JPH01261685A - Image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus capable of forming double-sided or composite images and having a pre-transfer exposure step.

BACKGROUND ART In an image forming apparatus using an electrostatic photographic process such as an electrophotographic copying machine or an electrostatic printer, an electrostatic latent image is formed by exposing a photoreceptor uniformly charged with a charger to image light.
It is developed into a toner image by a developing device, and the toner image is transferred to transfer paper by the action of a transfer charger.
The transferred transfer paper is separated from the photoreceptor and then fixed to form an image.

Between the above-mentioned development process and transfer process, the photoconductor on which the toner image is formed is irradiated with light to attenuate the charge of the electrostatic latent image under the toner image, and the transfer current in the transfer process is efficiently transferred to the transfer material. Pre-transfer exposure (pre-exposure) that allows stable transfer efficiency to be obtained from low to high transfer currents by
transfer light-ting, P T
The process (abbreviated as L) is well known.

In addition, in recent years, the toner image has been transferred and fixed, and the transfer paper on which the image has been formed is automatically circulated within the main body of the machine and fed again to the transfer section along the photoreceptor, so that it can be printed again on the same surface. Many devices have appeared that perform compositing to create a transferred image and double-sided image formation to create a transferred image on the other side.

FIG. 1 is a diagram showing a schematic configuration of an example of a multicolor copying machine that has a PTL process and is capable of forming double-sided and composite images.

In FIG. 1, around the photosensitive drum 1.

Charger 2, exposure position 3. a first developing device 4, a second developing device 5, a pre-transfer exposure device 6, a transfer/separation charger 7,
A cleaning device 8 and a static eliminator 9 are provided. An electrostatic latent image formed on the photoreceptor 1 by being charged by the charger 2 and subjected to image exposure by the exposure section 3 is developed by either the developer 4 or 5 to form a toner image. After being subjected to pre-transfer exposure in the PTL 6, the toner image is transferred to a transfer paper by a transfer separation charger 7, separated across the photoreceptor 1, and fixed by a heat roller fixing device 8 in the case of a one-sided single copy. 5 were ejected from the aircraft.

Circulating conveyance path 9 when performing composite copying or double-sided copying
is automatically circulated, and in the case of double-sided copying, the front and back sides are reversed at a reversing section (not shown), and the photoreceptor 1 is transferred through the registration rollers 10.
The paper is re-fed to the transfer section between the transfer charger and the transfer charger, and the second transfer is performed.

As shown in this example, when a heat roller fixing device is used as the fixing device, the leading edge of the transfer paper after fixing is curled, and in the case of 1 composite 1 double-sided copying, the curled area toward the photoconductor during the second transfer is Separation failure occurs, causing an abnormal image in which the transferred toner image is transferred to the photoreceptor again.

It has been confirmed that PTL is effective in preventing this phenomenon as well. However, in order to completely prevent reverse transfer, it is necessary to attenuate the electrostatic latent image under the toner image until it almost disappears, and the amount of light must be considerably greater than the amount of light required to obtain stable transfer efficiency. There was found.

Since PTL is performed from above the toner after development and acts on the latent image under the toner, it causes optical fatigue in most areas to which no toner is attached. Specifically, it appears as an afterimage phenomenon due to the memory effect at short ranges, and as changes in charging and light attenuation characteristics at long ranges. From these facts, it was concluded that it is better to have a smaller amount of light irradiated by PTL, and it was found that the direction does not match that of PTL, which is aimed at preventing reverse transfer during compositing and duplexing.

FIG. 2 is a graph showing the effect of PTL on improving transfer efficiency and the effect of preventing reverse transfer when separated from the photoreceptor after transfer. In FIG. 9 to 1,0 mg/d This shows the potential on the photoreceptor and toner after PTL when toner is attached, and the smaller the potential, the larger the amount of PTL light.
For the transfer efficiency indicated by the O symbol, a stable region can be obtained with the amount of light required to attenuate to 300 V or less, but for the reverse transfer of toner, the amount of light that is attenuated to zo○■ is obtained as indicated by the mark. is necessary.

FIG. 3 shows the degree of influence on the residual potential among the electrostatic characteristics of the photoreceptor with respect to the number of sheets passed using the PTL light intensity in FIG. 2 as a parameter.

From this, it can be seen that the amount of light when the potential after PTL is Ov causes more than twice as much deterioration on the photoreceptor as the amount of light when the potential after PTL is 200V.

In view of the above-mentioned fact regarding improvement of transfer efficiency and prevention of toner reversal in pre-transfer exposure, the present invention provides an image forming apparatus that performs pre-transfer exposure so as to maximize both effects. The purpose is to

[1] In order to achieve the above object, the present invention is characterized in that the exposure amount in the pre-transfer exposure step can be switched between large and small, and this is switched within the image area on the photoreceptor.

The switching method is preferably such that the exposure amount before switching is greater than the exposure amount after switching. The timing of this switching is determined by the pre-transfer exposure, when the device irradiates a position away from the leading edge of the image by a length exceeding the curl length of the front edge of the transfer paper, or by the separation charger that separates the transfer paper from the photoreceptor. The point at which the pre-transfer exposure device irradiates the toner image may be set at a position that is away from the leading edge of the toner image on the photoreceptor by at least the distance up to the nail.

The exposure amount of the pre-transfer exposure device which has been switched to a small capacity may be switched to a high light amount just when the leading edge of the next toner image on the photoreceptor approaches the irradiation surface of the pre-transfer exposure device.

Furthermore, if the pre-transfer exposure device is turned off while the non-image area passes through, it is more effective to prevent deterioration of the electrostatic characteristics of the photoreceptor.

EMBODIMENT OF THE INVENTION Below, one embodiment of the present invention will be described in detail based on the drawings.

Now, the inventor conducted an experiment and confirmed that the area where toner reverse transfer occurs is the curl area that occurs at the leading end of the transfer material 11 after passing through the heat roller fixing device 8, as shown in FIG. (denoted by Ql in the figure), or as shown in FIG. ) was the front end of the transfer material 11. If this is expressed using the angle θ with respect to the center of the photoreceptor, it becomes θ Q2=2πrX −□ 360′.

From the above, the amount of light that sets the potential after PTL to 0 (v) only needs to be irradiated to the portions of the image area on the photoreceptor corresponding to these areas. In other areas, if the amount of light is set such that the potential after PTL reaches 200 V, which is the limit of transfer efficiency, deterioration of the electrostatic characteristics of the photoreceptor and abnormal images due to afterimages can be reduced. Therefore, PTL
The exposure amount can be switched between two types, large and small, and the area Q4. where the above-mentioned reverse transfer of toner occurs. By switching to irradiate the image area on the photoreceptor corresponding to Q with a large amount of light and irradiate other parts with a small amount of light, reverse transfer of the toner image can be prevented and the transfer reversal rate can be improved. In addition, it is possible to reduce abnormal images and deterioration of electrostatic characteristics due to afterimages due to deterioration of the photoreceptor.

From the above, it is possible to switch the PTL light intensity within the image area on the photoconductor 1 into two types: E, , E, (E
TL When the exposure area is as close as possible to the irradiation area.

For example, if the developing bias value is controlled for the non-image area and the image area on the photoconductor, the device has the following settings: the timing of applying bias to the image area, the on-timing of the registration roller that conveys the transfer paper to the transfer charger, etc. You can select and use the appropriate one from each timing.

Also, the timing for switching to the low light amount E2 is as described in 21. above.
α8 in the range beyond Q2. Let it be a point close to Q, and El
Similarly to the switching to E2, an appropriate timing may be selected from among the timings provided in the device, or a timer may be used to count the time from the time of E□ large input to switch to E2 manual power.

Note that when there is no toner image on the photoreceptor, control may be performed so that PTL irradiation is not performed in order to prevent deterioration of the photoreceptor due to direct light irradiation on the photoreceptor.

As means for switching the light amount of the PTL, (a) change the voltage (current) input to the lamp.

(b) For devices such as LED arrays that consist of multiple light emitters, change the number of light emitters lit.

(c) The amount of light from the lamp is always constant, and a filter or the like is mechanically switched and inserted into the optical path.

(d) It is possible to adopt a method such as preparing two types of lamps with different amounts of light and switching the lamp that emits light.

As described above, according to the present invention, by appropriately controlling the amount of PTL light, it is possible to improve transfer efficiency and prevent toner reverse transfer, while at the same time reducing unnecessary irradiation onto the photoreceptor. By reducing the amount of light, it is possible to prevent afterimages and deterioration of electrostatic characteristics.

[Brief explanation of the drawing]

FIG. 1 is a side view showing a schematic configuration of an example of a copying apparatus to which the present invention is applied, FIG. 2 is a graph showing the relationship between the potential after PTL, transfer efficiency, and toner reverse transfer level, and FIG. 3 is a paper passing A graph showing the change in residual potential with respect to the number of sheets using the post-PTL potential as a parameter, and FIGS. 4 and 5 are explanatory diagrams showing portions where toner reverse transfer is likely to occur, respectively. 1...Photoconductor 4.5...Developer 6...Pre-transfer exposure device (PTL) 7...Transfer/separation charger 8...Heat roller fixing device 11...Transfer paper 12...・Separated claw transfer 2 volumes ('/,) Toner Okahira Eisha Rehercil Rujo II (V)

Claims (6)

[Claims] (1) It has the following steps: developing and transferring the electrostatic latent image formed on the photoconductor by the electrophotographic process, separating the transfer paper, and fixing it with a heat roller fixing device, and automatically fixes the transfer paper after fixing. It is possible to form a double-sided image or a composite image by refeeding the paper, and between the development process and the transfer process, the photoreceptor is irradiated with light to attenuate the electrostatic latent image charge under the toner image. An image forming apparatus having a pre-transfer exposure step, characterized in that the exposure amount in the pre-transfer exposure step can be changed in magnitude, and the exposure amount can be changed within an image area on a photoreceptor. (2) The image forming apparatus according to claim 1, wherein the exposure amount switched within the image area in the pre-transfer exposure step is larger than the exposure amount after switching. (3) The timing of switching the pre-transfer exposure amount to a small light amount is the time when the pre-transfer exposure device irradiates a position away from the leading edge of the image by a length that exceeds the curled length of the leading edge of the transfer paper. The image forming apparatus according to claim 2, characterized in that: (4) The timing of switching the pre-transfer exposure amount to a small light amount is at least the length of the total surface distance from the separator that separates the transfer material from the photoreceptor to the mechanical separation means, and the distance from the leading edge of the toner image on the photoreceptor. 3. The image forming apparatus according to claim 2, wherein the position is at the time when a pre-transfer exposure device irradiates the position. (5) The timing of switching the exposure amount from the small light amount to the high light amount in the above pre-transfer exposure step is when the leading edge of the next toner image on the photoconductor has not yet arrived and is as close as possible to the irradiation surface of the pre-transfer exposure device. The image forming apparatus according to claim 2, wherein the image forming apparatus is a period. (6) The image forming apparatus according to claim 1, wherein the pre-transfer exposure device is turned off while the non-image area of the photoreceptor passes through an irradiation section of the pre-transfer exposure device.