JP2012173732A - Developing device, and process cartridge and image forming apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress, in a developing device including a developer supplying conveyance path disposed below a developer collecting conveyance path, unevenness in image density caused because a developer moves from the developer collecting conveyance path to the developer supplying conveyance path in an effective imaging range.SOLUTION: A developing device comprises a developer stirring conveyance path C which is a conveyance path different from a developer supplying conveyance path A and a developer collecting conveyance path B, so as to circularly convey a developer by allowing the developer conveyed to a downstream region of the developer collecting conveyance path to be conveyed from a main communicating path 62 communicated with the downstream region through the developer stirring conveyance path to an upstream region of the developer supplying conveyance path. The developing device further comprises a sub communicating path 60, separately from the main communicating path, having an opening in a position opposing an excessive portion of the developer exceeding an allowable capacity of the developer collecting conveyance path for transferring the excessive portion of the developer to the developer stirring conveyance path.

Description

  The present invention relates to a developing device using a two-component developer including toner and a carrier, and a process cartridge and an image forming apparatus provided with the developing device.

  This type of developing device used in an image forming apparatus such as a printer, a facsimile machine, and a copying machine is generally transported along a developer carrying body in a developer supply carrying path extending in the direction of the developer carrying body rotation axis. A two-component developer (hereinafter simply referred to as “developer”) is carried on the surface of the rotating developer carrying member, and the developer is supplied to the developing region by the rotation of the developer carrying member. Some conventional developing devices employ a supply / recovery integrated system in which the developed developer on the surface of the developer carrying member that has consumed toner in the development region is returned to the developer supply / conveyance path. In this supply / collection-integrated developing device, the toner density of the developer flowing in the developer supply / conveyance path becomes lower toward the downstream side in the developer conveyance direction (hereinafter, simply referred to as “downstream”), and thus is supplied to the development region. In the developer, there is a drawback that unevenness of toner density occurs in the direction of the rotation axis of the developer carrier. Such toner density unevenness is likely to appear as density unevenness in the image formed on the recording material, and is therefore desired to be eliminated.

  As a developing device that can eliminate this drawback, the developed developer on the surface of the developer carrying member that has consumed toner in the developing region is collected in a developer collecting conveyance path that is a conveyance path different from the developer supply conveyance path. There is one that employs a supply / recovery separation system (for example, Patent Document 1). In the supply / separation type developing device, the toner concentration of the developer flowing in the developer supply / conveyance path is maintained constant over the developer conveyance direction. Therefore, in the developer supplied to the development area, toner density unevenness does not occur in the direction of the rotation axis of the developer carrying member, and the above-described drawbacks are solved.

  The developing device described in Patent Document 1 has a configuration in which a developer regulating member is disposed above a developer carrying member, and the developer supply conveyance path is disposed above the developer collection conveyance path. Yes. In such a configuration, the surface of the developer carrying member moves from the top to the bottom in the developing region facing the latent image carrying member. For this reason, when the forward development method in which the developer carrying member is moved in the same direction as the surface moving direction of the latent image carrying member in the developing region is adopted, the transfer region for transferring an image from the latent image carrying member to the transferred member is a latent region. A layout configuration in which the transfer region is disposed above the latent image carrier cannot be employed because it is necessary to position the image carrier below the image carrier. Similarly, when a reverse development method in which the developer carrying member is moved in the direction opposite to the surface moving direction of the latent image carrier in the development region, the transfer region needs to be positioned above the latent image carrying member. A layout configuration in which the area is arranged below the latent image carrier cannot be employed.

On the other hand, Patent Document 2 discloses a developing device in which a developer regulating member is disposed oppositely below a developer carrier. In this developing device, the developer supply transport path is disposed below the developer recovery transport path, and the surface of the developer carrying member moves from the bottom to the top in the development region. Therefore, when adopting the forward development method in which the developer carrier is moved in the same direction as the surface movement direction of the latent image carrier in the development area, a layout configuration is adopted in which the transfer area is arranged above the latent image carrier. can do. Similarly, when adopting a reverse development method in which the developer carrying member is moved in the direction opposite to the surface moving direction of the latent image carrier in the developing region, a layout configuration in which the transfer region is arranged below the latent image carrying member. Can be adopted.
Therefore, according to the developing device described in Patent Document 2, it is possible to cope with an image forming apparatus that needs to adopt a combination of such a developing method and a layout configuration.

However, as described in Patent Document 2, in the configuration in which the developer supply transport path is disposed below the developer recovery transport path, the following problem occurs.
In general, in a supply / separation type developing device, a developer (developed developer having a reduced toner concentration) in a developer collection conveyance path within a developing area (effective image forming range) in the direction of the rotation axis of the developer carrier. If mixed into the developer supply transport path, the density of the image portion corresponding to the mixed portion becomes light. Therefore, density unevenness occurs on the image due to the relationship with other image portions. Accordingly, the developer recovery transport path and the developer supply transport path in the effective image forming range are separated by the partition member, and the developer in the developer recovery transport path is within the effective image forming range. It is important to prevent the occurrence of image density unevenness without moving directly to the image.

Here, in the supply and recovery separation type developing device, the developer is collected to the downstream end while collecting the developer from the developer carrier disposed along the developer collecting and conveying path in the developer collecting and conveying path. Is transported. Therefore, the amount of the developer flowing in the developer recovery conveyance path increases toward the downstream side. Therefore, the bulk of the developer increases in the vicinity of the downstream end portion of the developer recovery conveyance path.
At this time, if the developer supply transport path is arranged above the developer recovery transport path, the developed developer near the downstream end of the developer recovery transport path fills the transport path. In other words, as long as the bulk does not increase so that it protrudes from the gap between the partition member formed on the ceiling of the developer recovery transport path and the developer carrier to the developer supply transport path, the developed development in the developer recovery transport path The agent does not move directly to the developer supply conveyance path. Therefore, in such a configuration, image density unevenness caused by the developer in the developer recovery transport path moving directly to the developer supply transport path within the effective image forming range is unlikely to occur.

  On the other hand, when the developer supply transport path is arranged below the developer recovery transport path, the developed developer in the developer recovery transport path is separated from the developer carrying member by the partition member facing the developer carrier. The developed developer falls from the gap between the partition member and the developer carrying member and moves directly to the developer supply / conveyance path only by increasing the bulk of the end portion. Therefore, in the vicinity of the downstream end portion of the developer recovery conveyance path where the developer bulk increases, the developed developer in the developer recovery conveyance path easily moves directly to the developer supply conveyance path within the effective image forming range. Therefore, there arises a problem that image density unevenness is likely to occur.

  In a configuration in which the developer supply transport path is disposed below the developer recovery transport path, in many cases, the developer that has reached the downstream end region of the developer recovery transport path falls downward due to its own weight. In this way, it is transferred to the developer supply conveyance path. In this case, the developer does not stay in the downstream end region of the developer recovery conveyance path, but the developer bulk increases in the region adjacent to the upstream side of the downstream end region. Therefore, in this case, in the region adjacent to the upstream side of the downstream end region, the developed developer in the developer recovery transport path is likely to move to the developer supply transport path, and thus image density unevenness is likely to occur. The problem arises. In this case, the developer in a region adjacent to the upstream side of the downstream end region of the developer recovery transport path is improved by increasing the transport capability of the developer by the transport member that transports the developer in the developer recovery transport path. The above problem can also be solved if the bulk of the substrate can be stably reduced. However, increasing the developer transport capability usually involves various adverse effects. For example, when a conveying screw is used as the conveying member, if a large screw is used in order to increase the developer conveying ability, the developing device is increased in size. Further, if the number of rotations of the screw is increased in order to increase the developer conveying capability, energy consumption is increased and the temperature in the developing device is excessively increased, which adversely affects the developer.

  In addition, if the partition member and the developing case are integrally configured so that the gap between the partition member and the developer carrier can be set with high accuracy, the gap between the partition member and the developer carrier can be narrowed. It is possible to reduce the amount of developer falling from the gap. However, in the vicinity of the downstream end region of the developer recovery conveyance path, the volume of the developed developer increases and the gap is pushed out to the gap. Developer drops. For this reason, it is difficult to suppress a decrease in density of the image portion corresponding to the vicinity of the downstream end region of the developer recovery conveyance path, and it is difficult to avoid occurrence of uneven image density.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a developer supply transport path in a configuration in which the developer supply transport path is disposed below the developer recovery transport path. A developing device capable of suppressing the occurrence of image density unevenness due to the direct movement of the developer to the developer supply / conveyance path within the effective image forming range, and a process cartridge and an image forming apparatus provided with the developing device are provided. It is.

In order to achieve the above object, the invention of claim 1 includes a toner and a carrier that are transported in a developer supply transport path extending in the direction of the rotation axis of the developer support along the developer support. By carrying the component developer on the surface of the rotating developer carrier, the two-component developer carried on the surface of the developer carrier is transported to the development area, and the two components are developed in the development area. The toner in the developer is attached to the latent image on the surface of the latent image carrier to develop the latent image, and the two-component developer on the developer carrier that has passed through the development area is applied to the developer carrier. A developer carrying member that extends in the direction of the rotation axis of the developer carrying member and collects in a developer collecting and conveying path disposed above the developer supplying and conveying path. And a developer agitation transport path different from these transport paths. A circulating transport mechanism for circulating and transporting the two-component developer, wherein the circulating transport mechanism transports the two-component developer transported to the downstream end region in the developer transport direction of the developer recovery transport path. In addition to the transport path that discharges from the main communication path communicating with the area and transports it to the upstream end area in the developer transport direction of the developer supply transport path, development exceeding the allowable volume in the developer recovery transport path From a sub-communication path different from the main communication path for opening the developer portion and transferring the developer part to the developer stirring and conveying path, via the developer stirring and conveying path. A transport path for transporting the developer supply transport path to the upstream end region in the developer transport direction is provided.
According to a second aspect of the present invention, in the developing device according to the first aspect, the sub-communication path is on the downstream side in the developer transport direction of the developer recovery transport path and is an effective image forming area on the developer carrier. It is provided over the range including the edge part of this.
According to a third aspect of the present invention, in the developing device according to the first or second aspect, the sub-communication path is higher than a height of a partition wall interposed between the developer recovery conveyance path and the developer carrier surface. It is characterized by opening at a low position.
According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, the developer stirring and conveying path is disposed at a position lower than the developer collecting and conveying path. The sub communication path extends downward from the developer collecting and conveying path side toward the developer stirring and conveying path side.
According to a fifth aspect of the present invention, in the developing device according to any one of the first to fourth aspects, the toner replenishing port for replenishing toner to the two-component developer has the developer collection transport path. This is characterized in that an opening is made in the upstream portion in the developer transport direction.
According to a sixth aspect of the present invention, there is provided a process in which the latent image carrier and the developing device for developing the latent image on the latent image carrier are integrally supported and detachable from the main body of the image forming apparatus. 6. The cartridge according to claim 1, wherein the developing device according to claim 1 is used as the developing device.
According to a seventh aspect of the present invention, there is provided a latent image bearing member, a latent image forming means for forming a latent image on the latent image bearing member, and a two-component developer containing toner and a carrier on the latent image bearing member. An image forming apparatus including: a developing device that develops a latent image; and a toner image formed on the latent image carrier by the developing device is finally transferred to a recording material to form an image on the recording material In the apparatus, the developing device according to any one of claims 1 to 5 is used as the developing device.

  In the present invention, a developer agitation conveyance path as a third conveyance path different from the developer supply conveyance path and the developer recovery conveyance path is provided, and the developer collection conveyance path and the developer agitation conveyance path are connected by a sub-communication path. Communicate. Since this sub-communication path opens at a position opposite to the developer portion exceeding the allowable volume in the developer recovery conveyance path, the developer portion exceeding the allowable volume in the developer recovery conveyance path The developer is transferred to the developer stirring and conveying path through the passage. Therefore, there is no developer exceeding the allowable volume in the developer recovery conveyance path, and the developer (developed developer) in the developer recovery conveyance path exceeding the allowable volume is within the effective image forming range. Therefore, it is possible to suppress the occurrence of a situation where the developer moves directly to the developer supply / conveyance path. The developer that has moved from the sub-communication path to the developer agitation transport path is circulated and transported by the circulation transport mechanism, and is finally transported to the upstream end of the developer supply transport path.

  As described above, according to the present invention, in the configuration in which the developer supply transport path is disposed below the developer recovery transport path, the developer in the developer recovery transport path is within the effective image forming range. There is an excellent effect that it is possible to suppress the occurrence of image density unevenness due to movement to the road.

1 is a configuration diagram illustrating a printer in an embodiment. FIG. FIG. 2 is a cross-sectional view of a process cartridge constituting an image forming unit of the printer. It is sectional drawing when the developing device in embodiment is seen from the developing roller rotating shaft direction. It is explanatory drawing when the lower internal structure (Developer supply conveyance path A and Developer stirring conveyance path C) in the developing device is seen from above. It is explanatory drawing when the upper internal structure (developer collection conveyance path B and developing roller) in the developing device is seen from above. 6 is a schematic diagram illustrating a developer bulk distribution in a developer supply transport path A and a developer recovery transport path B. FIG. FIG. 2 is an explanatory diagram for further detailed description of the developing device. It is sectional drawing of the location shown with the code | symbol X in FIG.4 and FIG.5. It is sectional drawing of the location shown with the code | symbol Y in FIG.4 and FIG.5. It is sectional drawing of the location shown with the code | symbol Z in FIG.4 and FIG.5. It is explanatory drawing when the lower internal structure (developer supply conveyance path A and developer stirring conveyance path C) in the developing device of a modification is seen from the upper part. It is explanatory drawing when the upper internal structure (developer collection conveyance path B and developing roller) in the developing device is seen from above.

Hereinafter, an embodiment of an image forming apparatus according to 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.

FIG. 1 is a configuration diagram illustrating a printer as an image forming apparatus according to the present exemplary embodiment.
FIG. 2 is a cross-sectional view of the process cartridge constituting the image forming unit of the printer.
As shown in FIG. 1, image forming portions 6Y, 6M, 6C, 6K corresponding to the respective colors (yellow, magenta, cyan, black) are arranged in parallel so as to face the intermediate transfer belt 8 of the intermediate transfer unit 10. Yes. Note that the four image forming units 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. 6, the color-coded codes (Y, M, C, K) in the photosensitive drum 1, the primary transfer bias roller 9 are omitted.

  Referring to FIG. 2, the image forming unit 6 includes a photosensitive drum 1 as a latent image carrier, a charging unit 4 disposed around the photosensitive drum 1, a developing device 5 as a developing unit, and a cleaning unit. 2 and so on (only the developing device 5 is shown in FIG. 1). An image forming process (charging process, exposure process, developing process, transfer process, cleaning process) is performed on the photosensitive drum 1, and a desired toner image is formed on the photosensitive drum 1.

  The photosensitive drum 1, the charging unit 4, the developing device 5, and the cleaning unit 2 constituting the image forming unit 6 are configured so as to be detachable from the apparatus main body 100. When it is done, it may be replaced with a new one. In the present embodiment, the photosensitive drum 1, the charging unit 4, the developing device 5Y, and the cleaning unit 2 constituting the image forming unit 6 are integrated into a process cartridge that is detachably installed in the apparatus main body 100. Thereby, workability at the time of performing maintenance of the image forming unit 6 is improved.

  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 (charging process). Thereafter, the surface of the photosensitive drum 1 reaches an irradiation position of a laser beam L emitted from an exposure unit (not shown), and an electrostatic latent image is formed by exposure scanning at this position (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). Thereafter, 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 onto the intermediate transfer belt 8 at this position. (Primary transfer process). At this time, a small amount of untransferred toner remains on the photosensitive drum 1. Thereafter, the surface of the photosensitive drum 1 reaches a position facing the cleaning unit 2, and untransferred toner remaining on the photosensitive drum 1 at this position is collected by the cleaning blade 2a (cleaning step). 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.

  Note that the above-described image forming process is performed by each of the four image forming units 6Y, 6M, 6C, and 6K. That is, referring to FIG. 1, laser light L based on image information is exposed on the photosensitive drums of image forming units 6Y, 6M, 6C, and 6K from an exposure unit disposed below the image forming unit. Irradiated toward. Specifically, the exposure unit 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.

  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 primary transfer nips. 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 onto the intermediate transfer belt 8 while being superimposed. 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 transfer material P that is a recording material such as transfer paper conveyed to the position of the secondary transfer nip. At this time, the untransferred toner that has not been transferred to the transfer material P remains on the intermediate transfer belt 8. Untransferred toner remaining on the intermediate transfer belt is removed by a cleaning unit (not shown) to return to the initial state. Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

  Here, the transfer material P transported to the position of the secondary transfer nip is transported from a paper feed unit 26 disposed below the apparatus main body 100 via a paper feed roller 27, a registration roller pair 28, and the like. It has been done. Specifically, a plurality of transfer materials P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is rotated in the counterclockwise direction in FIG. 1, the uppermost transfer material P is fed between the rollers of the registration roller pair 28. The transfer material P conveyed to the registration roller pair 28 is temporarily stopped at the position of the roller nip of the registration roller pair 28 that has stopped rotating. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the transfer material P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the transfer material P.

  Thereafter, the transfer material P on which the color image has been 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 to the surface is fixed on the transfer material P by heat and pressure generated by the fixing roller and the pressure roller. Thereafter, the transfer material P is discharged out of the apparatus through the rollers of the discharge roller pair 29. The transfer material 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.

Next, the configuration and operation of the developing device 5 will be described in more detail.
FIG. 3 is a cross-sectional view of the developing device 5 according to the present embodiment as viewed from the direction of the rotation axis of the developing roller 51 as a developer carrier.
The developing device 5 includes a developing roller 51 as a developer carrying member facing the photosensitive drum 1, a doctor blade 52 as a developer regulating member installed below the developing roller 51, and three developer conveying paths A and B. , C are provided with three conveying screws 53, 54, 55. The three developer transport paths A, B, and C contain a two-component developer (hereinafter simply referred to as “developer”) composed of a carrier and a toner. Further, the developing device 5 is provided with a toner concentration sensor 61 for detecting the toner concentration in the developer.

  As shown in FIG. 3, the developing roller 51 includes a magnet roller 56 fixed inside, and a sleeve that rotates around the magnet roller 56. On the magnet roller 56 of the developing roller 51, five magnetic poles of P1 to P5 are formed. Then, when the sleeve rotates around the magnet roller 56 on which the five magnetic poles are formed, the developer is conveyed along with the rotation. In addition, the radial line attached | subjected to the developing roller 51 of FIG. 3 shows the position where each magnetic force of P1 pole-P5 pole becomes a peak.

  In the developing device 5, as an initial developer, a developer in which a toner mainly composed of a polyester resin (average particle diameter of 5.8 μm) and a magnetic fine particle carrier (average particle diameter of 35 μm) are uniformly mixed to 7 wt% is constant. The amount is filled. In the developer supply conveyance path A, a supply screw 53 that is a conveyance member for conveying the developer along the rotation axis direction of the developing roller 51 is disposed. In the developer collection conveyance path B, a collection screw 54 that is a conveyance member for conveying the developer along the rotation axis direction of the developing roller 51 is disposed. In the developer agitation conveyance path C, an agitation screw 55 that is a conveyance member for conveying the developer along the rotation axis direction of the developing roller 51 is disposed. These conveying screws 53, 54, and 55 are driven to rotate at 600 to 800 rpm, thereby conveying the developer in each conveying path along the direction of the screw axis, and stirring to make the toner and carrier uniform. Mix and charge.

  The developer transported in the developer supply transport path A by the supply screw 53 arranged so as to face the developing roller 51 is caused by the magnetic force of the P4 and P5 magnetic poles of the magnet roller 56 included in the developing roller 51. It is carried on the outer peripheral surface of the sleeve. Then, the developing roller 51 rotates as shown by the arrow in the drawing, and is carried to the developing area formed by the photosensitive drum 1 and the developing roller 51. A developing bias is applied to the developing roller 51 by a high voltage power source (not shown), and the toner develops the electrostatic latent image on the photosensitive drum 1 by the action of the developing electric field formed in the developing region. The developed developer is collected in the developer collection conveyance path B in the developing device 5 as the developing roller 51 rotates. In the present embodiment, the developer recovery transport path B is disposed above the developer supply transport path A, and the separation between the developer recovery transport path B and the developer supply transport path A is a partition member. Partitioned by a plate 57.

FIG. 4 is an explanatory diagram when the lower internal structure (developer supply transport path A and developer stirring transport path C) in the developing device 5 of the present embodiment is viewed from above (in the direction of arrow A in FIG. 3). .
FIG. 5 is an explanatory diagram when the upper internal structure (developer recovery conveyance path B and developing roller 51) in the developing device 5 of the present embodiment is viewed from above (in the direction of arrow A in FIG. 3).
The arrows in FIGS. 4 and 5 indicate the flow of the developer.

  As shown in FIG. 3, the developer supply transport path A and the developer stirring transport path C are partitioned by a passage wall 58. The passage wall 58 has an opening in a downstream end region (region b in FIG. 4) of the developer supply transport path A, and the developer supply transport path A of the developer supply transport path A is formed through the main communication path formed by the opening. The developer is transferred from the downstream end region to the upstream end region of the developer stirring and conveying path C through the main communication path.

  The passage wall 58 is formed by an upstream end region (region a in FIG. 4) of the developer supply transport path A opening to a downstream end region of the developer stirring transport path C. The developer is transferred through the main communication path from the downstream end area of the developer agitation transport path C to the upstream end area of the developer supply transport path A through the main communication path. In the present embodiment, the part of the stirring screw 55 that faces the main communication path is formed in a paddle, a reversely wound screw, or the like, and is in the developer transport direction of the developer stirring transport path C. The conveyance ability toward the transfer direction to the developer supply conveyance path which is the vertical direction is enhanced.

  Further, as shown in FIG. 3, the developer recovery conveyance path B is partitioned from both the developer supply conveyance path A and the developer agitation conveyance path C by the separation plate 57. In the separation plate 57, a downstream end region (region c in FIG. 5) of the developer recovery conveyance path B opens to an upstream end region of the developer agitation conveyance path C, and a main communication formed by this opening. The developer is transferred from the downstream end region of the developer recovery transport path B to the upstream end region of the developer agitation transport path C through the main communication path. At this time, the developer that has reached the downstream end region of the developer recovery conveyance path B is subjected to the action of gravity, falls or slides down the main conveyance path, and is transferred to the upstream end region of the developer agitation conveyance path C. Is done.

  Further, in the developer agitation transport path C, a toner replenishing port 63 is opened upstream of the main communication path in the upstream end region. The agitating screw 55 conveys the toner replenished from the toner replenishing port 63 to the downstream side, and further to the downstream side together with the developer transferred from the main communication path in the region b in FIG. 4 or the region c in FIG. Thus, the replenishing toner and the developer are agitated and mixed in the developer agitating / conveying path C.

FIG. 6 is a schematic diagram illustrating the bulk distribution of the developer in the developer supply transport path A and the developer recovery transport path B.
Since the developing device 5 of the present embodiment employs a supply / recovery separation system, as shown in FIG. 6, the developer in the developer supply transport path A has a lower volume on the downstream side, and the developer recovery transport path. The bulk of the developer in B becomes higher toward the downstream side. When the relationship between the developer conveyance capacity Wm obtained from the diameter, pitch, and rotation speed of the supply screw 53 and the developer conveyance capacity Ws on the developing roller 51 is Wm> Ws, the developer is uniformly developed. It is conveyed onto the roller 51. If this condition is not satisfied, the developer is insufficient on the downstream side of the developer supply conveyance path A, and the developer supplied to the developing roller 51 is insufficient.

FIG. 7 is an explanatory diagram for further explaining the developing device 5 in the present embodiment.
In the present embodiment, the center height d of the recovery screw 54 is located between the upper vertex e and the lower vertex f of the developing roller 51, and the separation plate 57 is interposed between the recovery screw 54 and the developing roller 51. As a result, the developer is peeled off from the second quadrant area on the developing roller defined by the vertical line g and the horizontal line h passing through the center of the developing roller 51 as indicated by an arrow i in the drawing, and the inside of the developer collecting conveyance path B. It is configured to be collected. The developer peeling force from the developing roller 51 is ensured by applying a repulsive force with the P3 and P4 magnetic poles of the included magnet roller 56 as the same polarity and applying a centrifugal force due to the rotation of the developing roller. .

  In addition, the separation plate 57 functions as a partition wall whose front end partitions the developer collection conveyance path B and the outer peripheral surface of the developing roller 51. The tip of the separation plate 57 is located downstream of the peeling point where the developer is peeled off from the developing roller 51 in the developing roller rotation direction, and the developer peeled off from the developing roller 51 enters the developer supply transport path A. It collects so as not to fall and guides it to the developer recovery conveyance path B.

FIG. 8 is a cross-sectional view of a portion indicated by a symbol X in FIGS. 4 and 5.
The cross-sectional view shown in FIG. 8 shows a cross section orthogonal to the developing roller rotation axis at a location upstream of the developer recovery transport path. On the upstream side of the developer recovery transport path B, the bulk of the developer is low, so that the developer in the developer recovery transport path B approaches the gap between the tip of the separation plate 57 and the developing roller 51. Must not. Therefore, the developer does not fall from the gap between the front end of the separation plate 57 and the developing roller 51, and the developed developer in the developer recovery transport path B is not mixed into the developer supply transport path A.

FIG. 9 is a cross-sectional view of a portion indicated by a symbol Y in FIGS. 4 and 5.
The cross-sectional view shown in FIG. 9 shows a cross section orthogonal to the developing roller rotation axis in the downstream end region of the developer recovery transport path. In the downstream end region of the developer recovery transport path B, the main communication path 62 is opened at the bottom surface thereof, so that the developer that has reached the downstream end area of the developer recovery transport path B falls from the main communication path 62. To the upstream end region of the developer stirring and conveying path. As shown in FIG. 6, the bulk of the developer in the developer recovery transport path B becomes higher on the downstream side, but the developer that has reached the downstream end region of the developer recovery transport path B falls from the main communication path 62. The bulk is reduced. Therefore, in the downstream end region of the developer recovery transport path B, the volume does not increase as the developer in the developer recovery transport path B approaches the gap between the tip of the separation plate 57 and the developing roller 51.

FIG. 10 is a cross-sectional view of a portion indicated by a symbol Z in FIGS. 4 and 5.
The cross-sectional view shown in FIG. 10 shows a cross section orthogonal to the developing roller rotation axis on the upstream side of the downstream end region (that is, the region where the main communication passage 62 is open) of the developer collection conveyance path.
As shown in FIG. 6, the bulk of the developer in the developer recovery conveyance path B becomes higher toward the downstream side. Therefore, the bulk increases as it approaches the downstream end region of the developer collection conveyance path, and the volume may increase as the developer in the developer collection conveyance path B approaches the gap between the tip of the separation plate 57 and the developing roller 51. There is. When the bulk increases in this way, the developer falls from the gap between the tip of the separation plate 57 and the developing roller 51, and the developed developer in the developer recovery transport path B enters the developer supply transport path A. As a result, image density unevenness occurs as described above.

  Therefore, in the present embodiment, as shown in FIG. 10, an opening is made at a location facing the developer portion exceeding the allowable volume in the developer collection conveyance path B, and the developer portion exceeding the allowable volume is disposed. A sub-communication path 60 for transferring to the developer stirring and conveying path C is provided. In the present embodiment, as shown in FIG. 10, the sub-communication path 60 includes a rear end portion of a separation plate 57 that constitutes a side wall opposite to the developing roller 51 of the developer recovery transport path, and an inner wall of the developing case. Formed between. The height of the rear end portion of the separation plate 57 is formed lower than the height of the front end portion of the separation plate 57. As a result, before the bulk of the developer in the developer recovery conveyance path B exceeds the height of the front end portion of the separation plate 57, the upper portion of the developer gets over the rear end portion of the separation plate 57 and the sub communication path. 60, and falls to the developer stirring conveyance path C. As a result, the developer does not increase in volume as the developer in the developer recovery transport path B approaches the gap between the tip of the separation plate 57 and the development roller 51, and the gap between the tip of the separation plate 57 and the development roller 51 does not increase. It is possible to prevent the developer from dropping and causing uneven image density.

  In the present embodiment, the developing roller rotation axis direction (width direction) region forming the sub-communication path 60 is on the downstream side of the developer collection conveyance path B and is an effective image forming region (developing roller) on the developing roller 51. 51 covers the range including the end of the maximum width that can hold the developer. This range is a range in which there is a high possibility that the volume of the developer in the developer collection conveyance path B increases as the developer approaches the gap between the tip of the separation plate 57 and the developing roller 51. By forming, the amount of the developer moving to the developer stirring and conveying path C through the sub communication path 60 can be minimized. That is, when the amount of the developer moving to the developer stirring / conveying path C through the sub-communication path 60 becomes larger than necessary, the developer is developed via the main communication path 62 after reaching the downstream end region of the developer collecting / conveying path B. The amount of developer passing through the main circulation path that is transferred to the upstream end region of the agent stirring and conveying path C is relatively small. The sub-circulation path passing through the sub-communication path 60 has a shorter path length than the main circulation path, so that the distance for stirring and mixing before the developed developer is transported to the developer supply transport path A is large. short. Since it is desired that the developed developer is stirred and mixed as much as possible before being transported to the developer supply transport path A, it moves to the developer stirring transport path C through the sub-communication path 60. It is preferred to minimize the amount of developer.

[Modification]
Next, a modified example of the developing device 5 of the present embodiment will be described.
FIG. 11 is an explanatory diagram of the lower internal structure (developer supply / conveyance path A and developer stirring / conveyance path C) in the developing device 5 of this modification as viewed from above.
FIG. 12 is an explanatory view of the upper internal structure (developer recovery / conveying path B and developing roller 51) in the developing device 5 of this modification as viewed from above.
In the developing device of this modification, the developer transport directions of the developer supply transport path A, the developer recovery transport path B, and the developer agitation transport path C are all opposite to those in the above embodiment. .

  The developer supply transport path A and the developer agitation transport path C are partitioned by a passage wall 58 as in the above embodiment. The passage wall 58 is open at the downstream end region (region b in FIG. 11) of the developer supply transport path A, and the developer supply transport path A of the developer supply transport path A is formed through the main communication path formed by the opening. The developer is transferred from the downstream end region to the upstream end region of the developer stirring and conveying path C through the main communication path.

  The passage wall 58 is formed by the upstream end region (region a in FIG. 11) of the developer supply transport path A opening to the downstream end region of the developer stirring transport path C. The developer is transferred through the main communication path from the downstream end area of the developer agitation transport path C to the upstream end area of the developer supply transport path A through the main communication path. In this modification as well, the portion of the stirring screw 55 facing the main communication path is formed in a paddle, a reversely wound screw, or the like, and is in the developer transport direction of the developer stirring transport path C. The conveyance ability toward the transfer direction to the developer supply conveyance path which is the vertical direction is enhanced.

  Further, the developer recovery conveyance path B is partitioned from both the developer supply conveyance path A and the developer agitation conveyance path C by the separation plate 57 as in the above embodiment. In the separation plate 57, a downstream end region (region c in FIG. 12) of the developer recovery conveyance path B opens to an upstream end region of the developer agitation conveyance path C, and a main communication formed by this opening. The developer is transferred from the downstream end region of the developer recovery transport path B to the upstream end region of the developer agitation transport path C through the main communication path. At this time, the developer that has reached the downstream end region of the developer recovery conveyance path B is subjected to the action of gravity, falls or slides down the main conveyance path, and is transferred to the upstream end region of the developer agitation conveyance path C. Is done.

  In the present modification, the toner replenishing port 63 is opened upstream of the main communication path in the upstream end region of the developer recovery conveyance path B. Therefore, the collecting screw 54 conveys the toner replenished from the toner replenishing port 63 to the downstream side, and further conveys the toner to the downstream side while being stirred and mixed together with the developed developer sequentially collected from the developing roller 51. To do. Then, the developer stirred and mixed with the replenishment toner in the developer recovery conveyance path B is transferred from the main communication path to the upstream end area of the developer stirring conveyance path C in the region b in FIG. In the stirring conveyance path C, stirring and mixing are performed.

As described above, the printer according to the present embodiment includes a photosensitive drum 1 as a latent image carrier, an exposure unit as a latent image forming unit that forms a latent image on the photosensitive drum 1, and a two-component including toner and carrier. A developing device 5 that develops the latent image on the photosensitive drum 1 with a developer, and the toner image formed on the photosensitive drum 1 by the developing device 5 is finally transferred to a transfer material P as a recording material. An image forming apparatus that forms an image on a transfer material P by transferring the image. The developing device 5 used in this printer is a developer that rotates a developer conveyed in a developer supply conveyance path A extending in the direction of the developing roller rotation axis along a developing roller 51 as a developer carrying member. By carrying on the surface of the roller 51, the developer carried on the surface of the developing roller 51 is conveyed to the developing area, and the toner in the developer adheres to the latent image on the surface of the photosensitive drum 1 in the developing area. In addition to developing the latent image, the developer on the developing roller 51 that has passed through the developing region extends along the developing roller 51 in the direction of the developing roller rotation axis and is disposed above the developer supply conveyance path A. This is a developing device of a supply recovery separation system that recovers to the developer recovery conveyance path B. The developing device 5 includes a developer agitation transport path C which is a transport path different from the developer supply transport path A and the developer recovery transport path B, and is transported to the downstream end region of the developer recovery transport path B. Circulation transport for circulating and transporting the developer by transporting the developer from the main communication path 62 communicating with the downstream end area to the upstream end area of the developer supply transport path A via the developer stirring transport path C. It has a mechanism. In this embodiment, the sub-connection for opening the developer portion to the developer agitating / conveying path C by opening the developer collecting / conveying path B in a position facing the developer portion exceeding the allowable volume. A passage 60 is provided separately from the main communication passage 62. As a result, the developer portion exceeding the allowable volume in the developer recovery conveyance path B is transferred to the developer agitation conveyance path C through the sub-communication path 60. Therefore, there is no developer exceeding the allowable volume in the developer recovery conveyance path B, and the developer (developed developer) in the developer recovery conveyance path B exceeding the allowable volume is supplied as a developer. Occurrence of a situation of moving to the conveyance path A can be suppressed, and uneven image density can be suppressed.
In the present embodiment, the sub-communication path 60 is provided on the downstream side of the developer recovery transport path B in the developer transport direction and including the end of the effective image forming area on the developing roller 51. This range is a range in which there is a high possibility that the developer in the developer recovery transport path B will fall into the developer supply transport path A. By forming the sub-communication path 60 in this range, the developer recovery transport path It is possible to more reliably prevent the developer in B from dropping into the developer supply transport path A.
Further, in the present embodiment, the sub communication path 60 is opened at a position lower than the height of the leading end portion of the separation plate 57 that is a partition wall interposed between the developer recovery conveyance path B and the outer peripheral surface of the developing roller 51. Therefore, before the volume of the developer in the developer recovery transport path B exceeds the height of the tip of the separation plate 57 and falls to the developer supply transport path A, the developer is passed through the sub-communication path. 60 to the developer stirring and conveying path C. As a result, the developer does not increase in volume as the developer in the developer recovery transport path B exceeds the height of the tip of the separation plate 57, and the developer falls from the gap between the tip of the separation plate 57 and the developing roller 51. Thus, it is possible to prevent image density unevenness.
In this embodiment, the developer agitation transport path C is disposed at a position lower than the developer recovery transport path B, and the auxiliary communication path 60 is connected to the developer agitation transport path B from the developer recovery transport path B side. It extends downward toward the C side. As a result, the developer portion exceeding the allowable volume in the developer recovery conveyance path B moves to the developer agitation conveyance path C in the sub-communication path 60 by the action of gravity. Therefore, the moving mechanism can be simplified.
Further, in the above modification, the toner replenishing port 63 for replenishing the toner with respect to the developer is opened in the upstream portion of the developer collecting and conveying path B. If new toner is replenished to a location where the amount of developer is large, the replenished toner may move while being deposited on the upper layer of the developer and may not be dispersed in the developer. In this modification, since the toner is replenished to the upstream portion of the developer collection transport path B with a small amount of developer, the replenished toner can be easily dispersed in the developer. In addition, since the developed developer is gradually added from the developing roller 51 during the conveyance of the developer recovery conveyance path B, the toner density unevenness (circulation conveyance direction) in the developer circulated and conveyed in the developing device 5 is performed. It is easy to correct toner density unevenness. In particular, in this modification, the developer transported to the downstream end region of the developer recovery transport path B is transported to the upstream end region of the developer supply transport path A via the developer stirring transport path C. Therefore, the replenished toner can be agitated and mixed with the developer not only in the developer recovery conveyance path B but also in the developer agitation conveyance path C, so that insufficient frictional charging and toner density unevenness can be solved stably.

In the present embodiment, the developing device having only one developer stirring conveyance path C and including three conveyance paths including the developer supply conveyance path A and the developer recovery conveyance path B has been described. The present invention can be similarly applied to a configuration in which two or more developer stirring conveyance paths C are provided and four or more conveyance paths are provided.
In the present embodiment, the developer transported to the downstream end region of the developer recovery transport path B is transported to the upstream end region of the developer supply transport path A via the developer stirring transport path C. However, the developer transported to the downstream end region of the developer recovery transport path B is transported directly to the upstream end region of the developer supply transport path A without going through the developer stirring transport path C. It is good also as a structure. As the main circulation path in this case, for example, the developer is transferred from the downstream end region of the developer supply transport path A to the developer stirring transport path C, and the developer recovery transport is performed from the downstream end area of the developer stirring transport path C. A configuration in which the developer is transferred to the path B can be mentioned.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Cleaning part 4 Charging part 5 Developing device 6 Image forming part 8 Intermediate transfer belt 51 Developing roller 52 Doctor blade 53 Supply screw 54 Recovery screw 55 Stirring screw 56 Magnet roller 57 Separating plate 58 Passage wall 60 Secondary communication path 62 Main communication path 63 Toner replenishment port 100 Device body A Developer supply transport path B Developer recovery transport path C Developer stirring transport path

JP-A-5-333691 Japanese Patent Laid-Open No. 11-174810

Claims (7)

A two-component developer containing toner and a carrier conveyed in a developer supply conveyance path extending in the direction of the developer carrier rotation axis along the developer carrier is transferred to the rotating developer carrier. By carrying the toner on the surface of the developer carrying member, the two-component developer carried on the surface of the developer carrying member is conveyed to the developing region, and in the developing region, the toner in the two-component developer is transferred onto the latent image carrier surface. The two-component developer on the developer carrying member that has passed through the development area is extended along the developer carrying member in the direction of the rotation axis of the developer carrying member. In the developing device that collects in the developer collection conveyance path disposed above the agent supply conveyance path,
A circulation conveyance mechanism that circulates and conveys the two-component developer using the developer supply conveyance path, the developer recovery conveyance path, and a developer agitation conveyance path different from these conveyance paths,
The circulation transport mechanism discharges the two-component developer transported to the downstream end region in the developer transport direction of the developer recovery transport path from the main communication path communicating with the downstream end region, and supplies and transports the developer. In addition to the transport path for transporting to the upstream end area in the developer transport direction of the path, the developer portion is opened at a position facing the developer portion exceeding the allowable volume in the developer recovery transport path, and the developer portion is developed as described above. From the sub-communication path different from the main communication path for transferring to the developer stirring and conveying path, the developer is conveyed to the upstream end region in the developer conveying direction of the developer supply and conveying path through the developer stirring and conveying path. A developing device comprising a transport path. The developing device according to claim 1.
The sub-communication path is provided on a downstream side of the developer recovery transport path in the developer transport direction and over a range including an end of an effective image forming area on the developer carrier. apparatus. The developing device according to claim 1 or 2,
The developing device, wherein the sub-communication path is opened at a position lower than a height of a partition wall interposed between the developer collection transport path and the developer carrier surface. The developing device according to any one of claims 1 to 3,
The developer stirring conveyance path is disposed at a position lower than the developer recovery conveyance path,
The developing device, wherein the sub-communication path extends downward from the developer collecting and conveying path side toward the developer stirring and conveying path side. The developing device according to any one of claims 1 to 4,
A developing device characterized in that a toner replenishing port for replenishing toner to the two-component developer is opened at a portion upstream of the developer collection transport path in the developer transport direction. In a process cartridge that integrally supports a latent image carrier and a developing device that develops a latent image on the latent image carrier and is configured to be detachable from the image forming apparatus main body,
A process cartridge using the developing device according to claim 1 as the developing device. A latent image carrier, a latent image forming unit that forms a latent image on the latent image carrier, and a developing device that develops the latent image on the latent image carrier using a two-component developer containing toner and a carrier. An image forming apparatus for forming an image on the recording material by finally transferring the toner image formed on the latent image carrier by the developing device to the recording material,
An image forming apparatus using the developing device according to claim 1 as the developing device.

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