JPH05297724A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device provided with a transfer belt device whereby transfer can be satisfactorily and steadily carried out irrespective of environment such as temperature and humidity. CONSTITUTION:In the image forming device provided with the transfer belt device which transfer a toner image, formed on a photosensitive drum 10, to a recording sheet by the use of a transfer belt 31 and by carrying out corona discharge from the back of the belt 31 by the use of a corona discharger 36, a pressure roller 39 composed of a metal roller covered with an elastic body 39a such as an elastic rubber or foamed resin is set inside the transfer belt 31 further upstream than a transfer area (nip part), and the transfer belt 31 is pressed against the photosensitive drum; the pressure roller 39 is grounded, or bias having the same polarity as transfer bias is applied to the roller 39.

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 attached thereto onto a recording sheet by a physical means, and then conveys the recording sheet to a fixing means for fixing.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, after the peripheral surface of a photosensitive drum, which is an image carrier, is uniformly charged by a charger, the peripheral surface of the photosensitive drum is exposed to an image. 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 photoconductor drum is transferred by a physical means onto the recording paper fed at a timing, and the recording paper on which the toner image has been transferred is separated from the photoconductor drum and fixed by the fixing means. The toner image is fixed on the recording paper and then discharged to the outside of the apparatus.

As a transfer means for transferring the toner image adhered on the peripheral surface of the photosensitive drum onto the recording paper, a 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 it is difficult to separate, especially when the drum diameter of the photoconductor drum is large, and the recording paper on which the toner image has been transferred 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 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. In such a transfer belt device, excellent transfer efficiency and separation effect can be obtained in the transfer section.

Such a transfer belt device is used as a particularly preferable device in a color image forming device in which toner images are 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 on the peripheral portion of the photosensitive drum in order to superimpose toner images on the photosensitive member, the drum diameter becomes large, and sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation method. Therefore, more reliable separation performance is required, and in the method of superposing toner images, a large amount of toner is attached, and thus a large amount of transfer charge is required.Therefore, it is necessary to have a large transfer charge holding ability. 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.
At the nip portion 135 where the transfer belt 131 ′ stretched between the holding rollers 132 ′ and 133 comes into contact with the 110, the transfer belt 13
When a corona discharger 136 is provided on the back surface of 1'to perform corona discharge and transfer to the recording paper P adhered and conveyed to the transfer belt 131 ', sufficient transferability is not always obtained at low humidity. In some cases, no transfer was made, or transfer dropout occurred due to carrier adhesion. Further, when a pressing roller is provided for auxiliary pressing of the transfer belt against the photosensitive drum, transfer unevenness occurs unless the pressing force is uniform in the conveyance width direction. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus having a transfer belt device that always ensures good transferability without such unstable transfer.

[0007]

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 recording paper by corona discharge from the transfer belt and its back surface. In the image forming apparatus having the above, a pressing roller is installed inside the transfer belt on the upstream side of the contact position between the photosensitive drum and the transfer belt, and the pressing roller covered with a non-metallic elastic body is used. An image forming apparatus characterized in that the transfer belt is pressed against the photosensitive drum.

[0008]

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 obtained by coating an OPC photosensitive layer on the drum, and is grounded and rotated clockwise. 12 is a scorotron charger, which is _VH (-600 to -800V) with respect to the peripheral surface of the photosensitive drum 10.
Grid and the corona discharge wire which uniform charging has been potential held in the V _G (-550~-850V) of given by a corona discharge by. 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 photoconductor, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 via 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 ferrite is used as a core and an insulating resin is coated around the core, polyester is used as a main material, and a pigment and a charge control agent are used according to the color.
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).
1.0mm, _{AC of} VAC (1.5 to 3.0KV _PP ) during this period
A DC bias of Ba _dc and _VDC (-500 to -700V) 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 process proceeds to the image forming process of the second color, the uniform charging is performed again by the scorotron charger 12, and the 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 sudden decrease in the potential around the image.

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 no image of the first color is developed, but the portion of the photoreceptor having the first color image is developed again. At the portion to be performed, the latent image of V _M ′ is formed by the toner attached to the first color to shield the light 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 ′. At 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 (-1
It may be an intermediate potential such that 00-300V)> _VL .

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 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 collectively fed 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 with 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 as long as 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 to 3.0KV) is applied, and this shaft 32
A conductive brush 34 is grounded as a means for imparting a charge to the recording paper P at a position where it is installed on 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 a nip portion (transfer area) 35 formed by the photosensitive drum 10 and the transfer belt 31, and a transfer electric field is generated from the back surface of the transfer belt 31 by a corona discharger 36 or a bias roller instead. The multicolor image is transferred onto the recording paper P. In the present invention, a pressing roller 39 is newly provided in order to perform this transfer stably and surely, which will be described later with reference to FIGS. 2 and 3.

The recording paper P separated from the photosensitive drum 10 is
Shaft 33a of the holding roller 33 on the downstream side that stretches the transfer belt 31
Transfer belt 31 after being subjected to neutralization by AC corona discharge with the counter electrode as the opposite electrode or while receiving DC corona discharge.
Separate from. A cleaning blade 37 removes the toner attached to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is separated from the photoconductor drum 10 about the shaft 33a of the holding roller 33 on the downstream side as a rotation center during the formation of the multicolor image.

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 has come into contact with the photosensitive member to a cleaning device 16. 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 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.

FIG. 2 shows a transfer belt device provided with a pressing roller 39 of the present invention. The pressing roller 39 is inside the transfer belt 31 upstream of the nip portion (transfer area) 35 where the photosensitive drum 10 and the transfer belt 31 having the corona discharger 36 on the back surface are in contact, and there is no pressing roller 39. At this time, the transfer belt device 30 is attached at a position where the outer circumference of the pressing roller 39 projects outside the belt from the common tangent line between the holding roller 32 and the photosensitive drum 10 formed by the belt being pressed against the drum. The transfer belt device 30 is capable of swinging about a shaft 33a of a holding roller 33 on the downstream side as a rotation center. During transfer of a multicolor image, as shown in FIG. 31 is in a separated position. Figure 2
(A) shows a posture at the time of transfer, in which the transfer belt 31 is pressed closely from the nip portion 35 toward the upstream side by the newly provided pressing roller 39 so as not to be close to the photosensitive drum 10. It has a region, and FIG.
As shown in the sectional view of (a) showing the pressing state of the pressing roller 39 against the photosensitive drum 10, the peripheral surface of the pressing roller 39, whose both ends are supported by bearing members 41 such as ball bearings, is made of elastic rubber or foam. The pressing roller 39 is covered with an elastic body 39a such as a resin material, and the pressing roller 39 is connected to the photosensitive drum via the transfer belt 31.
Abut on 10 with even pressing force. 3 (b) is shown in FIG.
The XX cross section in (a) is shown. The photosensitive drum 10 of this embodiment is a drum having a diameter of about 100 mm, the pressing roller 39 is a metal roller made of stainless steel or the like having a diameter of 6 to 10 mm and a length of about 300 mm, and the outer periphery thereof has a thickness of about 1 to 4 mm. It is covered with an elastic body 39a having a rubber hardness of about 25 to 45 °, both ends are supported by bearings 42, and is located at a position of about 10 to 30 mm upstream from the corona discharger 36 for transfer which is a transfer part,
The elastic body 39a is pressed and appropriately compressed and deformed, and is brought into contact with the photosensitive drum 10 in the axial direction (the recording paper conveyance width direction) with substantially the same pressing force, so that the photosensitive drum 10 and the transfer belt 31 come into contact with each other. By eliminating the air, a better contact state is obtained, and uniform transferability can be obtained with the elastic body 39a absorbing the effects of irregularities on the surface of the recording paper P and carrier adhesion.

Further, the pressing roller 39 in which carbon or the like is mixed in the material of the elastic body 39a and which is covered with a conductive metal roller as a conductive elastic body is rotated with the movement of the transfer belt 31, The flexible pressing roller 39 is grounded directly or through a non-linear element or a resistor. Transfer belt
The static electricity generated by the movement of 31 accumulates in the pressing roller 39 and discharges and causes noise.Therefore, in the present embodiment, the roller 39 is grounded to prevent accidents and noise due to discharge such as leakage. Will be prevented.

Furthermore, when a bias having the same polarity as the transfer bias applied to the corona discharger 36 is applied to the conductive pressing roller 39, the transfer is performed with the transfer area in the nip portion enlarged. Therefore, the transferability can be improved.

[0028]

According to the present invention, the transferability is improved by increasing the nip width by the transfer roller, and the unevenness of the thickness of the transfer belt or the recording paper and the unevenness of the pressing force due to the deflection of the pressing roller are observed. Transfer that is absorbed and is uniform and uniform in the width direction of the recording paper, good transferability is always secured, and reliable images can be obtained without causing accidents or noise due to discharge in the transfer section. An image forming apparatus having a belt device 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.

FIG. 3 is a cross-sectional view showing a state in which a pressing roller according to the present invention presses a photosensitive drum.

FIG. 4 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 16 Cleaning device 21 Paper 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 (transfer area) 36 Corona discharger (for transfer) 37 Cleaning blade (transfer belt) 39 Pressing roller 39a Elastic body 41 Bearing member

Claims (2)

[Claims] 1. An image forming apparatus having a transfer belt device for transferring a toner image formed on a rotating photoconductor drum onto a recording sheet by corona discharge from a transfer belt and a back surface thereof. A pressure roller is installed inside the transfer belt on the upstream side of the contact position with the belt, and the transfer belt is pressed against the photosensitive drum by the pressure roller covered with a non-metallic elastic body. An image forming apparatus characterized by the above. 2. The image forming apparatus according to claim 1, wherein the pressing roller is a conductive roller covered with an elastic body of elastic rubber or foaming resin.