JP7703380B2 - Developing device - Google Patents

Description

The present invention relates to a developing device that uses a developer containing toner and carrier.

The developing device includes a developing container that contains a developer containing toner and a carrier, and a developing rotor that carries and transports the developer to develop an electrostatic latent image formed on an image carrier. The developing container has a partition wall, a first chamber (supply chamber) that supplies developer to the developing rotor, and a second chamber (mixing chamber) that is partitioned from the first chamber by the partition wall and in which developer circulates between the first chamber and the second chamber. The developing rotor is disposed at the opening of the first chamber.

In the developing device, air flows into the developing container through the gap between the opening of the first chamber and the developing rotor due to the rotation of the developing rotor. When air flows into the developing container and the internal pressure inside the developing container rises, the air inside the developing container is discharged outside the developing container through the gap between the opening of the first chamber and the developing rotor, which may cause toner to scatter.

In the developing device described in Patent Document 1, an opening through which air can pass in order to reduce the internal pressure in the developing container (hereinafter referred to as the pressure relief opening) is provided above the first chamber, and a filter is disposed in the pressure relief opening.

JP 2007-140288 A

However, the air in the first chamber (supply chamber) contains a large amount of toner that has been liberated from the developing rotor, resulting in a high toner concentration. For this reason, in the case of the configuration described in Patent Document 1, the amount of toner contained in the air that is discharged from inside the developing container to the outside of the developing container through the pressure relief opening provided above the first chamber tends to be large. Furthermore, if a filter is provided in the pressure relief opening provided above the first chamber, the filter provided in the pressure relief opening is likely to become clogged with toner, which may shorten the life of the filter.

The present invention has been made in consideration of the above problems. The object of the present invention is to provide a developing device that can reduce the amount of toner contained in the air discharged from inside the developing container to the outside of the developing container through an opening through which air can pass.

In order to achieve the above object, a developing device according to one aspect of the present invention has the following configuration: That is, a developer carrier that is rotatably provided and carries and transports a developer containing toner and a carrier to develop an electrostatic latent image formed on an image carrier, a magnet that is fixedly arranged inside the developer carrier and non-rotatably, the magnet having a first magnetic pole and a second magnetic pole that is arranged downstream of the first magnetic pole in the rotation direction of the developer carrier and adjacent to the first magnetic pole and has the same polarity as the first magnetic pole, a developing container that contains the developer, the developing container having a first chamber that supplies the developer to the developer carrier, a second chamber in which the developer circulates between the first chamber and the second chamber, and a partition wall that partitions the first chamber and the second chamber, a first communication portion that communicates between the first chamber and the second chamber, the first communication portion that allows the developer to move from the second chamber to the first chamber, and a second communication portion that communicates between the first chamber and the second chamber. a second communication portion configured to allow the developer to move from the first chamber to the second chamber, a first conveying screw disposed in the first chamber and conveying the developer in a first direction from the first communication portion toward the second communication portion, a second conveying screw disposed in the second chamber and conveying the developer in a second direction from the second communication portion toward the first communication portion, and a third communication portion configured to communicate the first chamber and the second chamber, the third communication portion being provided downstream of the first communication portion and upstream of the second communication portion with respect to the first direction, and being disposed vertically above a rotation axis of the first conveying screw and vertically above a rotation axis of the second conveying screw, and the developing container further has a third chamber disposed vertically above the second chamber, and the third chamber is configured to include a developer conveying portion that conveys the developer from the first chamber to the second chamber. an opening is provided for discharging the air from the developing container to the outside, the opening is disposed vertically above an uppermost end of the third communicating portion, a peak position of the magnetic flux density of the second magnetic pole in a normal direction of the developer carrier is vertically below a peak position of the magnetic flux density of the first magnetic pole in the normal direction of the developer carrier, and an uppermost end of the third communicating portion is vertically below a peak position of the magnetic flux density of the first magnetic pole in the normal direction of the developer carrier, a sealing member is attached to the developing container, and in a sealed state in which the second chamber and the third chamber are not in communication with each other, an initial developer is sealed in the third chamber by the sealing member attached to the developing container, and air inside the developing container is discharged between the first chamber and the second chamber via the third communicating portion. and in an unsealed state in which the air inside the developing container does not communicate between the second chamber and the third chamber, the sealing member is not attached to the developing container, and the second chamber and the third chamber are in communication with each other, the initial developer is not sealed in the third chamber, and the air inside the developing container communicates between the first chamber and the second chamber via the third communication part, and the air inside the developing container communicates between the second chamber and the third chamber, and in the unsealed state, the air inside the first chamber is allowed to move to the second chamber via the third communication part, and the air inside the second chamber is allowed to move to the third chamber, and the air inside the third chamber can be discharged to the outside of the developing container through the opening.

According to the present invention, it is possible to reduce the amount of toner contained in the air discharged from inside the developing container to the outside of the developing container through an opening through which air can pass.

1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a cross-sectional view showing a schematic configuration of an image forming unit according to the embodiment. FIG. 2 is a schematic cross-sectional view showing the basic configuration of a developing device according to the embodiment. FIG. 2 is a vertical cross-sectional view showing a schematic configuration of a developing device according to the embodiment. 5 is a schematic diagram showing the relationship between the magnetic flux density on the developing sleeve and the magnetic brush angle. FIG. 4 is a schematic diagram for explaining the behavior of the magnetic brush on the developing sleeve in the vicinity of the N2 pole. FIG. 4 is a schematic cross-sectional view of an airflow exhaust path of the developing device according to the embodiment. FIG. 2 is a cross-sectional view of a developing device according to the embodiment. FIG. 2 is a perspective view of the developing device according to the embodiment, as viewed obliquely from above. 6A to 6C are diagrams illustrating a method for removing an initial developer sealing sheet from the developing device according to the embodiment. 11 is a graph comparing the number of scattered toner particles between a comparative example and an embodiment.

The embodiment will be described with reference to Figures 1 to 11. First, the schematic configuration of the image forming apparatus of the embodiment will be described with reference to Figures 1 and 2.

[Image forming apparatus]
The image forming apparatus 100 of this embodiment is an electrophotographic tandem-type full-color printer equipped with four image forming units PY, PM, PC, and PK, each of which has a photosensitive drum 1 as an image carrier. The image forming apparatus 100 forms a toner image (image) on a recording material in response to an image signal from a document reading device (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 so as to be able to communicate with the apparatus main body 100A. 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 of the image forming device 100 have substantially the same configuration, except for the different developing colors. Therefore, we will explain the image forming unit PY as a representative, and omit explanations of the other image forming units.

As shown in FIG. 2, the image forming unit PY is provided with a cylindrical photosensitive member, i.e., photosensitive drum 1, as an image carrier. The photosensitive drum 1 is driven to rotate in the direction of the arrow in the figure. Around the photosensitive drum 1, there are arranged a charging roller 2 as a charging means, a developing device 4, a primary transfer roller 52 as a transfer means, and a cleaning device 7 as a cleaning means. Below the photosensitive drum 1 in the figure, there is arranged an exposure device (a laser scanner in this embodiment) 3 as an exposure means.

A transfer device 5 is disposed above each image forming unit in FIG. 1. The transfer device 5 is configured such that an endless intermediate transfer belt 51 serving as an intermediate transfer body is stretched across multiple rollers and moves (rotates) in the direction of the arrow. The intermediate transfer belt 51 carries and transports the toner image that has been primarily transferred to the intermediate transfer belt 51, as described below. A secondary transfer outer roller 54 serving as a secondary transfer means is disposed at a position opposite to a secondary transfer inner roller 53, one of the rollers that stretch the intermediate transfer belt 51, with the intermediate transfer belt 51 in between. This constitutes a secondary transfer unit T2 that transfers the toner image on the intermediate transfer belt 51 to a recording material. A fixing unit 6 is disposed downstream of the secondary transfer unit T2 in the recording material transport direction.

At the bottom of the image forming apparatus 100, a cassette 9 containing recording material S is disposed. The recording material S fed from the cassette 9 is transported by a transport roller 91 toward a registration roller 92. The leading edge of the recording material S then strikes the registration roller 92, which is in a stopped state, forming a loop to correct any skew in the recording material S. The registration roller 92 then starts to rotate in synchronization with the toner image on the intermediate transfer belt 51, and the recording material S is transported to the secondary transfer section T2.

The process of forming, for example, a four-color full-color image using 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 to laser light 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 toner contained as a developer in the development device 4, becoming 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 section T1 (FIG. 2) that is configured between the photosensitive drum 1 and a primary transfer roller 52 arranged with the intermediate transfer belt 51 in between. At this time, a primary transfer bias is applied to the primary transfer roller 52. Toner remaining on the surface of the photosensitive drum 1 after the primary transfer (transfer residual toner) is removed by a cleaning device 7.

This operation is performed in sequence at each image forming section for yellow, magenta, cyan, and black, and the four color toner images are superimposed on the intermediate transfer belt 51. After that, in time with the formation of the toner images, the recording material S stored in the cassette 9 is transported to the secondary transfer section T2. Then, by applying a secondary transfer bias to the outer secondary transfer roller 54, the four color toner images on the intermediate transfer belt 51 are secondarily transferred all at once onto the recording material S. Any toner that was not transferred at the secondary transfer section T2 and remains on the intermediate transfer belt 51 is removed by the intermediate transfer belt cleaner 55.

The recording material S is then conveyed to the fixing device 6 as a fixing means. The fixing device 6 includes a fixing roller 61 and a pressure roller 62, which have a heat source such as a halogen heater inside, and the fixing roller 61 and the pressure roller 62 form a fixing nip portion. The recording material S, onto which the toner image has been transferred, is passed through the fixing nip portion of the fixing device 6, whereby the recording material S is heated and pressurized. The toner on the recording material S is then melted and mixed, and fixed onto the recording material S as a full-color image. The recording material S is then discharged onto the discharge tray 102 by the discharge rollers 101. This completes the image formation process.

In addition, the image forming device 100 of this embodiment can also form a single-color or multi-color image, such as a black single-color image, by using image forming units for a desired single color or for several of the four colors.

[Developing device]
Next, the basic configuration of the developing device 4 will be described with reference to Figures 3 and 4. The developing device 4 has a developing container 41 that contains a developer containing a non-magnetic toner and a carrier having magnetism, and a developing sleeve 44 as a developer carrier that rotates while carrying the developer in the developing container. In the developing container 41, a first conveying screw 43a and a second conveying screw 43b are arranged as a first conveying member and a second conveying member that circulate the developer in the developing container while stirring and conveying the developer in the developing container. In addition, inside the developing sleeve 44, a magnet roll 44a as a magnetic field generating means having a plurality of magnetic poles aligned in the rotation direction is arranged in a non-rotating manner. Furthermore, a developing blade 42 is arranged as a regulating member that forms a thin layer of developer on the surface of the developing sleeve 44.

The developing container 41 has a developing frame 41j in which the developer is contained, and a top lid 41k as a cover member that covers the upper part of the developing frame 41j. The developing frame 41j and the top lid 41k are separate bodies, and the developing container 41 is formed by providing the top lid 41k to the developing frame 41j. The inside of the developing container 41 is divided horizontally into a developing chamber (first chamber) 41a and an agitating chamber (second chamber) 41b by a partition wall 41c that extends in the direction perpendicular to the paper surface at the approximate center, and the developer is contained in the developing chamber 41a and the agitating chamber 41b. That is, the developing container 41 is composed of a first frame (developing frame 41j) in which the first conveying screw 43a and the second conveying screw 43b are arranged and for containing the developer, and a second frame (top lid 41k) that is attached to the first frame and for covering a part of the outer circumferential surface of the developing sleeve 44.

A first conveying screw 43a and a second conveying screw 43b are disposed in the developing chamber 41a and the stirring chamber 41b, respectively. That is, the first conveying screw 43a and the second conveying screw 43b are disposed in the developing frame 41j, and the tops of the first conveying screw 43a and the second conveying screw 43b are covered by the top cover 41k. A first communicating portion 41d and a second communicating portion 41e that allow the developer to pass between the developing chamber 41a and the stirring chamber 41b are provided at both longitudinal ends of the partition 41c (both ends in the direction of the rotation axis of the developing sleeve 44, the left and right sides in FIG. 4).

The first transport screw 43a and the second transport screw 43b are each formed with a spiral blade around a shaft (rotation shaft) as a transport section. In addition to the spiral blade, the second transport screw 43b is provided with an agitation rib 43b1 that protrudes radially from the shaft and has a predetermined width in the developer transport direction. The agitation rib 43b1 agitates the developer as the shaft rotates.

The first transport screw 43a, which serves as the first transport member, is disposed at the bottom of the developing chamber 41a along the rotation axis of the developing sleeve 44. The rotation axis is rotated by a motor (not shown), transporting the developer in the developing chamber 41a along the axis in the first direction (the direction of the arrow α in FIG. 4) while supplying the developer to the developing sleeve 44. The developer carried by the developing sleeve 44, from which the toner has been consumed in the developing process, is collected in the developing chamber 41a.

The second transport screw 43b, which serves as a second transport member, is disposed at the bottom of the stirring chamber 41b along the rotation axis of the developing sleeve 44. In this embodiment, the first transport screw 43a and the second transport screw 43b are disposed substantially parallel to each other. The second transport screw 43b transports the developer in the stirring chamber 41b along the axial direction in a second direction (the direction of the arrow β in FIG. 4) opposite to the first direction. In this way, the developer is transported by the first transport screw 43a and the second transport screw 43b, and circulates in the developing container 41 via the first communicating portion 41d and the second communicating portion 41e.

At the upstream end in the conveying direction of the second conveying screw 43b of the stirring chamber 41b, i.e., in the second direction, a developer supply port 46 is provided for replenishing developer including toner in the developing container 41. The developer supply port 46 is connected to a developer container 8 (FIG. 1, toner bottle) that contains replenishing developer. The replenishing developer is supplied into the stirring chamber 41b directly from the developer container 8, or via a developer replenishing device that temporarily stores the developer in the developer container 8 and then supplies it to the developing device 4.

Toner replenishment from the developer container 8 is performed by automatic toner replenishment control (hereinafter referred to as "ATR: Automatic Toner Replenishing" control). Specifically, the operation of the replenishment developer container 8 or the developer replenishment device is controlled according to the image ratio during image formation and the patch image density detection results by the inductance sensor 45 and the patch image density sensor 103 (Figure 1), and developer is replenished to the developer replenishment port 46.

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 concentration in the developing container 41. In this embodiment, the inductance sensor 45 is provided downstream of the stirring chamber 41b in the developer transport direction.

As shown in FIG. 1, the patch image density sensor 103 is disposed 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, facing the surface of the intermediate transfer belt 51. In control using the patch image density sensor 103, a control toner image (patch image) is transferred onto the intermediate transfer belt 51, for example, at the start of an image formation job or after a predetermined number of images have been formed. The density of the patch image is then detected by the patch image density sensor 103. Based on the detection result, developer replenishment control from the developer storage container 8 is performed.

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

The second transport screw 43b transports the developer supplied from the developer supply port 46 while stirring the developer already in the stirring chamber 41b, making the toner concentration uniform. The transport forces of the first transport screw 43a and the second transport screw 43b move the developer in the development chamber 41a, whose toner concentration has decreased due to toner consumption in the development process, into the stirring chamber 41b through the first communication part 41d (left side of Figure 4), which is one of the transfer parts. The developer that has moved into the stirring chamber 41b is then transported while being mixed with the supplied developer, and moves to the development chamber 41a through the second communication part 41e (right side of Figure 4), which is the other transfer part.

In the developing chamber 41a of the developing container 41, an opening 41h is formed at a position corresponding to the facing area (developing area) A facing the photosensitive drum 1, and the developing sleeve 44 is arranged rotatably so that a part of it is exposed toward the photosensitive drum 1 at the opening 41h. On the other hand, the magnet roll 44a contained in the developing sleeve 44 is fixed so as not to rotate. Such a developing sleeve 44 is rotated by a motor (not shown) to transport the developer to the facing area A, and supplies the developer to the photosensitive drum 1 in the facing area A. That is, the facing area (developing area) A is an area where the magnetic brush formed by the carrier on the developing sleeve 44 magnetized by the magnet roll 44a contacts the electrostatic latent image formed on the photosensitive drum 1. In this embodiment, the developing sleeve 44 is formed in a cylindrical shape using a non-magnetic material such as aluminum or stainless steel. In addition, the developing sleeve 44 rotates in the facing area A from below to above in the direction of gravity, that is, in the counterclockwise direction (arrow γ direction) in FIG. 3. Additionally, the photosensitive drum 1 rotates in the same direction as the developing sleeve 44 (direction of arrow δ) in the opposing region A.

A developing blade 42 is fixed to the upstream side of the opening 41h in the rotation direction of the developing sleeve 44 as a regulating member that regulates the amount (layer thickness) of developer carried on the developing sleeve 44. In this embodiment, the developing sleeve 44 rotates from below toward above in the direction of gravity in the opposing region A, so the developing blade 42 is located below the opposing region A in the direction of gravity.

As shown in FIG. 3, the magnet roll 44a has a total of five magnetic poles, S1, S2, S3, N1, and N2, in the circumferential direction, and is formed in a roller shape. Such a magnet roll 44a generates a magnetic field that causes the developing sleeve 44 to carry the developer, and also generates a magnetic field that causes the developer to peel off from the developing sleeve 44 in a peeling area described later. That is, the developer in the developing chamber 41a is supplied from the developing chamber 41a to the developing sleeve 44. Then, a predetermined amount of the developer supplied to the developing sleeve 44 is carried on the developing sleeve 44 (on the developer carrier) by the magnetic field generated by the attraction magnetic pole S2 of the magnet roll 44a, forming a developer reservoir. That is, the attraction magnetic pole S2 corresponds to the second magnetic pole that causes the developer in the developing container to be carried on the developing sleeve 44.

The developer on the developing sleeve 44 passes through the developer reservoir as the developing sleeve 44 rotates, and is raised at the regulating magnetic pole N1, and the layer thickness is regulated by the developing blade 42 that faces the regulating magnetic pole N1. The developer whose layer thickness has been regulated is then transported to the facing area A that faces the photosensitive drum 1, and is raised at the developing magnetic pole S1 to form a magnetic brush. This magnetic brush comes into contact with the photosensitive drum 1 that rotates in the same direction as the developing sleeve 44 in the facing area A, and develops the electrostatic latent image into a toner image with charged toner. In other words, the developing magnetic pole S1 corresponds to the first magnetic pole that is located at the position where the developing sleeve 44 is closest to the photosensitive drum 1.

The developer on the developing sleeve 44, whose toner concentration has decreased due to toner consumption, is then transported into the developing container 41 by the rotation of the developing sleeve 44 while the transport magnetic pole N2 maintains the developer's adhesion to the surface of the developing sleeve 44. The developer carried on the developing sleeve 44 is then peeled off from the surface of the developing sleeve 44 in a peeling region formed by the peeling magnetic pole S3 and the attraction magnetic pole S2 of the same polarity, which are arranged in order in the rotation direction of the developing sleeve 44. The peeled off developer is collected in the developing chamber 41a of the developing container 41. That is, the peeling magnetic pole S3 corresponds to a third magnetic pole of the same polarity as the attraction magnetic pole S2, which is arranged adjacent to the attraction magnetic pole S2 as the second magnetic pole in the rotation direction of the developing sleeve 44.

[Scattering of developer]
Here, the scattering of developer generated from the developing device will be described. First, in an image forming device, there is a demand for faster output images and higher image quality, as well as simplified maintenance. One of the ways to simplify maintenance is to reduce contamination caused by developer inside the image forming device. If the inside of the image forming device is contaminated by developer, image defects such as stains on the output image will occur, and cleaning work will be required when replacing the developing device, photosensitive drum unit, etc. Furthermore, if developer adheres to each driving system such as gears, there is a risk that slippage will occur in the driving system.

One of the causes of developer contamination inside image forming devices is the scattering of developer from within the developing device. For example, in the case of two-component developers, the toner and carrier are usually charged by friction inside the developing device, so the toner and carrier adhere to each other due to electrostatic forces. However, there is a risk that this adhesion will be released due to some kind of impact, and the toner that has become detached from the carrier will be discharged from inside the developing device along with the air current, causing the developer to scatter.

A typical route for toner scattering from inside the developing device is the intake port 47 between the opening 41h of the developing container 41 and the developing sleeve 44, where the developer on the developing sleeve 44 is taken into the developing container 41 by the rotation of the developing sleeve 44 (see FIG. 3). The intake port 47 (inflow path) is the gap between the developing sleeve 44 and the opening end 41i downstream of the development area A of both ends of the opening 41h in the rotation direction of the developing sleeve 44. On the other hand, on the opposite side of the intake port 47 (lower side in FIG. 3), the developing blade 42 faces the developing sleeve 44 in close proximity. Therefore, at this position, the layer thickness of the developer carried on the developing sleeve 44 is regulated by the developing blade 42, and air is unlikely to flow out from the gap between the developing sleeve 44 and the developing blade 42. Therefore, toner scattering to the outside of the developing container mainly occurs at the intake port 47.

First, an overview of toner scattering from the intake port 47 will be described using Figures 5 and 6 with reference to Figure 3. Here, toner scattering refers to free toner that is generated in the developing container 41 due to the stirring and transport of the developer and the toner replenishment, is discharged to the outside of the developing container 41 through the intake port 47, and cannot be collected in the developing container 41.

Now, let us explain toner liberation. The toner and carrier contained in the developing container 41 are frictionally charged in the stirring chamber 41b and the developing chamber 41a, and are attached to each other by electrostatic adhesion forces generated by the frictional charging and non-electrostatic adhesion forces generated by intermolecular forces. When an impact or shear force is applied to the toner that is attached to the carrier, the toner is torn off from the carrier by inertial forces and the like, and becomes liberated within the developing container 41. The impact and shear force at this time include the behavior of the developer when it is transported by the developing sleeve 44.

As shown in FIG. 5, the developer forms magnetic ears on the developing sleeve 44, which are chain-like structures that follow the magnetic lines of force of the internal magnetic poles. That is, the developer forms magnetic ears on each magnetic pole of the developing sleeve 44, which are chain-like structures that follow the angle Φ of the magnetic flux density (magnetic flux lines) B that passes through that point. The angle Φ of the magnetic flux lines is determined by the magnitude Br of the normal component of the magnetic flux density B and the magnitude Bθ of the tangential component of the magnetic flux density B. The angle Φ of the magnetic flux density (magnetic flux lines) is the angle that the magnetic flux density makes with the tangent to the developing sleeve 44.

Therefore, at point Pa near magnetic pole N2, the normal magnitude Bra of the magnetic flux density is large and the tangential magnitude Bθa is small, so the angle Φa of the magnetic flux density (magnetic flux line) Ba approaches 90 degrees (normal direction). On the other hand, at point Pb away from magnetic pole N2, the normal magnitude Brb of the magnetic flux density is small compared to point Pa, and the tangential magnitude Bθb is large, so the angle Φb of the magnetic flux density (magnetic flux line) Bb with respect to the tangential direction of the developing sleeve 44 is small. Therefore, as shown in FIG. 6, the magnetic brush rises before passing the magnetic pole due to the magnetic flux density B created by the magnetic pole of the magnet roll 44a, and the magnetic brush falls when it passes over the magnetic pole. That is, the magnetic brush rises forward in the direction of rotation just before the magnetic pole due to the rotation of the developing sleeve 44, and falls forward in the direction of rotation when it passes over the magnetic pole. At this time, the rotation direction of the magnetic brush is the same as the rotation direction of the developing sleeve 44. In particular, the impact and inertial force generated when the magnetic brush falls over causes the toner to be torn off from the carrier, which causes the toner to become loose.

The magnetic pole that contributes most to toner liberation when developer is transported by the developing sleeve 44 is the peeling magnetic pole (stripping pole) S3, which generates a repulsive magnetic field between itself and the attraction magnetic pole S2. In order to peel off the developer from the developing sleeve 44, the peeling magnetic pole S3 applies a magnetic force in the opposite direction to the rotational direction of the developing sleeve 44, slowing down the speed of the developer being transported and causing the developer to accumulate. At this time, the flow rate of developer transported on the surface of the developing sleeve 44 is conserved, so the length of the magnetic wire becomes longer along the magnetic flux lines. As the magnetic wire becomes longer, the impact and inertial force when the magnetic wire falls over become larger, which tends to increase the amount of toner liberation.

Next, the airflow inside and near the developing device 4 will be described. The developing sleeve 44 and the photosensitive drum 1 are what generate the airflow near the developing device 4. Each will be described here. First, an airflow is generated in approximately the same direction as the rotation direction of the developing sleeve 44 due to the rotation of the developing sleeve 44 and the behavior of the magnetic wires on the magnetic pole. This airflow generated in approximately the same direction as the rotation direction of the developing sleeve 44 draws air into the developing container 41 from the intake port 47, which serves as a communication port between the inside of the developing container 41 and the outside of the developing container 41.

If we assume that the developing container 41 is a substantially closed space, the continuity equation can be applied since air is a fluid. If the flow velocity of air is v and the density is ρ, the following equation (1) holds.

Furthermore, when considering a steady state, since the internal pressure is constant and stable at a state higher than atmospheric pressure, the density ρ can be regarded as not changing with time in each region within the developing container 41, and equation (1) can be written as the following equation (2).

From this formula (2), the air flow rate ρv is preserved. In the cross section in the longitudinal direction (the direction of the rotation axis of the developing sleeve 44) near the developing device 4, the balance of the flow rate ρv becomes 0, and the same amount of air flow rate as the air flow rate flowing in through the developing sleeve 44 and replenishment is discharged outside the developing device 4. Here, the air flow rate flowing into the developing container 41 with the rotation of the developing sleeve 44 through the inlet 47 formed by the upper lid 41k of the developing container 41 and the developing sleeve 44 is Ia (sleeve inlet). In addition, the air flow discharged from the inlet 47 passes through the upper lid 41k side so as to face the flow taken in from this inlet 47. The air flow rate discharged in this way is Ib (sleeve outlet). If the air flow discharged from the developing container 41 through other gaps, ends, etc. is Ic (other leaks), the following formula (3) holds true.
Ia (sleeve inflow) = Ib (sleeve outflow) + Ic (other leaks) (3)

The airflow taken in by the developing sleeve 44 and flowing along the developing sleeve 44 is turned around and discharged inside the developing container 41. The above-mentioned free toner is caught in the flow that turns around inside the developing device and is carried out of the developing device, which is called toner scattering. In particular, when the amount of air taken into the developing device 4 by the rotation of the developing sleeve 44 is discharged to the outside of the developing device, the air inside the developing device 4 passes near the peeling magnetic pole S3. Therefore, if the developing container does not have an exhaust port for sufficiently discharging the air inside, the amount of air discharged from the intake port 47 between the developing sleeve 44 and the upper cover 41k is approximately the same as the amount of air taken into the developing device 4. In other words, the airflow discharged from inside the developing device 4 entrains the air with a high concentration of free toner near the peeling magnetic pole S3, and is discharged from the intake port 47 between the developing sleeve 44 and the upper cover 41k, causing toner scattering.

[Measures to prevent toner scattering]
Next, a toner scattering countermeasure in this embodiment will be described. In this embodiment, in order to reduce toner scattering, the air flow rate Ib passing through the vicinity of the peeling magnetic pole S3 and escaping from the intake port 47 between the developing sleeve 44 and the upper cover 41k is reduced. The configuration of the developing device 4 that reduces the air flow rate Ib will be described with reference to FIG. 7. Also, the details of the configuration of the developing device 4 in this embodiment will be described with reference to FIGS. 8, 9, and 10. FIG. 8 is a cross-sectional view of the developing device 4 according to this embodiment. FIG. 9 is a perspective view of the developing device 4 according to this embodiment, as viewed obliquely from above. FIG. 10 is a diagram showing a method of removing the initial developer sealing sheet from the developing device 4 according to this embodiment.

The developing container 41 is formed with an outlet 48 that connects the stirring chamber 41b to the outside and allows air to be discharged from the developing container 41. The outlet 48 is formed above the third communicating portion 1000 described below and above the developing sleeve 44. In particular, in this embodiment, the outlet 48 is formed in the upper cover 41k (above the stirring chamber 41b) and opens above the developing device 4. The outlet 48 is provided with an air filter 49 made of nonwoven fabric that allows air to pass through and serves as a collecting member that collects toner. That is, the opening of the outlet 48 is covered with the air filter 49, allowing ventilation between the developing device 4 and the outside.

The discharge port 48 is formed over almost the entire length of the developing container 41 (the direction of the rotation axis of the developing sleeve 44), and is capable of discharging air from within the developing container 41 over almost the entire length of the developing container 41.

In addition to the first and second communication parts 41d and 41e (FIG. 4), the partition 41c has a third communication part 1000 that communicates the developing chamber 41a with the stirring chamber 41b and allows air inside the developing container 41 to move between the developing chamber 41a and the stirring chamber 41b. The first communication part 41d, the second communication part 41e, and the third communication part 1000 are all openings formed to communicate the developing chamber 41a with the stirring chamber 41b. However, while the first communication part 41d and the second communication part 41e are formed at positions where the developer contained in the developing container 41 can pass through, the third communication part 1000 is formed above the first communication part 41d and the second communication part 41e. In addition, the third communication part 1000 is formed along the longitudinal direction of the developing container 41 (the direction of the rotation axis of the developing sleeve 44), and communicates the developing chamber 41a and the stirring chamber 41b over almost the entire longitudinal area. Since the third communication part 1000 communicates the developing chamber 41a and the stirring chamber 41b over almost the entire longitudinal area, it is possible to ensure a sufficient amount of air movement inside the developing container 41 between the developing chamber 41a and the stirring chamber 41b, compared to when they are partially or locally connected.

In this embodiment, the third communicating portion 1000 is deemed to be formed over substantially the entire longitudinal area of the developing container 41 when any of the conditions described below is satisfied. For example, when the third communicating portion 1000 is formed over 90% or more of the area downstream of the first communicating portion 41d and upstream of the second communicating portion 41e in the conveying direction of the second conveying screw 43b, it is deemed to be formed over substantially the entire longitudinal area. Also, when the third communicating portion 1000 is formed over 90% or more of the area (image forming area) in which the developing sleeve 44 has a developer conveying capacity, it is deemed to be formed over substantially the entire longitudinal area of the developing container 41. The area in which the developing sleeve 44 has a developer conveying capacity is, for example, an area in which grooves are formed on the outer surface of the developing sleeve 44 along the rotation axis direction of the developing sleeve 44 and periodically spaced in the circumferential direction of the developing sleeve 44.

That is, a portion of the third communication part 1000 may be covered with a filter or blocked with a film or sponge, and it is sufficient that the third communication part 1000 is formed over 90% or more of the aforementioned area when covered with a filter or blocked with a film or sponge. Similarly, even if the third communication part 1000 is formed discontinuously by providing ribs locally in the aforementioned area, it is sufficient that the third communication part 1000 is formed over 90% or more of the aforementioned area when the ribs are locally provided in the aforementioned area.

In addition, even if the exhaust outlet 48 is formed intermittently by providing ribs locally in the aforementioned region, it is sufficient that the exhaust outlet 48 is formed over 90% or more of the aforementioned region with the ribs provided locally in the aforementioned region.

The third communication portion 1000 opens below the position on the surface of the developing sleeve 44 where the normal component of the magnetic field of the peeling magnetic pole S3 is at its maximum, and above the developer surface of the developer contained in the developing container 41 (the developer surface in the steady state of the developing device 4). The developer surface height of the developing device 4 reaches the steady state by rotating the developing device 4 for two minutes from a state in which the developing device 4 is not in operation.

Hereinafter, the position where the component of the magnetic field of the peeling magnetic pole S3 on the surface of the developing sleeve 44 in the normal direction of the developing sleeve 44 is maximum is referred to as the maximum peak position. In FIG. 7, the third communicating portion 1000 is formed between A, which indicates the height of the maximum peak position of the peeling magnetic pole S3, and D, which indicates the height of the developer surface, in the vertical direction. Note that the height of the developer surface here is the maximum height of the developer surface that contacts the partition wall 41c when the first conveying screw 43a and the second conveying screw 43b are rotating during image formation. In addition, the third communicating portion 1000 is a long rectangle along the longitudinal direction of the developing container 41 (the direction of the rotation axis of the developing sleeve 44).

Here, the partition wall 41c is composed of a first wall portion 41c1 formed on the developing frame body 41j and a second wall portion 41c2 formed on the upper cover 41k. The third communication portion 1000 is formed between the first wall portion 41c1 and the second wall portion 41c2. That is, the second wall portion 41c2 is formed to protrude downward from the upper cover 41k, and divides the developing chamber 41a and the stirring chamber 41b above the first conveying screw 43a and the second conveying screw 43b. On the other hand, the first wall portion 41c1 is provided between the first conveying screw 43a and the second conveying screw 43b of the developing frame body 41j, and divides the developing chamber 41a and the stirring chamber 41b in the area where the developer is present. In addition, the first communication portion 41d and the second communication portion 41e are formed in the first wall portion 41c1. The space between the tip of the first wall portion 41c1 and the tip of the second wall portion 41c2 is the third communication portion 1000.

In the present embodiment, when the developing device 4 is new (at the time of shipping), the initial developer is enclosed in the space above the second transport screw 43b in the stirring chamber 41b (the upper space of the stirring chamber 41b, the initial developer storage chamber 50). In the present embodiment, the initial developer storage chamber 50 is provided on the upper lid 41k side of the developing frame 41j in which the developer is stored and the upper lid 41k which serves as a cover member covering the upper part of the developing frame 41j.

By shipping the developing device 4 with the initial developer sealed in the initial developer storage chamber 50, it is possible to prevent developer from leaking out of the gaps in the developing device 4 during the logistics period until the development device 4 is first used, thereby preventing the development device 4 itself from becoming contaminated even before it is first used.

When sealing the initial developer, for example, the end of the top cover 41k facing the second wall portion 41c2 is extended toward the developing frame 41j, and the initial developer is sealed in the space (initial developer storage chamber 50) between this extended portion (extension portion 41k2) and the second wall portion 41c2. At this time, the second wall portion 41c2 of the top cover 41k and the extension portion 41k2 are used as attachment portions for a sheet (initial developer sealing sheet 60) for sealing the initial developer in the initial developer storage chamber. In this embodiment, a PET sheet with a thickness of 0.5 mm is used for the initial developer sealing sheet 60, but the material and shape are not limited to this.

The upper cover 41k is attached to the developing frame 41j with the opening of this space (initial developer storage chamber 50) on the side of the developing frame 41j sealed with an initial developer sealing sheet 60 or the like. This results in a developing device 4 in which the initial developer is sealed in the space (initial developer storage chamber 50) above the second conveying screw 43b. Before installing this brand new developing device 4 in the image forming device 100 and starting to use it, as shown in FIG. 10, the initial developer sealing sheet 60 is slid toward the back of the developing device 4. Then, as shown in FIG. 10, the initial developer sealing sheet 60 is removed by pulling it out, so that the sealed initial developer falls to the bottom of the stirring chamber 41b. After that, the first conveying screw 43a and the second conveying screw 43b are driven to distribute the developer throughout the stirring chamber 41b and the developing chamber 41a.

As described above, as shown in FIG. 9, an air filter 49 made of nonwoven fabric is installed on the upper part of the initial developer storage chamber 50, allowing ventilation between the interior and exterior of the developing device 4. As shown in FIG. 10, after the initial developer sealing sheet 60 is removed and the initial developer is dropped into the stirring chamber 41b, the stirring chamber 41b and the initial developer storage chamber 50 are in communication with each other. Therefore, the air in the stirring chamber 41b moves to the emptied initial developer storage chamber 50 and can flow outside the developing device 4 through the air filter 49. This configuration can suppress an increase in the internal pressure in the developing device 4, and therefore suppresses toner from scattering from gaps in the developing device 4, such as the gap between the developing sleeve 44 and the developing container 41 above it.

As shown in FIG. 9, a filter cover 70 made of a 0.1 mm thick PET sheet is placed on top of the air filter 49. The filter cover 70 has multiple holes (hole diameter: 5 mm) so as not to impede the flow of air from inside the developing device 4 through the air filter 49 to the outside of the developing device 4. In addition, a filter cover 70 for covering the air filter 49 is placed vertically above the air filter 49 so as to overlap the air filter 49. This prevents the air filter 49 from being damaged even if an operator (serviceman) touches the filter cover 70 with his or her hand.

In this manner, in this embodiment, the initial developer is sealed in the upper part of the stirring chamber 41b (initial developer storage chamber 50), so the initial developer can be sealed without sealing the third communication part 1000, and further the first communication part 41d and the second communication part 41e with a sheet or the like. Note that the first communication part 41d, the second communication part 41e, and the third communication part 1000 may be sealed with a sheet, and the initial developer may be sealed in the stirring chamber 41b including the space in which the second conveying screw 43b is present.

The configuration of the developing device 4 of this embodiment will be described in more detail with reference to FIG. 7. First, the vertical opening width of the third communicating portion 1000 that communicates with the partition wall 41c that separates the developing chamber 41a and the stirring chamber 41b over the entire longitudinal area will be described. The vertical height of the maximum peak position of the peeling magnetic pole S3 is A, the vertical height of the upper opening end of the third communicating portion 1000 is B, and the vertical height of the lower opening end of the third communicating portion 1000 is C. In addition, the height of the higher contact point between the developer surface (the developer surface in the steady state of the developing device 4) of the developer circulating in the developing chamber 41a and the stirring chamber 41b and the partition wall 41c is D. In this case, the vertical opening width of the third communicating portion 1000 is configured so that the relationship of the following formula (4) is established.
A>B>C>D...(4)

In other words, the vertical opening width of the third communicating portion 1000 is below the maximum peak position A of the peeling magnetic pole S3 and above the developer surface height D in the steady state of the developing device 4. By having the third communicating portion 1000 below the maximum peak position of the peeling magnetic pole S3, the air flow Ia with a high toner concentration mixed with the free toner generated at the peeling magnetic pole S3 is more likely to flow into the stirring chamber 41b through the third communicating portion 1000. In addition, by having the third communicating portion 1000 above the developer surface (the developer surface in the steady state of the developing device 4) of the developer circulating in the developing chamber 41a and the stirring chamber 41b, it is possible to prevent the developer in the developing chamber 41a and the stirring chamber 41b from communicating and circulating through the third communicating portion 1000.

The discharge port 48 is formed by providing an opening in the top cover 41k (initial developer storage chamber 50) vertically above the stirring chamber 41b. That is, when the developing device 4 is in a new state, the opening of the initial developer storage chamber 50 on the development frame body 41j side is sealed with an initial developer sealing sheet 60, and initial developer is enclosed in the initial developer storage chamber 50. When the developing device 4 is in a new state, the discharge port 48 that allows air to pass from inside the developing container 41 to outside the developing container 41 is provided above the stirring chamber 41b. In addition, an air filter 49 is provided in the discharge port 48 as a member for collecting scattered toner.

The air filter 49 then captures the toner that is carried by the air flow Id and is about to be discharged outside the machine. In this embodiment, the air filter 49 is a nonwoven fabric with a thickness of 0.20 mm, and has an air resistance of 0.94 sec at a pressure difference of 5 Pa when measured using the Gurley tester.

If the air resistance is too high, the toner collection ability is high but the device is prone to clogging, causing the internal pressure of the developing container 41 to rise. And while it is desirable to reduce the internal pressure in the developing container 41 with the airflow Id discharged from the discharge port 48, the internal pressure is reduced in the direction of the airflow Ib' discharged from the intake port 47, causing air with a high toner concentration to be discharged outside the developing device 4 from the intake port 47. In other words, scattering toner cannot be sufficiently suppressed.

On the other hand, if the air resistance is too small, the toner collection capacity is low, and there is a possibility that the toner may blow out and soil the recording material. In this embodiment, the air resistance of the air filter 49 is preferably in the range of 0.1 to 10 sec (0.1 sec or more and 10 sec or less) at a pressure difference of 5 Pa in the Gurley test method. However, depending on the configuration of the developing device, the toner particle size, and other conditions, it is preferable to appropriately select the material, mesh size, thickness, air resistance, etc. of the air filter 49 so that the toner in the developing container 41 does not scatter to the outside, but this is not limited to this. In addition, it is preferable that the air filter 49 is configured to be replaceable depending on the usage status of the developing device 4.

In this embodiment, the third communicating portion 1000 is formed to communicate the partition wall 41c separating the developing chamber 41a and the stirring chamber 41b over the entire lengthwise direction, and an exhaust port 48 is formed in the developing container 41 (above the stirring chamber 41b) to exhaust air from the developing container 41 to the outside. As a result, the internal pressure of the developing chamber 41a increases when air flows into the developing container 41 from the inlet 47 due to the rotation of the developing sleeve 44, and the internal pressure difference between the developing chamber 41a and the stirring chamber 41b causes some air to flow from the developing chamber 41a to the stirring chamber 41b through the third communicating portion 1000 (Ie). As a result, the internal pressure of the stirring chamber 41b increases, and the air in the stirring chamber 41b is exhausted to the outside of the developing device 4 through the exhaust port 48 provided above the stirring chamber 41b.

At this time, the flow rate of air flowing in from intake port 47 due to the rotation of developing sleeve 44 is defined as Ia. The flow rate of air exhausted to the outside of developing device 4 through intake port 47 is defined as Ib', the amount of air leakage from the end or the like is defined as Ic, and the flow rate of air exhausted to the outside of developing device 4 through exhaust port 48 is defined as Id. Then, the relationship of the following formula (5) is established.
Ia=Ib'+Ic+Id...(5)

In other words, from the above formulas (3) and (5), the amount of air flow that passes through the vicinity of the stripping magnetic pole S3 and is exhausted from the intake port 47 between the developing sleeve 44 and the upper cover 41k can be reduced by the amount of air flow Id (Ib' < Ib).

Here, the amount of free toner contained in the airflow Ib and the airflow Id will be described. The amount of free toner contained in the airflow Ib is high because it contains a large amount of free toner generated at the peeling magnetic pole S3 for the reasons described above. On the other hand, the airflow Id passes through the stirring chamber 41b, which has a low free toner concentration, so the free toner concentration of the discharged air is reduced. In addition, before the air discharged to the discharge port 48 through the third communication portion 1000 and the stirring chamber 41b reaches the inlet 48a of the discharge port 48, the free toner is subjected to a force in the direction of gravity and is again taken up into the circulating developer. For this reason, the free toner concentration of the air discharged from the discharge port 48 is reduced. In other words, the amount of toner contained in the air discharged from inside the developing container 41 to outside the developing container 41 through the discharge port 48 through which air can pass can be reduced. In addition, by reducing the amount of toner contained in the air discharged from inside the developing container 41 to the outside of the developing container 41 through the discharge port 48, the air filter 49 covering the opening of the discharge port 48 is less likely to become clogged with toner, which extends the life of the air filter 49.

In addition, in this embodiment, because the initial developer is sealed in the upper part of the stirring chamber 41b as described above, a wide space exists above the third communication part 1000, and the airflow path from the third communication part 1000 to the discharge port 48 is long. As a result, the time during which the free toner is subjected to a force in the direction of gravity before the air discharged to the discharge port 48 through the third communication part 1000 and the stirring chamber 41b reaches the inlet 48a of the discharge port 48 is longer, and the free toner contained in this air is more likely to fall. As a result, the free toner concentration in the air discharged from the discharge port 48 can be further reduced.

As described above, by providing the third communication section 1000 that communicates the development chamber 41a and the stirring chamber 41b over the entire longitudinal direction, and the stirring chamber 41b with an exhaust port 48 that exhausts air outside the development device 4, it is possible to reduce the amount of toner scattered from the intake port 47. As a result, according to this embodiment, it is possible to provide a development device that can suppress toner scattering.

In this embodiment, in order to seal as much initial developer as possible in the initial developer storage chamber 50, the communication opening for communication between the initial developer storage chamber 50 and the stirring chamber 41b is located at a low position. Therefore, in this embodiment, as shown in FIG. 8, the uppermost end of the third communication part 1000 is located vertically below the attachment part of the initial developer sealing sheet 60 located on the partition wall 41c side. That is, in this embodiment, as shown in FIG. 8, the uppermost end of the third communication part 1000 is located vertically below the attachment part of the initial developer sealing sheet 60 on the second wall part 41c2 side of the upper cover 41k, of the second wall part 41c2 of the upper cover 41k, of the extension part 41k2.

In addition, in this embodiment, as shown in FIG. 8, the bottom end of the third communication portion 1000 is positioned vertically above the rotation axis of the first conveying screw 43a and vertically above the rotation axis of the second conveying screw 43b.

[experiment]
An experiment was conducted to confirm the effect of the present embodiment as described above, as follows: In the experiment, the amount of scattered toner was examined by preparing a configuration of the present embodiment as shown in Fig. 7 (Example) and a configuration in which the third communication portion 1000, the discharge port 48, and the air filter 49 were removed from the configuration of Fig. 7 (Comparative Example).

The scattered toner in the developing device 4 mainly passes through the intake port 47 and scatters to the outside. Therefore, a line laser was irradiated at approximately the center of the airflow so that it was perpendicular to the developing sleeve 44. A line laser is a laser that is irradiated in a line shape with a certain line width and forms a fan-shaped, two-dimensional flat light path. The scattered toner flying on the light path of the line laser scatters the laser light. Therefore, by observing with a high-speed camera from a direction approximately perpendicular to the line laser irradiation direction, it is possible to measure the number and trajectory of scattered toner present in the area irradiated by the laser.

The line laser used a YAG laser manufactured by Nippon Laser Co., Ltd. as the light source, and was irradiated by adjusting the cylindrical lens so that the line width was 0.5 mm. A high-speed camera SA-3 manufactured by Photron was used for observation, and the settings of the high-speed camera (frame rate and exposure time) and the optical system (lens, etc.) were selected so that the scattered toner on the line laser could be observed.

Using the above method, the number of scattered toner particles from the center of the longitudinal direction (rotation axis direction) of the developing sleeve 44 was measured, and converted into the number of scattered toner particles equivalent to one sheet of A4 paper from the line width and observation time. The results of measuring the number of scattered particles in the comparative example and the example are shown in Figure 11. As is clear from Figure 11, it was found that the number of scattered particles could be reduced by using the configuration of the example, which is the configuration of this embodiment.

<Other embodiments>
In each of the above-described embodiments, a printer is used as the image forming apparatus. However, the present invention is also applicable to image forming apparatuses other than printers, such as copiers, facsimiles, and multifunction machines.

4 Developing device 41 Developing container 41a Developing chamber 41b Stirring chamber 41c Partition 41d First communicating portion 41e Second communicating portion 43a First conveying screw 43b Second conveying screw 44 Developing sleeve 48 Discharge port 1000 Third communicating portion

Claims (8)

a developer carrier that is rotatably provided and carries and transports a developer containing toner and carrier for developing an electrostatic latent image formed on the image carrier;
a magnet disposed inside the developer carrier in a non-rotatable and fixed manner, the magnet having a first magnetic pole and a second magnetic pole disposed adjacent to the first magnetic pole downstream of the first magnetic pole in the rotational direction of the developer carrier, the second magnetic pole having the same polarity as the first magnetic pole;
a developing container including a first chamber for supplying the developer to the developer carrier, a second chamber in which the developer circulates between the first chamber and the second chamber, and a partition wall for separating the first chamber from the second chamber, and containing the developer;
a first communication portion that communicates the first chamber with the second chamber, the first communication portion allowing the developer to move from the second chamber to the first chamber;
a second communication portion that communicates the first chamber with the second chamber, the second communication portion allowing the developer to move from the first chamber to the second chamber;
a first conveying screw disposed in the first chamber and configured to convey the developer in a first direction from the first communicating portion toward the second communicating portion;
a second conveying screw disposed in the second chamber and configured to convey the developer in a second direction from the second communicating portion toward the first communicating portion;
a third communication portion that communicates the first chamber with the second chamber, the third communication portion being provided downstream of the first communication portion and upstream of the second communication portion in the first direction, and disposed vertically above the rotation axis of the first conveying screw and vertically above the rotation axis of the second conveying screw;
Equipped with
the developing container further includes a third chamber disposed vertically above the second chamber,
the third chamber is provided with an opening for discharging air inside the developing container to the outside of the developing container,
the opening is disposed vertically above an uppermost end of the third communication portion,
a peak position of the magnetic flux density of the second magnetic pole in the normal direction of the developer carrier is vertically lower than a peak position of the magnetic flux density of the first magnetic pole in the normal direction of the developer carrier, and an uppermost end of the third communicating portion is vertically lower than the peak position of the magnetic flux density of the first magnetic pole in the normal direction of the developer carrier,
a sealing member is attached to the developing container, and in a sealed state in which the second chamber and the third chamber are not in communication with each other, an initial developer is sealed in the third chamber by the sealing member attached to the developing container, air inside the developing container communicates between the first chamber and the second chamber via the third communication portion, and air inside the developing container does not communicate between the second chamber and the third chamber,
in an unsealed state in which the sealing member is not attached to the developing container and the second chamber and the third chamber are in communication with each other, the initial developer is not sealed in the third chamber, air inside the developing container communicates between the first chamber and the second chamber via the third communication portion, and air inside the developing container communicates between the second chamber and the third chamber,
a developing device characterized in that, in the unsealed state, air inside the first chamber is allowed to move to the second chamber via the third communication portion, and air inside the second chamber is allowed to move to the third chamber, and air inside the third chamber can be discharged to the outside of the developing container via the opening. 2 . The developing device according to claim 1 , wherein in the sealed state, air communicates between the third chamber and the outside of the developing container through the opening. 3. The developing device according to claim 1, wherein in the sealed state, an uppermost end of the third communication portion is located vertically below an attachment portion located on the partition side for attaching the sealing member to the developing container. 4. The developing device according to claim 1, wherein the opening is disposed vertically above the developer carrier . the developing container is composed of a first frame in which the first conveying screw and the second conveying screw are arranged and which accommodates the developer, and a second frame which is attached to the first frame and which covers a part of an outer circumferential surface of the developer carrier,
The developing device according to claim 1 , wherein the third chamber is provided in the second frame. The developing device according to any one of claims 1 to 5, wherein the third communicating portion is formed over an area of 90% or more of an area from a downstream end of the first communicating portion to an upstream end of the second communicating portion in the first direction. 7. The developing device according to claim 1, further comprising a filter provided in the opening for collecting toner. 8. The developing device according to claim 7, further comprising a filter cover provided vertically above the filter and overlapping the filter to cover the filter.

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