JP6458773B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method.

  Patent Document 1 discloses an image forming apparatus that develops an electrostatic latent image formed on a photoreceptor using a magnetic toner including hydrophobic silicon dioxide fine particles and organic fine particles as external additives. In the method for producing a magnetic toner used in such an image forming apparatus, magnetic toner base particles (powder) and external additives (hydrophobic silicon dioxide fine particles and organic fine particles) are mixed to form an external surface on the magnetic toner base particles. After adhering the additive, the magnetic toner base particles (powder) are dispersed and jetted in a hot air stream to fix external additives (hydrophobic silicon dioxide fine particles and organic fine particles) on the surface of the magnetic toner base particles. doing.

JP 7-271090 A

  However, with the technology disclosed in Patent Document 1 alone, sufficient heat-resistant storage stability and fixing property of the toner are ensured, and in continuous printing, the deposits on the image carrier are accurately removed by the cleaning member, and continuously. It is difficult to provide an image forming apparatus and an image forming method that can continue to form high-quality images. For example, in the image forming apparatus described in Patent Document 1, it is considered that the external additive is firmly adhered to the surface of the toner base particles, and organic fine particles are hardly detached from the toner particles. In such an image forming apparatus, when the substance attached to the surface of the photosensitive drum is removed by the cleaning member, the deposit on the photosensitive drum easily slips through the gap between the surface of the photosensitive drum and the cleaning member. It is difficult to sufficiently remove the deposits on the top. Further, in the image forming apparatus described in Patent Document 1, the release agent is likely to ooze out on the surface of the toner particles due to heat when fixing the external additive on the surface of the toner base particles. When the release agent oozes out on the surface of the toner particles, the toner particles tend to aggregate together, and the toner (more specifically, a carrier, a photosensitive drum, a developing roller, or the like) existing in the image forming apparatus has toner. Becomes easy to stick.

  The present invention has been made in view of the above circumstances, ensuring sufficient heat-resistant storage stability and fixability of toner, and in continuous printing, while accurately removing deposits on the image carrier with a cleaning member, An object of the present invention is to provide an image forming apparatus and an image forming method capable of continuously forming high-quality images.

An image forming apparatus according to the present invention includes an image carrier, an image forming unit, a developing device, a toner replenishing unit, and a cleaning member for removing substances adhering to the surface of the image carrier. The image forming unit is configured to form an electrostatic latent image on the image carrier. The developing device includes a first storage unit for storing a developer including toner and a carrier, and is configured to develop the electrostatic latent image formed on the image carrier with the toner. . The toner replenishing portion has a second housing portion for housing the replenishing toner, and is configured to replenish the replenishing toner into the first housing portion of the developing device. The developing device further includes a developer carrier and a toner carrier. The developer carrier is configured to receive and carry the developer from the first storage unit. The toner carrier is configured to receive and carry the toner in the developer from the developer carrier. The developing device is configured to develop the electrostatic latent image by causing the toner carried on the toner carrier to fly toward the image carrier. The replenishment toner includes a plurality of toner particles including toner base particles and an external additive attached to the surface of the toner base particles. The toner particles include inorganic particles and resin particles as the external additive. In the replenishment toner stored in the second storage unit, a first coverage ratio _RA indicating an area ratio of a region covered by the resin particles in a surface region of the toner base particles, and the toner carrier in the replenishment toner carrying state, the toner base and the second coverage R _B indicating the area ratio of the resin particles is covered regions of the surface area of the particles, the following equation (1), ( 2) and (3) are satisfied.
40.0% ≦ R _A (1)
30.0% ≦ R _B ≦ 55.0% (2)
0.70 ≦ R _B / R _A ≦ 0.90 (3)

The image forming method according to the present invention includes formation of an electrostatic latent image, formation of a toner image, transfer of the toner image, cleaning of the image carrier, and toner replenishment. In forming the electrostatic latent image, the image forming unit forms an electrostatic latent image on the image carrier. In the formation of the toner image, a developing device having a first storage portion for storing a developer containing toner and a carrier, a developer carrier, and a toner carrier is provided in the developer in the first storage portion. A step of carrying the toner on the developer carrier, a step of carrying the toner in the developer carried on the developer carrier on the toner carrier, and the toner carried on the toner carrier. A toner image is formed on the surface of the image carrier by flying toward the image carrier and developing the electrostatic latent image with the toner. In the transfer of the toner image, a transfer device transfers the toner image formed on the surface of the image carrier to an intermediate transfer member or a recording medium. In cleaning the image carrier, a cleaning member that comes into contact with the surface of the image carrier removes substances remaining on the surface of the image carrier after the transfer. In the toner replenishment, the toner replenishing unit having a second accommodating unit that accommodates toner for replenishment supplements the toner in the first accommodating unit consumed by the development of the electrostatic latent image. The replenishment toner is replenished into the first storage portion of the developing device. The replenishment toner includes a plurality of toner particles including toner base particles and an external additive attached to the surface of the toner base particles. The toner particles include inorganic particles and resin particles as the external additive. In the replenishment toner stored in the second storage unit, a first coverage ratio _RA indicating an area ratio of a region covered by the resin particles in a surface region of the toner base particles, and the toner carrier in the replenishment toner carrying state, the toner base and the second coverage R _B indicating the area ratio of the resin particles is covered regions of the surface area of the particles, the following equation (1), ( 2) and (3) are satisfied.
40.0% ≦ R _A (1)
30.0% ≦ R _B ≦ 55.0% (2)
0.70 ≦ R _B / R _A ≦ 0.90 (3)

  According to the present invention, sufficient heat-resistant storage stability and fixing property of the toner are ensured, and in continuous printing, high-quality images are continuously formed while accurately removing the deposits on the image carrier with a cleaning member. It is possible to provide an image forming apparatus and an image forming method that can continue to be performed.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating a photosensitive drum and a developing device of the image forming apparatus illustrated in FIG. 1. FIG. 3 is a diagram illustrating an example of a surface structure of toner particles used in an image forming apparatus according to an embodiment of the present invention.

  An embodiment of the present invention will be described. Note that the evaluation results (values indicating shape, physical properties, etc.) regarding the powder (more specifically, toner base particles, external additives, toner, carrier, etc.) are average values from the powder unless otherwise specified. This is the number average of the values measured for each of the average particles by selecting a significant number of such particles.

The number average particle diameter of the powder is the number average value of the equivalent circle diameter of primary particles (diameter of a circle having the same area as the projected area of the particles) measured using a microscope unless otherwise specified. . Moreover, the measured value of the volume median diameter (D ₅₀ ) of the powder is measured using a laser diffraction / scattering particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value. The glass transition point (Tg) is measured in accordance with “JIS (Japanese Industrial Standard) K7121-2012” using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) unless otherwise specified. It is the value. In the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) at the second temperature rise measured by the differential scanning calorimeter, the change point of the specific heat (outside the extrapolated line of the baseline and the falling line) The temperature (onset temperature) at the intersection with the insertion line corresponds to Tg (glass transition point).

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. When the name of a polymer is expressed by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Acrylic and methacrylic are sometimes collectively referred to as “(meth) acrylic”. Further, acrylonitrile and methacrylonitrile may be collectively referred to as “(meth) acrylonitrile”. Further, the silica particles mean dry silica particles unless otherwise specified.

  The image forming apparatus (image forming apparatus 100) according to the present embodiment will be described below with reference to FIGS.

  The image forming apparatus 100 is a tandem electrophotographic apparatus. As illustrated in FIG. 1, the image forming apparatus 100 includes developing devices 11 a to 11 d, photosensitive drums 12 a to 12 d, a transfer device 10, a fixing device 17, and a cleaning device 18. The transfer device 10 includes a transfer belt 13, a drive roller 14a, a driven roller 14b, a tension roller 14c, primary transfer rollers 15a to 15d, and a secondary transfer roller 16. The transfer belt 13 is stretched around a driving roller 14a, a driven roller 14b, and a tension roller 14c. The transfer belt 13 is driven by a driving roller 14a and rotates in a direction indicated by an arrow in FIG. The fixing device 17 is, for example, a nip fixing type fixing device including a heating roller and a pressure roller. The cleaning device 18 removes the toner remaining on the transfer belt 13. When an image is formed using the image forming apparatus 100, for example, a two-component developer is set in each of the developing devices 11a to 11d. The image forming apparatus 100 includes a control unit 20 that electronically controls the operation of the image forming apparatus 100 based on outputs from various sensors. The control unit 20 includes, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), and a storage device that stores a program and rewritable data. The user can give an instruction (electric signal) to the control unit 20 through an input unit (for example, a keyboard, a mouse, or a touch panel) (not shown).

  The two-component developer includes a toner and a carrier. The toner and the carrier are each a powder composed of a large number of particles. The toner includes a plurality of toner particles having the configuration described below. The carrier includes a plurality of carrier particles having the configuration described below. The toner contained in the two-component developer can be used as, for example, a positively chargeable toner. The positively chargeable toner is positively charged by friction with the carrier. Carrier particles contained in the carrier have magnetism. In order to impart magnetism to the carrier particles, at least a part of the carrier particles may be formed of a magnetic material (for example, a ferromagnetic material such as ferrite), or the carrier particles may be formed of a resin in which the magnetic particles are dispersed. You may form at least one part.

  The image forming apparatus 100 forms an electrostatic latent image on each surface layer portion (photosensitive layer) of the photoconductive drums 12a to 12d based on the image data. Next, the formed electrostatic latent image is developed using a two-component developer (toner and carrier) set in each of the developing devices 11a to 11d. Each of the developing devices 11a to 11d has a configuration shown in FIG. Hereinafter, when it is not necessary to distinguish (when common properties are described), each of the developing devices 11a to 11d is described as the developing device 11, and each of the photosensitive drums 12a to 12d is described as the photosensitive drum 12. To do. FIG. 2 shows the internal structure of the developing device 11 and the configuration of the photosensitive drum unit (photosensitive drum 12 or the like).

  As the photoconductor drum 12, for example, an organic photoconductor (OPC) drum is preferably used. The photosensitive drum 12 has a cylindrical outer shape. The photosensitive drum 12 includes a metal cylinder (for example, an aluminum pipe) as a core material, and a single-layer type photosensitive layer or a multilayer type photosensitive material containing a charge generating agent and a charge transport agent on the outside of the core material. Further provided are layers (eg, an undercoat layer, a charge generation layer, and a charge transport layer). A protective layer for protecting the photosensitive layer may be provided on the surface of the photosensitive layer. The photosensitive drum 12 is supported by, for example, a housing of the image forming apparatus 100 in a rotatable manner, and is driven by, for example, a motor (not shown) to rotate in the direction of the arrow in FIG.

  As shown in FIG. 2, the image forming apparatus 100 includes a charging device for uniformly charging the photosensitive layer of the photosensitive drum 12 with static electricity. The charging device includes a charging member 21 (for example, a charging roller) that contacts the surface F3 of the photosensitive drum 12, and is configured to charge the photosensitive layer by a contact charging method. The charged charging member 21 (for example, a member charged by applying a DC voltage or an AC superimposed DC voltage obtained by superimposing an AC voltage on the DC voltage) comes into contact with the photosensitive layer, thereby charging the photosensitive layer. To do. Further, as shown in FIG. 1, the image forming apparatus 100 includes an exposure device 22 for forming an electrostatic latent image on each photosensitive layer of the photosensitive drums 12a to 12d. The exposure device 22 includes, for example, an LED (light emitting diode) head as a light source. The exposure device 22 is configured to selectively irradiate each photosensitive layer of the photosensitive drums 12a to 12d with, for example, light emitted from an LED head based on the image data. When the exposure device 22 exposes the charged photosensitive layer, an electrostatic latent image is formed on the photosensitive layer. In the image forming apparatus 100, the charging device and the exposure device 22 as described above correspond to an image forming unit.

  Further, as shown in FIG. 2, the image forming apparatus 100 includes a cleaning blade 23 (for example, a rubber plate) for removing a substance (attachment) attached to the surface F3 of the photosensitive drum 12. The cleaning blade 23 is in contact with the surface F3 of the photosensitive drum 12. The cleaning blade 23 is pressed against the surface F3 of the photosensitive drum 12 by a biasing force of a spring, for example, and is configured to scrape off deposits on the photosensitive drum 12. As the photosensitive drum 12 rotates, the cleaning blade 23 slides relative to the surface F3 of the photosensitive drum 12.

  When the image forming apparatus 100 forms an image on the recording medium P, the image forming unit (the charging device and the exposure device 22 described above) forms an electrostatic latent image on the photosensitive layer of the photosensitive drum 12. Specifically, the charging device uniformly charges the photosensitive layer of the photosensitive drum 12. Subsequently, the exposure device 22 selectively irradiates the photosensitive layer of the photosensitive drum 12 with light. The light irradiation position is determined according to the image data. In the photosensitive layer, the potential of the portion irradiated with light decreases. By such light irradiation (exposure), an electrostatic latent image is formed on the photosensitive drum 12. Thereafter, the developing device 11 supplies charged toner (for example, toner charged by friction with the carrier) to the photosensitive drum 12 to develop the electrostatic latent image.

  As shown in FIG. 2, the developing device 11 includes a developing roller 111, a magnetic roller 112, a regulating blade 112 d, a first stirring shaft 113, and a second stirring shaft 114. Further, the developing device 11 includes storage units R2 and R3 and a transport unit R4. The transport unit R4 accommodates the developing roller 111 and the magnetic roller 112. The accommodating portion R3 accommodates the first stirring shaft 113, and the accommodating portion R2 accommodates the second stirring shaft 114. The developing roller 111 is disposed in the vicinity of the photosensitive drum 12. In the example shown in FIG. 2, a gap is provided between the developing roller 111 and the photosensitive drum 12 so that the toner can fly from the developing roller 111 toward the photosensitive drum 12.

  The developing device 11 is configured to develop the electrostatic latent image with toner. In the image forming apparatus 100 in the initial state (unused state), the storage units R2 and R3 each store a two-component developer including toner (initial toner) and a carrier.

  A replenishing toner container 115 as a toner replenishing unit is provided above the developing device 11. The replenishment toner container 115 has a storage portion R1 that stores replenishment toner, and is configured to replenish replenishment toner into the developing device 11. The supply toner is supplied from the storage portion R1 of the supply toner container 115 to the storage portion R2 of the developing device 11. The replenishment toner container 115 includes a replenishment amount adjusting member 115a. The supply amount of toner (the amount of toner supplied from the supply toner container 115 to the developing device 11) can be controlled by the supply amount adjusting member 115a. The replenishment amount adjusting member 115a is constituted by an elastic roller whose rotation operation is controlled by the control unit 20, for example.

  The initial toner and the replenishing toner may be the same toner or different toners. However, in order to stably form a suitable image, the initial toner and the replenishing toner are preferably the same toner. Note that the fact that two or more toners are the same means that there is substantially no difference in properties between the toners so that the toners are compatible.

  Each of the first stirring shaft 113 and the second stirring shaft 114 has a spiral stirring blade. When the first stirring shaft 113 and the second stirring shaft 114 rotate in the circumferential direction of the shaft, the developer is conveyed in the axial direction of each shaft. The first agitation shaft 113 and the second agitation shaft 114 convey the developer in opposite directions while agitating the developer in the developing device 11 (specifically, the accommodating portions R2 and R3). By stirring the developer, the toner in the developer is charged by friction with the carrier, and the carrier in the developer carries the toner.

  The magnetic roller 112 includes a magnet roll and a sleeve. The sleeve is a nonmagnetic cylinder (for example, an aluminum pipe). The shaft of the magnet roll and the sleeve are connected via a flange so that the sleeve can rotate around the non-rotating magnet roll. The magnetic roller 112 is driven by, for example, a motor (not shown) and rotates in the direction of the arrow in FIG.

  The magnet roll of the magnetic roller 112 has a plurality of magnetic poles (for example, a magnetic pole based on a fixed magnet) around the shaft. Specifically, the magnet roll includes a cylindrical fixed magnet (a cylindrical magnet fixed to the shaft) having a plurality of magnetic poles divided along the circumferential direction of the shaft. Hereinafter, among the magnetic poles of the magnet roll (specifically, the fixed magnet) of the magnetic roller 112, the magnetic pole for pumping up the developer in the storage portion (specifically, the storage portion R3) of the developing device 11 is referred to as “pump top pole”. The magnetic pole facing the developing roller 111 is described as “main pole”, and the magnetic pole facing the regulating blade 112d is described as “regulating pole”. The pumping pole is opposed to the first stirring shaft 113. In the developing device 11 shown in FIG. 2, the upper drawing pole and the regulation pole are shared. Specifically, the magnetic pole 112a (single magnetic pole) serves as both the upper and lower poles. The magnetic pole 112b corresponds to the main pole.

  The magnetic roller 112 attracts the carrier in the housing portion R3 by the magnetic force of the magnetic pole 112a (the common magnetic pole serving as the pumping pole and the regulating pole) while rotating the sleeve in the direction of the arrow in FIG. A developer (carrier and toner) is carried on F1. The developer is carried on the surface F1 of the magnetic roller 112 with the toner carried on the surface of the carrier. As a result, a magnetic brush by the carrier is formed on the surface F1 of the magnetic roller 112. The magnetic brush is a carrier particle cluster raised on the surface F1 of the magnetic roller 112. Toner adheres to the surface of the carrier particles connected in spikes. The thickness of the developer on the magnetic roller 112 (the height of the head of the magnetic brush) is regulated to a predetermined thickness by the regulating blade 112d. The regulating blade 112d is a plate-like magnetic member that can be magnetized by the magnetic force of the magnetic pole 112a, for example. The developing roller 111 and the magnetic roller 112 are arranged at an interval such that the magnetic brush on the magnetic roller 112 is in contact with the developing roller 111. The magnetic force of the magnetic pole 112b (main pole) acts to supply only the toner to the developing roller 111 out of the developer (toner and carrier) carried on the surface F1 of the magnetic roller 112.

  The developing roller 111 includes a magnet roll and a developing sleeve. The developing sleeve is a nonmagnetic cylinder (for example, an aluminum pipe). The magnet roll is located in the developing sleeve (in the cylinder), and the developing sleeve is located in the surface layer portion of the developing roller 111. The shaft of the magnet roll and the developing sleeve are connected via a flange so that the developing sleeve can rotate around the non-rotating magnet roll. The developing roller 111 is driven by, for example, a motor (not shown) and rotates in the direction of the arrow in FIG.

  In order to supply the toner in the developer carried on the magnetic roller 112 to the photosensitive drum 12, for example, by applying a bias (voltage) to at least one of the developing roller 111 and the magnetic roller 112, the surface potentials of both are developed. A potential difference is generated between the two. Due to this potential difference, the toner in the developer carried on the magnetic roller 112 moves to the developing roller 111 and is carried on the surface F 1 of the developing roller 111. Specifically, the developer carried on the surface F1 of the magnetic roller 112 (particularly, carried on the surface of the carrier) by rotating the sleeve of the developing roller 111 and the sleeve of the magnetic roller 112 in the direction of the arrow in FIG. Toner) and the developing roller 111 rub against each other. The toner in the developer carried on the surface F <b> 1 of the magnetic roller 112 is electrically attracted to the developing roller 111. As a result, a toner layer is formed on the surface F2 of the developing roller 111. As described above, in the image forming apparatus 100, the developing roller 111 and the magnetic roller 112 are configured to rotate while the developer (magnetic brush) carried on the magnetic roller 112 is in contact with the developing roller 111, respectively. The

  Furthermore, by applying a bias (voltage) to at least one of the developing roller 111 and the photosensitive drum 12, a potential difference is generated between the surface potentials of the two. This potential difference makes it easier for the toner carried on the developing roller 111 to move to the photosensitive drum 12. The toner carried on the developing roller 111 is electrically attracted to the exposed portion of the electrostatic latent image formed on the photosensitive drum 12 (for example, the portion whose potential is lower than the surroundings due to exposure), and the photosensitive drum. Fly to 12 As a result, a toner image is formed on the surface F3 of the photosensitive drum 12. As described above, in the image forming apparatus 100, the developing roller 111 and the photosensitive drum 12 cause the toner carried on the developing roller 111 to fly toward the photosensitive drum 12 and the electrostatic latent image on the photosensitive drum 12. It is comprised so that it may develop. Undeveloped toner (toner remaining on the developing roller 111) is collected by a magnetic brush on the magnetic roller 112. Specifically, the undeveloped toner is dropped in the housing portion R3 of the developing device 11 or attached to the magnetic brush and used for the next development (formation of a toner layer).

  The description will be continued with reference to FIG. As described above, in the image forming apparatus 100, the developing devices 11a, 11b, 11c, and 11d respectively develop the electrostatic latent images formed on the photosensitive drums 12a, 12b, 12c, and 12d (each image carrier). . The image forming apparatus 100 forms a toner image on each photoconductive drum 12 and then applies a bias (voltage) to each of the primary transfer rollers 15a to 15d to adhere the toner adhered to each of the photoconductive drums 12a to 12d. The (toner image) is primarily transferred onto the transfer belt 13 (intermediate transfer member). Further, by applying a bias (voltage) to the secondary transfer roller 16, the toner image on the transfer belt 13 is secondarily transferred to the transported recording medium P (transfer object). Thereafter, the fixing device 17 heats the toner transferred to the recording medium P to fix the toner to the recording medium P. Thereby, an image is formed on the recording medium P. Note that the toner remaining on the photosensitive drum 12 after the transfer process is removed together with other deposits on the photosensitive drum 12 by cleaning. In the cleaning process, the surface F3 of the photosensitive drum 12 is rubbed with the edge portion of the cleaning blade 23 to scrape and remove the deposits on the photosensitive drum 12.

  The image forming apparatus 100 includes a plurality of photosensitive drums 12a to 12d. For this reason, the image forming apparatus 100 sequentially transfers the toner images formed on each of the plurality of photosensitive drums 12a to 12d to the transfer belt 13 in the primary transfer step, thereby transferring a plurality of toner images onto the transfer belt 13. Different types of toner images (eg, toner images of different colors) can be superimposed. In the image forming apparatus 100, the toner images superimposed on the transfer belt 13 can be collectively transferred to the recording medium P in the secondary transfer process. For example, a full color image can be formed on the recording medium P by superimposing four color toner images of black, yellow, magenta, and cyan. As the recording medium P, for example, printing paper can be used. The transfer method may be a direct transfer method in which the toner image on the photosensitive member is directly transferred to the recording medium without using the intermediate transfer member.

  The image forming apparatus 100 is a touchdown image forming apparatus configured to develop an electrostatic latent image by the following touchdown development method.

(Touch-down development method)
The image forming method includes forming a magnetic brush, forming a toner layer, forming an electrostatic latent image, and forming a toner image. In the formation of the magnetic brush, a two-component developer containing toner and carrier is carried on the surface of a magnetic carrier (for example, the magnetic roller 112 shown in FIG. 2) in a state where the toner is carried on the surface of the carrier. By carrying the two-component developer on the magnetic carrier, a magnetic brush by the carrier is formed on the surface of the magnetic carrier. In the formation of the toner layer, the toner of the two-component developer carried on the surface of the magnetic carrier is moved to a toner carrier (for example, the developing roller 111 shown in FIG. 2) facing the magnetic carrier, A toner layer is formed on the surface of the toner carrier. In forming an electrostatic latent image, an electrostatic latent image is formed on the surface of an image carrier (for example, the photosensitive drum 12 shown in FIG. 2) facing the toner carrier. In the formation of the toner image, the toner in the toner layer formed on the surface of the toner carrier is caused to fly toward the image carrier to form a toner image on the surface of the image carrier.

  The image forming apparatus according to the present embodiment has the following configuration (hereinafter referred to as a basic configuration).

(Basic configuration of image forming apparatus)
The image forming apparatus includes an image carrier (for example, the photosensitive drum 12 illustrated in FIG. 2), an image forming unit, a developing device (for example, the developing device 11 illustrated in FIG. 2), and a toner replenishing unit (for example, 2 and a cleaning member (for example, the cleaning blade 23 shown in FIG. 2) for removing substances adhering to the surface of the image carrier. The image forming unit is configured to form an electrostatic latent image on the image carrier. In the image forming apparatus 100 illustrated in FIG. 1, the charging device including the charging member 21 and the exposure device 22 correspond to an image forming unit. The developing device has a first storage portion (for example, storage portions R2 and R3 shown in FIG. 2) for storing a developer including toner and carrier, and an electrostatic latent image formed on the image carrier. Is developed with toner. The toner replenishment unit has a second storage unit (for example, storage unit R1 shown in FIG. 2) that stores replenishment toner, and is configured to replenish replenishment toner into the first storage unit of the developing device. Is done. The developing device includes a developer carrier (for example, the magnetic roller 112 shown in FIG. 2) configured to receive and carry the developer from the first container, and the toner in the developer from the developer carrier. It further includes a toner carrier (for example, the developing roller 111 shown in FIG. 2) configured to receive and carry the toner. The developing device is configured to develop the electrostatic latent image by causing the toner carried on the toner carrier to fly toward the image carrier. The replenishing toner includes a plurality of toner particles including toner mother particles and an external additive attached to the surface of the toner mother particles. The toner particles include inorganic particles and resin particles as external additives. In the replenishment toner stored in the second storage unit, the first coverage ratio _RA indicating the area ratio of the region covered with the resin particles in the surface region of the toner base particles, and the state of being supported on the toner carrier in replenishment toner, and the second coverage R _B indicating the area ratio of a region where the resin particles are covered in the surface area of the toner base particles, the following equation (1), (2), and (3) Fulfill.
40.0% ≦ R _A (1)
30.0% ≦ R _B ≦ 55.0% (2)
0.70 ≦ R _B / R _A ≦ 0.90 (3)

  The initial toner and the replenishment toner are distinguished as shown below. The replenishment toner is toner that is replenished to the housing portion of the developing device after the start of use of the initial toner. The initial toner is toner that is substantially housed in the housing portion of the developing device in the initial state. The initial state of the image forming apparatus means an unused state (for example, when a product is sold). The initial toner includes not only the toner stored in the developing device storage unit in the initial state of the image forming apparatus, but also the initial setting (installation operation) at the start of use of the image forming apparatus. In addition, the toner to be charged automatically is also included.

In the above basic configuration, the first coverage ratio R _A (unit:%) and the second coverage ratio R _B (unit:%) are each expressed by the formula “coverage ratio = 100 × area of the coating region / area of the surface region”. Is done. In the formula, “area of the surface region” corresponds to the sum of the area of the covering region and the area of the exposed region. The “covered area” is covered with the resin particles (external additive) in the surface area of the toner base particles, and the “exposed area” is covered with resin particles (external additive) in the surface area of the toner base particles. It corresponds to each area that is not. Even a region covered with inorganic particles (external additive) corresponds to an “exposed region” if it is not covered with resin particles (external additive). A coverage of 100% means that the entire surface of the toner base particles is covered with resin particles (external additive). The first coverage ratio R _A is measured for the replenishment toner in a state of being accommodated in the toner replenishing portion accommodation portion (second accommodation portion). Second coverage R _B is measured for replenishing toner in a state of being carried on the toner carrying member. Method of measuring each of the first coverage R _A and the second coating rate R _B is the same method or an alternative method to Example described below.

  An example of the surface structure of toner particles comprising inorganic particles and resin particles as external additives is shown in FIG. The toner particles shown in FIG. 3 include toner base particles 30 and external additives (inorganic particles 31 and resin particles 32) attached to the surface of the toner base particles 30. The inorganic particles 31 are, for example, silica particles.

  In the above basic configuration, satisfying the relational expression (1) makes it easy to ensure sufficient heat-resistant storage stability of the replenishing toner. When the relational expression (1) is satisfied, it is considered that the toner base particles are sufficiently covered with the resin particles (external additive), and the heat resistance of the toner particles is improved.

In the above basic configuration, satisfying the relational expression (2) makes it possible to form a solid image and a halftone image with high image quality while ensuring sufficient fixability of the replenishment toner. Specifically, if the second coverage R _B is too large, excessive amounts of the resin particles (external additive) is apt to inhibit the fixation of the toner. In the image forming apparatus having the above basic configuration, by the second coverage R _B is less than 55%, is easy to ensure a sufficient fixing property of the replenishment toner. Also, if the second coverage R _B is 30% or more, the toner is easily separated from the sleeve, the toner is liable to fly toward the sleeve to the photosensitive drum. For this reason, jumping development between the toner carrier and the image carrier is preferably performed.

  In the image forming apparatus having the above basic configuration, the resin particles (external additive) are appropriately detached from the toner particles by satisfying the relational expression (3). Therefore, it is possible to suppress the phenomenon (carrier contamination) that the resin particles (external additive) adhere to the surface of the carrier particles while improving the cleaning properties of the image carrier. When carrier contamination occurs, the charge imparting property of the carrier (the ability to charge the toner) tends to decrease. Hereinafter, the action of the resin particles (external additive) relating to the cleaning property of the image carrier will be described based on the knowledge obtained by the inventors through experiments and the like with reference to FIG.

  By collecting resin particles at the edge portion (tip portion) of the cleaning blade 23 on the surface F <b> 3 of the photosensitive drum 12, it becomes possible to dam the deposits on the photosensitive drum 12 by the edge portion of the cleaning blade 23. . Due to the presence of an appropriate amount of resin particles at the edge portion of the cleaning blade 23, deposits (especially inorganic particles) on the photosensitive drum 12 pass between the surface F 3 of the photosensitive drum 12 and the edge portion of the cleaning blade 23. It becomes difficult to slip through. If the deposit on the photosensitive drum 12 passes between the surface F3 of the photosensitive drum 12 and the edge portion of the cleaning blade 23, the charging member 21 (for example, a charging roller) is easily contaminated. In the image forming apparatus having the above basic configuration, the resin particles (external additive) are appropriately detached from the toner particles, so that an appropriate amount of the resin particles can be present at the edge portion of the cleaning blade 23.

By adjusting the magnitude of the stress applied to the developer in the developing device, we can be adjusted ratio of the second coverage R _B for the first coverage _{R A (R B / R A} ). Specifically, when the stress applied to the developer increases in the developing device, the resin particles (external additive) are buried in the surface layer portion of the toner particles, and the amount of the resin particles (external additive) released from the toner particles is small. Tend to be. Such a tendency becomes particularly remarkable when the toner base particles include a toner core and a shell layer (for example, a resin film harder than the toner core) covering the surface of the toner core. For example, the image forming apparatus having the above basic configuration further includes a regulating blade (for example, regulating blade 112d shown in FIG. 2) for regulating the thickness of the developer on the developer carrying body, and the developer carrying body. However, it has a common magnetic pole (for example, the magnetic pole 112a shown in FIG. 2) that serves as both a drawing upper pole (a magnetic pole for pumping up the developer in the first container) and a regulating pole (a magnetic pole facing the regulating blade). when provided with a magnet roll is easily adjusted ratio of the second coverage R _B for the first coverage R _a and (R _B / R _a) in the range of 0.7 to 0.9. By sharing the upper electrode and the regulating electrode without forming them separately, the stress applied to the developer in the developing device is reduced, and the amount of resin particles (external additive) released from the toner particles increases. , the ratio of the second coverage _{R B (R B / R a} ) is reduced with respect to the first coverage R _a. However, the stirring speed of the developing device (more specifically, the rotational speed of the agitating shaft) by fast, that the ratio of the second coverage R _B for the first coverage R _A and (R _B / R _A) is increased it can. It is also possible to adjust the magnitude of stress applied to the developer in the developing device by changing the shape or density of the carrier.

  In the above basic configuration, the number average primary particle diameter of the resin particles (external additive) is preferably 50 nm or more and 200 nm or less. If the number average primary particle diameter of the resin particles (external additive) is too small, the resin particles do not function sufficiently as a spacer between the toner particles, and the durability of the toner tends to be insufficient. On the other hand, if the number average primary particle diameter of the resin particles (external additive) is too large, the fluidity of the toner is deteriorated or the resin particles collected on the edge of the cleaning member (for example, the photoconductor). The photosensitive layer of the drum) is likely to be scraped off. The particle diameter of the resin particles can be adjusted based on, for example, polymerization conditions (particularly stirring conditions) during resin synthesis. In the above basic configuration, when the number average primary particle diameter of the resin particles (external additive) is 50 nm or more and 200 nm or less, the number average primary particle diameter of the inorganic particles (external additive) is 5 nm or more and 50 nm or less. Even if it exists, it is thought that the slipping-through of the inorganic particles at the edge portion of the cleaning member can be suitably suppressed.

  In order to ensure sufficient heat-resistant storage stability and fixability of toner and to continuously form high-quality images while accurately removing deposits on the image carrier with a cleaning member in continuous printing, It is preferable to form an image by the following method using the image forming apparatus having the above basic configuration.

(Preferable image forming method)
The image forming method includes formation of an electrostatic latent image, formation of a toner image, transfer of the toner image, cleaning of the image carrier, and toner replenishment. In forming an electrostatic latent image, the image forming unit forms an electrostatic latent image on an image carrier (for example, the photosensitive drum 12 shown in FIG. 2). In the formation of the toner image, a first accommodating portion (for example, accommodating portions R2 and R3 shown in FIG. 2) for accommodating a developer including toner and a carrier, and a developer carrier (for example, shown in FIG. 2). A developing device (for example, the developing device 11 shown in FIG. 2) having a magnetic roller 112) and a toner carrying member (for example, the developing roller 111 shown in FIG. 2) converts the developer in the first container into the developer. A step of carrying the toner on the carrier, a step of carrying the toner in the developer carried on the developer carrier on the toner carrier, and causing the toner carried on the toner carrier to fly toward the image carrier. And a step of developing the electrostatic latent image to form a toner image on the surface of the image carrier. In the transfer of the toner image, the transfer device (for example, the transfer device 10 shown in FIG. 1) transfers the toner image formed on the surface of the image carrier to the intermediate transfer member (in the image forming apparatus 100 shown in FIG. 1). Transfer to a belt 13) or a recording medium. In cleaning the image carrier, a cleaning member that contacts the surface of the image carrier (for example, the cleaning blade 23 shown in FIG. 2) removes the material remaining on the surface of the image carrier after the transfer. In toner replenishment, a toner replenishing portion (for example, the replenishing toner container 115 shown in FIG. 2) having a second housing portion (for example, the housing portion R1 shown in FIG. 2) containing replenishing toner is Replenishment toner is replenished into the first storage portion of the developing device so as to supplement the toner in the first storage portion consumed in developing the electrostatic latent image.

  Hereinafter, the toner and carrier used in the image forming apparatus according to the present embodiment will be described in detail.

  The toner particles contained in each of the initial toner and the replenishing toner may be toner particles in which the toner base particles do not have a shell layer (hereinafter referred to as non-capsule toner particles), or the toner base particles are in the shell layer. Toner particles (hereinafter referred to as capsule toner particles). Capsule toner particles can be produced by forming a shell layer on the surface of toner base particles (toner core) of non-capsule toner particles. The shell layer may be substantially composed of only a thermosetting resin (for example, a “preferable thermosetting resin” described later), or substantially a thermoplastic resin (for example, a “preferable thermoplastic resin described later). ]) Or may contain both a thermoplastic resin and a thermosetting resin.

  Non-capsule toner particles can be produced, for example, by a pulverization method or an aggregation method. In these methods, the internal additive is easily dispersed well in the binder resin of the non-capsule toner particles.

  In an example of the pulverization method, first, a binder resin, a colorant, a charge control agent, and a release agent are mixed. Subsequently, the obtained mixture is melt-kneaded using a melt-kneading apparatus (for example, a single-screw or twin-screw extruder). Subsequently, the obtained melt-kneaded product is pulverized and classified. Thereby, toner mother particles are obtained. When the pulverization method is used, the toner base particles can often be produced more easily than when the aggregation method is used.

  In an example of the aggregation method, first, these fine particles are aggregated in an aqueous medium containing fine particles of a binder resin, a release agent, a charge control agent, and a colorant until a desired particle size is obtained. Thereby, aggregated particles containing a binder resin, a release agent, a charge control agent, and a colorant are formed. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. Thereby, toner mother particles having a desired particle diameter are obtained.

  Preferred examples of the resin constituting each of the toner particles and carrier particles are shown below.

<Preferable thermoplastic resin>
Suitable examples of thermoplastic resins include styrene resins, acrylic resins (more specifically, acrylic ester polymers or methacrylic ester polymers), olefin resins (more specifically, polyethylene). Resin or polypropylene resin), vinyl chloride resin, polyvinyl alcohol, vinyl ether resin, N-vinyl resin, polyester resin, polyamide resin, or urethane resin. Further, a copolymer of each of these resins, that is, a copolymer in which an arbitrary repeating unit is introduced into the resin (specifically, a styrene-acrylic acid resin or a styrene-butadiene resin) is used. May be.

  The thermoplastic resin can be obtained by addition polymerization, copolymerization, or condensation polymerization of one or more thermoplastic monomers. The thermoplastic monomer is a monomer that becomes a thermoplastic resin by homopolymerization (more specifically, an acrylic acid monomer or a styrene monomer), or a monomer that becomes a thermoplastic resin by condensation polymerization (for example, by condensation polymerization). A combination of a polyhydric alcohol and a polyhydric carboxylic acid to be a polyester resin.

  The styrene-acrylic acid resin is a copolymer of one or more styrene monomers and one or more acrylic monomers. In order to synthesize a styrene-acrylic acid resin, for example, a styrene monomer and an acrylic acid monomer as shown below can be suitably used.

  Preferable examples of the styrene monomer include styrene, alkyl styrene (more specifically, α-methyl styrene, p-ethyl styrene, 4-tert-butyl styrene, etc.), p-hydroxy styrene, m-hydroxy styrene. , Vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, or p-chlorostyrene.

  Preferable examples of the acrylic acid monomer include (meth) acrylic acid, (meth) acrylonitrile, (meth) acrylic acid alkyl ester, or (meth) acrylic acid hydroxyalkyl ester. Suitable examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic. Examples include n-butyl acid, iso-butyl (meth) acrylate, or 2-ethylhexyl (meth) acrylate. Suitable examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or (meth) acrylic. The acid 4-hydroxybutyl is mentioned.

  The polyester resin is obtained by polycondensation of one or more polyhydric alcohols and one or more polyhydric carboxylic acids. As the alcohol for synthesizing the polyester resin, for example, dihydric alcohols (more specifically, diols or bisphenols) as shown below or trihydric or higher alcohols can be suitably used. As the carboxylic acid for synthesizing the polyester resin, for example, divalent carboxylic acids or trivalent or higher carboxylic acids as shown below can be suitably used.

  Preferable examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-butene-1,4. -Diol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol.

  Preferable examples of the bisphenol include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, or bisphenol A propylene oxide adduct.

  Preferable examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butane. Triol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5- Trihydroxymethylbenzene is mentioned.

  As preferable examples of the divalent carboxylic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid Succinic acid, alkyl succinic acid (more specifically, n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, etc.), or alkenyl succinic acid (more specific Specifically, n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, or isododecenyl succinic acid, etc.) may be mentioned.

  Preferred examples of the trivalent or higher carboxylic acid include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) Examples include methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

<Preferable thermosetting resin>
Preferable examples of the thermosetting resin include an aminoaldehyde resin, a polyimide resin (more specifically, a maleimide polymer or a bismaleimide polymer), or a xylene-based resin. An aminoaldehyde resin is a resin produced by condensation polymerization of a compound having an amino group and an aldehyde (for example, formaldehyde). Examples of aminoaldehyde resins include melamine resins, urea resins, sulfonamide resins, glyoxal resins, guanamine resins, or aniline resins.

The thermosetting resin can be obtained by crosslinking (polymerizing) one or more thermosetting monomers. Moreover, a thermosetting resin can also be synthesize | combined with a thermoplastic monomer by using a crosslinking agent. The thermosetting monomer is a monomer having crosslinkability. For example, when monomers of the same kind are three-dimensionally connected via “—CH ₂ —” to become a thermosetting resin, the monomer corresponds to a “thermosetting monomer”. Specifically, the melamine used for the synthesis of the melamine resin corresponds to a “thermosetting monomer”.

  Preferable examples of the thermosetting monomer include methylol melamine, melamine, methylolated urea (more specifically, dimethylol dihydroxyethylene urea), urea, benzoguanamine, acetoguanamine, or spiroguanamine. When synthesizing an aminoaldehyde resin, it is possible to proceed with resin synthesis (polymerization reaction) without adding an aldehyde separately by using methylolated product as a resin raw material (monomer or prepolymer). Become.

  Next, preferred examples of the configurations of the capsule toner particles and the carrier particles will be described.

[Capsule toner particles: toner mother particles]
The toner base particles contain a binder resin. The toner base particles may contain an internal additive (for example, a colorant, a release agent, a charge control agent, and a magnetic powder).

(Binder resin)
In the toner base particles, generally, the binder resin occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the overall properties of the toner base particles. In order to achieve both the heat-resistant storage stability and the low-temperature fixability of the toner, the toner base particles preferably contain the above-mentioned “suitable thermoplastic resin” as the binder resin. The polyester resin and the styrene-acrylic acid are preferable. It is particularly preferable to contain at least one of the resin.

(Coloring agent)
The toner base particles may contain a colorant. As the colorant, a known pigment or dye can be used according to the color of the toner. In order to form a high-quality image using toner, the amount of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

  The toner base particles may contain a black colorant. An example of a black colorant is carbon black. The black colorant may be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

  The toner base particles may contain a color colorant such as a yellow colorant, a magenta colorant, or a cyan colorant.

  As the yellow colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds can be used. Examples of the yellow colorant include C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191, or 194), naphthol yellow S, Hansa yellow G, or C.I. I. Vat yellow can be preferably used.

  The magenta colorant is, for example, selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. One or more compounds can be used. Examples of the magenta colorant include C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254) can be preferably used.

  As the cyan colorant, for example, one or more compounds selected from the group consisting of a copper phthalocyanine compound, an anthraquinone compound, and a basic dye lake compound can be used. Examples of cyan colorants include C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue can be preferably used.

(Release agent)
The toner base particles may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  Examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or aliphatic hydrocarbon wax such as Fischer-Tropsch wax; oxidized polyethylene wax or a block thereof Oxides of aliphatic hydrocarbon waxes such as copolymers; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax; animal properties such as beeswax, lanolin, or whale wax Waxes; mineral waxes such as ozokerite, ceresin, or petrolatum; waxes based on fatty acid esters such as montanate ester wax or castor wax; fats such as deoxidized carnauba wax The wax portion of the ester or the whole was deoxygenated can be suitably used. One type of release agent may be used alone, or multiple types of release agents may be used in combination.

(Charge control agent)
The toner base particles may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charge stability or charge rising property of the toner. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

  By adding a positively chargeable charge control agent (more specifically, pyridine, nigrosine, quaternary ammonium salt, or the like) to the toner base particles, the cationicity of the toner base particles can be increased. However, if sufficient chargeability is ensured in the toner, it is not necessary to add a charge control agent to the toner base particles.

(Magnetic powder)
The toner base particles may contain magnetic powder. Examples of magnetic powder materials include ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys containing one or more of these metals), ferromagnetic metal oxides (more specifically, Ferrite, magnetite, chromium dioxide, or the like) or a material subjected to ferromagnetization treatment (more specifically, a carbon material or the like imparted with ferromagnetism by heat treatment) can be suitably used. In order to suppress elution of metal ions (for example, iron ions) from the magnetic powder, it is preferable to use the surface-treated magnetic particles as the magnetic powder. One type of magnetic powder may be used alone, or a plurality of types of magnetic powder may be used in combination.

[Capsule toner particles: shell layer]
For example, by chemically reacting the toner core and the shell material in the liquid, the shell layer is bonded (chemically bonded) to the surface of the toner core. The shell layer may cover the entire surface of the toner core or may partially cover the surface of the toner core. The shell layer may be a film without graininess or a film with graininess. When a shell layer is formed in an aqueous medium using a water-soluble material as the shell material, it is considered that a film having no graininess is formed as the shell layer. When resin particles are used as the shell material, it is considered that if the material (resin particles) is completely melted and cured in a film-like form, a film having no graininess is formed as the shell layer. On the other hand, if the material (resin particles) is not completely melted and cured in a film form, a film having a form in which the resin particles are two-dimensionally connected (a film having a granular feeling) is formed as a shell layer. it is conceivable that. For example, the resin particles are attached to the surface of the toner core in the liquid and the liquid is heated, whereby the resin particles can be dissolved (or deformed) to form a film. However, the resin particles may be formed into a film by being heated in the drying step or receiving a physical impact force in the external addition step. The entire shell layer is not necessarily formed integrally. The shell layer may be a single film or an assembly of a plurality of films (islands) that are separated from each other.

  In order to ensure sufficient heat-resistant storage stability of the toner, the shell layer preferably contains a thermosetting resin (more specifically, a “suitable thermosetting resin” or the like). In order to ensure sufficient heat-resistant storage stability of the positively chargeable toner, it is particularly preferable that the shell layer contains a melamine resin and / or a urea resin. The melamine resin is a condensation polymer of melamine and formaldehyde (or a polymer of methylol melamine). The urea resin is a condensation polymer of urea and formaldehyde (or a polymer of methylolated urea). In order to improve the heat resistant storage stability of the toner, it is preferable that 80% by mass or more of the resin contained in the shell layer is a thermosetting resin, and 90% by mass or more of the resin is thermoset. More preferably, the resin is a thermosetting resin, and more preferably 100% by mass of the resin is a thermosetting resin. When the shell layer is substantially composed of melamine resin or urea resin, the thickness of the shell layer is preferably 1 nm or more and 20 nm or less.

  In order to achieve both heat-resistant storage stability and fixing property of the toner, the shell layer has a glass transition point (Tg) of 60 ° C. or higher and 80 ° C. or lower (more specifically, “preferable thermoplastic resin” or the like) ) Is preferably contained. In order to achieve both heat-resistant storage stability and fixability of the positively chargeable toner, the shell layer particularly preferably contains a styrene-acrylic acid resin having a glass transition point (Tg) of 60 ° C. or higher and 80 ° C. or lower. . When the shell layer is substantially composed of a thermoplastic resin having a glass transition point (Tg) of 60 ° C. or more and 80 ° C. or less, the thickness of the shell layer is preferably 20 nm or more and 30 nm or less.

  The thickness of the shell layer can be measured by analyzing a TEM (transmission electron microscope) image of a cross section of the toner particles using commercially available image analysis software (for example, “WinROOF” manufactured by Mitani Corporation). . If the thickness of the shell layer is not uniform in one toner particle, four equally spaced locations (specifically, two perpendicular lines are drawn at the approximate center of the cross section of the toner particle, and the two straight lines are drawn. The thickness of the shell layer is measured at each of the four points intersecting the shell layer, and the arithmetic average of the four measured values obtained is taken as the evaluation value (shell layer thickness) of the toner particles. The boundary between the toner core and the shell layer can be confirmed, for example, by selectively dyeing only the shell layer of the toner core and the shell layer. When the boundary between the toner core and the shell layer is unclear in the TEM photographed image, a characteristic element contained in the shell layer in the TEM photographed image is formed by combining TEM and electron energy loss spectroscopy (EELS). By performing the mapping, the boundary between the toner core and the shell layer can be clarified.

[Method for forming shell layer]
Preferable examples of the method for forming the shell layer include an in-situ polymerization method, a liquid-cured coating method, and a coacervation method. More specifically, after the toner core is placed in an aqueous medium in which a water-soluble shell material is dissolved, the aqueous medium is heated to advance the polymerization reaction of the shell material, thereby forming a shell layer on the surface of the toner core. A forming method (hereinafter referred to as a first shell forming method) is preferable.

  The aqueous medium is a medium containing water as a main component (more specifically, pure water or a mixed liquid of water and a polar medium). As a polar medium in the aqueous medium, for example, alcohol (more specifically, methanol or ethanol) can be used. The boiling point of the aqueous medium is about 100 ° C.

  In order to uniformly adhere the shell material to the surface of the toner core, it is preferable to highly disperse the toner core in a liquid containing the shell material. In order to highly disperse the toner core in the liquid, a dispersant may be included in the liquid. However, the amount of the dispersant contained in the liquid is preferably 75 parts by mass or less with respect to 100 parts by mass of the toner core. Examples of the dispersant include sodium polyacrylate, polyparavinylphenol, partially saponified polyvinyl acetate, isoprenesulfonic acid, polyether, isobutylene-maleic anhydride copolymer, sodium polyaspartate, starch, gum arabic, polyvinyl Pyrrolidone or sodium lignin sulfonate can be preferably used. One type of dispersant may be used alone, or two or more types of dispersants may be used in combination.

  When a shell layer containing a melamine resin and / or a urea resin is formed by the first shell formation method, the temperature of the aqueous medium during shell layer formation is 40 The temperature is preferably from 80 ° C. to 80 ° C., more preferably from 55 ° C. to 70 ° C.

  In forming the shell layer, resin particles (for example, a resin dispersion) may be used as the shell material. More specifically, in the liquid containing the resin particles and the toner core, the resin particles are adhered to the surface of the toner core, and then the temperature of the liquid is heated to a temperature higher than the Tg of the resin particles. A method in which film formation is advanced to form a shell layer on the surface of the toner core (hereinafter referred to as a second shell forming method) is preferable.

  In the second shell forming method, a resin dispersion can be used as the shell material. For example, in the case of forming a shell layer substantially containing a polymer of a vinyl compound, an emulsion polymerization reaction is allowed to proceed in a liquid (for example, an aqueous medium) containing a vinyl compound and an ionic surfactant. A dispersion (shell material) is obtained. When forming a shell layer containing an oily resin (a resin having a relatively low solubility in water), the oily resin is dissolved in a solvent (for example, an organic solvent), and then the resulting solution is used as an ionic surfactant. And a polyelectrolyte together with an aqueous medium, for example, using a homogenizer, the material in the aqueous medium is subjected to a dispersion treatment (specifically, microparticulation by shearing force or impact force) to obtain a resin dispersion ( Shell material) is obtained. The solvent used can be evaporated by heating and / or reduced pressure.

[Capsule toner particles: external additive]
An external additive (specifically, a powder containing a plurality of external additive particles) adheres to the surface of the toner base particles. Specifically, the toner particles include inorganic particles and resin particles as external additives. For example, the toner base particles (powder) and the external additive (powder) are stirred together, so that the external additive adheres (physically bonds) to the surface of the toner base particles with a physical force.

  As the inorganic particles (external additives), silica particles or metal oxide particles (more specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, etc.) are preferable. One or more types of particles selected from the group consisting of silica particles and titanium oxide particles are particularly preferable.

  The resin particles (external additives) are preferably resin particles containing one or more resins selected from the group consisting of a crosslinked acrylic resin and a crosslinked styrene-acrylic resin, and the crosslinked styrene-acrylic resin. Particles are particularly preferred. The cross-linked acrylic acid resin and the cross-linked styrene-acrylic acid resin each have excellent chargeability and are easier to produce fine particles than melamine resins and the like.

  The external additive particles may be surface-treated. For example, when silica particles are used as the external additive particles, hydrophobicity and / or positive chargeability may be imparted to the surface of the silica particles by the surface treatment agent. Examples of the surface treatment agent include a coupling agent (more specifically, a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent), or silicone oil (more specifically, dimethyl silicone oil). Etc.) can be suitably used. When the surface of the silica substrate (untreated silica particles) is treated with the surface treatment agent, a large number of hydroxyl groups (—OH) present on the surface of the silica substrate are partially or entirely derived from the surface treatment agent. Substituted with a functional group. As a result, silica particles having a functional group derived from the surface treating agent (specifically, a functional group that is more hydrophobic and / or positively charged than the hydroxyl group) on the surface can be obtained.

[Carrier particles]
The carrier particles may be carrier particles without a coat layer (for example, ferrite carrier particles), or may be carrier particles with a coat layer (hereinafter referred to as coated carrier particles). In order to form a high-quality image over a long period of time using a developer, it is preferable to use coated carrier particles. The coated carrier particles include a carrier core and a coat layer that covers the surface of the carrier core. It is preferable that the coat layer covers the entire surface of the carrier core.

  Hereinafter, suitable examples of the coated carrier particles will be described. The coated carrier particle includes a carrier core and a coat layer. In addition, you may use the carrier core which has the following structure as carrier particles as it is, without covering with a coating layer.

(Career core)
The carrier core preferably contains a magnetic material. The carrier core may be magnetic material particles, or the magnetic material particles may be dispersed in the binder resin of the carrier core. Examples of the magnetic material contained in the carrier core include magnetite, barium ferrite, maghemite, Mn—Zn ferrite, Ni—Zn ferrite, Mn—Mg ferrite, Ca—Mg ferrite, Li ferrite, and Cu—Zn ferrite. Magnetic iron oxide is preferred, and magnetite is particularly preferred. As a material for each carrier core, one type of magnetic material may be used alone, or two or more types of magnetic materials may be used in combination. A commercially available product may be used as the carrier core. Also, the carrier core may be made by pulverizing and firing the magnetic material. In the production of the carrier core, the saturation magnetization of the carrier can be adjusted by changing the amount of magnetic material added (particularly, the proportion of the ferromagnetic material). Further, in the production of the carrier core, the circularity of the carrier can be adjusted by changing the firing temperature.

(Coat layer)
The coat layer is formed on the surface of the carrier core so as to cover the carrier core. The coat layer is substantially composed of a resin. Additives may be dispersed in the resin constituting the coat layer. Examples of the method for forming the coat layer include a method of immersing the carrier core in a liquid containing a resin (or resin material), or a liquid containing a resin (or resin material) in the carrier core in the fluidized bed. The method of spraying is mentioned.

  As the resin constituting the coat layer, a thermoplastic resin (more specifically, the “preferable thermoplastic resin” described above, or a fluororesin) may be used, or a thermosetting resin (more specifically, The above-mentioned “preferable thermosetting resin” or silicone resin may be used. Moreover, you may provide crosslinking | crosslinked property to a thermoplastic resin by mixing a thermoplastic monomer and a hardening | curing agent. The coat layer may have a sea-island structure.

  Examples of the present invention will be described. Table 1 shows devices FA-1 to FA-5, FB-1 to FB-4, FC-1 to FC-4, and FD-1 to FD-4 (image forming apparatuses, respectively) according to examples or comparative examples. Indicates. Table 2 shows toners T-1 to T-5 (each electrostatic latent image developing toner) used in each apparatus shown in Table 1. Table 3 shows developing devices D-1 to D-4 used in each device shown in Table 1. The “stirring speed” in Table 3 is “100” as the stirring speed of the developing device of the multifunction machine (“TASKalfa 500ci” manufactured by Kyocera Document Solutions Co., Ltd.). In this case, the stirring speed of each developing device is shown. For example, the stirring speed of the developing device D-2 is 80% of the stirring speed of the unmodified developing device.

  Hereinafter, manufacturing methods, evaluation methods, and evaluation results of the devices FA-1 to FA-5, FB-1 to FB-4, FC-1 to FC-4, and FD-1 to FD-4 will be described in order. . In the evaluation in which an error occurs, a considerable number of measurement values with sufficiently small errors are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value. A field emission scanning electron microscope (FE-SEM) was used for the measurement of the number average primary particle diameter.

[Preparation of materials]
(Shell material S-2: Preparation of St-Ac suspension)
A 1 L three-necked flask equipped with a thermometer and a stirring blade was set in a water bath at a temperature of 30 ° C., and 815 mL of ion-exchanged water and a cationic surfactant (“Cootamin (registered trademark) 24P manufactured by Kao Corporation) were placed in the flask. , Lauryltrimethylammonium chloride 25 mass% aqueous solution) 75 mL. Thereafter, the temperature in the flask was raised to 80 ° C. using a water bath. Subsequently, two kinds of liquids (first liquid and second liquid) were dropped into the contents of the flask at 80 ° C. over 5 hours. The first liquid was a mixed liquid of 68 mL of styrene and 12 mL of n-butyl acrylate. The second liquid was a solution in which 0.5 g of potassium persulfate was dissolved in 30 mL of ion exchange water. Subsequently, the temperature in the flask was kept at 80 ° C. for another 2 hours to polymerize the flask contents. As a result, a suspension of a styrene-acrylic acid resin having a solid content concentration of 8% by mass (hereinafter referred to as St-Ac suspension) was obtained. Regarding the resin particles contained in the obtained St-Ac suspension, the number average primary particle diameter was 31 nm, and Tg was 68 ° C.

(External additive: Preparation of crosslinked St-Ac resin particles)
In a 4-liter flask having a capacity of 1 L equipped with a stirrer, a cooling tube, a thermometer, and a nitrogen introduction tube, 600 g of ion-exchanged water, 6 g of emulsifier (DBS: sodium dodecylbenzenesulfonate), and n-butyl methacrylate 100 g of (BMA), 20 g of styrene, 15 g of an initiator (BPO: benzoyl peroxide), and 80 g of a crosslinking agent (DVB: divinylbenzene) were added. The purity (mass fraction) of divinylbenzene (DVB) used as a crosslinking agent was 80%. Specifically, p-divinylbenzene (CAS No. 105-06-6: manufactured by Sigma-Aldrich) was distilled to obtain divinylbenzene having a purity of 80%.

  Subsequently, while stirring the contents of the flask, nitrogen gas was introduced into the flask to create a nitrogen atmosphere inside the flask. Further, while stirring the flask contents, the temperature of the flask contents is increased to 90 ° C. in a nitrogen atmosphere, and the flask contents are reacted for 3 hours (specifically, a polymerization reaction) in a nitrogen atmosphere and a temperature of 90 ° C. It was. As a result, an emulsion was obtained in the flask. Subsequently, the obtained emulsion was cooled, and through a washing step and a dehydration step, resin particles having a number average primary particle size of 80 nm (specifically, particles of a crosslinked styrene-acrylic acid resin) were obtained. Hereinafter, the obtained resin particles (crosslinked styrene-acrylic acid resin particles) are referred to as crosslinked St-Ac resin particles.

[Production of toner]
(Production of toner core)
Using an FM mixer (manufactured by Nippon Coke Industries Co., Ltd.), 100 parts by mass of a polyester resin (Toughton (registered trademark) NE-410 manufactured by Kao Corporation) and polypropylene wax (manufactured by Sanyo Kasei Kogyo Co., Ltd.) Trademark) 660P ") 5 parts by mass, carbon black (" REGAL (registered trademark) 330R "manufactured by Cabot Corporation) 5 parts by mass, and quaternary ammonium salt (" BONTRON (registered trademark) P-51 manufactured by Orient Chemical Industry Co., Ltd.) " ]) 1 part by mass was mixed.

Subsequently, the obtained mixture was melt-kneaded using a twin-screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.). Subsequently, the obtained kneaded product was cooled and then pulverized using a pulverizer (“Turbo Mill” manufactured by Freund Turbo). Subsequently, the obtained pulverized product was classified using a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, a toner core having a volume median diameter (D ₅₀ ) of 7 μm was obtained.

(Formation of shell layer)
A 1 L three-necked flask equipped with a thermometer and a stirring blade was prepared, and the flask was set in a water bath. Subsequently, 300 mL of ion-exchanged water was put in the flask, and the temperature in the flask was kept at 30 ° C. using a water bath. Subsequently, dilute hydrochloric acid was added to the flask to adjust the pH of the flask contents to 4.

  Subsequently, the shell material shown in Table 2 (the shell material S-1 or S-2 shown in Table 2 defined for each toner) was added to the flask. Specifically, the shell material S-2 was added in the production of the toner T-4, and the shell material S-1 was added in the production of the other toners (toners T-1 to T-3 and T-5). As shell material S-1, 75 parts by mass of partially saponified polyvinyl acetate (“GOHSENOL (registered trademark) GM-14L” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) and water-soluble methylol melamine (manufactured by Nippon Carbide Industries Co., Ltd. (Registered trademark) S-260 ") 1.4 parts by mass was added. As the shell material S-2, 18 parts by mass of a St-Ac suspension (solid content concentration 8% by mass) prepared by the above-described procedure was added. The addition amounts of each of the shell materials S-1 and S-2 (75 parts by weight, 1.4 parts by weight, and 18 parts by weight) indicate relative amounts with respect to 100 parts by weight of the toner core added later. ing.

  Subsequently, 300 g of the toner core prepared by the above-described procedure was added to the flask, and the flask contents were stirred for 1 hour under the conditions of a rotation speed of 200 rpm and a temperature of 40 ° C. Subsequently, 300 mL of ion-exchanged water was added to the flask, and the temperature in the flask was increased to 70 ° C. at a rate of 1.0 ° C./min while stirring the flask contents at a rotation speed of 100 rpm. The flask contents were held for 1 hour at a speed of 100 rpm. As a result, a shell layer was formed on the surface of the toner core, and a dispersion of toner base particles was obtained. In either case of using the shell materials S-1 and S-2, a resin film harder than the toner core was formed as the shell layer. Thereafter, the pH of the dispersion of the toner base particles was adjusted to 7 (neutralized) using sodium hydroxide, and the dispersion of the toner base particles was cooled to room temperature (about 25 ° C.).

(Washing process)
The dispersion of toner base particles obtained as described above was filtered (solid-liquid separation) using a Buchner funnel. As a result, toner base particles in the form of wet cake were obtained. Thereafter, the obtained wet cake-like toner base particles were redispersed in ion-exchanged water. Further, dispersion and filtration were repeated 5 times to wash the toner base particles.

(Drying process)
Subsequently, the washed toner base particles (powder) were dispersed in an aqueous ethanol solution having a concentration of 50% by mass to obtain a slurry of toner base particles. Subsequently, the toner base particles in the slurry were removed under the conditions of a hot air temperature of 45 ° C. and a blower air volume of 2 m ³ / min using a continuous surface reformer (“Coat Mizer (registered trademark)” manufactured by Freund Sangyo Co., Ltd.). Dried. As a result, dried toner base particles (powder) were obtained.

(External addition process)
Using an FM mixer having a capacity of 10 L (manufactured by Nippon Coke Industries Co., Ltd.), 100 parts by mass of toner base particles prepared by the above-mentioned procedure, and conductive titanium oxide particles (“EC-100” manufactured by Titanium Industry Co., Ltd., substrate: TiO ₂ particles, coating layer: 1.5 parts by mass of Sb-doped SnO ₂ film) and 0.5 parts by mass of hydrophobic dry-type fumed silica particles (“Reolosil (registered trademark) HG-09” manufactured by Tokuyama Corporation) The amount of the resin particles shown in Table 2 (crosslinked St-Ac resin particles prepared by the above-described procedure) was mixed. In Table 2, the amount of resin particles (unit: parts by mass) indicates a relative amount with respect to 100 parts by mass of toner base particles. For example, in the production of the toner T-1, the amount of resin particles (crosslinked St—Ac resin particles) was 1.6 parts by mass with respect to 100 parts by mass of the toner base particles.

  By the above mixing, external additives (titanium oxide particles, silica particles, and resin particles) adhered to the surface of the toner base particles. After the above mixing, the obtained mixture (powder) was sieved using a 200 mesh (aperture 75 μm) sieve. As a result, toners (toners T-1 to T-5) containing a large number of toner particles (capsule toner particles) were obtained.

Regarding the toners T-1 to T-5 obtained as described above, the area ratio (first coverage R _A ) of the region covered with the resin particles in the surface region of the toner base particles was measured. Further, the heat resistant storage stability of each toner was evaluated. The measurement results of the first coverage _RA and the evaluation results of the heat resistant storage stability were as shown in Table 2, respectively. For example, in the toner T-1, the first coverage ratio _RA was 40.8%. Further, in the evaluation of heat resistant storage stability, the aggregation degree of the toner T-1 was 15.5% by mass. The measurement method of 1st coverage _RA and the evaluation method of heat-resistant preservation | save property were as follows, respectively.

<Measurement method of first coverage ratio _RA >
Of the surface area of the toner particles contained in the measurement target (toner), an area with less unevenness is selected, and the area is selected as a field emission scanning electron microscope (FE-SEM) (“JSM-7600F” manufactured by JEOL Ltd.). ) To obtain a reflected electron image (surface photographed image) of toner particles.

Subsequently, the obtained surface image of the toner particles was taken into image analysis software (“WinROOF” manufactured by Mitani Corporation), and image analysis was performed using the image analysis software (WinROOF). Specifically, in the surface photographed image of the toner particle, the pen tool of the image analysis software (WinROOF) is checked while visually confirming the outline of the surface area (covering area) covered with the resin particles (external additive) in the surface area of the toner base particle. Was used to draw a line along the contour of the covered area. Then, using the automatic measurement function of the image analysis software (WinROOF), the area (projected area) of the area (covered area) surrounded by the line was calculated. When there are a plurality of island-shaped covering regions in the surface photographed image of toner particles (one field of view: 1 μm × 1 μm), the area (projected area) of each of these island-shaped covering regions is calculated, The total area of the covering regions (each island-like region) was determined. Then, the area ratio (first coverage R _A ) of the area covered by the resin particles (external additive) in the surface area of the toner base particles was determined. The first coverage R _A was measured with 10 fields of view for each toner particle, and the arithmetic average of the 10 measured values obtained was used as the evaluation value (first coverage R _A ) of the toner particles. Further, the first coverage _RA is measured for each of the 10 toner particles contained in the measurement object (toner), and the arithmetic average of the measured values of the 10 toner particles obtained is evaluated for the measurement object (toner). The value (first coverage R _A ) was used.

<Method for evaluating heat-resistant storage stability>
3 g of the evaluation object (toner) was placed in a 20 mL polyethylene container, and the container was covered. The sealed container was left in an oven set at 58 ° C. for 3 hours. Thereafter, the container taken out from the oven was cooled to room temperature (about 25 ° C.), and the toner was taken out from the container to obtain an evaluation toner (heat-treated toner).

Subsequently, the obtained toner for evaluation was placed on a sieve (metal mesh) having an aperture of 106 μm having a known mass. Then, the mass of the sieve containing the toner was measured, and the mass of the toner on the sieve (the mass of the toner before sieving) was determined. Subsequently, the sieve was set on a powder tester (manufactured by Hosokawa Micron Co., Ltd.), and according to the manual of the powder tester, the sieve was vibrated for 30 seconds under the condition of the rheostat scale 5, and the evaluation toner was sieved. Then, the mass of the toner remaining on the sieve (the mass of the toner after sieving) was determined by measuring the mass of the sieve containing the toner after sieving. From the mass of the toner before sieving and the mass of the toner after sieving, the degree of aggregation (unit: mass%) was determined based on the following formula.
Aggregation degree = 100 × mass of toner after sieving / mass of toner before sieving

  When the degree of aggregation was 20% by mass or less, it was evaluated as “good”, and when the degree of aggregation exceeded 20% by mass, it was evaluated as “poor” (not good).

[Manufacture of image forming apparatus]
(Preparation of developing device)
By removing the developing device from the multifunction peripheral (“TASKalfa 500ci” manufactured by Kyocera Document Solutions Co., Ltd., developing method: touch-down developing method), and modifying the developing device as shown in Table 3, developing devices D-1 to D-1 D-4 was obtained.

  In the developing device D-1, the upper electrode and the regulating electrode of the magnet roll of the developer carrier are shared. In developing device D-2, the stirring speed was reduced to 80% of the stirring speed of an unmodified developing device. In the developing device D-3, the upper electrode of the magnet roll of the developer carrying member and the regulating electrode were made common, and the stirring speed was reduced to 80% of the stirring speed of the unmodified developing device. In the developing device D-4, the stirring speed was reduced to 90% of the stirring speed of the unmodified developing device. In each of the developing devices D-1 and D-3, the upper and lower poles are formed by a single magnetic pole (common magnetic pole) of a fixed magnet. In each of the developing devices D-2 and D-4, the upper and lower poles are formed by separate magnetic poles of the fixed magnet.

  The developing device modified as described above (any of the developing devices D-1 to D-4 shown in Table 1 defined for each device) is returned to the multi-function device (TASKalfa 500ci) and replenishment toner A two-component developer containing the same toner (any one of toners T-1 to T-5 shown in Table 1 defined for each device) for replenishment in the housing portion (first housing portion) of the developing device Toner (any one of toners T-1 to T-5 shown in Table 1 defined in each apparatus) is put into a storage part (second storage part) of a replenishing toner container. 1 to FA-5, FB-1 to FB-4, FC-1 to FC-4, and FD-1 to FD-4 were obtained. For example, in the manufacture of the apparatus FA-1, a mixture (two-component developer) of the toner T-1 and the carrier is put into the housing portion of the developing device D-1, and the toner T-1 is placed in the housing portion of the replenishment toner container. Was introduced. The method for preparing the two-component developer was as follows.

<Preparation of two-component developer>
The ferrite carrier and the toner (any one of the toners T-1 to T-5 shown in Table 1 defined in each apparatus) were mixed for 30 minutes using a ball mill to prepare a two-component developer. The proportion of toner in the two-component developer was 10% by mass. A ferrite carrier is obtained by spraying 230 parts by mass of a resin solution (resin: 30 parts by mass of a silicone resin, solvent: 200 parts by mass of toluene) on 1000 parts by mass of a Mn—Mg ferrite core (powder) having a number average primary particle size of 35 μm. After coating, it was produced by performing a heat treatment at a temperature of 200 ° C. for 60 minutes.

Regarding the devices FA-1 to FA-5, FB-1 to FB-4, FC-1 to FC-4, and FD-1 to FD-4 obtained as described above, the first coverage _RA and each of the measurement results of the second coverage R _B are as shown in Table 1. As a result of the second coverage R _B divided by the first coverage _{R A (R B / R A} ) it is also shown in Table 1. For example, in the apparatus FA-1, the first coverage ratio R _A is 40.8%, the second coverage ratio R _B is 30.6%, and “R _B / R _A ” is 0.75 (= 30). .6 / 40.8). Second method for measuring coverage R _B were as follows. The first coverage _RA shown in Table 1 is a value measured for the replenishment toner by the method described above.

<Measurement method of the second coverage R _B>
After performing calibration using the system menu of the target device (any one of the devices FA-1 to FD-4) and adjusting the image density, a sample image with a printing rate of 5% is recorded on the recording medium (printing paper) using the target device. ) Was subjected to a printing durability test for continuous printing of 10,000 sheets. After the printing endurance test, the target device is instructed to print a halftone image having a resolution of 600 dpi and a printing rate of 50% on the entire surface of the A4 size printing paper. In the middle of printing (specifically, a thin toner layer is formed on the surface of the toner carrier). The printing operation of the target device was suddenly stopped at the time of formation). Then, the power of the target device was turned off, and the developing device was taken out from the target device. Since the initial toner in the developing device is consumed by the printing durability test, the toner in the housing portion (first housing portion) of the developing device after the printing durability test is stored in the housing portion (first container) of the replenishment toner container. 2 is a replenishment toner replenished from (2 storage section).

Subsequently, a small amount of toner was collected from the toner layer (toner carried on the toner carrier) formed on the surface of the toner carrier of the developing device. Specifically, toner was collected from a portion of the toner layer on the toner carrier before the development position (position where the toner flies toward the image carrier). For collected toner was measured second coverage R _B in the first coverage R _A similar method. Specifically, a reflection electron image (surface image) of toner particles is obtained using a field emission scanning electron microscope (FE-SEM), and an image is analyzed using image analysis software (“WinROOF” manufactured by Mitani Corporation). By performing the analysis, the area ratio (second coverage R _B ) of the area covered by the resin particles (external additive) in the surface area of the toner base particles was obtained. The second coverage R _B measured in the toner particles, one for ten fields of view, the arithmetic mean of the ten measurements obtained, and the evaluation value of the toner particles (second coverage R _B). Further, measuring a second coverage R _B respectively, for the 10 toner particles contained in a measurement target (toner), the arithmetic mean of the measured values of ten toner particles obtained, evaluation of the measurement object (toner) The value (second coverage R _B ) was used.

[Evaluation method]
The evaluation methods of the devices FA-1 to FA-5, FB-1 to FB-4, FC-1 to FC-4, and FD-1 to FD-4 (hereinafter referred to as target devices) are as follows. It is.

(Fixing rate)
In an environment with a temperature of 23 ° C. and a humidity of 50% RH, using the target device (any one of the devices FA-1 to FD-4), the size of the evaluation paper (“Multi Paper Super Economy + A4” manufactured by ASKUL Corporation) A solid image (specifically, an unfixed toner image) of 20 mm × 20 mm was formed. Thereafter, the paper on which the image (unfixed toner image) was formed was passed through the fixing device of the evaluation machine. Subsequently, using a reflection densitometer (“SpectroEye (registered trademark)” manufactured by X-Rite), the image density (hereinafter referred to as pre-rubbing ID) of the image on the paper passed through the fixing device was measured. Subsequently, an image on the evaluation sheet was rubbed 5 times with no weight (using only the weight of the weight) using a 500 g weight coated with a fabric. Subsequently, using a reflection densitometer (SpectroEye), the image density of the image on the evaluation paper (hereinafter referred to as post-rubbing ID) was measured. Subsequently, the fixing rate (unit:%) was determined according to the formula “fixing rate = 100 × ID after rubbing / ID before rubbing” and evaluated according to the following criteria. Prior to image formation, the development bias of the target apparatus was adjusted so that the pre-rub ID was about 1.3.
○ (Good): The fixing rate was 90% or more.
X (not good): The fixing rate was less than 90%.

  The fixing rate indicates how much the image density (ID) decreases after rubbing, based on the image density (ID) before rubbing. That is, the fixing rate is an index indicating the ratio of the toner that is sufficiently fixed in the toner constituting the image.

(Charge amount maintenance rate)
In an environment with a temperature of 23 ° C. and a humidity of 50% RH, calibration is performed using the system menu of the target device (any one of the devices FA-1 to FD-4) to adjust the image density, and then printing is performed using the target device. A press life test was performed in which a sample image having a rate of 5% was continuously printed on a recording medium (printing paper) by 10,000 sheets. Prior to printing the test, remove the two-component developer from the receiving portion of the developing device (first housing part), the charge amount of the toner contained in the two-component developer (hereinafter, described as printing before the charge amount E _A Measured). Furthermore, after the printing test, take out the two-component developer from the accommodating portion (first housing portion) of the developing device, the charge amount of the toner contained in the two-component developer (hereinafter, and printing the charged amount E _B Described). Then, the printing before the charge amount E _A, based on the printing after charge E _B, charging retention (unit:%) according to the following equation was calculated.
Charge amount retention rate = 100 × E _B / E _A

  A Q / m meter (“MODEL210HS-1” manufactured by Trek) was used for the measurement of the charge amount of the toner. Specifically, the toner charge amount (unit: μC / g) was determined based on the formula “total amount of electricity of sucked toner (unit: μC) / mass of sucked toner (unit: g)”.

  When the charge amount maintenance rate was 80% or more, it was evaluated as ◯ (good), and when it was less than 80%, it was evaluated as x (not good).

(Image irregularities, charging roller contamination)
In an environment with a temperature of 23 ° C. and a humidity of 50% RH, calibration is performed using the system menu of the target device (any one of the devices FA-1 to FD-4) to adjust the image density, and then printing is performed using the target device. A press life test was performed in which a sample image with a rate of 5% was continuously printed on a recording medium (printing paper) 10,000 sheets. After the printing durability test, a halftone image having a resolution of 600 dpi and a printing rate of 50% was formed on the entire surface of the A4 size printing paper. Subsequently, it was visually confirmed whether or not there was a streak pattern in the formed halftone image. Further, after the halftone image was formed, it was visually confirmed whether or not the surface of the charging roller (charging device) of the target device was dirty (particularly, adhesion of toner components).

  Regarding the evaluation of the image unevenness of the halftone image, if a streak pattern (image unevenness) cannot be confirmed in the halftone image by visual observation, it is evaluated as “good”, and when it does not correspond to “○”. Was evaluated as x (not good).

  Regarding the evaluation of the charging roller contamination, it was evaluated as ◯ (good) when the surface of the charging roller could not be confirmed by visual observation, and evaluated as x (not good) when it did not correspond to “◯”.

[Evaluation results]
For each of the devices FA-1 to FA-5, FB-1 to FB-4, FC-1 to FC-4, and FD-1 to FD-4, fixing rate, image unevenness (presence of image unevenness), charging Table 4 shows the results of evaluating roller contamination (presence or absence of dirt) and charge amount maintenance rate.

The apparatuses FA-1 to FA-4 and FB-1 to FB-3 (image forming apparatuses according to Examples 1 to 7) each had the above-described basic configuration. Specifically, each of the devices FA-1 to FA-4 and FB-1 to FB-3 includes an image carrier (specifically, a photosensitive drum), an image forming unit (specifically, a contact charging type charging device, and An exposure device), a developing device (specifically, a touch-down developing type developing device), a toner replenishing portion (specifically, a toner container for replenishment), and a cleaning member (specifically, a cleaning blade). The toner particles of the replenishing toner were provided with inorganic particles and resin particles as external additives. As shown in Table 1, the first coverage R _A (the area ratio of the area covered by the resin particles in the surface area of the toner base particles in the toner for supply in the state of being accommodated in the second accommodating portion) and the second The coverage ratio R _B (area ratio of the area covered by the resin particles in the surface area of the toner base particles in the toner for replenishment carried on the toner carrier) is expressed by the following relational expressions (1) and (2 ) And (3).
40.0% ≦ R _A (1)
30.0% ≦ R _B ≦ 55.0% (2)
0.70 ≦ R _B / R _A ≦ 0.90 (3)

  As shown in Tables 2 and 4, in the devices FA-1 to FA-4 and FB-1 to FB-3, sufficient heat-resistant storage stability and fixing property of the toner are ensured, respectively. Thus, it was possible to continuously form high-quality images while accurately removing the deposits on the image carrier.

  The image forming apparatus and the image forming method according to the present invention can be used to form an image in, for example, a copying machine, a printer, or a multifunction peripheral.

DESCRIPTION OF SYMBOLS 10 Transfer device 11, 11a-11d Developing device 12, 12a-12d Photoconductor drum 13 Transfer belt 14a Drive roller 14b Driven roller 14c Tension roller 15a-15d Primary transfer roller 16 Secondary transfer roller 17 Fixing device 18 Cleaning device 20 Control Part 21 Charging member 22 Exposure device 23 Cleaning blade 30 Toner mother particle 31 Inorganic particle 32 Resin particle 100 Image forming device 111 Developing roller 112 Magnetic roller 112a Magnetic pole 112b Magnetic pole 112d Regulating blade 113 First stirring shaft 114 Second stirring shaft 115 Replenishment Toner container 115a replenishment amount adjusting member P recording medium R1, R2, R3 container R4 transport unit

Claims (5)

An image carrier;
An image forming unit configured to form an electrostatic latent image on the image carrier;
A developing device having a first containing portion for containing a developer including toner and a carrier, and configured to develop the electrostatic latent image formed on the image carrier with the toner;
A toner replenishing portion that has a second housing portion that contains a replenishing toner and is configured to replenish the replenishing toner into the first housing portion of the developing device;
A cleaning member for removing substances adhering to the surface of the image carrier;
With
The developing device includes:
A developer carrier configured to receive and carry the developer from the first container;
A toner carrier configured to receive and carry the toner in the developer from the developer carrier;
And developing the electrostatic latent image by causing the toner carried on the toner carrier to fly toward the image carrier,
The replenishment toner includes a plurality of toner particles including toner base particles and an external additive attached to the surface of the toner base particles,
The toner particles include inorganic particles and resin particles as the external additive,
In the replenishment toner stored in the second storage unit, a first coverage ratio _RA indicating an area ratio of a region covered by the resin particles in a surface region of the toner base particles, and the toner carrier in the replenishment toner carrying state, the toner base and the second coverage R _B indicating the area ratio of the resin particles is covered regions of the surface area of the particles, the following equation (1), ( An image forming apparatus satisfying 2) and (3).
40.0% ≦ R _A (1)
30.0% ≦ R _B ≦ 55.0% (2)
0.70 ≦ R _B / R _A ≦ 0.90 (3) A regulation blade for regulating the thickness of the developer on the developer carrier,
2. The developer carrying member includes a magnet roll having a common magnetic pole that serves as both a pumping pole for pumping up the developer in the first housing portion and a regulating pole facing the regulating blade. The image forming apparatus described in 1.   The image forming apparatus according to claim 2, wherein the toner base particles of the replenishing toner include a toner core and a shell layer that covers a surface of the toner core.   The image forming apparatus according to claim 1, wherein the resin particles contain one or more resins selected from the group consisting of a crosslinked acrylic resin and a crosslinked styrene-acrylic resin. . The image forming unit forms an electrostatic latent image on the image carrier;
A developing device having a first containing portion for containing a developer including toner and a carrier, a developer carrying member, and a toner carrying member, the developer in the first containing portion as the developer carrying member. A step of carrying, the step of carrying the toner in the developer carried on the developer carrier on the toner carrier, and the toner carried on the toner carrier directed toward the image carrier. Forming a toner image on the surface of the image carrier by flying and developing the electrostatic latent image with the toner; and
A transfer device transfers the toner image formed on the surface of the image carrier to an intermediate transfer member or a recording medium;
A cleaning member in contact with the surface of the image carrier removes a substance remaining on the surface of the image carrier after the transfer;
The first replenishing portion having a second housing portion that contains replenishing toner supplements the toner in the first housing portion consumed by the development of the electrostatic latent image. Replenishing the toner for replenishment into one container,
Including
The replenishment toner includes a plurality of toner particles including toner base particles and an external additive attached to the surface of the toner base particles,
The toner particles include inorganic particles and resin particles as the external additive,
In the replenishment toner stored in the second storage unit, a first coverage ratio _RA indicating an area ratio of a region covered by the resin particles in a surface region of the toner base particles, and the toner carrier in the replenishment toner carrying state, the toner base and the second coverage R _B indicating the area ratio of the resin particles is covered regions of the surface area of the particles, the following equation (1), ( An image forming method satisfying 2) and (3).
40.0% ≦ R _A (1)
30.0% ≦ R _B ≦ 55.0% (2)
0.70 ≦ R _B / R _A ≦ 0.90 (3)

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