JP4710454B2 - Cleaning device and image forming apparatus - Google Patents

Description

  The present invention relates to a cleaning device and an image forming apparatus, and more particularly to a cleaning device for collecting residual toner on an image carrier such as a photosensitive member or an intermediate transfer member in an electrophotographic copying machine or printer, and the cleaning device. The present invention relates to an image forming apparatus provided.

  Conventionally, in an electrophotographic image forming apparatus, the surface of a photosensitive drum is charged, image exposed, and developed with toner to transfer a toner image onto a transfer material such as paper, or from the photosensitive drum to an intermediate transfer member. After the toner image is transferred and synthesized, the synthesized toner image is transferred to a transfer material such as paper, and then the toner image is fixed, and then the toner image is formed on the transfer material.

  Incidentally, in the above image forming process, it is necessary to collect residual toner from an image carrier such as a photosensitive drum or an intermediate transfer member. The toner is charged to a predetermined polarity (hereinafter referred to as normal polarity) in the developing device. However, after the transfer, a part of which is charged with a reverse polarity remains on the image carrier, and the charge distribution is non-uniform. Various cleaning devices have been proposed in order to efficiently collect such toner.

  For example, in Patent Document 1, a rotating body provided with a potential difference with respect to an image carrier and a conductive member grounded are provided, and toner charged with a reverse polarity remaining on the image carrier by the conductive member is provided. A cleaning device is disclosed that is adjusted to have a normal polarity and electrostatically adsorbs the toner having the normal polarity to the rotating member for recovery.

By using the cleaning device, most of the residual toner has the charged polarity aligned with the normal polarity and can be collected by the rotating member. However, when the amount of toner charged to a reverse polarity due to fluctuations in transfer current or the like increases, the conductive member does not function sufficiently, and the rotating member cannot fully collect the toner, which may cause a cleaning failure. This is because if the amount of the reversely charged toner is excessive, the toner charged to the opposite polarity to the conductive member cannot be sufficiently contacted, and as a result, the charged polarity may not pass the normal polarity and pass through the conductive member. caused by.
JP 2004-310060 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cleaning device and an image forming apparatus capable of maintaining an appropriate cleaning performance for residual toner on an image carrier.

  In order to achieve the above object, a cleaning device according to the present invention has a conductive rotating member that is rotationally driven in contact with the surface of an image carrier that moves in one direction, and an image carrier than the rotating member. A conductive member that contacts the surface of the image carrier on the upstream side in the moving direction of the body, and the conductive member is made of a material that charges the toner to a polarity opposite to the normal polarity due to a frictional charge series with the toner. The charged polarity of the toner remaining on the surface of the toner is made regular to the normal polarity by the conductive member, and the toner having the regular polarity is collected from the image carrier by the rotating member.

  In the cleaning device according to the present invention, the conductive member provided on the upstream side in the moving direction of the image carrier is made of a material that charges the toner to a polarity opposite to the normal polarity in the frictional charging series with the toner. The toner is charged with a normal polarity by rubbing. Therefore, toner charged to a reverse polarity due to fluctuations in transfer current or the like is easily adsorbed by the conductive member and is collected by the conductive member. The collected reverse polarity toner is injected with a normal polarity charge from the conductive member, and the toner is charged with the normal polarity. The toner whose polarity has been adjusted in this way (becomes normal polarity) leaves the conductive member and is conveyed to the rotating member, and is collected from the image carrier by the rotating member.

  On the other hand, the toner charged to the normal polarity tends to have a reverse polarity when rubbed with the conductive member, but since the time for rubbing with the conductive member is short, an electric charge that causes the reverse polarity is injected. However, it is conveyed to the rotating member with the normal polarity, and is collected from the image carrier by the rotating member.

  That is, in the cleaning device according to the present invention, not only the toner charged to the normal polarity but also the toner charged to the reverse polarity is adjusted to the normal polarity by the conductive member, and then the rotating member is used. It is possible to maintain an appropriate cleaning performance for the residual toner collected from the image carrier and remaining on the image carrier.

In the cleaning device according to the present invention , the rotating member may be connected to a DC power source via a collecting member provided directly or in contact with the rotating member, and the conductive member may be grounded, or the conductive member may be a DC power source. The rotating member may be grounded.

  Furthermore, the DC power source is preferably a constant current DC power source. When the conductive member or the rotating member contains toner, the apparent circuit resistance increases. Therefore, when a constant voltage DC power source is used, the current flowing through the conductive member and the rotating member is reduced, and the toner recoverability is lowered. . However, if a constant current DC power supply is used, a necessary current value can be secured, and a decrease in toner recoverability can be prevented.

  The image forming apparatus according to the present invention includes the cleaning device, and has the operational effects of the cleaning device.

  Embodiments of a cleaning device and an image forming apparatus including the cleaning device according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus)
An image forming apparatus 1 shown in FIG. 1 is an electrophotographic color printer, and is configured to synthesize four color images in a so-called tandem system.

  The outline of the print head 20 includes a photosensitive drum 21, a developing device 22, a primary transfer roller 23, a charging device (not shown), an image exposure device, and the like. 20M, 20C, 20K) are juxtaposed directly below the intermediate transfer belt 10. The process of forming a toner image on the photosensitive drum 21 in each print head 20 is well known, and the description thereof is omitted.

  The intermediate transfer belt 10 is rotationally driven in the direction of arrow A by the driving roller 11 and the support rollers 12 and 13, and the portion facing the driving roller 11 through the intermediate transfer belt 10 (secondary transfer unit 14) is secondary. A transfer roller 15 is disposed.

  In the lower part of the image forming apparatus 1, an automatic paper feeding unit (not shown) that feeds stacked sheets one by one is installed. A toner fixing device (not shown) is installed immediately above the secondary transfer unit 14.

  The color-specific toner images formed on the respective photosensitive drums 21 are sequentially primary-transferred onto the intermediate transfer belt 10 that is rotationally driven in the direction of arrow A, and four-color images are synthesized. On the other hand, the sheets are fed one by one from the direction of arrow B, and are sandwiched between the intermediate transfer belt 10 and the transfer roller 15 by the secondary transfer unit 14, and the composite image is secondarily transferred. Thereafter, the sheet is heated and fixed with toner by a fixing device, and is discharged onto a tray (not shown).

  Here, the toner accommodated in each developing device 22 is negatively charged (in the present embodiment, normal polarity means negative polarity). For applying a positive electric field from the primary transfer roller 23. Then, the image is transferred to the intermediate transfer belt 10 and further transferred to the sheet by applying a positive electric field from the secondary transfer roller 15. Most of the residual toner on the intermediate transfer belt 10 is charged to the normal polarity, but includes toner charged to the reverse polarity due to fluctuations in the transfer current or the like. These residual toners are collected by a cleaning device 30 described below.

(Cleaning device)
As shown in FIGS. 1 and 2, the cleaning device 30 includes a conductive rotating member 31 that is driven to rotate in the direction of arrow C while being in contact with the surface of the intermediate transfer belt 10 at a portion facing the support roller 13. The conductive member 35 is in contact with the surface of the intermediate transfer belt 10 between the support rollers 12 and 13, and the recovery roller 32 is rotated in the same direction (arrow C) while being in contact with the rotating member 31. Yes.

  The rotating member 31 is a rotating brush having an axial length equal to the width dimension of the intermediate transfer belt 10, planted in a circular shape in cross section, and positive charge is injected from a constant current DC power supply 33 connected to the recovery roller 32. Is done. The conductive member 35 is a long brush having a length equal to the width of the intermediate transfer belt 10 and is grounded. The conductive member 35 is made of a material that charges the toner to a polarity opposite to the normal polarity due to the frictional charging series with the toner. That is, when the conductive member 35 and the toner are rubbed in a neutral state, the toner whose negative polarity is normal polarity is charged to positive polarity, and the conductive member 35 is charged to negative polarity.

  In this embodiment, the toner is mainly composed of a styrene acrylic resin. The conductive member 35 is a brush using fibers mainly composed of a polyethylene-based resin, and tends to be negatively charged by friction with toner. Incidentally, the intermediate transfer belt 10 is mainly composed of polyimide.

  By the way, the distribution of the charge amount of the toner in each portion of the intermediate transfer belt 10 is shown in FIGS. 3A to 3D, and the hatched portion is the toner charged to the reverse polarity. The charge amount of the toner on the intermediate transfer belt 10 after the primary transfer and before the secondary transfer has a distribution shown in FIG. Most toners are charged with normal polarity, but a small amount is charged with reverse polarity. Further, most of the toner charged to the normal polarity in the secondary transfer is transferred to the sheet by applying a positive electric field from the secondary transfer roller 15. Accordingly, the charge amount of the toner remaining on the intermediate transfer belt 10 after the secondary transfer has a distribution shown in FIG. The residual toner here is one in which the charge is not normal polarity or the charge amount is very small and the toner is not transferred to the paper by the secondary transfer electric field, and the secondary transfer current becomes excessive and the vicinity of the secondary transfer portion 14. In other words, abnormal charge is generated and the toner is no longer charged with normal polarity, and the percentage of toner charged with reverse polarity is increasing.

  Since it is difficult to collect the toner having the charge amount distribution shown in FIG. 3B by the rotating member 31 as it is, conventionally, the charging polarity of the toner is set to the normal polarity by the conductive member on the upstream side of the rotating member 31. It was aligned. The charge amount distribution after passing through this conventional conductive member is shown in FIG. Although the ratio of the toner charged to the reverse polarity is smaller than that after the secondary transfer, a considerable amount of the reverse polarity toner is present and cannot be collected by the rotating member 31.

  Therefore, in this embodiment, the conductive member 35 is made of a material that charges the toner with a polarity opposite to the normal polarity due to the frictional charging series with the toner. The charge amount distribution after passing through the conductive member 35 is shown in FIG. Here, most of the reverse polarity toner is adjusted to the normal polarity, collected by the rotating member 31, and further collected by adhering to the outer peripheral surface of the collecting roller 32 into which the positive charge is injected. The configurations of the rotating member 31 and the collection roller 32 are well known.

  Next, the operation of the conductive member 35 will be described. When the toner remaining on the intermediate transfer belt 10 is conveyed to the conductive member 35 in the secondary transfer unit 14 and rubs against the conductive member 35, the conductive member 35 is charged with a normal polarity with respect to the toner. When the conductive member 35 is charged with normal polarity (here, negative polarity), the toner that passes through the secondary transfer portion 14 and is conveyed to the cleaning device 30 is charged with reverse polarity (here, positive polarity). The toner is collected by the conductive member 35.

  The reverse polarity toner collected in the conductive member 35 in this way is firmly adsorbed to the flocked hair of the conductive member 35 by the electrostatic attractive force with the conductive member 35. Further, since the conductive member 35 is grounded and forms a part of the toner recovery bias circuit, a negative charge is injected into the reverse polarity toner adsorbed on the conductive member 35 to charge the toner to the normal polarity. The toner whose polarity has been adjusted in this way (becomes normal polarity) leaves the conductive member 35 and is conveyed to the rotating member 31, and is collected from the intermediate transfer belt 10 by the rotating member 31.

  On the other hand, toner that has been charged with a normal polarity tends to have a reverse polarity when rubbed with the conductive member 35, but since the time for rubbing with the conductive member 35 is short, a charge that would cause a reverse polarity is generated. It is not injected and is conveyed to the rotating member 31 with the normal polarity, and is collected from the intermediate transfer belt 10 by the rotating member 31.

  As described above, according to the present embodiment, the toner that has passed through the conductive member 35 is extremely rarely charged with a reverse polarity, and most of the toner after the secondary transfer is transferred from the intermediate transfer belt 10 by the rotating member 31. Collected and proper cleaning performance is maintained.

  The current value of the secondary transfer current is a factor for charging the toner with a reverse polarity, and the cleaning performance tends to deteriorate as the current value increases. Conventionally, when the secondary transfer current is about 80 μA or more, the cleaning performance is deteriorated so that it cannot be used practically. However, in this example, cleaning performance with no practical problem was shown even with a secondary transfer current of 80 μA.

(Other examples)
The cleaning device and the image forming apparatus according to the present invention are not limited to the above-described embodiments, and can be variously modified within the scope of the gist.

  For example, the present invention can be applied to various image forming apparatuses such as a monochrome printer, a color / monochrome copying machine, and a facsimile, not limited to the tandem type color printer shown in the above embodiment.

  Moreover, although the case where the DC power source 33 is connected to the collection roller 32 has been described in the above embodiment, it may be connected to the rotating member 31 or the conductive member 35. When the DC power source 33 is connected to the rotating member 31, the conductive member 35 is grounded. When the DC power source 33 is connected to the conductive member 35, the rotating member 31 is grounded. In addition, a ground location can be selected arbitrarily. The image carrier may be in the form of a belt or a roller, and the present invention may be applied as a cleaning device for the photosensitive drum 21 of the print head 20.

  Various materials other than the above-described embodiment can be used as the material of the rotating member 31 and the conductive member 35, and the material may be a felt shape instead of the flocking type.

  In the above-described embodiment, the toner having negative polarity with normal polarity is used. However, the present invention can be applied to the case of using toner with positive polarity having normal polarity. In this case, a brush using a fiber mainly composed of a polyamide-based resin as a conductive member can be used for a toner mainly composed of a styrene-acrylic resin or a polyester-based resin.

1 is a schematic configuration diagram illustrating an image forming apparatus including a cleaning device according to the present invention. It is a principal part enlarged view of the said cleaning apparatus. 6 is a graph illustrating a toner charge amount distribution state at each position of an intermediate transfer belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Intermediate transfer belt 14 ... Secondary transfer part 30 ... Cleaning device 31 ... Rotating member 32 ... Collection roller 33 ... DC power supply 35 ... Conductive member

Claims (5)

A rotating member having conductivity that is rotationally driven in contact with the surface of the image carrier that moves in one direction, and a conductive member that contacts the surface of the image carrier upstream of the rotating member in the moving direction of the image carrier. With members,
The conductive member is made of a material that charges the toner to a polarity opposite to the normal polarity on the frictional charging series with the toner,
Aligning the charged polarity of the toner remaining on the surface of the image carrier to the normal polarity by the conductive member, and collecting the toner having the normal polarity from the image carrier by the rotating member;
A cleaning device characterized by. The cleaning apparatus according to claim 1, wherein the rotating member is connected to a DC power source through a recovery member provided directly or in contact with the rotating member, and the conductive member is grounded. The cleaning device according to claim 1, wherein the conductive member is connected to a DC power source, and the rotating member is grounded. The DC power supply cleaning device according to claim 2 or claim 3, characterized in that a constant-current DC supply. An image forming apparatus comprising the cleaning apparatus according to any one of claims 1 to 4.

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