JP5526048B2 - Developing device and image forming apparatus having the same - Google Patents

Description

  An object of the present invention is to provide a developing device that forms a toner image by supplying a developer containing magnetic toner to a predetermined image carrier, and an image forming apparatus including the developing device.

  A developing device of an image forming apparatus using an electrophotographic system such as a copying machine or a printer includes a developing roller that conveys a developer onto an image carrier such as a photosensitive drum and forms a toner image on the image carrier. And a seal member that suppresses leakage of the developer to the outside (Patent Document 1). The developing roller includes a plurality of magnetic poles arranged along the circumferential direction, and conveys the magnetic toner to the image carrier using the magnetic force of the plurality of magnetic poles. The seal member is disposed so as to face each of both end portions in the axial direction of the developing roller, and forms a magnetic field with a plurality of magnetic poles built in the developing roller, and magnetically restrains the magnetic toner in the magnetic field. As a result, leakage of the magnetic toner to the outside is suppressed.

  In the developing device of Patent Document 1, the plurality of magnetic poles and the seal member are configured such that the longitudinal ends of the magnetic poles extending in the axial direction of the developing roller are positioned between the inner end and the outer end of the seal member. doing. With this configuration, the strength of the magnetic field between the seal member and the magnetic pole is increased, so that the magnetic binding force for the magnetic toner is increased. Thereby, the sealing performance which suppresses the leakage of the magnetic toner to the outside is ensured.

JP 10-39629 A

  The developing device of Patent Document 1 employs a configuration that suppresses leakage of magnetic toner by using a magnetic field formed between a plurality of magnetic poles built in a developing roller and a seal member. Therefore, the angle between the magnetic poles is adjusted so as to obtain a desired magnetic field strength between the magnetic pole and the seal member. However, there are cases where the angle between the magnetic poles cannot be appropriately adjusted from the viewpoint of sealing performance due to the layout restrictions of the entire apparatus such as the arrangement of the photosensitive drums.

  In particular, when the arrangement of the photosensitive drum is limited, the angle between the magnetic pole for adjusting the magnetic toner layer thickness on the developing roller and the magnetic pole for supporting the magnetic toner on the developing roller becomes large. There is a case. In that case, the magnetic flux density decreases at the boundary between the magnetic flux distribution of one magnetic pole and the magnetic flux distribution of the other magnetic pole. For this reason, the strength of the magnetic field is reduced, and the sealing performance is reduced. As a result, leakage of magnetic toner can occur.

  In order to compensate for such a decrease in magnetic flux density, it is conceivable to provide an additional magnetic pole, but in the case of this configuration, an increase in cost is inevitable. In particular, an image forming apparatus such as a low-cost printer is required to minimize the number of magnetic poles.

  SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a developing device capable of ensuring toner leakage sealing performance even when the angle between the magnetic poles built in the developing roller is large, and an image forming apparatus having the developing device The purpose is to provide.

In order to achieve the above object, a developing device according to the present invention includes a housing and a developing roller rotatably arranged in the housing, and includes a plurality of magnetic poles arranged along the circumferential direction, A developing roller that forms a toner image on the predetermined image carrier by transporting a developer containing magnetic toner to the predetermined image carrier using the magnetic force of the plurality of magnetic poles in accordance with the rotation; And a gap formed between the developing roller and the developing roller in the housing, and a magnetic field is formed between the plurality of magnetic poles in the gap, and the magnetic field A seal member that restrains the magnetic toner from leaking to the outside by magnetically constraining the magnetic toner, and the developing roller includes a first region facing the predetermined image carrier, and the shim. A second region opposite to the magnetic member, wherein the second region has a magnetic binding force for magnetically binding the magnetic toner, and the first region is the magnetic region of the second region. The developing roller has a cylindrical sleeve base material, an intermediate layer laminated on the outer peripheral surface of the sleeve base material, and a laminate on the intermediate layer. It includes a developing sleeve having a surface layer was, the intermediate layer is a layer having a magnetic, the surface layer, that have a higher hardness than the intermediate layer.

  According to the developing device of the present invention, the second region of the developing roller facing the seal member has a magnetic restraining force that magnetically restrains the magnetic toner. Therefore, even if the angle between the plurality of magnetic poles built in the developing roller increases due to the layout restriction of the developing device, and the strength of the magnetic field between the magnetic pole and the sealing member decreases, that is, the sealing member Even if the magnetic restraining force decreases, the magnetic toner can be magnetically restrained between the second region and the seal member by the magnetic restraining force of the second region. Thereby, the sealing performance of the developing device is ensured.

  In addition, since the first area facing the predetermined image carrier on which the toner image is formed has a magnetic restraining force lower than the magnetic restraining force of the second area, the first area is carried on the first area. The magnetic toner that is present can move to a predetermined image carrier without being greatly hindered by the magnetic restraining force of the first region. Thereby, it can be ensured that a good toner image is formed on a predetermined image carrier.

  As described above, the developing device according to the present invention can ensure the sealing performance without being affected by the layout restriction of the developing device by giving the second region a strong magnetic binding force. By suppressing the magnetic binding force of one area to a low level, the formation of a good toner image is ensured.

In a preferred embodiment of the present invention, the intermediate layer, the Oite in the second region, a ferromagnetic metal layer having a magnetic degree capable of exerting the magnetic binding force, the first region Oite is Ru weak magnetic metal layer der having a weaker magnetism than the magnetism of the ferromagnetic metal layer.

  According to this configuration, since the ferromagnetic metal layer is formed in the second region, the magnetic binding force for the magnetic toner can be easily ensured. On the other hand, since the weak magnetic metal layer is formed in the first region, smooth movement of the magnetic toner to the predetermined image carrier can be easily ensured.

  In another preferred embodiment of the present invention, the ferromagnetic metal layer and the weak magnetic metal layer are both nickel-plated layers containing phosphorus, and the ferromagnetic metal layer has a lower phosphorus than the weak magnetic metal layer. It has a content rate.

  According to this configuration, both the ferromagnetic metal layer and the weak magnetic metal layer are nickel plating layers and contain phosphorus. The phosphorus content is an element that affects the degree of magnetism of both metal layers. As the phosphorus content decreases, the magnetism increases, and as the phosphorus content increases, the magnetism decreases. In the above configuration, the ferromagnetic metal layer has a lower phosphorus content than the weak magnetic metal layer. Thus, by appropriately setting the phosphorus content, it is easy to apply a strong magnetic binding force to the ferromagnetic metal layer, and to ensure the transportability of the magnetic toner to a predetermined image carrier. Becomes easy.

  In still another preferred embodiment of the present invention, the phosphorus content of the ferromagnetic metal layer is 5% or less.

  According to this configuration, a strong magnetic binding force can be reliably applied to the ferromagnetic metal layer, and the reliability of the sealing performance of the developing device can be ensured even when the angle between the magnetic poles of the developing roller becomes large. Can be secured.

  The image forming apparatus according to the present invention includes: an image carrier on which a toner image is formed; and a developer that conveys a developer containing magnetic toner to the image carrier and forms the toner image on the image carrier. The developing device having the above structure is used as the developing device.

  The image forming apparatus according to the present invention includes a developing device that can ensure sealing performance without being affected by layout restrictions of the configuration. As a result, the degree of freedom in designing the image forming apparatus is increased, and contamination in the apparatus that may occur due to leakage of the magnetic toner is suppressed.

  According to the developing device and the image forming apparatus according to the present invention, it is possible to ensure the sealing performance of toner leakage even when the distance between the magnetic poles built in the developing roller is large.

1 is a diagram schematically illustrating an internal structure of an image forming apparatus. 2 is a diagram illustrating an internal configuration of a developing device used in the image forming apparatus. FIG. FIG. 3 is a view of the developing sleeve 24 as viewed from the photosensitive drum 10 side. It is sectional drawing cut | disconnected along the III-III line of FIG. It is a schematic diagram which shows the developing sleeve of the developing device in cross section. FIG. 6 is an enlarged view of a portion surrounded by a circle in FIG. 5 and shows a three-layer structure of a developing sleeve. It is a perspective view of a developing sleeve. It is sectional drawing cut | disconnected along the VII-VII line of FIG. It is a figure which shows the relationship between phosphorus content rate and a saturation magnetic flux density. It is a schematic diagram which shows magnetic flux distribution of the some magnetic pole incorporated in the image development sleeve. It is a figure which shows the result of the experiment conducted in order to test the sealing performance of a sealing member in the developing device of the conventional structure. FIG. 10 is a diagram for schematically explaining a toner leakage suppressing operation in the developing device according to the embodiment. It is a figure which shows the result of the experiment conducted in order to test the sealing performance of a sealing member in the developing device which concerns on this embodiment.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings. In the following description, a monochrome type printer is shown as an image forming apparatus as an embodiment of the present invention. However, the present invention is not limited to this, and a copying machine, a facsimile apparatus, and the functions thereof are described. The present invention can also be applied to other image forming apparatuses such as multifunction peripherals that are also included.

  FIG. 1 is a diagram schematically showing the internal structure of the image forming apparatus 1. The image forming apparatus 1 includes an image forming unit 4 that forms a toner image on the sheet P based on image data from the outside (for example, a personal computer), and the toner image formed on the sheet P by heating the sheet P A fixing unit 5 for fixing the sheet P, a sheet feeding cassette 7 for storing the sheet P, a sheet discharge tray 12 for discharging the sheet P, and a sheet discharged from the sheet feeding cassette 7 via the image forming unit 4 and the fixing unit 5. A conveyance path 6 that conveys the sheet P toward the tray 12, a manual feed tray 3 provided on the right side surface of the image forming apparatus 1 in FIG. 1, and a plurality of menu setting keys for setting various menus are arranged. And an operation unit (not shown).

  The image forming unit 4 irradiates the photosensitive drum 10 (image carrier), the charger 42 that performs a charging process on the photosensitive drum 10, and the laser beam L to the charged photosensitive drum 10, thereby electrostatically charging the photosensitive drum 10. An exposure device 43 that forms a latent image, a developing device 20 that electrostatically attaches toner to the electrostatic latent image formed on the photosensitive drum 10 to visualize the toner image, and develops the toner filled therein A toner cartridge 45 to be supplied to the apparatus 20, a transfer roller 46 (transfer member) for transferring the developed toner image to the sheet P, and a toner remover for removing and collecting toner remaining on the drum surface of the photosensitive drum 10. 47. Note that the charger 42, the developing device 20, the transfer roller 46, and the toner remover 47 are arranged in this order along the circumferential direction of the photosensitive drum 10 when viewed from the rotation direction of the photosensitive drum 10 (clockwise direction in FIG. 1). Are arranged. The exposure unit 43 is disposed above the charger 42.

  The photoconductor drum 10 is a drum having a photoconductor in which an amorphous silicon layer, which is a positively chargeable photoconductor, is deposited on the surface of an aluminum cylinder, for example.

  The charger 42 includes a charging roller 50, for example. The charging roller 50 uniformly charges the surface potential of the drum surface by applying a predetermined reference charging voltage (reference charging bias) in which a DC voltage and an AC voltage are superimposed on the drum surface.

  The exposure device 43 has a polygon mirror (not shown) that guides laser light L based on image data input from an external PC (personal computer) or the like to the drum surface of the photosensitive drum 10. The polygon mirror scans the laser beam L on the drum surface of the photosensitive drum 10 while rotating by a predetermined drive source, and forms an electrostatic latent image on the drum surface. The developing device 20 performs a developing operation of supplying toner to the electrostatic latent image to form a toner image on the drum surface.

  The transfer roller 46 is in pressure contact with the drum surface of the photosensitive drum 10 in the conveyance path 6, and a nip portion N is formed between the transfer roller 46 and the drum surface. Since a voltage having a polarity opposite to the surface potential of the drum surface is applied to the transfer roller 46, the toner image on the drum surface is transferred onto the sheet P when the sheet P passes through the nip portion N. The sheet P that has passed through the nip N is conveyed to the fixing unit 5 through the conveyance path 6.

  After the toner image on the sheet P is heated and fixed on the sheet P in the fixing unit 5, the sheet P is conveyed to the paper discharge tray 12 through the conveyance path 6.

  Hereinafter, the developing device 20 will be described in detail with reference to FIG. 2 in addition to FIG. FIG. 2 is a diagram illustrating an internal configuration of the developing device 20. The developing device 20 uses a one-component developer containing a magnetic toner having charging properties. As shown in FIGS. 1 and 2, a developing container 21 that defines an internal space of the developing device 20. The developer storage unit 11 that stores the developer, the developing roller 22 that faces the drum surface of the photosensitive drum 10, the regulating blade 30, and the seal member 38 are included as basic components. The developing device 20 can also use a two-component developer containing a non-magnetic toner and a magnetic carrier.

  The developing container 21 (housing) includes a bottom frame 21b and a main body frame 21a that covers the bottom frame 21b from above, and an internal space is defined between the two frames 21a and 21b.

  The developer storage unit 11 occupies most of the internal space and stores the developer, and the developer storage space S is formed in the bottom frame 21 b in the developer storage space S and extends in the longitudinal direction of the developing device 20. Adjacent developer circulation paths 14 and 15 are included.

  The developer circulation paths 14 and 15 are partitioned from each other in the longitudinal direction by a partition plate 17 made of a metal such as aluminum, for example, but communicate with each other at both ends in the longitudinal direction. Screw feeders 18 and 19 that convey the developer while being agitated by rotation are rotatably mounted on the developer circulation paths 14 and 15, respectively. Since the screw feeders 18 and 19 are set so that the conveying directions are opposite to each other, the developer is conveyed between the developer circulation path 14 and the developer circulation path 15 while being stirred. The developer storage unit 11 receives toner from the toner cartridge 45 into the developer storage space S through a supply port (not shown).

  The developing roller 22 is a roller member that conveys the developer to the photosensitive drum 10 to form a toner image on the photosensitive drum 10, and is between 0.2 mm and 0. The photoconductor drum 10 is disposed so as to face a gap of 4 mm. The developing roller 22 is a cylindrical developing sleeve 24 extending in the longitudinal direction of the developing device 20 (that is, the axial direction of the photosensitive drum 10), and the developing sleeve 24 is rotated in a counterclockwise direction in FIG. A roller member including a rotation shaft. The developing sleeve 24 receives the developer from the developer circulation path 14 and carries it on the outer peripheral surface 36, and conveys the developer in the order of a regulation blade 30, which will be described later, and the photosensitive drum 10 with rotation.

  A magnet roll 25 is built in the developing sleeve 24. The magnet roll 25 extends in the longitudinal direction of the developing sleeve 24 and is fixedly supported by the support shaft 28 with a minute gap formed between the inner surface of the developing sleeve 24.

  The magnet roll 25 is formed with a pumping pole 27. The scooping pole 27 is a magnetic pole, for example, an N pole, disposed opposite to the developer circulation path 14 via the developing sleeve 24. The scooping pole 27 magnetically adheres the toner in the developer circulation path 14 onto the outer peripheral surface 36 of the rotating developing sleeve 24 and carries it on the outer peripheral surface 36 as a developer layer. The toner is conveyed toward the regulating portion R as the developing sleeve 24 rotates.

  The restricting portion R is provided to make the layer thickness of the developer layer on the outer peripheral surface 36 thinner and uniform. The restricting portion R includes a restricting blade 30, a restricting pole 29, and a magnet member 35.

  The regulating blade 30 is a thin SUS member that is disposed above the developing sleeve 24 so as to face the developing sleeve 24 and extends in the longitudinal direction of the developing sleeve 24. The regulating blade 30 has a leading end portion 31 extending toward the developing sleeve 24, and a regulating gap G 1 of about 0.3 mm is formed between the leading end surface of the leading end portion 31 and the outer peripheral surface 36 of the developing sleeve 24. ing.

  The restriction pole 29 is a magnetic pole, for example, an S pole, formed on the magnet roll 25 so as to face the tip surface of the restriction blade 30. The magnet member 35 is a plate-like magnet that is joined to the upstream surface of the regulating blade 30 as viewed from the rotation direction of the developing sleeve 24 and extends in the longitudinal direction of the developing sleeve 24. The magnet member 35 has a distal end portion that extends toward the developing sleeve 24, and a magnetic pole having the same polarity as the regulation pole 29, for example, an S pole is formed at the distal end portion.

  The tip 31 of the regulation blade 30 is induced by a magnetic field of the regulation pole 29 and a magnetic field of the magnet member 35, and a magnetic pole, for example, an N pole, opposite to the regulation pole 29 and the tip of the magnet member 35 is induced. 30, a magnetic path, a so-called magnetic shield is formed between the regulation pole 29 and the magnet member 35. When the developer layer reaches the restricting portion R with the rotation of the developing sleeve 24, the developer layer is cut off by the restricting blade 30 while being magnetically restrained in the restricting gap G1 by the magnetic field of the magnetic shield. Thereby, the layer thickness of the developer layer is appropriately adjusted.

  Since the toner in the developer layer is brought into frictional contact with the outer peripheral surface 36 when being carried on the outer peripheral surface 36 of the developing sleeve 24, the toner is charged positively, for example. The toner is charged by frictional contact with the regulating blade 30 even when regulated by the regulating portion R. The toner in the regulated developer layer is conveyed toward the photosensitive drum 10 as the developing sleeve 24 rotates in such a charged state.

  In the magnet roll 25, a transport pole 39 is formed in addition to the draw-up pole 27 and the regulation pole 29. The transport pole 39 is a magnetic pole facing the photosensitive drum 10 via the developing sleeve 24, for example, an N pole. The transport pole 39 is arranged so that the magnetic lines of force are concentrated on the photosensitive drum 10. The toner that has passed through the regulating portion R is applied to the drum surface of the photosensitive drum 10 by the magnetic force of the transport pole 39 and by the potential difference between the developing bias applied to the developing sleeve 24 and the drum bias applied to the photosensitive drum 10. Adhere to the electrostatic latent image. Thereby, a toner image is formed on the drum surface.

  The seal member 38 is a member for suppressing the leakage of toner from the inside of the developing container 21, particularly from the developing sleeve 24 that carries the toner. The seal member 38 will be described with reference to FIGS. 3 and 4 in addition to FIG. 3 is a view of the developing sleeve 24 viewed from the photosensitive drum 10 side, and FIG. 4 is a cross-sectional view taken along the line III-III of FIG.

  The seal member 38 has a curved shape toward the inner space of the developing container 21 and along the outer peripheral surface 36 of the developing sleeve 24, and is disposed so as to face the end portion in the axial direction of the developing sleeve 24. Although not shown, a seal member 38 is also disposed opposite to the other axial end of the developing sleeve 24. A gap G <b> 2 of about 0.5 mm is formed along the outer peripheral surface 36 between the inner peripheral surface of the seal member 38 and the outer peripheral surface 36 of the developing sleeve 24. One end 381 of the seal member 38 viewed from the circumferential direction of the developing sleeve 24 faces the regulating blade 30 from the inner space side of the developing container 21. The other end 382 of the seal member 38 faces the photosensitive drum 10 from the inner space side of the developing container 21.

  On the magnet roll 25, a scattering prevention electrode 37 for preventing toner scattering is formed in addition to the drawing pole 27, the regulation electrode 29, and the conveyance pole 39. The anti-scattering pole 37 is a magnetic pole, for example, an S pole, located on the opposite side of the regulating pole 29 with the support shaft 28 interposed therebetween. As described above, the magnetic pole 25 has the four magnetic poles 27, 29, 37, and 39 arranged along the inner peripheral surface of the developing sleeve 24.

  The seal member 38 is made of a magnetic material such as SECC (electrogalvanized steel sheet). Since the seal member 38 faces the pumping pole 27, the regulation pole 29 and the scattering prevention pole 37 of the magnet roll 25 via the developing sleeve 24, the seal member 38 is magnetized by the magnetic force of the pumping pole 27, the regulation pole 29 and the scattering prevention pole 37. Then, a magnetic field is formed between the magnetic poles 27, 29, and 37. The seal member 38 magnetically restrains the toner in the gap G <b> 2 between the outer peripheral surface 36 and the seal member 38 at the axial end of the developing sleeve 24 by the action of the magnetic field. Therefore, the toner carried on the outer peripheral surface 36 of the developing sleeve 24 is prevented from leaking outside from the axial end of the developing sleeve 24.

  Next, the developing sleeve 24 will be referred to with reference to FIG. FIG. 5 is a schematic view showing the developing sleeve 24 in cross section. As shown in the figure, the developing sleeve 24 includes a cylindrical sleeve base material 32, a nickel plating layer 33 laminated on the outer peripheral surface 36 of the sleeve base material 32, and chromium laminated on the nickel plating layer 33. It has a three-layer structure including a plating layer 34.

  The sleeve base material 32 is an element tube made of a nonmagnetic metal such as aluminum. The nickel plating layer 33 is formed on the outer peripheral surface 36 by electroless plating. The kind of nickel plating is nickel (Ni) -phosphorus (P). The layer thickness of the nickel plating layer 33 is set to any value in the range of 0.3 μm to 10 μm.

  The chromium plating layer 34 is formed by electrolytic plating. The chromium plating layer 34 has a higher hardness (Vickers hardness) than the nickel plating layer 33. The layer thickness of the chromium plating layer 34 is set to any value in the range of 0.06 μm to 0.2 μm. The chromium is preferably trivalent chromium.

  FIG. 6 is an enlarged view of a portion CA surrounded by a circle in FIG. As shown in the figure, irregularities are formed on the outer peripheral surface 36 of the sleeve base 32 by blasting or the like. The surface roughness Rz of the outer peripheral surface 36 is set according to the average particle diameter of the toner. Specifically, the surface roughness Rz of the outer peripheral surface 36 is set slightly larger than the average particle diameter of the toner. When toner having an average particle diameter of 7.1 μm is used, the surface roughness Rz of the outer peripheral surface 36 is set to about 7.5 μm with a ten-point average roughness.

  The nickel plating layer 33 is formed along the unevenness of the outer peripheral surface 36 of the sleeve base material 32. Further, the upper layer 34 is formed along the unevenness of the outer peripheral surface 36 of the sleeve base material 32 through the nickel plating layer 33. A decrease in the degree of unevenness (surface roughness Rz) due to the formation of the nickel plating layer 33 and the upper layer 34 on the outer peripheral surface 36 is suppressed as much as possible.

  FIG. 7 is a perspective view of the developing sleeve 24. The developing sleeve 24 has a first area A1 that faces the drum surface of the photosensitive drum 10 and a second area A2 that faces the seal member 38 as the drum rotates. The second region A2 is set at each of both end portions of the developing sleeve 24 in the axial direction. The first area A1 is set between the pair of second areas A2.

  8 is a cross-sectional view taken along line VII-VII in FIG. The nickel plating layer 33 laminated on the outer peripheral surface 36 of the developing sleeve 24 extends from the first region A1 to the second region A2. In this embodiment, the nickel plating layer 33 has different phosphorus contents in the first portion 331 corresponding to the first region A1 and the second portion 332 corresponding to the second region A2.

  Specifically, the phosphorus content of the second portion 332 of the nickel plating layer 33 is set smaller than that of the first portion 331. The phosphorus content is an element that affects the degree of magnetism of the first portion 331 and the second portion 332. As the phosphorus content decreases (that is, as the nickel purity increases), the magnetism of the nickel plating increases. On the other hand, as the phosphorus content increases, the nickel plating becomes amorphous and the crystallinity decreases, so the magnetism becomes weaker. From the viewpoint of saturation magnetization, the saturation magnetization of nickel plating decreases as the phosphorus content increases, and the saturation magnetization of nickel plating increases as the phosphorus content decreases.

  In the present embodiment, in the second portion 332, the phosphorus content is set to 5% or less (that is, the nickel purity is set to 95% or more). In contrast, the first portion 331 is set to exceed 5%. Therefore, the second portion 332 is configured as a ferromagnetic metal layer having strong magnetism, and the first portion 331 is configured as a weak magnetic metal layer having magnetism weaker than that of the second portion.

  Accordingly, the saturation magnetization is different between the weak magnetic metal layer 331 and the ferromagnetic metal layer 332. FIG. 9 is a diagram showing the relationship between phosphorus content and saturation magnetic flux density. As shown in FIG. 9, the saturation magnetic flux density of nickel plating decreases as the phosphorus content increases, while the saturation magnetic flux density of nickel plating increases as the phosphorus content decreases.

  In the present embodiment, the ferromagnetic metal layer 332 has a higher saturation magnetic flux density than the weak magnetic metal layer 331. Therefore, the ferromagnetic metal layer 332 is more easily magnetized than the weak magnetic metal layer 331 due to the magnetic forces of the drawing pole 27, the regulation pole 29, and the scattering prevention pole 37 built in the developing sleeve 24. For this reason, the ferromagnetic metal layer 332 has a larger magnetic force acting on the toner carried on the outer peripheral surface 36 of the developing sleeve 24 than the magnetic force of the weak magnetic metal layer 331. As a result, the ferromagnetic metal layer 332 has a magnetic binding force that magnetically restrains (attaches) the toner carried on the outer peripheral surface 36 to the outer peripheral surface 36, and the magnetic binding force of the weak magnetic metal layer 331. Higher than.

  Incidentally, in the developing device 20 having the above-described configuration, the scooping pole 27, the regulating electrode 29, the transporting electrode 39, and the scattering prevention electrode 37 are configured to transport toner from the developing sleeve 24 to the photosensitive drum 10 and to seal the sealing member 38. The magnetic force of each magnetic pole 27, 29, 37, 39, the angle between the magnetic poles 27, 29, 37, 39, etc. are set appropriately. However, the top pole 27, the regulation pole 29, the transport pole 39, and the scattering prevention pole 37 are formed on the magnetic pole 27 due to restrictions on the layout of the developing device 20 and the layout of the entire image forming apparatus 1, for example, on the arrangement of the photosensitive drum 10. 29, 37, 39, for example, the angle α (FIG. 4) between the scooping pole 27 and the regulating pole 29 may become large. The angle α between the pumping pole 27 and the regulation pole 29 is an angle that is separated in the circumferential direction of the developing sleeve 24 when viewed from the rotation center of the developing sleeve 24 (that is, the magnet roll 25).

  FIG. 10 is a schematic diagram showing the magnetic flux distribution of the magnetic poles 27, 29, 37, 39 of the developing sleeve 24. In FIG. 10, the magnetic flux distribution is indicated by a one-dot chain line. When the angle α between the pumping pole 27 and the regulation pole 29 increases, the magnetic flux density greatly decreases at the boundary MB between the magnetic flux distribution of the pumping pole 27 and the flux distribution of the regulation pole 29 as shown in FIG. Therefore, the strength of the magnetic field decreases at the boundary MB. Thereby, the magnetic restraint force (seal performance) of the part corresponding to boundary MB in seal member 38 falls. As a result, the toner may leak from the corresponding portion to the outside.

FIG. 11 is a diagram showing the results of an experiment conducted for testing the sealing performance of a sealing member in a developing device having a conventional configuration. In the experiment, the sealing performance of the seal member was evaluated with respect to the change in the angle between the upper electrode and the regulating electrode (angle α in FIG. 10). The experimental conditions are listed below.
Development sleeve outer diameter: 20 mm
Development sleeve rotation speed: 496 mm / s
Toner: Magnetic toner Average particle diameter of toner: 7.1 μm
Regulating blade: SUS430
Development sleeve surface roughness: 7.5 μm
Magnetic force of the upper pole: 85mT
Magnetic force of regulation pole: 90mT
Magnetic force of transport pole: 89mT
Magnetic force of peeling pole: 80mT
In the experiment, after the developing device was continuously driven for 30 minutes without toner consumption, the sealing performance of the sealing member was evaluated. In addition, the angle between the pumping pole and the regulation pole was changed between 50 degrees and 160 degrees. Evaluation was performed in five stages of 1-5.
1: Completely sealed (the toner is blocked at the edge portion of the seal member).
2: Although the seal is made, the toner slightly enters the inside of the seal member.
3: The axial end of the developing sleeve is soiled with toner, but there is no leakage of toner.
4: There is some toner leakage.
5: The sealing member does not fulfill the sealing performance.

  As shown in FIG. 11, it was confirmed that the sealing performance of the sealing member deteriorated as the angle between the upper electrode and the regulating electrode increased. This is because, as described above, the magnetic flux density decreases at the boundary between the magnetic flux distribution of the pumping pole and the magnetic flux distribution of the regulating pole as the angle between the pumping pole and the regulating pole increases. Thus, it was confirmed that the sealing performance of the sealing member depends on the angle between the magnetic poles.

  However, in the developing device 20 according to the present embodiment, the leakage of toner can be suppressed without being affected by the angle between the magnetic poles, that is, without being influenced by the layout of the developing device 20 and the entire image forming apparatus 1. . With reference to FIG. 12, the toner leakage suppression operation in the developing device 20 will be described.

  That is, as described above, the ferromagnetic metal layer 332 made of nickel plating having a phosphorus content of 5% or less is formed in the second region A2 facing the seal member 38 in the developing sleeve 24. The ferromagnetic metal layer 332 has a strong magnetic binding force for magnetically binding the toner. Due to the layout restrictions of the developing device 20 and the image forming apparatus 1 as a whole, for example, the angle α (FIG. 10) between the pumping pole 27 and the regulating electrode 29 increases, and the space between the pumping pole 27 and the regulating electrode 29 and the seal member 38 is increased. When the strength of the magnetic field decreases, the magnetic binding force of the seal member 38 on the toner decreases. Therefore, the toner T <b> 2 tends to leak outside from the axial end portion of the developing sleeve 24.

  However, the toner T2 is magnetically restrained on the outer peripheral surface 36 of the developing sleeve 24 by the action of the ferromagnetic metal layer 332. In particular, the toner T2 on the outer peripheral surface 36 corresponding to the boundary MB (FIG. 10) between the magnetic flux distribution of the upper pole 27 and the magnetic flux distribution of the regulating pole 29 is magnetically constrained by the ferromagnetic metal layer 332. Is done. Thereby, the toner T2 is magnetically restrained between the outer peripheral surface 36 and the seal member 38, and leakage of the toner T2 to the outside is suppressed. As a result, the sealing performance of the developing device 20 is ensured. Thus, the ferromagnetic metal layer 332 of the developing roller 22 supplements the magnetic restraining force of the seal member 38 and suppresses the leakage of the toner T2.

  In addition, a weak magnetic metal layer 331 is formed in the first region A1 facing the photosensitive drum 10 in the developing sleeve 24. Since the weak magnetic metal layer 331 has a phosphorus content exceeding 5%, the degree of magnetism is significantly lower than that of the ferromagnetic metal layer 332 as shown in FIG. Therefore, the magnetic binding force of the toner of the weak magnetic metal layer 331 is considerably weaker than the magnetic binding force of the ferromagnetic metal layer 332. Therefore, the toner T1 carried on the outer peripheral surface 36 in the first region A1 can smoothly move to the photosensitive drum 10 without being largely hindered by the magnetic binding force of the weak magnetic metal layer 331. . Thereby, it can be ensured that a good toner image is formed on the photosensitive drum 10.

  As described above, the developing device 20 according to the present embodiment forms the ferromagnetic metal layer 332 having a strong magnetic binding force in the second region A2 of the developing sleeve 24, so that the developing device 20 and the image forming apparatus are formed. 1. A weak magnetic metal layer 331 having a low level of magnetic restraining force can be formed in the first region A1 of the developing sleeve 24 while being able to ensure sealing performance without being affected by the layout restrictions of the whole. Thus, the formation of a good toner image is ensured.

  In the developing device 20 according to the present embodiment, nickel plating is used to form the ferromagnetic metal layer 332 and the weak magnetic metal layer 331, and the phosphorus content in the nickel plating is appropriately set. It is easy to adjust the degree of magnetism of the ferromagnetic metal layer 332 and the weak magnetic metal layer 331.

  Further, since the ferromagnetic metal layer 332 is set to a phosphorus content of 5% or less, even when the angle between the magnetic poles (for example, the angle α between the pumping pole 27 and the regulating pole 29) is increased, A strong magnetic restraining force can be easily and reliably applied to the ferromagnetic metal layer 332. On the other hand, by appropriately setting the phosphorus content of the weak magnetic metal layer 331 within a range exceeding 5%, smooth transportability of the toner to the photosensitive drum 10 can be easily ensured.

  Next, an experiment performed using the developing device 20 according to the present embodiment will be described with reference to FIG. The experiment was conducted to test the sealing performance of the entire developing device 20. In the experiment, Example 1, Example 2, and Comparative Example 1 were used. In Example 1, the phosphorus content of the ferromagnetic metal layer 332 is set to 2%, and in Example 2, the phosphorus content is set to 4%, while in Comparative Example 1, the phosphorus content is 6%. Was set. Further, in the experiment, for each of Example 1, Example 2, and Comparative Example 1, the seal when the angle α (FIG. 10) between the pumping pole 27 and the regulating pole 29 is changed in the range of 50 degrees to 160 degrees. Performance was evaluated.

The experimental conditions are listed below.
Development sleeve outer diameter: 20 mm
Development sleeve rotation speed: 496 mm / s
Toner: Magnetic toner Average particle diameter of toner: 7.1 μm
Regulating blade: SUS430
Development sleeve surface roughness: 7.5 μm
Magnetic force of the upper pole: 85mT
Magnetic force of regulation pole: 90mT
Magnetic force of transport pole: 89mT
Magnetic force of peeling pole: 80mT

In the experiment, the sealing performance was evaluated after the developing device was continuously driven for 30 minutes without toner consumption. Further, the angle α between the pumping pole 27 and the regulating pole was changed between 50 degrees and 160 degrees. Evaluation was performed in five stages of 1-5.
1: Completely sealed (the toner is blocked at the edge portion of the seal member).
2: Although the seal is made, the toner slightly enters the inside of the seal member.
3: The axial end of the developing sleeve is soiled with toner, but there is no leakage of toner.
4: There is some toner leakage.
5: The sealing member does not fulfill the sealing performance.

  As shown in FIG. 13, in Example 1, it was confirmed that the sealing performance was good even when the angle α was increased to 160 degrees. Further, in Example 2, it was confirmed that the outer peripheral surface of the developing sleeve was slightly soiled in the range of the angle α of 140 to 160 degrees, but no toner leaked and the sealing performance was good. This is because the phosphorus content of the ferromagnetic metal layer 332 is set to 5% or less, so even if the angle α is increased and the sealing performance of the sealing member is reduced, the reduction amount of the ferromagnetic metal layer 332 is reduced. It is thought that it was compensated by magnetic restraint force.

  On the other hand, in Comparative Example 1, toner leakage was confirmed when the angle α was set to 160 degrees. This is presumably because the decrease in the sealing performance of the sealing member was not compensated by the magnetic binding force of the ferromagnetic metal layer because the phosphorus content of the ferromagnetic metal layer was 6%.

  From the above results, the phosphorus content of the ferromagnetic metal layer 332 is set to 5% or less, so that the development can be achieved even when the angle α between the scooping pole 27 and the regulating pole 29 is set to 160 degrees. It was confirmed that the sealing performance of the entire device could be secured.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Photosensitive drum 20 Developing device 22 Developing roller 24 Developing sleeve 32 Sleeve base material 33 Nickel plating layer 331 Weak magnetic metal layer 332 Ferromagnetic metal layer 34 Chrome plating layer 36 Outer peripheral surface 38 Seal member A1 First region A2 Second area

Claims (5)

A housing;
A developing roller rotatably disposed in the housing, and includes a plurality of magnetic poles arranged in a circumferential direction, and the developer containing magnetic toner is made to move along with the magnetic force of the plurality of magnetic poles along with the rotation. A developing roller that forms a toner image on the predetermined image carrier by conveying the image to the predetermined image carrier using
A gap is formed between the developing roller and the developing roller in the housing, and a magnetic field is formed between the plurality of magnetic poles in the gap, and the magnetic field A sealing member for restraining leakage of the magnetic toner to the outside by magnetically restraining the toner;
With
The developing roller includes a first region facing the predetermined image carrier and a second region facing the seal member;
The second region has a magnetic binding force for magnetically binding the magnetic toner,
The first region has a magnetic restraining force lower than the magnetic restraining force of the second region ;
The developing roller includes a developing sleeve having a cylindrical sleeve base, an intermediate layer laminated on the outer peripheral surface of the sleeve base, and a surface layer laminated on the intermediate layer,
The intermediate layer is a magnetic layer,
The surface layer, the developing device that have a higher hardness than the intermediate layer. The developing device according to claim 1,
The intermediate layer Oite the second region is a ferromagnetic metal layer having a magnetic degree capable of exerting the magnetic binding force,
The Oite the first region, the Ru said weakly magnetic metal layer der having a weaker magnetism than the magnetism of the ferromagnetic metal layer developing device. The developing device according to claim 2,
The ferromagnetic metal layer and the weak magnetic metal layer are both nickel-plated layers containing phosphorus,
The developing device wherein the ferromagnetic metal layer has a lower phosphorus content than the weak magnetic metal layer. The developing device according to claim 3,
The developing device in which the phosphorus content of the ferromagnetic metal layer is 5% or less. An image carrier on which a toner image is formed;
A developing device that conveys a developer containing magnetic toner to the image carrier and forms the toner image on the image carrier;
With
An image forming apparatus in which the developing device according to claim 1 is used as the developing device.

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