JP2007121719A - Image forming apparatus and waste toner collecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus where waste toner is collected in the inside and the discharge of the waste toner to the outside is reduced, to provide and a waste toner collecting method. <P>SOLUTION: The tandem-type image forming apparatus is provided with a cleaning brush 1 for collecting the waste toner corresponding to each color image carrier 41, and the collected waste toner is discharged to the image carrier by the application of alternating voltage by a power source 3. The image carrier 41 is charged again to make the polarities of the waste toner uniform, and intermittent exposure voltage is applied to the image carrier 41 corresponding to respective colors Y, M and C. The waste toner is transferred to an intermediate transfer belt 50 at the position of a primary transfer roller 45. The waste toner is collected in the K image carrier 41K from the intermediate transfer belt 50 and is stored in a K developing device 44K. The applying time of the alternating voltage to the cleaning brush 1, the absolute value thereof and the interval of the exposure voltage are made different among the respective colors. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that collects waste toner inside the apparatus and reduces discharge to the outside, and a waste toner collection method.

  In general, an electrophotographic toner image forming unit includes a photosensitive member as an image bearing member having a photosensitive layer on an outer peripheral surface, a charging unit that uniformly charges the outer peripheral surface of the photosensitive member, and a uniform charging unit using the charging unit. An exposure unit that selectively exposes the outer peripheral surface charged to form an electrostatic latent image, and a toner as a developer is applied to the electrostatic latent image formed by the exposure unit to form a visible image ( Developing means for forming a toner image).

  As a tandem type image forming apparatus for forming a color image, a plurality (for example, four) of toner image forming means as described above are arranged on the intermediate transfer belt. The toner image on the photosensitive member by the single color toner image forming unit is sequentially transferred to the intermediate transfer belt, and the toner images of a plurality of colors (for example, yellow, cyan, magenta, and black (black)) are superimposed on the intermediate transfer belt. There is an intermediate transfer belt type that obtains a color image on an intermediate transfer belt.

  By the way, in the image forming apparatus, a technique has been developed in which waste toner remaining on the photosensitive member after the printing process is collected to prevent image quality deterioration. For example, Japanese Patent Application Laid-Open No. 63-247781 discloses that a transfer roller performs a cleaning action. Patent Document 2 (Japanese Patent Laid-Open No. 5-19670) describes that a toner remaining on the photosensitive member is attracted by electrostatic action using a cleaning brush.

JP 63-247781 A Japanese Patent Laid-Open No. 5-19670

  The conventional techniques described in Patent Document 1 and Patent Document 2 are applied to a monochrome image forming apparatus, and cannot be applied to the tandem color image forming apparatus.

  The present invention has been made in view of such problems of the prior art, and an object thereof is to form an image in which waste toner is effectively collected from a photoreceptor in a tandem color image forming apparatus. An apparatus and a waste toner collecting method are provided.

An image forming apparatus of the present invention that achieves the above object includes a black image forming station in which image forming units including a charging unit, an exposure unit, a developing unit, and a transfer unit are arranged around an image carrier. An image forming apparatus in which at least two image forming stations are provided, and a transfer medium passes through each station to form an image in a tandem manner.
Waste toner cleaning mode setting means after image formation, cleaning means provided corresponding to each image carrier and collecting waste toner remaining on each image carrier, and waste collected by each cleaning means A power source that applies an alternating voltage to the cleaning means and an absolute value of the alternating voltage are different for each color so that toner is discharged to each image carrier, and an application time of the alternating voltage is different for each color. A first control unit, a second control unit that outputs a charging voltage from the charging unit to align the polarity of the waste toner discharged to the image carrier, and an exposure voltage from the exposure unit to the image carrier. And the waste toner discharged to the image carrier is transferred to a third control unit that varies the interval at which the exposure voltage is applied at each station. A power source for applying a voltage to said transfer means,
In the station forming a black image,
A power source for applying a voltage to the transfer means so as to collect the waste toner transferred to the transfer medium on the image carrier, and the waste toner from the image carrier for forming a black image is collected in the developing means. And a power source for applying a voltage to the developing means. According to such a configuration, the waste toner remaining on the photosensitive member (image carrier) without being transferred is collected in a K (black) developing device, mixed with black toner, and used for printing. Therefore, it is possible to obtain an environment-friendly image forming apparatus by effectively using toner resources and collecting waste toner inside the apparatus to reduce discharge of the waste toner to the outside.

  In the image forming apparatus of the present invention, the cleaning unit is a rotating member that rotates in contact with the image carrier. According to such a configuration, since the rotating member rotates while elastically contacting the image carrier, the waste toner remaining on the image carrier can be collected by the cleaning means without unevenness.

  In the image forming apparatus of the present invention, the cleaning unit is a cleaning brush. According to such a configuration, waste toner can be effectively collected between the brushes.

  In the image forming apparatus of the present invention, the transfer medium is an intermediate transfer medium. According to such a configuration, in the image forming apparatus using the intermediate transfer medium, the waste toner discharged from the cleaning unit to the image carrier can be effectively transferred to the intermediate transfer medium.

  In the image forming apparatus according to the aspect of the invention, the station is provided corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black), and the traveling direction of the transfer medium The K (black) station is arranged on the most downstream side when viewed from the upstream side of the center. According to such a configuration, in a color image forming apparatus corresponding to four colors of Y (yellow), M (magenta), C (cyan), and K (black), Y (yellow), M (magenta), and C ( Since the waste toner of each color (cyan) is mixed and printed as black toner, it is possible to prevent image quality deterioration due to reuse of the waste toner.

  In the image forming apparatus of the present invention, the absolute value of the alternating voltage applied to the cleaning unit of each station is controlled to be large on the upstream side of the transfer medium and small on the downstream side. According to such a configuration, the thickness of the waste toner layer discharged from each cleaning unit and transferred from the photosensitive member is reduced from the upstream side to the downstream side in the moving direction of the transfer medium, and the transfer is performed as a whole. Since the waste toner is evenly transferred to the medium, the waste toner can be finally recovered without difficulty on the K (black) image carrier.

  The image forming apparatus of the present invention is characterized in that the application time of the alternating voltage applied to the cleaning unit of each station is controlled to be short on the upstream side of the transfer medium and long on the downstream side. To do. According to such a configuration, the thickness of the waste toner layer discharged from each cleaning unit and transferred from the photosensitive member is reduced from the upstream side to the downstream side in the moving direction of the transfer medium, and the transfer is performed as a whole. Since the waste toner is evenly transferred to the medium, the waste toner can be finally recovered without difficulty on the K (black) image carrier.

  In the image forming apparatus of the present invention, the voltage interval intermittently applied from the exposure unit of each station to the image carrier is set small on the upstream side in the traveling direction of the transfer medium and large on the downstream side. It is characterized by that. According to such a configuration, since the waste toner is evenly transferred from the upstream side to the downstream side in the traveling direction of the transfer medium, it can be recovered to the image carrier without difficulty.

In the waste toner collecting method of the present invention, at least two or more image forming stations in which image forming units including a charging unit, an exposure unit, a developing unit, and a transfer unit are arranged around an image carrier are provided. A process of forming an image in a tandem manner by passing a medium through each station;
In the waste toner cleaning mode after image formation,
A step of collecting waste toner remaining on each image carrier by a cleaning unit provided corresponding to each image carrier, and an absolute value of an alternating voltage output from a power source connected to each cleaning unit for each color And changing the application time of the alternating voltage for each color to discharge the waste toner collected by the cleaning means to the image carrier, and the image carrier from which the waste toner has been discharged. A step of recharging the image carrier, a step of intermittently exposing the image carrier at large intervals on the upstream side in the traveling direction of the transfer medium and a large interval on the downstream side, and a waste toner of the unexposed portion discharged onto the image carrier Transferring to the transfer means;
In the station forming a black image,
Recovering the waste toner transferred to the transfer medium to the image carrier, recovering the waste toner from the image carrier to the developing unit,
It is characterized by comprising. According to such a configuration, the waste toner remaining on the image carrier can be recovered to the K developing unit by a series of processes without waste using an existing apparatus.

  In the waste toner collecting method of the present invention, in the step of recharging the image carrier from which the waste toner has been discharged, the polarity of the charging voltage output from the charging unit is the same as the charging polarity of the image carrier. It is characterized by polarity. According to such a configuration, the polarity of the waste toner discharged from the cleaning unit to the image carrier is aligned, and the subsequent waste toner processing can be performed smoothly.

  Further, in the waste toner collecting method of the present invention, the step of transferring the unexposed portion of the waste toner discharged to the image carrier to the transfer unit includes an absolute value of a voltage applied to the transfer unit. It is smaller than the value used at the time of transfer. According to such a configuration, the waste toner discharged from the cleaning unit to the image carrier can be efficiently transferred to the transfer medium by applying a voltage lower than the voltage applied during toner image transfer.

Further, in the waste toner collecting method of the present invention, the step of collecting the waste toner transferred to the transfer medium on the image carrier is performed in the black image forming station.
The polarity of the voltage applied to the transfer means is the same as the charging polarity of the image carrier. According to such a configuration, the waste toner transferred to the transfer medium can be sucked into the image carrier and smoothly collected.

  In the present invention, waste toner remaining on the photosensitive member (image carrier) without being transferred is collected in a K (black) developing device, mixed with black toner, and used for printing. Therefore, it is possible to provide an image forming apparatus and a waste toner collecting method in which resources are effectively used and waste toner is collected inside the apparatus to reduce discharge of the waste toner to the outside. As described above, since waste toner is not discharged to the outside of the apparatus, it is possible to prevent environmental pollution.

  In the embodiment of the present invention, four photoconductors as shown in the cross-sectional view of FIG. 13 are exposed by four line heads to simultaneously form four color images, and one endless intermediate transfer belt (intermediate transfer medium) is formed. Tandem type color printer (image forming apparatus). In this image forming apparatus, exposure apparatuses 101K, 101C, 101M, and 101Y having the same configuration are placed at the exposure positions of four corresponding photosensitive drums (image carriers) 41K, 41C, 41M, and 41Y. Each is arranged. The exposure apparatuses 101K, 101C, 101M, and 101Y are composed of line heads using light emitting elements such as LEDs or organic EL elements as light sources. A scanning optical system that scans with laser light may be used as the exposure apparatus.

  The image forming apparatus is provided with a driving roller 51, a driven roller 52, and a tension roller 53. The intermediate roller is tensioned by the tension roller 53 and is circulated and driven in the direction indicated by the arrow (counterclockwise). A transfer belt (intermediate transfer medium) 50 is provided. Photosensitive members 41K, 41C, 41M, and 41Y having photosensitive layers are arranged on the outer peripheral surface as four image carriers arranged at predetermined intervals with respect to the intermediate transfer belt 50. K, C, M, and Y added after the reference sign mean black, cyan, magenta, and yellow, respectively, and indicate that the photoconductors are black, cyan, magenta, and yellow, respectively. The same applies to other members. The photoreceptors 41K, 41C, 41M, and 41Y are rotationally driven in the direction indicated by the arrow (clockwise) in synchronization with the driving of the intermediate transfer belt 50. Around each photoconductor 41 (K, C, M, Y), charging means (corona charger) 42 (K) for uniformly charging the outer peripheral surface of the photoconductor 41 (K, C, M, Y), respectively. , C, M, Y) and the outer peripheral surface uniformly charged by the charging means 42 (K, C, M, Y) are synchronized with the rotation of the photoconductor 41 (K, C, M, Y). An exposure apparatus (line head) 101 (K, C, M, Y) that sequentially scans lines is provided.

  In addition, a developing device 44 (K, C, and Y) that forms a visible image (toner image) by adding toner as a developer to the electrostatic latent image formed by the exposure device 101 (K, C, M, and Y). M, Y) and a primary transfer roller 45 (K, Y) as transfer means for sequentially transferring the toner image developed by the developing device 44 (K, C, M, Y) to the intermediate transfer belt 50 as a primary transfer target. C, M, Y) and a cleaning device 46 (K, C, M, Y) as a cleaning means for removing the toner remaining on the surface of the photoreceptor 41 (K, C, M, Y) after being transferred. ). The developing device 44 (K, C, M, Y) uses, for example, a non-magnetic one-component toner as a developer, and the one-component developer is conveyed to the developing roller by a supply roller, for example, and adheres to the surface of the developing roller. The film thickness of the developed developer is regulated by a regulating blade, and the developing roller is brought into contact with or increased in thickness by the photosensitive body 41 (K, C, M, Y), whereby the photosensitive body 41 (K, C, M, Y). The toner is developed as a toner image by attaching a developer according to the potential level.

  The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are intermediated by the primary transfer bias applied to the primary transfer roller 45 (K, C, M, Y). The toner image, which is sequentially primary transferred onto the transfer belt 50 and sequentially superposed on the intermediate transfer belt 50 to become a full color, is secondarily transferred to a recording medium P such as paper by a secondary transfer roller 66, and serves as a fixing unit. The toner is fixed on the recording medium P by passing through the fixing roller pair 61, and is discharged onto a paper discharge tray 68 formed in the upper part of the apparatus by a paper discharge roller pair 62.

  In FIG. 13, reference numeral 63 denotes a paper feed cassette in which a large number of recording media P are stacked and held, 64 denotes a pickup roller for feeding the recording media P one by one from the paper feed cassette 63, and 65 denotes a secondary transfer roller. 66, a pair of gate rollers for defining the supply timing of the recording medium P to the secondary transfer portion 66; a secondary transfer roller 66 as a secondary transfer means for forming a secondary transfer portion with the intermediate transfer belt 50; Is a cleaning blade as a cleaning means for removing the toner remaining on the surface of the intermediate transfer belt 50 after the secondary transfer.

  Next, an embodiment of the present invention will be described with reference to the explanatory diagrams shown in FIGS. FIG. 2 is an explanatory diagram of a cleaning process in which the transfer residual toner is collected from the photoreceptor (image carrier) 41 by the cleaning brush 1. The cleaning brush 1 is connected to the ground 6 and sucks normally charged toner 11 (black circle, negative polarity) and reversely charged toner 12 (white circle, positive polarity) while rotating in a certain direction. At this time, the alternating voltage generated by the alternating power supply 4 is not applied to the cleaning brush 1 because the power supply switch 5 is opened. A large number of brushes are formed in an arc shape in the cleaning brush 1, and the captured waste toner is stored in the space between the brushes without dropping off. In this way, waste toner can be effectively collected between the brushes. The cleaning unit that collects the transfer residual toner from the photoconductor 41 is not limited to the cleaning brush, and for example, a rotating member provided with a sponge or the like may be rotated in contact with the photoconductor 41. In this case, since the rotating member rotates while elastically contacting the image carrier, the waste toner can be collected from the image carrier to the cleaning unit without unevenness.

  FIG. 3 is an explanatory diagram of a process of discharging (discharging) the toner collected by the cleaning brush 1 in FIG. At this time, the switch 7 is opened, and an alternating voltage generated by the alternating power source 4 is applied to the cleaning brush 1. The period of the alternating voltage is longer than the time for which the cleaning brush 1 rotates once. Reference numeral 13 denotes toner discharged from the cleaning brush 1 to the photoreceptor 41. Since an alternating voltage is applied to the cleaning brush 1, the normally charged toner 11 (black circle, negative polarity) and the reversely charged toner 12 (white circle, positive polarity) collected by the cleaning brush 1 are both in one cycle. Alternately discharged to the photoreceptor 41.

  FIG. 4 is an explanatory diagram of a process for recharging the toner discharged from the cleaning brush 1 to the photosensitive member 41 in FIG. At this time, a constant voltage, for example, −500 V, is applied from the charging device 42 to the photosensitive member, so that the polarity of the reversely charged toner discharged to the photosensitive member is aligned with the polarity of the normally charged toner. In this way, the post-process can be smoothly performed by aligning the polarity of the toner discharged to the photoreceptor to the negative polarity.

  FIG. 5 is an explanatory diagram of a process for applying an exposure voltage to the toner recharged on the surface of the photoreceptor 41 as shown in FIG. At this time, an exposure voltage such as an exposure potential of −50 V is applied from the exposure apparatus 101 to the photoconductor 41. The exposure voltage applied here is not an applied voltage for image formation, but is a process performed so as not to transfer the toner from the region of the photoreceptor 41 to the intermediate transfer belt, as will be described later. For this reason, a potential difference is generated between the portion where the exposure voltage is applied to the photoreceptor 41 and the portion where the exposure voltage is not applied.

  FIG. 6 is an explanatory diagram of a process when the photoconductor 41 to which the exposure voltage is applied in FIG. 5 passes through the developing device 44. Here, since the power supply switch 71 of the power supply 70 of the developing device 44 is opened, the developing device 44 does not perform development processing. Therefore, the recharged toner 14 formed on the surface of the photoconductor 41 is not collected by the developing device 44 but passes through the position of the developing device 44 as it is and sent to the next process.

  FIG. 7 is an explanatory diagram of a process when the recharged toner 14 of the photoreceptor 41 that has passed through the developing device 44 in FIG. 6 is discharged to the intermediate transfer belt 50. In FIG. 7, the voltage applied from the power supply 2 to the primary transfer roller 45 is a positive / negative voltage, for example, 100 V, which is weaker than the charging voltage. The recharged toner on the photosensitive member 41 in the portion where the charged potential 21 (−500 V) exists has a large potential difference with the primary transfer roller 45, so that the degree of suction becomes strong and intermediate transfer progresses in the direction of the arrow 20. It is discharged to the belt 50. On the other hand, the recharged toner in the portion where the exposure potential 22 of the photoconductor 41 exists is weakly attracted because the potential difference from the primary transfer roller 45 is small, and remains as the residual toner 15 as it is. Adhering to

  Therefore, by changing the magnitude of the exposure voltage described with reference to FIG. 5, the difference in the potential level of the photoconductor 41 is changed, and the amount of toner remaining on the photoconductor 41 can be adjusted. As shown in FIG. 7, waste toner is discharged from the photoconductor 41 to the intermediate transfer belt 50 intermittently by applying an exposure voltage. By performing such processing, a large amount of waste toner is not transferred to the intermediate transfer belt 50 at one time, and on average, waste toner is transferred. Therefore, waste toner is collected on the photoconductor 41 in a later step. Can be performed smoothly. In the embodiment of the present invention, in the image forming apparatus using an intermediate transfer medium, waste toner discharged from the cleaning unit to the image carrier can be effectively transferred to the intermediate transfer medium. In this example, waste toner is transferred from the photoconductor to the intermediate transfer belt. However, in the present invention, transfer of the waste toner from the photoconductor is not limited to the intermediate transfer belt and can be applied to transfer media in general.

  FIG. 8 is an explanatory diagram of a process for collecting waste toner from the intermediate transfer belt 50 to the photoreceptor 41K in black (K) transfer. In FIG. 8, the primary transfer roller 45K is connected to a power source 2 that applies a voltage having the same polarity (negative potential) as that of the photoreceptor 41K. For this reason, the waste toner transferred to the intermediate transfer belt 50 is sucked by the photoreceptor 41K and conveyed to the developing device as the collected toner 17.

  FIG. 9 is an explanatory diagram of a process for collecting waste toner adhering to the photoconductor 41K in the black (K) developing device 44K. 9, in the black (K) cleaning mode, the processes of FIGS. 2 to 4 are performed, and the processes of FIGS. 5 to 7 are not performed. This process will be described below. The AC power supply 4 of the cleaning brush 1 opens the switch 7 and maintains a negative charging voltage until the waste toner collected from the intermediate transfer belt 50 by the photosensitive member 41K passes the position of the cleaning brush 1. After the waste toner passes through the position of the cleaning brush 1, the potential is reversed to positive polarity in order to discharge the reversely charged toner staying on the cleaning brush 1 to the photoreceptor 41K.

  Next, the charging device 42K applies −500 V to the photoconductor 41K as in FIG. 4 so that the polarity of the reversely charged toner discharged from the cleaning brush 1 to the photoconductor 41K is aligned with the polarity of the normal charged toner. Here, no exposure voltage is applied to the photoconductor 41K, and the photoconductor 41K recharged by the charging device 42K proceeds to the position of the developing device 44K. The developing device 44K is connected to a power source 70, and a voltage having the same polarity (negative polarity) as that of the photoreceptor 41K is applied. For this reason, the waste toner adhering to the photoreceptor 41K is collected by the developing device 44K (developing roller).

  The waste toner collected by the developing device 44K is stored in a black toner tank (not shown). This waste toner is reused when a K (black) image is formed. As described above, since the waste toner is reused without being discharged out of the image forming apparatus, resources can be effectively used. In FIG. 9, the photoconductor 41K and the developing device 44K are in contact with each other in actual arrangement, but are separated from each other for easy understanding.

  10 to 12 are timing charts showing the processing process of the present invention over time. In this image forming apparatus, the processing of Y (yellow), M (magenta), C (cyan), and K (black) is continuously performed, but it does not fit in one drawing, so FIGS. Are shown separately. That is, FIG. 10 shows Y (yellow) and M (magenta) processing, and FIGS. 11 and 12 show C (cyan) and K (black) processing.

  Taking Y (yellow) in FIG. 10 as an example, the image forming process and the cleaning process after the image forming process will be described. In the following description, the voltage values are approximate. A period from time tya to tyb indicates a change in the photoreceptor (OPC) potential due to exposure. The initial potential is −500 V, the exposure potential is −50 V, and when the exposure potential is −50 V, an image is formed on the photoreceptor. The period from time tyc to tyd is a development bias application period, and a development bias of DC -200 V + AC 2 kV is applied.

  The period from time ty to tyf is a transfer bias application period, and a DC-500V transfer bias is applied. When tyf, which is the end time of the transfer bias application period, elapses, a cleaning mode is set by a control device (not shown) at time tyx, and the process proceeds to a cleaning process after the image forming process. The period from time tyg to tyh is a cleaning bias application time t1, and a cleaning bias of V1 kV is applied. At this time, the waste toner collected by the cleaning brush is discharged to the photoreceptor. As the photoconductor rotates, the photoconductor is recharged during a period from time tyi to tyj, partially overlapping with the cleaning bias application period, and then an exposure voltage is intermittently applied to the photoconductor. A pulsed exposure voltage is applied in the period from time tyi to tyj, and details of the exposure time interval d1 are shown in the process timing on the right side.

  A part of the recharging and exposure periods of the photosensitive member overlaps, and during the period from time tyk to tyl, a voltage is applied to the transfer roller to transfer (discharge) the waste toner from the photosensitive member to the intermediate transfer belt. . The waste toner discharged to the intermediate transfer belt does not exist in the exposed portion Yx but exists sparsely in the unexposed portion Yw. At this time, the interval between the exposed portions is d1. As described above, in the waste toner cleaning mode, the sequence control is applied to the application of the cleaning bias, the recharging of the photosensitive member and the exposure voltage, and the application of the transfer bias to the intermediate transfer belt. Further, the lengths of the cleaning bias application times tyg to tyh, the recharging times tyi to tyj of the photosensitive member, and the transfer bias application times tyk to tyl are made equal to each other to perform synchronous control. In the example of FIG. 10, the absolute value of the voltage applied when transferring the waste toner to the transfer unit is the same voltage as the value used when transferring the toner image. In the embodiment of the present invention, the absolute value of the voltage at the time of waste toner transfer can be made smaller than the value used at the time of toner image transfer. In this case, waste toner discharged from the cleaning means to the image carrier by applying a voltage lower than the voltage applied during toner image transfer can be efficiently transferred to the transfer medium.

  After a time Ta from the Y (yellow) image forming process, an M (magenta) image forming process is performed, and subsequently, a waste toner cleaning process is performed. The suffixes (a to l) at the times tma to tml of each process of M (magenta) are the same as the processes of Y (yellow). In this case, the distribution of the exposed portion Mx and the unexposed portion My is further sparser than Y (yellow) (the interval between the exposed portions is d2, and d1 <d2). Here, the position where the waste toner is transferred on the intermediate transfer belt between the photoconductor 41M and the primary transfer roller 45M is different from the Y (yellow) waste toner transfer position.

  As described above, the reason why the relationship between the exposure intervals is set to d1 <d2 is that the waste toner accumulated on the downstream side of the intermediate transfer belt 50 increases as described above, and is therefore discharged from the photoreceptor 41 to the intermediate transfer belt 50. This is to reduce the amount of waste toner. That is, when discharging waste toner from the M (magenta) photoreceptor 41M to the intermediate transfer belt 50, waste toner from the upstream Y (yellow) photoreceptor 41Y has already adhered to the intermediate transfer belt 50. Yes.

  Therefore, the exposure interval d2 by the exposure apparatus 101M for M (magenta) is set longer than the exposure interval d1 for the exposure apparatus 101Y for Y (yellow) (exposure time is shortened), and the process described in FIG. The amount of waste toner remaining on the photoreceptor 41M is reduced. Similarly, the exposure time d3 by the C (cyan) exposure apparatus 101CM downstream of M (magenta) is longer than the exposure interval d2 by the M (magenta) exposure apparatus 101M. For this reason, the amount of waste toner remaining on the photoreceptor 41C is further reduced.

  The cleaning bias voltage is V2 kV, and V1> V2. The reason why the absolute value of the cleaning bias voltage is set large on the upstream side in the conveyance direction of the transfer medium and small on the downstream side will be described. In this example, waste toner for two colors, Y (yellow) and M (magenta), is accumulated on the image carrier on the downstream side of the transfer medium, and is collected by an M (magenta) cleaning brush. The amount of waste toner to be collected is larger than the amount of waste toner collected by the Y (yellow) cleaning brush.

  For this reason, when the same cleaning bias voltage as that for the Y (yellow) cleaning brush is applied, the amount of waste toner discharged to the image carrier increases, and as a result, the amount of waste toner discharged to the intermediate transfer medium also increases. To do. That is, the thickness of the waste toner discharged to the intermediate transfer medium may be different between the Y (yellow) portion and the M (magenta) portion, resulting in spots. Therefore, the process of finally collecting the waste toner in the K (black) developing unit cannot be smoothly performed. In order to avoid such inconvenience, the absolute value of the cleaning bias voltage is set to V1> V2 as described above, and the amount of waste toner discharged on the downstream side of the transfer medium is set to the same thickness as that on the upstream side. It is trying to become.

  The cleaning brushes 1Y to 1K are connected to power sources 3Y to 3K to apply a cleaning bias. The cleaning bias voltage application time is set to a relationship of t1 <t2. For this reason, the cleaning time of the cleaning brush installed at the downstream station in the conveyance direction of the intermediate transfer belt is set longer.

  With such a configuration, the waste toner discharged to the upstream side of the transfer medium and the waste toner discharged to the downstream side overlap to increase the thickness of the waste toner layer, thereby forming a local halftone memory. Can be prevented. That is, since the cleaning time is set to the same length as the transfer bias time to the transfer medium, the transfer time is shortened on the upstream side of the transfer medium, and overlapping with waste toner transferred on the downstream side can be prevented. .

  Similarly, after time Ta from the M (magenta) image forming process, a C (cyan) image forming process and a subsequent cleaning process for waste toner are performed. In this case, the distribution of the exposed portion Cx and the unexposed portion Cy is further sparser than M (magenta) (the interval between the exposed portions is d3, and d1 <d2 <d3). At this time, the transfer position of the waste toner on the intermediate transfer belt between the photoconductor 41C and the primary transfer roller 45C is different from the waste toner transfer positions of Y (yellow) and M (magenta). Further, the absolute value of the cleaning bias voltage is set to V3, and the relation of V1> V2> V3 is set.

  The reason why the absolute value of the C (cyan) cleaning bias voltage on the downstream side in the transfer direction of the transfer medium is set smaller than that on the upstream side is the same as that described in the process for M (magenta). By setting the absolute value of the cleaning bias voltage so as to satisfy the relationship of V1> V2> V3, the thickness of the toner layer corresponding to the unexposed portions Yw, Mw, and Cw on the transfer medium is equalized. ing. The cleaning bias application time is t3. The application time of the cleaning bias for each color is set to t1 <t2 <t3.

  After a time Ta from the C (cyan) image forming process, the K (black) image forming process, the subsequent cleaning processing of the waste toner, and the recovery to the developing device are performed. During the period from time tkr to tks, waste toner of Y, M, and C transferred onto the intermediate transfer belt is collected on the photoreceptor 41K. At this time, the transfer bias reverses the polarity and applies + 500V DC. Also, during the period from time tku to tkv, waste toners of Y, M, C, and K colors discharged to the photoreceptor 41K are collected by the developing device 44K. At this time, the developing device 44K is in contact with the photoconductor 41K, and a direct current of −200 V + AC of 2 kV is applied as a developing bias.

  The distribution of waste toner on the intermediate transfer belt in contact with the photoreceptor 41K is the sum of the waste toners of the respective colors Y (yellow), M (magenta), and C (cyan). That is, the waste toner is sparse in the length direction on the intermediate transfer belt corresponding to the unexposed portion Yw of Y (yellow), the unexposed portion Mw of M (magenta), and the unexposed portion Cw of C (cyan). , The intervals exist with an even distribution. Further, the transfer positions of the waste toners of Y (yellow), M (magenta), and C (cyan) are formed differently without overlapping on the intermediate transfer belt, so that the intermediate transfer belt has a fixed length. The transfer amount of the waste toner is constant as described above. For this reason, waste toner on the intermediate transfer belt can be collected smoothly without imposing an excessive burden on the photoconductor 41K.

  That is, in this embodiment, the exposure interval is d1 <d2 <d3, the absolute value of the cleaning bias voltage is V1> V2> V3, and the cleaning bias application time is t1 <t2 <t3. Since the relationship is set, the waste toner is thinly and uniformly discharged as a whole on the intermediate transfer medium. Therefore, finally, the waste toner is smoothly collected without difficulty in the K (black) developing device.

  FIG. 1 is an explanatory diagram illustrating a tandem image forming apparatus according to an embodiment of the present invention. The same parts as those in FIG. 12 are denoted by the same reference numerals, and detailed description thereof is omitted. In FIG. 1, the intermediate transfer belt 50 rotates in the arrow R direction, and Y (yellow), M (magenta), C (cyan), K (black) from the upstream side as viewed in the rotation direction of the intermediate transfer belt 50. ) Developing devices 44Y, 44M, 44C, and 44K. That is, the arrangement of the developing device is different from that shown in FIG.

  Y (yellow), M (magenta), and C (cyan) developing devices 44Y, 44M, and 44C are spaced apart from the photoconductors 41Y, 41M, and 41C to prevent color mixture during image formation. . An intermediate transfer belt cleaner 69a collects waste toner remaining on the intermediate transfer belt 50 by a rotating roller. The polarity of the power source 2K connected to the K primary transfer roller 45K is the same as that of the other Y, M, and C power sources 2Y, 2M, and 2C during image formation. In the waste toner cleaning mode, as described with reference to FIGS. 7 and 8, the polarity of the power source 2K is set to be opposite to that of the other Y, M, and C power sources 2Y, 2M, and 2C.

  In the cleaning mode, as described with reference to FIG. 5, the exposure voltage is applied for each of Y, M, and C colors. Y (yellow) exposure apparatus 101Y applies an exposure voltage whose exposure interval (interval between on pulse and off pulse) is d1. The exposure apparatus 101M with M (magenta) applies an exposure voltage with an exposure interval of d2, and the exposure apparatus 101CM with C (cyan) applies an exposure voltage with an exposure interval of d32. Here, the exposure interval is set to d1 <d2 <d3 as described above.

  The cleaning brushes 1Y to 1K are connected to power sources 3Y to 3K to apply a cleaning bias. As described above, the absolute value of the cleaning bias voltage applied to the cleaning brush is set to a relationship of V1> V2> V3. For this reason, when the toner charge amount decreases in the latter half of printing, the waste toner discharge voltage from the cleaning brush to the photoconductor decreases, so that the thickness of the waste toner layer discharged to the photoconductor can be reduced.

  If there is a difference in the contamination of the cleaning brush, it becomes difficult to maintain a thin waste toner layer at low charge, which may cause memory fogging due to deterioration in cleaning performance. However, in the embodiment of the present invention, since the absolute value of the cleaning bias voltage is lowered toward the downstream side of the recording medium (as the cleaning brush increases the amount of waste toner accumulated), the waste toner is discharged from the cleaning brush. Excessive discharge and deterioration of discharge performance can be prevented. Therefore, it is possible to suppress the occurrence of memory fogging due to deterioration of the cleaning performance. According to the configuration shown in FIG. 1, in a color image forming apparatus corresponding to four colors of Y (yellow), M (magenta), C (cyan), and K (black), Y (yellow), M (magenta), Since the waste toner of each color of C (cyan) is collected by the K developing device and mixed and printed as black toner, image quality deterioration due to reuse of the waste toner can be prevented.

  In the embodiment of the present invention, control of the power source, charging unit, and exposure unit connected to the cleaning unit as described with reference to FIGS. 1 and 10 to 12 is performed by, for example, a control device provided in the image apparatus. That is, the control device, in each color station, discharges the waste toner collected by each cleaning unit to each image carrier so that the absolute value of the alternating voltage of the power supply that applies the alternating voltage to the cleaning unit is obtained. In order to make the polarity of the waste toner discharged to the image carrier the same as the first control means that makes the alternating voltage application time different for each color and the charging voltage is outputted from the charging means This corresponds to the configuration of the second control means. Further, this corresponds to a configuration of a third control unit in which an exposure voltage is intermittently applied from the exposure unit to the image carrier, and an interval at which the exposure voltage is applied is varied at each station.

  Further, the relationship between the exposure intervals is set to d1 <d2 <d3, the cleaning bias voltage application time is set to the relationship t1 <t2 <t3, and the absolute value of the cleaning bias voltage is set to V1>. Since the relationship of V2> V3 is set, waste toner transferred to the transfer medium is dispersed by a synergistic effect, and the cleaning function in the cleaning unit can be maintained. As a result, high-quality image formation can be performed.

  According to the embodiment of the present invention, the amount of waste toner discharged from the image carrier (photoconductor) to the transfer medium is flattened, so that the amount of waste toner collected by the K (black) cleaning brush is constant. Become. For this reason, the cleaning performance of the K cleaning brush is maintained in a good state, and the image quality of K (black) can be stabilized. Thus, in the present invention, in a color image forming apparatus corresponding to four colors of Y (yellow), M (magenta), C (cyan), and K (black), Y (yellow), M (magenta), C Since the waste toner of each color of (cyan) is collected by the K developing device and mixed and printed as black toner, the waste toner can be reused and environmental pollution can be prevented.

  As described above, the image forming apparatus and the waste toner collecting method of the present invention have been described based on the principle and the embodiments. However, the present invention is not limited to these embodiments and can be variously modified.

It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a schematic explanatory view showing an embodiment of the present invention. It is a timing chart which shows embodiment of this invention. It is a timing chart which shows embodiment of this invention. It is a timing chart which shows embodiment of this invention. 1 is a schematic cross-sectional view showing an overall configuration of one embodiment of an image forming apparatus using an electrophotographic process applied to the present invention.

Explanation of symbols

  1 (K, C, M, Y): Cleaning brush, 2 (K, C, M, Y): Transfer device power supply, 3 (K, C, M, Y): Cleaning brush power supply, 4 ... AC power supply, 5, 7 ... Power switch, 6 ... Ground, 11 ... Normal charged toner, 12 ... Reversely charged toner, 13 ... Discharged toner, 15 ... Residual toner, 16 ... transfer toner, 17 ... collected toner, 21 ... charged potential, 22 ... exposure potential, 41 (K, C, M, Y) ... photosensitive drum (image carrier) Body), 42 (K, C, M, Y) ... charging means (corona charger), 44 (K, C, M, Y) ... developing device, 45 (K, C, M, Y) ... Primary transfer roller, 50 ... Intermediate transfer belt, 66 ... Secondary transfer roller, 69, 69a ... Intermediate transfer belt cleaning means 70 ... developing unit power, 71 ... power switching switch, 101K, 101C, 101M, 101Y ... exposure apparatus, P ... recording medium.

Claims (12)

At least two or more image forming stations including a black image forming station in which image forming units including a charging unit, an exposure unit, a developing unit, and a transfer unit are arranged around the image carrier are provided. An image forming apparatus that forms an image in a tandem manner by passing through each station,
Waste toner cleaning mode setting means after image formation, cleaning means provided corresponding to each image carrier and collecting waste toner remaining on each image carrier, and waste collected by each cleaning means A power source that applies an alternating voltage to the cleaning means and an absolute value of the alternating voltage are different for each color so that toner is discharged to each image carrier, and an application time of the alternating voltage is different for each color. A first control unit, a second control unit that outputs a charging voltage from the charging unit to align the polarity of the waste toner discharged to the image carrier, and an exposure voltage from the exposure unit to the image carrier. And the waste toner discharged to the image carrier is transferred to a third control unit that varies the interval at which the exposure voltage is applied at each station. A power source for applying a voltage to said transfer means,
In the station forming a black image,
A power source for applying a voltage to the transfer means so as to collect the waste toner transferred to the transfer medium on the image carrier, and the waste toner from the image carrier for forming a black image is collected in the developing means. A power source for applying a voltage to the developing means,
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the cleaning unit is a rotating member that rotates in contact with the image carrier. The image forming apparatus according to claim 2, wherein the cleaning unit is a cleaning brush. The image forming apparatus according to claim 1, wherein the transfer medium is an intermediate transfer medium. The station is provided corresponding to each color of Y (yellow), M (magenta), C (cyan), K (black), and K (black) as viewed from the upstream side in the traveling direction of the transfer medium. 5. The image forming apparatus according to claim 1, wherein the station is disposed on the most downstream side. 6. The absolute value of the alternating voltage applied to the cleaning means of each station is controlled to be large on the upstream side of the transfer medium and small on the downstream side. The image forming apparatus described. 7. The application time of the alternating voltage applied to the cleaning means of each station is controlled to be short on the upstream side of the transfer medium and long on the downstream side. The image forming apparatus according to any one of the above. The voltage interval intermittently applied to the image carrier from the exposure unit of each station is set to be small on the upstream side in the traveling direction of the transfer medium and large on the downstream side. The image forming apparatus according to claim 7. By providing at least two or more image forming stations each having image forming units of charging means, exposure means, developing means, and transfer means around the image carrier, the transfer medium passes through each station. A process of forming an image by a tandem method;
In the waste toner cleaning mode after image formation,
A step of collecting waste toner remaining on each image carrier by a cleaning unit provided corresponding to each image carrier, and an absolute value of an alternating voltage output from a power source connected to each cleaning unit for each color And changing the application time of the alternating voltage for each color to discharge the waste toner collected by the cleaning means to the image carrier, and the image carrier from which the waste toner has been discharged. A step of recharging the image carrier, a step of intermittently exposing the image carrier at large intervals on the upstream side in the traveling direction of the transfer medium and a large interval on the downstream side, and a waste toner of the unexposed portion discharged onto the image carrier Transferring to the transfer means;
In the station forming a black image,
Recovering the waste toner transferred to the transfer medium to the image carrier, recovering the waste toner from the image carrier to the developing unit,
A waste toner collecting method comprising: The step of recharging the image carrier from which the waste toner has been discharged is characterized in that the polarity of the charging voltage output from the charging means is the same as the charging polarity of the image carrier. 10. The waste toner collecting method according to 9. The step of transferring the unexposed portion of the waste toner discharged to the image carrier to the transfer unit is characterized in that the absolute value of the voltage applied to the transfer unit is smaller than the value used when transferring the toner image. The waste toner recovery method according to claim 9 or 10. In the black image forming station, the step of collecting the waste toner transferred to the transfer medium on the image carrier is such that the polarity of the voltage applied to the transfer means is the same as the charging polarity of the image carrier. The waste toner recovery method according to claim 9, wherein the waste toner recovery method is performed.

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