JPH052988B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a corona charging device capable of uniformly charging a surface potential.

PRIOR ART As a type of charging device that has been widely used in the past, there is a so-called corotron, which charges by ion discharge from a corona electrode connected to a DC high voltage source. Although this corotron has the advantage of being simple and inexpensive, it lacks stable and uniform charging performance. In other words, higher quality image reproduction,
Corotrons are no longer able to meet the image forming conditions required by the hardware.

For this reason, it is conceivable to adopt a DC scorotron in which a grid electrode is provided between the corona electrode and the photoreceptor, and a DC high voltage is applied to the corona electrode, and a DC bias voltage is applied to the grid electrode for charging. This type of scorotron has the advantage that the charging potential can be set approximately equal to the potential applied to the grid electrode. In this case, however,
A transformer is required to apply a DC bias voltage, which makes the structure larger and more expensive.
Therefore, as shown in Japanese Patent Publication No. 51-17419, if a constant voltage passive element functioning as a self-bias voltage applying means is connected to the grid electrode and the constant voltage value of the constant voltage element is set constant, the above-mentioned result can be achieved. Similarly, it can be charged to a potential approximately equal to the constant voltage value without requiring a transformer. However, it is insufficient from the viewpoint of uniformity of charging potential.Grid electrodes in particular, when used for a long time, that is, exposed to corona discharge for a long time, gradually form an insulating film on the surface, and this insulating film is exposed to corona discharge. Charges are trapped and the effective bias voltage value of the grid electrode changes, resulting in fluctuations in the charging potential. Furthermore, when toner adheres to the grid electrode, the charging potential varies locally.

Therefore, it is possible to use an AC scorotron that applies a DC bias voltage to the grid electrode and uses it as a voltage source for the corona electrode. However, this AC type scorotron can almost eliminate the above-mentioned drawbacks of the DC type and has excellent uniform charging properties, but cannot perform high-speed charging due to the small amount of corona discharge charge. Moreover, since the amount of corona discharge charge is small, the self-bias voltage function is low, and it is not possible to use a constant voltage passive element as in the above-mentioned Japanese Patent Publication No. 17419/1985, making it inevitable to increase the size of the structure.

Purpose of the invention The present invention has been made in view of the above facts.
The purpose is to provide a corona charging device that can always perform high-speed uniform charging without uneven charging.

Embodiment FIG. 1 shows a schematic configuration of a corona charging device according to the present invention, and its basic configuration is of the scorotron type, and a DC type corona charger 1 and an AC type corona charger 2 are arranged side by side. Specifically, 3 is a first corona electrode connected to a DC high voltage source 4, 5 is a second corona electrode connected to an AC high voltage source 6, and 7 has discharge openings 9 and 10 facing the photoreceptor 8. A conductive shield is provided as an integral unit surrounding each corona electrode 3, 5 from three sides, and is itself grounded. Reference numeral 11 denotes each corona electrode 3, 5 in a relationship facing the discharge openings 9, 10.
A constant voltage passive element 12 such as ZNR is connected to the grid electrode provided between the photoreceptor 8 and the photoreceptor 8, and the element 12 is grounded.

In the corona charging device having the above configuration, charging to a potential substantially equal to or close to the constant voltage value of the constant voltage passive element 12 is most excellent in terms of charging efficiency and performance. In the present invention, first, the photoreceptor is charged to a predetermined surface potential using the DC type corona charger 1. That is, the first corona electrode 3 connected to the DC high voltage source 4
The photoreceptor is primarily charged by the discharge action from the photoreceptor. At this time, the voltage source is DC and the first corona electrode 3
Since the amount of discharged charge from the grid electrode 1 is large,
The corona current flowing through 1 is guaranteed to be above a certain level, and the surface potential is charged to a desired level. The surface potential due to this primary charging may be approximately equal to the constant voltage value of the constant voltage passive element 12, or may be greater or less than that, as long as it is finally charged to a desired potential by secondary charging, which will be described later.

As mentioned above, the primary charging by the direct current type corona charger 1 alone is insufficient in terms of potential uniformity. Therefore, in the present invention, after the primary charging, secondary charging is performed by the AC corona charger 2. At this time, the corona discharge of the DC corona charger 1 is charged with a self-biasing function for the grid electrode 11. In other words, the grid electrode 8 is connected to a DC type corona charger and an AC type corona charger 1, 2.
If they are installed independently, there is no problem with the DC type, but with the AC type corona charger 2, both positive and negative ions are discharged from the second corona electrode 5 connected to the AC high voltage source 6, so the amount of charge is small and the grid It does not function as an effective means for applying a self-bias voltage to the electrodes. In other words, there is no point in providing a grid electrode. However, in the present invention,
Since the grid electrode 11 is provided across the discharge opening 9 of the DC type corona charger 1, during secondary charging by the AC type corona charger 2, a DC corona current due to a large corona discharge by the DC type corona charger 1 flows to the grid electrode 11. , the voltage generated by flowing to the constant voltage passive element 12 through it is guaranteed to have a high value, and as a result, the charging performance of the AC corrocharger 2 is greatly improved, and its original uniform charging property remains unchanged. be kept alive. Therefore, in the primary charging, it is charged to a constant potential without considering uniformity, and in the secondary charging, it is uniformly charged to a surface potential that is approximately equal to or close to the constant voltage value of the constant voltage passive element 11 without charging unevenness.

FIG. 2 shows a second embodiment according to the present invention,
Components that are the same as those in FIG. 1 are designated by the same reference numbers and their explanations will be omitted. In this example, a DC type corotron 1
The conductive shield 14 connects the first corona electrode 3, and the dielectric shield 15 connects the second corona electrode 5.
It is set up in such a way that it surrounds it from three sides. A grid electrode 16 is provided between the second corona electrode 5 and the photoreceptor 8, facing the discharge aperture 10, and is itself connected to the conductive shield 14 of the DC corotron and to a constant voltage passive element. . In this regard, a portion of the conductive shield 14 extends above the dielectric shield 15 and is connected to the grid electrode 16. The dielectric shield 15 is used in the AC scorotron because, in this embodiment, the grid electrode 16 faces only the discharge opening 10, and if a conductive shield is used, the AC from the second corona electrode 5 is This is because a corona current flows and the self-biasing function of the DC corotron with respect to the grid electrode 16 is significantly degraded.

In the configuration shown in FIG. 2, the photoreceptor 8 is first charged to a constant potential by the DC type corotron 13.
The potential at this time may be set appropriately as described in connection with FIG. 1, and uniformity need not be considered. Subsequently, the photoreceptor 8 is secondarily charged by the AC type scorotron 2, but at this time, the DC corona discharge current from the first corona electrode 3 of the DC type corotron is applied to the conductive shield 1.
4 to the constant voltage passive element 12, as a result of which a high bias voltage is guaranteed to the grid electrode.
Therefore, the photoreceptor 8 is uniformly charged by secondary charging to a potential substantially equal to or close to the constant voltage value.

Figure 3 uses the corona charging device configured in Figure 2,
It shows the charging characteristics when the DC corona discharge current of the DC type corotron 13 is changed. As the photoreceptor 8, a substrate with CdS.nCdCO ₃ photoconductive powder dispersed in a resin binder and coated to a thickness of 30 microns was used, the moving speed was 13 cm/sec, and the distance between the grid electrode 16 and the photoreceptor was The experiment was conducted under a setting of 1 mm. In addition, ZNR constant voltage passive element 1
The constant voltage value (V _ZNR ) of 2 is 630V, AC high voltage source 6
was 6.5KV, and the DC high voltage source 4 was variable within the range of 5 to 6.5KV.

In FIG. 3, the potential when only the AC scorotron 2 was charged was 150V. This shows that the AC corona discharge current has little self-biasing function for the grid electrode. Therefore, when a DC corona discharge current of 260 μA was used for primary charging and then secondary charging, the surface potential was 460 V. Incidentally, since the potential due to the primary charging was 580V, the potential due to the secondary charging of the AC scorotron was 120V.
This means that the static electricity has been removed. By increasing the DC corona discharge current, the surface potential increases and reaches 330 μA.
500V.410μA at 530V.530μA at 580V.650μA equals the constant voltage value (V _ZNR ) at 630V, 740μA
Charged to 700V at 60V.820μA. Therefore, in order to make the charging potential approximately equal to or close to the constant voltage value, it is sufficient to determine the DC corona discharge current. The charging potential also depends on the shape of the corotron itself, the distance between the grid electrode and the photoreceptor, the shape of the grid electrode, etc., and these must also be taken into consideration.

Under the same conditions as above, we investigated the image formation by varying the DC corona current to perform primary and secondary charging, followed by image exposure, development, and transfer, and clear images were obtained in all cases. . This means that the surface potential, which is determined by taking various conditions into account, is not only easily obtained by using the corona charging device of the present invention, but also guarantees the reproduction of clear images even if there are slight fluctuations. It means.

In the configuration shown in FIGS. 1 and 2, the grid electrodes 11 and 16 are, for example,
It is possible to use a mesh-like wire as shown in Japanese Patent No. 10240, or a wire in which a large number of wires 17 are stretched in parallel with fine intervals as shown in FIG. 4 and supported by a frame 18. can. In this case, it is preferable that the wire 18 be stretched in an inclined manner in the direction in which the photoreceptor 8 moves. Further, the constant voltage passive element 12 is not limited to ZNR, but a constant voltage diode, a constant voltage discharge tube, etc. can be used. In addition, the DC type scorotron 1 or corotron 13 and the AC type scorotron 2 do not need to be an integral structure, and may be separate bodies.
1 and 16, it is sufficient if the structure is configured to perform a self-biasing function.

Effects As is clear from the above explanation, according to the corona charging device according to the present invention, high-speed uniform charging can be performed without uneven charging. In addition, it is easy to set the charging potential, the structure is simple, and it has many effects such as guaranteeing the self-biasing function for the grid electrode without impairing the original excellent functions of the DC and AC corona chargers.

[Brief explanation of drawings]

Figures 1 and 2 are schematic configuration diagrams of a corona charging device according to the present invention, Figure 3 is a graph showing the relationship between DC corona discharge current and charging characteristics, and Figure 4 shows an example of the configuration of a grid electrode. It is a diagram. 1... DC scorotron, 2... AC scorotron, 3... First corona electrode, 4... DC high voltage source, 5... Second corona electrode, 6... AC high voltage source, 7, 14... ...Conductive shield, 11, 16
... Grid electrode, 12 ... Constant voltage passive element, 1
3...DC type corotron.

Claims (1)

[Scope of Claims] 1. A charging device for uniformly charging a photoreceptor, comprising: a first corona charger having a first corona electrode connected to a DC high voltage source; and a second corona charger connected to an AC high voltage source. a second corona charger having a corona electrode and applying an electric charge to the photoreceptor charged by the first corona charger; and a constant voltage passive element provided between the second corona electrode and the photoreceptor. a grid electrode grounded through the grid electrode; and a DC corona discharge from the first corona electrode, which is provided near the first corona electrode and electrically connected to the grid electrode side of the constant voltage passive element. A corona charging device comprising: a conductive member that receives a current and causes the resulting current to flow through the constant voltage element. 2. The corona charging device according to claim 1, wherein the first corona charger has a grounded conductive shield. 3. The corona charging device according to claim 2, wherein the conductive member is the grid electrode integrally extended between the first corona electrode and the photoreceptor. 4. The corona charging device according to claims 1 to 3, wherein the second corona charger has a grounded conductive shield. 5. The corona charging device according to claims 1 to 3, wherein the conductive member is a conductive shield provided around the first corona electrode and having an opening in a portion facing the photoreceptor. . 6. The corona charging device according to claim 5, wherein the second corona charger has a dielectric shield.