of the magnetic core particles is out of the range of 5.0% or more and 30% or less, even after long-term image formation under high temperature and high humidity. There is provided a carrier for electrostatic image development in which image defects caused by a reduction in carrier resistance are suppressed while stably securing high image quality.

  According to the third aspect of the present invention, the average spacing Sm of the concavities and convexities on the surface of the magnetic core particles is 1.0 μm ≦ Sm ≦ 5.0 μm, and the maximum height Ry of the magnetic particle surface is 0.5 μm ≦ As compared with the case of outside the range of Ry ≦ 3.0 μm, even after long-term image formation under high temperature and high humidity, image defects caused by a decrease in carrier resistance are stably maintained while securing high image quality. A carrier for electrostatic image development to be suppressed is provided.

  According to the invention of claim 4, the magnetic core particles of the carrier contain calcium of 0.05% by mass or more and 1.0% by mass or less, and the calcium content ratio of the inside of the magnetic core particles (a The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particle to the above b) is 5 or more, and the carrier is further coated with a resin coating layer to the calcium content ratio (b) Compared with the case where the ratio c / b of the calcium content ratio (c) of the carrier surface portion later is not 0.1 or more and 0.5 or less, even after long-term image formation under high temperature and high humidity There is provided a developer for electrostatic image development in which image defects caused by a decrease in carrier resistance are suppressed while securing high image quality stably.

  According to the invention of claim 5, the magnetic core particles of the carrier contain calcium of 0.05% by mass or more and 1.0% by mass or less, and the calcium content ratio of the inside of the magnetic core particles (a The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particle to the above b) is 5 or more, and the carrier is further coated with a resin coating layer to the calcium content ratio (b) Compared with the case where the ratio c / b of the calcium content ratio (c) of the carrier surface portion later is not 0.1 or more and 0.5 or less, even after long-term image formation under high temperature and high humidity There is provided a developer cartridge containing a developer for electrostatic image development, which stably suppresses image defects caused by a decrease in carrier resistance while securing high image quality.

  According to the invention of claim 6, the magnetic core particles of the carrier contain calcium of 0.05% by mass or more and 1.0% by mass or less, and the calcium content ratio of the inside of the magnetic core particles (a The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particle to the above b) is 5 or more, and the carrier is further coated with a resin coating layer to the calcium content ratio (b) Compared with the case where the ratio c / b of the calcium content ratio (c) of the carrier surface portion later is not 0.1 or more and 0.5 or less, even after long-term image formation under high temperature and high humidity There is provided a process cartridge containing a developer for electrostatic image development in which image defects caused by a decrease in carrier resistance are suppressed while securing high image quality stably.

  According to the invention of claim 7, the magnetic core particles of the carrier contain calcium of 0.05% by mass or more and 1.0% by mass or less, and the calcium content ratio of the inside of the magnetic core particles ((1) The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particles to a) is 5 or more, and the carrier is further coated with a resin coating layer to the calcium content ratio (b) Compared with the case where the ratio c / b of the calcium content ratio (c) of the carrier surface portion after this is not 0.1 or more and 0.5 or less, even after long-term image formation under high temperature and high humidity There is provided an image forming apparatus in which image defects caused by a decrease in carrier resistance are suppressed while stably securing high image quality.

FIG. 1 is a schematic configuration view showing an example of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a schematic configuration view showing another example of the image forming apparatus according to the embodiment of the present invention. It is a schematic block diagram which shows an example of the process cartridge which concerns on embodiment of this invention.

  Embodiments of the present invention will be described below. The present embodiment is an example for implementing the present invention, and the present invention is not limited to the present embodiment.

<Method for Producing Carrier for Developing Electrostatic Charge Image and Carrier for Developing Electrostatic Charge Image>
With the increase in printing speed by electrophotography and diversification of the use environment, it is desirable for the carrier having a resin coating layer to reduce the change in the chargeability of the carrier and the carrier resistance over a long period of time. If the thickness of the resin coating layer is thick, the chargeability may vary due to the adhesion of additives and the like contained in the toner of the developer, and if the resin coating layer is thinned, the magnetic core particles are exposed and the chargeability fluctuates. The resistance may decrease, and as a result, the printed image may be deteriorated. This phenomenon is noticeable when used under high temperature and high humidity (35 ° C, 85% RH), and the carrier resistance is reduced, especially during image formation after long-term continuous use under high temperature and high humidity. The carrier may contaminate or damage the charging roller, the photosensitive member, the photosensitive member cleaning member and the like, which may cause an image defect.

  As a result of intensive researches, the inventors of the present invention generated dielectric breakdown in the magnetic core particles in the carrier for electrostatic charge image development having the magnetic core particles and the resin coating layer covering the magnetic core particles. Calcium is contained, a large amount of calcium is present on the surface of the magnetic core particle, and the surface of the magnetic core particle in which a large amount of calcium is present is in advance against the surface of the carrier even after being coated with a coating resin. It is found that image defects caused by a decrease in carrier resistance are suppressed while ensuring high image quality stably even after long-term image formation under high temperature and high humidity by exposing at a constant ratio. The Furthermore, they also found that the image deterioration can be improved. This is because calcium which is hard to cause dielectric breakdown is contained in the surface portion of the magnetic core particle, and calcium on the surface of the magnetic core particle is exposed in advance to a part of the surface of the carrier, so that it is longer than the start of use. It is considered that the composition fluctuation of the carrier surface until the time after use decreases, the fluctuation of the carrier resistance is suppressed, and the charge injection due to the reduction of the carrier resistance is prevented. Thus, by maintaining the structure that stably holds the resistance even when the coating resin is worn, stable toner developability over a long period of time can be obtained even in a high temperature and high humidity environment, and a long period of time in a high temperature and high humidity environment It is considered that image defects such as image omission caused by composition fluctuation of the carrier surface are reduced in the image formation of the above.

  The carrier according to the embodiment of the present invention has magnetic core particles and a resin coating layer covering the surface of the magnetic core particles. Further, the magnetic core particles contain calcium of 0.05% by mass or more, and the calcium content ratio in the surface portion of the magnetic core particles is more pronounced than the calcium content ratio in the inside of the magnetic core particles. In the present specification, a mere "carrier" is assumed to have magnetic core particles and a resin coating layer, unless otherwise specified.

  The calcium content of the magnetic core particles is in the range of 0.05% by mass to 1.0% by mass, and preferably in the range of 0.1% by mass to 0.5% by mass. If the content of calcium in the magnetic core particles is less than 0.05% by mass, the effect of providing insulation resistance is small, and if it exceeds 1.0% by mass, the magnetization characteristics and the like are affected.

  The calcium content of the magnetic core particles is determined by dispersing the magnetic core particles in cellulose and molding the same using a fluorescent X-ray analyzer (for example, PRIMUS II (manufactured by RIGAKU CO., LTD.) Etc.) Is measured.

  In the carrier according to the embodiment of the present invention, more calcium is present on the surface portion of the magnetic core particle than the inside of the magnetic core particle, and the magnetic core material to the calcium content ratio (a) inside the magnetic core particle The ratio b / a of the calcium content ratio (b) of the particle surface portion is 5 or more. The upper limit of b / a is not particularly limited. For example, it is also possible to use magnetic core particles in which calcium is not contained inside the magnetic core particles and the a is zero or less than the detection limit. In particular, the b / a is preferably 10 or more and 100 or less. If the b / a is less than 5, the effect of providing insulation resistance to the surface of the magnetic core particle may be reduced, and the stability of the carrier resistance may be impaired.

  The calcium content ratio of the surface part and the inside of the magnetic core particles is measured by an electron beam microanalysis method using an electron beam microanalyzer (for example, EPMA-1610 (manufactured by Shimadzu Corporation) etc.). The surface of the magnetic core particles is analyzed to determine the calcium content ratio b (mass%) in the surface portion. Regarding the calcium content ratio a (mass%) inside the magnetic core particles, after the magnetic core particles are cut with a microtome, the cross section that appears is analyzed to determine the calcium content ratio a (mass%) inside. As a measurement value, a region of 5.0 μmφ on the surface and the inside of the magnetic core particle is measured at 10 points, and the average value is taken. With regard to the carrier having a resin coating layer, it is possible to measure the calcium content ratio of the surface portion or the inside of the magnetic core particles by removing the resin coating layer with a solvent.

  Here, in the present specification, the “surface portion” of the magnetic core particle means a portion up to 5% from the surface with respect to the particle diameter of the magnetic core particle, and the “inside” of the magnetic core particle And refers to a portion other than the portion up to 5% from the surface with respect to the particle diameter of the magnetic core particle.

  The calcium content ratio c of the carrier surface portion is measured by electron beam microanalysis. The surface of the carrier is analyzed using, for example, an electron probe microanalyzer EPMA-1610 to determine the calcium content ratio c (mass%) in the surface portion. The ratio c / b of the content ratio c (mass%) in the surface part of the carrier to the calcium content ratio b (mass%) in the surface part of the magnetic core particles is in the range of 0.1 or more and 0.5 or less More preferably, it is in the range of 0.2 or more and 0.4 or less. If the c / b is less than 0.1, the composition fluctuation during long-term use may increase, and if the c / b exceeds 0.5, the coating amount of the magnetic core particles with the coating resin is It may not be enough.

  In the present specification, the "surface portion" of the carrier refers to a portion up to 5% from the surface with respect to the particle size of the carrier. The calcium content of the carrier surface may be analyzed by the same method as the surface portion of the magnetic core particles. As a measurement value, a region of 0.5 μmφ on the carrier surface is measured at 10 points, and the average value is taken.

  The exposure ratio of the magnetic core particles in the carrier (hereinafter simply referred to as "core material exposure ratio") is the surface of the magnetic core particles in the carrier in which the surface of the magnetic core particles is covered with the resin coating layer. Is the area ratio of the exposed area (area not coated with the resin coating layer) to the total surface area. The core material exposure ratio of the carrier is obtained, for example, by photographing the surface of the carrier using a scanning electron microscope (SEM), and using an image analysis device to judge the exposed part of the magnetic core particle and the coated resin part It is measured by making a measurement.

  The average spacing Sm of irregularities on the surface of the magnetic core particles is preferably in the range of 1.0 μm to 5.0 μm, more preferably in the range of 1.2 μm to 2.5 μm, and 1.5 μm. More preferably, it is in the range of not less than 1.8 μm. When the average spacing Sm of the irregularities is less than 1.0 μm, the penetration of the solution for forming a coating resin layer may be deteriorated, and the adhesion may be reduced. If the average spacing Sm of the irregularities exceeds 5.0 μm, the adhesion may be reduced.

  The maximum height Ry of the irregularities on the surface of the magnetic core particles is preferably in the range of 0.5 μm to 3.0 μm, and more preferably in the range of 0.7 μm to 1.0 μm. When the maximum height Ry of the unevenness is less than 0.5 μm, it may be difficult to expose the core after forming the covering resin layer. When the maximum height Ry of the unevenness exceeds 3.0 μm, the strength of the magnetic core particles may be reduced.

  The average spacing Sm and the maximum height Ry of the unevenness of the surface of the magnetic core particles are measured in accordance with JIS B0601 (1994 version). As a specific measurement method of the average interval Sm and the maximum height Ry, for 50 magnetic particles, the magnification is 3000 times with an ultra-deep color 3D shape measurement microscope (for example, product name VK-9500 (manufactured by Keyence Co., Ltd.)) The surface is observed and measured.

  From the three-dimensional shape of the observed core surface, a roughness curve is obtained from the three-dimensional shape of the observed core surface, and the average value of peak-valley-cycle intervals obtained from the intersection where the roughness curve intersects the average line is obtained. The reference length for obtaining the Sm value is 10 μm, and the cutoff value is 0.08 mm.

  The maximum height Ry is obtained by obtaining a roughness curve and extracting a reference length in the direction of the average line, and the height Yp from the average line of the extracted portion to the highest peak and the depth Yv from the lowest valley bottom The maximum height Ry is obtained by finding the sum (Yp + Yv). The reference length for obtaining the Ry value is 10 μm, and the cutoff value is 0.08 mm.

  In order to measure the calcium content ratio of the surface portion of the carrier and the exposure ratio of the magnetic core particles on the surface of the carrier, the carrier obtained by detaching the toner from the developer for electrostatic charge image development is used as a measurement sample. use. As a more specific toner detachment method, for example, 10 g of a developer is taken in a 100 ml beaker, 50 ml of deionized water and a few drops of surfactant are added, ultrasonic waves are applied, and the carrier is adsorbed with a magnet from the bottom of the beaker. Perform the removal of the supernatant. The above operation is repeated several times to desorb the toner, and after washing several times with deionized water, the carrier can be obtained.

  In addition, for the magnetic core particles, to measure the calcium content, the calcium content ratio of the inner and surface portions, the average spacing Sm of the surface irregularities and the maximum height Ry, as described above, from the developer for electrostatic charge image development From the carrier obtained by desorbing the toner, magnetic core material particles obtained by removing the coating resin layer with a solvent or the like are used. As a more specific method of removing the coating resin layer, for example, a carrier and an appropriate solvent are added to a beaker and ultrasonic waves are applied to dissolve the coating resin, and then the carrier is adsorbed by a magnet from the bottom of the beaker and the supernatant is removed By repeating this, it is possible to obtain magnetic core particles from which the coating resin has been removed.

  The volume average particle diameter of the magnetic core particles is preferably in the range of 15 μm to 100 μm, and more preferably in the range of 15 μm to 50 μm. When the volume average particle diameter is less than 15 μm, the toner may not be held on the developer holding member and may be developed. When the volume average particle diameter exceeds 100 μm, the small particle diameter toner may not be uniformly charged.

  The saturation magnetization of the magnetic core particles is preferably 40 emu / g or more, and more preferably 50 emu / g or more and 75 emu / g or less. When the saturation magnetization of the magnetic core particles is less than 40 emu / g, the developer may be separated from the magnet roll of the developing machine during development to cause an image defect.

  In the present embodiment, the method of producing the magnetic core particles is not particularly limited, but an example of the method of producing the magnetic core particles will be described.

  The magnetic core particles are produced, for example, according to the following general method for producing ferrite core particles. An appropriate amount of each oxide is blended, water is added, and the mixture is pulverized and mixed, for example, for 1 hour or more, preferably 1 hour or more and 20 hours or less by a wet ball mill or a wet vibration mill. The slurry thus obtained is dried and further pulverized, and then calcined at a temperature of, for example, 700 ° C. or more and 1200 ° C. or less. After calcination, the resultant is further pulverized by a wet ball mill or a wet vibration mill to obtain a mixed powder having a particle size of 1 μm or less. The obtained mixed powder is granulated with granulation means, such as a spray dryer, for example, a method of performing main baking by holding at a temperature of 1000 ° C. or more and 1500 ° C. or less for 1 hour or more and 24 hours or less.

  In the present embodiment, the particle diameter of the mixed powder obtained by pulverizing with a mill or the like after temporary firing, and the adjustment of the granulation method and the adjustment of the sintering temperature make it possible to form irregularities on the surface of the magnetic core particles obtained. The average interval Sm and the maximum height Ry are controlled. For example, the average interval Sm can be increased by increasing the particle size of the mixed powder and raising the firing temperature to advance the sintering of the surface of the magnetic core particles, and the particle size of the mixed powder can be increased. By suppressing the temperature, the maximum height Ry can be increased.

  In the present embodiment, in the above granulation, a resin particle dispersion containing a binder resin is prepared by emulsion polymerization or another method, and is hetero-aggregated with the dispersion of the raw material composition of the magnetic core particles, and then fused. It may carry out by the emulsion polymerization aggregation method to unite.

  As the raw material of the magnetic core particles, conventionally known ones may be used, but ferrite and magnetite are preferably selected. For example, iron powder is known as another raw material. In the case of iron powder, since the specific gravity is large and the toner is easily deteriorated, ferrite and magnetite are more stable. As an example of the ferrite which is a raw material composition of magnetic core material particles, ferrite generally represented by the following formula is mentioned.

(MO) _X (Fe ₂ O ₃ ) _Y
(Wherein, M contains at least one selected from Cu, Zn, Fe, Mg, Mn, Li, Ti, Ni, Sn, Sr, Si, Al, Ba, Co, Mo, Ca, etc. X and Y show mass mol ratios, and satisfy the condition X + Y = 100).

  M needs to contain Ca. M includes one or more selected from Li, Mg, Mn, Sr and Sn in addition to Ca, and is a component other than Fe, Ca, Li, Mg, Mn, Sr, Sn and oxygen atom Ferrite particles having a content of 1% by mass or less are preferable as magnetic core particles. By adding Cu, Zn and Ni elements, magnetic core particles tend to have low resistance, charge leakage tends to occur, resin coating tends to be difficult, and environmental dependence tends to deteriorate. . Furthermore, since Cu, Zn and Ni are heavy metals, the stress given to the carrier becomes strong, which may adversely affect the service life. From the viewpoint of safety, ferrites to which Mn element or Mg element has been added are generally widely used in recent years.

  In the present embodiment, the magnetic core particles contain calcium in an amount of 0.05% by mass or more and 1.0% by mass or less. The presence of calcium in the magnetic core particles results in high resistance compared to the case where they do not exist, and charge injection hardly occurs.

  Although there is no restriction | limiting in particular as a method of making a magnetic core material particle contain calcium, For example, the method of making a raw material composition of a magnetic core particle particle contain calcium compounds (calcium inorganic salts, such as calcium oxide and calcium carbonate, etc.) Etc. When a calcium compound is added to the raw material composition of the magnetic core particle and sintered, the calcium compound is mixed with another oxide to obtain, for example, a ferrite represented by the above formula. The composition may then be sintered. In this case, for example, the ferrite composition containing calcium as a composition is coated on the surface of the magnetic core particles and then sintered, whereby the calcium content in the surface portion of the magnetic core particles is reduced to the magnetic core material Magnetic core particles are produced which are higher than the calcium content inside the particles.

  Furthermore, calcium carbonate particles are further dispersed in a solution in which resin is dispersed in a solvent of magnetic core particles, etc., and the obtained dispersion is applied on the surface of magnetic core particles, and then the solvent is removed by a kneader coater or the like. After decarburization baking (for example, 500 ° C. or more and 800 ° C. or less), baking may be performed again. By this method, the calcium content in the surface portion of the magnetic core particle is higher than the calcium content in the magnetic core particle. In addition, calcium on the surface portion of the magnetic core particles tends to sinter and appear in the convex portions of the sintered block convex and concave portions on the surface of the magnetic core particles.

  In these methods of producing magnetic core particles, the particle size distribution of the magnetic core particles may be narrow. In the production of the magnetic core particles, the sintered particles may be crushed if necessary, and particle size adjustment such as sieving or classification may be performed.

  In the present embodiment, the coating resin is used by coating on the surface of the magnetic core particles.

  As a typical method of coating and forming a coating resin on the surface of magnetic core particles, a coating resin and conductive particles are charged into a resin-soluble solvent to form a solution for forming a resin coating layer. An immersion method in which the powder is immersed in a solution for forming a resin coating layer, a spray method in which a solution for forming a resin coating layer is sprayed on the surface of the magnetic core particles, a resin coating layer in a state where the magnetic core particles are suspended by flowing air. Examples thereof include a fluidized bed method of spraying a forming solution, a kneader coater method of mixing magnetic core particles and a solution for forming a resin coating layer in a kneader, and then removing a solvent. It is preferable that the magnetic core particles and the solution for forming a resin coating layer are mixed in a kneader coater, and then manufactured by a kneader coater method in which the solvent is removed.

  The magnetic core particles include resin particles in which magnetic metals, magnetic oxides, or magnetic particles are internally dispersed. However, since these are hydrophilic and the chargeability may decrease under high humidity, the environmental change of the chargeability is large. Moreover, since these are high surface energy materials, they are easily contaminated with toner components, and the maintainability of the chargeability may be poor. Coating the surface of the carrier with a resin that is hydrophobic or low surface energy ameliorates the aforementioned problems with charging. On the other hand, when the surface of the magnetic core particles is coated with a high coverage ratio by the insulating resin, the electrical resistance as a carrier may increase, and the reproducibility of the solid image may be deteriorated. In this case, the conductive particles may be dispersed in the resin coating layer in order to avoid an increase in the electrical resistance.

  In addition, the resin coating layer may contain a wax. Waxes are hydrophobic and relatively soft even at room temperature and have low membrane strength. This is derived from the molecular structure of the wax, but if a wax is present in the resin coating layer due to this characteristic, toner components such as particles of external additives added to the toner surface or toner bulk components adhere to the carrier surface It is difficult to do. Also, even if it adheres, the wax on the attached portion is exfoliated at the molecular level, so that the surface is renewed and the carrier surface is less likely to be attached and contaminated.

  Usually, in the case of production by the kneader coater method, resin core layer particles and a solution for forming a resin coating layer in which conductive particles and the like are dispersed are mixed and heated and depressurized while stirring to remove the solvent, thereby removing resin coating. A layer is formed.

  As a coating resin (matrix resin) used for the resin coating layer, polyethylene, polypropylene, polystyrene, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone, vinyl chloride- Vinyl acetate copolymer, styrene-acrylic acid copolymer, straight silicone resin containing organosiloxane bond or its modified product, fluorocarbon resin, polyester, polyurethane, polycarbonate, phenol resin, amino resin, melamine resin, benzoguanamine resin, urea resin Although an amide resin, an epoxy resin, etc. are mentioned, it is not limited to these. Particularly preferred are polystyrene resins, acrylic resins, and styrene acrylic copolymers. When these resins are used, the strength of the resin coating film is high, and the conductive material and the charge control agent are well dispersed in the resin.

  The wax to be contained in the coating resin layer is not particularly limited. For example, paraffin wax and its derivative, montan wax and its derivative, microcrystalline wax and its derivative, Fischer-Tropsch wax and its derivative, polyolefin wax and its derivative, etc. Can be mentioned. The derivatives include the oxides, polymers with vinyl monomers, graft modified products and the like. Besides, alcohols, fatty acids, vegetable waxes, animal waxes, mineral waxes, ester waxes, acid amides and the like may be used. Also, other known ones may be used. The melting point of the wax is preferably in the range of 60 ° C. or more and 200 ° C. or less, and more preferably in the range of 80 ° C. or more and 150 ° C. or less. When the melting point of the wax is less than 60 ° C., the flowability as a carrier may be deteriorated.

  The resin coating layer may contain a charge control agent. Examples of charge control agents include nigrosine dyes, benzimidazole compounds, quaternary ammonium salt compounds, alkoxylated amines, alkylamides, molybdate chelate pigments, triphenylmethane compounds, salicylic acid metal salt complexes, azo chromium complexes, copper Although a phthalocyanine etc. are mentioned, you may contain any well-known charge control agent. Particularly preferred are quaternary ammonium salt compounds, alkoxylated amines and alkylamides. These charge control agents are easy to control the dispersion state and have good adhesion to the coating resin interface, so that the release of the charge control agent from the resin coating film is suppressed. In addition, the charge control agent acts as a dispersion aid for the conductive material, the dispersed state of the conductive material in the resin coating layer is substantially uniformed, and the change in carrier resistance is suppressed even if some resin coating layer is peeled off. The reason is that the conductive material to be described later is easily oxidized on the surface and easily affected by moisture, so it has a high hydrophilicity and is a structure that is easily aggregated by water on the particle surface or the like. Therefore, when the conductive material is dispersed in the coating resin, since the polarity of the coating resin is generally low, the aforementioned aggregation remains as it is, so that the conductive material tends to be unevenly distributed inside the coating resin. On the other hand, the above-mentioned charge control agent has good adhesion to the coating resin interface and also has high polarity to a certain extent, thus improving the adhesion to the conductive material, thereby improving the dispersibility of the conductive material. Presumed.

  The content of the charge control agent in the resin coating layer is preferably 0.001 parts by mass to 5 parts by mass, and more preferably 0.01 parts by mass or more, when the mass of the magnetic core particles is 100 parts by mass. The range of 0.5 parts by mass or less is more preferable. When the content of the charge control agent exceeds 5 parts by mass, the strength of the resin coating layer may be reduced, and the carrier may be denatured due to the stress during use, and when it is less than 0.001 part by mass, the charge control agent Not only may the function not be exhibited, but the dispersibility of the conductive material may not be improved.

  Examples of the conductive material include metals such as gold, silver and copper, titanium oxide, zinc oxide, barium sulfate, aluminum borate, potassium titanate, tin oxide, carbon black and the like, and carbon black is particularly preferred. It is preferable in terms of dispersibility in resin and resistance control. However, it is not limited to these. The content of the conductive material in the resin coating layer is preferably in the range of 1 part by mass to 50 parts by mass with respect to 100 parts by mass of the covering resin in order to make the carrier volume specific resistance a desired characteristic, and 3 parts by mass or more The range of 20 parts by mass or less is more preferable.

  The solvent used to prepare the solution for forming a resin coating layer is not particularly limited as long as it dissolves the coating resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene, acetone, methyl ethyl ketone and the like. Ketones, ethers such as tetrahydrofuran and dioxane, and halides such as chloroform and carbon tetrachloride may be used.

  In the present embodiment, the exposure ratio of the magnetic core particles of the carrier after coating is preferably 5.0% or more and 30% or less, and more preferably 10% or more and 20% or less. If it is less than 5.0%, the surface composition fluctuation of the carrier may become large when the coating resin is worn out after long-term use, and if it exceeds 30%, the toner may be charged because the amount of the coating resin is small. It may not be possible.

  The average film thickness of the resin coating layer is preferably in the range of usually 0.1 μm to 10 μm. In the present embodiment, the maximum height Ry of the unevenness of the surface of the magnetic core particle is preferably in the range of 0.5 μm to 3.0 μm, and is in the range of 0.4 μm to 2.8 μm. More preferably, the exposure ratio of the magnetic core particles is preferably in the range of 5.0% to 30% and more preferably in the range of 10% to 20%. The film thickness is more preferably in the range of 0.3 μm to 3 μm, and still more preferably in the range of 0.4 μm to 2.8 μm.

The volume specific resistance value of the carrier in this embodiment is 10 ⁶ Ω · cm or more and 10 ¹⁴ Ω · cm in the case of 1,000 V corresponding to the upper and lower limits of the normal development contrast potential in order to achieve high image quality. The following range is preferable, and a range of 10 ⁸ Ω · cm to 10 ¹³ Ω · cm is more preferable. If the volume specific resistance value of the carrier is less than 10 ⁶ Ω · cm, the reproducibility of the thin line may be poor, and the amount of carrier transferred to the photoreceptor (image carrier) may be increased, which may easily damage the photoreceptor. . On the other hand, when the volume specific resistance value of the carrier exceeds 10 ¹⁴ Ω · cm, the reproducibility of black solid and halftone may be deteriorated.

<Developer for electrostatic image development>
The developer for electrostatic charge image development (developer) according to the present embodiment contains the carrier for electrostatic charge image development (carrier) according to the present embodiment and a toner for electrostatic charge image development (toner). The developer according to the present embodiment is prepared by mixing the carrier according to the present embodiment and the toner according to an appropriate mixing ratio. The carrier content ((carrier) / (carrier + toner) × 100) is preferably in the range of 85% by mass to 99% by mass, more preferably in the range of 87% by mass to 98% by mass, 89% by mass or more The range of 97 mass% or less is more preferable.

  Hereinafter, the toner used for the developer for electrostatic charge image development concerning this embodiment is explained.

  The toner used in the present embodiment contains at least a binder resin and a colorant, and optionally contains a releasing agent and other components. In addition to the toner particles having the above-described configuration, an external additive (hereinafter, may be simply referred to as an “external additive”) may be added to the toner used in the present embodiment for various purposes. .

  For the toner used in the present embodiment, a known binder resin, various colorants, and the like may be used. As the binder resin in the toner used in the present embodiment, in addition to polyester resin, polyolefin resin, copolymer of styrene and acrylic acid or methacrylic acid, polyvinyl chloride, phenol resin, acrylic resin, methacrylic resin, poly Even if vinyl acetate, silicone resin, modified polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumarone indene resin, petroleum resin, polyether polyol resin, etc. are used alone You may use it together.

  As a coloring agent in the toner used in the present embodiment, for example, C.I. I. Pigment blue 1, 2, 3, 4, 5, 5, 6, 7, 7, 10, 11, 12, 13, 14, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17, 23, 23, 60, 65, 73, 83, 180, C.I. I. Battian 1, 3, 20, etc., bitumen, cobalt blue, alkali blue lake, phthalocyanine blue, non-metal phthalocyanine blue, partially chlorinated phthalocyanine blue, cyan pigments of fast sky blue, indaslen blue BC, C.I. I. Alternatively, cyan dyes such as solvent cyan 79 and 162 may be used.

  As a magenta colorant, for example, C.I. I. Pigment red 1, 2, 3, 4, 5, 5, 6, 7, 8, 9, 10, 11, 12, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 41, 48, 49, 50, 51, 52, 53, 54, 55, 57, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90 112, 114, 122, 123, 163, 184, 202, 206, 207, 209, etc., magenta pigments of pigment violet 19, C.I. I. Solvent Red 1, 3, 8, 23, 23, 24, 25, 30, 30, 49, 81, 82, 83, 84, 100, 109, 121, C . I. Disperse thread 9, C.I. I. Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 18. 22, 23, 24, 27, 29, 32, 32, 34, and so on. Magenta dyes such as 35, 36, 37, 38, 39, 40, etc., etc., bengara, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, resole red, pyrazolone red, watching red, calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rotamine Lake B, Alizarin Lake, Brilliant Carmine 3 B, etc. may be used.

  As a yellow colorant, for example, C.I. I. Pigment Yellow 2, 3, 15, 16, 17, 17, 97, 180, 185, 139, etc. may be used.

  Furthermore, in the case of a black toner, for example, carbon black, activated carbon, titanium black, magnetic powder, nonmagnetic powder containing Mn, etc. may be used.

  Also, the toner used in the present embodiment may contain a charge control agent, and may be nigrosine, quaternary ammonium salt, organic metal complex, chelate complex, or the like.

Furthermore, in the present embodiment, various resin powders or inorganic compounds may be added as external additives to the surface of the toner particles as a surface modifier. As the resin powder, spherical particles of polymethyl methacrylate resin (PMMA), nylon, melamine, benzoguanamine, fluorine resin and the like can be used. Various known inorganic compounds include, for example, SiO ₂ , TiO ₂ , Al ₂ O ₃ , MgO, CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , BaO, CaO, K ₂ O, Na ₂ O And ZrO ₂ , CaO · SiO ₂ , CaCO ₃ , K ₂ O (TiO ₂ ) _n , MgCO ₃ , Al ₂ O ₃ · ₂ SiO ₂ , BaSO ₄ , MgSO _{4 and the} like, preferably SiO ₂ , Although TiO ₂ and Al ₂ O ₃ may be mentioned, they are not limited to these, and one or two or more of these may be used in combination. The volume average particle diameter of the external additive is preferably 0.1 μm or less, and the addition amount of the external additive is, for example, 0.1% by mass or more and 20% by mass or less with respect to 100% by mass of toner particles. Range.

  In the present embodiment, the external additive is desirable for obtaining stable printing quality over a long period of time, but causes the carrier surface to be buried, deformed, or polished, and in particular, particles having a volume average particle diameter of 50 nm to 200 nm. When there is a large effect. In the present embodiment, when the toner for developing an electrostatic charge image having external additive particles having a volume average particle diameter of 50 nm to 200 nm is used, the effect of suppressing the burying, deformation, and polishing of the surface of the carrier of large.

  Furthermore, the toner used in the present embodiment preferably contains a release agent. As the mold release agent, ester wax, polyethylene, polypropylene or a copolymer of polyethylene and polypropylene, polyglycerin wax, microcrystalline wax, paraffin wax, carnauba wax, sasol wax, montanic acid ester wax, deacidified carnauba wax, etc. Polymers and waxes; unsaturated fatty acids such as palmitic acid, stearic acid, montanic acid, branzinic acid, eleostearic acid, valinaric acid; stearin alcohol, aralkyl alcohol, behenyl alcohol, carnauvir alcohol, Or saturated alcohols such as long chain alkyl alcohols having a long chain alkyl group; polyhydric alcohols such as sorbitol; linoleic acid amide, Fatty acid amides such as inic acid amide and lauric acid amide; Saturated fatty acid bisamides such as methylene bis stearic acid amide, ethylene bis capric acid amide, ethylene bis lauric acid amide, hexamethylene bis stearic acid amide, ethylene bis oleic acid amide, Unsaturated fatty acid amides such as hexamethylene bis oleic acid amide, N, N'-dioleyl adipic acid amide, N, N'-dioleyl sebacic acid amide; m-xylene bis-stearic acid amide, N, N 'di-amide Aromatic bisamides such as stearyl isophthalic acid amide; fatty acid metal salts such as calcium stearate, calcium laurate, zinc stearate, magnesium stearate etc. (generally referred to as metal soaps); aliphatic hydrocarbon waxes such as styrene Acrylic acid Waxes grafted with a vinyl monomer of the following; partially esterified fatty acid and polyhydric alcohol such as behenic acid monoglyceride; methyl ester compounds having a hydroxyl group obtained by hydrogenation of vegetable oil and the like .

  In the present embodiment, the method for producing the toner (toner particles) is not particularly limited, but in order to obtain high image quality, it is preferable to be produced by a wet production method. As a wet manufacturing method, the binder resin dispersion obtained by emulsion polymerization of the polymerizable monomer of the binder resin is mixed with a dispersion of a coloring agent, a releasing agent, and, if necessary, a charge control agent. Emulsion aggregation method to obtain toner particles; aqueous solution of polymerizable monomer for obtaining binder resin, coloring agent, releasing agent, charge control agent etc. as needed Suspension polymerization method for suspending and polymerizing in water; dissolution suspension method for suspending and granulating a solution such as a binder resin, a colorant, a mold release agent, and, if necessary, a charge control agent in an aqueous solvent; Can be mentioned. Alternatively, the toner particles obtained by the above method may be used as a core, and resin particles may be attached and heat fused to give a core-shell structure. In addition, toner particles obtained by a general pulverization classification method may be used.

<Image Forming Apparatus, Image Forming Method, and Process Cartridge>
The image forming apparatus according to the present embodiment includes an image carrier, an electrostatic charge image forming unit that forms an electrostatic charge image on the surface of the image carrier, and a development for developing an electrostatic charge image according to the present embodiment. And developing means for developing the toner image to form a toner image, and transferring means for transferring the developed toner image to a transfer target (recording medium). The image forming apparatus according to the present embodiment may charge the surface of the image carrier, fix the toner image on the recording medium, and clean the surface of the image carrier as necessary. A means etc. may be included.

  In the image forming apparatus, for example, a portion including the developing unit may have a cartridge structure (process cartridge) which can be detached from the image forming apparatus main body. The process cartridge contains the developer for electrostatic charge image development according to the present embodiment, and the electrostatic charge image formed on the surface of the image carrier is developed with the developer for electrostatic charge image development to form a toner image. Preferably, a process cartridge provided with a developing unit to be mounted on and removed from the image forming apparatus is used. As a result, the developer for electrostatic charge image development can be easily handled, and the adaptability to various configurations of the image forming apparatus can be enhanced.

  An image forming apparatus according to the present embodiment charges the surface of the image carrier, an electrostatic charge image forming process for forming an electrostatic charge image on the surface of the image carrier, and the electrostatic charge image according to the present embodiment. A developing step of developing with a developer for electrostatic charge image development to form a toner image, a transferring step of transferring the toner image to a recording medium, and a fixing step of fixing the toner image on the recording medium An image forming method according to an embodiment is implemented.

  Hereinafter, although an example of the image forming apparatus according to the present embodiment is shown, the present invention is not limited to this.

  FIG. 1 is a schematic configuration view showing an example of an image forming apparatus according to the present embodiment. The image forming apparatus 301 includes a charging unit 310, an exposure unit 312, an electrophotographic photosensitive member 314 as an image carrier, a developing unit 316, a transfer unit 318, a cleaning unit 320, and a fixing unit 322.

  In the image forming apparatus 301, around the electrophotographic photosensitive member 314, the charging unit 310, which is a charging unit that charges the surface of the electrophotographic photosensitive member 314, and the charged electrophotographic photosensitive member 314 are exposed to light according to the image information. Exposure unit 312, which is an electrostatic charge image forming unit that forms an electrostatic charge image, a developing unit 316, which is a development unit that develops an electrostatic charge image with a developer to form a toner image, The transfer unit 318, which is a transfer unit that transfers the toner image formed on the surface of the recording medium 324 to the surface of the recording medium 324, removes foreign matter such as toner remaining on the surface of the electrophotographic photosensitive member 314 after transfer. The cleaning unit 320, which is an image carrier cleaning unit that cleans the surface of the image forming apparatus, is disposed in this order. Further, a fixing unit 322, which is a fixing unit for fixing the toner image transferred to the recording medium 324, is disposed to the side of the transfer unit 318.

  The operation of the image forming apparatus 301 according to the present embodiment will be described. First, the surface of the electrophotographic photosensitive member 314, which is an image carrier, is charged by the charging unit 310 (charging step). Next, light is applied to the surface of the electrophotographic photosensitive member 314 by the exposure unit 312, the charge in the portion to which the light is applied is removed, and an electrostatic charge image is formed according to the image information (electrostatic charge image formation Process). Thereafter, the electrostatic charge image is developed by the developing unit 316, and a toner image is formed on the surface of the electrophotographic photosensitive member 314 (developing step). For example, in the case of a digital electrophotographic copying machine using an organic photosensitive member as the electrophotographic photosensitive member 314 and a laser beam as the exposing unit 312, the surface of the electrophotographic photosensitive member 314 is negatively charged by the charging unit 310. Then, a digital electrostatic charge image is formed in a dot shape by the laser beam light, and a toner is applied to the portion hit by the laser beam light at the developing portion 316 to be visualized. In this case, a negative bias is applied to the developing unit 316. Next, a recording medium 324 such as a sheet of paper is superimposed on the toner image at the transfer unit 318, and a charge of the opposite polarity to the toner is applied to the recording medium 324 from the back side of the recording medium 324. Transfer to 324 (transfer step). The transferred toner image is subjected to heat and pressure by the fixing member in the fixing unit 322, and is fused and fixed to the recording medium 324 (fixing step). On the other hand, foreign matter such as toner remaining on the surface of the electrophotographic photosensitive member 314 without being transferred is removed by the cleaning unit 320 (cleaning step). One cycle ends in a series of processes from charging to cleaning. Although the toner image is directly transferred to the recording medium 324 such as a sheet of paper at the transfer unit 318 in FIG. 1, the toner image may be transferred via a transfer body such as an intermediate transfer body.

  Hereinafter, the charging unit, the image carrier, the electrostatic charge image forming unit (exposure unit), the developing unit, the transfer unit, the image carrier cleaning unit, and the fixing unit in the image forming apparatus 301 of FIG. 1 will be described.

(Charging means)
For example, a charger such as corotron shown in FIG. 1 is used as the charging unit 310, which is a charging unit, but a conductive or semiconductive charging roll may be used. A contact type charger using a conductive or semiconductive charging roll may apply a direct current or an alternating current to the electrophotographic photosensitive member 314 in an overlapping manner. For example, the surface of the electrophotographic photosensitive member 314 is charged by generating a discharge in a minute space in the vicinity of the contact portion with the electrophotographic photosensitive member 314 by the charging unit 310. In addition, normally, it is charged to -1000V or more and -300V or less. The conductive or semiconductive charging roll may have a single layer structure or a multiple structure. In addition, a mechanism for cleaning the surface of the charging roll may be provided.

(Image holder)
The image carrier has a function of forming at least an electrostatic charge image (latent image). As an image carrier, an electrophotographic photosensitive member is suitably mentioned. The electrophotographic photosensitive member 314 has a coating film including an organic photosensitive member and the like on the outer peripheral surface of a cylindrical conductive substrate. The coating film is formed by forming a photosensitive layer including a subbing layer, if necessary, a charge generating layer containing a charge generating substance, and a charge transporting layer containing a charge transporting substance in this order on a substrate. is there. The stacking order of the charge generation layer and the charge transport layer may be reversed. These are laminated type photoreceptors in which a charge generation material and a charge transport material are contained in separate layers (charge generation layer, charge transport layer) and laminated, but the charge generation material and the charge transport material are the same. The photosensitive layer may be a single layer type photosensitive member contained in the layer of (1), and preferably a laminated type photosensitive member. In addition, an intermediate layer may be provided between the undercoat layer and the photosensitive layer. In addition to the organic photosensitive member, other types of photosensitive layers such as an amorphous silicon photosensitive film may be used.

(Electrostatic charge image forming means)
The exposure unit 312, which is an electrostatic charge image forming unit (exposure unit), is not particularly limited. For example, a light source such as semiconductor laser light, LED (Light Emitting Diode) light, or liquid crystal shutter light may be provided on the surface of the image carrier. The optical system apparatus etc. which expose in a desired image-like are mentioned.

(Developing means)
The developing unit 316, which is a developing unit, has a function of developing the electrostatic charge image formed on the image carrier with a developer containing toner to form a toner image. The developing device is not particularly limited as long as it has the above-described function, and may be selected according to the purpose. For example, a toner for developing an electrostatic charge image may be a brush, a roller, etc. Known developing devices having the function of adhering to Although a DC voltage is usually used for the electrophotographic photosensitive member 314, an AC voltage may be further superimposed and used.

(Transfer means)
As a transfer unit 318 which is a transfer unit, for example, a unit that applies an electric charge of reverse polarity to the toner to the recording medium 324 from the back side of the recording medium 324 shown in FIG. 1 and transfers the toner image to the recording medium 324 by electrostatic force. Alternatively, a transfer roll and a transfer roll pressing device using a conductive or semiconductive roll or the like which transfers directly in contact with the recording medium 324 may be used. A direct current may be applied to the transfer roll as a transfer current to be applied to the image carrier, or an alternating current may be superimposed and applied. The transfer roll may be appropriately set according to the image area width to be charged, the shape of the transfer charger, the opening width, the process speed (peripheral speed) and the like. In addition, a single-layer foam roll or the like is suitably used as the transfer roll for cost reduction. The transfer method may be a method of directly transferring to a recording medium 324 such as paper, or a method of transferring to a recording medium 324 via an intermediate transfer member.

  A well-known intermediate transfer body may be used as the intermediate transfer body. Materials used for the intermediate transfer member include polycarbonate resin (PC), polyvinylidene fluoride (PVDF), polyalkylene phthalate, thermosetting polyimide resin; and PC / polyalkylene terephthalate (PAT), ethylene tetrafluoroethylene copolymer Examples thereof include blend materials such as (ETFE) / PC and ETFE / PAT, but an intermediate transfer belt using a thermosetting polyimide resin is preferable from the viewpoint of mechanical strength.

(Image holder cleaning means)
If the cleaning unit 320, which is an image carrier cleaning unit, cleans foreign substances such as residual toner on the image carrier, a blade cleaning method, a brush cleaning method, a roll cleaning method or the like may be selected. Just do it.

(Fixing means)
The fixing unit 322, which is a fixing unit (image fixing device), fixes the toner image transferred to the recording medium 324 by heating, pressing, or heating and pressing, and includes a fixing member.

(recoding media)
Examples of the recording medium 324 on which the toner image is transferred include plain paper, an OHP sheet, and the like used in an electrophotographic copying machine or printer. In order to further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording medium is also smooth. For example, coated paper obtained by coating the surface of plain paper with a resin or the like, art paper for printing, etc. You may

  Further, by combining with the trickle development proposed in Japanese Examined Patent Publication No. 2-21591, stable image formation can be achieved in a longer period of time.

  FIG. 2 is a schematic configuration view showing a quadruple tandem type color image forming apparatus as another example of the image forming apparatus according to the present embodiment. The image forming apparatus shown in FIG. 2 outputs an image of each color of yellow (Y), magenta (M), cyan (C) and black (K) based on color separated image data. The fourth image forming units 10Y, 10M, 10C, and 10K (image forming means) are provided. These image forming units (which may be simply referred to as "units" hereinafter) 10Y, 10M, 10C, and 10K are arranged side by side at a predetermined distance from each other in the horizontal direction. The units 10Y, 10M, 10C, and 10K may be process cartridges detachable from the image forming apparatus main body.

  Above the respective units 10Y, 10M, 10C, and 10K in the drawing, an intermediate transfer belt 20 as an intermediate transfer member is extended through the respective units. The intermediate transfer belt 20 is provided by winding the inner surface of the intermediate transfer belt 20 so that the inner surface of the intermediate transfer belt 20 is in contact with the drive roller 22 and the support roller 24 arranged at a distance from each other in the left direction. The vehicle travels in the direction from 10Y to the fourth unit 10K. A force is applied to the support roller 24 in a direction away from the drive roller 22 by a spring or the like (not shown), and a tension is applied to the intermediate transfer belt 20 wound around both. Further, an intermediate transfer member cleaning device 30 is provided on the side of the image carrier of the intermediate transfer belt 20 so as to face the drive roller 22. Further, yellow, magenta, cyan and black contained in toner cartridges 8Y, 8M, 8C and 8K are respectively provided in developing devices (developing means) 4Y, 4M, 4C and 4K of the respective units 10Y, 10M, 10C and 10K. The four color toners are supplied.

  Since the first to fourth units 10Y, 10M, 10C, and 10K described above have the same configuration, here, the first to form a yellow image disposed on the upstream side in the traveling direction of the intermediate transfer belt The unit 10Y will be described as a representative. The second to fourth reference numerals are attached to portions equivalent to the first unit 10Y by substituting magenta (M), cyan (C), and black (K) instead of yellow (Y). Description of the units 10M, 10C, and 10K is omitted.

  The first unit 10Y has a photoreceptor 1Y acting as an image carrier. Around the photosensitive member 1Y, the electrostatic roller is exposed by the charging roller 2Y that charges the surface of the photosensitive member 1Y to a predetermined potential and the laser beam 3Y based on the color-separated image signal. An exposure device (electrostatic charge image forming means) 3 to be formed, a development device (development means) 4 Y for developing an electrostatic charge image by supplying toner charged to the electrostatic charge image, transfer the developed toner image onto the intermediate transfer belt 20 A primary transfer roller 5Y (primary transfer means) and a photoreceptor cleaning device (cleaning means) 6Y for removing toner remaining on the surface of the photoreceptor 1Y after primary transfer are sequentially disposed.

  The primary transfer roller 5Y is disposed on the inner side of the intermediate transfer belt 20, and is provided at a position facing the photosensitive member 1Y. Further, a bias power supply (not shown) for applying a primary transfer bias is connected to each primary transfer roller 5Y (5M, 5C, 5K). Each bias power supply varies the transfer bias applied to each primary transfer roller under control of a control unit (not shown).

Hereinafter, an operation of forming a yellow image in the first unit 10Y will be described. First, prior to the operation, the surface of the photosensitive member 1Y is charged to a potential of about -800 V or more and -600 V or less by the charging roller 2Y. The photoreceptor 1 </ ^b > Y is formed by laminating a photosensitive layer on a conductive (for example, having a volume resistivity at 20 ° C. of 1 × 10 ⁻⁶ Ωcm or less). This photosensitive layer usually has high resistance (having a resistivity similar to that of a general resin), but has the property that the specific resistance of the portion irradiated with the laser beam changes when the laser beam 3Y is irradiated. ing. Therefore, the laser beam 3Y is output to the charged surface of the photosensitive member 1Y through the exposure device 3 in accordance with the yellow image data sent from the control unit (not shown). The laser beam 3Y is applied to the photosensitive layer on the surface of the photoreceptor 1Y, whereby an electrostatic charge image of a yellow print pattern is formed on the surface of the photoreceptor 1Y.

  The electrostatic image is an image formed on the surface of the photosensitive member 1Y by charging, and the specific resistance of the irradiated portion of the photosensitive layer is reduced by the laser beam 3Y, and the charge on the surface of the photosensitive member 1Y flows On the other hand, it is a so-called negative latent image which is formed by the residual charge of the portion not irradiated with the laser beam 3Y. The electrostatic charge image thus formed on the photosensitive member 1Y is rotated to a predetermined development position as the photosensitive member 1Y travels. Then, at this developing position, the electrostatic charge image on the photosensitive member 1Y is visualized (developed) by the developing device 4Y.

  In the developing device 4Y, for example, a developer for electrostatic charge image development containing at least a yellow toner and a carrier is accommodated. The yellow toner is frictionally charged by being stirred inside the developing device 4Y, and has a charge of the same polarity (negative polarity) as the charged charge on the photosensitive member 1Y, and the developer roll (developer holding member) Held on top. When the surface of the photosensitive member 1Y passes through the developing device 4Y, yellow toner electrostatically adheres to the electrostatically charged image portion on the surface of the photosensitive member 1Y, and the electrostatic charge image is developed by the yellow toner. Be done.

  From the viewpoint of development efficiency, image granularity, tone reproducibility and the like, a bias potential (developing bias) in which an alternating current component is superimposed on a direct current component may be applied to the developer holding member. Specifically, when the developer holder direct current applied voltage Vdc is, for example, -700 V or more and -300 V or less, the developer holder AC voltage peak width Vp-p may be, for example, 0.5 kV or more and 2.0 kV or less. Good. The photoreceptor 1Y on which the yellow toner image is formed is subsequently traveled at a predetermined speed, and the toner image developed on the photoreceptor 1Y is conveyed to a predetermined primary transfer position.

  When the yellow toner image on the photosensitive member 1Y is conveyed to the primary transfer position, the primary transfer bias is applied to the primary transfer roller 5Y, and the electrostatic force from the photosensitive member 1Y toward the primary transfer roller 5Y causes the toner image to The toner image on the photosensitive member 1Y is transferred onto the intermediate transfer belt 20. The transfer bias applied at this time is the (+) polarity opposite to the polarity (−) of the toner, and is controlled to about +10 μA by the control unit (not shown) in the first unit 10Y, for example. On the other hand, the toner remaining on the photosensitive member 1Y is removed and collected by the cleaning device 6Y.

  In addition, the primary transfer bias applied to the primary transfer rollers 5M, 5C, and 5K after the second unit 10M is also controlled according to the first unit. Thus, the intermediate transfer belt 20 to which the yellow toner image is transferred in the first unit 10Y is sequentially conveyed through the second to fourth units 10M, 10C, and 10K, and the toner images of the respective colors are superimposed and transferred in multiples. Ru.

  The intermediate transfer belt 20 on which toner images of four colors are multiply transferred through the first to fourth units is disposed on the intermediate transfer belt 20 and the support roller 24 in contact with the inner surface of the intermediate transfer belt and the image holding surface side of the intermediate transfer belt 20 It leads to the secondary transfer portion constituted by the secondary transfer roller (secondary transfer means) 26 which has been carried out. On the other hand, the recording paper (recording medium) P is fed at a predetermined timing to a gap where the secondary transfer roller 26 and the intermediate transfer belt 20 are in pressure contact via the supply mechanism, and the secondary transfer bias is supported by the support roller. 24 is applied. The transfer bias applied at this time is the same as the polarity (−) of the toner (−) and the electrostatic force from the intermediate transfer belt 20 to the recording paper P acts on the toner image, and the transfer bias is applied on the intermediate transfer belt 20. Is transferred onto the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detection unit (not shown) that detects the resistance of the secondary transfer portion, and is voltage controlled.

  Thereafter, the recording paper P is sent to the pressure contact portion (nip portion) of the pair of fixing rolls in the fixing device (roll-like fixing means) 28, the toner image is heated, and the color superimposed toner image is melted. It is fixed on P.

  Examples of the recording medium to which the toner image is transferred include plain paper, an OHP sheet and the like used for electrophotographic copying machines or printers.

  The recording paper P for which the fixing of the color image is completed is carried out toward the discharge unit, and a series of color image forming operations are completed.

  Although the image forming apparatus exemplified above is configured to transfer the toner image to the recording paper P via the intermediate transfer belt 20, the present invention is not limited to this configuration, and the toner image is directly from the photosensitive member. The structure may be transferred to a recording sheet.

  FIG. 3 is a schematic configuration view showing an example of a process cartridge containing the developer for electrostatic charge image development according to the present embodiment. The process cartridge 200 includes a developing device 111, a photosensitive member 107, a charging roller 108, a photosensitive member cleaning device 113, an opening 118 for exposure, and an opening 117 for discharge exposure using a mounting rail 116. Combined and integrated. In FIG. 2, reference numeral 300 denotes a recording medium.

  The process cartridge 200 is detachably attachable to the image forming apparatus main body including the transfer device 112, the fixing device 115, and the other components (not shown). It constitutes the forming apparatus.

  The process cartridge 200 shown in FIG. 3 includes a photosensitive member 107, a charging device 108, a developing device 111, a cleaning device 113, an opening 118 for exposure, and an opening 117 for discharge exposure. The devices may be selectively combined. In the process cartridge according to the present embodiment, in addition to the developing device 111, the photosensitive member 107, the charging device 108, the cleaning device (cleaning means) 113, the opening 118 for exposure, and the opening for charge removal exposure It may comprise at least one selected from the group consisting of 117.

  Next, the toner cartridge and the developer cartridge will be described. The toner cartridge is detachably mounted to the image forming apparatus, and contains at least a toner to be supplied to the developing unit provided in the image forming apparatus. Note that at least the toner may be stored in the toner cartridge, and, for example, a developer may be stored depending on the mechanism of the image forming apparatus. The toner cartridge containing the developer is referred to as a developer cartridge.

  The image forming apparatus shown in FIG. 2 is an image forming apparatus having a configuration in which the toner cartridges 8Y, 8M, 8C and 8K can be attached and detached, and the developing devices 4Y, 4M, 4C and 4K are each developing devices ( The toner cartridge corresponding to color) is connected by a toner supply pipe (not shown). Further, when the toner stored in the toner cartridge runs low, the toner cartridge is replaced.

  The image forming apparatus and the image forming method according to the present embodiment use the developer for electrostatic charge image development (the carrier according to the present embodiment), so that the occurrence of image deterioration after long-term image formation is suppressed.

  Further, by combining with the trickle development proposed in Japanese Examined Patent Publication No. 2-21591, a long-term stable image formation can be performed without accumulating the separated spherical particles (carrier) on the developer support. .

  Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited to the following examples.

  The volume average particle sizes of the magnetic core particles, the raw material composition (mixture) of the magnetic core particles, and the carrier were measured using a laser diffraction type particle size distribution analyzer (LA-700, manufactured by Horiba, Ltd.).

  The calcium content of the magnetic core particles was measured using a fluorescent X-ray analyzer PRIMUS II (manufactured by RIGAKU Co., Ltd.). More specifically, 100 parts by mass of magnetic core particles and 10 parts by mass of cellulose were added to a vibrating crusher and dispersed, and the obtained mixture was molded with a die using a press and the above measurement was performed.

  The calcium content ratio in the surface part and the inside of the magnetic core particle and the calcium content ratio in the surface part of the carrier were measured using a microanalyzer EPMA-1610 (manufactured by Shimadzu Corporation). The calcium content ratio inside the magnetic core particles was obtained by cutting the magnetic core particles with a microtome, analyzing the cross section, and measuring and calculating the content ratio. The calcium content ratio in the surface portion of the magnetic core particle and the surface portion of the carrier was calculated by analyzing each surface portion and measuring the content ratio of each. As a measurement value, an area of 0.5 μmφ was measured at 10 points in each of the surface portion and the inside of the magnetic core particle and the surface portion of the carrier.

  The exposure rate of the magnetic core particles on the carrier surface was obtained by photographing each of 500 carriers at 1000 times using a field emission scanning electron microscope (FE-SEM), and the magnetic core particle exposed portion and the resin coated portion The surface area of each was measured by an image analyzer and determined by averaging the obtained exposure rates.

  The average spacing Sm and the maximum height Ry of the unevenness of the surface of the magnetic core particles are about 3000 times with an ultra-deep color 3D shape measuring microscope (product name VK-9500, manufactured by Keyence Co., Ltd.) for 50 magnetic particles. The surface was observed to determine Sm and Ry, which were determined by averaging.

Example 1
[Preparation of magnetic core particle 1]
-Mn ₃ O ₄ powder 25 parts by mass-Fe ₂ O ₃ powder 75 parts by mass-CaCO ₃ powder 0.2 parts by mass After mixing the above raw materials with a mixing mill, firing was carried out at 900 ° C for 1 hour.
To the fired mixed powder, 20 parts by mass of water and 3.0 parts by mass of polyvinyl alcohol were mixed to prepare a mixed solution. The prepared mixture was stirred by a wet ball mill for 12 hours. The volume average particle size of the mixed powder was 0.5 μm.

Next, the obtained mixed liquid was granulated with a spray dryer, and a sieve was used to obtain a granulated material having dried particles having a volume average particle diameter of about 42 μm. 0.3 parts by mass of CaCO ₃ powder was mixed with the obtained granulated product.

  The granulated product was charged into a calcining furnace and calcined at 1150 ° C. for 4 hours in a nitrogen gas atmosphere to obtain a massive calcined product. The obtained fired product was crushed by a hammer mill, and the ground product was subjected to an air classifier to classify and remove a fine powder part. Next, magnetic separation was performed to separate the nonmagnetic portion, and the particles were passed through a sieve to obtain a magnetic core particle 1 having a volume average particle diameter of 35 μm.

  The calcium content of the magnetic core particles obtained is 0.2% by mass, the calcium content ratio (a) inside the magnetic core particles is 0.05% by mass, and the calcium content of the surface portion of the magnetic core particles is The ratio (b) was 3.0% by mass, and b / a was 60. The average spacing Sm and the maximum height Ry of the unevenness of the magnetic core particle surface were 1.5 μm and 0.8 μm, respectively.

Magnetic core particles 1 100 parts by mass Toluene 8 parts by mass Styrene-methyl methacrylate copolymer (styrene: methyl methacrylate = 25: 75 (molar ratio)) 2 parts by mass Carbon black (VXC-72, manufactured by Cabot Corporation) 0 .2 parts by mass The styrene-methyl methacrylate copolymer as a coating resin and carbon black were charged into toluene and stirred and dispersed by a sand mill to prepare a solution for forming a resin coating layer. This solution was put in a vacuum degassing type kneader together with the magnetic core particles 1 and kept at a temperature of 60 ° C. and stirred for 10 minutes, then the current value of the stirring motor was monitored and the toluene was distilled off under reduced pressure. The resulting resin-coated layer-formed carrier was sieved with a mesh having an aperture of 75 μm to obtain a carrier 1.

  The calcium content (c) of the surface portion of the carrier 1 was 1.2% by mass, and c / b was 0.4. The core material exposure rate of Carrier 1 was 20%. In addition, the volume average particle size of Carrier 1 was 36 μm.

[Preparation of developer]
Eight parts by mass of the externally added toner and 100 parts by mass of the carrier 1 were stirred at 40 rpm for 20 minutes using a V blender, and then sieved using a sieve of 125 μm mesh to obtain a developer 1.

[Evaluation]
The image defect was evaluated after long-term image formation under high temperature and high humidity by the following three evaluation items of halftone image quality, image loss and thin line reproducibility. The results are shown in Table 1.

[Evaluation of carrier and developer]
Using the developer 1, 100,000 sheets of a 1% printing chart were printed on an A4 sheet under an environment of 35 ° C. and 85% RH by a copying machine Docu Center Color 500 manufactured by Fuji Xerox Co., Ltd. under an environment of 35 ° C. and 85% RH. Printing chart after printing initial (10th sheet), 10,000 sheets, 50,000 sheets, 80,000 sheets, and 100,000 sheets, and printing chart printed after leaving for 100,000 hours after printing 100,000 sheets. For the evaluation of halftone image quality and image loss, the following criteria were used. The obtained results are shown in Table 1.

(Half tone image quality)
In the print chart, deterioration in image quality such as uneven density and blur was visually observed and evaluated according to the following criteria.
○: When deterioration of the halftone image quality is not visually recognized at all :: When the deterioration of the halftone image quality is visually recognized while being unclear ×: When the deterioration of the halftone image quality is clearly recognized visually

(Image missing)
The number of missing images due to carrier skipping in 10 sheets of black solid images was visually measured and evaluated according to the following criteria.
○: 2 or less △: 3 or more and 9 or less ×: 10 or more

(Thin line reproducibility)
Using the developer 1 and the modified machine, 100,000 sheets of 1% print chart were printed on A4 paper under an environment of 35 ° C. and 85% RH. After printing the initial (10th sheet), 10,000 sheets, 50,000 sheets, 80,000 sheets, and 100,000 sheets and after leaving for 100,000 hours after printing 100,000 sheets, with a resolution of 2,400 dpi The 1 on 1 off image (an image in which 1 dot line is arranged in parallel at 1 dot intervals) is output as a 5 cm × 5 cm chart in the direction perpendicular to the developing direction on the upper left, center and lower right of A4 paper. The output sample was observed using a loupe with a scale of × 100 to check whether the line interval was narrowed at a portion where the toner spattered or the like, or at a portion where the thin line became thin. Based on the observation result and the line interval of the observed point, the grade evaluation was performed based on the following criteria. The obtained results are shown in Table 1.
○: In all charts, decrease in line spacing due to splintering, increase in thin line narrowing hardly observed Δ: decrease in line spacing, increase in some cases where there is at least one chart with visible thin lines ×: thin lines If the interval between can not be determined, or if there is at least one chart with missing gaps

Example 2
A magnetic core is prepared in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged into the mixing mill is 0.4 parts by mass and the amount of CaCO ₃ powder mixed after granulation is changed to 0.1 part by mass. Material particles 2 were obtained.

  The calcium content of the obtained magnetic core particles 2 is 0.2% by mass, the calcium content ratio (a) inside the magnetic core particles is 0.10% by mass, and the calcium content of the surface portion of the magnetic core particles is The content ratio (b) was 0.7% by mass, and b / a was 7. The average spacing Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particle were 2.5 μm and 0.8 μm, respectively.

  The magnetic core particles were coated with the coating resin in the same manner as the magnetic core particles 2 except that the magnetic core particles 1 were replaced with the magnetic core particles 2 to obtain a carrier 2. The calcium content (c) of the surface portion of the obtained carrier 2 was 0.5% by mass, and c / b was 0.5. The core material exposure rate of Carrier 2 was 28%. Moreover, the volume average particle diameter of the carrier 2 was 36 μm.

  Developer 2 was produced in the same manner as in Example 1 except that Carrier 2 was used, and evaluation of printed matter was carried out. The evaluation results are shown in Table 2.

Example 3
A magnetic core material is prepared in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged into the mixing mill is 0.05 parts by mass and the amount of CaCO ₃ powder mixed after granulation is 0.15 parts by mass. Particle 3 was obtained.

  The calcium content of the obtained magnetic core particle 3 is 0.08 mass%, the calcium content ratio (a) inside the magnetic core particle is 0.04 mass%, and the calcium content of the surface portion of the magnetic core particle is The content ratio (b) was 1.0% by mass, and b / a was 25. The average spacing Sm and the maximum height Ry of the unevenness of the magnetic core particle surface were 1.8 μm and 0.9 μm, respectively.

  The magnetic core particles were coated with a coating resin in the same manner as in the above except that the magnetic core particles 1 were replaced with the magnetic core particles 3, to obtain a carrier 3. The calcium content (c) of the surface part of the obtained carrier 3 was 0.4% by mass, and c / b was 0.4. The core material exposure rate of Carrier 3 was 15%. Moreover, the volume average particle diameter of the carrier 3 was 36 μm.

  Developer 3 was produced in the same manner as in Example 1 except that Carrier 3 was used, and evaluation of printed matter was carried out. The evaluation results are shown in Table 2.

Example 4
A magnetic core is prepared in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged to the mixing mill is 1.2 parts by mass and the amount of CaCO ₃ powder mixed after granulation is changed to 1.2 parts by mass. Material particles 4 were obtained.

  The calcium content of the obtained magnetic core particles 4 is 0.95% by mass, the calcium content ratio (a) inside the magnetic core particles is 0.20% by mass, and the calcium content of the surface portion of the magnetic core particles is The content ratio (b) was 7.0% by mass, and b / a was 35. The average spacing Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particle were 2.0 μm and 0.7 μm, respectively.

  The magnetic core particles were coated with the coating resin in the same manner as in the above except that the magnetic core particles 1 were replaced with the magnetic core particles 4, to obtain a carrier 4. The calcium content (c) of the surface portion of the obtained carrier 4 was 2.0%, and c / b was 0.29. The core material exposure rate of Carrier 4 was 18%. Moreover, the volume average particle diameter of the carrier 4 was 36 μm.

  A developer 4 was produced in the same manner as in Example 1 except that the carrier 4 was used, and evaluation of printed matter was performed.

Reference Example 5
A magnetic core is prepared in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged to the mixing mill is 0.05 parts by mass, and the amount of CaCO ₃ powder mixed after granulation is changed to 0.08 parts by mass. Material particles 5 were obtained.

  The calcium content of the obtained magnetic core particles X is 0.05% by mass, the internal calcium content ratio (a) is 0.01% by mass, and the calcium content ratio (b) of the surface portion is 0. It was 5% by mass, and b / a was 50. The average spacing Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particle were 1.8 μm and 0.8 μm, respectively.

  The magnetic core particles 5 were coated with a coating resin in the same manner as in Example 1 except that the magnetic core particles 1 were replaced with the magnetic core particles 5, to obtain a carrier 5. The calcium content (c) of the surface part of the obtained carrier 5 was 0.2% by mass, and c / b was 0.40. The core material exposure rate of Carrier 5 was 15%, and the volume average particle size was 36 μm.

  Developer 5 was produced by the same method as Example 1 except that carrier 5 was used, and evaluation of printed matter was carried out. The evaluation results are shown in Table 2.

Example 6
A magnetic core is prepared in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged into the mixing mill is 1.0 part by mass and the amount of CaCO ₃ powder mixed after granulation is changed to 1.5 parts by mass. Material particles 6 were obtained.

  The calcium content of the obtained magnetic core particle X is 1.0% by mass, the calcium content ratio (a) in the inside is 0.2% by mass, and the calcium content ratio (b) in the surface portion is 8. It was 0% by mass, and b / a was 40. The average spacing Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particle were 1.8 μm and 0.8 μm, respectively.

  The magnetic core particles 6 were coated with a coating resin in the same manner as in Example 1 except that the magnetic core particles 1 were replaced with the magnetic core particles 6, to obtain a carrier 6. The calcium content ratio (c) of the surface part of the obtained carrier X was 2.5 mass%, and c / b was 0.31. The core material exposure rate of Carrier 6 was 15%, and the volume average particle size was 36 μm.

  Developer 6 was produced in the same manner as in Example 1 except that Carrier 6 was used, and evaluation of printed matter was carried out. The evaluation results are shown in Table 2.

Example 7
Magnetic core particles 7 were obtained in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged to the mixing mill was 0.5 parts by mass, and the CaCO ₃ powder mixed after granulation was changed to nothing. .

  The calcium content of the obtained magnetic core particles 7 is 0.2% by mass, the internal calcium content ratio (a) is 0.1% by mass, and the calcium content ratio (b) of the surface portion is 0. It was 5% by mass, and b / a was 5. The average spacing Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particle were 1.7 μm and 0.9 μm, respectively.

  The magnetic core particles 7 were coated with the coating resin in the same manner as in Example 1 except that the magnetic core particles 1 were replaced with the magnetic core particles 7, to obtain a carrier 7. The calcium content (c) of the surface part of the obtained carrier 7 was 0.2% by mass, and c / b was 0.4. The core material exposure rate of Carrier 7 was 13%, and the volume average particle size was 36 μm.

  Developer 7 was produced in the same manner as in Example 1 except that carrier 7 was used, and evaluation of printed matter was carried out. The evaluation results are shown in Table 2.

Example 8
The magnetic core particles are prepared in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged into the mixing mill is 0.02 parts by mass, and the CaCO ₃ powder mixed after granulation is changed to 0.23 parts by mass. I got eight.

  The calcium content of the obtained magnetic core particles X is 0.2% by mass, the internal calcium content ratio (a) is 0.01% by mass, and the calcium content ratio (b) of the surface portion is 1. It was 0% by mass, and b / a was 100. The average spacing Sm and the maximum height Ry of the unevenness of the magnetic core particle surface were 1.8 μm and 1.0 μm, respectively.

The magnetic core particles 8 were coated with the covering resin in the same manner as in Example 1 except that the magnetic core particles 1 were replaced with the magnetic core particles 8, to obtain a carrier 8. The calcium content (c) of the surface portion of the obtained carrier 8 was 0.4% by mass, and c / b was 0.4. The core material exposure ratio of Carrier 8 was 10%, and the volume average particle diameter was 36 μm.
A developer 8 was produced in the same manner as in Example 1 except that the carrier 8 was used, and evaluation of printed matter was performed. The evaluation results are shown in Table 2.

Example 9
The magnetic core particles 1 are coated with the coating resin in the same manner as in Example 1 except that the styrene-methyl methacrylate copolymer is changed to 2.5 parts by mass and the carbon black to 0.25 parts by mass, and the carrier is used. I got nine. The calcium content (c) of the surface portion of the obtained carrier 9 was 0.3 mass%, and c / b was 0.1. The core material exposure rate of the carrier 9 was 5%, and the volume average particle size was 36 μm.

  A developer 9 was produced in the same manner as in Example 1 except that the carrier 9 was used, and evaluation of printed matter was performed. The evaluation results are shown in Table 2.

Example 10
The magnetic core particles 1 are coated with a coating resin in the same manner as in Example 1 except that the styrene-methyl methacrylate copolymer is changed to 1.5 parts by mass and the carbon black to 0.15 parts by mass, and the carrier is used. I got ten. The calcium content (c) of the surface part of the obtained carrier 10 was 1.5 mass%, and c / b was 0.50. The core material exposure rate of the carrier 10 was 4%, and the volume average particle size was 36 μm.

  The developer 10 was produced by the same method as Example 1 except that the carrier 10 was used, and the evaluation of the printed matter was performed. The evaluation results are shown in Table 2.

Example 11
The magnetic core material particles 8 are coated with the coating resin in the same manner as in Example 1 except that the styrene-methyl methacrylate copolymer is changed to 2.5 parts by mass and the carbon black to 0.25 parts by mass, and the carrier is used. I got eleven. The calcium content (c) of the surface portion of the obtained carrier 11 was 0.15 mass%, and c / b was 0.15. The core material exposure rate of the carrier 11 was 4%, and the volume average particle diameter was 36 μm.

  A developer 11 was produced in the same manner as in Example 1 except that the carrier 11 was used, and evaluation of printed matter was performed. The evaluation results are shown in Table 2.

Example 12
The magnetic core particles 2 are coated with the coating resin in the same manner as in Example 1 except that the styrene-methyl methacrylate copolymer is changed to 1.5 parts by mass and the carbon black to 0.15 parts by mass, and the carrier is used. I got twelve. The calcium content (c) of the surface part of the obtained carrier 12 was 0.35 mass%, and c / b was 0.50. The core material exposure rate of the carrier 12 was 32%, and the volume average particle size was 36 μm.

  A developer 12 was produced in the same manner as in Example 1 except that the carrier 12 was used, and evaluation of printed matter was performed. The evaluation results are shown in Table 2.

Comparative Example 1
The magnetic core particles 13 were obtained in the same manner as in Example 1 except that the CaCO ₃ powder was not mixed either at the time of mixing mill charging or after granulation as a raw material.

  The calcium content of the magnetic core particles 13 obtained is 0.01% by mass, the calcium content ratio (a) inside the magnetic core particles is 0.005% by mass, and the calcium content of the surface portion of the magnetic core particles is The content ratio (b) was 0.02 mass%, and b / a was 4. The average spacing Sm and the maximum height Ry of the unevenness of the surface of the magnetic core particle 13 were 1.0 μm and 1.2 μm, respectively.

  The magnetic core particles were coated with a coating resin in the same manner as in the above except that the magnetic core particles 1 were replaced with the magnetic core particles 13, to obtain a carrier X. The surface part calcium content ratio (c) of the obtained carrier 13 was not detected. The core material exposure rate of the carrier 13 was 25%, and the volume average particle size was 36 μm.

  A developer X was produced in the same manner as in Example 1 except that the carrier X was used, and evaluation of printed matter was performed.

Comparative Example 2
The magnetic core particles 14 were obtained in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged into the mixing mill was 0.1 parts by mass, and the CaCO ₃ powder mixed after granulation was changed to nothing. .

  The calcium content of the obtained magnetic core particles 14 is 0.08% by mass, the calcium content ratio (a) inside is 0.05% by mass, and the calcium content ratio (b) in the surface part is 0. 0. It was 2% by mass, and b / a was 4. The average spacing Sm and the maximum height Ry of the unevenness of the magnetic core particle surface were 1.0 μm and 0.9 μm, respectively.

  The magnetic core particles 14 were coated with the coating resin in the same manner as in Example 1 except that the magnetic core particles 1 were replaced with the magnetic core particles 14, to obtain a carrier 14. The calcium content (c) of the surface part of the obtained carrier 14 was 0.1% by mass, and c / b was 0.5. The core material exposure rate of the carrier 14 was 22%, and the volume average particle size was 36 μm.

  The developer 14 was produced in the same manner as in Example 1 except that the carrier 14 was used, and evaluation of printed matter was performed. The evaluation results are shown in Table 2.

Comparative Example 3
The magnetic core particles 1 are coated with the coating resin in the same manner as in Example 1 except that the styrene-methyl methacrylate copolymer is changed to 4.0 parts by mass and the carbon black to 0.4 parts by mass, and the carrier is used. I got fifteen.

  The calcium content (c) of the surface portion of the obtained carrier 15 was 0.2 mass%, and c / b was 0.07. The core material exposure rate of the carrier 15 was 0.2%, and the volume average particle size was 36 μm.

  A developer 15 was produced in the same manner as in Example 1 except that the carrier 15 was used, and evaluation of printed matter was performed. The evaluation results are shown in Table 2.

Comparative Example 4
The magnetic core particles 1 are coated with the coating resin in the same manner as in Example 1 except that the styrene-methyl methacrylate copolymer is changed to 1.0 part by mass and the carbon black to 0.1 parts by mass, and the carrier is used. I got sixteen.

  The calcium content (c) of the surface portion of the obtained carrier 16 was 1.8 mass%, and c / b was 0.6. The core material exposure rate of the carrier 15 was 35%, and the volume average particle size was 36 μm.

  The developer 16 was produced in the same manner as in Example 1 except that the carrier 16 was used, and evaluation of printed matter was performed. The evaluation results are shown in Table 2.

Comparative Example 5
A magnetic core is prepared in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged to the mixing mill is 1.5 parts by mass, and the amount of CaCO ₃ powder mixed after granulation is changed to 1.5 parts by mass. Material particles 17 were obtained.

  The calcium content of the obtained magnetic core particles 17 is 1.2% by mass, the internal calcium content ratio (a) is 0.4% by mass, and the calcium content ratio of the surface portion (b) is 10%. %, B / a was 25. The average spacing Sm and the maximum height Ry of the unevenness of the magnetic core particle surface were 2.0 μm and 0.8 μm, respectively.

  The magnetic core particles 17 were coated with a coating resin in the same manner as in Example 1 except that the magnetic core particles 1 were replaced with the magnetic core particles 17, to obtain a carrier 17.

  The calcium content (c) of the surface part of the obtained carrier 17 was 3.0 mass%, and c / b was 0.3. The core material exposure ratio of the carrier 17 was 20%, and the volume average particle diameter was 36 μm.

  The developer 17 was produced by the same method as Example 1 except that the carrier 17 was used, and the evaluation of the printed matter was performed. The evaluation results are shown in Table 2.

(Evaluation results)
As the results of Examples 1 to 12 show, the magnetic core particles contain 0.05% by mass or more and 1.0% by mass or less of calcium, and the magnetic core member to the calcium content ratio (a) inside the magnetic core particles. The ratio b / a of the calcium content ratio (b) of the particle surface part is 5 or more, and the carrier surface part after being coated with the resin coating layer to the calcium content ratio (b) of the core material particle surface part The ratio c / b of the calcium content ratio (c) is 0.1 or more and 0.5 or less, so that it is stably high even after long-term image formation under high temperature and high humidity as compared with the comparative example. There has been provided a carrier for electrostatic image development in which image defects caused by a decrease in carrier resistance are suppressed while securing image quality.

1Y, 1M, 1C, 1K photoconductor, 2Y, 2M, 2C, 2K charging roller, 3 Exposure device (electrostatic charge image forming means), 3Y, 3M, 3C, 3K laser beam, 4Y, 4M, 4C, 4K developing device (Developing means), 5Y, 5M, 5C, 5K Primary transfer roller (primary transfer means), 6Y, 6M, 6C, 6K Photosensitive member cleaning device (cleaning means), 8Y, 8M, 8C, 8K Toner cartridge, 10Y , 10M, 10C, 10K Image forming unit (image forming means), 20 intermediate transfer belt, 22 drive roller, 24 support roller, 26 secondary transfer roller (secondary transfer means), 28 fixing device (roll-like fixing means), Reference Signs List 30 intermediate transfer member cleaning device 107 photosensitive member 108 charging roller 111 developing device 112 transfer device 113 photosensitive member cleaning device 115 fixing device 116 mounting rail 117 opening for charge elimination exposure 118 opening for exposure 200 process cartridge 300 recording medium 301 image forming apparatus 310 charging unit 312 exposure unit ( Exposure unit, electrostatic charge image forming unit), 314 electrophotographic photosensitive member, 316 developing unit (developing unit), 318 transfer unit (transfer unit), 320 cleaning unit (image carrier cleaning unit), 322 fixing unit (image fixing device) , Fixing means), 324 recording medium, P recording paper (recording medium).

Claims (7)

Magnetic core particles containing calcium of 0.08% by mass or more and 1.0% by mass or less and having a ratio b / a of the calcium content ratio (b) of the surface part to the internal calcium content ratio (a) of 5 or more And a resin coating layer covering the surface of the magnetic core particles, and a ratio c / c of the calcium content ratio (c) of the surface portion coated with the resin coating layer to the calcium content ratio (b). The carrier for developing an electrostatic charge image, wherein b is 0.1 or more and 0.5 or less, and the exposure ratio of the magnetic core particles on the surface of the carrier is 4.0% or more and 32% or less .   The carrier for developing an electrostatic charge image according to claim 1, wherein an exposure rate of the magnetic core particles on the surface of the carrier is 5.0% or more and 30% or less.   The average spacing Sm of irregularities on the surface of the magnetic core particles is 1.0 μm ≦ Sm ≦ 5.0 μm, and the maximum height Ry of the magnetic particle surface is 0.5 μm ≦ Ry ≦ 3.0 μm. The carrier for electrostatic image development according to claim 1 or 2.   The developer for electrostatic image development containing the carrier for electrostatic image development of any one of Claims 1-3, and the toner for electrostatic charge image development.   A developer cartridge containing the developer for electrostatic image development according to claim 4.   A developer is provided which contains the developer for electrostatic charge image development according to claim 4 and develops the electrostatic charge image formed on the surface of the image carrier with the developer for electrostatic charge image development to form a toner image. , A process cartridge which is attached to and detached from the image forming apparatus.   An image carrier, electrostatic charge image forming means for forming an electrostatic charge image on the surface of the image carrier, and the electrostatic charge image developed using the developer for electrostatic charge image development according to claim 4 An image forming apparatus comprising: developing means for forming an image; and transfer means for transferring the developed toner image to a transfer target.

Images