JPH0635338A - Image forming device - Google Patents

Abstract

PURPOSE:To press-contact a transfer belt used for a transfer device with the surface of a photosensitive body with a uniform pressure distribution. CONSTITUTION:The device has such a structure for which a pair of substrates 2 for bearing and supporting holding rollers is supported so that they can be rocked by supporting one shaft end part of a driving shaft 32A for the holding roller for stretching a transfer belt 31 and which is positioned on a downstream side in a carrying direction in a U-shaped notched hole, and also, both shaft end parts of the holding roller on an upstream side in the carrying direction and the substrate 2 positioned on a side facing the notched hole are respectively energized upward by compression coil springs S1 and S2. Respective compression coil springs S1 and S2 are released from press-contacting by rotating an eccentric cam for pressing a roller member K for the substrate 2 and retreating upward at the time of transfer, and then, the transfer belt 31 is in press-contact with the peripheral surface of the photosensitive drum with the uniform pressure distribution.

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]

Since this transfer belt is of a type in which a recording paper is pressed against the peripheral surface of the photosensitive drum and the toner image is transferred while being conveyed at a constant speed, the width direction of the photosensitive drum is reduced. It is necessary to make a pressure contact state with a uniform pressure distribution over the entire area.

However, since it is well-known that the transfer belt is a wide belt, it is difficult to press the photosensitive drum evenly on the photosensitive drum. Therefore, there is a concern that unevenness in image density may occur due to the pressure difference.

The present invention solves this problem and improves the result.
An object of the present invention is to provide an image forming apparatus equipped with a transfer belt device capable of transferring a high-quality image having an average density by pressing the transfer belt against the drum surface with a uniform pressure distribution in the width direction.

[0009]

SUMMARY OF THE INVENTION The above object is to provide an image forming apparatus including a transfer belt device for transferring a toner image formed on a rotating photosensitive member onto a transfer belt stretched between a plurality of rollers. The plurality of rollers are supported between a pair of substrates integrated with each other, one shaft end of one roller is fixed, the other shaft end is movable in the vertical direction, and the rollers are pivoted as fulcrums. This is achieved by an image forming apparatus provided with a transfer belt device, which is supported as much as possible, and presses the substrate upward at the time of transfer to press the transfer belt against the peripheral surface of the photoconductor.

[0010]

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 structure 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 denotes a scorotron charger, which applies a uniform charge of V _{H to} the peripheral surface of the photosensitive drum 10 to V _G.
It is given by a corona discharge with a grid and a corona discharge wire that are held at a potential. This scorotron charger
Prior to charging by 12, the PCL 11 using a light emitting diode or the like is exposed to eliminate the history of the photoconductor until the previous printing, and the peripheral surface of the photoconductor is neutralized.

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.

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, D of the AC bias and V _DC of V _AC during this time
The C bias is superimposed and applied. Since V _DC and V _H and the toner are charged with the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion, which has a higher potential than V _{DC, and} has a potential higher than V _DC. attached to a lower V _L portion of visualized (reversal development) is carried out.

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 by 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
When the latent image of is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M > V
_It may be an intermediate potential that becomes _L.

An image forming process similar to that of 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.

The structure of the transfer belt device 30 will be described with reference to FIGS.

Transfer belt provided in the transfer belt device 30
31 is retracted to a position separated from the peripheral surface of the photosensitive drum 10 during non-transfer of an image, that is, during formation of a toner image,
The position is automatically switched so that it comes into pressure contact with the peripheral surface only during transfer.

2 and 3 are cross-sectional views and side views of the transfer belt device 30 during non-transfer, FIGS. 4 and 5 are cross-sectional views and side views during transfer, and FIG. 6 is a photosensitive drum. 3 is a plan view of the transfer belt device 30 viewed from the 10 side. FIG.

Reference numeral 1 is a casing of the transfer belt device 30, and 2 is a pair of rocking substrates for holding the transfer belt 1. The substrate 2 integrated via the connecting members 2A and 2B is:
During that time, the transfer belt 31 is held in a transportable state,
The casing 1 is housed in a rotatable state.

That is, the transfer belt 31 is stretched between a holding roller 32 on the downstream side of conveyance, a holding roller 33 on the upstream side of conveyance, and tension rollers 34 and 35, which are bearing-supported between the rocking substrates 2. It is conveyed counterclockwise by the drive of the holding roller 32.

The drive shaft 32A of the holding roller 32 is
As shown in FIG. 6, both shaft ends are rotatably supported by the casing 1, and a drive gear G0 for transmitting power from the main body of the apparatus is attached to the shaft end on the front side, while the rear side The bearing member B for supporting the shaft end portion of the above is engaged with the cutout hole 1A of the casing 1 so that only the shaft end portion can move slightly upward while maintaining the bearing state.

Each of the rocking substrates 2 is provided with a pair of compression coil springs S1 supported by the guide pins 3 of the casing 1.
Further, only the oscillating substrate 2 on the back side is biased upward by the compression coil spring S2 supported by the guide pin 4 via the receiving plate 2C.

On the other hand, each of the rocking substrates 2 has a rotatable roller member K projecting from the outer surface thereof, and abuts against a pair of eccentric cams C provided on both sides of the photosensitive drum 10. Has been done.

The eccentric cam C is rotated through gears G1 and G2 and G3 on both shaft ends of the parallel shaft 5 installed outside the peripheral surface of the photosensitive drum 10, and has a rotation phase. Similarly, the roller member K is contacted in a balanced manner.

At the time of non-transfer, the parallel shaft 5 is rotated by an image formation start signal from the controller to set the eccentric cam C to the angle shown in FIG. 3, whereby the roller member K is compressed by the compression coil spring S1. It is pressed so as to occupy the lowermost position against the bias of S2.

As a result, the transfer belt 31 is separated from the peripheral surface of the photosensitive drum 10 and retracts downward to enable the formation of the toner image described above.

On the other hand, at the time of transfer, the parallel shaft 5 is further rotated by 1/2 in response to an image formation end signal from the control section to set the eccentric cam C to the angle shown in FIG. Put K in a free state.

As a result, the oscillating base plate 2 has the compression coil spring S.
The drive shaft 32A of the holding roller 32 is oscillated in a clockwise direction by the urging force of 1, and the outer peripheral surface of the transfer belt 31 is pressed against the peripheral surface of the photosensitive drum 10 to form an image transfer area 38. Let

At this time, the transfer belt 31 is always in parallel with the rotation axis of the photosensitive drum 10 by the oscillating substrate 2 on the back side being further urged by the compression coil spring S2 as described above. Since it is pressed, the photosensitive drum
It is pressed against the peripheral surface of 10 with a uniform pressure in the depth direction.

The recording paper P supplied to the transfer area 38 is pressed against the peripheral surface of the photosensitive drum 10 by pressure contact of the transfer belt 31, and a transfer electric field is applied by corona discharge of the transfer device 36 to rotate the recording paper P around the drum. The multicolor image on the surface is transferred.

In this case, since the recording paper P is brought into close contact with the peripheral surface of the drum by the transfer belt 31 with an even pressure distribution, the transfer of the multicolor image on the peripheral surface of the drum is carried out evenly and the density is uniform. A copy of the color image is obtained.

The recording paper P to which the multicolor image has been transferred in the transfer area 38 is conveyed to the photosensitive drum by the transfer belt 31.
Fixing device consisting of two pressure rollers separated from the peripheral surface of 10 and then having a heater inside at least one of the rollers
It is fed to 23, and the heat and pressure are applied between the pressure-bonding rollers to melt the adhered toner, which is fixed on the recording paper P and then discharged to the outside of the apparatus.

On the other hand, in the transfer belt device 30, the parallel shaft 5 is further rotated 1/2 the angle shown in FIG. 5 in response to an image transfer end signal from the control unit, and the eccentric cam C again moves the roller member K downward. The transfer belt 31
Is separated from the peripheral surface of the drum and retracted.

On the other hand, the photosensitive drum 10 whose pressure contact with the transfer belt 31 has been released is subjected to static elimination by the static eliminator 15 using an AC corona discharger to remove the residual toner on the peripheral surface thereof, and then the cleaning device 16 is moved to the photosensitive drum. It is scraped off into the cleaning device 16 by the cleaning blade 16a made of a rubber material abutting against it, discharged by a screw or the like, and then stored in the recovery box. Depending on the arrangement of the static eliminator 15, the static eliminator 15 can also serve as static eliminator for 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.

[0041]

According to the present invention, the recording paper fed to the image transfer area is evenly adhered to the photosensitive surface,
As a result, an image forming apparatus provided with a transfer belt device capable of reliably transferring a toner image to obtain a high quality image is provided.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of a transfer belt device included in the above device at the time of non-transfer.

FIG. 3 is a side view of the transfer belt device.

FIG. 4 is a sectional view of the transfer belt device during transfer.

FIG. 5 is a side view of the transfer belt device.

FIG. 6 is a plan view of the transfer belt device.

[Explanation of symbols]

 10 Photosensitive drum 12 Charging device 13 Image exposure means 14 Developing device 16 Cleaning device 21 Paper feeding cassette 23 Fixing device 30 Transfer belt device 31 Transfer belt 32, 33 Holding roller 32A Drive shaft 34, 35 Tension roller 36 Transfer device 37 Cleaning blade K Roller member S1, S2 Compression coil spring

Claims (1)

[Claims] 1. An image forming apparatus including a transfer belt device for transferring a toner image formed on a rotating photosensitive member onto a transfer belt stretched between a plurality of rollers, wherein the plurality of rollers are integrated. Supports between a pair of substrates, 1
One of the rollers has one shaft end fixed and the other shaft end movable in the vertical direction to swingably support the roller as a fulcrum. An image forming apparatus comprising a transfer belt device, wherein the transfer belt is brought into pressure contact with the peripheral surface of a photoconductor.