Developing device

Abstract

To provide a structure that can suppress an excessive discharge of a developer.SOLUTION: A discharge path 70 is provided outside a circulation route for a developer to connect to a first conveyance path 52, and has a discharge port 100 for discharging an excessive developer in a development container 2. A discharge conveyance unit 71 is provided below a blade 58b of a first conveyance screw 58 and conveys the developer to the discharge port 100. A magnet member 101 is arranged below an upper stream 103 of the discharge port 100 in a direction of conveying the developer in the discharge conveyance unit 71.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a developing device that develops an electrostatic latent image formed on an image carrier with a developer containing toner and carrier.

Background Art

[0002] In an image forming apparatus using an electrophotographic method or the like, an electrostatic latent image formed on a photosensitive drum is developed as a toner image by a developing device. As such a developing device, one using a two-component developer containing toner and carrier has been conventionally used. In a developing device using a two-component developer, for the purpose of suppressing deterioration of carrier particles, a so-called trickle developing method is widely used in which an excessive amount of the developer is discharged from a discharge port while toner containing a small amount of carrier is replenished (for example, Patent Document 1).

[0003] In a developing device, the internal pressure in the developing container may increase due to driving, and an air flow may blow out from the discharge port. The developer in the developing container may be excessively discharged by riding on this air flow. Patent Document 1 describes a configuration in which a regulating unit for regulating the blowing out of the air flow from the discharge port is provided in order to suppress such excessive discharge of the developer due to the air flow. In the case of the configuration described in Patent Document 1, a part of the regulating unit is missing, and the developer is discharged through this missing area, and the upper space where the developer does not exist is blocked by the area where the regulating unit is not missing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the case of the configuration described in Patent Document 1, since the regulating portion has a region with partial deficiency, there may be a slight gap in the path to the discharge port. In order to further increase the speed of the developing device, there is a risk that air flow may flow out from the slight gap, leading to excessive discharge of the developer.

[0006] An object of the present invention is to provide a configuration capable of suppressing excessive discharge of the developer.

Means for Solving the Problems

[0007] The developing device of the present invention includes a developing container that houses a developer containing toner and carrier, and has a first chamber and a second chamber that forms a circulation path of the developer with the first chamber, a first conveying unit that conveys the developer in the first direction in the first chamber, a second conveying unit that conveys the developer in a second direction opposite to the first direction in the second chamber, a discharge port provided outside the circulation path and having a discharge path for discharging the excess developer in the developing container and connecting to the first chamber, a discharge conveying unit provided on the downstream side in the first direction of the first conveying unit for conveying the developer toward the discharge port, and magnetic field generating means disposed on the downstream side of the upstream end of the discharge port with respect to the conveying direction of the developer of the discharge conveying unit.

Effects of the Invention

[0008] According to the present invention, excessive discharge of the developer can be suppressed.

Brief Description of the Drawings

[0009]

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Embodiments for Carrying Out the Invention

[0010] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 12. First, the schematic configuration of the image forming apparatus of this embodiment will be described with reference to FIG. 1.

[0011] [Image Forming Apparatus] The image forming apparatus 200 is an electrophotographic full-color printer provided corresponding to four colors of yellow, magenta, cyan, and black and having four image forming units PY, PM, PC, and PK. In this embodiment, the image forming units PY, PM, PC, and PK are arranged in a tandem type along the rotation direction of the intermediate transfer belt 10 described later. The image forming apparatus 200 forms a toner image (image) on a recording material in response to an image signal from a document reading apparatus (not shown) connected to the image forming apparatus main body or a host device such as a personal computer communicably connected to the image forming apparatus main body. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0012] To explain the outline of such an image forming process, first, in each of the image forming units PY, PM, PC, and PK, toner images of respective colors are formed on the photosensitive drums 13Y, 13M, 13C, and 13K. The toner images of respective colors thus formed are transferred onto the intermediate transfer belt 10, and then transferred from the intermediate transfer belt 10 onto the recording material. The recording material onto which the toner image has been transferred is conveyed to the fixing device 11, and the toner image is fixed to the recording material. Details will be described below.

[0013] Note that the four image forming units PY, PM, PC, and PK included in the image forming apparatus 200 have substantially the same configuration except that the developing colors are different. Therefore, hereinafter, the image forming unit PY will be described as a representative, and the configurations of the other image forming units are shown by replacing the subscript "Y" of the reference numerals attached to the configuration in the image forming unit PY with M, C, and K, respectively, and the description thereof will be omitted.

[0014] In the image forming unit PY, a cylindrical photoreceptor, that is, a photosensitive drum 13Y is disposed as an image carrier. Around the photosensitive drum 13Y, a charging roller 12Y (charging device), a developing device 1Y, a primary transfer roller 17Y, and a cleaning device 15Y are arranged. Below the photosensitive drum 13Y in the drawing, an exposure device (laser scanner) 14Y is arranged.

[0015] The charging roller 12Y rotates in a driven manner with respect to the photosensitive drum 13Y during image formation. The charging roller 12Y is biased by a pressure spring (not shown) toward the photosensitive drum 13Y. Further, a charging bias is applied to the charging roller 12Y from a high-voltage power source. Thereby, the photosensitive drum 13Y is charged substantially uniformly by the charging roller 12Y.

[0016] Further, an intermediate transfer belt 10 is disposed facing the photosensitive drums 13Y, 13M, 13C, and 13K. The intermediate transfer belt 10 is stretched by a plurality of stretching rollers and moves in a circular motion by the driving of a driving roller which is one of the plurality of stretching rollers. At a position facing the secondary transfer inner roller 18 among the plurality of stretching rollers with the intermediate transfer belt 10 interposed therebetween, a secondary transfer outer roller 16 as a secondary transfer member is arranged, which constitutes a secondary transfer unit T2 for transferring the toner image on the intermediate transfer belt 10 to a recording material. A fixing device 11 is arranged downstream in the recording material conveyance direction of the secondary transfer unit T2. Further, a feeding unit (not shown) is arranged at the lower part of the image forming apparatus 200. The recording material fed from the feeding unit at the start of the image forming operation is conveyed to the secondary transfer unit T2 at a predetermined timing.

[0017] A process of forming an image by the image forming apparatus 200 configured as described above will be described. First, when the image forming operation starts, the surface of the rotating photosensitive drum 13Y is uniformly charged by the charging roller 12Y. Next, the photosensitive drum 13Y is exposed by laser light corresponding to the image signal emitted from the exposure device 14Y. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 13Y. The electrostatic latent image on the photosensitive drum 13Y is visualized by the toner contained in the developing device 1Y and becomes a visible image (toner image).

[0018] The toner image formed on the photosensitive drum 13Y is primarily transferred to the intermediate transfer belt 10 at the primary transfer unit T1Y formed between the primary transfer roller 17Y disposed with the intermediate transfer belt 10 interposed therebetween. The toner remaining on the surface of the photosensitive drum 13Y after the primary transfer (transfer residual toner) is removed by the cleaning device 15Y.

[0019] Such operations are sequentially performed in each of the magenta, cyan, and black image forming units, and the four-color toner images are superimposed on the intermediate transfer belt 10. Thereafter, the recording material accommodated in the recording material storage cassette (not shown) of the feeding unit is conveyed to the secondary transfer unit T2 in accordance with the formation timing of the toner image, and the four-color toner images on the intermediate transfer belt 10 are collectively secondarily transferred onto the recording material. The toner remaining on the intermediate transfer belt 10 without being completely transferred at the secondary transfer unit T2 is removed by the intermediate transfer belt cleaner 19.

[0020] Next, the recording material is conveyed to the fixing device 11. The fixing device 11 includes a fixing roller 20 having a heat source such as a halogen heater inside and a pressure roller 21, and forms a fixing nip portion by the fixing roller 20 and the pressure roller 21. By passing the recording material conveyed to the fixing device 11 through the fixing nip portion, the toner image is fixed to the recording material. Thereafter, the recording material is discharged outside the machine. Thus, a series of image forming processes is completed. It is also possible to form a monochromatic or multi-color image of a desired color using only a desired image forming unit.

[0021] [Developer] Here, the two-component developer used in this embodiment will be described. The developer is a mixture of a negatively charged non-magnetic toner and a positively charged magnetic carrier. The non-magnetic toner is obtained by encapsulating a colorant, a wax component, etc. in a resin such as polyester or styrene-acrylic, pulverizing or polymerizing it into a powder, and adding fine powders such as titanium oxide and silica to the surface. The magnetic carrier is obtained by applying a resin coat to the surface layer of a core composed of resin particles kneaded with ferrite particles or magnetic powder.

[0022] [Developing Device] Next, the detailed configuration of the developing device 1Y will be described with reference to FIGS. 2 and 3. The same applies to the developing devices 1M, 1C, and 1K. The developing device 1Y includes a developing container 2 that houses a developer composed of a magnetic carrier and a non-magnetic toner, and a developing sleeve 54 as a developer carrier that carries and conveys the developer in the developing container. The surface of the developing sleeve 54 is rotatably held, while a magnet roll 54a composed of a plurality of magnetic poles (S1, S2, S3, N1, N2) is non-rotatably disposed inside.

[0023] The developing container 2 is partitioned by a partition wall 51 into a first conveyance path (agitation chamber) 52 as a first chamber and a second conveyance path (developing chamber) 53 as a second chamber. The first conveyance path 52 and the second conveyance path 3 communicate with each other through communication ports at both ends. Thereby, a circulation path for the developer is formed by the first conveyance path 52 and the second conveyance path 53.

[0024] Two screw members are provided in the developing container 2 as conveyance members for conveying the developer while agitating it. That is, a first conveyance screw 58 is provided in the first conveyance path 52, and a second conveyance screw (second conveyance part) 59 is provided in the second conveyance path 53. The first and second conveyance screws 58 and 59 each have a rotation shaft 58a and 59a, and blades 58b and 59b provided spirally around the rotation shafts 58a and 59a (on the rotation shafts).

[0025] When the first conveying screw 58 rotates around the rotation axis 58a, the developing agent in the first conveying path 52 is conveyed in the direction of arrow α (first direction), which is one side in the longitudinal direction of the developing device 1Y (axial direction of the rotation axis 58a), by the spiral blades 58b. When the second conveying screw 59 rotates around the rotation axis 59a, the developing agent in the second conveying path 53 is conveyed in the direction of arrow β (second direction), which is the other side in the longitudinal direction of the developing device 1Y (axial direction of the rotation axis 58a), by the spiral blades 59b. Thereby, the developing agent is circulated between the first conveying path 52 and the second conveying path 53.

[0026] The developing device 1Y has a toner concentration sensor (permeability sensor) 61 as a concentration detecting means capable of detecting the toner concentration (the ratio of the weight of toner particles to the total weight of carrier particles and toner particles, T / D ratio) in the developing container 2. The toner concentration sensor 61 is provided at a predetermined position in the first direction of the first conveying path 52 and detects the toner concentration in the first conveying path 52. In the present embodiment, an inductance sensor is used as the toner concentration sensor 61, and the sensor surface (detection surface) of the inductance sensor is exposed in the first conveying path 52. The inductance sensor detects the permeability of a predetermined detection range from the sensor surface. When the toner concentration of the developing agent changes, the permeability also changes due to the mixing ratio of the magnetic carrier and the non-magnetic toner. Therefore, the toner concentration can be detected by detecting the change in the permeability with the inductance sensor.

[0027] The developing agent in the second conveying path 53 is pumped up within the magnetic force range of the S2 pole by the second conveying screw 59 installed below the developing sleeve 54 inside the second conveying path 53 and is carried on the surface of the developing sleeve 54. The carried developing agent is conveyed as the surface of the developing sleeve 54 rotates. Near the N1 pole of the magnetic pole of the developing sleeve 54, a regulating blade 55 is arranged with a predetermined gap from the surface of the developing sleeve 54 as a member for forming a thin layer of the developing agent. Generally, the gap between the developing sleeve 54 and the regulating blade 55 is set to about 200 to 500 μm. The wider the gap, the larger the amount of the developing agent carried on the developing sleeve 54.

[0028] The conveyed developer forms a magnetic brush at the N1 pole, and a desired amount of the developer is formed into a thin layer on the surface of the developing sleeve 54 by a regulating blade 55 installed at a predetermined interval from the developing sleeve 54. Then, the developer conveyed to the opposing portion of the photosensitive drum 13Y forms a magnetic brush again at the S1 pole and forms a developing nip with the photosensitive drum 13Y.

[0029] As described above, the surface of the photosensitive drum 13Y is charged to a certain potential by the charging roller 12Y, and the image portion is exposed by the exposure device 14Y to form an exposure potential. On the other hand, a developing bias is applied to the developing sleeve 54 through a high-voltage circuit (not shown). The developing bias is, for example, a bias in which a rectangular AC waveform is superimposed on a DC waveform of a constant voltage. The toner charged in the developing device 1Y obtains a driving force due to the potential difference between the developing bias and the surface potential of the drum in the developing nip and adheres to the exposed portion, thereby completing the developing process.

[0030] The carrier and the toner that has not been developed are further conveyed downstream in the rotation direction of the developing sleeve 54, lose the magnetic restraint force in the zero-gauss zone (a region where the radial magnetic flux density becomes zero) formed between the S2 pole and the S3 pole, and are recovered into the second conveyance path 53 again.

[0031] When the developing operation is performed, only the toner among the developer is consumed, so the weight ratio (T / D ratio) of the developer to the toner decreases. Therefore, the T / D ratio is controlled to a predetermined value by performing the toner replenishment operation. In this embodiment, the predetermined T / D ratio is set to 8%.

[0032] As shown in FIG. 4, a hopper 75 containing a replenishing developer composed of toner and magnetic carrier is installed above the developing device 1Y, and a mechanism is provided to supply the amount of toner used for image formation to the developing device 1Y. The replenishment amount of toner is controlled by a control unit (not shown) rotating a supply screw 76. Specifically, the control unit calculates the toner consumption amount used for image formation based on the image ratio during image formation, the result of magnetically detecting the T / D ratio in the developing container 2 by a toner density sensor 61 (FIGS. 2 and 3), etc., and determines the toner replenishment amount. For example, a control toner image (patch image) is formed on the intermediate transfer belt 10 every time a predetermined number of images are formed, and the result detected by a reflection density sensor (not shown) is also used to determine the toner replenishment amount.

[0033] Toner replenishment is performed from a toner replenishment port 40 provided in the developing container 2 (see FIG. 3). In the present embodiment, the toner replenishment port is provided above and outside the conveyance path of the first conveyance screw 58 at the upstream end in the first direction of the first conveyance screw 58. However, the position of the replenishment port can be installed in various places depending on the main body configuration of the image forming apparatus and the like, and is not limited to this location. The replenished toner circulates while being agitated and conveyed together with the developer by the first conveyance screw 58 and the second conveyance screw 59 through the first conveyance path 52 and the second conveyance path 53.

[0034] [Trickle development method] In the developing device 1Y in the present embodiment, a trickle development method (hereinafter referred to as trickle) for suppressing the deterioration of the carrier in the developer is adopted. Trickle is a development method in which when the bulk of the developer in the developing container 2 becomes a certain level or more, surplus developer is discharged from a discharge port 100 (see FIG. 8, etc.) provided in the developing container 2, and carrier replenishment is performed by a small amount of carrier contained in the replenishing toner.

[0035] Figs. 5(a) and 5(b) are diagrams for explaining an example of the configuration and mechanism of a general trickle. Hereinafter, when using the terms "upstream" and "downstream", the upstream (right side of the paper) and downstream (left side of the paper) in the conveying direction (first direction) by the blades 58b of the first conveying screw 58 shall be indicated.

[0036] The first conveying screw 58 includes a rotating shaft 58a, blades 58b for conveying the developer in the first direction in the first conveying path 52, and a reverse conveying portion 58c as a reverse conveying portion for pushing back the developer in the upstream direction at the downstream end of the first conveying screw 58. A discharge path 70 for discharging the excess developer is connected downstream of the first conveying path 52, and a discharge port 100 is opened downward in the gravitational direction downstream thereof. The discharge path 70 is provided outside the circulation path of the developing container 2 and is connected to the first conveying path 52.

[0037] A discharge conveying portion 71 is provided in the discharge path 70. The discharge conveying portion 71 is a conveying screw having spiral blades formed on a rotating shaft 58a which is the same rotating shaft as the first conveying screw 58, and has a role of conveying the developer in the downstream direction toward the discharge port 100. The inner diameter of the discharge path 70 and the outer diameter of the discharge conveying portion 71 are formed to be smaller than the inner diameter of the first conveying path 52 and the blades 58b, respectively.

[0038] In Figs. 5(a) and 5(b), the matte portions are those that ostensibly show the regions where the developer exists. As shown in Fig. 5(a), when the bulk of the developer in the first conveying path 52 is small and the agent surface is low, all of the developer conveyed by the blades 58b is pushed back by the reverse conveying portion 58c. On the other hand, as shown in Fig. 5(b), when the bulk of the developer in the first conveying path 52 increases and the agent surface rises above a certain level, the developer that cannot be completely pushed back by the reverse conveying portion 58c climbs over the reverse conveying portion 58c. Then, when the climbed-over developer accumulates until it exceeds a step 60 between the first conveying path 52 and the discharge path 70, it can be conveyed by the discharge conveying portion 71, is carried to the discharge port 100, and is discharged as excess developer.

[0039] As the use of the developing device 1Y progresses, it is known that the charging ability of the carrier decreases as the external additive contained in the toner adheres to the surface of the carrier. FIG. 6 is a graph showing the average residence time (representing the degree of deterioration of the carrier) of the carrier in the developing container 2 when trickle is not performed (a) and when it is performed (b). The conditions for this calculation were calculated with an image density of 5%, a developer amount of 250 g in the developing container 2, a T / D ratio of the developer of 8%, and a weight ratio of the carrier in the replenishing toner of 10%.

[0040] In FIG. 6(a), the average residence time increases in proportion to the usage period (number of image formations). On the other hand, in FIG. 6(b), since the old carrier is consumed and new carrier replenishment is supplied, the average residence time of the carrier is shorter than in the case of FIG. 6(a) and converges to a certain time (saturation residence time). That is, the deterioration of the carrier does not progress beyond a certain level, and the toner charging ability by the carrier can be maintained.

[0041] As described above, in the trickle development method, a trace amount of carrier is contained in the replenishing toner. Therefore, the amount of the developer in the developing container 2 increases with the replenishment operation, and when the bulk becomes a certain level or more, a part spills further into the back of the reverse conveyance section 58c, and the developer is discharged from the discharge port 100. In this way, by a mechanism in which the discharge stops when the bulk of the developer is small and the developer is discharged when the bulk is large, the amount of the developer in the developing container 2 is maintained within a certain range.

[0042] [Regarding Excessive Discharge of Developer] As described above, the trickle development method is an effective technique for suppressing carrier deterioration in the developer. However, the discharge of the developer by the trickle development method may become excessive compared to the assumption. For example, as the driving speed of the developing device 1Y increases with the recent high-speed operation of the image forming apparatus, the amount of air taken into the developing container 2 increases as the developing sleeve 54 rotates, and the internal pressure of the developing container 2 rises. As a result of the internal pressure of the developing container 2 rising while the outside of the developing container 2 is at atmospheric pressure, an air pressure difference occurs between the inside and outside, and an air flow is generated that blows out from the discharge port 100 to the outside of the developing container 2 as shown in FIG. 7. Since this air flow contains the developer lifted by the screw, the developer reaches the discharge path 70 and is conveyed downstream by the discharge conveyance unit 71. In this way, even in a case where the developer should not be discharged, a small amount of the developer flows out from the discharge port 100.

[0043] If such a state of "excessive discharge" where trickle discharge occurs despite the small amount of the developer continues, the developer in the developing container 2 gradually decreases, and there is a risk that the developer cannot be satisfactorily supplied to the developing sleeve 54.

[0044] [Measures against Excessive Discharge of Developer] Therefore, in the present embodiment, as shown in FIG. 8, by disposing a ring-shaped magnet member 101, which is a magnetic field generating means, downstream in the conveyance direction of the discharge conveyance unit 71 from the end of the discharge port 100, excessive discharge of the developer in the developing container 2 is suppressed. This will be described in detail below. Hereinafter, in the discharge path 70, "upstream" and "downstream" shall be the upstream and downstream in the developer conveyance direction by the discharge conveyance unit 71, respectively.

[0045] First, also in the case of the configuration of the present embodiment, the first conveyance screw 58 that conveys the developer in the first conveyance path 52 in the first direction has a rotation shaft 58a and blades 58b as a first conveyance part provided spirally on the rotation shaft. Further, the discharge conveyance part 71 is provided on the downstream side in the first direction of the blades 58b and conveys the developer toward the discharge port 100. The discharge conveyance part 71 is configured by providing spiral blades on the rotation shaft 58a and conveys the developer in the same direction as the first direction. Furthermore, in the first direction, a reverse conveyance part 58c that conveys the developer in the direction opposite to the first direction is provided between the blades 58b and the discharge conveyance part 71. The reverse conveyance part 58c is also a blade provided spirally on the rotation shaft 58a.

[0046] Particularly in the case of the present embodiment, regarding the conveyance direction of the developer in the discharge conveyance part 71, a magnet member 101 as a magnetic field generation means is disposed on the downstream side of the upstream end 103 of the discharge port 100. The magnet member 101 is formed in a ring shape and is fixed to the inner wall of the discharge path 70 over the entire circumference on the downstream side of the discharge conveyance part 71. Specifically, the magnet member 101 is disposed at a predetermined interval in the first direction from the upstream end 103 of the discharge port 100.

[0047] Such a ring-shaped magnet member 101 has a shape as shown in FIG. 9, and in the present embodiment, the outer diameter is 14 mm, the inner diameter is 8 mm, and the thickness is 1.5 mm. And the rotation shaft 58a is configured to penetrate the central part thereof. Thereby, the inner peripheral surface 101a of the magnet member 101 faces the outer peripheral surface of the rotation shaft 58a over the entire circumference with a slight gap therebetween.

[0048] The magnet member 101 has one side surface magnetized to the S pole and the other side surface magnetized to the N pole, and a magnet member with a surface magnetic flux density of 50 mT or more and 60 mT or less (measured with a GX-100 manufactured by Nippon Denshi Sokki Co., Ltd.) was used. Also, in this embodiment, the N-pole surface is arranged so as to face the discharge port 100 side, but there is no particular problem regardless of which pole faces the discharge port 100 side. If the magnetic flux density of the magnet member 101 is too large, the friction between the attached developer and the rotating shaft 58a of the discharge conveyance unit 71 will become strong and there is a risk that the toner will adhere. Also, if the magnetic flux density is too small, the effects of this embodiment cannot be obtained. For this reason, in this embodiment, the magnetic flux density is set within the above range, but the magnetic flux density can be appropriately set depending on the configuration of the apparatus.

[0049] The developer conveyed by the discharge conveyance unit 71 is discharged by falling from the discharge port 100, but a part of the discharged developer is attracted by the magnetic force of the magnet member 101 and adheres to the surface of the magnet member 101. As the amount of developer adhering to the surface of the magnet member 101 gradually increases, as shown in FIG. 10, a reservoir region 102 is formed by the adhered developer.

[0050] Since this reservoir region 102 is formed so as to extend from the magnet member 101 toward the upstream end 103 of the discharge port 100 (right direction in FIG. 10), the discharge port 100 is covered by the reservoir region 102 formed as shown in FIG. 10. In the illustrated example, a part of the magnet member 101 is exposed at the discharge port 100, and the reservoir region 102 is formed so as to protrude below the discharge port 100. Note that the magnet member 101 does not have to be exposed at the discharge port 100, and it is sufficient that the magnet member 101 is arranged such that at least the discharge port 100 is covered by the reservoir region 102.

[0051] When the discharge port 100 is covered by the reservoir region 102, the flow path that blows out from the discharge port 100 to the outside of the developing container 2 as shown in FIG. 7 is blocked by this reservoir region 102, so the flow rate of the airflow that tries to flow out to the outside can be reduced. For this reason, it is possible to suppress the developer from being discharged to the outside from the discharge port 100 due to this airflow.

[0052] On the one hand, although the discharge port 100 is covered by the agent reservoir area 102, the developer being conveyed by the discharge conveyance unit 71 is pushed in the direction of the agent reservoir area 102 by the conveying force of the discharge conveyance unit 71. Then, when the amount of the developer exceeds the amount that can be supported by the magnetic force of the magnet member 101, the developer is naturally discharged downward from the discharge port 100 due to gravity. Therefore, the developer does not get clogged in the vicinity of the discharge port 100. In this way, it is possible to achieve both suppression of excessive developer discharge due to air flow and normal developer discharge by the discharge conveyance unit 71.

[0053] In the configuration of the present embodiment, the distance A between the upstream end 103 of the discharge port 100 and the magnet member 101 is set to 11.5 mm. However, since it is important to appropriately set this distance A, the reason will be described below.

[0054] As shown in FIG. 11(a), when the above distance A is set too wide, the formed agent reservoir area 102 cannot sufficiently cover the discharge port 100. For this reason, a gap through which the air flow passes is generated, and it becomes impossible to sufficiently suppress the air flow flowing to the outside and the developer being discharged by the air flow.

[0055] On the other hand, as shown in FIG. 11(b), when the distance A is set too narrow, the substantial opening width of the discharge port 100 becomes small, so the amount of the developer that can be discharged per unit time decreases. Therefore, when a high-image ratio image is continuous or the like, that is, when the supply amount of the developer per unit time is large, if the amount of the developer that can be discharged is less than the supply amount, the amount of the developer in the developing container 2 becomes excessive. As a result, problems such as developer leakage and poor agitation of the replenished toner occur.

[0056] Therefore, it is preferable that the distance A is such that the tip of the agent reservoir region 102 carried by the magnet member 101 reaches the upstream end 103 of the discharge port 100. For this purpose, in this embodiment, the distance A is set to 11.5 mm. However, the appropriate value of the distance A varies depending on the configuration near the discharge port 100, the size of the magnet member 101, and the magnetic force. Therefore, an appropriate value is set according to the configuration of the developing device.

[0057] Further, in this embodiment, a magnetic material is used as the material of the rotating shaft 58a of the discharge conveyance unit 71. When the material of the rotating shaft 58a is a magnetic body, the rotating shaft 58a passing through the center of the ring-shaped magnet member 101 is magnetized by the magnetic force of the magnet member 101. Therefore, a magnetic seal is formed between the inner peripheral surface 101a of the magnet member 101 and the rotating shaft 58a. Therefore, it is possible to suppress the developer from passing through the center of the ring-shaped magnet member 101 due to this magnetic seal.

[0058] Note that since the agent reservoir region 102 formed by the magnet member 101 only needs to cover the upper part of the discharge port 100, it is also possible to use a shape in which the upper part of the ring-shaped magnet member 101 is cut, for example, a semi-circular shape. That is, the magnet member 101 only needs to be arranged in a range including at least one end to the other end of the opening width of the discharge port 100 in the circumferential direction of the rotating shaft 58a. In other words, when viewed from the axial direction of the rotating shaft 58a, the magnet member 101 is located in the same phase as the discharge port 100 in the circumferential direction of the rotating shaft 58a and has a width equal to or greater than the width of the discharge port 100.

[0059] Further, the magnet member may be fixed to the rotating shaft 58a. In this case, it is preferable to provide the magnet member over the entire circumference of the rotating shaft 59a so as to have a slight gap with the inner peripheral surface of the discharge path 70. Further, the magnet member may be provided on the outer wall of the discharge path 70. In this case, the discharge path 70 is made of a non-magnetic member, and a magnetic force is applied to the inside of the discharge path 70 to form an agent reservoir region inside the discharge path 70.

[0060] In addition, as shown in FIG. 10, it is preferable that the discharge conveyance unit 71, which has spiral vanes, is arranged to extend to the downstream side in the conveyance direction from the upstream end 103 of the discharge port 100. Of course, the downstream end of the discharge conveyance unit 71 is positioned on the upstream side of the magnet member 101. With such a configuration, the conveyance force of the discharge conveyance unit 71 can surely push the developer storage area 102 in the conveyance direction, so that even when the supply amount of the developer is large, the developer can be discharged more surely.

[0061] Further, in the case of the present embodiment, since the magnet member 101 is located on the downstream side of the upstream end 103 of the discharge port 100 and the downstream end of the discharge conveyance unit 71, it is difficult for the developer to reach the downstream side of the magnet member 101 in the discharge path 70. For this reason, usually, a sealing member such as an oil seal provided at the downstream end of the discharge path 70 to prevent the developer from leaking may be omitted.

[0062] [Examples] Next, the experiment conducted to confirm the effects of the present embodiment will be described. In the experiment, an example of an image forming apparatus provided with the magnet member 101 as in the present embodiment and a comparative example of an image forming apparatus not provided with the magnet member were used, and the transition of the amount of developer in the image forming apparatus when continuously forming images with an image ratio of 0.5% was examined. In the example and the comparative example, the configurations are the same except for the presence or absence of the magnet member 101. The results are shown in FIG. 12.

[0063] In the case of an image with an image ratio of 0.5%, since the supply amount of the developer is very small, if the discharge amount from the image forming apparatus is large, the amount of developer in the image forming apparatus will gradually decrease. As is clear from FIG. 12, in the image forming apparatus having the configuration of the comparative example, the amount of developer gradually decreases as image formation continues, whereas in the case of the image forming apparatus having the configuration of the present example, the amount of developer in the image forming apparatus remains stable even when image formation continues.

[0064] As described above, with the configuration of the present embodiment, by covering the discharge port 100 with the agent storage region 102 formed by the magnet member 101, the air flow flowing out from the discharge port 100 can be suppressed, and excessive developer discharge due to the air flow can be suppressed. Therefore, even when the amount of developer supplied per unit time is small, the amount of developer in the developing device can be appropriately maintained.

[0065] <Second Embodiment> The second embodiment will be described with reference to FIG. 13. In the case of the configuration of the above-described first embodiment, the case where a ring-shaped magnet member is used was described. In contrast, in the present embodiment, a flat plate-shaped magnet member 101A is used. Since the other configurations and employments are the same as those of the first embodiment, the same reference numerals are given to the same configurations, and the description and illustration are omitted or simplified. Hereinafter, the description will focus on the parts different from the first embodiment.

[0066] In the present embodiment, a flat plate-shaped magnet member 101A as a magnetic field generating means is set at a position spaced by a distance A from the upstream end 103 of the discharge port 100. The magnet member 101A is fixed to the inner peripheral surface of the discharge path 70 in a range including at least one end to the other end of the opening width of the discharge port 100 in the circumferential direction of the rotation axis 58a. In the present embodiment, since the magnet member 101A is not arranged over the entire circumference of the discharge path 70, an oil seal 72 as a sealing member for preventing the developer from leaking is provided on the downstream side of the magnet member 101A of the discharge path 70.

[0067] Also in the case of such a present embodiment, the agent storage region 102 is formed by the developer adhering to the surface attracted by the magnetic force of the magnet member 101A, and the discharge port 100 is sealed by this agent storage region 102. Therefore, since the flow path blowing out from the discharge port 100 to the outside of the developing container 2 is blocked by the agent storage region 102, the flow rate of the air flow flowing out to the outside can be reduced. Therefore, it is possible to suppress the developer from being discharged to the outside from the discharge port 100 by this air flow.

[0068] Further, the developer conveyed by the discharge conveyance unit 71 is pushed downstream in the conveyance direction by the conveyance force of the discharge conveyance unit 71, but an oil seal 72, which is a sealing member, is provided further downstream than the magnet member 101A. For this reason, the developer is not conveyed beyond the oil seal 72, and the developer that has exceeded the magnet member 101A is pulled back by the magnetic force of the magnet member 101A and becomes part of the agent reservoir region 102.

[0069] When the amount of the developer exceeds the amount that can be supported by the magnetic force of the magnet member 101A, the developer is naturally discharged downward from the discharge port 100 by gravity. In this way, it is possible to achieve both suppression of excessive developer discharge due to the air flow and normal developer discharge by the discharge conveyance unit 71.

[0070] As described above, even with the configuration of the present embodiment, it is possible to suppress excessive developer discharge due to the air flow flowing out from the discharge port 100, and the amount of the developer in the developing device can be appropriately maintained even when the amount of the developer supplied per unit time is small.

[0071] <Third Embodiment> The third embodiment will be described with reference to FIG. 14. In the case of the configurations of the above-described first and second embodiments, the configuration in which the magnet member is provided in the discharge path 70 has been described. In contrast, in the present embodiment, the magnet member 101B is provided in the discharge connection path 104 connected to the discharge port 100. Since the other configurations and employments are the same as those of the first embodiment, the same reference numerals are given to the same configurations, and the description and illustration are omitted or simplified. Hereinafter, the description will focus on the parts different from the first embodiment.

[0072] First, a discharge connection path 104 as a second discharge path is connected to the discharge port 100 of the discharge path 70 as the first discharge path. The discharge connection path 104 discharges the developer to the outside from the discharge port 100. For example, the discharge connection path 104 is connected to a recovery container for the developer provided outside, and the developer discharged from the discharge port 100 is recovered into the recovery container through the discharge connection path 104. Such a discharge connection path 104 is formed of a non-magnetic material such as resin. For example, it is integrally formed with the developing container 2 by resin. Note that the discharge connection path is usually provided also in the configurations of the first and second embodiments.

[0073] Particularly, in the present embodiment, a magnet member 101B as a magnetic field generating means is provided on the outer wall of the discharge connection path 104. The magnet member 101B is formed in a flat plate shape and is provided on the downstream end side of the discharge port 100 among the outer walls of the discharge connection path 104. Note that the magnet member 101B may be arranged so as to cover the entire circumference of the outer wall of the discharge connection path 104, or may be provided on the upstream end side of the discharge port 100. Further, it may be provided on the inner wall of the discharge connection path 104. In any case, the magnet member 101B may be arranged so that the agent accumulation region 102 formed by the magnetic force of the magnet member 101B blocks the discharge connection path 104.

[0074] Also, in the case of the present embodiment, the magnet member 101B is arranged at the upstream end portion in the direction in which the developer in the discharge connection path 104 passes. And in the vicinity of the discharge port 100, the discharge connection path 104 is blocked by the agent accumulation region 102.

[0075] Also, in the case of the present embodiment, different from the first and second embodiments, since no magnet member is provided in the discharge path 70, a pushing-back portion 71a for pushing back the developer is provided on the downstream side of the discharge port 100. The pushing-back portion 71a is a spiral blade in the direction opposite to the spiral blade of the discharge conveyance portion 71, and conveys the developer in the direction opposite to the developer conveyance direction of the discharge conveyance portion 71. Further, in the case of the present embodiment, an oil seal 72 is provided on the downstream side (the left side in FIG. 14) of the pushing-back portion 71a, similarly to the second embodiment.

[0076] Also in the case of such an embodiment of the present invention, the agent storage region 102 is formed by the developer adhering to the inner peripheral surface of the discharge connection path 104 and attracted by the magnetic force of the magnet member 101B, and the discharge connection path 104 is sealed by this agent storage region 102. Therefore, since the flow path blowing out from the discharge port 100 to the outside of the developing container 2 is blocked by this agent storage region 102, the flow rate of the air flow flowing out to the outside can be reduced. For this reason, it is possible to suppress the developer from being discharged to the outside from the discharge port 100 due to this air flow.

[0077] The developer conveyed by the discharge conveyance unit 71 is pushed in the left direction of FIG. 14 by the conveying force of the discharge conveyance unit 71. However, an oil seal 72 which is a sealing member and a pushing-back portion 71a for pushing back the developer are installed at the downstream end of the discharge port 100. For this reason, the developer is not conveyed ahead of the oil seal 72 and is pushed in the direction of the discharge port 100 installed below. When the amount of the developer pushed in exceeds the amount of the developer that can be supported by the magnetic force of the magnet member 101B, the developer is naturally discharged downward from the discharge port 100 by gravity. In this way, it is possible to achieve both suppression of excessive developer discharge due to the air flow and normal developer discharge by the discharge conveyance unit 71. Note that the pushing-back portion 71a may be omitted.

[0078] As described above, also in the configuration of the present embodiment, it is possible to suppress excessive developer discharge due to the air flow flowing out from the discharge port 100, and even when the amount of the developer supplied per unit time is small, the amount of the developer in the developing apparatus can be appropriately maintained.

[0079] <Fourth Embodiment> The fourth embodiment will be described with reference to FIGS. 15 to 19. In the case of the configurations of the above-described first and second embodiments, a configuration in which the magnet member is provided on the downstream side of the upstream end 103 of the discharge port 100 was described. In contrast, in the present embodiment, the magnet member 101C is provided upstream of the upstream end 103 of the discharge port 100. Since the other configurations and employment are the same as those of the first embodiment, the same reference numerals are given to the same configurations, and the description and illustration are omitted or simplified. Hereinafter, the description will focus on the parts different from the first embodiment.

[0080] In the present embodiment, as shown in FIG. 15, a part of the blades of the discharge conveyance unit 71 is notched, and a magnet member 101C as a magnetic field generating means is fixed around the rotation shaft 58a over the entire circumference. Specifically, the flat magnet member 101C is fixed by attaching it so as to wind around the entire circumference of the rotation shaft 58a. The developer carried on the outer peripheral surface of the magnet member 101C forms a magnetic brush between the inner peripheral surface of the discharge path 70 and the rotation shaft 58a. As a result, the air flow path in the discharge path 70 is blocked by the magnetic brush.

[0081] The attachment position of the magnet member 101C in the longitudinal direction (the axial direction of the rotation shaft 58a) is downstream in the first direction from the reverse conveyance unit 58c. The reason is as follows. If the magnet member 101C is arranged upstream in the first direction from the reverse conveyance unit 58c and a magnetic brush is formed at a position upstream of the reverse conveyance unit 58c, the air flow path leading to the discharge port 100 cannot be sufficiently blocked, and excessive discharge of the developer cannot be sufficiently suppressed.

[0082] Also, a configuration in which the blades of the reverse conveyance unit 58c are notched in the middle to provide the magnet member 101C is also assumed. However, since the reverse conveyance unit 58c is a member that conveys the developer upstream in the first direction, even when the bulk of the developer increases, the sealing by the magnetic brush cannot be broken, and the discharge function of the developer is impaired. The above is the reason why the attachment position in the longitudinal direction of the magnet member 101C is downstream of the reverse conveyance unit 58c. If it is downstream in the first direction from the reverse conveyance unit 58c, the magnet member 101C may be provided in the first conveyance path 52, but as in this embodiment, it is preferable to arrange the magnet member 101C in the discharge path.

[0083] FIG. 16(a) is a perspective view of the magnet member 101C, and FIG. 16(b) is a cross-sectional view of the magnet member 101C when cut in the axial direction of the rotating shaft 58a. The magnet member 101C is composed of a flexible plate-shaped magnet member 110 and a seal surface 111 of a double-sided tape attached to one surface of the magnet member 110. The magnet member 101C has exactly the same length as one round of the rotating shaft 58a, and there is no gap when viewed from the cross-section when wound around the shaft.

[0084] FIG. 17 shows the magnetization pattern of the magnet member 101C in this embodiment. The plate-shaped magnet member 101C is magnetized on both sides, with the seal surface 111 side being the S pole and the surface being the N pole. However, the reverse direction may be reversed.

[0085] The outer diameter of the position where the magnet member 101C is attached to the rotating shaft 58a is preferably designed to be an appropriate size according to the magnitude of the magnetic force and the thickness of the magnet member 101C. Since the height of the bristles of the magnetic brush depends on the magnitude of the magnetic force of the magnet member 101C, in order to block the air flow path by the magnetic brush, it is desirable to keep the gap between the magnet member 101C and the discharge path 70 at an appropriate distance. If the gap between the magnet member 101C and the discharge path 70 is too close to the strength of the magnetic force, when the bulk density of the developer increases, the discharge of the excess developer is not satisfactorily performed. Conversely, if the magnetic force is too weak, the sealing property is insufficient and the air flow cannot be blocked. In the present embodiment, the gap between the outer peripheral surface of the magnet member 101C and the inner peripheral surface of the discharge path 70 is set to 1 mm or more.

[0086] Also, in the present embodiment, as the magnet member 101C, one having a thickness of 1.0 mm, a width of 3 mm, and a surface magnetic force of 60 mT (measured with a GX-100 manufactured by Nihon Denshi Sokki Co., Ltd.) was used. The height of the bristles of the magnetic brush was calculated as the average bristle height from an image three-dimensionally acquired using a 3D laser microscope (VK-8700 manufactured by Keyence Corporation). When the average bristle height of the above-described magnet member 101C was measured, it was 1.2 mm. Therefore, by setting the outer diameter of the position where the magnet member 101C is attached to the rotating shaft 58a to 8 mm and the inner diameter of the discharge path 70 to 12 mm, the gap between the magnet member 101C and the discharge path 70 was set to 1 mm. Then, the magnetic brush was brought into contact with the inner wall of the discharge path 70 to block the air flow.

[0087] Next, the discharge mechanism of the developer in the present embodiment will be described. FIG. 18(a) is a diagram showing the state of the surface of the developer when the bulk density of the developer is low, and FIG. 18(b) is a diagram showing the state of the surface of the developer when the bulk density of the developer has increased.

[0088] Considering a state where a certain amount of developer has already been discharged by the trickle development method, a magnetic brush along the magnetic field lines as shown in Figs. 18(a) and (b) is formed around the magnet member 101C. As shown in Fig. 18(a), when the bulk density of the developer is low, the magnetic brush formed around the magnet member 101C blocks the path through which air escapes toward the discharge port 100. Therefore, the air flow as shown in Fig. 7 does not occur, or even if it occurs, the air flow rate is reduced. As a result, the developer hardly reaches the discharge path 70, and excessive discharge of the developer is less likely to occur.

[0089] On the other hand, as shown in Fig. 18(b), when the bulk density of the developer increases, the developer that cannot be pushed back by the reverse conveyance unit 58c reaches the discharge path 70 and is conveyed downstream by the discharge conveyance unit 71. When the amount of the conveyed developer increases and the agent pressure rises, the developer breaks through the restraining force of the magnetic brush and is conveyed to the most downstream, reaches the discharge port 100, and is discharged as surplus developer.

[0090] In the above description, the discharge conveyance unit 71 also exists downstream of the magnet member 101C. However, if the magnet member 101C is close to the discharge port 100, the discharge conveyance unit 71 may not be provided downstream of the magnet member 101C. That is, the discharge conveyance unit 71 only needs to be provided upstream of the magnet member 101C at least.

[0091] As described above, by sealing the space between the discharge path 70 and the rotating shaft 58a with a magnetic brush by the magnet member 101C, it is possible to effectively suppress the excessive discharge of the developer riding on the air flow without impairing the discharge performance of the developer.

[0092] Note that the magnetization pattern of the magnet member 101C is not limited to that shown in FIG. 17, and various patterns are conceivable. Examples of the magnetization pattern are shown in FIGS. 19(a) to (c). The magnet member 101Ca in FIG. 19(a) has the magnetization pattern of the magnet member 110A in the vertical direction instead of the front and back. The magnet member 101Cb in FIG. 19(b) is obtained by further magnetizing both the front and back surfaces of the magnet member 110B with respect to FIG. 19(a). The magnet member 101Cc in FIG. 19(c) is obtained by alternately magnetizing the N pole and the S pole in a diagonal stripe pattern on the surface of the magnet member 110C. Even with these patterns, by making the magnetic brush contact the discharge path 70, it is possible to effectively suppress the excessive discharge of the developer riding on the air flow.

[0093] In addition to those exemplified in FIGS. 19(a) to (c), various implementable magnetization patterns can be considered. Needless to say, the effect of the present invention can be obtained as long as the magnetic brush contacts the inner wall of the discharge path 70.

[0094] <Fifth Embodiment> The fifth embodiment will be described with reference to FIGS. 20 and 21. In the case of the configuration of the above-described fourth embodiment, the configuration in which a magnetic brush is formed by a magnet member was described. In contrast, in the present embodiment, a brush member 120 is provided instead of the magnetic brush by the magnet member. Since the other configurations and applications are the same as those of the fourth embodiment, the same reference numerals are given to the same configurations, and the description and illustration are omitted or simplified. Hereinafter, the description will focus on the parts different from the fourth embodiment.

[0095] The brush member 120 is provided over the entire circumference between the rotary shaft 58a and the inner wall of the discharge path 70. In the present embodiment, as shown in FIG. 20, a part of the blades of the discharge conveyance unit 71 is cut out, and the brush member 120 is fixed over the entire circumference around the rotary shaft 58a. The fixing position of the brush member 120 is the same as the fixing position of the magnet member 101C in the fourth embodiment.

[0096] As shown in FIG. 21, the brush member 120 has fibers 122 implanted on one surface of a flexible base material 121, and a double-sided tape 123 is attached to the other surface to form an attachment surface. It is fixed by being wound around the rotating shaft 58a. Also in the case of this embodiment, as shown in FIG. 20, the hairs of the fibers 122 are in contact with the inner wall of the discharge path 70. Note that the brush member 120 may be fixed to the inner wall of the discharge path 70 so that the brush is in contact with the outer peripheral surface of the rotating shaft 58a.

[0097] This embodiment is different from the fourth embodiment in that the structure for sealing the air leakage path is made of implanted fibers instead of a magnetic brush. However, the mechanism for suppressing the excessive discharge of the excess developer is the same as that of the fourth embodiment. Also in the case of this embodiment, as in the fourth embodiment, it is possible to effectively suppress the excessive discharge of the developer riding on the air flow.

[0098] <Other Embodiments> In each of the above-described embodiments, the configuration in which the image forming apparatus is a printer has been described. However, the present invention is also applicable to a copying machine, a facsimile machine, a multifunction machine, and the like. Also, in each of the above-described embodiments, as a developing device, the configuration in which the developer is supplied from the developing chamber (second conveyance path 53, second chamber) to the developing sleeve and the developer is recovered from the developing sleeve in the developing chamber has been described. However, the present invention is also applicable to a configuration in which the developer is supplied from the developing chamber and the developer is recovered in a stirring chamber (first conveyance path 52, first chamber) disposed with a partition wall interposed therebetween. Furthermore, the present invention is applicable not only to a developing device in which the first chamber and the second chamber are arranged side by side in the horizontal direction, but also to a configuration in which the first chamber and the second chamber exist in a positional relationship such that they are in the vertical direction or inclined with respect to the horizontal direction. Note that the first chamber may be a developing chamber and the second chamber may be a stirring chamber.

Explanation of Reference Numerals

[0099] 1Y, 1M, 1C, 1K ··· Developing device / 2 ··· Developing container / 52 ··· First conveyance path (first chamber) / 53 ··· Second conveyance path (second chamber) / 54 ··· Developing sleeve / 58 ··· First conveyance screw / 58a ··· Rotation shaft / 58b ··· Blade (first conveyance section) / 58c ··· Reverse conveyance section / 59 ··· Second conveyance screw (second conveyance section) / 70 ··· Discharge path (first discharge path) / 71 ··· Discharge conveyance section / 100 ··· Discharge port / 101, 101A, 101B, 101C, 101Ca, 101Cb, 101Cc ··· Magnet member (magnetic field generating means) / 104 ··· Discharge connection path (second discharge path) / 120 ··· Brush member

Claims

【Claim 1】 A developing container that houses a developer containing toner and carrier, and has a first chamber and a second chamber that forms a circulation path of the developer with the first chamber; A first conveying unit that conveys the developer in a first direction in the first chamber; A second conveying unit that conveys the developer in a second direction, which is opposite to the first direction, in the second chamber; A discharge path that is provided outside the circulation path, has a discharge port for discharging excess developer in the developing container, and is connected to the first chamber; A discharge conveying unit that is provided on the downstream side in the first direction of the first conveying unit and conveys the developer toward the discharge port; Magnetic field generating means that is disposed on the downstream side of the upstream end of the discharge port with respect to the conveying direction of the developer of the discharge conveying unit; A developing device characterized by the above.

Images