JP2013171265A - Image forming apparatus - Google Patents

Abstract

A complex mechanism for supplying an external additive for image defects such as image density reduction and fogging caused by the external additive being buried in a toner surface when a low printing rate image is output for a long period of time. It is to solve without having.
An electrostatic latent image carrier, a two-component developer containing toner and a magnetic carrier, and developing the electrostatic latent image on the electrostatic latent image carrier using the two-component developer. An image forming apparatus having a developing device for replenishing and a replenishing device for replenishing the developing device with a replenishing developer,
An external additive supply carrier 101 exists in the developing device,
The external additive supply carrier has pores, and the external additive 103 is filled in the pores.
[Selection] Figure 3

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that obtains an image by visualizing an electrostatic image formed on an image carrier with toner. More specifically, the present invention relates to an image forming apparatus using a developer including toner and a carrier as a developer.

  An image forming apparatus such as a copying machine or a printer using an electrophotographic system visualizes an electrostatic image formed on a photoreceptor as a toner image using a developer, and transfers the toner image to a transfer material. The toner image is fixed on the material to form an image.

  A plurality of external additives are added to the normal toner in order to obtain the desired toner performance. However, if the image forming operation is performed for a long period of time, the toner repeatedly receives pressure and frictional heat at various locations in the developing device, and the external additive added to the toner surface gradually becomes buried in the toner surface. As a result, the external additive cannot perform its intended function.

  For example, if an external additive added to adjust the toner charge amount is buried in the toner surface, the toner charge amount is remarkably reduced, and the toner does not adhere to the non-image area where the toner should not adhere. An image defect called fogging will occur.

  In addition, in a two-component developer in which toner and carrier are mixed, an external additive that acts as a spacer is added in order to reduce the adhesion between the two and efficiently supply the toner onto the photoconductor in the developing section. Has been. When this external additive is buried in the toner surface, the adhesion between the toner and the carrier increases, and even when an electric field is applied, a sufficient amount of toner cannot be supplied to the photoreceptor, resulting in a decrease in image density. The problem will arise.

  The problem of burying external additives occurs due to repeated application of pressure and frictional heat generated in the developing device, so the smaller the amount of developer in the developing device and the lower the melting point of the toner, the more prominent it is. This is a great barrier to downsizing the image forming apparatus, which is a strong need. In addition, it is a great barrier when the toner fixing temperature is lowered to save energy in the apparatus.

  On the other hand, various methods have been proposed so far in order to improve various problems caused by burying the external additive of the toner. For example, as disclosed in Patent Document 1, a method is proposed in which the concentration of the external additive added to the toner contained in the toner supply bottle is set high and the external additive is replenished in the developing device simultaneously with the toner supply. Has been. Further, as in Patent Document 2, there is a container for storing an external additive in the vicinity of the developing device, and when the external additive is buried, the external additive is supplied into the developing device from the container for storing the external additive. This method has been proposed. Further, as in Patent Document 3, a method is proposed in which an external additive is re-added to the toner collected in the cleaning device and then returned to the developing device.

JP 2009-151120 A JP 2007-310191 A JP 2001-66960 A

  However, the configuration in which the external additive concentration of the toner contained in the toner supply bottle as in Patent Document 1 is high may not function effectively depending on the print rate of the output image.

  More specifically, a large amount of toner in the developing device is consumed when outputting an image with a high printing rate, so that the toner supply from the toner supply bottle to the developing device is frequently performed and the external additive is supplied. On the other hand, when image output with a low printing ratio continues for a long time, the toner in the developing device is hardly consumed, and therefore, toner with a high external additive concentration is not supplied into the developing device from the toner supply bottle. As a result, the external additive is not supplied into the developing device even if it is configured as in Patent Document 1, so that the toner in the developing device is buried in the external additive, causing various image defects such as fogging and density reduction. There is a problem that it occurs.

  On the other hand, a configuration having a container for storing and supplying an external additive in the image forming apparatus as in Patent Document 2, or a developer that re-adds the external additive in the image forming apparatus as in Patent Document 3 Although the configuration such as this can return the external additive into the developing unit without being affected by the printing rate of the output image, there is a mechanism for supplying the external additive and a space for arranging the external additive. Necessary. As a result, it is inevitable that the image forming apparatus becomes complicated and large, and there is a problem that it becomes a big barrier to downsizing that the user demands.

  Accordingly, an object of the present invention is to solve the above-mentioned problems by performing image output with a low printing rate for a long time without having a complicated mechanism for supplying an external additive that causes the apparatus to be enlarged. Another object of the present invention is to provide an image forming apparatus that does not cause image defects caused by burying external additives.

  The above object is achieved by the image forming apparatus according to the present invention.

In summary, an electrostatic latent image carrier, a two-component developer containing toner and a magnetic carrier, and an electrostatic latent image on the electrostatic latent image carrier are developed using the two-component developer. An image forming apparatus having a developing device for replenishing and a replenishing device for replenishing the developing device with a replenishing developer,
An external additive supply carrier exists in the developing device,
The image forming apparatus is characterized in that the external additive supply carrier has holes, and the holes are filled with the external additive.

  By using the image forming apparatus as described above, the external additive can be stably supplied to the toner in the developing device over a long period of time even when image output with a low printing rate continues for a long time. Even without providing a special mechanism, it is possible to solve image defects such as a decrease in image density and fog caused by burying the external additive.

1 is a schematic cross-sectional configuration diagram of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional configuration diagram of a developing device in Embodiment 1. FIG. 1 is a cross-sectional configuration diagram of an external additive supply carrier in Example 1. FIG. FIG. 4 is a diagram illustrating a toner charge amount and development efficiency in Example 1. 6 is a cross-sectional configuration diagram of an external additive supply carrier in Example 2. FIG. FIG. 6 is a diagram illustrating a toner charge amount and development efficiency in Example 2.

  Hereinafter, an image forming apparatus according to the present invention will be described in detail with reference to the drawings.

[Schematic Configuration and Operation of Image Forming Apparatus]
FIG. 1 shows a schematic cross-sectional configuration of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus according to this embodiment is a quadruple tandem type image forming apparatus, and performs image formation using toners of four colors of yellow (Y), magenta (M), cyan (C), and black (K). Device.

  The image forming apparatus has image forming portions P (PY, PM, PC, PK) for forming yellow, magenta, cyan, and black images, respectively, and toner images created in the respective image forming portions are intermediately transferred. As the body T passes, it is superimposed on the intermediate transfer body. The multiple toner images superimposed on the intermediate transfer member T are transferred to a recording material (paper, plastic sheet, etc.) in the secondary transfer unit 8, and the recording material separated from the intermediate transfer member is conveyed to the fixing device 9. The The multiple toner image on the recording material is heated and pressed by a fixing device, whereby the toner is fixed on the surface of the recording material. Thereafter, the recording material is discharged out of the apparatus as an output image.

  In this embodiment, each image forming unit P has the same configuration except that the color of the toner is different. Therefore, the subscripts Y, M, C, and K representing the colors are omitted unless otherwise distinguished. Explained.

  The image forming unit P includes a cylindrical photoreceptor 1 as an electrostatic latent image carrier. Around the photosensitive member 1, there are a charging device 2 as a charging means, an exposure device 3 as an exposure means, a developing device 4 as a developing means, a primary transfer device 5 as a transfer means, a cleaner device 6 as a cleaning means, a static elimination device. A static eliminator 7 as a means is arranged.

  The photoreceptor 1 is rotationally driven at a predetermined peripheral speed in the direction of the arrow shown in the drawing, and the surface is charged substantially uniformly by the charging device 2. Next, when a position facing the exposure device 3 is reached, a laser beam is emitted from the exposure device 3 in accordance with the image signal, and an electrostatic image corresponding to the document image is formed on the photoreceptor 1.

  When the electrostatic latent image formed on the photosensitive member 1 reaches a position facing the developing device 4 by the rotation of the photosensitive member 1, the electrostatic latent image is formed from non-magnetic toner particles (toner) and magnetic carrier particles (carrier) in the developing device 4. The resulting developer is developed as a toner image. The electrostatic latent image is developed with substantially toner alone of the developer.

  Next, the toner image formed on the photosensitive member 1 is transferred onto the intermediate transfer member T by the action of a bias applied to the transfer member in the primary transfer portion 5 where the intermediate transfer member T and the photosensitive member 1 abut. Is done. For example, when a four-color full-color image is formed, toner is transferred from the photoreceptor 1 onto the intermediate transfer member T sequentially from the first image forming unit PY, and the four-color toner images are superimposed on the intermediate transfer member T. A toned multiple toner image is formed.

  On the other hand, the toner remaining on the photoreceptor 1 after the transfer process is removed by the cleaner 6. Thereafter, the photosensitive member cleaned by the cleaner 6 is electrically initialized by light irradiation from the static eliminator 7, and the above-described image forming operation is repeated.

  The present invention is characterized in that a stable image formation can be performed over a long period of time by holding an external additive replenishing carrier in the developing unit that has an external additive inside the carrier. The deep developer structure and developer (carrier, toner, external additive) will be described in detail.

[Developer configuration]
FIG. 2 shows a cross-sectional configuration of the developing device. The developing device 4 includes a developing container 401 that stores a developer composed of a nonmagnetic toner and a magnetic carrier. The developing container is divided into a developing chamber 403 and an agitating chamber 404 by a partition wall 402. A first screw 405 is arranged in the developing chamber, and a second screw 406 is arranged in the agitating chamber. Both ends in the longitudinal direction of the partition wall 402 have no partition wall so that the developer can circulate between the developing chamber 403 and the stirring chamber 404.

  A position corresponding to the developing area facing the photoreceptor 1 is opened in the developing chamber 403, and a developing sleeve 408 is rotatably installed so as to be partially exposed to the opening. A magnet roll 409 having a plurality of magnetic poles along the circumferential direction is fixed inside the developing sleeve 408 as a magnetic field generating means. Further, a regulating blade for regulating the amount of the developer is disposed close to the surface of the developing sleeve.

  The developer in the developing chamber is supplied to the developing sleeve 408 by the first screw 405, and the developer having a predetermined layer thickness is conveyed to the developing region facing the photoreceptor by the rotation of the developing sleeve 408 and the regulating blade 407. In the development region, the developer is sprinkled by the magnetic field generated by the magnet roll 409 to form a magnetic brush. In this embodiment, this electrostatic brush is brought into contact with the surface of the photosensitive member 1 and a developing bias is applied to the developing sleeve 408 from a power source (not shown) to visualize the electrostatic latent image on the photosensitive member as a toner image. . In general, a developing bias voltage in which a DC voltage and an AC voltage are superimposed is applied.

  The developing device also includes a developer replenishing device 420 (hereinafter referred to as a hopper) for supplying a replenishing developer containing toner into the developing device, and a discharging device 430 for discharging excess developer in the developing device. have.

  The developer container contains a predetermined amount of toner and carrier at a predetermined ratio at the time of shipment. However, since the toner is consumed as the image is formed and the toner concentration in the developing device is lowered, the toner concentration in the developing device is reduced. Thus, the replenishment developer containing toner is discharged from a replenishment developer container 421 (hereinafter referred to as a hopper) and supplied into the developing device through the transport path 422. On the other hand, the discharge device 430 includes a discharge port 431, a conveying member 432, and a storage unit (not shown). When the developer surface in the developer container reaches a predetermined height or more, the developer passes through the discharge port 431. It is ejected after overcoming it and sent to the storage unit by the conveying member 432.

  While being replenished, the developer is gradually discharged out of the developing device, and the developer in the developing device is gradually replaced.

  Next, the developer in the developing device and the hopper will be described in detail.

[Developer]
A major feature of the present invention is that the developer in the developing device and the hopper is composed of toner and a magnetic carrier, and the magnetic carrier is composed of two types of carriers.

  Of the two types of magnetic carriers, one is a general carrier used in a conventional two-component developer, and the other is a feature of the present invention, and supplies an external additive into the developing device. It is an external additive supply carrier.

  FIG. 3 shows a cross-sectional configuration of the external additive supply carrier which is a feature of the present invention.

  The external additive supply carrier 105 is one in which a hole portion of a ferrite carrier (porous ferrite core) 101 having pores is filled and contained with an external additive 103. On the other hand, a general carrier in the present embodiment is a bulk ferrite carrier that has been subjected to a silicone coating process that does not have pores therein.

  In order to appropriately charge the toner, a surface coat 102 such as a charge adjusting resin is applied to the surface of the porous ferrite core 101 of the external additive supply carrier. This surface treatment is preferably the same as that of the bulk ferrite carrier, and in this embodiment, a silicone coating treatment is performed.

  The external additive filled in the carrier for supplying the external additive is preferably one contained in the external additive added to the toner. For example, in this embodiment, the one filled with about 100 nm of hydrophobic silica is used. ing.

  In order to supply the filled external additive little by little from the external additive supply carrier in the developing unit, the average pore diameter of the external additive supply carrier core is 0.8 to 0.8 of the average particle diameter of the filled external additive. About 1.5 times is preferable, and the same level is more preferable. The average pore diameter in this example was 100 nm, which is the same average particle diameter as that of the external additive.

  In order to supply sufficient external additive into the developing device from the external additive supply carrier, the pore volume ratio of the external additive supply carrier core is preferably about 25 to 50%. A volume ratio of 40% was used.

  In order to appropriately charge the toner, it is preferable that the surface of the porous ferrite core of the external additive supply carrier is subjected to a surface treatment such as a coating agent. Silicone coat treatment is applied in the same way as ferrite carriers.

  In order to stably output a low-printed image for a long period of time, a carrier for supplying an external additive always exists in the developing unit so that the external additive can be stably supplied to the toner in the developing unit. It is necessary to. For this reason, a predetermined amount of an external additive supply carrier is mixed with the developer in the hopper, and the external additive supply carrier is supplied into the developing device simultaneously with the replenishment of toner into the developing device. The mixing ratio of the external additive supply carrier in the hopper varies depending on various conditions such as the proper amount of toner in the developing unit and the melting characteristics of the toner, and the appropriate range varies depending on various conditions such as the toner melting characteristics. Then, toner: general carrier: carrier for supplying external additive = 90: 9.35: 0.65 (mass ratio).

  In addition, in order to perform stable image output immediately after shipment (that is, when the developing device is new), even if a low-printed image is performed over a long period of time (that is, even in a situation where developer supply from the hopper is hardly performed). It is preferable that a predetermined amount of the external additive supply carrier is mixed in the developing device at the time of shipment. The mixing ratio of the external additive supply carrier in the developing device is in an appropriate range depending on various conditions such as the amount of toner in the developing device, the amount and characteristics of the external additive added to the toner, and the pore volume of the external additive supply carrier. Although different, in this embodiment, toner: general carrier: carrier for supplying external additive = 8: 86: 6 (mass ratio).

  When the developer is replenished from the hopper into the developing device and the toner in the developing device corresponding to the volume is discharged from the discharging device, the developer is replaced little by little, but not all of the developer is replaced. Some of the toner may remain in the developing unit even after the external additive has been used up. Even in such a case, since the external additive supply carrier is coated in the same manner as the normal carrier, it can function as a carrier for normalizing the toner in the same manner as the normal carrier.

  As a method for producing such a carrier for supplying an external additive, the following method can be exemplified.

First, a predetermined amount of iron oxide (Fe ₂ O ₃ ) and additives as used in a general ferrite carrier are weighed and mixed. Examples of the additive include one or more oxides belonging to groups IA, IIA, IIIA, IVA, VA, IIIB and VB of the periodic table, for example, BaO, Al ₂ O ₃ , TiO ₂ , SiO ₂ , SnO. ₂ and Bi ₂ O ₅ . The obtained mixture is calcined in the range of 700 to 1000 ° C. for 5 hours, and then pulverized to a particle size of about 0.3 to 3 μm. If necessary, a binder and further a foaming agent are added to the obtained pulverized product, followed by spray drying in a heated atmosphere at 100 to 200 ° C., and granulated to a size of about 20 to 50 μm. Thereafter, firing is performed at an sintering temperature of 1000 to 1400 ° C. for 8 to 12 hours in an atmosphere of an inert gas (for example, N ₂ gas) having an oxygen concentration of 5% or less. Thereby, a porous ferrite core is obtained. The pore size can be controlled by controlling the inert gas concentration and the sintering temperature.

  Furthermore, about 0.1 to 1.0% by mass of a resin such as a silicone resin is coated on the surface of the porous ferrite core by a dipping method and dried under an inert gas.

  Next, the porous ferrite core is immersed in a solution in which a desired external additive is dispersed, and dried under an inert gas to obtain a carrier for supplying an external additive in which pores are filled with the external additive. be able to.

  The porosity and resistance value of the ferrite core can be controlled by controlling the amount of the foaming agent, the inert gas concentration for controlling the firing atmosphere, and the sintering temperature.

  On the other hand, as a general ferrite carrier, the following methods can be mentioned.

  The pulverized ferrite composition is mixed with a binder, water, a dispersant, an organic solvent, and the like, and particles are formed using a spray dryer method or a fluidized granulation method. Thereafter, firing is performed at 700 to 1400 ° C., preferably 800 to 1300 ° C., in a rotary kiln or batch-type firing furnace. Furthermore, a general ferrite carrier can be obtained by coating the ferrite surface with a resin such as a silicone resin in an amount of about 0.1 to 1.0% by mass.

  The pore volume and average pore diameter of the external additive supply carrier core are measured using mercury porosimeters Pascal 140 and Pascal 240 (manufactured by ThermoFisher Scientific). CD3P (for powder) is used as the dilatometer, and the sample is put in a commercially available gelatin capsule with a plurality of holes, degassed in the dilatometer, filled with mercury, and the low pressure region (0 to 400 kPa) is set. Measurement was made to be 1st Run. Next, deaeration and measurement of the low pressure region (0 to 400 kPa) were performed again to obtain 2nd Run. After 2nd Run, the combined mass of the dilatometer, mercury, capsule and sample was measured. Next, the high pressure region (0.1 MPa to 200 MPa) was measured, and the pore volume, the pore size distribution, and the peak pore size of the porous ferrite core material were determined from the mercury intrusion amount obtained by the measurement of the high pressure part. Further, when determining the pore diameter, the surface tension of mercury was 480 dyn / cm and the contact angle was 141.3 °.

  In this example, both an external additive supply carrier and a general carrier having an average particle diameter of 35 μm were used. The particle diameter of the carrier is not particularly limited, but it is preferable that the particle diameters of the external additive supply carrier and the general carrier are approximately the same. If the particle diameters of the two are greatly different, when developing toner on the photoconductor in the development area, large unevenness occurs in the size of the oyster streak caused by the magnetic spikes being dragged over the toner on the photoconductor. This is because the uniformity (graininess) of the image may be impaired.

  The toner is not particularly limited, and a general toner prepared by a pulverization method or a polymerization method may be used. In this embodiment, pulverized toner having an average particle diameter of 6 μm was used.

The external additive added to the toner is not particularly limited, and the type of external additive to be added may be selected in accordance with desired characteristics. In this embodiment, negatively chargeable 20 nm hydrophobic silica for adjusting the toner charge amount and electrically neutral silica having an average particle diameter of 100 nm for improving developability and transferability are added in the following amounts. did.
20 nm hydrophobic silica (negatively charged) 0.5 parts by mass with respect to 100 parts by mass of toner 100 nm hydrophobic silica (neutral) 1 part by mass with respect to 100 parts by mass of toner

  The particle size of the external additive is a value obtained by randomly extracting 500 or more particles with a scanning electron microscope (50,000 times), measuring the major axis and the minor axis with a digitizer, and averaging them.

[Verification experiment]
Using the image forming apparatus and the developer described above, durability tests of 50,000 sheets each in image patterns having greatly different printing rates, that is, in a low printing rate mode (printing rate 2%) and a high printing rate mode (printing rate 40%). Went. Table 1 shows the results of examining the occurrence of image defects during the durability test.

  FIG. 4A shows the development transition of the development efficiency in the low printing ratio mode, and FIG. 4B shows the durability transition of the toner charge amount in the low printing ratio mode. Note that x in FIG. 4A indicates the lower limit of the development efficiency for obtaining an image density acceptable by the user in the image forming apparatus used in this embodiment, and in FIG. 4B. y indicates the lower limit value of the toner charge amount for obtaining the fog level acceptable by the user in the image forming apparatus used in the present embodiment. This is a standard for recognizing the problem.

  Condition 1 is according to the present invention, and conditions 2 and 3 are comparative examples. Condition 2 is a configuration in which the carrier for supplying the external additive is not included in the developing device and the hopper, and Condition 3 is a configuration in which the external additive concentration of the toner in the hopper is cited as an example of the prior art.

  Condition 1 according to the present invention is that the developing efficiency and the toner charge amount greatly exceed the image density and the allowable level of fog x and y in both the low printing rate mode and the high printing rate mode, and a good image is obtained until the end. I was able to. This is because even in the low printing rate mode in which almost no toner is consumed, 100 nm hydrophobic silica, which serves as a spacer, is constantly supplied to the toner in the developing unit little by little from the external additive supply carrier in the developing unit. In addition, in the second half of the endurance test, the external additive is supplied little by little from the new external additive supply carrier supplied into the developing unit to the toner in the developing unit little by little at the time of toner replenishment. A high level of development efficiency can be maintained over time and a sufficient image density can be ensured.

  In addition, since the spacer particles of 100 nm exist on the toner surface in the developing device for a long time, 20 nm hydrophobic silica for adjusting the charge amount is difficult to be buried in the toner surface, and the toner charge amount is slightly lower than the initial value. The acceptable level can be greatly exceeded over time, and a good image without fogging can be obtained over a long period of time.

  On the other hand, Condition 2 in which the carrier for supplying the external additive is not provided in the developing device and the hopper, the developing efficiency and the toner charge amount are greatly reduced as the durability test proceeds in the low printing rate mode, and the image density and fogging are reduced. An image failure occurred. This is because the toner in the developing device is hardly consumed and the external additive is not supplied at all, so that the burying of the external additive proceeds rapidly.

  Even in the high printing rate mode, although the development efficiency and the toner charge amount decrease rate are moderate as compared with the low printing rate, an image defect such as a decrease in image density and fogging eventually occurred. This promotes the replacement of the toner in the developing device compared to the low printing rate, but not all the toner in the developing device is completely replaced and the external additive is not supplied at all. This is because the development efficiency and the toner charge amount are greatly reduced.

  Condition 3 is a configuration in which the external additive concentration of the toner in the hopper mentioned as an example of the prior art is increased. To the toner in the hopper, 20 nm hydrophobic silica (negatively charged) is added by 0.5 parts by mass with respect to 100 parts by mass of the toner, and 100 nm hydrophobic silica (neutral) is added by 3 parts by mass with respect to 100 parts by mass of the toner. In comparison with conditions 1 and 2, the amount of 100 nm hydrophobic silica is tripled.

  Under condition 3, a good image could be obtained in the high printing rate mode until the end, but in the low printing rate mode, as the durability test progressed, the development efficiency and the toner charge amount drastically decreased, and the image density decreased. An image defect called fogging occurred.

  In the low printing mode, the external additive is supplied together with the toner from the hopper to the developing device at the time of toner replenishment. However, no external additive is supplied until the next replenishment timing. The diffusion of the external additive is mainly performed through contact between the toner supplied from the hopper and the toner in the developing device. However, since toner with a high external additive concentration progresses as the external additive diffuses simultaneously with the diffusion of the external additive, the external additive replenished from the hopper does not reach the toner in the developing device. As a result, the development efficiency and the toner charge amount as a whole are greatly reduced, and image defects such as image density reduction and fogging finally occur.

  In order to prevent this, a technique for increasing the concentration of the external additive in the hopper is also conceivable. However, as a result of studies by the present inventors, the fluidity and chargeability of the toner in the hopper and the toner in the developing device are considered. Therefore, the toner could not be uniformly mixed in the developing device. As a result, fog and coating failure of the developing sleeve occurred, and the same effect as in the present invention could not be obtained.

  As described above, the carrier for supplying the external additive is mixed in the hopper, and supplied to the developing device at the same time as the replenishment of toner, so that a high level of development efficiency and toner can be obtained in both the low printing rate mode and the high printing rate mode. The charge amount can be maintained, and good image output without image density reduction or fogging can be performed over a long period of time.

  In Example 1, one type of external additive was filled in the carrier for supplying the external additive, but in this example, a large feature is that a plurality of types of external additives are filled in the carrier for supplying the external additive. It is.

  FIG. 5 shows a cross-sectional configuration of the external additive supply carrier, which is a feature of this embodiment.

  As in Example 1, external additives 103 and 104 are filled in the pores of a ferrite carrier (porous ferrite core) 101 having pores. The types of external additives filled in the radial direction are different, negatively charged 20 nm hydrophobic silica (104) is near the center of the carrier, and electrically neutral 100 nm hydrophobicity is far from the center. Silica (103) is filled.

  Further, in order to appropriately charge the toner, a surface coat 102 such as a charge adjusting resin is applied to the surface of the porous ferrite core 101 of the carrier for supplying the external additive. A coating treatment is applied.

  As a method for producing such a carrier for supplying an external additive, the following method can be exemplified.

  A porous ferrite core is produced in the same manner as in Example 1, and the surface thereof is coated with a resin such as a silicone resin in an amount of about 0.1 to 1.0% by mass.

  Next, the porous ferrite core is immersed in a solution in which negatively charged 20 nm hydrophobic silica is dispersed and dried while flowing. A porous ferrite core is immersed in a solution in which negatively charged 20 nm hydrophobic silica is dispersed and dried while flowing. Thereafter, the porous ferrite core is immersed in a solution in which 100 nm hydrophobic silica (103) is dispersed, and dried under an inert gas while flowing to fill the pores with a plurality of external additives in layers. A carrier for supplying external additives can be obtained.

[Verification experiment]
Using the same image forming apparatus and developer as in Example 1, a durability test of 50,000 sheets was performed in the low printing rate mode (printing rate 2%) and the high printing rate mode (printing rate 40%). Table 2 shows the results of examining the occurrence of image defects during the durability test.

  Further, FIG. 6A shows the durability transition of the development efficiency in the low printing rate mode in this embodiment, and FIG. 6B shows the durability transition of the toner charge amount in the low printing rate mode. Note that X in FIG. 6A and y in FIG. 6B are development efficiency for obtaining an image density acceptable by the user in the image forming apparatus used in this embodiment, as in the first embodiment. The lower limit value and the lower limit value of the toner charge amount for obtaining the fog level acceptable by the user are shown.

  Condition 4 is according to the present invention, and condition 5 is a comparative example. Condition 5 is a configuration in which the external additive concentration of the toner in the hopper mentioned as an example of the prior art is increased. In the toner in the hopper of Condition 5, 20 nm hydrophobic silica (negatively charged) is 1.5 parts by mass with respect to 100 parts by mass of toner, and 100 nm hydrophobic silica (neutral) is 3 parts by mass with respect to 100 parts by mass of toner. The amount of 20 nm hydrophobic silica and 100 nm hydrophobic silica is three times that of the toner of Condition 4.

  In condition 4 which is the configuration of the present embodiment, as in the first embodiment, the development efficiency and the toner charge amount greatly exceed the allowable levels x and y of the image density and fog in both the low print rate mode and the high print rate mode. A good image was obtained until the end. In particular, in the low printing rate mode, the development efficiency was the same level as in Example 1, and the toner charge amount was further improved from that in Example 1.

  In Example 1, compared with Conditions 2 and 3, 20 nm hydrophobic silica for adjusting the charge amount is less likely to be embedded in the toner surface, but it is embedded in a small amount. Condition 2 of 2 is that 20 nm hydrophobic silica is directly supplied to the toner from the external additive supply carrier, so that the toner charge amount can be maintained at a higher level.

  Also, when the printing rate is high, 20 nm hydrophobic silica for adjusting the charge amount is discharged out of the developing device by the discharging device before coming out of the carrier, so that the toner is not excessively charged. Therefore, a good image can be obtained over a long period of time.

  On the other hand, Condition 5 is a configuration in which the external additive concentration of the toner in the hopper, which is cited as an example of the prior art, is increased. To the toner in the hopper, 20 nm hydrophobic silica (negatively charged) is added by 0.5 parts by mass with respect to 100 parts by mass of the toner, and 100 nm hydrophobic silica (neutral) is added by 3 parts by mass with respect to 100 parts by mass of the toner. Compared with condition 4, the amount of 100 nm hydrophobic silica is tripled.

  In condition 5, a good image could be obtained until the end in the high printing rate mode. However, in the low printing rate mode, the toner charge amount decrease rate was somewhat slower than in condition 1 of Example 1, but the durability test. As the process progressed, the development efficiency and the toner charge amount drastically decreased, and image defects such as a decrease in image density and fogging occurred.

  The reason for this is the same as described in Example 1. Also, the 20 nm hydrophobic silica was not easily spread by the external additive replenished from the hopper to the toner in the developing device. This is because the amount is greatly reduced.

  As described above, the external additive supply carrier in which a plurality of external additives are filled in the hopper is mixed and supplied into the developing device at the same time as toner replenishment. In this case, a high level of development efficiency and toner charge amount can be maintained, and good image output without image density reduction or fogging can be performed over a long period of time.

  In the second embodiment, the external additive for adjusting the toner charge amount is supplied at a time difference. However, the present invention is not limited to this, and a configuration according to the purpose and function of the external additive to be added is used. For example, a configuration in which a plurality of external additives that are uniformly mixed is filled in an external additive supply carrier may be employed.

  DESCRIPTION OF SYMBOLS 1 Photoconductor, 2 Charging apparatus, 3 Exposure apparatus, 4 Developing apparatus, 5 Primary transfer apparatus, 6 Cleaning apparatus, 7 Static elimination apparatus, 8 Secondary transfer apparatus, 9 Fixing apparatus, 101 Porous core, 102 Coating agent, 103, 104 external additive, 105 external additive supply carrier, 420 developer supply device, 430 discharge device

Claims (4)

Electrostatic latent image carrier, two-component developer having toner and magnetic carrier, and developing device for developing electrostatic latent image on electrostatic latent image carrier using the two-component developer And an image forming apparatus having a replenishing device for replenishing the developing device with a replenishing developer,
An external additive supply carrier exists in the developing device,
The image forming apparatus, wherein the external additive supply carrier has pores, and the pores are filled with the external additive.   2. The image forming apparatus according to claim 1, wherein the replenishment developer contains the external additive supply carrier.   The image forming apparatus according to claim 1, wherein the developing device includes a discharge device that discharges the developer.   4. The image forming apparatus according to claim 1, wherein a plurality of types of external additives are filled in the external additive supply carrier. 5.

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