JP2008102438A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of recovering residual toner accumulated on a cleaning member by static electricity, without providing a special bias device to it. <P>SOLUTION: The image forming apparatus includes: a primary transfer bias applying means for applying a bias so as to primarily transfer a toner image formed on an image carrier onto an intermediate transfer body; the cleaning member for electrostatically attracting the residual toner left on the intermediate transfer body; a cleaning bias applying means for applying a bias reverse to the electrification characteristics of the residual toner on the cleaning member. During a non-image formation period, the cleaning bias apply means stops the operation of applying the cleaning bias on the cleaning member, and the cleaning member is rotated so as to attain self-triboectrification generated by contact friction with the intermediate transfer body, then, an electrical field equivalent to the bias to peel the residual toner from the cleaning member is formed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that collects toner remaining on an intermediate transfer body after transfer.

In an image forming apparatus such as a copying machine, a toner image is formed on an image carrier by developing the electrostatic latent image formed on the image carrier with a developing device. There is a color image forming apparatus provided with an intermediate transfer member so as to transfer the toner image onto the paper and transfer it again to the paper.
In a color image forming apparatus provided with such an intermediate transfer member, there is a toner remaining on the intermediate transfer member after transfer to a sheet, and means for cleaning this residual toner is provided.

As a means for cleaning the residual toner on the intermediate transfer body after the transfer, an electrostatic cleaning means for collecting the toner by using an electrostatic force such as a fur brush, and a machine for scraping the blade by contacting the blade with the intermediate transfer body Cleaning means.
According to the electrostatic cleaning means, since the load for driving the intermediate transfer member can be set small, it is possible to reduce color registration displacement. Also, an intermediate transfer drum or intermediate transfer belt is used as the intermediate transfer member, but when an intermediate transfer belt is used and an elastic material such as rubber is used as the belt material, mechanical cleaning means cannot be used, but electrostatic cleaning is possible. Means can be preferably used.

However, toner attracted to a cleaning member such as a fur brush using electrostatic force is collected by a collecting roller or the like, but toner that cannot be collected accumulates in the fur brush. There is a problem that the toner accumulated in the fur brush returns to the intermediate transfer member during image formation to cause an image defect.
As a technique using an electrostatic cleaning means for solving such a problem, for example, the following Patent Document 1 can be cited. This technology is the opposite of the normal cleaning bias between the fur brush and the intermediate transfer body during warm-up when the power is turned on or during non-image formation after a specific number of transfers to the recording medium. A toner peeling bias voltage is applied. The electrostatic force generated by this voltage application causes the toner accumulated in the fur brush to move to the intermediate transfer member side, and the toner is further moved to the image carrier side to be collected by a cleaning process on the image carrier. ing.

  However, in such electrostatic cleaning means, it is necessary to separately prepare a device for applying a toner stripping bias voltage opposite to that at the time of normal cleaning bias, leading to an increase in cost.

JP 2002-72697 A

  The present invention has been made to solve the above-described problems of the prior art, and can collect the residual toner accumulated on the cleaning member by electrostatic force without providing a special bias device. An image forming apparatus is provided.

  According to a first aspect of the present invention, there is provided an image forming apparatus including an intermediate transfer body for performing a primary transfer of a toner image formed on an image carrier and then a secondary transfer to a transfer material. A primary transfer bias applying unit that applies a bias to a contact portion with the intermediate transfer member and primarily transfers a toner image formed on the image carrier onto the intermediate transfer member; and is provided in contact with the intermediate transfer member. A cleaning member that electrostatically adsorbs the residual toner remaining on the intermediate transfer member after the secondary transfer to the transfer material, and a bias reverse to the charging characteristics of the residual toner is applied to the cleaning member. A cleaning bias applying unit, and the cleaning bias applying unit stops applying the cleaning bias to the cleaning member and rotates the cleaning member during non-image formation to rotate the intermediate member. Self frictional charging by contact friction with the transfer member, an image forming apparatus, and forming a bias equivalent electric field for peeling the residual toner from the cleaning member.

  According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, wherein the cleaning member has a charging series closer to a toner charging characteristic side than the intermediate transfer member.

  The invention according to claim 3 is characterized in that a plurality of the image bearing members are arranged around the intermediate transfer member so as to be in contact with the intermediate transfer member, respectively. The present invention relates to an image forming apparatus.

  According to a fourth aspect of the present invention, the image carrier further comprises an image carrier cleaning means for removing toner remaining on the surface of the image carrier after the primary transfer, and the cleaning member is rotated during the non-image formation. 4. The image forming apparatus according to claim 1, wherein the intermediate transfer member is driven and the primary transfer bias applying unit applies a reverse bias to that during image formation.

  According to the first aspect of the present invention, the cleaning bias applying means stops the application of the cleaning bias to the cleaning member (fur brush) and rotates the cleaning member at the time of non-image formation to make contact friction with the intermediate transfer member. By self-friction charging, an electric field equivalent to a bias for peeling off the residual toner from the cleaning member is formed, so that it is opposite to the bias for applying the residual toner to the cleaning member during image formation. Even if this bias is not applied, an electric field equivalent to this can be formed, and the residual toner accumulated in the cleaning member can be moved to the intermediate transfer member side. Accordingly, the residual toner accumulated in the cleaning member can be collected by electrostatic force without providing a special bias device.

  According to the second aspect of the present invention, since the cleaning member has a charging series closer to the charging characteristics of the toner than the intermediate transfer member, the cleaning member is charged to the same plus or minus as the toner. By forming a positive or negative electric field equivalent to a bias for peeling off the residual toner from the member, the residual toner accumulated in the cleaning member can be moved to the intermediate transfer member side.

  According to the third aspect of the present invention, a so-called tandem intermediate transfer type image forming in which a plurality of image carriers (photoconductors) are arranged around the intermediate transfer member so as to be in contact with the intermediate transfer member, respectively. Even in the case of an image forming apparatus, exactly the same as a so-called 1-drum intermediate transfer type image forming apparatus, it is possible to apply a bias opposite to a bias applied to a cleaning member to adsorb residual toner during image formation. It is possible to move the residual toner accumulated in the cleaning member to the intermediate transfer member side by forming an electric field equivalent to.

  According to the invention of claim 4, the image carrier further comprises an image carrier cleaning means for removing toner remaining on the surface after the primary transfer, and when the cleaning member is rotated during non-image formation, the intermediate transfer member is When the toner is driven and the primary transfer bias applying means applies a bias opposite to that at the time of image formation, the toner moved from the cleaning member to the intermediate transfer member is further moved to the image carrier, and the image carrier in the image carrier It can be recovered by a cleaning means (drum cleaning device).

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of an image forming apparatus according to the invention will be described with reference to the drawings.
FIG. 1 is a simplified configuration diagram illustrating an example of a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a partially enlarged view showing the intermediate transfer member cleaning unit in FIG. 1 in an enlarged manner.
The image forming apparatus 100 is a one-drum intermediate transfer type, and includes a photosensitive drum 1 that is an image carrier on which a toner image is formed, an intermediate transfer member 7 to which the toner image is transferred, and the transferred toner image on a sheet. And a secondary transfer belt 9 for retransferring to the transfer material 13.

Around the photosensitive drum 1, in order from the upstream side in the rotation direction, a charger 6 for charging the surface of the photosensitive drum 1, an exposure device 2 for exposing to form an electrostatic latent image, and an electrostatic latent image A developing unit 3 for developing and forming a toner image, a drum cleaning unit 4 for cleaning toner remaining on the photosensitive drum 1 after the toner image is transferred to the intermediate transfer body 7, and the surface of the photosensitive drum 1 are neutralized. The static eliminator 5 is provided. In the illustrated example, the developing device 3 is composed of four developing devices 3 each including a color.
Further, in order to apply a bias to a contact portion between the photosensitive drum 1 and the intermediate transfer member 7, a primary transfer bias applying unit (not shown) is provided at or near the contact portion.

The intermediate transfer body 7 has a support roller 24 on the inner side, and on the downstream side in the rotation direction, intermediate transfer that cleans residual toner on the surface of the intermediate transfer body 7 after secondary transfer to the secondary transfer belt 9. A body cleaner 11 is provided. The intermediate transfer body cleaning device 11 includes a fur brush 21 that removes residual toner from the surface of the intermediate transfer body 7, cleaning bias means (not shown) that applies a bias opposite to the toner charging characteristics to the fur brush 21, and A recovery roller 22 that removes residual toner from the fur brush 21, a cleaning blade 23 that scrapes off residual toner from the recovery roller 22, and a power source 26 for applying a bias are provided.
The registration roller 8 that conveys the transfer material 13 to the secondary transfer belt 9 and the transfer material 13 from the secondary transfer belt 9 are conveyed to the fixing device 12 on the downstream and upstream sides of the rotation of the secondary transfer belt 9, respectively. A conveyor belt 10 is provided.

In the image forming apparatus 100 configured as described above, a cleaning bias applying unit (not shown) stops applying the cleaning bias to the fur brush 21 during non-image formation, and rotates the fur brush 21 to intermediate transfer member. 7 is characterized in that it is self-frictionally charged by contact friction with 7 and forms an electric field equal to or higher than a bias for peeling off the remaining toner from the fur brush 21.
For this reason, if the charging series of the fur brush 21 is closer to the toner charging characteristics than the intermediate transfer member 7, it is equivalent to a bias for peeling off the remaining toner by contact friction between the fur brush 21 and the intermediate transfer member 7. The above electric field can be formed.

Here, the case where the charging characteristic of the photosensitive drum 1 is plus (+) and the toner is developed by reversal development and the toner charging characteristic becomes plus (+) will be described as an example.
For example, when an intermediate transfer belt composed of a resin layer, an elastic layer, and a release layer from the inside is adopted as the intermediate transfer member 7, the charge series of the release layer as the surface layer is compared with the fur brush 21. It becomes a target. As the release layer, PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) FEP (hexafluoropropylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride) ) And the like are used.

Since the charging characteristic of the toner is plus (+), the charging series of the fur brush 21 is from the intermediate transfer body 7 so that a positive electric field (positive potential) equal to or greater than the bias for peeling off the remaining toner is formed. A toner on the plus (+) side which is the charging characteristic of the toner is employed.
There are polyester, acrylic, rayon, and nylon types that are on the plus (+) side of the fluororesin, and this is close to the charging series of fluororesins in this order. It is farthest from the resin charging series.

Here, the frictional charging potential suddenly rises from 0V, and there is no potential of 0 to less than 100V. If there is a potential of 100 V or higher, a potential equal to or higher than the bias for peeling off the remaining toner is formed.
In order to form a potential equal to or higher than the bias for peeling off such residual toner, the charging series of the material of the frictional brush 21 and the intermediate transfer member 7 must be separated from each other to some extent. The farther away, the better.
For example, when the intermediate transfer member 7 is made of a fluororesin, it is preferable to use a nylon system in which the fur brush 21 is not charged with a polyester system or an acrylic system and the charging series is farthest away.

Next, an operation for cleaning the residual toner on the intermediate transfer body 7 in the image forming apparatus 100 made of such a material will be described.
(During image formation)
First, at the time of image formation, the surface of the photosensitive drum 1 is charged by the charger 6, and the surface is exposed by the exposure device 2 to form an electrostatic latent image (step 1).
The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by the developing device 3 to form a toner image (step 2).

Next, a bias (minus) is applied to the contact portion between the photosensitive drum 1 having a positive charging characteristic and the intermediate transfer member 7 by a primary transfer bias applying means (not shown), whereby a positive charge on the photosensitive drum 1 is obtained. The charged toner image is primarily transferred onto the intermediate transfer body 7 (step 3).
After the primary transfer, the toner remaining on the surface of the photosensitive drum 1 is scraped off by the drum cleaner 4, and then the surface of the photosensitive drum 1 is discharged by the charge eliminator 5 and then charged again (step). 4).

The toner image primarily transferred to the intermediate transfer member 7 is secondarily transferred onto the transfer material 13 conveyed from the registration roller 8 between the secondary transfer belt 9 and transferred onto the conveyance belt 10. The toner image on the material 13 is fixed by the fixing device 12 and discharged from the image forming apparatus 100 (step 5).
After the secondary transfer, the residual toner on the surface of the intermediate transfer member 7 is electrostatically charged by applying a reverse bias to the toner charging characteristics to the fur brush 21 by a cleaning bias means (not shown) of the intermediate transfer member cleaner 11. The remaining toner is adsorbed to the fur brush 21 (step 6).

The residual toner adsorbed by the fur brush 21 is collected by the collecting roller 22 by the contact rotation with the fur brush 21 (step 7).
The residual toner that has moved onto the collection roller 22 is scraped off and collected by the cleaning blade 23 (step 8).

(Non-image formation)
When the image forming operations in steps 1 to 8 are repeated, residual toner that has not been collected by the collection roller 22 and the cleaning blade 23 is accumulated in the fur brush 21.
Therefore, during non-image formation, for example, when the image forming apparatus 100 is powered on, before warming up before starting image formation, or at the end of a specific number of transfers to the transfer material 13, the fur brush 21 is rotated to rotate the intermediate transfer member. 7 and contact friction (step 11). At this time, the cleaning bias means (not shown) stops applying the bias.

Due to this contact friction, the fur brush 21 is self-frictionally charged, and an electric field equal to or greater than a bias for peeling off the residual toner from the fur brush 21 is formed, and the residual toner accumulated in the fur brush 21 is transferred to the intermediate transfer member 7 side. (Step 12).
The intermediate transfer body 7 is driven to rotate, and a primary transfer bias applying means (not shown) applies a reverse bias to that at the time of image formation to the contact portion between the photosensitive drum 1 and the intermediate transfer body 7. The residual toner discharged to the body 7 side moves to the photosensitive drum 1 side at the contact portion, contrary to the time of image formation (step 13).
The residual toner that has moved to the photosensitive drum 1 is scraped off by the drum cleaning device 4 in the same manner as in the image formation as in step 4 (step 14).

FIG. 3 is a simplified configuration diagram showing an example of the second embodiment of the image forming apparatus according to the present invention. The same configurations as those in FIGS. 1 and 2 are denoted by the same reference numerals, and different configurations will be mainly described.
The image forming apparatus 200 according to the second embodiment is a tandem intermediate transfer body type, and is different from the first embodiment of a one-drum intermediate transfer type. A plurality of photosensitive drums 1 a to 1 d are arranged around the intermediate transfer member 7 so as to be in contact with the intermediate transfer member 7. Further, primary transfer rollers 32 a to 32 d each provided with primary transfer bias applying means (not shown) for applying a transfer bias to the contact portions between the respective photosensitive drums 1 a to 1 d and the intermediate transfer body 7 are provided. About another structure, it is the same as that of 1st Embodiment.

  The intermediate transfer member 7 is an intermediate transfer belt that moves endlessly. On the downstream side in the rotation direction, the intermediate transfer member 7 is subjected to the secondary transfer onto the secondary transfer belt (roller) 9 after the secondary transfer, as in the first embodiment. An intermediate transfer member cleaning device (not shown) for cleaning residual toner on the surface of the toner is provided. The intermediate transfer member cleaning device includes a fur brush 21 that removes residual toner from the surface of the intermediate transfer member 7, cleaning bias means (not shown) that applies a bias reverse to the charging characteristics of the toner to the fur brush 21, A recovery roller 22 that removes residual toner from the brush 21 and a cleaning blade 23 that scrapes off residual toner from the recovery roller 22 are provided.

In the tandem intermediate transfer body type image forming apparatus 200 configured as described above, the cleaning bias applying means (not shown) is a non-image, similarly to the one-drum intermediate transfer type image forming apparatus 100 of the first embodiment. At the time of formation, the application of the cleaning bias to the fur brush 21 is stopped, the fur brush 21 is rotated and self-friction charged by contact friction with the intermediate transfer member 7, and is equivalent to a bias for peeling off the remaining toner from the fur brush 21. The above electric field is formed.
For this reason, if the charging series of the fur brush 21 is closer to the toner charging characteristics than the intermediate transfer member 7, it is equivalent to a bias for peeling off the remaining toner by contact friction between the fur brush 21 and the intermediate transfer member 7. The above electric field can be formed.
Accordingly, the materials exemplified in the first embodiment can also be used for the materials of the intermediate transfer body 7 and the fur brush 21.

Next, an operation for cleaning the residual toner on the intermediate transfer body 7 in the image forming apparatus 200 of the second embodiment will be described.
(During image formation)
First, at the time of image formation, the surface of each of the photosensitive drums 1a to 1d is charged by the chargers 6a to 6d, and is exposed by an exposure device (not shown) to form an electrostatic latent image (step 21).
The electrostatic latent images formed on the surfaces of the photosensitive drums 1a to 1d are developed by the developing devices 3a to 3d to form toner images (step 22).

Next, a bias (minus) is applied to contact portions between the photosensitive drums 1a to 1d having positive charging characteristics and the intermediate transfer member 7 by primary transfer bias applying means provided in the primary transfer rollers 32a to 32d. The positively charged toner images on the photosensitive drums 1a to 1d are sequentially primary-transferred onto the intermediate transfer body 7 (step 23).
After the primary transfer, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is scraped off by the drum cleaners 4a to 4d. Thereafter, the surfaces of the photosensitive drums 1a to 1d are discharged by a discharging device (not shown) and then charged again. (Step 24).

As in the first embodiment, the toner image primarily transferred to the intermediate transfer body 7 is secondarily transferred onto the transfer material conveyed with the secondary transfer belt (roller) 9 and is transferred onto the transfer material. The toner image is fixed by the fixing device 12 and discharged from the image forming apparatus 200 (step 25).
After the secondary transfer, the residual toner on the surface of the intermediate transfer body 7 is collected by a cleaning bias means (not shown) as in Steps 6 to 8 as in the first embodiment (Step 26).

(Non-image formation)
As in the first embodiment, after the power supply to the image forming apparatus 200 is turned on, the fur brush 21 is rotated to warm up the intermediate transfer member 7 at the time of warming up before starting image formation or at the end of a specific number of times of transfer to the transfer material. (Step 31). At this time, the cleaning bias means (not shown) stops applying the bias.

Due to this contact friction, the fur brush 21 is self-frictionally charged, and an electric field equal to or greater than a bias for peeling off the residual toner from the fur brush 21 is formed, and the residual toner accumulated in the fur brush 21 is transferred to the intermediate transfer member 7 side. (Step 32).
The intermediate transfer member 7 is driven to rotate, and a primary transfer bias applying means (not shown) applies a bias opposite to that at the time of image formation to the contact portion between the photosensitive drums 1a to 1d and the intermediate transfer member 7. The residual toner discharged to the intermediate transfer body 7 side moves to the photosensitive drums 1a to 1d side at the contact portion, contrary to the time of image formation (step 33).
The residual toner that has moved to the photosensitive drums 1a to 1d is scraped off by a drum cleaner (not shown) in the same manner as in the image formation (step 34).

Examples of the image forming apparatus according to the present invention will be described below. This embodiment relates to a tandem intermediate transfer member type image forming apparatus, and will be described with reference to FIG.
(Implementation conditions)
In an image forming apparatus (KM-C3232 manufactured by Kyocera Mita Co., Ltd.), the a-Si photosensitive member was used to make the charging characteristics positive, and the reversal development method was used to make the toner positively charged. The materials of the intermediate transfer member 7 and the fur brush 21 were as follows.
<Intermediate transfer member (belt)>
Resin layer: PI (polyimide) 100 μm
Elastic layer: NBR (nitrile rubber) 230 μm
Release layer: PTFE (polytetrafluoroethylene) 5 μm
Volume resistivity: 1E + 10Ω · cm
Surface resistivity: 1E + 11Ω / □

<Fur brush>
Material: 6 nylon (Made by Unitika)
Outer diameter: Φ17mm
Hair length: 4.5mm
Fineness: 6D (denier)
Raw yarn resistance: 11.5th power Brush density: 120KF / inch ²
Biting distance between belt and brush: 1.5mm
Fur brush charging potential by frictional charging: + 250V

  Since the toner is positively charged, the material of the fur brush 21 is a nylon whose charging series is more positive than the charging series of the release layer of the intermediate transfer body 7 and is further away from the charging series of the intermediate transfer body 7. The system was adopted. As a preliminary test, when the relationship between the charging potential of the fur brush 21 and the residual toner discharge effect from the fur brush 21 to the intermediate transfer member 7 side was examined, a potential of 100 V or more was obtained as shown in Table 1 below. We confirmed that there was effect if there was.

Image formation is performed as in steps 21 to 26 described above, and after 100 times of transfer to A4 paper is completed, the sheet is idled (aged) for 3 minutes as described in steps 31 to 34 and accumulated in the fur brush 21. The residual toner thus discharged was discharged to the intermediate transfer member 7 side and collected by a drum cleaner (not shown) of the photosensitive drums 1a to 1d.
At the end of the transfer, the residual toner accumulated in the fur brush 21 could be clearly confirmed by visual observation, but after the idling, the residual toner was hardly recognized in the fur brush 21.
As described above, the fur brush 21 is rotated to contact the intermediate transfer member 7 without applying a reverse bias to the bias applied to the fur brush 21 by the cleaning bias means during image formation. It was found that by self-friction charging by contact friction, an electric field equal to or higher than a bias for peeling off the residual toner from the fur brush 21 can be formed, and the residual toner accumulated in the fur brush 21 can be collected.

  The present invention is suitably used for an image forming apparatus that employs a system in which a toner image is secondarily transferred to a transfer material after primary transfer to an intermediate transfer member.

1 is a simplified configuration diagram showing an example of a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a partially enlarged view showing an enlarged portion of an intermediate transfer member cleaning device in FIG. 1. It is a simplified block diagram which shows an example of 2nd Embodiment of the image forming apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Exposure device 3 Developing device 4 Drum cleaning device 5 Charger 6 Charger 7 Intermediate transfer body 8 Registration roller 9 Secondary transfer belt 10 Conveying belt 11 Intermediate transfer cleaning 12 Fixing device 13 Transfer material

Claims (4)

An image forming apparatus comprising an intermediate transfer body for primary transfer of a toner image formed on an image carrier to a transfer material after primary transfer,
A primary transfer bias applying unit that applies a bias to a contact portion between the image carrier and the intermediate transfer member, and primarily transfers a toner image formed on the image carrier onto the intermediate transfer member;
A cleaning member that is provided in contact with the intermediate transfer member and electrostatically adsorbs residual toner remaining on the intermediate transfer member after secondary transfer to the transfer material;
Cleaning bias applying means for applying a bias opposite to the charging characteristics of the remaining toner to the cleaning member;
The cleaning bias application unit stops applying the cleaning bias to the cleaning member during non-image formation, rotates the cleaning member, and self-frictions due to contact friction with the intermediate transfer member, and remains from the cleaning member. An image forming apparatus, wherein an electric field equivalent to a bias for peeling off toner is formed.   The image forming apparatus according to claim 1, wherein the cleaning member has a charging series closer to a toner charging characteristic side than the intermediate transfer member.   3. The image forming apparatus according to claim 1, wherein a plurality of the image bearing members are arranged around the intermediate transfer member so as to be in contact with the intermediate transfer member, respectively. The image carrier further comprises image carrier cleaning means for removing toner remaining on the surface of the image carrier after the primary transfer,
4. The first transfer bias applying unit applies a reverse bias to that during image formation while driving the intermediate transfer member when rotating the cleaning member during the non-image formation. The image forming apparatus according to any one of the above.

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