JP5139921B2 - Developing device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a developing device for developing an electrostatic latent image formed on an image carrier by an electrophotographic process using a developer, and an image forming apparatus such as a copying machine, a printer, and a facsimile equipped with the developing device. It is.

  In an image forming apparatus such as a copying machine or a printer that forms an image on a sheet by electrophotography, an electrostatic latent image formed on an image carrier is developed by a developing device and visualized as a developed image. The developed image is transferred onto the paper. Then, the sheet onto which the developed image has been transferred is conveyed to a fixing device, and after the developed image is fixed by heat and pressure by the fixing device, it is discharged out of the apparatus, thereby completing a series of image forming operations. .

  By the way, as a developing method using dry toner as a developer, a one-component developing method and a two-component developing method are known. In the one-component development method, since the developer to be used does not include a carrier, in the two-component development method in which a two-component developer composed of toner and carrier is used, a static brush on the image carrier is formed by a magnetic brush formed by the carrier and toner. Since the electrostatic latent image is not disturbed, high image quality can be achieved.

  However, in the one-component development method, it is difficult to stably maintain the toner charge amount. Further, in the case of a color toner, since high transparency is required, the color toner needs to be a non-magnetic toner.

  Therefore, in a full-color image forming apparatus, a two-component developing system using a two-component developer composed of toner as a developer and a carrier as a medium for charging and transporting the toner is often employed.

  In a developing device employing a two-component developing system, a thin toner layer is formed on a developing roller by a magnetic brush formed on a magnetic roller carrying a two-component developer, and an image is carried by the toner thin layer on the developing roller. Some employ a touch-down development method in which an electrostatic latent image on a body is developed and visualized as a toner image.

  Such a touch-down development method has a problem that toner accumulates in the lower part of the developing roller due to scattering of the toner. In order to solve this problem, Patent Document 1 discloses a recovery roller in the vicinity of the magnetic roller and the developing roller. A configuration has been proposed in which the toner is provided so as to be rotatable, the scattered toner is collected by the collecting roller, and the collected toner is peeled off from the collecting roller and returned to the developing device.

Further, in Patent Document 2, an electrode plate is disposed at a position facing the developing roller of the housing of the developing device, and a voltage having the same polarity as the toner charging polarity is applied to the electrode plate, thereby developing from the electrode plate side. There has been proposed a configuration in which scattered toner is pushed back to the developing roller side by the force of the electric field directed to the roller side.
JP 2005-242194 A JP 2001-066886 A

  By the way, in the developing device, preventing toner scattering is an important factor in realizing high image quality and long life, but in the developing device adopting the touch-down developing method described in Patent Document 1, Since the layout of the magnetic roller and the developing roller is limited, it is difficult to prevent the toner from scattering from the magnetic roller.

  Further, as disclosed in Patent Document 2, by simply applying a voltage having the same polarity as the charging polarity of the toner to the electrode plate, the insufficiently charged toner can easily be separated from the carrier on the magnetic roller, and the centrifugal force and There is a problem of falling from the magnetic roller due to gravity and scattering. In addition, if the voltage applied to the electrode plate is too large, the carrier adheres to the electrode plate, and the surface of the magnetic roller is damaged by this carrier, or the gap between the magnetic roller and the electrode plate is narrowed. The problem of overflowing careers occurs.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a developing device that can effectively prevent toner scattering in a touch-down developing method, and an image forming apparatus including the developing device. It is in.

In order to achieve the above object, a first aspect of the present invention provides a magnetic roller for magnetically holding a two-component developer composed of toner and a carrier, an electrode member disposed below the magnetic roller, and the magnetic roller. in the developing apparatus having a developing roller which carries the toner thin layer on the surface by the toner to be transferred from the set smaller than the distance between the developing roller and the said and the magnetic roller the distance between the electrode members electrode member In addition, an AC voltage having the same polarity as the toner is applied to the electrode member, and an absolute value of an effective value of the AC voltage is set larger than an absolute value of an effective value of the AC voltage applied to the magnetic roller. To do.

According to a second aspect of the present invention, in the first aspect, wherein the phase of the AC voltage applied to the electrode member is synchronized with the phase of the AC voltage applied to the magnetic roller.

According to a third aspect of the present invention, in the second aspect of the present invention, the electrode member is constituted by a rotatable collection roller.

An image forming apparatus according to a fourth aspect includes the developing device according to any one of the first to third aspects.

According to the first and third aspects of the present invention, the distance between the developing roller and the electrode member is set smaller than the distance between the magnetic roller and the electrode member. It is collected again by the electrode member or the developing roller in a narrow gap between the electrode member and the developing roller, and the leakage of the toner to the outside of the housing from the opening of the developing roller of the housing is surely prevented.

In addition , since an AC voltage having the same polarity as that of the toner is applied to the electrode member, the toner is hardly separated from the carrier carried on the surface of the magnetic roller, and the scattering of the toner from the magnetic roller is effectively prevented.

Furthermore, since the set larger than the absolute value of the effective value of the AC voltage applied absolute value of the effective value of the AC voltage applied to the electrode member to the magnetic roller, the scattered toner is collected and returned to the magnetic roller side, the magnetic roller The toner is prevented from scattering from the surface and the carrier is prevented from adhering to the collecting roller. In addition, the toner that is insufficiently charged or the toner charged to the opposite polarity is collected by the collecting roller, and the scattering thereof is prevented.

According to the invention of claim 2, since the phase of the AC voltage applied to the electrode member is synchronized with the phase of the AC voltage applied to the magnetic roller , a constant potential difference is always generated between the electrode member and the magnetic roller, Due to this potential difference, the scattered toner moves to the magnetic roller side and is collected.

According to the fourth aspect of the present invention, toner scattering is effectively prevented, a high-quality image is stably obtained, and the problem of in-machine contamination is solved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

[Image forming apparatus]
FIG. 1 is a cross-sectional view of a color laser printer as an embodiment of an image forming apparatus according to the present invention. The illustrated color laser printer is a tandem type, and a magenta image forming unit 1M is provided at the center of the main body. The cyan image forming unit 1C, the yellow image forming unit 1Y, and the black image forming unit 1K are arranged in tandem at regular intervals.

  Each of the image forming units 1M, 1C, 1Y, and 1K includes photosensitive drums 2a, 2b, 2c, and 2d as image carriers, developing devices 3a, 3b, 3c, and 3d, transfer rollers 4a, 4b, 4c, and 4d. It is configured to include.

  The developing devices 3a to 3d contain magenta (M) toner, cyan (C) toner, yellow (Y) toner, and black (K) toner, respectively, and are formed on the photosensitive drums 2a to 2d. Each color toner is attached to the electrostatic latent image to visualize each electrostatic latent image as a toner image of each color, the details of which will be described later.

  The transfer rollers 4a to 4d are disposed so as to be in contact with the photosensitive drums 2a to 2d via the intermediate transfer belt 5 at each primary transfer portion. Here, the intermediate transfer belt 5 is stretched between the secondary transfer counter roller 6, the driving roller 7, and the tension roller 8, and is disposed on the lower surface side of each of the photosensitive drums 2a to 2d. The secondary transfer counter roller 6 is disposed so as to be in contact with the secondary transfer roller 9 via the intermediate transfer belt 5 in the secondary transfer portion.

  A paper feed cassette 10 is detachably installed at the bottom of the apparatus main body 100, and a paper discharge tray 11 is provided at the top of the main body 100. Here, a plurality of sheets (not shown) are stacked and accommodated in the paper feed cassette 10, and the paper is taken out from the paper feed cassette 10 one by one by the pickup roller 12. , 14 and 15 are sent to the transport path L. In the transport path L, a registration roller pair 16, a fixing device 17, a transport roller pair 18, and a paper discharge roller pair 19 are arranged. The fixing device 17 includes a heating roller 20 and a pressure roller 21 that rotate in contact with each other.

  Next, an image forming operation by the color laser printer having the above configuration will be described.

  When an image formation start signal is issued, the photosensitive drums 2a to 2d are driven to rotate at a predetermined process speed in the direction of the arrow in FIG. 1 (counterclockwise) in each of the image forming units 1M, 1C, 1Y, and 1K. The photosensitive drums 2a to 2d are irradiated with laser light modulated by a color image signal for each color to form an electrostatic latent image corresponding to the color image signal for each color.

  First, the electrostatic latent image formed on the photosensitive drum 2a of the magenta image forming unit 1M is developed by the developing device 3a to be visualized as a magenta toner image. This magenta toner image is transferred to the arrow shown in FIG. 1 by the action of the transfer roller 4a to which a primary transfer bias opposite in polarity to the toner is applied at the primary transfer portion (transfer nip portion) between the photosensitive drum 2a and the transfer roller 4a. Primary transfer is performed on the intermediate transfer belt 5 that is rotationally driven in the direction.

  The intermediate transfer belt 5 on which the magenta toner image has been primarily transferred as described above moves to the next cyan image forming unit 1C. In the cyan image forming unit 1C as well, the cyan toner image formed on the photosensitive drum 2b is transferred to the magenta toner image on the intermediate transfer belt 5 at the primary transfer portion in the same manner as described above.

  Similarly, yellow and black toners respectively formed on the photosensitive drums 2c and 2d of the yellow and black image forming units 1Y and 1K on the magenta and cyan toner images superimposed and transferred on the intermediate transfer belt 5, respectively. The images are sequentially superimposed on each primary transfer portion, and a full-color toner image is formed on the intermediate transfer belt 5.

  Then, the full color toner image on the intermediate transfer belt 5 is taken out from the paper feed cassette 10 in accordance with the timing at which the leading end of the full color toner image reaches the secondary transfer portion (transfer nip portion) between the secondary transfer counter roller 6 and the secondary transfer roller 9. Then, the paper that has been sent to the registration roller pair 16 and temporarily waiting is conveyed to the secondary transfer portion. Then, a full-color toner image is collectively transferred from the intermediate transfer belt 5 onto the sheet conveyed to the secondary transfer unit by the secondary transfer roller 9 to which a secondary transfer bias having a polarity opposite to that of the toner is applied. .

  Thus, the sheet on which the full-color toner image has been transferred is conveyed to the fixing device 17, where the full-color toner image is heated and pressurized and thermally fixed on the surface of the sheet, and the sheet on which the toner image is fixed Then, the paper is transported upward along the transport path L by the transport roller pair 18 and discharged onto the paper discharge tray 11 by the paper discharge roller pair 19 to complete a series of image forming operations.

[Developer]
Next, details of the developing devices 3a to 3d according to the present invention will be described with reference to FIGS.

  The four developing devices 3a to 3d employ a touch-down developing method using a two-component developer, and all the configurations are the same. Therefore, only the magenta developing device 3a will be described below.

  FIG. 2 is a cross-sectional view of the main part of the developing device. A housing 22 of the developing device 3a shown in FIG. 2 contains a two-component developer composed of toner and a carrier and magnetically holds the two-component developer. A roller 23, a developing roller 24 that carries a toner thin layer on the surface thereof by toner transferred from the magnetic roller 23, and a recovery member that is disposed below the magnetic roller 23 and is an electrode member for recovering scattered toner The roller 25 and stirring members 26 and 27 for stirring the two-component developer are accommodated. Further, in the vicinity of the magnetic roller 23 at the upper part in the housing 22, a regulating blade 28 for fixing the height of the magnetic brush (protrusion) formed on the surface of the magnetic roller 23 is fixed. A cleaning blade 29 slidably in contact with the outer peripheral surface of the collection roller 25 is provided at the lower portion.

  The magnetic roller 23, the developing roller 24, and the collecting roller 25 are long and parallel to each other in the direction perpendicular to the paper surface of FIG. 2, and both ends of the axial direction (perpendicular to the paper surface in FIG. 2) can be rotated by bearings (not shown). The bias power sources 30, 31, and 32 are electrically connected to these. Here, the bias power supplies 30, 31, and 32 are for applying a bias voltage in which an AC voltage and a DC voltage are superimposed to the magnetic roller 23, the developing roller 24, and the collecting roller 25, respectively.

  Thus, the present embodiment is characterized in that the distance A between the developing roller 24 and the collection roller 25 is set smaller than the distance B between the magnetic roller 23 and the collection roller 25 (A <B). Here, the distance A between the developing roller 24 and the collecting roller 25 is such that the bias voltage applied to the collecting roller 25 does not leak to the developing roller 24, and the toner scattered from the magnetic brush on the magnetic roller 23 is again removed. A value that can be collected by the developing roller 24 or the collecting roller 25, specifically, 0.5 mm to 2.0 mm is set. The distance B between the magnetic roller 23 and the collection roller 25 is such that the tip of the magnetic brush formed on the magnetic roller 23 rubs the outer peripheral surface of the collection roller 25, that is, the ejection of toner from the inside of the housing 22. It is set to a value that can prevent physical adhesion of the carrier to the collection roller 25 while being prevented, specifically 1.5 mm to 3.0 mm.

  FIGS. 3A and 3B show waveforms of bias voltages (a superimposed voltage of an AC voltage and a DC voltage) applied to the magnetic roller 23 and the recovery roller 25, respectively. The effective AC voltage applied to the recovery roller 25 is shown in FIGS. The value Vdc is set to 400 V having the same polarity (positive polarity) as that of the toner, and the phase of the AC voltage applied to the recovery roller 25 is synchronized with the phase of the AC voltage applied to the magnetic roller 23.

  In this embodiment, the absolute value of the effective value Vdc of the alternating voltage applied to the recovery roller 25 is set to 400 V, and this value is set to be larger than the absolute value 200 V of the effective value Vdc of the alternating voltage applied to the magnetic roller 23. It is set large. Therefore, the AC component is canceled between the collection roller 25 and the magnetic roller 23, and the potential difference becomes 200V. In this embodiment, the peak-to-peak voltage Vpp applied to the magnetic roller 23 and the collection roller 25 is set to 1.2 kV for all, and the frequency is set to 2 kHz for both. Here, the effective value Vdc of the alternating voltage is equal to the area S1 of the waveform rising to the positive side and the area S2 of the waveform rising to the negative side in the voltage waveforms shown in FIGS. 3A and 3B (S1 = S2) Say voltage.

  Thus, in the developing device 3a, the two-component developer accommodated in the housing 22 is agitated by the rotation of the agitating members 26 and 27, so that the toner is triboelectrically charged to the positive polarity. The two-component developer is charged on the carrier and its surface magnetically constrained by a fixed magnet contained in the magnetic roller 23 as the magnetic roller 23 rotates in the direction of the arrow (clockwise) in FIG. A magnetic brush is formed on the surface of the magnetic roller 23 by the held toner, and this magnetic brush is conveyed to the developing roller 24.

  The magnetic brush on the magnetic roller 23 is layer-regulated at a certain height by the regulating blade 28, and only the toner rotates in the arrow direction (clockwise) in FIG. 2 due to the potential difference between the magnetic roller 23 and the developing roller 24. A toner layer is formed on the developing roller 24 by flying to the roller 24, and this toner layer is used for developing the electrostatic latent image formed on the photosensitive drum 2a shown in FIG.

After the development is performed as described above, the developing roller 24 having the residual toner layer is closest to the magnetic roller 23 having the developer layer at the facing position, and the magnetic brush on the magnetic roller 23 is located at the facing position. The residual toner layer on the developing roller 24 is scraped off by the mechanical force. At the same time, toner is supplied from the developer layer on the magnetic roller 23 to the developing roller 24 according to a potential difference (electric field) formed between the magnetic roller 23 and the developing roller 24.

  By the way, although toner scattering inevitably occurs in the housing 22 of the developing device 3a, in this embodiment, the effective value Vdc of the AC voltage applied to the collecting roller 25 has the same polarity as that of the toner (as described above). (Positive polarity) is set to 400V, and this value is set to be larger than the absolute value 200V of the effective value Vdc of the AC voltage applied to the magnetic roller 23. Therefore, an AC component is generated between the recovery roller 25 and the magnetic roller 23. Is offset and the potential difference becomes 200V. Accordingly, the positively charged scattered toner is returned to the magnetic roller 23 and collected, preventing the toner from scattering from the surface of the magnetic roller 23 and preventing the carrier from adhering to the collecting roller 25. Further, the toner that is insufficiently charged or the toner charged to the opposite polarity (negative polarity) is collected by the collecting roller 25, and the scattering thereof is prevented.

  In particular, in the present embodiment, since the AC voltage having the same polarity (positive polarity) as that of the toner is applied to the recovery roller 25, the toner is difficult to be separated from the carrier carried on the surface of the magnetic roller 23. The scattering of toner from the magnetic roller 23 is effectively prevented.

  In this embodiment, since the phase of the AC voltage applied to the recovery roller 25 is synchronized with the phase of the AC voltage applied to the magnetic roller 23, a potential difference of 200 V is always generated between the recovery roller 25 and the magnetic roller 23. The scattered toner moves to the magnetic roller 23 side due to the potential difference and is collected. In the present embodiment, the effective value Vdc of the AC voltage applied to the recovery roller 25 is set to 400V, and the absolute value of the effective value Vdc of the AC voltage applied to the magnetic roller 23 is set to 200V. 200V is generated between the magnetic roller 23 and the magnetic roller 23. However, if the potential difference between the recovery roller 25 and the magnetic roller 23 is in the range of 100 to 300V, the recovery roller 25 is prevented from scattering toner from the surface of the magnetic roller 23. The carrier can be prevented from sticking to the surface.

  Thus, when the carrier is prevented from adhering to the collection roller 25 as described above, the burden on the cleaning blade 29 for slidingly contacting the outer peripheral surface of the collection roller 25 to clean the collection roller 25 is reduced. Therefore, the cleaning blade 29 is prevented from being damaged or deteriorated, and its durability is enhanced.

In this embodiment, the distance A between the developing roller 24 and the collection roller 25 is set smaller than the distance B between the magnetic roller 23 and the collection roller 25 (A <B), and this distance A is set to the collection roller 25. The applied voltage is such that the applied toner does not leak to the developing roller 24 and the toner scattered from the magnetic brush on the magnetic roller 23 can be collected again by the developing roller 24 (specifically, 0.5 mm to 2.0 mm), even if the toner scatters from the magnetic roller 23, the scattered toner is collected again by the recovery roller 25 or the development roller 24 in a narrow gap between the recovery roller 25 and the development roller 24. Is done. Therefore, developing a low-La 24 toner leakage from the opening which opens to the outside of the housing 22 of the housing 22 is prevented reliably, the machine contamination due to toner problem can be solved. The distance B between the magnetic roller 23 and the collection roller 25 is such that the tip of a timing brush (bump) formed on the magnetic roller 23 rubs the outer peripheral surface of the collection roller 25 (specifically, 1.5 mm to 3.0 mm), it is possible to prevent physical adhesion of the carrier to the collection roller 25 while preventing the ejection of toner from the inside of the housing 22.

  In the above, the embodiment in which the present invention is applied to the color laser printer and the developing device provided in the color laser printer has been described. However, the present invention is not limited to a copying machine other than a printer, a facsimile machine, or any combination image of these multifunction machines. Of course, the present invention can be similarly applied to a forming apparatus and a developing device provided in the forming apparatus.

1 is a cross-sectional view of a color laser printer according to the present invention. 1 is a cross-sectional view of a developing device according to the present invention. (A) is a waveform diagram of the bias voltage applied to the magnetic roller, (b) is a waveform diagram of the bias voltage applied to the recovery roller.

Explanation of symbols

1M Magenta image forming unit 1C Cyan image forming unit 1Y Yellow image forming unit 1K Black image forming unit 2a to 2d Photosensitive drum 3a to 3d Developing device 4a to 4d Transfer roller 5 Intermediate transfer belt 6 Secondary transfer counter roller 7 Drive roller 8 Tension Roller 9 Secondary transfer roller 10 Paper feed cassette 11 Paper discharge tray 12 Pickup roller 13-15 Transport roller 16 Registration roller pair 17 Fixing device 18 Transport roller pair 19 Paper discharge roller pair 20 Heating roller 21 Pressure roller 22 Developing device housing 23 Magnetic roller 24 Developing roller 25 Collection roller (electrode member)
26, 27 Stirring member 28 Regulating blade 29 Cleaning blade 30-32 Bias power supply 100 Apparatus body A Distance between developing roller and collection roller B Distance between magnetic roller and collection roller L Conveyance path

Claims (4)

A magnetic roller for magnetically holding a two-component developer composed of toner and a carrier, an electrode member disposed below the magnetic roller, and a toner thin layer supported on the surface by the toner transferred from the magnetic roller In a developing device provided with a developing roller,
A distance between the developing roller and the electrode member is set to be smaller than a distance between the magnetic roller and the electrode member, and an AC voltage having the same polarity as the toner is applied to the electrode member, and an effective value of the AC voltage is determined. A developing device characterized in that an absolute value is set larger than an absolute value of an effective value of an alternating voltage applied to the magnetic roller . A developing device according to claim 1, wherein the phase of the AC voltage applied to the electrode member is synchronized with the phase of the AC voltage applied to the magnetic roller. 3. The developing device according to claim 1, wherein the electrode member is constituted by a rotatable collection roller. An image forming apparatus comprising the developing device according to any one of claims 1-3.

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