JP2018036537A - Developing device - Google Patents

Abstract

Provided is a developing device capable of suppressing an increase in developer surface even when the flowability of the developer is lowered when the ACR system is applied to a function separation type developing device. Two discharge ports, a first discharge port and a second discharge port, are provided on the upstream side and the downstream side of the stirring chamber. The second discharge port 51 is provided at a position away from the first discharge port 50 by a predetermined distance or more. The second discharge port 51 is located at a position where the length to the first discharge port 50 is more than half of the length between the first communication part 17 and the second communication part 18, and at least a part thereof is the second communication part 18. It is provided in the position which overlaps. The second discharge port 51 is provided at a position where the lower end is higher than the lower end of the first discharge port 50 with respect to the arrangement position in the vertical direction. As a result, the excess developer discharged along with the replenishment of the replenisher is discharged from the first discharge port 50, and the developer discharged when the surface of the developer rises due to the decrease in the fluidity of the developer is discharged to the second discharge port. Since the process is carried out from No. 51, when the flowability of the developer is lowered, the rise in the surface of the developer is suppressed. [Selection] Figure 3

Description

  The present invention relates to a developing device suitable for an image forming apparatus using electrophotographic technology such as a printer, a copying machine, a facsimile machine, or a multifunction machine.

  2. Description of the Related Art Image forming apparatuses such as printers, copiers, facsimile machines, and multifunction machines include a developing device that develops an electrostatic latent image formed on a photosensitive drum with a developer to make a visible image. As a developing device, a developing chamber for supplying a developer to the developing sleeve and a stirring chamber for collecting the developer peeled from the developing sleeve, and a function separation type configuration for circulating the developer between the developing chamber and the stirring chamber Is known (Patent Document 1). The developer is circulated and conveyed in the developing container while being stirred by the developing screw in the developing chamber and by the stirring screw in the stirring chamber.

  In the developing device, a two-component developer (hereinafter simply referred to as a developer) composed of a non-magnetic toner and a magnetic carrier is used. In this case, the toner is consumed during image formation, and the carrier is used repeatedly without being consumed. However, a carrier that has been repeatedly used over a long period of time has deteriorated charging performance with respect to the toner, and if a developer containing a large amount of such a carrier is used as it is, image defects such as density unevenness and fog easily occur. Therefore, a carrier refresh method (ACR) that replenishes approximately the same amount of toner that has been consumed and suppresses the deterioration of the carrier while replenishing the replenishment agent including the toner and the carrier and discharging the excess developer. (Patent Document 2, Patent Document 3). In the ACR type developing device, one or more discharge ports are provided in the developing container so that excess developer (excess developer) overflows from the discharge port, that is, excess developer overflows the discharge port. Discharged.

Japanese Patent No. 5610920 JP 2005-283865 A JP 2010-204402 A

  The ACR method can be applied to a function separation type developing device. However, when the ACR method described in Patent Document 2 or Patent Document 3 is applied, the developer amount decreases every time the replenishment agent is replenished when the flowability of the developer decreases and the excess developer becomes difficult to be discharged from the discharge port. And the developer surface may be higher than the upper end of the stirring screw. As a result, the stirring screw is buried in the developer, and the developer stirring ability of the stirring screw is lowered, so that image defects such as density fluctuations due to poor stirring may occur. In addition, since the load applied to the stirring screw when the developer is conveyed increases, the motor or the like that drives the stirring screw may break down. Alternatively, the developer can leak out of the developing container.

  This is because it is difficult to adjust the surface of the discharge port as described in Patent Document 2 and Patent Document 3 due to the decrease in the fluidity of the developer. Since it is difficult to adjust the surface of the developer, when the fluidity of the developer decreases, the amount of developer in the developing container (stirring chamber) increases each time the replenisher is replenished, causing the surface of the developer to rise. Therefore, when the ACR method is applied to a function-separated type developing device, a developing device that can suppress the rise in the surface of the developer even if the fluidity of the developer is reduced has been desired. However, such a device has not yet been proposed. Not.

  The present invention has been made in view of the above problems. When the ACR method is applied to a function-separated type developing device, the developing device can suppress an increase in the developer surface even if the developer fluidity is lowered. The purpose is to provide.

  A developing device according to the present invention includes a developer carrying member that carries and rotates a developer containing a non-magnetic toner and a magnetic carrier, a first chamber that supplies developer to the developer carrying member, and the first chamber A developer container having a second chamber for forming a developer circulation path with the chamber and collecting the developer from the developer carrier, and the first chamber in the first direction. A first conveying screw that conveys the developer, and is disposed in the second chamber so that at least a part of the first conveying screw overlaps the first conveying screw when viewed from the horizontal direction; Developing from the first chamber to the second chamber on the upstream side in the second direction by separating the first chamber and the second chamber in the developer container with a second conveying screw that conveys the developer in two directions A first series passing portion for delivering the agent, and the second chamber downstream from the second chamber A partition wall having a second communication portion for delivering the developer to one chamber, and the developer container is provided on a side wall facing the partition wall of one of the first chamber and the second chamber, A first discharge port that is provided upstream of the central portion of the partition wall in the second direction and that overflows and discharges the developer conveyed through the one chamber; The one chamber is provided on the side wall of the one chamber so that the lower end is located on the downstream side in the second direction with respect to the downstream end in the second direction and the lower end is higher than the lower end of the first discharge port. And a second discharge port for discharging the conveyed developer to overflow.

  According to the present invention, in the function separation type and ACR system configuration, when the developer fluidity decreases and the developer surface tends to rise, the developer from the first discharge port and the second discharge port The developer level of the developer is adjusted by discharging, and an increase in the level of the developer is suppressed.

1 is a schematic diagram illustrating a configuration of an image forming apparatus to which a developing device according to an exemplary embodiment is applied. FIG. 3 is a cross-sectional view illustrating a configuration of the developing device according to the first embodiment. FIG. 3 is a top cross-sectional view illustrating a configuration of the developing device according to the first embodiment viewed in a horizontal cross section including an axial direction. The figure explaining the arrangement position of the longitudinal direction of the discharge outlet of a first embodiment. The figure explaining the arrangement position of the perpendicular direction of the discharge outlet of a first embodiment. FIG. 6 is a top cross-sectional view illustrating a configuration of a developing device according to a second embodiment viewed in a horizontal cross section including an axial direction. The figure explaining the arrangement position of the longitudinal direction of the discharge outlet of a second embodiment.

  Hereinafter, the developing device of this embodiment will be described. First, the configuration of an image forming apparatus to which the developing device of this embodiment is applied will be described with reference to FIG. An image forming apparatus 100 illustrated in FIG. 1 is a tandem intermediate transfer type full-color printer in which image forming units PY, PM, PC, and PK are arranged along an intermediate transfer belt 25.

[Image forming apparatus]
In the image forming unit PY, a yellow toner image is formed on the photosensitive drum 10Y and transferred to the intermediate transfer belt 25. In the image forming unit PM, a magenta toner image is formed on the photosensitive drum 10M and transferred to the intermediate transfer belt 25. In the image forming units PC and PK, a cyan toner image and a black toner image are formed on the photosensitive drums 10C and 10K, respectively, and transferred to the intermediate transfer belt 25. The four-color toner images transferred to the intermediate transfer belt 25 are transported to a secondary transfer portion (secondary transfer nip portion) T2 and are collectively transferred to a recording material S (sheet material such as paper or an OHP sheet). Is done.

  The image forming units PY, PM, PC, and PK are configured substantially the same except that the colors of toner used in the developing devices 1Y, 1M, 1C, and 1K are different from yellow, magenta, cyan, and black. Hereinafter, the configuration and operation of the image forming units PY to PK will be described by omitting Y, M, C, and K at the end of the code representing the distinction between the image forming units PY, PM, PC, and PK.

  In the image forming portion P, a primary charging roller 21, an exposure device 22, a developing device 1, a transfer roller 23, and a drum cleaning device 24 are disposed so as to surround the photosensitive drum 10 as an image carrier. The photosensitive drum 10 has a photosensitive layer formed on the outer peripheral surface of an aluminum cylinder, and is rotated in the direction of arrow R1 in FIG. 1 at a predetermined process speed.

  The primary charging roller 21 is applied with a charging bias voltage to come into contact with the photosensitive drum 10 to charge the photosensitive drum 10 to a uniform negative dark potential. The exposure device 22 scans the scanning line image data obtained by developing the separation color image of each color with a rotating mirror, and writes an electrostatic image of the image on the surface of the charged photosensitive drum 10. The developing device 1 supplies toner to the photosensitive drum 10 to develop the electrostatic image into a toner image. Details of the developing device 1 will be described later.

  The transfer roller 23 presses the intermediate transfer belt 25 to form a primary transfer portion (primary transfer nip portion) of the toner image between the photosensitive drum 10 and the intermediate transfer belt 25. A toner image carried on the photosensitive drum 10 is primarily transferred to the intermediate transfer belt 25 by applying a DC voltage having a polarity opposite to the charging polarity of the toner to the transfer roller 23. The drum cleaning device 24 rubs the photosensitive drum 10 with a cleaning blade to remove the primary transfer residual toner slightly remaining on the photosensitive drum 10 after the primary transfer.

  The intermediate transfer belt 25 is supported around a tension roller 26, a secondary transfer inner roller 27, a driving roller 28, and the like, and is driven by the driving roller 28 to rotate in the direction of arrow R2 in FIG. The secondary transfer portion T <b> 2 is a toner image transfer nip portion to the recording material S formed by contacting the secondary transfer inner roller 27 with the intermediate transfer belt 25 supported by the secondary transfer outer roller 29. In the secondary transfer portion T2, a predetermined secondary transfer voltage is applied to the secondary transfer inner roller 27, whereby the toner image is transferred to the recording material S that is nipped and conveyed from the intermediate transfer belt 25 to the secondary transfer portion T2. Next transferred. Secondary transfer residual toner remaining on the intermediate transfer belt 25 after the secondary transfer is removed by the belt cleaning device 30 rubbing the intermediate transfer belt 25. The belt cleaning device 30 removes the secondary transfer residual toner by sliding the cleaning blade against the intermediate transfer belt 25.

  The recording material S onto which the four color toner images have been transferred by the secondary transfer portion T2 as described above is conveyed to the fixing device 31. The fixing device 31 melts and fixes the toner image on the recording material S by applying pressure from an opposing roller or belt or the like and generally heat from a heat source (not shown) such as a heater. The recording material S having the toner image fixed on the surface in this manner is discharged out of the machine.

<First embodiment>
The developing device 1 according to the first embodiment will be described with reference to FIGS. 2 and 3, the developing device 1 includes a developing container 2 forming a housing, a developing sleeve 3 as a developer carrier, a regulating blade 5, a developing screw 13 as a first conveying screw, and a second conveying element. A stirring screw 14 as a screw is provided.

  The developing container 2 contains a two-component developer (hereinafter, developer). The developer includes a non-magnetic toner having negative charging characteristics and a magnetic carrier having positive charging characteristics. The non-magnetic toner is obtained by encapsulating a colorant, a wax component, etc. in a resin such as polyester or styrene acrylic, and pulverizing or polymerizing it. The magnetic carrier is obtained by applying a resin coat to the surface layer of a core made of resin particles kneaded with ferrite particles or magnetic powder. In this embodiment, the toner concentration (weight ratio of toner contained in the developer) in the developer in the initial state not used for image formation is, for example, 8%.

  As shown in FIG. 2, a part of the developing container 2 facing the photosensitive drum 10 is opened, and a developing sleeve 3 as a developer carrying member is rotatably arranged so that a part of the developing container 2 is exposed to the opening. Has been. The developing sleeve 3 is formed in a cylindrical shape from a nonmagnetic material such as an aluminum alloy, and is driven to rotate in the direction of arrow R3 in FIG. Inside the developing sleeve 3, a magnet roller 4 as a magnetic field generating means composed of a plurality of magnetic poles is disposed so as not to rotate. The developing sleeve 3 rotates in the direction of the arrow R3 at a predetermined process speed, and carries and conveys the developer adsorbed at the position of the pumping magnetic pole N1 of the magnet roller 4 in the direction of the regulating blade 5. The developer spiked by the regulating magnetic pole S1 is subjected to a shearing force by the regulating blade 5 when passing through the gap between the developing sleeve 3 and the regulating blade 5, and the amount thereof is regulated, and a predetermined layer thickness is formed on the developing sleeve 3. The developer layer is formed. The formed developer layer is carried and conveyed to a development area facing the photosensitive drum 10 and develops the electrostatic latent image formed on the surface of the photosensitive drum 10 with magnetic spikes formed by the development magnetic pole N2. After being subjected to development, the developer is peeled off from the developing sleeve 3 by a non-magnetic band formed by adjoining the same pole between the stripping magnetic pole N3 and the pumping magnetic pole N1.

  As shown in FIG. 3, the developing sleeve 3 has a coat region H (carrying region) capable of carrying the developer at an intermediate portion in the rotation axis direction. The coat region H has irregularities formed on the surface. The non-carrying regions that are out of the coating region H at both ends in the rotation axis direction of the developing sleeve 3 are smooth surfaces on which no irregularities are formed.

  As shown in FIG. 2, the developing container 2 is provided between the developing chamber 11 as the first chamber, the stirring chamber 12 as the second chamber, and the developing chamber 11 and the stirring chamber 12. And a partition wall 15 that partitions the chamber 12. The partition wall 15 separates the developing chamber 11 and the stirring chamber 12 so as to protrude from the bottom surface portion 2 a into the developing container 2 (inside the developing container). The partition wall 15 extends in the rotation axis direction (longitudinal direction) of the developing sleeve 3. In the developing device 1 of the present embodiment, the developing chamber 11 and the stirring chamber 12 are arranged so as to be aligned in a substantially horizontal direction.

  As shown in FIG. 3, the partition wall 15 has a first communication part 17 and a second communication part 18 as a delivery part for communicating the developing chamber 11 and the stirring chamber 12 on both ends in the longitudinal direction. In the case of the present embodiment, the both ends of the partition wall 15 do not reach the inner walls of both end portions in the longitudinal direction of the developing container 2, and thereby the first series of communication portions 17 for delivering the developer from the developing chamber 11 to the stirring chamber 12. As a result, a second communication portion 18 for transferring the developer from the stirring chamber 12 to the developing chamber 11 is formed. The first communication portion 17 and the second communication portion 18 are formed outside the range of the coating region H of the developing sleeve 3. A guide member 16 is provided above the partition wall 15 so as to extend toward the developing sleeve 3 and guide the developer collected from the developing sleeve 3 into the stirring chamber 12.

  The developing chamber 11 is provided with a developing screw 13 for conveying the developer in the developing chamber 11 in a predetermined first direction. The stirring chamber 12 is provided with a stirring screw 14 for transporting the developer in the second direction opposite to the developer transport direction (first direction) of the developing screw 13 in the stirring chamber 12. The developing screw 13 and the stirring screw 14 are configured by forming a blade 13b as a first blade and a blade 14b as a second blade in a spiral shape around the rotation shafts 13a and 14a, respectively. Both end portions of the rotary shafts 13a and 14a are rotatably supported by bearings with respect to the developing container 2, respectively. The developing screw 13 and the stirring screw 14 may be arranged so that at least a part thereof is overlapped when viewed from the horizontal direction. In the present embodiment, as shown in FIG. 2, the developing screw 13 and the stirring screw 14 are disposed so as to be substantially horizontal.

  In the following description, the term “upstream or downstream of the developing chamber 11” refers to the upstream or downstream of the developer screw 13 in the developer transport direction without particular notice. Similarly, when referring to the upstream or downstream side of the stirring chamber 12, the upstream side or downstream side of the stirring screw 14 in the developer conveyance direction is used.

  As shown in FIG. 3, a return screw 141 is provided coaxially with the rotating shaft 14 a of the stirring screw 14 at the downstream end portion in the developer conveying direction (second downstream end portion in the second direction) of the stirring screw 14. The return screw 141 has a blade 141b wound in the opposite direction to the blade 14b on the rotating shaft 14a, and develops in the first direction opposite to the developer conveying direction (second direction) of the stirring screw 14 in the stirring chamber 12. Transport the agent.

  The developing sleeve 3, the developing screw 13, and the stirring screw 14 (including the return screw 141) are connected and driven by a gear train (not shown), and rotate through a gear train from a drive motor (not shown). To do. As shown in FIG. 2, the developing screw 13 rotates in the direction of arrow R <b> 5 in FIG. 2 from the lower side to the upper side on the side wall side of the developing chamber 11 on the side opposite to the partition wall 15, and the stirring screw 14 is on the side opposite to the partition wall 15. It rotates in the direction of arrow R4 in FIG. 2 from below to above on the side wall side of the stirring chamber 12. As the developing screw 13 and the agitating screw 14 rotate in this way, the developer is circulated and conveyed as shown by the arrows in FIG. At this time, with respect to the developer conveying direction (second direction) of the stirring screw 14, the developer is transferred from the developing chamber 11 to the stirring chamber 12 in the first communication section 17 on the upstream side in the second direction, and on the downstream side in the second direction. The developer is transferred from the stirring chamber 12 to the developing chamber 11 by the two communicating portions 18. Thus, the developer chamber 11 and the stirring chamber 12 form a developer circulation path, and the developer is mixed and stirred by circulating through this circulation path.

  In the developing chamber 11, the developer is supplied to the coating region H of the developing sleeve 3, and in the stirring chamber 12, the developer peeled from the developing sleeve 3 is collected. That is, the developer in the developing chamber 11 is adsorbed to the developing sleeve 3 at the position of the pumping magnetic pole N1 of the magnet roller 4 while being conveyed by the developing screw 13. A guide member 16 is provided above the partition wall 15. The guide member 16 extends from the upper end of the partition wall 15 so as to be close to the developing sleeve 3 in the vicinity of the non-magnetic band of the developing sleeve 3, and after the developer on the developing sleeve 3 is peeled off and peeled off by the magnetic pole N3, the developing chamber. It is configured to be accommodated in the stirring chamber 12 without returning to 11. In the stirring chamber 12, the collected developer is conveyed by the stirring screw 14 while collecting the developer.

  As described above, the developing device 1 of the present embodiment has a so-called function separation type configuration in which the developer is supplied to the developing sleeve 3 in the developing chamber 11 and the developer is recovered from the developing sleeve 3 in the stirring chamber 12. . In the function separation type developing device 1, the developer on the developing sleeve 3 is collected in the longitudinal direction of the stirring chamber 12. For this reason, the developer passes through two paths: a path where the developer is transported from the developing chamber 11 to the stirring chamber 12 without passing through the developing sleeve 3, and a path where the developer is transported directly from the developing sleeve 3 to the stirring chamber 12. It is circulated and tends to be unevenly distributed in the developing container 2. In particular, the developer tends to accumulate on the downstream side of the stirring chamber 12, and the developer surface of the developer tends to be high. That is, the surface of the downstream of the stirring chamber 12 is higher than that of the upstream. In the developing chamber 11, the upstream surface of the developing chamber 11 is higher than the downstream surface.

  As described above, when developing is performed using a developer, the charging performance of the carrier with respect to the toner decreases as the image is formed. As a result, the charge amount of the toner is reduced, and image defects are likely to occur. Therefore, the function separation type developing apparatus 1 also employs an ACR system in which a replenisher is replenished to refresh the carrier in order to restore the charging performance of the carrier. In the present embodiment, in order to realize the ACR method, a developer replenishing device 32 is provided via a replenishing port 42 above the developing container 2 on the upstream side of the stirring chamber 12 in the vertical direction.

  The developer replenishing device 32 shown in FIG. 2 can replenish the developing device 1 with an amount of toner corresponding to the amount of consumed toner in accordance with the consumption of the toner of the developing device 1 during image formation. . The amount of the replenishment agent replenished by the developer replenishing device 32 is roughly determined by the number of rotations of the replenishment screw 33, and this number of rotations is determined based on the detection result of a toner replenishment amount control means (not shown). Examples of the toner replenishment amount control means include one that optically or magnetically detects toner density, and one that develops a reference latent image formed on the photosensitive drum 10 and detects the density of the toner image.

  When the ACR method is adopted, if the developer in the developing container 2 becomes too much as the replenisher is replenished and the developer is not sufficiently stirred, an image defect may occur. Therefore, as described above, the excessive developer is discharged from the discharge port to the outside of the developing container so that the developer in the developing container 2 does not become excessive. In the case of this embodiment, the developing container 2 is provided with two discharge ports (a first discharge port 50 and a second discharge port 51). The first discharge port 50 and the second discharge port 51 will be described later. The developer discharged from the first discharge port 50 and the second discharge port 51 is conveyed to a collected developer storage (not shown) by the collection screw 43.

  By the way, when the developer circulated and conveyed in the developing container 2 is repeatedly used for a long time, the fluidity is lowered. When the flowability of the developer is lowered, the developer conveying efficiency of the stirring screw 14 is lowered, and the distribution of the developer amount in the longitudinal direction is changed in the stirring chamber 12. As a result, the inclination of the developer surface of the developer in the stirring chamber 12 (specifically, the difference between the upstream agent surface height and the downstream agent surface height of the stirring chamber 12) is larger than that of the developer in the initial state. growing. In the stirring chamber 12, the surface of the developer is inclined so that the developer surface of the developer increases from the upstream side to the downstream side of the stirring chamber 12. In the developing device 1, for example, the rotation speed of the developing sleeve 3, the stirring screw 14, and the like can be changed according to the type of the recording material S. At this time, if the rotation speed of the stirring screw 14 is slowed, the developer conveying efficiency of the stirring screw 14 decreases, and in this case also, the inclination of the developer surface of the developer becomes larger than in the initial state. Note that when the developer fluidity decreases, the developer conveying efficiency of the developing screw 13 also decreases, and the inclination of the developer surface of the developer increases in the developing chamber 11 as compared with the initial state. In order to make it easy, the case where it provided in the stirring chamber 12 is demonstrated to the example.

  If a single discharge port is provided on the upstream side of the stirring chamber 12 as in the prior art, the developer agent in the stirring chamber 12 is reduced by only one discharge port when the flowability of the developer is reduced. It is difficult to adjust the surface. That is, as the developer fluidity decreases, the developer becomes difficult to be discharged from the discharge port. Then, the developer increased with the replenishment of the replenishment agent is biased to the downstream side, and the stirring chamber 12 without the discharge port is compared with the amount of increase in the agent level on the upstream side of the stirring chamber 12 with the discharge port. The amount of increase in the surface of the agent on the downstream side increases. Therefore, the surface of the agent is greatly increased on the downstream side of the stirring chamber 12 as compared with the upstream side. Even if one discharge port is provided on the downstream side of the stirring chamber 12, if the flowability of the developer decreases, the developer relatively increases on the upstream side than the downstream side. The surface rises on the side. Thus, when one discharge port is provided, as the supply of the replenishment agent is repeated, the surface of the agent tends to be high either on the downstream side or the upstream side of the stirring chamber 12 where no discharge port is provided. is there. That is, the developer amount increases. When the surface of the agent becomes higher than the upper end of the stirring screw 14, an image defect due to the stirring failure can be caused. In addition, a motor or the like (not shown) for driving the agitating screw 14 may break down due to an increase in load caused by the developer, or the developer may leak out of the developing container 2. As described above, even if only one discharge port is provided, it is difficult to adjust the developer surface that fluctuates with a decrease in the fluidity of the developer to a predetermined height depending on the single discharge port.

  In view of the above points, in the developing device 1 of the present embodiment, two discharge ports are provided on the side wall of the developing container 2 facing the partition wall 15. As will be described later, a first discharge port 50 is provided on the upstream side of the stirring chamber 12, and a second discharge port 51 is provided on the downstream side of the stirring chamber 12 spaced from the first discharge port 50 by a predetermined distance or more. Yes. Hereinafter, the first discharge port 50 and the second discharge port 51 will be described with reference to FIGS. 3 to 5.

[First outlet]
The first discharge port 50 will be described. As shown in FIG. 3, the first discharge port 50 is provided on the upstream side of the stirring chamber 12 where the surface of the developer is lowered in a steady state in the function-separated type developing device 1 with respect to the position in the longitudinal direction of the developing container 2. . As shown in FIG. 4, the first discharge port 50 is provided on the upstream side of the stirring chamber 12 with respect to the central portion M in the longitudinal direction of the partition wall 15.

  The first discharge port 50 is preferably provided in the vicinity of the first series passage portion 17. In the case of the present embodiment, as shown in FIGS. 3 and 4, the first discharge port 50 does not overlap the first communication part 17 but overlaps the partition wall 15, rather than the first communication part 17. It is provided on the downstream side. This is because the developer is discharged more than necessary from the first discharge port 50 and is extremely reduced, and the amount of developer in the developing container 2 is less than the amount capable of stably supplying toner to the developing sleeve 3. Is to avoid. Therefore, if the developer amount does not extremely decrease, the first discharge port 50 may be provided so that at least a part thereof overlaps with the first series passage portion 17 or all of the first discharge ports 50 may be provided. 17 may be provided so as to overlap.

  The first discharge port 50 is provided at a height position at which excess developer can be discharged from the stirring chamber 12 with respect to the arrangement position in the vertical direction. As shown in FIG. 5, the first discharge port 50 has a lower end 50 a that is greater than or equal to the rotational axis center of the stirring screw 14 (shown by a dotted line F in FIG. 5) and a straight line connecting the upper ends of the blades 14 b of the stirring screw 14 (FIG. 5). (Indicated by a dotted line G). This range is a range in which the amount of developer in the developing container 2 does not fall below the amount necessary to stably supply the toner to the developing sleeve 3. When the amount of developer in the developing container 2 increases with the replenishment of the replenisher, a part of the developer overflows from the first discharge port 50 and is discharged. The discharge of excess developer stops when the surface of the developer falls below the lower end 50a of the first discharge port 50.

[Second outlet]
The second discharge port 51 will be described. The second discharge port 51 is provided at a position where the surface of the developer container 2 is likely to rise in a steady state with a decrease in the fluidity of the developer with respect to the position in the longitudinal direction of the developer container 2. This is because a developer is discharged in an emergency manner so that the developer surface is not raised more than expected because the developer is biased in the agitating chamber 12 due to the decrease in the fluidity of the developer. This is because it is intended to be provided in the area. By providing the second discharge port 51 at a position where the surface of the developer is likely to rise, it is possible to suppress an increase in the surface of the material due to a decrease in the fluidity of the developer.

  As shown in FIG. 3, the second discharge port 51 is formed from the first discharge port 50 so that the downstream end 51 b (downstream end in the second direction) is on the downstream side of the stirring chamber 12 with respect to the downstream end 15 b of the partition wall 15. Is also provided downstream of the stirring chamber 12. However, if the interval between the second discharge port 51 and the first discharge port 50 is too close, it is difficult to obtain the effect of suppressing the increase in the dosage level by providing a plurality of discharge ports. Therefore, the second outlet 51 is provided at a position away from the first outlet 50 by a predetermined distance or more. As shown in FIG. 4, the second discharge port 51 is at least half the length between the first communication portion 17 and the second communication portion 18, that is, the length in the longitudinal direction (second direction length) of the partition wall 15. Are provided in the vicinity of the second communication portion 18 at a position spaced apart. Here, the vicinity of the second communication portion 18 may be a position where at least a part of the second discharge port 51 overlaps the second communication portion 18. However, if even a part of the second discharge port 51 overlaps the partition wall 15, the developer may be discharged due to the jumping up by the stirring screw 14 at the portion overlapping the partition wall 15. In order to avoid this, it is preferable that the second outlet 51 is provided so as to overlap the second communication portion 18 in the whole or as large range as possible.

  The second discharge port 51 is provided at a height position where the developer can be discharged from the developer container 2 in accordance with the rise in the surface of the developer due to the lowered fluidity of the developer with respect to the vertical arrangement position. As shown in FIG. 5, the second outlet 51 is provided such that the lower end 51 a is higher than the lower end 50 a of the first outlet 50. If the lower end 51 a of the second discharge port 51 is provided at a position lower than the lower end 50 a of the first discharge port 50, the developer is more easily discharged from the second discharge port 51 than the first discharge port 50. The amount of developer in the developing container 2 is reduced more than expected. In order to avoid this, the second discharge port 51 is provided at a position where the lower end 51 a is higher than the lower end 50 a of the first discharge port 50.

  The above-described poor stirring and increased load accompanying the increase in the surface of the agent is remarkable when the stirring screw 14 is deeply buried in the developer. In order to avoid this, the second discharge port 51 is provided at a position below a straight line (indicated by a dotted line G in FIG. 5) where the lower end 51 a connects the upper ends of the blades 14 b of the stirring screw 14. In this way, the second discharge port 51 has a level before the level of the developer becomes higher than expected due to a decrease in the fluidity of the developer. The developer overflows from the second discharge port 51 before being discharged. In the case of the present embodiment, the surface of the agent is in a range from the center of the rotation axis of the stirring screw 14 (shown by a dotted line F in FIG. 5) to a straight line (shown by the dotted line G in FIG. 5) connecting the upper ends of the blades 14b of the stirring screw 14. It is suppressed.

  As shown in FIG. 5, the second discharge port 51 is provided such that the width W <b> 2 of the second discharge port 51 is smaller than the width W <b> 1 of the first discharge port 50. Since the developer overflows and is discharged from the first discharge port 50 and the second discharge port 51, if these widths W1 and W2 are reduced, the amount of developer discharged per unit time at these discharge ports is suppressed. it can. However, if the developer discharge amount is excessively suppressed with respect to the first discharge port 50, the excess developer that should be discharged is not discharged, and the developer amount in the developing container 2 may be excessively increased. On the other hand, regarding the second discharge port 51, when the developer is biased in the developer container 2 due to a decrease in the fluidity of the developer, an emergency response is made so that the surface of the developer does not become higher than expected. As long as the developer can be discharged, the width W <b> 2 may be smaller than that of the first discharge port 50.

  Although the developer mainly overflows and is discharged from the second discharge port 51, the developer can be discharged not only by the splashing of the developer by the stirring screw 14. The amount of developer discharged by the raising of the stirring screw 14 is approximately proportional to the opening area of the second discharge port 51. In the case of the present embodiment, since the width W2 of the second outlet 51 is smaller than the width W1 of the first outlet 50 as described above, the opening area of the second outlet 51 is the first outlet 50. It is smaller than the opening area. Therefore, the discharge of the developer from the second discharge port 51 due to the raising of the stirring screw 14 can be suppressed.

  As described above, in this embodiment, the two discharge ports, the first discharge port 50 and the second discharge port 51, are provided on the upstream side and the downstream side of the stirring chamber 12. As described above, the first discharge port 50 and the second discharge port 51 are provided apart from each other by a predetermined distance or more in the longitudinal direction of the developing container 2 and are provided at different heights in the vertical direction. In this way, the excess developer discharged due to the replenishment of the replenishment agent is discharged from the first discharge port 50, while the developer discharge when the developer level rises due to the decrease in developer fluidity is discharged to the second discharge. Taken from the exit 51. Since the developer is discharged from the second discharge port 51 when the flowability of the developer is lowered, the increase in the surface of the developer is suppressed. Accordingly, the surface of the agent does not become higher than the upper end of the stirring screw 14, and image defects due to poor stirring are unlikely to occur. Further, a motor or the like (not shown) for driving the stirring screw 14 does not break down due to an increase in load caused by the developer, or the developer does not leak out of the developing container 2.

  In the developing device 1 of the first embodiment described above, the width W2 of the second discharge port 51 is made smaller than the width W1 of the first discharge port 50, and the developer discharge due to the jumping up of the stirring screw 14 is suppressed as much as possible. doing. However, even if it does so, there is a possibility that the developer may be discharged by the splashing. As already described, since the developer is to be discharged from the second discharge port 51 in an emergency when the surface level rises more than expected, the discharge of the developer due to the jumping up of the stirring screw 14 can be further suppressed. In addition, it is preferable to provide the second discharge port 51.

<Second embodiment>
In view of the above points, in the developing device of the second embodiment, the second discharge port 51 is provided at a position away from the developer circulation path on the end portion side of the developing container 2 with respect to the second communication portion 18. A developing apparatus 1A according to the second embodiment will be described with reference to FIGS. However, in the developing device 1A shown in FIGS. 6 and 7, the same components as those of the developing device 1 of the first embodiment described above are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIGS. 6 and 7, the developing device 1 </ b> A of the present embodiment is provided with a partition wall 20 that abuts against the side wall of the developing container 2 with the second communication portion 18 interposed therebetween at one end side in the longitudinal direction of the partition wall 15. . The partition wall 20 forms a developer discharge portion 60 adjacent to the stirring chamber 12 in the developing container 2 on the downstream side of the second communication portion 18. The second discharge port 51 is provided in the developer discharge unit 60. A return screw 141 is disposed in the developer discharge portion 60. That is, the second discharge port 51 is provided in a range facing the return screw 141.

  As shown in FIG. 6, the return screw 141 has a return blade 141 b capable of transporting the developer on the side (first direction) opposite to the blade 14 b of the stirring screw 14. The return screw 141 pushes the developer conveyed by the stirring screw 14 back to the stirring screw 14 side. When the return screw 141 pushes back the developer, the developer conveyed through the stirring chamber 12 by the stirring screw 14 easily passes through the second communication portion 18 and is delivered to the developing chamber 11. Further, due to the return screw 141, when the surface of the developer is not high, it is difficult for the developer to enter the developer discharge section 60.

  The pitch of the return blade 141b of the return screw 141 is formed narrower than the pitch of the blade 14b of the stirring screw 14. When the pitch of the return blade 141b is narrow, the inclination angle of the return blade 141b with respect to the rotation shaft 14a is larger than when the pitch is large. When the inclination angle is large, compared with the case where the inclination angle is small, the force exerted by the return blade 141b as the return screw 141 rotates is greater in the rotation axis direction than in the radial direction of the rotation shaft 14a. The function to push back to the 14 side becomes high. If the developer is more directed in the direction of the rotation axis, the developer jumps up in proportion thereto. As a result, unnecessary discharge due to the jumping up by the return screw 141 can be suppressed.

  In the second embodiment described above, the developer enters the developer discharge portion 60 provided with the second discharge port 51 from the stirring chamber 12 in response to the rising of the agent level in the stirring chamber 12. Therefore, if the surface of the liquid does not rise, the developer is hardly discharged from the second discharge port 51, and the developer can be discharged from the second discharge port 51 only when the surface of the liquid rises. That is, the developer can be discharged from the second discharge port 51 in an emergency manner when the surface of the liquid rises more than expected.

<Other embodiments>
In each of the above-described embodiments, the first discharge port 50 and the second discharge port 51 are provided in the stirring chamber 12, but the present invention is not limited thereto. Both the first discharge port 50 and the second discharge port 51 may be provided in the developing chamber 11. In this case, the first discharge port 50 is provided on the downstream side in the developer conveyance direction of the development screw 13, and the second discharge port 51 is provided on the upstream side in the developer conveyance direction of the development screw 13.

  In each of the above-described embodiments, after the primary transfer of the toner images of the respective colors from the photosensitive drums 10Y to 10K of the respective colors to the intermediate transfer belt 25, the intermediate transfer of the secondary transfer of the composite toner images of the respective colors onto the recording material S is performed. Although the transfer type image forming apparatus 100 has been described, the present invention is not limited to this. For example, the developing devices of the above-described embodiments may be applied to a direct transfer type image forming apparatus that directly transfers from the photosensitive drums 10Y to 10K to the recording material S carried and conveyed by the transfer material conveyance belt.

DESCRIPTION OF SYMBOLS 1 (1Y-1K, 1A) ... developing apparatus, 2 ... developing container, 3 ... developer carrier (developing sleeve), 11 ... first chamber (developing chamber), 12 ... second chamber (stirring chamber), 13 ... 1st conveying screw (developing screw), 14 ... 2nd conveying screw (stirring screw), 15 ... partition, 17 ... first communicating part, 18 ... second communicating part, 50 ... first outlet, 51 ... second Discharge port, 141 ... Return screw

Claims (5)

A developer carrier that carries and rotates a developer containing a non-magnetic toner and a magnetic carrier;
A developer container having a first chamber for supplying a developer to the developer carrier, and a second chamber for forming a developer circulation path in the first chamber and collecting the developer from the developer carrier. When,
A first conveying screw disposed in the first chamber and conveying the developer in the first direction in the first chamber;
A second transport that is disposed in the second chamber so as to at least partially overlap the first transport screw when viewed from the horizontal direction, and transports the developer in a second direction opposite to the first direction in the second chamber. Screw,
A second communication section that transfers the developer from the first chamber to the second chamber on the upstream side in the second direction across the first chamber and the second chamber in the developer container; A partition wall having a second communication portion that transfers the developer from the second chamber to the first chamber on the downstream side in the direction,
The developing container is provided on the side wall facing the partition wall of either the first chamber or the second chamber on the upstream side in the second direction from the central portion of the partition wall, and the one chamber A first discharge port for overflowing and discharging the developer conveyed,
The second chamber downstream end is located on the downstream side in the second direction with respect to the second direction downstream end of the partition wall, and the lower end is higher than the lower end of the first discharge port. A second discharge port provided on the side wall and configured to overflow and discharge the developer conveyed through the one chamber,
A developing device. The first discharge port and the second discharge port are arranged with an interval of at least half of the second direction length of the partition wall,
The developing device according to claim 1. The second discharge port has a width in the second direction smaller than a width in the second direction of the first discharge port.
The developing device according to claim 1, wherein Either the first conveying screw or the second conveying screw arranged in the one chamber rotates from the lower side to the upper side on the side wall side,
The developing device according to claim 3. A return screw provided at the downstream end of the second conveying screw in the second direction and conveying the developer in the first direction in the second chamber;
The second discharge port is provided in a range facing the return screw on the side wall,
The developing device according to claim 1, wherein

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