JPH10133486A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stable clean 2nd image carrier by using a specified frequency in the case of superposing AC on a bias impressed on an electrifying means in order to remover toner left after secondary transfer on the 2nd image carrier. SOLUTION: As the electrifying means for the toner left after the secondary transfer of the 2nd image carrier 10, a contact type electrifying means, concretely, an elastic roller having plural layers is used as an intermediate transfer belt cleaning device 8. A DC power source 8a and an AC power source 8b are connected to the device 8 so as to apply the bias obtained by superimposing DC voltage on AC voltage. In such a case, the frequency of the AC component superimposed on the bias impressed on the device 8 is set to 1000-6000Hz, more desirably, 3000-5000Hz. Thus, the 2nd image carrier 10 is excellently cleaned.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus for transferring a toner image formed on an image carrier to a transfer material via an intermediate transfer member.

[0002]

2. Description of the Related Art FIG. 4 shows a schematic configuration of a four-color full-color image forming apparatus.

The image forming apparatus shown in FIG. 1 includes a photosensitive drum 1 as a first image carrier and a contact type roller charger 2. Further, a plurality of developing devices are provided on the left side of the photosensitive drum 1. A developing device in which 4a, 4b, 4c, and 4d are supported by a rotatable support 3 is provided. Further, the developing devices 4a,
4b, 4c and 4d include yellow (hereinafter abbreviated as [Y]), magenta (hereinafter abbreviated as [M]), cyan (hereinafter abbreviated as [C]), and black (hereinafter abbreviated as [K]) toners The developing devices 4a, 4b, 4c, and 4d attached to the support 3 are driven such that the developing opening surface always faces the photosensitive drum surface. An exposure device 11 is arranged above the photosensitive drum 1.

The photosensitive drum 1 is formed by applying a photoconductor such as an organic photoconductor (OPC), A-Si, CdS, or Se on the outer peripheral surface of an aluminum cylinder, and is driven by driving means (not shown). It is driven in the direction indicated by the arrow.

[0005] The transfer device 5 includes three support rollers 5a, 5b, and 5c as a transfer body support. One of these
The book is a driving roller, and the remaining two are driven rollers.
An intermediate transfer belt (second image carrier) 1 is attached to this support roller.
The endless rubber belt is wound as 0, and is driven by a driving means (not shown) in a direction indicated by an arrow. Specific materials of the intermediate transfer belt 10 include acrylonitrile butadiene rubber (NBR), styrene butadiene rubber, butadiene rubber, ethylene propylene rubber, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, acrylic rubber, fluorine rubber, and urethane rubber And the like. A primary transfer roller 5a is disposed at a position substantially opposed to the photosensitive drum 1 via an intermediate transfer belt 10, and a secondary transfer for transferring a toner image to a transfer material (not shown) is provided at a position opposed to the support roller 5c. A roller 6 is arranged. An intermediate transfer belt cleaning device 8 is provided between the secondary transfer roller 6 and the primary transfer roller 5a.

[0006] By the contact type roller charger 2 described above,
The AC voltage is superimposed on the DC voltage to uniformly charge the photosensitive drum 1. When a signal according to the Y image pattern is input to the laser driver, a laser beam is emitted from the exposure device 11 to the photosensitive drum 1 through the optical path L, and an electrostatic latent image is formed on the photosensitive drum 1. When the photosensitive drum 1 further rotates in the direction of the arrow, the electrostatic latent image is visualized by the developing device 4a to become a toner image.

The toner image on the photosensitive drum 1 is transferred (primary transfer) by a voltage applied to the intermediate transfer belt 10 from a power supply (not shown). M, C, K
The multicolor toner image formed on the intermediate transfer belt 10 for each color is transferred (secondarily transferred) to a transfer material by a voltage applied to the intermediate transfer belt 10 from a power supply (not shown), and is conventionally known. Is fused and fixed by the heating and pressurizing fixing device 9 to obtain a color image. After the development, the transfer residual toner on the photosensitive drum 1 is cleaned by the photosensitive drum cleaning device 7. The transfer residual toner on the transfer belt after the completion of the secondary transfer is charged to the opposite polarity by the charging device 8 which is an intermediate transfer belt cleaning device, and is reversely transferred to the photosensitive drum 1 and cleaned.

Here, the intermediate transfer belt cleaning will be described in detail.

The secondary transfer residual toner is transferred to the intermediate transfer belt 10.
When the toner is transferred from the toner to the transfer material, it receives a strong electric field having a polarity opposite to that of the toner, and is charged to a polarity (positive in this conventional example) opposite to the normal charging polarity (negative in this conventional example) The toner remaining on the intermediate transfer belt 10 is large. However, not all toners are inverted to the positive polarity, and some toners are partially neutralized and have no charge, and other toners maintain the negative polarity.

Therefore, a charging device 8 is provided immediately after the secondary transfer, and the secondary transfer residual toner on the intermediate transfer belt 10 is
The neutralized toner having no charge and the toner maintaining the negative polarity are also charged to the opposite polarity. Then, the secondary transfer residual toner charged to the opposite polarity is reverse transcribed onto the photosensitive drum 1 at the primary transfer nip N _1, the intermediate transfer belt 10 is cleaned.

Even during continuous printing, the mutual charge of the oppositely charged secondary transfer residual toner on the intermediate transfer belt 10 and the regular toner of the primary transfer on the photosensitive drum 1 are equal to each other.
Since the short-time contact does not cancel each other, the secondary transfer residual toner reversely charged in the primary transfer nip portion N ₁ between the photosensitive drum 1 and the intermediate transfer belt 10 is transferred to the photosensitive drum 1, which is normally charged. The upper toner can be transferred to the intermediate transfer belt 10 in the reverse direction, and an appropriate image is output without transferring the secondary transfer residual toner onto the transfer material at the time of the next printing.

[0012]

In order to perform the above-described cleaning of the intermediate transfer member, it is preferable that the secondary transfer residual toner on the intermediate transfer belt 10 is as small as possible. If the residual toner amount is large, it is necessary to apply a strong cleaning bias to the charging device 8 in order to charge the residual toner with the charging device 8 and return the toner to the photosensitive drum 1. If the intermediate transfer member cleaning is performed with a strong bias, the toner that has already been charged to the opposite polarity (positive in this embodiment) in the secondary transfer among the secondary transfer residual toners is further strongly charged. A toner having a high positive charge is generated.

FIG. 3 is a diagram schematically showing the above phenomenon.

The secondary transfer residual toner 21 on the intermediate transfer belt 10 is dominated by positive polarity toner which has been inverted to a polarity opposite to the normal polarity in the secondary transfer process. The tribo on the intermediate transfer belt 10 at this time was +10 to +20 (μC / g).

Further, by applying a bias to the intermediate transfer member cleaning roller 8 and inverting most of the remaining toner 22 to the opposite polarity, the tribo of the toner 21 after passing the intermediate transfer member cleaning roller 8 is +30 to +40 (μC / μC /
g).

As described above, since the toner has a strong positive charge, the secondary transfer residual toner is efficiently re-transferred to the photosensitive drum 1 and returned.

However, the intermediate transfer member cleaning roller 8
As shown in FIG. 3, when a part of the toner is charged to an abnormally strong positive polarity due to the charge application,
In the toner 21 and the primary transfer nip N ₁ of returning the toner 20 and the photosensitive drum 1 to be primarily transferred at the primary transfer, since the charge amount of the toner 21 of returning is large, it attracts toner 20 to transfer primary Is returned to the photosensitive drum 1 again.

As an actual image, after the remaining toner at the time of the previous print, the image appears as a negative ghost in the second and subsequent images of the continuous print. Hereinafter, this phenomenon will be referred to as a cleaning ghost.

As described above, when there is a large amount of secondary transfer residual toner, it is necessary to strongly charge the residual toner in order to prevent defective cleaning, but there is a possibility that abnormally strongly charged toner may be generated. In order to prevent this, the secondary transfer residual toner may be kept small.

However, when environmental fluctuations or durability fluctuations occur, there is a possibility that the secondary transfer residual toner may inevitably be large.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image forming apparatus capable of satisfactorily cleaning a second image carrier (the above-described intermediate transfer belt).

[0022]

According to a first aspect of the present invention, a plurality of color toner images sequentially formed on a first image carrier are sequentially transferred to a second image carrier in a primary transfer. In an image forming apparatus for forming a color image on a transfer material by collectively and secondarily transferring a plurality of color toner images on the second image carrier onto a transfer material, an AC component is superimposed on a DC component. By applying a bias to apply electric charge to the secondary transfer residual toner on the second image carrier, the secondary transfer residual toner on the second image carrier is removed from the first image simultaneously with the primary transfer. Charging means for performing reverse transfer onto the image bearing member, wherein the frequency of the AC component of the bias applied to the charging means is 1000 to 6000H
z.

The present invention according to claim 2 is characterized in that the frequency of the AC component is 3000 to 5000 Hz.

According to a third aspect of the present invention, the second charging means is a roller charger arranged in contact with the second image carrier.

The present invention according to claim 4 is characterized in that the second charging means is a charging electrode which is arranged in a non-contact and opposed relationship with the second image carrier.

[Operation] Based on the above configuration, when the second image carrier is cleaned, an alternating current component is superimposed on the bias of the charging means, so that reciprocating motion of the remaining toner occurs.
Charge can be uniformly applied to the remaining toner. The frequency of the AC component is preferably 1000 to 6000 Hz, more preferably 3000 to 5000 Hz.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a sectional view of a color image forming apparatus according to the present embodiment. In addition, the same reference numerals are given to the same components and operation members as those of the image forming apparatus shown in FIG. 4, and the description thereof will be omitted as appropriate.

In the first embodiment, a contact-type charging unit, specifically, an elastic roller having a plurality of layers is used as the transfer-member cleaning roller 8 as a charging unit for the secondary transfer residual toner on the intermediate transfer belt 10. Used. And
A DC power supply 8a and an AC power supply 8b are connected to the transfer cleaning roller 8 to apply a bias in which a DC voltage and an AC voltage are superimposed. The occurrence of cleaning failure and cleaning ghost was confirmed under the following conditions. (Common conditions) Environment: temperature 30 ° C., humidity 80% RH Secondary transfer bias (constant current control): +10 μA Cleaning charging AC voltage: 2500 V _PP or less FIGS. 5 shows the occurrence of cleaning failure and cleaning ghost when the frequency of the DC component and the AC component of the cleaning bias applied to the cleaning bias is changed. X indicates a case where cleaning failure or cleaning ghost has occurred in the entire image, and 場合 indicates a case where cleaning ghost has occurred in a part of the image. 〇 indicates a case where no occurrence has occurred.

FIG. 5 shows a case where no alternating current is superimposed. There is no area where neither the cleaning failure nor the cleaning ghost has occurred, and the charge application is still uneven.

FIG. 6 shows a case where an AC component of 500 Hz is superimposed. In the case where the alternating current of 500 Hz is superimposed, there is no area where neither the cleaning failure nor the cleaning ghost occurs, almost in the same manner as in the case where the alternating current is not superimposed, and it can be said that the application of electric charge is still non-uniform.

FIG. 7 shows a case where an AC component of 1000 Hz is superimposed. At 1000 Hz, a condition is found under which neither cleaning failure nor cleaning ghost occurs. However, the margin of the DC component current is narrow.

FIG. 8 shows a case where a 3000 Hz alternating current is superimposed. When the frequency is increased to 3000 Hz, the area where neither cleaning failure nor cleaning ghost occurs is widened. This is presumably because the reciprocating movement of the toner due to the AC voltage is increased and the charge is more uniformly applied.

FIG. 9 shows a case where a 5000 Hz AC component is superimposed. In the case of 5000 Hz, as in the case of 3000 Hz, there is a wide area where neither cleaning failure nor cleaning ghost occurs. However, the area is slightly narrower than in the case of 3000 Hz. This is probably because the frequency has increased and the toner has become unable to follow.

FIG. 10 shows a case where an alternating current of 6000 Hz is superimposed. When the frequency is increased to 6000 Hz, an area where neither cleaning failure nor cleaning ghost occurs is narrowed. This is probably because the frequency became too high and the toner could not follow.

FIG. 11 shows a case where an AC of 7000 Hz is superimposed. It is considered that the frequency is too high, so that the toner can no longer follow, and the effect of the superposition of the AC component cannot be seen.

As described above, the frequency of the AC component superimposed on the bias applied to the transfer body cleaning roller 8 is 100
0 to 6000 Hz is preferable, and 3000 to 5 is more preferable.
It can be seen that 000 Hz is good. <Second Embodiment> FIG. 2 is a sectional view of a color image forming apparatus according to a second embodiment. In addition, the same reference numerals are given to the same components and operation members as those of the image forming apparatus shown in FIG. 4, and the description thereof will be omitted as appropriate.

In the first embodiment, a contact-type roller charger is used as the charger after the secondary transfer. However, since a high-frequency region is used, a weak charging noise occurs. In addition, there is a disadvantage that using a roller that is resistant to environmental changes slightly increases the cost.

In the second embodiment, the secondary transfer residual toner charging means on the intermediate transfer belt 10 is
A non-contact charging electrode 8A was used.

The charging electrode 8A has an electrode width of 10 mm in the traveling direction (the direction of the arrow) of the intermediate transfer belt 10 and has a width of 10 mm.
The gap width between A and the intermediate transfer belt 10 is 70 μm.
And Using the non-contact type charging electrode 8A, cleaning failure and generation of a cleaning ghost are described in Embodiment 1.
As a result, the same effects as in the first embodiment were obtained, and the charging noise could be eliminated and the cost could be reduced while preventing the occurrence of cleaning failure and cleaning ghost.

Although the embodiment of the present invention is used with the intermediate transfer belt 10, it goes without saying that a similar effect can be obtained with the intermediate transfer drum.

[0041]

As described above, according to the present invention,
When the alternating current is superimposed on the bias applied to the charging means in order to remove the secondary transfer residual toner on the second image carrier (in the above-described case, the intermediate transfer belt), the frequency is set to 1000 to 60.
00Hz, more preferably 3000Hz-5000H
By setting z, stable cleaning of the second image carrier can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram illustrating a state of toner on an intermediate transfer belt.

FIG. 4 is a schematic configuration diagram of a conventional image forming apparatus.

FIG. 5 shows a cleaning failure when AC is not superimposed.
The figure which shows the state of a cleaning ghost.

FIG. 6 is a diagram showing a state of a cleaning failure and a cleaning ghost when an alternating current of 500 Hz is superimposed.

FIG. 7 is a diagram illustrating a state of cleaning failure and a cleaning ghost when an alternating current of 1000 Hz is superimposed.

FIG. 8 is a diagram illustrating a state of cleaning failure and a cleaning ghost when an alternating current of 3000 Hz is superimposed.

FIG. 9 is a diagram illustrating a state of cleaning failure and a cleaning ghost when an alternating current of 5000 Hz is superimposed.

FIG. 10 is a diagram illustrating a state of a cleaning failure and a cleaning ghost when an alternating current of 6000 Hz is superimposed.

FIG. 11 is a diagram illustrating a state of a cleaning failure and a cleaning ghost when an AC of 7000 Hz is superimposed.

[Description of Signs] 1 First image carrier (photosensitive drum) 2 Contact type roller charger 3 Supporters 4a, 4b, 4c, 4d developing device 5 Transfer device 5a Primary transfer roller 6 Secondary transfer roller 7 Photosensitive drum cleaning Apparatus 8 Charging device (intermediate transfer belt cleaning device) 8A Charging device (charging electrode) 9 Fixing device 10 Second image carrier (intermediate transfer belt) 11 Exposure device

Claims (4)

[Claims] A first transfer unit configured to sequentially transfer a plurality of color toner images sequentially formed on a first image carrier to a second image carrier;
In an image forming apparatus for forming a color image on a transfer material by collectively and secondarily transferring a plurality of color toner images on the second image carrier onto a transfer material, a bias in which an AC component is superimposed on a DC component is provided. Is applied to impart a charge to the secondary transfer residual toner on the second image carrier, so that the secondary transfer residual toner on the second image carrier is transferred to the first toner simultaneously with the primary transfer. A color image forming apparatus, comprising: charging means for performing reverse transfer onto an image carrier, wherein a frequency of an AC component of a bias applied to the charging means is 1000 to 6000 Hz. 2. The frequency of the alternating current component is 3000 to 50.
The color image forming apparatus according to claim 1, wherein the frequency is set to 00 Hz. 3. The color image forming apparatus according to claim 1, wherein the second charging unit is a roller charger arranged in contact with the second image carrier. 4. The color image according to claim 1, wherein the second charging means is a charging electrode which is arranged in a non-contact and opposed manner to the second image carrier. Forming equipment.