JPS58122565A - Electrophotographic picture stabilizing method - Google Patents

Abstract

PURPOSE:To make a good constant continuous pictures formation possible, by changing the strength of exposure or charging for formation of a latent image in accordance with the change of the surface potential of a photoreceptor which is generated according to the number of continuously formed copies. CONSTITUTION:In case that images are formed repeatedly in a high speed, the potential of the surface of the photoreceptor tends to rise, and the image density becomes higher according as the number of formed copies is increased. This inclination cannot be resolved by dimming of a single time constant. Therefore, an original picture exposure means 14 is controlled by an original picture exposure controlling means 30. For example, in a graph where the number of continuously formed copies is indicated on the axis of abscissas and the voltage of an original picture exposure lamp which is the original picture exposure strength to be given by the expsoure means 14 is indicated on the axis of ordinates, the voltage of the lamp is changed in accordance with an exponential function curve (a), and the voltage of the lamp is changed in accordance with a curve (b), which is connected to the curve (a) and has a time constant longer than that of the curve (a), after the curve (a) is saturated approximately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic image forming method, and in particular, to a method for forming an image on a photoreceptor (also referred to as a latent image carrier), which always produces a good and constant image. The present invention relates to an image stabilization method in electrophotographic image formation that makes it possible to obtain images.

Conventionally, there have been methods such as the Carlson method, in which image formation is performed through the processes of charging, exposure of the original image, and development, or the NP method, in which image formation is performed through the processes of -order charging, original image lightless simultaneous secondary charging, and development. When the photoreceptor is repeatedly used in an electrophotographic image forming method, the photoreceptor receives the history of the previous image formation, subsequent image erasure, and rest time, so that an image of exactly the same level as the previous image is obtained. There may be no. That is, when image formation is repeated at high speed, image quality defects appear when image formation is performed using conventional processes. In particular, as a defect in image quality, a memory phenomenon is observed in which a previously formed image appears superimposed on a repeatedly formed image copy. There is also a phenomenon in which the image quality differs between each copy, and the image quality of the copy image formed later is higher than that of the first copy image.

The latter phenomenon indicates that the surface potential of the photoreceptor is low at the time of initial copy formation and tends to gradually increase as image formation is repeated. For example, in NP Glossene, this phenomenon may be found when image formation is repeated within 3 seconds.

Although this difference in image quality becomes smaller as the image forming machine is repeatedly operated, the difference in image quality becomes more noticeable when the machine is stopped and restarted.

This phenomenon is particularly noticeable when forming images repeatedly at high speed, especially when using a photoreceptor with good photosensitivity. The causal mechanism of this phenomenon F
Although it is not clear, since the photoreceptor is repeatedly used for image formation at high speed, it is subjected to charging and exposure R for image formation, and this rapidly accumulates, so that the dark resistance of the photoreceptor is substantially reduced. This is thought to be the result of an increase in the number of children. When the continuously formed copy image density k becomes darker one after another as image formation is repeated, it is called a rise-up mark, and conversely, when it becomes gradually lighter, it is called a fall-off mark. The time until this rising edge (lower edge) reaches saturation is called the rise time, and the density difference or latent image potential difference between the first copy and the copy when the density is saturated is called the rising edge (lower edge) width.

Conventionally, as a method for correcting such changes in the surface potential of the photoreceptor during continuous repeated use, the photoreceptor has a correction amount that increases exponentially depending on the machine's down time, and further increases the amount of correction for the number of copies made. There is a non-light adjustment method (hereinafter abbreviated as dimming) that provides an original image exposure that changes exponentially, and a charging current adjustment method that provides a charge similar to the above (hereinafter abbreviated as current adjustment). There is.

However, since this method can only provide a certain amount of correction, it cannot respond to changes in the usage history of the photoreceptor or the usage atmosphere, and a phenomenon occurs in which the amount of correction does not perfectly match. That is, as the usage history of the photoreceptor progresses, the rise width becomes larger and the rise time becomes longer, and similar phenomena appear as the relative humidity of the atmosphere decreases. Therefore, simple light adjustment or flow adjustment cannot fully respond to the usage conditions of the electrophotographic image forming apparatus, and it is difficult to maintain a constant density of continuously formed copy images.

In view of the above-mentioned points, the present invention provides an electrophotographic image stabilization method that solves the above-mentioned problems and makes it possible to form good and constant continuous images.

In the electrophotographic image stabilization method of the present invention, when forming a latent image continuously and repeatedly on a latent image carrier, IIA that contributes to latent image formation is used.
IIhi Image exposure intensity, charging intensity, or both intensities are changed over time as a substantially exponential function with the start of continuous repeated formation of a latent image, and after #1 is saturated, the intensities are continuously changed and It is characterized in that it changes over time as a different exponential function with a time constant substantially different from the above-mentioned exponential function.

Next, embodiments of the present invention will be described in detail.

FIG. 1 is a side view of an example of an electrophotographic image forming apparatus capable of performing a non-explosion process. The photosensitive drum 1 has an insulating layer on its surface so that an electrostatic latent image can be formed by an electrophotographic method based on the NP process described above, and is supported rotatably in the direction of the arrow in the figure. Tangnutensin, which acts as a pre-exposure means, is on its circumferential surface! A light source 11 such as the like, a static eliminator 12 for erasing the residual charge on the photoreceptor are arranged first, and then a primary corona discharger 13 for applying primary corona radiation to form a latent image;
For example, at the same time as the original image is exposed by the A image recording means 14, -
DC corona discharge with opposite polarity to the next corona discharge, AC: ffO
a secondary corona discharger 15 that generates a secondary corona discharge, or a combination of both; and a light source 1 for full-surface exposure.
6 are arranged, and a round developing device 17 that develops the electrostatic latent image formed on the photoreceptor drum, a round transfer corona discharger 18 that transfers the developed image to the transfer material 20, and a post-transfer photosensitive device. A cleaning means 19 and the like are arranged to remove developer remaining on the body. Note that the original image exposure means 14 is connected to an original image exposure control means 30, which will be described in detail later. The photosensitive drum used is an aluminum cylinder on which a photosensitive layer made of 4-doped cadmium sulfide and a resin is provided, and the surface is an insulating resin layer. The steps to obtain the image are as follows.

First, the photoreceptor is exposed to light by the front lightless means 11.

□ Apply +7.0 kV to the primary corona discharger 13,
Uniformly charges the surface of the photoreceptor. Next, at step i, the original image exposure means 14 exposes the photoreceptor surface to 6.5 kV.
Corona static elimination is performed by the secondary corona discharger 15 to which an AC voltage of . Next, the surface of the photoreceptor is uniformly irradiated by the entire surface exposure source 16 to complete latent image formation1.The electrostatic latent image thus formed is developed by, for example, sleeve development in the developing device 17. Ru.

A transfer material 20 is superimposed on this developed image, and a transfer corona is applied from the back side using the transfer corona discharger 18.

After the transfer is completed, the transfer material 20 is separated from the photoreceptor 1,
The images are fixed using a fixing device as shown in the figure, and a copy is provided.

On the other hand, residual developer L91J on the surface of the photoreceptor after completion of transfer
- removed by Jung means 19; and on photoreceptor 1
When forming an image in step 9, the pre-exposure means 11 and the static eliminator 1
2 is applied to erase the exposure history and charging history.

Incidentally, as described above, the potential on the surface of the photoreceptor tends to increase when image formation is performed repeatedly at high speed, and the image density increases as the number of copies formed increases. This tendency cannot be eliminated by conventional dimming or flow adjustment using a single time constant. Ki 2 is the reason.
This is a correlation diagram showing the number of continuous copies made on the horizontal axis and the surface potential of the photoreceptor on the vertical axis. FIG. 3 is a diagram showing a case where a photoconductor that has undergone a usage history of 200 days is used in an atmosphere at a temperature of 20° C. and a relative humidity of 30° C. In the curve in Figure 2, ■D
is the mflll potential of the dark part of the original (density 1.2 or higher), vH
T#i represents the latent image potential of the original density of 0.3, and vL represents the latent image potential of the bright area of the original density of 0.07. In this way, a photoreceptor that has been used many times shows a large rise phenomenon as continuous copies are made in a low humidity atmosphere, and the way it rises is an exponential function until the first 10 copies are made. However, when the number of copies exceeds 1, it increases slightly with respect to the number of copies made. Conventional dimming, the charging of a capacitor when a DC voltage is applied to a circuit consisting of a Choryusha capacitor and a resistor, or the voltage change due to discharge during a short circuit is used as a signal source for correcting the rise of the photoreceptor. It is something. Therefore,
Since the time constant is equal to the value of the capacitor capacitance multiplied by the resistance, the above voltage change curve is also a constant exponential function.
If the potential change of the photoreceptor has a curve different from the function as shown in FIG. 2, even if the above-mentioned dimming and flow adjustment is applied, the yield difference between copies cannot be completely eliminated. This is the reason why it has not been possible to completely correct a photoreceptor exhibiting a rise as shown in FIG. 2 in the past.

According to the present invention, in order to eliminate the drawbacks of the conventional light control or flow adjustment method, the photoreceptor surface potential changes as shown in FIG. 2 according to the number of continuous copies made. The intensity of exposure or charging of the original image to be applied to form a latent image is changed as the total number of continuous copies to be made, and therefore the time, increases. That is, the third
The figure shows an example of changing the intensity of original image exposure according to the present invention, where the horizontal axis shows the number of continuous copies (and thus the continuous copy forming time), and the vertical axis shows the original image exposure intensity. 14 indicates the voltage of the original image exposure lamp which is the original image exposure intensity to be given. The Lanzo voltage is continuous
At the same time as the start of formation #! This song +Vi! is changed according to an exponential curve a. After a is almost saturated, the time constant is changed in accordance with the longer curve line than that of the curve number. If the time constants of curves a- and b are selected according to the change characteristics of the photoreceptor potential as shown in Fig. 2, it is possible to automatically obtain a copy image that is sufficiently corrected for such rising characteristics. Ru. The control of the original image exposure intensity as described above is shown in FIG.
This is done by controlling the original image exposure means 14 by the g-light control means 30.

Although FIG. 3 shows the case where the intensity of exposure of the original image is controlled, it is alternatively possible to control the intensity of charging for forming an electrostatic latent image on the photoreceptor in the same way, or to control both of the above-mentioned intensities. may be similarly controlled.

The results of experimental examples using the image stabilization method of the present invention are described below.

Experimental Example □ Process Nupid 300w/@.cO Original image exposure voltage control according to the image stabilization method of the present invention was applied to an electrophotographic image forming apparatus as shown in FIG. The initial voltage change (Fig. 3) is determined by the time constant τ1 = 1.
0 seconds, and the change in rung voltage in the latter half (song 11i1 b
K phase 'A) is timed to -60 seconds ft-
0 Using a photoreceptor that has been used for approximately 50,000 sheets, the temperature is 15.
Continuous copying was performed in an atmosphere of .degree. C. and relative humidity [25 Is. As a result, the image density did not change even after 99 continuous copies were made.

For comparison, when the time constant was set to only 10 seconds under the same conditions, images with constant saponification were obtained up to the 10th image, but after that, the density gradually increased, and by the 99th image, 1~lO
A difference in concentration of approximately 0.3 was observed from the 1st sheet to the 1st sheet.Also, when the time constant was set to only 60 seconds, the concentration increased exponentially from the 1st sheet, and from about the 10th sheet Although there was no change in image density until the 9th image, the difference in density between the 1st image and the 99th image was approximately 0.064.

As described above, the image stabilization method of the present invention has a remarkable effect of correcting the inconvenient 1-up characteristic due to the usage history of the photoreceptor, compared to the conventional single index yAe dimming or 1-stream dimming. This greatly improves the durability of photoreceptors in electrophotographic image forming apparatuses.

[Brief explanation of the drawing]

FIG. 1 shows an example of an electrophotographic image forming apparatus to which the present invention can be applied, FIG. 2 shows an example of changes in photoreceptor surface potential during continuous copy formation, and FIG. 3 shows an example of an electrophotographic image forming apparatus to which the present invention is applied. An example of how to change the image exposure voltage is shown below.

Claims (1)

[Claims] When continuously and repeatedly forming a latent image on a latent image carrier, the original image mist intensity, charging intensity, or both of them, which contribute to latent image formation, are substantially reduced at the same time as the continuous and repeated formation of the latent image begins. The term "percentage sign" means that the index function changes over time as an exponential function, and after it becomes almost saturated, it changes over time as another exponential function that is continuous with it and has a time constant substantially different from that of the above exponential function. An electrophotographic image stabilization method.