Image forming apparatus with cleaning bias feature

Details Image forming apparatus with cleaning bias feature Image forming apparatus with cleaning bias feature

2000-07-27

2002-01-22

Brase, Sandra (Department: 2852)

Electrophotography

Internal machine environment

Particle or contaminant control

C399S066000

Reexamination Certificate

active

06341205

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic system, such as a copying machine or a laser printer, in which an image is formed by secondarily transferring a toner image to a recording medium from an intermediate transfer body on which the toner image has been transferred, and particularly to a cleaning technique of a transfer part in a secondary transfer portion.
2. Description of the Related Art
Conventionally, as an image forming apparatus using an electrophotographic system, such as the copying machine or laser printer, there is an image forming apparatus constructed such that toner images of yellow, magenta, cyan, black, etc. sequentially formed on a photoreceptor drum are transferred onto an intermediate transfer belt in a state where they overlap with each other, the multiple toner images of the respective colors transferred onto the intermediate transfer belt are transferred to a recording medium at the same time by pressing force and electrostatic attraction force of a backup roll and a secondary transfer roll, and then, the unfixed toner images of the respective colors are fixed onto the recording medium by a fixing device, whereby a color image is formed.
In the image forming apparatus, the secondary transfer roll is brought into press contact with the intermediate transfer belt on which the toner images of the respective colors have been transferred, and the multiple transferred toner images on the intermediate transfer belt are secondarily transferred onto the recording medium, so that the color image is formed. Thus, in the image forming apparatus, when the toner image transferred onto the intermediate transfer belt comes in contact with the secondary transfer roll, the toner is shifted to the secondary transfer roll by the pressing force, and the toner sticking to the secondary transfer roll adheres to the rear surface of the recording medium next conveyed to a secondary transfer position, which becomes a cause of rear surface stain of the recording medium.
For the purpose of preventing such rear surface stain of a recording medium caused by adhesion of toner to a secondary transfer roll, in an image forming apparatus using a transfer roll including a secondary transfer roll, a technique of cleaning the secondary transfer roll or the like has been already proposed in Japanese Patent Unexamined Publication No. Hei. 8-272235, No. Hei. 8-328401, and No. Hei. 9-6146.
An image forming apparatus disclosed in Japanese Patent Unexamined Publication No. Hei. 8-272235 includes an image carrier which electrostatically holds a toner image, a transfer member which comes in contact with the surface of the image carrier and applies a transfer bias, and a bias application part which sequentially applies bias currents having different polarities to the transfer member when a transfer material does not exist at a transfer position. In the image forming apparatus, the bias application part applies the same polarity current having the same polarity as the toner constituting the toner image, and then, applies the opposite polarity current having the polarity opposite to the toner and having a current value of an absolute value not lower than an absolute value of the same polarity current.
An image forming apparatus disclosed in Japanese Patent Unexamined Publication No. Hei. 8-328401 includes an image carrier which electrostatically holds a toner image, a transfer member which comes in contact with the surface of the image carrier and applies a transfer bias, and a bias application part which applies the transfer bias to the transfer member when a transfer material passes between the image carrier and the transfer member so as to transfer the toner image formed on the image carrier to the transfer material, and applies a current having a polarity opposite to the charged polarity of the toner to the transfer member after applying a current having the same polarity as the charged polarity of the toner at the time of cleaning when the transfer material does not exist at a transfer position. In the image forming apparatus, a bias having the same polarity as the transfer bias is applied to the transfer member at least in the period from the start of first image formation immediately after the cleaning to the application of the transfer bias.
An image forming apparatus disclosed in Japanese Patent Unexamined Publication No. Hei. 9-6146 includes a photoreceptor on which a toner image corresponding to an image to be formed is formed, a primary transfer member which transfers the toner image on the photoreceptor onto an intermediate transfer body, a secondary transfer member which is provided to be freely pressed on and separated from the intermediate transfer body and transfers the toner image on the intermediate transfer body onto a recording sheet, and an intermediate transfer body driving part which rotates and drives the intermediate transfer body. The image forming apparatus further includes a cleaner blade which is provided to be freely pressed on and separated from the intermediate transfer body and removes the toner image on the intermediate transfer body, a secondary transfer member holding part which holds the secondary transfer member while selectively changing a press contact state and a separating state to the intermediate transfer body, a cleaner blade holding part which holds the cleaner blade while selectively changing a press contact state and a separating state to the intermediate transfer body, a paper jam detection part which detects a paper jam in a recording sheet conveying passage, a paper jam release detection part which detects that a paper jam state is released, a voltage application part which applies a voltage to the secondary transfer member, and a control part which controls the operation of the respective holding parts, the driving part, and the voltage application part on the basis of detection signals by the respective detection parts. The control part performs such control that after the release of the paper jam state is detected, the cleaner blade is held in the press contact state to the intermediate transfer body, the secondary transfer member is held in the separating state to the intermediate transfer body, cleaning on the intermediate transfer body is performed while the intermediate transfer body is caused to make at least one rotation, the secondary transfer member is held while the press contact state to the intermediate transfer body is changed after the intermediate transfer body is cleaned, a voltage is applied to the secondary transfer member, and cleaning of the secondary transfer member is performed while the secondary transfer member is caused to make at least one rotation.
However, the foregoing prior art has the following problems. That is, in the technique disclosed in Japanese Patent Unexamined Publication No. Hei. 8-272235 or No. Hei. 8-328401, at the time of cleaning when the recording medium does not exist at the transfer position, the voltage having the same polarity as the charged polarity of the toner is applied to the transfer part, and then, the voltage having the polarity opposite to the charged polarity of the toner is applied, so that the toner sticking to the transfer part is completely reversely transferred onto the image carrier, and the rear stain of the recording medium is prevented. In the technique disclosed in Japanese Patent Unexamined Publication No. Hei. 9-6146, the contact and separation control of the cleaner blade and the secondary transfer member is performed, so that cleaning of the toner remaining on the intermediate transfer body and the secondary transfer member after the release of the paper jam can be effectively performed, and in the image forming operation carried out after the release of the paper jam, the stain such as fogging or stripes due to the remaining toner is not produced, a clear image can be formed, and the image quality of the formed image is improved.
However, there has been a problem that even

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