JPH0635340A - Image forming device - Google Patents

Abstract

PURPOSE:To realize an image recorder provided with a transfer belt device which keeps a transfer belt clean without belt wear, and ensures satisfactorily recorded images over a long period of time. CONSTITUTION:The image forming device provided with the transfer belt device 31 which transfers a toner image formed on a rotating photosensitive drum 10 to the surface of recording paper P by means of the transfer belt 31 and a corona discharger 36 situated on the back of the belt is further provided with a cleaning means which makes a cleaning roller 37 abut to holding rollers 32 and 33 via the transfer belt 31 and carries out cleaning by the application of a bias between the rollers 33 and 37.

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, and particularly 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 adheres to 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 an 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]

It is an object of the present invention to use a transfer belt for a long period of time, and toner, paper dust, etc. will gradually adhere to the transfer belt. Also, when a toner image on the photoconductor drum is transferred onto recording paper, if a jam occurs during transfer and corona discharge occurs without the recording paper reaching the transfer area, the toner image on the photoconductor drum Is transferred onto the transfer belt, and the transfer belt is greatly soiled. When the transfer belt is dirty, the back surface of the recording paper is soiled and the quality is degraded, so the transfer belt is cleaned. As a cleaning means for the transfer belt, a blade or a fur brush is brought into contact with the transfer belt for cleaning. However, when a blade cleaning means is used, the transfer belt and the blade are worn, the durability is shortened, and the cleaning performance is deteriorated. Further, the fur brush has a problem that the capability is insufficient at the time of jamming and the like, and the removed toner is scattered.

It is an object of the present invention to provide an image forming apparatus equipped with a transfer belt device which is excellent in durability and maintains good cleaning performance with little abrasion of the transfer belt.

[0008]

SUMMARY OF THE INVENTION The present invention achieves the above object. The present invention records a toner image formed on a rotating photoconductor drum by corona discharge from a transfer belt stretched between holding rollers and its back surface. In an image forming apparatus having a transfer belt device for transferring onto paper, a roller is brought into contact with one of the holding rollers via a transfer belt, and the roller is interposed between the two rollers with respect to the holding roller. It is an object of the present invention to provide an image forming apparatus characterized in that cleaning means for cleaning a transfer belt by applying a bias so as to have a potential difference of the same polarity as that of corona discharge is provided.

[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
Is not adhering to the portion, but is adsorbed to the portion of V _{L having} a lower potential than V _DC to be visualized (reverse development).

After the visualization of the first color is completed, the image forming process for the second color is started, the uniform charging is performed again by the scorotron charger 12, and a latent image based on the image data for 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 adsorbed on the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, V is applied over the entire peripheral 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. the part for a latent image of V _M 'is formed by the charge possessed by the shading and toner itself by adsorption toner of the first color, 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 feed cassette 21 by the paper feed mechanism 22 is transferred to the transfer belt 31 which will be described later.
The multi-color image on the peripheral surface of the photoconductor drum 10 is fed all at once to the recording paper P by the transfer belt device 30 which is stretched.
Moved to the top.

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 provided 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.
A voltage of _PC (1.0 to 3.0 kV) is applied, and this shaft 32
A conductive brush 34 is grounded as a means for applying a charge to the recording paper P at a position where it is installed on the sheet a through the transfer belt 31, or is grounded via a non-linear element or a resistor. The fed recording paper P enters between the brush 34 and the transfer belt 31, and the brush 34 injects an electric charge into the recording paper P, so that an attraction force is exerted between the recording paper P and the transfer belt 31. Occurs. 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. A pressure roller 39 is provided close to the upstream side of the nip portion 35 in order to ensure pressure contact and transfer.

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.
Transfer belt 31 after receiving static electricity by AC corona discharge with the counter electrode as the counter electrode, or while receiving AC corona discharge.
Separate from. The toner attached to the transfer belt 31 is cleaned by a cleaning unit using a cleaning roller 37, which will be described later with reference to FIG.

The recording paper P, which holds 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, and then is removed from a rubber material which is in a cleaning device 16 and abuts on the photosensitive body. It is scraped off into the cleaning device 16 by the cleaning blade 16a, discharged by a screw or the like, and then stored in the recovery box. Depending on the arrangement, the above-mentioned static eliminator 15 can be arranged at a position as shown in FIG. 1 and can also serve as static erasing of the recording paper at the same time.

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.

2 shows the transfer belt device 30 of the image forming apparatus shown in FIG. 1 taken out, and FIG. 2 (b) shows the transfer belt 31 separated from the photosensitive drum 10. (A) shows a transfer state in which the transfer belt 31 is in contact with the photosensitive drum 10 via the recording paper P. Holding roller
A cleaning roller 37, which is made of metal or conductive resin and is rotatable, is brought into contact with the transfer roller 33 via the transfer belt 31. The holding roller 33 is grounded and the cleaning roller 37 is grounded.
The cleaning power source E (37) applies a positive bias (2 KV) to 37. In addition, this cleaning device has a switch S (37)
The switch S (37) may be turned on in conjunction with the transfer operation shown in FIG. 2 (a) to apply a cleaning bias, or may be turned on only while the transfer belt 31 is rotating for cleaning. A bias may be applied, or it may remain ON regardless of the operating state of the transfer belt 31.

Since the toner that has moved from the photosensitive drum 10 to the transfer belt 31 before and after the transfer or during the transfer is negatively charged by the peeling discharge, the toner attached to the transfer belt 31 comes into contact with the cleaning roller 37 and passes through. At this time, the transfer belt 31 is cleaned by being attracted to the cleaning roller 37 to which a positive bias is applied. The toner attracted to the cleaning roller 37 is the cleaning roller.
It is scraped off by an elastic blade 37a made of PET, rubber, or the like, which is in sliding contact with 37. When the cleaning means having such a structure is used, the belt is hardly worn and the cleaning means is also excellent in durability, so that good cleaning performance is maintained for a long period of time.

In an image forming apparatus using such a belt transfer device, if a recording sheet is not present in the nip portion 35 at the time of transfer due to a jam or the like immediately before transfer, a large amount of toner is attracted to the transfer belt 31. To do. In such a case, if the cleaning belt is only passed once, the transfer belt
31 cleaning is inadequate. Therefore, when such a jam occurs, a jam program is prepared in advance, and the cleaning roller in the state in which the bias with the switch S (37) turned on in the recovery operation is applied.
By allowing the transfer belt 31 to pass through the 37 part multiple times and repeating insufficient cleaning once,
A complete cleaning can be done. Further, the rotational driving for cleaning the transfer belt 31 is performed such that the transfer belt 31 is in contact with the photoconductor drum 10 as shown in FIG. 2A, and the transfer discharge is also performed by the corona discharger 36 to clean the transfer belt 31. Will improve further. Also, during rotation driving for cleaning the transfer belt 31, the photosensitive drum
10 also rotates without image formation, cleaning device
By sliding the cleaning blade 16a of 16 onto the photosensitive drum, not only the transfer belt 31 but also the photosensitive drum 10
Also, the recovery operation after the jam is performed.

[0028]

According to the present invention, the transfer belt is always kept in a clean state without fear of wear and the like.
An image forming apparatus having a highly reliable transfer belt device capable of obtaining a good recorded image for a long period of time is provided.

[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 an explanatory diagram showing a configuration of a transfer belt device of the present invention.

[Explanation of symbols]

 10 Photoconductor drum 11 PCL 12 Scorotron charger 13 Image exposure means 14 Developing device 15 Static eliminator 16 Cleaning device 21 Paper feeding cassette 22 Paper feeding mechanism 23 Fixing device 30 Transfer belt device 31 Transfer belt 32, 33 Holding roller 34 Brush (charge Applying means) 35 Nip part (transfer area) 36 Corona discharger (for transfer) 37 Cleaning roller (transfer belt) 37a Blade (cleaning roller) 39 Pressing roller E (37) Power supply (for cleaning) S (37) Switch (cleaning) (For power supply)

Claims (3)

[Claims] 1. An image forming apparatus having a transfer belt in which a toner image formed on a rotating photosensitive drum is stretched between holding rollers and a transfer belt device for transferring the toner image onto a recording sheet by corona discharge from the back surface thereof. A roller is brought into contact with any one of the holding rollers via a transfer belt, and a bias is applied to the holding roller so that the roller has a potential difference of the same polarity as the corona discharge to clean the transfer belt. An image forming apparatus provided with a cleaning unit for performing. 2. The image forming apparatus according to claim 1, wherein when a jam occurs, the transfer belt operates so as to pass through the cleaning means a plurality of times. 3. The image forming apparatus according to claim 2, wherein the corona discharge is performed during the operation.