JP6344366B2 - Developing device and image forming apparatus including the same - Google Patents

Description

  The present invention relates to a two-component developing type developing device used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system, and an image forming apparatus including the same.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. In addition, a two-component development method is known in which an electrostatic latent image on a photoreceptor is developed by a magnetic brush composed of toner and a carrier formed on a developing roller.

  In such a developing device using a two-component developer, a so-called carrier jump, in which a frictionally charged carrier moves to the surface of the photosensitive member due to a reverse electric field formed in a non-image portion on the photosensitive member, becomes a problem. The carrier that has moved to the surface of the photoconductor is sandwiched between the photoconductor and a cleaning blade that removes residual toner on the photoconductor, and is strongly pressed against the photoconductor, whereby the coating agent on the surface of the carrier adheres to the photoconductor. As a result, there occurs an image defect in which the attached streaks appear as white lines on the image.

  In both the two-component development method and the one-component development method, the toner scattered at the opposite portion (development region) between the photosensitive member and the developing roller is external to the developing device along with the air flow generated by the rotation of the photosensitive member. There is also a problem that the inside of the image forming apparatus is contaminated.

  Therefore, a method of collecting a carrier adhering to the photoconductor by arranging a carrier collecting roller on the downstream side of the developing area with respect to the rotation direction of the photoconductor, or arranging a toner scattering prevention roller to prevent toner scattering. Has been proposed. For example, Patent Document 1 includes a carrier recovery sleeve that is provided on the downstream side of the developing roller in the surface movement direction of the photoconductor and that supports the carrier attached to the photoconductor on the surface and is rotatable, and is included in the carrier recovery sleeve. A developing device provided with a carrier recovery roller having a carrier recovery magnet roller fixedly arranged and having a plurality of magnetic poles is disclosed.

JP 2014-81405 A

  By the way, when recovering the carrier from the photoconductor, the carrier cannot be recovered completely unless a magnetic field or a strong electric field stronger than the developing area is applied. Usually, since the carrier recovery roller has a smaller diameter than the developing roller, it has been difficult to obtain a strong magnetic force with a magnet disposed in the carrier recovery roller. Therefore, in order to obtain a strong magnetic field or electric field, it is necessary to make the carrier recovery roller face the photoconductor with a gap smaller than the gap between the developing roller and the photoconductor. However, if the gap between the carrier recovery roller and the photoconductor is reduced, the surface of the photoconductor is damaged due to contact with the carrier recovery roller, the photosensitive layer is scraped, or the carrier recovery roller is smeared with toner or an external toner additive. There was a fear.

  SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a developing device that can effectively recover a carrier attached on an image carrier using a carrier recovery member, and an image forming apparatus including the developing device.

  In order to achieve the above object, a first configuration of the present invention includes a casing, a developer carrier, and a carrier recovery member, and an electrostatic latent image formed on the image carrier is converted into a toner image. A developing device for developing. The housing accommodates a two-component developer including a magnetic carrier and toner. The developer carrier is rotatably supported so as to face the image carrier from the opening of the housing, and carries the developer on the outer peripheral surface. The carrier recovery member is rotatably supported so as to face the image carrier on the downstream side of the developer carrier with respect to the rotation direction of the image carrier, and collects the carrier attached to the surface of the image carrier. The carrier recovery member includes a conductive knitted fabric knitted in a cylindrical shape using a twisted yarn in which a plurality of metal fibers are twisted together, a cylindrical support member inserted into the conductive knitted fabric, a plurality of carrier recovery members fixed inside the support member, And a recovery magnet having a magnetic pole. A recovery voltage is applied to the conductive knitted fabric in a direction in which the carrier attached to the image carrier moves toward the carrier recovery member.

  According to the first configuration of the present invention, the conductive carrier knitted with metal fibers is mounted on the surface of the carrier recovery member, and the magnetic field and electric field concentrate on the metal fibers. It is possible to set a wide gap between the two. As a result, it is possible to prevent the surface of the image carrier from being scratched, the photosensitive layer from being scraped, or the carrier recovery member from being contaminated by toner or a toner external additive. Therefore, a stable carrier recovery effect can be maintained over a long period.

  In addition, the numerous irregularities formed on the surface of the conductive knitted fabric generate an air flow in the rotation direction of the carrier recovery member by the rotation of the carrier recovery member. Since the direction of the air flow is from the outside to the inside of the opening of the housing, toner scattering from the opening of the housing can be suppressed. In addition, it is possible to increase the charge amount of the toner developed on the image carrier by discharging from the metal fiber, which is also effective for lowering transferability caused by a decrease in the charge amount of the toner at high humidity. is there.

1 is a schematic diagram showing an overall configuration of an image forming apparatus 100 including a developing device 16 of the present invention. Side surface sectional view of developing device 16 concerning one embodiment of the present invention. Enlarged view around the developing roller 25 and carrier recovery roller 29 in FIG. Exploded perspective view of carrier recovery roller 29 Enlarged photo of the surface of the conductive knitted fabric 29c

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating the overall configuration of the image forming apparatus 100 according to the first embodiment of the present invention, and the right side is illustrated as the front side of the image forming apparatus 100. As shown in FIG. 1, an image forming apparatus 100 (in this case, a monochrome printer) includes a paper feed cassette 2 that accommodates sheets stacked on the lower part of the apparatus body 1. Above the sheet feeding cassette 2, a sheet conveyance path 4 is formed that extends substantially horizontally from the front to the rear of the apparatus main body 1 and further extends upward to reach the paper discharge unit 3 formed on the upper surface of the apparatus main body 1. A pickup roller 5, a feed roller 6, an intermediate conveyance roller 7, a registration roller pair 8, an image forming unit 9, a fixing device 10, and a discharge roller pair 11 are arranged in this order along the paper conveyance path 4 from the upstream side. ing. Further, in the image forming apparatus 100, a control unit (CPU) 70 for controlling the operation of each of the rollers, the image forming unit 9, the fixing device 10 and the like is disposed.

  The paper feed cassette 2 is provided with a paper stacking plate 12 that is rotatably supported with respect to the paper feed cassette 2 by a rotation fulcrum 12a provided at the rear end in the paper transport direction. The paper (recording medium) stacked on the paper 12 is pressed by the pickup roller 5. A retard roller 13 is disposed in front of the paper feed cassette 2 so as to be in pressure contact with the feed roller 6. When a plurality of sheets are simultaneously fed by the pickup roller 5, these feed rollers 6 are fed. The paper is rolled by the roller 6 and the retard roller 13 so that only the uppermost sheet is conveyed.

  Then, the paper rolled by the feed roller 6 and the retard roller 13 is conveyed to the registration roller pair 8 by changing the conveyance direction to the rear of the apparatus by the intermediate conveyance roller 7, and the timing is adjusted by the registration roller pair 8. Are supplied to the image forming unit 9.

  The image forming unit 9 forms a predetermined toner image on a sheet by an electrophotographic process. The image forming unit 9 is a photosensitive drum 14 that is an image carrier that is rotatably supported in the clockwise direction in FIG. A charging device 15, a developing device 16, a cleaning device 17, a static eliminator (not shown) disposed around the body drum 14, and a transfer roller disposed so as to face the photosensitive drum 14 with the paper conveyance path 4 interposed therebetween. 18 and an exposure unit (LSU) 19 disposed above the photosensitive drum 14. A toner container 20 for supplying toner to the developing device 16 is disposed above the developing device 16.

  In this embodiment, the photoconductor drum 14 is an amorphous silicon (a-Si) photoconductor, and an a-Si photoconductive layer is formed as a photoconductive layer on a conductive substrate (tubular body) such as aluminum. A surface protective layer made of an inorganic insulator or an inorganic semiconductor such as a-Si based SiC, SiN, SiO, SiON, SiCN or the like is laminated on the upper surface.

  The charging device 15 includes, in a housing, a charging roller that contacts the photosensitive drum 14 and applies a charging bias to the drum surface, and a charging roller cleaning brush for cleaning the charging roller. The charging roller is made of conductive rubber, and is disposed so as to contact the photosensitive drum 14.

  The developing device 16 supplies toner to the electrostatic latent image formed on the photosensitive drum 14 by the developing roller 25 (see FIG. 2). The toner is supplied to the developing device 16 by the toner container 20. Here, a two-component developer (hereinafter also simply referred to as a developer) containing a magnetic carrier and toner is accommodated in the developing device 16.

  The cleaning device 17 has a cleaning blade that contacts the photosensitive drum 14 and removes residual toner on the drum surface. As the cleaning blade, for example, a polyurethane rubber blade having a JIS hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photosensitive drum 14 at the contact point. The material, hardness and dimensions of the cleaning blade, the amount of biting into the photosensitive drum 14, the pressure contact force, and the like are appropriately set according to the specifications of the photosensitive drum 14.

  The transfer roller 18 transfers the toner image formed on the surface of the photoconductive drum 14 to the sheet conveyed through the sheet conveyance path 4 without disturbing the toner image. The transfer roller 18 is connected to a transfer bias power source and a bias control circuit (both not shown) for applying a transfer bias having a polarity opposite to that of the toner.

  When image data is input from a host device such as a personal computer, first, the surface of the photosensitive drum 14 is uniformly charged by the charging device 15. Next, an electrostatic latent image based on the image data input on the photosensitive drum 14 is formed by the laser beam from the exposure device (LSU) 19. Further, the developing device 16 attaches toner to the electrostatic latent image and forms a toner image on the surface of the photosensitive drum 14. The toner image formed on the surface of the photoconductive drum 14 is transferred by the transfer roller 18 to the paper supplied to the nip portion (transfer position) between the photoconductive drum 14 and the transfer roller 18.

  The sheet onto which the toner image has been transferred is separated from the photosensitive drum 14 and conveyed toward the fixing device 10. The fixing device 10 is disposed downstream of the image forming unit 9 in the paper conveyance direction, and the paper on which the toner image has been transferred in the image forming unit 9 is applied to a heating roller and a heating roller provided in the fixing device 10. The toner image that is heated and pressed by the pair of fixing rollers 10a including a pressure roller that is in pressure contact is transferred to the paper and fixed. The paper on which the image is formed in the image forming unit 9 and the fixing device 10 is discharged to the paper discharge unit 3 by the discharge roller pair 11.

  After the transfer, the residual toner on the surface of the photosensitive drum 14 is removed by the cleaning device 17, and the residual charge on the surface of the photosensitive drum 14 is neutralized by the static eliminator. The photosensitive drum 14 is charged again by the charging device 15 and image formation is performed in the same manner.

  2 is a side cross-sectional view of the developing device 16 of the present embodiment, and FIG. 3 is an enlarged cross-sectional view of the vicinity of the developing roller 25 in FIG. As shown in FIG. 2, the housing 21 (housing) of the developing device 16 is partitioned into a first storage chamber 22a and a second storage chamber 22b by a partition wall 21a formed integrally with the housing 21. A first stirring screw 23 is disposed in the first storage chamber 22a, and a second stirring screw 24 is disposed in the second storage chamber 22b.

  Each of the first stirring screw 23 and the second stirring screw 24 has a configuration in which a spiral blade is provided around a supporting shaft (rotating shaft), and is rotatably supported by the housing 21 in a state of being parallel to each other. . In addition, the partition wall 21a does not exist in the both ends of the longitudinal direction (direction perpendicular to the paper surface of FIG. 2) of the housing 21, which is the axial direction of the first stirring screw 23 and the second stirring screw 24, and the first stirring screw. 23, the toner can be transferred between the second stirring screws 24. Thus, the first stirring screw 23 conveys the developer in the first storage chamber 22a to the second storage chamber 22 while stirring, and the second stirring screw 24 develops the transported to the second storage chamber 22b. The agent is conveyed while stirring and supplied to the developing roller 25.

  The developing roller 25 is exposed from the opening 21 b of the housing 21 and faces the photosensitive drum 14, and rotates in accordance with the rotation of the photosensitive drum 14, whereby developer is applied to the photosensitive layer of the photosensitive drum 14. Supply. The developing roller 25 includes a rotatable nonmagnetic developing sleeve 25a and a developing magnet 25b made of a permanent magnet having a plurality of magnetic poles fixed inside the developing sleeve 25a. As shown in FIG. 3, in the developing magnet 25b, five magnetic poles including an S1 pole, an S2 pole, and an N1, N2, and N3 pole are disposed along the inner peripheral surface of the developing sleeve 25a. A magnetic brush is formed by attaching (carrying) developer to the surface of the developing sleeve 25a by the magnetic force of the developing magnet 25b. The developing magnet 25b is not limited to the 5-pole configuration, and may be a 3-pole configuration or a 7-pole configuration, for example.

  The developing roller 25 is rotatably supported by the housing 20 in a state parallel to the first stirring screw 23 and the second stirring screw 24. The first stirring screw 23, the second stirring screw 24, and the developing roller 25 are rotationally driven by a motor (not shown). Further, a voltage applying device 30 is connected to the developing roller 25, and a developing bias in which an AC voltage is superimposed on a DC voltage is applied.

  The regulating blade 27 is formed such that its longitudinal direction (direction perpendicular to the paper surface of FIG. 2) is larger than the maximum developing width, and is arranged at a predetermined interval from the developing roller 25, whereby the photosensitive drum 14 is arranged. A regulating portion 31 that regulates the amount of developer supplied to is formed. As the material of the regulating blade 27, magnetic SUS (stainless steel) or the like is used.

  A developer amount detection sensor (not shown) for detecting the amount of developer stored in the housing 21 is provided on the bottom surface of the second storage chamber 22 facing the second stirring screw 24. In accordance with the detection result of the developer amount detection sensor, the toner stored in the toner container 20 (see FIG. 1) passes through the developer supply port (not shown) provided in the upper portion of the housing 21 and enters the housing 21. To be supplied.

  A DS roller (not shown) is rotatably attached to the rotation shaft of the developing roller 25. The DS roller strictly abuts the distance (DS gap) d1 between the developing roller 25 and the photosensitive drum 14 by contacting both ends of the outer peripheral surface of the photosensitive drum 14. The DS roller has a built-in bearing, and the drum surface can be prevented from being worn by being rotated by being driven by the photosensitive drum 14. Further, magnetic seal members (not shown) for preventing leakage of the developer from the gap between the housing 21 and the developing roller 25 are disposed at both ends of the developing roller 25.

  Since the regulation blade 27 is made of a magnetic material, an S pole is induced at the tip of the regulation blade 27. As a result, a magnetic field in a direction attracting the restriction portion 31 is generated between the tip of the restriction blade 27 and the N3 pole (regulation pole) of the developing magnet 25b.

  By this magnetic field, a magnetic brush in which magnetic carriers are continuous is formed between the regulating blade 27 and the developing roller 25, and the layer is regulated to a desired height when the magnetic brush passes through the regulating portion 31. Thereafter, the developing sleeve 25a rotates clockwise, and a magnetic field in the direction along the outer peripheral surface of the developing sleeve 25a is applied by the S1 pole (conveying pole), so that the magnetic brush faces the photosensitive drum 14 (developing area). Move to. Then, since a magnetic field is applied by the N1 pole (main pole), the magnetic brush on the developing sleeve 25a rises and contacts the surface of the photosensitive drum 14. As a result, the electrostatic latent image formed on the surface of the photosensitive drum 14 is developed into a toner image by the toner in the magnetic brush.

  Further, when the developing sleeve 25a rotates in the clockwise direction, a magnetic field in the direction along the outer peripheral surface of the developing sleeve 25a is applied by the S2 pole (conveying pole), and the developing that has not been used to form the toner image together with the magnetic brush is applied. The agent is collected on the developing sleeve 25a. Further, the magnetic brush separates from the developing sleeve 25a and falls into the second storage chamber 22b at the same polarity portion (N2 pole and N3 pole) of the developing magnet 25b. Then, after being stirred and conveyed by the second stirring screw 24, a magnetic brush is formed again on the developing sleeve 25a by the magnetic field of the N3 pole (pump upper pole).

  A carrier recovery roller 29 that recovers the magnetic carrier attached to the surface of the photosensitive drum 14 is disposed above the developing roller 25 in the housing 21. The carrier recovery roller 29 is arranged in non-contact with the surface of the photosensitive drum 14 on the downstream side of the developing roller 25 with respect to the rotation direction of the photosensitive drum 14, and in the opposite direction (counter direction) on the surface facing the photosensitive drum 14. Rotate to.

  The carrier recovery roller 29 includes a cylindrical support member 29a, a recovery magnet 29b fixed inside the support member 29a, and a conductive knitted fabric 29c attached to the outer peripheral surface of the support member 29a. The support member 29a is made of metal, and support shafts are formed at both ends in the longitudinal direction. In the recovery magnet 29b, three magnetic poles composed of S3 pole, S4 pole, and N4 pole are arranged along the inner peripheral surface of the support member 29a. Note that the recovery magnet 29b is not limited to a three-pole configuration, and may have a five-pole configuration, for example.

  The conductive knitted fabric 29c is a knitted fabric knitted in a cylindrical shape using a twisted yarn obtained by twisting a plurality of metal fibers. For example, stainless steel fibers are used as the metal fibers. The “knitted fabric” as used in this specification is formed “one by one” in the manner of knotting with a single twisted yarn, and has a structure in which a large number of warp yarns and weft yarns intersect. It is clearly distinguished from the “woven fabric” that is formed one by one.

  Since the conductive knitted fabric 29c has elasticity, the inner diameter of the conductive knitted fabric 29c is formed smaller than the outer diameter of the support member 29a. When assembling the carrier recovery roller 29, as shown in FIG. 4, while extending the conductive knitted fabric 29c in the radial direction, the support member 29a having the recovery magnet 29b disposed therein is inserted inside the conductive knitted fabric 29c. As a result, the conductive knitted fabric 29c is mounted on the outer peripheral surface of the support member 29a. The conductive knitted fabric 29c is held on the outer peripheral surface of the support member 29a by a restoring force (shrinking force). Further, a gap roller (not shown) is rotatably attached to the support shafts provided at both ends of the support member 29a. The gap roller abuts on both ends of the outer peripheral surface of the photosensitive drum 14 to strictly regulate the distance (DC gap) d2 between the carrier recovery roller 29 and the photosensitive drum 14.

  In addition, a voltage application device 30 is connected to the carrier recovery roller 29. When the carrier attached to the surface of the photosensitive drum 14 is collected by the carrier collecting roller 29, the carrier moves to the conductive knitted fabric 29c via the support member 29b in the direction in which the carrier moves from the photosensitive drum 14 side to the carrier collecting roller 29 side. Apply recovery voltage. As the recovery voltage, it is preferable to apply a voltage obtained by superimposing an AC voltage on a DC voltage.

  FIG. 5 is an enlarged photograph of the surface of the conductive knitted fabric 29c. As shown in FIG. 5, a large number of metal fibers protrude from the surface of the conductive knitted fabric 29c. When a voltage having a polarity opposite to that of the carrier is applied to the support member 29a, the electric field is concentrated on the tip of the metal fiber. Further, the magnetic lines of force generated from the N4 pole of the recovery magnet 25b facing the photosensitive drum 14 are also concentrated on the tip of the metal fiber. The carrier attached to the surface of the photosensitive drum 14 is attracted to the carrier recovery roller 29 by the electric field and magnetic field collected at the tip of the metal fiber. As a result, the carrier adhering to the surface of the photosensitive drum 14 can be efficiently collected.

  The carrier recovered by the carrier recovery roller 29 is collected at the same polarity portion (S3 pole and S4 pole) of the recovery magnet 29b, and when it cannot be held, it is separated from the carrier recovery roller 29 (conductive knitted fabric 29c) and developed. It is held at the S2 pole at 25 opposing positions. Here, the S pole is arranged at a position opposite to the developing roller 25. If the N pole is arranged here, a magnetic brush is formed between the developing roller 25 and the carrier recovery roller 29, and each other. This is because toner development occurs in any of the rollers due to the voltage difference. Thereafter, the carrier collected on the developing roller 25 is detached from the developing sleeve 25a at the same polarity portion (N2 pole and N3 pole) of the developing magnet 25b, and falls into the second storage chamber 22b.

  According to the configuration of the present embodiment, the conductive knitted fabric 29c knitted with metal fibers is mounted on the surface of the carrier recovery roller 29, and the magnetic field and the electric field concentrate on the metal fibers. It can be set wider than the gap d1. As a result, it is possible to prevent the surface of the photosensitive drum 14 from being scratched, the photosensitive layer from being scraped, or the carrier recovery roller 29 from being contaminated by toner or a toner external additive. Therefore, a stable carrier recovery effect can be maintained over a long period of time.

  Moreover, since the conductive knitted fabric 29C used for the carrier recovery roller 29 is formed by weaving a twisted yarn obtained by twisting metal fibers, a large number of irregularities are formed on the surface. The unevenness generates an air flow in the rotation direction of the carrier recovery roller 29 (counterclockwise direction in FIG. 3) by the rotation of the carrier recovery roller 29. As shown in FIG. 3, the direction of the air flow generated by the rotation of the carrier recovery roller 29 is the direction from the outside to the inside of the opening 21 b of the housing 21, so that the toner scattering from the opening 21 b of the housing 21 is prevented. Suppress. Further, it becomes possible to increase the charge amount of the toner developed on the photosensitive drum 14 by the discharge from the metal fiber, and it is also effective in reducing the transferability caused by the decrease in the charge amount of the toner at high humidity. There is.

  Further, the stretchability of the conductive knitted fabric 29c can be used to fix the conductive knitted fabric 29c to the support member 29a without using an adhesive or the like. In this case, the holding performance of the conductive knitted fabric 29c can be further improved by making the outer peripheral surface of the support member 29a rough.

  In addition, although the fineness of the metal fiber used for twisting yarn (fiber is thin) becomes easy to concentrate a magnetic field and an electric field, if the fiber is too thin, the durability of the carrier recovery roller 29 is lowered. The diameter of the metal fiber is preferably 8 μm or more and 30 μm or less. Further, if the thickness of the conductive knitted fabric 29c is too large, the magnetic lines of force pass through the conductive knitted fabric 29c toward the adjacent pole, and the number of magnetic lines of force in the direction of the photosensitive drum 14 is reduced. The same applies to the case where the conductive knitted fabric 29c is used in a state where the degree of stretching is low. Therefore, it is preferable that the thickness of the conductive knitted fabric 29c is 0.7 mm or more and 1.2 mm or less, and the degree of stretching is 1.2 times or more.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, instead of the contact charging type charging device 15 using the charging roller as shown in the above embodiment, a corona charging type charging device including a corona wire and a grid may be used.

  Furthermore, the image forming apparatus of the present invention is not limited to the monochrome printer as shown in FIG. 1, and may be other image forming apparatuses such as monochrome and color copiers, digital multifunction peripherals, color printers, and facsimiles. . Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

  The carrier recovery performance when using the developing device 16 of the present invention was evaluated. As shown in FIGS. 2 and 3, the test method includes the developing device 16 of the present embodiment (the present invention) including the carrier recovery roller 29 with the conductive knitted fabric 29c mounted thereon, and the conventional method without the conductive knitted fabric 29c mounted. A developing device (comparative example) equipped with a carrier recovery roller 29 is mounted on a testing machine (FS-13200 modified machine, manufactured by Kyocera Document Solutions), and 100,000 character images with a printing rate of 5% are output as test images. The presence or absence of a streak image due to carrier adhesion was confirmed.

  As test conditions, a photosensitive drum 14 having a diameter of 30 mm with an organic photosensitive layer (OPC) formed on the outer peripheral surface was used, and the linear speed of the photosensitive drum 14 was 180 mm / sec (process speed 30 sheets / min). Further, the white background potential (bright potential) V0 of the photosensitive drum 14 was set to + 430V, and the image portion potential (dark potential) was set to + 100V. As the developing roller 25, a developing roller 25a having a diametrically asymmetrical developing magnet 25b fixed in a developing sleeve 25a having a diameter of 20 mm whose outer peripheral surface is knurled is used. The developing roller 25 was applied with a developing bias obtained by superimposing an AC voltage of 310 V on a DC voltage of Vpp = 1500 V, a frequency of 3.7 kHz, and a duty = 50%. The gap between the photosensitive drum and the developing roller (DS gap) was set to 0.35 mm.

  The carrier recovery roller 29 is a twisted yarn prepared by fixing a tripolar asymmetric recovery magnet 25b in a metal support member 29a having a diameter of 12 mm, collecting a plurality of stainless steel (SUS316L) fibers on the outer peripheral surface, and adding twist. A conductive knitted fabric 29c having a thickness of 0.7 mm knitted into a cylindrical shape was used. In addition, a recovery voltage obtained by superimposing an AC voltage of 700 V on a DC voltage of Vpp = 650 V, a frequency of 3.7 kHz, and a duty = 50% was applied to the carrier recovery roller 29. The gap between the photosensitive drum and the carrier recovery roller (DC gap) was set to 0.4 to 1.0 mm.

  As a result of the test, in the developing device 16 of the present invention in which the conductive knitted fabric 29c is mounted on the carrier recovery roller 29, the carrier adhering to the photosensitive drum 14 is efficiently recovered by the carrier recovery roller 29 and after 100,000 durable prints. In addition, no streak image was observed due to carrier adhesion.

  On the other hand, in the developing device of the comparative example in which the conductive knitted fabric 29c is not mounted on the carrier recovery roller 29, a cleaning failure occurs due to carrier adhesion to the photosensitive drum 14, and the carrier adhesion occurs after 100,000 durable prints. Generation of muscle images was observed.

  The present invention is a developing device using a two-component developer containing a magnetic carrier and a toner, and can be used for a developing device provided with a carrier recovery roller for recovering a magnetic carrier attached on an image carrier.

9 Image forming unit 10 Fixing device 14 Photosensitive drum (image carrier)
DESCRIPTION OF SYMBOLS 15 Charging device 16 Developing device 17 Cleaning device 18 Transfer roller 25 Developing roller (developer carrier)
25a Developing sleeve 25b Developing magnet 27 Regulating blade 29 Carrier recovery roller (carrier recovery member)
29a Support member 29b Recovery magnet 29c Conductive knitted fabric 30 Voltage application device 41 Charging roller (charging member)
47 Cleaning blade 100 Image forming apparatus

Claims (7)

A housing for storing a two-component developer containing a magnetic carrier and toner;
A developer carrier that is rotatably supported so as to face the image carrier from the opening of the housing, and carries the developer on an outer peripheral surface;
A carrier recovery member that is rotatably supported so as to face the image carrier on the downstream side of the developer carrier relative to the rotation direction of the image carrier and collects the carrier attached to the surface of the image carrier. When,
A developing device for developing an electrostatic latent image formed on the image carrier into a toner image,
The carrier recovery member is
A conductive knitted fabric knitted into a tubular shape using twisted yarns obtained by twisting a plurality of metal fibers;
A cylindrical support member inserted into the conductive knitted fabric,
A recovery magnet fixed inside the support member and having a plurality of magnetic poles;
Have
A developing device in which a collection voltage in a direction in which the carrier attached to the image carrier moves to the carrier collection member is applied to the conductive knitted fabric.   The developing device according to claim 1, wherein the recovery voltage is a voltage obtained by superimposing an AC voltage on a DC voltage.   The developing device according to claim 1, wherein a gap between the image carrier and the carrier recovery member is larger than a gap between the image carrier and the developer carrier.   The developing device according to claim 1, wherein a fiber diameter of the metal fiber is 8 μm or more and 30 μm or less.   The developing device according to claim 1, wherein a thickness of the conductive knitted fabric is 0.7 mm or greater and 1.2 mm or less. The developer carrier has a developing sleeve rotatably supported by the housing, and a developing magnet fixed to the inside of the developing sleeve and having a plurality of magnetic poles,
2. The magnetic pole of the recovery magnet disposed at a portion facing the developer carrying member has the same polarity as the magnetic pole of the development magnet disposed at a portion facing the carrier recovery member. The developing device according to claim 5.   An image forming apparatus comprising the developing device according to claim 1.