Image forming apparatus

Abstract

An image forming apparatus including a first transfer section for transferring a toner image, formed on an image carrier by utilizing a charging section, an exposing section and a developing section, onto a belt shaped intermediate transfer member; and a second transfer section for transferring the toner image on the intermediate transfer member onto a recording material by applying an electric field between a second transfer roller being provided outside the intermediate transfer member and a backup roller being provided inside the intermediate transfer member, the second transfer roller and the backup roller sandwiching the intermediate recording member and the recording material, wherein the second transfer roller is grounded and a bias voltage is applied to the backup roller, and further provided is a second charging section for charging a surface of the second transfer roller with a predetermined polarity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a total image forming apparatus having a tandem configuration, which is capable of generating a full color image;

FIG. 2 illustrates a block diagram schematically showing a controller;

FIG. 3 illustrates a drawing for explaining unwanted toner;

FIG. 4 illustrates a drawing for magnifying a main point for showing the schematic configuration of the second transfer section illustrated in FIG. 1; and

FIG. 5 illustrates a timing chart for showing a sheet conveying signal of a sheet in a transfer section, pressing/releasing of the second transfer roller against the backup roller, bias voltage switch for the backup roller and the control for the second charging section.

Claims

1. An image forming apparatus comprising: a first transfer section for transferring a toner image, which is formed on an image carrier by utilizing a charging section, an exposing section and a developing section, onto an intermediate transfer member having a belt shape; anda second transfer section for transferring the toner image transferred on the intermediate transfer member onto a recording material by applying an electric field between a second transfer roller being provided outside the intermediate transfer member and a backup roller being provided inside the intermediate transfer member, the second transfer roller and the backup roller sandwiching the intermediate recording member and the recording material,wherein the second transfer roller is grounded and a bias voltage is applied to the backup roller, and further provided is a second charging section for charging a surface of the second transfer roller with a predetermined polarity.

2. The image forming apparatus of claim 1, wherein a bias voltage having a same polarity as a polarity of toner forming the toner image to be transferred is applied to the backup roller when transfer operation is conducted by the second transfer section, and bias voltage having an opposite polarity to the polarity of toner is applied to the backup roller when transfer operation is not conducted by the second transfer section.

3. The image forming apparatus of claim 1, wherein the predetermined polarity, with which the second charging section charges the surface of the second transfer roller, is a same polarity as a polarity of toner forming the toner image to be transferred.

4. The image forming apparatus of claim 1, wherein the second charging section charges a surface of the second transfer roller when a transfer operation by the second transfer section is not conducted.

5. The image forming apparatus of claim 1, wherein the second charging section comprises a corona discharging electrode.

6. The image forming apparatus of claim 1, wherein the second charging section has a structure such that a conductive member, on which a voltage is applied, contacts directly the surface of the second transfer roller.

7. The image forming apparatus of claim 1, wherein the second charging section is enable to apply a bias voltage, on which AC voltage is superimposed, to the surface of the second transfer roller.

8. The image forming apparatus of claim 1, wherein the second transfer roller press to the backup roller.