JP4387226B2 - Developing device, process cartridge, image forming apparatus - Google Patents

Description

The present invention relates to a developing device that develops an electrostatic image on an image carrier with a two-component developer, a process cartridge and an image forming apparatus using the developing device, and an image forming apparatus using the process cartridge.

  A non-magnetic toner that is a non-magnetic toner that is a non-magnetic toner that is a rotatable non-magnetic cylinder and a magnetic roller and a magnetic substance generating means in which a magnet for forming a plurality of magnetic poles is immovably installed. A developer container that contains the two-component developer, a stirring / conveying means that stirs and conveys the two-component developer in the developer container, and a case member that surrounds the developing roller. There is a two-component developing device that conveys by rotation of a nonmagnetic cylinder and develops an electrostatic latent image on an image carrier with a magnetic brush (see, for example, Patent Documents 1 and 2).

  These developing devices include a developing container that contains the two-component developer (hereinafter simply referred to as a developer), a developing roller that is a developing carrier, and a magnet roller that is included in the developing roller. Regarding the developing roller, of the plurality of magnetic poles provided on the magnet roller, the magnetic pole disposed closest to the developing container is configured to reach the inside of the developing container. The developer pumped up and carried on the surface of the developing roller is regulated in its layer thickness when it passes through a position facing a regulating member such as a regulating blade as the developing roller rotates.

  Then, the toner is conveyed to a developing position where a latent image carrier such as a photosensitive drum and a developing roller face each other, and toner is electrostatically attached to the latent image on the latent image carrier. The developer that has passed through the developing position is a portion where the magnetic force at the middle position between the two magnetic poles becomes almost zero due to the repulsive magnetic field created by the magnetic poles of the same polarity adjacent to each other among the magnet rollers included in the developing roller. And released from the surface of the developing roller by being released from the binding force of the magnet. The developer separated from the developing roller is mixed and agitated with the developer moving in the developing container, and is again pumped up by the developing roller, and the above cycle is repeated.

  In recent years, the proportion of space saving and printing speed has increased as an important factor in user machine selection, and the development device has become smaller, resulting in a smaller development roller diameter, a smaller cover to cover it, At present, it is inevitable to narrow the gap between the developing roller and the cover and increase the developing roller rotation speed.

  In such a space-saving and high-speed developing device, the developer separated by the repulsive magnetic force is sufficiently mixed and stirred with the developer moving in the developer container to refresh the toner concentration, toner charge amount, etc. Therefore, repeated development has become difficult. That is, the developer after development separated by the repulsive magnetic force is pumped up again by the developing roller without being sufficiently refreshed, reaches the development position and is developed, and unevenness in image density is likely to occur. Yes.

JP-A-10-31362 Japanese Patent No. 266050

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a developing device capable of suppressing abnormal images such as image density unevenness in a developing device having a space-saving and high-speed configuration, and the developing device. A process cartridge and an image forming apparatus including the image forming apparatus , and an image forming apparatus in which the process cartridge can be attached to and detached from the main body at low cost.

In order to achieve the above object, the present invention has the following configuration.
(1) a developing roller having a rotatable nonmagnetic cylinder and a magnetic field generating means in which a magnet for forming a plurality of magnetic poles is fixedly installed, a magnetic carrier, and a nonmagnetic toner. A developer container containing the two-component developer, a stirring / conveying means for stirring and transporting the two-component developer in the developer container, and a case member surrounding the developing roller. In a two-component developing device that conveys by rotating a magnetic cylinder and develops an electrostatic latent image on an image carrier with a magnetic brush,
Among the magnetic poles constituting the magnetic field generating means, a repulsive magnetic field is formed between two magnetic poles of the same polarity that separate the developer that has passed the development position from the developing roller, and two repulsive magnetic fields are formed. Among the polar magnetic poles, the magnetic pole located downstream in the rotation direction of the developing roller is used as a pumping magnetic pole for pumping up the developer from the stirring and conveying means, and the peak magnetic force in the normal direction of the pumping magnetic pole is the stirring and conveying means towards the developer conveying direction upstream side and a Rukoto it is set higher than the downstream side (claim 1).
(2). In the process cartridge which integrally supports these members including the image carrier and the developing device and is detachable from the image forming apparatus main body,
The developing device includes:
A developing roller having a rotatable nonmagnetic cylinder and a magnetic roller generating means in which non-moving magnets for forming a plurality of magnetic poles are fixed, and a two component component comprising a magnetic carrier and a nonmagnetic toner A developer container for containing the developer; agitating and conveying means for agitating and conveying the two-component developer in the developer container; and a case member surrounding the developing roller; It consists of a two-component developing device that conveys by rotation and develops the electrostatic latent image on the image carrier with a magnetic brush.
Among the magnetic poles constituting the magnetic field generating means, a repulsive magnetic field is formed between two magnetic poles of the same polarity that separate the developer that has passed the development position from the developing roller, and two repulsive magnetic fields are formed. Among the polar magnetic poles, the magnetic pole located downstream in the rotation direction of the developing roller is used as a pumping magnetic pole for pumping up the developer from the stirring and conveying means, and the peak magnetic force in the normal direction of the pumping magnetic pole is the stirring and conveying means The upstream side in the developer transport direction is set higher than the downstream side (claim 2).
(3). An image forming apparatus comprising an image bearing member and a developing unit that develops an electrostatic latent image formed on the image bearing member, wherein the developing unit is the developing device according to claim 1. 3).
(4). In the image forming apparatus in which the process cartridge is detachable from the main body of the image forming apparatus, the process cartridge is the process cartridge according to claim 2 (claim 4).

According to the present invention, the developer separated by the repulsive magnetic forces, sufficiently stirred and mixed with the developer coming move the developing container, Ri by the fact refresh, also the peak of the normal direction of the magnetic pole magnetic force By setting the upstream side in the developer conveying direction of the agitating and conveying means higher than the downstream side, it is possible to suppress abnormal images due to image density unevenness and image density differences between the upstream and downstream sides in the developer conveying direction .

Embodiments of the present invention will be described below with reference to the accompanying drawings.
(Image forming process in image forming apparatus)
A process for obtaining a color image will be described for a color image forming apparatus as an example of the image forming apparatus of the present invention. In FIG. 1, the color image forming apparatus is provided with a transfer belt device 10 having an intermediate transfer belt 11 and four image stations. Each image station has a photosensitive drum 20Y, 20C, 20M, 20Bk as an image carrier. Is provided.

  Around these photosensitive drums 20Y, 20C, 20M, and 20Bk, dedicated charging devices 30Y, 30C, 30M, and 30Bk, developing devices 50Y, 50C, 50M, and 50Bk, and cleaning devices 40Y, 40C, 40M, and 40Bk are provided, respectively. It has been. In the upper part of the image forming apparatus main body 70, toner bottles 9Y, 9C, 9M, and 9Bk for replenishing toner are arranged from the left in the drawing, and these toner bottles are yellow (Y), cyan (C), Magenta (M) and black (Bk) toners are filled, and toner of each color is replenished to the developing devices 50Y, 50C, 50M, and 50Bk by a predetermined replenishment amount through a conveyance path (not shown).

  Regarding the operation, the transfer paper 2 is fed from the paper feed cassette 1 by the paper feed roller 3, and when the leading edge of the transfer paper 2 reaches the registration roller pair 4, it is detected by a sensor (not shown). While taking timing with this detection signal, the transfer paper 2 is conveyed to the nip portion between the secondary transfer roller 5 and the intermediate transfer belt 11 by the registration roller pair 4.

  The photosensitive drums 20Y, 20C, 20M, and 20Bk uniformly charged in advance by the charging devices 30Y, 30C, 30M, and 30Bk are exposed and scanned with laser light by the optical writing device 8, and the photosensitive drums 20Y, 20C, and 20M are scanned. , An electrostatic latent image is formed on 20 Bk.

  The electrostatic latent images are developed by the developing devices 50Y, 50C, 50M, and 50Bk for the respective colors, and yellow, cyan, magenta, and black toner images are formed on the surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk.

  Next, a voltage is applied to the primary transfer rollers 12Y, 12C, 12M, and 12Bk, and the toner on the photosensitive drums 20Y, 20C, 20M, and 20Bk is sequentially transferred onto the intermediate transfer belt 11. At this time, the image forming operation of each color is performed by shifting the timing from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 11 so that the toner image is transferred to the same position on the intermediate transfer belt 11. Executed.

  The superimposed toner image formed on the intermediate transfer belt 11 is conveyed to the position of the secondary transfer roller 5 and is secondarily transferred to the transfer paper 2. The transfer paper 2 onto which the toner images of the respective colors are transferred is conveyed to the fixing device 6 and thermally fixed, discharged by the paper discharge roller 7, and stacked on the paper discharge tray 7T.

The residual toner on the photoconductive drums 20Y, 20C, 20M, and 20Bk is cleaned by the respective cleaning devices 40Y, 40C, 40M, and 40Bk, and then a charging voltage in which an AC component bias is superimposed and applied to the DC is applied. The electrification devices 30Y, 30C, 30M, and 30Bk to be applied are charged simultaneously with static elimination to prepare for the next image formation. The residual toner on the intermediate transfer belt 11 is cleaned by the intermediate transfer belt cleaning device 13 to prepare for the next image forming process.
(Image station, development device)
Here, FIG. 2 is an enlarged view of one of the image stations in FIG. 1, FIG. 3 shows an external view of the developing device 50, various dimensions and magnetic field lines on the figure representing the same developing device as shown in FIG. This will be described with reference to FIG. In the following description, since it is a description of a structure common to the developing devices 50Y, 50C, 50M, and 50Bk, it is displayed with only numerals except the Y, C, M, and Bk signs that represent the color distinction, explain.

  The developing device 50 includes a developing case 55 as a case member having an opening, a developing roller 51 disposed so as to be close to and opposed to the surface of the photosensitive drum 20, and a blade that regulates the developer on the developing roller 51 to a certain height. The first conveying screw 53 disposed at a position opposed to the lower side of the developing roller 51, the second conveying screw 54 provided in parallel with the first conveying screw 53 in the horizontal direction, and the like. Has been.

  From the toner bottle, the toner passes through a conveyance path (not shown) and a replenishment section, and the toner is fed upstream of the second conveyance screw 54 in the developer container 56b (not shown in FIG. 3, see FIGS. 2, 4, 5, and 9) in the developer feeding direction. The toner is replenished on the second conveying screw 54 in FIG. 3 or in the developing container 56b and upstream in the developer feeding direction indicated by arrow A, that is, the left end portion.

  The replenished toner is mixed and charged with the carrier in the developer while being sent in the direction of arrow A in the developing container 56b (not shown in FIG. 3) by the second conveying screw 54, and the second conveying screw in FIG. At the end on the downstream side in the feed direction of 54, that is, the right end, it is delivered in the direction indicated by the arrow B to the first transport screw 53 side that rotates in conjunction with the second transport screw 54 via a gear (not shown). The partition plate 56a1 is cut out at the delivery portion. This time, the toner is fed in the direction of arrow C opposite to the direction of arrow A in the developing container 56a, and is supplied to the developing roller 51 in the process. Then, the conveyance end in the direction of arrow C, that is, the left end, proceeds in the direction of arrow D changed from the direction of arrow C to the right angle direction, and is transferred to the second conveyance screw 54 and in the direction of arrow A. Sent. The partition plate 56a1 is also cut out at this transfer portion.

  As shown in FIG. 4, the developing roller 51 is disposed at an angle θ from the vertical direction with respect to the first conveying screw 53. Further, the developing roller 51 and the first conveying screw 53 have a center-to-center distance of δ. In this example, the photosensitive drum is a drum whose outer peripheral portion is made of an OPC (optical photo conductor), and has a diameter of 30 mm and a rotational outer peripheral linear velocity of 155 mm / sec. The developing roller 51 has a diameter of 18 mm and a rotational velocity of 329 rpm. The conveying screws 53 and 54 are stirring and conveying means having a stirring function, have a screw shape, have an outer diameter of 15 mm, a rotational speed of 469 rpm, θ = 25.5 degrees, and δ = 24.4 mm.

  The distance between the centers of the developing roller 51 and the first conveying screw 53 in the horizontal direction is 10 mm, the distance between the centers in the vertical direction is 21 mm, and the opening width of the developing container 56a in FIGS. The magnetic poles P3 and P4 and the inclined inner wall surface of the developing case 55 (part where a normal vector A described later is reflected) are located. The inclination angle β between the inner wall surface and the horizontal line LL1 is 44 degrees, and the inner wall extends to the position of the partition plate 56c that forms the opening of the developing container 56a.

  The cleaning device 40 includes a cleaning case 43 having an opening, a cleaning blade 41 for cleaning residual toner on the photosensitive drum 20, a waste toner screw 42 for transporting the cleaned waste toner to a waste toner bottle (not shown), and the like. It is configured.

  1 and 2, a transfer belt device 10 includes an intermediate transfer belt 11, a primary transfer roller 12 for transferring a toner image on the photosensitive drum 20 to the intermediate transfer belt 11, and an intermediate transfer belt for holding these components. It is comprised by the case 14 grade | etc.,.

  The photosensitive drum 20 between the charging roller 30R and the developing roller 51 is irradiated with the laser light L from the optical writing device 8.

  FIG. 5 is an enlarged view of the magnetic force distribution shown in FIG. 4 and 5, around the developing roller 51, “the magnetic poles P 1 to P 5 are moved in the developing sleeve rotation direction P 2, P 3, P 4 by the magnetic field generating means in which magnets for forming a plurality of magnetic poles are fixedly installed. , P5 poles are arranged in this order.

That is, the developing roller 51 starts from the P1 pole (N pole) set to the center of the photosensitive drum 20 (image carrier) in the rotation direction, and starts from the P2 pole (in the rotation direction of the developing roller 51). S poles), P3 poles (N poles), P4 poles (N poles), P5 poles (S poles) are arranged in this order, and two adjacent magnetic poles of the same polarity are P3 poles (N poles) and P4 poles. an (N-pole), these in two same polarity magnetic poles, the magnetic poles located downstream in the rotational direction of the developing roller 51 P4 poles (N-pole) Ru der.

  These magnetic poles are magnetic forces in the normal direction of the developing roller 51, and supply the developer for developing the latent image on the photoconductor 20 is the magnetic pole P1 (N pole), and the developing position (developing roller) 51 and the photosensitive drum 20 are in close proximity to each other, and the developer used for development is developed in the developing container 56a (around the first conveying screw 53) by a synergistic action with the rotation of the developing roller 51. It is the magnetic pole P2 (S pole) that is attracted to this side, and the magnetic pole P4 (N pole) that attracts the developer from the first conveying screw 53 onto the developing roller 51 is the same pole as the magnetic pole P4. The magnetic pole P3 (N pole) is configured to be located between the magnetic pole P2 and the magnetic pole P4, and to release the developer attracted by the magnetic pole P2 by the repulsive magnetic field with the magnetic pole P4 from the developing roller 51. Developing low by the magnetic force of The developer that is bound to 51 surface, to move attracted to the regulating member 52 for regulating the thickness of the developer is a magnetic pole P5 (S pole). The magnetic pole P5 also has a function of pumping up the developer conveyed by the first conveying screw 53 in the conveying process. The repulsive magnetic field (hereinafter referred to as magnetic pole P3-4) formed by the magnetic pole P3 and the magnetic pole P4 has a magnetic force of 10 mT or less in both the horizontal direction and the normal direction.

  In the illustrated example, when the developing roller 51 is regarded as a clock face, the developing position is 3 o'clock, the magnetic pole P1 is 2 o'clock to 4 o'clock, and the magnetic pole P2 is 12 o'clock to 2 o'clock. The position of the magnetic pole P3 is from 10 o'clock to 12 o'clock, the position of the magnetic pole P4 is from 8 o'clock to 9 o'clock, and the position of the magnetic pole P5 is from 5 o'clock to 7 o'clock. The peak position in the normal direction of each magnetic pole is at the center in the circumferential direction of each magnetic pole.

  4 and 5, the normal vector A raised on the peripheral surface of the developing roller 51 in the region where the normal magnetic field of the P3-4 pole is the lowest is reflected by the inner wall surface of the developing case 55 surrounding the developing roller 51. Let B be the reflected vector. The angle from the intersection of the vector B to the horizontal line LL1 to the vector B measured in the counterclockwise direction starting from the horizontal line on the left side of the intersection is defined as an angle α.

  The peak magnetic force in the normal direction of the magnetic pole P4 is M (mT). FIGS. 6 and 7 summarize the haze density unevenness rank and the image density ID value when the angle α and the peak magnetic force M are leveled (developed with different values). In the experiment, the entire surface exposure image (solid image) was continuously 20 while supplying the toner in an environment of room temperature 27 ° C., relative humidity 80%, and room temperature 10 ° C., relative humidity 15% while maintaining the toner concentration at 7 wt%. This is an evaluation of the image when the sheet is output, and in the case of the haze density unevenness, it can be determined that rank 4 or higher is a level with no problem in actual use. The image density ID was measured at the center of the image using a measuring instrument X-Rite 938 (X-Rite, USA). As the toner, black toner (average particle size: 6.8 μm), which is easy to determine the haze density unevenness, was used.

According to this, on the peripheral surface of the developing roller 51 at the lowest part of the repulsive magnetic field formed between the poles of the two same-polarity magnetic poles P3 and P4 that are arranged adjacently in order from the upstream side in the rotation direction of the developing roller. with respect to the normal reflection vector B direction and is, the normal vector direction of the horizontal line LL1 made reflected the inner wall surface of the case member serving developing case 55 surrounding the normal vector and the developing roller 51 stood on, “Angle α = 0 ° to 70 °” and the peak magnetic force in the normal direction of the magnetic pole P4 downstream of the developing roller 51 in the rotation direction of the developing roller 51 in the two same-polarity magnetic poles P3 and P4 is 35 mT or more and 55 mT or less. in some cases, it reaches smoke-like density unevenness, and the level image density ID is no practical problem together. 4 and 5 show the structure of the apparatus used in the experiment at the actual size ratio. Incidentally, the peak magnetic force in the normal direction of the magnetic pole P1 is 95 mT, and the peak magnetic force in the normal direction of the magnetic pole P5 is 65 mT.

  By setting the direction of the normal reflection vector B and the peak magnetic force of the magnetic pole P4 within the above range, the developer circulation, that is, the developer used for development is released at the magnetic pole P3-4, and the released developer is directly Alternatively, it bounces off the inner wall of the developing case 55 above the developing roller 51 and falls into the first conveying screw 53 or the developing container 56a surrounding the first conveying screw 53, and the dropping position is away from the magnetic pole P5 that pumps up the developer. This is because the first conveying screw 53 is further conveyed while being sufficiently mixed and agitated with the subsequent developer conveyed without being attracted by the magnetic pole P5 immediately after dropping, and pumped up again by the magnetic pole P4.

  On the other hand, when the angle α is set to be greater than 70 degrees, the developer separated by the magnetic pole P3-4 falls into the developing container 56a surrounding the first transport screw 53, and the subsequent transport that the first transport screw 53 has transported. The ratio of what is immediately pumped up by the magnetic pole P4 or the magnetic pole P5 without being sufficiently mixed and stirred with the developer increases. Therefore, a developer having a low toner concentration is partially pumped up, so that a haze-like toner density unevenness occurs during development.

  Further, when the peak magnetic force M in the normal direction of the magnetic pole P4 is larger than 55 mT, the force that pulls the developer separated by the magnetic pole P3-4 directly by the magnetic pole P4 is increased, and the developer is rotated on the developing roller 51. In the same manner, a haze-like toner density unevenness is generated during development. When the peak magnetic force M is smaller than 35 mT, the force of pumping up the developer in the developing container surrounding the lower portion of the first conveying screw 53 is weakened, resulting in a problem that the image density ID is lowered as a whole.

  Here, for example, in order to adapt to high speed, the linear velocity of the photoconductor 20 is set to 186 mm / sec, and the image output speed is set to 1.2 times the above. Accordingly, the speed of the developing roller 51, the first transport screw 53, and the second transport screw 54 is also increased by 1.2 times.

  As a result, the density (ID) is lower in the right part of the image than in the center and the left part, and further, it becomes easy to generate a haze-like density unevenness as a whole. This is because the developer transfer speeds of the developer transfer section from the second transfer screw 54 to the first transfer screw 53 and the developer transfer section of the developer transfer section from the first transfer screw 53 to the second transfer screw 54 are different from each other. The developer feeding speed by the screw becomes slower, and the developer amount at the uppermost stream side of the first conveying screw 53, that is, the right side of the developing roller 51 in FIG. Because it is less than that.

  This tendency tends to become more pronounced as the rotational speed of the photosensitive drum 20, the developing roller 51, and the first and second conveying screws 53 and 54 for stirring the developer is higher, and as the developer filling amount is lower.

  FIG. 8 shows the result of measuring the density of each part on the image when the entire exposure image is output. The magnetic pole P4 is 45 mT and the angle α is 35 degrees. However, in FIG. 3, only the magnetic force of the P4 pole on the most upstream side (right side on the image position) of the developing roller 51 is leveled to 45 mT, 47 mT, and 50 mT.

In this case, that has a magnetic force of the magnetic pole P4 varied over the lengthwise direction of the developing roller 51. In this example, the most upstream side (F side) in the developer transport direction by the first transport screw 53 along the longitudinal direction of the developing roller 51 is set higher than the most downstream side (R side) and the central side (C side). This makes it easy to draw up the developer. Thus, the image right portions and the center, the density difference of the left section that a small.

  That is, the peak magnetic force in the normal direction of the magnetic pole P4 located on the downstream side in the rotation direction of the developing roller 51 among the two same-polarity magnetic poles P3 and P4 is applied from one end side to the other end side in the longitudinal direction of the developing roller 51. By making them partially different, the pumping amount is set to be constant in the longitudinal direction of the developing roller 53 in accordance with the volume balance of the developer in the developing container surrounding the lower portion of the first conveying screw 53, and an image having no image density unevenness is set. Can be provided.

  FIG. 9 shows a process cartridge 60 in which a developing device 50 according to the present invention is supported by a frame integrally with a photosensitive drum 20, a charging roller 30R as a charging means and its incidental equipment, a cleaning device 40 as a cleaning means, and the like. It is composed. The frame that is integrally supported is a frame that integrates the developing case 55, the developing containers 56a and 56b, the cleaning case 43, and the like, as described with respect to the members that have come out so far. FIG. 9 shows a frame that connects these members together.

The process cartridge 60 is configured to be detachable from the image forming apparatus main body 70 through appropriate attachment standards and guide means. Since various unit members that execute the image forming process are integrated as a process cartridge 60, it is easy for users and service personnel to carry around, and the photosensitive drum 20, charging means, developing means, and cleaning device are not easily damaged and replaced. A cartridge with good operability can be provided .

FIG. 10 is a schematic view of an image forming apparatus in which the process cartridges 60Y, 60M, 60C, and 60Bk of the respective colors are detachable from the image forming apparatus main body 70. In the figure, the process cartridges 60Y, 60M, 60C, and 60Bk are shown in the middle of being extracted (or mounted) from the image forming apparatus main body 70. Each of these process cartridges 60Y, 60C, 60M, and 60Bk can be developed with yellow, cyan, magenta, and black developers (developing devices 50Y, 50C, 50M, and 50Bk in this example, although not shown). Is a process cartridge containing. As a result, it is possible to provide a main unit with a small number of units and excellent maintainability .

1 is a diagram illustrating a configuration of a color image forming apparatus. It is a figure explaining the structure of the image station. 1 is an external perspective view of a developing device. FIG. 6 is a diagram illustrating an internal configuration of the developing device and a magnetic force distribution around the developing roller. It is a figure explaining magnetic force distribution around a developing roller. It is the figure which plotted the data which evaluated the image quality when changing the normal direction peak magnetic force etc. of the magnetic pole P4. It is the figure which plotted the data which evaluated the image quality when changing the normal direction peak magnetic force etc. of the magnetic pole P4. FIG. 6 is a graph of data obtained by evaluating image quality when the normal direction peak magnetic force of the magnetic pole P4 is changed in the longitudinal direction of the developing roller. It is explanatory drawing of a process cartridge. FIG. 3 is an external perspective view illustrating a state in the middle of assembling process cartridges for respective colors to the image forming apparatus main body.

Explanation of symbols

51 Developing roller 55 Developing case P4 Magnetic pole

Claims (4)

A developing roller having a rotatable nonmagnetic cylinder and a magnetic roller generating means in which non-moving magnets for forming a plurality of magnetic poles are fixed, and a two component component comprising a magnetic carrier and a nonmagnetic toner A developer container for containing the developer; agitating and conveying means for agitating and conveying the two-component developer in the developer container; and a case member surrounding the developing roller; In a two-component developing device that conveys by rotation and develops an electrostatic latent image on an image carrier with a magnetic brush,
Among the magnetic poles constituting the magnetic field generating means, a repulsive magnetic field is formed between two magnetic poles of the same polarity that separate the developer that has passed the development position from the developing roller, and two repulsive magnetic fields are formed. Among the polar magnetic poles, the magnetic pole located downstream in the rotation direction of the developing roller is used as a pumping magnetic pole for pumping up the developer from the stirring and conveying means, and the peak magnetic force in the normal direction of the pumping magnetic pole is the stirring and conveying means The developing device is characterized in that the upstream side in the developer conveying direction is set higher than the downstream side . In the process cartridge which integrally supports these members including the image carrier and the developing device and is detachable from the image forming apparatus main body,
The developing device includes:
A developing roller having a rotatable nonmagnetic cylinder and a magnetic roller generating means in which non-moving magnets for forming a plurality of magnetic poles are fixed, and a two component component comprising a magnetic carrier and a nonmagnetic toner A developer container for containing the developer; agitating and conveying means for agitating and conveying the two-component developer in the developer container; and a case member surrounding the developing roller; It consists of a two-component developing device that conveys by rotation and develops the electrostatic latent image on the image carrier with a magnetic brush.
Among the magnetic poles constituting the magnetic field generating means, a repulsive magnetic field is formed between two magnetic poles of the same polarity that separate the developer that has passed the development position from the developing roller, and two repulsive magnetic fields are formed. Among the polar magnetic poles, the magnetic pole located downstream in the rotation direction of the developing roller is used as a pumping magnetic pole for pumping up the developer from the stirring and conveying means, and the peak magnetic force in the normal direction of the pumping magnetic pole is the stirring and conveying means the process cartridge towards the developer conveyance direction upstream side, characterized that you have been set higher than the downstream side of the. In an image forming apparatus comprising an image carrier and developing means for developing an electrostatic latent image formed on the image carrier,
The image forming apparatus according to claim 1, wherein the developing unit is the developing device according to claim 1 . 3. An image forming apparatus according to claim 2, wherein the process cartridge is a process cartridge according to claim 2, wherein the process cartridge is detachable from the main body of the image forming apparatus .

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