JPH0810370B2 - Multiple image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Use of the Invention] The present invention supports a transfer material on a rotating transfer material carrying sheet and applies a transfer electric field to the transfer material on the transfer material carrying sheet to form a photosensitive drum. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus that sequentially superimposes a plurality of toner images sequentially formed on an image carrier such as an insulating drum on a transfer material and transfers the toner images, for example, a multiple image forming apparatus such as a color copying machine or a color printer.

[Prior art]

FIG. 1 is an explanatory view of a conventional color electrophotographic copying machine for forming a conventional full-color copied image to which the present invention is applicable. In the figure, a corona charger 2, an exposure system 3, a developing device 4, a transfer drum 5, and a cleaner 6 are placed around the photosensitive drum 1. The optical system 3 comprises a document scanning section 3a and a color separation filter 3b. The developing device 4 has four developing devices around the central axis 4b, 4Y is a yellow developing device and 4M is a developing device.
Is a magenta developing device, 4C is a cyan developing device, and 4B is a black developing device. Further, the entire developing device is rotated to sequentially develop each of the four colors. The transfer drum 5 includes a cylinder 5a, a transfer charger 5b, and a transfer material gripper.
5c, an inner charger 5d as a static eliminator, and an outer charger 5e, and a transfer material carrying sheet is stretched over the peripheral opening area.

To form a full-color image, first, a blue color-separated electrostatic latent image is formed on the photosensitive drum 1 and developed by the yellow developing device 4Y. On the other hand, the transfer material is gripped by the gripper 5c of the transfer drum 5 from the transfer material cassette 7 via the transport system. As the rotation of the transfer drum 5 progresses, the toner image on the photosensitive drum 1 is transferred onto the transfer material by the transfer charger 5b, and at the same time, the transfer material is
Adsorbed on the transfer material carrying sheet. For example, an AC voltage is applied to the inner charger 5d, and discharge is started at the same time as the transfer charger 5b, so that the charge remaining on the transfer material carrying sheet due to the discharge of the inner charger 5d is neutralized or reduced. In addition to an AC voltage, an AC voltage, which is a DC voltage having a polarity opposite to that of transfer charging or a DC voltage having a polarity opposite to that of transfer charging, is applied to the inner charger. Here, the inner charger 5d continues discharging from the start of the front rotation to the end of the rear rotation.

This operation is repeated three more times, that is, magenta, cyan, and black, as in the known full-color image forming method. When the transfer of the four-color toner images is completed in this way, the outer charger 5e starts discharging (in the opposite phase AC when the inner charger is AC), and is separated from the transfer drum 5 by the separating claw 8 and fixed to the heat roller fixing device. It is discharged to the tray 10 via 9.

FIG. 2 shows an example of the time sequence of the color electrophotographic copying machine, in which the diameter of the photosensitive drum 1 is, for example,
When the diameter of the transfer drum 5 is 80 mm and the diameter of the transfer drum 5 is 160 mm (ratio to the diameter of the photosensitive drum is 2: 1), the image exposure time, the charging time by the transfer charger, and the inner charging with respect to the rotation speed of the photosensitive drum and the transfer drum. The charge removal time by the charger and the charge removal time by the outer charger are shown separately for the transfer material size of A4 (JIS standard) size and A3 size. It should be noted that the transfer charging does not necessarily have to be turned off in the non-transfer area, but it is shown in order to make it easy to understand the transfer timing due to the difference in the size of the transfer material.

As can be seen from the on / off timing of each charger, starting with the image exposure in Fig. 2, there is little A3 size full-color copying, and the image exposure interval is open for one rotation of the co-transfer drum. This is due to the fact that it takes time to return to the start position after scanning of the original scanning optical system, or to move with the replacement of the developing device.
In some cases, copying to a transfer material of the same size is not possible with the same rotation speed of the transfer drum as A4 size. In this case, the transfer drum 1
It requires idling for the amount of rotation. That is, until the second color toner image as the second toner image is transferred after the first color toner image as the first toner image is transferred, the second color toner image as the first toner image is transferred. Until the third color toner image as the second toner image is transferred after the transfer of
After the transfer of the third color toner image as the second toner image and before the transfer of the fourth color toner image as the second toner image, the transfer material is conveyed to the transfer portion of the photosensitive drum on which the toner image is not formed. And a step of contacting the photosensitive drum is required.

Conventionally, the so-called offset phenomenon in which the toner transferred to the transfer material adheres to the photosensitive drum in the above idle rotation, and the resulting image has unevenness or a decrease in density, which causes A3 size copy. There was a problem that the image quality of was significantly inferior to that of A4 size.

One of the reasons why the above-mentioned problem occurs is that the inner charger is continuously operated as shown in FIG. 2 so that the electric charge is gradually reduced even during idling. That is, the charge of the transfer material carrying sheet that holds the toner transferred onto the transfer material is neutralized or reduced, the attraction force of the toner to the transfer material is reduced, and the photosensitive drum is brought into contact with the photosensitive drum during idle rotation. Was off set.

The above problem also occurs in a multicolor image forming apparatus proposed by the present applicant, for example, when a color copy for color proofing is created from a color separation film for printing. That is, in the above-described multicolor image forming apparatus, in order to accurately place the color separation film or the like at the same position on the platen glass, a register bin for normal printing is used. It takes a certain amount of time to attach and detach such punch holes. Therefore, the photosensitive drum and the transfer drum are rotated for a sufficient time to replace the original such as the color separation film in a short time between the four original illuminations in the full-color copy mode. During this idle rotation, the transfer material faces the photosensitive drum on which the toner image is not formed, and the toner image once transferred on the transfer material is offset to the photosensitive drum.

[Problems to be solved by the invention]

The present invention is a means for eliminating the problems described in the preceding paragraph,
An object of the present invention is to provide a transfer device capable of preventing or reducing an offset phenomenon that occurs when a transfer material faces a photosensitive drum that does not carry a toner image in multiple transfer.

〔Example〕

The present invention is shown using the time sequence of the color electrophotographic machine of FIG. FIG. 3 is the same as the contents of the conventional sequence of FIG. 2, in which the diameter of the photosensitive drum 1 is, for example, 80 mm,
When the diameter of the transfer drum 5 is 160 mm, the image exposure time, the charging time by the transfer charger, the slow charging time by the inner charger, and the time by the outer charger with respect to the rotation speed of the photosensitive drum and the transfer drum are set to the transfer material. It is shown separately for sizes A4 and A3.

During A4 size and full color copying, there is no idle rotation as described above, so the same sequence as the operation of the inner charger may be used. This is during A3 size full-color copying, but in this case there is idle rotation, so it is necessary to turn it on and off as shown in the timing chart. That is, the operation of the inner charger is turned off immediately after the transfer of the first color yellow is started. Further, the operation is restarted by passing the nip between the photosensitive drum and the transfer drum when the front end of the transfer material idles. These off and on are repeated three times in the same manner. However, since the transfer material is immediately discharged after the transfer of the fourth color black, this off / on operation is not required.

By a series of these operations, it is possible to obtain the effect of preventing offset or reducing it to the extent that it does not affect the image quality.

When the applied voltage of the inner charger is turned on and off, instead of turning it off, control may be performed such that the charge removal is weaker than when the applied voltage is turned on.

〔effect〕

As described above, during full-color copying in which the inner charger operates even during transfer, the phenomenon in which the toner on the transfer material offsets to the photosensitive drum when the transfer material faces the photosensitive drum that does not carry toner is suppressed. Mura,
Alternatively, a good image without density reduction can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view of a main part of a conventional color electrophotographic copying machine, and FIG. 2 is an explanatory view showing a part of a timing chart in a system in which an inner charger of the color copying machine of FIG. 1 operates every time.
FIG. 3 shows a timing chart when the present invention is applied to the color copying machine of FIG. In the figure, 1 is a photosensitive drum, 2 is a primary charger, 3 is an exposure system, 4 is a developing device, 5 is a transfer drum, 5b is a transfer charger, 5d is an inner charger, and 5e is an outer charger. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Aoki ▲ Takao Man 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) Reference JP-A-59-154465 (JP, A)

Claims (1)

[Claims] 1. An image carrier for carrying a toner image, a transfer material carrying sheet for carrying a transfer material to a transfer portion of the image carrier, and a transfer charger for transferring the toner image to the transfer material. And an image carrier that does not carry the toner image on the transfer material having the first toner image after transferring the first toner image onto the transfer material on the transfer material carrying sheet conveyed to the transfer section. The transfer material having the first toner image is conveyed to the transfer portion of the image carrier, the second toner image is transferred, and the first and second toner images are transferred. In a multiple image forming apparatus that sequentially forms layers on a transfer material, a static eliminator that removes electric charges from the transfer material carrying sheet is provided,
Immediately before the transfer material having the first toner image passes through the transfer portion of the image carrier that does not carry the toner image, rather than the charge of the transfer material carrying sheet immediately before the transfer of the second toner image, A multiple image forming apparatus characterized in that the amount of static elimination by the static eliminator is controlled so as to increase the charge of the transfer material carrying sheet.