JP2011164309A - Cleaning device, belt device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning device configured to clean up a belt member more satisfactorily than in a conventional manner, suppress damages of the belt member and the cleaning rotating body due to discharge, and also, maintain good cleaning performance, irrespective of a lapse of time, and to provide a belt device and an image forming apparatus. <P>SOLUTION: The center (center line L1) of a cleaning nip (point F to point C) in a belt moving direction is positioned upstream of the center (center line L2) of a belt winding area (point B to point G) in the belt moving direction, and a cleaning brush 102 is brought into contact with a intermediate transfer belt 8 to form the cleaning nip so that the center of the cleaning nip in the belt moving direction may be positioned upstream of the center of the belt winding area in the belt moving direction, and also the winding area may be located within the range of the cleaning nip. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a cleaning device that cleans deposits adhering to the front surface of an endless belt member with a cleaning rotator, a belt device including the same, and an image forming apparatus.

  Toners used for image formation have become mainstream due to the polymerization method rather than the pulverization method with the recent increase in image quality. The toner particles obtained by the polymerization method have a spherical shape and a small diameter as compared with the toner particles obtained by the pulverization method, so that even a small dot corresponding to a high resolution can exhibit excellent reproducibility. On the other hand, the blade cleaning method by scraping with a cleaning blade has a problem that it tends to cause a cleaning failure. This is because, since it is close to a sphere and has a small diameter, it passes through a slight gap formed between the cleaning blade and the object to be cleaned.

  If the electrostatic cleaning method is employed as in the cleaning device described in Patent Document 1, it is possible to satisfactorily clean even the toner produced by the polymerization method. Specifically, the cleaning device described in Patent Document 1 includes a cleaning brush roller that rotates while contacting a drum-shaped photoconductor as a member to be cleaned, a recovery roller that rotates while contacting this, and a recovery roller. And a scraping blade that abuts. The cleaning brush roller includes a rotating shaft member that is rotatably supported, and a brush roller portion that includes a plurality of raised brushes that are erected on the peripheral surface thereof. A cleaning voltage having a polarity opposite to the normal charging polarity of the toner is applied to the cleaning brush roller. A recovery voltage having the same polarity as the cleaning voltage and a value larger than the cleaning voltage is applied to the recovery roller. The untransferred toner remaining on the surface of the photoconductor after the transfer process is brushed by the electric field between the photoconductor and the brush roller unit while being scratched by the brush roller unit of the rotating cleaning brush roller. Electrostatic transfer occurs in the roller section. Then, after further electrostatic transfer from the inside of the brush roller portion to the collecting roller, it is scraped off from the surface of the collecting roller by a scraping blade. In such an electrostatic cleaning method, it is possible to clean the toner by the polymerization method better than in the blade cleaning method.

  In the electrostatic cleaning system, when a belt member such as an intermediate transfer belt is to be cleaned, a cleaning counter roller is generally provided at a position facing the cleaning brush roller as a cleaning rotating body via the belt member. (For example, Patent Documents 2 and 3). The cleaning counter roller is grounded, an electric field is formed between the cleaning counter roller and the cleaning brush roller, and the toner on the belt member is electrostatically transferred to the cleaning brush roller.

  When a toner pattern is formed on the belt member by control for adjusting image density and correcting color misregistration, the density is read by a photo sensor, and the image forming conditions are controlled by the detection result, the toner after reading The pattern is not transferred onto the transfer paper but is removed by the cleaning device. In addition, the toner image is not transferred to the transfer paper but removed by the cleaning device even if the toner is consumed to refresh the toner in the developing unit or if a jam occurs due to poor paper conveyance. become. As described above, the cleaning device may remove not only the transfer residual toner but also an untransferred toner image in which a large amount of toner adheres to the belt member, such as a toner pattern, from the belt member.

  In order to electrostatically attach a large amount of toner such as an untransferred toner image from the belt member to the cleaning brush roller, it is necessary to form a strong electric field between the cleaning brush roller and the cleaning counter roller. However, when the electric field is increased, an electric current (hereinafter referred to as a cleaning current) flowing in a path from the cleaning brush roller to the cleaning counter roller via the belt member becomes excessive. As a result, charge injection having a polarity opposite to the normal polarity occurs with respect to the toner, and the toner may be reversely charged. Such reverse charging of the toner causes the cleaning property to deteriorate.

The reverse charging of the toner will be described in more detail. FIG. 8 is an enlarged configuration diagram illustrating an example of a configuration around a cleaning nip in a conventional cleaning device. In the drawing, an intermediate transfer belt 901 as a belt member is moved endlessly while being stretched between a cleaning facing roller 902 shown in the figure and a plurality of rollers (not shown). The inside of the loop of the intermediate transfer belt 901, a cleaning opposed roller 902, among the entire area of its peripheral surface, is wound around the intermediate transfer belt 901 in the range of over-turning the width W ₁ shown. On the other hand, on the outer side of the loop of the intermediate transfer belt 901, the cleaning brush roller 903 abuts against the belt front surface to form a cleaning nip. The cleaning brush roller 903 is driven by a driving means (not shown) while rotating its surface in a counter direction that moves the surface of the cleaning nip in a direction opposite to the belt, and the brush of the brushes of the intermediate transfer belt 901 is driven. The surface is rubbed. Transfer residual toner adhering to the front surface of the intermediate transfer belt 901 is scraped off by a cleaning brush roller to which a cleaning bias having a polarity opposite to that of the toner is applied. Nip width W ₂ this scraping is the length of the belt moving direction of the cleaning nip to be performed is larger than the over-turning the width W ₁ of the above. The cleaning brush roller 903 is in contact with the belt extension region that is not wrapped around the roller at the upstream end and the downstream end of the cleaning nip in the belt moving direction. Hereinafter, a region of the cleaning nip where the cleaning brush roller 903 is in contact with the belt extension region on the upstream side in the belt moving direction is referred to as an “upstream belt extension nip region”. In the upstream belt extension nip region, although the cleaning brush roller 903 is in contact with the belt front surface, the cleaning counter roller 902 is not in contact with the back surface of the belt, so that the cleaning current does not flow so much. In contrast, in the belt receiving turning area cleaning facing roller 902 is in contact with the intermediate transfer belt 901 (region indicated by over-turning width W _1), the cleaning current flows to many. In particular, in the vicinity of the center of the belt running area where the nip pressure is strongest, a larger amount of cleaning current flows than at both ends of the belt running area. For this reason, when the toner enters the vicinity of the center of the belt wrapping region, the toner is easily reversely charged.

Therefore, in order to obtain a good cleaning property, it is necessary to transfer most of the untransferred toner to the cleaning brush roller in the following areas among all the areas in the belt moving direction in the cleaning nip. That is, the amount of cleaning current hardly becomes excessive, (area indicated by a width W ₃₎ upstream belt stretched nip region and a vicinity of the inlet of the belt Kakemawa Shi region (region indicated by over-turning width W _1). However, the upstream belt stretched nip area around the entrance as indicated by the width W _3, in a state where the hair raising constituting the brush as shown is brought into contact with the tip only belt. It is difficult for the transfer residual toner to transfer to the raised hair in such a state. Good transfer of the transfer residual toner occurs when the side surface of the brush is in contact with the belt while the brushed portion is greatly bent. Of upstream belt stretched nip area indicated by a width W _3, the raising is such a condition is limited to very small area relatively distant from the vicinity of the inlet. Also, of the width W belt receiving turning area indicated by ₁ Shi Kakemawa, regions oppositely charged toner by the cleaning current is not significantly occur is limited to very small area near the inlet. As a result, it has been found that in the conventional cleaning device, the transfer residual toner that enters the central portion of the belt wrapping region without being transferred to the cleaning brush roller is inevitably generated, resulting in cleaning failure.

In view of this, the applicants proposed in Japanese Patent Application No. 2009-248415 a cleaning device in which the center of the cleaning nip is positioned upstream of the center of the belt wrapping region with respect to the cleaning counter roller in the belt moving direction. In the belt movement direction, the center of the cleaning nip is positioned on the upstream side of the center of the belt wrapping area with respect to the cleaning counter roller. The nip area can be increased. For example, as shown in FIG. 9, the nip center line L ₁ , which is the center line of the cleaning nip in the belt moving direction, is upstream of the wrap center line L _2, which is the center line of the belt wrap region with respect to the cleaning roller 902. It is located on the side. In this way, as is apparent from a comparison between FIG. 8 showing a conventional example, it is the increase than before the upstream belt stretched nip area indicated by a width W _3. Then, the area where the toner on the belt can be favorably transferred to the cleaning brush roller on the upstream side of the central portion of the belt running area with respect to the cleaning counter roller, which easily causes reverse charging of the toner, is increased as compared with the conventional case. The belt member can be cleaned better than before.

  However, it has been found that the cleaning apparatus described in Japanese Patent Application No. 2009-248415 has the following problems. That is, as shown in FIG. 9, the exit point C in the belt-wrapping region of the cleaning counter roller 902 is located downstream of the cleaning nip exit point G in the belt member moving direction. In other words, a part of the wrapping region in the belt member 901 protrudes downstream of the cleaning nip range in the belt moving direction. In such a configuration, the electric field in the region between the exit point G and the exit point C becomes strong, and peeling discharge occurs in the region between the exit point G and the exit point C. Due to such discharge, there is a problem in that the belt member 901 and the cleaning brush roller 903 are damaged, and the cleaning brush roller 903 and the belt member 901 are shortened in life early.

  In addition, when a large amount of toner is removed from the belt member 901 by the cleaning brush roller 903, the toner attached to the cleaning brush roller 903 may not be collected by a collection roller (not shown) serving as a collection unit. In this case, the brush with the uncollected toner that has not been collected on the collection roller enters the region between the exit point G and the exit point C. The cleaning brush roller 903 is applied with a polarity opposite to the normal charging polarity of the toner, for example, a positive voltage, and the cleaning counter roller 902 is grounded, so that the region between the exit point G and the exit point C is When electric discharge occurs, negative charge (electrons) moves from the cleaning facing roller 902 toward the cleaning brush roller 903. For this reason, negative charge is injected into the uncollected toner adhering to the brush. Therefore, the uncollected toner adhering to the brush due to the discharge is charged up to negative polarity, and the electrostatic adhesion force with the brush is increased. As the electrostatic adhesion force between the unrecovered toner and the brush increases in this way, when the brush to which the unrecovered toner adheres again enters the contact area with the recovery roller, the unrecovered toner is It remains without moving electrostatically to the surface of the collecting roller. This is because when the uncollected toner is charged up, the force to move the toner to the surface of the collection roller due to the collection electric field between the collection roller and the cleaning brush roller 903 increases, but the electrostatic force between the toner and the brush exceeds the increased amount. The amount of increase in attractive adsorption power is larger. For this reason, the relationship between the force that moves the toner to the surface of the collecting roller before charge-up is greater than the electrostatic force that attracts the brush. Changes to a relationship larger than the force that moves the toner to the surface of the collecting roller. As a result, unrecovered toner remains on the brush without electrostatically moving to the surface of the recovery roller. As described above, the uncollected toner is not collected by the collecting roller and remains on the cleaning brush roller 903. Therefore, the uncollected toner accumulates over time, and good cleaning properties are obtained over time. The problem is that it cannot be obtained.

  In the above description, the case where the positive polarity voltage is applied to the cleaning brush roller 903 and the negative polarity toner is electrostatically adsorbed is described as an example. However, the negative polarity voltage is applied to the cleaning brush roller 903. The same problem occurs when the toner is electrostatically adsorbed by applying the positive polarity toner. In this case, when a discharge occurs at the exit of the cleaning nip, negative charges (electrons) move from the cleaning brush roller side to the cleaning counter roller side. At this time, negative charge is also discharged from the uncollected toner adhering to the brush toward the cleaning facing roller, and the uncollected toner is charged up to the positive polarity. As a result, the electrostatic attraction force of the unrecovered toner with the cleaning brush roller increases, and the electrostatic recovery force does not move to the recovery roller as the recovery means, and the unrecovered toner accumulates on the cleaning brush roller 903. It becomes impossible to maintain a good cleaning property.

  Further, the case where a cleaning brush roller is used as the cleaning rotating member has been described as an example. However, even when a cleaning roller such as a cleaning roller that does not have a brush is used, discharge occurs near the cleaning nip outlet and adheres to the cleaning roller. Uncollected toner is charged up. As a result, the electrostatic attraction force with the cleaning roller increases, and the electrostatic transfer to the recovery roller as the recovery means stops, and unrecovered toner accumulates, making it impossible to maintain good cleaning properties over time.

  The present invention has been made in view of the above problems, and the object of the present invention is to be able to clean the belt member better than before and to suppress damage due to discharge of the belt member and the cleaning rotator. And providing a cleaning device, a belt device, and an image forming apparatus capable of maintaining good cleaning properties over time.

In order to achieve the above object, the invention according to claim 1 is directed to a region where the belt member is wound around the cleaning counter roller which is one of a plurality of stretching rollers disposed inside the loop of the endless belt member. In the state where a cleaning nip is formed in contact with the belt front surface to contact the belt front surface, the surface of the belt moves in the cleaning nip in the direction opposite to the belt moving direction. A cleaning rotator for cleaning by electrostatically transferring an adherent having a polarity opposite to the polarity of the voltage applied to the belt front surface while rotating to cause the belt to rotate. In a cleaning apparatus comprising: a collection unit that electrostatically transfers the deposits attached to the cleaning rotator to collect the deposits from the cleaning rotator; The center of the cleaning nip in the belt movement direction is located upstream of the center of the wrapping area in the belt movement direction in the belt movement direction, and the wrapping area is within the cleaning nip range. The cleaning rotator is brought into contact with the belt member to form the cleaning nip.
According to a second aspect of the present invention, there is provided an endless belt member that is endlessly moved in a state of being stretched by a plurality of stretching rollers disposed inside its own loop, and attached to the surface of the belt member. A belt device provided with a cleaning means for cleaning adhering deposits, wherein the cleaning device according to claim 1 is used as the cleaning means.
According to a third aspect of the present invention, in the belt device of the second aspect, a conductive wire is used as the cleaning counter roller.
According to a fourth aspect of the present invention, there is provided a toner image carried on the front surface of an endless belt member or a toner image carried on a recording member held on the front surface of the belt member. An image forming apparatus comprising: a belt device that conveys the belt member as the belt member moves endlessly; and a toner image forming unit that forms a toner image on a front surface of the belt member or a recording member. The belt device according to claim 2 or 3 is used.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the belt member includes an elastic layer having a thickness of 0.07 [mm] or more and 0.5 [mm] or less. Is.

According to the present invention, in the belt moving direction, the center of the cleaning nip is positioned upstream of the center of the belt wrapping region with respect to the cleaning counter roller, so that the center is located at the same position as compared to the conventional case. Thus, the upstream belt extension nip region can be increased. As a result, the area where the deposit on the belt can be transferred to the cleaning rotating body can be increased on the upstream side of the central portion of the belt running area with respect to the cleaning counter roller, which is better than before. In addition, the belt member can be cleaned.
In addition, since the hanging region of the belt member is within the cleaning nip range, the portion of the hanging region of the belt member protrudes downstream of the cleaning nip range in the belt moving direction, compared with the case where the cleaning nip is not. The electric field near the exit can be weakened. As a result, the discharge near the cleaning nip exit can be suppressed, and damage due to the discharge of the cleaning rotator and the belt member can be suppressed. Therefore, the lifetime of the belt member and the cleaning rotator can be extended. In addition, it is possible to suppress unrecovered deposits adhering to the cleaning rotator from being charged up to a polarity opposite to the charging polarity of the cleaning rotator due to discharge. Therefore, it is possible to suppress the electrostatic attracting force of the uncollected deposits on the cleaning rotator from becoming larger than the force of electrostatically moving to the collecting means. As a result, when the unrecovered deposit again enters the region where the deposit is electrostatically moved to the recovery means, the unrecovered deposit moves electrostatically to the recovery means, It can be recovered. Thereby, accumulation of unrecovered deposits on the cleaning rotator over time can be suppressed, and good cleaning properties can be maintained over time.

1 is a schematic configuration diagram illustrating a main part of a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating a belt cleaning device of the printer and its surroundings in an enlarged manner. FIG. 3 is an enlarged configuration diagram illustrating a cleaning counter roller and an intermediate transfer belt in the printer. FIG. 3 is an enlarged configuration diagram illustrating a cleaning counter roller, an intermediate transfer belt, and a cleaning brush roller in the printer. FIG. 6 is an enlarged configuration diagram showing a belt cleaning device and its surroundings in a first modification of the printer according to the embodiment. The graph which shows the result of a verification experiment. FIG. 2 is a schematic configuration diagram illustrating a main part of a tandem direct transfer type printer. FIG. 9 is an enlarged configuration diagram illustrating an example of a peripheral configuration of a cleaning nip in a conventional cleaning device. The expanded block diagram which shows an example of the surrounding structure of the cleaning nip in the cleaning apparatus of a prior application.

  Hereinafter, as an embodiment of an image forming apparatus to which the present invention is applied, a so-called tandem type intermediate transfer type printer (hereinafter simply referred to as a printer) will be described. First, the basic configuration of the printer will be described. FIG. 1 is a schematic configuration diagram showing a main part of the printer. The printer includes four process units 6Y, 6M, 6C, and 6K for generating toner images of yellow, magenta, cyan, and black (hereinafter referred to as Y, M, C, and K). The four process units 6Y, 6M, 6C, and 6K have drum-shaped photoreceptors 1Y, 1M, 1C, and 1K, respectively. Around the photoreceptors 1Y, 1M, 1C, 1K, charging devices 2Y, 2M, 2C, 3K, developing devices 5Y, 2M, 3C, 3K, drum cleaning devices 4Y, 4M, 4C, 4K, a neutralization device (not shown) ) Etc. The process units 6Y, 6M, 6C, and 6K use Y, M, C, and K toners of different colors, but have the same configuration. Above the process units 6Y, 6M, 6C, and 6K, there is an optical writing unit (not shown) for irradiating the surface of the photoreceptors 1Y, 1M, 1C, and 1K with laser light L to write an electrostatic latent image. It is arranged.

  Below the process units 6Y, 6M, 6C, and 6K, a transfer unit 7 is disposed as a belt device including an endless intermediate transfer belt 8 that is a belt member. In addition to the intermediate transfer belt 8, a plurality of stretching rollers disposed inside the loop, a secondary transfer roller 15, a pressing roller 16, and a belt cleaning device 100 disposed outside the loop are included.

  Inside the loop of the intermediate transfer belt 8 are four primary transfer rollers 9Y, 9M, 9C, 9K, a tension roller 10, a post-primary transfer roller 11, a secondary transfer counter roller 12, and two cleanings. Opposing rollers 13 and 14 are disposed. Each of these rollers functions as a stretching roller that stretches the intermediate transfer belt 8 around a part of its peripheral surface to stretch the belt. The intermediate transfer belt 8 is moved endlessly in the clockwise direction in the drawing by the rotation of the driving roller 12 that is driven to rotate clockwise in the drawing by a driving means (not shown).

  The four primary transfer rollers 9Y, 9M, 9C, and 9K disposed inside the belt loop sandwich the intermediate transfer belt 8 between the photoreceptors 1Y, 1M, 1C, and 1K. As a result, primary transfer nips for Y, M, C, and K where the front surface of the intermediate transfer belt 8 and the photoreceptors 1Y, 1M, 1C, and 1K come into contact are formed. A primary transfer bias having a polarity opposite to that of the toner is applied to the primary transfer rollers 9Y, 9M, 9C, and 9K by a power source (not shown).

  Further, the intermediate transfer belt 8 is sandwiched between the secondary transfer counter roller 12 disposed inside the belt loop and the secondary transfer roller 12 disposed outside the belt loop. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 8 and the secondary transfer roller 12 abut is formed. Note that a secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 12 by a power source (not shown).

  Further, the intermediate transfer belt 8 is sandwiched between the cleaning counter rollers 13 and 14 disposed inside the belt loop and the cleaning brush rollers 102 and 106 of the belt cleaning device 100 disposed outside the belt loop. Accordingly, a cleaning nip is formed in which the front surface of the intermediate transfer belt 8 and the cleaning brush rollers 102 and 106 come into contact with each other. The belt cleaning device 100 can be integrally replaced with the intermediate transfer belt 8. However, when the belt cleaning device 100 and the intermediate transfer belt 8 have different life settings, the belt cleaning device 100 is referred to as an intermediate transfer belt. The printer main body may be independently detachable.

  The printer includes a paper feed unit (not shown) having a paper feed cassette for storing the recording paper P and a paper feed roller for feeding the recording paper P from the paper feed cassette to the paper feed path. In addition, a registration roller pair (not shown) that receives the recording paper sent from the paper feeding unit and feeds it at a predetermined timing toward the secondary transfer nip is provided on the right side of the secondary transfer nip in the drawing. In addition, a fixing device (not shown) that receives the recording paper P sent out from the secondary transfer nip and fixes the toner image to the recording paper P is provided on the left side of the secondary transfer nip in the drawing. . Further, Y, M, C, and K toner supply devices (not shown) for supplying Y, M, C, and K toners to the developing devices 5Y, M, C, and K are provided as necessary.

  In recent years, in addition to plain paper that has been widely used as recording paper, special recording paper that is used for thermal transfer such as special paper having an uneven surface or iron print as a design has been increasingly used. When such special paper is used, transfer defects are more likely to occur when the toner image on the intermediate transfer belt 8 on which the color toners are superimposed is secondarily transferred onto the paper, as compared with conventional plain paper. Therefore, in this printer, the contact property with the recording paper is improved by giving the intermediate transfer belt 8 elasticity.

As the intermediate transfer belt 8, a multilayer structure is used. As the base layer, an appropriate amount of a conductive agent such as carbon black is contained in a synthetic resin such as polyimide, polyimide amide, polycarbonate, polyester, or polypropylene, or various rubbers, and the volume resistivity is 10 ⁶ to 10 ¹⁴ Ω · What becomes cm is used. Further, in the case of using a belt having elasticity, a conductive elastic layer of 0.07 mm or more and 0.5 mm or less is provided. Silicone rubber, NBR, H-NBR, CR, EPDM, urethane rubber or the like is used as the main base material of the conductive elastic layer. The material of the conductive protective layer is not particularly limited as long as it can achieve the objectives of reducing the frictional resistance, stability of the electrical characteristics to the environment, and improving the residual toner cleaning performance by reducing the surface roughness. Fluororesin polymers such as tetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA), PVDF, alcohol soluble nylon, silicone resin, silane coupler, urethane resin emulsions and A paint dissolved and dispersed in an organic solvent can be used. These protective layers can be provided by dip coating, spray coating, electrostatic coating, roll coating, or the like. Furthermore, by subjecting the protective layer to surface treatment or polishing, it is possible to improve mold release properties, conductivity, wear resistance, surface cleaning properties, and the like. The elastic intermediate transfer belt 8 and the drum-shaped photoconductor 1 are arranged in contact with each other in a relatively wide contact area, and are elastically pressed by the intermediate transfer belt 8. The tack pressure between the intermediate transfer belt 8 and the intermediate transfer belt 8 is not so high, and the toner image is wrapped by the intermediate transfer belt 8 so that the toner images on the photoreceptors 1Y, 1M, 1C, and 1K are transferred to the intermediate transfer belt 8. Primary transfer to the side. At this time, the transfer image onto the intermediate transfer belt 8 has no image defect such as a holo character due to a large tack surface pressure, and is transferred with high transfer efficiency, so that it is on a recording material (particularly, special paper having irregularities). Color image quality is kept very good.

  When image information is sent from a personal computer or the like, the printer rotates the drive roller 12 to move the intermediate transfer belt 8 endlessly. The stretching rollers other than the driving roller 12 are driven to rotate by the belt. At the same time, the photosensitive members 1Y, 1M, 1C, and 1K of the process units 6Y, 6M, 6C, and 6K are rotationally driven. Further, an electrostatic latent image is formed by irradiating the charged surface with laser light L while uniformly charging the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K with the charging devices 2Y, 2M, 2C, and 2K. To do. The electrostatic latent images formed on the surfaces of the photoconductors 1Y, 1M, 1C, and 1K are developed on the photoconductors 1Y, M, C, and K by developing the electrostatic latent images on the photoconductors 1Y, M, C, and K, respectively. , K toner images are obtained. The Y, M, C, and K toner images are primarily transferred while being superimposed on the front surface of the intermediate transfer belt 8 in the above-described primary transfer nips for Y, M, C, and K. As a result, a four-color superimposed toner image is formed on the front surface of the intermediate transfer belt 8.

  On the other hand, in the paper feed unit, the recording paper P is sent out from the paper feed cassette one by one by the paper feed roller 27 and conveyed to the registration roller pair. Then, at a timing that can be synchronized with the four-color superimposed toner image on the intermediate transfer belt 8, the registration roller pair is driven to feed the recording paper P to the secondary transfer nip, and the four-color superimposed toner image on the belt is transferred. Batch transfer onto the recording paper P is performed. Thereby, a full-color image is formed on the surface of the recording paper P. The recording paper P after the formation of the full-color image is conveyed from the secondary transfer nip to a fixing device and subjected to a toner image fixing process.

  For the photoreceptors 1Y, M, C, and K after the Y, M, C, and K toner images are primarily transferred to the intermediate transfer belt 8, the remaining toner is cleaned by the drum cleaning devices 4Y, 4M, 4C, and 4K. Apply. Then, after neutralizing with a neutralizing lamp (not shown), it is uniformly charged with the charging devices 2Y, 2M, 2C, and 3K, and is ready for the next image formation.

  Here, problems of the conventional blade cleaning method will be described. As described above, in recent years, there has been an increasing demand for higher image quality, and the toner tends to have a smaller particle size. In addition, there is a tendency to use a spheroidized toner by a polymerization method or the like instead of a pulverized toner because of a demand for reduction in toner manufacturing cost and improvement in transfer rate. The blade cleaning method, which has been used mainly as a means to remove the toner remaining on the image bearing member with the use of toner having a smaller particle size and spheroidization, is used for the accuracy of adhesion between the blade and the surface of the image bearing member. If it is low, the toner slips through and the cleaning property tends to be lowered. In order to prevent this, if the blade is pressed with a strong contact pressure, the blade is turned over, causing a so-called streak-like or belt-like cleaning failure, and it is difficult to keep stable cleaning performance. In addition, spherical toner can be cleaned by increasing the linear pressure to an extremely high level (specifically, linear pressure of 100 gf / cm or more). However, the life of the toner is extremely shortened due to wear of the cleaning blade or scratches on the belt. The life of the cleaning blade at a normal linear pressure of 20 gf / cm (the life when a cleaning failure occurs due to shaving) is about 120K. When the linear pressure is 100 gf / cm, the life of the cleaning blade is about 20K sheets. Further, it is well known that the blade cleaning property is inferior to the cleaning property for the pulverized (atypical) toner with respect to the spherical toner whose transferability is good.

  Therefore, this printer employs a belt cleaning apparatus 100 of an electrostatic cleaning system that can clean the spheroidized toner better than the blade cleaning system.

  FIG. 2 is an enlarged configuration diagram showing the belt cleaning device 100 of the printer and its surroundings in an enlarged manner. The belt cleaning device 100 includes a first cleaning unit 100a for cleaning negative toner having a normal charging polarity among toners on the intermediate transfer belt 8 as a belt member, and normal charging among toners on the intermediate transfer belt 8. And a second cleaning unit 100b for cleaning positive polarity toner having a polarity opposite to that of the polarity.

  The first cleaning unit 100a contacts the first cleaning brush roller 102 as a cleaning rotator, the first recovery roller 103 as a recovery unit that recovers toner attached to the first cleaning brush roller 102, and the first recovery roller 103. And a first toner scraping blade 104 as a toner scraping member for scraping the toner from the surface of the first recovery roller.

  The first cleaning brush roller 102 includes a metal rotating shaft member that is rotatably supported, and a brush roller portion that includes a plurality of raised brushes (conductive fibers) that are erected on the peripheral surface thereof. A positive first cleaning bias having a polarity opposite to the normal charging polarity of the toner is applied by a brush power source (not shown). Further, a first recovery bias having a positive polarity and a value larger than the first cleaning bias is applied to the first recovery roller 103 from a recovery power source (not shown). In addition, the first scraping blade 104 may be conductive, and a bias may be applied to maintain the surface potential of the first recovery roller 103. In addition, when a large amount of toner is collected on the first cleaning brush roller 102, the potential at the brush tip may decrease. For this reason, brush surface charge applying means for applying charge to the surface of the first cleaning brush roller 102 may be provided. The brush surface charge imparting member abuts a contact member such as a metal round bar or a metal plate member on the first cleaning brush roller 102 and applies a positive bias to the contact member, whereby the brush surface Is charged. By applying a charge to the brush surface, the potential can be compensated even if the potential at the tip of the brush decreases.

  The second cleaning unit 100b is disposed downstream of the first cleaning unit 100a in the moving direction of the intermediate transfer belt 8, and, like the first cleaning unit 100a, the cleaning brush roller 106 as a cleaning rotating body and the recovery roller as a recovery unit. 107, a scraping blade 108 is provided.

  The second cleaning brush roller 106 includes a metal rotating shaft member that is rotatably supported, and a brush roller portion that includes a plurality of raised brushes (conductive fibers) that are erected on the peripheral surface thereof. A negative second cleaning bias having the same polarity as the normal charging polarity of the toner is applied by a brush power source (not shown). Further, a second recovery bias having a negative polarity and a value larger than the second cleaning bias is applied to the second recovery roller 107 from a recovery power source (not shown). Further, the second scraping blade 108 may be conductive, and a negative bias may be applied to maintain the surface potential of the second recovery roller 107. Further, in order to suppress a decrease in the potential of the brush tip of the second cleaning brush roller 106, a brush charge applying unit having the same configuration as described above may be provided.

  Further, the belt cleaning apparatus 100 includes a discharge screw 109 that conveys the toner removed by the first and second cleaning units 100a and 100b toward one end of the apparatus casing and discharges the toner out of the belt cleaning apparatus 100 casing. Is provided. The toner discharged from the cleaning device by the discharge screw 109 falls into a waste toner tank (not shown) provided in the printer main body. Further, it may be returned to the developing device instead of the waste tank.

  In order to protect the surface of the intermediate transfer belt 8, a lubricant may be applied to the surface of the intermediate transfer belt 8 with the second cleaning brush roller 106. In this case, the solidified lubricant is brought into contact with the second cleaning brush roller 106 to apply the lubricant. Further, a leveling blade for leveling the lubricant applied to the surface of the intermediate transfer belt may be provided downstream of the second cleaning brush roller 106 in the moving direction of the intermediate transfer belt 8. In addition to the second cleaning brush roller 106, a lubricant application brush may be provided. By providing a brush for applying a lubricant separately from the second cleaning brush roller 106, when the lubricant is applied by the second cleaning brush roller 106, the toner is always collected on the second cleaning brush roller 106. In some cases, the toner and the lubricant are mixed with each other, and the toner once collected at the time of applying the lubricant adheres again to the intermediate transfer belt. On the other hand, by providing a brush for applying a lubricant separately from the second cleaning brush roller 106, it is possible to suppress the collected toner from reattaching to the intermediate transfer belt 8.

An example of specific configuration conditions in the belt cleaning apparatus 100 of the printer is as follows in a normal environment (other than a high temperature and high humidity environment).
<Conditions of the first cleaning brush roller 102>
Brush material: Conductive polyester (contains conductive carbon inside the fiber and the fiber surface is polyester, so-called core-sheath structure)
Brush resistance: 1 × 10 ⁷ Ω (measured in the whole axial direction under a voltage application condition of 1000 V)
Brush shaft applied voltage (cleaning bias): + 2000V
Brush flocking density: 100,000 / inch ² , fiber diameter of about 25 to 35 μm, with bevel treatment at brush tip Brush diameter: 15 mm
The amount of brush biting into the intermediate transfer belt 8: 1 mm
Rotation direction: Counter direction with respect to the belt

<Conditions of Second Cleaning Brush Roller 106>
Brush material: Conductive polyester (contains conductive carbon inside the fiber and the fiber surface is polyester, so-called core-sheath structure)
Brush resistance: 1 × 10 ⁷ Ω (measured in the whole axial direction under a voltage application condition of 1000 V)
Brush shaft applied voltage (cleaning bias): -1600V
Brush flocking density: 100,000 / inch ² , fiber diameter of about 25 to 35 μm, with bevel treatment at the brush tip Brush diameter: 16 mm
The amount of brush biting into the intermediate transfer belt 8: 1 mm
Rotation direction: Counter direction with respect to the belt

  The brush fibers of the first and second cleaning brush rollers 102 and 106 are conductive as a whole, but the fiber surface is covered with an insulating layer. By having an insulating layer on the fiber surface, it becomes difficult for current to flow when the cleaning brush rollers 102 and 106 and the intermediate transfer belt 8 come into contact with each other, and excess current is generated when the brush fiber electrostatically attracts toner from the belt. Becomes difficult to flow. For this reason, the toner of the opposite polarity is not given to the toner, and the possibility that the toner once captured in the brush is reattached to the intermediate transfer belt 8 is reduced. However, even if such a brush is used, if a voltage that breaks the insulation of the fiber surface and flows current is applied to the rotating shaft, the toner is returned to the intermediate transfer belt 8 as a result. Care must be taken when setting the voltage value.

  If each cleaning brush roller 102, 106 is formed in a brush roll shape and then subjected to bevel hair treatment that tilts the hair in one direction, it becomes difficult to bring the conductive agent exposed on the fiber cross section into contact with the intermediate transfer belt 8. Thereby, the charge injection property to the toner is reduced, and the margin of cleaning property is improved. The fiber is generally made of an insulating material such as nylon, polyester, or acrylic, and the same effect can be obtained with any material. Representative fibers of the core-sheath structure are disclosed in JP-A-10-310974, JP-A-10-131035, JP-A-01-292116, JP 07-033637, JP 07-036066, This is disclosed in Japanese Patent Publication No. 03-064604.

<Conditions of the first collection roller 103>
Recovery roller core material: SUS
Recovery roller surface material: Acrylic UV curable resin layer (3-5 μm thickness) on the surface layer of PVDF (100 μm thickness)
Roller diameter: 14mm
The amount of brush fiber biting into the collection roller: 1.5mm
Collecting roller cored bar applied voltage (collecting bias): + 2400V
Rotation direction: counter direction with respect to the first cleaning brush roller 102

<Conditions of second collection roller 107>
Recovery roller core material: SUS
Recovery roller surface material: Acrylic UV curable resin layer (3-5 μm thickness) on the surface layer of PVDF (100 μm thickness)
Roller diameter: 14mm
The amount of brush fiber biting into the collection roller: 1.5mm
Recovery roller mandrel applied voltage (recovery bias): -2000V
Rotation direction: counter direction with respect to the second cleaning brush roller 106

  Each of the collection rollers 103 and 107 is a core metal (made of SUS) having a PVDF thickness of 100 μm and an acrylic UV curable resin layer on the surface (medium resistance roller). The same performance can be obtained not only with the collection rollers 103 and 107 used in the present embodiment, but also with a conductive core metal covered with a high resistance elastic tube of about several μm to 100 μm, or further with an insulating coating. Examples of the material for the surfaces of the collection rollers 103 and 107 include a PVDF tube, a PFA tube, a PI tube, an acrylic coat, a silicone coat (for example, coated with PC (polycarbonate) containing silicone particles), ceramics, and a fluorine coating.

<Conditions of first scraping blade 104>
Material: SUS
Thickness: 100 μm
Blade contact angle: 20 °
Amount of blade biting into the first collection roller 103: 0.6 mm

<Conditions of second scraping blade 108>
Material: SUS
Thickness: 100 μm
Blade contact angle: 20 °
Blade bite amount into the second collection roller 107: 0.6 mm

  A collection bias is applied to the core metal to each of the collection rollers 103 and 107, and when the surface potential is measured, it is almost the same as the collection bias. However, when a large amount of toner is input during the cleaning operation, The surface potential of each of the collecting rollers 103 and 107 decreases as the toner is input. As a result, it becomes impossible to secure a necessary potential difference (collection potential difference) between the collection rollers 103 and 107 and the cleaning brush rollers 102 and 106, and the ability to collect toner from the cleaning brush rollers 102 and 106 is reduced. For this reason, for example, a print potential difference of a required size can be secured if printing is performed for one A4 size sheet, but if the amount of toner input to the brush is large in a continuous printing operation, the collection potential difference cannot be secured. May cause things. Then, there is a problem that toner is accumulated in the cleaning brush rollers 102 and 106 and the toner is discharged from the brush to the belt. For this reason, the scraping blades 104 and 108 may be made conductive, and a scraping voltage may be applied to the scraping blades 104 and 108 to apply charges to the surfaces of the collection rollers 103 and 107. By applying a charge to the surface of the collection roller, the collection potential difference can be increased and the collection performance can be improved.

The conditions of the intermediate transfer belt 8 and the cleaning counter rollers 13 and 14 of the present embodiment are as follows.
<Conditions for intermediate transfer belt>
Material: Elastic belt Layer thickness: 250μm
<Conditions for cleaning counter rollers 13 and 14>
Material: Aluminum Diameter: 14mm

  The untransferred toner that has passed through the secondary transfer nip is transferred to the position of the first cleaning brush roller 102 by the rotation of the intermediate transfer belt 8. A voltage having a polarity (positive polarity) opposite to the normal charging polarity of the toner is applied to the first cleaning brush roller 102, and an electric field formed by a potential difference between the intermediate transfer belt 8 and the surface potential of the first cleaning brush roller 102. Thus, the negatively charged toner on the intermediate transfer belt 8 is electrostatically attracted and moved to the first cleaning brush roller 102. The negative polarity toner that has moved to the first cleaning brush roller 102 is transferred to a contact position with the first recovery roller 103 to which a positive polarity voltage having a value larger than that of the first cleaning brush roller 102 is applied. Then, the toner that has moved onto the first cleaning brush roller 102 is electrostatically adsorbed by the electric field formed by the potential difference between the surface potential of the first cleaning brush roller 102 and the surface potential of the first recovery roller 103, thereby The negative toner moved to the first collection roller 103 and moved to the first collection roller 103 is scraped off from the surface of the collection roller by the first scraping blade 104. The toner scraped off by the first scraping blade 104 is discharged out of the apparatus by the discharge screw 109.

  The positive transfer residual toner on the intermediate transfer belt 8 that could not be removed by the first cleaning brush roller 102 is transferred to the position of the second cleaning brush roller 106. A voltage having the same polarity (negative polarity) as the normal charging polarity of the toner is applied to the second cleaning brush roller 106, and an electric field formed by a potential difference between the intermediate transfer belt 8 and the surface potential of the second cleaning brush roller 106. Thus, the positively charged toner on the intermediate transfer belt 8 is electrostatically attracted and moved to the second cleaning brush roller 106. The positive toner moved to the second cleaning brush roller 106 is transferred to a contact position with the second recovery roller 107 to which a negative voltage having a value larger than that of the second cleaning brush roller 106 is applied. Then, the toner that has moved onto the second cleaning brush roller 106 is electrostatically adsorbed by the electric field formed by the potential difference between the surface potential of the second cleaning brush roller 106 and the surface potential of the second collection roller 107, and the 2 Move to the collection roller 107. The positive toner moved to the second collection roller 107 is scraped off from the surface of the second collection roller by the second scraping blade 108. The toner scraped off by the second scraping blade 108 is discharged out of the apparatus by the discharge screw 109.

  In the above description, the first cleaning unit 100a removes the negative polarity toner on the intermediate transfer belt 8, and the second cleaning unit 100b removes the positive polarity toner. However, the first cleaning unit 100a removes the positive polarity toner. A configuration in which the toner is removed and the negative polarity toner is removed by the second cleaning unit 100b may be employed.

Next, the features of the present invention will be described using the first cleaning unit 100a, but the second cleaning unit 100b also has similar features described below.
FIG. 3 is an enlarged configuration diagram showing the cleaning counter roller 13 and the intermediate transfer belt 8 in the printer. In the figure, the cleaning counter roller 13 is made of an aluminum roller having a diameter of 14 mm, and is driven to rotate in the clockwise direction in the drawing along with the endless movement of the intermediate transfer belt 8. The intermediate transfer belt 8 is wound around an arcuate region from point B to point C in the figure on the entire circumference of the cleaning counter roller 13. The length is multiplied by turning the width of the belt moving direction of the belt receiving turning region is indicated with W ₁ in FIG. In the figure, two-dot chain line indicated by reference numeral L ₂ illustrates the over-turning center line is a belt length in the moving direction of the belt receiving turning region (arc BC). Further, the two-dot chain line indicated by reference numeral L ₃ shows the extension that extends as a belt movement direction immediately before going into the point B.

FIG. 4 is an enlarged configuration diagram illustrating the cleaning facing roller 13, the intermediate transfer belt 8, and the first cleaning brush roller 102 in the printer. In the drawing, the first cleaning brush roller 102 has a diameter of 15 mm and is disposed so as to bite into the front surface of the intermediate transfer belt 8 by 1 mm. Against the front surface of the intermediate transfer belt 8 to form a cleaning nip contact in the area of the nip entrance point F to the nip exit point G (the area indicated by the nip width W _2). Then, in the cleaning nip, it rotates in the counter direction (clockwise direction in the figure) so as to move its own surface in the opposite direction to the intermediate transfer belt 8.

The lengths of the wrapping width W ₁ and the cleaning nip width W ₂ are measured from the dimensions on the drawing layout. Alternatively, a color material such as toner is attached to the front and back surfaces of the intermediate transfer belt 8, and the cleaning counter roller 13 and the first cleaning brush roller 102 are set and fixed so that the belt does not move. It can also be measured by rotating the one cleaning brush roller 102 and measuring the length of the range where the color material on the belt has been removed.

The two-dot chain line indicated by reference numeral L ₁ in the figure is a nip center line located in the center of the belt moving direction of the cleaning nip. In this printer, as shown, than turning center line L ₂ times the nip center line L ₁ is positioned on the upstream side of the belt moving direction, and, in the cleaning nip from nip entrance point F to the nip exit point G The upstream end of the belt moving direction is an upstream belt extension nip region where the brush contacts the belt extension region. Such a configuration, as compared with the turning center line L ₂ over the nip center line L ₁ in the conventional apparatus which has be located in the same place, over from the upstream side belt stretched nip area (nip entrance point F represented by the width W ₃ The area up to the turning entry point B) is increased. As a result, an area where toner on the belt can be favorably transferred to the cleaning brush roller 102 on the upstream side of the central portion of the belt running area, which easily causes reverse charging of the toner, is increased compared to the conventional case. The intermediate transfer belt 8 can be cleaned well.

Moreover, over-turning width W ₁ is shorter than the cleaning nip width W _2, multiplied by turning width W ₁ is within the range of the cleaning nip. In this configuration, the separation discharge in the vicinity of the cleaning nip outlet point G is suppressed as compared with the configuration in which the cleaning nip outlet point G is positioned upstream of the belt wrapping region (arc BC) outlet point C. Can do. This is because the cleaning opposing roller 13 is not in contact with the belt in the vicinity of the cleaning nip exit point G, and thus the electric field formed is weaker than the conventional configuration shown in FIG. 8 and can suppress discharge. Thereby, it is possible to suppress damage caused by the discharge of the first cleaning brush roller 102 and the intermediate transfer belt 8.

  In addition, when a large amount of toner such as a control pattern or untransferred toner during jamming continuously enters the cleaning nip, toner movement to the first collection roller 103 may not be in time. In this case, the uncollected toner that is not collected by the collection roller 103 and remains on the first cleaning brush roller 102 moves to the cleaning nip again. At this time, if a discharge occurs near the cleaning nip exit point G, the uncollected toner adhering to the brush of the first cleaning brush roller 102 is charged up. This is because a positive first cleaning bias is applied to the first cleaning brush roller 102 by a brush power source (not shown), and the cleaning counter roller 13 is grounded. When this occurs, the negative charge moves from the cleaning counter roller 13 toward the first cleaning brush roller 102. As a result, negative charge is injected into the negative uncollected toner adhering to the first cleaning brush roller 102, and the uncollected toner is charged up. As described above, due to the discharge near the cleaning nip exit point G, the electrostatic charge of the uncollected toner charged up with the cleaning brush roller 102 increases. Although the force for electrostatically moving the uncollected toner to the first collection roller 103 increases due to the charge-up of the uncollected toner, the amount of increase in the electrostatic adsorption force with the first cleaning brush roller 102 is larger. . Therefore, before the uncollected toner is charged up, the force to electrostatically move to the first collecting roller 103 is larger than the electrostatic attracting force to the brush. The electrostatic attraction force is larger than the force for electrostatically moving the first collection roller 103. As a result, the uncollected toner is not collected by the first collecting roller 103 and continues to adhere to the first cleaning brush roller 102. As a result, there is a problem that unrecovered toner that adheres to the first cleaning brush roller 102 with use over time increases and good cleaning properties cannot be obtained. Further, due to the discharge near the cleaning nip exit point G, the negative charge moves from the positive toner adhering to the intermediate transfer belt 8 to the first cleaning brush roller 102, and the positive toner is charged up. . As a result, the electrostatic adsorption force between the positive toner on the intermediate transfer belt 8 and the intermediate transfer belt 8 increases. As a result, the suction force to the intermediate transfer belt 8 becomes larger than the force to transfer the positive toner on the intermediate transfer belt 8 to the second cleaning brush roller 106. As a result, the positive toner may not be removed satisfactorily by the second cleaning unit 100b.

However, in this printer, the over-turning width W _1, housed within the cleaning nip, thereby suppressing separation discharge in the vicinity of the cleaning nip exit point G. As a result, it is possible to suppress charge-up of unrecovered toner adhering to the first cleaning brush roller 102 and positive toner adhering to the intermediate transfer belt 8. As a result, when unrecovered toner enters the contact area with the first recovery roller 103 next time, it can be electrostatically moved to the first recovery roller 103, and the unrecovered toner is transferred to the first cleaning brush. It is possible to suppress the adhesion to the roller 102. As a result, the cleaning property of the first cleaning roller 102 can be maintained over time. Further, the positive toner on the intermediate transfer belt 8 can be satisfactorily cleaned with the second cleaning brush roller 106.

Further, in this printer, over-turning width W ₁ is shorter than the cleaning nip width W _2. Upon application of a first cleaning bias to the first cleaning brush roller 102, the cleaning current flows through the cleaning counter roller 13 from the first cleaning brush roller 102 via the intermediate transfer belt 8, but the over-turning width W _1, the cleaning nip width by shorter than W _2, it is possible to narrow the region where the cleaning current flows. As a result, it is possible to prevent the toner on the intermediate transfer belt 8 from being charged to a reverse polarity due to charge injection by the cleaning current.

In this printer, the cleaning nip width W _{2 is} about 6 mm and the running width W _{1 is 1} mm, and the center of the cleaning nip is shifted to the upstream of the 2 mm belt from the center of the opposing nip.

  In the second cleaning unit 100b, the same configuration can also be used to suppress peeling discharge near the cleaning nip exit point, and charge up of unrecovered toner adhering to the second cleaning brush roller 106. Can be suppressed. In the case of the second cleaning unit 100b, the second cleaning brush roller 106 is negatively charged, and positive uncollected toner adheres to the brush. When discharge occurs near the cleaning nip exit point, negative charges move from the second cleaning brush roller 106 toward the cleaning counter roller 14, and are attached to the second cleaning brush roller 106 at this time. Negative charge is also discharged from the uncollected toner toward the cleaning facing roller 14. As a result, the uncollected toner adhering to the second cleaning brush roller 106 is charged up to positive polarity. Therefore, in the second cleaning unit 100b as well, the unrecovered toner of the second cleaning brush roller 106 is brought into contact with the second recovery roller 107 next time by adopting the arrangement relationship shown in FIG. It can be moved electrostatically to the second collection roller side. As a result, the cleaning property of the second cleaning brush roller 106 can be maintained over time.

Next, a modified example of the printer will be described.
FIG. 5 is an enlarged configuration diagram showing the belt cleaning device 100 and its surroundings of a modified printer in an enlarged manner. In the printer of the first modification, the cleaning facing rollers 13 and 14 are configured by conductive wire members 131 and 141.
The conductive wire members 131 and 141 are fixed so as to fit into grooves (not shown) of semicircular insulating support members 132 and 142 provided at both ends of the intermediate transfer belt 8. The diameters of the support members 132 and 142 were 14 mm, and the diameters of the wire members 131 and 141 were 0.18 mm or less although they could not be measured accurately with thin wires. Each of the wire members 131 and 141 was disposed 2 mm downstream from the center of the cleaning nip on the downstream side in the belt moving direction.

Thus, the cleaning counter roller 13 and 14 by the wire member 131 and 141, it is possible to narrow the multiplying turning width W ₁ further, the width cleaning current flows more can be narrowed further. Thereby, it is possible to suppress the toner on the intermediate transfer belt 8 from being charged to a reverse polarity due to charge injection by the cleaning current. Further, the cleaning counter roller can be separated from the vicinity of the cleaning nip outlet point G, and the discharge near the cleaning nip outlet point G can be further suppressed. Furthermore, it is possible to increase the upstream belt extension nip region (the region from the nip entry point F to the entry point B). Thereby, the cleaning property of the intermediate transfer belt 8 can be further improved.

Next, a verification experiment will be described.
In the verification experiment, a printer configured as follows was prepared.
<Example 1>
Printer Example 1, using a cleaning opposed roller diameter 14 mm, shift the cleaning nip width W ₂ of about 6 mm, a width W ₁ 1 mm once over, upstream of 2mm belt than the center of the over-turning area the center of the cleaning nip It has been made.
<Example 2>
Printer Example 2, using a wire member having a diameter of 0.18mm as cleaning facing roller, the cleaning nip width _{W 2} of about 6 mm, with the following over-turning width _W 1 0.18mm, than the center of the cleaning nip wire member It is shifted upstream of the 2 mm belt.
<Comparative Example 1>
The printer of Comparative Example 1 uses a cleaning counter roller having a diameter of 40 mm, the cleaning nip width W ₂ and the wrapping width W ₁ are set to 6 mm, and the center of the cleaning nip is aligned with the center of the wrapping area. Is.

In the evaluation method, the secondary transfer current is set to 0, and all three solid images of three colors of A3 are overlapped. As an input to the cleaning device, a total solid 10 of 1.2 mg / cm ^{2 in} terms of toner adhesion amount is used. It becomes the number of sheets. After passing the paper, the intermediate transfer belt that passed through the cleaning was transferred with a tape, and the density (ID) of the tape attached to the mount was measured. A range in which the ID is 0.15 or less of the target value was determined by varying the cleaning bias applied to the brush.

The results are shown in FIG. 6 and Table 1.

  It can be seen that the bias range (see ΔV in Table 1) where the cleaning is OK is wider in the first embodiment than in the first comparative example. It can also be seen that the bias range for cleaning OK is wider in the second embodiment than in the first embodiment. The cleaning OK range varies depending on the environment such as temperature and humidity, the toner adhesion amount, and the charge amount. Therefore, it can be said that a wider bias range that is equal to or less than the target value is more stable against changes in the environment.

  In addition, the cleaning device of the present invention is not limited to the belt cleaning device 100 that cleans the front surface of the intermediate transfer belt, but may be applied to the transport belt cleaning device 500 of the paper transport belt 51 as shown in FIG. Can do. As shown in FIG. 7, a paper transport belt 51 as a member to be cleaned used in an image forming apparatus of a tandem type direct transfer system comes into contact with the photoreceptors 1Y, 1M, 1C, 1K, and Y, M, C, A primary transfer nip for K is formed. Then, in the process of conveying the recording paper P from the left side to the right side in the figure along with its endless movement while holding the recording paper P on its surface, the primary transfer nip for Y, M, C, K is used. In order. As a result, the Y, M, C, and K toner images are superimposed and primarily transferred onto the recording paper P. Contamination such as toner adhering to the paper transport belt 51 after passing through the primary transfer nip for K is removed by the transport belt cleaning device 500. The optical sensor unit 150 is disposed so as to face the front surface of the paper transport belt 51 with a predetermined gap. In the printer shown in FIG. 7, image density control and positional deviation amount correction control are performed at a predetermined timing, a predetermined toner pattern (gradation pattern, chevron patch) is formed on the paper transport belt 51, and the optical sensor unit 150. Then, the toner pattern is detected, and a predetermined correction process is executed based on the detection result. A toner pattern which is an untransferred toner image detected by the optical sensor unit 150 is removed by the conveyor belt cleaning device 500. Thus, the paper transport belt 51 has a function as an image carrier that carries a toner image.

  By applying the cleaning device of the present invention to the transport belt cleaning device 500, the paper transport belt 51 can be satisfactorily cleaned over time.

As described above, the printer according to the present embodiment includes the cleaning device having the following cleaning configuration. In other words, the belt is attached to the region where the intermediate transfer belt 8 is wound around the cleaning counter roller 13 which is one of a plurality of stretching rollers disposed inside the loop of the intermediate transfer belt 8 which is an endless belt member. A cleaning brush roller is provided as a cleaning rotary member that forms a cleaning nip that abuts from the surface side and abuts against the belt front surface. This cleaning brush roller performs cleaning by transferring the toner, which is attached to the front surface of the belt, to itself while rotating so that the surface moves in the cleaning nip in the direction opposite to the belt moving direction. . The cleaning device also includes a brush power supply as a voltage applying means for applying a cleaning bias as a cleaning voltage to the cleaning brush roller, and electrostatically transfers the toner adhering to the cleaning brush roller to the toner from the cleaning brush roller. And a collecting roller as a collecting means for collecting the. Then, the center of the cleaning nip in the belt moving direction is positioned on the upstream side in the belt moving direction with respect to the center of the wrapping area in the belt moving direction, and cleaning is performed so that the wrapping area is within the cleaning nip range. A cleaning nip was formed by bringing the brush roller into contact with the intermediate transfer belt.
By having such a configuration, the upstream belt extension nip region can be increased as compared with the case where the center of the cleaning nip and the center of the wrapping region are located at the same place. As a result, the area where the toner on the intermediate transfer belt can be satisfactorily transferred to the cleaning brush roller on the upstream side of the central portion of the belt running area with respect to the cleaning counter roller can be increased as compared with the prior art. The intermediate transfer belt can be cleaned well.
In addition, since the encircled area of the intermediate transfer belt is within the cleaning nip range, the electric field near the cleaning nip exit is reduced, and a part of the encircled area of the belt member is located downstream of the cleaning nip range in the belt moving direction. It can be weakened compared to the case of protruding. As a result, the discharge near the exit of the cleaning nip can be suppressed, and damage due to the discharge of the cleaning brush roller and the intermediate transfer belt can be suppressed. Therefore, the life of the intermediate transfer belt and the cleaning brush roller can be extended. Further, it is possible to prevent the uncollected toner adhering to the cleaning brush roller from being charged up to a polarity opposite to the charging polarity of the cleaning brush roller due to discharge. Therefore, it is possible to suppress the electrostatic attracting force of the uncollected toner to the cleaning brush roller from becoming larger than the force of electrostatically moving to the collecting roller. As a result, when the uncollected toner again enters the contact area with the collection roller, the uncollected toner can be electrostatically moved to the collection roller and removed from the cleaning brush roller. As a result, accumulation of unrecovered toner on the cleaning brush roller over time can be suppressed, and good cleaning properties can be maintained over time.

  In addition, by using a conductive wire as the cleaning counter roller, the width of the winding region can be narrowed, and the width of the cleaning current flowing from the cleaning brush roller to the conductive wire via the intermediate transfer belt can be narrowed. Can do. Thereby, it is possible to suppress the toner from being reversely charged due to the influence of the cleaning current. Further, the cleaning nip exit point G and the exit point C in the winding region can be separated, and the occurrence of discharge near the cleaning nip exit point can be suppressed. Further, the upstream belt extension nip region can be widened, and good cleaning properties can be maintained.

  Further, the intermediate transfer belt is provided with an elastic layer having a thickness of 0.07 [mm] or more and 0.5 [mm] or less, so that the contact with the recording paper can be improved and the secondary transfer efficiency can be increased. . A cleaning device that employs an electrostatic cleaning system as a cleaning device for such an intermediate transfer belt having elasticity can obtain good cleaning performance.

8: intermediate transfer belt 51: transfer conveyance belt 100: belt cleaning device 100a: first cleaning unit 100b: second cleaning unit 102: first cleaning brush roller 103: first recovery roller 106: second cleaning brush roller 107: first 2 recovery rollers 131, 141: wire member 500: transport belt cleaning device

JP 2009-20249 A JP 2007-78803 A JP 2009-134153 A

Claims (5)

Abutting from the belt front surface side on the belt member wrapping region with respect to the cleaning counter roller which is one of a plurality of stretching rollers disposed inside the loop of the endless belt member, While forming a cleaning nip that contacts the belt front surface, the surface of the belt adheres to the belt front surface while rotating so that its surface moves in the direction opposite to the belt moving direction in the cleaning nip. A cleaning rotator that electrostatically transfers to the object an object having a polarity opposite to the polarity of the voltage applied to itself, and cleaning it;
In a cleaning apparatus comprising: a collection unit that electrostatically transfers the deposits attached to the cleaning rotator to collect the deposits from the cleaning rotator;
The center of the cleaning nip in the belt movement direction is located upstream of the center of the wrapping area in the belt movement direction in the belt movement direction, and the wrapping area is within the cleaning nip range. The cleaning nip is formed by bringing the cleaning rotator into contact with the belt member. An endless belt member that can be moved endlessly in a state of being stretched by a plurality of stretching rollers disposed inside its own loop;
A belt device comprising: cleaning means for cleaning deposits adhering to the surface of the belt member;
A belt device using the cleaning device according to claim 1 as the cleaning means. The belt device according to claim 2.
A belt device using a conductive wire as the cleaning counter roller. The toner image carried on the front surface of the endless belt member or the toner image carried on the recording member held on the front surface of the belt member is used for endless movement of the belt member. In an image forming apparatus comprising: a belt device that conveys the toner image; and a toner image forming unit that forms a toner image on a front surface of the belt member or a recording member;
An image forming apparatus using the belt device according to claim 2 or 3 as the belt device. The image forming apparatus according to claim 4.
The belt member includes an elastic layer having a thickness of 0.07 [mm] or more and 0.5 [mm] or less.

Images