JP4387281B2 - Development device - Google Patents

Description

  The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic system or an electrostatic recording system.

  In general, in an image forming apparatus such as a copying machine, a printer, or a facsimile machine, an electrostatic latent image is formed on a photosensitive member, a developer is supplied from the developing device to the photosensitive member, and the developer is subjected to static on the photosensitive member. The electrostatic latent image is developed to form a developer image on the photoconductor, the developer image is transferred from the photoconductor to the recording paper, the recording paper is heated and pressurized, and the developer image is recorded on the recording paper. It is fixed on the top.

  In the developing device, for example, a two-component developer obtained by mixing a toner and a magnetic carrier is stirred, the toner is charged, and the two-component developer is adhered to the surface of the developing roller while rotating the developing roller. The developer is conveyed and supplied to the developing area between the developing roller and the photosensitive member, and the electrostatic latent image on the photosensitive member is developed with the toner of the two-component developer. The developing roller includes a cylindrical sleeve and a magnet disposed in the sleeve. While rotating the sleeve, the two-component developer is adsorbed on the sleeve surface by the magnetic field of the magnet in the sleeve. The agent is conveyed and supplied from the sleeve to the photoreceptor.

  In such a developing device, the potential and charging polarity on the surface of the photoconductor, the potential and magnetic polarity on the surface of the developing roller (sleeve), and the charging polarity of the toner are set appropriately, and the toner is electrostatically latent on the surface of the photoconductor. The electrostatic latent image is developed by attaching it to the image. For example, as shown in FIG. 8A, the potential Vo of the non-carrying area of the electrostatic latent image on the surface of the photoconductor is set to −650V, and the potential VL of the carrying area of the electrostatic latent image is set to −100V. Then, the bias Vb on the surface of the developing roller is set to -500V. Further, as shown in FIG. 8B, the toner is charged to a negative polarity, and the magnetic carrier is set to a positive polarity. In this case, since the potential Vo (−650 V) in the non-carrying area of the electrostatic latent image is lower by +150 V than the potential Vb (−500 V) on the developing roller surface, negative polarity toner is transferred from the developing roller surface to the electrostatic latent image. The toner does not move to the non-carrying region, and toner is not carried in the non-carrying region of the electrostatic latent image. Further, since the potential VL (−100 V) of the electrostatic latent image carrying area is higher by +400 V than the potential Vb (−500 V) of the developing roller surface, negative polarity toner is carried from the developing roller surface to the electrostatic latent image carrying area. And the toner is carried on the electrostatic latent image carrying region. As a result, a toner image is formed on the surface of the photoreceptor.

  By the way, in the conventional developing device, for example, when an electrostatic latent image such as a character document having a high occupancy ratio in a white region or a low density region is repeatedly formed on the surface of the photosensitive member, it moves from the developing roller surface to the photosensitive member surface. The amount of toner is reduced, and the toner remaining on the surface of the developing roller is likely to be generated. If the image forming apparatus is not operated at night or on holidays, and the toner remaining on the surface of the developing roller is left unattended, the toner may be fused to the surface of the developing roller due to environmental (temperature and humidity) changes. The image quality was degraded.

  For this reason, for example, in Patent Document 1, a conductive blade that is in sliding contact with the sleeve surface of the developing roller is provided, and a DC voltage having the same polarity as the charging polarity of the toner is applied to the conductive blade. By injecting, the charged polarity of the toner is charged to the original polarity to prevent the toner from fusing to the sleeve surface.

Further, in Patent Document 2, after the developer is constrained on the surface of the developing sleeve by the conveying magnetic pole (pumping pole), only the low tribo toner on the surface of the developing sleeve is removed by the low tribo toner removing member to which a bias voltage is applied. Thus, the low tribo toner is removed, whereby the tribo of the developer is stabilized without lowering the toner concentration in the developer, and the image quality is maintained over a long period of time.
JP 2001-242714 A JP 2001-281998 A

  However, in Patent Document 1, since the conductive blade is slidably contacted with the sleeve surface, the toner is rubbed against the sleeve surface by the conductive blade. Could not be prevented sufficiently.

  Further, in Patent Document 2, since only the low tribo toner in the developer constrained on the surface of the developing sleeve is removed, all of the toner adhering to the surface of the developing roller cannot be removed, and the toner is fused. Could not be prevented.

  Accordingly, the present invention has been made in view of the above-described conventional problems, and provides a developing device capable of more reliably preventing toner of a two-component developer from fusing to the surface of the developer carrying member. The purpose is to do.

In order to solve the above-described problems, the present invention provides a two-component developer obtained by mixing a chargeable toner and a magnetic carrier while rotating the developer carrier, and the surface of the developer carrier by a magnetic field of the developer carrier. by adhering to, the developing device transporting supplies to the developing region between the two-component developer a developer carrying member and the image bearing member, is disposed opposite in non-contact with said developer carrying member surface, the developer carrying a charge imparting means which is applied a voltage such as to suck the chargeable toner of the body surface, on the upstream side of the charge providing means in the conveying direction of the two-component developer by said developer carrying member, the developer carrying member surface And an electrode plate to which an AC voltage is applied. The developer electrode is disposed on the upstream side in the transport direction of the two-component developer by the developer carrier. Arranged to approach the surface It has been.

  Further, in the present invention, a release portion for releasing the two-component developer from the surface of the developer carrier is provided outside the region where the two-component developer is attached to the surface of the developer carrier by the magnetic field of the developer carrier. In addition, a charging means is provided in the vicinity of the release location.

  In the present invention, the charging means is provided upstream of the release position in the transport direction of the two-component developer by the developer carrier.

  Further, in the present invention, the gap between the developer carrying member and the charging means is set to be larger than the diameter of the magnetic carrier and set to be equal to or less than the distance at which the chargeable toner on the surface of the developer carrying member can be sucked. Yes.

  In the present invention, the charging means is a rod-shaped body made of a conductive material.

  Furthermore, in the present invention, the charge applying means and the electrode plate are non-magnetic materials.

  In the present invention, the polarity of the voltage applied to the charging means is set to be opposite to the charging polarity of the chargeable toner.

  Further, in the present invention, the respective voltages are applied to the charging means and the electrode plate after the image forming operation for forming the toner image on the surface of the image carrier is completed.

  In the present invention, the respective voltages are not applied to the charging means and the electrode plate during the period in which the toner image is formed on the surface of the image carrier.

On the other hand, according to the present invention, a two-component developer obtained by mixing a chargeable toner and a magnetic carrier is attached to the surface of the developer carrier by the magnetic field of the developer carrier while rotating the developer carrier. In the developing device that conveys and supplies the component developer to the developing area between the developer carrier and the image carrier, the developer is disposed in a non-contact manner along the surface of the developer carrier, and the AC voltage and the chargeability of the developer carrier surface And an electrode plate that is applied with a DC voltage superimposed so as to attract toner, and the electrode plate moves toward the upstream side in the transport direction of the two-component developer by the developer carrier. It is arranged to approach.

  In the present invention, a release point for releasing the two-component developer from the surface of the developer carrier is provided outside the region where the two-component developer is attached to the surface of the developer carrier by the magnetic field of the developer carrier. The electrode plate is provided on the upstream side of the release location.

  Further, in the present invention, after the image forming operation for forming the toner image on the surface of the image carrier, the AC voltage and the DC voltage are superimposed and applied to the electrode plate.

  In the present invention, AC voltage and DC voltage are not applied to the electrode plate during the period of forming the toner image on the surface of the image carrier.

  According to the developing device of the present invention, the two-component developer is adhered to the surface of the developer carrier by the magnetic field of the developer carrier while rotating the developer carrier, and the two-component developer is attached to the developer carrier. Is conveyed to the development area between the image carrier and the image bearing member, and the charging means is disposed so as to face the developer carrier surface in a non-contact manner, and on the upstream side, the electrode plate extends along the surface of the developer carrier. It is arranged without contact. Then, an AC voltage is applied to the electrode plate, and a voltage that attracts the chargeable toner on the surface of the developer carrying member is applied to the charging device. An alternating magnetic field is generated by the AC voltage of the electrode plate, and this alternating magnetic field vibrates the magnetic carrier and the chargeable toner of the two-component developer on the surface of the developer carrier, and the magnetic carrier is developed by the magnetic field of the developer carrier. The toner is sucked onto the surface of the carrier, and the chargeable toner and the chargeable toner are separated into layers on the surface of the developer carrier. Subsequently, the charging toner is easily released from the surface of the developer carrying member by suction of the charging toner by the charging means. Further, since the electrode plate and the charge applying means do not contact the surface of the developer carrying member, the charging toner is not rubbed against the surface of the developer carrying member by the electrode plate and the charge applying means. Thereby, it is possible to reliably prevent the charging toner from being fused to the surface of the developer carrying member.

  Further, the electrode plate is disposed so as to approach the surface of the developer carrier as it goes upstream in the transport direction of the two-component developer by the developer carrier. Therefore, on the upstream side in the transport direction, the electrode plate approaches the developer carrier surface, the alternating magnetic field due to the AC voltage of the electrode plate is strong, the magnetic carrier and the chargeable toner vibrate greatly, and the downstream side in the transport direction The alternating magnetic field due to the AC voltage on the electrode plate becomes weaker and the vibration of the magnetic carrier and the chargeable toner becomes smaller. Through such a process, the magnetic carrier is attracted to the surface of the developer carrier by the magnetic field of the developer carrier, and the chargeable toner and the chargeable toner are separated into layers on the surface of the developer carrier.

  For example, a release point for releasing the two-component developer from the developer carrier surface is provided outside the region where the two-component developer is adhered to the developer carrier surface by the magnetic field of the developer carrier. A charging means is provided in the vicinity of the location. In this case, after the chargeable toner and the chargeable toner are separated into layers on the surface of the developer carrier by the alternating magnetic field of the electrode plate, the chargeable toner is easily released from the surface of the developer carrier by the suction of the charging means. At substantially the same time, the two-component developer is released from the surface of the developer carrier, and the chargeable toner is reliably released from the surface of the developer carrier.

  In addition, a charging unit is provided on the upstream side of the release position in the transport direction of the two-component developer by the developer carrier. In this case, the chargeable toner and the chargeable toner are separated into layers on the surface of the developer carrier by the alternating magnetic field from the electrode plate, and then the chargeable toner is released from the surface of the developer carrier by the suction of the charging means. Immediately after this, the two-component developer is released from the surface of the developer carrier, and the chargeable toner is reliably released from the surface of the developer carrier.

  Furthermore, the gap between the developer carrying member and the charging means is set larger than the diameter of the magnetic carrier. In general, since the diameter of the magnetic carrier is larger than the diameter of the chargeable toner, such a setting allows both the chargeable toner and the magnetic carrier on the surface of the developer carrier to pass through the gap. The conductive toner and the magnetic carrier do not have to be rubbed against the surface of the developer carrying member. Since the gap between the developer carrying member and the charging means is set to be equal to or less than the distance at which the chargeable toner on the surface of the developer carrying member can be sucked, the charging toner can be reliably sucked. .

  For example, the charging means is a rod-shaped body made of a conductive material. The charging means and the electrode plate are non-magnetic materials. For this reason, the charging means and the electrode plate do not have a strong influence on the surrounding magnetic field, and the flow and circulation of the two-component developer are not hindered in the vicinity of the charging means and the electrode plate.

  In addition, the polarity of the voltage applied to the charging means is set to be opposite to the charging polarity of the chargeable toner. Thereby, the charging toner and the charging toner on the surface of the developer carrying member are attracted to each other, and the charging toner is easily released from the surface of the developer carrying member.

  Further, after the image forming operation for forming the toner image on the surface of the image carrier, the respective voltages are applied to the charging unit and the electrode plate. Alternatively, the respective voltages are not applied to the charging means and the electrode plate during the period of forming the toner image on the surface of the image carrier. For this reason, the voltage of the electrode plate and the charging means does not affect the toner image forming process on the surface of the image carrier.

  On the other hand, according to the present invention, the charging means is omitted, the electrode plate is disposed in a non-contact manner along the surface of the developer carrier, and the AC voltage and the chargeable toner on the surface of the developer carrier are applied to the electrode plate. A DC voltage that sucks in is superimposed and applied. An alternating magnetic field is generated by the AC voltage of the electrode plate, and this alternating magnetic field vibrates the magnetic carrier and the chargeable toner of the two-component developer on the surface of the developer carrier, and the magnetic carrier is developed by the magnetic field of the developer carrier. The toner is sucked onto the surface of the carrier, and the chargeable toner and the chargeable toner are separated into layers on the surface of the developer carrier. At the same time, the charging toner is easily released from the surface of the developer carrying member by suction of the charging toner by the DC voltage of the electrode plate. Further, since the electrode plate does not contact the surface of the developer carrier, the toner is not rubbed against the surface of the developer carrier by the electrode plate. This can more reliably prevent the toner from fusing to the surface of the developer carrying member.

  For example, a release point for releasing the two-component developer from the developer carrier surface is provided outside the region where the two-component developer is adhered to the developer carrier surface by the magnetic field of the developer carrier. An electrode plate is provided upstream of the location. In this case, immediately after the chargeable toner and the chargeable toner are separated into layers on the surface of the developer carrier by the alternating magnetic field of the electrode plate, and the residual toner is easily released from the surface of the developer carrier by the suction of the electrode plate. The two-component developer is released from the surface of the developer carrier, and the chargeable toner is reliably released from the surface of the developer carrier.

  In addition, an AC voltage and a DC voltage are applied to the electrode plate after completion of the image forming operation for forming a toner image on the surface of the image carrier. Alternatively, AC voltage and DC voltage are not applied to the electrode plate during the period of forming the toner image on the surface of the image carrier. For this reason, the voltage of the electrode plate does not affect the toner image forming process on the surface of the image carrier.

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

  FIG. 1 is a side view schematically showing an image forming apparatus to which a developing device according to a first embodiment of the present invention is applied. In this image forming apparatus, an image is formed by an electrophotographic method, and a developing device 12, a transfer roller 13, a static elimination lamp 14, a cleaning device 15, a charging roller 16, an exposure device 17, and the like rotate the photosensitive drum 11. It arranges in order from the upstream of the direction. Further, power sources 22, 23, and 24 that apply voltages to the developing roller 21, the transfer roller 13, and the charging roller 16 of the developing device 12 are provided. Further, a fixing device 18 is disposed on the downstream side in the conveyance direction of the recording paper P.

  In this image forming apparatus, the surface of the photosensitive drum 11 is uniformly charged by the charging roller 16 while rotating the photosensitive drum 11 in the direction of arrow A. Then, while modulating the light beam irradiated from the exposure device 17 to the photosensitive drum 11 based on the image data, the surface of the photosensitive drum 11 is scanned by this light beam, and the electrostatic latent image is formed on the photosensitive drum 11. Form an image. Further, toner is attached to the electrostatic latent image on the photosensitive drum 11 by the developing roller 21 of the developing device 12 to form a toner image, and this toner image is transferred from the photosensitive drum 11 to the recording paper P by the transfer roller 13. And the toner image on the recording paper P is fixed by heating and pressing by the fixing device 18. Thereafter, the charge on the surface of the photosensitive drum 11 is removed by the charge eliminating lamp 14, and the residual toner on the photosensitive drum 11 is removed by the cleaning device 14, thereby cleaning the surface of the photosensitive drum 11.

  In addition, you may apply the thing of another system as the photosensitive drum 11, each apparatus, and the rollers 13-18.

  FIG. 2 is a side view showing the vicinity of the developing device 12 of the present embodiment. FIG. 3 is a side view showing the developing device 12 of this embodiment.

  The developing device 12 of this embodiment is built in an electrophotographic image forming apparatus. The developing device 12 is connected to an intermediate hopper 31, and the intermediate hopper 31 is connected to a toner bottle 32.

  The toner bottle 32 contains toner and can replenish the toner little by little to the intermediate hopper 31 through the toner replenishment paths 32a and 31a, or can stop the toner replenishment.

  The intermediate hopper 31 is supplied with toner from the toner bottle 32 and temporarily stores it, and supplies the toner to the developing device 12 through the toner supply paths 31b and 12a. In the intermediate hopper 31, the stirring member 33 is rotated to stir the toner in the intermediate hopper 31, and the replenishing roller A34a and the replenishing roller B34b are rotated to remove the toner in the intermediate hopper 31 from the toner replenishment path 31b, It is moved to the 12a side. Further, the flexible belt-like member 35 is connected to one end of the stirring member 33, and the detected body 36 is fixedly supported at the tip thereof. Further, the electrostatic capacity sensor 37 is fixed to the bottom of the intermediate hopper 31 and detects the electrostatic capacity between the electrostatic capacity sensor 37 and the detection object 36 at the tip of the flexible belt-shaped member 35.

  Here, in a state where the toner in the intermediate hopper 31 is reduced, the vicinity of the tip of the flexible belt-like member 35 slides on the toner surface, and the detection object 36 also slides and moves on the toner surface. When the toner surface height decreases as the toner in the intermediate hopper 31 decreases, the position of the detected object 36 that slides and moves on the toner surface gradually decreases, and the detected object 36 that slides on the toner surface. And the distance between the capacitance sensor 37 is shortened. Therefore, the capacitance between the capacitance sensor 37 and the detected body 36 is detected by the capacitance sensor 37 at the timing when the detection target 36 moves immediately above the capacitance sensor 37, and this capacitance is detected. A separation distance between the corresponding capacitance sensor 37 and the detection target 36 is obtained, and a remaining amount of toner corresponding to the separation distance is obtained. Then, in accordance with the decrease in the remaining amount of toner, notification is made that the toner is replenished from the toner bottle 32 to the intermediate hopper 31 or the replacement of the toner bottle is urged.

  The developing device 12 stores a developer mixed with a magnetic carrier and toner in the case 12b, supplies the toner in the developer to the photosensitive drum 11 of the image forming apparatus, and electrostatically charges the surface of the photosensitive drum 11. The latent image is developed to form a toner image on the surface of the photosensitive drum 11. In the developing device 12, the agitation roller 41 is rotated to agitate the developer, and the magnetic carrier and the toner are frictionally charged by the agitation to apply a charge to the magnetic carrier and the toner.

  The developing roller 21 has a rod-like multipolar magnetized magnet 21b fixed thereto, and a nonmagnetic material (aluminum alloy, stainless steel, etc.) sleeve 21a rotatably supported around the multipolar magnetized magnet 21b. The developer is attracted to and carried on the outer periphery of the sleeve 21a by the magnetic force of the magnet 21b while rotating the sleeve 21a.

  The multipolar magnetized magnet 21b includes a plurality of S poles 21c, 21e, 21g, and 21i and a plurality of N poles 21d, 21f, and 21h that are alternately arranged, and the N pole 21d that is a developing pole from the S pole 21c. The developer is attracted to and supported on the outer periphery of the sleeve 21a by the magnetic force of the magnet 21b in a range that reaches the S pole 21i via the.

  With the rotation of the sleeve 21a, the developer layer thickness on the outer periphery of the sleeve 21a is regulated by the tip of the second regulating member 42, and the developer layer thickness on the outer circumference of the sleeve 21a is regulated again by the first regulating member 43. Then, the developer layer on the outer periphery of the sleeve 21 a is conveyed to the developing region D between the sleeve 21 a and the photosensitive drum 11.

  The toner in the developer layer on the outer periphery of the sleeve 21 a is frictionally charged by the stirring roller 41 with a polarity opposite to that of the electrostatic latent image on the surface of the photosensitive drum 11. For this reason, when the developer layer on the outer periphery of the sleeve 21a reaches the developing region D between the sleeve 21a and the photosensitive drum 11, the toner of the developer layer adheres to the electrostatic latent image on the surface of the photosensitive drum 11, This electrostatic latent image becomes a toner image.

  Further, surplus developer is generated due to the layer thickness regulation of the first regulating member 43. This excess developer flows to the reflux port 45, slides down the back surface of the second regulating member 42, and returns to the stirring roller 41 side.

  A well-known toner concentration sensor 46 is provided on the bottom of the case 12 b of the developing device 12. The toner concentration sensor 46 is a magnetic permeability sensor, for example, and detects a toner concentration corresponding to the magnetic permeability of the developer. The developer is a non-magnetic toner mixed with a magnetic carrier. For this reason, when the amount of toner per unit volume of the developer increases, the amount of magnetic carrier per unit volume decreases, and the magnetic resistance of the developer increases. Conversely, when the amount of toner per unit volume decreases, the amount of magnetic carrier per unit volume increases and the magnetic resistance of the developer decreases. The toner density sensor 46 detects the magnetic resistance of such a developer, and detects the amount of toner per unit volume corresponding to the magnetic resistance, that is, the toner density.

  For the toner concentration of the developer in the case 12b, a target specified range is set in advance, so that the toner concentration of the developer in the case 12b detected by the toner concentration sensor 46 falls within the specified range. Then, the replenishing roller 47 of the developing device 12 is rotated to replenish toner from the intermediate hopper 31 to the case 12b of the developing device 12 through the toner replenishing paths 31b and 12a.

  By the way, in such a developing device 12, for example, when an electrostatic latent image such as a character document having a high occupation ratio in a white area or a low density area is repeatedly formed on the surface of the photosensitive drum 11, the surface of the sleeve 21 a of the developing roller 21. The amount of toner that moves from the surface of the photosensitive drum 11 to the surface of the photosensitive drum 11 is reduced, and the toner that remains attached to the surface of the sleeve 21a is likely to be generated. When the image forming apparatus is not operated at night or on holidays, and the toner remaining on the surface of the sleeve 21a is left, the toner is fused to the surface of the sleeve 21a due to environmental (temperature and humidity) changes. The image quality is degraded.

  Therefore, in this embodiment, the developer on the surface of the sleeve 21a is once released on the downstream side of the developing region D in the rotation direction B (developer transport direction) of the sleeve 21a of the developing roller 21, and then the surface of the sleeve 21a. Then, the developer is adsorbed again to prevent the toner from fusing to the surface of the sleeve 21a.

  Next, the configuration and operation for releasing the developer on the surface of the sleeve 21a of the developing roller 21 will be described with reference to FIGS. FIG. 4 is a side view schematically showing a part of the developing device.

  In the developing device 12, in order to release the developer on the surface of the sleeve 21a of the developing roller 21, the two S poles 21c and 21i of the multipolar magnet 21b are moved at a position shifted by 180 degrees from the developing region D around the developing roller 21. Provided so as to be adjacent to each other, a repulsive magnetic field is formed between the S poles 21c and 21i, and a position outside the developing roller 21 on a straight line passing through the center of the repelling magnetic field from the axis of the developing roller 21 is developed. It is set as the release point Q of the agent. At the release point Q, the magnetic force between the S poles 21c and 21i becomes 0 Tesla, the developer magnetic carrier is peeled off from the surface of the sleeve 21a, and the developer toner is also peeled off from the surface of the sleeve 21a together with the magnetic carrier. .

  The release of the developer from the surface of the sleeve 21a at the release portion Q is performed at any time as long as the sleeve 21a of the developing roller 21 is rotating. Accordingly, during the image forming process, the loading and releasing of the developer on the surface of the sleeve 21a is repeated.

  On the other hand, a charging member 48 is provided at a position slightly spaced upstream from the release point Q in the rotation direction of the sleeve 21a of the developing roller 21, and the voltage of the DC power supply 49 is applied to the charging member 48. The toner charged to the (−) polarity on the surface of the sleeve 21 a is sucked by the DC voltage of the charging member 48. The DC voltage of the DC power supply 49 is set to a polarity (+) opposite to the toner charging polarity (−), and its voltage level is set to + 300V.

  The charging member 48 is a round bar having a diameter of about several millimeters made of a conductive material and a non-magnetic material (copper or the like), and is arranged in parallel with a slight distance from the sleeve 21a. For example, the gap between the charging member 48 and the sleeve 21a is set to a level slightly exceeding the particle size of the developer. Generally, the particle size of the magnetic carrier is larger than the particle size of the toner. For this reason, for example, if the particle size of the magnetic carrier is 37 μm to 80 μm, the gap between the charging member 48 and the sleeve 21 a is set to a value slightly exceeding the particle size of 37 μm to 80 μm of the magnetic carrier. As a result, the developer on the surface of the sleeve 21a passes through the gap, and the toner and the magnetic carrier are not rubbed against the surface of the sleeve 21a by the charging member 48.

  Further, the electrode plate 51 is disposed so as to approach the surface of the sleeve 21a as it goes upstream of the charging member 48 in the rotation direction of the sleeve 21a of the developing roller 21 and upstream in the rotation direction of the sleeve 21a. . An AC voltage of an AC power source 52 is applied between the electrode plate 51 and the sleeve 21a, an alternating magnetic field is generated by the AC voltage of the electrode plate 51, and the magnetic carrier on the surface of the sleeve 21a is vibrated by the alternating magnetic field. The magnitude of this alternating magnetic field is set to 1 to 10 kV / mm (pp), and the frequency is set to 1 to 5 kHz.

  The sleeve 21 a is connected to an AC power supply 52 and a DC power supply 53 through the shaft of the developing roller 21, and is applied with a (−) bias voltage of the DC power supply 53.

  The electrode plate 51 has a plate shape made of a conductive material and a non-magnetic material (such as copper).

  Here, the effect | action of the electrode plate 51 is demonstrated, referring FIG. 5 (a), (b).

  First, when an AC voltage of an AC power source 52 is applied between the electrode plate 51 and the sleeve 21a, an alternating electric field is generated between the electrode plate 51 and the sleeve 21a as shown in FIG. Electric field lines are formed. The strength of this alternating electric field decreases as the distance between the electrode plate 51 and the sleeve 21a increases. When charged particles are present in the alternating electric field, the charged particles receive an electrostatic force having a magnitude proportional to the strength of the electric field along the direction of the alternating electric field.

  Therefore, the alternating electric field is strong at a place where the distance between the electrode plate 51 and the sleeve 21a is narrow, and the charged particles receive a large electrostatic force corresponding to the strong alternating electric field, and vibrate with a large amplitude. It becomes easy to collide with the sleeve 21a.

  As the charged particles move in the rotation direction B of the sleeve 21a, the distance between the electrode plate 51 and the sleeve 21a gradually increases, the alternating electric field around the charged particles becomes weak, and the electrostatic force received by the charged particles also decreases. , The amplitude of the charged particles is reduced. When the alternating electric field around the charged particles reaches a certain value or less, the charged particles are pulled back in the opposite direction before reaching one of the electrode plate 51 and the sleeve 21a, and do not collide with the electrode plate 51 and the sleeve 21a. Thus, the vibration of the charged particles gradually converges.

  Such a phenomenon occurs under the condition that the charged particles move in a direction in which the distance between the electrode plate 51 and the sleeve 21a gradually increases. If the electrode plate 51 and the sleeve 21a are parallel to each other, the charged particles do not vibrate or continue to vibrate with a very small amplitude in a weak alternating electric field. It only collides violently with the plate 51 and the sleeve 21a.

  Further, the vibration amplitude of the charged particles depends on the mass and the charge amount of the charged particles. For example, the smaller the mass and the larger the charge amount, the larger the vibration amplitude in the alternating electric field. In general, the absolute value of the specific charge (charge amount per unit mass) of the toner is about 10 to 50 times that of the magnetic carrier. Therefore, when this charged particle is replaced with a charged magnetic carrier and toner, it can be seen that the magnetic carrier and the toner vibrate with respective amplitudes. Further, when the magnetic carrier and the toner have particularly high resistance, their charging polarities are different from each other, so that they vibrate in opposite phases (in the opposite direction). For this reason, the magnetic carrier and the toner are gradually separated from each other regardless of the initial conditions.

  At this time, since the toner is easily separated from the magnetic carrier, variation in the charge amount of the toner can be reduced. In particular, even when the toner particle size is small and the adhesion force between the magnetic carrier and the toner (which is said to depend on van der Waals force or mirror image force) is large, the toner particles are separated by applying an external force such as a strong alternating electric field. Can be made.

  Even in the case of a one-component developer (toner), if the toner is agglomerated and placed between the electrode plate 51 and the sleeve 21a, the toner vibrates in an alternating electric field, and the toner moves to the electrode plate 51 and the sleeve 21a. Since the toner collides, the agglomeration of the toner is solved by the collision energy. Therefore, the toner is separated and moves individually.

  That is, as shown in FIG. 5B, when a magnetic carrier and toner are placed between the electrode plate 51 and the sleeve 21a, the magnetic carrier and toner are separated from each other while oscillating in opposite phases. Further, even if the aggregation of only the toner is placed between the electrode plate 51 and the sleeve 21a, the aggregation is dissolved and each toner particle moves individually.

  As the sleeve 21a rotates, the magnetic carrier and toner on the surface of the sleeve 21a move from a portion where the distance between the electrode plate 51 and the sleeve 21a is narrow to a wide portion. In places where the distance between the electrode plate 51 and the sleeve 21a is narrow, the alternating electric field is strong, and the magnetic carrier and the toner vibrate vigorously in opposite phases and are separated from each other.

  As the distance between the electrode plate 51 and the sleeve 21a increases, the vibration amplitude of the magnetic carrier and the toner decreases as the alternating electric field decreases. At this time, the magnetic carrier is less likely to move than the toner, and is attracted to the surface of the sleeve 21a by the magnetic force of the south pole 21i of the multipolar magnet 21b, so that a magnetic brush is formed as a layer on the surface of the sleeve 21a. Go. Part of the toner is captured by the magnetic brush on the surface of the sleeve 21a, and most of the toner continues to vibrate.

  Further, when the distance between the electrode plate 51 and the sleeve 21a is increased, the vibration of most of the toner is reduced. Then, the adhesion of most of the toner to the surface of the sleeve 21a gradually decreases, and this most of the toner is gradually captured by the tip of the magnetic brush on the surface of the sleeve 21a. As a result, the toner density near the tip of the magnetic brush is increased, and the magnetic carrier and toner are separated into layers on the surface of the sleeve 21a.

  In this manner, in the state where the magnetic carrier and the toner are separated in layers on the surface of the sleeve 21a, as will be described later, the toner is effectively sucked at the position where the charging member 48 and the sleeve 21a face each other, and the subsequent development is performed. The agent can be easily peeled off and collected.

  In the image forming apparatus, even after the image forming process is completed, the photosensitive drum 11, the roller 21 of the developing device 12, the other rollers 13, 16 and the like are subsequently rotated. Then, during this subsequent rotation, an AC voltage from the AC power source 52 is applied to the electrode plate 51 for a certain period. At the same time, the (+) voltage from the DC power source 49 is also applied to the charging member 48 for a certain period.

  For example, as shown in FIG. 6, in the image forming process period T 1, the photosensitive drum 11, each device, the rollers 13 to 18, and the like are operating, and the surface of the photosensitive drum 11 is charged to −650 V by the charging roller 16. Thus, the surface of the sleeve 21a of the developing roller 21 is also charged with a (−) voltage. Even after the period T1 of the image forming process is completed, the photosensitive drum 11, the roller 21 of the developing device 12, the other rollers 13, 16 and the like are subsequently rotated for a while. An AC voltage is applied from the AC power supply 52 to the electrode plate 51 and a voltage of about +300 V is applied from the DC power supply 49 to the charge applying member 48 for a certain period T2 during the subsequent rotation.

  The voltage of the AC power supply 52 is set to be less than the discharge start voltage between the electrode plate 51 and the developing roller 21, and the voltage of the DC power supply 49 is set to be less than the discharge start voltage between the charge applying member 48 and the developing roller 21.

  When an AC voltage is applied, the electrode plate 51 forms an alternating magnetic field between the electrode plate 51 and the sleeve 21a as described above, and this alternating magnetic field vibrates the magnetic carrier and toner on the surface of the sleeve 21a. Then, the magnetic carrier and toner on the surface of the sleeve 21a are separated into layers.

  As the sleeve 21a rotates, the portion of the sleeve 21a where the magnetic carrier and toner are separated in layers moves to a position where the charging member 48 and the sleeve 21a face each other.

  Since the (+) voltage is applied to the charging member 48, the toner charged to the (−) polarity on the surface of the sleeve 21a is attracted by the (+) potential of the charging member 48. At this time, as described above, since the gap between the charging member 48 and the sleeve 21a is set to be slightly larger than the particle diameter of the magnetic carrier, the toner on the surface of the sleeve 21a is strongly attracted by the charging member 48. Is done. This suction facilitates the release of toner from the surface of the sleeve 21a.

  Further, as the sleeve 21a rotates, the magnetic carrier and the toner on the surface of the sleeve 21a are separated into layers and the portion where the toner is easily released moves to the release location Q between the S poles 21c and 21i. Then, at the release point Q, the developer is released from the surface of the sleeve 21a.

  As described above, in this embodiment, the magnetic carrier and the toner on the surface of the sleeve 21a are separated into layers by the alternating magnetic field between the electrode plate 51 and the sleeve 21a, and then the toner on the surface of the sleeve 21a is sucked by the charging member 48, The toner is easily released from the surface of the sleeve 21a, and then the developer is released from the surface of the sleeve 21a at the release point Q. Therefore, the developer can be reliably released, and the toner on the surface of the sleeve 21a can be reliably released. Can be prevented.

  Further, the AC voltage of the AC power supply 52 is applied to the electrode plate 51 and the voltage of the DC power supply 49 is applied to the charging member 48 only for a certain period T2 after the image forming process is completed. The potential of the applying member 48 does not affect the image forming process. In addition, since the electrode plate 51 and the charge imparting member 48 are non-magnetic, the electrode plate 51 and the charge imparting member 48 do not have a strong influence on the surrounding magnetic field, and in the vicinity of the electrode plate 51 and the charge imparting member 48. The flow and circulation of the two-component developer are not hindered.

  FIG. 7 is a side view schematically showing a part of the second embodiment of the developing apparatus of the present invention. In the developing device of this embodiment, the charging member 48 of FIGS. 2 to 4 is omitted, and the DC voltage of the DC power source 49 and the AC voltage of the AC power source 52 are superimposed and applied to the electrode plate 51.

  Also in this developing device, the DC voltage of the DC power source 49 and the AC voltage of the AC power source 52 are superimposed and applied to the electrode plate 51 only for a certain period T2 after the image forming process as shown in FIG.

  At this time, an alternating magnetic field is formed by an alternating voltage between the electrode plate 51 and the sleeve 21a, and the magnetic carrier and toner on the surface of the sleeve 21a vibrate by this alternating magnetic field, and the magnetic carrier and toner on the surface of the sleeve 21a are separated into layers. To do. At the same time, the toner charged to the (−) polarity on the surface of the sleeve 21a is sucked by the (+) potential of the electrode plate 51 by the DC voltage, and the toner is easily released from the surface of the sleeve 21a by this suction.

  Subsequently, along with the rotation of the sleeve 21a, the magnetic carrier and the toner on the surface of the sleeve 21a are separated into layers and the portion where the toner is easily released moves to the release location Q between the S poles 21c and 21i. With Q, the developer is reliably released from the surface of the sleeve 21a. This prevents the toner from being fused to the surface of the sleeve 21a.

  Further, since the DC voltage of the DC power source 49 and the AC voltage of the AC power source 52 are applied to the electrode plate 51 only for a certain period T2 after the image forming process is completed, the potential of the electrode plate 51 affects the image forming process. Never give. Moreover, since the electrode plate 51 is a non-magnetic material, the electrode plate 51 does not have a strong influence on the surrounding magnetic field, and the flow and circulation of the two-component developer are not hindered in the vicinity of the electrode plate 51. .

  In addition, this invention is not limited to the said Example, It can deform | transform variously. For example, when a toner charged to (+) polarity is used as the toner, a (−) voltage is applied to the charging member 48. Further, the positions of the electrode plate 51 and the charging member 48 may be moved as appropriate, or the period during which the voltage is applied to the electrode plate 51 and the charging member 48 may be changed as appropriate.

1 is a side view schematically showing an image forming apparatus to which a first embodiment of a developing device of the present invention is applied. FIG. 2 is a side view showing the vicinity of the developing device in FIG. 1. It is a side view which shows the developing device of FIG. FIG. 2 is a side view schematically showing a part of the developing device of FIG. 1. (A) is a figure which shows the electric field between an electrode plate and a sleeve, (b) is a figure which shows the motion of the magnetic carrier and toner between an electrode plate and a sleeve. It is a figure which shows the electrical potential change of a photoconductive drum, a developing device, and a charge provision member. It is a side view which shows roughly a part of Example 2 of the developing device of the present invention. FIG. 5 is a diagram illustrating a potential on the surface of a photoconductor, a potential on a surface of a developing roller, and a charging polarity of toner.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Photosensitive drum 12 Developing device 13 Transfer roller 14 Static elimination lamp 15 Cleaning device 16 Charging roller 17 Exposure device 18 Fixing device 21 Developing roller 21a Sleeve 21b Magnet 22-24 Power supply 48 Charging member 49 DC power supply 51 Electrode plate 52 AC power supply

Claims (13)

While rotating the developer carrier, a two-component developer obtained by mixing a chargeable toner and a magnetic carrier is attached to the surface of the developer carrier by the magnetic field of the developer carrier, and the two-component developer is developed as a developer. In the developing device that conveys and supplies the developing area between the carrier and the image carrier,
Noncontact arranged opposite the charge imparting means which is applied a voltage such as to suck the charged toner of the developer carrying member surface to the surface of the developer carrying member,
Wherein upstream from said charge providing means in the conveying direction of the two-component developer by the developer carrying member, disposed along the surface of the developer carrying member in a non-contact, and an electrode plate which is applied an AC voltage,
The developing device according to claim 1, wherein the electrode plate is disposed so as to approach the surface of the developer carrier as it goes upstream in the transport direction of the two-component developer by the developer carrier . A release point for releasing the two-component developer from the surface of the developer carrier is provided outside the region where the two-component developer is attached to the surface of the developer carrier by the magnetic field of the developer carrier. The developing device according to claim 1, further comprising a charging unit. The developing device according to claim 2, wherein the charge imparting unit is provided upstream of the release position in the transport direction of the two-component developer by the developer carrier. The gap between the developer carrying member and the charge applying unit is set to be larger than the diameter of the magnetic carrier and set to be equal to or less than a distance at which the chargeable toner on the surface of the developer carrying member can be attracted. Item 2. The developing device according to Item 1. The developing device according to claim 1, wherein the charging unit is a rod-shaped body made of a conductive material. The developing device according to claim 1, wherein the charging unit and the electrode plate are made of a non-magnetic material. The developing device according to claim 1, wherein the polarity of the voltage applied to the charging unit is set to be opposite to the charging polarity of the chargeable toner. 2. The developing device according to claim 1, wherein after the image forming operation for forming a toner image on the surface of the image carrier, the respective voltages are applied to the charge applying unit and the electrode plate. 2. The developing device according to claim 1, wherein each voltage is not applied to the charging unit and the electrode plate during a period in which a toner image is formed on the surface of the image carrier. While rotating the developer carrier, a two-component developer obtained by mixing a chargeable toner and a magnetic carrier is attached to the surface of the developer carrier by the magnetic field of the developer carrier, and the two-component developer is developed as a developer. In the developing device that conveys and supplies the developing area between the carrier and the image carrier,
An electrode plate is disposed in a non-contact manner along the surface of the developer carrying member, and is applied with an alternating voltage and a DC voltage applied so as to attract the chargeable toner on the surface of the developer carrying member,
The developing device according to claim 1, wherein the electrode plate is disposed so as to approach the surface of the developer carrier as it goes upstream in the transport direction of the two-component developer by the developer carrier . A release point for releasing the two-component developer from the surface of the developer carrier is provided outside the region where the two-component developer is attached to the surface of the developer carrier by the magnetic field of the developer carrier. The developing device according to claim 10, wherein an electrode plate is provided upstream of the developing device. The developing device according to claim 10, wherein an AC voltage and a DC voltage are superimposed and applied to the electrode plate after the period of forming the toner image on the surface of the image carrier. The developing device according to claim 10, wherein an AC voltage and a DC voltage are not applied to the electrode plate during a period in which a toner image is formed on the surface of the image carrier.

Images