JP2018169568A - Developing device and image forming apparatus - Google Patents

Abstract

A configuration capable of sufficiently suppressing scattering of a developer is provided. A developing container (41B) has an outer cover (47B) and an inner cover (48B). The outer cover (47B) is arranged downstream of the facing area (A) in the rotational direction (R) and covers the developing sleeve (44) through a gap. In the outer cover 47B, a third facing portion 47Bd that faces the photosensitive drum 1 with a gap is formed downstream of the facing area A in the rotation direction of the photosensitive drum 1. The gap between the third facing portion 47Bd and the photosensitive drum 1 is smaller in the end region in the longitudinal direction than in the central region in the longitudinal direction. The inner cover 48B is disposed with a gap between the outer cover 47B and the developing sleeve 44, and covers the developing sleeve 44. A part of the inner cover 48B faces a part of the outer cover 47B in the rotation direction R with a gap therebetween. The rotation direction downstream end 48Bb of the inner cover 48B is located downstream of the upstream minimum value of the pair of minimum values related to the rotation direction R of the absolute value of the magnetic flux density distribution of the peeling magnetic pole. [Selection] Figure 12

Description

  The present invention relates to a developing device provided with a developer carrying member that carries and rotates a developer, and a copier, a printer, a facsimile, and a multi-function device equipped with such a function. The present invention relates to an image forming apparatus.

  An image forming apparatus using an electrophotographic system or an electrostatic recording system has a developing device that develops an electrostatic latent image formed on a photosensitive drum as an image carrier with a developer such as toner. The developing device has a developing sleeve as a developer carrying member that carries and rotates the developer, and the developer carried on the developing sleeve is placed on a photosensitive drum arranged with a gap (gap) from the developing sleeve. I am trying to supply.

  In the case of such a developing device, the air pressure in the developing container rises as air flows into the developing container constituting the developing device by the rotation of the developing sleeve from the gap with the photosensitive drum, and the developer in the developing container May fly out of the container through the gap with the photosensitive drum. Therefore, an inner cover is provided between the outer cover of the developing container and the developing sleeve, and air flowing into the developing container through the developing sleeve and the inner cover is allowed to flow between the inner cover and the outer cover. A configuration has been proposed in which the toner is discharged out of the developing container through the gap (Patent Document 1).

Japanese Patent Laying-Open No. 2015-72331

  However, in the case of the configuration described in Patent Document 1, the air containing the developer passes through the inflow path between the developing sleeve that allows air to flow into the developing container and the inner cover in the direction opposite to the inflow direction. May be discharged out of the developing container through the gap between the developing sleeve and the photosensitive drum. Therefore, there is a possibility that the scattering of the developer cannot be sufficiently suppressed.

  An object of this invention is to provide the structure which can fully suppress the scattering of the developer to the exterior of a developing container.

  The developing device according to the present invention has a developing container in which a developer is accommodated and a developer carrying region capable of carrying the developer, and carries and rotates the developer in the developing container and rotates the image carrying A developer carrying member capable of transporting the developer to a facing region facing the body, a first magnetic pole disposed downstream of the facing region with respect to a rotation direction of the developer carrying member, and downstream of the first magnetic pole. A developer having a first magnetic pole and a second magnetic pole that are adjacent to each other and disposed inside the developer carrier, the developer carried on the developer carrier by the first magnetic pole. Magnetic flux generating means for generating magnetic flux to be peeled off from the developer carrier, and the developer container is disposed downstream of the facing region in the rotation direction and covers the developer carrier via a gap. Between the first cover and the first cover and the developer carrier Between the first covering portion and the developer carrying member so that a gap is provided between the first covering portion and the developer carrying member, and a part of the first covering portion is disposed between the first covering portion and the rotation direction via the gap. Oppositely, the rotation direction downstream end is positioned downstream of the upstream minimum value of the pair of minimum values with respect to the rotation direction of the absolute value of the magnetic flux density distribution of the first magnetic pole. A second covering portion covering the developer carrying member, wherein the first covering portion is located upstream of the rotation direction upstream of a portion of the second covering portion facing the upstream end in the rotation direction. A first facing portion facing the body, a second facing portion facing a portion between the upstream end and the downstream end of the second covering portion with respect to the rotation direction, and an upstream end of the first facing portion, Opposite the image carrier with a gap on the downstream side in the rotation direction of the image carrier from the facing region A third opposing portion, and the third opposing portion includes a part of the developer carrying region located on both end sides of the developer carrying body with respect to a rotation axis direction of the developer carrying body. An end region and a central region closer to the center than the end region, so that a gap between the end region and the image carrier is smaller than a gap between the central region and the image carrier. It is characterized by being formed.

  The developing device according to the present invention has a developing container in which a developer is accommodated and a developer carrying region capable of carrying the developer, and carries and rotates the developer in the developing container and rotates the image carrying A developer carrying member capable of transporting the developer to a facing region facing the body, a first magnetic pole disposed downstream of the facing region with respect to a rotation direction of the developer carrying member, and downstream of the first magnetic pole. A developer having a first magnetic pole and a second magnetic pole that are adjacent to each other and disposed inside the developer carrier, the developer carried on the developer carrier by the first magnetic pole. Magnetic flux generating means for generating magnetic flux to be peeled off from the developer carrier, and the developer container is disposed downstream of the facing region in the rotation direction and covers the developer carrier via a gap. Between the first cover and the first cover and the developer carrier Between the first covering portion and the developer carrying member so that a gap is provided between the first covering portion and the developer carrying member, and a part of the first covering portion is disposed between the first covering portion and the rotation direction via the gap. Oppositely, the rotation direction downstream end is positioned downstream of the upstream minimum value of the pair of minimum values with respect to the rotation direction of the absolute value of the magnetic flux density distribution of the first magnetic pole. A second covering portion covering the developer carrying member, wherein the first covering portion is located upstream of the rotation direction upstream of a portion of the second covering portion facing the upstream end in the rotation direction. A first facing portion facing the body, a second facing portion facing a portion between the upstream end and the downstream end of the second covering portion with respect to the rotation direction, and an upstream end of the first facing portion, Opposite the image carrier with a gap on the downstream side in the rotation direction of the image carrier from the facing region A third opposing portion, and the third opposing portion includes a part of the developer carrying region located on both end sides of the developer carrying body with respect to a rotation axis direction of the developer carrying body. An end region, and a central region closer to the center than the end region, and a rotational direction length of the image carrier in the end region is larger than a rotational direction length of the image carrier in the central region. It is formed so that it may become long.

  According to the present invention, the scattering of the developer outside the developing container can be sufficiently suppressed.

1 is a schematic sectional view of an image forming apparatus according to a first embodiment. FIG. 2 is a schematic cross-sectional view of an image forming unit according to the first embodiment. 1 is a schematic cross-sectional view of a developing device according to a first embodiment. 1 is a schematic longitudinal sectional view of a developing device according to a first embodiment. 1 is a schematic cross-sectional view of a replenishing device and a developing device according to a first embodiment. Sectional drawing which shows typically the airflow of the developing device which concerns on a comparative example. FIG. 3 is a cross-sectional view around the developing sleeve of the developing device according to the first embodiment. FIG. 3 is a cross-sectional view schematically showing an air flow around a developing sleeve of the developing device according to the first embodiment. FIG. 3 is a cross-sectional view schematically showing an air flow around a combined flow path of the developing device according to the first embodiment. The graph which shows the result of a comparative experiment. Sectional drawing around the developing sleeve of the developing device according to the second embodiment. Sectional drawing around the developing sleeve of the developing device according to the third embodiment. FIG. 10 is a top view of a schematic configuration of a developing device according to a third embodiment. Sectional drawing which shows the magnetic seal structure of an image development sleeve edge part. Sectional drawing around the developing sleeve of the developing device according to the fourth embodiment.

<First Embodiment>
A first embodiment will be described with reference to FIGS. 1 to 10. First, a schematic configuration of the image forming apparatus according to the present exemplary embodiment will be described with reference to FIGS. 1 and 2.

[Image forming apparatus]
The image forming apparatus 100 of this embodiment is an electrophotographic tandem full-color printer including four image forming units PY, PM, PC, and PK each having a photosensitive drum 1 as an image carrier. The image forming apparatus 100 receives a toner image (image) in response to an image signal from a document reading apparatus (not shown) connected to the apparatus main body 100A or a host device such as a personal computer connected to the apparatus main body 100A. ) On the recording material. Examples of the recording material include sheet materials such as paper, plastic film, and cloth. The image forming units PY, PM, PC, and PK form yellow, magenta, cyan, and black toner images, respectively.

  The four image forming units PY, PM, PC, and PK included in the image forming apparatus 100 have substantially the same configuration except that the development colors are different. Therefore, the image forming unit PY will be described as a representative, and description of the other image forming units will be omitted.

  As shown in FIG. 2, the image forming unit PY is provided with a cylindrical photosensitive member, that is, a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotationally driven in the arrow direction in the figure. Around the photosensitive drum 1, a charging roller 2 as a charging unit, a developing device 4, a primary transfer roller 52 as a transfer unit, and a cleaning device 7 as a cleaning unit are arranged. An exposure device (a laser scanner in the present embodiment) 3 as an exposure unit is disposed below the photosensitive drum 1 in the drawing.

  A transfer device 5 is disposed above each image forming unit in FIG. The transfer device 5 is configured such that an endless intermediate transfer belt 51 as an intermediate transfer member is stretched around a plurality of rollers, and rotates (rotates) in an arrow direction. The intermediate transfer belt 51 carries and conveys the toner image primarily transferred to the intermediate transfer belt 51 as will be described later. Out of the rollers that stretch the intermediate transfer belt 51, a secondary transfer outer roller 54 as a secondary transfer means is disposed at a position facing the secondary transfer inner roller 53 and the intermediate transfer belt 51 across the intermediate transfer belt 51. A secondary transfer portion T2 is configured to transfer the toner image on the belt 51 to the recording material. A fixing device 6 is disposed downstream of the secondary transfer portion T2 in the recording material conveyance direction.

  Under the image forming apparatus 100, a cassette 9 in which the recording material S is accommodated is disposed. The recording material S fed from the cassette 9 is transported toward the registration roller 92 by the transport roller 91. Then, the leading edge of the recording material S comes into contact with the registration roller 92 in the stopped state, and a skew is formed to correct the skew of the recording material S. Thereafter, the registration roller 92 starts to rotate in synchronization with the toner image on the intermediate transfer belt 51, and the recording material S is conveyed to the secondary transfer portion T2.

  A process for forming, for example, a four-color full-color image by the image forming apparatus 100 configured as described above will be described. First, when the image forming operation starts, the surface of the rotating photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the photosensitive drum 1 is exposed with a laser beam corresponding to an image signal emitted from the exposure device 3. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 1. The electrostatic latent image on the photosensitive drum 1 is visualized by a toner as a developer accommodated in the developing device 4 and becomes a visible image.

  The toner image formed on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 51 at a primary transfer portion T1 (FIG. 2) configured with the primary transfer roller 52 disposed with the intermediate transfer belt 51 interposed therebetween. Transcribed. At this time, a primary transfer bias is applied to the primary transfer roller 52. The toner remaining on the surface of the photosensitive drum 1 after the primary transfer (transfer residual toner) is removed by the cleaning device 7.

  Such an operation is sequentially performed in each of the yellow, magenta, cyan, and black image forming units, and the four color toner images are superimposed on the intermediate transfer belt 51. Thereafter, the recording material S accommodated in the cassette 9 is conveyed to the secondary transfer portion T2 in accordance with the toner image formation timing. Then, by applying a secondary transfer bias to the secondary transfer outer roller 54, the four color toner images on the intermediate transfer belt 51 are secondarily transferred onto the recording material S at once. The toner remaining on the intermediate transfer belt 51 without being completely transferred at the secondary transfer portion T2 is removed by the intermediate transfer belt cleaner 55.

  Next, the recording material S is conveyed to a fixing device 6 as a fixing unit. The fixing device 6 includes a fixing roller 61 having a heat source such as a halogen heater and a pressure roller 62 inside, and the fixing roller 61 and the pressure roller 62 form a fixing nip portion. By passing the recording material S on which the toner image has been transferred through the fixing nip portion of the fixing device 6, the recording material S is heated and pressurized. The toner on the recording material S is melted and mixed to be fixed on the recording material S as a full-color image. Thereafter, the recording material S is discharged to the discharge tray 102 by the discharge roller 101. This completes a series of image forming processes.

  Note that the image forming apparatus 100 according to the present embodiment forms a single-color or multi-color image using an image forming unit for a desired single color or some of four colors, such as a black single-color image. Is also possible.

[Developer]
Next, a detailed configuration of the developing device 4 will be described with reference to FIGS. 3 and 4. The developing device 4 includes a developing container 41 that stores a developer containing non-magnetic toner and a magnetic carrier, and a developing sleeve 44 that serves as a developer carrying member that carries and rotates the developer in the developing container. In the developing container 41, conveying screws 43a and 43b are arranged as developer conveying members that circulate in the developing container while stirring and conveying the developer in the developing container. A magnet 44a as a magnetic flux generating means having a plurality of magnetic poles in the circumferential direction is disposed in the developing sleeve 44 so as not to rotate. Further, a developing blade 42 as a regulating member for forming a thin layer of developer on the surface of the developing sleeve 44 is disposed.

  The inside of the developing container 41 is divided into a developing chamber 41a and a stirring chamber 41b horizontally by a partition wall 41c extending in a direction perpendicular to the paper surface, and the developer is divided into the developing chamber 41a and the stirring chamber. 41b. Conveying screws 43a and 43b are disposed in the developing chamber 41a and the stirring chamber 41b, respectively. At both ends in the longitudinal direction of the partition wall 41c (both ends in the rotational axis direction of the developing sleeve 44, the left side and the right side in FIG. 4), a delivery unit 41d that allows the developer to pass between the developing chamber 41a and the stirring chamber 41b, 41e is provided.

  Each of the conveying screws 43a and 43b is formed by providing a spiral blade as a conveying unit around the axis (rotation axis) of the magnetic body. In addition to the spiral blades, the conveying screw 43b is provided with a stirring rib 43b1 protruding in the radial direction from the shaft and having a predetermined width in the developer conveying direction. The stirring rib 43b1 stirs the developer as the shaft rotates.

  The conveying screw 43a is disposed along the rotational axis direction of the developing sleeve 44 at the bottom of the developing chamber 41a. The developer in the developing chamber 41a is fed along the axial direction by rotating the rotating shaft by a motor (not shown). The developer is supplied to the developing sleeve 44 while being conveyed. The developer carried on the developing sleeve 44 and having consumed the toner in the developing process is collected in the developing chamber 41a.

  The conveying screw 43b is disposed along the rotational axis direction of the developing sleeve 44 at the bottom of the stirring chamber 41b, and conveys the developer in the stirring chamber 41b along the axial direction opposite to the conveying screw 43a. In this way, the developer is transported by the transport screws 43a and 43b, and circulates in the developing container 41 via the delivery portions 41d and 41e.

  A developer replenishing port 46 for replenishing developer containing toner in the developing container 41 is provided at the upstream end of the agitating chamber 41b in the conveying direction of the conveying screw 43b. The developer replenishing port 46 is connected to a replenishment conveyance unit 83 of a developer replenishing device 80 shown in FIG. Accordingly, the replenishing developer is supplied from the developer replenishing device 80 into the agitating chamber 41 b via the replenishing conveyance unit 83 and the developer replenishing port 46. The conveying screw 43b conveys the developer replenished from the developer replenishing port 46 and the developer already in the agitating chamber 41b while agitating to uniformize the toner density.

  Therefore, the developer in the developing chamber 41a in which the toner is consumed in the developing process due to the conveying force of the conveying screws 43a and 43b and the toner concentration is reduced is transferred to the stirring chamber via one delivery portion 41d (left side in FIG. 4). Move into 41b. Then, the developer that has moved into the agitating chamber 41b is conveyed while being agitated with the replenished developer, and moves to the developing chamber 41a via the other delivery portion 41e (right side in FIG. 4).

  In the developing chamber 41a of the developing container 41, there is an opening 41h at a position corresponding to a facing area (developing area) A facing the photosensitive drum 1, and the developing sleeve 44 partially extends in the direction of the photosensitive drum 1 in the opening 41h. It is rotatably arranged so as to be exposed. On the other hand, the magnet 44a included in the developing sleeve 44 is fixed in a non-rotating manner. Such a developing sleeve 44 is rotated by a motor (not shown) so that the developer can be conveyed to the facing area A, and the developer is supplied to the photosensitive drum 1 in the facing area A. In the present embodiment, the developing sleeve 44 is formed in a cylindrical shape using, for example, aluminum or stainless steel as a nonmagnetic material. Further, the developing sleeve 44 rotates from the lower side to the upper side in the gravity direction in the facing region A, that is, in the counterclockwise direction of FIG.

  A developing blade 42 as a regulating member for regulating the amount of developer carried on the developing sleeve 44 is fixed on the upstream side of the opening 41 h in the rotation direction of the developing sleeve 44. In the present embodiment, since the developing sleeve 44 rotates from the lower side to the upper side in the gravitational direction in the facing area A, the developing blade 42 is positioned below the facing area A in the gravitational direction.

  As shown in FIG. 3, the magnet 44a has a total of five poles of a plurality of magnetic poles S1, S2, S3, N1, and N2 in the circumferential direction, and is formed in a roller shape. The developer in the developing chamber 41a is supplied to the developing sleeve 44 by the conveying screw 43a, and the developer supplied to the developing sleeve 44 is predetermined on the developing sleeve 44 by a magnetic field generated by the magnetic pole S2 for attracting the magnet 44a. Is carried to form a developer reservoir.

  When the developing sleeve 44 rotates, the developer on the developing sleeve 44 passes through the developer pool, rises at the regulating magnetic pole N1, and has a layer thickness by the developing blade 42 facing the regulating magnetic pole N1. Be regulated. Then, the developer whose layer thickness is regulated is conveyed to the facing area A facing the photosensitive drum 1 and spikes at the developing magnetic pole S1 to form magnetic spikes. The magnetic spike contacts the photosensitive drum 1 that rotates in the same direction as the developing sleeve 44 in the facing area A, and the electrostatic latent image is developed as a toner image by the charged toner.

  Thereafter, the developer on the developing sleeve 44 is conveyed into the developing container 41 by the rotation of the developing sleeve 44 while maintaining the adsorption of the developer to the surface of the developing sleeve 44 by the conveying magnetic pole N2. The developer carried on the developing sleeve 44 is peeled off from the surface of the developing sleeve 44 by the peeling magnetic pole S3 and collected in the developing chamber 41a of the developing container 41.

  As shown in FIG. 4, the developing container 41 is provided with an inductance sensor 45 as a toner concentration sensor that detects the toner density in the developing container 41. In the present embodiment, the inductance sensor 45 is provided on the downstream side of the stirring chamber 41b in the developer conveyance direction.

[Developer supply device]
Next, the developer supply device 80 will be described with reference to FIG. The developer supply device 80 includes a storage container 8 that stores a developer for supply, a supply mechanism 81, and a supply conveyance unit 83. The container 8 has a structure in which a spiral groove is dug in the inner wall of a cylindrical container, and the container 8 itself rotates to generate a developer conveying force in the longitudinal direction (rotation axis direction). Let A supply mechanism 81 is connected to the downstream end of the container 8 in the developer transport direction. The replenishment mechanism 81 has a pump part 81 a that discharges from a discharge port 82 through which developer is conveyed from the storage container 8. The pump portion 81 a is formed in a bellows shape, and is rotationally driven to change its volume and generate air pressure. The developer conveyed from the storage container 8 is discharged from the discharge port 82.

  The discharge port 82 is connected to the upper end of the replenishment transport unit 83, and the lower end of the replenishment transport unit 83 is connected to the developer replenishment port 46 of the developing device 4. That is, the replenishment conveyance unit 83 communicates the discharge port 82 with the developer replenishment port 46. Therefore, the developer discharged from the discharge port 82 by the pump unit 81 a is supplied into the developing container 41 of the developing device 4 through the supply conveyance unit 83.

  In the developing device 4 described above, the developer supply port 46 is located at the upstream end of the stirring chamber 41b in the developer transport direction and outside the developer circulation path formed by the developing chamber 41a and the stirring chamber 41b. Is provided. Specifically, the developer supply port 46 is provided on the upstream side in the developer transport direction of the stirring chamber 41b with respect to the one transfer portion 41d. Therefore, in the vicinity of the developer supply port 46, there is almost no developer in the developer circulation path, and only the supply developer passes.

  Such replenishment by the developer replenishing device 80 is performed by automatic toner replenishment control (hereinafter referred to as ATR (Automatic Toner Replenisher) control). In this ATR control, the operation of the developer supply device 80 is controlled in accordance with the density detection result of the patch image by the image sensor, the inductance sensor 45, and the density sensor 103 (FIG. 1) that detects the density of the toner image. Thus, the developer is supplied to the developing device 4.

  As shown in FIG. 1, the density sensor 103 faces the surface of the intermediate transfer belt 51 downstream of the most downstream image forming unit PK and upstream of the secondary transfer unit T2 in the rotation direction of the intermediate transfer belt 51. Are arranged. In the control using the density sensor 103, for example, a control toner image (patch image) is transferred onto the intermediate transfer belt 51 at the start of an image forming job or every time a predetermined number of images are formed. Thus, the density of the patch image is detected. Based on the detection result, developer replenishment control by the developer replenishing device 80 is performed.

  The configuration for supplying the developer to the developing device 4 is not limited to this configuration, and a conventionally known configuration may be used.

[Developer splash]
Here, the scattering of the developer generated from the developing device will be described. First, an image forming apparatus is required to increase the speed and quality of an output image and to simplify maintenance. One of the maintenance simplifications is reduction of contamination due to the developer inside the image forming apparatus. When the inside of the image forming apparatus is contaminated with the developer, an image defect such as a dirty output image may occur, or a cleaning operation may occur when the developing device or the photosensitive drum unit is replaced. Further, when the developer adheres to each drive system such as a gear, there is a possibility that the drive system may slip.

  One cause of such contamination by the developer inside the image forming apparatus is that the developer is scattered from the inside of the developing apparatus. For example, in the case of a two-component developer, since the toner and the carrier are usually frictionally charged inside the developing device, the toner and the carrier are adhered by electrostatic force. However, this adhesion is released by some impact, and there is a risk of the developer scattering, in which the toner released from the carrier is discharged together with air from the inside of the developing device.

  A specific example of such developer scattering will be described using a developing device 400 of a comparative example shown in FIG. The developing device 400 is the same as the developing device 4 described above except that the configuration of the developing container 401 is different. For this reason, the same code | symbol is attached | subjected and demonstrated to the same structure. Further, similarly to the developing device 4 described above, the replenishing conveyance unit 83 of the developer replenishing device 80 is connected to the developing device 400.

  The developing container 401 includes an upper lid 402 that covers the top of the developing sleeve 44. Between the upper lid 402 and the developing sleeve 44, an air flow path is formed in which air flows into the developing container 401 by the rotation of the developing sleeve 44. This flow path is opened at a position facing the photosensitive drum 1, and the scattering of the developer from the inside of the developing container 401 mainly occurs from this flow path. This is because the developing blade 42 is opposed to the developing sleeve 44 in the vicinity of the flow path (the lower side in FIG. 6). That is, at this position, the developer carried on the developing sleeve 44 is in a state where the layer thickness is regulated by the developing blade 42, and air does not easily flow out from the gap between the developing sleeve 44 and the developing blade 42. is there.

  Here, the scattering of the developer means that the developer such as free toner generated in the developer container 401 by stirring and transporting the developer or replenishing the developer is discharged to the outside of the developer container 401 through the opening of the flow path. This means that the developer container 401 cannot be fully collected.

  First, toner release will be described. The toner and the carrier stored in the developing container 401 are frictionally charged in the stirring chamber 41b and the developing chamber 41a, and are adhered to each other by the electrostatic adhesion force generated by the frictional charging and the non-electrostatic adhesion force generated by the surface property. Yes. When an impact or shear force is applied to the toner adhering to the carrier, the toner is peeled off from the carrier and released in the developing container 401. As the impact and shear force at this time, there is a developer behavior when the developer is conveyed by the developing sleeve 44.

  On the developing sleeve 44, the developer forms a magnetic spike having a chain-like structure along the magnetic field lines of the internal magnetic poles. The magnetic spike rises forward in the rotational direction immediately before the magnetic pole by the rotation of the developing sleeve 44, and falls forward in the rotational direction when passing over the magnetic pole. At this time, the rotation direction of the magnetic spike is the same as the rotation direction of the developing sleeve 44. The toner is released due to the toner being peeled off from the carrier by the impact and centrifugal force when the magnetic spike falls.

  The magnetic pole that greatly contributes to the release of the toner when the developer is conveyed by the developing sleeve 44 is a peeling magnetic pole S3 that generates a repulsive magnetic field with the attracting magnetic pole S2. In this peeling magnetic pole S3, in order to peel the developer from the developing sleeve 44, a magnetic force in the direction opposite to the rotation direction of the developing sleeve 44 is applied by the magnetic pole, the speed of the conveyed developer is reduced, and the developer is retained. . At this time, since the length of the magnetic spike becomes long, the impact and centrifugal force when the magnetic spike falls down tend to increase, and the amount of released toner tends to increase.

  Further, when the developer is supplied from the developer supply device 80 to the developer supply port 46, the developer that has swollen before being sufficiently agitated also causes free toner in the developer container 401. . The toner supplied to the developer supply port 46 is conveyed while being stirred with the developer already in the stirring chamber 41b. At this time, in the mixed region of the replenishment developer and the existing developer, the mixing ratio of the toner and the developer is temporarily increased. When the mixing ratio of the toner and the developer is high, the charge amount of the toner decreases, and the electrostatic adhesion force between the toner and the carrier decreases. The toner that could not be mixed with the developer is released as it is or by the impact of the developer stirring and transporting by the transport screws 43a and 43b, and the free toner rises in the developing container 401.

  Further, when the developer replenishing device 80 discharged by the air pressure generated by the pump unit 81a is used, the air pressure propagates through the replenishment transport unit 83 and air flows into the developing container 401 from the developer replenishing port 46. There is. The airflow that flows in at this time winds up the free toner in the developing container 401 at a portion where the mixing ratio of the toner and the developer near the developer supply port 46 is high. The air pressure propagation to the developing container 401 causes an unsteady rise in air pressure from the developer supply port 46 to the stirring chamber 41b. This increase in atmospheric pressure causes free toner to flow out of the developing container 401 as described later. In particular, the inflowing air due to such developer replenishment is one of the causes of the developer scattering at the end including the developer replenishing port 46 in the longitudinal direction of the developing container 401 (the rotational axis direction of the developing sleeve 44). Become one.

  Next, the airflow in and near the developing device 400 will be described with reference to FIG. The developing sleeve 44 and the photosensitive drum 1 generate airflow in the vicinity of the developing device 400. Each will be described here. First, due to the rotation of the developing sleeve 44 and the behavior of the magnetic spike on the magnetic pole, an air flow is generated in substantially the same direction as the rotating direction of the developing sleeve 44. The airflow generated in the substantially same direction as the rotation direction of the developing sleeve 44 takes air into the developing container 401 from the communication port inside the developing container 401 and the developing container 401. Further, air flows into the developing container 401 even when the developer is replenished.

Assuming that the developer container 401 is a substantially closed space, since air is a fluid, a continuous equation can be applied. Assuming that the flow velocity of air is v and the density is ρ, the following equation (1) holds because there is no air springing up in the developing container 401.

Further, considering the steady state, since the density ρ is approximately constant in each region in the developing container 401, the expression (1) can be expressed as the following expression (2).

From this equation (2), the flow rate ρv of air is preserved. In the longitudinal section in the vicinity of the developing device 400, the balance of the flow rate ρv is 0, and the same amount as the flow rate of air flowing in by the replenishment with the developing sleeve 44 is discharged out of the developing device 400. Here, the flow rate of air flowing into the developing container 401 as the developing sleeve 44 rotates through the communication port constituted by the upper lid 402 of the developing container 401 and the developing sleeve 44 is defined as Qa (sleeve inflow). Further, the air flow discharged from the communication port inside the developing container 401 and the outside of the developing container 401 passes through the upper lid 402 side so as to face the flow taken in from this communication port. The air flow rate discharged in this way is defined as Qb (sleeve discharge). Further, when the air flow rate that flows in along with replenishment to the developing device 400 is Qd (replenishment inflow), the relationship of the following equation (3) is established.
Qa (sleeve inflow) + Qd (replenishment inflow) = Qb (sleeve discharge) (3)

  The airflow taken in by the developing sleeve 44 and flowing along the developing sleeve 44 is folded back in the developing container 401 and discharged. At this time, when the air flow is folded back at the developer retaining portion of the peeling magnetic pole S3 including the developer peeled from the developing sleeve 44, the air flow causes the developer such as free toner generated in the developing container 401 to flow. It will go in the direction of discharge including many.

  There are mainly two processes in which the developer contained in the sleeve discharge air (flow rate Qb) is discharged out of the developing container 401. First, the sleeve discharge air (flow rate Qb) discharged out of the developing device 400 from the communication port is directly discharged from the gap between the upper lid 402 and the photosensitive drum 1. Secondly, the air discharged from the sleeve (flow rate Qb) is mixed with the developer carried on the developing sleeve 44 in the vicinity of the photosensitive drum 1, or the developer is generated by the rotation of the photosensitive drum 1 with inertial force. By moving to the airflow g, the airflow g is discharged.

  The scattering of the developer is discharged out of the developing container 401 due to at least one of the above two factors. The scattered developer contaminates the periphery of the developing device 400, the outer wall of the developing container 401, the photosensitive drum 1, the exposure device 3, and the transfer device 5.

[Configuration of Developer Container of this Embodiment]
Therefore, in the present embodiment, the configuration of the developing container 41 of the developing device 4 is as follows. A detailed configuration of the developing container 41 of the present embodiment will be described with reference to FIG. The angles θ1 to θ6 in the figure are based on a horizontal plane H passing through the center O of the developing sleeve 44, and a vertical segment (vertical plane) with respect to a line segment connecting the center O and the target position and the horizontal plane H passing through the center O. ) An angle formed by the horizontal plane H on the photosensitive drum 1 side with respect to P.

  A curve C shown around the developing sleeve 44 in FIG. 7 shows the distribution of the magnetic flux density of each magnetic pole of the magnet 44a. The rotation direction of the developing sleeve 44 is R. Of the magnetic poles of the magnet 44a, with respect to the rotational direction R, the peeling magnetic pole S3 disposed downstream of the facing area A is the first magnetic pole and is disposed adjacent to the downstream of the peeling magnetic pole S3. The attracting magnetic pole S2 having the same polarity as S3 corresponds to the second magnetic pole. In FIG. 7, the position of each magnetic pole is indicated by a line indicating the peak position of the magnetic flux density.

  The developing container 41 of the present embodiment has an upper lid 41f that covers the developing sleeve 44 on the downstream side in the rotation direction R of the developing sleeve 44 with respect to the facing area A. The upper lid 41f includes an outer cover 47 as a first cover part and an inner cover 48 as a second cover part. The outer cover 47 is disposed downstream of the facing area A with respect to the rotation direction R, and covers the developing sleeve 44 through a gap.

  The inner cover 48 is disposed between the outer cover 47 and the developing sleeve 44 so as to cover the developing sleeve 44 with a gap between the outer cover 47 and the developing sleeve 44. A part of the inner cover 48 faces a part of the outer cover 47 in the rotation direction R with a gap. In the present embodiment, the upstream end 48a in the rotation direction of the developing sleeve 44 of the inner cover 48 is opposed to a part of the outer cover 47 in the rotation direction R with a gap.

  In addition, the upstream end 48 a in the rotational direction of the inner cover 48 is located on the downstream side in the rotational direction R with respect to the vertical surface (vertical surface) P passing through the uppermost point in the vertical direction above the developing sleeve 44. That is, the upstream end 48 a of the inner cover 48 is positioned on the downstream side in the rotation direction R with respect to the top of the apex of the developing sleeve 44. In other words, the upstream end 48 a of the inner cover 48 is positioned on the inner side (downstream in the rotation direction R) of the developing container 41 with respect to the vertical plane P passing through the center O of the developing sleeve 44.

  The downstream end 48b in the rotation direction of the developing sleeve 44 of the inner cover 48 is higher than the upstream minimum value M1 of the pair of minimum values M1 and M2 with respect to the rotation direction R of the absolute value of the magnetic flux density distribution of the peeling magnetic pole S3. Located downstream.

  The downstream end 48b in the rotation direction of the inner cover 48 is located downstream of the upstream end W1 in the rotation direction of the developing sleeve 44 having the half width W of the magnetic flux density distribution of the peeling magnetic pole S3 or the upstream end W1 in the half width W. It is preferable to do. More preferably, the rotation direction downstream end 48b of the inner cover 48 is positioned on the downstream side in the rotation direction R from the peak position or peak position of the magnetic flux density of the separation magnetic pole S3. By disposing the position of the rotation direction downstream end 48b of the inner cover 48 at a position that satisfies these conditions, the range in which the peeling magnetic pole S3 is covered by the inner cover 48 can be made wider.

  However, it is preferable that the downstream end 48 b in the rotation direction of the inner cover 48 is positioned on the upstream side in the rotation direction R from the position of the horizontal plane H passing through the center O of the developing sleeve 44 or the position of the horizontal plane H. This is because if the downstream end 48b in the rotation direction of the inner cover 48 is located further downstream, it is difficult to take the developer peeled from the developing sleeve 44 into the developing chamber 41a. For this reason, in this embodiment, the rotation direction downstream end 48b of the inner cover 48 is positioned within the range of the half-value width W of the magnetic flux density distribution of the separation magnetic pole S3.

  This will be described more specifically. The outer cover 47 is formed to bend toward the photosensitive drum 1 so as to cover the developing sleeve 44 from the upper end of the side wall 41g opposite to the photosensitive drum 1 across the developing sleeve 44 of the developing container 41. The outer cover 47 includes a first facing portion 47a on the photosensitive drum 1 side, a second facing portion 47b on the side wall 41g side, a continuous portion 47c that connects the first facing portion 47a and the second facing portion 47b, and And a third facing portion 47d provided at the tip of the first facing portion 47a.

  The first facing portion 47 a faces the developing sleeve 44 on the upstream side in the rotational direction R of the developing sleeve 44 with respect to a part (continuous portion 47 c) facing the upstream end 48 a in the rotational direction of the inner cover 48. The second facing portion 47b faces the portion between the upstream end 48a and the downstream end 48b of the inner cover 48 in the rotation direction R.

  Since the inner cover 48 is disposed between the second facing portion 47 b and the developing sleeve 44, the second facing portion 47 b is disposed outside the first facing portion 47 a in the radial direction of the developing sleeve 44. For this reason, the continuous part 47c which continues the upstream end of the rotation direction R of the 2nd opposing part 47b and the downstream end of the rotation direction R of the 1st opposing part 47a is provided. The continuous portion 47c is formed to bend toward the developing sleeve 44 from the upstream end in the rotation direction R of the second facing portion 47b. And the continuous part 47c opposes the rotation direction upstream end 48a of the inner cover 48 in the rotation direction R through a gap.

  The third facing portion 47 d is formed so as to be bent from the upstream end in the rotation direction R of the first facing portion 47 a toward the radially outer side of the developing sleeve 44, and faces the surface of the photosensitive drum 1. The third facing portion 47d faces the photosensitive drum 1 with a gap in a predetermined range downstream of the facing area A in the rotation direction of the photosensitive drum 1. In the present embodiment, the third facing portion 47d is formed so that the length of the photosensitive drum 1 in the rotation direction is 3 mm or more and 10 mm or less. Further, the gap between the third facing portion 47d and the photosensitive drum is the same in both the rotational direction and the longitudinal direction of the photosensitive drum 1 (the rotational axis direction of the developing sleeve 44).

  Next, the angles θ1 to θ6 will be described. The angle θ1 is an angle from the horizontal plane H to the opening 41h of the developing container 41. That is, θ1 is an angle formed by the horizontal plane H and a line segment connecting the center O of the developing sleeve 44 and the upstream end of the first facing portion 47a of the outer cover 47 in the rotation direction R. The angle θ2 is an angle from the horizontal plane H to the downstream end in the rotation direction R of the first facing portion 47a. That is, θ2 is an angle formed by the horizontal plane H and the line segment connecting the center O of the developing sleeve 44 and the downstream end in the rotation direction R of the first facing portion 47a. Therefore, the range from the angle θ1 to θ2 is the first facing portion 47a.

  The angle θ3 is an angle from the horizontal plane H to the upstream end 48a in the rotation direction of the inner cover 48. That is, θ3 is an angle formed by the horizontal plane H and a line segment connecting the center O of the developing sleeve 44 and the upstream end 48a. The angle θ4 is an angle from the horizontal plane H to the downstream end 48b in the rotation direction of the inner cover 48. That is, θ4 is an angle formed by the horizontal plane H and a line segment connecting the center O of the developing sleeve 44 and the downstream end 48b. Therefore, the range from the angle θ3 to θ4 is the inner cover 48.

  The angle θ5 is an angle from the horizontal plane H to the peak position of the peeling magnetic pole S3. That is, θ5 is an angle formed by the horizontal plane H and the line segment connecting the center O of the developing sleeve 44 and the peak position of the peeling magnetic pole S3. The angle θ6 is an angle from the horizontal plane H to the peak position of the transfer magnetic pole N2 adjacent to the upstream side in the rotation direction R of the peeling magnetic pole S3. That is, θ6 is an angle formed by a line segment connecting the center O of the developing sleeve 44 and the peak position of the conveying magnetic pole N2 and the horizontal plane H.

  In the present embodiment, the relationship θ1 <θ6 <θ2 is satisfied. That is, the first facing portion 47a is formed so as to cover at least the peak position of the transport magnetic pole N2. In the present embodiment, the upstream end in the rotation direction R of the first facing portion 47a is in the vicinity of the upstream minimum value of the pair of minimum values related to the rotation direction R of the absolute value of the magnetic flux density distribution of the transport magnetic pole N2. Is located.

  Further, a relationship of θ2 <θ3 is satisfied, and a gap in which the above-described continuous portion 47c and the upstream end 48a of the inner cover 48 face each other is provided in this range. Further, the relationship θ3 <θ5 <θ4 is satisfied. That is, the inner cover 48 is formed so as to cover at least the peak position of the peeling magnetic pole S3. Further, θ3 is positioned downstream of the angle (90 °) formed by the vertical plane P and the horizontal plane H. The developing sleeve 44 has a cylindrical shape, and the vertical plane P passes through the apex (upper end position) of the developing sleeve 44. Accordingly, the upstream end 48 a of the inner cover 48 is positioned downstream in the rotation direction R from the apex of the developing sleeve 44.

  Here, the gap between the first facing portion 47a and the developing sleeve 44 (the gap in the region from the angle θ1 to θ2) is defined as a first gap (first flow path) F1. A gap between the inner cover 48 and the developing sleeve 44 (a gap in an area from the angle θ3 to θ4) is defined as a second gap (second flow path) F2. A gap between the second facing portion 47b and the inner cover 48 is defined as a third gap (third flow path) F3.

  Regarding the cross section perpendicular to the rotation direction R of the developing sleeve 44 (the radial cross section passing through the central axis of the developing sleeve 44), the minimum gap in the rotation direction R of the first gap F1 is L1, and the minimum cross-sectional area is A1. Similarly, the minimum gap in the rotation direction R of the second gap F2 is L2, the minimum cross-sectional area is A2, the minimum gap in the rotation direction R of the third gap F3 is L3, and the minimum cross-sectional area is A3.

  In the present embodiment, since the first facing portion 47a is formed along the peripheral surface of the developing sleeve 44, the gap and the cross-sectional area of the first gap F1 are substantially the same with respect to the rotation direction R. Further, since the inner cover 48 is also formed along the peripheral surface of the developing sleeve 44, the gap and the cross-sectional area of the second gap F2 are substantially the same with respect to the rotation direction R. On the other hand, with respect to the rotation direction R, the clearance and the cross-sectional area of the third clearance F3 gradually increase from the upstream side to the center side and gradually decrease from the center side to the downstream side.

  As described above, the continuous portion 47c that connects the second facing portion 47b and the first facing portion 47a faces the upstream end 48a of the inner cover 48 in the rotational direction R with a gap therebetween. In the present embodiment, a gap between the continuous portion 47c and the upstream end 48a and between the first gap F1, the second gap F2, and the third gap F3 in the rotation direction R (a region between angles θ2 and θ3). Is a fourth gap (joining flow path) F4. That is, the fourth gap F4 is a gap where the second gap F2 and the third gap F3 communicate with the first gap F1. Such a fourth gap F4 is formed such that a gap L4 related to a cross section perpendicular to the rotation direction R of the developing sleeve 44 becomes larger toward the downstream side in the rotation direction R.

  Further, a fifth gap (branch path) F5 is provided downstream of the inner cover 48 in the rotation direction downstream end 48b. The fifth gap F5 is a gap between the developing sleeve 44 and the outer cover 47 or the side wall 41g downstream of the second gap F2 and the third gap F3.

In the present embodiment, the above-described minimum gaps L1, L2, and L3 and minimum cross-sectional areas A1, A2, and A3 satisfy the following relationship.
A1 ≦ A2 + A3
A2 ≦ A3
L1 ≦ L2 + L3
L2 ≦ L3

[Air flow around the developing sleeve]
Next, the air flow (air flow) around the developing sleeve 44 will be described with reference to FIGS. In the present embodiment, as described above, by providing the first gap F1 to the fifth gap F5 around the developing sleeve 44, an airflow as shown in FIG. 8 is generated. First, in the vicinity of the developing sleeve 44 in the first gap F <b> 1, an air flow “a” is generated so as to be involved with the rotation of the developing sleeve 44, and air flows into the developing container 41. As air flows in, the internal pressure in the developing container 41 increases, and an air flow b is generated on the first facing portion 47a side of the first gap F1 so as to keep the internal pressure in an equilibrium state from the inside of the developing container 41 toward the outside of the apparatus. .

  Further, in the vicinity of the developing sleeve 44 in the second gap F2, an airflow c is generated along with the movement of the magnetic spikes at the peeling magnetic pole S3 (see FIG. 7), and the air taken into the developing container by the airflow c is an airflow. Back flow by d and air flow e. That is, the airflow c flowing downstream of the second gap F2 branches at the fifth gap F5 and flows back to the second gap F2 and the third gap F3, and the airflow d flows on the inner cover 48 side of the second gap F2. The air flow e is generated in the third gap F3.

  As described above, since a lot of toner is released when the magnetic spike falls at the separation magnetic pole S3, the air flow d in the second gap F2 contains a lot of free toner generated in this way. For this reason, in this embodiment, the downstream end 48b of the inner cover 48 is positioned downstream of the upstream minimum value M1 of the magnetic flux density distribution of the separation magnetic pole S3, thereby at least a part of the separation magnetic pole S3. Is covered with an inner cover 48 (see FIG. 7). In particular, in this embodiment, since the downstream end 48b of the inner cover 48 is positioned downstream of the peak position of the peeling magnetic pole S3, an area where free toner is generated when the magnetic spike is tilted by the peeling magnetic pole S3. Many can be covered by the inner cover 48.

  An inner cover 48 is provided between the developing sleeve 44 and the outer cover 47, a second gap F 2 is provided between the inner cover 48 and the developing sleeve 44, and a third gap is provided between the inner cover 48 and the outer cover 47. F3 is provided. Therefore, the airflow e that flows backward by the airflow c can be formed in the third gap F3. Since the third gap F3 is separated from the second gap F2 by the inner cover 48, the air flow e becomes air with a small amount of the released toner as described above.

  The upstream end 48a in the rotation direction of the inner cover 48 is opposed to the continuous portion 47c of the outer cover 47 in the rotation direction R via the fourth gap F4. For this reason, the airflow e passing through the third gap F3 merges with the airflow b in the first gap F1 via the fourth gap F4. At this time, as shown in FIG. 9, the airflow f flowing through the fourth gap F4 serving as the combined flow path becomes an air curtain, and the airflow d in the second gap F2 is easily returned to the flow of the airflow c. As a result, the air flow d containing a large amount of free toner becomes difficult to be discharged from the developing container 41, and scattering of the developer can be suppressed.

  In particular, in the present embodiment, the minimum cross-sectional area A1 of the first gap F1 is equal to or smaller than the sum of the minimum cross-sectional area A2 of the second gap F2 and the minimum cross-sectional area A3 of the third gap F3 (A1 ≦ A2 + A3). In the present embodiment, the first gap F <b> 1 to the fifth gap F <b> 5 are formed in substantially the same shape with respect to the rotation axis direction of the developing sleeve 44. For this reason, the above-mentioned relationship can be expressed as the minimum gap L1 of the first gap F1 being equal to or less than the sum of the minimum gap L2 of the second gap F2 and the minimum gap L3 of the third gap F3 (L1 ≦ L2 + L3). Even if the shape of each gap is different with respect to the rotation axis direction of the developing sleeve 44, the average of the gaps in the position where the radial gap in the developing sleeve 44 at that position is the smallest in the rotation direction R is the average. The minimum gap may be set.

  In any case, by satisfying the above-described conditions, an area where the upstream end 48a of the inner cover 48 and the continuous portion 47c face each other can be secured, and the effect of the air curtain by the airflow f can be enhanced. In order to enhance the effect of the air curtain, it is preferable to satisfy A1 <A2 + A3 (L1 <L2 + L3). However, even if A1 = A2 + A3 (L1 = L2 + L3), A1 <A2 + A3 + (cross-sectional area of the inner cover 48) or L1 <L2 + L3 + (thickness of the inner cover 48). And the area where the continuous portion 47c faces can be secured.

  Here, the portion of the inner cover 48 that faces the continuous portion 47c, which is a part of the outer cover 47, is not limited to the upstream end 48a. For example, even if the upstream end of the inner cover 48 in the rotation direction R is not opposed to a part of the outer cover 47 (for example, a position radially inward of a part of the outer cover 47), It suffices if a part of the upstream end on the downstream side in the rotational direction faces a part of the outer cover 47. However, in this case, the minimum gap of the second gap F2 between the inner cover 48 and the developing sleeve 44 may be smaller than the gap of the first gap F1. In consideration of the conveyance of the magnetic spike by the developing sleeve 44, it is not preferable that there is a portion where the gap of the second gap F2 becomes extremely small. For this reason, it is preferable that the upstream end 48 a of the inner cover 48 is configured to face a part of the outer cover 47.

  In the present embodiment, the minimum cross-sectional area A2 of the second gap F2 is set to be equal to or smaller than the minimum cross-sectional area A3 of the third gap F3 (A2 ≦ A3). Thereby, the pressure loss of the flow path of the 3rd clearance F3 is made smaller than the pressure loss of the flow path of the 2nd clearance F2. Then, the flow rate of the air flow e passing through the third gap F3 is increased, and the flow rate of the air flow d passing through the second gap F2 is decreased. As a result, the above-described air curtain effect can be more easily obtained, and more airflow e, which is air with less free toner, can flow through the discharge path than airflow d, which is air with more free toner. From the developer can be suppressed.

  In order to make the pressure loss of the flow path of the third gap F3 smaller than the pressure loss of the flow path of the second gap F2, it is preferable to satisfy A2 <A3. However, even if A2 = A3, the second gap F2 has an airflow c that opposes the airflow d as the developing sleeve 44 rotates, so the pressure loss in the flow path of the second gap F2 is the third gap. It becomes larger than the pressure loss of the flow path of F3.

  In order to satisfy such a relationship, the minimum gap L2 of the second gap F2 may be equal to or smaller than the minimum gap L3 of the third gap F3 (L2 ≦ L3). The reason is the same as described above for A2 ≦ A3. Also in this case, L2 <L3 is preferable, but L2 = L3 may be satisfied due to the presence of the air flow c as described above.

  However, if the minimum cross-sectional area A3 or the minimum gap L3 is too small, the flow of the airflow c that takes in the scattered toner into the developing container 41 may be hindered, and the flow rate of the airflow e may drop extremely. For this reason, it is preferable to set the minimum gap L2 to 1.5 mm to 3.0 mm and the minimum gap L3 to 2.0 mm to 3.5 mm.

  In the present embodiment, the fourth gap F4 is arranged so as not to overlap the peak position (angle θ6) of the transport magnetic pole N2. In other words, the second gap F4 is formed at a position deviating from the peak position of the transport magnetic pole N2 with respect to the rotation direction R, and in the present embodiment, is disposed downstream of the peak position in the rotation direction R. This is because if the peak position of the fourth gap F4 and the conveying magnetic pole N2 overlap, the scattered toner generated when the magnetic spike of the conveying magnetic pole N2 starts to fall is diffused by the air flow f, and the air curtain This is because the effect is reduced.

  Further, in the present embodiment, the upstream end 48 a of the inner cover 48 is positioned on the downstream side in the rotational direction R with respect to the vertical top of the developing sleeve 44. In other words, the upstream end 48 a of the inner cover 48 is positioned on the inner side of the developing container 41 with respect to the vertical plane P passing through the center O of the developing sleeve 44. The toner tends to adhere to the upper surface of the inner cover 48 and the upstream end 48a. For this reason, there is a possibility that the toner adhered for some reason may fall from the upstream end 48a. Here, if the adhered toner falls to the upstream side of the apex of the developing sleeve 44, the dropped toner may adhere to the photosensitive drum 1 and affect the image formed on the photosensitive drum 1.

  In contrast, in the present embodiment, the upstream end 48a of the inner cover 48 is positioned downstream of the developing sleeve 44 in the rotation direction R, so that the toner adhering to the inner cover 48 has an upstream end 48a. From the top of the developing sleeve 44 to the downstream side. Therefore, the dropped toner is taken into the developing container 41 as the developing sleeve 44 rotates, and it is possible to suppress the influence on the image formed on the photosensitive drum 1.

  In the case of this embodiment, a third facing portion 47 d that faces the photosensitive drum 1 in a predetermined range in the rotational direction of the photosensitive drum 1 is provided at the tip of the outer cover 47 on the photosensitive drum 1 side. A sixth gap (sixth flow path) F6 is formed between the third facing portion 47d and the photosensitive drum 1 along the rotational direction of the photosensitive drum 1. As shown in FIG. 8, an air flow g is generated in the sixth gap F <b> 6 as the photosensitive drum 1 rotates. The air flow g is a flow in a direction discharged from the sixth gap F6. On the other hand, in order to make the inflow and outflow of air in the sixth gap F6 equivalent to the sixth gap F6, an airflow h in the opposite direction to the airflow g flows from the outside air. The air flow h is rectified by the third facing portion 47d and flows into the developing container 41.

  If the third facing portion 47d is not provided, the airflow h can cause turbulence near the junction with the airflow b in the first gap F1. When a turbulent flow is generated in the vicinity of the confluence of the air flow h and the air flow b, the magnetic spikes of the developer formed on the developing sleeve 44 are disturbed and the toner can be released. As a result, the released toner is caught in the air flow b and the air flow g, and the free toner contained in the air flow b and the air flow g can be increased. The amount of free toner contained in the airflow b is limited by the magnetic spikes, and the amount of free toner contained in the airflow g that adheres to the photosensitive drum 1 is limited. Therefore, the developer is likely to be scattered outside the developing container 41 by the air flow b and the air flow g.

  In view of this point, in the present embodiment, the airflow h is rectified by the third facing portion 47d, thereby suppressing the scattering of the developer to the outside due to the airflow b or the airflow g. That is, when the air flow h is rectified, turbulence hardly occurs in the vicinity of the joining portion of the air flow h and the air flow b, and the free toner contained in the air flow b and the air flow g is difficult to increase. The rectified airflow h forms an air curtain in the vicinity of the junction of the airflow h and the airflow b. When the air curtain is formed in the vicinity of the merged portion of the airflow h and the airflow b, the airflow b is easily returned to the first gap F1 and easily joined with the airflow a. In other words, a part of the air current can circulate in the developing container 41. When the air flow b joins the air flow a, the air flow b is hardly discharged to the outside of the developing container 41. Further, a part of the air flow b that has not been circulated joins the air flow h, and the free toner contained in the air flow b is easily caught by the magnetic spikes formed on the developing sleeve 44 in the vicinity of the facing region A. Further, since a small amount of free toner adheres to the photosensitive drum 1 in the vicinity of the photosensitive drum 1 in the airflow g, the free toner contained in the airflow g hardly leaks to the outside.

  As described above, according to the configuration of the present embodiment, scattering of the developer can be sufficiently suppressed. Further, even if the developer scatters, the amount of scatter is small, so even if the developer adheres to the image, the amount of adhesion cannot be visually recognized, and it is possible to suppress degradation in image quality.

[Comparison experiment]
Next, in order to confirm the effect of the present embodiment, an experiment in which the amount of scattered toner is compared between the configuration of the comparative example and the configuration of the present embodiment will be described. First, an outline of the toner scattering amount measurement method employed in this experiment will be described with reference to FIG. The apparatus used in the experiment is the same as the apparatus except for the developing device, the photosensitive drum, and the exposure device around the photosensitive drum. In the experiment, as in normal image formation, the amount of toner scattering was measured in the following manner with the photosensitive drum rotating, charging, developing driving, and bias applied.

  In the region excluding both ends in the longitudinal direction of the developing device 4, the toner inside the device passes through the sixth gap F <b> 6 between the third opposing portion 47 d of the outer cover 47 facing the photosensitive drum 1 and the photosensitive drum 1. Spatter to the outside. Therefore, the line laser is applied to the approximate center in the longitudinal direction of the sixth gap F6 (in the rotational axis direction of the developing sleeve 44) so as to be perpendicular to the developing sleeve 44 and the photosensitive drum 1. A line laser is a laser that forms a fan-shaped two-dimensional plane optical path by irradiating in a line shape with a certain line width, and is usually created by scattering a dot laser in a certain direction by a cylindrical lens or a rod lens. . The scattered toner flying on the optical path of the line laser scatters the laser light. Therefore, by observing with a high speed camera or the like from a direction substantially perpendicular to the irradiation direction of the line laser, it is possible to measure the number and locus of scattered toner existing in the laser irradiation range.

  The line laser used was a YAG laser (DPGL-5W) manufactured by Nippon Laser Co., Ltd. as a light source. Then, an optical system using a cylindrical lens (attached to the product) was adjusted so that the line width was 0.5 mm in the sixth gap F6, and the laser was irradiated. For observation, a high speed camera SA-3 manufactured by Photoron Co., Ltd. was used. Also, the shooting conditions (frame rate and exposure time) of the high-speed camera and the optical system (lens, etc.) were selected so that the scattered toner on the line laser can be observed.

  The number of scattered toner passing through the longitudinal center of the sixth gap F6 obtained by the above method was converted to the number of scattered toner corresponding to one A4 sheet (210 mm × 297 mm) from the line width and observation time. Since the experimental apparatus is configured as described above, this conversion does not consider the contribution to the edge of the image area, the contribution of toner replenishment, and the influence of the air flow inside the image forming apparatus on the toner scattering.

  In the comparative experiment, the same L2 ≦ L3 configuration as in the above embodiment (Example 1), the configuration shown in FIG. 6 (Comparative Example 1), and the configuration in which L2> L3 unlike the embodiment (Comparative Example 2). The experiment apparatus was prepared and each experiment was performed under the above-mentioned conditions. In Example 1, L2 = 2 mm and L3 = 2.5 mm, and in Comparative Example 2, L2 = 2.5 mm and L3 = 2 mm. In Comparative Example 1, there was no inner cover, and the distance between the developing sleeve 44 and the upper lid 402 was 2.5 mm. Further, in Comparative Example 1, although there is no third facing portion 47d, the laser is irradiated to the substantially central portion in the longitudinal direction on the portion of the upper lid 402 facing the photosensitive drum 1. Other configurations are common to each other.

  The result of this experiment is shown in FIG. First, when Comparative Example 1 and Comparative Example 2 were compared, Comparative Example 2 had fewer scattered toners than Comparative Example 1. However, the number of scattered toners could not be reduced much compared to Comparative Example 1. This is because although the air flow e is generated in the third gap F3, the air flow d is also generated due to the pressure loss of the second gap F2 and the third gap F3, and the free toner is generated near the S3 pole. It is estimated that there is a large amount that is directly transported to the airflow g.

  Next, when Comparative Example 1 and Example 1 were compared, Example 1 was able to significantly reduce the number of scattered toner compared to Comparative Example 1. This is presumably because the airflow e is larger than the airflow d due to the pressure loss between the second gap F2 and the third gap F3, and the amount of scattered toner contained in the airflow g is relatively reduced. As described above, Example 1 which is the configuration of the present embodiment was able to greatly reduce toner scattering as compared with Comparative Examples 1 and 2.

<Second Embodiment>
A second embodiment will be described with reference to FIG. The meaning of each line in FIG. 11 is the same as that in FIG. In the first embodiment described above, the upstream end 48 a of the inner cover 48 is positioned on the downstream side in the rotation direction R with respect to the apex of the developing sleeve 44. On the other hand, in the developing device 4A of the present embodiment, the upstream end 48Aa of the inner cover 48A is positioned upstream of the apex of the developing sleeve 44 in the rotation direction R. Except for the configuration of the developing container 41A of the developing device 4A, the configuration is the same as that of the first embodiment. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted or simplified, and the following description will be focused on portions different from those in the first embodiment.

  The developing container 41A has an upper lid 41Af that covers the developing sleeve 44 on the downstream side in the rotation direction R of the developing sleeve 44 with respect to the facing area A. The upper lid 41Af has an outer cover 47A as a first cover portion and an inner cover 48A as a second cover portion. The outer cover 47A is disposed downstream of the facing area A with respect to the rotation direction R, and covers the developing sleeve 44 through a gap. The inner cover 48 </ b> A is disposed between the outer cover 47 </ b> A and the developing sleeve 44 so as to cover the developing sleeve 44 with a gap between the outer cover 47 </ b> A and the developing sleeve 44.

  The outer cover 47A has a first facing portion 47Aa on the photosensitive drum 1 side and a second facing portion 47Ab on the side wall 41g side. The first facing portion 47Aa faces the developing sleeve 44 on the upstream side in the rotational direction R of the developing sleeve 44 with respect to a part facing the upstream end 48Aa in the rotational direction of the inner cover 48A. The second facing portion 47Ab faces the portion between the upstream end 48Aa and the downstream end 48Ab of the inner cover 48A with respect to the rotation direction R.

  In the case of the present embodiment, the first facing portion 47Aa is formed so as to be bent from the end of the second facing portion 47Ab on the photosensitive drum 1 side to the developing sleeve 44 side, and the tip is interposed between the developing sleeve 44 and the first gap F1. Facing each other. Further, the side surface of the first facing portion 47Aa is opposed to the photosensitive drum 1 through the sixth gap F6 within a predetermined range in the rotational direction of the photosensitive drum 1.

  The upstream end 48Aa of the inner cover 48A is located upstream of the apex of the developing sleeve 44 in the rotational direction R, and in this embodiment, is located upstream of the peak position (angle θ6) of the transport magnetic pole N2. ing. On the other hand, the downstream end 48Ab of the inner cover 48A is at a position that substantially overlaps the peak position (angle θ5) of the peeling magnetic pole S3. The position of the downstream end 48Ab may be the same as in the first embodiment.

  In this embodiment, since the inner cover 48A covers the transport magnetic pole N2 beyond the peak position, scattering due to the toner released by the transport magnetic pole N2 can be reduced. The other requirements for each component are the same as those in the first embodiment.

  In this embodiment as well, a comparative experiment was performed as in the first embodiment. The result is shown in FIG. In Example 2 having the same configuration as that of the present embodiment shown in FIG. 11, the number of scattered toner was smaller than that in Example 1. This is the same mechanism as in the first embodiment, and the air flow including the free toner generated in the conveying magnetic pole N2 is also discharged around the third gap F3, so that the air flow g (see, for example, FIG. 8) is relatively. It is predicted that the amount of scattered toner contained in () is reduced.

<Third Embodiment>
A third embodiment will be described with reference to FIGS. 12 and 13. In the first embodiment described above, the gap between the third facing portion 47d of the outer cover 47 and the photosensitive drum 1 is the same in the longitudinal direction (the rotational axis direction of the developing sleeve 44). In contrast, in the case of the developing device 4B of the present embodiment, the gap between the third facing portion 47Bd of the outer cover 47B and the photosensitive drum 1 is made smaller in the longitudinal end region than in the longitudinal central region. . Except for the configuration of the developing container 41B of the developing device 4B, the configuration is the same as that of the first embodiment. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted or simplified, and the following description will be focused on portions different from those in the first embodiment.

  As illustrated in FIG. 12, the developing container 41 </ b> B includes an upper lid 41 </ b> Bf that covers the developing sleeve 44 on the downstream side in the rotation direction R of the developing sleeve 44 with respect to the facing area A. The upper lid 41Bf has an outer cover 47B as a first cover part and an inner cover 48B as a second cover part. The outer cover 47B is disposed downstream of the facing region A in the rotation direction R and covers the developing sleeve 44 through a gap. The inner cover 48B is disposed between the outer cover 47B and the developing sleeve 44 so as to cover the developing sleeve 44 with a gap between the outer cover 47B and the developing sleeve 44, respectively.

  The outer cover 47B includes a first facing portion 47Ba on the photosensitive drum 1 side, a second facing portion 47Bb, a continuous portion 47Bc that connects the first facing portion 47Ba and the second facing portion 47Bb, and the first facing portion 47Ba. And a third facing portion 47Bd provided at the tip. The first facing portion 47Ba faces the developing sleeve 44 on the upstream side in the rotational direction R of the developing sleeve 44 from a part (continuous portion 47Bc) facing the upstream end 48Ba in the rotational direction of the inner cover 48B. The second facing portion 47Bb faces the portion between the upstream end 48Ba and the downstream end 48Bb of the inner cover 48B with respect to the rotation direction R.

  The third facing portion 47Bd is formed so as to be bent from the upstream end in the rotation direction R of the first facing portion 47Ba toward the radially outer side of the developing sleeve 44, and faces the surface of the photosensitive drum 1. The third facing portion 47Bd faces the photosensitive drum 1 within a predetermined range in the rotational direction of the photosensitive drum 1 as described above.

  Here, in the vicinity of the longitudinal center of the photosensitive drum 1 and the developing sleeve 44, even if a small amount of toner floats, it adheres to the photosensitive drum 1 to the extent that it cannot be visually recognized on the image. On the other hand, at the end of the imageable area, which is the longitudinal end of the photosensitive drum 1 and the developing sleeve 44, or the outside thereof, the force of the toner adhering to the developing sleeve 44 is weak, so that the toner may be scattered outside. is there. Therefore, in the present embodiment, toner scattering near the end of the imageable area is reduced.

  As shown in FIG. 13, the imageable area of the developing sleeve 44 (developer carrying area that has been roughened so that the developer can be carried) is designated as B1. Then, in the third facing portion 47Bd, a region having a length in the longitudinal direction that is not less than half the length in the longitudinal direction of the imageable region B1 with the center in the longitudinal direction of the imageable region B1 as a center is defined as a central region B2. . Moreover, the area | region of the longitudinal direction both ends side of center area | region B2 is made into edge part area | region B3 among 3rd opposing part 47Bd. The end region B3 is a region located on both ends of the developing sleeve 44 including a part of the imageable region B1.

  The center region B2 and the end region B3 will be described using specific examples. Both ends of the developing sleeve 44 are sealed. As a seal structure for sealing both ends of the developing sleeve 44, a magnetic seal structure for magnetically blocking the outside and the inside of the developing container 41 (see FIG. 2) is used. FIG. 14 shows an example of the magnetic seal configuration. In the magnetic seal configuration shown in FIG. 14, the plate-like magnetic plate 11 and the magnet sheet 12 are rotated at the end 44b of the developing sleeve 44 that has not been subjected to the roughening treatment, that is, the developing sleeve 44 rotates more than the imageable region B1. The configuration is arranged outside in the axial direction (outside the developer carrying region).

  The magnetic plate 11 as a magnet member can form a magnetic spike by covering the developing sleeve 44 in a non-contact manner along the outer periphery of the developing sleeve 44. That is, since a magnetic force is generated between the magnetic plate 11 and the magnet 44a in the developing sleeve 44, the developer that has entered between the magnetic plate 11 and the developing sleeve 44 forms a magnetic spike. This magnetic spike closes the gap between the magnetic plate 11 and the developing sleeve 44 to prevent developer leakage from the sleeve end 44b. Further, the magnet sheet 12 is provided on the outer side of the developing sleeve 44 in the rotational axis direction than the magnetic plate 11. The magnet sheet 12 holds the developer leaking from between the magnetic plate 11 and the developing sleeve 44 by a magnetic force. By providing the magnetic plate 11 and the magnet sheet 12 in this way, developer leakage from the sleeve end 44b is suppressed.

  The central region B2 is formed so that both end portions are positioned at a distance of 10 mm or more and 30 mm or less from the position of the magnetic plate 11 to the center side, for example. In this way, the end region B3 can cover both ends of the imageable region B1. In the present embodiment, the longitudinal length of the central region B2 is 290 mm to 310 mm, and the longitudinal length of the end region B3 is 20 to 40 mm. In such a case, the end region B3 of the third facing portion 47Bd is closer to the photosensitive drum 1 than the central region B2. That is, when the gap between the end region B3 and the photosensitive drum 1 is L5, and the gap between the central region B2 and the photosensitive drum 1 is L6, the third facing portion 47Bd is formed so as to satisfy L5 <L6. . As an example, the gap L5 in the end region B3 is 2 mm to 4 mm, and the gap L6 in the central region B2 is 4 mm to 8 mm.

  Thereby, the inflow / outflow of the airflow g and the airflow h in the center region B2 in the sixth gap F6 is larger than the inflow / outflow of the airflow g2 and the airflow h2 in the end region B3. For this reason, toner scattering in the end region B3 is reduced, and image defects and in-machine contamination due to toner scattering in the image forming apparatus can be reduced. Other requirements for each component are the same as those in the first embodiment.

<Fourth Embodiment>
A fourth embodiment will be described with reference to FIG. In the third embodiment described above, the gap between the third facing portion 47Bd of the outer cover 47B and the photosensitive drum 1 is made smaller in the longitudinal end region than in the longitudinal central region. In contrast, in the case of the developing device 4C of this embodiment, the length of the third opposing portion 47Cd of the outer cover 47C in the rotation direction of the photosensitive drum 1 is set to be longer in the longitudinal end region than in the longitudinal central region. ing. Except for the configuration of the third facing portion 47Cd, the third embodiment is the same as the third embodiment. Hereinafter, the same components as those in the third embodiment are denoted by the same reference numerals, description thereof will be omitted or simplified, and the following description will be focused on portions that are different from those in the third embodiment.

  The developing container 41 </ b> C has an upper lid 41 </ b> Cf that covers the developing sleeve 44 on the downstream side in the rotation direction R of the developing sleeve 44 with respect to the facing area A. The upper lid 41Cf has an outer cover 47C as a first cover portion and an inner cover 48B as a second cover portion. The outer cover 47C has a third facing portion 47Cd provided at the tip of the first facing portion 47Ba. The third facing portion 47Cd is formed so as to be bent from the upstream end in the rotation direction R of the first facing portion 47Ba toward the radially outer side of the developing sleeve 44, and faces the surface of the photosensitive drum 1.

  In the present embodiment, a portion corresponding to the end region B3 (FIG. 12) of the third facing portion 47Cd is a first region 471, and a portion corresponding to the central region B2 (FIG. 12) is a second region 472. The length of the first region 471 in the rotation direction of the photosensitive drum 1 is longer than the length of the second region 472 in the rotation direction of the photosensitive drum 1. That is, when the length of the first region 471 is L7 and the length of the second region 472 is L8, the third facing portion 47Cd is formed so as to satisfy L7> L8. As an example, the length L8 of the second region 472 is 3 mm to 6 mm, and the length L7 of the first region 471 is 7 mm to 10 mm.

  Thereby, the inflow / outflow of the airflow g and the airflow h in the second region 472 in the sixth gap F6 is larger than the inflow / outflow of the airflow g3 and the airflow h3 in the first region 471. For this reason, toner scattering in the end region B3 provided with the first region 471 is reduced, and image defects and in-machine contamination due to toner scattering in the image forming apparatus can be reduced. Other requirements for each component are the same as those in the first embodiment.

<Other embodiments>
In each of the above-described embodiments, the configuration using the two-component developer including toner and carrier as the developing device has been described. However, the present invention can be applied to a configuration having the above-described peeling magnetic pole, even when using a one-component developer containing magnetic toner. In addition, the configurations of the above-described embodiments can be implemented in combination as appropriate. For example, the configuration of the third embodiment and the configuration of the fourth embodiment may be combined. That is, the length in the rotation direction of the photosensitive drum 1 in the end region B3 of the third facing portion 47Bd in the third embodiment may be longer than the length in the rotation direction of the photosensitive drum 1 in the central region B2. Moreover, you may combine the combination of these 3rd, 4th embodiment, or 3rd Embodiment or 4th Embodiment with the structure of 2nd Embodiment.

  Further, the present invention separates the function of supplying and recovering the developer in addition to the configuration of supplying the developer to the developing sleeve and recovering the developer from the developing sleeve in the developing chamber as described above. The present invention can also be applied to a function separation type developing device. For example, referring to FIG. 3, even if the developer is supplied from the developing chamber 41a to the developing sleeve 44 and the developer peeled off from the developing sleeve 44 is collected by the stirring chamber 41b, The invention can be applied.

  DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum (image carrier) / 4, 4A, 4B, 4C ... Developing device / 11 ... Magnetic plate (magnet member) / 41, 41A, 41B, 41C ... Developing container / 42 ... Developing blade (regulating member) / 44 ... Developing sleeve (developer carrier) / 44a ... Magnet (magnetic flux generating means) / 47, 47A, 47B, 47C ... Outer cover (first covering) Part) / 47a, 47Aa, 47Ba ... first opposing part / 47b, 47Ab, 47Bb ... second opposing part / 47d, 47Bd, 47Cd ... third opposing part / 48, 48A, 48B ... Inner cover (second cover) / 48a, 48Aa, 48Ba... Upstream end / 48b, 48Ab, 48Bb... Downstream end / 100... Image forming apparatus / B1. Area) / B2... Central area / 3 ... end region / S2 ... adsorption magnetic pole (second pole) / S3 ... peeling magnetic pole (first magnetic pole)

Claims (7)

A developer container containing a developer;
A developer carrying region having a developer carrying region capable of carrying the developer, carrying the developer in the developer container and rotating, and capable of transporting the developer to a facing region facing the rotating image carrier; ,
With respect to the rotation direction of the developer carrier, a first magnetic pole disposed downstream of the facing region, and a second magnetic pole having the same polarity as the first magnetic pole disposed adjacent to the downstream of the first magnetic pole. And a magnetic flux generating means that is disposed inside the developer carrier and generates a magnetic flux for separating the developer carried on the developer carrier by the first magnetic pole from the developer carrier. ,
The developer container is disposed downstream of the facing region with respect to the rotation direction, and includes a first cover portion that covers the developer carrier through a gap, the first cover portion, and the developer carrier. Between the first cover part and the developer carrier, and a part of the first cover part is opposed to a part of the first cover part via the gap. The developing direction is such that the downstream end in the rotation direction is located downstream of the upstream minimum value of the pair of minimum values related to the rotation direction of the absolute value of the magnetic flux density distribution of the first magnetic pole. A second cover for covering the agent carrier,
The first cover portion includes a first facing portion that faces the developer carrying member on the upstream side in the rotational direction with respect to a portion facing the upstream end in the rotational direction of the second cover portion, and the rotational direction with respect to the rotation direction. A second facing portion facing a portion between the upstream end and the downstream end of the second covering portion; and an upstream end of the first facing portion, and downstream of the facing region in the rotation direction of the image carrier. A third facing portion facing the image carrier via a gap;
The third facing portion includes an end region including a part of the developer carrying region located on both end sides of the developer carrying member with respect to a rotation axis direction of the developer carrying member, and an end region. Also has a central region on the center side, and is formed such that a gap between the end region and the image carrier is smaller than a gap between the central region and the image carrier.
A developing device. A developer container containing a developer;
A developer carrying region having a developer carrying region capable of carrying the developer, carrying the developer in the developer container and rotating, and capable of transporting the developer to a facing region facing the rotating image carrier; ,
With respect to the rotation direction of the developer carrier, a first magnetic pole disposed downstream of the facing region, and a second magnetic pole having the same polarity as the first magnetic pole disposed adjacent to the downstream of the first magnetic pole. And a magnetic flux generating means that is disposed inside the developer carrier and generates a magnetic flux for separating the developer carried on the developer carrier by the first magnetic pole from the developer carrier. ,
The developer container is disposed downstream of the facing region with respect to the rotation direction, and includes a first cover portion that covers the developer carrier through a gap, the first cover portion, and the developer carrier. Between the first cover part and the developer carrier, and a part of the first cover part is opposed to a part of the first cover part via the gap. The developing direction is such that the downstream end in the rotation direction is located downstream of the upstream minimum value of the pair of minimum values related to the rotation direction of the absolute value of the magnetic flux density distribution of the first magnetic pole. A second cover for covering the agent carrier,
The first cover portion includes a first facing portion that faces the developer carrying member on the upstream side in the rotational direction with respect to a portion facing the upstream end in the rotational direction of the second cover portion, and the rotational direction with respect to the rotation direction. A second facing portion facing a portion between the upstream end and the downstream end of the second covering portion; and an upstream end of the first facing portion, and downstream of the facing region in the rotation direction of the image carrier. A third facing portion facing the image carrier via a gap;
The third facing portion includes an end region including a part of the developer carrying region located on both end sides of the developer carrying member with respect to a rotation axis direction of the developer carrying member, and an end region. And a central region on the center side, and the rotational direction length of the image carrier in the end region is longer than the rotational direction length of the image carrier in the central region.
A developing device. The central region is formed to have a length that is at least half of the length of the developer carrying region with respect to the rotation axis direction of the developer carrying member, with the center of the developer carrying region as the center.
The developing device according to claim 1, wherein The developer carrier is a cylindrical developing sleeve,
The developer sleeve is provided so as to face along the circumferential surface of at least a part of both ends in the rotation axis direction of the developing sleeve outside the developer carrying region, and between the opposite circumferential surfaces of the both ends. It has a magnet member that can form magnetic ears,
Both end portions of the central region are located at positions away from the position of the magnet member by 10 mm or more and 30 mm or less on the center side.
The developing device according to claim 1, wherein The developer carrier rotates from the lower side to the upper side in the direction of gravity in the facing region.
The developing device according to claim 1, wherein A regulating member that regulates the amount of developer carried on the developer carrying body upstream of the facing region and downstream of the second magnetic pole with respect to the rotation direction;
The developing device according to claim 1, wherein: A developing device according to any one of claims 1 to 6,
An image carrier that carries an electrostatic latent image developed by the developing device and rotates in the same direction as the developer carrier in the facing region;
An image forming apparatus.

Images