JPS6279479A - Multiple image forming device - Google Patents

Abstract

PURPOSE:To prevent toner on a transfer material from being transferred reversely to a photosensitive drum at a transfer position during additional rotation and to obtain an image of high quality which is neither irregular nor out of focus by separating the transfer material from on a support after the completion of final transfer and rotating the support additionally. CONSTITUTION:The photosensitive drum 1 of a multiple image forming device is supported rotatably on a shaft 2 and rotated as shown by an arrow with a copy instruction. When this drum 1 rotates until a fixed position, an original O is lighted by an illumination lamp 5 and an exposed part 13 is exposed to its reflected light. Further, slit exposure is carried out after the drum 1 is charged electrostatically by a primary charger 3, and the electrostatic latent image is visualized in respective colors by a developing device 14. Then when a transfer material 171 from a cassette 17 passes the transfer position T between a transfer discharger 27 and the drum 1, the toner image on the drum 1 is transferred to a transfer drum 15. When the final-color transfer of this developing device 14 is finished, the transfer material 17 is separated from the drum 15 by a separation claw 15 at a separation position S and the drum 15 is rotated additionally to prevent the reverse transfer of the toner to the drum 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field of the Invention] The present invention relates to a multiple image forming apparatus, and in particular, to a multiple image forming apparatus in which a transfer material is supported on a drum-shaped support, and a toner image on an image carrier is multiple-transferred to the transfer material. The present invention relates to image forming apparatuses such as electrophotographic copying machines and printers.

[Prior art]

Conventionally, in multicolor image forming apparatuses such as color copying machines, a drum-shaped transfer material support that contacts an image bearing member (hereinafter representatively referred to as a photosensitive drum) such as a drum or a belt-shaped photoreceptor and rotates synchronously with it. The leading end of the transfer material is gripped by a gripper and wrapped around the body (referred to as the lower transfer drum), and each color (for example, yellow, magenta) is developed on the photosensitive drum.

Cyan, black) toner images are multiple-transferred onto the above-mentioned transfer material in 1110th order.

The transfer dome is generally a cylindrical rigid body with a notch leaving a part connecting both ends, and a dielectric insulating sheet or screen stretched over the outer circumferential surface. A corona discharger is installed inside the transfer drum to face the photosensitive drum at a position in contact with it (hereinafter referred to as the transfer section), and a charge of opposite polarity to the toner is applied from the back side of the screen etc. Transfer the toner image electrostatically to a transfer material. Then, the transfer material that has been transferred is released from the transfer tram by opening the gripper, and at the same time is peeled off from the transfer drum by a separation claw or the like, and is further transported to a fixing device by a transport means and output.

[Problem that the invention attempts to solve]

In the process of writing L, there were the following problems. Conventionally, due to the configuration of the device, the device in which the transfer material is a transfer drum is located immediately downstream near the transfer section, and as soon as the final color toner image is transferred, the clipper opens and the transfer material is transferred from the tip to the transfer drum. Separate (see control in Figure 3)
. However, when this gripper opens, at the transfer position, transfer is still being performed at the rear of the transfer material. A latent image is also formed in the exposed area.

Conventionally, the opening/closing mechanism of a gripper is performed by, for example, sliding a cam and displacing a cam follower attached to the gripper. Due to the force in the direction opposite to the rotational direction of the transfer drum, the photosensitive drum may rotate unevenly, resulting in positional deviation in the exposed area with respect to the final color image (misalignment of the exposed image on the photosensitive drum with the page image).
or a transfer shift occurred at the transfer portion, resulting in color shift on the transfer material.

Furthermore, there has been another problem in that the shock caused by the leading end of the transfer material hitting the separating claw or the shock or vibration caused by the downstream conveyance belt is transmitted to the transfer position, resulting in uneven transfer.

A method to solve these problems is to give the transfer drum additional rotation so that the transfer material is separated from the transfer drum and conveyed after the final toner image has been completely transferred. It will be achieved (No. 4)
(see control in figure), this also has the following problems. That is,
Applying additional rotation to the transfer drum causes the transfer material wrapped around the transfer tram to pass through the transfer position at least once after the final color transfer. For this reason, at the transfer position, the photosensitive drum and the transfer material are in a positional relationship in which they are in contact with each other, so that the toner that has been transferred on the transfer material is instead transferred to the photosensitive drum, causing image unevenness and blurring.

The present invention has been made in view of the above-mentioned conventional circumstances, and when the transfer material is separated from the transfer drum and during additional rotation to prevent exposure deviation and transfer deviation, the toner of the transfer material is transferred to the photosensitive drum at the transfer position. The present invention provides an apparatus that prevents reverse transfer and obtains high-quality multicolor images without image unevenness or blur.

[Means to solve the problem]

The multi-hair image forming R& device of the present invention has the advantage that when the transfer material is separated from the transfer drum and undergoes additional rotation to prevent exposure deviation and transfer deviation, when the transfer material reaches the transfer section again, A transfer discharger generates a charge of opposite polarity to the toner.
Furthermore, it is possible to prevent the toner on the transfer material from being offset to the image carrier due to contact with the image carrier, and also to prevent the toner from being disturbed due to misalignment with the image carrier.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

In FIG. 2, the photosensitive drum 1 is rotatably supported by a shaft 2, and starts rotating in the direction of the arrow in response to a copy command. When the drum l rotates to a fixed position, the original 0 placed on the original glass 4 is illuminated by the illumination lamp 5 which is integrated with the first scanning mirror 6, and the reflected light is transmitted to the second scanning mirror 7,
An image is formed on the exposure section 13 through the third scanning mirror 8, lens 9, fourth scanning mirror IO, and color separation filter 11.

The photosensitive drum 1 is charged (for example, positively charged) by the primary charger 3 and then subjected to slit exposure in the exposure section 13 .

Then, the electrostatic latent image is visualized with toner in a developing device 14. The four developing units, yellow 141, magenta 142, cyan 143, and black 144, are supported by a frame rotatable around a rotating shaft 145, and are designated in correspondence with the color separation filter 11. The developing device works to obtain a toner image of the desired color (yellow in FIG. 2).

The transfer material 171 in the cassette 17 is fed into the machine by the paper feed roller 18, approximate timing is determined by the second register roller 20, accurate timing is determined by the second register roller 20, and then by the guide 21. Transfer drum 1
It is gripped by the gripper 151 on 5. The toner image on the photosensitive drum 1 is transferred onto the transfer material while the transfer material 171 is conveyed while being wrapped around the drum 15 as the transfer drum 15 rotates, and passes between the transfer discharger 27 and the photosensitive drum 10 (transfer position). is transcribed. The transfer drum 15 has a gripper 151
While gripping the tip of the transfer material 171, the transfer material 171 is rotated by the required number of rotations, and an image of the required number of colors is transferred.

After the final color toner image is transferred, the transfer material does not separate from the transfer drum immediately, but rotates while being held by the transfer drum. Due to this rotation, the transfer material is wrapped around the transfer drum and transferred. The final color toner image is transferred to the trailing edge of the material. After the transfer is completely completed, the transfer material is transferred to a static eliminator 28.
．． 29, the gripper 151 is released from adsorption to the transfer drum 15, and at the separation position S, the gripper 151 rides on the cam 3I and opens. At the same time, it is released from the gripper and is guided to the conveyor belt 33 by the separation claw 32, and then the fixing device 34. The image is fixed by the paper ejection roller pair 35 and ejected onto the tray 36 . After the transfer, the surface of the photosensitive drum l is cleaned by a cleaning device 16 composed of a blade, and the photosensitive drum l proceeds to the next cycle.

FIG. 1 shows a timing chart of an embodiment of the present invention. When the final toner image is transferred by overlapping four colors,
It starts at point A, just before the end of four rotations of the transfer drum.

At this time, the gripper 151 does not open during exposure and transfer of the final color, and the transfer drum 15 enters additional rotation with the transfer material 171 wound thereon. When the transfer is completely completed by additional rotation, the transfer discharger 27 is also turned off, but the transfer drum 1
Immediately before the leading edge of the transfer material 171 on the transfer material 171 reaches the point A again, discharge with a polarity opposite to that of the toner starts. Conventionally, the idea of giving additional rotation to the transfer drum in order to prevent color shift and image unevenness caused by the laser sequence when the final color is being exposed and transferred during one separation is insufficient. The mechanical contact between the transfer drum 15 and the photosensitive drum 1, or the shock caused by the gripper 151 riding on the cam during separation, causes rotational misalignment between the transfer drum 15 and the photosensitive drum 1, which causes the toner image on the transfer material to become photosensitive. There is a drawback that the image is transferred to the drum 1 in the opposite direction.

Furthermore, the reverse transfer to the photosensitive drum l differs depending on the potential of the surface of the photosensitive drum.

The surface of the photosensitive drum usually settles down to approximately Ov when the transfer is completed, but some charge of the opposite polarity to that of the toner may remain. In this case, even if the drum transfer material is not in mechanical contact with the toner, the toner is electrostatically attracted to the photosensitive drum, resulting in disturbance of color balance.

However, as in the present invention, when a charge with a polarity opposite to that of the toner is applied from a transfer charger to the back surface of the transfer material during the additional rotation, reverse transfer to the photosensitive drum can be prevented. Also, of course, adjusting the drum potential can also enhance this result.

Therefore, there is no problem in keeping the transfer discharger ON until the separation is completed.

After the additional rotation, the transfer material is neutralized by the separation charger, and when the gripper rides on the cam and opens, it is separated, conveyed, and fixed and discharged.

As a result of the above configuration, the resulting image becomes a high-quality picture free of color shift due to shock during separation and image unevenness due to reverse transfer to the photosensitive drum during additional rotation.

[Other Examples]

The above has described the case of multiple transfer in a color copying machine, but it goes without saying that it is also highly effective to apply the present invention to the sequence of monochrome image formation by avoiding a sequence in which separation occurs immediately after transfer. .

〔Effect of the invention〕

As explained above, when the transfer material is separated from the transfer material support and additional rotation is performed to prevent exposure deviation and transfer deviation, when the transfer material returns to the transfer position, the transfer discharge device is discharged again. This prevents the toner on the transfer material to the image carrier during additional rotation from being offset to the image carrier, thereby making it possible to obtain a high-quality image without image unevenness or blur.

In the above embodiments, a full-color electrophotographic apparatus is exemplified, but the present invention is also effective for an apparatus that transfers different patterns using toner of the same color in an overlapping manner. Further, the image carrier may be not only a photoreceptor but also an insulator that carries a static image, and its shape is not limited to a drum but may be a belt. Further, the transfer material support is not limited to a drum shape, but may be an endlessly movable belt shape.

[Brief explanation of drawings]

FIG. 1 is a timing chart showing the timing of transfer and separation and the operation timing of the transfer discharger according to an embodiment of the present invention; FIG. 3 and 4 show conventional transfer/separation timing and operation timing charts of a transfer discharger. In the figure, 1-----1 photosensitive drum, 15-----1 transfer drum, 27-----transfer discharger, 151--1--
Clipper, 32------- One-separate claw, T----
--1--transcription position. 5--------- Indicates one minute position.

Claims (1)

[Scope of Claims] A multiple image in which the leading end of a transfer material is gripped by a support that is synchronously and integrally driven in close proximity to or in contact with the image carrier, and the toner images on the image carrier are sequentially superimposed and transferred onto the transfer material. In the forming device, in order to separate the transfer material from the support after the final transfer in the overlapping transfer, additional rotation is applied to the support, and during this additional rotation, at least the transfer material remains at the transfer position. A multiplex image forming apparatus characterized in that when the toner is used, the transfer discharge device performs discharge with a polarity opposite to that of the toner.