JPS6139667B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to xerography, in particular, to an AC corona generator in which the electrostatic adhesion force between a transfer paper and a photoreceptor surface generated by electrostatic transfer is applied to a DC bias voltage. The present invention relates to a method of reducing toner-laden transfer paper (hereinafter referred to as "separation charge"), thereby easily separating toner-laden transfer paper from a photoreceptor.

In conventional xerography, the surface of the photoreceptor is uniformly electrostatically charged, the charged surface is exposed to a light image of the original image to be reproduced, and areas of the surface that are struck by the light are discharged. In this way, the areas that are not discharged form an electrostatic latent image that follows the outline of the original pattern. Next, this electrostatic latent image is brought into contact with toner having a polarity opposite to the above-mentioned charge to be developed. In this case, the image density is adjusted by a developing bias voltage applied to a developing roller facing the photoreceptor. The amount of toner attached increases or decreases depending on the amount of electrostatic charge on the surface of the photoreceptor and the amount of developing bias. The transfer paper is then advanced in synchronous contact with the toner image thus formed.
During this synchronous contact period, a voltage with a polarity opposite to that of the toner is applied from the back side of the transfer paper to electrostatically attract the toner image from the photoreceptor to the transfer paper, thereby performing transfer. The transfer paper is then subjected to a corona discharge by a separation charger to reduce the electrostatic charge holding the transfer paper on the photoreceptor, and the transfer paper is separated from the photoreceptor by a suitable separation means, such as the transfer paper's own weight. .

However, conventional static elimination of transfer paper using separated corona is performed with a certain level of strength. It is known that the amount of static electricity removal can be switched between the leading edge and the trailing part of the transfer paper, but the strength of static elimination at the leading edge or the trailing part of the transfer paper is still constant. In order to achieve this, efforts are being made to make the AC high voltage power source of the separation charger constant current. However, there were still cases where the transfer paper did not separate from the photoreceptor, and poor separation occurred in 10/10,000 times.

An object of the present invention is to improve the probability of separation of transfer paper from a photoreceptor.

The inventors believe that the above decrease in separation probability is due to
We found that the following two reasons were the cause.

One reason is that, as shown in FIG. 1, the common separation range B with respect to the separable range A becomes narrower due to fluctuations in the background potential of the photoreceptor. The background potential on the horizontal axis, that is, the potential of the bright area of the photoreceptor surface that is illuminated by light, changes depending on the color of the copy original, dirt on the exposure optical system, the aperture value, etc.
Figure 1 shows the case where the surface of the selenium drum is positively charged.
AC voltage is applied from a distance of 12 mm to the transfer paper on the surface of the selenium drum rotating at 134 mm/sec.
This is an example in which a separate corona was applied at a constant 5.0KV-rms. Separable range A is from (+) 450V to (-) 250V when the ground potential is 50V, and 500V.
There is a DC bias voltage range from (+) 200V to (+) 920V, while the ground potential is from 50V to
When the voltage varies up to 500V, the common separation range B becomes extremely narrow, ranging from DC bias voltage (+) 200V to (+) 450V. Therefore, if the voltage setting of the DC bias of the separation charger is kept constant as in the conventional case, the establishment of separation becomes poor. For example, now
Assuming that the DC bias of the separation charger is set to (+) 200V, if the skin potential is 50V,
In other words, at point E in Figure ₁ , the positive side is 7.2KV-
0.05KV=7.15KV and negative side is 6.8KV+0.05KV
Discharge occurs at =6.85KV. On the other hand, when the skin potential is 500V, that is, at point E ₂ in Figure 1, the positive side is 7.2KV - 0.5KV = 6.7KV and the negative side is 7.2KV - 0.5KV = 6.7KV.
Discharge occurs at 6.8KV + 0.5KV = 7.3KV. Therefore, even when the skin potential is 500V, the separation range is
In order to achieve the same conditions as when using 50V, it is necessary to change the DC bias from 200V to 650V. Note that while the AC applied voltage is 7.0 KV, the discharge AC voltage in the above example is different on the positive and negative sides because the ground potential on the surface of the photoreceptor is positive, so the separation is due to this potential. This is because positive discharge of the corona is suppressed and negative discharge increases accordingly.

Therefore, in order not to narrow the separable range, it is necessary to increase the DC bias voltage of the separation charger as the ground potential rises. Specifically, this can be done by changing the DC bias in conjunction with the aperture value of the exposure optical system, or by receiving a portion of the exposure light beam with a light receiving element and changing the photoelectric conversion output.
Just change your bias.

Another reason for decreasing the separation probability is as shown in FIG.
This is because the common separation range B becomes extremely narrow. In FIG. 2, the background potential is kept constant at (+) 100 V and the DC bias voltage applied to the developing roller is varied. The developing roller used is 60 mm in diameter and rotates at four times the speed of the selenium drum.
It's a roller. As can be seen from this figure, when the amount of toner adhering to the background portion is changed by changing the developing bias, not only does the separation range shift, but the separation range also becomes smaller. In particular, when the developing bias changes from around 300V DC to around 450V, which is accompanied by a change in toner adhesion amount, the separable range A decreases to 1/2 to 1/4, and in extreme cases, it is necessary to switch the polarity. I understand that.

In order to avoid such a reduction in the common separation range, the DC bias of the separation charger is changed in conjunction with the development bias. This is, for example, a potentiometer that is linked to the density adjustment knob of a copying machine, and has a distribution such that the change in resistance value with respect to the rotational angular displacement of the slider follows the curve shown in Figure 2. This is achieved by using
However, the simplest and most effective method would be to switch the strength of static elimination of the separated corona in conjunction with switching the developing bias.

The present invention shifts the static elimination strength of the separation charger in accordance with the shift of the separable range caused by fluctuations in the background potential of the photoreceptor, fluctuations in the developing bias voltage, etc., so that the separation probability can be reduced. can be maintained in the best conditions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the range of separable DC bias voltage when the AC applied voltage to the separation charger is kept constant and the surface potential of the photoreceptor is varied;
FIG. 2 is a diagram showing the range of the DC bias voltage of the separable separation charger when the background potential of the photoreceptor is constant and the DC bias of the developing roller is varied. A...Separable range, B...Common separation range.

Claims (1)

[Claims] 1. The electrostatic adhesion force between the transfer paper and the photoconductor surface generated by electrostatic transfer is reduced by an AC corona generator to which a DC bias voltage is applied, thereby transferring the toner-bearing transfer paper to the photoconductor surface. A method for separating transfer paper, characterized in that the intensity of static elimination by the corona generator is changed in accordance with the potential of the background part of a photoreceptor or the amount of toner adhering to the background part.