JP2019028315A - Developing device - Google Patents

Abstract

To provide a developing device capable of suppressing generation of an unsatisfactorily image due to supply of supplement.SOLUTION: A developing device makes screw pitches of supply screws 60 of a first conveyance part 70a and a second conveyance part 70b different from each other in a supply chamber 70. In this way, a difference is generated in a conveyance amount between the first conveyance part 70a and the second conveyance part 70b. If a supplement conveyance amount of the first conveyance part 70a is larger than that of the second conveyance part 70b, a difference in height of the supplement surface of the supplement generated in the second conveyance part 70b is eliminated by the first conveyance part 70a. Consequently, even if a large amount of the supplement is supplied and a peak of the supplement is formed by the second conveyance part 70b, the peak is eliminated during the conveyance by the first conveyance part 70a, and then, the supplement is supplied to a circulation passage. In other words, the supplement amount does not fluctuate largely at a point when supplied to the circulation passage. As a result, even if the large amount of the supplement is supplied, the supplement is not supplied suddenly in a large amount to the circulation passage, and generation of the unsatisfactory image due to the supply of the supplement can be suppressed.SELECTED DRAWING: Figure 4

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 multi-function machines are provided with a developing device that develops an electrostatic latent image formed on a photosensitive drum with a developer to make a visible image. In the developing device, a two-component developer (hereinafter also simply referred to as a developer) composed of a nonmagnetic toner and a magnetic carrier is used. In the developing device, a developing chamber for supplying the developer to the developing sleeve and a stirring chamber for collecting the developer separated from the developing sleeve are formed in the developing container, and the developing chamber and the stirring chamber are connected to the developer. Is circulated (Patent Document 1). In order to do so, in the developing device, the developing chamber and the stirring chamber are communicated with each other through a communication port, and a developing screw and a stirring screw for conveying the developer are provided in each chamber. The developer is transferred from the stirring chamber to the developing chamber through the downstream communication port on the downstream side in the developer conveying direction of the stirring screw, and from the developing chamber through the upstream communication port on the upstream side in the developer conveying direction of the stirring screw. It is circulated in the developing container so as to be delivered to the stirring chamber.

  In the case of the above developing device, when the developer reaches a stable state (so-called steady state), in the developing chamber, the developer surface of the developer gradually decreases from the upstream to the downstream in the developer conveying direction of the developing screw. Cheap. On the other hand, in the stirring chamber, the developer surface tends to gradually increase from the upstream to the downstream in the developer conveying direction of the stirring screw. In this specification, the term “upstream” or “downstream” refers to the upstream of the stirring screw in the developer conveyance direction or the downstream of the developer conveyance direction without particular notice.

  By the way, in the image forming apparatus, toner is consumed as the image is formed. Therefore, like the apparatus described in Patent Document 1, the developing device is supplied with a replenisher through a replenishing port by a replenishing device. The replenished replenisher is mixed with the developer circulated in the developing container by a stirring screw that also serves as a replenishing screw. In order to sufficiently mix the replenisher and the developer, the replenishment port is generally formed upstream of the stirring screw in the stirring chamber in the stirring chamber.

JP 2009-192554 A

  As described above, in the stirring chamber, the developer surface tends to be lower on the upstream side than on the downstream side, that is, the amount of developer at the upstream communication port tends to be smaller than the amount of developer at the downstream communication port. Particularly when toner consumption is rapid, the amount of developer at the upstream communication port can be extremely reduced until the replenisher is replenished. If a large amount of replenishment agent is replenished at such time, the developer is supplied to the developing sleeve without being sufficiently mixed, resulting in image defects such as density unevenness. It was. In addition, when a large amount of replenishment agent is replenished at a time, a part of the replenishment agent scatters out of the developing chamber and hence the developing container through the upstream communication port (referred to as toner scattering), resulting in image defects such as fogging. Can be.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a developing device that can suppress the occurrence of image defects associated with replenishment of a replenisher.

  The developing device according to the present invention includes a developer container having a developer circulation path, a replenisher supply path communicating with the circulation path, a transport screw that transports the developer in the circulation path, a rotating shaft, and the rotation shaft. A replenishing screw having a spiral blade formed around a rotation shaft and transporting the replenisher of the replenishment path toward the circulation path, the replenishment path being downstream in the replenisher transport direction The first conveying unit is formed so that the amount of replenisher conveyed per one rotation of the replenishing screw is larger than that of the second conveying unit upstream of the first conveying unit in the replenisher conveying direction. It is characterized by.

  In the developing device according to the present invention, a developer carrying body that rotates while carrying a developer, a first chamber that supplies the developer to the developer carrying body, and a circulation path of the developer between the first chamber A developer container having a second chamber for forming and collecting the developer from the developer carrying member; a replenishment chamber communicating with the second chamber to form a replenishment path for the replenisher; and provided in the first chamber A first conveying screw that conveys the developer in a first direction; a second conveying screw that is provided in the second chamber and conveys the developer in a second direction opposite to the first direction; and the replenishing chamber A replenishing screw connected to the second conveying screw and rotating together with the second conveying screw to convey the replenisher in the second direction, and the first chamber and the second chamber in the developing container, With the second direction downstream from the second chamber to the first chamber A partition wall having a first communication port for transferring the image agent and a second communication port for transferring the developer from the first chamber to the second chamber on the upstream side in the second direction. Is formed upstream of the second communication port in the second direction, and the replenishment path is configured such that the first transport unit on the downstream side in the second direction is the first transport unit on the upstream side in the second direction from the first transport unit. It is characterized in that it is formed so that the amount of replenisher transported per one rotation of the replenishing screw is larger than that of the two transporting portions.

  According to the present invention, a large amount of replenishment agent can be replenished at a time by varying the amount of replenisher transport per revolution of the replenishment screw between the downstream side and the upstream side in the replenishment agent transport direction in the replenishment path. Therefore, it is possible to suppress the occurrence of image defects due to the replenishment of the replenisher.

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 the developing device according to the embodiment. FIG. 3 is a top cross-sectional view illustrating the developing device of the present embodiment. Side surface sectional drawing which shows the replenishment screw of 1st embodiment. The graph showing the relationship between screw pitch and the replenishment agent conveyance amount per rotation of a screw. The graph showing the time transition of the amount of replenishment agents when a replenishment agent arrives at the stirring chamber. The graph showing the relationship between the peak value of a replenishment agent at the time of reaching | attaining a stirring chamber, and its half value width. Side surface sectional drawing which shows the replenishment screw of 2nd embodiment. Side surface sectional drawing which shows the replenishment screw of 3rd embodiment.

[First embodiment]
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 shown 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 recording material S is taken out one by one from a paper feed cassette (not shown) and conveyed to the secondary transfer portion T2.

  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 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 charging roller 21 is charged with a charging voltage and contacts the photosensitive drum 10, thereby charging the photosensitive drum 10 to a uniform negative-polarity dark portion potential. The exposure device 22 generates a laser beam obtained by ON-OFF modulation of scanning line image data obtained by developing a separation color image of each color from a laser light emitting element, and scans this with a rotating mirror on the surface of the photosensitive drum 10 that is charged. Write an electrostatic image of the image. 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 (see FIGS. 2 and 3).

  The transfer roller 23 is disposed opposite to the photosensitive drum 10 with the intermediate transfer belt 25 interposed therebetween, and forms a primary transfer portion (primary transfer nip portion) T1 of the toner image between the photosensitive drum 10 and the intermediate transfer belt 25. In the primary transfer portion T1, a toner image is primarily transferred from the photosensitive drum 10 to the intermediate transfer belt 25 by applying a primary transfer voltage to the transfer roller 23 by, for example, a high voltage power source (not shown). That is, when a primary transfer voltage opposite to the toner charging polarity is applied to the transfer roller 23, the toner image on the photosensitive drum 10 is electrostatically attracted to the intermediate transfer belt 25 and transferred. 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 on which the four-color toner images are secondarily transferred by the secondary transfer portion T2 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 a roller or a belt (not shown) and a heat source (not shown) such as a heater. The recording material S on which the toner image is fixed by the fixing device 31 is discharged out of the machine body.

  A replenishing device 32 is connected to the developing device 1, and the replenishing device 32 replenishes the developing device 1 with toner (specifically a replenisher) in accordance with the consumption of the toner of the developing device 1 during image formation. As will be described in detail later, a replenishing port is formed in the developing device 1 to connect a replenishing device 32. Further, a discharge port is formed in order to discharge the excess developer generated by the replenishment of the replenisher to the outside.

<Developing device>
The developing device 1 of this embodiment will be described with reference to FIGS. As shown in FIG. 2, 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 screw. A stirring screw 14 and the like are provided.

  The developing container 2 contains a two-component developer containing a nonmagnetic toner and a magnetic carrier. In this embodiment, a two-component development system is used as a development system, and a non-magnetic toner having a negative charge polarity and a magnetic carrier having a positive charge polarity are mixed and used as a developer. The non-magnetic toner is obtained by encapsulating a colorant, a wax component and the like in a resin such as polyester or styrene acryl, and pulverizing or polymerizing the powder. 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 (ratio of toner weight to the total weight of the developer (TD ratio)) in a new (initial state) developer that has not yet been developed is, for example, 8%. .

  As shown in FIG. 2, the developing container 2 has a part facing the photosensitive drum 10 (see FIG. 1), and a developing sleeve as a developer carrying member is partly exposed in the opening. 3 is rotatably arranged. 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. The developing sleeve 3 has a coat region M (carrying region, see FIG. 3) capable of carrying the developer on the surface. A magnet roller 4 composed of a plurality of magnetic poles is disposed inside the developing sleeve 3 so as not to rotate.

  The developing sleeve 3 rotates in the direction of the arrow R3 in FIG. 2, and carries the developer adsorbed at the position of the 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.

  In the developing container 2, a developing chamber 11 as a first chamber and a stirring chamber 12 as a second chamber are formed, and the developing chamber 11 and the stirring chamber 12 are partitioned between the developing chamber 11 and the stirring chamber 12. A partition wall 15 is provided. The partition wall 15 separates the developing chamber 11 and the stirring chamber 12 so as to protrude from the bottom surface portion 2 c into the developing container. The partition wall 15 extends in the rotation axis direction of the developing sleeve 3, and the developing chamber 11 and the stirring chamber 12 are formed along the rotating axis direction of the developing sleeve 3. In this embodiment, the developing chamber 11 and the stirring chamber 12 have a difference in height when viewed from the horizontal direction so that the bottom surface portion 12a on the stirring chamber 12 side is above the bottom surface portion 11a on the developing chamber 11 side. Are arranged. In the present specification, “upper” and “lower” refer to the upper direction of gravity and the lower side of direction of gravity, respectively.

  As illustrated in FIG. 3, the partition wall 15 includes a first communication port 16 and a second communication port 17 that allow the developing chamber 11 and the stirring chamber 12 to communicate with each other on both ends in the rotation axis direction (longitudinal direction) of the stirring screw 14. Have The first communication port 16 allows the developer to be transferred from the stirring chamber 12 to the developing chamber 11 on the downstream side (downstream side in the second direction), and the second communication port 17 develops on the upstream side (upstream side in the second direction). This is a developer delivery section that enables delivery of the developer from the chamber 11 to the stirring chamber 12. The first communication port 16 is formed on the downstream side of the coating region M of the developing sleeve 3, and the second communication port 17 is formed on the upstream side of the coating region M of the developing sleeve 3. With respect to the longitudinal direction of the partition wall 15, the first communication port 16 is formed with a width of 30 mm, for example, and the second communication port 17 is formed with a width of 30 mm, for example.

  The developing chamber 11 is provided with a developing screw 13 that conveys the developer in a predetermined first direction in the developing chamber 11. The stirring chamber 12 is provided with a stirring screw 14 that conveys the developer in the second direction opposite to the developing screw 13 in the stirring chamber 12. The developing screw 13 and the stirring screw 14 are configured by forming blades 13b and 14b in a spiral shape around the rotary shafts 13a and 14a, respectively. Both ends of the rotation shafts 13a and 14a are rotatably supported by the developing container 2, respectively. As the developing screw 13, for example, a screw having a blade pitch (hereinafter referred to as a screw pitch) of 20 mm, a screw shaft (rotating shaft 13a) of 8 mm in diameter, and a screw outer diameter of 16 mm is used. On the other hand, as the stirring screw 14, for example, a screw having a screw pitch of 20 mm, a screw shaft (rotating shaft 14a) having a shaft diameter of 6 mm, and a screw outer diameter of 16 mm is used.

  The developing sleeve 3, the developing screw 13, and the agitation screw 14 are connected and driven by a gear train (not shown), and rotate through a gear train from a driving motor (not shown). As the developing screw 13 and the agitating screw 14 rotate, the developer is circulated and conveyed in the direction indicated by the arrow R4 in FIG. At this time, the developer is transferred from the stirring chamber 12 to the developing chamber 11 through the first communication port 16, and the developer is transferred from the developing chamber 11 to the stirring chamber 12 through the second communication port 17. As a result, a developer circulation path is formed between the developing chamber 11 and the stirring chamber 12 in the developing container, and the developer is mixed and stirred by circulating through the circulation path.

  In the developing chamber 11, the developer is supplied to the developing sleeve 3, and the developer separated from the developing sleeve 3 is collected. That is, as shown in FIG. 2, the developer in the developing chamber 11 is attracted to the developing sleeve 3 at the position of the pumping magnetic pole N <b> 1 of the magnet roller 4 while being conveyed by the developing screw 13. Further, the developer separated from the developing sleeve 3 by the peeling magnetic pole N3 is collected in the developing chamber 11. Then, the developer conveyed by the developing screw 13 is moved into the stirring chamber 12 through the second communication port 17. In the stirring chamber 12, the developer is transported by the stirring screw 14 and moved into the developing chamber 11 through the first series opening 16.

  In the case of this embodiment, the developing screw 13 and the stirring screw 14 are arranged so that at least a part thereof is overlapped when viewed from the horizontal direction. As shown in FIG. 2, for example, the developing screw 13 and the stirring screw 14 are arranged so that the lower end 14 e of the stirring screw 14 is higher than the lower end 13 e of the developing screw 13 when viewed from the horizontal direction.

  By the way, in the developing device 1 that performs development using a two-component developer, the developing characteristics of the developer can change with image formation, such as, for example, the charging performance of the carrier with respect to toner decreases. When the charging performance of the carrier is deteriorated, image defects such as density fluctuation and scattering fogging may occur. Therefore, in order to restore the charging performance of the carrier, for example, a replenisher in which toner and carrier are mixed at a weight ratio of 9: 1 is replenished from a replenishing device 32 (see FIG. 1) connected to the developing device 1. Control for refreshing is performed.

<Replenishment of developer>
As shown in FIG. 3, a replenishment chamber 70 is formed in the developing container 2 at a position outside the developer circulation path upstream of the second communication port 17 of the stirring chamber 12. The replenishing chamber 70 communicates with the agitating chamber 12 and forms a replenishing agent replenishing path to the agitating chamber 12. A supply port 40 is formed in the supply chamber 70, and a supply device 32 (see FIG. 2) is connected to the supply port 40. Although not shown, the replenishing device 32 has, for example, a toner bottle containing a replenishing agent and a drive unit that rotates the toner bottle. By rotating the toner bottle, replenishment is performed from an opening formed in the toner bottle. The replenisher is supplied to the stirring chamber 12 through the mouth 40. A supply screw 60 is provided in the supply chamber 70. The replenishing screw 60 conveys the replenisher in the replenishing chamber 70 toward the stirring chamber 12. That is, the replenishing screw 60 conveys the replenisher in the same second direction as the stirring screw 14. The replenishing screw 60 will be described later (see FIG. 4).

<Discharge of developer>
As described above, the replenishing agent is replenished by the replenishing device 32. However, if the developer is excessively increased in the developing container as the replenishing agent is replenished, the developer is not sufficiently stirred, causing density fluctuations and scattering fog. Such image defects are likely to occur. Therefore, the developer container 2 is formed with a discharge port 50 for discharging the excess developer to the outside of the developing container so that the developer that becomes excessive due to the replenishment of the replenishing agent is discharged from the developing container 2.

  In the present embodiment, the discharge port 50 is formed on the downstream side of the first series port 16 of the stirring chamber 12. This is because, for example, if the discharge port 50 is formed on the wall surface in the middle of the stirring chamber 12, the developer may be discharged more than necessary due to the jumping up by the stirring screw 14. That is, the developer is easily discharged regardless of the amount of the developer, and in some cases, the developer becomes too small. As a result, a sufficient amount of developer is not ensured in the developing chamber 11 on the upstream side in the developer conveying direction of the developing screw 13, and the coating region M of the developing sleeve 3 is difficult to be uniformly coated. When such a coating defect occurs, image defects such as image unevenness and white stripes may occur. In order to avoid this, it is preferable that the discharge port 50 is formed on the downstream side of the first continuous port 16, which is less affected by the developer splashing by the stirring screw 14.

  In the developing device 1, the developer on the developing sleeve is collected over the longitudinal direction of the stirring chamber 12 (the rotational axis direction of the stirring screw 14). Therefore, the developer is divided into a first path that is transported from the developing chamber 11 to the stirring chamber 12 without going through the developing sleeve 3, and a second path that is transported directly from the developing sleeve 3 to the stirring chamber 12. The developer is circulated through the two paths, and the developer distribution tends to be non-uniform in the developing container. Specifically, in the developing chamber 11 and the stirring chamber 12, the developer surface tends to be lower on the upstream side than on the downstream side. Therefore, the amount of developer delivered from the developing chamber 11 to the stirring chamber 12 via the second communication port 17 is the amount of developer delivered from the stirring chamber 12 to the developing chamber 11 via the first communication port 16. Less likely to be less.

  By the way, in the conventional developing device, as described above, when a large amount of replenishment agent is replenished at once from the replenishing port 40, a large amount of replenishment agent conveyed by the replenishment screw 60 into the replenishment chamber becomes a mountain. It is easy to flow into the second communication port 17 as it is. When a large amount of replenisher flows into the second communication port 17 with a small amount of developer as it is, even if the replenisher is conveyed by the stirring screw 14, it is difficult for the replenisher to be sufficiently mixed with the developer. Then, a difference in toner density occurs in the developer, and as a result of such developer being supplied to the developing sleeve 3, image defects such as density unevenness may occur. Further, when a large amount of replenisher is replenished, a part of the replenisher is likely to be scattered at the second communication port 17, and image defects such as fogging may occur due to the scattered replenisher.

<Supply screw>
Therefore, in the present embodiment, even when a large amount of replenisher is replenished, in order to prevent the replenisher from flowing all at once into the second communication port 17 by the replenishment screw 60, in the replenishment chamber 70, the upstream side in the replenisher transport direction. A difference was made in the amount of replenisher transported on the downstream side. Hereinafter, the replenishing screw 60 of the first embodiment will be described with reference to FIG.

  As shown in FIG. 4, in the case of the present embodiment, the replenishing screw 60 is connected to the stirring screw 14 and rotated together with the stirring screw 14. The replenishment screw 60 and the agitation screw 14 are connected and provided so that their connection location (seam) is located upstream of the second communication port 17. Further, the replenishing screw 60 has a full length so as to cover almost the entire replenishing chamber 70. The replenishing screw 60 has a rotating shaft 60a and a spiral blade 60b formed around the rotating shaft 60a. Here, as with the stirring screw 14, the shaft diameter of the screw shaft (rotating shaft 60a) is 6 mm. The outer diameter of the screw is 16 mm. Note that the replenishing screw 60 and the stirring screw 14 may be provided integrally with a common rotating shaft.

  The replenishment chamber 70 can be roughly divided into a first transport unit 70a and a second transport unit 70b. The 2nd conveyance part 70b is an area | region including immediately under the supply port 40 of the replenisher conveyance direction upstream (2nd direction upstream). The replenishment agent replenished from the replenishing port 40 is first accommodated in the second transport unit 70b. On the other hand, the 1st conveyance part 70a is an area | region which extends to the 2nd communicating port 17 in the replenisher conveyance direction downstream (2nd direction downstream) adjacent to the 2nd conveyance part 70b.

  The screw pitch of the replenishment screw 60 in the first transport unit 70a is different from the screw pitch of the replenishment screw 60 in the second transport unit 70b. Specifically, the screw pitch of the second transport unit 70b is 10 mm, which is smaller than the screw pitch of the stirring screw 14, and the screw pitch of the first transport unit 70a is, for example, 20-30 mm, which is larger than the second transport unit 70b. Moreover, the screw pitch of the 1st conveyance part 70a may not be uniform, for example, may differ for every pitch. However, in that case, the upstream side may be formed, for example, at 20 mm on the upstream side and 30 mm on the downstream side so that the downstream side is larger than the upstream side in the replenisher conveyance direction. In the case of this embodiment, the replenishment screw 60 is formed to have the same overall length as the replenishment chamber 70 of 60 mm, the second transport unit 70b has a screw pitch of 10 mm, and the first transport unit 70a has a screw pitch of 20 mm and 30 mm. Yes. That is, the replenishing screw 60 is formed at three different pitches of 10 mm, 20 mm, and 30 mm from the upstream side to the downstream side in the replenisher transport direction. The replenishing screw 60 may be formed so that the screw pitch continuously increases from the upstream side to the downstream side in the replenisher transport direction.

  Here, the screw pitch will be described with reference to FIG. FIG. 5 is a graph showing the relationship between the screw pitch and the replenisher transport amount per rotation of the screw. Here, the case where the outer diameter of the screw is 20 mm is given as an example. As can be understood from FIG. 5, the replenisher transport amount per rotation varies depending on the screw pitch. As shown in FIG. 5, the replenisher transport amount per one rotation becomes maximum when the screw pitch is 30 mm. Therefore, in the case of the present embodiment, the screw pitch of the first transport unit 70a is on the downstream side close to the stirring chamber 12 in order to quickly transport the replenisher in the replenishment chamber on the downstream side rather than the upstream side in the replenisher transport direction. It is formed so that the replenisher transport amount per rotation is 30 mm at the maximum. On the other hand, in order to reduce the replenisher transport amount per rotation as compared with the first transport unit 70a, the screw pitch of the second transport unit 70b is formed to 10 mm.

  As described above, by making the screw pitches of the first transport unit 70a and the second transport unit 70b different, the transport speed of the replenisher becomes faster than the transport speed of the second transport unit 70b in the first transport unit 70a. As a result, the replenishment agent replenished in the second conveyance unit 70b is delivered to the first conveyance unit 70a at a relatively slow speed, but the replenishment agent delivered in the first conveyance unit 70a is delivered to the second conveyance unit 70b. Compared to the above, it is delivered to the stirring chamber 12 at a higher speed. That is, there is a difference in the replenisher transport amount between the first transport unit 70a and the second transport unit 70b. Then, even if there is a height difference in the level of the replenisher in the second transport unit 70b, the replenisher is loosened in the first transport unit 70a and the level difference in the level of the replenisher disappears. That is, when a large amount of replenishment agent is replenished and a crest of replenishment agent is formed immediately below the replenishment port 40, the second conveyance unit 70b conveys the crest while maintaining the crest substantially, but the first conveyance unit 70a. Then, the crest is eliminated during conveyance, and the height difference is eliminated. As a result, the amount of the replenishment agent when it reaches the stirring chamber 12 cannot vary greatly, so that the replenishment agent is stably supplied from the replenishment path to the circulation path.

  In order to confirm the effect of the present embodiment, the inventors replenish a predetermined amount of replenisher from the replenishment port 40, and the replenisher amount when the replenisher is conveyed to the replenishment screw 60 and reaches the stirring chamber 12. An experiment was conducted to examine the time transition of. The same experiment was performed by dividing the replenishment amount of one replenisher into 0.4 g in three times, and the average value of the three times is shown in FIG. The horizontal axis in FIG. 6 is the time immediately after replenishment, and the vertical axis is the amount of replenisher that has reached the stirring chamber 12. In addition, FIG. 7 shows the relationship between the peak value of the replenishment agent and its half-value width when it reaches the stirring chamber 12. In FIGS. 6 and 7, experimental results when the screw pitch of the replenishing screw 60 is the same at 20 mm for both the first transport unit 70 a and the second transport unit 70 b are shown as “comparative examples”, and the experiment of this embodiment is performed. The result was expressed as “Embodiment 1”.

  As shown in FIGS. 6 and 7, the first embodiment compared to the comparative example has a smaller peak value of the replenisher reaching the stirring chamber 12, a later peak time, and a larger half-value width of the peak value. It can be understood from the experimental results. This indicates that, in the case of the present embodiment, the replenishment agent replenished in the replenishment chamber 70 expands in the replenishment agent conveyance direction until the replenishment agent distribution in the replenishment chamber 70 reaches the agitation chamber 12 as the replenishment agent 60 conveys the replenishment agent. ing.

  In addition, the inventors set the screw pitch combinations of the replenishing screw 60 to “20, 20, 20 (Comparative Example 1)”, “20, 20, 30 (Comparative Example 2)”, “10, 20, 30 (main). In place of “Embodiment)”, an experiment for forming an image on a recording material was performed. In this experiment, the occurrence of image defects such as fogging and density unevenness when continuous image formation was performed on 10,000 recording materials was examined. The experimental results are shown in Table 1. In Table 1, a circle mark indicates that no image defect has occurred, and a cross mark indicates that an image defect has occurred. A triangle mark indicates that an image defect has occurred compared to the circle mark but has not occurred compared to the x mark.

  As can be understood from Table 1, in the case of Comparative Example 1, fogging and density unevenness occurred. On the other hand, in the case of the comparative example 2 in which the screw pitch on the downstream side close to the stirring chamber 12 in the first transport unit 70a is 30 mm, as compared with the comparative example 1, the fogging and the concentration are as shown by Δ. Unevenness is less likely to occur. In the case of the present embodiment in which the replenishing screw 60 is formed at three different pitches of 10 mm, 20 mm, and 30 mm from the upstream side to the downstream side in the replenisher transport direction, as shown by the circles, the fog and density Unevenness (image defect) hardly occurred.

  As described above, in the present embodiment, in the replenishment chamber 70 that forms the circulation path, the screw pitches of the replenishment screws 60 of the first transport unit 70a and the second transport unit 70b are made different from each other, so A difference is generated in the transport amount of the replenishment agent with the transport unit 70b. If the replenisher transport amount of the first transport unit 70a is larger than that of the second transport unit 70b, the difference in height of the surface of the replenishment agent generated in the second transport unit 70b is eliminated by the first transport unit 70a. . Therefore, even if a large amount of replenishment agent is replenished and a crest of replenishment agent is formed in the second conveyance unit 70b, the replenishment agent distribution will be resolved after the crest is eliminated during conveyance in the first conveyance unit 70a. Is expanded in the replenisher transport direction, and the replenisher is supplied to the circulation path. Thus, since the amount of the replenishment agent does not vary greatly at the time when it is supplied to the circulation path, even if a large amount of replenishment agent is replenished, a large amount of replenishment agent is not supplied to the circulation path all at once. In that case, the replenisher is sufficiently mixed with the developer by the stirring screw 14, and the developer is supplied to the developing sleeve 3 by the developing screw 13. As a result, image defects such as density unevenness hardly occur. In addition, a part of the replenisher is less likely to be scattered through the second communication port 17. As described above, in the present embodiment, it is possible to suppress the occurrence of image defects such as fogging and density unevenness due to the replenishment of the replenisher.

[Second Embodiment]
As described above, in the first embodiment, the screw pitch of the replenishment screw 60 is varied in order to cause a difference in the replenisher transport amount between the first transport unit 70a and the second transport unit 70b. In contrast, in the second embodiment, the shaft diameter and blade diameter of the rotation shaft of the replenishing screw 60 are made different. FIG. 8 shows a supply screw according to the second embodiment. In the second embodiment shown in FIG. 8, the shape of the replenishing screw 601 is different from that in the first embodiment shown in FIG. Since other configurations and operations are the same as those in the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 8, the replenishing screw 601 has a rotary shaft 601a formed so that the shaft diameter of the first transport portion 70a is smaller than the shaft diameter of the second transport portion 70b. Both the first transport unit 70a and the second transport unit 70b are formed such that the rotation shaft 601a continuously becomes thinner as the replenisher transport direction proceeds from the upstream side to the downstream side. In this case, the rotating shaft 601a is formed in a conical shape, for example. In the present embodiment, the rotation shaft 601a is formed so that the shaft diameter at the most downstream end in the replenisher transport direction is 6 mm, which is the same as that of the stirring screw 14, and the shaft diameter at the most upstream end in the replenisher transport direction is 10 mm. In such a case, the distance between the inner wall surface of the replenishment chamber 70 and the rotation shaft 601a is lower than the rotation center of the rotation shaft 601a in the gravity direction and viewed from the upstream side in the replenisher transport direction as viewed from the rotation axis direction of the rotation shaft 601a. It becomes wider as it goes downstream. However, the distance between the inner wall surface of the replenishment chamber 70 and the outer peripheral surface of the blade 601b is a constant distance below the rotation center of the rotation shaft 601a in the gravity direction when viewed from the rotation axis direction of the rotation shaft 601a. To do so, the replenishing screw 601 is formed such that the area of the blade 601b of the first transport unit 70a is larger than the area of the blade 601b of the second transport unit 70b when viewed from the direction of the rotational axis of the rotary shaft 601a. That is, the blade 601b is formed to have a smaller blade diameter in proportion to an increase in the shaft diameter of the rotary shaft 601a. The screw pitch may be formed at the same pitch of, for example, 30 mm for both the first conveyance unit 70a and the second conveyance unit 70b, or the first conveyance unit 70a and the second conveyance unit as in the first embodiment described above. It may be different from 70b.

  Thus, in the present embodiment, in the replenishment chamber 70 that forms the circulation path, the first conveyance unit 70a and the second conveyance unit 70b have different shaft diameters of the rotation shaft 601a and the blade diameter of the blade 601b. A difference is generated in the amount of replenisher transported between the portion 70a and the second transport portion 70b. By doing so, even when a large amount of replenishment agent is replenished, a large amount of replenishment agent is not supplied to the circulation path all at once. Accordingly, even in the case of the second embodiment, the same effect as in the case of the first embodiment described above that the occurrence of image defects such as fogging and density unevenness due to the replenishment of the replenishment agent can be suppressed. .

[Third embodiment]
As described above, in the first embodiment and the second embodiment, the screw pitch of the replenishing screw 60 and the replenishment in order to cause a difference in the replenisher transport amount between the first transport unit 70a and the second transport unit 70b. The shaft diameter and blade diameter of the rotating shaft of the screw 60 are varied. On the other hand, in the third embodiment, the replenisher is used in the first transport unit 70a and the second transport unit 70b without changing the screw pitch of the replenishment screw 602 and the shaft diameter and blade diameter of the rotation shaft of the replenishment screw 60. This causes a difference in the transport amount. A third embodiment will be described with reference to FIG. In the third embodiment shown in FIG. 9, a paddle 60 c is formed around the rotation shaft 60 a as a protrusion that protrudes in the radial direction from the rotation shaft 60 a and extends in the rotation axis direction in the replenishment screw 602. Since other configurations and operations are the same as those in the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted. However, the replenishing screw 602 of the third embodiment is formed so that the pitch of the blades 60b, the area of the blades 60b, and the shaft diameter of the rotation shaft 60a are the same over the entire region in the rotation axis direction.

<Paddle>
In the case of the present embodiment, for example, four paddles 60c are arranged in the second transport unit 70b so that the phase is shifted by 90 ° in the circumferential direction of the rotation shaft 60a, for example, within one pitch. On the other hand, in the first transport unit 70a, for example, two paddles 60c are arranged in one pitch on the upstream side in the replenisher transport direction so that the phase is shifted by 180 ° in the circumferential direction of the rotation shaft 60a. Yes. In other words, the number of paddles 60c per unit length in the replenisher transport direction is less in the first transport unit 70a than in the second transport unit 70b. Here, in this embodiment, the paddle 60c is not disposed on the downstream side in the replenisher transport direction in the first transport unit 70a, but the paddle 60c may be disposed on the downstream side in the replenisher transport direction. However, fewer paddles 60c are formed per unit length in the replenisher transport direction on the downstream side in the replenisher transport direction than on the upstream side. In this way, by reducing the number of paddles 60c from the upstream side to the downstream side in the replenisher transport direction, a difference in the transport amount of the replenisher is caused between the first transport unit 70a and the second transport unit 70b. Can do. Specifically, the replenisher transport amount per rotation of the replenishment screw 602 is made larger in the first transport unit 70a than in the second transport unit 70b.

  When the replenishment screw 602 of the third embodiment shown in FIG. 9 is used to replenish a predetermined amount of replenishment agent from the replenishment port 40 described above, the replenishment agent is conveyed to the replenishment screw 602 and reaches the stirring chamber 12. An experiment was conducted to examine the time course of the amount of replenishing agent in Japan. In FIG. 6 and FIG. 7, experimental results in the case of the third embodiment are shown as “Embodiment 2”. As shown in FIGS. 6 and 7, in the case of this embodiment as well, until the replenishment agent supplied in the replenishment chamber 70 reaches the stirring chamber 12 as the replenishment replenishment agent is conveyed by the replenishment screw 602. It shows that it spreads in a replenisher conveyance direction. Further, as a result of conducting an experiment (see Table 1 above) for checking whether or not image defects such as fogging and density unevenness occur when continuous image formation is performed on 10,000 recording materials, replenishment is also possible in the third embodiment. The occurrence of image defects such as fogging and density unevenness due to the replenishment of the agent could be suppressed.

  Thus, also in the third embodiment, it is possible to cause a difference in the amount of replenisher transported between the first transport unit 70a and the second transport unit 70b. Therefore, even if a large amount of replenishment agent is replenished, a large amount of replenishment agent is not supplied to the circulation path all at once, thus suppressing the occurrence of image defects such as fogging and density unevenness due to replenishment of replenishment agent. The effect that it can do is acquired.

<Other embodiments>
In each of the above-described embodiments, the replenishment chamber 70 is disposed on the upstream side of the stirring chamber 12 in the developer conveyance direction, but the present invention is not limited to this. The replenishment chamber 70 may be disposed upstream of the developing chamber 11 in the developer conveyance direction.

  In each of the above-described embodiments, an intermediate transfer method in which a toner image of each color is primarily transferred from the photosensitive drum 10 of each color to the intermediate transfer belt 25, and then a composite toner image of each color is collectively transferred to the recording material S. Although the image forming apparatus 100 has been described, the present invention is not limited to this. For example, the image forming apparatus may be a direct transfer type that directly transfers from a photosensitive drum to a recording material carried and conveyed by a transfer material conveyance belt.

  In each of the above-described embodiments, the developing container 2 is divided into the developing chamber 11 and the stirring chamber 12 in the horizontal direction, or the developing container 2 is divided into the developing chamber 11 and the stirring chamber 12. The present invention can also be applied to a vertical stirring type developing device partitioned in the vertical direction.

  Each of the above-described embodiments has a function of supplying and recovering the developer in addition to the configuration in which the developer is supplied to the developing sleeve 3 and the developer is recovered from the developing sleeve 3 in the developing chamber 11 as described above. It can also be applied to a so-called function separation type developing device. That is, referring to FIG. 2, a guide member is extended above the partition wall 15 so as to be close to the developing sleeve 3, and the developer separated from the developing sleeve 3 is guided to the stirring chamber 12 by the guide member. It may be. In this case, the developer is supplied from the developing chamber 11 to the developing sleeve 3, while the developer separated from the developing sleeve 3 is collected in the stirring chamber 12.

DESCRIPTION OF SYMBOLS 1 ... Developing device, 2 ... Developing container, 3 ... Developer carrier (developing sleeve), 11 ... First chamber (developing chamber), 12 ... Second chamber (stirring chamber) , 13 ... conveying screw (first conveying screw, developing screw), 14 ... conveying screw (second conveying screw, stirring screw), 15 ... partition wall, 16 ... first series opening, 17 ... Second communication port, 32 ... Supply device, 60 (601, 602) ... Supply screw, 60a ... Rotary shaft, 60b ... Vane, 60c ... Projection (paddle), 70: Replenishment chamber, 70a: First transport unit, 70b: Second transport unit, 100: Image forming apparatus

Claims (8)

A developer container having a developer circulation path, and a replenisher supply path communicating with the circulation path;
A conveying screw for conveying the developer in the circulation path;
A replenishing screw having a rotating shaft and a spiral blade formed around the rotating shaft, and transporting the replenishing agent of the replenishing path toward the circulation path,
The replenishment path is such that the first transport unit downstream in the replenisher transport direction transports the replenisher per rotation of the replenishment screw more than the second transport unit upstream in the replenisher transport direction from the first transport unit. Is formed to be more,
A developing device. The replenishing screw is formed such that the blade pitch of the first transport unit is larger than the pitch of the blades of the second transport unit.
The developing device according to claim 1. The replenishing screw is formed such that the area of the blades of the first transport unit is larger than the area of the blades of the second transport unit as viewed from the direction of the rotation axis of the rotation shaft.
The developing device according to claim 1, wherein The replenishing screw is formed such that the shaft diameter of the rotating shaft of the first transport unit is smaller than the shaft diameter of the rotating shaft of the second transport unit,
The developing device according to claim 3. The replenishing screw has a protrusion protruding in the radial direction of the rotating shaft around the rotating shaft, and the protruding portion of the first conveying portion rotates the rotating shaft more than the protruding portion of the second conveying portion. The number per unit length in the axial direction is small.
The developing device according to claim 1, wherein The replenishing screw is formed such that the pitch of the blades, the area of the blades, and the shaft diameter of the rotation shaft are the same in the first transport unit and the second transport unit
The developing device according to claim 5. The replenishing screw is connected to the conveying screw and rotated integrally.
The developing device according to claim 1, wherein A developer carrying member that carries the developer and rotates;
A first chamber for supplying a developer to the developer carrier, a second chamber for forming a developer circulation path in the first chamber and collecting the developer from the developer carrier, and the second chamber. A developer container having a replenishment chamber that communicates with the chamber and forms a replenishment path for the replenisher;
A first conveying screw provided in the first chamber for conveying the developer in a first direction;
A second conveying screw provided in the second chamber for conveying the developer in a second direction opposite to the first direction;
A replenishment screw provided in the replenishment chamber, connected to the second transport screw and rotating with the second transport screw to transport the replenisher in the second direction;
A first series of openings for separating developer from the second chamber to the first chamber on the downstream side in the second direction, separating the first chamber and the second chamber in the developer container; A partition wall having a second communication port for transferring developer from the first chamber to the second chamber on the upstream side in the direction,
The replenishing chamber is formed upstream of the second communication port in the second direction,
In the replenishment path, the amount of replenisher transported per rotation of the replenishment screw is greater in the first transport unit downstream in the second direction than in the second transport unit upstream in the second direction from the first transport unit. Is formed to be more,
A developing device.

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