JP2016008987A - Carrier for electrostatic charge image development, developer for electrostatic charge image development, developer cartridge, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for electrostatic charge image development, configured to prevent an image defect due to reduction in carrier resistance, while ensuring a high-quality image stably, even after long-term image formation in a high-temperature/high-humidity environment, developer for electrostatic charge image development, a developer cartridge, a process cartridge, and an image forming apparatus.SOLUTION: A carrier for electrostatic charge image development contains: a magnetic core material particle including calcium of at least 0.05 to 1.0 mass%, and having a ratio b/a of 5 between an internal calcium content ratio (a) and a calcium content ratio (b) of a surface section; and a resin coating layer covering a surface of the magnetic core material particle. A ratio c/b between the calcium content ratio (b) and a calcium content ratio (c) of the surface section covered with the resin coating layer is 0.1 to 0.5.

Description

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

  Electrophotographic methods for visualizing image information through an electrostatic charge image (electrostatic latent image) 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 member using various means, and the electrostatic charge image developing developer (hereinafter simply referred to as an electrostatic charge image developing agent). The electrostatic image is developed and visualized by attaching electro-sensitive particles called electrostatic charge image developing toner (hereinafter sometimes simply referred to as “toner”) included in the “developer”. The method is commonly used. The developer used here includes a two-component developer that imparts an appropriate amount of positive or negative charge to the toner by triboelectrically charging both a holding particle called a carrier and the toner, and a magnetic toner. It is roughly classified into a one-component developer used solely for toner. In particular, two-component developers are widely used for reasons such as ease of design because the carrier itself has functions such as stirring, transport, and charging, and the functions required for the developer can be separated. ing.

  Carriers are generally classified into a resin-coated carrier having a resin coating layer on the surface of magnetic core particles (carrier core particles) and an uncoated carrier having no coating layer on the surface. Considering the developer life and the like, since the resin-coated carrier is superior, various types of resin-coated carriers have been developed and put into practical use.

  In recent years, with the reduction of toner particles, the carrier has been studied to reduce the particle size, 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.

Patent Document 1 discloses that in a two-component developer composed of 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. However, it has a resin coating layer in the form of ferrite particles, has a number average particle diameter in a specific range, and a ratio between the fluorescent X-ray intensity of iron element and the fluorescent X-ray intensity of calcium element by a fluorescent X-ray analysis is specific. Two-component developers in the range are described.

  Patent Document 2 discloses a carrier core material for an electrophotographic developer 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 in which the material is resin-coated is described.

JP 2006-276354 A JP 2006-259294 A

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

  The invention according to claim 1 includes at least 0.05 mass% or more and 1.0 mass% or less of calcium, and the ratio b / a of the calcium content ratio (b) of the surface portion to the internal calcium content ratio (a). The surface after covering with the resin coating layer with respect to the said calcium content ratio (b) containing the magnetic core particle which is 5 or more, and the resin coating layer which coat | covers the surface of the said magnetic core particle The electrostatic charge image developing carrier has a calcium content ratio (c) ratio c / b of 0.1 to 0.5.

  The invention according to claim 2 is the electrostatic image developing carrier, wherein an exposure rate 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, the average interval Sm of the irregularities on the surface of the magnetic core particles is 1.0 μm ≦ Sm ≦ 5.0 μm, and the maximum height Ry of the surface of the magnetic core particles is 0.5 μm. ≦ Ry ≦ 3.0 μm The carrier for developing an electrostatic charge image.

  According to a fourth aspect of the present invention, there is provided an electrostatic charge image developing developer comprising the electrostatic charge image developing carrier and the electrostatic charge image developing toner.

  The invention according to claim 5 is a developer cartridge for storing the developer for developing an electrostatic image.

  The invention according to claim 6 contains the developer for developing an electrostatic image, and develops the electrostatic image formed on the surface of the image carrier with the developer for developing the electrostatic image to form a toner image. And a process cartridge that is detachably attached to the image forming apparatus.

  According to a seventh aspect of the present invention, there is provided an image carrier, an electrostatic image forming means for forming an electrostatic image on the surface of the image carrier, and developing the electrostatic image using the developer for developing an electrostatic image. An image forming apparatus comprising: a developing unit that forms a toner image; and a transfer unit that transfers the developed toner image to a transfer target.

  According to the invention of claim 1, the magnetic core particles contain 0.05 mass% or more and 1.0 mass% or less of calcium, and the calcium content ratio (a) inside the magnetic core particles. The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particles to 5 is 5 or more, and the carrier surface portion after being coated with the resin coating layer with respect to the calcium content ratio (b) Compared with the case where the ratio c / b of the calcium content ratio (c) is not 0.1 or more and 0.5 or less, it is stably high even after long-term image formation under high temperature and high humidity. Provided is an electrostatic charge image developing carrier in which image defects due to a decrease in carrier resistance are suppressed while ensuring image quality.

  According to the second aspect of the present invention, even after long-term image formation under high temperature and high humidity, the exposure rate of the magnetic core particles is outside the range of 5.0% to 30%. There is provided a carrier for developing an electrostatic charge image in which image defects due to a decrease in carrier resistance are suppressed while ensuring high image quality stably.

  According to the invention of claim 3, the average interval Sm of the 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 ≦ Compared to the case outside the range where Ry ≦ 3.0 μm, image defects caused by a decrease in carrier resistance are ensured while stably ensuring high image quality even after long-term image formation under high temperature and high humidity. A suppressed electrostatic charge image developing carrier is provided.

  According to the invention of claim 4, the magnetic core particles of the carrier contain 0.05 mass% or more and 1.0 mass% or less of calcium, and the calcium content ratio (a ) The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particle to 5) is 5 or more, and the carrier was coated with a resin coating layer with respect to the calcium content ratio (b). Compared to the case where the ratio c / b of the calcium content ratio (c) on the carrier surface portion 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 developing an electrostatic image in which image defects due to a decrease in carrier resistance are suppressed while ensuring high image quality stably.

  According to the invention of claim 5, the magnetic core particles of the carrier contain 0.05 mass% or more and 1.0 mass% or less of calcium, and the calcium content ratio (a ) The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particle to 5) is 5 or more, and the carrier was coated with a resin coating layer with respect to the calcium content ratio (b). Compared to the case where the ratio c / b of the calcium content ratio (c) on the carrier surface portion 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 developing an electrostatic image in which image defects caused by a decrease in carrier resistance are suppressed while ensuring high image quality stably.

  According to the invention of claim 6, the magnetic core particles of the carrier contain 0.05 mass% or more and 1.0 mass% or less of calcium, and the calcium content ratio (a ) The ratio b / a of the calcium content ratio (b) of the surface portion of the magnetic core particle to 5) is 5 or more, and the carrier was coated with a resin coating layer with respect to the calcium content ratio (b). Compared to the case where the ratio c / b of the calcium content ratio (c) on the carrier surface portion 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 developing an electrostatic charge image in which image defects caused by a decrease in carrier resistance are suppressed while ensuring high image quality stably.

  According to the invention of claim 7, the magnetic core particles of the carrier contain 0.05 mass% or more and 1.0 mass% or less of calcium, and the calcium content ratio in the magnetic core particles ( 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 coated with a resin coating layer with respect 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 is not 0.1 or more and 0.5 or less, even after long-term image formation under high temperature and high humidity An image forming apparatus is provided in which image defects caused by a decrease in carrier resistance are suppressed while ensuring high image quality stably.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. It is a schematic block diagram which shows the other example of the image forming apparatus which concerns on embodiment of this invention. It is a schematic structure figure showing an example of a process cartridge concerning an embodiment of the present invention.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

<Electrostatic charge image developing carrier and method for producing electrostatic charge image developing carrier>
With the increase in printing speed by electrophotography and the diversification of usage environment, it is desirable for carriers with a resin coating layer to reduce fluctuations in carrier chargeability and carrier resistance over a long period of time. If the film is made thick, there may be fluctuations in chargeability due to adhesion of additives contained in the developer toner, and if the resin coating layer is made thin, the magnetic core particles are exposed and the chargeability fluctuates. The resistance may decrease, and as a result, the print image may deteriorate. This phenomenon is prominent when used in a high-temperature and high-humidity environment (35 ° C. and 85% RH environment). In particular, in image formation after long-term continuous use in a high-temperature and high-humidity environment, carrier resistance decreases and charge injection occurs. In some cases, the charged carrier contaminates or damages the charging roll, the photosensitive member, the photosensitive member cleaning member, and the like, thereby causing image defects.

  As a result of diligent research, the present inventors have found that dielectric breakdown occurs in the magnetic core particles in the carrier for developing an electrostatic image having the magnetic core particles and the resin coating layer covering the magnetic core particles. The surface of the magnetic core particles containing a large amount of calcium is added to the surface of the carrier in advance, even after the calcium is contained in the surface portion of the magnetic core particles, and after being coated with the coating resin. It has been found that by exposing at a constant ratio, image defects caused by a decrease in carrier resistance can be suppressed while stably ensuring high image quality even after long-term image formation under high temperature and high humidity. It was. Furthermore, it discovered that image degradation could be improved. This is because the surface of the magnetic core particles contains calcium that hardly causes dielectric breakdown, and the surface calcium of the magnetic core particles is exposed in advance to a part of the surface of the carrier, so that it can be used for a long time. It is considered that the change in the composition of the carrier surface until after use is reduced, the change in the carrier resistance is suppressed, and charge injection due to the decrease in the carrier resistance is prevented. Thus, by maintaining a structure that stably maintains resistance even when the coating resin is worn, stable toner developability can be obtained over a long period of time even in a high-temperature and high-humidity environment. It is considered that image defects such as image omission caused by composition variation on the carrier surface are reduced in the image formation.

  The carrier which concerns on embodiment of this invention has a magnetic core particle and the resin coating layer which has coat | covered the surface of a magnetic core particle. Further, the magnetic core material particles contain 0.05% by mass or more of calcium, and the calcium content ratio in the surface portion of the magnetic core material particles is manifested higher than the calcium content ratio inside the magnetic core material particles. In the present specification, unless otherwise specified, it is assumed that a simple “carrier” has magnetic core particles and a resin coating layer.

  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 calcium content of the magnetic core particles is less than 0.05% by mass, the effect of imparting insulation resistance is small, and if it exceeds 1.0% by mass, the magnetization characteristics and the like are affected.

  The content of calcium in the magnetic core particles is analyzed by using a fluorescent X-ray analyzer (for example, PRIMUS II (manufactured by Rigaku Corporation)) to disperse the magnetic core particles in cellulose and molding them. Is measured.

  In the carrier according to the embodiment of the present invention, more calcium is present in the surface portion of the magnetic core particle than in the magnetic core particle, and the magnetic core material with respect to the calcium content ratio (a) in the magnetic core particle The ratio b / a of the calcium content ratio (b) in the particle surface portion is 5 or more. The upper limit of b / a is not particularly limited. For example, it is possible to use magnetic core particles that do not contain calcium in the magnetic core particles and that a is zero or below 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 imparting insulation resistance to the surface of the magnetic core particles is reduced, and the stability of carrier resistance may be impaired.

  The calcium content ratio in the surface portion and 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)). The surface of the magnetic core particle is analyzed to determine the calcium content ratio b (mass%) in the surface portion. About the calcium content ratio a (mass%) in the inside of a magnetic core material particle, after cutting a magnetic core material particle with a microtome, the appeared cross section is analyzed and the calcium content ratio a (mass%) in an inside is calculated | required. As measurement values, 10 points of the 5.0 μmφ region on the surface and inside of the magnetic core particles are measured, and the average value is obtained. About the carrier which has a resin coating layer, it is possible to measure the calcium content ratio of the surface part of a magnetic core material particle, or an inside by removing a resin coating layer with a solvent.

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

  The calcium content ratio c in the carrier surface portion is measured by electron beam microanalysis. For example, the surface of the carrier is analyzed using an electron beam 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 portion of the carrier to the calcium content ratio b (mass%) in the surface portion of the magnetic core particles is in the range of 0.1 to 0.5. More preferably, it is in the range of 0.2 to 0.4. 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 may be increased. It may not be enough.

  In this specification, the “surface portion” of the carrier refers to a portion from the surface to 5% of the particle size of the carrier. The calcium content on the surface of the carrier may be analyzed by the same method as that for the surface portion of the magnetic core particle. As a measurement value, 10 points of the 0.5 μmφ region on the carrier surface are measured, and the average value is obtained.

  The exposure rate of the magnetic core particles in the carrier (hereinafter also simply referred to as “core exposure rate”) refers to the surface of the magnetic core particles in the carrier in which the surface of the magnetic core particles is coated with a resin coating layer. Is the area ratio of the exposed area (area not covered with the resin coating layer) to the total surface area. The core exposure rate of the carrier is determined by, for example, photographing the surface of the carrier using a scanning electron microscope (SEM), determining the exposed part of the magnetic core particle and the coating resin part using an image analyzer, and It is measured by measuring.

  The average spacing Sm of the 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 more preferably 1.5 μm. More preferably, it is in the range of 1.8 μm or less. If the average interval Sm of the irregularities is less than 1.0 μm, the penetration of the coating resin layer forming solution may be deteriorated, and the adhesion may be lowered. If the average interval Sm of the unevenness exceeds 5.0 μm, the adhesion may be lowered.

  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 material after forming the coating resin layer. When the maximum unevenness height Ry exceeds 3.0 μm, the strength of the magnetic core particles may be lowered.

  The average spacing Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particles are measured according to JIS B0601 (1994 edition). As a specific measuring method of the average interval Sm and the maximum height Ry, a magnification of 3000 times was obtained for 50 magnetic particles using an ultra-deep color 3D shape measuring microscope (for example, product name VK-9500 (manufactured by Keyence Corporation)). Measured by observing the surface.

  The average interval Sm of the unevenness is obtained from a three-dimensional shape of the observed core surface, and a roughness curve is obtained, and an average value of the intervals between the valleys and the cycles obtained from the intersection where the roughness curve intersects the average line is obtained. The reference length for determining the Sm value is 10 μm, and the cutoff value is 0.08 mm.

  For the maximum height Ry, a roughness curve is obtained, and a reference length is extracted in the direction of the average line. The height Yp from the average line of this extracted part to the highest peak and the depth Yv to the lowest valley bottom The maximum height Ry is obtained by calculating the sum (Yp + Yv). The reference length for determining 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 rate of the magnetic core particles on the surface of the carrier, a carrier obtained by detaching the toner from the developer for developing an electrostatic charge image is used as a measurement sample. use. As a more specific toner desorption method, for example, 10 g of developer is placed 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 by a magnet from the bottom of the beaker. Supernatant removal is performed. The above operation is repeated several times to remove the toner, washed several times with deionized water and dried to obtain a carrier.

  Further, for the magnetic core particles, to measure the calcium content, the calcium content ratio of the inside and the surface portion, the average interval Sm and the maximum height Ry of the surface irregularities, from the developer for developing an electrostatic charge image as described above. Magnetic core particles obtained by removing the coating resin layer with a solvent or the like from the carrier obtained by detaching the toner are used. As a more specific method for 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. Then, the carrier is adsorbed with a magnet from the bottom of the beaker to remove the supernatant. By repeating this, magnetic core material particles from which the coating resin has been removed can be obtained.

  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. If the volume average particle diameter is less than 15 μm, the toner may not be held on the developer holder and may be developed. If the volume average particle diameter exceeds 100 μm, the toner having a small particle diameter may not be uniformly charged.

  The saturation magnetization of the magnetic core particles is preferably 40 emu / g or more, and more preferably in the range of 50 emu / g or more and 75 emu / g or less. If the saturation magnetization of the magnetic core particles is less than 40 emu / g, the magnetic core particles may be separated from the developing machine magnet roll during development and cause image defects.

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

  The magnetic core particles are manufactured, for example, according to the following general method for manufacturing ferrite core particles. An appropriate amount of each oxide is blended, water is added, and pulverized and mixed, for example, for 1 hour or more, preferably 1 hour or more and 20 hours or less in 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 the preliminary firing, the mixture 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 by a granulating means such as a spray dryer, for example, held at a temperature of 1000 ° C. or more and 1500 ° C. or less for 1 hour or more and 24 hours or less, and a method of performing main firing is exemplified.

  In the present embodiment, by adjusting the particle size of the mixed powder obtained by pulverizing with a mill or the like after provisional firing, and adjusting the granulation method and the firing temperature, unevenness on the surface of the obtained magnetic core particles is obtained. The average interval Sm and the maximum height Ry are controlled. For example, by increasing the particle size of the mixed powder, raising the firing temperature and proceeding the sintering of the magnetic core particle surface, the average interval Sm can be increased, and the particle size of the mixed powder is increased and sintered. By suppressing the temperature, the maximum height Ry can be increased.

  In this embodiment, in the above granulation, a resin particle dispersion containing a binder resin is prepared by emulsion polymerization or other methods, heteroaggregated with the dispersion of the raw material composition of magnetic core particles, and then fused. Alternatively, the emulsion polymerization aggregation method may be used.

  As the raw material for the magnetic core particles, conventionally known ones may be used, but ferrite or magnetite is preferably selected. As another raw material, for example, iron powder is known. In the case of iron powder, since the specific gravity is large and the toner is likely to be deteriorated, ferrite and magnetite are more stable. Examples of ferrite that is a raw material composition of magnetic core particles generally include ferrite represented by the following formula.

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

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

  In the present embodiment, the magnetic core particles contain 0.05 mass% or more and 1.0 mass% or less calcium. When calcium is present in the magnetic core particles, the resistance becomes higher than when no calcium is present, and charge injection is less likely to occur.

  The method for containing calcium in the magnetic core particles is not particularly limited, but for example, a method of adding a calcium compound (calcium inorganic salt such as calcium oxide or calcium carbonate) to the raw material composition of the magnetic core particles. Etc. When the raw material composition for magnetic core particles is sintered with a calcium compound, the calcium compound is mixed with other oxides to obtain, for example, the ferrite represented by the above formula. And then the composition may be sintered. In this case, for example, by covering the surface of the magnetic core particle with a ferrite composition containing calcium as a composition and then sintering, the calcium content in the surface portion of the magnetic core particle is reduced to the magnetic core material. Magnetic core particles that are higher than the calcium content inside the particles are produced.

  In addition, in the solution in which the resin is dispersed in the solvent of the magnetic core particles, the calcium carbonate particles are further dispersed, and after the obtained dispersion is applied to the surface of the magnetic core particles, the solvent is removed with a kneader coater, After decarburization firing (for example, 500 ° C. or more and 800 ° C. or less), firing may be performed again. This is because the calcium content in the surface portion of the magnetic core particles becomes higher than the calcium content in the magnetic core particles by this method. Further, the calcium in the surface portion of the magnetic core material particles tends to be manifested by sintering to the convex portions of the ingot indentations on the surface of the magnetic core particle.

  In these magnetic core particle production methods, the particle size distribution of the magnetic core particles may be narrowed. In the production of the magnetic core particles, the sintered particles may be crushed as necessary to adjust the particle size such as sieving and classification.

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

  A typical method for coating the surface of the magnetic core particles with the coating resin is to inject a coating resin and conductive particles into a resin-soluble solvent to form a resin coating layer forming solution. Immersion method in which powder is immersed in resin coating layer forming solution, spray method in which resin coating layer forming solution is sprayed on the surface of magnetic core material particles, resin coating layer in a state where magnetic core material particles are suspended by flowing air Examples thereof include a fluidized bed method in which the forming solution is sprayed, a kneader method in which the magnetic core particles and the resin coating layer forming solution are mixed in a kneader coater, and then the solvent is removed. It is preferable that the magnetic core material particles and the resin coating layer forming solution are mixed in a knea coater and then the solvent is removed to produce the knea coater method.

  Magnetic core material particles include resin particles in which magnetic metal, magnetic oxide, magnetic particles or the like are dispersed internally. However, since these are hydrophilic and the chargeability may be reduced under high humidity, the environmental change of chargeability is large. In addition, since these are high surface energy materials, they are easily contaminated with toner components, and the chargeability may not be maintained. By coating the surface of the carrier with a resin having hydrophobicity or low surface energy, the above-mentioned problems relating to charging are improved. On the other hand, when the surface of the magnetic core particles is coated with a high coverage with an insulating resin, the electrical resistance as a carrier increases, and the reproducibility of a solid image may deteriorate. In this case, in order to avoid an increase in electrical resistance, it is sufficient to take measures such as dispersing conductive particles in the resin coating layer.

  Further, the resin coating layer may contain a wax. Wax is hydrophobic, is relatively soft even at room temperature, and has low film strength. This originates from the molecular structure of the wax, but due to this property, when wax is present in the resin coating layer, toner components such as external additive particles added to the toner surface or toner bulk components adhere to the carrier surface. It is hard to do. Moreover, even if it adheres, the surface of the carrier is renewed by peeling off the wax at the adhesion part at the molecular level, and the carrier surface is less likely to be adhered and contaminated.

  Usually, when manufacturing by the kneader coater method, the resin coating layer is prepared by mixing the magnetic core particles and the resin coating layer forming solution in which conductive particles are dispersed, heating and depressurizing while stirring, and removing the solvent. A layer is formed.

  Examples of the coating resin (matrix resin) used in the resin coating layer include polyethylene, polypropylene, polystyrene, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone, and vinyl chloride. Vinyl acetate copolymer, styrene-acrylic acid copolymer, straight silicone resin containing organosiloxane bond or modified product thereof, fluororesin, polyester, polyurethane, polycarbonate, phenol resin, amino resin, melamine resin, benzoguanamine resin, urea resin Amide resin, epoxy resin and the like, but are not limited thereto. Particularly preferred are polystyrene resin, acrylic resin, and styrene acrylic copolymer. 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 included in the coating resin layer is not particularly limited, and examples thereof include paraffin wax and derivatives thereof, montan wax and derivatives thereof, microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and derivatives thereof, and the like. Is mentioned. Derivatives include oxides thereof, polymers with vinyl monomers, graft modified products, and the like. In addition, alcohol, fatty acid, plant wax, animal wax, mineral wax, ester wax, acid amide, and the like may be used. In addition, other known ones may be used. The melting point of the wax is preferably in the range of 60 ° C. or higher and 200 ° C. or lower, and more preferably in the range of 80 ° C. or higher and 150 ° C. or lower. When the melting point of the wax is less than 60 ° C., the fluidity as a carrier may be deteriorated.

  A charge control agent may be contained in the resin coating layer. Examples of the charge control agent include nigrosine dye, benzimidazole compound, quaternary ammonium salt compound, alkoxylated amine, alkylamide, molybdate chelate pigment, triphenylmethane compound, salicylic acid metal salt complex, azo chromium complex, copper Examples thereof include phthalocyanine, but any known charge control agent may be contained. 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 desorption 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 dispersion state of the conductive material in the resin coating layer is substantially uniformed, and the change in carrier resistance is suppressed even if a slight amount of the resin coating layer is peeled off. The reason for this is that the conductive material described later is easily oxidized on the surface and easily affected by moisture, and therefore has a high hydrophilicity and a structure that easily aggregates due to water on the particle surface. Therefore, when the conductive material is dispersed in the coating resin, since the polarity of the coating resin is generally low, the above-described aggregation remains as it is, so that the conductive material is likely 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 has a certain degree of polarity, so that the adhesion to the conductive material is also improved, and therefore the dispersibility of the conductive material is improved. Presumed.

  The content of the charge control agent in the resin coating layer is preferably in the range of 0.001 to 5 parts by mass, and 0.01 to 0 parts by mass when the mass of the magnetic core particles is 100 parts by mass. The range of 5 parts by mass or less is more preferable. If 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 altered by stress during use. If the content is less than 0.001 parts by mass, In addition to not functioning, 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, and carbon black. It is preferable in terms of dispersibility in the 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 coating 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 for preparing the resin coating layer forming solution is not particularly limited as long as it dissolves the coating resin. For example, 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 rate of the magnetic core particles of the coated carrier 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 of the carrier may fluctuate when the coating resin is worn after long-term use. If it exceeds 30%, the toner may be charged because 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 or more and 10 μm or less. In the present embodiment, 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 preferably in the range of 0.4 μm to 2.8 μm. More preferably, since the exposure rate of the magnetic core particles is preferably in the range of 5.0% to 30%, more preferably in the range of 10% to 20%, the average of the resin coating layer 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 when 1,000 V corresponding to the upper and lower limits of a 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 fine lines is poor, and the amount of carrier transferred to the photoconductor (image carrier) increases, which may easily damage the photoconductor. . On the other hand, if the volume resistivity value of the carrier exceeds 10 ¹⁴ Ω · cm, the black solid and halftone reproducibility may deteriorate.

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

  Hereinafter, the toner used in the developer for developing an electrostatic charge image according to the exemplary embodiment will be described.

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

  For the toner used in this embodiment, a known binder resin, various colorants, and the like may be used. As the binder resin in the toner used in this embodiment, in addition to the polyester resin, polyolefin resin, copolymer of styrene and acrylic acid or methacrylic acid, polyvinyl chloride, phenol resin, acrylic resin, methacrylic resin, poly 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. may be used alone You may use together.

  Examples of the colorant in the toner used in the exemplary embodiment include cyan colorants such as C.I. I. Pigment Blue 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 13, 15, 15: 1, 15: 2, 15: 3, 15: 4, 15: 6, 16, 17, 17, 23, 60, 65, 73, 83, 180, C.I. I. Vat cyan 1, 3 and 20, etc., bitumen, cobalt blue, alkali blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, first sky blue, indanthrene blue BC cyan pigment, C.I. I. Cyan dyes such as solvent cyan 79 and 162 may be used.

  Examples of magenta colorants include C.I. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 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, and 209, pigment violet 19 magenta pigments, C.I. I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 30, 49, 81, 82, 83, 84, 100, 109, 121, C . I. Disper thread 9, C.I. I. Basic Red 1, 2, 9, 9, 13, 14, 15, 17, 17, 18, 22, 23, 24, 27, 29, 32, 34, the same 35, 36, 37, 38, 39, 40, etc. Magenta dyes, etc., Bengala, Cadmium Red, Lead Tan, Mercury Sulfide, Cadmium, Permanent Red 4R, Resol Red, Pyrazolone Red, Watching Red, Calcium Salt, lake red D, brilliant carmine 6B, eosin lake, rotamin lake B, alizarin lake, brilliant carmine 3B and the like may be used.

  Examples of yellow colorants include C.I. I. Pigment Yellow 2, 3, 15, 15, 16, 17, 97, 180, 185, 139, and the like may be used.

  Further, in the case of black toner, for example, carbon black, activated carbon, titanium black, magnetic powder, Mn-containing nonmagnetic powder, or the like may be used.

  The toner used in the exemplary embodiment may contain a charge control agent, and nigrosine, a quaternary ammonium salt, an organometallic complex, a chelate complex, or the like may be used.

Furthermore, in this embodiment, various resin powders and inorganic compounds may be added as external additives to the surface of the toner particles as a surface modifier. As the resin powder, polymethyl methacrylate resin (PMMA), nylon, melamine, benzoguanamine, spherical particles such as fluorine resin, and the like can be used. Examples of various known inorganic compounds include SiO ₂ , TiO ₂ , Al ₂ O ₃ , MgO, CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , BaO, CaO, K ₂ O, and Na ₂ O. , ZrO ₂ , CaO · SiO ₂ , CaCO ₃ , K ₂ O (TiO ₂ ) _n , MgCO ₃ , Al ₂ O ₃ · 2SiO ₂ , BaSO ₄ , MgSO _{4 and the} like, preferably SiO ₂ , Examples thereof include TiO ₂ and Al ₂ O _3, but are not limited to these, and one or more of these may be used in combination. The volume average particle size of the external additive is preferably 0.1 μm or less, and the addition amount of the external additive is, for example, from 0.1% by mass to 20% by mass with respect to 100% by mass of the toner particles. Range.

  In the present embodiment, the external additive is desirable for obtaining a stable print quality over a long period of time, but causes burial, deformation, polishing, etc. of the carrier surface, and in particular, particles having a volume average particle diameter of 50 nm to 200 nm. The effect is great when In the present embodiment, when an electrostatic charge image developing toner having external additive particles having a volume average particle diameter of 50 nm or more and 200 nm or less is used, the effect of suppressing the embedding, deformation, and polishing of the surface of the carrier of this embodiment is particularly significant. large.

  Furthermore, the toner used in the exemplary embodiment preferably contains a release agent. Examples of the release agent include ester wax, polyethylene, polypropylene, or a copolymer of polyethylene and polypropylene, polyglycerin wax, microcrystalline wax, paraffin wax, carnauba wax, sazol wax, montanic ester wax, deoxidized carnauba wax, and the like. Polymers and waxes; unsaturated fatty acids such as palmitic acid, stearic acid, montanic acid, brandic acid, eleostearic acid, valinalic acid; stearic alcohol, aralkyl alcohol, behenyl alcohol, carnauvyl alcohol, seryl alcohol, melyl alcohol Or a saturated alcohol such as a long-chain alkyl alcohol having a long-chain alkyl group; a polyhydric alcohol such as sorbitol; a linoleic acid amide, Fatty acid amides such as inamide, lauric acid amide; saturated fatty acid bisamides such as methylenebisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, hexamethylene bisstearic acid amide, ethylene bisoleic acid amide, Unsaturated fatty acid amides such as hexamethylenebisoleic acid amide, N, N′-dioleyl adipic acid amide, N, N′-dioleyl sebacic acid amide; m-xylene bisstearic acid amide, N, N′di Aromatic bisamides such as stearyl isophthalic acid amide; fatty acid metal salts such as calcium stearate, calcium laurate, zinc stearate, magnesium stearate (generally referred to as metal soap); aliphatic hydrocarbon wax with styrene or Acrylic acid Waxes grafted using vinyl monomers of the above; partially esterified products of fatty acids such as behenic acid monoglycerides and polyhydric alcohols; methyl ester compounds having hydroxyl groups obtained by hydrogenation of vegetable oils and the like .

  In this embodiment, the method for producing the toner (toner particles) is not particularly limited, but it is preferably produced by a wet production method in order to obtain high image quality. As a wet manufacturing method, the polymerizable monomer of the binder resin is emulsion-polymerized, and the formed binder resin dispersion is mixed with a dispersion of a colorant, a release agent, and, if necessary, a charge control agent. An emulsion aggregation method in which toner particles are obtained by agglomeration and heat fusion; a solution of a polymerizable monomer and a colorant, a release agent, and a charge control agent as required in order to obtain a binder resin in an aqueous solvent Suspension polymerization method in which the polymer is suspended and polymerized; a suspension method in which a binder resin, a colorant, a release agent, and a charge control agent, if necessary, are suspended in an aqueous solvent and granulated; etc. Is mentioned. In addition, a manufacturing method may be performed in which the toner particles obtained by the above method are used as a core, and resin particles are further adhered and heat-fused to have a core-shell structure. Further, 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 image forming unit that forms an electrostatic image on the surface of the image carrier, and the electrostatic charge image developing developer according to the embodiment. The image forming apparatus includes a developing unit that forms a toner image by developing using an agent, and a transfer unit that transfers the developed toner image to a transfer target (recording medium). The image forming apparatus according to this embodiment includes a charging unit that charges the surface of the image carrier, a fixing unit that fixes the toner image on the recording medium, and an image carrier cleaning that cleans the surface of the image carrier, as necessary. Means and the like may be included.

  In this image forming apparatus, for example, the part including the developing unit may have a cartridge structure (process cartridge) that can be attached to and detached from the main body of the image forming apparatus. The process cartridge contains the developer for developing an electrostatic image according to the present embodiment, and the electrostatic image formed on the surface of the image carrier is developed with the developer for developing the electrostatic image to form a toner image. A process cartridge that includes a developing unit that is attached to and detached from the image forming apparatus is preferably used. This facilitates the handling of the developer for developing an electrostatic image, and enhances the adaptability to image forming apparatuses having various configurations.

  The image forming apparatus according to the present embodiment uses the charging process for charging the surface of the image carrier, the 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 book including a developing step of developing with a developer for developing an electrostatic charge image to form a toner image, a transfer step of transferring the toner image to a recording medium, and a fixing step of fixing the toner image on the recording medium. The image forming method according to the embodiment is performed.

  Hereinafter, an example of the image forming apparatus according to the present embodiment will be described, but the present invention is not limited thereto.

  FIG. 1 is a schematic configuration diagram illustrating 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 that is an image holding member, 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, a charging unit 310 that is a charging unit that charges the surface of the electrophotographic photosensitive member 314 and the charged electrophotographic photosensitive member 314 are exposed according to image information. An exposure unit 312 that is an electrostatic image forming unit that forms an electrostatic image, a developing unit 316 that is a developing unit that develops the electrostatic image with a developer to form a toner image, and the surface of the electrophotographic photoreceptor 314 The transfer unit 318 that is a transfer unit that transfers the toner image formed on the surface of the recording medium 324 and foreign matters such as toner remaining on the surface of the electrophotographic photosensitive member 314 after the transfer are removed to remove the toner image. And a cleaning unit 320 which is an image carrier cleaning means for cleaning the surface of the lens is arranged in this order. A fixing unit 322 that is a fixing unit that fixes the toner image transferred to the recording medium 324 is disposed on the side of the transfer unit 318.

  The operation of the image forming apparatus 301 according to this embodiment will be described. First, the charging unit 310 charges the surface of the electrophotographic photosensitive member 314 that is an image holding member (charging step). Next, light is applied to the surface of the electrophotographic photosensitive member 314 by the exposure unit 312, and the charged charge in the exposed part is removed, and an electrostatic image is formed according to image information (electrostatic 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 photoconductor as the electrophotographic photoconductor 314 and using a laser beam as the exposure unit 312, the surface of the electrophotographic photoconductor 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 toner is applied to a portion irradiated with the laser beam light by the developing unit 316 to be visualized. In this case, a negative bias is applied to the developing unit 316. Next, a recording medium 324 such as paper is superimposed on the toner image at the transfer unit 318, and a charge having a polarity opposite to that of the toner is applied to the recording medium 324 from the back side of the recording medium 324. 324 is transferred (transfer process). The transferred toner image is heated and pressed by a fixing member in the fixing unit 322, and is fused and fixed to the recording medium 324 (fixing step). On the other hand, foreign matters such as toner remaining on the surface of the electrophotographic photosensitive member 314 without being transferred are removed by the cleaning unit 320 (cleaning step). One cycle is completed in a series of processes from charging to cleaning. In FIG. 1, the toner image is directly transferred to the recording medium 324 such as paper by the transfer unit 318, but may be transferred via a transfer body such as an intermediate transfer body.

  Hereinafter, the charging unit, the image carrier, the electrostatic 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)
As the charging unit 310 serving as a charging unit, for example, a charger such as a corotron shown in FIG. 1 is used, but a conductive or semiconductive charging roll may be used. A contact charger using a conductive or semiconductive charging roll may apply a direct current to the electrophotographic photosensitive member 314 or may apply an alternating current superimposed thereon. For example, the charging unit 310 charges the surface of the electrophotographic photosensitive member 314 by generating a discharge in a minute space near the contact portion with the electrophotographic photosensitive member 314. Normally, it is charged at a voltage of −1000V or more and −300V. The conductive or semiconductive charging roll may have a single layer structure or a multiple structure. Further, a mechanism for cleaning the surface of the charging roll may be provided.

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

(Static charge image forming means)
The exposure unit 312 which is an electrostatic charge image forming unit (exposure unit) is not particularly limited, and for example, a light source such as a semiconductor laser beam, LED (Light Emitting Diode) light, or liquid crystal shutter light is provided on the surface of the image carrier. Examples thereof include an optical device that exposes a desired image.

(Development means)
The developing unit 316 serving as 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. And a known developing device having a function of adhering to the surface. The electrophotographic photosensitive member 314 normally uses a DC voltage, but may be used with an AC voltage superimposed thereon.

(Transfer means)
As the transfer unit 318 that is a transfer unit, for example, a charge opposite in polarity to the toner is applied to the recording medium 324 from the back side of the recording medium 324 shown in FIG. 1, and the toner image is transferred to the recording medium 324 by electrostatic force. Alternatively, a transfer roll and a transfer roll pressing device using a conductive or semiconductive roll that directly contacts and transfers to the recording medium 324 may be used. A direct current may be applied to the transfer roll as a transfer current applied to the image carrier, or an alternating current may be applied in a superimposed manner. The transfer roll may be appropriately set depending on the width of the image area to be charged, the shape of the transfer charger, the opening width, the process speed (circumferential speed), and the like. Further, a single layer foam roll or the like is suitably used as a transfer roll for cost reduction. As a transfer method, 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 may be used.

  A known intermediate transfer member may be used as the intermediate transfer member. 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. From the viewpoint of mechanical strength, an intermediate transfer belt using a thermosetting polyimide resin is preferable.

(Image carrier cleaning means)
As for the cleaning unit 320 that is an image carrier cleaning means, a blade cleaning method, a brush cleaning method, a roll cleaning method, or the like may be selected as long as it cleans foreign matters such as residual toner on the image carrier. That's fine.

(Fixing means)
The fixing unit 322 as a fixing unit (image fixing device) fixes a 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 to which the toner image is transferred include plain paper, an OHP sheet, and the like used for an electrophotographic copying machine or printer. In order to further improve the smoothness of the image surface after fixing, the surface of the recording medium is also preferably smooth. For example, coated paper with the surface of plain paper coated with resin, art paper for printing, etc. are used. May be.

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

  FIG. 2 is a schematic configuration diagram illustrating a quadruple tandem color image forming apparatus as another example of the image forming apparatus according to the present exemplary embodiment. The image forming apparatus shown in FIG. 2 is a first to first electrophotographic method that outputs yellow (Y), magenta (M), cyan (C), and black (K) images based on color-separated image data. Fourth image forming units 10Y, 10M, 10C, and 10K (image forming means) are provided. These image forming units (hereinafter sometimes simply referred to as “units”) 10Y, 10M, 10C, and 10K are juxtaposed at predetermined distances in the horizontal direction. The units 10Y, 10M, 10C, and 10K may be process cartridges that can be attached to and detached from the image forming apparatus main body.

  Above each unit 10Y, 10M, 10C, 10K in the drawing, an intermediate transfer belt 20 as an intermediate transfer member is extended through each unit. The intermediate transfer belt 20 is provided so that the inner surface of the intermediate transfer belt 20 is in contact with a drive roller 22 and a support roller 24 that are spaced apart from each other in the left-to-right direction in the drawing. The vehicle travels in the direction from 10Y to the fourth unit 10K. The support roller 24 is applied with a force in a direction away from the driving roller 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wound around the 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 driving roller 22. Further, yellow, magenta, cyan, and black, which are housed in toner cartridges 8Y, 8M, 8C, and 8K, are respectively provided in the developing devices (developing units) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K. The four colors of toner are supplied.

  Since the first to fourth units 10Y, 10M, 10C, and 10K described above have the same configuration, here, a first image that forms a yellow image disposed on the upstream side in the intermediate transfer belt traveling direction is formed. The unit 10Y will be described as a representative. It should be noted that reference numerals with magenta (M), cyan (C), and black (K) are attached to the same parts as those of the first unit 10Y instead of yellow (Y). The description of the units 10M, 10C, and 10K will be omitted.

  The first unit 10Y includes a photoreceptor 1Y that functions as an image holding member. Around the photosensitive member 1Y, a charging roller 2Y for charging the surface of the photosensitive member 1Y to a predetermined potential, and the charged surface is exposed by a laser beam 3Y based on the color-separated image signal to form an electrostatic charge image. An exposure device (electrostatic image forming means) 3 for forming, a developing device (developing means) 4Y for supplying the charged toner to the electrostatic image and developing the electrostatic image, and transferring the developed toner image onto the intermediate transfer belt 20 A primary transfer roller 5Y (primary transfer unit) that performs the transfer and a photoconductor cleaning device (cleaning unit) 6Y that removes toner remaining on the surface of the photoconductor 1Y after the primary transfer are sequentially arranged.

  The primary transfer roller 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. Further, a bias power source (not shown) for applying a primary transfer bias is connected to each primary transfer roller 5Y (5M, 5C, 5K). Each bias power source varies the transfer bias applied to each primary transfer roller under the 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 photoreceptor 1Y is charged to a potential of about −800 V or more and −600 V or less by the charging roller 2Y. The photoreceptor 1Y is formed by laminating a photosensitive layer on a conductive substrate (for example, a volume resistivity at 20 ° C. is 1 × 10 ⁻⁶ Ωcm or less). This photosensitive layer usually has a high resistance (having a resistivity equivalent to that of a general resin), but has a property that the specific resistance of the portion irradiated with the laser beam changes when irradiated with the laser beam 3Y. ing. Therefore, a laser beam 3Y is output to the surface of the charged photoreceptor 1Y via the exposure device 3 in accordance with yellow image data sent from a 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 charge image is an image formed on the surface of the photoreceptor 1Y by charging, and the specific resistance of the irradiated portion of the photosensitive layer is lowered by the laser beam 3Y, and the charged charge on the surface of the photoreceptor 1Y flows. On the other hand, this is a so-called negative latent image formed by the charge remaining in the portion not irradiated with the laser beam 3Y. The electrostatic charge image formed on the photoreceptor 1Y in this way is rotated to a predetermined development position as the photoreceptor 1Y travels. At this development position, the electrostatic charge image on the photoreceptor 1Y is visualized (developed) by the developing device 4Y.

  In the developing device 4Y, for example, an electrostatic image developing developer containing at least yellow toner and a carrier is accommodated. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y, and has a charge of the same polarity (negative polarity) as the charged electric charge on the photoreceptor 1Y, and a developer roll (developer holder). Is held on. As the surface of the photoreceptor 1Y passes through the developing device 4Y, yellow toner adheres electrostatically to the static image portion that has been neutralized on the surface of the photoreceptor 1Y, and the electrostatic image is developed with the yellow toner. Is done.

  From the viewpoint of development efficiency, image graininess, gradation reproducibility, and the like, a bias potential (development bias) in which an AC component is superimposed on a DC component may be applied to the developer holder. Specifically, when the developer holding member DC applied voltage Vdc is set to, for example, −700 V or more and −300 V or less, the developer holding member AC voltage peak width Vp−p is set to a range of, for example, 0.5 kV or more and 2.0 kV or less. Good. The photoconductor 1Y on which the yellow toner image is formed continues to run at a predetermined speed, and the toner image developed on the photoconductor 1Y is conveyed to a predetermined primary transfer position.

  When the yellow toner image on the photoreceptor 1Y is conveyed to the primary transfer position, a primary transfer bias is applied to the primary transfer roller 5Y, and electrostatic force directed from the photoreceptor 1Y to the primary transfer roller 5Y is applied to the toner image. The toner image on the photoreceptor 1 </ b> Y is transferred to the intermediate transfer belt 20. The transfer bias applied at this time is a (+) 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 photoreceptor 1Y is removed and collected by the cleaning device 6Y.

  Further, 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 onto which the yellow toner image has been transferred by 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 a multiple manner. The

  The intermediate transfer belt 20 onto which the four color toner images have been transferred in multiple passes through the first to fourth units is disposed on the image transfer surface side of the intermediate transfer belt 20, the support roller 24 that is in contact with the inner surface of the intermediate transfer belt 20. The secondary transfer roller (secondary transfer means) 26 is connected to a secondary transfer portion. On the other hand, a recording paper (recording medium) P is fed at a predetermined timing into a gap where the secondary transfer roller 26 and the intermediate transfer belt 20 are pressed against each other via a supply mechanism, and the secondary transfer bias is supplied to the support roller. 24. The transfer bias applied at this time is a (−) polarity that is the same polarity as the polarity (−) of the toner, and an electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, and the transfer bias is applied to the intermediate transfer belt 20. The toner image 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 means (not shown) for detecting the resistance of the secondary transfer portion, and is voltage-controlled.

  Thereafter, the recording paper P is fed to the pressure contact portion (nip portion) of the pair of fixing rolls in the fixing device (roll-type fixing means) 28, the toner image is heated, and the color-superposed toner image is melted to record the recording paper. Fixed onto P.

  Examples of the recording medium to which the toner image is transferred include plain paper and OHP sheet used in an electrophotographic copying machine or printer.

  The recording paper P on which the color image has been fixed is carried out toward the discharge unit, and a series of color image forming operations is completed.

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

  FIG. 3 is a schematic configuration diagram illustrating an example of a process cartridge containing the developer for developing an electrostatic charge image according to the present embodiment. The process cartridge 200 includes, together with the 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 static elimination exposure using an attachment rail 116. Combined and integrated. In FIG. 2, reference numeral 300 indicates a recording medium.

  The process cartridge 200 is detachable from an image forming apparatus main body including a transfer device 112, a fixing device 115, and other components (not shown). It forms a 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 static elimination 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 static elimination exposure. You may provide at least 1 sort (s) selected from the group comprised from 117.

  Next, the toner cartridge and the developer cartridge will be described. The toner cartridge is detachably attached to the image forming apparatus, and contains at least toner to be supplied to a developing unit provided in the image forming apparatus. The toner cartridge only needs to contain at least toner, and may contain developer, for example, depending on the mechanism of the image forming apparatus. A 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 ( And a toner supply pipe (not shown). Further, when the toner stored in the toner cartridge becomes low, the toner cartridge is replaced.

  Since the image forming apparatus and the image forming method according to the present embodiment use the developer for developing an electrostatic image (the carrier according to the present embodiment), the occurrence of image deterioration after long-term image formation is suppressed.

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

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

  The volume average particle diameters of the magnetic core particles, the raw material composition (mixture) of the magnetic core particles and the carrier were measured using a laser diffraction 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 Corporation). More specifically, 100 parts by mass of magnetic core particles and 10 parts by mass of cellulose were added to a vibration pulverizer and dispersed. The obtained mixture was molded with a press using a die, and the above measurement was performed.

  The calcium content ratio in the surface part and inside of the magnetic core particles 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 calculated by cutting the magnetic core particles with a microtome, analyzing the cross section, and measuring 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, measuring each content ratio. The measured value was an average value when 10 points of a 0.5 μmφ region were measured in each of the surface and inside of the magnetic core particles and the surface of the carrier.

  The exposure rate of the magnetic core material particles on the carrier surface was determined by photographing each of the 500 carriers at 1000 times using a field emission scanning electron microscope (FE-SEM). Each surface area was measured with an image analyzer, and the obtained exposure rate was averaged.

  The average interval Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particles were measured at a magnification of 3000 times with respect to 50 magnetic particles using an ultra-depth color 3D shape measurement microscope (product name VK-9500, manufactured by Keyence Corporation) The surface was observed and Sm and Ry were measured and determined by averaging.

<Example 1>
[Preparation of magnetic core particle 1]
· _Mn 3 _{O 4} after the powder 25 parts by mass · _Fe 2 _{O 3} powder 75 parts by mass · CaCO ₃ powder 0.2 parts by mass The above raw materials were mixed in a mixing mill to conduct the calcination of 1 hour at 900 ° C..
To the baked mixed powder, 20 parts by mass of water and 3.0 parts by mass of polyvinyl alcohol were prepared to obtain a mixed solution. The prepared mixed liquid was stirred with a wet ball mill for 12 hours. The volume average particle size of the mixed powder was 0.5 μm.

Subsequently, after granulating the obtained liquid mixture with a spray dryer, the granulated material which has a dry particle | grain with a volume average particle diameter of about 42 micrometers was obtained using the sieve. 0.3 parts by mass of CaCO ₃ powder was mixed with the obtained granulated product.

  The granulated product was filled in a firing furnace and fired at 1150 ° C. for 4 hours in a nitrogen gas atmosphere to obtain a massive fired product. The obtained fired product was crushed with a hammer mill, and the pulverized product was applied to an air classifier to classify and remove the fine powder portion. Next, magnetic separation was performed to separate nonmagnetic portions, and magnetic core particles 1 having a volume average particle size of 35 μm were obtained through a sieve.

  The obtained magnetic core particles have a calcium content of 0.2% by mass, the calcium content ratio (a) in the magnetic core particles is 0.05% by mass, and the calcium content in the surface 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 irregularities on the surface of the magnetic core particle were 1.5 μm and 0.8 μm, respectively.

Magnetic core particle 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 A styrene-methyl methacrylate copolymer and carbon black, which are coating resins, were added to toluene and stirred and dispersed in a sand mill to prepare a resin coating layer forming solution. This solution was put in a vacuum degassing kneader together with the magnetic core material particles 1 and stirred at a temperature of 60 ° C. for 10 minutes. The current value of the stirring motor was monitored and the pressure was reduced to distill off toluene. The obtained resin coating layer-formed carrier was sieved with a mesh having an opening of 75 μm to obtain Carrier 1.

  The calcium content ratio (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%. The volume average particle diameter of the carrier 1 was 36 μm.

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

[Evaluation]
Image defects after long-term image formation under high temperature and high humidity were evaluated according to the following three evaluation items of halftone image quality, image omission, and fine line reproducibility. The results are shown in Table 1.

[Evaluation of carrier and developer]
Using the developer 1, 100,000 copies of a 1% printing chart were printed on A4 paper in a 35 ° C. and 85% RH environment using a modified copy machine Docu Center Color 500 manufactured by Fuji Xerox Co., Ltd. Initial (10th), 10,000, 50,000, 80,000, and 100,000 print charts after printing, and a print chart printed after standing for 72 hours after printing 100,000 sheets The evaluation of halftone image quality and image loss was performed according to the following criteria. The obtained results are shown in Table 1.

(Halftone image quality)
In the print chart, image quality deterioration such as density unevenness and blurring was visually observed and evaluated according to the following criteria.
○: When the halftone image quality degradation is not visually recognized △: When the halftone image quality degradation is unclearly visually recognized x: When the halftone image quality degradation is clearly recognized visually

(Image missing)
The number of image omissions due to carrier skipping in 10 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

(Fine line reproducibility)
Using the developer 1 and the modified machine, 100,000 sheets of a 1% printing chart were printed on A4 paper in an environment of 35 ° C. and 85% RH. Initial (10th sheet) After printing 10,000 sheets, 50,000 sheets, 80,000 sheets, and 100,000 sheets, and after leaving for 72 hours after printing 100,000 sheets, with a resolution of 2,400 dpi A 1 on 1 off image (an image in which one dot line is arranged in parallel at an interval of one dot) was output as a 5 cm × 5 cm chart perpendicular to the developing direction to the upper left, center and lower right of A4 paper. The output sample was observed using a magnifying glass with a scale of x100 times to see if there was a portion where the line spacing was narrowed due to toner scattering or the like, or a portion widened by narrowing the thin line. Grade evaluation was performed based on the following criteria from the observation results and the line spacing of the observed locations. The obtained results are shown in Table 1.
○: In all charts, the decrease in line spacing due to scattering and the increase due to thin line thinning are hardly observed. Δ: When there is at least one chart in which the line spacing decreases and increases but the thin line can be confirmed. If there is at least one chart that cannot be distinguished, or the thin line is missing

<Example 2>
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 to be mixed after granulation is changed to 0.1 parts by mass. Material particles 2 were obtained.

  The obtained magnetic core particle 2 has a calcium content of 0.2% by mass, the calcium content ratio (a) inside the magnetic core particle is 0.10% by mass, and the calcium in the surface part of the magnetic core particle 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 particles were 2.5 μm and 0.8 μm, respectively.

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

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

<Example 3>
The magnetic core material is the same 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 to be mixed after granulation is 0.15 parts by mass. Particle 3 was obtained.

  The obtained magnetic core particle 3 has a calcium content of 0.08% by mass, the calcium content ratio (a) in the magnetic core particle is 0.04% by mass, and the calcium in the surface part of the magnetic core particle. The content ratio (b) was 1.0% by mass, and b / a was 25. The average interval Sm and maximum height Ry of the irregularities on the surface of the magnetic core particles were 1.8 μm and 0.9 μm, respectively.

  A carrier 3 was obtained by coating the magnetic core particles with a coating resin in the same manner except that the magnetic core particles 1 were replaced with the magnetic core particles 3. The calcium content ratio (c) of the surface portion of the obtained carrier 3 was 0.4 mass%, and c / b was 0.4. The core 3 exposure rate of the carrier 3 was 15%. The volume average particle diameter of the carrier 3 was 36 μm.

  A developer 3 was produced in the same manner as in Example 1 except that the carrier 3 was used, and the printed matter was evaluated. The evaluation results are shown in Table 2.

<Example 4>
In the same manner as in Example 1, except that the amount of CaCO ₃ powder charged into the mixing mill is 1.2 parts by mass and the amount of CaCO ₃ powder to be mixed after granulation is changed to 1.2 parts by mass. Material particles 4 were obtained.

  The obtained magnetic core particle 4 has a calcium content of 0.95% by mass, the calcium content ratio (a) inside the magnetic core particle is 0.20% by mass, and the calcium in the surface part of the magnetic core particle. 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.

  A carrier 4 was obtained by coating the magnetic core particles with a coating resin in the same manner except that the magnetic core particles 1 were replaced with the magnetic core particles 4. The calcium content ratio (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 the carrier 4 was 18%. The volume average particle diameter of the carrier 4 was 36 μm.

  A developer 4 was prepared in the same manner as in Example 1 except that the carrier 4 was used, and the printed matter was evaluated.

<Example 5>
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 to be mixed after granulation is changed to 0.08 parts by mass. Material particles 5 were obtained.

  The obtained magnetic core particle X has a calcium content of 0.05% by mass, an internal calcium content ratio (a) of 0.01% by mass, and a calcium content ratio (b) of the surface portion of 0.00%. 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 particles were 1.8 μm and 0.8 μm, respectively.

  A carrier 5 was obtained by coating the magnetic core particles 5 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. The calcium content ratio (c) of the surface portion of the obtained carrier 5 was 0.2% by mass, and c / b was 0.40. The core 5 exposure rate of the carrier 5 was 15%, and the volume average particle diameter was 36 μm.

  A developer 5 was prepared in the same manner as in Example 1 except that the carrier 5 was used, and the printed matter was evaluated. The evaluation results are shown in Table 2.

<Example 6>
The magnetic core is the same 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 to be mixed after granulation is changed to 1.5 parts by mass. Material particles 6 were obtained.

  The obtained magnetic core particle X has a calcium content of 1.0 mass%, an internal calcium content ratio (a) of 0.2 mass%, and a calcium content ratio (b) of the surface portion of 8. 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 particles were 1.8 μm and 0.8 μm, respectively.

  A carrier 6 was obtained by coating the magnetic core particles 6 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. The calcium content ratio (c) of the surface portion of the obtained carrier X was 2.5% by mass, and c / b was 0.31. The core 6 exposure rate of the carrier 6 was 15%, and the volume average particle diameter was 36 μm.

  A developer 6 was prepared in the same manner as in Example 1 except that the carrier 6 was used, and the printed matter was evaluated. The evaluation results are shown in Table 2.

<Example 7>
Magnetic core material particles 7 were obtained in the same manner as in Example 1 except that the amount of CaCO ₃ powder charged into the mixing mill was 0.5 parts by mass and the CaCO ₃ powder mixed after granulation was changed to none. .

  The obtained magnetic core particle 7 has a calcium content of 0.2% by mass, an internal calcium content ratio (a) of 0.1% by mass, and a calcium content ratio (b) of the surface portion of 0.2% by mass. It was 5 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 particles were 1.7 μm and 0.9 μm, respectively.

  A carrier 7 was obtained by coating the magnetic core particles 7 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 7. The calcium content ratio (c) of the surface portion of the obtained carrier 7 was 0.2% by mass, and c / b was 0.4. The core material exposure rate of the carrier 7 was 13%, and the volume average particle diameter was 36 μm.

  A developer 7 was prepared in the same manner as in Example 1 except that the carrier 7 was used, and the printed matter was evaluated. The evaluation results are shown in Table 2.

<Example 8>
Magnetic core material particles 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 to be mixed after granulation is changed to 0.23 parts by mass. 8 was obtained.

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

A carrier 8 was obtained by coating the magnetic core particles 8 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 8. The calcium content ratio (c) of the surface portion of the obtained carrier 8 was 0.4 mass%, and c / b was 0.4. The core 8 exposure rate of the 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 the printed matter was evaluated. The evaluation results are shown in Table 2.

<Example 9>
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 2.5 parts by mass and the carbon black is changed to 0.25 parts by mass. 9 was obtained. The calcium content ratio (c) of the surface portion of the obtained carrier 9 was 0.3% by mass, and c / b was 0.1. The core 9 exposure rate of the carrier 9 was 5%, and the volume average particle diameter was 36 μm.

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

<Example 10>
The magnetic core particle 1 is 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 is changed to 0.15 parts by mass. 10 was obtained. The calcium content ratio (c) of the surface portion 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 diameter was 36 μm.

  A developer 10 was produced in the same manner as in Example 1 except that the carrier 10 was used, and the printed matter was evaluated. The evaluation results are shown in Table 2.

<Example 11>
The magnetic core particles 8 were coated with a coating resin in the same manner as in Example 1 except that the styrene-methyl methacrylate copolymer was changed to 2.5 parts by mass and the carbon black was changed to 0.25 parts by mass. 11 was obtained. The calcium content ratio (c) of the surface portion of the obtained carrier 11 was 0.15% by 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 the printed matter was evaluated. The evaluation results are shown in Table 2.

<Example 12>
The magnetic core particles 2 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 is changed to 0.15 parts by mass. 12 was obtained. The calcium content ratio (c) of the surface portion of the obtained carrier 12 was 0.35% by mass, and c / b was 0.50. The core 12 exposure rate of the carrier 12 was 32%, and the volume average particle size was 36 μm.

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

<Comparative Example 1>
Magnetic core material particles 13 were obtained in the same manner as in Example 1 except that the CaCO ₃ powder was not mixed as a raw material both when the mixing mill was charged and after granulation.

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

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

  A developer X was prepared in the same manner as in Example 1 except that the carrier X was used, and the printed matter was evaluated.

<Comparative Example 2>
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 none. .

  The obtained magnetic core particles 14 have a calcium content of 0.08% by mass, an internal calcium content ratio (a) of 0.05% by mass, and a calcium content ratio (b) of the surface portion of 0.2%. 2% by mass and b / a was 4. The average interval Sm and the maximum height Ry of the irregularities on the surface of the magnetic core particle were 1.0 μm and 0.9 μm, respectively.

  A carrier 14 was obtained by coating the magnetic core particles 14 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 14. The calcium content ratio (c) of the surface portion of the obtained carrier 14 was 0.1% by mass, and c / b was 0.5. The core 14 exposure rate of the carrier 14 was 22%, and the volume average particle size was 36 μm.

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

<Comparative Example 3>
A magnetic core material particle 1 is coated with a 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 is changed to 0.4 parts by mass. 15 was obtained.

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

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

<Comparative Example 4>
A magnetic core material particle 1 is coated with a 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 is changed to 0.1 part by mass. 16 was obtained.

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

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

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

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

  A carrier 17 was obtained by coating the magnetic core particles 17 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.

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

  A developer 17 was prepared in the same manner as in Example 1 except that the carrier 17 was used, and the printed matter was evaluated. 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 mass% or more and 1.0 mass% or less of calcium, and the magnetic core material with respect 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 portion is 5 or more, and the carrier surface portion after being coated with the resin coating layer with respect to the calcium content ratio (b) of the core particle surface portion When the ratio c / b of the calcium content ratio (c) is 0.1 or more and 0.5 or less, the ratio is stable and high even after long-term image formation under high temperature and high humidity as compared with the comparative example. Provided is a carrier for developing an electrostatic image in which image defects due to a decrease in carrier resistance are suppressed while ensuring 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 Photoconductor 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-type fixing means), 30 Intermediate transfer member cleaning device, 107 photoconductor, 108 charging roller, 111 developing device, 112 transfer device, 113 photoconductor cleaning device (cleaning device) 115 fixing device, 116 mounting rail, 117 opening for static 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 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 material containing at least 0.05 mass% to 1.0 mass% of calcium, and the ratio b / a of the calcium content ratio (b) of the surface portion to the internal calcium content ratio (a) is 5 or more A ratio of the calcium content ratio (c) of the surface portion coated with the resin coating layer to the calcium content ratio (b), including particles and a resin coating layer covering the surface of the magnetic core particle A carrier for developing an electrostatic charge image, wherein c / b is 0.1 or more and 0.5 or less.   The electrostatic charge image developing carrier 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 interval Sm of the 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 developing an electrostatic charge image according to claim 1 or 2.   An electrostatic charge image developing developer comprising the electrostatic charge image developing carrier according to claim 1 and an electrostatic charge image developing toner.   A developer cartridge containing the developer for developing an electrostatic charge image according to claim 4.   5. A developing means for storing the developer for developing an electrostatic charge image according to claim 4 and developing the electrostatic charge image formed on the surface of the image carrier with the developer for developing an electrostatic charge image to form a toner image. A process cartridge to be attached to and detached from the image forming apparatus. An image carrier, an electrostatic image forming means for forming an electrostatic image on the surface of the image carrier, and the electrostatic image developed with the developer for developing an electrostatic image according to claim 4. An image forming apparatus comprising: a developing unit that forms an image; and a transfer unit that transfers the developed toner image to a transfer target.

Images