JP5962023B2 - Developing device, image forming apparatus - Google Patents

Description

  The present invention relates to a developing device which is a means for visualizing an electrostatic latent image and an image forming apparatus using the developing device.

  As a developing device used in an image forming apparatus such as a printer, a facsimile machine, and a copying machine, a one-component developing device using a one-component developer, and a two-component developing device using a two-component developer composed of toner and a magnetic carrier. Both developing devices are well known. Conventionally, as a small-sized developing device, a one-component developing device is often used. However, it is known that a two-component developing device is more advantageous in terms of durability and image characteristics. In recent years, there has been a demand for developing devices with high image quality, small size, and long life, and there is an increasing demand for miniaturization of two-component developing devices.

  In order to reduce the size of the two-component developing device, it is usually necessary to arrange two developer conveying screws in the vertical direction and to reduce the diameter of the developing roller. However, if the conventional developing device is simply reduced in size, the toner easily scatters in the portion where the developer passes through the developing region and enters the developing case. Conventionally, the gap between the developing roller (sleeve) and the case is managed, and a suction airflow is used to accommodate the toner scattered in this portion in the case. However, in order to generate a suction airflow by reducing the diameter of the developing roller Can't take enough distance. Even if the developing roller is simply rotated, the toner accumulated in the apparatus cannot be discharged outside the container unless the developer touches it.

  In JP 2009-258276 A (Patent Document 1), for the purpose of removing the toner accumulated on the developer regulating member, the developing sleeve is reversely rotated to scrape the toner adhering to the developer regulating member from the developing device. It is disclosed to reduce toner dropping. However, in order to discharge the scattered toner accumulated in the developing container to the outside of the container, it is not sufficient to reverse the developing sleeve alone, and the problem of discharging the accumulated toner has not been solved.

  The developer regulating member is always in contact with the developer, and the toner attached to the regulating member can be removed by reversing the developing sleeve. However, toner deposited on the developing case below the developing roller (near the end of the opening) is usually deposited in a place where it does not come into contact with the developer, so the deposited toner is discharged even if the developing roller is simply reversed. I can't do it. When the distance (gap) between the sleeve and the case is reduced so that the developer (developer carried and carried by the sleeve) contacts the accumulated toner, the developer that must be collected in the developing container is contained in the container (case). ), The gap cannot be reduced (a gap is necessary to some extent), and conventionally, toner deposited near the developing case opening end below the developing roller cannot be effectively discharged. .

  Along with the miniaturization of the developing device, a phenomenon has occurred in which scattered toner accumulates in the device and causes an abnormal image due to toner dropping during image formation. In conventional devices, the accumulated toner is sufficiently discharged outside the device. There was a problem that I could not.

  SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact developing device and an image forming apparatus that can solve the above-mentioned problems in the prior art and that can discharge accumulated toner to the outside of the apparatus and that does not cause toner drop during image formation. And

According to the present invention, there is provided a developer carrying body that includes a magnetic field generating means and carries a two-component developer comprising a toner and a carrier on the surface, and supplies the developer to the developer carrying body. A first conveying member that conveys the developer while the second conveying member is disposed below the first conveying member and conveys the developer while collecting the developer from the developer carrying member, and the developer carrying A developer carrying body, wherein the developer carrying body includes a developing case that includes a developing body that supports the developer carrying body in an opening facing the developing region. Is provided so as to be rotatable in the direction opposite to that during the developing operation, and the developer on the developer carrying member is brought into contact with the opening end of the developing case located below the developer carrying member during the developing operation. not, positioned below the developer carrying member That from the open end of the developing case, the said developer carrying member downstream side in the rotational direction of the developing operation, the developer staying portion is formed, the open end when the developing operation is driven to rotate in the opposite direction This is solved by extruding the accumulated toner of the developer by the developer in the developer retaining portion .

  According to the developing device of the present invention, the developer retaining portion is formed in the vicinity of the downstream side of the developing case opening end (downstream in the developer carrying member rotation direction) below the developer carrying member (developing roller). Since the developer carrying member is rotated in the direction opposite to that during the developing operation, the accumulated toner (toner deposited near the opening end of the case) is developed by the developer accumulated in the developer retaining portion. It can be pushed out of the case, and it is possible to prevent the occurrence of abnormal images such as toner dropping.

1 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus equipped with a developing device to which the present invention is applied. FIG. 2 is a schematic configuration diagram illustrating an example of a developing device applicable to the image forming apparatus. It is a schematic diagram explaining the flow of the developer in a developing container. It is a schematic diagram explaining the mode of the developer in the supply and recovery screw longitudinal direction. It is a schematic diagram for explaining the flow of the developer around the developing sleeve 34a. It is a schematic diagram for demonstrating the behavior of the developer around the developing roller in the developing device of the comparative example. 6 is a graph showing a comparison of toner drop occurrence rates in developing devices of an example and a comparative example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, an example of an image forming apparatus equipped with a developing device to which the present invention is applied will be described with reference to FIG.

  A printer 100 shown in FIG. 1 is a color image forming apparatus that can form a full color image by adopting a tandem method, and each color toner of black, magenta, yellow, and cyan (hereinafter referred to as K, M, Y, and C). Image forming devices 17K, M, Y, and C for forming an image are provided. Below these image forming devices 17K, 17M, 17C, and 17C, the recording paper P is carried on the surface and conveyed around the downstream stretching roller 18 and the upstream stretching roller 19, and each image forming device is conveyed. A transfer / conveying belt 15 that moves on the surface while facing the devices 17K, M, Y, and C is disposed. Transfer bias rollers 5K, M, Y, and C that face the image forming devices 17K, M, Y, and C with the transfer conveyance belt 15 interposed therebetween are provided.

  Further, a fixing device 24 that fixes unfixed toner on the recording paper P separated from the transfer conveyance belt 15 is provided downstream of the downstream tension roller 18 in the recording paper conveyance direction by the transfer conveyance belt 15. . In addition, a discharge tray 25 for stacking recording paper P that has passed through the fixing device 24 and has a toner image fixed thereon is provided at the top of the main body of the printer 100.

  A plurality of paper feed cassettes 20, 21, and 22 that store the recording paper P are provided below the transfer conveyance belt 15. In addition, a paper feeding / conveying device serving as a recording paper supply unit that supplies recording paper P from each of the paper feeding cassettes 20, 21, 22 to a transfer region where the transfer / conveying belt 15 and the image forming devices 17 K, M, Y, and C face each other. 26, and a registration roller 23 for supplying the recording paper P conveyed from each of the paper feed cassettes 20, 21, and 22 in accordance with the image forming timing by the image forming devices 17K, M, Y, and C.

  In FIG. 1, the transfer conveyance belt 15 is disposed in an oblique direction so that the printer 100 is small in the left-right direction in FIG. 1, and the conveyance direction of the recording paper P indicated by an arrow is an oblique direction. Accordingly, in the printer 100, the width of the housing in the left-right direction in FIG. 1 is slightly longer than the length in the longitudinal direction of the A3 size recording paper. That is, the printer 100 is greatly reduced in size by being the minimum size required to accommodate the recording paper therein.

  Each image forming device 17K, M, Y, C has a drum-shaped photoconductor 1K, M, Y, C as a latent image carrier. In order with respect to the rotation direction of the photoreceptors 1K, M, Y, and C, there are charging devices 2K, M, Y, and C, developing devices 3K, M, Y, and C, cleaning devices 6K, M, Y, and C, respectively. doing. Further, the writing light L is radiated from the exposure devices 16K, M, Y, C between the charging devices 2K, M, Y, C and the developing devices 3K, M, Y, C. The photoreceptors 1K, M, Y, and C may be belt-shaped instead of drum-shaped.

  In the printer 100 having such a configuration, each color toner image is formed by each image forming device 17K, M, Y, and C at the start of image formation. In each of the image forming devices 17K, M, Y, and C, the photoreceptors 1K, M, Y, and C are rotationally driven by a main motor (not shown) and are uniformly charged by the charging devices 2K, M, Y, and C. The exposure device 16K, M, Y, C emits the writing light L according to image information for each color obtained by color separation of the image, and an electrostatic latent image is formed. The electrostatic latent images formed on the photoreceptors 1K, M, Y, and C are developed by the developing devices 3K, M, Y, and C, and toner images of the respective colors are formed on the surfaces of the photoreceptors 1K, M, Y, and C. Is formed. On the other hand, the recording paper P fed and conveyed from the paper feeding cassette (one of 20 to 22) is transferred and conveyed by the registration rollers 23 in accordance with the image forming timings of the image forming devices 17K, M, Y, and C. Supplied on the surface of the belt 15. Then, the recording paper P carried on the transfer conveyance belt 15 is conveyed to the transfer area of each color by the surface movement of the transfer conveyance belt 15.

  The toner images formed on the photoconductors 1K, 1M, 1C, 1C are transferred to the transfer bias rollers 5K, 5M, 5B, and 5C, which are transfer bias means, at the facing portions of the photoconductors 1K, 1M, 1C, 1C and the transfer conveyance belt 15, respectively. The images are sequentially transferred onto the recording paper P carried on the transfer conveyance belt 15 by Y and C. In this way, the toner images formed on the respective photoreceptors 1K, M, Y, and C are transferred in the order of K (black), M (magenta), Y (yellow), and C (cyan), and the superimposed color. A toner image is formed on the recording paper P. The recording paper P onto which the toner image has been transferred is separated from the transfer conveyance belt 15 and conveyed to the fixing device 24 where the toner image is fixed and discharged to a paper discharge tray 25 outside the apparatus.

  On the other hand, after the toner image is transferred onto the recording paper P, the transfer residual toner is removed by the cleaning devices 6K, M, Y, and C, and the charge removal (not shown) is performed as necessary. After being neutralized by the lamp, the operation of being uniformly charged by the charging devices 2K, M, Y, and C is repeated again.

  Next, the developing device 3 will be described in detail. The developing devices 3K, M, Y, and C of the printer 100 according to the present embodiment use toners of different colors (K, M, Y, and C) as image forming materials, but the other configurations are the same. Yes. For this reason, hereinafter, the subscripts K, M, Y, and C are omitted, and the developing device 3 will be described.

FIG. 2 is a schematic configuration diagram illustrating an example of the developing device 3 applicable to the printer 100 according to the present embodiment.
The developing device 3 is disposed to face the photoconductor 1, and the photoconductor 1 is rotated in the clockwise direction in FIG. 2 as indicated by an arrow a in FIG.

  A developer container 33 that is a casing of the developing device 3 contains a developer 32 that is a powdery two-component developer composed of a magnetic carrier and magnetic or non-magnetic toner. The developing device 3 carries the developer 32 in the developing container 33 to the developing area A where the toner is supplied to the electrostatic latent image formed on the surface of the photoreceptor 1 to perform development, and is transported by moving the surface. A developing sleeve 34a is provided as a developer carrying member. Further, a magnet roller 34b composed of a plurality of magnets fixed to the developing device 3 is provided inside the developing sleeve 34a, and the developing roller 34 is configured by the developing sleeve 34a and the magnet roller 34b. Further, it has an agent regulating member 35 that regulates the layer thickness of the developer carried on the developing sleeve 34a.

  As two transport screws as developer transport means, a supply screw 39 and a recovery screw 40 are provided substantially parallel to the rotation axis direction of the developing sleeve 34a. Each transport screw includes a rotating shaft and a wing portion spirally provided on the rotating shaft, and transports the developer 32 in one direction along the axial direction of the rotating shaft by rotating. The interior of the developing container 33 is partitioned by an inner wall of the developing container 33 and a partition plate 36, and a supply transport path 37 and a recovery transport path 38 are formed vertically with a partition plate 36 interposed therebetween as a developer transport path. Further, openings are provided at both ends of the front and rear sides of the partition plate 36 in FIG. 2, and the supply conveyance path 37 and the collection conveyance path 38 are communicated with each other by two openings. ing.

  Further, the partition plate 36 is erected so that the end on the developing sleeve 34 a side surrounds the supply screw 39, and a barrier 43 described later is formed by the erected portion. An opening is formed on the developing sleeve 34a side by the end of the barrier 43 and the inner wall of the developing device 3, and the developer 32 is supplied from the opening to the developing sleeve 34a. The opening extends in the longitudinal direction of the developing sleeve 34a, and the developer 32 can be supplied to the developing sleeve 34a over the developing width.

  In the developing device 3 in this embodiment, as described later, the amount of the developer 32 in the supply conveyance path 37 tends to decrease as it goes downstream, so that the end of the barrier 43 follows the phenomenon of that amount. The height of the portion is formed so as to decrease as it goes from upstream to downstream.

  As shown in FIG. 2, a supply screw 39 and a collection screw 40 are disposed in the supply conveyance path 37 and the collection conveyance path 38, respectively, and the developer 32 in the developing container 33 is supplied to the supply conveyance path 37 and the collection conveyance path 38. Is housed in. The collection screw 40 is disposed substantially parallel to the supply screw 39, and the developer 32 in the collection conveyance path 38 is conveyed by the collection screw 40 in the direction opposite to the conveyance direction of the supply screw 39.

  The developer 32 in the developing container 33 is circulated between the supply conveyance path 37 and the collection conveyance path 38 through openings provided at both ends of the partition plate 36 by conveyance by rotation of the supply screw 39 and the collection screw 40. To do. The supply screw 39 rotates clockwise in FIG. 2, and the recovery screw 40 rotates counterclockwise similarly to the developing sleeve 34a.

  Of the developer 32 in the developing container 33, the developer in the supply conveyance path 37 is supplied to the surface of the developing sleeve 34 a while being conveyed by the rotation of the supply screw 39. The developer 32 is supplied from the supply conveyance path 37 to the developing sleeve 34a by the rotation of the supplying screw 39 over the end portion of the barrier 43 between the supplying screw 39 and the developing sleeve 34a, or the developing sleeve 34a. The developer 32 is attracted to the developing sleeve 34a by the magnetic force of the magnet roller 34b provided therein.

  The developer 32 supplied to the developing sleeve 34a is carried on the surface of the developing sleeve 34a by the rotation of the developing sleeve 34a and the magnetic force of the magnet roller 34b provided therein, and in the direction of arrow B in FIG. Be transported. That is, a certain amount of the developer 32 supplied and carried on the developing sleeve 34a passes through the portion facing the agent regulating member 35 as shown by the arrow B while being carried on the developing sleeve 34a. At this time, excessive developer 32 out of the developer 32 carried on the surface of the developing sleeve 34a passes through the portion facing the agent regulating member 35 as indicated by an arrow B1 in FIG. It is scraped off by the member 35.

  An appropriate amount of the developer 32 that has passed through the portion facing the agent regulating member 35 passes through the developing area A between the developing sleeve 34a and the photosensitive member 1 as shown by an arrow B2 in FIG. , And flows to the bottom 33 b of the developing container 33 and is delivered to the collection conveyance path 38.

  That is, the developer 32 that is carried on the developing sleeve 34a, conveyed to the developing area A, passes through the developing area A, and remains on the developing sleeve 34a without being supplied to the surface of the photoreceptor 1 in the developing area A. Instead of being collected again in the supply conveyance path 37 with the rotation of the developing sleeve 34a, it is once collected in the collection conveyance path 38. Then, the collected developer 32 is conveyed while being agitated with the toner replenished in the collection conveyance path 38 and transferred to the supply conveyance path 37 again. For this reason, only the developer sufficiently stirred in the collection conveyance path 38 is always present in the supply conveyance path 37.

  The developer 32 that has reached the downstream end of the supply conveyance path 37 and the developer that has passed through the development region A and separated from the surface of the developing sleeve 34 a are conveyed by the collection conveyance path 38 and are upstream of the supply conveyance path 37. Is passed on. Since the developer 32 in the collection conveyance path 38 includes the developer 32 having passed through the development region A and having a lowered toner density, it is necessary to replenish the toner. Therefore, the toner is replenished to the developer 32 in the collection conveyance path 38 according to the toner consumption calculated from the image information of the latent image or according to the measurement result of the toner density of the developer in the collection conveyance path 38. Thus, the developer 32 having an appropriate toner concentration can be transferred to the supply conveyance path 37.

  FIG. 3 is a schematic diagram illustrating the flow of the developer 32 in the developing container 33 when the developing device 3 is viewed from the direction of arrow C in FIG. FIG. 4 is a cross-sectional explanatory view in the vicinity of the screw rotation axis when the developing device 3 is viewed from the direction of arrow C in FIG. The arrows in FIGS. 3 and 4 indicate the flow of the developer 32 in the developing container 33.

As shown in FIGS. 1, 3, and 4, the developing device 3 is configured such that the positional relationship between the supply conveyance path 37 and the collection conveyance path 38 is aligned vertically. For this reason, among the openings provided at both ends of the partition plate 36, development is performed from the downstream end of the supply conveyance path 37 to the upstream end of the collection conveyance path 38 at the drop opening 42 that is the opening on the right side in FIGS. The agent 32 moves from top to bottom.
On the other hand, of the openings provided at both ends of the partition plate 36, the developer 41 from the downstream end of the collection conveyance path 38 to the upstream end of the supply conveyance path 37 at the lifting opening 41, which is the opening on the left side in FIGS. 32 moves from bottom to top. The movement of the developer from the collection conveyance path 38 to the supply conveyance path 37 at the lifting port 41 is pushed up from below by the pressure of the developer 32 accumulated at the downstream end in the conveyance direction in the collection conveyance path 38. Developer is delivered.

  Further, the developing device 3 replenishes toner from the toner replenishing port 45 to the upstream side of the collection conveyance path 38 as indicated by an arrow T in FIGS. 3 and 4. The toner replenished in the developing container 33 by this toner replenishment can fall from the drop opening 42 to the upstream end portion in the transport direction of the recovery transport path 38 and supply the developer 32 in the recovery transport path 38 with toner. .

  In the developing device 3, not all of the developer 32 transferred from the recovery conveyance path 38 to the supply conveyance path 37 reaches the downstream end in the conveyance direction of the supply screw 39 in the supply conveyance path 37. As indicated by an arrow B in FIG. 3, there is a component that is supplied to the surface of the developing sleeve 34 a while being transported in the supply transport path 37, passes through the developing region A, and is recovered in the recovery transport path 38. To do. The delivery of the developer 32 to the surface of the developing sleeve 34a is performed over substantially the entire width of the developing sleeve 34a in the rotation axis direction.

  For this reason, the amount of the developer 32 that is transported with the transport force applied by the supply screw 39 in the supply transport path 37 is recovered from the surface of the developing sleeve 34a to the recovery transport path 38 as described above. As a result, there is a tendency to gradually decrease from the upstream end to the downstream end in the supply conveyance path 37.

  On the other hand, the amount of the developer 32 that is conveyed with the conveying force applied by the circulation screw 40 in the collection conveyance path 38 tends to gradually increase from the upstream end to the downstream end in the collection conveyance path 38. That is, there is a deviation in the distribution of the amount of the developer 32 in the developing device 3.

  In the developing device 3 according to the embodiment, the developer whose toner density is reduced by being supplied from the supply conveyance path 37 to the development sleeve 34 a and passing through the development area A is separated from the surface of the development sleeve 34 a at a position facing the recovery conveyance path 38. Then, it is collected in the collection conveyance path 38. The developer collected in the collection conveyance path 38 is agitated in the collection conveyance path 38 with the toner replenished at the upstream end in the conveyance direction in the collection conveyance path 38, and in a state where a desired toner concentration is obtained. It is supplied to the supply conveyance path 37. As described above, in the developing device 3 according to the first embodiment, the developer whose toner density has decreased after passing through the developing region A is not collected in the supply conveyance path 37, and thus is supplied on the upstream side and the downstream side in the conveyance direction by the supply screw 39. The toner density of the developer 32 in the transport path 37 does not change.

FIG. 5 is a schematic diagram for explaining the behavior of the developer around the developing roller.
The magnet roller built in the developing roller 34 of this embodiment includes magnets indicated by S1, N1, and N2, and magnetic poles P1, P2, and P3 are formed corresponding to the magnets. The P1 electrode (developing electrode) has a function of causing the developer in the developing area to rise and bringing the toner held by the carrier into contact with the photosensitive member. The P2 electrode (collection electrode) is responsible for the developer transport and developer separation functions. The P3 pole (pumping pole) has a function of holding the developer in the buffer section and a function of controlling the developer layer thickness by compressing the agent by the doctor 35 (see FIG. 2).

  In the developing device, toner easily scatters at a portion where the developer enters the developing case after passing through the developing region, and that portion (a portion where the sleeve and the opening end of the case face each other immediately downstream of the developing region). ) Easily accumulates toner. The toner accumulation portion is surrounded by a broken line in the figure and is shown as an ellipse. In the developing device of the present invention, the device is so formed that a developer retaining portion (indicated by an ellipse surrounded by a dotted line in the figure) is formed in the vicinity of the downstream side of the toner accumulation portion (near the downstream side in the developing roller rotation direction). It is composed.

  In the embodiment, the magnetic pole is set so that the position of the opening end of the developing container (developing case) 33 (the opening end of the developing case located below the developing roller 34) is located near the boundary between the P1 pole and the P2 pole. Is arranged (magnets indicated by S1 and N1 are arranged in the figure). Furthermore, the magnet N2 (magnet forming the P3 pole) is greatly separated from the magnet N1 (about 180 degrees at the central angle of the developing roller), and the magnetic flux density after the agent separation portion downstream of the P2 pole is reduced to hold the developer. It is configured so that there is no power to do.

  With such a configuration, the toner accumulation portion is located at the beginning of the P2 pole, and a developer retention portion is formed in the latter half of the P2 pole. That is, the developer retaining portion is formed adjacent to the toner accumulation portion at the opening end portion of the developing case and in the vicinity of the downstream side thereof. Then, by rotating the developing roller 34 (developing sleeve 34a) at an appropriate timing, the toner accumulated in the developer accumulating portion can be discharged out of the container by the developer accumulated in the developer accumulating portion. Become.

  In some conventional developing devices, the accumulated toner is discharged by reversing the developing roller (sleeve). However, even if the developing roller is simply reversed, if the developer does not touch it, it accumulates in the device. The toner could not be discharged out of the container. On the other hand, in the developing device of the present example, the developer staying portion is formed adjacent to the toner accumulation portion and in the vicinity of the downstream side as described above, so that the staying portion is kept at the time of reverse rotation of the developing roller. The accumulated toner can be effectively discharged out of the container by the staying developer.

The flow of the developer around the developing roller in the developing device of the embodiment will be further described with reference to FIG.
The developer sent from the supply screw 39 to the buffer unit is held in the buffer unit by the magnetic force of the P3 pole of the magnet roller built in the developing roller 34 and falls to the collection unit from between the developing roller 34 and the partition plate 36. There is nothing. For this reason, the developer in the buffer section is always conveyed to the developing area (the portion having the P1 pole).

  As described above, the magnetic flux density is small after the agent separation part on the P2 pole downstream side, and there is no force to hold the developer. For this reason, the developer stays in front of the out-of-agent portion. The gap between the developing roller 34 and the case under the roller is 1.2 mm, and the developer on the developing roller (the developer carried on the sleeve 34a) does not touch the lower case.

  Further, when the developing roller is reversely rotated, the developer retaining portion (developer staying in the developer) needs to move to the toner accumulation portion. In the configuration of this embodiment, when the developing roller 34 (sleeve 34a) is reversed by 30 degrees, the staying developer has an effect of pushing the accumulated toner (toner accumulated in the accumulation portion) out of the developing device.

  By the way, once the accumulated toner is discharged, the toner does not accumulate in the toner accumulation portion for a while. Therefore, it is not necessary to perform the reverse operation of the developing roller every time (a series of developing operations: each time a print job is performed once), and the reverse operation of the developing roller may be performed before the accumulated toner starts to fall in the image. The reverse operation of the developing roller is performed at the time of non-image formation after completion of the image forming operation. For example, an appropriate reverse operation is performed when a predetermined developing device driving time (driving time in the developing operation direction) elapses, or a reverse operation is performed when a predetermined number of prints are performed in the image forming apparatus. By performing the reverse operation at the timing, it is possible to discharge the accumulated toner and prevent an abnormal image due to toner dropping.

FIG. 6 is a schematic diagram for explaining the behavior of the developer around the developing roller in the developing device of the comparative example.
In this figure, the developing roller has five magnetic poles. In such a configuration, the toner accumulation portion (portion surrounded by a broken line in the drawing and indicated by an ellipse) formed in the vicinity of the container end is in the vicinity of the center of the P2 pole immediately downstream of the P1 pole as the development pole. positioned. In addition, a small magnetic pole P3 is formed in a portion facing the recovery screw on the P2 pole downstream side, and a developer retaining portion (portion surrounded by a dotted line in the drawing and shown in an ellipse shape) is formed in the P3 pole portion. ing. For this reason, the toner accumulation portion and the developer retention portion are far from each other, and even if the developing roller (sleeve) is reversed, the developer in the retention portion does not move to a portion where the accumulated toner is pushed out. Therefore, the configuration of FIG. 6 does not have a function of removing the accumulated toner. In addition, if the developing sleeve is reversed too much, the developer accumulates in front of the developing nip and the developer regulating member. If the developer accumulates in the development nip, the developer may fall. If the developer restricting member (doctor) accumulates, the accumulated developer cannot enter the developing nip at once, and the agent accumulates on the nip, and only that portion becomes an abnormal image (a hazy image).

  Further, since there is a deviation in the amount of the developer present in the collecting unit in the longitudinal direction of the collecting screw, the developer is clogged downstream in the developer conveying direction of the collecting unit, and the portion downstream of P2 pole in FIG. There is a place where the developer is clogged. For this reason, if the reversal is excessive, the developer on the downstream side of the collecting unit comes out of the developing case and falls. Therefore, the reverse rotation amount is about 40 deg at most, and the accumulated toner cannot be pushed out because the toner accumulation portion and the developer retention portion are separated.

FIG. 7 is a graph showing a toner drop occurrence rate in the developing device of the embodiment and the developing device of the comparative example described in FIG.
In this graph, the toner drop occurrence rate is represented by a bar graph with a diagonal line. In both the example and the comparative example, the toner drop occurrence rate is about 3% when the sleeve is not reversed, but in the comparative example. When the sleeve reversal is performed, the toner drop occurrence rate is about 2.5%, and only a slight effect is obtained. On the other hand, in the example, when the sleeve reverse rotation is performed, the toner drop occurrence rate is almost 0%, and a large toner drop improvement effect is obtained.

  As described so far, the developing device of the present invention is configured such that the developer retaining portion is formed in the vicinity of the downstream side of the developing case opening end (downstream of the developing roller rotation direction) below the developing roller. Therefore, by rotating the developing roller (sleeve) in the direction opposite to that during the developing operation, the accumulated toner (toner accumulated near the opening end of the case) is developed by the developer accumulated in the developer retaining portion. It can be pushed out of the case, and it is possible to prevent the occurrence of abnormal images such as toner dropping.

  Further, the magnet roller (magnetic field generating means) built in the developing roller includes a developing pole (P1 pole), a collecting pole (P2 pole) on the downstream side of the developing pole, and a pumping pole (P3 pole) on the upstream side of the developing pole. The magnetic pole has a magnetic flux density between the terminal end of the recovery pole (P2 pole) and the start end of the pumping pole (P3 pole), so that the developer is not retained. ) On the rear side (second half portion) of the toner), and the developer staying in the staying portion can be used for discharging the accumulated toner.

  Further, the position of the opening end of the developing case located below the developing roller is provided near the boundary between the developing electrode (P1 electrode) and the collecting electrode (P2 electrode). The toner accumulation portion formed near the opening end is located at the beginning of the collection electrode (P2 pole), and the developer retention portion is formed in the vicinity of the downstream side adjacent to the toner accumulation portion. The accumulated toner can be reliably discharged out of the case by the developer staying in the developer staying portion.

  In the image forming apparatus of this embodiment, the developing roller (sleeve) is reversely rotated during the non-image forming operation after the image forming operation is completed. When the toner accumulated in the toner accumulation portion is discharged out of the developing container due to the reverse rotation of the sleeve, there is a transfer portion below the developing device or the recording medium is conveyed below the developing device. When toner falls from the apparatus, a toner drop image is formed. Therefore, even if the discharged toner falls on the transfer unit or the conveying belt 15 (FIG. 1) by performing the reverse operation of the developing roller (sleeve) during the non-image forming operation after the image forming operation is completed. As the transport belt moves, the fallen toner is carried to a cleaning unit (cleaning means for cleaning the transport belt 15; not shown), so that no toner drop image is generated. In other words, when the toner is removed by performing the reverse operation of the developing roller (sleeve) during the non-image forming operation after the image forming operation is completed, if a toner drop image is generated during image formation Can be prevented.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. For example, the number and arrangement of the magnetic poles of the developing roller are examples, and are not limited to the examples. As the developer supply means and the recovery means, screws having appropriate configurations can be used. In addition, the configuration of each part of the developing device can be appropriately changed within the scope of the present invention.

  The configuration of the image forming apparatus is not limited to the tandem system, and any appropriate system can be employed. The present invention is applicable not only to the direct transfer system and the indirect transfer system. Further, the image forming apparatus is not limited to a full-color machine, and may be a multi-color machine or a monochrome apparatus having a plurality of colors. Of course, the image forming apparatus is not limited to a printer, and may be a copier, a facsimile machine, or a multifunction machine having a plurality of functions.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 3 Developing device 32 Developer 33 Developing container 34 Developing roller 34a Developing sleeve 34b Magnet roller 35 Agent regulating member 36 Partition plate 37 Supply conveyance path 38 Collection conveyance path 39 Supply screw 40 Collection screw 100 Printer

JP 2009-258276 A

Claims (7)

A developer carrying body containing a magnetic field generating means and carrying a two-component developer comprising a toner and a carrier on the surface;
A first conveying member that conveys the developer while supplying the developer to the developer carrying member;
A second conveying member that is disposed below the first conveying member and conveys the developer while collecting the developer from the developer carrying member;
In the developing device including the developer carrier, the first transport member, and the second transport member inside, and having a developing case that supports the developer carrier in an opening facing the development region,
The developer carrying member is provided so as to be rotatable in the direction opposite to that during the developing operation,
The developer on the developer carrier is not in contact with the open end of the developer case located below the developer carrier during the development operation,
From the opening end of the developing case located below the developer carrying member, a developer retaining portion is formed on the downstream side in the developer carrying member rotating direction during the developing operation ,
A developing device characterized in that when the toner is rotated in the direction opposite to that during the developing operation, the developer in the developer retaining portion pushes out the accumulated toner at the opening end portion . The magnetic field generating means includes a developing pole, the said collecting pole of the developer carrying member downstream side in the rotational direction of the developing operation of the developing pole, during the developing operation of the developing pole of the developer carrier rotating direction upstream side Each of the pumping poles has a magnetic pole, and has an agent separating portion that separates the developer from the developer carrier between the recovery pole and the pumping pole that is the same polarity as the recovery pole . The developing device according to claim 1. The developing device according to claim 2, wherein an opening end portion of the developing case located below the developer carrying member is provided in the vicinity of a magnetic flux density boundary between the developing electrode and the recovery electrode. .   An image forming apparatus comprising the developing device according to claim 1.   The image forming apparatus according to claim 4, wherein the rotation of the developer carrying member in a direction opposite to that during the developing operation is performed during non-image formation after the image forming operation. 6. The image forming apparatus according to claim 5, wherein the rotation of the developer carrying member in the direction opposite to that during the developing operation is performed when a predetermined developing drive operation time has elapsed in the developing device. .   6. The image forming apparatus according to claim 5, wherein the rotation of the developer carrying member in the direction opposite to that during the developing operation is performed when a predetermined number of prints are performed.

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