Image forming apparatus

Abstract

To provide a configuration capable of suppressing scattering of toner to the outside of a developing device.SOLUTION: A developing roller 50 is disposed opposed to a photosensitive drum and rotates to convey a developer to a developing position where an electrostatic latent image formed on the photosensitive drum is developed. A supply roller 51 is disposed opposed to the developing roller 50 and rotates to supply the developer inside a developing container 40 to the developing roller 50. A shielding roller 53 is disposed at a position opposed to the supply roller 51 between a wall portion 71 and the developing roller 50 and downstream of the closest position P1 between the developing roller 50 and the supply roller 51 in a rotational direction of the supply roller 51.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a developing device used in an image forming apparatus such as a copier, a printer, a facsimile, or a multifunction machine having a plurality of these functions. [Background technology]

[0002] Conventionally, there has been known a developing device that uses a two-component developer (hereinafter, abbreviated as developer) containing non-magnetic toner particles and magnetic carrier particles. As such a developing device, a configuration using a so-called hybrid development method has been proposed, which has a developing roller as a developing rotor arranged opposite a photosensitive drum as an image carrier, and a supply roller as a supply rotor arranged opposite the developing roller (Patent Document 1).

[0003] In the case of the developing device described in Patent Document 1, a first toner shielding member is disposed downstream in the rotation direction of the supply roller from the closest position between the developing roller and the supply roller, and in the space between the wall of the developing container and the developing roller. This prevents toner floating in the vicinity of this space from scattering outside the developing device. In addition, in the case of the developing device described in Patent Document 1, in addition to the first toner shielding member, a second toner shielding member is provided between the wall and the first toner shielding member. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-21278 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of the developing device described in Patent Document 1, the pressure inside the developing device increases, and there is a possibility that the floating toner near the above-mentioned space will scatter to the outside of the developing device through the gap between the first toner shielding member and the developing roller, or the gap between the developing roller and the supply roller.

[0006] An object of the present invention is to provide a configuration capable of suppressing toner from scattering outside a developing device. [Means for solving the problem]

[0007] The developing device of the present invention is characterized by comprising a developing container having a wall portion and containing a developer including toner and a carrier, a developing roller arranged opposite an image carrier and rotating to transport the developer to a development position where an electrostatic latent image formed on the image carrier is developed, a supply roller arranged opposite the developing roller and rotating to supply the developer in the developing container to the developing roller, and a rotating member arranged downstream in the rotational direction of the supply roller from the closest position between the developing roller and the supply roller, and between the wall portion and the developing roller, and rotating in a position opposite the supply roller. Effect of the Invention

[0008] According to the present invention, it is possible to prevent the toner from scattering outside the developing device. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of the developing device according to the first embodiment. [Diagram 3] FIG. 4 is a cross-sectional view showing a schematic configuration of a developing device according to a comparative example. [Figure 4] FIG. 4 is a schematic diagram showing a driving configuration on the rear side of the device according to the first embodiment. [Diagram 5] FIG. 2 is a schematic diagram showing a driving configuration on the front side of the device according to the first embodiment. [Figure 6] FIG. 11 is a schematic cross-sectional view of a developing device according to a second embodiment. [Figure 7] FIG. 11 is a schematic diagram showing a driving configuration on the front side of an apparatus according to a second embodiment. [Figure 8]FIG. 13A is a perspective view of a shielding roller according to a third embodiment, and FIG. 13B is an enlarged schematic view of a groove portion of the shielding roller according to the third embodiment. [Figure 9] FIG. 13 is a schematic cross-sectional view of a developing device according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <First embodiment> The first embodiment will be described with reference to Figures 1 to 5. In this embodiment, a developing device is applied to a tandem type full-color printer as an example of an image forming apparatus.

[0011] [Image forming equipment] First, a schematic configuration of an image forming apparatus 100 according to the present embodiment will be described with reference to FIG. 1. The image forming apparatus 100 shown in FIG. 1 is an electrophotographic full-color printer having image forming units PY, PM, PC, and PK of four colors (yellow, magenta, cyan, and black) in the main body of the apparatus. In this embodiment, an intermediate transfer tandem type is adopted in which the image forming units PY, PM, PC, and PK are arranged along the rotation direction of an intermediate transfer belt 6, which will be described later. The image forming apparatus 100 forms a toner image (image) on a recording material S in response to an image signal from a document reading device (not shown) connected to the main body of the apparatus or a host device such as a personal computer connected to the main body of the apparatus so as to be able to communicate with the main body of the apparatus. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

[0012] The toner image forming process will be described. First, the image forming units PY, PM, PC, and PK will be described. However, the image forming units PY, PM, PC, and PK are configured almost identically except for the toner colors, yellow, magenta, cyan, and black. Therefore, the following description will be given using the yellow image forming unit PY as an example, and the description of the other image forming units PM, PC, and PK will be omitted.

[0013] The image forming unit PY is mainly composed of a photosensitive drum 1, a charging device 2, a developing device 4, a static eliminator 5, a cleaning device 8, etc. In this embodiment, an intermediate transfer belt 6 is disposed above each of the image forming units PY, PM, PC, and PK, and an exposure device 3 is disposed below them. The photosensitive drum 1, which serves as an image carrier and photosensitive member, has a photosensitive layer formed to have a negative or positive charging polarity on the outer circumferential surface of an aluminum cylinder, and rotates in the direction of arrow R2 in the figure at a predetermined process speed (circumferential speed).

[0014] The charging device 2 charges the surface of the photosensitive drum 1 to a uniform negative or positive dark potential according to the charging characteristics of the photosensitive drum 1. In this embodiment, the charging device 2 is a charging roller that rotates in contact with the surface of the photosensitive drum 1. After charging the surface of the photosensitive drum 1, an electrostatic latent image (electrostatic image) is formed on the surface of the photosensitive drum 1 by an exposure device (laser scanner) 3 based on image information. The photosensitive drum 1 carries the formed electrostatic latent image and moves around, and the image is developed with toner by the developing device 4. The detailed configuration of the developing device 4 will be described later. The toner in the developer consumed in image formation is replenished together with carrier from a toner cartridge (not shown).

[0015] A predetermined pressure and a primary transfer bias are applied to the developed toner image by a primary transfer roller 61 disposed opposite the photosensitive drum 1 with the intermediate transfer belt 6 sandwiched therebetween, and the toner image is primarily transferred onto the intermediate transfer belt 6. After the primary transfer, the surface of the photosensitive drum 1 is neutralized by a static eliminator 5. A cleaning device 8 cleans off residual matter such as transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer.

[0016] The intermediate transfer belt 6 is tensioned by a tension roller 62 and a secondary transfer inner roller 63. The intermediate transfer belt 6 is driven by the secondary transfer inner roller 63, which is also a drive roller, so as to move in the direction of the arrow R1 in the figure. The image forming process of each color processed by the above-mentioned image forming units PY, PM, PC, and PK is performed at a timing to sequentially superimpose the toner image of the color upstream in the moving direction that has been primarily transferred onto the intermediate transfer belt 6. As a result, a full-color toner image is finally formed on the intermediate transfer belt 6 and is conveyed to the secondary transfer unit T2. The secondary transfer unit T2 is a transfer nip portion formed by a part of the intermediate transfer belt 6 tensioned by the secondary transfer inner roller 63 and the secondary transfer outer roller 64. Note that the transfer residual toner after passing through the secondary transfer unit T2 is removed from the intermediate transfer belt 6 by a belt cleaning device (not shown).

[0017] A process of transporting the recording material S to the secondary transfer portion T2 is executed at the same timing as the process of forming the toner image sent to the secondary transfer portion T2. ​​In the transport process, the recording material S is fed from the sheet cassette 11 and sent to the secondary transfer portion T2 in accordance with the image formation timing. In the secondary transfer portion T2, a secondary transfer voltage is applied to the inner secondary transfer roller 63.

[0018] Through the above image forming process and conveying process, the toner image is secondarily transferred from the intermediate transfer belt 6 to the recording material S at the secondary transfer portion T2. ​​Thereafter, the recording material S is conveyed to the fixing device 7, and is heated and pressurized by the fixing device 7, thereby melting and fixing the toner image onto the recording material S. The recording material S on which the toner image has been fixed in this manner is discharged by discharge rollers 12 onto a discharge tray (not shown).

[0019] [Two-component developer] Next, the developer used in this embodiment will be described. In this embodiment, a two-component developer is used as the developer, in which the mixture coverage of the toner with respect to the carrier containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) is 8.0% by weight. The toner is a colored resin particle containing a binder resin, a colorant, and other additives as necessary, and an external additive such as colloidal silica fine powder is added to the surface of the toner. The toner is, for example, a polyester resin with negative or positive charging properties according to the charging properties of the photosensitive drum 1, and has a volume average particle size of about 7.0 μm. The carrier is, for example, made of magnetic metal particles such as iron, nickel, cobalt, etc., whose surfaces are oxidized, and has a volume average particle size of about 40 μm to 50 μm.

[0020] In this embodiment, the developer used is a carrier mainly composed of Mn-Mg with a weight average diameter of 45 μm and a saturation magnetization of 60 emu / g as determined by the MSV method, and the toner particles are 7 μm in median diameter of the volume distribution measured by a Coulter counter. The toner and carrier are mixed to a toner concentration of 12%, and used as the developer. The toner has a positive charging characteristic.

[0021] [Developing device] Next, the developing device 4 will be described in detail with reference to Fig. 2. The developing device 4 of this embodiment is a so-called touch-down developing type developing device, which forms a thin layer of only toner on the developing roller 50 with a magnetic brush made of a two-component developer formed on a supply roller 51, and develops the toner by flying it to the electrostatic latent image formed on the photosensitive drum 1 with a developing bias in which a direct current and an alternating current are superimposed and applied to the developing roller 50.

[0022] As shown in FIG. 2, the developing device 4 includes a developing container 40, a developing roller 50 as a developing rotator, a supply roller 51 as a supply rotator, and a shielding roller 53 as a rotating member. The developing container 40 includes a housing 70 and a developer storage section 40a disposed at a lower portion of the housing 70. The housing 70 includes a wall portion 71 and an opening 72. The wall portion 71 is disposed at a position facing a part of the supply roller 51. In the case of the present embodiment, the wall portion 71 is disposed on the opposite side of the regulating blade 52 described later, with the supply roller 51 interposed therebetween. At this position, the wall portion 71 is disposed so as to follow the outer peripheral surface of the supply roller 51. The opening 72 is formed at a position facing the photosensitive drum 1 of the developing container 40, and the developing roller 50 faces the photosensitive drum 1 through the opening 72.

[0023] The developer storage section 40a stores a developer including a non-magnetic toner and a magnetic carrier. The developer storage section 40a has a developing chamber 42 as a first chamber, a stirring chamber 43 as a second chamber, and a partition wall 41 as a partition wall. The stirring chamber 43 is disposed adjacent to the developing chamber 42 so that at least a part of the stirring chamber 43 overlaps with the developing chamber 42 when viewed in the horizontal direction. The partition wall 41 separates the developing chamber 42 from the stirring chamber 43. The partition wall 41 has openings as communication parts that communicate the developing chamber 42 and the stirring chamber 43 at both ends in the longitudinal direction (the direction of the rotation axis of the developing roller 50 and the supply roller 51). The developer storage section 40a forms a circulation path that circulates the developer between the developing chamber 42 and the stirring chamber 43 via the openings provided in the partition wall 41.

[0024] In this embodiment, a partition wall 41 is provided in the approximate center of the developer accommodating section 40a. As a result, the developer accommodating section 40a is partitioned by the partition wall 41 so that the developing chamber 42 and the stirring chamber 43 are adjacent to each other in the horizontal direction. A first transport screw 44 and a second transport screw 45 that can rotate to stir and circulate the developer are disposed in the developing chamber 42 and the stirring chamber 43, respectively.

[0025] The first transport screw 44 as the first transport member is disposed at the bottom of the developing chamber 42 (inside the first chamber) along the rotation axis direction (longitudinal direction) of the supply roller 51, facing the supply roller 51 substantially parallel to the supply roller 51. The first transport screw 44 has a rotating shaft 44a and a blade 44b provided in a spiral shape around the rotating shaft 44a. The second transport screw 45 as the second transport member is disposed at the bottom of the mixing chamber 43 (inside the second chamber) substantially parallel to the first transport screw 44. The second transport screw 45 has a rotating shaft 45a and a blade 45b provided in a spiral shape around the rotating shaft 45a.

[0026] The first transport screw 44 and the second transport screw 45 rotate in the directions of arrows R4 and R3, respectively, to transport the developer within the developing chamber 42 and the mixing chamber 43. The developer transported by the rotation of the first transport screw 44 and the second transport screw 45 circulates between the developing chamber 42 and the mixing chamber 43 through openings at both ends of the partition wall 41. The toner is stirred by the first transport screw 44 and the second transport screw 45, and rubs against the carrier, becoming frictionally charged to a negative or positive polarity.

[0027] As shown in FIG. 2, the developing roller 50 and the supply roller 51 are disposed vertically above the developing chamber 42 and the stirring chamber 43 inside the housing 70. The developing roller 50 is disposed between the photosensitive drum 1 and obliquely above the supply roller 51 when viewed from the direction of the rotation axis of the supply roller 51. That is, the developing roller 50 is disposed so that its rotation axis is located above the rotation axis of the supply roller 51. The supply roller 51 and the developing roller 50 are disposed facing each other at the closest position P1 with their rotation axes substantially parallel to each other. The closest position P1 is a position where the supply roller 51 and the developing roller 50 face each other on a line connecting the rotation centers of the supply roller 51 and the developing roller 50.

[0028] The developing roller 50 faces the photosensitive drum 1 on the opening 72 side of the housing 70. The developing roller 50 and the supply roller 51 are each provided so as to be rotatable about their respective rotation axes. The developing roller 50 and the supply roller 51 are driven to rotate counterclockwise in FIG. 2 (in the direction of arrows R6 and R5). That is, the developing roller 50 and the supply roller 51 rotate in the opposite direction (reverse direction) at the closest position P1, and the rotation speed is variable.

[0029] The supply roller 51 is a non-magnetic cylindrical roller that rotates counterclockwise in Fig. 2, and is provided rotatably around a cylindrical magnetic roller 51a that is a magnetic field generating means and a second magnet provided on the inner circumference side and does not rotate. That is, the magnetic roller 51a is fixedly arranged inside the supply roller 51 so as not to rotate. The magnetic roller 51a has five pieces, and five magnetic poles are arranged in order in the rotation direction. Note that, although a magnetic roller with five poles is used in this embodiment, it may be other than five poles, for example, a magnetic roller with seven poles may be used.

[0030] The supply roller 51 carries a developer having non-magnetic toner and a magnetic carrier, and rotates to transport it to a closest position P1 to the developing roller 50. That is, the supply roller 51 is disposed opposite the developing roller 50, and supplies the developer in the developer accommodating portion 40a (in the developing container) to the developing roller 50 by rotating.

[0031] The regulating blade 52 as a regulating member is disposed upstream of a position (closest position P1) facing the developing roller 50 in the rotation direction of the supply roller 51, and regulates the amount of developer carried by the supply roller 51. That is, the regulating blade 52 is a plate-shaped member, and is provided in the developing container 40 so that its tip faces the outer circumferential surface of the supply roller 51 on which a regulating pole, which is one of the magnetic poles of the magnet roller 51a, is disposed. A predetermined gap is provided between the tip of the regulating blade 52 and the outer circumferential surface of the supply roller 51. Then, the magnetic brush of the developer carried on the surface of the supply roller 51 is cut off by the regulating blade 52, thereby regulating the layer thickness of the developer.

[0032] The developing roller 50 is disposed opposite the photosensitive drum 1, and conveys a developer to a developing position where the electrostatic latent image formed on the photosensitive drum 1 is developed by rotating. That is, the developing roller 50 is a non-magnetic roller that rotates counterclockwise in FIG. 2, and is provided rotatably around a magnet roller 50a as a first magnet that does not rotate and has one receiving pole, which is a magnetic pole provided on the inner circumference side. The developing roller 50 can develop the electrostatic latent image on the photosensitive drum 1 in a developing area P2, which is an opposing area facing the photosensitive drum 1, by rotating while carrying toner. The supply roller 51 and the developing roller 50 face each other with a predetermined gap at their closest position P1. The receiving pole of the magnet roller 50a in the developing roller 50 is of a polarity opposite to the main pole, which is one of the magnetic poles of the magnet roller 51a that faces the developing roller 50 via the supply roller 51 and the developing roller 50.

[0033] A supply bias in which a DC voltage and an AC voltage are superimposed is applied to the supply roller 51. A development bias in which a DC voltage and an AC voltage are superimposed is also applied to the development roller 50. The development bias and the supply bias are applied to the development roller 50 and the supply roller 51 from a bias power supply 54 as an example of a voltage application unit via a bias control circuit. That is, the bias power supply 54 applies a voltage including a DC component and an AC component between the development roller 50 and the supply roller 51. Due to the potential difference between the voltage applied to the supply roller 51 and the voltage applied to the development roller 50, the toner is supplied from the supply roller 51 to the development roller 50, and due to the effect of the AC component, the toner on the development roller 50 after the development is completed is collected by the supply roller 51.

[0034] As described above, by repeating the delivery of toner between the supply roller 51 and the developing roller 50, floating toner is likely to accumulate near the closest position P1 between the supply roller 51 and the developing roller 50. In general, in the space S between the supply roller 51, the developing roller 50, and the wall portion 71, air flows due to the rotation of the supply roller 51 and the rotation of the developing roller 50. Therefore, the pressure inside the housing 70 becomes higher than the pressure outside the housing 70. As a result, in the space S, toner that is not used for development and is separated from the developing roller 50 by the magnetic brush, and floating toner near the closest position P1 described above, may scatter to the outside of the developing device 4 through the opening 72 of the housing 70.

[0035] [Shielding roller] As a countermeasure against such scattering, in this embodiment, a shielding roller 53 as a rotating member and a toner shielding member is disposed downstream in the rotation direction of the supply roller 51 from the closest position P1 between the developing roller 50 and the supply roller 51, and at a position facing the supply roller 51 between the wall portion 71 and the developing roller 50. The shielding roller 53 is disposed so as to substantially face both the developing roller 50 and the supply roller 51. The shielding roller 53 is also disposed at a position closer to the developing roller 50 than the supply roller 51. Specifically, the shielding roller 53 is disposed at a position above the supply roller 51 and close to the developing roller 50. By disposing the shielding roller 53, it is possible to suppress scattering of toner from the opening 72 to the outside of the developing device through the gap between the wall portion 71 and the developing roller 50.

[0036] The shielding roller 53 is configured to be rotatable as described later, and its outer circumferential surface is a cylindrical surface centered on the rotation axis. That is, the shielding roller 53 is preferably formed in a cylindrical or columnar shape. The toner shielding member corresponding to the shielding roller 53 may have a different configuration with the outer circumferential surface being a cylindrical surface, for example, a rectangular parallelepiped shape having corners on the outer circumferential surface. However, compared to such a shape, the shielding roller 53 having a cylindrical or columnar shape is less likely to warp on the surface, and the shielding roller 53 can be manufactured with high precision. In this embodiment, the shielding roller 53 is formed in a columnar shape, and the diameter of the shielding roller 53 is, for example, 4 mm or more.

[0037] The shielding roller 53 is rotatably supported by the housing 70. The shielding roller 53 is a weakly magnetic or non-magnetic metal member, and if the shielding roller 53 is weakly magnetic, it is preferable that the shielding roller 53 is made of austenitic stainless steel. Furthermore, the shielding roller 53 is made of a conductive material.

[0038] Here, as described above, simply providing the shielding roller 53 in the space surrounded by the developing roller 50, the supply roller 51, and the wall portion 71 cannot completely block the flow of toner, so that the toner leaking from the gap will scatter to the outside. In addition, the toner will adhere to the shielding roller 53, accumulate and fall, so-called dripping may occur, which may affect the image. In particular, when the shielding roller 53 is disposed above the supply roller 51 as in this embodiment, the dripped toner falls onto the supply roller 51, so that the toner concentration in the part on the supply roller 51 where the toner has fallen becomes high, and there is a risk of image defects occurring in which the image concentration of the toner image formed on the photosensitive drum 1 becomes high in part. This is similar to the case where the shielding roller 53 is disposed above the developing roller 50, although it is different from this embodiment.

[0039] Therefore, in this embodiment, when the supply roller 51 and the development roller 50 are driven, a DC voltage of the same polarity as the normal charging polarity of the toner and equal in absolute value to that of the supply roller 51 is applied to the shielding roller 53. That is, a voltage of the same potential as that of the supply roller 51 is applied to the shielding roller 53. By setting in this manner, the toner is pressed from the shielding roller 53 to the development roller 50 due to the potential difference. As a result, it is possible to prevent the toner from leaking out of the gap and scattering to the outside. It is also possible to prevent the toner from adhering to the surface of the shielding roller 53 and dripping off.

[0040] However, simply setting the potential as described above makes it difficult to capture the toner between the shielding roller 53 and the supply roller 51 by electric field, and it is not possible to prevent the toner from scattering from the gap between the wall portion 71 and the shielding roller 53.

[0041] One possible configuration for preventing such toner scattering is to provide a seal-like toner shielding member 55 between the wall portion 71 and the shielding roller 53 to block the gap, as in the comparative developing device 4A shown in Fig. 3. However, with this configuration, the pressure inside the housing 70 increases, and there is a possibility that the floating toner near the space S will scatter to the outside of the developing device 60 through the gap between the shielding roller 53 and the developing roller 50, or the gap between the developing roller 50 and the supply roller 51.

[0042] Therefore, in this embodiment, by rotating the shielding roller 53 in the rotation direction R7, air is drawn in between the wall portion 71 and the shielding roller 53, and the air is discharged while shielding the toner by the electric field generated between the developing roller 50 and the shielding roller 53. This makes it possible to suppress the increase in pressure inside the housing 70 while suppressing toner scattering.

[0043] [Drive configuration of the development device] 4 and 5, the drive configuration of the developing device 4 according to this embodiment will be described. In this embodiment, the shielding roller 53 is rotatable in the forward direction with respect to the rotation direction R6 of the developing roller 50 by the gear configurations 90 and 91. That is, the rotation direction of the shielding roller 53 is the same as the rotation direction of the developing roller 50.

[0044] Here, the gear configuration 90 shown in Fig. 4 indicates the drive configuration on the rear side of the device, as viewed from the rear side of the device. The gear configuration 91 shown in Fig. 5 indicates the drive configuration on the front side of the device, as viewed from the front side of the device. The front side of the device is the front side of the image forming device 100, for example, the side where an operation unit for accepting operations by an operator is provided (the front side of the paper in Figs. 1 and 2). The rear side of the device is the opposite side to the front side of the device (the rear side of the paper in Figs. 1 and 2).

[0045] 4, in this embodiment, a drive motor 900 is disposed at the rear side of the developing device 4 as a drive source. The drive motor 900 is directly connected to a gear 901 of the gear configuration 90. The gear 901 is provided at one end (the end at the rear side of the device) of the supply roller 51. In addition, a gear 907 is provided at one end of the developing roller 50, a gear 903 is provided at one end of the first transport screw 44, and a gear 905 is provided at one end of the second transport screw 45.

[0046] The operation of the gear configuration 90 will be described with reference to FIG. 2. During image formation, the gear 901 is rotated by the drive motor 900, and the supply roller 51 on which the gear 901 is provided rotates in a rotation direction R5. An idler gear 902 is provided adjacent to the lower side of the gear 901, and the idler gear 902 rotates following the rotation of the gear 901. A gear 903 is provided adjacent to the idler gear 902, and the rotation of the gear 901 is transmitted to the gear 903 via the idler gear 902, and the first conveying screw 44 on which the gear 903 is provided rotates in a rotation direction R4. The rotation of the gear 903 is transmitted to the gear 905 via the idler gear 904, and the second conveying screw 45 on which the gear 905 is provided rotates in a rotation direction R3.

[0047] Meanwhile, an idler gear 906 is provided adjacent to and above the gear 901, and the idler gear 906 rotates in response to the rotation of the gear 901. In addition, a gear 907 is provided adjacent to the idler gear 906, and the rotation of the gear 901 is transmitted to the gear 907 via the idler gear 906, causing the developing roller 50 on which the gear 907 is provided to rotate in the rotation direction R6.

[0048] As shown in FIG. 5, a gear 911 is provided at the other end (the end on the front side of the device) of the second conveying screw 45. A gear 916 is provided at the other end of the shielding roller 53. A plurality of idler gears 912 to 915 are disposed between the gears 911 and 916. When rotation is transmitted to the gear 905 in FIG. 4, the gear 911 provided at the other end of the second conveying screw 45 rotates because the gear 905 is provided at one end of the second conveying screw 45. Then, following the rotation of the gear 911, an idler gear 912 adjacent to the gear 911 and an idler gear 913 adjacent to the idler gear 912 rotate in the rotation direction R9. Furthermore, following the rotation of the idler gear 914, the gear 916 rotates via the idler gear 915 adjacent to the idler gear 914, and the shielding roller 53 on which the gear 916 is provided rotates in the rotation direction R7.

[0049] The peripheral speed of the shielding roller 53 is preferably 1 / 20 to 1 / 1 of the peripheral speed of the supply roller 51, and more preferably 1 / 10 to 3 / 20 of the peripheral speed of the supply roller 51. If the peripheral speed of the shielding roller 53 is less than 1 / 20 of the peripheral speed of the supply roller 51, there is a risk that the rotation of the shielding roller 53 will not generate a sufficient air flow between the wall portion 71 and the shielding roller 53, and air will not be drawn in. Furthermore, if the peripheral speed of the shielding roller 53 exceeds 1 / 1 of the peripheral speed of the supply roller 51, the air drawn in from between the wall portion 71 and the shielding roller 53 will be carried around between the shielding roller 53 and the supply roller 51, and toner may easily accumulate in the space S.

[0050] Therefore, by setting the peripheral speed of the shielding roller 53 to be 1 / 20 or more and 1 / 1 or less relative to the peripheral speed of the supply roller 51, and more preferably 1 / 10 or more and 3 / 20 or less, it is possible to make it difficult for toner to accumulate in the space S while discharging air to the outside, thereby suppressing an increase in pressure inside the developing device 4.

[0051] In the case of this embodiment, since the shielding roller 53 is configured to rotate, air is drawn in between the wall portion 71 and the shielding roller 53 and the air is expelled. This makes it possible to suppress toner scattering while suppressing an increase in pressure inside the developing device 4. As a result, it is possible to suppress contamination of the inside of the image forming apparatus 100 by scattered toner.

[0052] In addition, because a DC voltage of the same polarity as the normal charging polarity of the toner and equal in absolute value to that of the supply roller 51 is applied to the shielding roller 53, the toner is shielded by the electric field generated between the developing roller 50 and the shielding roller 53, and it is possible to prevent the toner from leaking out of the gap and scattering to the outside. Furthermore, by applying such a voltage to the shielding roller 53, it is possible to prevent the toner from being pressed from the shielding roller 53 to the developing roller 50, causing the toner to adhere to the surface of the shielding roller 53 and drop off. As a result, it is possible to prevent the occurrence of image defects due to drop off.

[0053] <Second embodiment> The second embodiment will be described with reference to Figures 6 and 7. This embodiment differs from the first embodiment in the rotation direction of the shielding roller 53. Other configurations and functions are similar to those of the first embodiment described above, so the same reference numerals are used for similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0054] In the first embodiment, the shielding roller 53 is rotatable in the forward direction relative to the rotation direction of the developing roller 50. In contrast, in the developing device 4B of the present embodiment, as shown in FIG. 6, the shielding roller 53 is rotatable in a rotation direction R8 which is the opposite direction to the rotation direction R6 of the developing roller 50. In other words, the rotation direction of the shielding roller 53 is the opposite direction to the rotation direction of the developing roller 50.

[0055] The gear configuration 92 shown in FIG. 7 shows the drive configuration on the front side of the device, and shows the state seen from the front side of the device. In this embodiment, the gear configuration 90 on the rear side of the device is the same as that shown in FIG. 4 in the first embodiment, but the gear configuration 92 on the front side of the device is different from that in the first embodiment. That is, as shown in FIG. 7, in the gear configuration 92 of this embodiment, the idler gear 915 and the gear 916 are not adjacent to each other, but an idler gear 921 is added to the gear configuration 91 of the first embodiment so as to be adjacent to both the idler gear 915 and the gear 916. As a result, the shielding roller 53 provided with the gear 916 rotates in a rotation direction R8 as shown in FIG. 6. The rotation direction R8 is opposite to the rotation direction R6 of the developing roller 50.

[0056] As for the embodiment, the first embodiment is more preferable than the second embodiment. This is because, in the second embodiment, when toner is accumulated on the shielding roller 53, the accumulated toner is shaken off and adheres to the developing roller 50 as the shielding roller 53 rotates in the rotation direction R8, which may cause image defects such as stains. In addition, since toner suspended in the space S is likely to accumulate, when the shielding roller 53 rotates in the rotation direction R8, an airflow is generated in the direction toward the space S from the gap between the shielding roller 53 and the developing roller 50, which may increase the pressure in the vicinity of the space S and may lead to toner scattering.

[0057] However, even in the present embodiment, since the shielding roller 53 is rotated, it is possible to draw in air between the wall portion 71 and the shielding roller 53 and expel the air. Therefore, it is possible to suppress the toner scattering while suppressing the increase in pressure inside the developing device 4, compared to the case where the shielding roller 53 is not rotated.

[0058] <Third embodiment> The third embodiment will be described with reference to Fig. 8. This embodiment differs from the first embodiment in the configuration of the shielding roller 53A. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the similar configurations, and the description and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0059] FIG. 8(a) is a schematic perspective view of the shielding roller 53A according to this embodiment. FIG. 8(b) is a schematic view of a part of the surface of the shielding roller 53A enlarged and linearly developed. The arrow h in the figure indicates the rotation direction of the shielding roller 53A with the rotation axis j in FIG. 8(a) as the axis of rotation. As shown in FIG. 8(a), the shielding roller 53A has a plurality of grooves 531 formed along the longitudinal direction over the entire circumference of the outer circumferential surface. That is, the shielding roller 53A has a plurality of grooves 531 formed along the longitudinal direction of the surface with respect to the surface shape of the shielding roller 53 shown in the first embodiment.

[0060] 8(b), the plurality of grooves 531 are regularly formed around the entire circumference of the shielding roller 53A. The depth of the grooves 531 formed on the surface of the shielding roller 53A is, for example, 50 μm or more. The number of the grooves 531 formed on the surface of the shielding roller 53A is, for example, 20 or more.

[0061] In this way, by providing the grooves 531 on the surface of the shielding roller 53A, the generation of airflow caused by the rotation of the shielding roller 53A is promoted, and scattering of toner to the outside of the developing device can be suppressed. Note that the numerical values ​​and dimensions of the groove shape described above are merely examples and are not particularly limited. The configuration of this embodiment may be applied to the second embodiment. That is, the shielding roller 53A may be configured to rotate in the rotation direction R8 shown in FIG. 7.

[0062] <Fourth embodiment> A fourth embodiment will be described. This embodiment differs from the first embodiment in the voltage applied to the shielding roller 53. Other configurations and functions are similar to those of the first embodiment described above, so the same reference numerals are used for similar configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0063] In the above-described first embodiment, biases of the same potential are applied to the shielding roller 53 and the supply roller 51. In contrast to this, in this embodiment, the absolute value of the DC component of the voltage applied to the shielding roller 53 is greater than the absolute value of the DC component of the voltage applied to the supply roller 51. In other words, a bias having a DC component Vdc2 of the same polarity as the toner and greater in absolute value than the DC component Vdc1 of the bias applied to the supply roller 51 is applied to the shielding roller 53.

[0064] By setting the bias as in this embodiment, the potential difference causes the toner to be pressed from the shielding roller 53 toward the supply roller 51. As a result, it is possible to prevent the toner from adhering to the surface of the shielding roller 53 and dripping. In this embodiment, the potential difference between Vdc1 and Vdc2 is set to 400 V. The bias relationship in this embodiment may also be applied to the second and third embodiments.

[0065] <Fifth embodiment> The fifth embodiment will be described with reference to FIG. 9. In the above-described embodiments, a so-called touch-down type developing device having a developing roller and a supply roller has been described. In contrast, the developing device 4C of this embodiment has only a developing roller 50A. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the similar configurations, and the description and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0066] The developing device 4C of this embodiment has only the developing roller 50A, and the shielding roller 53 is rotated, but the same effect as that of the first embodiment can be obtained. The developing device 4C of this embodiment includes a developing container 40A, a developing roller 50A as a developing rotator, and a shielding roller 53 as a rotating member. The developing container 40A has a housing 70A and a developer accommodating portion 40Aa arranged at the bottom of the housing 70A. The housing 70A has a wall portion 71A and an opening 72A.

[0067] The wall portion 71A is disposed at a position facing a part of the developing roller 50A. In the case of the present embodiment, the wall portion 71A is disposed on the opposite side of the developing roller 50A from the regulating blade 52. At this position, the wall portion 71A is disposed so as to follow the outer circumferential surface of the developing roller 50A. The opening 72A is formed at a position facing the photosensitive drum 1 of the developing container 40A, and the developing roller 50A faces the photosensitive drum 1 through the opening 72A.

[0068] The developer storage section 40Aa stores a developer including non-magnetic toner and magnetic carrier. A partition wall 41 is provided in the approximate center of the developer storage section 40Aa. As a result, the developer storage section 40a is partitioned by the partition wall 41 so that a developing chamber 42 and a stirring chamber 43 are horizontally adjacent to each other. A first transport screw 44 and a second transport screw 45 that can rotate to stir and circulate the developer are disposed in the developing chamber 42 and the stirring chamber 43, respectively. The configuration for circulating the developer inside the developer storage section 40Aa is generally similar to that of the first embodiment.

[0069] The developing roller 50 is disposed opposite the photosensitive drum 1, and rotates to transport developer to a development position where the electrostatic latent image formed on the photosensitive drum 1 is developed. That is, the developing roller 50A rotates to carry and transport the developer in the developer accommodating section 40a (inside the developing container) and supply it to the photosensitive drum 1. The regulating blade 52 is disposed upstream of the development position in the rotation direction of the developing roller 50A, and regulates the amount of developer carried by the developing roller 50A.

[0070] In such a developing device 4C, the toner suspended between the left side of the developing roller 50A in the figure and the wall portion 71A scatters to the outside of the developing device 4C in the flow path toward the opening 72A. As a countermeasure against this toner scattering, a sheet may be attached to the wall portion 71A near the opening 72A facing the developing roller 50A to seal the airflow from the opening 72A to the outside of the developing device 4C. However, the pressure inside the developing device 4C may rise, causing the toner to scatter from between the developing roller 50A and the regulating blade 52.

[0071] Therefore, in this embodiment, the shielding roller 53 is rotatably installed between the upper left part of the developing roller 50A in the figure and the wall part 71A, and rotated in a rotation direction R10. The rotation direction of the shielding roller 53 is the same as that of the developing roller 50A. By rotating the shielding roller 53 in the rotation direction R10, an airflow is generated between the wall part 71A and the shielding roller 53 in a direction that draws air into the inside of the developing device 4C, and it is possible to suppress toner scattering from the opening 72A to the outside of the developing device 4C.

[0072] In this embodiment, the developing roller 50A and the shielding roller 53 may be at the same potential, similar to the relationship between the supply roller 51 and the shielding roller 53 in the first embodiment, and even in this case, toner scattering and dripping can be suppressed to some extent. However, similar to the relationship between the supply roller 51 and the shielding roller 53 in the fourth embodiment, it is preferable to provide a potential difference between the developing roller 50A and the shielding roller 53. In this case, toner scattering and dripping can be further suppressed.

[0073] <Other embodiments> In the above-described embodiments, the present invention has been described as being applied to a developing device used in a tandem-type image forming apparatus. However, the present invention can also be applied to developing devices used in other types of image forming apparatus. In addition, the image forming apparatus is not limited to being full-color, and may be monochrome or mono-color. Alternatively, by adding necessary devices, equipment, and housing structures, the present invention can be embodied in various applications such as printers, various printing machines, copiers, FAX machines, and multi-function machines.

[0074] In addition, the configuration of the developing device is not limited to the above-mentioned configuration in which the developing chamber and the stirring chamber are arranged horizontally, but may be arranged in a direction inclined with respect to the horizontal direction. In short, it is sufficient that the developing chamber as the first chamber and the stirring chamber as the second chamber are arranged adjacent to each other so as to overlap at least partially when viewed from the horizontal direction. [Explanation of symbols]

[0075] 1...Photosensitive drum (image carrier) 4, 4B, 4C...Developing device 40, 40A...Developing container 50, 50A...Developing roller 51 Supply roller 52 Regulating blade (regulating member) 53, 53A: Shielding roller (rotating member) 71, 71A...Wall section

Claims

1. Image carrier and, A developing apparatus comprising: a developing container for containing a developer including toner and a carrier; a developing roller for carrying and transporting the toner to a developing position for developing an electrostatic image formed on the image carrier; a supply roller positioned opposite the developing roller for carrying and transporting the developer supplied from the developing container and supplying only the toner to the developing roller; a first magnet having a first magnetic pole, fixedly positioned in a non-rotating manner inside the developing roller; and a second magnet having a second magnetic pole opposite the first magnetic pole and fixedly positioned in a non-rotating manner inside the supply roller. A conductive roller is positioned opposite the supply roller and the developing roller, with respect to the rotational direction of the developing roller, downstream of the developing position and upstream of the closest proximity position between the developing roller and the supply roller, A drive source for rotating each of the supply roller, the developing roller, and the conductive roller, The system includes a bias application unit that applies a bias to each of the supply roller, the developing roller, and the conductive roller, At the position on the developing roller where the supply roller is closest to the developing roller, the rotation direction of the developing roller is opposite to the rotation direction of the supply roller. The shortest distance between the conductive roller and the developing roller is shorter than the shortest distance between the conductive roller and the supply roller. During the image formation process, With the supply roller, the developing roller, and the conductive roller each being driven to rotate, a bias is applied to each of the supply roller, the developing roller, and the conductive roller. The polarity of the first potential obtained by subtracting the DC potential of the developing roller from the DC potential of the supply roller is the same as the normal charging polarity of the toner. and, The polarity of the second potential obtained by subtracting the DC potential of the developing roller from the DC potential of the conductive roller is the same as the normal charging polarity of the toner. An image forming apparatus characterized by the following features.

2. During the image forming operation, the DC potential of the conductive roller and the DC potential of the supply roller are the same. The image forming apparatus according to feature 1.

3. During the image forming operation, the polarity of the third potential obtained by subtracting the DC potential of the supply roller from the DC potential of the conductive roller is the same as the normal charging polarity of the toner. The image forming apparatus according to feature 1.

4. During the aforementioned image forming operation, The supply roller is subjected to a bias in which a DC voltage and an AC voltage are superimposed. and, The developing roller is subjected to a bias that is a superposition of a DC voltage and an AC voltage. The image forming apparatus according to feature 1.

5. During the image forming operation, the peripheral speed of the conductive roller is between 1 / 20 and 1 / 1 of the peripheral speed of the supply roller. The image forming apparatus according to feature 1.

6. During the image forming operation, the peripheral speed of the conductive roller is between 1 / 10 and 3 / 20 of the peripheral speed of the supply roller. The image forming apparatus according to feature 1.

7. At the position on the developing roller where the conductive roller is closest to the developing roller, the rotation direction of the developing roller is the same as the rotation direction of the conductive roller. The image forming apparatus according to feature 1.

8. At the position on the developing roller where the conductive roller is closest to the developing roller, the rotation direction of the developing roller is opposite to the rotation direction of the conductive roller. The image forming apparatus according to feature 1.

9. Multiple grooves are formed on the outer circumferential surface of the conductive roller along the rotation axis direction of the conductive roller. The plurality of grooves are formed around the entire circumference of the conductive roller. The image forming apparatus according to feature 1.

10. The developing apparatus further comprises a first gear provided at the end of the supply roller in the direction of its rotation axis, a second gear provided at the end of the developing roller in the direction of its rotation axis, and a third gear provided at the end of the conductive roller in the direction of its rotation axis. The aforementioned drive source is a motor, As the driving force of the motor is transmitted to the first gear, the second gear, and the third gear, the supply roller, the developing roller, and the conductive roller are each rotated. The image forming apparatus according to feature 1.

11. The motor is directly connected to the first gear. The image forming apparatus according to feature 10.

12. It is further equipped with an operating section for receiving input from the operator, The motor, the first gear, and the second gear are each positioned on the opposite side of the image forming apparatus from the side where the operating unit is located, with respect to the front-to-back direction. The third gear is positioned on the same side as the operating unit with respect to the front-to-back direction of the image forming apparatus. The image forming apparatus according to feature 10.

13. The motor, the first gear, and the second gear are each located on the rear side in the front-rear direction of the image forming apparatus. The third gear is located on the front side in the direction of the image forming apparatus. The image forming apparatus according to feature 10.

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