JP2011150185A - Developing device and image forming apparatus equipped therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that solves the nonconformities of developing "image ghosts", by fully scraping off a highly charged toner and small-particle diameter toner on a toner carrier, and to provide an image forming apparatus equipped with the device. <P>SOLUTION: The developing device 10 includes a developer carrier 33 for carrying a developer layer D by means of the magnetic force of first and second magnetic poles 57 and 58; a first toner carrier 34 for supplying toner T, received from the developer layer D, to an image carrier 17; a second toner carrier 35, disposed downstream of the first toner carrier 34 and used for supplying the toner T, received from the developer layer D, to the image carrier 17; the first toner carrier 34 has a third magnetic pole 63 located opposite the first magnetic pole 57 and having the reverse polarity of the first magnetic pole 57; the second toner carrier 35 has a fourth magnetic pole 66 located opposite the second magnetic pole 58 and having the reverse polarity of the second magnetic pole 58; and the magnetic force of the fourth magnetic pole 66 is set larger than that of the third magnetic pole 63. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a developing device used for electrophotographic image formation, and an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

  An image forming apparatus such as a copying machine, a printer, or a facsimile using an electrophotographic system supplies a developer to an electrostatic latent image formed on an image carrier (for example, a photosensitive drum or a transfer belt) and supplies the developer. A developing device that forms a toner image on the image carrier by developing the electrostatic latent image is included.

  Recent development apparatuses are required to further increase the development speed while maintaining high image quality of toner images. As a developing device that meets the demand for higher speed, for example, the one disclosed in Patent Document 1 is known.

  The developing device of Patent Document 1 is provided with a developer carrying member carrying a developer including toner and a carrier, a first developing roller arranged on the upstream side when viewed from the rotation direction of the developer carrying member, and a downstream side. And a second developing roller. The first developing roller and the second developing roller receive only toner from the developer carrier due to a potential difference between the developer carrier and develop the electrostatic latent image on the image carrier with the toner. In the developing device of Patent Document 1, the first developing roller and the second developing are set by setting the bias voltage applied to the first developing roller to be larger than the bias voltage applied to the second developing roller. The ratio of development is made substantially uniform between the rollers. Thereby, the developing operation can be speeded up.

JP 2005-37523 A

  However, in the developing device of Patent Document 1, toner that has not been used for development in the first developing roller on the upstream side is supplied to the second developing roller. Therefore, highly charged toner or small particles are placed on the second developing roller. There will be a large number of toners having a diameter. Highly charged toner and small particle size toner are difficult to peel off from the second developing roller by a magnetic brush on the developer carrying member. Therefore, the highly charged toner and the small particle size toner are not sufficiently peeled off, and the high charged toner and the small particle size toner are likely to be deposited on the second developing roller. As a result, inconvenience such as so-called development ghost occurs.

  Therefore, the present invention provides a developing device capable of sufficiently removing the highly charged toner and the small particle size toner on a toner carrying member such as a developing roller to eliminate problems such as a developing ghost, and the like. Another object of the present invention is to provide an image forming apparatus.

  In order to achieve the above object, a developing device according to the present invention includes a developer storage section that stores a developer containing non-magnetic toner and a magnetic carrier while stirring, and a first magnetic pole having different polarities. A developer carrying member having the second magnetic pole and rotating in a predetermined direction, receiving the developer from the developer reservoir and carrying the developer layer by the magnetic force of the first magnetic pole and the second magnetic pole. And a first toner carrier that is disposed opposite to the developer carrier and carries the toner received from the developer layer on the developer carrier and supplies the toner to a predetermined image carrier. The developer layer disposed opposite to the developer carrier and disposed downstream of the first toner carrier as viewed from the rotation direction of the developer carrier, and the developer layer on the developer carrier Carrying the toner received from A second toner carrier for supplying the toner to the predetermined image carrier, and the first toner carrier has a polarity opposite to the first magnetic pole at a position facing the first magnetic pole. The second toner carrier has a fourth magnetic pole having a polarity opposite to the second magnetic pole at a position opposite to the second magnetic pole, and the magnetic force of the fourth magnetic pole is The magnetic force of the third magnetic pole is set larger.

  In the developing device according to the present invention, the total amount of toner received from the developer layer on the developer carrier by the first toner carrier is not supplied to the image carrier. Toner and toner having a small particle diameter are likely to remain on the first toner carrier. However, the third magnetic pole can peel the residual toner from the first toner carrier by its magnetic force, and the peeled toner acts between the third magnetic pole and the first magnetic pole opposite to the third magnetic pole. It is recovered in the developer layer by a magnetic field.

  As the developer carrier rotates, the second toner carrier located downstream from the first toner carrier is supplied with toner from the developer layer. The toner supplied onto the second toner carrier contains a large amount of highly charged toner and small particle size toner that the first toner carrier could not supply to the image carrier. For this reason, the proportion of the high-charged toner and the small particle size toner in the toner existing on the second toner carrier is larger than that in the case of the first toner carrier. However, since the magnetic force of the fourth magnetic pole is set larger than the magnetic force of the third magnetic pole, even when a large amount of highly charged toner or small particle size toner is attached to the second toner carrier, Such toner can be peeled off from the second toner carrier. The peeled toner is collected in the developer layer by a magnetic field that acts between the fourth magnetic pole and the second magnetic pole opposite to the fourth magnetic pole. As a result, it is possible to suppress the occurrence of inconveniences such as a development ghost caused by the highly charged toner or the small particle size toner remaining and depositing on the second toner carrier.

  In a preferred embodiment of the present invention, the third magnetic pole is arranged so as to be shifted downstream by a first angle from a position facing the first magnetic pole when viewed from the rotation direction of the developer carrier. The fourth magnetic pole is arranged to be shifted to the downstream side by a second angle from a position facing the second magnetic pole when viewed from the rotation direction of the developer carrier.

  According to this configuration, the range covered by the magnetic field between the third magnetic pole and the first magnetic pole can be increased downstream, and the range covered by the magnetic field between the fourth magnetic pole and the second magnetic pole can be reduced downstream. Therefore, the recoverability of recovering residual toner from the first toner carrier to the developer layer and the recoverability of recovering residual toner from the second toner carrier can be improved.

  In another preferred embodiment of the present invention, the second angle is set larger than the first angle.

  According to this configuration, since the second angle is set to be larger than the first angle, the range covered by the magnetic field between the fourth magnetic pole and the second magnetic pole can be further increased. Thereby, the recoverability of recovering the residual toner from the second toner carrier can be further improved.

  An image forming apparatus according to the present invention includes an image carrier on which a toner image is formed, a developing device that supplies toner to the image carrier and forms the toner image on the image carrier, and the toner image The image forming apparatus includes a transfer member to be transferred onto a sheet and a fixing unit that fixes the toner image on the sheet onto the sheet.

  Since the image forming apparatus according to the present invention employs a developing device that is highly recoverable for highly charged toner and small particle size toner that are difficult to supply to the image carrier, image ghost caused by such toner is used. And inconveniences such as a decrease in image density can be suppressed from occurring in the toner image on the image carrier.

  According to the developing device and the image forming apparatus of the present invention, it is possible to sufficiently remove the highly charged toner and the small particle size toner on the toner carrying member such as the developing roller, thereby eliminating problems such as a developing ghost. It is.

1 is a cross-sectional view illustrating an internal structure of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view schematically showing an internal structure of a developing device used in an image forming apparatus. It is sectional drawing which shows the other structure of a developing device. FIG. 4 is a partially enlarged view of the developing device and shows a developing operation of the developing device. It is a figure which shows the result of the experiment about the development ghost and image density which were performed using the image development apparatus. It is a figure which shows the example of the image printed in experiment. FIG. 7 is a diagram illustrating a state where a development ghost has occurred in the printed image of FIG. 6.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing the internal structure of the image forming apparatus. In this embodiment, a color printer is illustrated as an example of an image forming apparatus. The image forming apparatus 1 is connected to a personal computer (not shown) or the like directly or via a LAN. The image forming apparatus 1 is provided below the apparatus main body 200 and is configured to be able to supply paper to the apparatus main body 200. Supply unit 130. The image forming apparatus 1 also includes other components provided in a general image forming apparatus such as a control circuit that controls the operation of the image forming apparatus 1.

  As shown in FIG. 1, the apparatus main body 200 includes an image forming unit 93, an exposure device 94, an intermediate transfer unit 92, a fixing unit 97, and a paper discharge unit 96.

  The image forming unit 93 includes a photosensitive drum 17 (image carrier) that carries a corresponding color toner image, and a developing device 10 that supplies the corresponding color toner to the photosensitive drum 17 (yellow developing device 10Y, magenta). Development device 10M, cyan development device 10C, and black development device 10K).

  As the photoreceptor drum 17, a photoreceptor drum using an amorphous silicon (a-Si) material can be used.

  Around the photosensitive drum 17, in addition to the developing device 10 (10Y, 10M, 10C, 10K), a charger 15, a transfer roller 19, and a cleaning device (not shown) are arranged. The charger 15 uniformly charges the drum surface of the photosensitive drum 17. The charged drum surface of the photosensitive drum 17 is exposed by an exposure device 94 to form an electrostatic latent image. Each of the developing devices 10Y, 10M, 10C, and 10K uses a toner of each color supplied from a yellow toner container 900Y, a magenta toner container 900M, a cyan toner container 900C, and a black toner container 900K. The electrostatic latent image formed on the drum surface of the drum 17 is developed (visualized). As a result, a toner image is formed on the drum surface of the photosensitive drum 17. The transfer roller 19 forms a nip portion with the photosensitive drum 17 across the intermediate transfer belt 921, and primarily transfers the toner image on the photosensitive drum 17 onto the intermediate transfer belt 921. The cleaning device cleans the drum surface of the photosensitive drum 17 after the toner image is transferred.

  The intermediate transfer unit 92 includes an intermediate transfer belt 921, a driving roller 922, and a driven roller 923. On the intermediate transfer belt 921, toner images are primarily transferred from the plurality of photosensitive drums 17 in an overcoated state. This toner image is secondarily transferred to the paper supplied from the paper supply unit 130 by the secondary transfer unit 98. The driving roller 922 and the driven roller 923 drive the intermediate transfer belt 921 to rotate.

  The fixing unit 97 performs a fixing process on the toner image on the sheet on which the toner image is secondarily transferred, and forms a fixing roller 971 with a built-in heat source, and a fixing nip portion with the fixing roller 971. Pressure roller 972. The sheet on which the fixing process has been completed is conveyed toward a discharge unit 96 formed on the upper part of the apparatus main body 200.

  The paper discharge unit 96 includes a discharge roller pair 961, and discharges the paper conveyed from the fixing unit 97 onto the paper discharge tray 911 by the rotation of the discharge roller pair 961.

  The paper supply unit 130 is detachably attached to the housing 90 of the apparatus main body 200 and is detachably attached to the front cover 23 of the apparatus main body 200 in the front (rightward in the drawing). And a manual feed tray 40. Between the paper supply unit 130 and the secondary transfer unit 98, a paper feed conveyance path 24 through which the paper from the paper supply unit 130 is conveyed is provided. A plurality of conveyance roller pairs 27 for feeding paper to the secondary transfer unit 98 are provided in the paper feed conveyance path 24.

  The papers placed on the paper placement surface 42 of the manual feed tray 40 are fed one by one to the paper feed conveyance path 24 and introduced into the secondary transfer unit 98 by the rotation of the conveyance roller pair 27. On the other hand, the paper placed on the paper placement surface 43 of the paper cassette 41 is fed out one by one to the paper feed conveyance path 24 by driving the pickup roller 44 and the like, and is rotated by the rotation of the conveyance roller pair 27. It is introduced into the next transfer section 98.

  In the image forming apparatus 1 described above, the image forming unit 93 has a configuration capable of forming a full-color image as described above, but is not limited to this, and is not limited to a monochrome image or a color that is not full-color. It may be configured to form an image.

  FIG. 2 is a cross-sectional view schematically showing the internal structure of the developing device 10. The developing device 10 includes a developing container 31 that defines an internal space thereof. Within the internal space, the developing device 10 includes a developer reservoir 32 formed at the bottom of the developer container 31, a magnet roller 33 (developer carrier) disposed above the developer reservoir 32, and A first developing roller 34 (first toner carrier) and a second developing roller 35 (second toner carrier) disposed opposite to the magnet roller 33 at a position above the magnet roller 33, and opposed to the magnet roller 33. Developer control blade 36.

  The developer storage unit 32 stores a developer containing non-magnetic toner and a magnetic carrier, and can transport the developer while stirring. It is composed of two adjacent developer storage chambers 32a and 32b extending in the direction. The developer storage chambers 32 a and 32 b are partitioned from each other in the longitudinal direction by a partition plate 37 formed integrally with the developing container 31, but communicate with each other at both ends in the longitudinal direction. Further, screw feeders 38 and 39 for stirring the developer by rotation are rotatably mounted in the developer storage chambers 32a and 32b. Since the screw feeders 38 and 39 are set to rotate in opposite directions, the developer is conveyed between the developer storage chamber 32a and the developer storage chamber 32b while being stirred. By this stirring, the toner made of a non-magnetic material and the carrier made of a magnetic material are mixed to charge the toner.

  The magnet roller 33 is disposed so as to extend in the longitudinal direction of the developing device 10, and includes a hollow magnet sleeve 51 that can rotate clockwise in FIG. 2 and a rotation shaft (not shown) that rotates the magnet sleeve 51. A so-called magnet roll extending in the axial direction of the magnet sleeve 51 is incorporated in the internal space of the magnet sleeve 51. The magnet roll is supported in a fixed state on the support shaft 56 and does not rotate with the magnet sleeve 51. The magnet roll is formed with a pumping pole 53 for magnetically pumping up the developer from the developer reservoir 32 onto the peripheral surface 52 of the magnet sleeve 51. The developer thus pumped up is magnetically held as a developer layer on the peripheral surface 52 of the magnet sleeve 51 and is conveyed toward the developer regulating blade 36 as the magnet sleeve 51 rotates.

  The developer regulating blade 36 regulates the layer thickness of the developer layer that is magnetically attached to the peripheral surface 52 of the magnet sleeve 51. The developer regulating blade 36 is a plate member made of a magnetic material extending along the longitudinal direction of the magnet sleeve 51, and is supported at an appropriate position of the developing container 31. Further, the developer regulating blade 36 has a front end portion 54 that forms a predetermined regulating gap with the peripheral surface 52 of the magnet sleeve 51.

  The magnet roll in the magnet sleeve 51 is provided with a regulating pole 55 disposed opposite to the tip 54 of the developer regulating blade 36 in addition to the scooping pole 53. Therefore, the developer regulating blade 36 made of a magnetic material is magnetized by the regulating pole 55 of the magnet roller 33 and is magnetized between the tip 54 of the developer regulating blade 36 and the regulating pole 55, that is, in the regulating gap. A path is formed.

  The magnet roll further includes a first transport pole 57 (first magnetic pole), a second transport pole 58 (second magnetic pole), and a separation pole 59. The first transport pole 57 is a magnetic pole formed on the downstream side of the regulation pole 55 when viewed from the rotation direction of the magnet sleeve 51. The second transport pole 58 is a magnetic pole formed on the downstream side of the first transport pole 57 when viewed from the rotation direction of the magnet sleeve 51. The first transport pole 57 and the second transport pole 58 have different polarities from each other, and the developer layer formed on the peripheral surface 52 is in contact with the first developing roller 34 and the second developing roller (to be described later) as the magnet sleeve 51 rotates. When being conveyed toward the developing roller 35, the developer layer is held on the peripheral surface 52. The peeling pole 59 is a magnetic pole formed on the downstream side of the second conveying pole 58 when viewed from the rotation direction of the magnet sleeve 51, and after the developer layer on the peripheral surface 52 has passed through the second developing roller 35, It has a polarity for returning the developer layer to the developer reservoir. Note that the pumping pole 53, the regulation pole 55, the first transport pole 57, the second transport pole 58, and the peeling pole 59 have substantially the same longitudinal dimension as the magnet sleeve 51.

  The first developing roller 34 is disposed so as to extend in parallel to the magnet sleeve 51. In FIG. 2, a hollow first developing sleeve 61 that can rotate clockwise, and a first developing sleeve 61 that rotates the first developing sleeve 61 are omitted. Rotation axis. As will be described later, the first developing sleeve 61 receives only toner from the developer layer on the circumferential surface 52 of the magnet sleeve 51 and carries the toner on the circumferential surface 67 thereof.

  A magnet roll extending in the axial direction of the first developing sleeve 61 is built in the internal space of the first developing sleeve 61. The magnet roll is supported in a fixed state on the support shaft 62 and does not rotate with the first developing sleeve 61. The magnet roll is first peeled off at a position facing the first transport pole 57 of the magnet roller 33 and at a position where the peripheral surface 67 of the first developing sleeve 61 is closest to the peripheral surface 52 of the magnet sleeve 51. A pole 63 (third magnetic pole) is formed. In FIG. 2, the first transport pole 57 and the first stripping pole 63 are on a virtual line L1 connecting the axis C1 (FIG. 4) of the magnet roller 33 and the axis C2 (FIG. 4) of the first developing roller 34. It is set to be located.

  The second developing roller 35 is disposed downstream of the first developing sleeve 61 as viewed from the rotation direction of the magnet sleeve 51 and so as to extend in parallel to the magnet sleeve 51 and the first developing sleeve 61. 2 includes a hollow second developing sleeve 64 that can rotate clockwise, and an unillustrated rotating shaft that rotates the second developing sleeve 64. The second developing sleeve 64 receives only the toner from the developer layer on the peripheral surface 52 of the magnet sleeve 51 and carries the toner on the peripheral surface 68 as will be described later.

  A magnet roll extending in the axial direction of the second developing sleeve 64 is incorporated in the internal space of the second developing sleeve 64. The magnet roll is supported in a fixed state on the support shaft 65 and does not rotate with the second developing sleeve 64. The magnet roll is second peeled off at a position facing the second transport pole 58 of the magnet roller 33 and at a position where the peripheral surface 68 of the second developing sleeve 64 is closest to the peripheral surface 52 of the magnet sleeve 51. A pole 66 (fourth magnetic pole) is formed. In FIG. 2, the second transport pole 58 and the second stripping pole 66 are positioned on a virtual line L2 connecting the axis C1 of the magnet roller 33 and the axis C3 of the second developing roller 64 (FIG. 4). Is set.

  The first stripping pole 63 of the first developing roller 34 is set so as to have a polarity opposite to that of the first conveying pole 57 of the magnet roller 33 and to have a polarity opposite to the charging polarity of the toner. Yes. Further, the second stripping pole 66 of the second developing roller 35 is set to have a polarity opposite to that of the second transport pole 58 of the magnet roller 33 and to a polarity opposite to the charging polarity of the toner. Has been. The magnetic force of the second stripping pole 66 is set larger than the magnetic force of the first stripping pole 63. For example, the magnetic force of the second stripping pole 66 is set to 45 mT, and the magnetic force of the first stripping pole 63 is set to 35 mT. The first stripping electrode 63 and the second stripping electrode 66 have longitudinal dimensions that are substantially the same as the longitudinal dimensions of the first transport pole 57 and the second transport pole 58.

  As described above, the first stripping electrode 63 may be disposed opposite to the first transport pole 57 and the second stripping electrode 66 may be disposed facing the second transport pole 58. As viewed from the rotational direction of the magnet sleeve 51 and shifted to the downstream side by a predetermined angle from the position facing the first conveying pole 57, and the second stripping pole 66 is viewed from the rotational direction of the magnet sleeve 51. Thus, it may be arranged so as to be shifted downstream by a predetermined angle from the position facing the second transport pole 58. In the preferred embodiment of the present invention, as shown in FIG. 3, the first stripping pole 63 is arranged to be shifted to the downstream side by the first angle α with respect to the virtual line L1, and the second stripping pole. 66 is arranged to be shifted downstream by the second angle β with respect to the virtual line L2. The first angle α and the second angle β are set to 5 °, for example.

  As described above, the first stripping pole 63 and the second stripping pole 66 are arranged so as to be shifted to the downstream side, so that the range of the magnetic field generated between the first stripping pole 63 and the first transport pole 57 is covered. (So-called development nip width) can be increased on the downstream side in the rotational direction in the circumferential direction of the first developing roller 34 and the magnet sleeve 51, and between the second stripping electrode 66 and the second transporting pole 58. The range (development nip width) covered by the magnetic field generated in (2) can be increased on the downstream side in the rotational direction in the circumferential direction of the second developing roller 35 and the magnet sleeve 51.

  In a preferred embodiment of the present invention, the second angle β of the second stripping pole 66 is set larger than the first angle α of the first stripping pole 63. By doing so, the range covered by the magnetic field between the second stripping pole 66 and the second transport pole 58 is further increased on the downstream side in the rotational direction in the circumferential direction of the second developing roller 35 and the magnet sleeve 51. be able to. In this case, for example, the first angle α is set to 5 °, and the second angle β is set to 7.5 °.

  Hereinafter, the developing operation and its action by the developing device 10 configured as described above will be described with reference to FIGS.

  First, the non-magnetic toner is charged by being stirred together with the magnetic carrier in the developer reservoir 32. The developer containing the carrier and the charged toner is pumped up from the developer reservoir 32 onto the peripheral surface 52 of the magnet sleeve 51 by the magnetic force of the pumping pole 53 of the magnet roller 33. The developer thus pumped up is magnetically held as a developer layer on the peripheral surface 52 of the magnet sleeve 51 and is conveyed toward the developer regulating blade 36 as the magnet sleeve 51 rotates.

  The developer regulating blade 36 regulates the developer layer on the peripheral surface 52 in the regulation gap to make it uniform and thin. As a result, a developer layer (hereinafter referred to as a magnetic brush layer D) having a predetermined thickness is formed on the peripheral surface 52.

  The magnetic brush layer D on the peripheral surface 52 is conveyed toward the first developing roller 34 as the magnet sleeve 51 rotates. A predetermined bias is applied to each of the magnet sleeve 51 and the first developing sleeve 61, and only the toner T from the magnetic brush layer D is first in the position upstream of the first transport pole 57 due to the potential difference therebetween. It moves to the peripheral surface 67 of the developing sleeve 61. As a result, a toner layer having a predetermined thickness is formed on the peripheral surface 67.

  The toner layer on the peripheral surface 67 is conveyed toward the drum surface of the photosensitive drum 17 as the first developing sleeve 61 rotates. Since a predetermined bias is also applied to the photosensitive drum 17, the toner T in the toner layer moves to the drum surface of the photosensitive drum 17 due to a potential difference between the photosensitive drum 17 and the first developing sleeve 61. Thereby, the electrostatic latent image on the drum surface is developed.

  Incidentally, the degree of charging of the toner T varies. Therefore, the entire amount of toner T received by the first developing sleeve 61 from the magnetic brush layer D on the magnet sleeve 51 does not move to the photosensitive drum 17, but a part of toner TA, for example, highly charged toner or small particles The toner having the diameter tends to remain on the peripheral surface 67 of the first developing sleeve 61 after passing through the photosensitive drum 17. The residual toner TA is conveyed toward the magnetic brush layer D on the peripheral surface 52 of the magnet sleeve 51 with the rotation of the first developing sleeve 61. However, since the adhesive force to the peripheral surface 67 is strong, the magnetic brush layer D. Difficult to be recovered by.

  However, in the present embodiment, the first developing roller 34 is provided with the first stripping pole 63 having a polarity opposite to the charging polarity of the toner, so that the residual toner TA on the peripheral surface 67 is the first stripping. It is peeled off from the peripheral surface 67 by the magnetic force of the electrode 63. The residual toner TA thus peeled off is collected in the magnetic brush layer D by a magnetic field generated between the first stripping pole 63 and the first transport pole 57 substantially opposite to the first stripping pole 63. In the present embodiment, the magnetic field between the first stripping pole 63 and the first transport pole 57 is arranged by shifting the first stripping pole 63 downstream from the virtual line L1 by the first angle α. Therefore, the recoverability of recovering the residual toner TA to the magnetic brush layer D can be improved.

  The magnetic brush layer D from which the residual toner TA has been collected is transported toward the second developing sleeve 64 as the magnet sleeve 51 rotates. Since a predetermined bias is also applied to the second developing sleeve 64, only the toner T from the magnetic brush layer D is positioned upstream of the second conveying pole 58 due to the potential difference between the magnet sleeve 51 and the second developing sleeve 64. Moves to the peripheral surface 68 of the second developing sleeve 64. As a result, a toner layer having a predetermined thickness is formed on the peripheral surface 68.

  The toner layer on the peripheral surface 68 contains a large amount of the highly charged toner TA and the small particle size toner TA that the first developing sleeve 61 could not supply to the photosensitive drum 17. The ratio of the charged toner TA and the small particle size toner TA is larger than that of the toner layer on the first developing sleeve 61. Therefore, although the toner layer is conveyed toward the photosensitive drum 17 as the second developing sleeve 64 rotates, only a small amount of toner T in the toner layer develops the electrostatic latent image on the photosensitive drum 17. Most of the toner (that is, the highly charged toner TA and the small particle size toner TA) remains on the peripheral surface 68 after passing through the photosensitive drum 17. The residual toner TB is conveyed toward the magnetic brush layer D on the peripheral surface 52 of the magnet sleeve 51 as the second developing sleeve 64 rotates, but has a strong adhesion to the peripheral surface 68. Difficult to be recovered by.

  When the residual toner TB on the peripheral surface 68 is not collected by the magnetic brush layer D and is accumulated on the peripheral surface 68 and is transported to the photosensitive drum 17 again as the second developing sleeve 64 rotates, a part of the residual toner TB is collected. In some cases, the toner TB moves to the photosensitive drum 17 to generate a so-called development ghost.

  However, in the present embodiment, the second developing roller 35 has a magnetic force set larger than the magnetic force of the first stripping pole 63 and has a polarity opposite to the charging polarity of the toner. 66 is provided, so that even when a large amount of highly charged toner TB or small particle size toner TB adheres to the peripheral surface 68, such residual toner TB is removed from the magnetic force of the second stripping pole 66. Can be peeled off from the peripheral surface 68. The residual toner TB that has been peeled off is collected in the magnetic brush layer D by a magnetic field generated between the second stripping pole 66 and the second transport pole 58 that is substantially opposite to the second stripping pole 66. Thereby, generation | occurrence | production of a development ghost can be suppressed.

  In the present embodiment, the magnetic field between the second stripping pole 66 and the second transport pole 58 is arranged by shifting the second stripping pole 66 to the downstream side by the second angle β with respect to the virtual line L2. Therefore, the recoverability of recovering the residual toner TB to the magnetic brush layer D can be improved.

  Further, in the present embodiment, since the second angle β is set to be larger than the first angle α, the range covered by the magnetic field between the second stripping pole 66 and the second transport pole 58 is set within the first stripping pole. It can be made larger than that of the magnetic field between 63 and the first transport pole 57. Thereby, the recoverability of the residual toner TB by the magnetic brush layer D can be further improved.

  Further, in the present embodiment, the magnetic force (for example, 35 mT) of the first stripping pole 63 ensures the stripping property that the first stripping pole 63 strips the residual toner TA from the peripheral surface 67 of the first developing sleeve 61. In addition, it is set smaller than the magnetic force (for example, 45 mT) of the second stripping pole 66 to such an extent that the strength of the magnetic field between the first stripping pole 63 and the first transport pole 57 can be kept appropriate.

  If the magnetic field between the first stripping pole 63 and the first transport pole 57 is too strong, the toner T in the magnetic brush layer D is restrained by the magnetic field and cannot move onto the peripheral surface 67. The thickness of the toner layer formed in this is less than a predetermined layer thickness. If the electrostatic latent image on the photosensitive drum 17 is developed in this state, the image density of the toner image tends to decrease.

  However, in this embodiment, since the magnetic field strength between the first stripping pole 63 and the first transport pole 57 is kept appropriate, the toner T is removed from the magnetic brush layer D that has passed through the developer regulating blade 36. 1 can be smoothly moved onto the peripheral surface 67 of the developing sleeve 61. Thereby, since a toner layer having a predetermined layer thickness can be formed on the peripheral surface 67, it is possible to suppress a decrease in image density of the toner image.

  Note that the magnetic brush layer D from which the residual toner TB has been collected from the peripheral surface 68 of the second developing sleeve 64 is transported toward the peeling pole 59 positioned on the downstream side of the second transport pole 58 as the magnet sleeve 51 rotates. Is done. Then, the magnetic brush layer D is peeled off from the peripheral surface 52 of the magnet sleeve 51 by the magnetic force of the peeling pole 59, and the developer including the residual toner TB and the carrier is returned to the developer storage section 32.

  Hereinafter, an experiment performed using the developing device 10 will be described. In the experiment, the first peeling pole 63, the second peeling pole 66, the first angle α and the second angle β were set as appropriate, and the presence / absence of development ghost and the image density of the toner image were examined. In the experiment, Examples 1 and 2 and Comparative Examples 1 and 2 shown in FIG. In Example 1, the magnetic force of the first stripping pole 63 was set to 35 mT, the magnetic force of the second stripping pole 66 was set to 45 mT, the first angle α was set to 5 °, and the second angle β was set to 5 °. In Example 2, the magnetic force of the first stripping pole 63 was set to 35 mT, the magnetic force of the second stripping pole 66 was set to 45 mT, the first angle α was set to 5 °, and the second angle β was set to 7.5 °. In Comparative Example 1, the magnetic force of the first stripping pole 63 was set to 35 mT, the magnetic force of the second stripping pole 66 was set to 35 mT, the first angle α was set to 5 °, and the second angle β was set to 5 °. In Comparative Example 2, the magnetic force of the first stripping pole 63 was set to 45 mT, the magnetic force of the second stripping pole 66 was set to 45 mT, the first angle α was set to 7.5 °, and the second angle β was set to 7.5 °.

  The determination of the presence or absence of the development ghost is performed by developing and outputting an image having a solid portion 71 having a high toner concentration and a half portion 72 having a toner concentration lower than that of the solid portion 71 shown in FIG. 7 was performed by visually checking whether or not a history (ghost) 73 of the solid portion 71 as shown in FIG. 7 occurred. The image density was determined by printing 100 images shown in FIG. 6 and measuring the image density of the solid portion 71 using a Macbeth reflection densitometer. When the image density was 1.2 or more, it was determined that the image density was good, and when the image density was less than 1.2, it was determined that the image density was lowered. The result of Experiment 1 is shown in FIG.

  As shown in FIG. 5, in Example 1, the development ghost did not occur, and the image density did not decrease. This is because, by setting the magnetic force of the second stripping pole 66 to be larger than the magnetic force of the first stripping pole 63, the residual toner stripping property by the second stripping pole 66 can be secured. At the same time, by setting the magnetic force of the first stripping pole 63 to an appropriate value (35 mT), the strength of the magnetic field between the first stripping pole 63 and the first transport pole 57 can be set appropriately. In Example 2, the development ghost did not occur, and the image density did not decrease. In particular, in Example 2, since the second angle β was set larger than the first angle α, it is considered that the residual toner recoverability by the magnetic brush layer D was superior to that in Example 1.

  On the other hand, in Comparative Example 1, a development ghost occurred although there was no decrease in image density. This is because the magnetic force of the second stripping pole 66 is set to be the same as the magnetic force of the first stripping pole 63, so that a large amount of highly charged toner or small particle size toner is likely to adhere from the peripheral surface 68 of the second developing roller 35. This is because such toner could not be removed sufficiently. In Comparative Example 2, a development ghost did not occur, but a decrease in image density was confirmed. This is because the magnetic force of the first stripping pole 63 is set to 45 mT, which is larger than an appropriate value, so that the magnetic field strength between the first stripping pole 63 and the first transport pole 57 becomes too large, and the toner in the magnetic brush This is because it is restrained by the magnetic field.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Developing apparatus 17 Photosensitive drum (image carrier)
32 Developer storage unit 33 Magnet roller (developer carrier)
34 First developing roller (first toner carrier)
35 Second developing roller (second toner carrier)
57 First conveying pole (first magnetic pole)
58 Second transport pole (second magnetic pole)
63 First stripped pole (third pole)
66 Second stripped pole (fourth pole)
D Developer layer T Toner TA, TB Residual toner

Claims (4)

A developer storage section for storing a developer containing a non-magnetic toner and a magnetic carrier while stirring;
The first magnetic pole and the second magnetic pole having different polarities from each other, rotating in a predetermined direction, receiving the developer from the developer storage section, and separating the developer layer from the magnetic force of the first magnetic pole and the second magnetic pole. A developer carrier carried by
A first toner carrier that is disposed opposite to the developer carrier and carries the toner received from the developer layer on the developer carrier and supplies the toner to a predetermined image carrier;
The developer carrier is disposed opposite to the developer carrier, and is disposed downstream of the first toner carrier as viewed from the rotation direction of the developer carrier, and from the developer layer on the developer carrier. A second toner carrier for carrying the received toner and supplying the toner to the predetermined image carrier;
With
The first toner carrier has a third magnetic pole having a polarity opposite to the first magnetic pole at a position facing the first magnetic pole,
The second toner carrier has a fourth magnetic pole having a polarity opposite to the second magnetic pole at a position facing the second magnetic pole,
The developing device, wherein the magnetic force of the fourth magnetic pole is set larger than the magnetic force of the third magnetic pole. 2. The developing device according to claim 1, wherein the third magnetic pole is arranged to be shifted to the downstream side by a first angle from a position facing the first magnetic pole when viewed from the rotation direction of the developer carrier. ,
The developing device, wherein the fourth magnetic pole is arranged to be shifted downstream by a second angle from a position facing the second magnetic pole when viewed from the rotation direction of the developer carrier.   The developing device according to claim 2, wherein the second angle is set larger than the first angle. An image carrier on which a toner image is formed;
A developing device for supplying toner to the image carrier and forming the toner image on the image carrier;
A transfer member for transferring the toner image onto a sheet;
A fixing unit for fixing the toner image on the sheet onto the sheet;
With
An image forming apparatus in which the developing device according to claim 1 is employed as the developing device.

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