Developing device and image forming apparatus including the same

Abstract

To provide a developing device that has developer conveying chambers arranged in the vertical direction, and that can achieve good developer separability without increasing the size of the developing device, and an image forming apparatus including the same.SOLUTION: A developing device comprises: a developer container that has a first conveying chamber and a second conveying chamber arranged above the first conveying chamber; a first stirring and conveying member; a second stirring and conveying member; a developer carrier; and a regulation blade. The developer carrier has a magnet member having a plurality of magnetic poles including a regulation pole, a main pole, a separation pole separating developer carried on the developer carrier, and a pump-up pole pumping up the developer onto the developer carrier. A separation starting position at which the magnetic force of the separation pole is 5 mT or less is located below a horizontal straight line L1 passing through the center of a rotation axis of the second stirring and conveying member. When the central angle of a developer separation area where the magnetic force between the separation pole and the pump-up pole is 5 mT or less is defined as X°, and the peak magnetic force of the pump-up pole as Y mT, Y≤2.1X-32.7 is satisfied.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a developing device and an image forming apparatus equipped with the same, and in particular to a developing device having a first transport chamber in which a stirring and transporting member that stirs and transports developer is disposed, and a second transport chamber disposed above the first transport chamber, and an image forming apparatus equipped with the same. [Background technology]

[0002] In image forming apparatuses, a latent image formed on an image carrier such as a photosensitive member is developed by a developing device to be visualized as a toner image. One known example of such a developing device is one that includes a developer container that contains developer, a first agitation / transport member and a second agitation / transport member that agitate and transport the developer, and a developing roller (developer carrier) that carries the developer supplied from the second agitation / transport member. The first agitation / transport member transports the developer to one side of the axial direction of the developing roller, and the second agitation / transport member transports the developer to the other side (the opposite side) while supplying it to the developing roller.

[0003] In recent years, there has been an increasing demand for smaller image forming apparatuses, particularly in color machines that use multiple developing devices. To address this, a developing device has been proposed that includes a first transport chamber containing a first agitating / transporting member and a second transport chamber located above the first transport chamber and containing a second agitating / transporting member. In this developing device, the first and second transport chambers are arranged vertically, thereby enabling the developing device to be smaller in the horizontal direction than in a configuration in which the first and second transport chambers are arranged horizontally. This reduces the space required for the developing device, enabling the image forming apparatus to be more compact.

[0004] For example, Patent Document 1 discloses a configuration in which, in a developing device having a lower transport chamber and an upper transport chamber, the developer on the developing roller is separated above the developer transport mixer in the lower transport chamber and the developer is recovered in the lower transport chamber. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-66377 Summary of the Invention [Problem to be solved by the invention]

[0006] In two-component development, which uses a two-component developer containing a magnetic carrier and toner, a developing roller equipped with a magnetic member inside the developing sleeve rubs the developer in the form of a magnetic brush against the surface of a photosensitive drum, transferring only the toner to the photosensitive drum surface to develop an electrostatic latent image. After development, the developer adhering to the surface of the developing roller must be peeled off because the toner has been consumed and the toner concentration has decreased. If the developer is not sufficiently peeled off from the developing roller, the developer with consumed toner will immediately be scooped up onto the developing roller. As a result, the toner concentration of the developer will differ between areas where toner has been consumed and areas where toner has not been consumed, causing localized unevenness in image density.

[0007] The configuration of Patent Document 1 achieves good removability by collecting the developer separated from the developing roller in the lower stirring chamber. However, in order to collect the developer in the lower stirring chamber, the housing of the lower stirring chamber must face (overlap) the lower side of the developing roller. As a result, the lower transport chamber and the photosensitive drum cannot be closer than a certain distance, requiring extra space for installation.

[0008] In view of the above problems, the present invention aims to provide a developing device in which developer transport chambers are arranged above and below, which can achieve good developer separation performance without increasing the size of the developing device, and an image forming apparatus equipped with the same. [Means for solving the problem]

[0009] To achieve the above object, a first configuration of the present invention is a developing device that includes a developing container, a first agitating / transporting member, a second agitating / transporting member, a developer carrier, and a regulating blade, and develops an electrostatic latent image formed on an image carrier into a toner image. The developing container has a first transport chamber and a second transport chamber disposed above the first transport chamber across a partition, and contains a two-component developer containing a carrier and a toner. The first agitating / transporting member is rotatably supported within the first transport chamber and transports the developer in the first transport chamber in a first direction while agitating it. The second agitating / transporting member is rotatably supported within the second transport chamber and parallel to the first agitating / transporting member, and transports the developer in the second transport chamber in a second direction opposite to the first direction while agitating it. The developer carrier is rotatably supported in the developing container and carries the developer in the second transport chamber on its surface. The regulating blade is disposed opposite the developer carrier and regulates the thickness of the developer layer on the developer carrier. The developing device supplies developer to the developer carrier and collects developer from the developer carrier in a second transport chamber. The developer carrier has a rotatable cylindrical developing sleeve and a magnet member non-rotatably fixed inside the developing sleeve. The magnet member has multiple magnetic poles, including a regulating pole facing the regulating blade, a main pole facing the image carrier, a stripping pole for stripping the developer carried on the developer carrier, and a pumping pole for pumping the developer onto the developer carrier, along the rotation direction of the developing sleeve. The separation start position, where the magnetic force of the stripping pole is 5 mT or less, is located below a horizontal line L1 passing through the center of the rotation axis of the second stirring / transporting member. The central angle of the developer separation region, where the magnetic force between the stripping pole and the pumping pole is 5 mT or less, is X [°], and the peak magnetic force of the pumping pole is Y [mT], satisfies the following formula (1). Y≦2.1X-32.7 (1) [Effects of the Invention]

[0010] According to the first configuration of the present invention, the separation start position where the magnetic force of the separation pole becomes 5 [mT] or less is located below the straight line L1, and the central angle of the developer separation area between the separation pole and the pumping pole where the magnetic force becomes 5 [mT] or less is set to X [°], and the peak magnetic force of the pumping pole N1 is set to Y [mT] so as to satisfy formula (1), thereby ensuring good separation and pumping properties of the developer. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus 100 equipped with developing devices 3a to 3d of the present invention. [Figure 2] FIG. 10 is a side cross-sectional view showing the structure of the agitation unit of the developing device 3a according to one embodiment of the present invention. [Figure 3] 1 is a longitudinal cross-sectional view of a developing device 3a according to an embodiment of the present invention, taken along a direction perpendicular to the longitudinal direction thereof. [Figure 4] FIG. 4 is an enlarged cross-sectional view of the periphery of the second transport chamber 22c in FIG. 3, showing the magnetic force distribution of the magnet member 20b of the developing roller 20 and the developer separation region R. [Figure 5] Graph showing the experimental results of developer separation performance when the separation area width [°] and the peak magnetic force of the pumping pole N1 are changed DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view of an image forming apparatus 100 equipped with developing devices 3a to 3d of the present invention, showing a tandem color printer. Four image forming units Pa, Pb, Pc, and Pd are arranged in the main body of the image forming apparatus 100, in the order of Pd to Pa, from the upstream side in the transport direction (the right side in Fig. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta, and black), and sequentially form images of yellow, cyan, magenta, and black through the processes of charging, exposure, development, and transfer, respectively.

[0013] Each of the image forming stations Pa to Pd is provided with a photosensitive drum 1a, 1b, 1c, and 1d that carries a visible image (toner image) of each color. An intermediate transfer belt 8 that rotates clockwise in FIG. 1 is provided adjacent to each of the image forming stations Pa to Pd.

[0014] When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a-1d are uniformly charged by the charging devices 2a-2d. Next, the exposure device 5 irradiates the surfaces of the photosensitive drums 1a-1d with light according to the image data, forming electrostatic latent images on each of the photosensitive drums 1a-1d in accordance with the image data. The developing devices 3a-3d are filled with a predetermined amount of two-component developer (hereinafter simply referred to as developer) containing yellow, cyan, magenta, and black toner and magnetic carriers supplied from toner containers 4a-4d. The developing devices 3a-3d supply the toner in the developer onto the photosensitive drums 1a-1d, where it electrostatically adheres to them. This forms a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5.

[0015] Then, primary transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d, and the yellow, cyan, magenta, and black toner images on the photosensitive drums 1a to 1d are primarily transferred onto the intermediate transfer belt 8. After the primary transfer, toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d are removed by cleaning devices 7a to 7d.

[0016] The transfer paper P onto which the toner image is transferred is stored in a paper cassette 16 located at the bottom of the image forming apparatus 100. The transfer paper P is transported at a predetermined timing via a paper feed roller 12a and a pair of registration rollers 12b to a nip portion (secondary transfer nip portion) between the intermediate transfer belt 8 and a secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8. The transfer paper P onto which the toner image has been secondarily transferred is transported to a fixing unit 13.

[0017] The transfer paper P conveyed to the fixing unit 13 is heated and pressurized as it passes through the nip between the fixing belt and pressure roller, and the toner image is fixed to the surface of the transfer paper P, forming a predetermined full-color image. The transfer paper P on which the full-color image has been formed is then discharged onto a discharge tray 17 by a pair of discharge rollers 15 as is (or after being diverted to a reversing conveyance path 18 by a branching unit 14 and images formed on both sides).

[0018] 2 is a vertical cross-sectional view showing the structure of an agitation unit of a developing device 3a according to one embodiment of the present invention, which is mounted on an image forming apparatus 100. While the developing device 3a disposed in the image forming section Pa of FIG. 1 will be described here, the developing devices 3b to 3d disposed in the image forming sections Pb to Pd have basically the same configuration, and therefore description thereof will be omitted. For ease of explanation, the position of the developing roller 20 is shifted above the first transport chamber 22b in FIG. 2.

[0019] As shown in FIG. 2, the developing device 3a includes a developing roller (developer carrier) 20, a first spiral (first agitating / transporting member) 43, a second spiral (second agitating / transporting member) 44, and a developing container 22. The developing container 22 forms the outer shell of the developing device 3a and includes a partition 22a, a first transport chamber 22b, a second transport chamber 22c, a first communication portion 22d, and a second communication portion 22e. A two-component developer consisting of a magnetic carrier and toner is stored in the first transport chamber 22b and the second transport chamber 22c. The developing container 22 rotatably holds the first spiral 43, the second spiral 44, and the developing roller 20.

[0020] The partition 22a extends in the longitudinal direction of the developer container 22 and partitions the first transport chamber 22b and the second transport chamber 22c so that they are arranged vertically side by side. The first communication portion 22d and the second communication portion 22e are formed on one and the other longitudinal sides (the downstream side in the A1 direction and the downstream side in the A2 direction) of the partition 22b, respectively. The first communication portion 22d connects the downstream ends of the first transport chamber 22b and the second transport chamber 22c in the A1 direction (first direction) with each other. The second communication portion 22e connects the downstream ends of the first transport chamber 22b and the second transport chamber 22c in the A2 direction (second direction) with each other. The developer circulates through the first transport chamber 22b, the first communication portion 22d, the second transport chamber 22c, and the second communication portion 22e.

[0021] The first spiral 43 is disposed in the first transport chamber 22b. The first spiral 43 has a rotary shaft 43b rotatably supported in the developing container 22 and a first spiral blade 43a integrally provided on the rotary shaft 43b and spirally formed at a constant pitch in the axial direction of the rotary shaft 43b. The first spiral 43 rotates in a predetermined direction (counterclockwise in FIG. 3) by a drive mechanism (not shown). By rotating in the predetermined direction, the first spiral blade 43a transports the developer in the first transport chamber 22b in the A1 direction (one side in the axial direction of the developing roller 20) while stirring the developer.

[0022] Furthermore, a toner supply port 23 for supplying toner to the developing container 22 is provided on the end surface of the first conveying chamber 22b in the A2 direction. A toner supply path 24, which is connected to the toner container 4a (see FIG. 1), is connected to the toner supply port 23. The rotating shaft 43b passes through the toner supply port 23 and is disposed within the toner supply path 24. A supply blade 43c is formed integrally with the portion of the rotating shaft 43b disposed within the toner supply path 24, and is spirally shaped at a constant pitch in the axial direction of the rotating shaft 43b. The supply blade 43c is formed by a spiral blade facing in the same direction (in the same phase) as the first spiral blade 43a. The supply blade 43c is formed with a smaller pitch and a smaller diameter than the first spiral blade 43a.

[0023] The second spiral 44 is disposed in the second transport chamber 22c. The second spiral 44 has a rotation shaft 44b rotatably supported in the developer container 22 parallel to the rotation shaft 43b, and a second spiral blade 44a integrally provided on the rotation shaft 44b and formed in a spiral shape with blades facing in the opposite direction (opposite phase) to the first spiral blade 43a. The second spiral 44a is rotated in a predetermined direction (counterclockwise in FIG. 3) by a drive mechanism (not shown). The second spiral blade 44a rotates in the same direction as the first spiral blade 43a, thereby agitating and transporting the developer in the second transport chamber 22c in the A2 direction (opposite the A1 direction) and supplying the developer to the developing roller 20.

[0024] The first spiral 43 and the second spiral 44 agitate the developer, charging the toner in the developer to a predetermined level. This causes the toner to be held by the carrier. When the first spiral 43 and the second spiral 44 rotate, the developer is transported from one of the communication portions (first communication portion 22d) provided in the partition portion 22b to the second spiral 44, and then from the other communication portion (second communication portion 22e) to the first spiral 43, circulating between the first transport chamber 22b and the second transport chamber 22c. The developer is then supplied from the second spiral 44 to the developing roller 20, forming a magnetic brush on the developing roller 20.

[0025] The developing roller 20 includes a developing sleeve 20a rotatably supported in a developing container 22, and a magnetic pole member 20b having a plurality of magnetic poles and fixed to a fixed shaft (not shown) within the developing sleeve 20a. The developing sleeve 20a rotates in the direction of the arrow (counterclockwise) in Fig. 3 by a drive mechanism (not shown). A developing voltage, which is a DC voltage superimposed with an AC voltage, is applied to the developing sleeve 20a.

[0026] In this developing device 3a, as shown in FIG. 2, the developer in the first transport chamber 22b is stirred and transported in the A1 direction (toward the first communicating portion 22d) by the first spiral 43, and gradually accumulates on one side of the first transport chamber 22b. On one side of the first transport chamber 22b, the developer is pushed by the following developer and is pushed up into the second transport chamber 22c via the first communicating portion 22d. The developer in the second transport chamber 22c is supplied to the developing roller 20 while being stirred and transported in the A2 direction (toward the second communicating portion 22e) by the second spiral 44. The developer transported to the other side of the second transport chamber 22c falls into the first transport chamber 22b via the second communicating portion 22e.

[0027] FIG. 3 is a longitudinal cross-sectional view of the developing device 3a of this embodiment, taken in a direction perpendicular to the longitudinal direction (cross-sectional view taken along the arrow XX' in FIG. 2). As shown in FIG. 3, a regulating blade 27 is attached to the developer container 22. More specifically, the regulating blade 27 is attached along the longitudinal direction of the developing roller 20 (the direction perpendicular to the paper surface of FIG. 3). A small gap (regulating gap) is provided between the tip of the regulating blade 27 and the outer circumferential surface of the developing roller 20, forming a regulating portion. As the developing sleeve 20a rotates, the developer (magnetic brush) passes through the regulating portion, thereby regulating the layer thickness of the developer carried on the surface of the developing roller 20. In this embodiment, a magnetic blade made of stainless steel (SUS430) is used as the regulating blade 27.

[0028] The magnetic pole member 20b of the developing roller 20 has, along the rotation direction of the developing sleeve 20a (counterclockwise in FIG. 3), a regulating pole (pumping pole) N1 arranged in the region facing the regulating blade 27 (regulating portion), a main pole S1 arranged in the region facing the photosensitive drum 1a (developing region), and a peeling pole N3 that peels off the developer carried on the developing roller 20. In addition, a five-pole configuration is formed, with transport poles N2 and S2 arranged between the regulating pole (pumping pole) N1 and the main pole S1. The regulating pole N1 also serves as a pumping pole that pumps developer onto the developing roller 20, so its magnetic pole width (central angle) is larger than those of the other magnetic poles. When a driving force is input to the developing device 3a, the developing sleeve 20a rotates, but the magnetic member 20b does not rotate.

[0029] A magnetic field is generated between the regulating pole N1 of the magnet member 20b and the regulating blade 27 in an attractive direction, forming a magnetic brush of developer between the regulating blade 27 and the developing roller 20. The magnetic brush passes through the regulating blade 27 (regulating portion), thereby regulating the layer thickness to a desired height. When the developing sleeve 20a subsequently rotates counterclockwise, the transport poles S2 and N2 apply a magnetic field in a direction along the outer circumferential surface of the developing sleeve 20a, causing the magnetic brush to move to the development region. Then, the main pole S1 applies a magnetic field in an attractive direction between the magnetic brush and the photosensitive drum 1a, causing the magnetic brush to come into contact with the surface of the photosensitive drum 1a and develop the electrostatic latent image. Additionally, toner not used in development is collected by the magnetic brush on the developing sleeve 20a.

[0030] When the developing sleeve 20a further rotates counterclockwise, the magnetic brush is detached from the developing roller 20 by the repulsive magnetic field between the peeling pole N3 and the regulating pole (pumping pole) N1 and is collected into the second transport chamber 22c. Then, after being stirred and transported by the second spiral 44, the magnetic brush is again formed on the developing sleeve 20a by the magnetic field of the regulating pole (pumping pole) N1.

[0031] In the developing device 3a of this embodiment, the second transport chamber 22c is disposed above the first transport chamber 22b. That is, the first transport chamber 22b and the second transport chamber 22c are disposed one above the other. This allows the developing device 3a to be made smaller in the horizontal direction. Since the four developing devices 3a to 3d are disposed horizontally in the image forming apparatus 100, making the developing devices 3a to 3d smaller is particularly effective in making the image forming apparatus 100 smaller. Furthermore, the developing roller 20 is disposed below the second spiral 44 in the second transport chamber 22c. This allows the developing device 3a to be made smaller in the vertical direction as well.

[0032] The developing device 3a of this embodiment supplies developer from the second spiral 44 in the second transport chamber 22c to the developing roller 20. Then, the developer that has passed through the development area and consumed toner during development is collected in the second transport chamber 44 in which the second spiral 44 is arranged.

[0033] Also, as shown in Figure 3, when a horizontal line passing through the center of the rotation axis 44b of the second spiral 44 in the second conveying chamber 22c is defined as L1, a horizontal line passing through the rotation center of the developing roller 20 is defined as L2, and a horizontal line passing through the center of the rotation axis 43b of the first spiral 43 in the first conveying chamber 22b is defined as L3, L2 is at a lower position than L1, and L3 is at a lower position than L2.

[0034] Fig. 4 is an enlarged cross-sectional view of the periphery of the second transport chamber 22c in Fig. 3. The magnetic force distribution of the magnet member 20b of the developing roller 20 and the developer separating region R will be described with reference to Fig. 4.

[0035] In the developing device 3a of this embodiment, the separation start position is defined as point P1 (the falling position of the magnetic force peak of the separation pole N3 between the separation pole N3 and the pumping pole N1) where the magnetic force of the separation pole N3, which separates the developer from the developing roller 20 after passing through the development region, becomes 5 mT or less. The region between the separation pole N3 and the pumping pole N1 of the developing roller 20 where the magnetic force is 5 mT or less is defined as the developer separation region R. The pumping start position is defined as point P2 (the rising position of the magnetic force peak of the pumping pole N1 between the separation pole N3 and the pumping pole N1) where the magnetic force of the pumping pole N1, which scoops up the developer onto the developing roller 20 after passing through the developer separation region R, becomes 5 mT or more.

[0036] At this time, the separation start position P1 is below the straight line L1 and is at the same height as the upper surface of the partition portion 22a. With this configuration, the developer is separated (separated) from the developing roller 20 below the second spiral 44 in the second transport chamber 22c, and the developer separated from the developing roller 20 is collected in the location in the second transport chamber 22c where the developer G is filled. Therefore, toner scattering from the gap between the developing roller 20 and the developing container 22 can be effectively suppressed.

[0037] Furthermore, the scooping start position P2 is located below the upper end of the second spiral 44. With this configuration, the developer stirred by the second spiral 44 is easily supplied to the developing roller 20 by the scooping pole N1. Therefore, a magnetic brush can be stably formed on the developing roller 20.

[0038] Next, we will explain the relationship between the width (central angle) of the developer separation region R, the peak magnetic force of the pumping pole (regulating pole) N1, and developer separation performance. The narrower the width of the developer separation region R and the stronger the peak magnetic force of the pumping pole N1, the lower the developer separation performance. More specifically, the developer separated in the developer separation region is immediately pumped up by the pumping pole N1, resulting in developer with a reduced toner concentration being used for development. As shown in the examples below, by designing the separation region width to satisfy the following formula (1), where X [°] is the width of the separation region and Y [mT] is the peak magnetic force of the pumping pole N1, good separation performance of developer used for development and with a reduced toner concentration, and pumping performance of developer sufficiently stirred in the second transport chamber 22c with a stable toner concentration, can be ensured. Y≦2.1X-32.7 (1)

[0039] Furthermore, although the wider the developer separation region R, the better the separation performance, it is difficult to set the width (central angle) of the developer separation region R to 60° or more due to layout constraints of the developing devices 3a-3d. Furthermore, if the peak magnetic force of the pumping pole N1 is 30 mT or less, when the regulating blade 27 regulates the thickness of the developer (magnetic brush) layer, it is necessary to set a small gap (regulating gap) with the developing roller 20, which is undesirable because it is susceptible to the influence of component tolerances and installation tolerances of the regulating blade 27. Furthermore, if the peak magnetic force of the pumping pole N1 is 60 mT or more, the mechanical stress on the developer increases when the magnetic brush passes through the regulating blade 27, which is undesirable because it reduces the durability of the developer when used for long periods of time.

[0040] Therefore, by designing to satisfy the following formulas (2) and (3), it becomes possible to design developing devices 3a to 3d that maintain good developer detachability while improving the stability of the magnetic brush and the durability of the developer. X≦60 (2) 30≦Y≦60 (3)

[0041] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, in the above-described embodiment, an example in which developer is supplied from the second spiral 44 to the developing roller 20 is shown, but the present invention is not limited to this. For example, a magnetic roller (developer carrier) may be provided adjacent to the second spiral 44, and after the developer is supplied from the second spiral 44 to the magnetic roller, toner may be supplied from the magnetic roller to the developing roller (toner supply member).

[0042] In addition, in the above embodiment, the magnetic pole width of the regulating pole N1 is increased so that it also serves as a pumping pole, but a separate pumping pole may be provided upstream of the regulating pole N1 in the rotation direction of the developing roller 20. Furthermore, in the above embodiment, two transport poles N2 and S2 are arranged, but one or three or more transport poles may be arranged.

[0043] 1, the present invention is not limited to direct transfer color printers, but can also be applied to various image forming apparatuses equipped with a developing device including a first transport chamber and a second transport chamber located above the first transport chamber, such as intermediate transfer color printers that have an intermediate transfer belt and a secondary transfer roller instead of the transport belt 8, and digital or analog monochrome copiers, color copiers, and facsimiles.The effects of the present invention will be described more specifically below using examples. [Example]

[0044] [Relationship between the width of the developer separation area, the peak magnetic force of the pumping pole, and developer separation performance] The developer separation property in the developer separation region R was investigated when the width (central angle) of the developer separation region R and the peak magnetic force of the pumping pole (regulating pole) N1 were changed.

[0045] The test machine used was an image forming apparatus 100 (manufactured by Kyocera Document Solutions Inc.) as shown in Figure 1, with a paper transport speed (process linear speed) of 195 mm / sec. The outer diameter of the developing roller 20 was 16 mm, and the linear speed ratio of the developing roller 20 to the photosensitive drums 1a to 1d was 1.8. The gap between the developing roller 20 and the regulating blade 27 (regulation gap) was 0.40 mm, and the gap between the photosensitive drums 1a to 1d and the developing roller 20 (development gap) was 0.34 mm.

[0046] To evaluate developer release performance, we varied the width (central angle) of the developer release region R and the peak magnetic force of the pumping pole (regulating pole) N1 between multiple levels, outputting solid images, and then measured the density difference ΔID between the leading and trailing edges of the image using an image densitometer. When developer release failure occurs, the trailing edge of the image is used for development with consumed toner (lower toner concentration), resulting in lower image density compared to the leading edge. In other words, when developer release failure occurs, ΔID increases. We set the target value for ΔID at 0.10 or less, and confirmed the relationship between the width (central angle) of the developer release region R and the peak magnetic force of the pumping pole N1 that met the target value. The results are shown in Figure 5. The numbers labeled on the plots in Figure 5 indicate the ΔID values.

[0047] As shown in Figure 5, the narrower the width (central angle) of the developer separation area R and the stronger the peak magnetic force of the pumping pole N1, the lower the developer separation property, and therefore the larger the value of ΔID. If the width (central angle) of the developer separation area R is X [°] and the peak magnetic force of the pumping pole N1 is Y [mT], then ΔID can be kept below the target value of 0.10 in the area that satisfies the relationship Y≦2.1X-32.7 (the area to the right of line L4 in Figure 5).

[0048] Furthermore, the region where X≦60 and 30≦Y≦60 (the hatched region in FIG. 5) is the designable region OW (operation window) of the developing devices 3a to 3d. It has been confirmed that within this region, good developer separation performance can be achieved, and the stability of the magnetic brush and the durability of the developer are also improved.

[0049] Furthermore, if the relationship Y≦2.1X-32.7 is satisfied, there is no risk that the developer separated in the developer separation region R will be immediately drawn up by the drawing pole N1 and used for development. Furthermore, if the relationships X≦60 and 30≦Y≦60 are satisfied, the stability of the magnetic brush and the durability of the developer are improved. Therefore, even if development conditions such as the outer diameter of the developing roller 20, the linear velocity ratio of the developing roller 20 to the photosensitive drums 1a-1d, the regulating gap, and the development gap change, the desired actions and effects can be obtained by satisfying formulas (1) to (3). [Industrial Applicability]

[0050] The present invention can be applied to a developing device having a first transport chamber and a second transport chamber disposed above the first transport chamber. By utilizing the present invention, it is possible to provide a developing device that can achieve good developer releasability without increasing the size of the developing device, and an image forming apparatus equipped with the same. [Explanation of symbols]

[0051] 3a~3d developing device 20 Developing roller (developer carrier) 20a developing sleeve 20b Magnet member 22 Developer container 22a Partition 22b 1st transfer room 22c Transport Room 2 22d 1st communication part 22e 2nd communication part 23 Toner supply port 27 Regulatory Blade 43 First spiral (first stirring and conveying member) 44 Second spiral (second stirring and conveying member) 43a First spiral blade 44a Second spiral blade 43b, 44b Rotation axis 100 Image forming device N1 Regulating pole (pumping pole) S1 main pole N2, S2 carrying pole N3 Peeling pole P1 Peeling start position P2 Pumping start position R Developer separation area

Claims

1. a developing container having a first transport chamber and a second transport chamber disposed above the first transport chamber across a partition, the developing container containing a two-component developer containing a carrier and a toner; a first stirring and conveying member that is rotatably supported in the first conveying chamber and that conveys the developer in the first conveying chamber in a first direction while stirring the developer; a second agitating / transporting member that is rotatably supported in the second transport chamber and parallel to the first agitating / transporting member, and that agitates the developer in the second transport chamber and transports it in a second direction that is opposite to the first direction; a developer carrier that is rotatably supported by the developing container and that carries the developer in the second transport chamber on its surface; a regulating blade disposed opposite the developer carrier and regulating the thickness of the developer layer on the developer carrier; A developing device for developing an electrostatic latent image formed on an image carrier into a toner image, comprising: supplying the developer to the developer carrier and recovering the developer from the developer carrier in the second transport chamber; the developer carrier includes a rotatable cylindrical developing sleeve, and a magnet member that is fixed non-rotatably inside the developing sleeve and has a plurality of magnetic poles, including a regulating pole that faces the regulating blade along the rotation direction of the developing sleeve, a main pole that faces the image carrier, a separating pole that separates the developer carried on the developer carrier, and a pumping pole that pumps up the developer onto the developer carrier; A developing device characterized in that the peeling start position, where the magnetic force of the peeling pole is 5 [mT] or less, is located below a horizontal line L1 passing through the center of the rotation shaft of the second stirring and conveying member, and the central angle of the developer peeling region, where the magnetic force between the peeling pole and the pumping pole is 5 [mT] or less, is X [°], and the peak magnetic force of the pumping pole is Y [mT], such that the following formula (1) is satisfied. Y≦2.1X-32.7...(1)

2. 2. The developing device according to claim 1, wherein the following formula (2) is satisfied: X≦60 (2)

3. 2. The developing device according to claim 1, wherein the following formula (3) is satisfied: 30≦Y≦60 (3)

4. 2. The developing device according to claim 1, wherein the straight line L1 is located above a horizontal straight line L2 that passes through the center of the rotation shaft of the developer carrier, and the straight line L2 is located above a horizontal straight line L3 that passes through the center of the rotation shaft of the first stirring / conveying member.

5. 2. The developing device according to claim 1, wherein the separation start position, which is the falling position of the magnetic force peak of the separation pole between the separation pole and the pumping pole, is at the same height as the upper surface of the partition portion.

6. 2. The developing device according to claim 1, wherein a pumping start position, which is a position where a magnetic force peak of the pumping pole rises between the peeling pole and the pumping pole, is located below an upper end of the second stirring / transporting member.

7. 7. An image forming apparatus comprising the developing device according to claim 1.

Images