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 prevent, with a simple configuration, scattering of toner to the outside 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, and stores two-component developer including carrier and toner; a first stirring and conveying member and a second stirring and conveying member that convey the developer in the first conveying chamber and the second conveying chamber in directions opposite to each other, while stirring the developer; a developer carrier that carries the developer in the second conveying chamber on its surface; and a regulation blade that regulates the layer thickness of the developer on the developer carrier. Supply of the developer to the developer carrier and recovery of the developer from the developer carrier are performed inside the second conveying chamber. A horizontal straight line L1 passing through the center of a rotation axis of the second stirring and conveying member is located above a horizontal straight line L2 passing through the center of a rotation axis of the developer carrier, and the straight line L2 is located above a horizontal straight line L3 passing through the center of a rotation axis of the first stirring and conveying member.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 Documents 1 and 2 disclose 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 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-129905 Summary of the Invention [Problem to be solved by the invention]

[0006] In the configurations disclosed in Patent Documents 1 and 2, in which the developer that has passed through the development area is collected from the developing roller into the lower transport chamber, the developer separated from the developing roller is collected in a location above the developer transport mixer in the lower transport chamber that is not filled with developer. At this time, there is a problem in that the separated developer rises up inside the developing container, causing toner to scatter outside the developing device through the gap between the developing roller and the housing.

[0007] In the configuration of Patent Document 1, in order to collect the developer separated from the developing roller into the lower stirring chamber, the housing of the lower stirring chamber must be positioned facing (overlapping) below the developing roller. This prevents the lower transport chamber and the photosensitive drum from being closer than a certain distance, requiring additional space for installation. In addition, in the configuration of Patent Document 2, the developer separated from the developing roller is collected through a developer guide member installed in the lower transport chamber, preventing toner from scattering near the gap between the developing roller and the housing. This increases the number of parts and requires space for developer transport, leading to larger and more costly developing devices.

[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 suppress toner scattering outside the developing device with a simple configuration, 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 supply of developer to the developer carrier and the recovery of developer from the developer carrier are performed in the second transport chamber. A horizontal line L1 passing through the center of the rotation shaft of the second agitating / transporting member is located above a horizontal line L2 passing through the center of the rotation shaft of the developer carrier, and line L2 is located above a horizontal line L3 passing through the center of the rotation shaft of the first agitating / transporting member. [Effects of the Invention]

[0010] According to the first configuration of the present invention, the developer separated from the developer carrier can be collected in the lower part of the second transport chamber filled with the developer. This suppresses the toner from flying up inside the developing container and the toner from scattering outside the developing device through the gap between the developer carrier and the developing container. Furthermore, since there is no need to provide a developer guide member, the number of components used in the developing device can be reduced. Furthermore, since there is no need to provide a distance between the image carrier and the developing device, the image carrier and the developing device can be placed closer to each other, enabling the image forming device to be made more compact. [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, illustrating the transfer of developer between the developing roller 20 and the first transport chamber 22b. [Figure 5] FIG. 4 is an enlarged cross-sectional view of the periphery of the second transport chamber 22c in FIG. 3, illustrating the positional relationship between the developing roller 20 and the second spiral 44. [Figure 6] Graph showing the measurement results of the density difference ΔID between the leading edge and trailing edge of an image when a solid image is output while changing d2 using a developing roller 20 in which the width of the developer peeling region R is 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 this order from the upstream side in the transport direction (the right side in Fig. 1) to Pa to Pd within the main body of the image forming apparatus 100. 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. A conveyor belt 8 that rotates counterclockwise in Fig. 1 is provided adjacent to each of the image forming stations Pa to Pd. The conveyor belt 8 is wound around a drive roller 10 and a driven roller 11.

[0014] When image data is input from a host device such as a personal computer, first, the charging devices 2a-2d uniformly charge the surfaces of the photosensitive drums 1a-1d. Next, the exposure devices 5a-5d irradiate the surfaces of the photosensitive drums 1a-1d with light according to the image data, forming electrostatic latent images on each photosensitive drum 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 devices 5a-5d.

[0015] 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 in the paper cassette 16 is fed to the paper transport path 14 by a paper feed roller 12a, and is transported to the transport belt 8 at a predetermined timing via a pair of registration rollers 12b.

[0016] Then, transfer rollers 6a to 6d apply an electric field at a predetermined transfer voltage between the 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 attracted to and transferred sequentially onto the transfer paper P being transported by the transport belt 8. After transfer, toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d are removed by cleaning devices 7a to 7d.

[0017] The transfer paper P onto which the toner image has been secondarily transferred is transported to the fixing unit 13. The transfer paper P transported to the fixing unit 13 is heated and pressurized as it passes through the nip between the fixing roller and the pressure roller, so that the toner image is fixed onto the surface of the transfer paper P, and a predetermined full-color image is formed. The transfer paper P with the full-color image formed thereon is discharged to the discharge unit 17 by the discharge roller pair 15.

[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 S2 and N2 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 peeling start position P1 is below the straight line L1 and is at the same height as the upper surface of the partition portion 22a. The pumping start position P2 is located below the upper end of the second spiral 44.

[0037] Next, the transfer of developer between the developing roller 20 and the second transport chamber 22c will be described. In the developing device 3a of this embodiment, the positional relationship of the straight lines L1 to L3 is defined as shown in FIG. 3, so that the supply of developer to the developing roller 20 is performed above the second spiral 44 in the second transport chamber 22c, as shown in FIG. 4. The separation (peeling) of the developer from the developing roller 20 is performed below the second spiral 44 in the second transport chamber 22c. With this configuration, the developer separated from the developing roller 20 is collected in a location in the second transport chamber 22c where the developer G is filled.

[0038] In conventional developing devices with a second transport chamber located above the first transport chamber, the developer separated from the developing roller is collected in the first transport chamber. In this case, toner often rises from the developer when the developer is separated from the developing roller, scattering from the gap between the developing roller and the developing container. To prevent this, measures have been taken, such as installing a developer guide member to prevent the separated developer from reaching the gap between the developing roller and the developing container, and providing a distance between the photosensitive drum and the gap to prevent scattered toner from affecting image quality.

[0039] In contrast, in the developing devices 3a to 3d of this embodiment, the developer separated from the developing roller 20 is collected in the lower part of the second transport chamber 22c filled with the developer. This makes it possible to suppress the toner from flying up inside the developing container 22 and to suppress the toner from scattering outside the developing devices 3a to 3d through the gap between the developing roller 20 and the developing container 22.

[0040] In addition, since there is no need to provide a developer guide member, the number of components used in the developing devices 3a to 3d can be reduced. Furthermore, since there is no need to provide a distance between the photosensitive drums 1a to 1d and the developing devices 3a to 3d, the photosensitive drums 1a to 1d and the developing devices 3a to 3d can be placed closer to each other, making it possible to reduce the size of the image forming apparatus 100.

[0041] Furthermore, by setting the separation start position P1 below the straight line L1 and at the same height as the upper surface of the partition portion 22a, 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, it is possible to effectively prevent toner from scattering from the gap between the developing roller 20 and the developing container 22.

[0042] Furthermore, by positioning the scooping start position P2 below the upper end of the second spiral 44, the developer stirred by the second spiral 44 is more 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.

[0043] Next, the positional relationship between the developing roller 20 and the second spiral 44 in the developing devices 3a to 3d of this embodiment will be described with reference to Fig. 5. In Fig. 5, d1 indicates the length of the line segment connecting the rotation center O1 of the developing roller 20 and the rotation center O2 of the second spiral 44. In Fig. 5, d2 indicates the length of the line segment connecting the rotation center O2 of the second spiral 44 and the peeling start position P1.

[0044] If the distance d1 between the developing roller 20 and the second spiral 44 is too short, the developer layer formed on the outer peripheral surface of the developing roller 20 is easily affected by the uneven shape of the second spiral 44. As a result, the developer layer will have thickness variations (mixer variations) at the screw pitch intervals of the second spiral 44. On the other hand, if the distance d1 between the developing roller 20 and the second spiral 44 is too far, the distance d2 between the second spiral 44 and the peeling start position P1 will also increase. As a result, the developer collection performance by the second spiral 44 will be insufficient, resulting in poor developer peeling. In other words, there are preferred ranges for d1 and d2. Therefore, the following test was conducted to determine the preferred ranges for d1 and d2.

[0045] First, to investigate the preferable range of d1, a developing roller with the peak magnetic force of the pumping pole N1 changed to three levels: 35mT, 45mT, and 55mT was used, and halftone images with a printing rate of 50% were output while changing d1, and the occurrence of mixer unevenness was confirmed.The test was conducted on the black image forming section Pd using a tandem color printer as shown in Figure 1.

[0046] The test conditions were: linear speed of photosensitive drum 1d (process linear speed) 195 mm / sec, diameter of developing roller 20 16 mm, linear speed ratio of developing roller 20 to photosensitive drum 1d 1:8, gap between developing roller 20 and regulating blade 27 (blade gap) 0.4 mm, and gap between photosensitive drum 1d and developing roller 20 (DS gap) 0.34 mm. The results are shown in Table 1.

[0047] [Table 1]

[0048] As is clear from Table 1, for all of the developing rollers 20 in which the peak magnetic force of the pumping pole N1 was changed to one of three levels, when d1 was smaller than 2.0 mm, there was a tendency for mixer unevenness to deteriorate significantly. This is because if the distance between the developing roller 20 and the second spiral 44 is too close, the thin developer layer formed on the outer peripheral surface of the developing roller 20 is easily affected by the uneven shape of the second spiral blade 44a of the second spiral 44.

[0049] Next, to investigate the preferred range of d2, we used a developing roller 20 with two settings for the width (separation area width) of the developer separation area R (where the magnetic force between the separation pole N3 and the pumping pole N1 of the developing roller 20 is 5 mT or less): 42° and 51°. Solid images were printed while varying d2, and the density difference ΔID between the leading and trailing edges of the image was measured. The test equipment and test conditions were the same as above. The results are shown in Figure 6. When developer separation failure occurs, the image density decreases at the trailing edge of the image because developer with consumed toner is supplied.

[0050] As is clear from Fig. 6, when the peeling region width of the developing roller 20 is 42° (solid line in Fig. 6) or 51° (dashed line in Fig. 6), ΔID tends to increase when d2 exceeds 7 mm. This is thought to be because, although the developer peeled off at the peeling start position P1 of the developer peeling region R of the developing roller 20 is collected and stirred by the second spiral 44, when d2 becomes large, the developer collection performance by the second spiral 44 becomes insufficient, resulting in poor developer peeling.

[0051] From the above results, it was confirmed that it is preferable to satisfy the following formulas (1) and (2), where R is the radius of the developing roller 20 and r is the radius of the second spiral 44. d1≧R+r+2 [mm] (1) d2≦r+7[mm] (2)

[0052] Although the formulas (1) and (2) do not specify the upper limit of d1 or the lower limit of d2, by arranging the developing roller 20 and the second spiral 44 so as to satisfy both formulas (1) and (2), the upper limit of d1 and the lower limit of d2 will also fall within a certain range.

[0053] 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. A developer carrier such as a magnetic roller may be further provided between the second spiral 44 and the developing roller 20, 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 20.

[0054] 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.

[0055] Furthermore, the present invention is not limited to direct transfer color printers such as those shown in FIG. 1, but can also be applied to various image forming devices 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, digital or analog monochrome copiers, color copiers, and facsimiles. [Industrial Applicability]

[0056] 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 suppress toner scattering to the outside of the developing device with a simple configuration, and an image forming apparatus equipped with the same. [Explanation of symbols]

[0057] 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 O1 Center of rotation (developing roller) O2 Rotation center (second spiral) 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; A developing device characterized in that a horizontal line L1 passing through the center of the rotation shaft of the second agitating and conveying member is located above a horizontal line L2 passing through the center of the rotation shaft of the developer carrier, and the line L2 is located above a horizontal line L3 passing through the center of the rotation shaft of the first agitating and conveying member.

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

3. 3. The developing device according to claim 2, 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.

4. 3. The developing device according to claim 2, wherein, when a radius of the developer carrier is R and a radius of the second agitating and transporting member is r, a length d1 of a line segment connecting the rotation center of the developer carrier and the rotation center of the second agitating and transporting member, and a length d2 of a line segment connecting the rotation center of the second agitating and transporting member and the peeling start position satisfy the following expressions (1) and (2): d1≧R+r+2 [mm] (1) d2≦r+7[mm] (2)

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

Images