JP6460022B2 - Developing device and image forming apparatus having the same - Google Patents

Description

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

  Conventionally, image forming apparatuses such as printers and copiers that employ an electrophotographic method have a photosensitive drum carrying an electrostatic latent image, and toner is supplied to the photosensitive drum so that the electrostatic latent image becomes visible as a toner image. And a transfer device that transfers a toner image from the photosensitive drum to a sheet.

  Patent Document 1 discloses a developing roller that supplies toner to a photosensitive drum and a conveyance roller that supplies developer to the developing roller. Each of the developing roller and the transporting roller includes a magnet having a plurality of magnetic poles fixed and a sleeve that rotates around the magnet. The developer is supplied from the conveyance roller to the developing roller by a magnetic force generated between the first S pole on the conveyance roller side and the first N pole on the development roller side. The developer is collected from the developing roller to the transport roller by a magnetic force generated between the second N pole on the developing roller side and the second S pole on the transport roller side.

Japanese Patent Laid-Open No. 04-107586

  In the developing device as described above, the south pole and north pole on the developing roller side are attracted to the north pole and south pole on the transport roller side, respectively. For this reason, a strong magnetic attractive force is generated between the two rollers, and the shaft supporting the magnet may be deformed. When the shaft is greatly deformed, there are problems that the inner peripheral surface of the rotating sleeve comes into contact with the magnet, and that the magnet falls off the shaft.

  The present invention has been made in view of the above problems, and can reduce the magnetic attraction generated between a plurality of rollers each having a magnet therein, and can stably deliver developer between the rollers. An object of the present invention is to provide a developing device and an image forming apparatus including the developing device.

  A developing device according to one aspect of the present invention includes a first magnet fixed including a plurality of magnetic poles along a circumferential direction, and a toner and a magnetic carrier on a circumferential surface rotating around the first magnet in a first rotation direction. And a first sleeve that carries a developer containing the toner, and is disposed to face a photosensitive drum on which an electrostatic latent image is formed at a predetermined development position, and supplies the toner to the photosensitive drum. A developing roller, a roller disposed so as to face the developing roller at a predetermined facing position, a second magnet including a plurality of magnetic poles fixed along a circumferential direction, and the first magnet at the facing position A second sleeve that rotates around the second magnet in a second rotation direction set to oppose the rotation direction and carries the developer on a peripheral surface, and supplies the developer to the developing roller A transporting roller, and A developer agitating unit that agitates the image agent and supplies the developer to the conveyance roller, and a first delivery that is disposed adjacent to the facing position and delivers the developer from the conveyance roller to the development roller And a second delivery part that is disposed so as to sandwich the facing position between the developing part and the first delivery part, and delivers the developer from the developing roller to the transport roller, and the first delivery part And one of the second delivery parts, a first magnetic pole having a predetermined polarity, disposed on a side from which the developer is fed out of the first magnet and the second magnetic pole, and the first magnet and the second magnetic pole. The developer is delivered by a magnetic field formed by a second magnetic pole different from the first magnetic pole, which is disposed on the magnet receiving side of the magnet so as to face the first magnetic pole. The other of the first delivery part and the second delivery part is arranged on the side of the developer receiving side of the first magnet and the second magnet, and is a third magnetic pole different from the first magnetic pole. Between the first magnet and the second magnet and the non-magnetic region where the magnetic pole formed so as to oppose the third magnetic pole is not disposed on the developer delivery side. The plurality of magnetic poles of the first magnet and the second magnet are respectively arranged so as to be passed.

  According to this configuration, the developer is supplied from the developer stirring unit to the conveyance roller, and the developer is supplied from the conveyance roller to the development roller. Part of the toner is supplied from the developer to the photosensitive drum at the development position, and then the developer is collected from the development roller to the transport roller. On one of the first delivery portion and the second delivery portion, the developer is stably delivered by the first magnetic pole and the second magnetic pole having different polarities. Further, on the other of the first delivery part and the second delivery part, the developer is delivered between the third magnetic pole and the non-magnetic pole region. As a result, a stronger magnetic attractive force acts between the developing roller and the transport roller than in the case where the developer is delivered by the magnetic poles of different polarities in both the first delivery unit and the second delivery unit. Is reduced. For this reason, in each roller, it is suppressed that a magnet falls and that a magnet and a sleeve contact. Further, it is possible to stably deliver the developer between the rollers.

  In the above configuration, the second magnet disposed between the first magnet and the second magnet in which the non-magnetic pole region is formed is sandwiched between the second magnetic pole and the second magnetic pole region. A fourth magnetic pole different from the magnetic pole is provided, and the first reference position where the magnetic force of the vertical component of the second magnetic pole is 0 on the non-magnetic pole region side and the magnetic force of the vertical component of the fourth magnetic pole is the non-magnetic It is desirable that the magnetic force of the horizontal component of the magnet is set to be larger than 0 in a region between the second reference position that is 0 on the magnetic pole region side.

  According to this configuration, the developer conveyed from the fourth magnetic pole to the non-magnetic pole region is peeled off from the first sleeve or the second sleeve by the non-magnetic pole region. As a result, the separated developer is attracted by the opposing third magnetic pole, and the delivery of the developer is realized.

  In the above configuration, it is desirable that an angle between the peak position of the magnetic force of the vertical component of the second magnetic pole and the peak position of the magnetic force of the vertical component of the fourth magnetic pole is set to 100 degrees or more. .

  According to this configuration, the non-magnetic pole region from which the developer can be peeled can be stably formed by setting a large angle between the second magnetic pole and the fourth magnetic pole.

  In the above configuration, in the region between the first reference position and the second reference position, it is preferable that the magnetic force of the horizontal component of the magnet is set to 10 mT or less.

  According to this configuration, the developer can be more stably peeled off in the non-magnetic pole region.

  In the above configuration, the second magnetic pole, the fourth magnetic pole, and the non-magnetic pole region are disposed in the first magnet of the developing roller, and the first magnetic pole and the third magnetic pole are the second magnet of the transport roller. It is desirable to be arranged in.

  According to this configuration, the developer before going to the developing position is stably delivered by the first magnetic pole of the transport roller and the second magnetic pole of the developing roller. Further, the developer after passing through the development position is delivered from the non-magnetic region of the developing roller toward the third magnetic pole of the transport roller. Therefore, the distribution of the developer at the development position is stabilized, and a strong magnetic attraction force between the developing roller and the transport roller is reduced.

  In the above configuration, the first magnet of the developing roller is disposed adjacent to the fourth magnetic pole on the upstream side in the first rotation direction of the fourth magnetic pole, and has the same polarity as the fourth magnetic pole. It is desirable to have five magnetic poles.

  According to this configuration, the developer is partially retained by the fourth and fifth magnetic poles having the same polarity. For this reason, even when the history of toner consumed at the development position remains on the first sleeve, the history of toner is eliminated by the magnetic brush of the developer staying at the staying portion. For this reason, generation | occurrence | production of a ghost is suppressed.

  In the above-described configuration, it is desirable to further include a layer thickness regulating member that is disposed to face the conveyance roller and regulates the layer thickness of the developer supplied from the developer stirring unit to the conveyance roller.

  According to this configuration, the developer layer thickness can be stably regulated before the developer is transferred from the transport roller to the developing roller. As a result, compared to the case where the layer thickness regulating member is arranged on the developing roller side, a large amount of developer is prevented from being conveyed on the conveying roller and the developing roller, and the driving torque of the developing roller and the conveying roller is reduced. Can be reduced.

  In the above configuration, it is preferable that the first sleeve of the developing roller includes a base material having a surface blasted.

  According to this configuration, the developer retaining portion can be stably formed on the first sleeve.

  In the above configuration, it is preferable that the first sleeve of the developing roller includes a plating layer applied to the surface of the substrate.

  According to this configuration, the developer retaining portion can be more stably formed on the first sleeve, the adhesion of the toner to the sleeve surface is reduced, and the toner layer on the developing roller is eliminated. It becomes easy.

  In the above configuration, the axis of the developing roller is disposed below the axis of the photosensitive drum, and the axis of the transport roller is disposed below the axis of the developing roller. Is desirable.

  According to this configuration, the developer flying from the non-magnetic pole region is stably delivered to the transport roller side together with the action of gravity.

  In the above configuration, it is preferable that a developing bias in which an AC bias is superimposed on a DC bias is applied to the developing roller.

  According to this configuration, even when an oscillating electric field composed of an AC bias is formed at the development position and a ghost is likely to occur, the occurrence of the ghost is suppressed by the magnetic brush of the developer in the staying portion.

  An image forming apparatus according to another aspect of the present invention includes the developing device according to any one of the above, the photosensitive drum that is supplied with the toner from the developing device and carries a toner image on the peripheral surface, And a transfer unit that transfers the toner image from the photosensitive drum to a sheet.

  According to this structure, it is reduced that a strong magnetic attraction force acts between the developing roller and the transport roller. For this reason, in each roller, it is suppressed that a magnet falls and that a magnet and a sleeve contact. Further, it is possible to stably deliver the developer between the rollers.

  According to the present invention, there is provided a developing device capable of reducing magnetic attraction generated between a plurality of rollers each having a magnet therein, and capable of stably delivering developer between the rollers, and the developing device. An image forming apparatus is provided.

1 is a cross-sectional view illustrating an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the internal structure of the developing device according to the embodiment of the present invention. It is typical sectional drawing which shows magnetic pole arrangement | positioning of the developing roller which concerns on embodiment of this invention, and a conveyance roller. It is a typical sectional view showing magnetic pole arrangement of a development roller concerning an embodiment of the present invention. It is sectional drawing which shows the magnetic pole pattern of the developing roller which concerns on embodiment of this invention. It is typical sectional drawing which shows magnetic pole arrangement | positioning of the conveyance roller which concerns on embodiment of this invention. It is sectional drawing which shows the magnetic pole pattern of the conveyance roller which concerns on embodiment of this invention. FIG. 2 is a schematic cross-sectional view illustrating a structure of a housing of a developing device according to an embodiment of the present invention and a state where a developer pool is generated. It is the schematic diagram which showed a mode that the perpendicular direction component of the magnetic force of the developing roller which concerns on embodiment of this invention was measured. It is the schematic diagram which showed a mode that the horizontal direction component of the magnetic force of the developing roller which concerns on embodiment of this invention was measured. It is a schematic diagram which shows a mode that the ghost generate | occur | produced on the print. It is typical sectional drawing which shows magnetic pole arrangement | positioning of the developing roller of a developing device and the conveyance roller which concern on the deformation | transformation embodiment of this invention.

  Hereinafter, an image forming apparatus 10 according to an embodiment of the present disclosure will be described in detail with reference to the drawings. In this embodiment, a tandem color printer is illustrated as an example of an image forming apparatus. The image forming apparatus may be, for example, a copying machine, a facsimile machine, and a complex machine of these.

  FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus 10. The image forming apparatus 10 includes an apparatus main body 11 having a box-shaped housing structure. In the apparatus main body 11, a sheet feeding unit 12 that feeds the sheet P, an image forming unit 13 that forms a toner image to be transferred to the sheet P fed from the sheet feeding unit 12, and the toner image are primarily transferred. Intermediate transfer unit 14, secondary transfer roller 145, toner replenishing unit 15 for replenishing toner to the image forming unit 13, and fixing unit for performing a process of fixing an unfixed toner image formed on the sheet P to the sheet P 16 are decorated. Further, a discharge unit 17 that discharges the sheet P that has been subjected to the fixing process by the fixing unit 16 is provided on the upper portion of the apparatus main body 11.

  In the apparatus main body 11, a sheet conveying path 111 extending in the vertical direction is further formed on the right side of the image forming unit 13. The sheet conveyance path 111 is provided with a conveyance roller pair 112 that conveys a sheet to an appropriate position. A registration roller pair 113 that corrects the skew of the sheet and feeds the sheet to a nip portion of secondary transfer described later at a predetermined timing is also provided on the upstream side of the nip portion in the sheet conveyance path 111. The sheet conveyance path 111 is a conveyance path that conveys the sheet P from the paper feeding unit 12 to the paper discharge unit 17 via the image forming unit 13 (secondary transfer nip unit) and the fixing unit 16.

  The paper feed unit 12 includes a paper feed tray 121, a pickup roller 122, and a paper feed roller pair 123. The sheet feeding tray 121 is detachably mounted at a lower position of the apparatus main body 11 and stores a sheet bundle P1 in which a plurality of sheets P are stacked. The pickup roller 122 feeds the uppermost sheet P of the sheet bundle P1 stored in the sheet feeding tray 121 one by one. The pair of paper feed rollers 123 sends out the sheet P fed out by the pickup roller 122 to the sheet conveyance path 111.

  The image forming unit 13 forms a toner image to be transferred to the sheet P, and includes a plurality of image forming units that form toner images of different colors. As this image forming unit, in this embodiment, a magenta (M) color which is sequentially arranged from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 141 described later (from the left side to the right side in FIG. 1). A magenta unit 13M using a developer, a cyan unit 13C using a cyan (C) developer, a yellow unit 13Y using a yellow (Y) developer, and a black (Bk) developer are used. A black unit 13Bk is provided. Each of the units 13M, 13C, 13Y, and 13Bk includes a photosensitive drum 20, and a charging device 21, a developing device 23, and a cleaning device 25 disposed around the photosensitive drum 20. An exposure device 22 common to the units 13M, 13C, 13Y, and 13Bk is disposed below the image forming unit.

  The photosensitive drum 20 is driven to rotate about its axis, and an electrostatic latent image and a toner image are formed on its peripheral surface. As this photosensitive drum 20, a photosensitive drum using an amorphous silicon (a-Si) material can be used. The photosensitive drums 20 are arranged corresponding to the image forming units of the respective colors. The charging device 21 uniformly charges the surface of the photosensitive drum 20. The charging device 21 includes a charging roller and a charging cleaning brush for removing toner attached to the charging roller. The exposure device 22 has various optical system devices such as a light source, a polygon mirror, a reflection mirror, and a deflection mirror, and irradiates light that has been modulated based on image data onto the circumferential surface of the uniformly charged photoreceptor drum 20. Thus, an electrostatic latent image is formed. The cleaning device 25 cleans the peripheral surface of the photosensitive drum 20 after the toner image is transferred.

  The developing device 23 supplies toner to the peripheral surface of the photosensitive drum 20 in order to develop the electrostatic latent image formed on the photosensitive drum 20. The developing device 23 is for a two-component developer composed of toner and carrier. In this embodiment, the toner has a characteristic of being charged to a positive polarity.

  The intermediate transfer unit 14 is disposed in a space provided between the image forming unit 13 and the toner supply unit 15. The intermediate transfer unit 14 includes an intermediate transfer belt 141, a driving roller 142, a driven roller 143, and a primary transfer roller 24.

  The intermediate transfer belt 141 is an endless belt-like rotating body, and is stretched between the driving roller 142 and the driven roller 143 so that the circumferential surface side thereof is in contact with the circumferential surface of each photosensitive drum 20. The intermediate transfer belt 141 is driven to circulate in one direction, and carries the toner image transferred from the photosensitive drum 20 on the surface.

  The drive roller 142 stretches the intermediate transfer belt 141 on the right end side of the intermediate transfer unit 14 and drives the intermediate transfer belt 141 to rotate. The driving roller 142 is a metal roller. The driven roller 143 stretches the intermediate transfer belt 141 on the left end side of the intermediate transfer unit 14. The driven roller 143 applies tension to the intermediate transfer belt 141.

  The primary transfer roller 24 forms a primary transfer nip portion with the photosensitive drum 20 with the intermediate transfer belt 141 interposed therebetween, and primarily transfers the toner image on the photosensitive drum 20 onto the intermediate transfer belt 141. A primary transfer roller 24 is disposed to face the photosensitive drum 20 of each color.

  The secondary transfer roller 145 is disposed to face the driving roller 142 with the intermediate transfer belt 141 interposed therebetween. The secondary transfer roller 145 is pressed against the peripheral surface of the intermediate transfer belt 141 to form a secondary transfer nip portion. The toner image primarily transferred onto the intermediate transfer belt 141 is secondarily transferred to the sheet P supplied from the paper feeding unit 12 at the secondary transfer nip portion. The intermediate transfer unit 14 and the secondary transfer roller 145 of this embodiment constitute a transfer unit of the present invention. The transfer unit transfers the toner image from the photosensitive drum 20 to the sheet P.

  The toner replenishing unit 15 stores toner used for image formation, and includes a magenta toner container 15M, a cyan toner container 15C, a yellow toner container 15Y, and a black toner container 15Bk in this embodiment. The toner containers 15M, 15C, 15Y, and 15Bk replenish toner of each color to the developing devices 23 of the image forming units 13M, 13C, 13Y, and 13Bk corresponding to the respective colors of MCYBk through a toner transport unit (not shown).

  The sheet P supplied to the fixing unit 16 is heated and pressed by passing through the fixing nip. As a result, the toner image transferred to the sheet P at the secondary transfer nip is fixed to the sheet P.

  The paper discharge unit 17 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 171 for receiving the discharged sheet P is formed at the bottom of the concave portion. The sheet P on which the fixing process has been performed is discharged toward the discharge tray 151 via the sheet conveyance path 111 extending from the upper part of the fixing unit 16.

  Next, the developing device 23 according to the present embodiment will be described in more detail with reference to FIGS. 2 to 6 in addition to FIG. FIG. 2 is a schematic cross-sectional view showing the internal structure of the developing device 23 according to this embodiment. In FIG. 2, the rotation direction of each rotation member of the developing device 23 is indicated by an arrow. FIG. 3 is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231 and the transport roller 232 according to this embodiment. FIG. 4A is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231. FIG. 4B is a cross-sectional view showing a magnetic pole pattern of the developing roller 231. FIG. 5A is a schematic cross-sectional view showing the magnetic pole arrangement of the transport roller 232. FIG. 5B is a cross-sectional view showing a magnetic pole pattern of the transport roller 232. FIG. 6 is a schematic cross-sectional view showing the structure of the housing 23 </ b> H and a state where a developer reservoir (retention portion TD) is generated in the developing device 23 according to the present embodiment.

  1 to 6, the developing device 23 includes a housing 23H, a developing roller 231, a transport roller 232, two stirring screws 233 (developer stirring unit), a partition plate 234, and a layer thickness. A restricting member 235. The housing 23H is a housing portion that supports each member of the developing device 23.

  The developing roller 231 is arranged to face the photosensitive drum 20 on which the electrostatic latent image is formed at a predetermined developing position NP (FIG. 3), and supplies toner to the photosensitive drum 20. The developing roller 231 includes a first magnet 231A and a first sleeve 231B (FIG. 3). In the present embodiment, the development position NP includes the closest position between the photosensitive drum 20 and the development roller 231. The first magnet 231A is a columnar magnet including a plurality of magnetic poles along the circumferential direction and fixed to the housing 23H. The first sleeve 231B rotates around the first magnet 231A in the first rotation direction (the direction of arrow D1 in FIGS. 2 and 3), and carries a developer containing toner and a magnetic carrier on the peripheral surface. In the present embodiment, the first sleeve 231B is made of an aluminum circular pipe member (base material). The circumferential surface of the circular pipe member of the first sleeve 231B is subjected to sandblasting (blasting) and further includes a Ni plating layer applied on the circumferential surface. The surface of the Ni plating layer of the first sleeve 231B has a predetermined surface roughness. In the present embodiment, the surface roughness Rzjis of the first sleeve 231B is set in the range of 4.0 μm to 14.0 μm. The first sleeve 231B of the developing roller 231 is rotatably supported by the housing 23H.

  The transport roller 232 is disposed so as to face the developing roller 231 at a predetermined facing position TP (FIG. 3), and supplies the developer to the developing roller 231. In the present embodiment, the facing position TP includes the closest position between the transport roller 232 and the developing roller 231. The transport roller 232 includes a second magnet 232A and a second sleeve 232B. The second magnet 232A includes a plurality of magnetic poles along the circumferential direction, and is fixed to the housing 23H. The second sleeve 232B rotates around the second magnet 232A in the second rotation direction (the direction of arrow D2 in FIGS. 2 and 3), and carries a developer containing toner and carrier on the peripheral surface. A known groove shape is provided on the surface of the second sleeve 232B. The second sleeve 232B is rotatably supported by the housing 23H.

  A developing bias in which an AC bias is superimposed on a DC bias is applied to the developing roller 231 and the transport roller 232 (FIG. 2). As shown in FIG. 3, the first rotation direction D1 in which the developing roller 231 rotates and the second rotation direction D2 in which the transport roller 232 rotates are set so as to face each other at the facing position TP (counter). direction).

  The stirring screw 233 charges the toner by circulating and conveying the two-component developer while stirring. The stirring screw 233 includes a first screw 233A and a second screw 233B. Although not shown in FIG. 2, the housing 23H includes a first agitation unit (not shown) in which the first screw 233A is arranged and a second agitation unit (not shown) in which the second screw 233B is arranged. Provided (see developing device 23 in FIG. 1). The developer is circulated and conveyed between the first screw 233A and the second screw 233B. Then, the first screw 233 </ b> A supplies the developer to the transport roller 232. The partition plate 234 is a plate-like member provided in the housing 23H. The partition plate 234 partitions the first stirring portion and the second stirring portion along the axial direction of the first screw 233A and the second screw 233B. Further, the toner replenished from the toner replenishing portion 15 flows into the housing 23H from one end side in the axial direction of the second screw 233B, and is agitated with the other developer.

  The layer thickness regulating member 235 is a plate-like member made of a nonmagnetic metal that is disposed so as to face the peripheral surface of the transport roller 232. In another embodiment, a magnetic member may be fixed to the upstream side surface of the layer thickness regulating member 235. The layer thickness regulating member 235 regulates the layer thickness of the developer supplied from the first screw 233 </ b> A of the stirring screw 233 to the transport roller 232.

  As shown in FIG. 2, the axis of the developing roller 231 is disposed below the axis of the photosensitive drum 20, and the axis of the transport roller 232 is further below the axis of the developing roller 231. Has been placed.

  Referring to FIG. 2, the developer composed of toner and carrier and circulated and conveyed by stirring screw 233 is supplied from first screw 233 </ b> A to conveying roller 232. Thereafter, after the layer thickness of the developer is regulated by the layer thickness regulating member 235, the developer is supplied to the developing roller 231. When a part of the toner is supplied to the photosensitive drum 20 at the development position NP (FIG. 3), the developer is collected from the development roller 231 to the transport roller 232. Thereafter, the developer collected on the transport roller 232 again flows into the first stirring unit around the first screw 233A. Referring to FIG. 6, a region that is disposed adjacent to the facing position TP (FIG. 3) and delivers the developer from the transport roller 232 to the developing roller 231 is defined as a first delivery unit K1. Further, a region where the opposing position TP is sandwiched between the first delivery unit K1 and the developer is delivered from the developing roller 231 to the transport roller 232 is defined as a second delivery unit K2.

  With reference to FIGS. 3, 4A, and 4B, in the present embodiment, the first magnet 231A of the developing roller 231 includes five magnetic poles along the circumferential direction. An N11 pole (second magnetic pole) is arranged on the downstream side in the first rotation direction (D1) of the facing position TP between the developing roller 231 and the transport roller 232. Further, the S11 pole is disposed downstream of the N11 pole in the first rotation direction. The S11 pole functions as a transport pole for transporting the developer received from the transport roller 232 to the photosensitive drum 20 side. Further, an N12 pole that functions as a main pole that supplies toner to the photosensitive drum 20 is disposed downstream of the S11 pole in the first rotation direction. The N12 pole is disposed in the vicinity of the development position NP.

  Further, the first magnet 231A includes two magnetic poles (S12, S13) in the first region R downstream of the developing position NP in the first rotational direction and upstream of the facing position TP in the first rotational direction. ing. The S12 pole (fifth magnetic pole) is disposed downstream of the N12 pole in the first rotation direction. The S13 pole (fourth magnetic pole) is a magnetic pole having the same polarity as the S12 pole, arranged further downstream in the first rotation direction of the S12 pole. The N11 pole described above is disposed adjacent to the S13 pole on the downstream side in the first rotation direction with the opposite position TP interposed therebetween, and is a magnetic pole different from the S13 pole.

  Table 1 shows examples of the angles and magnetic forces (peak values of vertical components) of five magnetic poles as the first magnet 231A according to the present embodiment. In addition, the angle of each magnetic pole shown in Table 1 is shown along the 1st rotation direction from the opposing position TP of FIG. 4A as a starting point (angle 0 degree). In FIG. 4A, a straight line CL that connects the facing position TP and the rotation axis of the developing roller 231 (a straight line that connects the rotation axis of the developing roller 231 and the rotation axis of the transport roller 232) is shown as the starting point. .

  Further, referring to FIG. 4B, the first magnet 231A of the developing roller 231 includes a non-magnetic pole region NM sandwiched between the S13 pole and the N11 pole. The first magnet 231A does not have a manufacturing magnetic pole in the non-magnetic pole region NM. The first magnet 231A is formed by fixing a plurality of magnet pieces formed in a substantially fan shape in a cross-sectional view corresponding to each magnetic pole such as the N11 pole, to a shaft (not shown). The magnet piece is not arranged at a position corresponding to the non-magnetic pole region NM in FIG. 4B. In other embodiments, the first magnet 231A may be formed by inserting a shaft through a cylindrical magnet. In this case, at the manufacturing stage of the first magnet 231A, the magnetizing yoke is oriented corresponding to the position of each magnetic pole. Also in this case, the magnetizing yoke is not disposed at the position corresponding to the non-magnetic pole region NM.

  Referring to FIG. 4B, there is a slight magnetic force even in such a non-magnetic pole region NM. This is due to the magnetic field lines extending from the N11 pole and the S13 pole adjacent to the non-magnetic pole region NM. In this embodiment, as shown in Table 1, as an example, the peak position of the vertical component of the magnetic force of the N11 pole is arranged at a position of 30 degrees from the straight line CL (FIG. 4A), and The peak position is arranged at a position of 264 degrees from the straight line CL (FIG. 4A). In other words, the interval between the peak positions of both poles is set to 126 degrees. As described above, when the interval between the two different poles is set larger than 100 degrees, as shown in FIG. 4B, the non-magnetic pole region NM has a weak N pole (N) and a weak S pole ( S) is triggered. As a result, in the first magnet 231A, the S poles, the N poles, the S poles, and the N poles are alternately formed in the first rotation direction from the S13 poles.

  Further, the non-magnetic pole region NM will be described in more detail. In this embodiment, the first reference position J1 (FIG. 4B) where the magnetic force of the vertical component of the N11 pole becomes 0 on the non-magnetic pole region NM side and the vertical of the S13 pole. In a region between the second reference position J2 (FIG. 4B) where the magnetic force of the directional component is 0 on the non-magnetic pole region NM side, the magnetic force of the horizontal component of the first magnet 231A is set to be greater than 0 and 10 mT or less. Has been. Thus, in the flat region where the magnetic force of the horizontal component is weak, the developer holding force on the developing roller 231 is weakened.

  FIG. 7A is a schematic diagram illustrating a state in which a vertical component (also referred to as a radial component, a component perpendicular to the circumferential surface of the developing roller 231) of the magnetic force of the developing roller 231 according to the present embodiment is measured. FIG. 7B is a schematic diagram illustrating a state in which a horizontal component (also referred to as a tangential component, a tangential component of the peripheral surface of the developing roller 231) of the magnetic force of the developing roller 231 according to the present embodiment is measured. When measuring the vertical component of the magnetic force of the first magnet 231A (arrow DP in FIG. 7A), as shown in FIG. 7A, the measurement element PB of the probe PA is substantially in contact with the first sleeve 231B ( The magnet shaft 231AS connected to the first magnet 231A is rotated in the direction of the arrow at a distance between them of 0 to 0.5 mm. As a result, the magnetic force pattern of the vertical component in FIG. 4B is measured. On the other hand, when measuring the horizontal component of the magnetic force of the first magnet 231A (arrow DQ in FIG. 7B, the direction orthogonal to the paper surface), as shown in FIG. 7B, the measuring element PB of the probe PA is moved from FIG. Rotate 90 degrees toward you. In this state, the magneto shaft 231AS is rotated in the direction of the arrow. As a result, the magnetic force pattern of the horizontal component in FIG. 4B is measured. In this case, an interval PH of 1 mm to 2 mm exists between the measuring element PB and the first sleeve 231B.

  Like the non-magnetic pole region NM of the first magnet 231A according to the present embodiment, the state where the horizontal magnetic field of the first magnet 231A does not become zero occurred from the S13 pole and the N11 pole arranged on both sides of the non-magnetic pole region NM. This means that the magnetic field lines are very strong and the horizontal magnetic field generated between (N) and (S) of the non-magnetic pole region NM is very small. In (N) and (S) of the non-magnetic pole region NM, a slight vertical component magnetic force is generated, so that a horizontal magnetic force is slightly generated between (N) and (S). Almost no magnetic field appears. In such a configuration, the developer is directed from the S13 pole to (N) of the non-magnetic pole region NM. However, the magnetic lines of force connecting (N) and (S) of the non-magnetic pole region NM are very small. Is peeled off from the developing roller 231.

  On the other hand, referring to FIG. 3, FIG. 5A and FIG. 5B, the second magnet 232A of the transport roller 232 includes five magnetic poles along the circumferential direction. An N1 pole (third magnetic pole) is arranged on the downstream side in the second rotational direction (D2) of the facing position TP between the developing roller 231 and the transport roller 232. Further, the S1 pole is disposed downstream of the N1 pole in the second rotation direction. Furthermore, the S2 pole is arranged at an interval on the downstream side of the S1 pole in the second rotation direction. The S1 pole functions as a peeling pole for peeling the developer from the transport roller 232. The S2 pole, which is the same polarity as the S1 pole, functions as a pumping top that pumps up the developer from the first screw 233A. An N2 pole and an S3 pole (first magnetic pole) are arranged downstream of the S2 pole in the second rotation direction. As shown in FIG. 5A, the layer thickness regulating member 235 is spaced a predetermined distance from the second sleeve 232B of the transport roller 232 between the N2 pole and the S2 pole, upstream of the S3 pole in the second rotational direction. Are arranged opposite to each other. In the present embodiment, the S2 pole mainly functions as a regulation pole. For this reason, the developer layer thickness can be stably regulated before the developer is transferred from the transport roller 232 to the developing roller 231. As a result, compared to the case where the layer thickness regulating member 235 is disposed on the developing roller 231 side, a large amount of developer is prevented from being conveyed on the conveying roller 232 and the developing roller 231, and the developing roller 231 and the conveying roller The driving torque of the roller 232 can be reduced. The S3 pole is disposed upstream of the opposing position TP in the second rotational direction, and the aforementioned N1 pole is disposed adjacent to the S3 pole downstream of the opposing rotational position in the second rotational direction. Yes.

  Table 2 shows the angles and magnetic forces (peak values of vertical components) of five magnetic poles as an example of the second magnet 232A according to the present embodiment. The angles of the magnetic poles shown in Table 2 are shown along the second rotation direction with the opposing position TP in FIG. 5A as the starting point (angle 0 °). In FIG. 5A, a straight line CL (a straight line connecting the rotation axis of the developing roller 231 and the rotation axis of the conveyance roller 232) connecting the facing position TP and the rotation axis of the conveyance roller 232 is shown as the start point. ing. The N1 pole of the second magnet 232A is arranged so that the peak position of the magnetic force faces the position at an angle of 330 degrees in Table 1 above.

  Further, the configuration and functions around the facing position TP of the first magnet 231A of the developing roller 231 and the second magnet 232A of the transport roller 232 will be additionally described. In the first delivery section K1 (FIG. 6), the S3 pole arranged in the second magnet 232A on the developer delivery side and the first magnet 231A on the developer reception side are arranged to face the S3 magnetic pole. The developer is delivered by a magnetic field formed by the N11 pole, which is different from the S3 pole. On the other hand, in the second delivery part K2, the N1 pole opposite to the S3 pole and the first magnet 231A on the developer delivery side are arranged on the second magnet 232A on the developer receiving side and opposite to the N1 pole. The developer is transferred to and from the non-magnetic pole region NM where the magnetic pole is not formed. The developer that has passed through the development position NP is transferred from the developing roller 231 to the transport roller 232 by flying from the non-magnetic pole region NM and attracted to the N1 pole. The developer supplied from the first screw 233A of the stirring screw 233 to the transport roller 232 is regulated by the layer thickness regulating member 235, and then developed from the transport roller 232 by the magnetic field formed by the S3 pole and the N11 pole. Delivered to the roller 231.

  With reference to FIG. 6, the housing 23 </ b> H includes a plurality of inner wall portions facing the developing roller 231 and the transport roller 232. Specifically, the housing 23H includes a first inner wall portion 23H1, a second inner wall portion 23H2, a third inner wall portion 23H3, and a fourth inner wall portion 23H4. The first inner wall portion 23H1 faces the S12 pole and the S13 pole and extends along the peripheral surface of the first sleeve 231B of the developing roller 231 from the developing position NP to a position facing the non-magnetic pole region NM (FIG. 4B). It is extended. The second inner wall portion 23H2 is connected to the first inner wall portion 23H1, is opposed to the N1 pole and the S1 pole, and extends along the peripheral surface of the second sleeve 232B of the transport roller 232. Similarly, the third inner wall portion 23H3 opposes the S11 pole and the N11 pole on the side opposite to the first inner wall portion 23H1, and the first sleeve 231B of the developing roller 231 from the developing position NP to a position facing the N11 pole. It is extended so that the surrounding surface of this may be followed. Between the first inner wall portion 23H1 and the third inner wall portion 23H3, the first sleeve 231B of the developing roller 231 is partially exposed and arranged to face the photosensitive drum 20. The fourth inner wall portion 23H4 is connected to the third inner wall portion 23H3, faces the N2 pole and the S3 pole, and extends along the peripheral surface of the second sleeve 232B of the transport roller 232. As shown in FIG. 6, a substantially uniform gap H (developer transport path) is formed between each inner wall and the first sleeve 231B of the developing roller 231 and the second sleeve 232B of the transport roller 232. Has been. In this embodiment, the height of the gap H is smaller than the radii of the developing roller 231 and the transport roller 232, and is set in the range of 0.5 mm to 2.0 mm. In addition, since it is necessary to adjust the position of the layer thickness regulating member 235, it is desirable that a part of the housing 23H including the third inner wall portion 23H3 and the fourth inner wall portion 23H4 is removable.

  As described above, a developing bias in which an AC bias is superimposed on a DC bias is applied to the developing roller 231 and the transport roller 232 during a developing operation for developing the electrostatic latent image on the photosensitive drum 20. As a result, an oscillating electric field due to an AC bias is formed at the development position NP (development nip), so that the fog toner adhered to the background portion on the photosensitive drum 20 can be collected. However, such an oscillating electric field attracts toner also onto the first sleeve 231B of the developing roller 231. As a result, a toner layer (toner film) is easily formed on the surface of the first sleeve 231B.

  The thickness of the toner layer formed on the first sleeve 231B of the developing roller 231 differs between the image portion and the background portion, and the difference in thickness remains as a history. FIG. 8 is a schematic diagram showing a ghost image generated on a halftone image due to such toner consumption history. A history of ring-shaped images formed on the upstream side in the process direction (sheet conveyance direction) appears on the subsequent halftone image. Such a history is based on the difference in toner consumption in the toner layer, and in the next halftone image, the potential difference between the first sleeve 231B and the photosensitive drum 20 is equal to the remaining toner charge. Is due to a partial shift.

  In this embodiment, in the developing device 23 in which two magnetic rollers (developing roller 231 and transport roller 232) are arranged, a thin toner layer is formed on the developing roller 231 that is one roller facing the photosensitive drum 20. The generation of the ghost image as described above is preferably suppressed. That is, in order to suppress such a ghost image, the developing roller 231 of the developing device 23 includes the S12 pole and the S13 pole (FIG. 6).

  Thus, the repulsive magnetic field is formed by the S12 pole and the S13 pole by arranging the magnetic poles of the same polarity adjacent to each other on the developing roller 231. Since the developer conveyed from the N12 pole of the developing roller 231 to the S12 pole is difficult to move to the S13 pole, it partially stays on the S12 pole. As a result, a developer retention portion TD is formed on the first sleeve 231B of the developing roller 231. In the stay part TD, the magnetic brush of the developer stays while slipping on the first sleeve 231B. Therefore, even if the history of the toner consumed at the development position NP remains in the toner layer on the first sleeve 231B, the toner history is eliminated (polished) by the magnetic brush of the developer staying in the stay portion TD. Is done. For this reason, the developing device 23 in which the occurrence of the ghost as described above is suppressed is provided. In particular, when the magnetic pole peak position does not exist at the opposing position TP between the developing roller 231 and the transport roller 232 as in the present embodiment, the polishing force (scraping power) of the developer magnetic brush on the transport roller 232 is high. It is difficult to reach the surface of the first sleeve 231B. Even in such a case, the staying part TD can be suitably formed by the repulsive force of the S12-S13 poles that the developing roller 231 has.

  In this embodiment, one developing roller 231 is disposed to face the photosensitive drum 20 and develops the electrostatic latent image on the photosensitive drum 20. Therefore, it is necessary to stably expose the electrostatic latent image at one development position NP as compared with other development devices in which a plurality of development rollers are arranged adjacent to each other along the circumferential surface of the photosensitive drum 20. There is. In other words, when a plurality of developing rollers are arranged along the rotation direction of the photosensitive drum 20 as described above, the downstream developing roller removes the density-decreasing portion of the ghost image formed by the upstream developing roller. It can be corrected. On the other hand, in the present embodiment, correction becomes difficult when the history of toner consumption formed on the first sleeve 231B of the developing roller 231 becomes a ghost image in the next round. Therefore, by providing the first magnet 231A with the S12 pole and the S13 pole, it is possible to suitably suppress the history of the toner layer from rotating toward the next development position NP. As a result, the structure of the developing device 23 is prevented from becoming complicated, and the cost of the developing device 23 is prevented from increasing.

  Further, in the present embodiment, the first sleeve 231B is made of an aluminum circular pipe member (base material). Further, the circumferential surface of the circular pipe member of the first sleeve 231B is subjected to sand blasting (blasting) and further includes a Ni plating layer applied on the circumferential surface. For this reason, the developer tends to slip due to the surface property of the first sleeve 231B subjected to the blasting process, and the developer retention portion TD is stably formed. Furthermore, the charge amount of the positively charged toner is likely to be reduced by the plating layer on the developing roller 231. As a result, the charge amount of the developer is reduced, the developer slip at the staying part TD is promoted, and the force with which the toner adheres to the sleeve surface is reduced. Therefore, the generation of ghost images is further suppressed. As will be described later, in other embodiments, the first sleeve 231B of the developing roller 231 is not subjected to blasting and may have a known groove shape. In this case, by performing peripheral polishing such as centerless processing before or after the groove formation, or by performing blasting after the groove formation, the adhesion force of the toner to the sleeve surface is reduced, and the ghost image is simply generated. Suppresses more than just the groove shape.

  The developer that can no longer be held by the magnetic force of the S12 pole will eventually fly from the staying part TD. As a result, the developer flying from the vicinity of the S12 pole moves to the S13 pole side and then moves to the non-magnetic pole region NM (FIG. 4B). As described above, in the non-magnetic pole region NM, the magnetic holding force of the developer is weak. For this reason, the developer is transferred from the developing roller 231 to the transport roller 232 by being attracted by the magnetic force of the opposing N1 pole. In other embodiments, even when the magnetic pole on the side of the transport roller 232 facing the non-magnetic pole region NM is composed of the S pole, the developer can be delivered in the same manner. Therefore, the developer can be transferred regardless of whether the magnetic pole on the downstream side of the reception of the second transfer portion K2 is the N pole or the S pole, and the degree of freedom in the arrangement of the magnetic pole of the second magnet 232A is increased.

  When the non-magnetic pole region NM is arranged opposite to the N1 pole as in the present embodiment, no strong magnetic attractive force is generated between the N1 pole and the non-magnetic pole region NM. For this reason, the magnetic attraction between the developing roller 231 and the transport roller 232 is stronger than in the case where the developer is delivered by the magnetic poles of different polarities in both the first delivery unit K1 and the second delivery unit K2. The force is reduced from working. Accordingly, the first magnet 231A and the second magnet 232A are prevented from bending along the axial direction inside the first sleeve 231B and the second sleeve 232B. As a result, in each roller, the magnets (magnet pieces) of the first magnet 231A and the first sleeve 231B drop off from a shaft (not shown), deformation of the shaft, and further, the first magnet 231A and the second magnet. It is suppressed that 232A, the 1st sleeve 231B, and the 2nd sleeve 232B contact. Further, it is possible to stably deliver the developer between the rollers.

  In this embodiment, as described above, the magnetic force of the vertical component of the N11 pole is zero on the non-magnetic pole region NM side, and the magnetic force of the vertical component of the S13 pole is non-magnetic. In the region between the second reference position J2 (FIG. 4B) that becomes 0 on the magnetic pole region NM side, the magnetic force of the horizontal component of the first magnet 231A is set to be larger than 0. For this reason, the developer conveyed from the S13 pole to the non-magnetic pole area NM is peeled off from the first sleeve 231B by the non-magnetic pole area NM. As a result, the separated developer is attracted by the opposing N1 pole, and stable delivery of the developer is realized. Further, in the region between the first reference position J1 and the second reference position J2, the magnetic force of the horizontal component of the first magnet 231A is set to 10 mT or less. For this reason, the developer can be peeled off more stably in the non-magnetic pole region NM. Further, in this embodiment, the interval between the peak positions of the N11 pole and the S13 pole is set to 100 degrees or more. For this reason, the non-magnetic pole region NM from which the developer can be peeled can be stably formed.

  The developer delivered from the transport roller 232 to the developing roller 231 is then used for developing the electrostatic latent image on the photosensitive drum 20 at the developing position NP. For this reason, it is desirable that the magnetic brush formed by the magnetic poles of different polarities be delivered smoothly without breaking the developer magnetic brush. In this case, the distribution of the developer amount at the development position NP can be made as uniform as possible along the axial direction. On the other hand, the developer from the developing roller 231 to the transport roller 232 is the developer after passing through the developing position NP. For this reason, the developer flying from the non-magnetic pole region NM may be delivered while the developer magnetic brush is broken by the N1 pole attracting the developer. Therefore, in this embodiment, it is preferable to form the non-magnetic pole region NM in the region where the developer is transferred from the developing roller 231 to the transport roller 232. As a result, the developer can be stably conveyed while weakening the magnetic attraction between the developing roller 231 and the conveying roller 232. Further, the non-magnetic pole region NM is arranged on the upstream side (development roller 231 side) of the second transfer portion K2, so that the peeling of the developer is promoted, and the developer on the development roller 231 moves toward the facing position TP. It is restrained from being conveyed.

  In this embodiment, as an example, the gap (development position NP) between the developing roller 231 and the photosensitive drum 20 is set to be larger than 0.25 mm and equal to or smaller than 0.40 mm. On the other hand, the gap (opposing position TP) between the developing roller 231 and the transport roller 232 is set to 0.18 mm or more and 0.25 mm or less. In other words, the gap between the developing roller 231 and the transport roller 232 is set to be narrower than the gap between the developing roller 231 and the photosensitive drum 20. Then, the developer is transferred between the developing roller 231 and the transport roller 232 so as to sandwich the opposing position TP set so narrow. As described above, the peak position of any magnetic pole does not face the facing position TP. For this reason, even if the gap at the facing position TP is set narrow as described above, the developer is prevented from sticking to the facing position TP due to the presence of the developer. Further, since two magnetic brushes for the developer to be transferred are formed so as to sandwich the facing position TP in the circumferential direction, even when the toner is scattered at the facing position TP, the toner can be contained.

  In this embodiment, with reference to FIG. 6, the axis of the developing roller 231 is disposed below the axis of the photosensitive drum 20, and the axis of the transport roller 232 is higher than the axis of the developing roller 231. It is arranged below. For this reason, the developer flying from the non-magnetic region NM is stably delivered to the conveying roller 232 side in combination with the action of gravity in addition to the magnetic force of the N1 pole. At this time, since the first inner wall portion 23H1 and the second inner wall portion 23H2 are connected to each other while being formed along the peripheral surfaces of the developing roller 231 and the conveying roller 232, the developer is supplied from the developing roller 231 to the conveying roller 232. It can be delivered smoothly.

  Further, as shown in FIG. 6, since the developer retaining portion TD is disposed in contact with or close to the first inner wall portion 23H1, the toner in the developer is prevented from scattering around the retaining portion TD. The Further, the toner in the developer is prevented from scattering to the development position NP side. Furthermore, since the developer transport path is limited, the developer movement range is restricted, and the developer retention portion TD can be formed stably. Similarly, in the first transfer portion K1 of the developer from the transport roller 232 to the developing roller 231, the developer is smoothly received from the transport roller 232 to the developing roller 231 by the third inner wall portion 23H3 and the fourth inner wall portion 23H4. Can pass.

Next, based on an Example, this invention is further demonstrated. In addition, this invention is not limited to a following example. In each experiment described later, the experiment was performed under the following experimental conditions.
<Experimental conditions>
Print speed: 55 sheets / min Photoconductor drum 20: Amorphous silicon photoconductor (a-Si), diameter φ30 mm, surface potential Vo (white background portion, background portion) = + 270 V, VL (image portion) = + 20 V, peripheral speed = 300mm / sec
A gap between the layer thickness regulating member 235 and the second sleeve 232B: 200 to 600 μm
-Developer conveyance amount (after layer thickness regulation) on the conveyance roller 232 and the developing roller 231: 100 to 300 g / m ²
Carrier: Volume average particle size 35 μm, magnetic force 80 emu / g, ferrite resin coated carrierToner: Volume average particle size 6.8 μm, toner concentration 7%, positive chargeability

The conditions of the developing roller 231 are as follows.
・ Developing roller 231: Diameter φ20 mm
-Peripheral speed ratio of the developing roller 231 to the photosensitive drum 20: 1.8 (same direction at the opposite position, with direction)
A gap between the developing roller 231 and the photosensitive drum 20: 300 μm
Development bias: DC bias = 170 V, AC bias = Vpp 1.4 kV, frequency f3.7 kHz, Duty 50%, rectangular wave (note that the transport roller 232 and the layer thickness regulating member 235 are also at the same potential).
Surface condition of the first sleeve 231B: sand blast (Rzjis 7 μm), Ni plating treatment The magnetic pole distribution of the developing roller 231 used in the experiment is the condition shown in Table 1 above. In addition, the magnetic force measurement of the following developing roller 231 and the conveyance roller 232 was performed using the Japan Electromagnetic Instrument Co., Ltd. In this case, the distance between the measuring element and each sleeve is 0.5 mm when measuring the magnetic force of the vertical component, and the distance between the measuring element and each sleeve is 1.5 mm when measuring the magnetic force of the horizontal component.

Moreover, the conditions of the conveyance roller 232 used for experiment are as follows.
・ Conveyance roller 232: Diameter φ20mm
-Surface condition of the second sleeve 232B: Knurled V groove (groove depth 80 μm, groove width 0.2 mm, number of grooves 120)
-Peripheral speed ratio of transport roller 232 to developing roller 231: 1.4 (reverse direction at counter position, counter direction)
-Gap between transport roller 232 and developing roller 231: 250 μm
Further, the magnetic pole distribution of the transport roller 232 used in the experiment is shown in Table 2 above.

  Under the above experimental conditions, the ghost confirmation pattern image shown in FIG. 8 was printed, and the number of generated ghosts was evaluated. The ghost confirmation pattern has five patterns (a donut-shaped original image) arranged in the horizontal direction, and a halftone image is formed behind the pattern. Each of the five halftone image patterns had different densities, and how many ghosts were generated in the halftone portion was evaluated. The ghost counts up to four laps from the original image, and a maximum of 20 ghosts are generated per print. Further, the above evaluation was performed by changing the development AC bias Vpp at five levels of 1.0 kV, 1.2 kV, 1.4 kV, 1.6 kV, and 1.8 kV (a total of 100 ghosts occurred). . As a result, the ghost was eliminated under any condition.

  In particular, ghosting was greatly improved by plating the first sleeve 231B. For positively charged toner, the first sleeve 231B is plated with Ni, whereby the chargeability of the toner is lowered and the staying portion TD is stably formed. In addition, when the aluminum or SUS background is exposed on the surface of the first sleeve 231B, a passive layer is formed on the surface. This passive layer is negatively charged and has the ability to increase the charge amount of positively charged toner. When the toner adhering on the first sleeve 231B of the developing roller 231 is charged in the above-described passive layer, the mirror image force of the toner is increased and the toner is more difficult to be separated from the surface of the first sleeve 231B. On the other hand, Ni plating is positively charged, and the charge amount of the toner can be easily reduced. As a result, the cleaning property at the S12 electrode is increased due to the slipperiness of the plated layer, and the charge of the toner is also reduced, so that the ghost is further eliminated.

  Further, after 1000 sheets were printed, the developing roller 231 and the transport roller 232 were disassembled, and the bending of the first magnet 231A and the second magnet 232A was measured. In both cases, an increase in the amount of bending was confirmed compared to before the experiment. There wasn't.

  In addition, about the 1st sleeve 231B, it turned out that the same result as the above was obtained as a result of performing the same evaluation in Rzjis 4 micrometers or more and 14 micrometers or less. Further, it was confirmed that there is no difference in Rzjis of the first sleeve 231B before and after plating when the Ni plating film thickness is in the range of 3 μm or more and 5 μm or less.

  In the above experiment, when the same evaluation as described above was performed in a toner concentration range of 5% to 12%, there was no change in the amount of developer stagnant portion TD, and the development ghost suppression effect was not changed. Similar results were obtained. Further, when the same evaluation is performed in the range where the diameter of the developing roller 231 and the conveying roller 232 is 16 mm or more and 35 mm or less and the peripheral speed of the photosensitive drum 20 is 200 mm / sec or more and 400 mm / sec or less, the development ghost Similar results were obtained with regard to the suppression effect and evaluation of the deflection of each magnet.

  The developing device 23 and the image forming apparatus 10 including the developing device 23 according to an embodiment of the present invention have been described in detail above, but the present invention is not limited to this. The present invention can take, for example, the following modified embodiments.

  (1) In the above embodiment, the non-magnetic pole region NM has been described as being disposed on the first magnet 231A side of the developing roller 231, but the present invention is not limited to this. FIG. 9 is a schematic cross-sectional view showing the magnetic pole arrangement of the developing roller 231M and the conveying roller 232M of the developing device according to a modified embodiment of the present invention. The developing roller 231M includes a first magnet 231AM and a first sleeve 231BM. Further, the transport roller 232M includes a second magnet 232AM and a second sleeve 232BM. In this modified embodiment, the developer is transferred from the S13 pole of the first magnet 231AM toward the N1 pole of the second magnet 232AM (corresponding to the second transfer portion K2). On the other hand, a non-magnetic pole region (not shown) is formed between the S2 pole and the N1 pole of the second magnet 232AM, similarly to the non-magnetic pole area NM according to the previous embodiment. Then, the developer is transferred from the non-magnetic region of the second magnet 232AM toward the N11 pole of the first magnet 231AM (corresponding to the first transfer portion K1). For this reason, compared with the case where a developer is delivered by magnetic poles of different polarities in both the first delivery unit and the second delivery unit, a stronger magnetic attraction force is generated between the developing roller 231M and the transport roller 232M. Work is reduced. For this reason, in each roller, it is suppressed that a magnet falls and that a magnet and a sleeve contact. Further, it is possible to stably deliver the developer between the rollers.

  (2) In the above-described embodiment, the layer thickness regulating member 235 has been described as being disposed so as to face the transport roller 232, but the present invention is not limited to this. The layer thickness regulating member 235 may be disposed to face the periphery of the S11 pole of the developing roller 231 and the like. In this case, another magnetic pole for transporting the developer may be added to the first magnet 231A.

  (3) In the above-described embodiments and examples, the developing roller 231, the transport roller 232, and the layer thickness regulating member 235 have been described as being set to the same potential. However, the present invention is limited to this. is not. Individual developing biases may be applied to the developing roller 231 and the transport roller 232. The layer thickness regulating member 235 may be in a floating state in terms of potential.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Apparatus main body 13 Image forming part 14 Intermediate transfer unit (transfer part)
145 Secondary transfer roller (transfer section)
20 Photosensitive drum (image carrier)
23 Developing device 231 Developing roller 231A First magnet 231B First sleeve 232 Conveying roller 232A Second magnet 232B Second sleeve 233 Stirring screw 233A First screw 233B Second screw 234 Partition plate 235 Layer thickness regulating member 23H Housing 23H1 First inner wall Part 23H2 Second inner wall part 23H3 Third inner wall part 23H4 Fourth inner wall part 24 Primary transfer roller K1 First delivery part K2 Second delivery part NM Non-magnetic pole area NP Development position TP Opposite position

Claims (9)

A first magnet including a plurality of magnetic poles fixed along the circumferential direction; a first sleeve that rotates around the first magnet in a first rotational direction and carries a developer containing toner and a magnetic carrier on the circumferential surface; A developing roller that is arranged opposite to a photosensitive drum on which an electrostatic latent image is formed at a predetermined development position and supplies the toner to the photosensitive drum;
A roller disposed to face the developing roller at a predetermined facing position, and a second magnet fixed including a plurality of magnetic poles along a circumferential direction, and facing the first rotation direction at the facing position A second roller that rotates around the second magnet in a second rotation direction set so as to carry the developer on a peripheral surface thereof, and a conveying roller that supplies the developer to the developing roller; ,
A developer agitating unit for agitating the developer and supplying the developer to the transport roller;
A first delivery section that is arranged adjacent to the facing position and delivers the developer from the transport roller to the development roller;
A second delivery unit that is disposed so as to sandwich the facing position with the first delivery unit, and delivers the developer from the development roller to the transport roller;
With
Wherein in one of the first transfer portion and the second transfer unit, a first pole of a predetermined polarity disposed on the side for feeding the developer of the first magnet and said second magnet, said first Of the one magnet and the second magnet, the developer is received by a magnetic field formed by a second magnetic pole different from the first magnetic pole, which is disposed on the side receiving the developer and opposed to the first magnetic pole. The other one of the first delivery portion and the second delivery portion is disposed on the side of the first magnet and the second magnet that receives the developer and has a polarity different from that of the first magnetic pole. The three magnetic poles and the development between the first magnet and the second magnet formed on the side where the developer is sent out so as to face the third magnetic pole, where no magnetic pole is disposed. The drug will be handed over To the plurality of magnetic poles of the first magnet and said second magnet is arranged,
Of the first magnet and the second magnet, the magnet in which the non-magnetic pole region is formed is different from the second magnetic pole disposed so as to sandwich the non-magnetic pole region with the second magnetic pole. The fourth magnetic pole
A first reference position where the magnetic force of the vertical component of the second magnetic pole is zero on the non-magnetic pole region side, and a second reference position where the magnetic force of the vertical component of the fourth magnetic pole is zero on the non-magnetic pole region side; In the region between, the magnetic force of the horizontal component of the magnet is set larger than 0,
In the region between the first reference position and the second reference position, the magnetic force of the horizontal component of the magnet is set to 10 mT or less . A first magnet including a plurality of magnetic poles fixed along the circumferential direction; a first sleeve that rotates around the first magnet in a first rotational direction and carries a developer containing toner and a magnetic carrier on the circumferential surface; A developing roller that is arranged opposite to a photosensitive drum on which an electrostatic latent image is formed at a predetermined development position and supplies the toner to the photosensitive drum;
A roller disposed to face the developing roller at a predetermined facing position, and a second magnet fixed including a plurality of magnetic poles along a circumferential direction, and facing the first rotation direction at the facing position A second roller that rotates around the second magnet in a second rotation direction set so as to carry the developer on a peripheral surface thereof, and a conveying roller that supplies the developer to the developing roller; ,
A developer agitating unit for agitating the developer and supplying the developer to the transport roller;
A first delivery section that is arranged adjacent to the facing position and delivers the developer from the transport roller to the development roller;
A second delivery unit that is disposed so as to sandwich the facing position with the first delivery unit, and delivers the developer from the development roller to the transport roller;
With
One of the first delivery part and the second delivery part is provided with a first magnetic pole having a predetermined polarity and disposed on a side of the first magnet and the second magnet for delivering the developer; Of the magnet and the second magnet, the developer is received by a magnetic field formed by a second magnetic pole which is disposed on the side receiving the developer and is opposed to the first magnetic pole and is different from the first magnetic pole. The other of the first delivery part and the second delivery part is arranged on the side of the first magnet and the second magnet that receives the developer and has a third polarity different from that of the first magnetic pole. The developer between a magnetic pole and a non-magnetic pole region in which the magnetic pole is not disposed and formed on the side of the first magnet and the second magnet that faces the third magnetic pole on the developer sending side Will be delivered To the plurality of magnetic poles of the first magnet and said second magnet is arranged,
Of the first magnet and the second magnet, the magnet in which the non-magnetic pole region is formed is different from the second magnetic pole disposed so as to sandwich the non-magnetic pole region with the second magnetic pole. The fourth magnetic pole
A first reference position where the magnetic force of the vertical component of the second magnetic pole is zero on the non-magnetic pole region side, and a second reference position where the magnetic force of the vertical component of the fourth magnetic pole is zero on the non-magnetic pole region side; In the region between, the magnetic force of the horizontal component of the magnet is set larger than 0 ,
The second magnetic pole, the fourth magnetic pole, and the non-magnetic pole region are disposed in the first magnet of the developing roller, and the first magnetic pole and the third magnetic pole are disposed in the second magnet of the transport roller;
The first magnet of the developing roller includes a fifth magnetic pole disposed adjacent to the fourth magnetic pole on the upstream side in the first rotation direction of the fourth magnetic pole and having the same polarity as the fourth magnetic pole. A developing device. Claim 1, the angle between the peak position of the magnetic force of the vertical direction component of the second magnetic pole of said fourth magnetic pole and the peak position of the magnetic force of the vertical direction component, characterized in that it is set to 100 degrees or more Or the developing device according to 2 ; Is arranged to face the conveying roller, wherein the developer agitating portion of the claims 1 to 3, characterized by further comprising a layer thickness regulating member for regulating the layer thickness of the developer supplied to the transport roller The developing device according to claim 1. Wherein the first sleeve of the developing roller, a developing apparatus according to any one of claims 1 to 4, characterized in that it comprises a substrate blast processing is applied to the surface. The developing device according to claim 5 , wherein the first sleeve of the developing roller includes a plating layer applied to the surface of the base material. The axial center of the developing roller is disposed below the axial center of the photosensitive drum,
The developing device according to claim 2 , wherein an axis of the transport roller is disposed below an axis of the developing roller. Wherein the developing roller, a developing apparatus according to any one of claims 1 to 7, characterized in that the developing bias AC bias on a DC bias is superposed is applied. A developing device according to any one of claims 1 to 8 ,
The photosensitive drum that is supplied with the toner from the developing device and carries a toner image on the peripheral surface;
A transfer unit for transferring the toner image from the photosensitive drum to a sheet;
An image forming apparatus comprising:

Images