JPS6345110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transfer device, and more particularly to a device for transferring a developed image formed on an image carrier onto a transfer material. A transfer device for an image forming apparatus such as an electrophotographic copying device generally uses an electrostatic transfer method such as bias roller transfer or corona discharge transfer. Among these, bias roller transfer applies a transfer bias voltage of opposite polarity to the charge of the toner on the photoreceptor to a transfer roller made of an insulating or conductive elastic member to transfer the toner onto the transfer paper. A variation of this method is to use an insulating or conductive endless belt as the support for the transfer paper, and apply a transfer electric field using a bias roller or corona discharge from the back side of the belt to transfer the toner to the transfer paper. be. However, in any case, bias roller transfer has the problem of toner being offset to the back surface of the transfer paper support, staining the back surface of the transfer paper, or causing uneven transfer. This occurs when copying is performed using transfer paper of different paper sizes. For example, when copying A4 size on a copying machine that can make A4 and B4 size copies, A4 and B4 size copies The toner image developed on the area corresponding to the difference in area is transferred to the transfer roller, and when a B4 size copy is made next time, problems such as back stains occur. In order to deal with these problems, conventional transfer rollers have required cleaning means such as rubber blades and fur brushes, similar to cleaning means for the surface of the photosensitive drum. However, these cleaning means are complicated, and the apparatus becomes expensive when storage or discharge of the toner after the cleaning process is taken into account. Moreover, since it is a mechanical means, when the transfer paper support is made of a thin polyester film or the like, it is undesirable because it affects the mechanical strength of the transfer paper support. The present invention has been made in view of the above problems. The present invention provides a transfer device that transfers a developed image formed on an image carrier onto a transfer material, including a transfer material holding means that is supported in an endlessly movable manner and has a holding surface that holds the transfer material; A means for applying a transfer bias of a predetermined polarity from the back side of the transfer material holding surface of the means to transfer the developed image on the image carrier onto the transfer material, and a means for transferring the developed image on the image carrier before the transfer material is held by the transfer material holding means. When the material holding means moves endlessly or after the transfer is completed, the transfer material is separated from the transfer material holding means and the transfer material holding means moves endlessly without holding the transfer material, the transfer material is transferred to the transfer material holding surface of the transfer material holding means. means for applying a corona discharge of the same polarity as the bias; the polarity of the developer attached to the transfer material holding surface of the transfer material holding means is reversed by the discharge of the corona discharge means; The present invention is characterized in that the developer whose polarity is reversed is moved from the transfer material holding means to the image carrier. Hereinafter, details of the present invention will be explained using specific examples with reference to the drawings. Figure 1 shows an example of a transfer-type color electronic copying machine, in which 1 is a CdS photosensitive drum with an insulating surface, which is rotatably supported by a shaft 2, and starts rotating in the direction of arrow 3 in response to a copy command. do. When the drum 1 rotates to the fixed position, the original O placed on the original platen glass 4 is moved to the first scanning mirror 5.
It is irradiated with an illumination lamp 6 that is integrally formed with the camera, and the reflected light is scanned by a second scanning mirror 7. The first scanning mirror 5 and the second scanning mirror 7 are 1:1/2.
By moving at a speed ratio of , the document is scanned while the optical path length between the document O and the lens 8 is always kept constant. After passing through the lens 8 and the third mirror 9, the reflected light image is color-separated by a color separation filter 10, and then passed through the fourth mirror 11 and the dust-proof sealing glass 1.
2, the image is formed on the drum 1 at the exposure section 13. The drum 1 is neutralized by a static eliminator 14, then charged (positive polarity) by a primary charger 15, and then an image irradiated by the illumination lamp 6 is slit exposed in the exposure section 13. At the same time, AC or primary static electricity removal with the opposite polarity (- polarity) is performed in the static eliminator 16, and then a high-contrast electrostatic latent image is formed on the drum 1, which has been entirely exposed by the full-surface exposure lamp 17. . The electrostatic latent image on the photosensitive drum 1 is then visualized as a toner image by a developing device 18 . Developing device 18
is yellow 181, magenta 182, cyan 18
It consists of four developing devices, 3 and 184 black, and each developing device contains a predetermined toner (- polarity). works to obtain a toner image of the desired color. The transfer paper 20 in the cassette 19 is transferred to the paper feed roller 21.
is sent into the machine by the first register roller 22, then the second register roller 23 takes accurate timing, and the leading end is gripped by the gripper 241 of the transfer drum 24 . Then, as the transfer drum 24 rotates, the transfer paper 20 is conveyed while being wrapped around the drum, and while the transfer paper 20 passes between the transfer charger 25 and the photosensitive drum 1,
The toner image on the photosensitive drum 1 is transferred onto the transfer paper. The transfer drum 24 is made by wrapping a polyester film 243 with a thickness of 200 .mu.m around a notch of a metal frame 242 shown in FIG. During transfer, a corona discharge current having a polarity opposite to that of the toner charge is applied to the back surface of the film 243 by the transfer charger 25. The transfer drum 24 rotates at a required number of rotations while gripping the leading edge of the transfer paper 20 with a gripper 241, and an image of the required number of colors is transferred. After the transfer is completed, the transfer paper is neutralized by the AC static eliminators 27 and 27', and then released from the gripper 241.
The sheet is guided to a conveyor belt 29 by a separating claw 28, further heat-fixed by a heat roller fixing device 30 , and then discharged onto a tray 31. Further, the surface of the photosensitive drum 1 after the transfer is cleaned by a cleaning device 32 composed of an elastic blade, and then the photosensitive drum 1 is allowed to proceed to the next cycle. Before the end of copying, the transfer drum 24 separates the transfer paper 20 and then performs a post-rotation without supporting the transfer paper on the surface of the transfer paper support. During subsequent rotation, that is, after separation of the transfer paper 20,
The tip of the transfer paper support of the transfer drum 24 is connected to the charger 26
When it reaches the vicinity, the charger 26 starts corona discharge of + polarity by a control means (not shown), and charges the surface of the transfer paper support 243 to + polarity. At the same time, the polarity of the toner attached to the surface of the support 243 is reversed to +. Note that, of course, this charging is not limited to the time of the rear rotation, but may also be performed during the front rotation or other times. Support 2 which became + polar due to the above + charging
The toner on the surface of the toner 43 is repelled by the positive charge on the back surface of the support 243 by the transfer charger 25, and is retransferred to the surface of the photosensitive drum 1, thereby cleaning the surface of the support 243. In this case, if the surface potential of the photosensitive drum 1 is set to the bright area potential (0 to -100 V) of the original by sequence control, the above-mentioned cleaning effect can be further enhanced. Prior to charging by the charger 26, the back side of the transfer paper support 243 is
By removing the charge, positive charging by the charger 26 can be performed efficiently. FIGS. 3 and 4 are sectional views illustrating another embodiment of the apparatus, and only the transfer portion shown in FIG. 1 is illustrated. In FIG. 3, an insulating film is provided on the surface of a conductive rubber roller to form a transfer roller 24' , and the transfer roller 24 is connected to a high-voltage power source for a transfer bias of positive polarity. The positive charging by the charger 26' is controlled in the same manner as in the case of FIG. FIG. 4 shows a transfer device 24'' using an insulating rubber belt, and a transfer charger 25'' performs positive corona discharge. The positive charge by the charger 26'' is controlled in the same way as in the case of FIG. This makes it possible to float the toner adhering to the body surface by Van der Waals force, which further enhances the effects of the present invention.As explained above, according to the present invention, the developer with reversed polarity is Since the transfer material can be moved from the transfer material holding means to the image carrier by a transfer bias having the same polarity as that polarity, it is possible to prevent the transfer material holding surface of the transfer material holding means from becoming dirty.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an electrophotographic apparatus to which a specific example transfer apparatus based on the present invention is applied. FIG. 2 is a partial perspective view of a specific example transfer device. FIG. 3 and FIG. 4 are schematic diagrams of different embodiment transfer devices. In the figure, 1: photosensitive drum, 2: support shaft, 4: document table glass, 5, 7: scanning mirror, 10: color separation filter, 24 : transfer drum.

Claims (1)

[Scope of Claims] 1. A transfer device that transfers a developed image formed on an image carrier onto a transfer material, comprising: a transfer material holding means that is supported in an endlessly movable manner and has a holding surface that holds the transfer material; means for applying a transfer bias of a predetermined polarity from the back side of the transfer material holding surface of the transfer material holding means to transfer the developed image on the image carrier onto the transfer material; and the transfer material being held by the transfer material holding means. When the transfer material holding means moves endlessly before or after the transfer is completed, when the transfer material is separated from the transfer material holding means and the transfer material holding means moves endlessly without holding the transfer material, the transfer material of the transfer material holding means means for applying a corona discharge of the same polarity as the transfer bias to the holding surface, and the polarity of the developer attached to the transfer material holding surface of the transfer material holding means is reversed by the discharge of the corona discharge means, and the transfer means A transfer device, wherein the developer whose polarity has been reversed is moved from the transfer material holding means to the image carrier by a transfer bias.