JP5459572B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a developing device and a process cartridge installed therein, and more particularly, a plurality of conveying members. The present invention relates to a developing device, a process cartridge, and an image forming apparatus that perform a developing process while circulating a two-component developer in the longitudinal direction.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a developing device that stores a two-component developer (including a case where an external additive or the like is added) composed of toner and a magnetic carrier and performs a developing process. Many are used.
In such a two-component development type developing device, for the purpose of reducing the size of the device, a developing roller (developer carrier) is circulated in the longitudinal direction of the developing device by two conveying screws (conveying members). There is known a technique for supplying a developer (see, for example, Patent Document 1 and Patent Document 2).

Specifically, the developing device includes a developing roller, two conveying screws, a doctor blade, and the like.
Then, according to toner consumption in the developing device, toner is appropriately supplied into the device from a toner supply port provided at one end of the developing device. The replenished toner is mixed with the developer in the developing device while being circulated in the longitudinal direction (the same direction as the longitudinal direction of the developing roller) by the two conveying screws. A part of the mixed developer is carried on a developing roller facing one conveying screw. After the developer carried on the developing roller is regulated to an appropriate amount by the doctor blade, the toner in the developer adheres to the latent image on the photosensitive drum at a position facing the photosensitive drum (image carrier). .

  In the developing device in Patent Document 1 or the like, a first conveying member (first conveying screw) and a second conveying member (second conveying screw) are juxtaposed in a horizontal direction via a partition member. A developer circulation path is formed by the conveying member. The first conveying member facing the developing roller supplies the developer to the developing roller while collecting the developer in the longitudinal direction and collects the developer separated from the developing roller. The second conveying member facing the first conveying member via the partition member causes the developer to move in the longitudinal direction (conveyed by the first conveying member) toward the relay unit communicating with the upstream side of the first conveying path by the first conveying member. The direction is opposite to the direction.) The downstream side of the conveyance path (first conveyance path) by the first conveyance member and the upstream side of the conveyance path (second conveyance path) by the second conveyance member communicate with each other via the first relay unit. Then, the developer that has reached the downstream side of the first transport path moves to the upstream side of the second transport path via the first relay unit. Here, a toner replenishing port is provided on the upstream side of the second transport path, and new toner (supplementary toner) is appropriately replenished. Further, the upstream side of the first transport path and the downstream side of the second transport path communicate with each other via a second relay unit (relay unit). Then, the developer that has reached the downstream side of the second transport path moves to the upstream side of the first transport path via the second relay unit.

  In such a biaxial agitation type developing device equipped with two conveying screws, the developer is positively conveyed in the longitudinal direction of the device, so that the deviation of the developer occurs in a part of the longitudinal direction. Defects are less likely to occur. As a result, the toner replenishing port can be provided at one end in the longitudinal direction rather than over the entire width in the longitudinal direction. Further, the conveying screw does not require much installation space in the short direction (the direction perpendicular to the longitudinal direction). Therefore, the developing device and the image forming apparatus can be reduced in size.

JP 2006-39250 A Japanese Patent No. 3379678

  In the conventional biaxial agitation type developing device described above, the developer is delivered to the first conveyance path via the relay unit in a state where the replenishment toner is not sufficiently dispersed in the developer in the second conveyance path. There was a case where it was done. Therefore, the developer supplied onto the developing roller in the first transport path contains a lot of replenished toner that is not sufficiently charged, resulting in image density unevenness and background stains on the output image, There has been a problem that toner is scattered from the developing device.

  The present invention has been made to solve the above-described problems. With a relatively simple configuration, the developer in a state where the replenishment toner is sufficiently dispersed can be supplied to the first transport path, and an output image can be obtained. It is an object of the present invention to provide a developing device, a process cartridge, and an image forming apparatus that do not cause image density unevenness or background stain or toner scattering.

  The inventor of the present application has conducted research to solve the above-described problems, and as a result, the positional relationship between the bottom surface of the first transport path and the bottom surface of the second transport path, the rotational directions of the first transport member and the second transport member, and However, it has been found that this greatly affects the dispersibility of the replenishment toner in the developer supplied to the first transport path via the relay unit.

The present invention is based on the matters described above. That is, the developing device according to the first aspect of the present invention accommodates a developer having a carrier and a toner and is formed on an image carrier. A developing device that develops a latent image to be opposed to the image carrier, and carries a developer carrier that carries a developer and a developer contained in the device in a longitudinal direction, and passes through a circulation path. A plurality of conveying members to be formed, and the plurality of conveying members are opposed to the developer carrier and supply the developer to the developer carrier while conveying the developer in the longitudinal direction. A first conveying member that conveys the developer separated from the developer carrying member in the longitudinal direction, and the first conveying member that faces the first conveying member via a partition member, and upstream of the first conveying path by the first conveying member Communicate with A second transport member that transports the developer in the longitudinal direction toward the joint, and the bottom surface of the first transport path is positioned at the bottom of the second transport path by the second transport member. The first transport member rotates in a direction in which the uppermost portion thereof is separated from the developer carrying member and approaches the second transport member, and the rotation direction of the second transport member is A toner density detecting means that rotates in the same direction and detects the toner density of the developer contained in the apparatus is provided in the vicinity of the relay section and in the second transport path. The second transport path is inclined so as to be higher from the second transport path side to the first transport path side. Formed to be smaller than the channel cross-sectional area at the position. A first inclined surface that is inclined downward from the upper wall to the surface closest to the toner concentration detecting means from the upstream side of the second transport path on the ceiling near the position where the toner concentration detecting means is installed And a second inclined surface that is inclined upward at a steeper angle than the first inclined surface from the surface closest to the toner density detecting means toward the downstream side of the second transport path. It was those.

  The developing device according to a second aspect of the present invention is the developing device according to the first aspect, wherein the position of the bottom surface of the first transport path is lower than the position of the rotation center of the second transport member. It is arranged like this.

  According to a third aspect of the present invention, in the developing device according to the first or second aspect, the outer diameter of the first conveying member is the same as the outer diameter of the second conveying member. The rotation center position is higher than the rotation center position of the second transport member.

  According to a fourth aspect of the present invention, there is provided the developing device according to the third aspect of the invention, wherein the first conveying member is arranged such that the position of the rotation center thereof does not exceed the uppermost part of the second conveying member. It is arranged.

The developing device according to a fifth aspect of the present invention is the developing device according to any one of the first to fourth aspects, wherein the toner concentration detecting means is within a range of 70 mm or less in the longitudinal direction from the relay portion. It is arranged.

The developing device according to a sixth aspect of the present invention is the developing device according to any one of the first to fifth aspects, wherein the carrier has a resin coating layer on the surface of the core material, The resin coating layer contains conductive particles formed by providing a conductive coating layer composed of a tin dioxide layer and an indium oxide layer containing tin dioxide provided on the tin dioxide layer on the surface of the substrate particles, The conductive particles are formed so that the oil absorption is 10 to 300 ml / 100 g. The toner includes a binder resin, a release agent, and a colorant. The binder resin includes a vinyl polymer and a polyester. And a hybrid resin having a base polymer, and the hybrid resin content with respect to the release agent content is in the range of 0.5 to 3.

According to a seventh aspect of the present invention, there is provided the developing device according to any one of the first to sixth aspects, wherein the carrier is formed such that a weight average particle diameter is in a range of 20 to 65 μm. It is a thing.

The developing device according to an eighth aspect of the present invention is the developing device according to any one of the first to seventh aspects, wherein the toner has an average particle size in the range of 3.5 to 7.5 μm. It is formed.

A developing device according to a ninth aspect of the present invention is the developing device according to any one of the first to eighth aspects, wherein the toner concentration of the developer contained in the device is in the range of 4 to 12% by weight. It is controlled to become.

A process cartridge according to a tenth aspect of the present invention is a process cartridge that is detachably installed on the main body of the image forming apparatus, and the developing device according to any one of the first to ninth aspects. And the image carrier.

An image forming apparatus according to an eleventh aspect includes the developing device according to any one of the first to ninth aspects and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing unit (developing device) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. At least one of the cleaning units and the image carrier are defined as a unit that is integrated and detachably installed on the image forming apparatus main body.

  Since the present invention optimizes the positional relationship between the bottom surface of the first transport path and the bottom surface of the second transport path and the rotational directions of the first transport member and the second transport member, the configuration is relatively simple. In the developing device and process, the developer in a state in which the replenishment toner is sufficiently dispersed can be supplied to the first conveyance path, and image density unevenness, background stains, and toner scattering do not occur on the output image. A cartridge and an image forming apparatus can be provided.

Embodiment.
Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

First, the image forming apparatus will be described in detail with reference to FIGS.
FIG. 1 is a configuration diagram illustrating a laser printer as an image forming apparatus. FIG. 2 is a cross-sectional view showing the vicinity of the process cartridge 6 installed therein. FIG. 3 is a cross-sectional view of the developing device 5 and the photosensitive drum 1 as viewed from above in the longitudinal direction (the vertical direction in FIG. 2). FIG. 4 is a cross-sectional view showing the developing device 5.

  As shown in FIG. 1, process cartridges 6Y, 6M, 6C, and 6K as image forming units corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged so as to face the intermediate transfer belt 8 of the intermediate transfer unit 15. It is installed side by side. Since the four process cartridges 6Y, 6M, 6C, and 6K installed in the apparatus main body 100 have substantially the same structure except that the color of the toner used in the image forming process is different, the process cartridges in FIGS. The alphabets (Y, M, C, K) of the reference numerals for the cartridge 6, the photosensitive drum 1, and the primary transfer bias roller 9 are omitted.

  Referring to FIG. 2, a process cartridge 6 includes a photosensitive drum 1 as an image carrier, a charging unit 4 disposed around the photosensitive drum 1, a developing device 5 (developing unit), and a cleaning unit 2. Are integrated with each other and are detachable from the apparatus main body 100. Thus, the maintainability of the image forming unit is improved by integrating the components of the image forming unit. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, charge eliminating process) is performed on the photosensitive drum 1 to form a desired toner image on the photosensitive drum 1. It will be.

  In the present embodiment, the photosensitive drum 1, the charging unit 4, the developing device 5, and the cleaning unit 2 are integrated to form the process cartridge 6. However, each component is formed as a single unit in the apparatus main body 100. It can also be installed detachably. Specifically, the developing device 5 can be configured to be detachable from the apparatus main body 100 as a single unit. Further, it can be configured to be detachable from the apparatus main body 100 as a unit in which at least one of the photosensitive drum 1, the charging unit 4, and the cleaning unit 2 and the developing device 5 are integrated.

Referring to FIG. 2, the photosensitive drum 1 is rotationally driven in a clockwise direction in FIG. 2 by a drive unit (not shown). Then, the surface of the photosensitive drum 1 is uniformly charged at the position of the charging unit 4 (a charging process).
Thereafter, the surface of the photosensitive drum 1 reaches the irradiation position of the laser beam L emitted from the exposure unit 7 (see FIG. 1), and an electrostatic latent image is formed by exposure scanning at this position. (It is an exposure process.)

Thereafter, the surface of the photosensitive drum 1 reaches a position facing the developing device 5, and the electrostatic latent image is developed at this position to form a desired toner image (developing process).
Specifically, a two-component developer G composed of toner and a carrier (magnetic carrier) is accommodated in the developing device 5. The developer G in the developing device 5 is adjusted so that the toner density (the ratio of the toner in the developer G) detected by the magnetic sensor 57 as the toner density detecting means is within a predetermined range. . That is, according to the toner consumption in the developing device 5, the toner is replenished from the toner transport pipe 43 (toner transport unit) into the second transport path 54 via the toner supply port 44. The magnetic sensor 57 is a sensor that detects a change in toner density from a change in magnetic permeability of the developer flowing around the magnetic sensor 57.

Referring to FIG. 1, the toner transport pipe 43 communicates with a corresponding toner bottle among the toner bottles 32 </ b> Y, 32 </ b> M, 32 </ b> C, and 32 </ b> K installed in the bottle container 31 above the apparatus main body 100. Although not shown in the figure, the toner transport unit includes a drive unit that rotationally drives the toner bottles 32Y, 32M, 32C, and 32K, a toner transport pipe 43, an air pump connected to the toner transport pipe 43, and the like. The toner transport unit configured as described above transports the respective color toners from the toner bottles 32Y, 32M, 32C, and 32K containing the respective color toners to the respective developing devices 5 through the toner transport pipe 43. .
The toner conveying unit is not limited to the above-described configuration, and various configurations can be used. For example, a configuration in which toner is supplied from the toner bottle to the developing device 5 via the relay hopper without using the toner transport pipe can be used.

  Thereafter, the toner replenished in the second transport path 54 is mixed and stirred together with the developer G by the second transport screw 56 and the first transport screw 55, and is separated by the partition member 58. Then, it circulates through the second transport path 54 (circulation in the direction of the broken line arrow in FIG. 3).

  Specifically, referring to FIG. 3, the developer G in the first conveyance path 53 (first developer accommodating portion) is developed from the right side to the left side of the sheet by the first conveyance screw 55 as the first conveyance member. It is conveyed along the longitudinal direction of the roller 51. On the other hand, the developer G in the second transport path 54 (second developer accommodating portion) is defined as the first transport path from the left side to the right side of the paper surface by the second transport screw 56 as the second transport member. It is conveyed in the reverse direction.

  In addition, the first transport path 53 and the second transport path 54 are separated from each other by a partition member 58 disposed in a region excluding both ends in the longitudinal direction, and both end portions in the longitudinal direction where the partition member 58 is not interposed (first The relay unit 63 and the second relay unit 64) communicate with each other. That is, the developer transported to the downstream side of the first transport path 53 by the first transport screw 55 flows to the upstream side of the second transport path 54 via the first relay portion 63, and then the second transport. It is conveyed by the screw 56. The developer transported to the downstream side of the second transport path 54 by the second transport screw 56 flows to the upstream side of the first transport path 53 via the second relay section 64 as a relay section, and thereafter It is conveyed by one conveying screw 55. Thus, a developer circulation path is formed between the two transport paths 53 and 54.

Thus, the toner in the developer G circulating in the circulation path is attracted to the carrier by frictional charging with the carrier, and a plurality of magnetic poles H1 to H4 formed on the developing roller 51 (see FIG. 4 can be referred to). ) Is carried on the developing roller 51 together with the carrier.
Here, referring to FIG. 3, the developing roller 51 includes a magnet 51b that is fixed inside and forms a plurality of magnetic poles on the peripheral surface of the roller, and a sleeve 51a that rotates around the magnet 23a1. . Then, when the sleeve 51a rotates around the magnet 51b in which a plurality of magnetic poles are formed, the developer G moves on the developing roller 51 (on the sleeve 51a) with the rotation.

The developer G carried on the developing roller 51 as the developer carrying member is conveyed as the developing roller 51 rotates in the direction of the arrow, and reaches the position of the doctor blade 52 as the developer regulating member. Then, after the developer G on the developing roller 51 is regulated to an appropriate amount at this position, the developer G is conveyed to a position facing the photosensitive drum 1 (developing area). The toner is attracted to the latent image formed on the photosensitive drum 1 by the electric field (developing electric field) formed in the developing area.
In the present embodiment, as the developing bias applied to the developing roller 51, the AC component developing bias is not applied, and only the DC component developing bias is applied. This simplifies the configuration and control of the power supply unit that supplies the developing bias, and can reduce the occurrence of a blurred image with respect to a carrier having a low resistance.

The developing roller 51 in the present embodiment is set to have an outer diameter of 18 mm and a length in the longitudinal direction of 326 mm. Further, the surface of the sleeve 51a of the developing roller 51 may be formed with V-shaped grooves at equal pitch intervals in the circumferential direction, or may be blasted.
The gap (development gap) between the developing roller 51 and the photosensitive drum 1 is set to 0.3 ± 0.05 mm, and the gap (doctor gap) between the developing roller 51 and the doctor blade 52 is 0.5 ± 0.00 mm. It is set to 04 mm. The doctor blade 52 is a plate-like member made of a stainless material.
Furthermore, each of the first conveying screw 55 and the second conveying screw 56 is formed by forming a screw portion (blade) having an outer diameter of 14 mm in a spiral shape at a pitch of 20 mm on a shaft portion having an outer diameter of 5 mm. is there.

FIG. 4 shows a plurality of magnetic poles H1 to H4 formed around the developing roller 51 (sleeve 51a) by the magnet 51b. As shown in FIG. 4, the plurality of magnetic poles are formed from a position facing the main magnetic pole H <b> 1 formed at the position facing the photosensitive drum 1 and the position facing the first conveying screw 55 to a position facing the doctor blade 52. The raising magnetic pole H2 (doctor counter magnetic pole), the agent separating magnetic pole H3 formed above the first conveying path 53, the conveying magnetic pole H4 formed between the main magnetic pole H1 and the agent separating magnetic pole H3, and the like.
First, the pumping magnetic pole H <b> 2 acts on a carrier as a magnetic body, and a part of the developer G that moves in the first transport path 53 is carried on the developing roller 51. Part of the developer G carried on the developing roller 51 is scraped off at the position of the doctor blade 52 (developer regulating member) and returned to the first transport path 53. On the other hand, the developer G carried on the developing roller 51 through the doctor gap between the doctor blade 52 and the developing roller 51 at the position of the doctor blade 52 where the magnetic force by the pumping magnetic pole H2 acts is the main magnetic pole H1. It rises at the position and becomes a magnetic brush in the developing area and slides on the photosensitive drum 1. Thus, the toner in the developer G carried on the developing roller 51 adheres to the latent image on the photosensitive drum 1. Thereafter, the developer G that has passed the position of the main magnetic pole H1 is transported to the position of the agent separating magnetic pole H3 by the transport magnetic pole H4. Then, the repelling magnetic field acts on the carrier at the position of the agent separating magnetic pole H 3, and the developer G after the developing process carried on the developing roller 51 is detached from the developing roller 51. The detached developer G is returned again to the first conveyance path 53, conveyed toward the downstream side of the first conveyance path 53, and upstream of the second conveyance path 54 via the first relay unit 63. Move to. Further, the developer that has moved to the upstream side of the second conveyance path 54 reaches the downstream side of the second conveyance path 54 together with the replenishment toner replenished from the toner replenishment port 44, and the second relay unit 64 (relay unit). To the upstream side of the first transport path 53. Such a series of circulation of the developer G is repeated.
A part of the developer G that is separated from the developing roller 51 at the position of the agent separating magnetic pole H 3 is held by the developing roller 51 again without falling to the first transport path 53.

After the development process described above, the surface of the photosensitive drum 1 reaches a position facing the intermediate transfer belt 8 and the first transfer bias roller 9, and the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 8 at this position. Transferred upward (this is a primary transfer step). At this time, a small amount of untransferred toner remains on the photosensitive drum 1.
Thereafter, the surface of the photoreceptor 1 reaches a position facing the cleaning unit 2, and untransferred toner remaining on the photoreceptor drum 1 at this position is collected by the cleaning blade 2a (cleaning process).
Finally, the surface of the photosensitive drum 1 reaches a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drum 1 is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drum 1 is completed.

  The image forming process described above is performed by each of the four process cartridges 6Y, 6M, 6C, and 6K. That is, referring to FIG. 1, laser light L based on image information is directed onto the photosensitive drums of the process cartridges 6Y, 6M, 6C, and 6K from the exposure unit 7 disposed below the process cartridge. Is irradiated. Specifically, the exposure unit 7 emits laser light L from a light source, and irradiates the photosensitive drum through a plurality of optical elements while scanning the laser light L with a polygon mirror that is rotationally driven. Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 8 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 8.

  Here, referring to FIG. 1, the intermediate transfer unit 15 includes an intermediate transfer belt 8, four primary transfer bias rollers 9Y, 9M, 9C, and 9K, a secondary transfer backup roller 12, a counter roller 13, and a tension roller 14. And the cleaning unit 10 and the like. The intermediate transfer belt 8 is stretched and supported by the three roller members 12 to 14 and is moved endlessly in the direction of the arrow in FIG.

The four primary transfer bias rollers 9Y, 9M, 9C, and 9K respectively sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. A transfer bias having a polarity opposite to the polarity of the toner is applied to the primary transfer bias rollers 9Y, 9M, 9C, and 9K.
The intermediate transfer belt 8 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred while being superimposed on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 19. At this position, the secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The color toner image formed on the intermediate transfer belt 8 is transferred onto a recording medium P such as transfer paper conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 8.
Thereafter, the intermediate transfer belt 8 reaches the position of the cleaning unit 10 for the intermediate transfer belt 8. At this position, the untransferred toner on the intermediate transfer belt 8 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip is transported from a paper feeding unit 26 disposed below the apparatus main body 100 via a paper feeding roller 27, a registration roller pair 28, and the like. It is a thing.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the rollers of the registration roller pair 28.

  The recording medium P transported to the registration roller pair 28 temporarily stops at the position of the roller nip of the registration roller pair 28 whose rotation drive has been stopped. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing unit 20. At this position, the color image transferred on the surface is fixed on the recording medium P by heat and pressure generated by the fixing roller and the pressure roller.
Thereafter, the recording medium P is discharged to the outside of the apparatus through the rollers of the discharge roller pair 29. The transferred P discharged from the apparatus main body 100 by the discharge roller pair 29 is sequentially stacked on the stack unit 30 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Hereinafter, the configuration and operation of the developing device 5 which are characteristic in the present embodiment will be described in detail.
Referring to FIG. 4, the first transport path 53 is disposed such that the position of the bottom surface thereof is higher than the position of the bottom surface of the second transport path 54 (the distance Y1 is disposed higher). ). Therefore, the bottom surface of the second relay unit 64 serving as a relay unit is inclined so as to increase from the second transport path 54 side to the first transport path 53 side (a diagram showing a cross section of the position of the second relay unit 64). 5).
The first transport screw 55 rotates in a direction in which the uppermost portion (the uppermost portion of the screw portion) is separated from the developing roller 51 and approaches the second transport screw 56, and the rotation direction of the second transport screw 56. It is comprised so that it may rotate in the same direction. That is, the rotation directions of the first conveyance screw 55 and the second conveyance screw 56 are set so as to be counterclockwise in FIG. By setting the rotation direction of the first conveying screw 55 counterclockwise, the developer surface can be brought closer to the developing roller 51 side as shown in FIGS. The magnetic force of H2 is likely to act, and the ability to pump the developer onto the developing roller 51 is improved.

  With such a configuration, the developer G is delivered to the first transport path 53 via the second relay unit 64 in a state where the replenishment toner is sufficiently dispersed in the developer G in the second transport path 54. It will be. Therefore, the replenishment toner that is not sufficiently charged is not included in the developer G supplied onto the developing roller 51 in the first transport path 53, and image density unevenness and background stains are generated on the output image. Inconveniences that the toner is scattered or the toner is scattered from the developing device 5 are suppressed.

The behavior of the developer G circulating in the developing device 5 in the present embodiment will be described in more detail with reference to FIGS.
FIG. 5 is a cross-sectional view at the position of the second relay portion 64 of the developing device 5, and FIG. 6 is a cross-sectional view at the position of the partition member 58 of the developing device 5.
Referring to FIG. 6, the developer G moving in the center in the longitudinal direction in the second transport path 54 has the partition surface 58 on the outer wall surface 54 a side due to the counterclockwise rotation of the second transport screw 56. Lower than the side surface. Accordingly, the replenished toner replenished from the toner replenishing port 44 that is not dispersed in the developer moves in the longitudinal direction along the outer wall surface 54a due to the inclination of the surface of the material. In this state, the developer that has reached the downstream side of the second conveyance path 54 is directed to the first conveyance path 53 disposed at a high position by the second relay unit 64 with reference to FIG. It flows at a relatively moderate momentum. At this time, since the replenishment toner that is not dispersed in the developer is on the outer wall surface 54a side, a sufficient amount of time is spent in the developer G along the counterclockwise rotation of the second conveying screw 56. While stirring and mixing, the fluid flows to the first transport path 53 side via the second relay portion 64. Therefore, the developer G in which the replenishment toner is sufficiently dispersed is supplied from the second conveyance path 54 to the first conveyance path 53.

Hereinafter, for comparison with the developing device 5 in the present embodiment, the behavior of the developer G circulating inside the developing devices of the three modes (Comparative Examples 1 to 3) will be described.
In the developing device 5 of Comparative Example 1 shown in FIGS. 8 and 9, the position of the bottom surface of the first transport path 53 is disposed lower than the position of the bottom surface of the second transport path 54, and the first transport screw 55 is provided. The second conveying screw 56 is rotated counterclockwise and clockwise. FIG. 8 is a cross-sectional view at the position of the second relay portion 64 of the developing device 5, and FIG. 9 is a cross-sectional view at the position of the partition member 58 of the developing device 5.
Referring to FIG. 9, the developer G moving in the center in the longitudinal direction in the second transport path 54 has the agent surface on the outer wall surface 54 a side turned to the partition member 58 side by the clockwise rotation of the second transport screw 56. It becomes higher than the surface. Accordingly, the replenished toner replenished from the toner replenishing port 44 that is not dispersed in the developer moves in the longitudinal direction along the partition member 58 side due to the inclination of the agent surface. Then, the developer that has reached the downstream side of the second transport path 54 in this state is directed toward the first transport path 53 disposed at a low position by the second relay unit 64 with reference to FIG. Flows vigorously. At this time, since the replenishment toner that is not dispersed in the developer is on the partition member 58 side, the first transport path is routed through the second relay portion 64 along the clockwise rotation of the second transport screw 56. It will flow to 53 side vigorously. Therefore, a large amount of the developer G in a state where the replenishment toner is not sufficiently dispersed is supplied from the second conveyance path 54 to the first conveyance path 53, thereby causing image density unevenness and background stains on the output image. Toner scattering will occur.

In the developing device 5 of Comparative Example 2 shown in FIGS. 10 and 11, the position of the bottom surface of the first transport path 53 is disposed lower than the position of the bottom surface of the second transport path 54, and the first transport screw 55 is provided. The second conveying screw 56 is also rotated counterclockwise in the counterclockwise direction. FIG. 10 is a cross-sectional view at the position of the second relay portion 64 of the developing device 5, and FIG. 11 is a cross-sectional view at the position of the partition member 58 of the developing device 5.
Referring to FIG. 11, the developer G moving in the center in the longitudinal direction in the second transport path 54 has its agent surface on the outer wall surface 54 a side turned to the partition member 58 side by the clockwise rotation of the second transport screw 56. It will be lower than the surface. Accordingly, the replenished toner replenished from the toner replenishing port 44 that is not dispersed in the developer moves in the longitudinal direction along the outer wall surface 54a due to the inclination of the surface of the material. In this state, the developer that has reached the downstream side of the second transport path 54 is directed toward the first transport path 53 disposed at a low position by the second relay unit 64 with reference to FIG. Flows vigorously. At this time, since the replenishment toner not dispersed in the developer is on the outer wall surface 54a side, the replenishment toner is less likely to flow to the first transport path 53 side than the first comparative example, but is disposed at a lower position. The fluid flows vigorously toward the one transport path 53 side. Therefore, a large amount of the developer G in a state where the replenishment toner is not sufficiently dispersed is supplied from the second conveyance path 54 to the first conveyance path 53, thereby causing image density unevenness and background stains on the output image. Toner scattering will occur.

In the developing device 5 of Comparative Example 3 shown in FIGS. 12 and 13, the position of the bottom surface of the first transport path 53 is disposed higher than the position of the bottom surface of the second transport path 54, and the first transport screw 55 is provided. The second conveying screw 56 is rotated counterclockwise and clockwise. 12 is a cross-sectional view at the position of the second relay portion 64 of the developing device 5, and FIG. 13 is a cross-sectional view at the position of the partition member 58 of the developing device 5.
Referring to FIG. 13, the developer G moving in the central portion in the longitudinal direction in the second transport path 54 has the agent surface on the outer wall surface 54 a side turned to the partition member 58 side by the clockwise rotation of the second transport screw 56. It becomes higher than the surface. Accordingly, the replenished toner replenished from the toner replenishing port 44 that is not dispersed in the developer moves in the longitudinal direction along the partition member 58 side due to the inclination of the agent surface. Then, the developer that has reached the downstream side of the second conveyance path 54 in this state is directed toward the first conveyance path 53 disposed at a high position by the second relay unit 64 with reference to FIG. It flows with a relatively low momentum. However, since the replenishment toner that is not dispersed in the developer is on the partition member 58 side, the first transport path 53 is connected via the second relay portion 64 along the clockwise rotation of the second transport screw 56. Will flow to the side. Accordingly, the developer G in a state in which the replenishment toner is not sufficiently dispersed is supplied from the second conveyance path 54 to the first conveyance path 53 to be output, although the degree is better than that of the comparative example 1 and the comparative example 2. Image density unevenness and background stains occur on the image, and toner scattering occurs.

  On the other hand, in the developing device 5 in the present embodiment, the position of the bottom surface of the first transport path 53 is disposed higher than the position of the bottom surface of the second transport path 54, and the first transport screw 55 and the first transport path 55 are arranged. 2 Since the transport screw 56 is rotated in the counterclockwise direction, the developer G in a state where the replenishment toner is sufficiently dispersed is supplied from the second transport path 54 to the first transport path 53, and the output image Therefore, it is possible to suppress problems such as image density unevenness and background stains, and toner scattering.

  Here, in the present embodiment, with reference to FIG. 4, the position of the bottom surface of the first transport path 53 is arranged to be lower than the position of the rotation center of the second transport screw 56 (distance). Y2 is arranged lower). This is because when the position of the bottom surface of the first transport path 53 becomes too high with respect to the position of the bottom surface of the second transport path 54, the second relay unit 64 moves from the second transport path 54 to the first transport path 53. This is because the delivery of the developer becomes insufficient and the amount of developer supplied from the first transport path 53 onto the developing roller 51 becomes insufficient. In such a case, the image density on the output image is lowered.

FIG. 14 is a graph showing the relationship between the inter-axis distance Y3 of the transport screws 55 and 56 and the amount of developer supplied to the first transport path 53. In FIG. 14, the horizontal axis indicates the axial distance Y3 (see FIG. 4) between the first transport screw 55 and the second transport screw 56 in the height direction. This is expressed as a ratio to the screw diameter (the same diameter as the screw diameter of the second conveying screw 56). In other words, the position “0” on the horizontal axis is the position where the inter-axis distance Y3 is zero, and the first transport screw 55 is disposed upward with respect to the second transport screw 56 as it proceeds in the right direction of the horizontal axis. Will be. In FIG. 14, the vertical axis indicates the amount of developer supplied from the second transport path 54 to the first transport path 53 in the second relay section 64, and the distance when the inter-axis distance Y3 is zero. This is expressed as a ratio (relative value) to the developer supply amount. Further, the amount of developer supplied is obtained by measuring the amount of developer pumped up onto the developing roller 51 (in the range from the second relay portion 64 side to the longitudinal direction 1/4) as a substitute characteristic. .
As shown in FIG. 14, it can be seen that the amount of developer supplied to the first transport path 53 is drastically reduced when the inter-axis distance Y3 exceeds 0.5. Accordingly, by arranging the bottom surface of the first transport path 53 so as to be lower than the position of the rotation center of the second transport screw 56 (the position of the rotation center of the first transport screw 55 is the second transport screw). The developer G in a state in which the replenishment toner is sufficiently dispersed is disposed from the second transport path 54 to the first transport path 53 by disposing it so as not to exceed the uppermost portion of 56 (disposed by a distance Y4). Can be supplied without excess or deficiency.

Here, in the present embodiment, the outer diameter (screw diameter) of the first conveying screw 55 is formed to be the same as the outer diameter (screw diameter) of the second conveying screw. The clearance between the screw portion of the first transport screw 55 and the bottom surface of the first transport path 53 and the clearance between the screw portion of the second transport screw 56 and the bottom surface of the second transport path 54 are both slight. Therefore, the developer is set so that the developer does not stay on the bottom surface due to the transport force of the first transport screw 55 and the second transport screw 56 acting on the bottom surfaces of the first transport path 53 and the second transport path 54.
Therefore, in the present embodiment, referring to FIG. 4, the position of the rotation center of the first transport screw 55 is arranged to be higher than the position of the rotation center of the second transport screw 56. (The distance Y3 (= distance Y1) is higher.) In other words, the position of the uppermost part of the first conveying screw 55 (the uppermost part of the screw part) is arranged to be higher than the position of the uppermost part of the second conveying screw 56 (the uppermost part of the screw part). (The distance Y3 (= distance Y1) is higher.)

In the present embodiment, the outer diameter of the first transport screw 55 is the same as the outer diameter of the second transport screw. However, the outer diameter of the first transport screw 55 is the outer diameter of the second transport screw. Even if it is formed to be different from the first embodiment, if it is formed so that the position of the bottom surface of the first transport path 53 is higher than the position of the bottom surface of the second transport path 54, Similarly, the developer G in a state where the replenishment toner is sufficiently dispersed can be supplied from the second conveyance path 54 to the first conveyance path 53.
For example, as shown in FIG. 16, even when the outer diameter of the first conveying screw 55 is formed to be smaller than the outer diameter of the second conveying screw, the position of the bottom surface of the first conveying path 53 is By forming so as to be higher than the position of the bottom surface of the second transport path 54, the same effect as in the present embodiment can be obtained.

Here, in the present embodiment, referring to FIG. 3, a magnetic sensor 57 as a toner concentration detecting means is installed in the vicinity of the second relay unit 64 (relay unit). Specifically, the magnetic sensor 57 is disposed in the second transport path 54 so that the distance X in the longitudinal direction from the second relay unit 64 is within 70 mm.
This is because the developer surface in the second transport path 54 is lower on the upstream side than on the downstream side. That is, if the magnetic sensor 57 is installed on the upstream side with a small amount of developer, the toner concentration is detected in a state where the replenishment toner is not sufficiently stirred and mixed in the developer. The detection accuracy of 57 becomes unstable.
The reason why the upstream surface of the second transport path 54 is lower than the downstream surface is that the second relay section 64 is located above the second transport path 54 as described above. Further, since the developer flows toward the first conveyance path 53 with a relatively gentle momentum, the swell due to the retention of the developer occurs on the downstream side of the second conveyance path 54. Further, the rotational speed of the second transport screw 56 is increased in order to push up the developer with a certain amount of force toward the first transport path 53 disposed upward from the second transport path 54 at the position of the second relay unit 64. In the case of speeding up, the developer transfer speed from the upstream side to the downstream side of the second transport path 54 is increased, and the upstream side is further lowered than the downstream side.

FIG. 15 is a graph showing the relationship between the distance X between the magnetic sensor 57 and the second relay unit 64 and the height of the agent surface in the vicinity of the magnetic sensor 57.
In FIG. 15, the “agent level near the magnetic sensor 57” shown on the vertical axis is a relative value with respect to the agent level when the magnetic sensor 57 is installed at the position of the second relay portion 64.
As shown in FIG. 15, it can be seen that if the distance X between the magnetic sensor 57 and the second relay portion 64 is within 70 mm, the surface height in the vicinity of the magnetic sensor 57 is sufficiently secured. Therefore, the detection accuracy of the magnetic sensor 57 is increased and stabilized.

In addition, referring to FIG. 7, the second transport path 54 in the present embodiment is a channel cross-sectional area in the vicinity of the position where the magnetic sensor 57 is installed (the cross-sectional area of the channel perpendicular to the longitudinal direction). However, it is formed so as to be smaller than the channel cross-sectional area at other positions. Specifically, as shown in FIG. 7, in the second conveyance path 54, a ceiling portion 59 close to the second conveyance screw 56 is provided on the upper wall in the vicinity of where the magnetic sensor 57 is installed.
With such a configuration, the developer flowing in the vicinity of the magnetic sensor 57 is clogged, and the variation in the bulk density of the developer is reduced. Therefore, the detection accuracy of the magnetic sensor 57 is increased and stabilized. In the present embodiment, the ceiling portion 59 is installed only in the vicinity of the magnetic sensor 57, but the ceiling portion 59 may be provided over the entire longitudinal direction of the second transport path 54.

With reference to FIG. 17, the configuration of the ceiling portion 59 described above will be described in more detail.
FIG. 17 is a rear view of the second transport path 54 as viewed in the longitudinal direction. As shown in FIG. 17, the ceiling portion 59 protrudes from the upper wall toward the second transport screw 56.
Further, the ceiling portion 59 extends downward from the upper wall from the upstream side in the transport direction of the second transport screw 56 to the surface closest to the magnetic sensor 57 (the portion where the flow path cross-sectional area is minimized). A gentle inclined surface 59a is provided. As a result, the developer is easily trapped between the magnetic sensor 57 and the ceiling portion 59.
Further, the surface closest to the magnetic sensor 57 in the ceiling portion 59 draws an arc along the shape of the second conveying screw 56, so that the developer pressure can be efficiently increased.
Furthermore, the ceiling 59 has an inclined surface 59b (on the upper wall) that is steeper than the above-described upstream inclined surface 59a from the portion having the smallest flow path cross-sectional area toward the downstream side of the second conveying screw 56. There is no problem even if it is vertical.) This prevents a problem that the developer flows backward in the vicinity of the magnetic sensor 57. Further, the developer in the vicinity of the second relay portion 64 is prevented from flowing back, and the developer stays in the vicinity of the second relay portion 64 to some extent. Therefore, the developer is transferred from the second transport path 54 to the first transport path 53. Will be performed smoothly.

Finally, the developer G used in the developing device 5 in the present embodiment will be described.
The carrier in the developer G has a resin coating layer on the surface of the core material. The resin coating layer of the carrier contains conductive particles in which a conductive coating layer comprising a tin dioxide layer and an indium oxide layer containing tin dioxide provided on the tin dioxide layer is provided on the surface of the substrate particles. ing. The conductive particles contained in the resin coating layer are formed so that the oil absorption is 10 to 300 ml / 100 g.
The oil absorption amount of the conductive particles can be measured according to “21 oil absorption amount” in JIS-K5101 “Pigment test method”.

  As the base particles of the conductive particles, at least one of aluminum oxide, titanium dioxide, zinc oxide, silicon dioxide, barium sulfide, and zirconium oxide can be used. The powder specific resistance of the conductive particles is formed to be 200 Ω · cm or less. The layer of the resin coating layer contains non-conductive particles in addition to the conductive particles. And it is formed so that the volume specific resistance of a carrier may be in the range of 10 to 16 Log (Ω · cm).

As described above, in the carrier of this embodiment, since the tin dioxide layer and the indium oxide layer containing tin dioxide are sequentially formed on the surface of the base particle, the conductive layer is uniformly and firmly formed on the particle surface. Fixed.
The conductive particles contained in the resin coating layer are formed so that the oil absorption is 10 to 300 ml / 100 g. Here, when the oil absorption is less than 10 ml / 100 g, the compatibility with the coating resin becomes insufficient, the adhesiveness is lowered, and the dispersibility is also lowered. Can not be. When the oil absorption exceeds 300 ml / 100 g, the adhesion with the binder resin becomes too strong and covers the surface of the conductive particles, so that the resistance cannot be adjusted sufficiently.
The carrier configured as described above is adjusted in resistance without containing carbon black as a resistance adjusting agent, and can prevent carrier adhesion and the like and stabilize the charge amount over time.

In the present embodiment, the carrier in the developer G is formed so that its weight average particle diameter is 35 μm. The weight average particle diameter of the carrier C is preferably in the range of 20 to 65 μm.
When the weight average particle size of the carrier is smaller than 20 μm, the magnetic force acting on each carrier is small, and thus carrier adhesion occurs. On the other hand, when the particle size of the carrier is larger than 65 μm, it becomes difficult for the toner to adhere faithfully to the latent image to which the toner should adhere, so that the granularity of the output image is lowered.

Further, the toner in the present exemplary embodiment is formed so that the average particle size is 5.2 μm.
The average particle diameter of the toner is preferably formed in the range of 3.5 to 7.5 μm. When the average particle diameter of the toner is smaller than 3.5 μm, the toner adhesion amount in the toner image is small, and therefore, the trailing edge white spot and the halo image are likely to occur. On the other hand, when the average particle diameter of the toner is larger than 7.5 μm, it becomes difficult for the toner to adhere faithfully to the latent image to which the toner should adhere, so that the granularity of the output image decreases. .

Further, the toner in the present embodiment is mainly composed of a binder resin, a release agent, and a colorant. The binder resin of the toner contains a hybrid resin having a vinyl polymer and a polyester polymer. Further, the content of the hybrid resin with respect to the content of the release agent is formed to be in the range of 0.5 to 3.
A hybrid resin can be obtained by performing a condensation polymerization reaction and an addition polymerization reaction simultaneously or independently in the same reaction vessel using a mixture containing a condensation polymerization resin raw material monomer and an addition polymerization resin raw material monomer. . As the release agent, carnauba wax, montan wax, oxidized rice wax or the like can be used, and the content thereof is preferably 3.5 to 10% by weight.
The toner configured in this manner provides an output image with high durability, high image quality without gloss unevenness, and less defects such as toner aggregation and fixing offset. On the other hand, since the specific gravity of the toner thus configured is smaller than that of the developer G (or carrier), the toner replenished from the toner replenishing port 44 is on the surface of the developer G in the second transport path. Easily floating in the developer G and hardly dispersed in the developer G. Therefore, as described above, the effect of optimizing the positional relationship and the rotation direction of the bottom surfaces of the first transport path 53 and the second transport path 54 is increased.

  Further, in the present embodiment, the toner concentration of the developer G accommodated in the developing device 5 is controlled so as to fall within the range of 4 to 12% by weight. As a result, the stress received by the developer G in the developing device 5 is reduced. Further, by controlling the toner density to 4% by weight or more, it is possible to prevent the image density of the output image from being lowered. In addition, by controlling the toner concentration to 12% by weight or less, the progress of toner spent is reduced, and the background charge and toner scattering are reduced without the toner charge amount (Q / M) being lowered.

  As described above, in the present embodiment, the positional relationship between the bottom surface of the first transport path 53 and the bottom surface of the second transport path 54, the first transport screw 55 (first transport member), and the second transport screw 56. Since the rotation direction of the (second transport member) is optimized, the developer G in a state where the replenishment toner is sufficiently dispersed can be supplied to the first transport path 53 with a relatively simple configuration. It is possible to suppress problems such as image density unevenness and background stains on the output image, and toner scattering.

  In the present embodiment, the present invention is applied to the developing device 13 in which two conveying screws as conveying members are installed. However, three or more conveying screws are installed, and at least two conveying screws are included. The present invention can also be applied to a developing device disposed at an adjacent position via a partition member. Even in this case, the same effect as in the present embodiment can be obtained by optimizing the positional relationship and the rotation direction of the bottom surfaces of two adjacent conveying screws.

  It should be noted that the present invention is not limited to the present embodiment, and it is obvious that each embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in the present embodiment. is there. In addition, the number, position, shape, and the like of the constituent members are not limited to the present embodiment, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which shows an image formation part. FIG. 4 is a cross-sectional view of the developing device and the photosensitive drum as viewed from above. It is sectional drawing which shows a developing device. It is sectional drawing in the position of the 2nd relay part of a developing device. It is sectional drawing in the position of the partition member of a developing device. It is sectional drawing in the position of the magnetic sensor of a developing device. FIG. 10 is a cross-sectional view of a second relay portion of the developing device in Comparative Example 1 at a position. FIG. 10 is a cross-sectional view of a partition member of a developing device in Comparative Example 1 at a position. FIG. 10 is a cross-sectional view of a second relay portion of the developing device in Comparative Example 2 at a position. FIG. 10 is a cross-sectional view of a partition member of a developing device in Comparative Example 2 at a position. FIG. 10 is a cross-sectional view of a second relay portion of the developing device in Comparative Example 3 at a position. FIG. 10 is a cross-sectional view at a position of a partition member of a developing device in Comparative Example 3. 6 is a graph showing the relationship between the inter-shaft distance of the transport screw and the amount of developer supplied to the first transport path. It is a graph which shows the relationship between the distance of a magnetic sensor and a 2nd relay part, and the agent surface height of a magnetic sensor vicinity. It is sectional drawing which shows the image development apparatus of another form. It is the rear view which looked at the 2nd conveyance path in the longitudinal direction.

Explanation of symbols

1, 1Y, 1M, 1C, 1K photosensitive drum (image carrier),
5 Development device (development unit),
6, 6Y, 6M, 6C, 6K process cartridge (imaging part),
51 Development roller (developer carrier),
52 Doctor blade,
53 1st conveyance path | route (1st developer accommodating part),
54 second transport path (second developer storage unit),
55 1st conveyance screw (1st conveyance member),
56 2nd conveyance screw (2nd conveyance member),
57 Magnetic sensor (toner concentration detection means),
58 partition members,
64 2nd relay part (relay part),
100 Image forming apparatus main body (apparatus main body), G developer.

Claims (11)

A developing device that contains a developer having a carrier and toner and that develops a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and carrying a developer;
A plurality of transport members that transport the developer contained in the apparatus in the longitudinal direction to form a circulation path;
With
The plurality of conveying members are:
First facing the developer carrying member, supplying the developer to the developer carrying member while conveying the developer in the longitudinal direction, and conveying the developer detached from the developer carrying member in the longitudinal direction. A conveying member;
A second conveying member that opposes the first conveying member via a partition member and conveys the developer in the longitudinal direction toward a relay unit that communicates with the upstream side of the first conveying path by the first conveying member;
Comprising
The first transport path is disposed such that the position of the bottom surface is higher than the position of the bottom surface of the second transport path by the second transport member,
The first transport member rotates in a direction in which an uppermost portion thereof is separated from the developer carrier and approaches the second transport member, and is rotated in the same direction as the rotation direction of the second transport member,
A toner concentration detecting means for detecting the toner concentration of the developer contained in the apparatus is provided in the vicinity of the relay unit and in the second transport path;
The relay portion is inclined so that a bottom surface thereof becomes higher from the second conveyance path side to the first conveyance path side,
The second transport path is
The flow path cross-sectional area in the vicinity of the position where the toner concentration detection means is installed is formed to be smaller than the flow path cross-sectional area at other positions,
A first inclined surface that inclines downward from the upper wall from the upstream side of the second transport path to the surface closest to the toner concentration detection unit is located on the ceiling near the position where the toner concentration detection unit is installed. A second inclined surface is provided, which is inclined from the surface closest to the toner density detecting means toward the downstream side of the second transport path at an angle steeper upward than the first inclined surface. A developing device.   The developing device according to claim 1, wherein the first transport path is disposed so that a position of a bottom surface thereof is lower than a position of a rotation center of the second transport member.   The first conveying member is formed such that the outer diameter thereof is the same as the outer diameter of the second conveying member, and the position of the rotation center thereof is higher than the position of the rotation center of the second conveying member. The developing device according to claim 1, wherein the developing device is provided.   The developing device according to claim 3, wherein the first conveying member is disposed such that a position of a rotation center thereof does not exceed an uppermost portion of the second conveying member.   5. The developing device according to claim 1, wherein the toner density detection unit is disposed within a range of 70 mm in the longitudinal direction from the relay unit. The carrier has a resin coating layer on the core surface,
The resin coating layer contains conductive particles formed by providing a conductive coating layer composed of a tin dioxide layer and an indium oxide layer containing tin dioxide provided on the tin dioxide layer on the surface of the substrate particles,
The conductive particles are formed so that the oil absorption is 10 to 300 ml / 100 g,
The toner includes a binder resin, a release agent, and a colorant,
The binder resin contains a hybrid resin having a vinyl polymer and a polyester polymer,
6. The developing device according to claim 1, wherein the content of the hybrid resin with respect to the content of the release agent is in a range of 0.5 to 3. The carrier, the developing device according to any one of claims 1 to 6, characterized in that the weight average particle diameter is formed to be in the range of 20～65Myuemu. The toner developing device according to any one of claims 1 to 7, characterized in that the average particle diameter is formed to be in the range of 3.5～7.5Myuemu. An apparatus according to any one of claims 1 to 8 in which the toner density of the developer contained in the apparatus is being controlled to be in the range of 4 to 12 wt%. A process cartridge that is detachably installed on the main body of the image forming apparatus,
10. A process cartridge in which the developing device according to claim 1 and the image carrier are integrated.   An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

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