JPS63149672A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce ground fogging at the time of forming a multiplex image by changing a developing bias to be impressed to a developing means at the time of forming normal image and at the time of forming a multiplex image. CONSTITUTION:A photosensitive drum 1 is electrostatically charged by a temporary charger 2 and an image is exposed 3 to the drum 1 to form an electrostatic latent image. The latent image is converted into a sensible image by toner supplied by a developing device 4, transferred to a transfer material 5 by the action of a transfer charger 6 and carried to a fixing device 7 so as to be fixed. In multiplex copying, the transfer material 5 is refed to the charger 6 through a transfer material returning carrying path 9, transferred again and then discharged from a transfer material carry-out line 8. When a switch 14 for selecting normal copy or multiplex copy is switched, a control circuit 15 switches a developing bias to be impressed from a bias power supply 13 to a developing sleeve 11 or a carrying course. Thus, ground fogging at the time of forming a multiplex image can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a method for transferring a plurality of original images onto the same side of the same transfer material.
The present invention relates to an image forming apparatus such as an electrophotographic apparatus having a multiple image forming mechanism for copying.

(Prior Art) Conventional image forming apparatuses of this type perform normal copying in which one document image is copied onto a transfer material, and two or more document images are copied onto the same side of the same transfer material. It is now possible to perform both multiple and multiple copies. In other words, 1. In normal copying, an electrostatic latent image is formed on the surface of a moving photoreceptor drum by image exposure corresponding to the original image, and a predetermined developing bias consisting of a DC component and an AC component is applied to a developing drum containing a developer. By applying Coulomb force to the developer, the developer adheres to the electrostatic Wi image to form a developed image. Thereafter, this developed image was transferred to a transfer material by a transfer charger and fixed by a fixing device.

In addition, in multiple copying, the normal copying is performed twice on the same side of the same transfer material by using a transfer material return conveyance path for copying again on the transfer material that has been subjected to the normal copying.
It is now possible to combine different original images by applying the process more than once.

(Problems to be Solved by the Invention) However, such prior art has the following problems. In other words, in normal copying, emphasis is placed on improving the image quality while also eliminating dirt in the background of the image.
A developing bias is applied to increase the image quality and density within an inconspicuous range. However, in multiple copying, since multiple transfers are made on the same side of the same transfer material, using a developing bias that focuses on image quality will result in the overlapping of soil blurring, which is not noticeable in normal copying. There was a problem with it being noticeable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to change the developing bias of the developing device between normal copying and multiple copying. The aim is to provide clear images with no background guff even at times.

(Means for Solving the Problems) In order to achieve the above object, in an image forming apparatus according to the present invention, a latent image formed on an image carrier corresponding to an original image is developed by a developing means. It is possible to perform normal image formation in which a developed image is formed, and this developed image is transferred and fixed onto a transfer material, and also to carry out multi-ITI: image formation in which the normal image formation is performed multiple times on the same side of the same transfer material. In this image forming apparatus, the development bias applied to the F stage of development is changed between normal image formation and multiple image formation.

(Function) In the present invention having the above configuration, by changing the developing bias applied to the developing means between normal image formation and multiple image formation, the blurring during multiple image formation is reduced. .

(Example) The present invention will be explained below based on the illustrated example. 1st
In the embodiment shown in the figures and FIG. 2, l is a photosensitive drum as an image carrier, 2 is a temporary charger, 3 is an image exposure device, 4 is a developer, 5 is a transfer material, 6 is a transfer charger, 7 is a fixing device; 8 is a transfer material discharge path; 9 is a transfer material return conveyance path; 10
is a cleaning device.

The photosensitive drum 1 is uniformly charged by a temporary charger 2 and then subjected to image exposure 3 to form an electrostatic latent image. Then, as the photosensitive drum 1 rotates, the latent image becomes a transferable developed image with toner supplied by the developing device 4. This I11 image is transferred to the transfer material 5 by the action of the transfer charger 6, and is conveyed to the fixing device 7 where it is fixed. Here, in normal copying in which one image is transferred onto the transfer material 5, the transfer material 5 is discharged from the transfer material discharge path 8.

In addition, in multiple copying where an image is transferred, for example, twice to the same side of the same transfer material 5, the transfer material 5 is re-fed onto the transfer charger 6 through the transfer material return conveyance path 9, and is then re-fed onto the transfer charger 6 again. After the transfer is performed, the transfer material is discharged from the transfer material discharge path 8. It should be noted that toner remaining on the photosensitive drums i, h without contributing to transfer reaches the cleaning device IO and is scratched off by a cleaning blade.

Further, this embodiment has the following configuration in addition to the above configuration. That is, 11 is a developing device sleeve disposed with a predetermined gap between the photosensitive drum 1 and the developing device sleeve 1.
1 includes a fixed magnet roller so as to hold magnetic toner on its surface. 12 is developer sleeve 1
The magnetic blade 12 is a magnetic blade disposed with a small gap from the developer sleeve 11, and the magnetic blade 12 scrapes off the magnetic toner adhering to the surface of the developer sleeve 11 to form a single layer of magnetic toner with a uniform thickness. A developing bias having a direct current component and an alternating current component is applied to the developing device sleeve 11 by a bias power supply 13, and jumping development is performed using magnetic toner charged with a negative 4n current. moreover,
The developing bias is set differently for normal copying and multiple copying, and when the selection switch 14 for selecting normal copying and multiple copying is changed to νJ4J, the control circuit 15 switches the bias power supply 13, the conveyance path, etc.

In the above configuration, the image density and latent image potential on the surface of the photoreceptor drum 1 when the DC component voltage VPC, the AC component voltage (peak-to-peak value: Vpp), and the frequency 1af of the developing bias are changed are shown in FIG. There is a similar relationship. That is, FIG. 2(a) shows the relationship between image density and latent image potential when the DC component voltage VDC of the developing bias is changed.As the DC component voltage VOC of the developing bias increases, the developing device sleeve 11 Since negatively charged magnetic toner is strongly attracted, a high latent image potential is required to obtain the same image density. FIG. 2(b) shows the relationship between the image density and the latent image potential when the AC component voltage VPP of the developing bias is changed. As the AC component voltage VPP of the developing bias increases, it transfers to the surface of the photoreceptor drum 1. As the amount of magnetic toner increases, the image density becomes higher. Figure 2 (C) shows the alternating current component frequency f of the developing bias.
This shows the relationship between image density and latent image potential when changing . As the frequency f increases, the number of transfers of magnetic toner during jumping development increases, so high image density can be obtained with a low latent image potential.

In the above configuration, in the image forming apparatus according to the present embodiment, ground force blur can be prevented in the following manner. That is, since the ground blur in the image background becomes more noticeable when the image density increases, the image density is reduced by changing the DC component voltage VDC1, AC component voltage VPP, and AC component frequency f of the developing bias during multiple copying as follows. In this embodiment, the developing bias during normal copying is set to oc=100V.
, Vpp=1200V, f=1500Hz, and during multiple copying, the developing bias is vDc=110V, Vpp=1
200V, f=1500Hz and DC component voltage VDC as I
By simply increasing the OV, there was no problem with the image quality, and multiple copies could be made without blurring. Also, the AC component voltage VPP
By lowering or lowering the frequency f by 1,
Alternatively, by combining changes in any one of the AC component voltage VPP, the frequency f, and the DC component voltage VDC, multiple copies can be performed without any problem in image quality and without local blurring.

In this embodiment, the developing bias during multiple copying is changed in all the steps of multiple copying. Only the first development bias may be changed.

Further, in this embodiment, a one-component magnetic toner was used as the developer, but a developing method using a two-component developer can also be used.

(Effects of the Invention) The present invention consists of one or more configurations and functions, and by changing the developing bias during normal copying and during multiple copying, it is possible to obtain clear images without blurring even during multiple copying. be able to.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention, and FIGS. 2(a), (b), and (C) show image density and latency in the same embodiment. It shows the relationship between image potentials, and Figure 2 (a
) is a graph when the DC component voltage VDC of the developing bias is changed, Figure 2 (b) is a graph when the AC component voltage VPP of the developing bias is changed, and Figure 2 (C) is a graph when the AC component voltage VPP of the developing bias is changed. It is a graph when the component frequency f is changed. Explanation of symbols 1... Photosensitive drum (image bearing member) 4... Developing device (developing means) 5... Transfer material Figure 1 (C) (b) tvj

Claims (1)

[Claims] A latent image formed on an image carrier corresponding to an original image is developed by a developing means to form a developed image, and this developed image is transferred and fixed onto a transfer material. In an image forming apparatus capable of performing multiple image formation in which normal image formation is performed multiple times on the same side of the same transfer material, a developing bias applied to the developing means is changed between normal image formation and multiple image formation. An image forming apparatus characterized by: