JP5046810B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device used for a copying machine, a facsimile, a printer, and the like, and more particularly to a developing device using a two-component developer composed of toner and a magnetic carrier and an image forming apparatus using the same.

  Conventionally, developing devices using a two-component developer composed of toner and a magnetic carrier have been widely used. In this developing device, an air flow generated on the surface of the developing roller as the developing roller rotates flows into the device through a gap between the developing roller and the casing on the downstream side of the developing region. The airflow that flows in increases the internal pressure because there is no escape in the device. When the internal pressure rises, an air flow that is jetted out of the apparatus from the gap between the developing roller and the casing on the downstream side of the developing region is generated due to a pressure difference with the external pressure. Due to the jetted airflow, toner having a weak electrostatic binding force by the carrier in the casing is jetted out of the casing, causing a problem of toner scattering.

  In order to prevent such toner scattering, the gap between the developing roller and the casing is narrowed. However, the gap cannot be eliminated, and the effect of suppressing the toner scattering is limited only by narrowing the gap. There is. Therefore, there has been proposed an apparatus that suppresses toner scattering by suppressing an increase in the internal pressure of the developing device that causes a jet air flow. For example, in Patent Document 1, an air flow path is formed so that air flowing from between the developing roller and the casing on the downstream side of the developing region is discharged out of the apparatus from an exhaust opening provided in the casing. What to do is described. Further, in Patent Document 2, the gap between the developing roller and the casing is narrowed at both ends of the developing roller where toner scattering is remarkable, and the gap between the developing roller and the casing is widened at the central portion of the developing roller to flow into the central portion. A device that suppresses an increase in internal pressure by reducing the flow velocity of the airflow is described.

JP 2005-346035 A JP 2006-113408 A

  By the way, in a conventional developing device using a two-component developer, a conveyance path for supplying a developer to a developing roller as a developer carrying member and a conveyance path for stirring the developer are provided separately, and two conveyance paths are provided. The developer is circulated by conveying the developer in the reverse direction. The developing roller carries the developer supplied by the magnetic force of the magnetic field generating means contained therein as a magnetic brush, and the developing roller is exposed from an opening provided in the casing so as to face the photosensitive member as a latent image carrier. The latent image on the photoreceptor is developed by transporting it to the developing area.

  However, in this developing apparatus, the conveyance path for supplying the developer to the developing roller and the conveyance path for collecting the developer that has been supplied to the developing roller and passed through the development region are common, and therefore the conveyance path for supplying the developing roller. There is a problem in that the toner concentration of the developer supplied to the developing roller decreases toward the downstream side in the transport direction. When the toner density supplied to the developing roller decreases, the image density during development also decreases.

  In order to solve such problems, a conveyance path for supplying the developer to the developing roller (hereinafter referred to as a supply conveyance path) and a conveyance path for collecting the developer that has passed through the development area from the developing roller (hereinafter referred to as collection conveyance). There is known a developing device provided with a separate path). In this developing device, the developed developer is collected in the collection conveyance path, so that it does not enter the supply conveyance path. Therefore, the toner density of the developer in the supply conveyance path does not change even on the downstream side, and the toner density of the developer supplied to the developing roller is also constant, resulting in uneven image density and reduced image density during development. Can be prevented.

  In a developing device provided with a separate collection conveyance path, an inflow air flow accompanying the rotation of the developing roller flows into the collection conveyance path on the downstream side of the development region, and an internal pressure rises. The developer is collected almost uniformly on the collection conveyance path. However, since the collected developer is conveyed from the upstream of the collection conveyance path to the downstream side, the developer on the downstream side is compared with the upstream side of the collection conveyance path. The dosage is increased. As a result, the gap in the collection conveyance path is wide on the upstream side and narrow on the downstream side, and the internal pressure due to the inflow airflow is likely to rise on the downstream side as compared with the upstream side. For this reason, it is easy to generate a blown air flow due to an increase in internal pressure on the downstream side in the transport direction of the recovery transport path, and toner scattering is likely to occur on the downstream side. Such a bias of an increase in internal pressure with respect to the transport direction of the recovery transport path is difficult to solve with the apparatus of Patent Document 1 or Patent Document 2.

  The present invention has been made in view of the above background. The object of the present invention is to use a two-component developer, a conveyance path for supplying the developer to the developer carrying member, and a developer that has passed through the development region. In the developing device separately provided with the transport path for collecting the toner from the developer carrier, the increase in the internal pressure of the device due to the rotation of the developer carrier can be suppressed from being biased in the developer transport direction, and toner scattering can be suppressed. A developing device and an image forming apparatus are provided.

In order to achieve the above object, the invention of claim 1 comprises a rotatable sleeve containing a magnetic field generating means having a plurality of magnetic poles, and carrying a two-component developer comprising a magnetic carrier and toner on the surface. A developer carrier that is transported to a portion facing the latent image carrier and develops the latent image on the latent image carrier, and an opening that exposes the developer carrier at a position facing the latent image carrier A developer casing having a portion, a developer supply transport path including a developer supply transport member that transports the developer along the axial direction of the developer carrier and supplies the developer to the developer carrier, The developer recovered from the developer carrier after passing through the portion facing the latent image carrier is along the axial direction of the developer carrier and in the same direction as the developer supply / conveying member. A developer recovery transport path with a developer recovery transport member that transports the And excess developer conveyed to the most downstream side in the transport direction of the developer supply conveyance path without being, conveyed from the developer carrying member to the lower stream side in the conveying direction of the collected developer collection conveyance path The supply with the collected developer is received, and the developer is conveyed along the axial direction of the developer carrier in the opposite direction to the developer supply and conveyance member while stirring the excess developer and the collected developer. In a developing device including a developer agitating / conveying member and a developer agitating / conveying path for supplying the developer to the developer supply / conveying path, the developer carrying body and the developer carrying body from the opening. gap between the developing casing in the downstream side in the rotational direction is one in which the lower stream side in respect developer conveying direction of the collected developer conveying path is equal to or greater than the upstream side.
According to a second aspect of the present invention, there is provided a rotatable sleeve containing a magnetic field generating means having a plurality of magnetic poles, and a two-component developer comprising a magnetic carrier and a toner is carried on the surface and the latent image carrier. A developer carrying member that is conveyed to the opposite portion of the latent image carrier and develops the latent image on the latent image carrier, and a developing casing having an opening that exposes the developer carrier at a position facing the latent image carrier. A developer supply transport path including a developer supply transport member that transports the developer along the axial direction of the developer support and supplies the developer to the developer support, and the latent image support; Developer recovery for transporting the developer recovered from the developer carrier after passing through the opposite part along the axial direction of the developer carrier and in the same direction as the developer supply transport member A developer recovery conveyance path provided with a conveyance member, and the developer supply without being used for development; Supply of excess developer transported to the most downstream side in the transport direction of the transport path and recovered developer recovered from the developer carrier and transported to the downstream side in the transport direction of the developer recovery transport path A developer agitating and conveying member that conveys in the direction opposite to the developer supply and conveying member while stirring the surplus developer and the recovered developer along the axial direction of the developer carrying member; In the developing device including the developer agitating / conveying path for supplying the developer to the developer supplying / conveying path, the developer carrying member, and a developing casing on the downstream side in the developer carrying member rotating direction with respect to the opening, Is characterized in that the side with a larger amount of developer is larger than the side with a smaller amount in the developer transport direction of the recovered developer transport path .
According to a third aspect of the present invention, in the developing device according to the first or second aspect , the developing casing on the downstream side in the rotation direction of the developer carrier relative to the opening has an arc shape concentric with the developer carrier. It is characterized by this.
According to a fourth aspect of the present invention, there is provided at least a latent image carrier, charging means for charging the surface of the latent image carrier, and formation of a latent image for forming an electrostatic latent image on the latent image carrier. And a developing device for developing the electrostatic latent image into a toner image, the developing device according to claim 1, 2 or 3 being used as the developing device. It is a feature.

  In the present invention, the size of the gap between the developing casing on the downstream side of the developing region and the developer carrying member is made different with respect to the developer carrying direction of the recovered developer carrying path, so that the gap enters the developing device. The flow velocity of the air flowing in can be made different with respect to the developer transport direction. As a result, even if there is a difference in the size of the gap in the collected developer conveyance path in the developer conveyance direction, the size of the gap is made different correspondingly, so that the flow velocity of the inflowing air current is increased. By providing the difference, it is possible to suppress the bias of the internal pressure increase due to the inflow airflow.

  According to the present invention, development using a two-component developer and separately providing a conveyance path for supplying the developer to the developer carrier and a conveyance path for collecting the developer that has passed through the development area from the developer carrier. In the apparatus, it is possible to suppress the increase in the internal pressure of the apparatus due to the rotation of the developer carrying member from being biased in the developer transport direction and to suppress toner scattering.

Hereinafter, as an image forming apparatus to which the present invention is applied, an embodiment of a tandem type color laser copying machine (hereinafter simply referred to as “copying machine”) in which a plurality of photoconductors are arranged in parallel will be described.
FIG. 1 is a schematic configuration diagram of a copying machine according to the present embodiment. The copier includes a printer unit 100, a paper feeding device 200 on which the printer unit 100 is placed, a scanner 300 fixed on the printer unit 100, and the like. An automatic document feeder 400 fixed on the scanner 300 is also provided.

  The printer unit 100 forms an image including four sets of process cartridges 18Y, 18M, 18C, and 18K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). A unit 20 is provided. Y, M, C, and K attached to the numbers of the respective symbols indicate members for yellow, cyan, magenta, and black (the same applies hereinafter). In addition to the process cartridges 18Y, 18M, 18C, and 18K, an optical writing unit 21, an intermediate transfer unit 17, a secondary transfer device 22, a registration roller pair 49, a fixing device 25, and the like are disposed.

  The process cartridges 18Y, 18M, 18C, and 18K include a drum-shaped photosensitive member 1, a charger, a developing device 4, a drum cleaning device, a static eliminator, and the like.

Hereinafter, the yellow process cartridge 18 will be described.
The surface of the photoreceptor 1Y is uniformly charged by a charger as charging means. The surface of the photoreceptor 1Y subjected to the charging process is irradiated with laser light by the optical writing unit 21, and an electrostatic latent image for Y is formed on the surface of the photoreceptor 1Y. The formed electrostatic latent image for Y is developed by the developing device 4Y as developing means to become a Y toner image. The Y toner image formed on the Y photoconductor 1Y is primarily transferred to an intermediate transfer belt 110 described later. The surface of the photoreceptor 1Y after the primary transfer is cleaned of the transfer residual toner by a drum cleaning device.
In the Y process cartridge 18Y, the photoconductor 1Y cleaned by the drum cleaning device is discharged by the charge eliminator. Then, it is uniformly charged by the charger and returns to the initial state. The series of processes as described above is the same for the other process cartridges (18M, C, K).

Next, the intermediate transfer unit will be described.
The intermediate transfer unit 17 includes an intermediate transfer belt 110, a belt cleaning device 90, primary transfer bias rollers 62Y, M, C, and K. The intermediate transfer belt 110 is endlessly moved clockwise in the drawing. The four primary transfer bias rollers 62Y, 62M, 62C, and 62K are disposed so as to be in contact with the inner peripheral surface side of the intermediate transfer belt 110, respectively, and receive primary transfer bias from a power source (not shown). Further, the intermediate transfer belt 110 is pressed toward the photoreceptors 1Y, 1M, 1C, and 1K from the inner peripheral surface side to form primary transfer nips. In each primary transfer nip, a primary transfer electric field is formed between the photosensitive member and the primary transfer bias roller due to the influence of the primary transfer bias.
The above-described Y toner image formed on the Y photoconductor 1Y is primarily transferred onto the intermediate transfer belt 110 due to the influence of the primary transfer electric field and nip pressure. On the Y toner image, the M, C, K toner images formed on the M, C, K photoconductors 1M, C, K are sequentially superposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) that is a multiple toner image is formed on the intermediate transfer belt 110.
The four-color toner image superimposed and transferred onto the intermediate transfer belt 110 is secondarily transferred onto a transfer sheet (not shown) as a recording sheet at a secondary transfer nip described later. Transfer residual toner remaining on the surface of the intermediate transfer belt 110 after passing through the secondary transfer nip is cleaned by a belt cleaning device 90 that sandwiches the belt with the driving roller 15 on the left side in the drawing.

Next, the secondary transfer device 22 will be described.
Below the intermediate transfer unit 17 in the figure, a secondary transfer device 22 is disposed in which a paper conveying belt 24 is stretched by two stretching rollers 23. The paper conveying belt 24 is moved endlessly counterclockwise in the drawing. One of the two stretching rollers 23 arranged on the right side in the drawing sandwiches the intermediate transfer belt 110 and the paper transport belt 24 between the secondary transfer backup roller 16 of the intermediate transfer unit 17. It is out. By this sandwiching, a secondary transfer nip is formed in which the intermediate transfer belt 110 of the intermediate transfer unit 17 and the paper transport belt 24 of the secondary transfer device 22 are in contact with each other. A secondary transfer bias having a polarity opposite to that of the toner is applied to the one stretching roller 23 by a power source (not shown). By applying this secondary transfer bias, the four-color toner image on the intermediate transfer belt 110 of the intermediate transfer unit 17 is electrostatically moved from the belt side toward the one stretching roller 23 side in the secondary transfer nip. A next transfer electric field is formed. The transfer paper fed into the secondary transfer nip so as to synchronize with the four-color toner image on the intermediate transfer belt 110 by a registration roller pair 49 to be described later has four colors affected by the secondary transfer electric field and nip pressure. The toner image is secondarily transferred.

  In the paper feeding device 200 provided at the lower part of the copying machine main body, a plurality of paper feeding cassettes 44 in which a plurality of transfer sheets can be stacked and accommodated in a bundle of sheets are arranged so as to overlap in the vertical direction. Has been. The uppermost transfer paper is sent out from each paper feed cassette 44 toward the paper feed path 46.

  The paper feed path 46 that receives the transfer paper fed from the paper feed cassette 44 has a plurality of conveying roller pairs 47 and a registration roller pair 49 provided near the end in the path. Then, the transfer paper is conveyed toward the registration roller pair 49. The transfer sheet conveyed toward the registration roller pair 49 is sandwiched between the rollers of the registration roller pair 49. On the other hand, in the intermediate transfer unit 17, the four-color toner image formed on the intermediate transfer belt 110 enters the secondary transfer nip as the belt moves endlessly. The registration roller pair 49 sends out the transfer paper sandwiched between the rollers at a timing at which the transfer paper can be brought into close contact with the four-color toner image at the secondary transfer nip. Thereby, in the secondary transfer nip, the four-color toner image on the intermediate transfer belt 110 is in close contact with the transfer paper. Then, it is secondarily transferred onto the transfer paper and becomes a full color image on the white transfer paper. The transfer paper on which the full-color image is formed in this manner exits the secondary transfer nip as the paper transport belt 24 moves endlessly, and then is sent from the paper transport belt 24 to the fixing device 25. The fixing device 25 sandwiches the transfer paper received from the paper transport belt 24 and fixes the full-color image on the transfer paper by heat and pressure.

  Next, the four process cartridges 18 (Y, M, C, K) will be described. The four process cartridges 18 (Y, M, C, K) have substantially the same configuration except that the colors of the toners to be handled are different from each other. The description is omitted. The surface of the photoreceptor 1 is charged by a charging device (not shown) while rotating in the direction of the arrow in the drawing. The charged surface of the photoreceptor 1 is supplied with toner from the developing device 4 to a latent image on which an electrostatic latent image is formed by laser light emitted from an exposure device (not shown), thereby forming a toner image.

  Next, the developing device 4 will be described. FIG. 2 is a schematic configuration diagram of the developing device. The developing device 4 supplies a toner to the latent image on the surface of the photoreceptor 1 while moving in the direction of arrow b in FIG. 2, and as a developer carrier for developing, a magnet roller as a magnetic field generating means having a plurality of magnetic poles The developing roller 5 includes a rotatable developing sleeve that encloses the toner. Further, a supply conveyance path 9 having a supply screw 8 as a developer supply conveyance member that conveys the developer in the depth direction of FIG. 2 while supplying the developer to the developing roller 5 is provided. A developing doctor 12 as a developer regulating member for regulating the developer supplied to the developing roller 5 to a thickness suitable for development is provided on the downstream side of the surface moving direction from the portion facing the supply screw 8 of the developing roller 5. ing. The developing roller 5 carries the developer supplied by the supply screw 8 as a magnetic brush by magnetic force, and conveys it by rotation. In the middle of the developer, the layer thickness is regulated by the developing doctor 12 to an appropriate layer thickness. At a position facing the photoreceptor 1, the developing roller 5 is exposed from an opening provided in the developing casing 13 to form a developing region. In this development area, the main pole of the magnet roller is disposed. By this magnetic field, a magnetic brush is formed with a two-component developer, and toner is supplied from the magnetic brush onto the photoreceptor 1 to develop the latent image. Further, on the downstream side of the development area, a recovery screw 6 is provided as a developer recovery transport member that recovers the developed developer that has passed through the development area and transports the recovered developer in the same direction as the supply screw 8. In addition, it has a collection conveyance path 7. In the developing device of FIG. 2, the supply conveyance path 9 is juxtaposed in the lateral direction of the development roller 5, and the collection conveyance path 7 is juxtaposed below the development roller 5. Further, a stirring conveyance path 10 which is a developer agitation conveyance path is provided below the supply conveyance path 9 in parallel with the collection conveyance path 7. The agitating and conveying path 10 includes an agitating screw 11 as a developer agitating and conveying member that conveys the developer to the front side in the figure, which is in the opposite direction to the supply screw 8 while agitating the developer.

  The supply conveyance path 9, the agitation conveyance path 10, and the collection conveyance path 7 are each partitioned by a partition member. In addition, the partition member which partitions the supply conveyance path 9 and the agitation conveyance path 10 has openings at the front side and the back side in the drawing, and the supply conveyance path 9 and the agitation conveyance path 10 communicate with each other. ing. Further, the partition member that partitions the supply conveyance path 9 and the collection conveyance path 7 is not provided with an opening. In addition, the partition member that divides the agitation conveyance path 10 and the collection conveyance path 7 has an opening on the front side in the figure, and the agitation conveyance path 10 and the collection conveyance path 7 communicate with each other.

  On the developing roller 5, the developer whose layer thickness is regulated by the developing doctor 12 is conveyed to the developing area and development is performed. The developer after development is collected in the collection conveyance path 7, conveyed to the front side of the cross section in FIG. 2, and the developer is supplied to the agitation conveyance path 10 through the opening of the partition member provided in the non-image area portion. Be transported. The toner is supplied to the stirring and conveying path 10 from a toner replenishing port provided on the upper side of the stirring and conveying path 10 in the vicinity of the opening of the partition member on the upstream side in the developer conveying direction in the stirring and conveying path 10.

  Next, the circulation of the developer in the three developer conveyance paths will be described. Note that arrows d1, d2, d3, and d4 in FIG. 2 indicate the flow of the developer in the developing device 4.

  In the supply conveyance path 9 that has received the developer supply (arrow d1 in FIG. 2) from the agitation conveyance path 10, while supplying the developer to the developing roller 5 (arrow d2 in FIG. 2), the supply screw 8 is downstream in the conveyance direction. Transport developer to the side. Then, the excess developer that is supplied to the developing roller 5 and is not used for development and transported to the downstream end in the transport direction of the supply transport path 9 is supplied to the stirring transport path 10 from the opening of the partition member. Further, the collected developer fed from the developing roller 5 to the collection conveyance path 7 (arrow d3 in FIG. 2) and conveyed to the downstream end in the conveyance direction of the collection conveyance path 7 by the collection screw 6 is stirred and conveyed from the opening of the partition member. It is supplied to the path 10 (arrow d4 in FIG. 2). The agitating and conveying path 10 agitates the supplied surplus developer and the recovered developer, conveys the agitating screw 11 to the downstream side in the conveying direction, and conveys it to the upstream side in the conveying direction of the supplying screw 8, and opens the partition member. Is supplied to the supply conveyance path 9 (arrow d1 in FIG. 2).

  In the agitating and conveying path 10, the agitating screw 11 agitates and conveys the collected developer, the surplus developer, and the toner replenished as necessary in the transfer unit in the direction opposite to the developer in the collecting and conveying path 7 and the supply conveying path 9. . Then, the agitated developer is transferred to the upstream side in the conveyance direction of the supply conveyance path 9 communicating with the downstream side in the conveyance direction. A toner concentration sensor (not shown) is provided below the agitation transport path 10, and a toner supply control device (not shown) is operated by the sensor output to supply toner from a toner storage portion (not shown).

  In the developing device 4 shown in FIG. 2, a supply conveyance path 9 and a recovery conveyance path 7 are provided, and developer supply and collection are performed in different developer conveyance paths, so that the developed developer is supplied to the supply conveyance path 9. There is no contamination. Accordingly, it is possible to prevent the toner density of the developer supplied to the developing roller 5 from decreasing toward the downstream side of the supply conveyance path 9 in the conveyance direction. Further, since the recovery conveyance path 7 and the agitation conveyance path 10 are provided and the developer recovery and agitation are performed in different developer conveyance paths, the developed developer does not fall during the agitation. Therefore, since the sufficiently agitated developer is supplied to the supply conveyance path 9, it is possible to prevent the developer supplied to the agent supply conveyance path 9 from being insufficiently agitated. In this way, the toner density of the developer in the supply conveyance path 9 can be prevented from decreasing, and the developer in the supply conveyance path 9 can be prevented from being insufficiently stirred. Can be constant.

  Here, as a reference example, FIG. 7 shows a schematic configuration diagram of a conventional general developing device, and FIG. 8 shows a magnetic force distribution diagram of a developing roller employed in a conventional general developing device. The conventional developing apparatus includes a supply conveyance path that accommodates a supply screw 3 that supplies the developer to the developing roller 5 while conveying the developer, and an agitation conveyance path that accommodates an agitation screw 4 that agitates and conveys the developer. The developer is circulated by conveying the developer in the reverse direction on the conveyance path. The developing device shown in FIG. 7 is different from the developing device shown in FIG. 2 in that the position of the developing doctor 12 is reversed and the rotation direction of the developing roller 5 is accordingly reversed. Will not change. In this developing device, the supply conveyance path for supplying the developer to the development roller 5 also functions as a collection conveyance path for collecting the developer supplied to the development roller 5 and passed through the development region. There is a problem in that the toner concentration of the developer supplied to the developing roller 5 decreases toward the downstream side in the conveying direction of the supply conveying path. When the density of toner supplied to the developing roller decreases, the image density during development also decreases.

Next, the characteristic part of this embodiment is demonstrated.
FIG. 3 is an enlarged view of the vicinity of the developing roller and the developing casing end on the downstream side of the developing region. When the developing roller 5 rotates (arrow direction b in FIG. 3), an air flow is generated on the surface of the developing roller with the rotation. On the downstream side of the developing region, as shown in FIG. 4, the generated airflow flows into the gap between the developing roller 5 and the developing casing 13 (arrow A in FIG. 4). This flowing airflow increases the internal pressure because there is no escape in the apparatus. When the internal pressure rises, a jet airflow is generated which is jetted out of the apparatus from the gap between the developing roller 5 and the developing casing 13 on the downstream side of the developing region due to a pressure difference with the external pressure. Due to the jetted airflow, toner having a weak electrostatic binding force from the carrier in the casing is jetted out of the casing, causing a problem of toner scattering. In the developing device in which the collection conveyance path 7 of this embodiment is provided separately, an inflow air flow accompanying the rotation of the developing roller 5 flows into the collection conveyance path 7 on the downstream side of the development region, and an internal pressure rises.

  5A and 5B show the amount of developer and the size of the gap in the recovery conveyance path. FIG. 5A is a view showing the state on the upstream side of the recovery conveyance path, and FIG. In the recovery conveyance path 7, the developer is recovered almost uniformly, but since the recovered developer is conveyed from the upstream side of the recovery conveyance path 7 to the downstream side, the downstream side compared to the upstream side of the recovery conveyance path 7 The amount of developer increases. As a result, the gap 15 in the collection conveyance path is wide on the upstream side and narrow on the downstream side. For this reason, the internal pressure due to the inflow airflow is likely to increase on the downstream side compared to the upstream side.

  Therefore, in the present embodiment, the gap between the developing roller 5 and the developing casing 13 on the downstream side of the developing region is made different between the downstream side and the upstream side. 6A and 6B show the gap between the developing roller 5 and the developing casing 13 on the downstream side of the developing region, where FIG. 6A shows the upstream side of the recovery conveyance path, and FIG. 6B shows the downstream side of the recovery conveyance path. As shown in FIG. 6, the gap h2 between the developing roller 5 and the developing casing 13 on the downstream side of the collection conveyance path is made larger than the gap h1 on the upstream side. As a result, the flow velocity of the airflow flowing into the developing device 4 can be reduced on the downstream side compared to the upstream side, and the gap 15 in the downstream collection conveyance path 7 is smaller than that on the upstream side. Moreover, it can suppress that the internal pressure of the downstream in the collection conveyance path 7 becomes high easily. Therefore, it is possible to suppress the generation of an air flow from the gap between the developing roller 5 and the developing casing 13 on the downstream side in the transport direction of the collection transport path 7 on the downstream side of the developing region, and to suppress toner scattering. .

  Further, the shape of the developing casing 13 on the downstream side of the developing region is preferably an arc shape that is concentric with the developing roller 5. As a result, the gap between the developer and the developing casing 13 can be made constant throughout the transport direction of the collection transport path 7, and toner scattering can be suppressed throughout the longitudinal direction.

As described above, according to the present embodiment, in the developing device having the supply conveyance path 9 as the developer supply conveyance path and the recovery conveyance path 7 as the developer collection conveyance path, the development roller 5 and the development casing on the downstream side of the development region. The size of the gap with respect to 13 is made different with respect to the developer transport direction of the collection transport path 7. Thereby, the flow velocity of the airflow flowing into the developing device from the gap can be made different with respect to the developer transport direction. Therefore, even if there is a difference in the size of the gap in the collection conveyance path 7 with respect to the developer conveyance direction, the difference in the flow velocity of the inflowing airflow can be made by changing the size of the gap correspondingly. By providing, it is possible to suppress the uneven increase in the internal pressure of the developing device due to the flowing airflow.
Further, since the collected developer is transported from the upstream side of the recovery transport path 7 toward the downstream side, the amount of developer on the downstream side is larger than the upstream side of the recovery transport path 7. As a result, the gap 15 in the collection conveyance path 7 is wide on the upstream side and narrow on the downstream side. For this reason, the internal pressure due to the inflow airflow is likely to increase on the downstream side compared to the upstream side.
Accordingly, by increasing the gap on the downstream side in the developer conveyance direction of the collection conveyance path 7 from the upstream side, the flow velocity of the airflow flowing into the developing device can be made smaller on the downstream side than on the upstream side. Therefore, even if the gap 15 in the downstream collection conveyance path 7 is smaller than that on the upstream side, it is possible to prevent the internal pressure on the downstream side in the collection conveyance path 7 from being easily increased.
Further, by making the gap larger on the side of the collection transport path 7 where the amount of developer is larger than on the side where the amount of developer is small, the flow velocity of the airflow flowing into the developing device can be made smaller on the downstream side than on the upstream side. Therefore, even if the amount of developer in the downstream collection conveyance path 7 is larger than that on the upstream side, it is possible to suppress the downstream internal pressure in the collection conveyance path 7 from being easily increased.
Further, the shape of the developing casing 13 on the downstream side of the developing region is an arc shape that is concentric with the developing roller 5, so that the gap between the developer and the developing casing 13 is made constant in the entire conveyance direction of the collection conveyance path 7. Can do. Therefore, toner scattering in the entire longitudinal direction can be suppressed.

1 is a schematic configuration diagram of a copier according to an embodiment. FIG. 2 is a schematic configuration diagram of a developing device of the present embodiment. FIG. 3 is an enlarged view of the development area downstream side. Explanatory drawing of the inflow airflow which generate | occur | produces in the development area downstream. 3A and 3B show the amount of developer and the size of a gap in the recovery conveyance path, where FIG. 4A shows the state on the upstream side of the recovery conveyance path, and FIG. FIG. 3A shows a gap between the developing roller and the developing casing on the downstream side of the developing region, and FIG. 4A shows the upstream side of the recovery conveyance path, and FIG. Schematic configuration diagram of a conventional developing device Explanatory drawing of magnetic force distribution of the conventional image development apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 4 Developing device 5 Developing roller 6 Collection screw 7 Collection conveyance path 8 Supply screw 9 Supply conveyance path 10 Stirring conveyance path 11 Stirring screw 12 Developing doctor 13 Developing casing
14 Developer 17 Intermediate transfer unit 18 Process cartridge 21 Optical writing unit

Claims (4)

It comprises a rotatable sleeve containing a magnetic field generating means having a plurality of magnetic poles, carries a two-component developer comprising a magnetic carrier and toner on the surface and conveys it to the opposite part of the latent image carrier, A developer carrier for developing a latent image on the image carrier;
A developing casing having an opening that exposes the developer carrier at a position facing the latent image carrier;
A developer supply transport path including a developer supply transport member that transports the developer along the axial direction of the developer support and supplies the developer to the developer support;
The developer recovered from the developer carrier after passing through the portion facing the latent image carrier is along the axial direction of the developer carrier and in the same direction as the developer supply / conveying member. A developer recovery transport path including a developer recovery transport member for transporting
And excess developer conveyed to the most downstream side in the transport direction of the developer supply conveyance path without being used for development, to the lower stream side in the transport direction of the recovered from the developer carrying member the developer collection conveyance path Receiving supply of the collected developer that has been conveyed, along the axial direction of the developer carrier, and in the direction opposite to the developer supply and conveying member while stirring the excess developer and the collected developer A developer agitating and conveying member that conveys the developer to the developer supplying and conveying path, and a developer agitating and conveying path that supplies the developer to the developer supply and conveying path;
The gap between the developer carrying member and the developing casing on the downstream side in the developer carrying member rotation direction from the opening is such that the downstream side in the developer carrying direction of the recovered developer carrying path is larger than the upstream side. Developing device . It comprises a rotatable sleeve containing a magnetic field generating means having a plurality of magnetic poles, carries a two-component developer comprising a magnetic carrier and toner on the surface and conveys it to the opposite part of the latent image carrier, A developer carrier for developing a latent image on the image carrier;
A developing casing having an opening that exposes the developer carrier at a position facing the latent image carrier;
A developer supply transport path including a developer supply transport member that transports the developer along the axial direction of the developer support and supplies the developer to the developer support;
The developer recovered from the developer carrier after passing through the portion facing the latent image carrier is along the axial direction of the developer carrier and in the same direction as the developer supply / conveying member. A developer recovery transport path including a developer recovery transport member for transporting
Excess developer transported to the most downstream side in the transport direction of the developer supply transport path without being used for development, and transported to the downstream side in the transport direction of the developer recovery transport path recovered from the developer carrier In response to the supply of the collected developer, the developer is conveyed in the direction opposite to the developer supply / conveyance member along the axial direction of the developer carrier and while stirring the excess developer and the collected developer. In a developing device including a developer agitating and conveying member for conveying, and a developer agitating and conveying path for supplying the developer to the developer supply and conveying path,
The gap between the developer carrying member and the developing casing on the downstream side in the developer carrying member rotation direction with respect to the opening is larger than the side where the developer amount is larger in the developer carrying direction of the recovered developer carrying path. A developing device. 3. The developing device according to claim 1, wherein the developing casing downstream of the opening in the direction of rotation of the developer carrier has an arc shape that is concentric with the developer carrier. 4. At least a latent image carrier, a charging unit for charging the surface of the latent image carrier, a latent image forming unit for forming an electrostatic latent image on the latent image carrier, and the electrostatic latent image In an image forming apparatus having a developing means for developing and forming a toner image,
As the developing means, the image forming apparatus, which comprises using one of the developing apparatus according to claim 1, 2 or 3.

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