JP4367040B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these, and more particularly to improvement of a cleaning technique in the image forming apparatus.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers using an electrophotographic system (electrostatic transfer system) are widely known. In such an image forming apparatus, the toner image is formed on the recording sheet by transferring the toner image onto the recording sheet by the final transfer member and fixing the toner image. The toner that has not been transferred onto the recording sheet is removed by a cleaning device in the image forming apparatus.

  As for cleaning in the image forming apparatus, the following techniques have been conventionally proposed. That is, a technique has been proposed in which residual toner on the intermediate transfer member or the final transfer member is collected on the final transfer member, and the residual toner is collectively cleaned by a cleaning device in contact with the final transfer member (for example, , See Patent Document 1).

Further, the multi-color toner is transferred onto the recording sheet between the final transfer body and the second intermediate transfer body, and the multi-color toner is normally negatively charged (this is referred to as a positive toner). The voltage of the final transfer body is set so that transfer failure of the multi-color toner onto the recording sheet does not occur, and the cleaning device avoids cleaning failure of the residual toner (positive electrode toner) in the multi-color toner. Based on voltage setting.
JP 2001-75448 A

  However, depending on the type and conveyance speed of the recording sheet, a single-color residual toner among the multi-color residual toners becomes a reverse polarity toner (positively charged) by the voltage (excess current) applied to the final transfer member. In other words, the single-color residual toner that has become the reverse polarity toner cannot be completely recovered by the cleaning device having the voltage setting. Therefore, as shown in FIG. 7, the residual toner (reverse polarity toner) that could not be collected overlaps with the next multi-color toner in the nip portion with the first intermediate transfer member on the upstream side, forming a so-called ghost. It sometimes appeared on the final image.

Therefore, in view of such problems, the present invention can reliably collect and remove residual toner even if the charged state (polarity) of the residual toner changes depending on the type of recording medium and the conveyance speed. The object is to obtain a forming device.

In order to achieve the above object, an image forming apparatus according to claim 1 according to the present invention includes an image carrier on which an electrostatic latent image is formed on a surface due to a difference in charging potential, and a surface of the image carrier. An image forming means for forming a toner image on the surface, a transfer body to which the toner image of the image carrier is transferred, a final transfer body for transferring the toner image from the transfer body to a recording medium, and a cleaning contact with the transfer body. And a control means for controlling a potential gradient between the image carrier, the transfer body, the final transfer body, and the cleaning body. In the image forming apparatus, the toner image of the transfer body is transferred to the cleaning body. A reverse polarity toner adhesion voltage for forming a potential gradient that causes the reverse polarity toner remaining on the transfer body to adhere to the cleaning body when transferred to the recording medium, and a toner image of the transfer body are the recording medium Is transcribed into And a positive toner adhesion voltage for forming a potential gradient that causes the positive toner remaining on the transfer body to adhere to the cleaning body, and a toner image on the transfer body is recorded on the recording body. The voltage of the cleaning body when transferring to the medium is switched between the reverse polarity toner adhesion voltage and the positive polarity toner adhesion voltage according to the type of the recording medium.

According to the first aspect of the present invention, the voltage of the cleaning body when the toner image on the transfer body is transferred to the recording medium is switched between the reverse polarity toner adhesion voltage and the positive polarity toner adhesion voltage according to the type of the recording medium . Therefore , even if the charging state (polarity) of the residual toner changes depending on the type of the recording medium, an appropriate voltage value is set according to the change, so that the residual toner can be reliably collected. Therefore, no ghost or the like occurs.

According to a second aspect of the present invention, there is provided an image forming apparatus comprising: an image carrier on which an electrostatic latent image is formed on a surface by a difference in charge potential; and an image that forms a toner image on the surface of the image carrier. Forming means; a transfer body to which a toner image of the image carrier is transferred; a final transfer body to transfer a toner image from the transfer body to a recording medium; a cleaning body in contact with the transfer body; and these image carriers. An image forming apparatus comprising: a transfer member; a final transfer member; and a control unit that controls a potential gradient between the cleaning member, and a toner image on the transfer member when the toner image on the transfer member is transferred to the recording medium. In addition, a reverse polarity toner adhesion voltage for forming a potential gradient that causes the reverse polarity toner remaining on the transfer body to adhere to the cleaning body, and when the toner image of the transfer body is transferred to the recording medium, Remaining on the transfer body A positive toner adhesion voltage to the positive toner to form a potential gradient as is attached to the cleaning member that is configured to is applied, the cleaning member at the time of transferring the toner image of the transfer member to the recording medium Is switched between the reverse polarity toner adhesion voltage and the positive polarity toner adhesion voltage according to the conveyance speed of the recording medium.

According to the second aspect of the present invention, the voltage of the cleaning body when transferring the toner image on the transfer body to the recording medium can be switched between the reverse polarity toner adhesion voltage and the positive polarity toner adhesion voltage according to the conveyance speed of the recording medium. . Therefore , even if the charging state (polarity) of the residual toner changes depending on the conveyance speed of the recording medium, an appropriate voltage value is set according to the change, so that the residual toner can be reliably collected. Therefore, no ghost or the like occurs.

The image forming apparatus according to claim 3 is the image forming apparatus according to claim 1 or claim 2, during continuous printing, when the voltage of the cleaning body is switched, without conveying the recording medium It is characterized by performing cleaning .

The image forming apparatus according to claim 4, in the image forming apparatus according to any one of claims 1 to 3, as the image bearing member, comprising a plurality of image bearing members for different colors As the transfer body, a first transfer body to which toner images are transferred from the plurality of image carriers, and a toner image is transferred from the first transfer body, and comes into contact with the final transfer body to be transferred to the recording medium. And a second transfer member that transfers the image .

The image forming apparatus according to claim 5, in the image forming apparatus according to any one of claims 1 to 3, as the image bearing member, comprising a plurality of image bearing members for different colors The transfer body includes a first upstream intermediate transfer body that contacts a part of the plurality of image carriers, a first downstream intermediate transfer body that contacts the rest of the plurality of image carriers, and these After the toner image is transferred from the first upstream intermediate transfer member in contact with the first upstream intermediate transfer member and the first downstream intermediate transfer member, the toner image is transferred from the first downstream intermediate transfer member. And a second intermediate transfer member to be transferred, wherein the final transfer member is in contact with the second intermediate transfer member .

Furthermore, the image forming apparatus according to claim 6, in the image forming apparatus according to any one of claims 1 to 3, as the image bearing member, for yellow, magenta, black, cyan A first upstream intermediate transfer member and a first downstream intermediate transfer member that are in contact with two of the four image carriers, respectively. After the toner image is transferred from the first upstream intermediate transfer member after contacting the first upstream intermediate transfer member and the first downstream intermediate transfer member, the toner is transferred from the first downstream intermediate transfer member. And a second intermediate transfer member to which an image is transferred, wherein the final transfer member contacts the second intermediate transfer member.

The image forming apparatus according to claim 7, in the image forming apparatus according to claim 5 or claim 6, as the cleaning member, a first upstream in contact with the first upstream side intermediate transfer member A cleaning body and a second cleaning body in contact with the second intermediate transfer body are provided .

Then, the image forming apparatus according to claim 8, in an image forming apparatus according to claim 7, wherein the control means, reverse polarity toner after the recording medium transfer, through the second intermediate transfer member, wherein An image forming potential gradient that adheres to the second cleaning body is formed, and the image forming apparatus according to claim 9 is the image forming apparatus according to claim 7, wherein the control unit includes: The positive toner after transfer of the recording medium forms an image forming potential gradient that adheres to the second cleaning member via the second intermediate transfer member .

The image forming apparatus according to claim 1 0, in the image forming apparatus according to any one of claims 5 to 7, wherein the control means, reverse polarity toner after the recording medium transfer, the A potential gradient that adheres to the first upstream cleaning member is formed through the second intermediate transfer member and the first upstream intermediate transfer member .

The image forming apparatus according to claim 1 1, in the image forming apparatus according to any one of claims 5 to 7, as the cleaning member, contacting the first downstream side intermediate transfer member first, further comprising a downstream cleaning body and as said, the image forming apparatus according to claim 12, in an image forming apparatus according to claim 11, wherein the control means is reversed on the final transfer body A potential gradient is formed such that the polar toner adheres to the first downstream cleaning body through the second intermediate transfer body and the first downstream intermediate transfer body .

The image forming apparatus according to claim 1 3, in the image forming apparatus according to any one of claims 1 to 12, wherein the cleaning body is that it is constituted by at least one roll It is a feature .

Further, the image forming apparatus according to claim 1 4, in the image forming apparatus according to any one of claims 1 to 12, wherein the cleaning member is a cleaning roller, pressed against the said cleaning roll cleaning A cleaning device having a blade and a container for collecting the toner cleaned by the cleaning roll and the cleaning blade is provided.

  The image forming means includes a charging means for uniformly charging the surface of the image carrier, a latent image forming means (exposure means) for forming an electrostatic latent image corresponding to the output image on the surface of the image carrier, Examples include a developing unit that selectively applies toner to the electrostatic latent image formed on the surface of the image carrier. Further, as one aspect of the charging means, a contact type charging body that comes into contact with the image carrier and uniformly charges the surface thereof can be cited. In this case, the control means controls the potential gradient between the contact-type charged bodies in addition to the image carrier, intermediate transfer body, final transfer body, and cleaning body.

  As described above, according to the present invention, since an optimum cleaning voltage is selected according to the type of recording medium and the conveyance speed, the residual toner can be reliably collected regardless of the polarity of the residual toner.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below in detail based on the embodiments shown in the drawings. FIG. 1 is a schematic side view showing a tandem type full color printer as an image forming apparatus according to the present invention, and FIG. 2 is a schematic side view showing a main part of the full color printer shown in FIG. The full color printer 10 is roughly composed of an image forming unit 12, an intermediate transfer device 14, a final transfer unit 16, a fixing device 18, and a paper feeding unit 20.

  The image forming unit 12 includes four image forming units 22Y, 22M, 22K, and 22C for yellow (Y), magenta (M), black (K), and cyan (C), and an exposure device 24. Has been. Each of the image forming units 22Y to 22C includes four photosensitive drums (image bearing members) 26Y, 26M, 26K, and 26C, and charging rolls (contact type charging members) 28Y and 28M that respectively contact the photosensitive drums 26Y to 26C. 28K, 28C, developing devices 30Y, 30M, 30K, 30C facing the photosensitive drums 26Y-26C, and photosensitive brush rolls 32Y, 32M, 32K, 32C respectively contacting the photosensitive drums 26Y-26C. It is configured.

  Here, with respect to the arrangement of each member around the photosensitive drum 26, the charging roll 28, the developing device 30, and the first to be described later are arranged around the photosensitive drum 26 from the upstream side to the downstream side in the rotation direction of the photosensitive drum 26. Upstream or downstream intermediate transfer rolls 34, 36 and a photosensitive brush roll 32 are arranged in this order.

  The photosensitive drums 26Y to 26C are applied with a DC voltage of about −900 V by the charging rolls 28Y to 28C, and are thereby uniformly charged to about −420V. When the electrostatic latent image is written by the exposure device 24, the surface potential is neutralized to about -70V.

The developing devices 30Y to 30C are magnetic brush contact type two-component developing type developing devices including a developing roll, a developer amount regulating member, a developer conveying member, and an auger for conveying and stirring the developer. Incidentally, amount of the developer conveyed to the developing portion is regulated by the developer amount regulating member is about ^{30g / m 2 ~45g / m 2} , the charge amount of the toner present on the developing roll to the lever is approximately - It is about 40 μC / g to −50 μC / g. The developing devices 30Y to 30C are developed by applying an AC + DC developing voltage. The developing voltage is 4 kHz for AC, 1.3 kVpp, and about −350 V for DC.

  The intermediate transfer device 14 includes a first upstream intermediate transfer roll (first upstream intermediate transfer member) 34 that contacts the photosensitive drums 26Y and 26M, and a first downstream side that contacts the photosensitive drums 26K and 26C. An intermediate transfer roll (first downstream intermediate transfer body) 36, a second intermediate transfer roll 38 (second intermediate transfer body) in contact with the two first intermediate transfer rolls 34, 36, and a second The toner sensor 40 optically detects the presence and density of the toner image on the intermediate transfer roll 38. Based on the detection result of the toner sensor 40, each charging bias, each developing bias, the amount of toner replenished in each developing device 30, and the like are controlled.

  Further, the first upstream intermediate transfer roll 34 includes a first upstream cleaning device 42. The first upstream cleaning device 42 includes a metal (stainless) cleaning roll 44 (cleaning body) that contacts the first upstream intermediate transfer roll 34, a cleaning blade 46 that contacts the cleaning roll 44, In the vicinity of the upstream side in the rotation direction of the first upstream intermediate transfer roll 34 relative to the cleaning roll 44, the brush roll 48 that contacts the intermediate transfer roll 34, and these cleaning roll 44, cleaning blade 46, and brush roll 48 are accommodated. A cleaner housing (container) 50 is provided.

  Similarly, the first downstream intermediate transfer roll 36 includes a first downstream cleaning device 52. The first downstream cleaning device 52 includes a metal (stainless) cleaning roll (cleaning body) 54 that contacts the first downstream intermediate transfer roll 36, a cleaning blade 56 that contacts the cleaning roll 54, In the vicinity of the upstream side in the rotation direction of the first downstream intermediate transfer roll 36 relative to the cleaning roll 54, the brush roll 58 that contacts the intermediate transfer roll 36, the cleaning roll 54, the cleaning blade 56, and the brush roll 58 are accommodated. A cleaner housing (container) 60 is provided.

  Further, the second intermediate transfer roll 38 includes a second cleaning device 62. The second cleaning device 62 includes a metal (stainless steel) cleaning roll (cleaning body) 64 that contacts the second intermediate transfer roll 38, a cleaning blade 66 that contacts the cleaning roll 64, and a cleaning roll 64. Also, in the vicinity of the downstream side in the rotation direction of the second intermediate transfer roll 38, the brush roll 68 that contacts the intermediate transfer roll 38, and the cleaner housing (container) that houses the cleaning roll 64, the cleaning blade 66, and the brush roll 68. 70.

  Here, the arrangement of the peripheral members in the first upstream intermediate transfer roll 34 is centered on the first upstream intermediate transfer roll 34 and the upstream side in the rotation direction of the first upstream intermediate transfer roll 34 from the upstream side. The photosensitive drum 26M, the photosensitive drum 26Y, the second intermediate transfer roll 38, the brush roll 48, and the cleaning roll 44 are sequentially arranged.

  The arrangement of the peripheral members in the first downstream intermediate transfer roll 36 is centered on the first downstream intermediate transfer roll 36 from the upstream side to the downstream side in the rotation direction of the first downstream intermediate transfer roll 36. The photosensitive drum 26C, the photosensitive drum 26K, the second intermediate transfer roll 38, the brush roll 58, and the cleaning roll 54 are disposed in this order.

  Further, the arrangement of the peripheral members in the second intermediate transfer roll 38 is such that the first upstream side is centered on the second intermediate transfer roll 38 from the upstream side to the downstream side in the rotation direction of the second intermediate transfer roll 38. An intermediate transfer roll 34, a first downstream intermediate transfer roll 36, a toner sensor 40, a final transfer roll 72, a cleaning roll 64, and a brush roll 68, which will be described later, are arranged in this order.

  The first intermediate transfer rolls 34 and 36 are formed by providing a silicon rubber layer on a metal pipe and further coating a high release layer thereon. The optimum value of the surface potential necessary for transferring the toner image from the photoconductive drums 26Y to 26C to the first intermediate transfer rolls 34, 36 is the type of the recording paper S, the conveying speed, and the charged state of the toner. It is set by the ambient temperature, humidity and the like.

  Similar to the first intermediate transfer rolls 34 and 36, the second intermediate transfer roll 38 is formed by providing a silicon rubber layer on a metal pipe and further coating a high release layer thereon. The optimum value of the surface potential necessary for transferring the toner image from the first intermediate transfer rolls 34 and 36 to the second intermediate transfer roll 38 is determined based on the type, transport speed, and toner charge of the recording paper S. It is set according to the state, ambient temperature, humidity, and the like.

  The final transfer roll 72 constituting the final transfer portion 16 is formed by providing a urethane rubber layer on a metal pipe and further applying a resin coating thereon. In order to transfer the toner image from the second intermediate transfer roll 38 onto the recording paper S, the optimum value of the transfer voltage applied to the final transfer roll 72 is determined based on the type of the recording paper S, the conveyance speed, and the toner. It is set according to the charging state, ambient temperature, humidity and the like. Usually, the transfer voltage applied to the final transfer roll 72 is in the range of about +1200 V to +4200 V. Here, the constant voltage control method is adopted, and the optimum value is about +2000 V in an environment of normal temperature and humidity.

  Unlike the first intermediate transfer rolls 34 and 36 and the second intermediate transfer roll 38, the final transfer roll 72 is configured such that a cleaning roll (cleaning body) is not in contact therewith. Further, the optimum value of the cleaning voltage to be applied to the cleaning rolls 44, 54, 64 and the brush rolls 48, 58, 68 of the cleaning devices 42, 52, 62 also depends on the type and conveyance speed of the recording paper S, the charged state of the toner, It is set by the ambient temperature, humidity, etc.

  In the fixing device 18, a heating roll 74 and a pressure roll 76 are pressed to form a fixing nip. A halogen lamp (not shown) as a heat source is disposed in the heating roll 74, and is configured to heat the surface of the heating roll 74 to a predetermined fixing temperature during fixing. A fixing discharge roll pair 78 is disposed downstream of the fixing nip in the conveyance direction of the recording paper S.

  The paper feed unit 20 is formed along a conveyance path (indicated by a dotted line) P of the recording paper S from the paper feed tray 80 to the discharge tray 82. A plurality of recording sheets S are accommodated in the paper feed tray 80, and from the paper feed tray 80 to the downstream side of the transport path P, a roll pair 84 and a transport roll pair 86 including a pickup roll 84 </ b> A and a retard roll 84 </ b> B. A resist roll pair 88 and a discharge roll pair 90 (via the final transfer roll 72 and the fixing device 18) are arranged in this order.

  In the full-color printer 10 having the above configuration, the potential control of each of the intermediate transfer rolls 34, 36, 38, each of the cleaning rolls 44, 54, 64, and each of the brush rolls 48, 58, 68 will be described. As described above, the voltage applied to each intermediate transfer roll 34, 36, 38, each cleaning roll 44, 54, 64, and each brush roll 48, 58, 68 depends on the type of recording paper S, the conveyance speed, and the charging of toner. It is set according to the state, ambient temperature, humidity, and the like, thereby forming an appropriate potential gradient.

  FIG. 3 shows voltage modes set according to the type of recording paper S, the conveyance speed, the charging state of the toner, the ambient temperature, the humidity, and the like. FIG. 4 shows, as an example, voltage mode values in normal temperature and normal humidity (environment No. 4), low temperature and low humidity (environment No. 0), and high temperature and high humidity (environment No. 8). The type of recording paper S is set such that the paper mode A is plain paper, the paper mode B is recycled paper, the paper mode C is thick paper, the paper mode D is coated paper, and the paper mode E is OHP. The conveyance speed of the recording paper S is set such that the paper modes A and B are full speed, and the paper modes C, D, and E are half speed.

  More specifically, for example, when the recording paper S is plain paper (paper mode A) under normal temperature and normal humidity (environment No. 4), the conveyance speed of the recording paper S is full speed, and the voltage mode in this case is It can be seen from FIG. 3 that the “reverse polarity toner catch” mode is set. Note that the type of the recording paper S is plain paper is set by a user appropriately inputting with a printer driver or the like on the computer. In addition, the ambient temperature and humidity may be automatically determined by providing a sensor in the printer 10 or may be appropriately input by a user using a printer driver on a computer, as described above.

  Thus, when it is determined that the “reverse polarity toner catch” mode is set, as shown in FIG. 4, the intermediate transfer rollers 34, 36, 38, the cleaning devices are cleaned for each environment, each paper type, and each transport speed. Since the voltage values to be applied to the rolls 44, 54, 64 and the brush rolls 48, 58, 68 are set in advance, the voltage value in the “reverse polarity toner catch” mode is selected from among the voltage values, and each intermediate transfer is performed. Applied to the rolls 34, 36, 38, the cleaning rolls 44, 54, 64, and the brush rolls 48, 58, 68, respectively.

  That is, as shown in FIG. 4A, the first intermediate transfer rolls 34 and 36 are 400V, the second intermediate transfer roll 38 is 850V, and the cleaning rolls 44 and 54 of the first cleaning devices 42 and 52 are 100V. The brush rolls 48 and 58 are applied to 750V, the cleaning roll 64 of the second cleaning device 62 is applied to 500V, and the brush roll 68 is applied to 1150V.

  This state is shown in FIG. FIG. 5 shows a movement state of a toner image as an output image in the “reverse polarity toner catch” mode under a normal temperature and humidity environment. The toner used in this embodiment is a negatively charged toner. Accordingly, the positive toner is negatively charged and the reverse toner is positively charged.

  The image forming units 22Y to 22C respectively form yellow, magenta, black, and cyan toner images on the photosensitive drums 26Y to 26C. That is, the surface of each photosensitive drum 26 is uniformly charged by the charging roll 28, and a laser beam L corresponding to an output image is irradiated from the exposure device 24 onto the surface of the photosensitive drum 26 after charging, and the exposed portion. An electrostatic latent image is formed on the photosensitive drum 26 due to the potential difference from the unexposed portion. The developing device 30 selectively applies toner to the electrostatic latent image, and a toner image is formed on the photosensitive drum 26.

  First, the magenta toner image is primarily transferred from the magenta photosensitive drum 26M to the first upstream intermediate transfer roll 34. Next, the yellow toner image is primarily transferred from the yellow photosensitive drum 26 </ b> Y to the first upstream intermediate transfer roll 34 and is superimposed on the magenta toner image. On the other hand, similarly, a cyan toner image is primarily transferred from the cyan photosensitive drum 26C to the first downstream intermediate transfer roll 36. Next, the black toner image is primarily transferred from the black photosensitive drum 26 </ b> K to the first downstream intermediate transfer roll 36.

  The primary-transferred magenta and yellow toner images are secondarily transferred to the second intermediate transfer roll 38. On the other hand, the primary transferred cyan and black toner images are also secondarily transferred to the second intermediate transfer roll 38, where the magenta and yellow toner images, the cyan toner image previously transferred, Are superimposed on each other to form a full-color toner image on the second intermediate transfer roll 38.

  The secondary transfer full color toner image and black toner image reach the nip portion between the second intermediate transfer roll 38 and the final transfer roll 72. In synchronization with the timing, the recording sheet S as a recording sheet is conveyed from the registration roll pair 88 (see FIG. 1) to the nip portion, and the full-color toner image and the black toner image are tertiary-transferred onto the recording sheet S (final transfer). )

  The recording sheet S then passes through the nip portion between the heating roll 74 and the pressure roll 76 of the fixing device 18 (see FIG. 1). At that time, the full color toner image and the black toner image are fixed on the recording paper S by the action of heat and pressure applied from both rolls 74 and 76 to form a permanent image. Further, thereafter, the recording paper S is discharged to the discharge tray 82 by the discharge roll pair 90, and the full color image formation is completed.

  On the other hand, among the toners constituting the toner image, there is residual toner that is not transferred even when it comes into contact with the recording paper S and moves as it is rotated by the second intermediate transfer roll 38. Most of the residual toner is negatively charged, but there is also a part of the reverse polarity toner that is positively charged due to contact with the final transfer roll 72.

  Therefore, in the “reverse polarity toner catch” mode, first, the second cleaning device 62 attaches positively charged reverse polarity residual toner to the cleaning roll 64 due to the potential relationship, and the cleaning blade 66 It is scraped off from the surface of the cleaning roll 64 and accommodated in the cleaner housing 70. Note that the toner accommodated in the cleaner housing 70 may be transported into a collection box (not shown).

  Further, at this time, the residual toner of the positive electrode that is negatively charged does not adhere to the cleaning roll 64 due to the potential relationship. The residual toner of the positive electrode that does not adhere to the cleaning roll 64 adheres to and is held by the brush roll 68 disposed downstream of the cleaning roll 64 due to the potential relationship, and is removed from the second intermediate transfer roll 38. The Therefore, no ghost is generated.

  Further, for example, when the recording paper S is recycled paper (paper mode B) under normal temperature and normal humidity (environment No. 4), the conveyance speed of the recording paper S is full speed, and the voltage mode in this case is shown in FIG. It can be seen that the “positive toner catch” mode is set. Therefore, in the same manner as described above, from FIG. 4A, the first intermediate transfer rolls 34 and 36 are 400 V, the second intermediate transfer roll 38 is 850 V, and the cleaning rolls 44 and 54 of the first cleaning devices 42 and 52 are the same. Is applied to 100 V, the brush rolls 48 and 58 are applied to 900 V, the cleaning roll 64 of the second cleaning device 62 is applied to 1250 V, and the brush roll 68 is applied to 1450 V.

  This state is shown in FIG. FIG. 6 shows a movement state of a toner image as an output image in the “positive toner catch” mode under a normal temperature and humidity environment. As described above, the toner used in this embodiment is a negatively charged toner. Accordingly, the positive toner is negatively charged and the reverse toner is positively charged.

  The image forming units 22Y to 22C respectively form yellow, magenta, black, and cyan toner images on the photosensitive drums 26Y to 26C. That is, the surface of each photosensitive drum 26 is uniformly charged by the charging roll 28, and a laser beam L corresponding to an output image is irradiated from the exposure device 24 onto the surface of the photosensitive drum 26 after charging, and the exposed portion. An electrostatic latent image is formed on the photosensitive drum 26 due to the potential difference from the unexposed portion. The developing device 30 selectively applies toner to the electrostatic latent image, and a toner image is formed on the photosensitive drum 26.

  First, the magenta toner image is primarily transferred from the magenta photosensitive drum 26M to the first upstream intermediate transfer roll 34. Next, the yellow toner image is primarily transferred from the yellow photosensitive drum 26 </ b> Y to the first upstream intermediate transfer roll 34 and is superimposed on the magenta toner image. On the other hand, similarly, a cyan toner image is primarily transferred from the cyan photosensitive drum 26C to the first downstream intermediate transfer roll 36. Next, the black toner image is primarily transferred from the black photosensitive drum 26 </ b> K to the first downstream intermediate transfer roll 36.

  The primary-transferred magenta and yellow toner images are secondarily transferred to the second intermediate transfer roll 38. On the other hand, the primary transferred cyan and black toner images are also secondarily transferred to the second intermediate transfer roll 38, where the magenta and yellow toner images, the cyan toner image previously transferred, Are superimposed on each other to form a full-color toner image on the second intermediate transfer roll 38.

  The secondary transfer full color toner image and black toner image reach the nip portion between the second intermediate transfer roll 38 and the final transfer roll 72. In synchronization with the timing, the recording sheet S as a recording sheet is conveyed from the registration roll pair 88 (see FIG. 1) to the nip portion, and the full-color toner image and the black toner image are tertiary-transferred onto the recording sheet S (final transfer). )

  Then, the recording sheet S passes through the nip portion between the heating roll 74 and the pressure roll 76 of the fixing device 18 (see FIG. 1). At that time, the full color toner image and the black toner image are fixed on the recording paper S by the action of heat and pressure applied from both rolls 74 and 76 to form a permanent image. Further, thereafter, the recording paper S is discharged to the discharge tray 82 by the discharge roll pair 90, and the full color image formation is completed.

  On the other hand, among the toners constituting the toner image, there is residual toner that is not transferred even when it comes into contact with the recording paper S and moves as it is rotated by the second intermediate transfer roll 38. Most of the residual toner is negatively charged, but there is also a part of the reverse polarity toner that is positively charged due to contact with the final transfer roll 72.

  Therefore, in the case of the “positive toner catch” mode, first, the negatively charged residual toner of the positive electrode is attached to the cleaning roll 64 due to the potential relationship by the second cleaning device 62, and the cleaning roll 66 removes the cleaning roll 66. 64 is scraped off from the surface and accommodated in the cleaner housing 70. Note that the toner contained in the cleaner housing 70 may be configured to be conveyed into a collection box (not shown) as described above.

  At this time, the positively charged residual toner having the opposite polarity does not adhere to the cleaning roll 64 due to the potential relationship. Residual toner having the opposite polarity that did not adhere to the cleaning roll 64 adheres to and is held on the brush roll 68 disposed downstream of the cleaning roll 64 due to the potential relationship, and is removed from the second intermediate transfer roll 38. Is done. Therefore, no ghost is generated.

  When each voltage is switched, that is, when the type or transport speed of the recording paper S is changed, the above-described voltage mode (“reverse polarity toner catch” mode or “positive polarity” is performed without transporting the recording paper S. Cleaning is preferably performed in the “toner catch” mode). Further, at this time, the second cleaning device 62 does not remove the residual toner, but the first upstream cleaning device 42 removes the residual toner via the first upstream intermediate transfer roll 34. The first downstream cleaning device 52 may remove the first downstream intermediate transfer roll 36.

  In any case, the potential gradient formed on each of the intermediate transfer rolls 34, 36, 38, each of the cleaning rolls 44, 54, 64, and each of the brush rolls 48, 58, 68 depends on the type of the recording paper S, the conveyance speed, the toner. Is determined in advance according to the charging state, ambient temperature, humidity, and the like, and an appropriate potential gradient is automatically formed when the user appropriately selects the type (sheet mode) of the recording sheet S, the conveyance speed, and the like. It has become. Therefore, the residual toner remaining on each of the intermediate transfer rolls 34, 36, and 38 is surely collected and removed even if the type of the recording paper S and the conveyance speed are changed.

  Further, the full-color printer 10 described above includes three intermediate transfer bodies including a first upstream intermediate transfer roll 34, a first downstream intermediate transfer roll 36, and a second intermediate transfer roll 38 as the intermediate transfer device 14. However, it goes without saying that the same effect can be obtained when the intermediate transfer device 14 includes only one intermediate transfer roll (not shown).

Schematic side view of a full-color printer according to the present invention Schematic side view of essential parts of a full-color printer according to the present invention Table showing voltage modes according to the present invention Table showing voltage mode values according to the present invention Operation explanatory diagram in “reverse polarity toner catch” mode according to the present invention Operation explanatory diagram in the “positive toner catch” mode according to the present invention Operation explanatory diagram of a conventional full color printer

Explanation of symbols

10 Printer (image forming device)
22 Image forming unit (image forming means)
26 Photosensitive drum (image carrier)
34 First upstream intermediate transfer roll (intermediate transfer member)
36 First downstream intermediate transfer roll (intermediate transfer member)
38 Second intermediate transfer roll (intermediate transfer member)
42 First upstream cleaning device 52 First downstream cleaning device 62 Second cleaning device 44, 54, 64 Cleaning roll (cleaning body)
46, 56, 66 Cleaning blade 48, 58, 68 Brush roll 50, 60, 70 Cleaner housing (container)
72 Final transfer roll (Final transfer body)

Claims (14)

An image carrier on which an electrostatic latent image is formed on the surface due to a difference in charging potential, an image forming means for forming a toner image on the surface of the image carrier, and a transfer body on which the toner image on the image carrier is transferred A final transfer member that transfers a toner image from the transfer member to a recording medium, a cleaning member that contacts the transfer member, and a potential gradient between the image carrier, the transfer member, the final transfer member, and the cleaning member. An image forming apparatus comprising: a control unit;
When the toner image on the transfer body is transferred to the recording medium, the cleaning body has a reverse polarity toner that forms a potential gradient that causes the reverse polarity toner remaining on the transfer body to adhere to the cleaning body. An adhesion voltage, and a positive toner adhesion voltage that forms a potential gradient that causes the positive toner remaining on the transfer body to adhere to the cleaning body when the toner image of the transfer body is transferred to the recording medium; Is configured to be applied,
The voltage of the cleaning body when transferring the toner image of the transfer body to the recording medium is switched between the reverse polarity toner adhesion voltage and the positive polarity toner adhesion voltage according to the type of the recording medium. Image forming apparatus. An image carrier on which an electrostatic latent image is formed on the surface due to a difference in charging potential, an image forming means for forming a toner image on the surface of the image carrier, and a transfer body on which the toner image on the image carrier is transferred A final transfer member that transfers a toner image from the transfer member to a recording medium, a cleaning member that contacts the transfer member, and a potential gradient between the image carrier, the transfer member, the final transfer member, and the cleaning member. An image forming apparatus comprising: a control unit;
When the toner image on the transfer body is transferred to the recording medium, the cleaning body has a reverse polarity toner that forms a potential gradient that causes the reverse polarity toner remaining on the transfer body to adhere to the cleaning body. An adhesion voltage, and a positive toner adhesion voltage that forms a potential gradient that causes the positive toner remaining on the transfer body to adhere to the cleaning body when the toner image of the transfer body is transferred to the recording medium; Is configured to be applied,
The voltage of the cleaning body when transferring the toner image on the transfer body to the recording medium is switched between the reverse polarity toner adhesion voltage and the positive polarity toner adhesion voltage according to the conveyance speed of the recording medium. An image forming apparatus. During continuous printing, when the voltage of the cleaning body is switched, the image forming apparatus according to claim 1 or claim 2, characterized in that for cleaning without conveying the recording medium. The image carrier includes a plurality of image carriers for different colors, and the transfer body includes a first transfer body to which a toner image is transferred from the plurality of image carriers, and a toner from the first transfer body. image is transferred, in contact with the final transfer body, according to any one of claims 1 to 3 for the second transfer member for transferring the toner image to a recording medium, comprising the Image forming apparatus. The image carrier includes a plurality of image carriers for different colors, and the transfer body includes a first upstream intermediate transfer member that contacts a part of the plurality of image carriers, and the plurality of image carriers. A first downstream intermediate transfer member in contact with the rest of the body, and the first upstream intermediate transfer member and the first downstream intermediate transfer member in contact with the first downstream intermediate transfer member. And a second intermediate transfer member to which a toner image is transferred from the first downstream intermediate transfer member after being transferred, and the final transfer member is in contact with the second intermediate transfer member. the image forming apparatus according to any one of claims 1 to 3,. As the image carrier, four image carriers for yellow, magenta, black, and cyan are provided. As the transfer member, the first image carrier is in contact with two of the four image carriers. The first upstream intermediate transfer member and the first downstream intermediate transfer member, the first upstream intermediate transfer member and the first downstream intermediate transfer member in contact with the first upstream intermediate transfer member, and the toner from the first upstream intermediate transfer member; A second intermediate transfer member to which a toner image is transferred from the first downstream intermediate transfer member after the image is transferred, and the final transfer member is in contact with the second intermediate transfer member. The image forming apparatus according to claim 1 , wherein the image forming apparatus is an image forming apparatus. The cleaning body includes: a first upstream cleaning body that contacts the first upstream intermediate transfer body; and a second cleaning body that contacts the second intermediate transfer body. The image forming apparatus according to claim 5 or 6 . The control means forms an image forming potential gradient such that the reverse polarity toner after transfer of the recording medium adheres to the second cleaning body via the second intermediate transfer body. Item 8. The image forming apparatus according to Item 7 . The control means forms an image forming potential gradient such that the positive toner after transfer of the recording medium adheres to the second cleaning body via the second intermediate transfer body. 8. The image forming apparatus according to 7 . The control means has a potential gradient such that the reverse polarity toner after transfer of the recording medium adheres to the first upstream cleaning body through the second intermediate transfer body and the first upstream intermediate transfer body. the image forming apparatus according to any one of claims 5 to 7, characterized in that to form the. The image forming apparatus according to claim 5 , further comprising a first downstream cleaning body that contacts the first downstream intermediate transfer body as the cleaning body. . The control means has a potential gradient that causes the reverse polarity toner on the final transfer body to adhere to the first downstream cleaning body via the second intermediate transfer body and the first downstream intermediate transfer body. the image forming apparatus according to claim 11, characterized by forming. The image forming apparatus according to claim 1, wherein the cleaning body includes at least one roll . The cleaning body is a cleaning roll, and includes a cleaning device having a cleaning blade pressed against the cleaning roll, and a container for collecting toner cleaned by the cleaning roll and the cleaning blade. the image forming apparatus according to any one of claim 1 to claim 12.

Images