JPH035587B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transfer method for an image forming apparatus that transfers a toner image on a photoreceptor to a transfer paper using a direct current corona charger (transfer charger) and then separates the transfer paper from the photoreceptor using a separation charger. Concerning Chajiya.

For example, in FIG. 1, a photoreceptor 1 is uniformly charged by a charger 2 and exposed to a light image 3 to form an electrostatic latent image on the photoreceptor 1. As shown in FIG. This electrostatic latent image is visualized by the developing device 4. On the other hand, transfer paper 9 is sent out by roller 5 in synchronization with the toner image on the photoreceptor and is overlapped with the toner image. In this state, the transfer paper 9 passes through the transfer charger 6 and then through the separation charger 7. At this time, the transfer charger 6 applies a charge of opposite polarity to the toner from the back side of the transfer paper 9, thereby transferring the toner image on the photoreceptor to the transfer paper. The separation charger 7 then applies an alternating current corona discharge, generally DC biased, to the transfer paper 9 to reduce the electrostatic adhesion force due to the transfer corona. The transfer paper is separated from the photoreceptor due to this action and its own weight, and then delivered to the conveying device 8. Note that the photoreceptor is cleaned and neutralized before being reused.

To explain the case where the original and the copy image are positive-positive, in the transfer process, the electric field acts only on the toner image area (image area), and the force is large enough to attract the toner image to the transfer paper. However, in reality, the electric field extends to the non-image area, and since the photoreceptor potential in the non-image area is low and the discharge potential difference is large, there is a stronger electric field there than the toner image (image area). It takes. Therefore, the non-image areas of the transfer paper will be more charged than the image areas, resulting in poor releasability when charge separation is used.

In FIG. 2, a is a solid black separable potential area, and b is a white solid separable potential area.
Since there is a difference in the separable area between the two, the commonly usable area is narrow as shown by the shaded area c. This is because the electrical action of the transfer charger is different as described above, and unless the electric potential of the black area is lowered or the electric potential of the white area is increased, the common usable range c cannot be increased.

Therefore, unless the transfer charger is set at a constant current to stabilize the discharge current to the photoreceptor, the separation width C cannot be expanded, and the reliability of the separation performance due to changes in the document or environment is lacking.

In connection with this point, only the power pack of the transfer charger is of a constant current type, but this alone cannot stabilize the current flowing to the photoreceptor. This is because the current changes depending on the potential of the photoreceptor depending on the white and black portions of the document.

Next, a current detection type that detects the current flowing to the photoreceptor of the transfer charger and feeds it back to the power pack is also known, but the charger structure is complicated and manufacturing costs are high, and a feedback circuit must also be included in the power pack. However, overall simplification has not been achieved, resulting in high cost and lack of reliability.

The purpose of the present invention is to make the current flowing through the photoreceptor a constant current with a simple structure, and further to make the transfer current caused by charge separation a constant current to stabilize the discharge current to the photoreceptor, thereby increasing the separation width. The aim is to achieve this goal.

The present invention will be explained below with reference to the drawings.

FIG. 3 shows an example of the use of the conventional transfer charger 10, in which the corona wire 12 is connected to the output terminal of a constant current high voltage power pack 13, and the casing 11 and photoreceptor 1 are grounded as usual. In the case of such a configuration, it has already been mentioned that the current flowing from the charger to the photoreceptor changes depending on the photoreceptor potential. This phenomenon can be explained as follows. That is, first, when the potential of the photoreceptor 1 is high, if the constant current power pack 13 is used, the photoreceptor 1
The current [Id] flowing through the casing 11 decreases, and the current [Ic] flowing through the casing 11 increases. Since the total current [I _T ] at that time will be the same, the voltage will increase by that amount. A constant current power supply works in this way to keep the current constant. However, the current Id to the photoreceptor that we need has changed and is no longer a constant current.

Therefore, in the present invention, as shown in FIG. 4, a voltage divider consisting of a series circuit of resistors R1 and R2 is connected between the power supply line for the corona wire 12 and the earth, while the charger casing 11 is suspended from the earth. It is connected to the resistance division point P of the voltage divider. The values of resistors R1 and R2 are, for example, R
1=50MΩ, R2=40MΩ.

At the connection point P, a voltage having a value obtained by dividing the applied voltage by the resistors R1 and R2 is generated. Since this is the voltage of the casing 11, when a high potential portion of the photoreceptor now comes, the applied voltage increases as explained in FIG. 3. Then, the voltage at point P increases and the voltage applied to the casing also increases, so the current flowing to the casing 11 is suppressed, and the current flowing to the photoreceptor increases accordingly.
In other words, when the potential of the photoreceptor is high, the voltage applied to the charger increases, and this voltage is fed back to the casing.

FIG. 5 shows changes in photoreceptor current (Id) with respect to photoreceptor potential (V), where curve A is for the conventional charger and curve B is for the charger of the present invention. By feeding back the variation of the applied voltage to the casing as described above, it is possible to flow a constant current to the photoreceptor, which does not vary much depending on the potential of the photoreceptor, as shown by curve B in FIG. 5, compared to conventional chargers. Therefore, the separation width C can be expanded. Furthermore, these effects can be easily obtained by floating the charger casing from the ground electrode and providing a resistive voltage divider.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an electronic copying machine to which the transfer charger of the present invention can be applied, Fig. 2 is an explanatory diagram showing the relationship between the separable range and the photoreceptor potential, and Fig. 3 is a schematic diagram of an electronic copying machine to which the transfer charger of the present invention can be applied. FIG. 4 is a schematic diagram of a transfer charger according to the present invention, and FIG. 5 shows a comparison of changes in photoreceptor current with respect to photoreceptor potential between a conventional charger and a transfer charger according to the present invention. This is a diagram. 1...Photoreceptor, 10...Transfer charger, 11
...Casing, 12...Corona wire, 13...
...Constant current high voltage power pack, R1, R2...Resistance voltage divider.

Claims (1)

[Claims] 1. A transfer charger for an image forming apparatus, which includes a transfer charger disposed facing a photoreceptor and for transferring a toner image on the photoreceptor onto a transfer paper, and a separation charger for separating the transfer paper from the photoreceptor. , connect the corona wire of the transfer charger to the output terminal of a constant current power pack, connect a resistor between the output terminal of the power pack and ground, and apply a voltage according to the voltage division ratio of the resistor to the casing of the transfer charger. A transcription charger featuring: