JP5834962B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus provided with a cleaning device, and more particularly to a technique for removing residual toner remaining on an image bearing surface of a rotating image bearing member.

In an image forming apparatus such as a printer or a copying machine, a toner image formed on an image bearing surface of a photosensitive drum is primarily transferred to an image bearing surface of an intermediate transfer belt, and then the paper is passed through a secondary transfer belt or the like. In some cases, an image is formed on a recording sheet by secondary transfer onto the recording sheet.
In such an image forming apparatus, not only a toner image transferred to a recording sheet but also a patch toner image (toner image not transferred to the recording sheet) for adjusting image density and gradation density is an image on the intermediate transfer belt. The patch toner image that has been primarily transferred onto the carrying surface and has been primarily transferred is then directly transferred onto the image carrying surface of the secondary transfer belt.

Then, on the image carrying surface of the intermediate transfer belt after the secondary transfer, a part of the toner that could not be fully transferred remains as residual toner, and on the image carrying surface of the secondary transfer belt, the secondary transfer belt The transferred patch toner image remains as residual toner.
For example, a rubber blade can be used as a cleaning device for removing residual toner remaining on an image bearing surface such as an intermediate transfer belt or a secondary transfer belt, but the toner has a spherical shape or a small particle size. In this case, the residual toner is easily slipped between the rubber blade and the image carrier, and the residual toner cannot be removed sufficiently.

  For this reason, in recent years, cleaning apparatuses that remove residual toner by electrostatically adsorbing residual toner remaining on the image carrying surface of the image carrier have come to be used. For example, Patent Document 1 discloses a cleaning device including two sets of cleaning units (first and second cleaning units) that can electrostatically remove residual toners having different polarities. . Each cleaning unit comes into contact with the image carrying surface of the image carrier while rotating and a cleaning brush that electrostatically attracts and removes residual toner on the image carrying surface, and contacts the cleaning brush while rotating, A recovery roller for electrostatically adsorbing the residual toner adsorbed on the cleaning brush is included, and a bias voltage having a polarity different between the cleaning units is applied to both.

  As a result, the negatively and positively charged residual spherical or small toner particles remaining on the image bearing surface are electrostatically adsorbed to the cleaning brush of the corresponding cleaning unit, and then electrostatically charged. By further electrostatically collecting the adsorbed toner with a recovery roller, it is possible to remove residual toner charged in both polarities.

JP 2011-164252 A

  However, the residual toner is charged by changing the charge amount before being collected by the collecting roller due to the influence of the bias voltage applied to the cleaning brush and the collecting roller in the cleaning process in the cleaning device. Some toner becomes weakly charged toner whose amount is 0 or in the vicinity of 0. In this way, when the residual toner is changed to weakly charged toner in the process of cleaning in the cleaning device, the weakly charged toner is not electrostatically attracted to the collection roller but is held physically attracted to the cleaning brush. Then, the toner is finally re-transferred onto the image bearing surface, and the toner is transferred to the recording sheet, causing the recording sheet to become dirty.

  The present invention has been made in view of the above-described problems, and prevents the image bearing surface and the recording sheet from being soiled due to weakly charged toner that occurs during the cleaning process of the image bearing surface of the image bearing member. It is an object of the present invention to provide an image forming apparatus capable of doing so.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention removes residual toner remaining on an image bearing surface of a rotating image bearing member and applies electrostatic transfer to the image bearing surface after removal. An image forming apparatus for forming a toner image, wherein a predetermined voltage is applied to the image bearing surface while rotating to contact the image bearing surface, and a residual toner on the image bearing surface is electrostatically adsorbed and removed. A voltage having the same polarity as the voltage and an absolute value greater than the voltage is applied to the rotating body, and the toner adhering to the first rotating body is further electrostatically contacted with the first rotating body while rotating. Two sets of cleaning units including the second rotating body to be adsorbed are provided, the polarity of the voltage applied to the first and second rotating bodies is different between the two sets of cleaning units, and one set of the first rotation Each time so that the body rotates in contact with the other pair of second rotating bodies. Body and disposed is set in the first rotary member of said one set, rather than the first rotary member of the other set, image bearing of said image bearing member in the upstream side in the rotational direction of said image bearing member The polarity of the voltage that is in contact with the surface and is applied to the first and second rotating bodies of the one set is different from the charging polarity of the toner of the toner image .
Also, an image forming apparatus according to an aspect of the present invention removes residual toner remaining on the image bearing surface of the rotating image bearing member, and forms a toner image on the image bearing surface after removal by an electrostatic transfer method. A first rotating body that is applied with a predetermined voltage and contacts the image carrying surface while rotating and electrostatically adsorbs and removes residual toner on the image carrying surface. A second voltage having the same polarity as the voltage and having an absolute value larger than the voltage is applied, contacts the first rotating body while rotating, and further electrostatically adsorbs the toner adsorbed on the first rotating body. Two cleaning units including a rotating body, the polarity of the voltage applied to the first and second rotating bodies differs between the two cleaning units, and the first rotating body of one set The arrangement of each rotating body is set so as to rotate while contacting the second rotating body of the set. Cage, a first rotary member of said one set, rather than the first rotary member of the other set is in contact with the image bearing surface of the image bearing member at a downstream side in the rotational direction of the image bearing member,
The polarity of the voltage applied to the first and second rotating bodies of the one set is different from the charging polarity of the toner of the toner image.

  Here, when a position where the one set of the first rotating bodies is in contact with the image bearing surface is defined as a starting point, the one set of the first rotating bodies and the one set of the one set from the starting point. The distance along the rotation direction of the one set of the first rotating bodies to the position where the second rotating body is in contact is the distance from the starting point to the one set of the first rotating bodies and the other set of the first rotating bodies. It may be shorter than the distance along the rotation direction to the position where the second rotating body of the set is in contact.

An image forming apparatus that removes residual toner remaining on an image bearing surface of a rotating image bearing member and forms a toner image on the image bearing surface after removal by an electrostatic transfer method, and applies a predetermined voltage. A first rotating body that contacts the image carrying surface while rotating and removes residual toner on the image carrying surface by electrostatic adsorption, and has the same polarity as the voltage and an absolute value of the voltage. 2 sets of cleaning units including a second rotating body that is applied with a larger voltage, contacts the first rotating body while rotating, and further electrostatically adsorbs the toner adsorbed on the first rotating body; The polarity of the voltage applied to the first and second rotating bodies is different between the two sets of cleaning units, and one set of the first rotating bodies is in contact with the other set of the second rotating bodies. so as to rotate, is set with the arrangement of the rotary member, a first rotary member of said one set The absolute value of the potential difference between the one set of second rotating bodies is greater than the absolute value of the potential difference between the one set of first rotating bodies and the other set of second rotating bodies. Can be small
An image forming apparatus that removes residual toner remaining on an image bearing surface of a rotating image bearing member and forms a toner image on the image bearing surface after removal by an electrostatic transfer method, and applies a predetermined voltage. A first rotating body that contacts the image carrying surface while rotating and removes residual toner on the image carrying surface by electrostatic adsorption, and has the same polarity as the voltage and an absolute value of the voltage. 2 sets of cleaning units including a second rotating body that is applied with a larger voltage, contacts the first rotating body while rotating, and further electrostatically adsorbs the toner adsorbed on the first rotating body; The polarity of the voltage applied to the first and second rotating bodies is different between the two sets of cleaning units, and one set of the first rotating bodies is in contact with the other set of the second rotating bodies. The arrangement of each rotating body is set so as to rotate, and the one set of the first rotating body and The contact area of the portion in contact with the second rotating body of the other set is the portion in which the first rotating body of the one set and the second rotating body of the one set are in contact. The contact area can be larger.
In addition, the rotation direction of the first rotating body of the one set is configured to be opposite to the rotating direction of the second rotating body at a portion in contact with the second rotating body of both sets. Can be.

  The first rotating bodies of the two sets of cleaning units may be conductive brushes.

  By providing the above configuration, the first rotating body of one set of the two cleaning units including the first and second rotating bodies, the polarity of the voltage applied to both rotating bodies being different between the units, Since each rotating body is arranged so as to rotate while being in contact with the second rotating body of the other set, in the process of cleaning the residual toner remaining on the image carrying surface, the residual toner is transferred to one set. When the toner is weakly charged by receiving charge injection from the first rotating body, the charge is injected from the second rotating body of either the one set or the other set, and the weakly charged toner is After changing to a charged toner having the same polarity as that of the second rotating body into which the charge has been injected, the charged toner can be collected by electrostatic adsorption through the second rotating body having the opposite polarity.

As a result, the weakly charged toner generated in the cleaning process can be collected in the cleaning device, and the weakly charged toner generated in the cleaning process is re-transferred from the cleaning device onto the image carrying surface. It is possible to prevent the recording sheet from being stained or the residual toner from being transferred from the image bearing surface to the recording sheet.
Here, the first rotating body of the one set is in contact with the image carrying surface of the image carrying body on the upstream side in the rotation direction of the image carrying body than the first rotating body of the other set. The polarity of the voltage applied to the first and second rotating bodies of the one set may be different from the charging polarity of the toner of the toner image.

  As a result, the first rotating body of one set of cleaning units that can collect the residual toner having the same polarity as the charged polarity of the toner image with the larger amount of toner remaining on the image carrying surface is more suitable for the other. Since it is in contact with the image carrying surface of the image carrier on the upstream side in the rotation direction of the image carrier relative to the first rotating body of the cleaning unit, many weaknesses generated in the process of cleaning the residual toner of the same polarity. The charged toner can be efficiently collected in the upstream cleaning unit. That is, after the remaining toners having the higher ratio of charged polarity are collected in order, and the residual toner is taken into the upstream cleaning unit, the remaining toner having the lower ratio of charged polarity is removed by the downstream cleaning unit. Since it is collected, the cleaning operation can proceed efficiently, and the cleaning effect can be further enhanced.

Here, the contact area of the part where the first rotating body of the one set and the second rotating body of the other set are in contact is the first rotating body of the one set and the one of the one rotating set. It can be made larger than the contact area of the part which the 2nd rotary body of a set is contacting.
Thereby, compared with the case where both contact area is made the same, it flows through the part which the 1st rotary body of one set and the 2nd rotary body of the other group of two different sets of cleaning units contact. Since the amount of current can be increased, the amount of charge injected into the weakly charged toner generated in the cleaning process can be increased, and the weakly charged toner can be made to have the same polarity as the second rotating body of the other set. After being reliably charged, the toner charged to the same polarity can be recovered through one set of opposite polarity second rotating bodies. As a result, the amount of weakly charged toner that is re-transferred to the image carrying surface can be reduced, and the image carrying surface and the recording sheet caused by re-transfer of the weakly charged toner onto the image carrying surface can be further reduced. Can be reduced.

Here, the voltages applied to the four rotating bodies of the two sets of cleaning units may be supplied from separate power sources.
As a result, a voltage can be applied to each rotating body from a separate power source. Therefore, the voltage application amount can be individually set for each rotating body so that the electric field strength does not become excessive or insufficient due to a change in state of the rotating body. Fine adjustments can be made, and in order to maintain the cleaning performance in a good state, a fine response can be taken.

1 is a diagram illustrating a configuration of a printer 1 according to the present embodiment. 2 shows a toner charge amount distribution in a patch toner image formed on an image bearing surface of a photosensitive drum. The toner charge amount distribution in the patch toner image after secondary transfer of the patch toner image formed on the image carrying surface of the photosensitive drum onto the image carrying surface of the secondary transfer belt 13 is shown. It is a figure which shows the structure of the cleaning apparatus 14 and its peripheral part. It is a figure which shows the structure of the cleaning apparatus 140 for a comparison. 6 is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when printing processing is performed while forming a patch toner image between sheets on the image carrying surface of the intermediate transfer belt using a comparative cleaning device. . The relationship between the cumulative number of printed sheets and the blackened area ratio when printing processing is performed while forming a patch toner image between sheets on the image carrying surface of the intermediate transfer belt using the cleaning device 14 of the present embodiment is shown. It is a graph. It is a figure which shows the modification of the cleaning apparatus 14 shown in FIG. FIG. 5 is a graph showing the relationship between the potential difference between the cleaning brush 141 and the recovery roller 144 and the amount of current flowing between the two when the second push amount is the same as the first push amount and when the second push amount is larger than the first push amount. is there. 4 is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when the same printing process as in the example is performed using the cleaning device 14 having the configuration shown in FIG. 4 when the second push-in amount is 1.4 mm. is there. 4 is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when the same printing process as in the example is performed using the cleaning device 14 having the configuration shown in FIG. 4 when the second push-in amount is 2.0 mm. is there.

Hereinafter, an embodiment of an image forming apparatus according to an embodiment of the present invention will be described with reference to an example in which the image forming apparatus is applied to a tandem color digital printer (hereinafter simply referred to as “printer”).
[1] Configuration of Printer First, the configuration of the printer 1 according to the present embodiment will be described. FIG. 1 is a diagram illustrating a configuration of a printer 1 according to the present embodiment. As shown in FIG. 1, the printer 1 includes an image process unit 3, a paper feed unit 4, a fixing device 5, and a control unit 60.

  When the printer 1 is connected to a network (for example, LAN) and receives a print instruction from an external terminal device (not shown) or an operation panel having a display unit (not shown), yellow, magenta, cyan, and black are received based on the instruction. A toner image of each color is formed, and these are multiplex-transferred onto a recording sheet to form a full-color image, thereby executing a printing process on the recording sheet. Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are expressed as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.

The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K, an exposure unit 10, an intermediate transfer belt 11, a secondary transfer belt 13, a secondary transfer roller 22, and the like. Since the image forming units 3Y, 3M, 3C, and 3K have the same configuration, the configuration of the image forming unit 3Y will be mainly described below.
The image forming unit 3Y includes a photosensitive drum 31Y, a developing device 32Y, a charger 33Y, a cleaner 34Y for cleaning the image bearing surface of the photosensitive drum 31Y, a primary transfer roller 35Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the image bearing surface of the photosensitive drum 31Y. The developing device 32Y faces the photosensitive drum 31Y and conveys charged toner to the image carrying surface of the photosensitive drum 31Y. The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 15 and a plurality of support rollers 16, 17, 18, 19, 20, and 21 and is driven to rotate in the direction of arrow A.

Further, residual toner on the image carrying surface of the intermediate transfer belt 11 is electrostatically charged on the circulation path of the intermediate transfer belt 11 (position facing the support rollers 18 and 19 across the image carrying surface of the intermediate transfer belt 11). A cleaning device 12 is provided for removal.
The exposure unit 10 includes a light emitting element such as a laser diode, emits laser light L for forming images of Y to K colors in response to a drive signal from the control unit 60, and each of the image forming units 3Y, 3M, 3C, and 3K. The image carrying surface of the photosensitive drum is exposed and scanned. By this exposure scanning, an electrostatic latent image is formed on the image bearing surface of the photosensitive drum 31Y charged by the charger 33Y. Similarly, electrostatic latent images are formed on the image bearing surfaces of the photosensitive drums of the image forming units 3M, 3C, and 3K.

The electrostatic latent image formed on the image bearing surface of each photosensitive drum is developed by the developing units of the image forming units 3Y, 3M, 3C, and 3K, and the corresponding color on the image bearing surface of each photosensitive drum. The toner image is formed. The formed toner image is labeled with a primary transfer roller of each of the image forming units 3Y, 3M, 3C, and 3K (in FIG. 1, only the primary transfer roller corresponding to the image forming unit 3Y is denoted by reference numeral 35Y). Are omitted in order from each other), so that the images are sequentially transferred onto the image carrying surface of the intermediate transfer belt 11 at different timings so as to be superimposed at the same position on the image carrying surface of the intermediate transfer belt 11. Thereafter, the toner image on the image carrying surface of the intermediate transfer belt 11 is secondarily transferred onto the recording sheet collectively by the action of electrostatic force by the secondary transfer roller 22.

The recording sheet onto which the toner image has been secondarily transferred is further conveyed to the fixing device 5 via the secondary transfer belt 13, and the toner image (unfixed image) on the recording sheet is heated and pressed in the fixing device 5. Then, after being thermally fixed to the recording sheet, it is discharged to a discharge tray 72 by a discharge roller 71.
The paper feed unit 4 includes a paper feed cassette 41 that stores recording sheets (denoted by reference numeral S in FIG. 1), a feed roller 42 that feeds the recording sheets in the paper feed cassette 41 one by one onto the transport path 43, and a feed roller 42. A timing roller 44 for conveying the recording sheet at a timing for sending the recording sheet to the secondary transfer position 24 is provided.

The number of paper feed cassettes is not limited to one and may be plural. As the recording sheet, paper sheets (plain paper, thick paper) having different sizes and thicknesses, and film sheets such as an OHP sheet can be used. When there are a plurality of paper feed cassettes, recording sheets having different sizes, thicknesses or materials may be stored in the paper feed cassettes.
The timing roller 44 is a timing at which the toner image primarily transferred onto the image carrying surface of the intermediate transfer belt 11 is conveyed to the secondary transfer position 24 so as to be superimposed at the same position on the image carrying surface of the intermediate transfer belt 11. At the same time, the recording sheet is conveyed to the secondary transfer position 24. Then, at the secondary transfer position 24, the toner images on the image carrying surface of the intermediate transfer belt 11 are secondarily transferred onto the recording sheet by the secondary transfer roller 22.

Each of the rollers such as the feeding roller 42 and the timing roller 44 is rotationally driven through a power transmission mechanism (not shown) such as a gear and a belt using a transport motor (not shown) as a power source. As the transport motor, for example, a stepping motor capable of controlling the rotational speed with high accuracy is used.
The secondary transfer belt 13 is an endless belt, is stretched around the secondary transfer roller 22, the drive roller 23, and the two opposing rollers 25 and 26, and is driven to rotate in the direction of arrow B. As the secondary transfer belt 13, for example, resin such as polyimide, polyester, polyvinylidene fluoride, rubber, or the like can be used. The surface resistance value of the secondary transfer belt 13 is preferably about 10 ⁵ to 10 ¹³ / □. The drive roller 23 is driven by a drive motor (not shown) controlled by the control unit 60, and the secondary transfer belt 13 is driven to rotate in the B direction by driving the drive motor.

  Further, on the circumference path of the secondary transfer belt 13 (position facing the opposing rollers 25 and 26 across the image carrying surface of the secondary transfer belt 13), there is a secondary on the image carrying surface of the secondary transfer belt 13. A cleaning device 14 for electrostatically removing the transferred residual toner is disposed. The residual toner that is secondarily transferred onto the image carrying surface of the secondary transfer belt 13 is transferred to a region between image areas on the image carrying surface of the intermediate transfer belt 11 that is secondarily transferred to the recording sheet. There are patch toner images for adjusting image density and gradation density, and fog toner between the image areas.

These residual toners are subjected to charge injection in the process from the image formation on the image bearing surface of the photosensitive drum to the secondary transfer on the image bearing surface of the secondary transfer belt 13, and the normal charging polarity ( Here, a broad charge distribution ranging from negative polarity) to normal charge polarity and reverse polarity (positive polarity) is shown.
Here, the “regular charging polarity” refers to the polarity of the average charge amount of the toner in the developing device or the toner image formed on the image carrying surface, and here, the negative polarity is the normal charging polarity. .
FIG. 2 shows the toner charge amount distribution in the patch toner image formed on the image bearing surface of the photosensitive drum. FIG. 3 shows the patch toner image on the image bearing surface of the secondary transfer belt 13. The toner charge amount distribution in the patch toner image after the next transfer is shown. In both figures, the horizontal axis indicates the charge amount of the toner, and the vertical axis indicates the ratio (%) of the number of toners of each charge amount. The charge amount distributions in both figures were measured using an E-Spart measuring device (Model EST-II; manufactured by Hosokawa Micron Corporation).

As is clear from comparison between the two figures, the charge distribution of the patch toner image after the secondary transfer is smaller than the charge distribution of the patch toner image formed on the image bearing surface of the photosensitive drum. The distribution width spreads to the bipolar side.
As described above, since the distribution range of the charge amount is widened, a weakly charged toner having a charge amount of 0 or in the vicinity of 0 or a positive toner is easily generated in the cleaning process in the cleaning device 14.

[2] Configuration of Cleaning Device The cleaning device 14 is configured to be able to remove weakly charged toner and positively charged toner generated in the process of cleaning charged toner. FIG. 4 is a diagram illustrating a configuration of the cleaning device 14 and its peripheral portion. A black circle indicated by reference numeral 401 in the figure is a negatively charged toner, a double-lined circle indicated by reference numeral 402 is a weakly charged toner, and a small spotted circle indicated by reference numeral 403 is a positively charged toner. Respectively.

  The cleaning device 14 includes a cleaning brush 141, a recovery roller 143, and a scraper 145. The cleaning device 14 includes a first cleaning unit 14A that electrostatically adsorbs and removes negatively charged toner, a cleaning brush 142, a recovery roller 144, and a scraper 146. And a second cleaning unit 14B for electrostatically adsorbing and removing the positively charged toner, and a conveying screw 147.

  The cleaning brush 141 of the first cleaning unit 14A is disposed so as to face and contact not only the recovery roller 143 of the first cleaning unit 14A but also the recovery roller 144 of the second cleaning unit 14B. On the other hand, the cleaning brush 142 of the second cleaning unit 14B is disposed so as to face and contact only the recovery roller 144 of the second cleaning unit 14B.

Further, the cleaning brushes 141 and 142 of the first and second cleaning units respectively face the opposing rollers 25 and 26 with the secondary transfer belt 13 interposed therebetween, and the opposing rollers via the secondary transfer belt 13 at the opposing positions. In contact with the secondary transfer belt 13 while being pushed in from 25 and 26.
Further, the cleaning brush 141 of the first cleaning unit 14 </ b> A is downstream of the position facing the opposing roller 25 in the rotation direction and is pressed from the recovery roller 143 of the first cleaning unit 14 </ b> A in a state where it is pushed in. Furthermore, in contact with the collection roller 144 in a state of being pushed from the collection roller 144 of the second cleaning unit 14B on the downstream side in the rotational direction from the opposed contact position. That is, the cleaning roller 143 of the first cleaning unit 14A has a cleaning brush from a position opposed to the counter roller 25 (contact position with the secondary transfer belt 13) rather than the collection roller 144 of the second cleaning unit 14B. The two collection rollers are in contact with the cleaning brush 141 in a non-contact state so that the distance in the rotation direction of 141 becomes closer.

  The cleaning brush 142 of the second cleaning unit 14B is opposed to and in contact with the recovery roller 144 of the second cleaning unit 14B on the downstream side of the position facing the facing roller 26 in the rotational direction. In FIG. 2, the recovery roller 144 is pressed against the recovery roller 144 and is in contact with the recovery roller 144. Further, the recovery roller 143 of the first cleaning unit 14A has a scraper 145 of the first cleaning unit 14A, and the recovery roller 144 of the second cleaning unit 14B has a scraper 146 of the second cleaning unit 14B. It is in contact.

  In the example of the figure, the collection roller 143 of the first cleaning unit 14A and the collection roller 144 of the second cleaning unit 14B are the rotation center point of the cleaning brush 141 of the first cleaning unit 14A and the collection roller 143. The straight line P connecting the rotation center point and the straight line Q connecting the rotation center point of the cleaning brush 141 and the rotation center point of the collection roller 144 are arranged at a position that is substantially orthogonal.

  Further, the cleaning brush 141 of the first cleaning unit 14A and the cleaning brush 142 of the second cleaning unit 14B have a rotation center point of the collection roller 144 and a rotation center point of the cleaning brush 141 of the second cleaning unit 14B. The connecting straight line Q and the straight line R connecting the rotation center point of the collection roller 144 and the rotation center point of the cleaning brush 142 are arranged at positions that are substantially orthogonal to each other. In addition, said arrangement | positioning relationship is an example and it cannot be overemphasized that the arrangement | positioning relationship between the cleaning brushes 141 and 142 and the collection | recovery rollers 143 and 144 is not limited to said example.

  In the cleaning brushes 141 and 142 and the collection rollers 143 and 144 of the first and second cleaning units 14A and 14B, a driving force from a drive motor (not shown) is applied to each cleaning brush and the collection roller via a drive transmission mechanism. Thus, it is rotationally driven in the directions of arrows C, D, E, and F shown in FIG. The opposing rollers 25 and 26 are driven to rotate in the directions of arrows G and H when the secondary transfer belt 13 is driven to rotate.

  The cleaning brush 141 of the first cleaning unit 14A is a region facing the recovery roller 143 and 144 of the opposing roller 25 and the first and second cleaning units 14A and 14B (recovery contact with the recovery rollers 143 and 144, respectively). The rotation direction of the counter roller 25, the rotation direction of the collection roller 143, and the rotation direction of the collection roller 144 (counter direction). The cleaning brush 142 of the second cleaning unit 14B rotates in the area facing the opposing roller 26 and the collection roller 144 of the second cleaning unit 14B (area facing the collection roller 144). And the rotation direction of the collecting roller 144 are rotated in the opposite direction (counter direction).

The cleaning brushes 141 and 142 of the first and second cleaning units 14A and 14B are each a metal core (core metal 141A and 142A) that is a solid or hollow cylindrical member made of a metal conductive material, It is comprised from the brush part (brush part 141B, 142B) which consists of an electroconductive brush fiber implanted by the outer periphery of the metal core 1. FIG.
The core bars 141A and 142A are made of a conductive metal, for example, aluminum, iron, stainless steel or the like, and both ends are pivotally supported by a bearing member (not shown) so as to be rotatable as a rotation shaft.

The brush portions 141B and 142B are made of conductive brush fibers planted on the outer periphery of the core bars 141A and 142A. The brush fibers are made of, for example, a material in which carbon is dispersed in a resin such as nylon, polyester, acrylic, or rayon to impart conductivity. Fineness is 1D to 10D, density is 50 to 300 [kF / inch ² ], A yarn resistance of 10 ⁵ to 10 ¹³ [Ω] can be used.

If the yarn resistance (volume resistance value) of the cleaning brushes 141 and 142 is too high, it is necessary to set a high bias voltage, and the power consumption becomes large. If the volume resistance value is too low, the electric field becomes strong and leaks. Is likely to occur.
The collection rollers 143 and 144 of the first and second cleaning units 14A and 14B are composed of metal rollers such as aluminum, stainless steel, and iron. Alternatively, a conductive resin layer may be formed on a metal roller, or plating may be performed for the purpose of maintaining surface smoothness and preventing corrosion such as rust.

  The conductive resin layer is formed by dispersing a conductive material in the resin, and as the resin material, materials having excellent wear resistance, such as polyester, polyvinylidene fluoride, polyamide, polyimide, etc. can be used. As the conductive material, for example, carbon black, metal fine particles, ionic conductive material, or the like can be used. The collection rollers 143 and 144 are pivotally supported so that both ends can rotate as a rotation shaft to a bearing member (not shown).

The volume resistance values of the collection rollers 143 and 144 can be 10 ⁵ to 10 ⁸ [Ω]. If the volume resistance value of the collection rollers 143 and 144 is too high, it is necessary to set the bias voltage high, and the power consumption becomes large. If the volume resistance value is too low, the electric field becomes strong and leakage tends to occur.
The scrapers 145 and 146 of the first and second cleaning units 14A and 14B are thin plate-like members made of a metal material such as iron or stainless steel. This is a cleaning member that scrapes off residual toner adsorbed on the surface. The conveying screw 147 is a conveying member that conveys residual toner scraped off by the scrapers 145 and 146 to a waste container (not shown). The opposing rollers 25 and 26 are composed of metal rollers such as aluminum, stainless steel, and iron, like the collection rollers 143 and 144.

  The cleaning brush 141 of the first cleaning unit 14A is connected to the high-voltage power supply 151 and the cleaning brush 142 of the second cleaning unit 14B is connected to the high-voltage power supply 152, respectively. In this case, a negative polarity) and a reverse polarity (positive polarity) bias voltage is applied to the cleaning brush 141 (the rotation shaft portion of the cleaning brush 141), and the high voltage power source 152 has the same polarity as the normal charging polarity of the toner (negative polarity). Is applied to the cleaning brush 142 (the rotating shaft portion of the cleaning brush 142).

  The collection roller 143 of the first cleaning unit 14A is connected to the high-voltage power supply 153, and the collection roller 144 of the second cleaning unit 14B is connected to the high-voltage power supply 154. From the high voltage power supply 153, a bias voltage having the same polarity as the high voltage power supply 151 and having a larger absolute value than the bias voltage applied from the high voltage power supply 151 to the cleaning brush 141 of the first cleaning unit 14A is applied to the first cleaning unit 14A. Bias voltage applied to the collection roller 143 (the rotation shaft portion of the collection roller 143), the same polarity as the high-voltage power supply 152 from the high-voltage power supply 154, and the bias voltage applied from the high-voltage power supply 52 to the cleaning brush 142 of the second cleaning unit 14B. A bias voltage having a larger absolute value than that is applied to the collection roller 144 of the second cleaning unit 14B (the rotation shaft portion of the collection roller 144).

  Thereby, between the cleaning brush 141 of the first cleaning unit 14A and the recovery roller 143 of the first cleaning unit 14A, the cleaning brush 142 of the second cleaning unit 14B, and the recovery roller 144 of the second cleaning unit 14B. In between, an electric field due to a potential difference is formed. In addition, an electric field due to a potential difference is also formed between the cleaning brush 141 of the first cleaning unit 14A having a different polarity and the recovery roller 144 of the second cleaning unit 14B.

  Moreover, since it is comprised so that a voltage may be applied to each cleaning brush and each collection roller of 1st and 2nd cleaning unit 14A, 14B from a respectively separate power supply, the state of each cleaning brush and each collection roller The amount of applied voltage can be fine-tuned individually so that the electric field strength does not become excessive or insufficient due to the change, and meticulous measures are taken to maintain the cleaning performance of the first and second cleaning units in good condition. Can be taken.

  For each cleaning brush and each collection roller, variations between production lots, environmental changes (for example, adhesion of moisture), and durability decrease (durability decrease due to adhesion of toner and toner external additives, deterioration of energization, etc.) The resistance changes due to a state change such as this, whereby the value of the current flowing through the rotating body changes, the voltage drop width in the rotating body changes, and the electric field strength may change. In such a case, it is possible to finely adjust the voltage application amount individually for each rotating body (for example, when each cleaning brush and each collection roller are turned on when the power is turned on or when a predetermined value of the durability counter is reached). It is possible to detect the value of the flowing current and make fine adjustments such as increasing or decreasing the voltage value based on the result), and maintain the cleaning performance of the first and second cleaning units 14A and 14B in a good state. In order to do so, we can take meticulous response.

  Further, the bias voltage values applied to the cleaning brush 141 of the first cleaning unit 14A, the recovery roller 143 of the first cleaning unit 14A, and the recovery roller 144 of the second cleaning unit 14B are the recovery roller 143 and the cleaning brush. The absolute value of the potential difference with respect to 141 is determined to be smaller than the absolute value of the potential difference between the collection roller 144 and the cleaning brush 141.

  As a result, a part of the weakly charged toner or the positively charged toner generated by being charged to the positive polarity side in the process of being collected by the cleaning brush 141 and the collecting roller 143 is charged to the negative polarity by the collecting roller 144. Can do. The negatively charged toner is transferred to the recovery roller 143 and recovered by the recovery roller 143 when the cleaning brush 141 is rotationally driven while being electrostatically attracted to the cleaning brush 141. It is possible to prevent the weakly charged toner or the like from re-transferring to the secondary transfer belt 13.

The opposing rollers 25 and 26 are grounded, respectively, between the cleaning brush 141 and the secondary transfer belt 13 of the first cleaning unit 14A, and between the cleaning brush 142 and the secondary transfer belt 13 of the second cleaning unit 14B. Each function as an electrode portion that takes an earth for forming an electric field between them.
[3] Operation of Cleaning Device Among the residual toners on the image carrying surface of the secondary transfer belt 13, the residual toners of normal charging polarity (negative polarity) are the first cleaning unit 14A to which a positive bias voltage is applied. Is electrostatically attracted to the cleaning brush 141. The negatively charged residual toner that has been electrostatically attracted is a collection roller to which a positive bias voltage greater than the bias voltage applied to the cleaning brush 141 is applied by rotating the cleaning brush 141 in the C direction. 143 is transferred to a region opposite to 143. Further, the negative residual toner is statically applied to the positive recovery roller 143 by the action of an electric field formed between the cleaning brush 141 of the first cleaning unit 14A and the recovery roller 143 of the first cleaning unit 14A. After being electroadsorbed and recovered, the scraper 145 of the first cleaning unit 14 </ b> A scrapes the recovery roller 143 and transports it to the disposal container by the transport screw 147.

In addition, when the residual toner of normal charging polarity is transferred to the area facing the cleaning brush 141 of the first cleaning unit 14A, positive charge injection is received from the cleaning brush 141 to which a positive bias voltage is applied. If the toner is weakly charged or positively charged, the residual toner is removed as follows.
The weakly charged toner is transferred to a region facing the recovery roller 143 of the first cleaning unit 14A when the cleaning brush 141 of the first cleaning unit 14A is rotationally driven in the C direction. Upon receiving positive charge injection from the roller 143, a positive charged toner is obtained. The positively charged toner is held by the cleaning brush 141 by the action of an electric field formed between the cleaning brush 141 of the first cleaning unit 14A and the recovery roller 143 of the first cleaning unit 14A. Thus, the second cleaning unit 14B to which the negative bias voltage is applied is transferred to a region facing the recovery roller 144. Further, the positively charged toner is electrostatically adsorbed to the recovery roller 144 by the action of an electric field formed between the cleaning brush 141 of the first cleaning unit 14A and the recovery roller 144 of the second cleaning unit 14B. Then, the scraper 146 of the second cleaning unit 14B scrapes the recovery roller 144 and transports it to the disposal container by the transport screw 147.

  On the other hand, the positively charged toner is transferred to a region facing the cleaning brush 142 of the second cleaning unit 14B to which the negative bias voltage is applied via the secondary transfer belt 13, and is statically transferred to the cleaning brush 142. Electroadsorbed. The positively charged toner that has been electrostatically adsorbed is rotated with the cleaning brush 142 of the second cleaning unit 14B in the direction D, so that the negatively charged second cleaning unit 14B and the collection roller 144 are rotated. It is transferred to the opposite area. Further, the positively charged toner is electrostatically attracted to the recovery roller 144 by the action of an electric field formed between the cleaning brush 142 of the second cleaning unit 14B and the recovery roller 144 of the second cleaning unit 14B. Then, the scraper 146 of the second cleaning unit 14B scrapes the recovery roller 144 and transports it to the disposal container by the transport screw 147.

Further, when the residual toner having the normal charging polarity is transferred to the area facing the recovery roller 143 of the first cleaning unit 14A, the toner of positive charge is injected from the recovery roller 143 and charged with a weak charge or positive charge. When toner is generated, residual toner is removed as follows.
The weakly charged toner is further transferred to a region facing the recovery roller 144 of the second cleaning unit 14B when the cleaning brush 141 of the first cleaning unit 14A is rotationally driven in the C direction. In the state where negative charge is injected from the collection roller 144 and electrostatically attracted to the cleaning brush 141 of the first cleaning unit 14A, the positive cleaning first 14A of the first cleaning unit 14A passes through the position facing the opposing roller 25. It is transferred to the area facing the collection roller 143. Then, after being electrostatically attracted to the positive recovery roller 143 and recovered by the action of an electric field formed between the cleaning brush 141 of the first cleaning unit 14A and the recovery roller 143 of the first cleaning unit 14A. The scraper 145 of the first cleaning unit 14A scrapes the recovery roller 143 and transports it to the disposal container by the transport screw 147.

  On the other hand, the positively charged toner is held by the cleaning brush 141 by the action of an electric field formed between the cleaning brush 141 of the first cleaning unit 14A and the recovery roller 143 of the first cleaning unit 14A. When the cleaning brush 141 is rotationally driven in the C direction, the cleaning brush 141 is transferred to a region facing the recovery roller 144 of the second cleaning unit 14B. Then, after being electrostatically adsorbed and recovered by the negative recovery roller 144 by the action of an electric field formed between the cleaning brush 141 of the first cleaning unit 14A and the recovery roller 144 of the second cleaning unit 14B. The scraper 146 of the second cleaning unit 14B scrapes the recovery roller 144 and transports it to the disposal container by the transport screw 147.

  Of the residual toner on the image carrying surface of the secondary transfer belt 13, the residual toner charged with a normal charge polarity (negative polarity) and a reverse polarity (positive polarity) is subjected to a second cleaning to which a negative bias voltage is applied. It is electrostatically attracted to the cleaning brush 142 of the unit 14B. Then, the cleaning brush 142 of the second cleaning unit 14B is rotationally driven in the D direction, so that the electrostatically adsorbed positive-polarity residual toner is in contact with the collection roller 144 of the negative-polarity second cleaning unit 14B. After being transferred to the opposite area and electrostatically attracted to the recovery roller 144 by the action of an electric field formed between the recovery roller 144 and recovered, the scraper 146 of the second cleaning unit 14B scrapes the recovery roller 144. And transported to a disposal container by a transport screw 147.

  As described above, in the cleaning device 14 according to the present embodiment, the recovery roller 143 of the first cleaning unit 14A, which has a different polarity from the cleaning brush 141 of the positive first cleaning unit 14A, and the second The collection roller 144 of the cleaning unit 14B is disposed so as to face the cleaning brush 141 at different positions on the rotation path of the cleaning brush 141 where they are not in contact with each other.

  As a result, in the course of cleaning, when the residual toner receives positively charged charge from the cleaning brush 141 or the collection roller 143 of the first cleaning unit 14A to generate weakly charged toner, the first cleaning unit 14A A charge is injected into the weakly charged toner from the recovery roller 143 of the first cleaning unit 14A or the recovery roller 144 of the second cleaning unit 14B that is in contact with the cleaning brush 141 at different positions on the rotation path, It can be changed to a charged toner having the same polarity as that of the collecting roller into which the charge has been injected. As a result, when the charged toner is transported to a position where the charged toner is not injecting electric charge and is in contact with the other collecting roller having the opposite polarity to the charged toner, the charged toner is transferred to the other collecting roller. It is electrostatically attracted and recovered.

  Therefore, the weakly charged toner generated in the cleaning process can be collected in the cleaning device 14, and the weakly charged toner is retransferred from the cleaning device 14 to the image carrying surface of the secondary transfer belt 13 as a residual toner. Thus, it is possible to prevent the image carrying surface of the secondary transfer belt 13 from becoming dirty, or the residual toner from being transferred from the image carrying surface of the secondary transfer belt 13 to the recording sheet and becoming dirty.

  Further, in the configuration of the cleaning device 14 of the present embodiment, as shown in FIG. 3, the charge polarity (regularity) of the toner image with the larger proportion of the amount of toner remaining on the image carrying surface of the secondary transfer belt 13. The first cleaning unit 14A capable of collecting the residual toner charged to the same polarity (negative polarity) as the charging polarity) is more suitable for the secondary transfer belt 13 than the second cleaning unit 14B capable of collecting the residual toner of the polarity. Since it is in contact with the image carrying surface of the secondary transfer belt 13 on the upstream side in the rotation direction, the weakly charged toner that frequently occurs in the process of cleaning the negative-polarity residual toner is efficiently processed in the first cleaning unit 14A on the upstream side. It can be recovered well. In other words, after the negative-polarity residual toner having the larger ratio is collected in order, and the residual toner is taken into the upstream first cleaning unit 14A, the positive-polarity residual toner having the smaller ratio is downstream. Because it is collected by the second cleaning unit 14B. The cleaning operation can proceed efficiently, and the cleaning effect can be further enhanced.

[4] Examples Experiments were conducted to compare the cleaning effects of the cleaning device 14 of the present embodiment and the cleaning device for comparison as follows. FIG. 5 is a diagram showing a configuration of the cleaning device 140 for comparison and comparison. In the figure, the same components as those of the cleaning device 14 are given the same numbers. As is clear from comparison between FIG. 4 and FIG. 5, the cleaning device 140 and the cleaning device 14 indicate whether the collection roller 144 of the second cleaning unit 14B is in contact with the cleaning brush 141 of the first cleaning unit 14A. However, the other two configurations are the same.

(1) Experimental conditions The cleaning brushes 141 and 142 of the first and second cleaning units 14A and 14B have an outer diameter of 18 mm, and the recovery rollers 143 and 144 of the first and second cleaning units 14A and 14B have an outer diameter. 16 mm, the opposing rollers 25 and 26 have an outer diameter of 10 mm, and the arrangement relationship between the cleaning brushes 141 and 142 and the collection rollers 143 and 144 of the first and second cleaning units 14A and 14B is shown in FIG. It is the same as the arrangement relationship.

  The bias voltage applied to the cleaning brushes 141 and 142 and the collection rollers 143 and 144 of the first and second cleaning units 14B is controlled by constant voltage control, and the bias applied to the cleaning brush 141 of the first cleaning unit 14A. The voltage is + 400V, the bias voltage applied to the cleaning brush 142 of the second cleaning unit 14B is -200V, the bias voltage applied to the recovery roller 143 of the first cleaning unit 14A is + 1200V, and the recovery of the second cleaning unit 14B. The bias voltage applied to the roller 144 was −1000V.

The rotational speed of the cleaning brushes 141 and 142 of the first and second cleaning units 14A and 14B is 300 mm / second, and the rotational speed of the collection rollers 143 and 144 of the first and second cleaning units 14A and 14B is 450 mm / second. The second rotation direction was the same as the rotation direction shown in FIG.
The amount of pressing from the opposing rollers 25 and 26 and the collection rollers 143 and 144 into the cleaning brushes 141 and 142 was as follows. Here, the “push-in amount” is the center of the cleaning brush when the cleaning brush is not pushed from the corresponding roller (the brush part of the cleaning brush is not crushed) and in contact with the corresponding roller. Cleaning in a state where the cleaning brush is pushed from the corresponding roller (a state where the brush portion of the cleaning brush is crushed) from the distance (D1) between the central axis of the gold and the rotation central axis of the corresponding roller This is expressed by the difference (D1−D2) between the center axis of the brush core and the distance (D2) between the corresponding rotation center axes of the rollers.

  The amount of pushing from the secondary transfer belt 13 to the cleaning brush 141 at the position facing the opposing roller 25 and the amount of pushing from the secondary transfer belt 13 to the cleaning brush 142 at the position facing the corresponding roller 26 are 1.2 mm. The push amount from the roller 143 to the cleaning brush 141 was 1.4 mm, the push amount from the collection roller 144 to the cleaning brush 141 was 1.6 mm, and the push amount from the collection roller 144 to the cleaning brush 142 was 1.4 mm. .

As the toner used in the experiment, 0.2 part by weight of the first hydrophobic silica and 100% by weight of the second hydrophobic silica are used for 100 parts by weight of the toner base material having a volume average particle diameter of about 6.5 μm prepared by wet granulation. A negative toner in which 0.5 part by weight of silica and 0.5 part by weight of hydrophobic titanium oxide were externally added was used.
In the experiment, a patch toner image was formed on the image carrying surface of the intermediate transfer belt 11 between the image area to be secondarily transferred to the recording sheet and the image area (hereinafter referred to as “inter-paper”) 300,000 sheets are continuously printed on paper (recording sheet) at a system speed (paper conveyance speed) of 600 mm / second, and the percentage of toner stain area on the back side of the coated paper during printing (area on the back side of the coated paper) The percentage of the area of the toner smudge with respect to 100%, hereinafter referred to as “blackened area ratio”) was measured using an optical microscope.

As the patch toner image, a patch toner image of each color of Y, M, C, and K with an adhesion amount of 5 g / m ² was formed between the papers. The length of each patch toner image in the axial direction is 12.6 mm (3% for A3 paper horizontal size 420 mm), 21 mm (5% for A3 paper horizontal size 420 mm), 29.4 mm (A3). The above-described continuous printing process was performed on patch toner images having respective lengths of 7% (percentage with respect to a paper lateral size of 420 mm).

(2) Experimental Results FIG. 6 is a graph showing the relationship between the cumulative number of printed sheets and the black area ratio when the above-described printing process is performed using the comparative cleaning device 140, and FIG. 14 is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when the above-described printing process is performed using 14.

  A solid line denoted by reference numeral 61 in FIG. 6 is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a patch toner image having an axial length of 12.6 mm is formed. A dotted line indicates a graph showing a relationship between the cumulative number of printed sheets and a blackened area ratio when a patch toner image having an axial length of 21 mm is formed. A one-dot chain line indicated by reference numeral 63 indicates an axial length. Is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a 29.4 mm patch toner image is formed.

  Similarly, the solid line denoted by reference numeral 71 in FIG. 7 shows a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a patch toner image having an axial length of 12.6 mm is formed. The two-dot chain line shown is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a patch toner image having an axial length of 21 mm is formed. 3 is a graph showing the relationship between the cumulative number of printed sheets and the black area ratio when a patch toner image having a length of 29.4 mm is formed.

  As shown in the experimental results shown in FIG. 6, when the cleaning device 140 is used, the blackened area ratio increases as the cumulative number of printed sheets increases until the cumulative number of printed sheets reaches 200,000. When the amount of toner smear increases and the cumulative number of printed sheets exceeds 100,000, coated paper is used when any patch toner image having an axial length of 12.6 mm, 21 mm, or 29.4 mm is formed. The blackening area ratio exceeds 0.6% (the level indicated by the dotted line 64), which is a level that affects quality.

  On the other hand, as shown in the experimental results of FIG. 7, when the cleaning device 14 is used, the axial lengths are 12.6 mm, 21 mm, and 29.4 mm even when the cumulative number of printed sheets reaches 300,000. Regardless of which patch toner image is formed, the blackened area ratio hardly increases and is lower than 0.6% (level indicated by a dotted line indicated by reference numeral 74) which is a level affecting the quality. As described above, the cleaning performance of the second cleaning unit 14B is made to contact the cleaning brush 141 of the first cleaning unit 14A as in the cleaning device 14, so that the cleaning performance is remarkably improved compared to the case where the recovery roller 144 is not contacted. Can be improved.

[5] Modifications Although the present invention has been described based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and the following modifications can be implemented. .
(1) In the present embodiment, as shown in FIG. 4, in the cleaning device 14, the collection roller 143 of the first cleaning unit 14 </ b> A disposed in contact with the cleaning brush 141 of the first cleaning unit 14 </ b> A, The arrangement order of the collection roller 144 of the second cleaning unit 14B in the rotation direction of the cleaning brush 141 is the order of the collection rollers 143 and 144, but the arrangement order is reversed (the order of the collection rollers 144 and 143). Alternatively, the collection roller 144 of the second cleaning unit 14B may be disposed upstream of the collection roller 143 of the first cleaning unit 14A in the rotation direction.

  For example, as shown in FIG. 8, the cleaning brush 142 of the second cleaning unit 14B is located upstream of the cleaning brush 141 of the first cleaning unit 14A in the rotational direction of the secondary transfer belt 13 (the B direction in the figure). The recovery roller 144 of the second cleaning unit 14B may be disposed in contact with the upstream side in the rotational direction of the cleaning brush 141 relative to the recovery roller 143 of the first cleaning unit 14A.

  Also in this case, when the residual toner on the image carrying surface of the secondary transfer belt 13 is transferred to a region facing the cleaning brush 141 of the first cleaning unit 14A, it is generated by receiving positive charge injection. The weakly charged toner is changed to negatively charged toner by injecting negative charge in a region facing the recovery roller 144 of the second cleaning unit 14B, and then facing the cleaning brush 141 on the downstream side thereof. Can be recovered by electrostatic adsorption to the recovery roller 143 of the first cleaning unit 14 </ b> A having the positive polarity disposed in contact therewith.

  (2) In this embodiment, the cleaning brush is used as a cleaning member that electrostatically attracts residual toner on the image carrying surface of the secondary transfer belt 13, but the shape of the cleaning member is not limited to the brush. The shape may also be For example, the peripheral surface may be a roller or belt in the form of a sponge or foam made of an electrically conductive and elastic resin.

(3) In the present embodiment, the recovery rollers 143 and 144 of the first and second cleaning units 14A and 14B are metal rollers, but the recovery roller is configured with a conductive resin instead of metal. Also good. Further, the recovery member of each cleaning unit is not limited to a roller shape, and may be, for example, a belt shape.
(4) The configuration of the cleaning device according to the present embodiment shown in FIG. 4 is such that residual toner on the image bearing surface of an image bearing member (for example, an intermediate transfer belt or a photosensitive drum) other than the secondary transfer belt. It can also be used for cleaning. For example, the configuration of the cleaning device 12 may be the same as the configuration of the cleaning device 14.

(5) In the present embodiment, the bias voltage is applied to the cleaning brush and the collection roller in each cleaning unit from separate high-voltage power sources. A bias voltage may be applied to the collection roller.
(6) In the present embodiment, the cleaning brush 141 indicates the rotation direction of the cleaning brush 141 of the first cleaning unit 14A, the recovery roller 143 of the first cleaning unit 14A, and the recovery roller 144 of the second cleaning unit 14B. In the areas where the recovery rollers 143 and 144 are opposed to and contacted with each other, the rotation direction of the cleaning brush 141 is the opposite direction (counter direction), but it may be the same direction. Alternatively, the direction may be the same only in a region where the recovery roller 144 is opposed to and contacted.

  (7) In this embodiment, the push amount from the collection roller 143 to the cleaning brush 141 (hereinafter referred to as “first push amount”) is 1.4 mm, and the push amount from the collection roller 144 to the cleaning brush 141 ( Hereinafter, “the second push amount” is set to 1.6 mm, and the second push amount is set to be larger than the first push amount. However, the push amount is limited to that of the present embodiment. It is good also as making the pushing amount of both into the same.

  As in this embodiment, when the second pushing amount is increased, the contact area between the cleaning brush 141 and the collection roller 144 is increased compared to the case where both contact areas are the same, and the amount of current flowing between both is increased. Since the charge injection amount for the weakly charged toner generated by receiving the positive charge injection from the collection roller 143 can be increased, and the weakly charged toner is more reliably charged to the negative polarity, The negatively charged toner can be recovered via the negative recovery roller 143.

As a result, the amount of weakly charged toner that is re-transferred to the image carrying surface can be reduced, and the image carrying surface and the recording sheet caused by re-transfer of the weakly charged toner onto the image carrying surface can be further reduced. Can be reduced.
FIG. 9 shows the relationship between the potential difference between the cleaning brush 141 and the recovery roller 144 and the amount of current flowing between the two when the second push amount is the same as the first push amount and when the second push amount is larger than the first push amount. It is a graph which shows.

  The graph shown in the figure was created by an experiment using the cleaning device 14 having the configuration shown in FIG. Also, graphs were prepared for each of the cases where the second push-in amount was 1.4 mm and 2 mm (reference numeral 91 is a graph when the second push-in amount is 2 mm, and reference numeral 92 is the second push-in. A graph in the case where the amount is 1.4 mm is shown, and the vertical axis of the graph shows the current amount and the horizontal axis shows the potential difference). About the other pushing amount, it was set as the pushing amount same as an Example. As shown in the figure, when the second pushing amount is larger (2 mm), the average current value is about 1.8 times higher than the smaller one (1.4 mm).

FIG. 10 shows the relationship between the cumulative number of printed sheets and the blackened area ratio when the second push-in amount is 1.4 mm and the same printing process as in the embodiment is performed using the cleaning device 14 having the configuration shown in FIG. It is a graph which shows.
Also, FIG. 11 shows the cumulative number of printed sheets and the blackened area ratio when the second push-in amount is 2.0 mm and the same printing process as in the embodiment is performed using the cleaning device 14 having the configuration shown in FIG. It is a graph which shows the relationship. In both figures, the bias voltage applied to the cleaning brush 141 of the first cleaning unit 14A is + 200V, the bias voltage applied to the cleaning brush 142 of the second cleaning unit 14B is -100V, and the first cleaning unit 14A. The bias voltage applied to the recovery roller 143 is +700 V, the bias voltage applied to the recovery roller 144 of the second cleaning unit 14B is −300 V, and the other experimental conditions are the same as in the example.

A two-dot chain line denoted by reference numeral 101 in FIG. 10 is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a patch toner image having an axial length of 21 mm is formed. The one-dot chain line shown is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a patch toner image having an axial length of 29.4 mm is formed.
Similarly, a two-dot chain line denoted by reference numeral 111 in FIG. 11 is a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a patch toner image having an axial length of 21 mm is formed. An alternate long and short dash line indicates a graph showing the relationship between the cumulative number of printed sheets and the blackened area ratio when a patch toner image having an axial length of 29.4 mm is formed.

  Comparing the two figures, in any case, even when the cumulative number of printed sheets reaches 300,000, the black area ratio is 0.6% (reference numeral 103 in FIG. 10, reference numeral 103 in FIG. 11). The level indicated by the dotted line 113 is below. On the other hand, when the 21 mm patch toner image is formed or when the 29.4 mm patch toner image is formed, the smaller second push amount (1.4 mm) is larger (1.4 mm). The value of the blackened area ratio tends to be larger than that of 2 mm), and the larger the second pushing amount (2 mm) indicates that the contamination is reduced.

  The present invention relates to an image forming apparatus provided with a cleaning device, and in particular, can be used as a technique for removing residual toner remaining on a rotating image carrier.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 4 Paper supply part 5 Fixing device 10 Exposure part 11 Intermediate transfer belts 12 and 14 Cleaning device 13 Secondary transfer belts 15 and 23 Driving rollers 16 to 21 Support roller 22 Secondary transfer roller 24 Secondary transfer position 25, 26 Opposite roller 31Y Photoconductor 32Y Developer 33Y Charger 34Y Cleaner 35Y Primary transfer roller 41 Paper feed cassette 42 Feeding roller 43 Transport path 44 Timing roller 45 Secondary transfer rollers 141, 142 Cleaning brushes 143, 144 Recovery roller 145, 146 Scraper 147 Conveying screw 151-154 High voltage power supply

Claims (8)

An image forming apparatus that removes residual toner remaining on an image bearing surface of a rotating image bearing member and forms a toner image on the image bearing surface after removal by an electrostatic transfer method,
A first rotating body that is applied with a predetermined voltage, contacts the image carrying surface while rotating, and electrostatically adsorbs and removes residual toner on the image carrying surface; and has the same polarity as the voltage A cleaning unit including a second rotating body that is applied with a voltage whose absolute value is greater than the voltage, contacts the first rotating body while rotating, and further electrostatically adsorbs the toner adsorbed on the first rotating body. 2 sets,
The polarity of the voltage applied to the first and second rotating bodies is different between the two sets of cleaning units, and one set of the first rotating bodies is in contact with the other set of the second rotating bodies. The arrangement of each rotating body is set to rotate ,
The one set of first rotating bodies is in contact with the image carrying surface of the image carrying body on the upstream side in the rotation direction of the image carrying body than the other set of first rotating bodies,
An image forming apparatus , wherein a polarity of a voltage applied to the first and second rotating bodies of the one set is different from a charging polarity of toner of a toner image . An image forming apparatus that removes residual toner remaining on an image bearing surface of a rotating image bearing member and forms a toner image on the image bearing surface after removal by an electrostatic transfer method,
A first rotating body that is applied with a predetermined voltage, contacts the image carrying surface while rotating, and electrostatically adsorbs and removes residual toner on the image carrying surface; and has the same polarity as the voltage A cleaning unit including a second rotating body that is applied with a voltage whose absolute value is greater than the voltage, contacts the first rotating body while rotating, and further electrostatically adsorbs the toner adsorbed on the first rotating body. 2 sets,
The polarity of the voltage applied to the first and second rotating bodies is different between the two sets of cleaning units, and one set of the first rotating bodies is in contact with the other set of the second rotating bodies. The arrangement of each rotating body is set to rotate,
The one set of first rotating bodies is in contact with the image carrying surface of the image carrying body on the downstream side in the rotation direction of the image carrying body than the other set of first rotating bodies,
An image forming apparatus , wherein a polarity of a voltage applied to the first and second rotating bodies of the one set is different from a charging polarity of toner of a toner image . When a position where the one set of first rotating bodies is in contact with the image bearing surface is defined as a starting point,
The distance along the rotation direction of the one set of first rotating bodies from the starting point to the position where the one set of first rotating bodies and the one set of second rotating bodies are in contact with each other Is shorter than the distance along the rotation direction from the starting point to the position where the first rotating body of the one set and the second rotating body of the other set are in contact with each other. The image forming apparatus according to claim 1. An image forming apparatus that removes residual toner remaining on an image bearing surface of a rotating image bearing member and forms a toner image on the image bearing surface after removal by an electrostatic transfer method,
A first rotating body that is applied with a predetermined voltage, contacts the image carrying surface while rotating, and electrostatically adsorbs and removes residual toner on the image carrying surface; and has the same polarity as the voltage A cleaning unit including a second rotating body that is applied with a voltage whose absolute value is greater than the voltage, contacts the first rotating body while rotating, and further electrostatically adsorbs the toner adsorbed on the first rotating body. 2 sets,
The polarity of the voltage applied to the first and second rotating bodies is different between the two sets of cleaning units, and one set of the first rotating bodies is in contact with the other set of the second rotating bodies. The arrangement of each rotating body is set to rotate,
The absolute value of the potential difference between the first rotating body of the one set and the second rotating body of the one set is the second value of the first rotating body of the one set and the second value of the other set. images forming device you wherein a smaller absolute value of the potential difference between the rotating member. An image forming apparatus that removes residual toner remaining on an image bearing surface of a rotating image bearing member and forms a toner image on the image bearing surface after removal by an electrostatic transfer method,
A first rotating body that is applied with a predetermined voltage, contacts the image carrying surface while rotating, and electrostatically adsorbs and removes residual toner on the image carrying surface; and has the same polarity as the voltage A cleaning unit including a second rotating body that is applied with a voltage whose absolute value is greater than the voltage, contacts the first rotating body while rotating, and further electrostatically adsorbs the toner adsorbed on the first rotating body. 2 sets,
The polarity of the voltage applied to the first and second rotating bodies is different between the two sets of cleaning units, and one set of the first rotating bodies is in contact with the other set of the second rotating bodies. The arrangement of each rotating body is set to rotate,
The contact area of the portion where the first rotating body of the one set and the second rotating body of the other set are in contact is the first rotating body of the one set and the first rotating body of the one set. images forming device you being greater than the contact area of the portion 2 of the rotary body is in contact. The rotation direction of the first rotating body of the one set is configured to be opposite to the rotating direction of the second rotating body at a portion in contact with the second rotating body of both sets. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The image forming apparatus according to claim 1, wherein voltages applied to the four rotating bodies of the two sets of cleaning units are respectively supplied from separate power sources. The image forming apparatus according to claim 1, wherein each first rotating body of the two sets of cleaning units is a conductive brush.

Images