JPH0635335A - Image forming device - Google Patents

Abstract

PURPOSE:To remove residual charges from the photosensitive drum periphery which has finished transfer while reducing the production of ozone to the lowest amount possible, in an image forming device with a transfer belt device. CONSTITUTION:The image forming device is provided with the transfer belt device which transfers a toner image formed on a photosensitive drum 10 to recording paper by means of a transfer belt 31 and corona discharge carried out from the back of the belt by a corona discharger 36. A destaticizing unit 15 which carries out AC destaticization from the periphery of the photosensitive drum 10 which has finished transfer is provided opposite the drum periphery, and it is turned on only for a dishcahrge area subjected to transfer discharge by the corona discharger 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine and uses a transfer belt device having a rotating transfer belt to transfer a toner image obtained by developing a latent image on an image carrier. The present invention relates to an image forming apparatus that transfers a recording sheet having a toner image to a fixing unit after transferring the recording sheet onto the recording sheet by a physical unit to fix the recording sheet.

[0002]

BACKGROUND OF THE INVENTION In an image forming apparatus such as an electrophotographic copying machine, after uniformly charging a peripheral surface of a photosensitive drum, which is an image carrier, by a charger, image exposure is performed on the peripheral surface of the photosensitive drum. To form an electrostatic latent image. This latent image is developed and visualized by developing means to become a toner image. The toner image formed on the peripheral surface of the photosensitive drum is transferred by a physical means onto the recording paper fed at a timing, and the recording paper on which the toner image is transferred is separated from the photosensitive drum and fixed by the fixing means. The toner image is conveyed onto the recording paper, fixed on the recording paper, and then discharged to the outside of the apparatus.

As a transfer means for transferring the toner image adhering to the peripheral surface of the photosensitive drum onto the recording paper, the toner having a polarity opposite to the charging polarity of the toner is applied by a transfer device which discharges from the back of the recording paper. The image is transferred to the recording paper,
After the transfer, a high voltage of alternating current is applied by the separator to eliminate the charge, and the recording paper is separated from the photosensitive drum. However, it is difficult to reliably maintain transferability and separability, especially when the drum diameter of the photoconductor drum is large, it is difficult to separate, and the recording paper after the transfer of the toner image is adsorbed on the photoconductor drum without being separated. It has the drawback that it tends to cause paper jams. A transfer belt device is used as a technique for improving this drawback.

The transfer belt device rotates a transfer belt stretched by a plurality of holding rollers at the same speed as the photosensitive drum. The transfer belt device is provided with a charge applying unit that applies an electric charge to the recording paper and causes the recording paper to be attracted to the transfer belt by electrostatic force. And a high voltage having a polarity opposite to the toner charging polarity is applied under constant current control at the transfer portion to transfer the toner image. With such a transfer belt device, excellent transfer efficiency and separation effect can be obtained at the transfer portion.

Such a transfer belt device is used as a particularly preferable device in a color image forming device in which a toner image is superposed on a photosensitive drum and transferred onto a recording sheet at a time. In such a color image forming apparatus, since a plurality of developing devices are provided at the peripheral portion of the photoconductor drum in order to superimpose toner images on the photoconductor, the drum diameter becomes large, and sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation system. Therefore, a more reliable separation performance is required, and a toner transfer amount is large in the method of superposing toner images, a large transfer charge amount is required, and thus a large transfer charge holding ability is required. This is because the transfer belt device is excellent in two respects.

[0006]

SUMMARY OF THE INVENTION However, a photosensitive drum as shown in FIG.
A corona discharger 136 is provided on the back surface of the transfer belt 131 at the nip portion 135 where the transfer belt 131 stretched between the holding rollers 132 and 134 contacts the 110, and corona discharge is performed, and the transfer belt 131 is attracted to the transfer belt 131. When the transfer is performed on the conveyed recording paper P, the recording paper P after the transfer is transferred to the photosensitive drum 11
When separated from 0, peeling discharge occurs between the recording paper P and the photoconductor drum 110, and the photoconductor drum 110 and the photoconductor drum 110
The residual toner that has adhered to the upper portion after the transfer is charged to the same polarity as that of the transfer. If the photoconductor drum 110 is in this charged state, it adversely affects the charging at the time of the next image formation, and if the residual toner is in this charged state, blade development due to cleaning is likely to occur. Therefore, a static eliminator is provided and an AC alternating bias voltage is applied to remove the static electricity.

However, when AC neutralization is performed, a large amount of ozone is generated at that time, and the discharge product adheres to the wire of the static eliminator to reduce the static elimination effect. An object of the present invention is to provide an image forming apparatus capable of obtaining a good image while preventing the generation of ozone from the static eliminator and the adhesion of discharge products as much as possible.

[0008]

SUMMARY OF THE INVENTION The present invention achieves the above object. The present invention is a transfer belt device for transferring a toner image formed on a rotating photosensitive drum onto a recording paper by corona discharge from the transfer belt and its back surface. In the image forming apparatus having the above, a static eliminator that performs AC static elimination from the peripheral surface of the photoconductor drum that has been transferred is provided to face the peripheral surface of the photoconductor drum, and the static eliminator is provided with respect to the discharge area where the transfer discharge is performed. An image forming apparatus characterized in that it is configured to be turned on only. It is a preferred embodiment that the static eliminator simultaneously performs AC static erasing on the recording paper before separation from the transfer belt.

[0009]

FIG. 1 is a sectional view showing the construction of a color image forming apparatus as an embodiment of the image forming apparatus of the present invention.

First, the configuration and operation will be described.

In the figure, reference numeral 10 is a photosensitive drum which is an image bearing member, which is formed by coating an OPC photosensitive layer on the drum and is grounded and rotated clockwise. Reference numeral 12 is a scorotron charger, and _VH (-600 to -800) is applied to the peripheral surface of the photosensitive drum 10.
The uniform charging of V) is given by a corona discharge by a grid and the corona discharge wire which is the potential held in the V _G (-550~-850V). Prior to the charging by the scorotron charger 12, the peripheral surface of the photoconductor is neutralized by exposure by the PCL 11 using a light emitting diode or the like in order to eliminate the history of the photoconductor until the previous printing.

After uniformly charging the photosensitive member, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 through a polygon mirror 131 that rotates using a laser diode (not shown) as a light emitting source, an fθ lens, and the like.
The optical path is bent by 32 and scanning is performed, and a latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10.
In this embodiment, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L (-100V to 0).

Yellow (Y) on the periphery of the photosensitive drum 10,
Developers each containing a developer composed of toner such as magenta (M), cyan (C), black (K), and a carrier.
14 is provided, and first, the development of the first color is performed by the developing sleeve 141 which contains a magnet and holds the developer and rotates. The developer is a carrier in which a ferrite core is coated with an insulating resin around it, a polyester as a main material, a pigment according to the color, and a charge control agent,
It consists of toner to which silica, titanium oxide, etc. have been added.
The layer is regulated to a layer thickness of ~ 600 μm and conveyed to the developing zone.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.4 to larger than the layer thickness (developer).
As 1.0mm, _{AC of} VAC (1.5 to 3.0KV _PP ) during this period
A DC bias of V _DC (−500 to −700 V) is superimposed and applied. V _DC and V _H, for charging the toner are both the same polarity, the toner given the opportunity to leave from the carrier by V _AC higher potential than V _DC V _H
The parts do not adhere, visualized attached to lower V _L portion of potential than V _DC (reversal development) is carried out.

After the visualization of the first color is completed, the process proceeds to the image forming process of the second color, uniform charging is performed again by the scorotron charger 12, and a latent image based on the image data of the second color is formed by the image exposing means 13. To be done. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Once again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M 'and V _M '. In the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
Performed to create a latent image, since the balance between the first color and the second color is lost, reducing the exposure amount of the first color V _H> V _M (-
It may be an intermediate potential such that 100 to −300 V)> _VL .

An image forming process similar to that for the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, the recording paper P fed from the paper feeding cassette 21 by the paper feeding mechanism 22 is fed to the transfer area by the transfer belt device 30 in which the transfer belt 31 is stretched, and the peripheral surface of the photosensitive drum 10 is fed. The above multicolor image is collectively transferred onto the recording paper P.

The transfer belt 31 has a thickness of 0.4 having a resistance of 10 ⁶ to 10 ¹⁴ Ω · cm formed by forming an outer FLC layer of a urethane rubber base.
An endless rubber belt of ~ 1.0mm, ribs may be provided at the ends to prevent deviation during rotation.

A film such as PET or a high resistance belt such as a film coated with these may be used if a charge removing mechanism is provided.

A holding roller 3 that stretches the transfer belt 31.
V is applied to the shaft 32a of the upstream holding rollers 32 of 2, 33.
The voltage of _PC (1.0-3.0KV) is applied, and this shaft 32
A conductive brush 34 is grounded as a means for applying a charge to the recording paper P or is grounded via a non-linear element resistor at a position where it is installed on a through the transfer belt 31. The recording paper P that has been fed enters between the brush 34 and the transfer belt 31, and electric charges are injected into the recording paper P by the brush 34,
A suction force is generated between the transfer belt 31 and the transfer belt 31. After that, the recording paper P enters the nip portion (transfer area) 35 formed by the photoconductor drum 10 and the transfer belt 31, and the transfer electric field is generated from the back surface of the transfer belt 31 by the corona discharger 36 or the bias roller instead. A multicolor image is transferred onto the recording paper P.

The recording paper P separated from the photosensitive drum 10 is
The shaft 33a of the holding roller 33 on the downstream side which stretches the transfer belt 31.
Is used as a counter electrode after being subjected to charge removal by AC corona discharge by a charge remover 15 to be described later, or separated from the transfer belt 31 while receiving AC corona discharge. A cleaning blade 37 removes the toner attached to the rotating transfer belt 31. The transfer belt 31 of this transfer belt device 30
During the formation of a multicolor image, is separated from the photoconductor drum 10 about the shaft 33a of the holding roller 33 on the downstream side as a rotation center.

The recording paper P holding the multicolor image separated from the transfer belt device 30 is conveyed to a fixing device 23 composed of two pressure-bonding rollers having a heater inside at least one roller, and is transferred between the pressure-bonding rollers. The applied toner is melted by applying heat and pressure, fixed on the recording paper P, and then discharged to the outside of the apparatus.

After the transfer, the residual toner remaining on the peripheral surface of the photosensitive drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, which will be described later in detail with reference to FIG. Cleaning device using a cleaning blade 16a made of a rubber material and abutting on the photoconductor
It is scraped off into the inside of the chamber 16, discharged by a screw, etc., and then stored in the collection box. The static eliminator shown in the above embodiment
Reference numeral 15 is arranged so that it also serves as static elimination of the recording paper as shown in FIG.

The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 16 is exposed by the PCL 11 and then uniformly charged by the scorotron charger 12.
Enter the next image forming cycle. The cleaning blade 16a is separated from the surface of the photoconductor during the formation of the multicolor image,
AC neutralization by 15 is kept in OFF state.

FIG. 2 shows the positional relationship of the static eliminator 15, FIG. 3 shows the structure of the static eliminator 15, and FIG. 4 shows a time table for the static eliminator 15 to perform AC corona discharge. Furthermore, FIG.
3A shows a cross-sectional shape of the static eliminator 15, and FIG. 3C shows a shape of the static eliminator 15 as seen from the photosensitive drum 10 side. The static eliminator 15 has both ends of a wire 151 stretched and supported by an insulating support body 152 made of a resin material, and has metal shield members 153 on both sides.
And the shield member 153 is grounded. As shown in FIG. 2, the wire 151 is stretched parallel to the axis of the photosensitive drum 10 and slightly shorter than the drum length. Since the wire 151 vibrates when an AC high voltage is applied, as shown in FIG. 3C, the static eliminator 15 is provided with a rib-shaped vibration preventive portion 152b on the insulating support 152 so that the wire 151 is removed. It prevents it from vibrating. Figure 3 (b)
Shows the cross-sectional shape of the portion of the static eliminator 15 where the vibration prevention portion 152b is provided. The static eliminator 15 having a front opening 154 having a width of about 9 mm faces the photoconductor drum 10 at intervals of about 2 mm, and the back surface of the static eliminator 15 has a rear opening 155 of about 3 mm, and the holding roller 33. About 6 mm on the transfer belt 31 that winds up
Are facing each other.

FIG. 4 shows a timetable in which the static eliminator 15 of the present invention arranged as shown in FIG. 2 performs AC corona discharge. The corona discharger 36 which gives a transfer electric field from the back surface of the transfer belt 31 is shown. The static eliminator 15 is approximately the same time T as the electric field application time T, and is delayed by a time t from the time when the corona discharger 36 is turned on (approximately the same time when the recording paper reaches the transfer area).
Is controlled to turn on. The time t is the time required for a point on the peripheral surface of the photoconductor drum 10 in the transfer area to reach a position facing the static eliminator 15. In the ON state, the static eliminator 15 has 650 Hz, V _PP 7 AC corona discharge of ~ 10KV is performed.

By performing the AC corona discharge, the post-transfer peeling discharge on the photosensitive drum 10 removes the positively charged portion having the same discharge polarity as that of the corona discharger 36, and moves to the cleaning device 16.

According to a study by the present inventor, when the charge removal by the charge remover 15 is insufficient and a positive charge remains on the photoconductor and the residual toner after transfer, not only is cleaning difficult. , The negative charge is also removed by the exposure of PCL11, so that a deterioration of the image quality of the image formed next is recognized as a history, but according to the present invention, the remaining charge of the image area is completely removed. No deterioration in image quality was observed in the image formed next.

When the recording paper is separated from the transfer belt 31 at the same time as the charge is removed from the photoconductor drum 10, the recording paper on the transfer belt 31 and immediately before the transfer is kept so that the toner on the recording paper is not scattered by the peeling discharge. Similarly, static elimination is performed.
In this case, since the color toner is electrostatically adhered on the recording paper, the static electricity removing electric field having a proper strength is used with the holding roller 33 as the counter electrode so that the toner image is not disturbed even by the AC corona discharge. Is granted. The recording paper P that has been adsorbed and conveyed to the transfer belt 31 is separated from the transfer belt 31 while being discharged by the holding roller 33 having a small diameter, and is conveyed to the fixing device 23.

[0031]

In the image forming apparatus having the transfer belt device of the present invention, although the AC charge is removed, ozone is not generated much and the discharge products on the wire are not attached, so that the image forming apparatus can be used for a long time. It is now possible to obtain good quality images.

[Brief description of drawings]

FIG. 1 is a configuration sectional view showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a layout view showing a layout positional relationship of the static eliminator of the present invention.

FIG. 3 is a cross-sectional view and a front view of a static eliminator.

FIG. 4 is a time table showing the operation of the static eliminator.

FIG. 5 is an explanatory diagram showing a configuration of a conventional transfer belt device.

[Explanation of symbols]

 10 Photoconductor drum 11 PCL 12 Scorotron charger 13 Image exposure unit 14 Developer 15 Static eliminator 151 Wire 152 Insulating support 153 Shield member 154 Front opening 155 Back opening 16 Cleaning device 21 Paper cassette 22 Paper feeding mechanism 23 Fixing Device 30 Transfer belt device 31 Transfer belts 32, 33 Holding roller 34 Brush (charge applying means) 35 Nip part (transfer area) 36 Corona discharger (for transfer)

Claims (2)

[Claims] 1. An image forming apparatus having a transfer belt device for transferring a toner image formed on a rotating photosensitive drum onto a recording sheet by corona discharge from a transfer belt and a back surface of the transfer belt. An image forming apparatus characterized in that a static eliminator that performs AC static erasing from the peripheral surface is provided so as to face the peripheral surface of the photoconductor drum, and the static eliminator is turned on only in the discharge region where the transfer discharge has been performed. . 2. The image forming apparatus according to claim 1, wherein the static eliminator simultaneously removes AC static electricity from the transfer belt to the recording paper before separation.