JP2011150220A - Developing device and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device that can suppress inconvenience such as a development hysteresis by improving the recovery property of residual toner on a toner carrier, and to provide an image forming apparatus equipped with the developing device. <P>SOLUTION: The developing device 10 includes: a developer carrier 56 having a first magnetic pole 71, and configured to receive developer from a developer storage section 51 to carry a developer layer by means of the magnetic force of the first magnetic pole 71; and a toner carrier 58 disposed opposite to the developer carrier 56 and carrying toner after receiving the toner from the developer layer while rotating in contact with the developer layer in the opposite position, to supply the toner to a predetermined image carrier 17. The toner carrier 58 includes a second magnetic pole 75 having a polarity reverse to that of the first magnetic pole 71 and forming a magnetic field between the first magnetic pole 71 and the second magnetic pole 75. The density of the magnetic flux of the second magnetic pole 75 is set so as to increase from the opposite position toward the upstream side in the rotating direction of the toner carrier 58. <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.

  In the developing device, for example, as basic components, a developer storage unit that stores a developer containing a non-magnetic toner and a magnetic carrier while stirring, and a developer received from the developer storage unit. Based on the potential difference between the developer carrier that carries the developer layer (so-called magnetic brush layer) and the developer carrier, only the toner is received from the magnetic brush layer and carried as a toner layer. And a toner carrier that supplies the toner to the image carrier based on a potential difference with the image carrier.

  In the developing device having the above configuration, the residual toner that is not supplied from the toner carrier to the image carrier and remains on the toner carrier is scraped and collected by the magnetic brush layer on the developer carrier. .

  However, there are cases where the residual toner is not sufficiently collected by the magnetic brush layer. In that case, on the toner carrier, there are formed a region where residual toner is not supplied from the toner carrier to the image carrier and a region where toner is supplied to the electrostatic latent image and no residual toner is present. The When toner is supplied from the developer carrier to the toner carrier for the next development operation in a state where the residual toner existence region and the residual toner non-existence region coexist, a uniform layer thickness is formed on the toner carrier. A toner layer is not formed. As a result, a so-called development history phenomenon occurs.

  Further, even when the toner is not sufficiently supplied from the developer carrier to the toner carrier, a toner layer having a uniform layer thickness is not formed on the toner carrier, and a development history phenomenon occurs.

  As a technique for suppressing the development history phenomenon, for example, one disclosed in Patent Document 1 is known. In the developing device of Patent Document 1, the developer carrier (magnetic roller) has two upstream S poles and downstream S poles disposed in the vicinity of a portion closest to the toner carrier (developing roller), The toner carrier has an N pole disposed substantially opposite the downstream S pole. Since a magnetic field is formed between the downstream S pole and the N pole, a good magnetic brush is formed in the magnetic field. Therefore, the residual toner on the toner carrier is scraped off by the magnetic brush and collected in the magnetic brush layer. In this way, the developing device of Patent Document 1 suppresses the development history phenomenon.

JP 2005-221800 A

  However, it is considered that the residual toner cannot be completely recovered simply by making the south pole of the developer carrier and the north pole of the toner carrier substantially opposite to each other. In particular, residual toner cannot be collected well when the diameter of the toner is reduced to improve the image quality, or when the rotation speed of the developer carrier and the toner carrier is increased to speed up the developing operation. it is conceivable that.

  Accordingly, in view of the above circumstances, the present invention provides a developing device capable of improving the recoverability of residual toner on a toner carrier and suppressing inconvenience such as a development history phenomenon, and an image forming apparatus including the same. The purpose is to provide.

  In order to achieve the above object, a developing device according to the present invention includes a developer storage unit that stores a developer containing a non-magnetic toner and a magnetic carrier while stirring, and a first magnetic pole, A developer carrier that receives the developer from the developer reservoir and carries the developer layer by the magnetic force of the first magnetic pole, and the developer carrier are disposed opposite to each other, and the developer layer is disposed at the opposite position. A toner carrier for receiving and carrying the toner from the developer layer and supplying the toner to a predetermined image carrier while rotating in contact with the toner layer, the toner carrier comprising the first magnetic pole Including a second magnetic pole that forms a magnetic field with the first magnetic pole, and the magnetic flux density of the second magnetic pole is upstream from the facing position in the rotation direction of the toner carrier. Set to increase toward the side That.

  According to the developing device of the present invention, the second magnetic pole of the toner carrier forms a magnetic field with the first magnetic pole that holds the developer layer on the developer carrier by magnetic force. The toner can be satisfactorily received from the developer layer at a position facing the developer carrier. As a result, the toner carrier can supply a sufficient amount of toner to the image carrier.

  In the developing device according to the present invention, the total amount of toner received by the toner carrier from the developer layer is not supplied to the image carrier, and a part of the toner remains on the toner carrier. Residual toner returns to the position facing the developer carrier as the toner carrier rotates. In the developing device according to the present invention, the magnetic flux density of the second magnetic pole is set so as to increase from the opposing position of the toner carrier and the developer carrier to the upstream side in the rotation direction of the toner carrier. The magnetic field formed between the second magnetic pole and the first magnetic pole covers a wide range from the facing position to the upstream side in the rotation direction of the toner carrier. Due to the influence of the magnetic field in such a wide range, the residual toner is scraped and collected by the developer layer on the developer carrier before returning to the facing position.

  As described above, the developing device according to the present invention can supply a sufficient amount of toner to the image bearing member and collect residual toner, thereby suppressing problems such as a development history phenomenon. Can do.

  In a preferred embodiment of the present invention, the second magnetic pole includes a counter magnetic pole disposed opposite to the first magnetic pole, an upstream side of the counter magnetic pole as viewed from a rotation direction of the toner carrier, and the counter magnetic pole. The upstream magnetic pole is disposed adjacent to the magnetic pole, and the magnetic flux density of the upstream magnetic pole is set larger than the magnetic flux density of the counter magnetic pole.

  According to this configuration, although the opposing magnetic pole and the upstream magnetic pole have the same polarity, the magnetic flux density of the upstream magnetic pole is set larger than the magnetic flux density of the opposing magnetic pole, and the upstream magnetic pole Since the opposing magnetic poles are arranged adjacent to each other, the magnetic flux density is distributed as if the two upstream magnetic poles and the opposing magnetic pole are one magnetic pole, and the range of the distribution becomes large. Thus, it is easy to set the magnetic flux density of the second magnetic pole so as to increase from the facing position toward the upstream side in the rotation direction of the toner carrier.

  In another preferred embodiment of the present invention, the developer carrying member is configured to be rotatable in a predetermined direction, and has a polarity opposite to that of the first magnetic pole, and the developer carrying member. And a third magnetic pole disposed downstream of the first magnetic pole and adjacent to the first magnetic pole as viewed from the direction of rotation of the first magnetic pole, the magnetic flux density of the third magnetic pole being the magnetic flux density of the counter magnetic pole Is set larger than.

  According to this configuration, the magnetic flux density of the third magnetic pole is set to be larger than the magnetic flux density of the counter magnetic pole, so that the magnetic force of the first magnetic pole is increased by the magnetic force of the third magnetic pole. As a result, the developer layer can be easily held on the developer carrier, and so-called carrier pulling in which the developer layer moves to the toner carrier can be suppressed.

  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.

  The image forming apparatus according to the present invention employs a developing device that can suppress inconveniences such as a development history phenomenon, so that a good toner image can be formed.

  According to the developing device and the image forming apparatus including the developing device according to the present invention, it is possible to improve the recoverability of the residual toner on the toner carrier and to suppress inconveniences such as a development history phenomenon. A toner image can be formed.

1 schematically shows an internal structure of an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which shows the internal structure of a developing device roughly. It is a figure which shows arrangement | positioning of the magnetic pole formed in the magnetic roller of a developing device, and a developing roller. It is a figure which shows the direction of the magnetic force line between a magnetic roller and a developing roller. It is a figure which shows distribution of the magnetic flux between a magnetic roller and a developing roller. It is a figure which shows distribution of the magnetic flux between a magnetic roller and a developing roller. It is a figure for demonstrating the image development operation | movement of a image development apparatus.

  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 16, a transfer roller 19, a cleaning device 18, and the like are arranged. The charger 16 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 18 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 50 that defines an internal space thereof. In the internal space, the developing device 10 includes a developer reservoir 51 formed at the bottom of the developer container 50, a magnetic roller 56 (developer carrier) disposed above the developer reservoir 51, and A developing roller 58 (toner carrier) disposed opposite to the magnetic roller 56 at a position obliquely above the magnetic roller 56; and a developer regulating blade 55 disposed opposite to the magnetic roller 56 at a side position of the magnetic roller 56. .

  The developer storage unit 51 is configured to store a developer containing a non-magnetic toner and a magnetic carrier and to convey the developer while stirring. The developer reservoir 51 is composed of two adjacent developer reservoirs 51 a and 51 b extending in the longitudinal direction of the developing device 10. The developer storage chambers 51a and 51b are partitioned from each other in the longitudinal direction by a partition plate 52 fixed to the bottom portion of the developing container 50, but communicate with each other at both ends in the longitudinal direction. Further, screw feeders 53 and 54 that stir the developer by rotation are rotatably mounted in the developer storage chambers 51a and 51b. Since the screw feeders 53 and 54 are set to have opposite rotation directions, the developer is conveyed between the developer storage chamber 51a and the developer storage chamber 51b while being stirred. By this stirring, the toner made of a non-magnetic material and the carrier made of a magnetic material are mixed, and the toner is charged positively, for example, and the carrier is charged negatively, for example. Further, the toner adheres to the carrier due to the electrostatic force between the carrier and the toner.

  The magnetic roller 56 is disposed so as to extend in the longitudinal direction of the developing device 10. In FIG. 2, a hollow magnetic sleeve 57 that can rotate counterclockwise as indicated by an arrow, and a magnetic sleeve 57 that rotates the magnetic sleeve 57 are omitted. Rotation axis. The magnetic sleeve 57 is made of a nonmagnetic material. A first magnet roll 63 extending in the axial direction of the magnetic sleeve 57 is built in the internal space of the magnetic sleeve 57. The first magnet roll 63 is supported in a fixed state on the support shaft 64 and does not rotate with the magnetic sleeve 57. The first magnet roll 63 is formed with a magnetic pole (not shown) for magnetically pumping the developer from the developer reservoir 51 onto the peripheral surface 61 of the magnetic sleeve 57. The developer pumped up on the peripheral surface 61 is magnetically held as a developer layer on the peripheral surface 61 of the magnetic sleeve 57 and is conveyed toward the developer regulating blade 55 as the magnetic sleeve 57 rotates. The magnetic sleeve 57, the first magnet roll 63, and the support shaft 64 are set coaxially with each other.

  The developer regulating blade 55 regulates the layer thickness of the developer layer on the peripheral surface 61 of the magnetic sleeve 57. The developer regulating blade 55 is a plate member made of a magnetic material that extends along the longitudinal direction of the magnetic sleeve 57, and is supported at an appropriate position of the developing container 50. Further, the developer regulating blade 55 has a tip portion that forms a predetermined regulating gap with the peripheral surface 61 of the magnetic sleeve 57.

  The first magnet roll 63 in the magnetic sleeve 57 is formed with a so-called restricting pole (not shown) that is disposed opposite to the tip of the developer restricting blade 55 in addition to the above-mentioned scooping pole. Therefore, the developer regulating blade 55 formed of a magnetic material is magnetized by the regulating pole of the magnetic roller 56, and the magnetic path is formed between the tip of the developer regulating blade 55 and the regulating pole, that is, in the regulating gap. Is formed.

  The developing roller 58 is disposed so as to extend in parallel to the magnetic sleeve 57, and supports a hollow developing sleeve 59 that can rotate counterclockwise as shown by an arrow in FIG. And a rotating shaft (not shown) for rotating the developing sleeve 59. As will be described later, the developing sleeve 59 receives only the toner from the developer layer on the peripheral surface 61 of the magnetic sleeve 57 and carries the toner on the peripheral surface 62. The developing sleeve 59 is made of a nonmagnetic material and has substantially the same longitudinal dimension as the magnetic sleeve 57. The diameter of the developing sleeve 59 and the diameter of the magnetic sleeve 57 may be set to be the same or may not be set to be the same.

  A gap G having a uniform size is formed in the axial direction between the peripheral surface 62 of the developing sleeve 59 and the peripheral surface 61 of the magnetic sleeve 57. The size of the gap G is set such that the developer layer on the circumferential surface 61 of the magnetic sleeve 57 can pass through the gap G while contacting the circumferential surface 62 of the developing sleeve 59 after being regulated by the developer regulating blade 55. Has been. In the present embodiment, the gap G is set to 0.3 mm, for example. If the size of the gap G exceeds a predetermined range, it becomes difficult to form a toner layer on the developing sleeve 59, and if it is less than the predetermined range, the developer layer cannot pass through the gap G, and the peripheral surface 62 of the developing sleeve 59 There is a risk of disturbing the toner layer formed thereon. A gap having a uniform size is also formed in the axial direction between the peripheral surface 62 of the developing sleeve 59 and the drum surface of the photosensitive drum. In the present embodiment, the gap is set to 0.12 mm, for example.

  A second magnet roll 65 extending in the axial direction of the developing sleeve 59 is built in the internal space of the developing sleeve 59. The second magnet roll 65 is supported by the support shaft 66 in a fixed state, and is configured not to rotate with the developing sleeve 59. The developing sleeve 59, the second magnet roll 65, and the support shaft 66 are set coaxially with each other.

  Next, with reference to FIG. 3, in addition to the upper drawing pole and the regulating pole, another plurality of magnetic poles formed on the first magnet roll 63 and a plurality of magnetic poles formed on the second magnet roll 65 will be described. To do. As shown in the figure, a first magnetic pole 71 is formed on the first magnet roll 63. The first magnetic pole 71 is a magnetic pole that extends in the axial direction of the first magnet roll 63 and has, for example, an N pole on the side facing the magnetic sleeve 57. The first magnetic pole 71 is formed at a position corresponding to the portion of the magnetic sleeve 57 facing the developing sleeve 59, that is, the portion of the magnetic sleeve 57 closest to the developing sleeve 59.

  On the other hand, a counter magnetic pole 73 is formed on the second magnet roll 65. The counter magnetic pole 73 is a magnetic pole that extends in the axial direction of the second magnet roll 65 and has, for example, an S pole on the side facing the developing sleeve 59. The counter magnetic pole 73 is formed so as to oppose the first magnetic pole 71 of the first magnet roll 63.

  The second magnet roll 65 is further formed with an upstream magnetic pole 74 on the upstream side of the counter magnetic pole 73 and adjacent to the counter magnetic pole 73 when viewed from the rotation direction of the developing sleeve 59. Similarly to the counter magnetic pole 73, the upstream magnetic pole 74 is a magnetic pole that extends in the axial direction of the second magnet roll 65 and has the S pole located on the side facing the developing sleeve 59. The opposing magnetic pole 73 and the upstream magnetic pole 74 of the second magnet roll 65 constitute a second magnetic pole 75 in the present invention, and form a magnetic field with the first magnetic pole 71.

  The first magnet roll 63 is further formed with a third magnetic pole 72 on the downstream side of the first magnetic pole 71 and adjacent to the first magnetic pole 71 when viewed from the rotation direction of the magnetic sleeve 57. The third magnetic pole 72 is a magnetic pole that extends in the axial direction of the first magnet roll 63 and has, for example, an S pole on the side facing the magnetic sleeve 57.

  In the present embodiment, the magnetic flux density of the second magnetic pole 75 composed of the opposing magnetic pole 73 and the upstream magnetic pole 74 is the opposing position between the magnetic sleeve 57 and the developing sleeve 59, that is, the closest position between the magnetic sleeve 57 and the developing sleeve 59. To the upstream of the developing sleeve 59 in the rotational direction. Thereby, the magnetic field formed between the second magnetic pole 75 and the first magnetic pole 71 extends over a wide range from the facing position to the upstream side in the rotation direction of the developing sleeve 59.

In the present embodiment, such a wide magnetic field is formed as follows. That is, assuming that the magnetic flux density peak value of the counter magnetic pole 73 is F1 and the magnetic flux density peak value of the upstream magnetic pole 74 is F2, F1 and F2 are set to satisfy the following relationship.
F2> F1 (1)
The magnetic flux density peak value F1 of the opposing magnetic pole 73 is set to 45 mT, for example, and the magnetic flux density peak value F2 of the upstream magnetic pole 74 is set to 60 mT, for example.

  In the present embodiment, the relationship (1) is satisfied, and the opposing magnetic pole 73 and the upstream magnetic pole 74 are disposed adjacent to each other. Therefore, even when the opposing magnetic pole 73 and the upstream magnetic pole 74 have the same polarity, the magnetic field lines F emitted from the first magnetic pole 71 are not limited to the opposing magnetic pole 73 as shown in FIG. It goes also to the upstream magnetic pole 74. The magnetic flux density between the first magnetic pole 71 and the upstream magnetic pole 74 is higher than the magnetic flux density between the first magnetic pole 71 and the counter magnetic pole 73. As a result, the magnetic flux is distributed between the second magnetic pole 75 and the first magnetic pole 71 as if the two opposing magnetic poles 73 and the upstream magnetic pole 74 are one magnetic pole, and the range of the distribution is large. Become.

  FIG. 5 shows a magnetic flux distribution between the first magnetic pole 71 and the second magnetic pole 75. As shown in the figure, in this embodiment, a magnetic flux is generated between a magnetic flux distribution E1 between the first magnetic pole 71 and the counter magnetic pole 73 and a magnetic flux distribution E2 between the first magnetic pole 71 and the upstream magnetic pole 74. No decrease in density is observed, and the magnetic flux density increases toward the upstream side in the rotation direction of the developing sleeve 59. As described above, by using the two opposing magnetic poles 73 and the upstream magnetic pole 74 that act as one magnetic pole, the magnetic flux density of the second magnetic pole 75 increases from the opposing position toward the upstream side in the rotation direction of the developing sleeve 59. It is easy to increase. On the other hand, when the opposing magnetic pole 73 and the upstream magnetic pole 74 are arranged apart from each other while not satisfying the relationship (1), the magnetic flux between the first magnetic pole 71 and the opposing magnetic pole 73 is shown in FIG. A decrease in magnetic flux density is observed between the distribution E1 and the magnetic flux distribution E2 between the first magnetic pole 71 and the upstream magnetic pole 74.

In the present embodiment, if the magnetic flux density peak value of the third magnetic pole 72 is F3, F3 is set to satisfy the following relationship with respect to the magnetic flux density peak value F1 of the counter magnetic pole 73.
F3> F1 (2)
The magnetic flux density peak value F3 of the third magnetic pole 72 is set to 55 mT, for example.

  In the present embodiment, the above relationship (2) is satisfied, and the third magnetic pole 72 and the first magnetic pole 71 are disposed adjacent to each other. It is possible to increase the magnetic force of the first magnetic pole 71 having the opposite polarity. Therefore, the developer layer can be easily held on the peripheral surface 61 of the magnetic sleeve 57. Thereby, the so-called carrier pulling in which the developer layer is magnetically attracted to the developing sleeve 59 and moves to the peripheral surface 62 can be suppressed.

  The magnetic flux density peak value of the first magnetic pole 71 is set to be higher than that of the other magnetic poles, for example, 95 mT. Further, the first magnetic pole 71 and the third magnetic pole 72 have a predetermined pole width extending in the circumferential direction with respect to the peripheral surface 61 of the magnetic sleeve 57, and the opposing magnetic pole 73 and the upstream magnetic pole 74 are also developed sleeve 59. It has a predetermined pole width extending in the circumferential direction with respect to the peripheral surface 62. In the present embodiment, the pole widths of the first magnetic pole 71 and the upstream magnetic pole 74 are set larger than the pole width of the counter magnetic pole 73.

  Next, the developing operation and its action by the developing device 10 having the above configuration will be described with reference to FIGS.

  First, the non-magnetic toner is charged by being agitated together with the magnetic carrier in the developer storage section 51, and adheres to the carrier. The developer including the carrier and the charged toner is pumped up from the developer storage portion 51 to the peripheral surface 61 of the magnetic sleeve 57 by the magnetic force of the pumping pole of the magnetic roller 56. The developer thus pumped up is magnetically held as a developer layer on the peripheral surface 61 of the magnetic sleeve 57 and is conveyed toward the developer regulating blade 55 as the magnetic sleeve 57 rotates.

  The developer regulating blade 55 regulates the developer layer on the peripheral surface 61 in the regulation gap to make it uniform and thin. As a result, a developer layer having a predetermined thickness (hereinafter referred to as a magnetic brush layer D) is formed on the peripheral surface 61.

  The magnetic brush layer D on the peripheral surface 61 is conveyed to a position where the magnetic sleeve 57 and the developing sleeve 59 face each other as the magnetic sleeve 57 rotates. Since the opposing position is in a strong magnetic field formed between the first magnetic pole 71 and the opposing magnetic pole 73 of the second magnetic pole 75, the magnetic brush DB made of the carrier C rises in the magnetic brush layer D and the developing sleeve. 59 is in contact with the peripheral surface 62. Thus, a good magnetic brush DB is formed by the magnetic field between the first magnetic pole 71 and the counter magnetic pole 73.

  Since a predetermined bias is applied to each of the magnetic sleeve 57 and the developing sleeve 59, the toner T adhering to the magnetic brush DB in contact with the peripheral surface 62 of the developing sleeve 59 is separated from the magnetic sleeve 57 and the developing sleeve 59. Due to the potential difference between the developing sleeves 59, the magnetic brush DB moves to the peripheral surface 62 of the developing sleeve 59. As a result, a toner layer having a predetermined thickness is formed on the peripheral surface 62. The carrier C constituting the magnetic brush DB is held on the peripheral surface 61 of the magnetic sleeve 57 by the magnetic force of the first magnetic pole 71 and does not move to the developing sleeve 59.

  The toner layer on the peripheral surface 62 is conveyed toward the drum surface of the photosensitive drum 17 as the developing sleeve 59 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 developing sleeve 59. Thereby, the electrostatic latent image on the drum surface is developed.

  On the other hand, the residual toner TA that does not move from the developing sleeve 59 to the drum surface and remains on the developing sleeve 59, that is, the residual toner TA that has not been used for development passes through the photosensitive drum 17, and then the magnetic sleeve 57. With this rotation, the magnetic sleeve 57 and the developing sleeve 59 return to the opposing positions.

  In the present embodiment, the upstream magnetic pole 74 of the second magnetic pole 75 is positioned upstream of the facing position when viewed from the rotation direction of the developing sleeve 59, and the upstream magnetic pole 74 and the first magnetic pole 71 A magnetic field is formed between them. As described above, the strength of the magnetic field increases from the facing position toward the upstream side in the rotation direction of the developing sleeve 59, that is, from the facing magnetic pole 73 toward the upstream magnetic pole 74. For this reason, the magnetic brush DB on the peripheral surface 61 of the magnetic sleeve 57 maintains a state where it rises within the range where the magnetic force of the upstream magnetic pole 74 reaches even after passing the facing position, and the peripheral surface 62 of the developing sleeve 59. Can contact. As described above, in the present embodiment, the distance that the magnetic brush DB contacts the circumferential surface 62 of the developing sleeve 59 in the circumferential direction is larger than in the configuration in which the upstream magnetic pole 74 is not provided. Accordingly, the residual toner TA can be scraped and collected by the magnetic brush DB before the residual toner TA reaches the facing position, and the recoverability of the residual toner TA can be improved.

  As is apparent from the above description, the developing sleeve 59 can receive the toner T satisfactorily from the magnetic sleeve 57, supply a sufficient amount of toner T to the photosensitive drum 17, and on the peripheral surface 61 of the magnetic sleeve 57. Since the magnetic brush DB can satisfactorily collect the residual toner TA on the peripheral surface 62 of the developing sleeve 59, inconveniences such as a development history phenomenon can be suppressed.

  Further, since the magnetic force of the first magnetic pole 71 is increased by the magnetic force of the third magnetic pole 72, the magnetic brush layer D can be easily held on the peripheral surface 61 of the magnetic sleeve 57. Thereby, the so-called carrier C pulling that the magnetic brush layer D is magnetically attracted to the developing sleeve 59 by the magnetic force of the counter magnetic pole 73 and moves to the peripheral surface 62 can be suppressed.

  In the embodiment described above, the case where the second magnetic pole 75 is composed of the opposing magnetic pole 73 and the upstream magnetic pole 74 has been described. However, the second magnetic pole 75 is upstream in the rotational direction of the developing sleeve 59 from the opposing position. You may comprise from three or more magnetic poles arrange | positioned toward. Even in this case, the magnetic flux density peak values of these magnetic poles are set so as to increase toward the upstream side in the rotation direction.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Developing apparatus 17 Photosensitive drum (image carrier)
56 Magnetic roller (developer carrier)
57 Magnetic sleeve 58 Developing roller (toner carrier)
59 Developing sleeve 71 First magnetic pole 72 Third magnetic pole 73 Opposing magnetic pole 74 Upstream magnetic pole 75 Second magnetic pole C Carrier D Magnetic brush layer DB Magnetic brush T Toner TA Residual toner

Claims (4)

A developer storage section for storing a developer containing a non-magnetic toner and a magnetic carrier while stirring;
A developer carrier having a first magnetic pole, receiving the developer from the developer reservoir, and carrying the developer layer by the magnetic force of the first magnetic pole;
The toner carrier is disposed opposite to the developer carrier and receives and carries the toner from the developer layer while rotating in contact with the developer layer at the opposite position, and the toner is transferred to a predetermined image carrier. A toner carrier to be supplied to
With
The toner carrier includes a second magnetic pole having a polarity opposite to that of the first magnetic pole and forming a magnetic field with the first magnetic pole;
The developing device, wherein the magnetic flux density of the second magnetic pole is set so as to increase from the facing position toward the upstream side in the rotation direction of the toner carrier. 2. The developing device according to claim 1, wherein the second magnetic pole includes a counter magnetic pole disposed opposite to the first magnetic pole, an upstream side of the counter magnetic pole as viewed from a rotation direction of the toner carrier, and the second magnetic pole. An upstream magnetic pole disposed adjacent to the opposing magnetic pole,
The developing device wherein the magnetic flux density of the upstream magnetic pole is set to be larger than the magnetic flux density of the counter magnetic pole. 3. The developing device according to claim 2, wherein the developer carrying member is configured to be rotatable in a predetermined direction, and has a polarity opposite to the first magnetic pole, and the developer carrying member. A third magnetic pole disposed further downstream than the first magnetic pole and adjacent to the first magnetic pole when viewed from the rotation direction of
The developing device wherein the magnetic flux density of the third magnetic pole is set to be larger than the magnetic flux density of the counter magnetic pole. 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.

Images