JPH04249281A - Toner image transfer device - Google Patents

Abstract

PURPOSE:To prevent the sticking of a toner image to a transfer roller and the generation of the soiling of the surface of a transfer material by adopting a constitution that only a part in an axial direction, configuration to the size of the transfer material of a transfer roller is abutted on a photosensitive body via the transfer material. CONSTITUTION:The transfer roller 15 is thinned from the central part toward both ends to obtain a spindle shape, and abutting force to the photosensitive body 10 can be adjusted, so that the nipp width of the transfer roller and the photosensitive body can be adjusted according to the size of the transfer material.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a toner image transfer device for transferring a toner image on a photoreceptor to a transfer material such as paper using a transfer roller in an image forming apparatus such as an electrostatic copying machine or printer. Regarding.

0002

2. Description of the Related Art One method of toner image transfer in an electrostatic image forming apparatus is to transfer a toner image to a photoreceptor.
A roller transfer method has already been proposed in which a conductive transfer roller to which a bias is applied is brought into pressure contact and a transfer material is passed between them to transfer a toner image onto the transfer material. Compared to the generally popular corona method, this roller transfer method achieves high transfer efficiency with a low bias, is less affected by temperature and humidity, and reliably holds the transfer material at the transfer site, making it resistant to transport. It has various advantages such as being able to give strength.

However, in the roller transfer method, since the transfer roller contacts the photoreceptor through the transfer material or directly in areas where there is no transfer material, toner adheres to the surface of the transfer roller and stains the back surface of the transfer material. There's a problem.

Therefore, in the past, the transfer roller was moved toward and away from the photoreceptor depending on the size of the transfer material (Japanese Unexamined Patent Publication No. 126875/1987), or the polarity of the bias applied to the transfer roller was changed during non-transfer. In order to prevent toner from adhering to the surface of the transfer roller, for example, the toner is reversed from that during transfer.

[0005]

[Problems to be Solved by the Invention] However, although these methods are effective as means for preventing toner from adhering to the transfer roller, the toner image forming area on the photoreceptor is smaller than the size of the transfer material. If the size of the transfer material is very large, even if the transfer rollers are spaced apart according to the size of the transfer material,
The toner image adheres to the outer portion of the transfer material in the axial direction of the transfer roller. In this case, even if a reverse bias is applied to the transfer roller, in the transfer area, an electric field acts in the direction of positively adhering the toner to the transfer roller, so switching to the reverse bias will cause the toner on the transfer roller to Even if you try to transfer it to the photoreceptor, it cannot be completely transferred.

An object of the present invention is to prevent toner images from adhering to the transfer roller by configuring only the axial portion of the transfer roller corresponding to the size of the transfer material to contact the photoreceptor through the transfer material. The objective is to prevent stains on the back side of the transfer material from occurring.

[0007]

SUMMARY OF THE INVENTION In the toner image transfer device according to the present invention, the transfer roller has a spindle shape that tapers from the center toward both ends.

This toner image transfer device has a transfer material size sensor that detects the size of the transfer material in order to automatically adjust the contact length of the transfer roller to the photoreceptor according to the size of the transfer material. It is preferable to include a detection means and a contact pressure adjustment means for adjusting the contact force of the transfer roller against the photoreceptor according to the size detected by the transfer material size detection means.

The contact pressure adjusting means can be composed of a stepping motor and a cam that applies pressure to the transfer roller by rotation of the stepping motor.

0010

[Operation] Since the transfer roller is spindle-shaped, by adjusting the contact force against the photoreceptor, the contact length (nip width) between the transfer roller and the photoreceptor can be adjusted according to the size of the transfer material.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 8 shows a schematic configuration of an image forming apparatus equipped with a toner transfer device according to the present invention. The surface of the photoreceptor 10 rotating in the direction of the arrow is uniformly charged by a charger 11, and an image-modulated laser beam 1 is emitted from a laser optical system 12.
3, an electrostatic latent image is formed on the surface of the photoreceptor. As the photoreceptor 10 rotates, the latent image reaches the developing device 14 and is visualized, forming a toner image. This toner image is transferred between the photoreceptor 10 and the transfer roller 1 in synchronization with a transfer material (not shown) conveyed by a paper feed conveyance system (not shown).
5 and is transferred to a transfer material. After that, the transfer material is conveyed to a fixing device (not shown), the toner image is fixed thereon, and then the transfer material is discharged to the outside of the device.

On the other hand, the surface of the photoreceptor that has passed through the transfer site 16 is cleaned of residual toner by a cleaning device 17, and is further neutralized by a charge eliminating means 18 in preparation for the next image formation.

A bias power source 19 applies to the transfer roller 15 a bias having the opposite polarity to that of the toner during transfer, and a bias having the same polarity as the toner during non-transfer.

As shown in FIG. 5, the transfer roller 15 is composed of a metal core shaft 15a and an elastic body 15b such as urethane rubber or silicone rubber in which a conductive material such as carbon is dispersed. It is spindle-shaped, tapering from the center toward both ends.

On the other hand, since the photoreceptor 10 has the same diameter throughout its entire length as shown in FIG. A gap 20 is formed which increases in size.

The transfer roller 15 can be brought into contact with and separated from the photoreceptor 10 by the following mechanism, and the pressure when brought into contact can be adjusted. That is, in FIG. 2, a cam 23 that rotates about a shaft 22 is in contact with a holder 21 bearing the transfer roller 15, and by pushing the holder 21 with the cam 23, the holder 21 is rotated as shown in FIGS. 3 and 4. The transfer roller 15 is pressed against the photoreceptor 10. In this case, since the elastic body 15b of the transfer roller 15 is spindle-shaped, the nip width between the photoreceptor 10 and the transfer roller 15 can be adjusted by changing the rotation angle of the cam 23.

Although it is possible to manually adjust the nip width according to the size of the transfer material by manually rotating the cam 23, it is preferable to detect the size of the transfer material and adjust it automatically. Figure 6
is an example of automatic adjustment, in which the stepping motor 24
The rotation is transmitted to cam 2 through gears 25 and 26.
3, and the rotation angle of the cam 23 is adjusted in stages.

FIG. 7 is a block diagram of the control system for automatic adjustment. A known transfer material size detection means 27 detects the size of the transfer material, and a microcomputer 28 calculates a control amount according to the size. Then, the motor driver 29 is controlled according to the control amount, and the stepping motor 24 is rotated so that the cam 23 has a predetermined rotation angle depending on the size of the transfer material. In addition, cam 2
3, the rotation angle when the power is turned on is detected by the cam angle detection means 30.

[0019]

According to the present invention, by making the transfer roller spindle-shaped and adjusting the force of contact with the photoreceptor, the nip width between the transfer roller and the photoreceptor can be adjusted according to the size of the transfer material. It is possible to prevent toner images from adhering to the transfer roller with a simple configuration, and to provide an inexpensive image forming apparatus in which the back surface of the transfer material is not stained by the transfer roller even when using a roller transfer method.

[Brief explanation of the drawing]

FIG. 1 is a schematic front view of a toner image transfer device according to the present invention.

FIG. 2 is a schematic side view of the same as above.

FIG. 3 is a front view of the device with the transfer roller in contact with the photoreceptor.

FIG. 4 is a side view of the same.

FIG. 5 is a front view of the transfer roller.

FIG. 6 is a perspective view of a part of a contact pressure adjustment mechanism that adjusts the contact pressure that brings the transfer roller into contact with the photoreceptor.

FIG. 7 is a block diagram of a control system of the contact pressure adjustment mechanism.

FIG. 8 is a schematic configuration diagram of an image forming apparatus equipped with a toner image transfer device according to the present invention.

[Explanation of symbols]

10 Photoreceptor 15 Transfer roller 23 Cam 24 Stepping motor 27 Transfer material size detection means

Claims (3)

[Claims] 1. A toner image transfer device that brings a transfer roller into contact with a photoreceptor and transfers a toner image on the photoreceptor to a transfer material conveyed between the photoreceptor and the transfer roller,
A toner image transfer device, wherein the transfer roller has a spindle shape that becomes thinner from the center toward both ends. 2. Transfer material size detection means for detecting the size of the transfer material; and contact pressure for adjusting the contact force of the transfer roller against the photoconductor according to the size detected by the transfer material size detection means. and an adjustment means,
The toner image transfer device according to claim 1. 3. The contact pressure adjusting means includes a stepping motor and a cam that applies pressure to the transfer roller by rotation of the stepping motor.
The toner image transfer device according to claim 2.