JP2018112712A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve both improvement of developer strippability in the vicinity of a stripping pole of magnet means and a reduction in size of the device by adjusting a pattern of a magnetic attraction force in the vicinity of the stripping pole of magnet means.SOLUTION: A guide part is arranged, at a predetermined clearance with a developer carrier, on a surface of the developer carrier on the downstream side of a maximum peak position of a magnetic flux density of a first magnetic pole and the upstream side of a maximum peak position of a magnetic flux density of a second magnetic pole in the direction of rotation of the developer carrier, and opposite to a magnetic force area having an absolute value of the magnetic flux density equal to or less than a predetermined value and for peeling a developer passing through a developing area from the surface of the developer carrier. A permanent magnet is arranged on a surface of the developer carrier on the downstream side of the guide part and the upstream side of the maximum peak position of the magnetic flux density of the second magnetic pole in the direction of rotation of the developer carrier and opposite to the magnetic force area, and a magnetic pole of the permanent magnet on a side opposite to the magnetic force area is the same pole as the second magnetic pole.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a developing device for developing an electrostatic latent image.

  The developing device described in Patent Document 1 has a so-called function separation in which a function of supplying a developer containing toner and a magnetic carrier to a developer carrying member and a function of collecting the developer from the developer carrying member are separated. This is a mold developing device. The developing device includes a developing chamber for supplying the developer to the developer carrying member and a partition member (partition) for separating the stirring chamber for stirring the developer, and is provided below the developer carrying member. A developing chamber is disposed, and an agitating chamber is disposed opposite the developer carrier. Further, in this developing device, the developer that has passed through the developing area facing the image carrier (hereinafter referred to as developer after the developing process) is the same magnetic pole (peeling pole and pumping pole) adjacent to the magnet. Is peeled off from the surface of the developer carrying member by the repulsive magnetic field formed by the above. Therefore, in this developing device, the partition wall is provided with a guide portion for guiding the developer after the developing process peeled off from the surface of the developer carrying member to be collected in the stirring chamber. This guide portion is disposed with a predetermined clearance between the developer carrier.

  In recent years, developing devices have been downsized, and accordingly, the diameter of the developer carrying member has been reduced. When the diameter of the developer carrier is small, the magnet disposed inside the developer carrier is small compared to the case where the diameter of the developer carrier is large. As a result, the distance between adjacent magnetic poles adjacent to each other in the rotation direction of the developer carrying member is shortened and the size of the repulsive magnetic field region (peeling region) is reduced. It tends to be difficult to peel off from the surface of the carrier.

  In the developer after the development process, the toner in the developer is consumed in the development process, and the toner concentration in the developer is lowered. When the developer after the development process is not sufficiently peeled off from the surface of the developer carrier in the peeling area, the guide is accompanied by the rotation of the developer carrier while being held on the surface of the developer carrier. If the clearance between the portion and the developer carrier is passed, the following problem occurs.

  In the developer after the development process that has passed a predetermined clearance between the guide portion and the developer carrier, the toner concentration in the developer is reduced because the toner in the developer is consumed in the development process. ing. If the developer after the development process that has not been peeled off from the surface of the developer carrier passes through a predetermined clearance between the guide portion and the developer carrier, the toner density remains low. There is a risk of being subjected to development again in the development region without being sufficiently stirred. This is particularly a problem when the developing device is downsized and the diameter of the developer carrying member is reduced accordingly (that is, when the size of the magnet disposed inside the developer carrying member is reduced). .

  In the developing device described in Patent Document 2, a rotatable stripping roller having a magnet body therein is disposed in the vicinity of a stripping pole of a magnet disposed inside the developer carrier. In this developing apparatus, the developer after the development process carried on the developer carrying member is sucked to the peeling roller side by the magnetic pole inside the peeling roller, so that the developer in the vicinity of the peeling pole is peeled off. Improves sex.

JP 2011-28216 A JP 2002-148921 A

  In the function separation type developing device, when a peeling roller as in Patent Document 2 is arranged, the developer after the developing process sucked to the peeling roller side is transferred to the stirring chamber without passing through the developing chamber. It is necessary to newly provide a circulation mechanism for circulating the developer. Therefore, in the function separation type developing device, when the peeling roller as in Patent Document 2 is arranged, a space for arranging the circulation mechanism is required, which leads to an increase in the size of the device.

  Therefore, in a function separation type developing device, there is a demand for a new configuration capable of improving the developer stripping property in the vicinity of the stripping pole of the magnet means with a simple configuration without increasing the size of the device. It is rare.

  The present invention has been made in view of the above problems. An object of the present invention is to improve the developer stripping property in the vicinity of the stripping pole by adjusting the magnetic attraction force pattern in the vicinity of the stripping pole of the magnet means in the function separation type developing device. An object of the present invention is to provide an apparatus that can achieve both miniaturization of the apparatus.

  In order to achieve the above object, a developing apparatus according to an aspect of the present invention has the following arrangement. That is, a developer carrier that is rotatably provided, carries a developer containing toner and a magnetic carrier, and transports the developer to a development area facing the image carrier, and is disposed below the developer carrier. A supply chamber for supplying a developer to the developer carrier, a recovery chamber disposed opposite to the developer carrier, and collecting the developer that has passed through the development region from the developer carrier; The first magnetic pole and the downstream side of the first magnetic pole in the rotation direction of the developer carrier and adjacent to the first magnetic pole. And a magnet means for generating a magnetic field for separating the developer that has passed through the development area from the surface of the developer carrier, and a second magnetic pole that is the same as the first magnetic pole. , Generated by the magnet means A partition that guides the developer separated from the surface of the developer carrying member by a boundary so as to be collected in the collection chamber; a partition that separates the supply chamber from the collection chamber; and a permanent magnet And the guide portion is downstream of the maximum peak position of the magnetic flux density of the first magnetic pole and in the rotational direction of the developer carrier and from the maximum peak position of the magnetic flux density of the second magnetic pole. The surface of the developer carrying member on the upstream side, the absolute value of the magnetic flux density being a predetermined value or less, and the magnetic force region for the developer that has passed through the developing region to peel from the surface of the developer carrying member The permanent magnet is disposed downstream of the guide portion in the rotation direction of the developer carrier and the second magnetic pole. Maximum magnetic flux density Is located on the surface of the developer carrying member upstream of the first magnetic position and opposite to the magnetic field, and the magnetic pole of the permanent magnet facing the magnetic field is the same as the second magnetic pole. It is a pole.

  According to the present invention, in the function separation type developing device, by adjusting the magnetic attraction force pattern in the vicinity of the stripping pole of the magnet means, the developer stripping property in the vicinity of the stripping pole is improved. It is possible to simultaneously reduce the size of the apparatus.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus. It is sectional drawing which shows the structure of a function separation type developing apparatus. FIG. 2 is a schematic diagram illustrating a configuration of a function separation type developing device. 1 is a cross-sectional view illustrating a configuration of a developing device according to a first embodiment. It is a graph which shows distribution of the magnitude | size of magnetic flux density, and the magnitude | size of a magnetic attraction force. It is a schematic diagram which shows distribution of a magnetic force line and a magnetic attraction force. It is a schematic diagram which shows the direction of the magnetic field in the vicinity of a partition. It is a schematic diagram which shows the motion of the developer in the vicinity of a partition.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all the combinations of features described in the present embodiments are not necessarily essential to the solution means of the present invention. . The present invention can be implemented in various applications such as printers, various printing machines, copiers, FAX machines, and multifunction machines.

[First Embodiment]
(Configuration of image forming apparatus)
First, the configuration of the image forming apparatus according to the first embodiment of the present invention will be described with reference to the cross-sectional view of FIG.

  As shown in FIG. 1, the image forming apparatus 100 includes an endless intermediate transfer belt (ITB) 7 serving as an intermediate transfer member, and a downstream side from the upstream side along the rotation direction of the intermediate transfer belt 7 (in the direction of arrow R7). Four image forming units S (Sa, Sb, Sc, Sd) are provided on the side.

  Each of the image forming units S (Sa, Sb, Sc, Sd) forms toner images of respective colors of Y (yellow), M (magenta), C (cyan), and Bk (black).

  The image forming unit S (Sa, Sb, Sc, Sd) includes a rotatable photosensitive drum 1 (1a, 1b, 1c, 1d) as an image carrier.

  Each of the photosensitive drums 1 (1a, 1b, 1c, 1d) is rotationally driven in the direction of arrow R1 (R1a, R1b, R1c, R1d) (clockwise). Around the photosensitive drum 1 (1a, 1b, 1c, 1d), along the rotation direction of the photosensitive drum 1 (1a, 1b, 1c, 1d), charging rollers 2 (2a, 2b, 2c, 2d) are arranged. Further, around the photosensitive drum 1 (1a, 1b, 1c, 1d), an exposure device 3 (latent image forming means) is provided along the rotation direction of the photosensitive drum 1 (1a, 1b, 1c, 1d). 3a, 3b, 3c, 3d) are arranged.

  Further, around the photosensitive drum 1 (1a, 1b, 1c, 1d), there are a developing device 4 (4a, 4b, 4c, 4d) as a developing unit, and a primary transfer roller 5 (5a, 5b) as a primary transfer unit. 5c, 5d). A photosensitive member cleaning blade 6 (6a, 6b, 6c, 6d) as a photosensitive member cleaner is disposed around the photosensitive drum 1 (1a, 1b, 1c, 1d).

  Each of the developing devices 4 can be attached to and detached from the image forming apparatus 100. Each of the developing devices 4 (4a, 4b, 4c, and 4d) is a developing container that contains a two-component developer (hereinafter also simply referred to as a developer) containing a non-magnetic toner (hereinafter also simply referred to as a toner) and a magnetic carrier. 41 (41Y, 41M, 41C, 41K).

  The intermediate transfer belt 7 is stretched around a primary transfer roller 5 (5a, 5b, 5c, 5d), a secondary transfer counter roller 8, a tension roller 17, and a tension roller 18. The secondary transfer counter roller 8 also serves as a drive roller.

  The intermediate transfer belt 7 is pressed from the back side of the intermediate transfer belt 7 by the primary transfer rollers 5 (5a, 5b, 5c, 5d).

  The surface of the intermediate transfer belt 7 is in contact with the photosensitive drum 1 (1a, 1b, 1c, 1d). Thus, primary transfer nip portions T1 (T1a, T1b, T1c, T1d) as primary transfer portions are formed between the photosensitive drums 1 (1a, 1b, 1c, 1d) and the intermediate transfer belt 7. Yes.

  Further, as the secondary transfer counter roller 8 rotates in the direction of arrow R8 (counterclockwise), the intermediate transfer belt 7 rotates in the direction of arrow R7. The rotational speed of the intermediate transfer belt 7 is set to be approximately the same as the rotational speed (process speed) of each of the photosensitive drums 1 (1a, 1b, 1c, 1d).

  A secondary transfer roller 9 as a secondary transfer unit is disposed at a position corresponding to the secondary transfer counter roller 8 on the surface of the intermediate transfer belt 7. The intermediate transfer belt 7 is sandwiched between the secondary transfer counter roller 8 and the secondary transfer roller 9. Thus, a secondary transfer nip portion T2 as a secondary transfer portion is formed between the secondary transfer roller 9 and the intermediate transfer belt 7.

  A belt cleaner 11 as an intermediate transfer member cleaner is in contact with a position corresponding to the tension roller 17 on the surface of the intermediate transfer belt 7.

  A recording material P (for example, paper, transparent film) used for image formation by the image forming unit S (Sa, Sb, Sc, Sd) is stored in a state of being stacked on a feeding cassette 10 as a recording material storage unit. Has been. Then, the recording material P is supplied to the secondary transfer nip T2 by a feeding / conveying device having a feeding roller, a conveyance roller, a registration roller, and the like. A fixing device 13 having a fixing roller 14 and a pressure roller 15 is disposed downstream of the secondary transfer nip T2 in the conveyance direction of the recording material P. Further, a discharge tray for loading the recording material P discharged outside the apparatus is disposed downstream of the fixing device 13 in the conveyance direction of the recording material P.

(Configuration of image forming unit)
The photosensitive drum 1 (1a, 1b, 1c, 1d) is a cylindrical (drum-type) electrophotographic photosensitive member having a photosensitive layer that is an organic optical semiconductor having negative charging characteristics. For example, the photosensitive drum 1 (1a, 1b, 1c, 1d) has a diameter of 30 mm, a length in the longitudinal direction of 360 mm, and a process speed (peripheral speed) of 250 mm / sec. Further, at the time of image formation, the photosensitive drum 1 (1a, 1b, 1c, 1d) is rotationally driven in the forward direction (arrow R1 (R1a, R1b, R1c, R1d) direction) by a motor.

  The charging roller 2 (2a, 2b, 2c, 2d) is in contact with the photosensitive drum 1 (1a, 1b, 1c, 1d) and is directed toward the photosensitive drum 1 (1a, 1b, 1c, 1d) by a pressure spring. Is energized. At the time of image formation, the charging roller 2 (2a, 2b, 2c, 2d) rotates following the photosensitive drum 1 (1a, 1b, 1c, 1d). The charging roller 2 (2a, 2b, 2c, 2d) has, for example, a diameter of 14 mm and a length in the longitudinal direction of 320 mm. For example, a charging bias (DC voltage: −900 V, AC peak-to-peak voltage: 1500 V) is applied to the charging roller 2 (2 a, 2 b, 2 c, 2 d) from a high voltage power source as an application unit. Thereby, the photosensitive drum 1 (1a, 1b, 1c, 1d) is uniformly charged.

  The exposure device 3 (3a, 3b, 3c, 3d) is a laser beam provided with a semiconductor laser for irradiating the photosensitive drum 1 (1a, 1b, 1c, 1d) charged by the charging roller 2 with a laser beam. It is a scanner. The exposure device 3 (3a, 3b, 3c, 3d) is a photosensitive drum 1 (1a) charged by a charging roller 2 (2a, 2b, 2c, 2d) based on an image signal input to the image forming apparatus 100. 1b, 1c, 1d) to form an electrostatic latent image.

  The developing device 4 (4a, 4b, 4c, 4d) generates an electrostatic latent image formed on the photosensitive drum 1 (1a, 1b, 1c, 1d) by the exposure device 3 (3a, 3b, 3c, 3d). Developer (development with toner. As a result, the toner adheres to the exposed portions (laser light irradiated portions) on the photosensitive drums 1 (1a, 1b, 1c, 1d) to form a visible image. Details of the developing device 4 will be described later with reference to FIG.

  The transfer device has a primary transfer portion provided with a primary transfer roller 5 (5a, 5b, 5c, 5d) and a secondary transfer portion provided with a secondary transfer roller 9.

  The primary transfer roller 5 (5a, 5b, 5c, 5d) is pressed against the surface of the intermediate transfer belt 7 sandwiched between the photosensitive drum 1 (1a, 1b, 1c, 1d) with a predetermined pressing force. . Thereby, primary transfer nip portions T1 (T1a, T1b, T1c, T1d) as primary transfer portions are formed.

  The secondary transfer roller 9 is pressed against the surface of the intermediate transfer belt 7 sandwiched between the secondary transfer counter roller 8 with a predetermined pressing force. Thereby, a secondary transfer nip portion T2 as a secondary transfer portion is formed.

  A transfer bias is applied to the primary transfer roller 5 (5a, 5b, 5c, 5d), and the toner image formed on the photosensitive drum 1 (1a, 1b, 1c, 1d) is transferred onto the intermediate transfer belt 7. Is done. The transfer residual toner slightly remaining on the photosensitive drum 1 (1a, 1b, 1c, 1d) after the primary transfer is scraped and collected by the photosensitive member cleaning blade 6 (6a, 6b, 6c, 6d). .

  The recording material P fed from the feeding cassette 10 is fed to the secondary transfer unit by a registration roller. A transfer bias is applied to the secondary transfer roller 9, and the toner image formed on the intermediate transfer belt 7 is transferred onto the recording material P. The transfer residual toner slightly remaining on the intermediate transfer belt 7 after the secondary transfer is scraped off and collected by the belt cleaner 11.

  The fixing device 13 fixes the toner image transferred onto the recording material P. The recording material P that has undergone the fixing process by the fixing device 13 is discharged to a discharge tray.

  A series of image forming processes by the image forming unit as described above is completed and prepared for the next image forming operation.

(Reference example of function-separated type development device)
In the developing device 4 according to the first embodiment, the function of supplying a developer containing toner and a magnetic carrier to the developer carrying member and the function of collecting the developer from the developer carrying member are separated, so-called, It is a function separation type developing device.

  Before describing the developing device 4 according to the first embodiment, the configuration of the function separation type developing device will be described with reference to the cross-sectional view of FIG. 2 and the schematic diagram of FIG.

  FIG. 2 is a cross-sectional view of the developing device 40 in a cross section orthogonal to the rotation axis of the developing sleeve 44 that is a developer carrying member. FIG. 3 is a top view (schematic diagram) of the developing device 40.

  The developing device 40 includes a developing container 41 that contains a two-component developer containing nonmagnetic toner and a magnetic carrier. Non-magnetic toner is a product in which a colorant, a wax component or the like is encapsulated in a resin such as polyester or styrene acrylic, and powdered by pulverization or polymerization, and a fine powder such as titanium oxide or silica is added to the surface. . The magnetic carrier is obtained by applying a resin coat to the surface layer of a core made of resin particles kneaded with ferrite particles or magnetic powder.

  The developing container 41 is provided with an opening at a position corresponding to the developing area facing the photosensitive drum 1. The developing sleeve 44 is rotatably arranged with respect to the developing container 41 so that a part of the developing sleeve 44 is exposed to the opening of the developing container 41. The developing sleeve 44 is made of a non-magnetic material, has a diameter of 20 mm, a length in the longitudinal direction of 334 mm, a process speed (circumferential speed) of 425 mm / sec, and in the direction of arrow R44 shown in FIG. Rotate. The developing container 41 is provided with a regulating blade 42 as a developer regulating member that forms a thin layer of developer on the surface of the developing sleeve 44.

  The inside of the developing container 41 is partitioned into a developing chamber 41a and a stirring chamber 41b by a partition wall 70 extending in the vertical direction. The developing chamber 41a and the stirring chamber 41b are arranged side by side in the horizontal direction. In the developing chamber 41a, a first screw portion 71 as a conveying means (a rotatable developer conveying member) for stirring and conveying the developer in the developing chamber 41a is provided in the longitudinal direction (rotational axis direction) of the developing sleeve 44. Are arranged substantially parallel to each other. The first screw portion 71 includes a magnetic rotating shaft 71a as a rotatable shaft portion, and a spiral blade portion 71b as a developer conveying portion provided along the outer periphery of the rotating shaft. The agitating chamber 41 b has a second screw portion 72 as a conveying means (rotatable developer conveying member) for agitating the developer in the agitating chamber 41 b and conveying it in the opposite direction to the first screw portion 71. The developing sleeve 44 is disposed substantially parallel to the longitudinal direction (rotational axis direction). The second screw portion 72 includes a magnetic rotating shaft 72a as a rotatable shaft portion, and a spiral blade portion 72b as a developer conveying portion provided along the outer periphery of the rotating shaft.

  The developing sleeve 44 includes a region where the developer is carried on the surface of the developing sleeve 44 (hereinafter referred to as a coated region) and a region where the developer is not carried on the surface of the developing sleeve 44 (hereinafter referred to as an uncoated region). It is configured. The coated area is located at the center in the longitudinal direction of the developing sleeve 44, and the non-coated areas are located at both ends in the longitudinal direction of the developing sleeve 44. In the non-coated region, a magnet sheet for magnetically capturing the developer at the end of the developing sleeve 44 is provided along the outer periphery of the end of the developing sleeve 44.

  Inside the developing sleeve 44, a magnet roll 44a is fixedly disposed as a magnet means (also referred to as a magnetic field generating means) for generating a magnetic field for separating the developer that has passed through the developing area from the surface of the developing sleeve 44. ing. The magnet roll 44a has a plurality of magnetic poles along the rotation direction of the developing sleeve 44 (arrow R44 direction). In the example of FIG. 2, the magnet roll 44a has five magnetic poles, that is, a pumping pole S2, a regulating pole N1, a developing pole S1, a conveying pole N2, and a stripping pole S3 along the rotation direction (arrow R44 direction) of the developing sleeve 44. Have

  The scooping pole S2 is a magnetic pole for attracting the developer in the developing chamber 41a to the surface of the developing sleeve 44, and is disposed facing the developing chamber 41a. The regulation pole N1 is disposed to face the regulation blade 42. The development pole S <b> 1 is disposed in a development area that faces the photosensitive drum 1. The transport pole N2 is disposed downstream of the development pole S1 and upstream of the stripping pole S3 in the rotation direction of the development sleeve 44 (in the direction of arrow R44). The stripping pole S3 is a magnetic pole for separating the developer carried on the surface of the developing sleeve 44 from the developing sleeve 44, and is disposed to face the stirring chamber 41b.

  In the example of FIG. 2, the maximum peak position of the magnetic flux density of each magnetic pole of the magnet roll 44a is an angle formed with a horizontal plane passing through the rotation center of the developing sleeve 44 along the rotation direction of the developing sleeve 44 (in the direction of arrow R44). Is defined as follows.

  The maximum peak position of the magnetic flux density of the stripping pole S3 is 150 degrees with respect to the horizontal plane passing through the rotation center of the developing sleeve 44 along the rotation direction (arrow R44 direction) of the developing sleeve 44. The maximum peak position of the magnetic flux density of the pumping pole S2 is 270 degrees with the horizontal plane passing through the rotation center of the developing sleeve 44 along the rotation direction (arrow R44 direction) of the developing sleeve 44. Further, the normal direction of the developing sleeve 44 is positive at a position where the angle between the developing sleeve 44 and the horizontal plane passing through the rotation center of the developing sleeve 44 (direction of arrow R44) is 200 degrees to 220 degrees. When the absolute value of the magnetic flux density is less than a predetermined value, a low magnetic field region is generated. The absolute value of the magnetic flux density in the low magnetic force region when the normal direction of the developing sleeve 44 is positive (hereinafter simply referred to as the absolute value of the magnetic flux density) is determined by the developer passing through the developing region. The value is such that it peels from the surface, and is, for example, 0 [mT] or more and 10 [mT] or less. This low magnetic force region is caused by a repulsive force caused by a repulsive magnetic field formed between the stripping pole S3 and the pumping pole S2.

  That is, the low magnetic force region is downstream of the maximum peak position of the magnetic flux density of the stripping pole S3 in the rotation direction of the developing sleeve 44 (in the direction of arrow R44) and upstream of the maximum peak position of the magnetic flux density of the pumping pole S2. To occur. In the low magnetic force region, the magnitude of the normal direction component (Fr) of the magnetic attraction force with respect to the surface of the developing sleeve 44 is small, and the force for attracting the developer toward the center of the developing sleeve 44 is weak. Therefore, the developer carried on the surface of the developing sleeve 44 is peeled off from the surface of the developing sleeve 44 in the low magnetic force region.

  That is, the low magnetic force region is a magnetic force region (hereinafter also referred to as a peeling region) for separating the developer that has passed through the development region (hereinafter referred to as a developer after the development process) from the surface of the developing sleeve 44. Yes. This low magnetic force region is on the surface of the developing sleeve 44 in the rotation direction of the developing sleeve 44 on the downstream side of the maximum peak position of the magnetic flux density of the stripping pole S3 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole S2. Is formed.

  The partition wall 70 has a guide portion 70b for guiding the developer peeled off from the surface of the developing sleeve 44 in the low magnetic force region (that is, the developer after the developing process) to be collected in the stirring chamber 41b. The guide portion 70b is formed with an inclined surface that is inclined with respect to a horizontal plane when the developing device 40 is attached to the image forming apparatus 100. In addition, an end portion 70a of the guide portion 70b facing the developing sleeve 44 (hereinafter simply referred to as the guide portion 70a) protrudes so as to face a low magnetic force region on the surface of the developing sleeve 44.

  The guide portion 70 a is disposed with a predetermined clearance (hereinafter referred to as “clearance A”) between the developing sleeve 44. As a result, as the developing sleeve 44 rotates during the developing operation, the guide portion 70a abuts against the surface of the developing sleeve 44, and the surface of the developing sleeve 44 is rubbed to prevent the surface of the developing sleeve 44 from being worn. Yes.

  The developer in the developing chamber 41 a is pumped up by the influence of the magnetic field generated by the pumping pole S <b> 2 and supplied to the developing sleeve 44. Thus, since the developer is supplied from the developing chamber 41a to the developing sleeve 44, the developing chamber 41a is also referred to as a supply chamber. The developer supplied to the developing sleeve 44 carries a predetermined amount of developer on the surface of the developing sleeve 44 by a magnetic field generated by the magnet roll 44a, thereby forming a developer pool. The developer carried on the surface of the developing sleeve 44 passes through the developer pool by the rotation of the developing sleeve 44, the layer thickness is regulated by the regulating blade 42, and the developing region facing the photosensitive drum 1. It is conveyed to.

  Subsequently, the developer carried on the surface of the developing sleeve 44 spikes in the developing area to form magnetic spikes. An electrostatic latent image formed on the surface of the photosensitive drum 1 is obtained by bringing the magnetic spikes formed in the development area into contact with the photosensitive drum 1 and supplying the toner in the developer to the photosensitive drum 1. Is developed as a toner image. At this time, in order to improve the toner application rate (development efficiency) to the electrostatic latent image, a development bias voltage in which a DC voltage and an AC voltage are superimposed is generally applied to the development sleeve 44.

  The developer on the surface of the developing sleeve 44 after supplying the toner to the photosensitive drum 1 (developer after the developing process) is repelled by the peeling pole S3 and the pumping pole S2 as the developing sleeve 44 rotates. It is peeled off from the surface of the developing sleeve 44 by a magnetic field. The developer after the development process peeled off from the surface of the developing sleeve 44 by the repulsive magnetic field falls on the inclined surface of the guide portion 70b, slides down the inclined surface of the guide portion 70b by gravity, and then the stirring chamber 41b. Is recovered into the stirring chamber 41b. That is, in the function separation type developing apparatus, the developer peeled off from the surface of the developing sleeve 44 is not collected in the developing chamber 41a but directly collected in the stirring chamber 41b. As described above, in the function separation type developing device, the developer peeled off from the surface of the developing sleeve 44 (developer after the developing process) is collected in the stirring chamber 41b, so that the stirring chamber 41b is recovered. Also called a room.

  The function separation type developing device has a path (hereinafter referred to as a circulation path C1) through which the developer is transported by the second screw portion 72 from upstream to downstream in the developer transport direction in the stirring chamber 41b. The function separation type developing device has a path (hereinafter referred to as a circulation path C2) in which the developer peeled off from the surface of the developing sleeve 44 is conveyed to the stirring chamber 41b via the guide portion 70b. As shown in FIG. 3, at one end portion of the partition wall 70 in the longitudinal direction of the partition wall 70, a first communication which is a transfer portion (first communication portion) for transferring the developer from the developing chamber 41a to the stirring chamber 41b. A mouth 41c is provided. That is, the developer can be communicated from the developing chamber 41a to the stirring chamber 41b via the first communication port 41c. The other end of the partition wall 70 in the longitudinal direction of the partition wall 70 is provided with a second communication port 41d which is a transfer portion (second communication portion) for transferring the developer from the stirring chamber 41b to the developing chamber 41a. ing. That is, the developer can be communicated from the stirring chamber 41b to the developing chamber 41a via the second communication port 41d.

  The first screw portion 71 and the second screw portion 72 convey the developer in opposite directions along the longitudinal direction (rotational axis direction) of the developing sleeve 44. A developer flow conveyed by the first screw portion 71 and a developer flow conveyed by the second screw portion 72 are formed via the first communication port 41c and the second communication port 41d. That is, the developer is transferred from the developing chamber 41a to the stirring chamber 41b via the first communication port 41c, and the developer is transferred from the stirring chamber 41b to the developing chamber 41a via the second communication port 41d. Is done.

  When the developing device 40 is attached to the image forming apparatus 100, a toner replenishing mechanism for replenishing toner is disposed above the stirring chamber 41b in the vertical direction. The agitation chamber 41b is a delivery unit (toner replenishment unit) for delivering the toner replenished by the toner replenishment mechanism to a circulation path through which the developer circulates between the agitation chamber 41b and the developing chamber 41a. A toner supply port 49 is provided. In the example of FIG. 3, the toner replenishing port 49 is provided at a position extending 30 mm further upstream than the most upstream part of the stirring chamber 41 b in the developer conveying direction of the second screw part 72.

  From the toner replenishing port 49, uncharged toner (hereinafter referred to as replenishing toner) is transferred to a circulation path through which the developer circulates between the stirring chamber 41b and the developing chamber 41a. The replenished toner delivered from the toner replenishing port 49 to the stirring chamber 41b is mixed and stirred with the developer in the stirring chamber 41b, thereby contacting the magnetic carrier in the developer in the stirring chamber 41b and friction charging. Is done. By frictional charging, the toner is negatively charged and the magnetic carrier is positively charged. The frictionally charged toner is attached and held on the surface of the magnetic carrier by electrostatic force. Therefore, the toner charge amount Q / M increases as the contact with the magnetic carrier increases. In the two-component developer, the smaller the toner density T / D, the greater the chance that the toner will come into contact with the magnetic carrier, so the toner charge amount Q / M increases. On the basis of developing the same electrostatic latent image formed on the surface of the photosensitive drum 1, the toner charge amount Q / M is larger when the toner charge amount Q / M is smaller than when the toner charge amount Q / M is small. The density of the image is reduced.

  When developing the electrostatic latent image formed on the surface of the photosensitive drum 1, the toner in the developer is consumed, but the magnetic carrier in the developer is not consumed. That is, since the toner in the developer is consumed in the developer after the development process, the toner concentration in the developer is lowered. In the function separation type developing device, the developer after the developing process in which the toner concentration is lowered is collected in the stirring chamber 41b. Therefore, the toner concentration T / D in the developer circulating in the circulation path through which the developer circulates between the stirring chamber 41b and the developing chamber 41a is determined by using a magnetic permeability sensor 48 provided in the stirring chamber 41b. Always detected. More specifically, the magnetic permeability sensor 48 detects the average magnetic permeability of the developer, and calculates the weight ratio of the toner in the developer from the detected value. The toner to be replenished by the toner replenishment mechanism so that the toner concentration T / D in the developer circulating in the circulation path through which the developer circulates between the stirring chamber 41b and the developing chamber 41a becomes substantially constant. The replenishment amount is adjusted.

  In recent years, the developing device has been downsized, and the diameter of the developing sleeve 44 has been reduced accordingly. When the diameter of the developing sleeve 44 is reduced, the size of the magnet roll 44a disposed inside the developing sleeve 44 is reduced as compared with the case where the diameter of the developing sleeve 44 is large. As a result, the distance between adjacent magnetic poles (peeling pole S3 and pumping pole S2) of adjacent magnet rolls 44a in the rotation direction of developing sleeve 44 is shortened, and the size of the repulsive magnetic field region (peeling region) is reduced. . Therefore, the developer after the development process tends to be hardly peeled off from the surface of the developing sleeve 44.

  As described above, in the developer after the development process, the toner in the developer is consumed in the development process, and the toner concentration in the developer is lowered. When the developer after the development process is not sufficiently peeled off from the surface of the developing sleeve 44 in the peeling region, the “clearance A” is accompanied by the rotation of the developing sleeve 44 while being held on the surface of the developing sleeve 44. If it passes, the following problem will arise.

  In the developer after the development process that has passed “clearance A”, the toner concentration in the developer is lowered because the toner in the developer is consumed in the development process. If the developer after the developing process that has not been peeled off from the surface of the developing sleeve 44 passes through the “clearance A”, the developer concentration is not sufficiently received in the developing region without being subjected to agitation while the toner concentration is lowered. There is a risk of being subjected to development again. This is particularly problematic when the developing device is downsized and the diameter of the developing sleeve 44 is reduced accordingly (that is, when the size of the magnet roll 44a disposed inside the developing sleeve 44 is reduced). .

  Therefore, in the present embodiment, by adopting the configuration described below, in the function separation type developing device, the magnetic attraction force pattern in the vicinity of the stripping pole of the magnet means is adjusted, and development in the vicinity of the stripping pole is performed. This improves both the stripping property of the agent and the downsizing of the apparatus.

  Specifically, the guide portion 70 a is disposed with a predetermined clearance (clearance A) between the developing sleeve 44 and a low magnetic force region where the absolute value of the magnetic flux density is a predetermined value or less. The low magnetic force region is the surface of the developing sleeve 44 on the downstream side of the maximum peak position of the magnetic flux density of the stripping pole S3 in the rotation direction of the developing sleeve 44 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole S2. This is a region for separating the developer that has passed through the development region. That is, in the low magnetic force region, the developer that has passed through the developing region (the developer after the developing step in which the toner concentration is lowered) is peeled off by the magnetic field generated by the magnet roll 44a. Further, the permanent magnet is on the surface of the developing sleeve 44 on the downstream side of the guide portion 70b in the rotation direction of the developing sleeve 44 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole S2, and faces the low magnetic force region. Are arranged. The magnetic pole on the side facing the low magnetic force region of the permanent magnet is the same as the pumping pole S2.

  By adopting such a configuration, in a function-separated type developing device, the developer can be easily peeled off in the vicinity of the stripping pole of the magnet means by a simple configuration without increasing the size of the device. It is. Details will be described below.

  The configuration of the developing device 4 (function-separated type developing device) according to the first embodiment will be described with reference to the cross-sectional view of FIG. FIG. 4 is a cross-sectional view of the developing sleeve 44 as viewed in a cross section orthogonal to the rotation axis. 4, the same reference numerals as those in FIG. 2 denote the same components. The configuration of the developing device 4 will be described below with a focus on differences from the configuration of the developing device 40 described above with reference to FIG.

  In the configuration of the developing device 4, the maximum peak position of the magnetic flux density of the stripping pole S <b> 3 is pumped up by 160 degrees with reference to the angle formed with the horizontal plane passing through the rotation center of the developing sleeve 44 along the rotation direction of the developing sleeve 44. The maximum peak position of the magnetic flux density of the pole S2 is 260 degrees. The maximum peak value of the magnetic flux density of the stripping pole S3 is 30 [mT], and the maximum peak value of the magnetic flux density of the pumping pole S2 is 30 [mT]. Then, the developer that has passed through the developing region is located at a position where the angle between the developing sleeve 44 and the horizontal plane passing through the center of rotation of the developing sleeve 44 is 200 degrees to 220 degrees along the rotating direction of the developing sleeve 44 (arrow R44 direction). A low magnetic force region for peeling from the surface of 44 is generated. The absolute value of the magnetic flux density in the low magnetic force region is a magnetic flux density such that the developer that has passed through the developing region peels off from the surface of the developing sleeve 44, and is equal to or less than a predetermined value (for example, 0 [mT] to 10 [MT] or less).

  In the configuration of the developing device 4, a magnet 90 that is a permanent magnet is provided so as to be close to the developing sleeve 44. The magnet 90 is disposed on the surface of the developing sleeve 44 on the downstream side of the guide portion 70b in the rotation direction of the developing sleeve 44 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole S2, and is opposed to the low magnetic force region. Has been. The closest distance between the magnet 90 and the developing sleeve 44 is set to 0.6 mm.

  Further, in the configuration of the developing device 4, the position of the magnet 90 is set to 210 degrees when the angle formed with the horizontal plane passing through the rotation center of the developing sleeve 44 along the rotation direction of the developing sleeve 44 is used as a reference. The magnet 90 is a magnet having a magnetic flux density of 30 [mT] when measured at a position of about 0.1 mm from the side 90a facing the low magnetic force region of the magnet 90. Further, the magnetic pole on the side 90a facing the low magnetic force region of the magnet 90 is the same pole as the pumping pole S2 (that is, the S pole), and the magnetic pole on the side opposite to the side 90a facing the low magnetic force region of the magnet 90 is It arrange | positions so that it may become a different pole (namely, N pole) with the pumping pole S2. The magnetic field generated by the magnet 90 and the magnetic field generated by the magnet roll 44a cooperate to generate a magnetic field for separating the developer that has passed through the developing region from the surface of the developing sleeve 44.

  In the first embodiment, the thickness of the magnet 90 is 2 mm, and the shape of the magnet 90 is a rectangular parallelepiped. A seal member 81 (for example, a polyester foam) is buried between the magnet 90 and the partition wall 70 in the longitudinal direction of the magnet 90. That is, the magnet 90 is attached to the partition wall 70 using the seal member 81.

  The graph of FIG. 5 shows the distribution of the magnetic flux density and the magnetic attraction force in the configuration of the developing device 4. The horizontal axis of the graph shown in FIG. 5 is an angle formed with a horizontal plane passing through the rotation center of the developing sleeve 44 along the rotation direction of the developing sleeve 44. Further, the vertical axis of the graph shown in FIG. 5 represents a normal direction component (Br) of the magnetic flux density with respect to the surface of the developing sleeve 44 and a normal direction component (Fr) of the magnetic attraction force with respect to the surface of the developing sleeve 44. .

  The schematic diagram of FIG. 6 shows the distribution of magnetic lines of force and magnetic attractive force in the configuration of the developing device 4. As shown in FIG. 6, in the vicinity of the developing sleeve 44, a magnetic field is generated between the magnet 90 and the magnet roll 44a. Further, a repulsive magnetic field is generated between the side 90a (S pole) facing the low magnetic force region of the magnet 90 and the stripping pole S3 (S pole).

  Therefore, the direction of the magnetic field generated in the vicinity of the partition wall 70 will be described with reference to the schematic diagram of FIG. FIG. 7 is a cross-sectional view (schematic diagram) when viewed in a cross-section orthogonal to the rotation axis of the developing sleeve 44.

  As shown in FIG. 7, a “low magnetic force region C” in which the absolute value of the magnetic flux density is 0 [mT] or more and 10 [mT] or less in a region from 200 degrees to 220 degrees along the rotation direction of the developing sleeve 44. Occurs. That is, the “low magnetic field region C” is formed downstream of the maximum peak position of the magnetic flux density of the stripping pole S3 in the rotation direction of the developing sleeve 44 and upstream of the maximum peak position of the magnetic flux density of the pumping pole S2. It is what is done. In the “low magnetic force region C”, the magnitude of the normal direction component (Fr) of the magnetic attraction force with respect to the surface of the developing sleeve 44 is small, and the force for attracting the developer toward the center of the developing sleeve 44 is weak. . Therefore, in the “low magnetic force region C”, the developer after the developing process carried on the surface of the developing sleeve 44 is peeled off from the surface of the developing sleeve 44.

  In the first embodiment, the magnet 90 is disposed at a position facing the “low magnetic force region C”. Thereby, a magnetic field is generated between the magnet 90 and the magnet roll 44a. As described above, the maximum peak position of the magnetic flux density of the stripping pole S3 is 160 degrees, the position of the magnet 90 is 210 degrees, and the maximum peak position of the magnetic flux density of the pumping pole S2 is 260 along the rotation direction of the developing sleeve 44. Set to degrees. Further, the magnetic pole on the side 90a of the magnet 90 facing the “low magnetic field region C” is set to the same polarity as the stripping pole S3 and the pumping pole S2. The magnitude of the magnetic flux density of the magnet 90 is set to be approximately the same as the maximum peak value of the magnetic flux density of the stripping pole S3 and the maximum peak value of the magnetic flux density of the pumping pole S2.

  In the first embodiment, the “low magnetic force region D” in which the absolute value of the magnetic flux density is 0 [mT] or more and 10 [mT] or less in a region from 180 degrees to 190 degrees along the rotation direction of the developing sleeve 44. Occurs. That is, the “low magnetic force region D” is formed on the surface of the developing sleeve 44 on the downstream side of the maximum peak position of the magnetic flux density of the stripping pole S3 in the rotation direction of the developing sleeve 44 and on the upstream side of the guide portion 70b. Is. In the “low magnetic field region D”, the magnitude of the normal component (Fr) of the magnetic attraction force with respect to the surface of the developing sleeve 44 is small, and the force for attracting the developer toward the center of the developing sleeve 44 is weak. . Therefore, in the “low magnetic force region D”, the developer after the developing process carried on the surface of the developing sleeve 44 is peeled off from the surface of the developing sleeve 44.

  As shown in FIG. 7, the “low magnetic force region D” is downstream of the maximum peak position of the magnetic flux density of the stripping pole S3 in the rotation direction of the developing sleeve 44 and upstream of the “low magnetic force region C”. It is in. For this reason, the developer after the development process carried on the surface of the developing sleeve 44 has an opportunity to be peeled off from the surface of the developing sleeve 44 in the “low magnetic field region D” before the “low magnetic field region C”. As a result, the developer stripping property in the vicinity of the stripping pole S3 can be improved.

  In the first embodiment, the guide portion 70 b is provided at a position facing the “low magnetic force region C”. As a result, the developer after the development process peeled off from the surface of the developing sleeve 44 in the “low magnetic field region D” or “low magnetic field region C” is not affected by the magnetic field by the stripping pole S3 or the pumping pole S2. The developer can be dropped on the slope of the guide portion 70b by its own weight.

  In the first embodiment, in the region from 230 degrees to 240 degrees along the rotation direction of the developing sleeve 44, the absolute value of the magnetic flux density is 0 [mT] or more and 10 [mT] or less. E "occurs. That is, the “low magnetic force region E” is formed on the surface of the developing sleeve 44 on the downstream side of the magnet 90 in the rotation direction of the developing sleeve 44 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole S2. It is. In the “low magnetic field region E”, the magnitude of the normal component (Fr) of the magnetic attraction force with respect to the surface of the developing sleeve 44 is small, and the force for attracting the developer toward the center of the developing sleeve 44 is weak. . Therefore, in the “low magnetic field region E”, the developer after the development process carried on the surface of the developing sleeve 44 is peeled off from the surface of the developing sleeve 44.

  The movement of the developer after the developing process carried on the surface of the developing sleeve 44 needs to consider the influence of gravity in addition to the influence of the magnetic field. Therefore, the movement of the developer in the vicinity of the partition wall 70 will be described with reference to the schematic diagram of FIG. FIG. 8 is a cross-sectional view (schematic diagram) when viewed in a cross section orthogonal to the rotation axis of the developing sleeve 44.

  In the first embodiment, the size of the “low magnetic force region D” is smaller than the size of the “low magnetic force region C”. Part of the developer after the developing process carried on the surface of the developing sleeve 44 is separated from the influence of the magnetic field in the “low magnetic force region D” and falls on the slope of the guide portion 70b due to the influence of gravity. On the other hand, the developer after the developing process that has not been peeled off from the surface of the developing sleeve 44 in the “low magnetic force region D” reaches the “low magnetic force region C” as the developing sleeve 44 rotates. Further, most of the developer after the development process that has not been peeled off from the surface of the developing sleeve 44 in the “low magnetic force region D” is separated from the influence of the magnetic field in the “low magnetic force region C”, and is guided by the influence of gravity. It falls on the slope of 70b.

  Then, the developer after the development process that has dropped onto the slope of the guide portion 70b slides down on the inclined surface of the guide portion 70b due to gravity, and is then collected into the stirring chamber 41b, and stirred by the second screw portion 72. receive.

  When the process speed at the time of image formation is high, the rotation speed of the developing sleeve 44 increases, and accordingly, the speed of the air flow on the surface of the developing sleeve 44 increases. At this time, the developer after the development process carried on the surface of the developing sleeve 44 is peeled off from the surface of the developing sleeve 44 by the repulsive magnetic field, but rides on the air flow on the surface of the developing sleeve 44 and a small amount of developer. May pass through “clearance A”. On the other hand, in this embodiment, even when a small amount of developer passes through the “clearance A” by riding on the air flow on the surface of the developing sleeve 44, the small amount of developer is reduced by the magnetic field generated by the magnet 90. It can be attracted to the side 90a opposite to the region C and kept.

  However, if the developer attracted to the side 90a of the magnet 90 facing the “low magnetic force region C” accumulates over time, the developer is applied to the side 90a of the magnet 90 facing the “low magnetic force region C”. It cannot be held. The developer that could not be held on the side 90 a of the magnet 90 facing the “low magnetic force region C” reaches the “low magnetic force region E” as the developing sleeve 44 rotates.

  As described above, in the “low magnetic force region E”, the magnitude of the normal component (Fr) of the magnetic attraction force with respect to the surface of the developing sleeve 44 is small, and the force attracts the developer toward the center of the developing sleeve 44. Is weak. Therefore, the developer carried on the surface of the developing sleeve 44 (that is, the developer after the developing process that has not passed through the “clearance A” and cannot be held on the side 90 a facing the “low magnetic field region C” of the magnet 90. ) Is peeled off from the surface of the developing sleeve 44 in the “low magnetic force region E”. Then, the developer after the development process peeled off in the “low magnetic force region E” is collected into the developing chamber 41 a by the dead weight of the developer and is subjected to stirring by the first screw portion 71.

  That is, the developer after the developing process in which the toner density is lowered passes through the “clearance A” and is carried again on the surface of the developing sleeve 44 without being sufficiently stirred, and faces the photosensitive drum 1. It is possible to suppress re-use in the development area.

  In the first embodiment, an example is described in which the magnitude of the magnetic flux density of the magnet 90 is substantially the same as the maximum peak value of the magnetic flux density of the stripping pole S3 and the maximum peak value of the magnetic flux density of the pumping pole S2. However, it is not limited to this.

  If the “low magnetic field region D” is formed in addition to the “low magnetic field region C”, the magnitude of the magnetic flux density of the magnet 90 is larger than 50% of the maximum peak value of the magnetic flux density of the pumping pole S2, and is 250. It should be smaller than%. The magnitude of the magnetic flux density of the magnet 90 may be larger than 50% and smaller than 250% of the maximum peak value of the magnetic flux density of the stripping pole S3. More preferably, in addition to the “low magnetic field region C”, both the “low magnetic field region D” and the “low magnetic field region E” are formed. That is, the magnitude of the magnetic flux density of the magnet 90 is larger than 90% of the maximum peak value of the magnetic flux density of the stripping pole S3 and smaller than 110%, and 90% of the maximum peak value of the magnetic flux density of the pumping pole S2. It is preferable that it is larger than 110%.

  In the present embodiment described above, the permanent magnet is located on the surface of the developing sleeve 44 on the downstream side of the guide portion 70b in the rotation direction of the developing sleeve 44 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole S2. It was placed opposite the magnetic field. The magnetic pole on the side facing the low magnetic force region of the permanent magnet is the same as the pumping pole S2. As a result, the pattern of the magnetic attractive force in the vicinity of the stripping pole S3 is adjusted, so that many opportunities for the developer after the development process to be stripped from the surface of the developing sleeve 44 are obtained. Therefore, according to the present embodiment, in the function separation type developing device, it is possible to improve the stripping property of the developer in the vicinity of the stripping pole S3 with a simple configuration without causing an increase in the size of the device. .

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

  In the above embodiment, the example in which the absolute value of the magnetic flux density in the low magnetic force region where the developer that has passed through the developing region peels from the surface of the developing sleeve 44 is 0 [mT] or more and 10 [mT] or less has been described. Not limited to. The range of the magnetic flux density at which the developer peels from the surface of the developing sleeve 44 varies depending on various parameters such as the diameter of the magnetic carrier and the specific gravity of the magnetic carrier. Therefore, if the developer that has passed through the developing region is peeled off from the surface of the developing sleeve 44, the upper limit of the absolute value of the magnetic flux density in the low magnetic force region may be larger than 10 [mT]. However, the upper limit of the absolute value of the magnetic flux density in the low magnetic force region is smaller than the maximum peak value of the magnetic flux density of the stripping pole S3 and the maximum peak value of the magnetic flux density of the pumping pole S2.

  In the above embodiment, as illustrated in FIG. 4, the magnet roll 44a has been described as having five magnetic poles along the rotation direction of the developing sleeve 44 (the direction of the arrow R44), but the present invention is not limited thereto. The present invention can also be applied to a developing device in which the magnet roll 44a has four or more magnetic poles or six or more magnetic poles along the rotation direction of the developing sleeve 44 (the direction of the arrow R44). Also in that case, the guide portion 70b is formed on the surface of the developing sleeve 44 on the downstream side of the maximum peak position of the magnetic flux density of the stripping pole in the rotation direction of the developing sleeve 44 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole. In this case, it may be arranged to face the low magnetic force region. Further, the permanent magnet is opposed to the low magnetic force region on the surface of the developing sleeve 44 on the downstream side of the guide portion 70b in the rotation direction of the developing sleeve 44 and on the upstream side of the maximum peak position of the magnetic flux density of the pumping pole S2. Can be arranged. The magnetic pole on the side facing the low magnetic force region of the permanent magnet is the same as the pumping pole S2.

  In the above embodiment, as illustrated in FIG. 1, the image forming apparatus 100 configured to use the intermediate transfer belt 7 as an image carrier has been described as an example, but the present invention is not limited thereto. The present invention can also be applied to an image forming apparatus configured to perform transfer by bringing a recording material into direct contact with the photosensitive drum 1 in order. In that case, the photosensitive drum 1 constitutes a rotatable image carrier that carries a toner image.

  In the above embodiment, as shown in FIG. 4, the developing device 4 having a configuration in which the developing sleeve 44 rotates counterclockwise and the regulating blade 42 is disposed below the developing sleeve 44 is taken as an example. Although explained, it is not limited to this. The present invention can also be applied to a developing device having a configuration in which the developing sleeve 44 rotates clockwise and the regulating blade 42 is disposed above the developing sleeve 44.

4 Developing Device 41a Developing Chamber 41b Agitation Chamber 44 Developing Sleeve 44a Magnet Roll 70 Partition 70b Guide Portion 90 Permanent Magnet

Claims (10)

A developer carrying member which is rotatably provided and carries a developer containing toner and a magnetic carrier and conveys the developer to a developing region facing the image carrier;
A supply chamber which is disposed below the developer carrier and supplies developer to the developer carrier;
A collection chamber disposed opposite to the developer carrier and collecting the developer that has passed through the development region from the developer carrier;
The first magnetic pole and the first magnetic pole are arranged downstream of the first magnetic pole in the rotation direction of the developer carrier and adjacent to the first magnetic pole. A magnet unit that is disposed and has a second magnetic pole that is the same as the first magnetic pole, and generates a magnetic field for separating the developer that has passed through the development region from the surface of the developer carrier;
A guide portion for guiding the developer separated from the surface of the developer carrier by the magnetic field generated by the magnet means to be collected in the collection chamber; the supply chamber; the collection chamber; A partition wall separating the
With permanent magnets,
With
The guide portion is located on the downstream side of the maximum peak position of the magnetic flux density of the first magnetic pole and the upstream side of the maximum peak position of the magnetic flux density of the second magnetic pole in the rotation direction of the developer carrier. The surface of the developer carrier, the absolute value of the magnetic flux density being equal to or less than a predetermined value, facing the magnetic region for separating the developer that has passed through the development region from the surface of the developer carrier, and Arranged between the developer carrier and a predetermined clearance,
The permanent magnet is a surface of the developer carrier on the downstream side of the guide portion in the rotation direction of the developer carrier and upstream of the maximum peak position of the magnetic flux density of the second magnetic pole. Placed opposite the magnetic field,
The developing device according to claim 1, wherein the magnetic pole of the permanent magnet on the side facing the magnetic region is the same as the second magnetic pole. The magnetic field for separating the developer that has passed through the development area from the surface of the developer carrying member is generated by the cooperation of the magnetic field by the permanent magnet and the magnetic field by the magnet means. Item 2. The developing device according to Item 1. The absolute value of the magnetic flux density is present on the surface of the developer carrier on the downstream side of the maximum peak position of the magnetic flux density of the first magnetic pole and on the upstream side of the guide portion in the rotation direction of the developer carrier. The development according to claim 1, wherein a magnetic force region is formed so that the developer that is not more than the predetermined value and passes through the development region is separated from the surface of the developer carrying member. apparatus. The absolute value of the magnetic flux density is present on the surface of the developer carrier downstream of the permanent magnet and upstream of the maximum peak position of the magnetic flux density of the second magnetic pole in the rotation direction of the developer carrier. 4. The magnetic field region for forming the developer that is equal to or less than the predetermined value and is separated from the surface of the developer carrying member is formed. The developing device according to item. The developing device according to any one of claims 1 to 4, wherein the predetermined value is 10 [mT]. The maximum peak value of the magnetic flux density of the permanent magnet is greater than 50% and less than 250% of the maximum peak value of the magnetic flux density of the first magnetic pole, and the maximum peak value of the magnetic flux density of the second magnetic pole. The developing device according to claim 1, wherein the developing device is larger than 50% and smaller than 250%. The maximum peak value of the magnetic flux density of the permanent magnet is greater than 90% and less than 110% of the maximum peak value of the magnetic flux density of the first magnetic pole, and the maximum peak value of the magnetic flux density of the second magnetic pole. The developing device according to claim 6, wherein the developing device is larger than 90% and smaller than 110%. The developing device according to claim 1, wherein a seal member is provided between the permanent magnet and the partition wall in a longitudinal direction of the permanent magnet. The developing device according to claim 1, further comprising a transport unit configured to transport the developer collected in the collection chamber to the supply chamber. 10. The supply chamber and the recovery chamber are arranged side by side in the horizontal direction when the developing device is mounted on an image forming apparatus that forms an image on a recording material. The developing device according to claim 1.

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