JPS639235B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Corona chargers are currently used in most electrophotographic equipment, but corona chargers use high pressure, which is dangerous, and pollutes the atmosphere and equipment due to ozone generation. There was a problem in that it was expensive. On the other hand, various charging methods using rollers and brushes have been tried for a long time, but none of these methods can be applied to photoreceptors that are used repeatedly because they cause mechanical damage or electrical damage to the photoreceptor.

The present invention has completed a contact-type charger by applying a DC voltage to an electrode placed on the back of a brush-like material with appropriate electrical resistance, and applying an attenuated AC voltage. It is.

The details are described below.

What is shown in FIG. 1 is one of the most typical embodiments. In the figure, 1 is a photosensitive drum whose surface is coated with a photosensitive material such as ZnO, which is supported by a grounded support part 1a, and 2 is a photosensitive drum that faces the photosensitive drum 1 with a small gap therebetween. 3 is a contact having a predetermined electrical resistance, such as a thin cloth with dense piles; 4 is a grounded DC power source that applies a DC voltage to the electrode 2;
5 is a grounded AC power supply for applying AC to the electrode 2 via the second capacitor 6;
Each shows a first capacitor for attenuating the AC electric field. The maximum voltage of the AC power source is lower than the voltage of the DC power source. FIG. 2 is a conceptual diagram for explaining the voltage applied to the photoreceptor. At point A in FIG. 1, the AC voltage is highest, and as it moves toward point B, the AC voltage attenuates. This can be easily achieved by making the electrode 2 have an appropriate resistance. For example, the voltage of the AC power supply 5 is
When the voltage is 500 volts, the resistance between AB is 1×
If set to ¹⁰⁶ ohms, there will always be 500 ohms between AB.
A microscopic current flows, and an alternating current voltage as shown in FIG. 2 is realized. For example, about 1000 volts is used as the DC voltage. The DC voltage is
If the electrical resistance of the resistive material, such as the cloth indicated by 3 in FIG. 1, is moderately high, it will remain almost constant between A and B, as shown in FIG. The electrical resistance of a material such as cloth, when measured in the thickness direction, is, for example, about 10 ⁸ ohms per cm ³ . Needless to say, setting the AC voltage to 0 at point B is a necessary condition for preventing charging from forming a striped pattern. The frequency of the AC power source should be determined from the relative speed with the photoreceptor and the distance between A and B.
For example, choosing a slightly higher frequency such as 1K cycle instead of 500 cycles has the advantage of being able to cope with any relative speed and making it easier to select the electrical resistor 3 such as cloth.

In experimentally conducted examples, a drum coated with a zinc oxide photoreceptor was used as the photoreceptor. AB
The distance between them was 20 mm, and the length of the charger was chosen to be 270 mm. Electrode 2 was filled with carbon.
SBR was used and the resistance between AB was 5 x 10 ⁵ ohms. Nylon velveteen with a pile of 1.5 mm was used as cloth 3. Velveteen was used by pasting it on the electrode 2 with a conductive adhesive. The resistance of the charger made in this way in the thickness direction of the cloth was measured and was approximately 10 ⁸ ohms per cm ² . Apply 500 volts AC and 1000 volts DC to this charger, and apply a relative velocity of 70 volts per second.
As a result of rotating the drum at mm, a stable surface potential of about 400 volts was obtained in the dark, and it dropped to almost 0 volts after exposure for about 20 lux seconds. This charging method shows extremely stable results, with both the results obtained when the photoreceptor is started operating after it has been stored in the dark for a long period of time, and the results obtained when it is operated continuously for a long period of time, both with and without exposure to light. In this case, there was almost no change in the charging potential. Furthermore, the advantages were found to be almost unchanged depending on the atmosphere such as temperature and humidity. Of course, it is a necessary condition that the density of the bristles of the brush be sufficiently high, and mechanical consideration must be taken so that the entire charger contacts the photosensitive drum evenly and softly.

It goes without saying that the numerical values in the above embodiments are merely examples. Moreover, the materials are also used by chance to realize the concept of the present invention, and are not limited to the materials of the examples. For example, as the electrode 2, carbon-filled paper, conductive rubber, etc. can be easily used, and nylon velveteen can be easily replaced with other cloth, a brush with electrostatic flocking, foamed plastic, etc. Ru.

As a result of experiments using a zinc oxide type photoreceptor, which is considered to be the most mechanically weak photoreceptor, almost no mechanical or electrical damage due to the charger was observed even after repeated charging and discharging more than 10,000 times, and corona radiation was not observed. I got much better results than if I used an electric appliance. This is thought to be due to several causes. The first is that the power supply voltage is much lower than that of the corona, so the electrical shock is much lower. Second, there is no ion bombardment, and third, there is no ozone generation, so there is no chemical damage. In particular, deterioration due to ozone has been a serious problem for ZnO systems, but the fact that there is no such problem is a big relief. It has been experimentally known that the current flowing through the photoreceptor is much smaller than when using a corona discharger. This also contributes to less deterioration of the photoreceptor. Of course, the photoreceptor is not limited.

With the power supply voltage being low and the current being small, the wattage of the power supply is reduced. This, together with the simplicity of the structure of the charger, contributes to a reduction in price.

The circuit shown in FIG. 1 can be further modified in various ways. If it is desired to further extend the life of the photoreceptor, it is possible to connect the wires as shown in FIG. Third
The figure shows the charger as a resistor, and the AC voltage becomes 0 even at point C, resulting in a voltage distribution as shown in FIG. This prevents sudden application of alternating current voltage.

Further, by using the circuit shown in FIG. 5, it is possible to give a slope to the DC voltage. The voltage distribution in this case is as shown in FIG.

A device that is electrically charged by bringing a mechanically flexible contactor having a predetermined electrical resistance into contact with a moving photoreceptor whose supporting portion is grounded, which supports said contactor and which is electrically charged. A backing electrode which is arranged opposite to the photoreceptor and has an appropriate resistance with a small enough distance to make contact with the photoreceptor, and a grounded first electrode which is connected to the downstream end of this electrode in the direction of movement of the photoreceptor. a grounded DC power supply connected to the electrode in parallel with the first capacitor, and a second capacitor connected to the upstream end of the power supply in the direction of movement of the photoreceptor; and a grounded AC power source whose voltage is lower than that of the DC power source, efficiency is improved, power supply voltage is reduced, ozone pollution is eliminated, and the life of the photoreceptor is extended as a result.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an embodiment of the present invention and shows the state in which the photoreceptor is charged, Fig. 2 is an explanatory diagram of the voltage applied to the photoreceptor, and Fig. 3 shows the charger as a resistor. Circuit diagram, Figure 4 is an explanatory diagram showing the voltage distribution in the case of Figure 3, Figure 5 is a circuit diagram of another embodiment in which the charger is shown as a resistor, Figure 6 is the voltage distribution in the case of Figure 5. FIG. 2 is an explanatory diagram showing the distribution of DESCRIPTION OF SYMBOLS 1... Photoreceptor, 1a... Support part, 3... Contact, 2... Backing electrode, 4... DC power supply, 5...
AC power supply, 6... second capacitor, 7... first
capacitor.

Claims (1)

[Claims] 1. A device that is electrically charged by bringing a mechanically flexible contactor having a predetermined electrical resistance into contact with a moving photoreceptor whose supporting portion is grounded, which supports the contactor, and A backing electrode is placed facing the photoconductor and has a moderate resistance while maintaining a very small distance between the two electrodes, and a grounded electrode is connected to the downstream end of this electrode in the direction of movement of the photoconductor. 1, a grounded DC power supply connected to the electrode in parallel with the first capacitor, and a second capacitor connected to the upstream end of the power supply in the direction of movement of the photoreceptor, A charging device comprising: a grounded AC power source whose voltage is lower than the voltage of the DC power source.