JPS63286878A - Image forming device - Google Patents

Abstract

PURPOSE:To effectively prevent lowering in transferring rate caused by contamination, by applying a bias voltage of polarity opposite to that of toner a transfer member at the time of transfer and another bias voltage of polarity equal to that of the toner at the time of non-transfer. CONSTITUTION:By applying a bias voltage Va of polarity opposite (plus in this case) to the toner to a transfer charger 6 during the period of tA-tB after a photosensitive body 1 is driven, the surface potential of a transfer roller 2 is maintained at Vc and the toner image on the surface of the photosensitive body 1 is transferred to a transfer material. Then, during the period of tB-tC after the transfer material passes the transferring section, another bias voltage Vb of polarity equal to that of the toner is applied to the charger 6 and the surface of the transfer roller 2 is electrostatically charged with surface potential Vd. As a result, not only the transfer of the toner existing on the surface of the photosensitive body to the transfer roller 2, but also that traction of the floating toner to the roller 2 can be prevented effectively. Therefore, the contamination of the succeeding transfer materials and the lowering in image quality can be avoided.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) This invention relates to image forming apparatuses that utilize an electrostatic recording process, such as electrostatic copying machines and printers, particularly transfer rollers, transfer belts, etc. The present invention relates to an image forming apparatus using an image forming apparatus.

(Prior art and issues to be solved) A transfer member such as a transfer roller made of an elastic material is placed in contact with or very close to a moving image carrier, and a sheet of paper or other material is transferred between the two. An image forming apparatus has already been proposed in which a transferable toner image formed on an image carrier is transferred to the transfer material by passing the transfer material therethrough.

In such an image forming apparatus, it is inevitable that the transfer roller etc. will be contaminated with toner and other foreign matter, and it is difficult to completely remove this, so the back side of the transfer material may become contaminated due to this, and This toner etc.
There have been problems such as problems such as re-adhesion to the image bearing member and deterioration of the image, and a reduction in transfer efficiency due to such stains on the rollers and the like.

In addition, in the case of a type that uses a conductive transfer roller, the bias applied to the roller cannot be set very high (usually less than IKV), which, together with the difficulty of cleaning the transfer roller as mentioned above, There were also problems such as difficulty in obtaining high-quality images.

The present invention has been made to deal with such a situation, and is to prevent toner from adhering to the roller in an image forming apparatus that uses a transfer member such as a transfer roller or a transfer belt. Accordingly, it is an object of the present invention to provide an image forming apparatus that can always obtain high-quality images at a high transfer rate.

(2) Object of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention provides a transfer method in an image forming apparatus using a transfer member such as an insulating transfer roller or belt. The present invention is characterized in that the member is charged to have the same polarity as the toner at times, and to have the opposite polarity to the toner when not being transferred.

With this configuration, when there is no transfer material between the image carrier carrying the toner image and the transfer roller, repulsion acts between the toner and the transfer roller, causing the transfer roller, etc. It is possible to prevent toner from adhering to the surface and prevent its contamination.

(Description of Embodiments) FIG. 1 is a side view of essential parts showing an embodiment in which the present invention is applied to a copying machine equipped with a rotating cylindrical photoreceptor, in which a photoreceptor 1 rotating in the direction of arrow A, It is provided with an elastic transfer roller 2 which is disposed in contact with or very close to this and whose surface is made of an insulating material at least.

It is assumed that the transfer roller 2 is configured to run synchronously at a portion facing the photoreceptor by appropriate means.

Transfer material (not shown) supplied from a cassette (not shown), etc.
arrives at the transfer site where the photoreceptor 1 and the transfer roller 2 face each other in time with the toner image formed on the surface of the photoreceptor by the registration roller pair 4 and progressing as the photoreceptor rotates, and at this time, As will be described later, the toner image is transferred to the transfer material by the action of a transfer roller to which a bias is applied with a polarity opposite to that of the toner.

Next, the transfer material is separated from the photoreceptor and transported to a fixing site (not shown) by the transport path 5.

As is well known, around the photoreceptor 1,
It goes without saying that means required for repeated image formation, such as a latent image forming means, a developing means, and a cleaning means, are provided, but since they are not directly related to the present invention, they are all omitted.

In such an image forming apparatus, the transfer roller 2 includes a core bar 20 made of a rigid material such as metal, an inner layer 2b surrounding the core bar 20 and made of an elastic material such as urethane rubber or silicone rubber with or without bubbles. Urethane rubber consists of an outer layer 2a made of an insulating and highly wear-resistant material, and the outer layer has a thickness of 0.1 to 2 mm and a hardness of 30.
It shall be determined as appropriate within the range of ~80°.

It is also assumed that the transfer roller 2 is elastically biased toward the photoreceptor 1 by a spring or the like in order to support the transfer material with a predetermined pressure between the transfer roller 2 and the photoreceptor l.

The inner layer 2b does not need to be insulating; rather, it is more convenient to be conductive in order to maintain a uniform surface potential of the insulating outer layer 2a, and in order to make it conductive, Conductive particles such as carbon may be dispersed.

A transfer charger 6 to which a transfer bias is applied by a power supply 7 is disposed near the transfer roller in order to charge the roller.The power supply 7 is further connected to a control circuit 8. The control circuit 8 sends timing control sequence signals to the registration roller pair 4. The signal is output to the transfer charger 6 to control the charging characteristics of the transfer roller.

FIG. 2 is a timing chart showing the relationship between the transfer operation and the charging characteristics of the transfer roller.

During the time tA"' tB after driving the photoreceptor,
Insert a transfer charger with a polarity opposite to that of the toner (in this case, positive).
By applying a bias va, the surface potential of the transfer roller 2 is set to Vc.
The toner image on the surface of the photoreceptor is thereby transferred to the transfer material.

Then, the time t, after the transfer material passes through the transfer site.
During tc, a bias vb having the same polarity as that of the toner is applied to the charger 6 to charge the surface potential of the transfer roller to 11. This not only effectively prevents the toner present on the surface of the photoreceptor from being transferred to the transfer roller, but also prevents floating toner from being attracted to the transfer roller, thereby preventing contamination and, therefore, the subsequent transfer material. , it is possible to avoid situations where image quality is impaired.

As can be seen from the behavior of the transfer roller at times t and tp in the figure, in order to prevent damage to the photoreceptor, it is preferable to apply an alternating current bias to the transfer charger 2 & to eliminate static electricity immediately before the photoreceptor is stopped. .

With this configuration, as described above, it is possible not only to prevent the transfer roller from being contaminated, but also to improve the transfer efficiency, making it possible to stably obtain high-quality images.

In the above device, a resist row was used to control the charging device when applying the ias, but it is also possible to use a jam detection means that is usually built into this type of device.
Further, at the same time as charging the transfer charger, a bias having the same polarity as this may be directly applied to the transfer roller.

Although the present invention is applied to a copying machine, the present invention is not limited to this and can be applied to various image forming apparatuses. It is easy to understand that it can also be used as a transfer member.

(3) Effect of sprouting As explained above, in the present invention, in an image forming apparatus in which a transfer member such as a transfer roller is disposed close to an image carrier, a bias having a polarity opposite to that of the toner is applied to the transfer member during transfer.
Since the configuration is such that a bias of the same polarity as the toner is applied during non-transferring, the transfer member can be kept clean at all times without the need for special cleaning means, effectively preventing a reduction in transfer rate due to contamination. At the same time, it is possible to stably obtain high-quality images without back staining over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a top-down view of essential parts of an embodiment in which the present invention is applied to a copying machine, and FIG. 2 is a timing chart illustrating the timing of zero impression force on the transfer member. 1. Red fist photoreceptor, 2. Fist-transfer roller, 4. Registration roller pair, 6. Transfer charger, 7. Bias power supply, 8. Red control circuit.

Claims (1)

[Claims] A moving image carrier and an insulating transfer member placed in contact with or close to the image carrier are provided, and a transfer material is inserted between the two to transfer the toner image on the image carrier to the transfer material. In an image forming apparatus configured to perform transfer, when a transfer material exists between the two, the transfer member has a polarity opposite to that of the toner, and when no transfer material exists and is not transferred, the transfer member has the same polarity as the toner. An image forming apparatus characterized in that a bias is applied to each of the following.