JP7621873B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus equipped with a developing device that develops an electrostatic image formed on an image 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 a development area where an electrostatic latent image formed on an image carrier is developed. While the developing device is operating, air flows into the developing container as the developing rotor rotates. In particular, when the rotation speed of the developing rotor is increased to increase the process speed, the amount of air flowing into the developing container per unit time increases, and the degree to which the internal pressure in the developing container increases increases. When the internal pressure in the developing container increases, the force of the air trying to be discharged from inside the developing container to the outside of the developing container through the opening of the developing container increases, and the amount of toner that scatters from inside the developing container to the outside of the developing container tends to increase.

The developing device described in Patent Document 1 has a discharge path forming member that covers the developing rotor along the outer peripheral surface of the developing rotor, and forms a discharge path that discharges air from within the developing container between the discharge path forming member and the inner wall surface of the developing container. This reduces the increase in internal pressure within the developing container and prevents air containing toner from being discharged to the outside of the developing container.

JP 2015-34965 A

When the developer is released from the developing rotor and returned to the screw, some of the toner in the developer may become suspended and fly up due to the impact of the fall or the rotation of the screw. In the configuration of Patent Document 1, if this toner enters the discharge path, there is a risk that the toner will be discharged out of the developing container through the discharge opening of the discharge path.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing a shortening of the life of a toner collecting member for collecting toner while reducing the amount of toner scattered outside a developing container.

In order to achieve the above object, an image forming apparatus according to one aspect of the present invention includes the following configuration: an image carrier on which an electrostatic image is formed, an exposure device that exposes the image carrier to light in order to form an electrostatic image on the image carrier, a rotatable developer carrier that carries and transports a developer containing a toner and a carrier to a development area in which the electrostatic image formed on the image carrier is developed, a developing frame that contains the developer and covers a part of the outer circumferential surface of the developer carrier, a flow path forming member that forms an inflow path having an inlet for introducing air and that causes air to flow into the inside of the developing frame through the inlet, and a discharge path having an outlet disposed adjacent to the inlet for discharging air and that causes air to be discharged to the outside of the developing frame through the outlet, a first electrode provided on the flow path forming member, and the flow path forming member of the developing frame. and a second electrode disposed opposite to the first electrode and provided at a portion facing the first electrode, and an electric field forming means for forming an electric field between the first electrode and the second electrode in the discharge path so that, during an image forming operation, normally charged toner moves to one side of the first electrode and the second electrode, and an oppositely charged toner, which is charged with a polarity opposite to that of the normally charged toner, moves to the other side of the first electrode and the second electrode, wherein a collecting member for collecting toner is provided in the discharge path, and the first electrode and the second electrode are disposed downstream of the collecting member in the discharge path in the rotational direction of the developer carrier .

According to the present invention, it is possible to reduce the amount of toner scattered outside the developing container , while preventing the life of the toner collecting member for collecting the toner from being shortened .

1 is a cross-sectional view showing an overall configuration of an image forming apparatus according to a first embodiment. 1 is a cross-sectional view illustrating a configuration of a developing device according to a first embodiment. FIG. 3 is an enlarged view of a region R0 shown in FIG. 2. 1 is a graph showing experimental results of Example 1 and a comparative example. FIG. 11 is a cross-sectional view showing a configuration of a developing device according to a second embodiment. FIG. 11 is a cross-sectional view showing a configuration of a developing device according to a third embodiment. 13 is a graph showing experimental results of Example 2, Example 3, and a comparative example.

The following describes in detail an embodiment of the present invention with reference to the accompanying drawings. Note that the following embodiment does not limit the scope of the present invention, and not all of the combinations of features described in the present embodiment are necessarily essential to the solution of the present invention. The present invention can be implemented in a variety of applications, including printers, various printing machines, copiers, fax machines, and multifunction machines.

[First embodiment]
(Overall configuration of image forming apparatus)
FIG. 1 is a diagram showing the overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. In the following, in the figure, in order to explain the arrangement of each component of the image forming apparatus 1, the space in which each component is arranged is represented as an xyz right-handed coordinate space. In addition, among the coordinate symbols shown in the figure, a symbol with a black circle inside a white circle represents an arrow pointing from the back side of the paper to the front side. In addition, a symbol with two intersecting lines inside a white circle represents an arrow pointing from the front side of the paper to the back side. The direction along the x-axis in space is called the x-axis direction. In addition, in the x-axis direction, the direction in which the x component increases is called the +x direction, and the direction in which the x component decreases is called the -x direction. For the y and z components, the y-axis direction, +y direction, -y direction, z-axis direction, +z direction, and -z direction are defined according to the above definitions.

As shown in FIG. 1, the image forming device 1 includes a control unit 11, an electric field forming means 12, developing units 13Y, 13M, 13C, and 13K, a transfer unit 14, a fixing unit 15, and a transport unit 16. The reference characters Y, M, C, and K indicate configurations corresponding to yellow, magenta, cyan, and black toners, respectively. The developing units 13Y, 13M, 13C, and 13K only differ in the toners they use, and there is no particular difference in their configurations. Hereinafter, when there is no need to distinguish between the developing units 13Y, 13M, 13C, and 13K, the letters at the end of the reference characters indicating the toner colors will be omitted and they will be referred to as the developing unit 13.

The control unit 11 has a CPU, ROM, RAM, and storage means such as a solid state drive and a hard disk drive. The CPU stands for Central Processing Unit. The ROM stands for Read Only Memory. The RAM stands for Random Access Memory. The CPU reads out and executes computer programs stored in these storage means to control each part of the image forming device 1 (e.g., the electric field forming means 12).

The transport unit 16 has a paper storage section and a transport roll. The paper storage section stores paper P as a medium that has been cut to a predetermined size. The paper P stored in the paper storage section is taken out one sheet at a time by the transport roll in response to instructions from the control unit 11, and is transported to the transfer unit 14 via the paper transport path. Note that the medium is not limited to paper, and may be, for example, a resin sheet. In short, the medium may be anything on whose surface an image can be recorded.

Each developing unit 13 includes a rotatable image carrier 31, a charging device 32, an exposure device 33, a developing device 34, a primary transfer roll 35, and a drum cleaner 36. The image carrier 31 is a photosensitive drum having a charge generating layer and a charge transport layer, and is rotated in the direction of the arrow D13 in the figure by the driving unit. The charging device 32 charges the surface of the image carrier 31. The exposure device 33 includes a laser light source and a polygon mirror, and irradiates the image carrier 31 after it has been charged by the charging device 32 with laser light according to the image data under the control of the control unit 11. As a result, a latent image (electrostatic image) is carried on each image carrier 31. The image data may be obtained by the control unit 11 from an external device via the communication unit. The external device may be, for example, a reading device that reads the original image or a storage device that stores data indicating the image. The developing device 34 supplies developer to the image carrier 31 in the development area. This causes an image to be formed (developed) on the image carrier 31.

The primary transfer roll 35 generates a predetermined potential difference at the position where the intermediate transfer belt 41 of the transfer section 14 faces the image carrier 31, and this potential difference transfers the image to the intermediate transfer belt 41. The drum cleaner 36 removes any untransferred toner remaining on the surface of the image carrier 31 after the image is transferred, and discharges the surface of the image carrier 31.

The transfer unit 14 includes an intermediate transfer belt 41, a secondary transfer roll 42, a belt transport roll 43, a backup roll 44, and a belt cleaner 49, and is a transfer unit that transfers the image formed by the development unit 13 to paper P. The intermediate transfer belt 41 is an endless belt member, and the belt transport roll 43 and the backup roll 44 stretch the intermediate transfer belt 41. At least one of the belt transport roll 43 and the backup roll 44 is provided with a drive unit, which moves the intermediate transfer belt 41 in the direction of arrow D14 in FIG. 1. The belt transport roll 43 or the backup roll 44, which does not have a drive unit, rotates with the movement of the intermediate transfer belt 41. As the intermediate transfer belt 41 moves and rotates in the direction of arrow D14 in FIG. 1, the image on the intermediate transfer belt 41 is moved to the area sandwiched between the secondary transfer roll 42 and the backup roll 44.

The secondary transfer roll 42 transfers the image on the intermediate transfer belt 41 to the paper P transported from the transport unit 16 by using a potential difference with the intermediate transfer belt 41. The belt cleaner 49 removes any untransferred toner remaining on the surface of the intermediate transfer belt 41. The transfer unit 14 or the transport unit 16 then transports the paper P to which the image has been transferred to the fixing unit 15. The fixing unit 15 fixes the image transferred to the paper P by heating.

(Configuration of the developing device)
FIG. 2 is a cross-sectional view showing the configuration of the developing device 34. FIG. 3 is an enlarged view of the region R0 shown in FIG. 2. As shown in FIG. 2, the developing device 34 is disposed on the lower side of the outer circumferential surface of the image carrier 31 in the +y direction, and has a developer carrier 340 and two screws 349. As shown in FIG. 3, the developing device 34 has a container 341 as a developing frame that contains a developer containing toner and a carrier and covers a part of the outer circumferential surface of the developer carrier 340, and a discharge path forming member 342. The discharge path forming member 342 is a member for forming an inflow path that causes air to flow into the container 34 and a discharge path that causes air to be discharged to the outside of the container 34.

The container 341 is a container (developing container) that contains a two-component developer containing toner of one of the colors Y, M, C, or K and a magnetic carrier such as ferrite powder, as well as the developer carrier 340 and two screws 349. The container 341 also has an opening 3410 on the side facing the image carrier 31 that exposes a portion of the developer carrier 340.

The developer carrier 340 is a cylindrical member (developing rotor) that carries the developer and rotates to supply the developer to the image carrier 31 on which an electrostatic latent image is formed. The developer carrier 340 is provided so as to face the image carrier 31 through the opening 3410 of the container 341. The developer carrier 340 has a magnet roller as a magnetic field generating means that generates a magnetic field, and a developing sleeve that carries the developer on its surface. The magnet roller is fixed inside the developing sleeve and forms multiple magnetic poles along the axial direction at predetermined angular positions. The multiple magnetic poles include a developing pole (S1) that is the magnetic pole located closest to the development region R1, and a peeling pole (S2) that is a magnetic pole that generates a magnetic field to peel the developer from the surface of the developing sleeve. The magnetic pole adjacent to the peeling pole downstream in the rotation direction of the developer carrier 340 has the same polarity as the peeling pole. For example, if the peeling pole is an S pole, the adjacent magnetic pole downstream of the peeling pole in the rotation direction of the developer carrier 340 is also an S pole. When the developing sleeve passes through a location corresponding to the magnetic pole of the magnet roller, a magnetic force acts on the developer on the developing sleeve.

The developing sleeve is a non-magnetic cylindrical member that covers the outer periphery of the magnet roller and has a voltage applied to it. This developing sleeve is rotated by the drive unit in the direction of arrow D0 shown in FIG. 2, that is, in the direction in which the part of the developer carrier 340 that is exposed from the opening 3410 and faces the image carrier 31 has a component that moves vertically from bottom to top. As a result, the developer that is subjected to the magnetic force from the magnet roller is transported in the direction of arrow D0.

The two screws 349 supply the developer to the developer carrier 340 while stirring it. The supplied developer is arranged in a bundle along the magnetic field lines by the magnetic force applied by the magnet roller, forming a so-called magnetic brush. The magnetic brush thus formed is carried on the developer carrier 340 and moves to a position facing the image carrier 31 as the developer carrier 340 rotates. Then, when the tip of the magnetic brush comes into contact with the surface of the image carrier 31, the toner adheres to the portion of the surface of the image carrier 31 exposed by the exposure device 33, that is, the image portion of the electrostatic latent image. That is, in the supply area (development area R1) in FIG. 2, the developer carried on the developer carrier 340 is supplied to the image carrier 31, and an image is formed on the image carrier 31.

The discharge path forming member 342 extends in the direction of the rotation axis of the developer carrier 340 along the outer peripheral surface of the developer carrier 340, covering a portion of the developer carrier 340, and forms a discharge path 343 between the discharge path forming member 342 and the inner wall surface of the container 341, which discharges air from the inside of the container 341 to the outside. The discharge path forming member 342 is supported by the container 341 by a rib installed on a portion of the inner wall surface of the container 341.

The discharge path forming member 342 is a flow path forming member that forms an inflow path 3411 having an inflow path inlet 3412 as an inlet through which air flows in, and a discharge path 343 having a discharge path outlet 3432 as an outlet through which air is discharged. The inflow path 3411 is a path (inflow path) that allows air to flow into the inside of the container 341 via the inflow path inlet 3412. The discharge path 343 is a path (discharge path) that allows air to be discharged to the outside of the container 341 via the discharge path outlet 3432. The discharge path outlet 3432 is provided with multiple ribs at intervals in the direction of the rotation axis of the developer carrier 340.

As shown in FIG. 3, the inlet 3412 is disposed downstream of the development area in the rotational direction of the developer carrier 340. More specifically, the inlet 3412 is disposed downstream of the development area in the rotational direction of the developer carrier 340 and upstream of the topmost part T (top) of the developer carrier 340. The inlet 3412 and the outlet 3432 are disposed adjacent to each other.

The discharge path forming member 342 covers the apex T (the top of the developer carrier 340), which is the highest position through which the outer circumferential surface of the developer carrier 340 passes. The discharge path outlet 3432 of the discharge path 343 is located closer to the image carrier 31 than the apex T.

Valves V1 and V2 are provided on the lower side of the opening 3410 of the container 341. Valve V1 contacts the developer carrier 340 at an angle where the distance from the surface of the developer carrier 340 decreases as the developer carrier 340 advances in the direction of arrow D0. Valve V1 restricts the flow of air so that the developer is less likely to blow out toward the image carrier 31 from the gap between the developer carrier 340 and the lower side of the opening 3410. Valve V2 also restricts the diffusion of the developer by contacting the image carrier 31.

The layer regulating member B (regulating blade) is a member known as a trimmer bar or the like, which comes into contact with the magnetic brush formed on the surface of the developer carrier 340 rotating in the direction of the arrow D0, scraping off a portion of it and adjusting the magnetic brush to approach a set height. The scraped off developer returns to the screw 349. The magnetic brush, whose height has been adjusted, passes a position facing the image carrier 31, supplies toner to the surface of the image carrier 31, and then moves to the region R covered by the discharge path forming member 342.

The discharge path forming member 342 is provided with a valve V3. The valve V3 contacts the developer carrier 340 at an angle such that the distance between the valve V3 and the surface of the developer carrier 340 decreases as the developer carrier 340 advances in the direction of the arrow D0. The valve V3 restricts the flow of air so that the developer is less likely to blow out toward the image carrier 31 from the gap between the developer carrier 340 and the upper side of the opening 3410.

In this way, valves V1 and V3 restrict the air inside container 341 so that it is difficult for it to flow in the direction from opening 3410 toward image carrier 31. Then, the magnetic brush that passes through valve V3 and reaches top portion T moves into container 341, sucking in air, and the internal pressure of container 341 rises.

As shown in FIG. 3, the discharge path forming member 342 covers an area R of at least one-quarter of the entire outer circumferential surface of the developer carrier 340, including the portion located at the apex T. In the first embodiment, the most downstream end 342e of the discharge path forming member 342 in the rotation direction of the developer carrier 340 is extended to a position below the rotation axis (center of rotation) of the developer carrier 340. This makes it difficult for floating toner from the developer carried by the developer carrier 340 to enter the discharge path inlet 3431.

In addition, a discharge passage outlet 3432 is formed adjacent to the opening 3410.

Furthermore, it is desirable that the discharge path inlet 3431, which is the inlet of the discharge path 343, is located vertically below the position of the center of the rotation axis of the developer carrier 340. This is because by locating the discharge path inlet 3431 vertically below the position of the center of the rotation axis of the developer carrier 340, the toner in the developer (floating toner in the container 341) that has detached from the developer carrier 340 near the peeling pole is less likely to enter the discharge path inlet 3431.

The discharge path forming member 342 is located in a position where it does not come into contact with the developer carried by the developer carrier 340. The air inside the container 341 enters the discharge path inlet 3431 of the discharge path 343 along the direction of arrow D1 shown in FIG. 3, and is discharged from the discharge path outlet 3432 of the discharge path 343 along the direction of arrow D2 toward the image carrier 31. This suppresses the rise in the internal pressure of the container 341, and reduces the risk of toner blowing out from the gap in the developing device 34 and soiling the medium, etc. However, after the developer transported by the developer carrier 340 passes through the top part T, the developer is detached from the developer carrier 340 at the peeling pole (S2) of the magnet roller and returned to the screw 349. At this time, there is a risk that some of the toner in the developer may become suspended due to the impact of the drop or the rotation of the screw 349, enter the discharge path inlet 3431, pass through the discharge path 343, and be discharged from the container 341 through the discharge path outlet 3432.

Here, we will explain toner release in detail. The two-component developer contained in the container 341 is triboelectrically charged, and the toner adheres to the carrier by electrostatic adhesion caused by triboelectric charging and non-electrostatic adhesion caused by surface properties. When an impact or shear force is applied to the toner attached to the carrier, the toner is peeled off from the carrier and released inside the container 341. The impact and shear force at this time include the behavior of the developer when the developer is transported by the developer carrier 340. The developer forms a magnetic chain-like structure along the magnetic field lines on the magnetic pole of the magnet roller. The magnetic chain rises forward just before the magnetic pole, and when it passes over the magnetic pole, it tilts forward and falls. At this time, the rotation direction of the magnetic chain is the same as the rotation direction of the developer carrier 340. The toner is peeled off from the carrier by the impact and centrifugal force when the magnetic chain falls, which is the cause of toner release.

Due to these factors, the scattered toner may be discharged outside the container 341 and contaminate the surroundings of the developing device 34, the outer walls of the container 341, the image carrier 31, the exposure device 33, and the intermediate transfer belt 41. This phenomenon becomes more pronounced as the process speed increases due to the high speed of the image forming device 1, and the circumferential speed of the developer carrier 340 increases accordingly, because the inflow airflow caused by the rotation of the developer carrier 340 increases.

The invention according to the first embodiment has been made in consideration of the above problems. In the invention according to the first embodiment, a pair of electrodes is disposed in the discharge path 343. During image formation operation, the electric field forming means 12 forms an electric field between the pair of electrodes disposed in the discharge path 343, and the force of the electric field generated between the electrodes presses floating toner that has entered the discharge path entrance 3431 against one of the electrodes, causing it to adhere to the electrode. This reduces the amount of toner that scatters outside the container 341, even if floating toner enters the discharge path entrance 3431. The details are described below.

As described above in FIG. 3, the developing device 34 according to the first embodiment has a discharge path forming member 342 that covers the developer carrier 340 along the outer peripheral surface of the developer carrier 340. In addition, the developing device 34 according to the first embodiment has a discharge path 343 formed between the discharge path forming member 342 and the inner wall surface of the storage section 341 to discharge air from inside the storage container 341.

In the developing device 34 according to the first embodiment, therefore, electrodes 345 and 346 are arranged opposite each other in the discharge path 343. During image formation, the force of the electric field generated between electrodes 345 and 346 arranged opposite each other in the discharge path 343 presses the toner against one of the electrodes, causing it to adhere to the other electrode. This prevents the toner from being discharged from the discharge path outlet 3432 to the outside of the container 341, even if some of the toner in the developer floats and enters the discharge path inlet 3431. This reduces the amount of toner that scatters outside the container 341.

The developing device 34 according to the first embodiment has the following configuration to suppress an increase in the internal pressure of the container 341 and reduce toner scattering from the discharge path 343. As shown in FIG. 3, the developing device 34 has electrodes 345 and 346 disposed on the container 341 and the discharge path forming member 342, which form the discharge path entrance 3431, so as to face each other within the discharge path 343.

The voltage (development bias) applied to the developer carrier 340 is a bias in which a direct current bias (DC) and an alternating current bias (AC) are superimposed, and the DC component of the development bias is -400 [V].

The AC wiring of the developing bias applied to the developer carrier 340 is rectified to a DC bias via a rectifier board provided in the container 341, and the rectified DC bias is applied to the electrode 346. In the first embodiment, a rectified DC bias of -800 [V] is applied to the electrode 346. This eliminates the need to provide a power supply for applying a bias to the electrode 346 in addition to a power supply for applying a bias to the electrode 345. In other words, the power supply for applying a bias to the electrode 346 and the power supply for applying a bias to the electrode 345 are the same power supply.

In addition, a modified example may be used in which a power supply for applying a bias to electrode 345 and a power supply for applying a bias to electrode 346 are provided separately. In other words, a modified example may be used in which a power supply for applying a bias to electrode 346 and a power supply for applying a bias to electrode 345 are provided as separate power supplies.

During image formation operation, a voltage is applied to electrode 345 such that the absolute value of the potential is smaller than the absolute value of the potential of electrode 346. In the first embodiment, electrode 345 is grounded, so the potential of electrode 345 is set to 0 [V]. In the first embodiment, the width of electrodes 345 and 346 is 5 mm, and the shortest distance between electrodes 345 and 346 is 3 mm.

During image formation, the normally charged toner among the floating toner that has entered the discharge path entrance 3431 is pressed against and adheres to electrode 345 by the force of the electric field generated between the electrodes (between electrode 345 and electrode 346) arranged in the discharge path 343. That is, during image formation, the electric field forming means 12 forms an electric field between electrodes 345 and 346 arranged in the discharge path 343 so that the normally charged toner moves from the electrode 346 side to the electrode 345 side.

On the other hand, during image formation operation, the oppositely charged toner among the floating toner that has entered the discharge path entrance 3431 is pressed against and adheres to electrode 346 by the force of the electric field generated between the electrodes (between electrode 345 and electrode 346) arranged in the discharge path 343. Note that the oppositely charged toner is toner that is charged with the opposite polarity to the normally charged toner. For example, when the normally charged toner is negatively charged, the oppositely charged toner is positively charged.

That is, during the image forming operation, the electric field forming means 12 forms an electric field between the electrodes 345 and 346 arranged in the discharge path 343 so that the oppositely charged toner moves from the electrode 345 side to the electrode 346 side. In addition, a modified example may be used in which the electric field forming means 12 forms an electric field between the electrodes 345 and 346 so that the normally charged toner moves from the electrode 345 side to the electrode 346 side and the oppositely charged toner moves from the electrode 346 side to the electrode 345 side during the image forming operation.

This reduces the amount of toner suspended in the air that is discharged from the discharge path outlet 3432 to the container 341, thereby reducing the amount of toner that scatters outside the developing container.

In addition, due to the force of the electric field generated between the electrodes (between electrodes 345 and 346) arranged in the discharge path 343, the toner adhering to electrode 345 or electrode 346 will fall under its own weight as it accumulates. Therefore, even if toner adheres to electrode 345 or electrode 346, there is no risk of it interfering with the discharge of discharge path 343 (discharging air to the outside of container 341 via discharge path outlet 3432). In addition, since the toner that falls under its own weight is mixed with the developer in screw 349 and then carried by developer carrier 340, there is no risk of image defects due to uneven toner concentration.

(Experimental Example)
Next, an experiment (hereinafter, referred to as this experiment) in which the amount of toner scattering was compared between the configuration of the comparative example and the configuration of the first embodiment in order to confirm the effect of the first embodiment will be described. The device used in this experiment was an assembly of the developing device 34, the image carrier 31, and the charging device 32. In this experiment, the amount of toner scattering was measured as follows, while driving the image carrier 31 for rotation, charging, and development, and applying a bias voltage, as in normal image formation.

In this experiment, an APS spectrometer Model 3321 was used as a device for measuring the amount of scattering. The particle size range for the APS spectrometer Model 3321 is 0.5 to 20 μm. In areas other than both ends of the longitudinal direction of the developing device 34, the toner inside the developing device 34 passes through a gap between the discharge path outlet 3432 and the image carrier 31 and scatters to the outside. Therefore, a suction tube for sucking up scattered toner was placed in the gap between the discharge path outlet 3432 and the image carrier 31, and at a position 5 mm vertically above the discharge path outlet 3432, and the amount of scattering was measured.

Measurement conditions were a temperature of 23°C and a relative humidity of 50%, a weight ratio of toner to developer in the two-component developer of 9%, a toner charge of 25 μC/g, a linear velocity of the image carrier 31 of 300 mm/sec, and a linear velocity of the developer carrier 340 of 540 mm/sec, and measurements were taken for 3 minutes. The number of scattered particles of each particle size per unit time was then measured. In addition, assuming that the toner of each particle size is spherical, the scattered weight per unit time was calculated from the volume of each particle size, the number of scattered particles per unit time, and the toner specific gravity. The toner specific gravity in this experiment was 1.2 g/cm3.

In addition, because the experimental equipment was configured as described above, the contribution of toner replenishment and the effect of airflow inside the image forming device on toner scattering were not taken into consideration.

In the comparative experiment, as in the first embodiment, an experimental device was created in which a pair of electrodes (electrodes 345, 346) were provided at the positions shown in FIG. 3 in the discharge path 343 of the developing device 34, electrode 345 was set to ground potential (0 V), and −800 V was applied to electrode 346 (Example 1). Furthermore, an experimental device was created in which a pair of electrodes was not provided at the positions shown in FIG. 3 in the discharge path 343 of the developing device 34 (Comparative Example). Note that the configurations of Example 1 and Comparative Example are the same, except for whether or not a pair of electrodes is provided at the positions shown in FIG. 3 in the discharge path 343 of the developing device 34. Then, experiments were performed under the above-mentioned conditions in each experimental device of Example 1 and Comparative Example.

The experimental results of Example 1 and Comparative Example are shown in the graph in Figure 4. Figure 4 is a diagram showing the particle size distribution of the number of toner particles scattered per unit time in each experimental device of Example 1 and Comparative Example. As shown in Figure 4, it can be seen that the number of toner particles scattered per unit time is significantly reduced in Example 1 compared to the Comparative Example. This confirms that Example 1, which is the configuration of the first embodiment, can significantly reduce the amount of toner scattering compared to the Comparative Example.

As described above, in the first embodiment, the electrodes 345 and 346 are installed in the container 341 and the discharge path forming member 342 that form the discharge path entrance 3431 so as to face each other in the discharge path 343. In the first embodiment, during the image forming operation, the force of the electric field generated between the electrodes 345 and 346 causes the normally charged toner of the floating toner that has entered the discharge path entrance 3431 to adhere to one electrode, and the oppositely charged toner to adhere to the other electrode. As a result, even if floating toner enters the discharge path entrance 3431, the amount of toner that scatters outside the container 341 can be reduced. Therefore, the increase in the internal pressure of the container 341 can be suppressed, and toner scattering from the discharge path 343 can be reduced.

In addition, in the first embodiment, the downstream end 342e of the discharge path forming member 342 in the rotation direction of the developer carrier 340 is extended to a position below the rotation axis (center of rotation) of the developer carrier 340. This makes it difficult for floating toner from the developer carried by the developer carrier 340 to enter the discharge path inlet 3431.

In addition to providing electrodes 345 and 346 in discharge path 343, a collection member (filter) for collecting toner may also be provided. By collecting toner with a filter provided in discharge path 343, even if floating toner enters discharge path inlet 3431 and passes between electrodes 345 and 346, it is possible to prevent the toner from being discharged outside container 341 from discharge path outlet 3432. This can further reduce the amount of toner that scatters outside container 341.

In view of the filter's lifespan due to clogging of the filter, it is preferable to make the toner adhere to one of the electrodes by the force of the electric field generated between electrodes 345 and 346 arranged in discharge path 343 before the toner is captured by the filter arranged in discharge path 343. That is, in a previous stage, it is preferable to block the toner that has entered discharge path inlet 3431 with an electric field by the action of electrodes 345 and 346 arranged in discharge path 343, and then collect the remaining toner that has not been blocked by the electric field with the filter.

Therefore, in order to maximize the life of the filter, it is more preferable to position the filter in the discharge path 343 at the discharge path outlet 3432 of the discharge path 343. Specifically, the filter is placed in a position that blocks the discharge path outlet 3432 over the entire longitudinal area of the discharge path 343 (the entire area corresponding to the maximum image area in which an image can be formed on the image carrier 31).

Second Embodiment
In the above-described first embodiment, an example was described in which the electrodes 345 and 346 are disposed on the container 341 and the discharge path forming member 342 that form the discharge path inlet 3431 so as to face each other in the discharge path 343. Also, in the first embodiment, an example was described in which the discharge path forming member 342 is extended to a position lower than the rotation axis (rotation center) of the developer carrier 340 in order to make it difficult for floating toner from the developer carried by the developer carrier 340 to enter the discharge path inlet 3431.

On the other hand, the second embodiment differs from the first embodiment in the configuration of the discharge path forming member 342 (specifically, the position of the downstream end 342e of the discharge path forming member 342 in the rotation direction of the developer carrier 340, and the position of the discharge path inlet 3431). In addition, the second embodiment differs from the first embodiment in the configuration of the discharge path forming member 342, and the shape of the electrode 345 disposed in the discharge path 343 is also different. The other basic configurations are common to the first and second embodiments. Therefore, the configuration of the developing device 34 according to the second embodiment will be described using the cross-sectional view of FIG. 5.

As shown in FIG. 5, in the second embodiment, the discharge path forming member 342 is shorter than in the first embodiment. Specifically, in the second embodiment, the position at which the discharge path forming member 342 is extended (the downstream end 342e of the discharge path forming member 342 in the rotation direction of the developer carrier 340) is above the rotation axis (center of rotation) of the developer carrier 340.

Also, as shown in FIG. 5, in the second embodiment, electrodes 345 and 346 are installed at the discharge path entrance 3431, and further, the extension 345e of the electrode 345 is extended to a position that does not face the discharge path forming member 342. That is, in the second embodiment, the extension 345e of the electrode 345 faces the developer carrier 340, and when viewed in a cross section perpendicular to the rotation axis of the developer carrier 340, the extension 345e of the electrode 345 is extended to a position that intersects with a horizontal line passing through the rotation center of the developer carrier 340. As a result, a part of the floating toner that is about to enter the discharge path entrance 3431 is pressed against the extension 345e of the electrode 345 by the weak electric field formed between the extension 345e of the electrode 345 and the developer carrier 340 during the image forming operation.

In this second embodiment, the discharge path forming member 342 is shorter than in the first embodiment, and the weak electric field formed between the extension 345e of the electrode 345 and the developer carrier 340 during image formation makes it difficult for floating toner to enter the discharge path inlet 3431.

[Third embodiment]
The third embodiment is different from the first and second embodiments in the configuration of the discharge path forming member 342 (specifically, the position of the most downstream end 342e of the discharge path forming member 342 in the rotation direction of the developer carrier 340 and the position of the discharge path inlet 3431). The other basic configurations are common to the first, second, and third embodiments.

The configuration of the developing device 34 according to the third embodiment will be described with reference to the cross-sectional view of FIG. 6.

As shown in FIG. 6, in the third embodiment, the discharge path inlet 3431 is disposed upstream in the rotation direction of the developer carrier 340 from the peak position where the magnetic flux density Br of the peeling pole (S2) in the normal direction of the developer carrier 340 is maximum. Also, the discharge path inlet 3431 is disposed downstream in the rotation direction of the developer carrier 340 from the peak position where the magnetic flux density Br of the development pole (S1) in the normal direction of the developer carrier 340 is maximum. That is, the electrode 346 is exposed on both sides of the discharge path forming member 342 so as to face the region of the developer carrier 340 upstream of the peak position of the magnetic flux density of the peeling pole and downstream of the peak position of the magnetic flux density of the development pole with respect to the rotation direction of the developer carrier 340.

Floating toner in the container 341 occurs not only when the developer is transported by the rotation of the developer carrier 340, or when it falls when peeled off, but also when the magnetic brush comes into contact with the valve V3. The toner floating in the valve V3 is pressed against the developer carrier 340 by the electric field between the electrode 346 and the developer carrier 340 at a position upstream of the peak position of the magnetic flux density of the peeling pole and downstream of the peak position of the magnetic flux density of the development pole in the direction of rotation of the developer carrier 340. This allows the floating toner to be returned to the developer again, thereby reducing the floating toner in the container 341, and reducing the amount of floating toner entering the discharge path inlet 3431, and suppressing the discharge of toner from the discharge path outlet 3432 to the outside of the container 341.

(Experimental Example)
In order to confirm the effects of the second and third embodiments, an experiment was conducted in the same manner as in the first embodiment to compare the amount of scattered toner between the configuration of the comparative example, the configuration of the second embodiment (Example 2), and the configuration of the third embodiment (Example 3). The apparatus and experimental conditions used in the experiment were the same as those described above in the first embodiment. That is, in the experiment, the amount of scattered toner was measured while driving the rotation, charging, and development of the image carrier 31 and applying a bias voltage, as in normal image formation. The experimental results of Examples 2 and 3 and the comparative example will be described with reference to the graph in FIG. 7.

In the second embodiment described above, the discharge path inlet 3431 is located near the peeling pole (S2), so the toner floating near the peeling pole (S2) is more likely to move toward the discharge path inlet 3431 than in the first embodiment. On the other hand, in the second embodiment, the weak electric field formed between the extension 345e of the electrode 345 and the developer carrier 340 during the image formation operation suppresses toner scattering, so the degree of reduction in toner scattering from the discharge path 343 can be made equivalent to that of the first embodiment. In addition, in the third embodiment, the floating toner in the container 341 is reduced by contact with the valve V3, and the floating toner entering the discharge path inlet 3431 can be reduced, so the degree of reduction in toner scattering from the discharge path 343 can be increased compared to the first and second embodiments.

Other Embodiments
The present invention is not limited to the above-described embodiments, and various modifications (including organic combinations of the respective embodiments) are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

In the above embodiment, as shown in FIG. 1, an image forming apparatus using an intermediate transfer belt 41 has been described as an example, but this is not limited to this. The present invention can also be applied to an image forming apparatus configured to transfer by directly contacting the paper P with the image carrier 3 in sequence.

REFERENCE SIGNS LIST 1 Image forming apparatus 12 Electric field forming means 31 Image carrier 33 Exposure device 34 Developing device 340 Developer carrier 341 Container 3411 Inflow path 3412 Inflow path inlet 342 Discharge path forming member 343 Discharge path 3431 Discharge path inlet 3432 Discharge path outlet 345 Electrode member 346 Electrode member

Claims (7)

an image carrier on which an electrostatic image is formed;
an exposure device that exposes the image carrier to light in order to form an electrostatic image on the image carrier;
a developing device including: a rotatable developer carrying member which carries and transports a developer containing a toner and a carrier to a development region where an electrostatic image formed on the image carrying member is developed; a developing frame which contains the developer and covers a part of an outer circumferential surface of the developer carrying member; a flow path forming member for forming an inflow path having an inlet for introducing air and for introducing air into the inside of the developing frame via the inlet; and a discharge path having an outlet disposed adjacent to the inlet for discharging air and for discharging air to the outside of the developing frame via the outlet; a first electrode provided on the flow path forming member; and a second electrode provided on a portion of the developing frame which faces the flow path forming member and which is disposed opposite to the first electrode;
an electric field forming means for forming an electric field between the first electrode and the second electrode in the discharge path so that, during an image forming operation, normally charged toner moves to one side of the first electrode and the second electrode, and an oppositely charged toner, which is charged with a polarity opposite to that of the normally charged toner, moves to the other side of the first electrode and the second electrode;
Equipped with
a collecting member for collecting toner is provided in the discharge path,
In the discharge path, the first electrode and the second electrode are disposed downstream of the collecting member in the rotation direction of the developer carrier.
1. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein during an image forming operation, the electric field forming means forms an electric field between the first electrode and the second electrode in the discharge path so that the normally charged toner adheres to the second electrode and the oppositely charged toner adheres to the first electrode. 3. The image forming apparatus according to claim 1, wherein the second electrode is grounded during an image forming operation. 4. The image forming apparatus according to claim 1, wherein a power supply for applying a bias to the first electrode and a power supply for applying a bias to the second electrode are the same power supply. 4. The image forming apparatus according to claim 1, wherein a power supply for applying a bias to the first electrode and a power supply for applying a bias to the second electrode are separate power supplies. 6. The image forming apparatus according to claim 1, wherein the inlet is disposed downstream of the development area and upstream of a top portion of the developer carrier in a rotational direction of the developer carrier. 7. The image forming apparatus according to claim 1, wherein the collection member is disposed at the discharge port.

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