JPH0836339A - Image-forming device - Google Patents

Abstract

PURPOSE:To prevent soiling on the rear face of transfer paper by applying a pressure roller a bias of polarity opposite to that of a transfer bias, and clearing away reversely electrified toner on an image carrier. CONSTITUTION:An image-forming device is equipped with a transfer member 24 which is applied with the transfer bias and pressed to the image carrier 11; and a transfer device 18 which transfers a visible image on the image carrier 11 to the transfer paper passing through the contact part with the image carrier 11. The image-forming device is provided with the pressure roller 14 which is rotatably provided in pressure-contact with the image carrier 11 between the developing device 13 and transfer device 18; and a pretransfer cleaner with a bias application means which applies the pressure roller 14 the biase of polarity opposite to that of the transfer bias.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a copying machine, a facsimile,
The present invention relates to an image forming apparatus such as a printer.

[0002]

2. Description of the Related Art In general, an image forming apparatus such as a copying machine, a facsimile, a printer, etc., has an image carrier on which an electrostatic latent image is formed and a visible image by developing the electrostatic latent image on the image carrier. And a transfer device for transferring the visible image on the image carrier to the transfer paper. Conventionally, the transfer device has often used a corona transfer system in which a visible image on the image carrier is transferred to a transfer paper by corona discharge. The contact transfer method has begun to be used because there is a possibility that the service life may be shortened due to the deterioration of the characteristics and the use environment may be adversely affected. This contact transfer system has a transfer member that is pressed against the image carrier by applying a transfer bias, and a visible image on the image carrier is transferred onto a transfer paper that passes through the pressure contact part between the transfer member and the image carrier. Is transferred.

Further, Japanese Patent Application Laid-Open No. 5-19645 discloses that
There is described a sheet guide device of an image forming apparatus in which a charging characteristic of a roll member for pressing a sheet against a photoconductor drum at a transfer section is controlled so that a toner image is effectively transferred.

[0004]

In the image forming apparatus adopting the contact transfer method, the reversely charged toner (background stain toner) adhered to the image carrier adheres to the transfer member and adheres to the back surface of the transfer paper. There is a problem that the back surface of the transfer paper becomes dirty.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of improving the above problems and preventing the back surface of a transfer sheet from being soiled.

[0006]

In order to achieve the above object, the invention according to claim 1 develops an image carrier on which an electrostatic latent image is formed and the electrostatic latent image on the image carrier. Visible image on the image carrier on a transfer device that passes through a pressure contact portion between the transfer member and the image carrier that is pressed against the image carrier by applying a transfer bias. An image forming apparatus having a transfer device for transferring the toner, a pressing roller rotatably provided in pressure contact with the image carrier between the developing device and the transfer device, and the transfer bias applied to the pressing roller. Is provided with a pre-transfer cleaning device having a bias applying means for applying a bias of opposite polarity.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, there is provided a contacting / separating mechanism for contacting / separating the transfer member with respect to the image carrier, and the bias applying unit includes the transfer member. A bias having the same polarity as the transfer bias is applied to the pressing roller when the pressure roller is separated from the image carrier.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the contacting / separating mechanism separates the transfer member from the image carrier each time one job is completed.

[0009]

According to the present invention, the pressing roller is pressed against the image carrier between the developing device and the transfer device, and a bias having a reverse polarity to the transfer bias is applied to the pressing roller from the bias applying means. The reversely charged toner on the image carrier is cleaned by the pressing roller.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the transfer member is brought into contact with and separated from the image carrier by a contacting / separating mechanism, and the bias applying means separates the transfer member from the image carrier. At this time, a bias having the same polarity as the transfer bias is applied to the pressing roller.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the contacting / separating mechanism separates the transfer member from the image carrier at the end of each job.

[0012]

FIG. 1 shows an embodiment of the present invention. This embodiment is an embodiment of the invention described in claim 1 and is an example of an electrophotographic image forming apparatus. Image carrier 1 made of a photoconductor
1 is, for example, a photosensitive drum, and is rotationally driven by a drive unit. The photoconductor drum 11 includes a charging device 12
Are uniformly charged, and an electrostatic latent image is formed by imagewise exposure by the exposure means. The charging device 12 is, for example, one that presses against the photoconductor drum 11 to apply an electric charge to the photoconductor drum 11, and the exposure unit exposes the original image to the photoconductor drum 11 or the photoconductor drum 11 according to an input image signal. Those that perform image exposure are used.

The electrostatic latent image on the photoconductor drum 11 is developed by the developing device 13 to become a visible image (toner image), and the photoconductor drum 11 passes through the developing device 13 and is cleaned before transfer including the pressing roller 14. The device cleans the oppositely charged toner. Further, the transfer paper 15 is fed from the paper feeding device to the registration roller 16, and the registration roller 16
Sends the transfer paper 15 according to the toner image on the photosensitive drum 11.

The transfer paper 15 delivered from the registration roller 16 is guided by a guide plate 17 and transferred to a transfer device 18.
Thus, the toner image on the photoconductor drum 11 is transferred and separated from the photoconductor drum 11. The static eliminator 19 is the transfer paper 1
By removing the electric charge from 5, the photosensitive drum 11 of the transfer paper 15
To improve the separation. The transfer paper 15 separated from the photoconductor drum 11 is conveyed by the conveying device 20, the toner image is fixed by the fixing device 21, and is discharged to the outside. After the transfer paper 15 is separated, the photoconductor drum 11 is cleaned by the cleaning device 22 to remove the residual toner, and the charge removal device 23 removes the charge to prepare for the next image forming operation.

As shown in FIG. 2, the transfer device 18 is a transfer member 2 including a transfer roller which is pressed against the photosensitive drum 11.
4 and a transfer bias applying unit 25 including a transfer bias applying unit 25 including a power source for applying a transfer bias to the transfer roller 24. The transfer roller 24 has a power source 25.
A transfer bias is applied to transfer the regular developing toner 26 on the photosensitive drum 11 to the transfer paper 15.

The pressing roller 14 is the photosensitive drum 1
A bias applying unit 27, which is rotatably provided in pressure contact with 1 and has a reverse polarity to the transfer bias, is composed of a power source.
Is applied more. Therefore, the reversely charged toner (background stain toner) 28 is transferred from the photosensitive drum 11 to the pressing roller 14 to clean the reversely charged toner 28 on the photosensitive drum 11, and the reversely charged toner 28 is transferred from the photosensitive drum 11 to the transfer device 18. Will not go.

In this embodiment, the pressing roller 14 which is in pressure contact with the image carrier 11 between the developing device 13 and the transfer device 18.
Since a bias having a polarity opposite to that of the transfer bias is applied from the power supply 27, the reverse charging toner 28 on the photosensitive drum 11 can be cleaned by the pressing roller 14, and the reverse charging toner 28 does not adhere to the transfer roller 24. Thus, the back surface of the transfer paper 15 can be prevented from being soiled.

FIG. 3 shows a part of another embodiment of the present invention.
This embodiment is an embodiment of the invention described in claims 2 and 3.
In this embodiment, the transfer device 18 is provided with a contact / separation mechanism for contacting / separating the transfer roller 24 with respect to the photosensitive drum 11 in the above embodiment. This contact / separation mechanism is configured using a transfer device contact / separation solenoid 29 and a spring (not shown).
The transfer roller 24 is pressed against the photosensitive drum 11 by a spring when the solenoid 29 is off, and is separated from the photosensitive drum 11 by the solenoid 29 when the solenoid 29 is on.

Regular development toner 26 on the photosensitive drum 11
Transfer roller 24 during transfer
Is pressed against the photosensitive drum 11 by the contact / separation mechanism to transfer the regular developing toner 26 on the photosensitive drum 11 onto the transfer paper 15. Further, the contact / separation mechanism separates the transfer roller 24 from the photosensitive drum 11 every time one job (one image forming operation or one transfer operation) is completed.

Further, the pressing roller 14 is switched and connected to the power sources 27 and 31 by the switch 30, and the switch 30 and the power sources 27 and 31 constitute bias applying means. At the time of transfer for transferring the regular developing toner 26 on the photoconductor drum 11 to the transfer paper 15, the switch 30 is switched to the power supply 27 side, and the pressing roller 14 has a bias having a polarity opposite to the transfer bias from the power supply 27 via the switch 30. The reversely charged toner 28 applied to the photosensitive drum 11 is cleaned. Therefore, the oppositely charged toner 28 on the photosensitive drum 11 is
To the transfer device 18, the reversely charged toner 28 does not adhere to the transfer roller 24, and the back surface of the transfer paper 15 is prevented from being soiled.

When the transfer roller 24 is separated from the photosensitive drum 11 by the contact / separation mechanism each time one job is completed, the switch 30 is switched to the power source 31 side, and the pressing roller 1 is pressed.
A bias having the same polarity as the transfer bias is applied from the power supply 31 to the switch 4 via the switch 30. Therefore, the reversely charged toner 28 attached to the pressing roller 14 moves to the photosensitive drum 11, and the reversely charged toner 28 on the photosensitive drum 11 passes through the transfer device 18 and is cleaned by the cleaning device 22. It is removed from the photoconductor drum 11.

In this embodiment, since the bias having the same polarity as the transfer bias is applied to the pressing roller 14 from the power source 31 via the switch 30 when the transfer member 24 is separated from the image carrier 11, it is attached to the pressing roller 14. The oppositely charged toner 28 that has been used can be moved to the photosensitive drum 11, and the oppositely charged toner 28 can be cleaned by the cleaning device 22 without contaminating the transfer device 18 with the oppositely charged toner 28. Further, since the transfer member 24 is moved away from the image carrier 11 by the contacting / separating mechanism every time one job is completed, the reversely charged toner 28 can be always reliably cleaned.

[0023]

As described above, according to the first aspect of the invention, an image bearing member on which an electrostatic latent image is formed, and an electrostatic latent image on the image bearing member is developed to form a visible image. Developing device, and a transfer device that transfers a visible image on the image carrier to a transfer paper that passes through a pressure contact portion between the transfer member and the image carrier that is pressed against the image carrier by applying a transfer bias. An image forming apparatus having: a pressing roller rotatably provided in pressure contact with the image carrier between the developing device and the transfer device; and a bias having a polarity opposite to the transfer bias on the pressing roller. Since the pre-transfer cleaning device having the bias applying means for applying the charge is provided, the reverse charging toner on the image carrier can be cleaned by the pressing roller, and the reverse charging toner does not adhere to the transfer member, and Prevents dirt on the back side It is possible.

According to a second aspect of the invention, in the image forming apparatus according to the first aspect, there is provided a contacting / separating mechanism for contacting / separating the transfer member with respect to the image carrier, and the bias applying means transfers the transfer member. When the member is separated from the image carrier, a bias having the same polarity as the transfer bias is applied to the pressing roller, so that the reversely charged toner adhering to the pressing roller is moved to the image carrier and the reversely charged toner is used. It is possible to clean the reversely charged toner without contaminating the transfer device.

According to the third aspect of the invention, in the image forming apparatus according to the second aspect, the contacting / separating mechanism separates the transfer member from the image carrier every time one job is completed. The charged toner can be cleaned.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a part of the embodiment.

FIG. 3 is a sectional view showing a part of another embodiment of the present invention.

[Explanation of symbols]

 11 Photosensitive Drum 13 Developing Device 14 Pressing Roller 18 Transfer Device 24 Transfer Member 27, 31 Power Supply 29 Transfer Device Contact / Separation Solenoid 30 Switch

Claims (3)

[Claims] 1. An image carrier on which an electrostatic latent image is formed, a developing device for developing the electrostatic latent image on the image carrier to a visible image, and a transfer bias applied to the image carrier. An image forming apparatus comprising: a transfer member that is pressed against a body; and a transfer device that transfers a visible image on the image carrier onto a transfer paper that passes through a pressure contact portion of the image carrier. A pre-transfer cleaning device having a pressing roller rotatably provided in pressure contact with the image carrier between the apparatus and a bias applying unit for applying a bias having a polarity opposite to the transfer bias to the pressing roller. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, further comprising a contacting / separating mechanism for contacting / separating the transfer member with respect to the image carrier, wherein the bias applying unit separates the transfer member from the image carrier. An image forming apparatus, wherein a bias having the same polarity as the transfer bias is applied to the pressing roller when the pressure roller is turned on. 3. The image forming apparatus according to claim 2, wherein the contacting / separating mechanism separates the transfer member from the image carrier at the end of each job.