Developing device and image forming apparatus

Abstract

To increase the stirring properties and conveyance properties of a developer to prevent the occurrence of printing unevenness.SOLUTION: A developing device 10 of an image forming apparatus 1 comprises: a developer tank 14 that stores a developer including toner and magnetic carrier; a developing roller 15 that carries the developer to convey it to an image carrier; and a first stirring and conveying paddle 11 and a second stirring and conveying paddle 12 that rotate inside the developer tank 14 to stir and convey the developer, wherein a conveying paddle 13 is provided between the developing roller 15 and the second stirring and conveying paddle 12. The conveying paddle 13 includes a rotation shaft 131, and a plurality of blade plate parts 132 disposed around an axis of the rotation shaft 131. The blade plate part 132 is disposed such that a base 133 is located on the downstream side and a tip 134 is located on the upstream side with respect to a rotation direction R3 of the conveying paddle 13.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a developing device and an image forming apparatus including the developing device.

Background Art

[0002] As a developing device provided in an image forming apparatus such as a copying machine or a printer, a two-component developing device that performs a developing process using a two-component developer containing toner and a magnetic carrier is widely known.

[0003] For example, in the developing device disclosed in Patent Document 1, there are provided a developing roller that carries a developer on its circumferential surface, a developer stirring member having an elliptical plate, a developer conveying member for supplying the developer to the developing roller, and a developer stirring auxiliary member for correcting unevenness in the amount of the developer. The developer is stored in a housing portion in which these members are arranged. Further, the developer stirring auxiliary member is arranged between the developer stirring member and the developer conveying member.

[0004] In the developing device, the toner stored in the toner hopper is appropriately replenished via a toner supply roller. The replenished toner is stirred by the developer stirring member together with the already stored toner, supplied onto the developing roller, and the toner carried on the developing roller is thinned to an appropriate amount by a doctor portion. Further, in the facing region with the photosensitive drum, the toner thinned on the developing roller is supplied to the latent image on the photosensitive drum, and a toner image is formed on the photosensitive drum.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Conventional developing devices have had difficulty accurately maintaining the amount of toner stored in the storage section at a target value. As a result, the amount of stored toner may be excessive or insufficient with respect to the target value. If the amount of toner is insufficient with respect to the target value, there is a risk of problems such as a decrease in image density. However, providing a developer agitation assisting member as in the conventional developing device is not preferable as it causes the device to become larger.

[0007] In recent years, in order to reduce costs, there have also been proposed image forming devices in which the developing device is unitized so that a common developing unit can be applied regardless of whether it is a high-speed machine or a low-speed machine in terms of process speed. In such cases, it becomes difficult to optimize the rotation speed of the developer conveying member and the like. As a result, the developer conveying member may act to hold the developer during rotation, or may not be sufficiently mixed with the developer conveyed from the developer agitation member, and a phenomenon in which a new developer is laminated on the surface layer portion of the storage section is likely to occur. As a result, there have been problems such as unevenness in the formed image and occurrence of printing unevenness.

[0008] The present invention has been made in view of the above problems, and an object thereof is to provide a developing device and an image forming device capable of enhancing the agitation property and conveyance property of the developer and suppressing the occurrence of printing unevenness.

Means for Solving the Problems

[0009] The solution means of the present invention for achieving the above object is premised on a developing device including a storage container for storing a developer containing toner and a magnetic carrier, a developer carrier for carrying the developer and conveying it to an image carrier, a plurality of stirring and conveying members that rotate in the storage container to stir and convey the developer, and a conveying member disposed between the developer carrier and the stirring and conveying members for conveying the developer to the developer carrier and recovering the developer from the developer carrier. Further, the conveying member includes a rotation shaft and a plurality of blade plate portions disposed around the rotation shaft. The blade plate portions are arranged such that the base side connected to the rotation shaft is located downstream and the tip side is located upstream with respect to the rotation direction of the conveying member.

[0010] By having such specific matters, it becomes possible to sufficiently stir the developer conveyed from the stirring and conveying member and the developer from the developer carrier in the developing device, and prevent the occurrence of a phenomenon in which a new developer is laminated.

[0011] Also, in the developing device having the above configuration, more preferably, the conveying member is provided to rotate in a direction opposite to the rotation direction of the adjacent stirring and conveying members.

[0012] Also, in the developing device having the above configuration, it is preferable that the blade plate portions are each provided in a flat plate shape.

[0013] Also, in the developing device having the above configuration, it is preferable that the blade plate portions extend in a tangential direction with respect to the outer peripheral surface of the rotation shaft.

[0014] Also, in the developing device having the above configuration, the blade plate portions may be continuously provided along the axial direction of the rotation shaft.

[0015] Also, in the developing device having the above configuration, it is preferable that the stirring and conveying member has a rotation shaft and spiral blades provided spirally around the rotation shaft.

[0016] In addition, an image forming apparatus including the developing device according to each of the above-described solution means is also within the scope of the technical idea of the present invention. Thereby, in the developing device and the image forming apparatus, it becomes possible to sufficiently agitate the developer from the developer carrier and the developer from the stirring and conveying member by operating the conveying member, and it becomes possible to suppress a decrease in image density and occurrence of printing unevenness.

Effects of the Invention

[0017] According to the present invention, it is possible to enhance the agitation property and conveyance property of the developer and suppress the occurrence of printing unevenness without causing an increase in the size of the apparatus.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0019] The developing device and the image forming device according to the embodiment of the present invention will be described with reference to the drawings.

[0020] (Image Forming Device) FIG. 1 is a cross-sectional view showing the schematic configuration of an image forming device 1 as an embodiment. In this embodiment, as an example, the case where the present invention is applied to a monochrome multifunction peripheral in which a single-color image (monochrome image) is formed on a recording medium P will be described. Note that the image forming device 1 is not limited to this, and the present invention is also applicable to various image forming devices including color printers, color multifunction peripherals, monochrome printers, and the like. As the recording medium P, paper, overhead projector sheets, and the like can be used.

[0021] Also, as shown in the figure, when the image forming device 1 is viewed from the front, among the front-rear direction X, the front side (front side) of the image forming device 1 is defined as the front direction X1, the rear side (rear side) of the image forming device 1 is defined as the rear direction X2, among the left-right direction Y, the left side is defined as the left direction Y1, the right side is defined as the right direction Y2, and among the up-down direction Z, the upper side is defined as the up direction Z1, and the lower side is defined as the down direction Z2, and the following description will be made.

[0022] The image forming device 1 is roughly divided into a document conveyance unit 201, an image reading unit 202, an image forming unit 203, a recording medium conveyance unit 204, and a paper feeding unit 205. In this image forming device 1, a two-component development method using a two-component developer containing toner and a magnetic carrier as the developer is adopted.

[0023] When at least one original document is set on the document tray 211, the document feeding unit 201 pulls out the documents one by one from the document tray 211 and conveys them, and guides this document to pass on the first platen glass 223 of the image reading unit 202.

[0024] The image reading unit 202 includes an optical unit including a first scanning unit 221 and a second scanning unit 222 below the first platen glass 223. When the document passes on the first platen glass 223, the surface of the document is exposed by the light source of the first scanning unit 221, and the reflected light from the surface of the document is guided to the imaging lens 224 by the mirrors of the first scanning unit 221 and the second scanning unit 222, and the image of the surface of the document is imaged on the CCD (Charge Coupled Device) 225 by the imaging lens 224. The CCD 225 repeatedly reads the image of the document surface in the main scanning direction and outputs image data indicating the image of the document surface.

[0025] When the document is placed on the second platen glass 226 on the upper surface of the image reading unit 202, while moving the first scanning unit 221 and the second scanning unit 222 in the sub-scanning direction while maintaining a predetermined speed relationship with each other, the surface of the document on the second platen glass 226 is exposed by the first scanning unit 221, and the reflected light from the surface of the document is further reflected by the first scanning unit 221 and the second scanning unit 222 and guided to the imaging lens 224, and the image of the surface of the document is imaged on the CCD 225 by the imaging lens 224.

[0026] The output image data is subjected to various image processes by the control circuit and output to the image forming unit 203. The image forming unit 203 includes a photosensitive drum 20 as an image carrier at its approximate center. Around the photosensitive drum 20, a developing device 10, a charging device 40, an optical scanning device 50, a transfer device 60, a cleaning device 70, etc. are arranged.

[0027] The photoreceptor drum 20 has a drum-shaped base material and a photoconductive layer formed in a thin film shape on the surface of the base material. The base material can be made of a metal such as aluminum, for example. The photoconductive layer can be made of, for example, an organic photoconductor (OPC), amorphous silicon (a-Si), or the like.

[0028] The developing device 10 develops the electrostatic latent image on the photoreceptor drum 20 with a developer (toner) to form a developer image on the photoreceptor drum 20. A toner cartridge 18 for supplying toner is connected to the developing device 10. Details of the developing device 10 will be described later.

[0029] The charging device 40 uniformly charges the surface of the photoreceptor drum 20 before the electrostatic latent image is formed. The charging device 40 can be composed of, for example, a charging wire such as a tungsten wire, a metal shield plate, a corona charger composed of a grit plate, a charging roller, or a charging brush.

[0030] The optical scanning device 50 scans the uniformly charged photoreceptor drum 20 with a light beam while modulating the intensity of the light beam according to the image data to write an electrostatic latent image. As the optical scanning device 50, a laser, an LED, or the like can be used.

[0031] The transfer device 60 transfers the developer image on the photoreceptor drum 20 to the recording medium P while sandwiching and conveying the recording medium P between the transfer belt 61 and the photoreceptor drum 20. As the transfer device 60, in addition to the transfer belt 61, for example, a transfer roller, a charging brush, or a corona charger can also be used.

[0032] The cleaning device 70 removes the toner remaining on the surface of the photoreceptor drum 20 after the toner image has been transferred to the recording medium P. The cleaning device 70 has, for example, a cleaning blade.

[0033] Above the image forming unit 203, a fixing device 80 is arranged. The fixing device 80 sandwiches the recording medium P onto which an image has been transferred between a fixing roller 81 having a heat source inside and a pressure roller 82, and fixes the image with heat and pressure. The recording medium P after fixing is conveyed by a conveying roller and discharged by a paper discharge roller 241 to a paper discharge tray 244 provided in the in-body paper discharge space between the image reading unit 202 and the image forming unit 203.

[0034] When forming images on both sides of the recording medium P, the recording medium P is reversely conveyed in the opposite direction by the paper discharge roller 241, further conveyed to the reverse conveyance path 243, reversed in its front and back, and then conveyed again to the image forming unit 203, and a developer image is transferred and fixed onto its back surface.

[0035] The paper feeding unit 205 includes a paper feeding cassette 251, and separates and supplies the recording media P one by one from the tray in the paper feeding cassette 251. The recording medium P is temporarily stopped by a registration roller 242 provided in front of the photosensitive drum 20 and the transfer device 60 among the conveying rollers, and is supplied between the photosensitive drum 20 and the transfer device 60 in accordance with the transfer timing, and the developer image on the photosensitive drum 20 is transferred.

[0036] (Developing device) FIG. 2 is a schematic cross-sectional view showing a developing device 10 according to an embodiment of the present invention. In the drawing, hatching indicating a cross-section is omitted for easy viewing of each component member.

[0037] In the present embodiment, the developing device 10 supplies the non-magnetic toner contained in the two-component developer onto the surface of the photosensitive drum 20 by a developing electric field formed between the photosensitive drum 20 and the developing device 10.

[0038] The developing device 10 has a developing tank (accommodation container) 14 in which a two-component developer containing toner and a magnetic carrier is accommodated. An opening is provided in the developing tank 14 at a position facing the photosensitive drum 20. The photosensitive drum 20 is disposed facing this opening.

[0039] The developing roller 15 is a magnet roller that functions as a developer carrier, and is disposed at a position facing the photosensitive drum 20. The developing roller 15 includes a rotatable sleeve portion formed in a non-magnetic cylindrical shape (not shown) around the rotation axis 151, and a columnar and magnetic tuna roll portion disposed inside the sleeve portion. On the circumferential surface of the developing roller 15, a plurality of magnetic poles each having a single polarity are formed due to the magnetism of the tuna roll portion. In the illustrated embodiment, the developing roller 15 is provided so that the sleeve portion rotates in the rotation direction R4 around the rotation axis 151 disposed along the axial direction X. The developing roller 15 carries the developer in the developing tank 14 on its surface, and conveys the toner contained in the carried developer to the surface of the photosensitive drum 20.

[0040] The rotation direction R4 of the developing roller 15 is set to be the same as the rotation direction R5 of the photosensitive drum 20 at the position facing the photosensitive drum 20. In the developing region where the photosensitive drum 20 and the developing roller 15 face each other, the electrostatic latent image formed on the surface of the photosensitive drum 20 is developed with toner.

[0041] The developed toner image is transferred to the recording medium P by the transfer device 60 and fixed by the fixing device 80 (see FIG. 1). The toner remaining on the surface of the photosensitive drum 20 is removed by the cleaning device 70, and the surface of the photosensitive drum 20 is discharged. In the image forming apparatus 1, such an image forming process is repeated at any time.

[0042] As shown in FIG. 2, the developing device 10 is provided with a first stirring and conveying paddle 11 and a second stirring and conveying paddle 12 as stirring and conveying members that rotate in the developing tank 14 to stir and convey the developer.

[0043] The first stirring and conveying paddle 11 and the second stirring and conveying paddle 12 are each provided with spiral blades 112 and 122. The spiral blades 112 and 122 are spirally formed on the outer peripheries of their respective rotating shafts 111 and 121. In the developing device 10, the first stirring and conveying paddle 11 and the second stirring and conveying paddle 12 are arranged with their respective rotating shafts 111 and 121 facing each other in parallel, and by rotating these, the developer is circulated while being stirred in the developing tank 14. Further, by this stirring, friction is generated between the toner and the magnetic carrier contained in the developer, and the non-magnetic toner is charged by the friction.

[0044] The developing tank 14 is provided with an upper surface cover 141 in the upward Z1 direction and its upper part is closed, and its interior is partitioned into a plurality by a partition wall 143 between the first stirring and conveying paddle 11 and the second stirring and conveying paddle 12. In the illustrated embodiment, the first stirring and conveying paddle 11 is the most separated from the developing roller 15 in the developing tank 14 and is disposed on the opposite side of the photosensitive drum 20. The second stirring and conveying paddle 12 is disposed in the developing tank 14 at a position closer to the developing roller 15 than the first stirring and conveying paddle 11. In the partition wall 143, communication parts (not shown) for allowing the developer to flow through by the first stirring and conveying paddle 11 and the second stirring and conveying paddle 12 are opened.

[0045] As shown in the figure, the first stirring and conveying paddle 11 is rotating in the rotation direction R1 about the rotating shaft 111. The first stirring and conveying paddle 11 rotates so as to move the developer from above to below on the side facing the partition wall 143. The second stirring and conveying paddle 12 rotates in the direction of the rotation direction R2 about the rotating shaft 121 so as to move the developer from above to below on the side facing the partition wall 143. The rotating shafts 111 and 121 are provided along the front-rear direction X parallel to each other. Therefore, in this case, the front-rear direction X corresponds to the axial direction of the rotating shafts 111 and 121 of the first stirring and conveying paddle 11 and the second stirring and conveying paddle 12.

[0046] In the developing device 10, a conveying paddle 13 as a conveying member is disposed between a developing roller 15 and a second stirring and conveying paddle 12. The conveying paddle 13 is provided so as to convey the developer to the developing roller 15 and recover the developer from the developing roller 15.

[0047] In the exemplary embodiment, the conveying paddle 13 includes a rotating shaft 131 and a plurality of blade plate portions 132 disposed around the axis of the rotating shaft 131. In this case, eight blade plate portions 132 are provided. While the second stirring and conveying paddle 12 rotates in the rotation direction R2, the adjacent conveying paddle 13 is provided to rotate in the rotation direction R3 which is the same direction in the region facing the second stirring and conveying paddle 12. Also, in order to enhance the conveying property and stirring property of the developer, the rotating shaft 131 of the conveying paddle 13 is provided in the developing tank 14 so as to be positioned below the rotating shaft 111 of the first stirring and conveying paddle 11 and the rotating shaft 121 of the second stirring and conveying paddle 12. The rotating shaft 131 of such a conveying paddle 13 is preferably provided at a height position that can be buried in the developer accommodated in the developing tank 14.

[0048] Therefore, as shown in FIG. 2, the conveying paddle 13 is provided to rotate in the direction (rotation direction R3) opposite to the rotation direction R2 of the adjacent second stirring and conveying paddle 12. Thereby, in the region where the conveying paddle 13 faces the second stirring and conveying paddle 12, the conveying paddle 13 is provided to rotate upward from below together with the second stirring and conveying paddle 12.

[0049] By the image forming operation, the developer on the developing roller 15 is supplied to the photosensitive drum 20. The toner constituting the developer is adsorbed by the photosensitive drum 20, so that the electrostatic latent image on the surface of the photosensitive drum 20 is developed and a toner image is formed. The developer remaining on the developing roller 15 is conveyed back to the developing tank 14 as the developing roller 15 rotates, but the toner concentration of the developer gradually decreases due to the formation of the toner image.

[0050] Therefore, the developing device 10 is provided with a toner supply port (not shown) for supplying toner to the developing tank 14. The toner supply port is connected to the toner cartridge 18 and is provided, for example, above the first agitation and conveyance paddle 11 and disposed on one side (e.g., closer to the forward direction X1) in the axial direction (front-rear direction X). The supplied toner is agitated while being mixed with the magnetic carrier from the first agitation and conveyance paddle 11 through the second agitation and conveyance paddle 12 and is conveyed.

[0051] The conveyance paddle 13 for conveying the developer to the developing roller 15 has each blade plate portion 132 provided in a flat plate shape. The blade plate portion 132 is preferably formed of a flexible plate-like member or sheet-like member (flexible sheet) made of, for example, PET (polyethylene terephthalate). Further, the blade plate portion 132 preferably has a stiffness enough to agitate the toner and has a flexibility to bend when contacting the second agitation and conveyance paddle 12 or the bottom surface 142 of the developing tank 14. The eight blade plate portions 132 are arranged at equal intervals in the circumferential direction around the rotation shaft 131.

[0052] FIG. 3 is an explanatory diagram schematically showing the configuration of the conveyance paddle 13 in the developing device 10 according to the present embodiment as viewed in the axial direction (front-rear direction X), and FIG. 4 is an explanatory diagram showing the state of agitation of the developer in the developing device 10.

[0053] As shown in FIG. 3, each blade plate portion 132 of the conveyance paddle 13 has a base portion 133 connected to the rotation shaft 131 and provided near the rotation shaft 131, and is continuously provided so as to extend outward from the base portion 133. The tip 134 on the opposite side of the base portion 133 of the blade plate portion 132 is separated from the rotation shaft 131 and is located radially outward of the rotation shaft 131. The conveyance paddle 13 is arranged such that, in each blade plate portion 132, the base portion 133 side is located downstream in the rotation direction R3 and the tip 134 side is located upstream in the rotation direction R3.

[0054] Further, as shown in FIG. 3, the blade portions 132 of the conveying paddles 13 are each extended in a direction (tangential direction) parallel to the tangent line L on the outer peripheral surface of the rotating shaft 131. The tip 134 side of the blade portion 132 is provided in a tapered shape along the bottom surface 142 of the developing tank 14. The blade portions 132 having such a shape are each continuously formed along the axial direction (front-rear direction X) of the rotating shaft 131.

[0055] Here, for the purpose of comparison with the developing device 10 according to the present embodiment, the configuration of the conventional developing device 900 will be briefly described with reference to FIG. 12.

[0056] As shown in FIG. 12, the conventional developing device 900 is configured such that a first stirring and conveying paddle 911 rotating in the rotation direction R11 and a second stirring and conveying paddle 912 rotating in the rotation direction R12 are provided in the developing tank 914, and the developer is conveyed to a developing roller 915 rotating in the rotation direction R14 facing the photosensitive drum 920. Further, there is also a configuration in which a conventional conveying paddle 913 rotating in the rotation direction R13 is provided between the second stirring and conveying paddle 912 and the developing roller 915. However, as shown in FIG. 12, the form of the blade portion 9132 of the conventional conveying paddle 913 is different from that of the present embodiment, and the base side closer to the rotating shaft 9131 is located upstream in the rotation direction R13, and the tip side away from the rotating shaft 9131 is arranged to be located downstream in the rotation direction R13.

[0057] Therefore, the conveying paddle 913 rotates in the rotation direction R13 while holding the developer between the plurality of blade portions 9132. As shown by the arrow in FIG. 12, although the developer returned from the developing roller 915 is held by the conveying paddle 913 and conveyed in the direction of the second stirring and conveying paddle 912, it is held between the blade portions 9132 as it is and may not be sufficiently mixed with the developer from the second stirring and conveying paddle 912 and may be conveyed back to the developing roller 915 again.

[0058] Therefore, the developer returned from the developing roller 915 has a low toner concentration due to toner consumption, and is supplied to the developing roller 915 without being sufficiently mixed with the developer from the second mixing and transporting paddle 912. Even if the developer is supplied to the photoconductor drum 20 due to insufficient mixing, there is a problem that the formed image has a shading effect and print unevenness occurs. This phenomenon is noticeable in the case of images that consume a large amount of toner, and also tends to occur on the toner supply port side in the axial direction (front-rear direction X) if the developer is not sufficiently mixed.

[0059] 3, the transport paddle 13 is provided such that the base 133 side of the vane plate portion 132 is located downstream in the rotation direction R3 and the tip 134 side of the vane plate portion 132 is located upstream in the rotation direction R3. Since the tip 134 side of the vane plate portion 132 is located upstream in the rotation direction R3 relative to the base 133 side, the rotation around the rotation shaft 131 acts to push the developer outward (for example, toward the second stirring transport paddle 12).

[0060] 4, the developer returned from developing roller 15 reaches transport paddle 13 along bottom surface 142 of developing tank 14, and is transported in rotation direction R3 by each vane portion 132 and sequentially pushed toward second agitation transport paddle 12. The pushed-out developer mixes with the developer transported by the rotation of second agitation transport paddle 12 in rotation direction R2, and is transported while being agitated. This promotes sufficient agitation of the developer in developing tank 14.

[0061] 5 is a plan view showing a schematic configuration inside developer tank 14 in developing device 10. As shown in the figure, a toner supply port 144 is provided near the end in the forward direction X1 above first stirring and transport paddle 11, and is configured so that new toner is supplied from toner cartridge 18 to developer tank 14 as toner is consumed.

[0062] In the developing tank 14, the developer D is conveyed backward in the X2 direction by the rotation of the first stirring and conveying paddle 11, and is sent to the adjacent second stirring and conveying paddle 12 through the partition wall 143. By the rotation of the second stirring and conveying paddle 12, the developer D is conveyed in the forward X1 direction and circulates while being stirred in the developing tank 14.

[0063] Here, in order to confirm the stirring property and conveying property of the developer in the developing device 10 according to the present embodiment, the toner concentration in the developing tank 14 was measured, and a test was conducted in comparison with the case of the conventional developing device 900. The measurement of the toner concentration was performed at four locations: the front end portion MXF and the rear end portion MXR of the second stirring and conveying paddle 12, and the front end portion MGF and the rear end portion MGR of the developing roller 15, as shown in FIG. 5. The toner concentration was also measured at the same locations in the conventional developing device 900.

[0064] FIGS. 6 to 8 show the measurement results of the developing device 10 according to the present embodiment. FIG. 6 is a graph showing the time change of the toner concentration when the amount of the developer is 300 g, FIG. 7 is a graph showing the time change of the toner concentration when the amount of the developer is 400 g, and FIG. 8 is a graph showing the toner concentration at different amounts of the developer. FIGS. 9 to 11 show the measurement results of the conventional developing device 900 for comparison. FIG. 9 is a graph showing the time change of the toner concentration when the amount of the developer is 300 g, FIG. 10 is a graph showing the time change of the toner concentration when the amount of the developer is 400 g, and FIG. 11 is a graph showing the toner concentration at different amounts of the developer.

[0065] In the figure, the temporal change in toner concentration is shown by the results measured at T1 before image formation (before printing) shown on the horizontal axis, T2 after performing three solid black prints on A3 paper, T3 after further performing three solid black prints (printing black over the entire surface) on A3 paper, T4 after performing agitation rotation for 3 seconds without image formation, and T5 after further performing agitation rotation for 3 seconds without image formation. Also, FIGS. 8 and 11 show the evaluation of the degree of occurrence of print unevenness when performing solid black printing on A3 paper with each developer amount. The white ○ marks indicate those where print unevenness was not confirmed by image analysis, the black-filled ○ marks indicate those where print unevenness was confirmed by image analysis but not visually, the △ marks indicate those where print unevenness was confirmed when visually observing carefully, and the × marks indicate those where obvious print unevenness was confirmed visually.

[0066] As shown in FIG. 5, since the developer D is circulated while being agitated in the developing tank 14, in this case, when comparing the forward direction X1 and the backward direction X2 in the front-rear direction X, usually, in the second agitation conveyance paddle 12, the toner concentration tends to be higher at the rear end portion MXR, which is before toner consumption, than at the front end portion MXF. Similarly, in the developing roller 15, the toner concentration tends to be higher at the rear end portion MGR than at the front end portion MGF. On the other hand, since there is a flow of the developer between the second agitation conveyance paddle 12 and the developing roller 15 that are parallel to each other, it is preferable that the difference in toner concentration is small between the respective front end portions MXF / MGF or between the rear end portions MXR / MGR. It is considered that a large difference leads to the occurrence of print unevenness.

[0067] When the developer amount is 300 g, as shown in FIG. 9, in the developing device 900 provided with the conventional conveyance paddle 913, a difference of about 0.5 to 1.5% in toner concentration occurred between the respective front end portions MXF / MGF and between the rear end portions MXR / MGR. In particular, the difference in toner concentration became large between the rear end portions MXR / MGR. In contrast, in the developing device 10 of the present embodiment, as shown in FIG. 6, the toner concentration changed over time without a large difference between the respective front end portions MXF / MGF and between the rear end portions MXR / MGR.

[0068] Also, when the developer amount is 400 g, as shown in FIG. 10, in the developing device 900 including the conventional conveying paddle 913, a difference of about 0.5 to 1.0% occurred in the toner concentration between the respective front end portions MXF / MGF and between the rear end portions MXR / MGR. On the other hand, in the developing device 10 of the present embodiment, as shown in FIG. 7, the toner concentration changed with almost no difference between the respective front end portions MXF / MGF and between the rear end portions MXR / MGR over time. Further, in FIG. 7, even between the front end portion MXF and the rear end portion MXR in the second agitation conveying paddle 12, the difference in toner concentration was relatively small and extremely good results were obtained.

[0069] Therefore, according to the developing device 10 of the present embodiment, it can be seen that sufficient agitation of the developer in the developing tank 14 is promoted by the action of the conveying paddle 13, and good image formation with reduced printing unevenness becomes possible.

[0070] For example, when the developer amount is 400 g rather than 300 g, the fluctuation of the toner concentration is smaller, and the larger the developer amount, the easier it is to maintain a stable toner concentration. However, in the conventional developing device 900, as shown in FIG. 11, even when the developer amount is 400 g, printing unevenness occurs as the toner concentration decreases, and obvious printing unevenness was confirmed at a toner concentration of about 4%. Further, even when the toner concentration is 6.5% or more, printing unevenness is recognized when the developer amount is less than 340 g.

[0071] On the other hand, in the developing device 10 of the present embodiment, since the conveying paddle 13 is provided, no occurrence of printing unevenness was recognized as shown in FIG. 8. That is, even when the developer amount is 400 g, even when it is 350 g or less, and even when the toner concentration drops to 5.5%, the occurrence of printing unevenness is suppressed, and it was confirmed that the developer was sufficiently agitated by the action of the conveying paddle 13.

[0072] From the above, it can be said that the developing device 10 according to this embodiment is equipped with the transport paddle 13, and can sufficiently mix the developer from the developing roller 15 and the developer from the second mixing transport paddle 12, significantly improving the mixing and transport properties of the developer, and making it possible to suppress the occurrence of print unevenness. It is also possible to make the developing device 10 a unit and apply it to various image forming apparatuses 1 in common, and it becomes possible to suppress uneven mixing of the developer and perform good image formation, regardless of whether the process speed is a high-speed or low-speed machine.

[0073] In the transport paddle 13 of the developing device 10, the plurality of vane plate portions 132 are not limited to being continuously formed along the axial direction (front-rear direction X) of the rotation shaft 131, but may be provided discontinuously, and may be provided primarily at a location corresponding to toner consumption, such as on the most downstream side with respect to the toner resupply port 144. Furthermore, a combination of continuously formed vane plate portions 132 and discontinuously formed vane plate portions 132 may be used.

[0074] Furthermore, toner supply port 144 is not limited to being provided closer to the front direction X1 of developer tank 14, and may be provided closer to the rear direction X2. In this case, too, it is preferable to circulate developer inside developer tank 14 in the front-to-rear direction X from first stirring and transport paddle 11 to second stirring and transport paddle 12, starting from the toner supply port. In either case, the developer can be transported while being sufficiently stirred by transport paddle 13 inside developer tank 14, improving the stirring and transport properties of the developer and making it possible to suppress the occurrence of print unevenness.

[0075] The present invention is not limited to the above-described embodiment, but can be embodied in various other forms. Therefore, the above-described embodiment is merely illustrative in all respects and should not be interpreted as being restrictive. The scope of the present invention is defined by the claims, and is not limited in any way by the text of the specification. Furthermore, all modifications and changes within the scope of the claims are within the scope of the present invention. [Explanation of symbols]

[0076] 1 Image forming apparatus 10 Developing device 11 First stirring and conveying paddle (stirring and conveying member) 111 Rotating shaft 112 Screw blade 12 Second stirring and conveying paddle (stirring and conveying member) 121 Rotating shaft 122 Screw blade 13 Conveying paddle (conveying member) 131 Rotating shaft 132 Blade plate part 133 Base part 134 Tip 14 Developing tank (accommodating container) 15 Developing roller (developer carrier) 18 Toner cartridge 20 Photoconductor drum (image carrier) 40 Charging device 50 Optical scanning device 60 Transfer device 70 Cleaning device 80 Fixing device

Claims

1. A storage container that stores a developer containing toner and a magnetic carrier, A developer carrier that carries the developer and transports it to an image carrier, A plurality of stirring and transporting members that rotate within the storage container to stir and transport the developer, A developing device provided with a transport member disposed between the developer carrier and the stirring and transport member, for transporting the developer to the developer carrier and recovering the developer from the developer carrier, The transport member includes a rotation shaft and a plurality of blade plate portions disposed around the rotation shaft, The rotation shaft is provided in the storage container so as to be positioned below the shaft portions of the plurality of stirring and transport members, The bottom surface of the storage container facing the transport member is formed to be lower than the bottom surface of the storage container facing the stirring and transport member adjacent to the transport member, The blade plate portion is A plate-like member or sheet-like member having flexibility, and the tip side of the blade plate portion is provided in a tapered shape along the bottom surface of the storage container, With respect to the rotation direction of the transport member, the base side connected to the rotation shaft is located downstream and the tip side is located upstream, and the rotation of the rotation shaft pushes the developer toward the stirring and transport member adjacent to the transport member. A developing device characterized by this.

2. In the developing device according to claim 1, The stirring and transport member adjacent to the transport member is provided so as to rotate upward from below in a region facing each other. A developing device characterized by this.

3. In the developing device according to claim 1 or 2, The blade plate portions are each provided in a flat plate shape. A developing device characterized by this.

4. In the developing device according to claim 3, The blade plate portion is extended in a tangential direction with respect to the outer peripheral surface of the rotating shaft. The developing device is characterized by this.

5. In the developing device according to any one of claims 1 to 4, The blade plate portions are continuously provided along the axial direction of the rotating shaft respectively. The developing device is characterized by this.

6. In the developing device according to any one of claims 1 to 5, The stirring and conveying member has a rotating shaft and spiral blades provided spirally around the axis of the rotating shaft. The developing device is characterized by this.

7. An image forming apparatus comprising the developing device according to any one of claims 1 to 6.

Images