JPS6115163A - Corona discharging device - Google Patents

Abstract

PURPOSE:To prevent a foreign matter adhering to a discharge electrode from going in, and to maintain a stable discharge characteristic which is excellent in durability, by constituting a titled device so that a wind velocity and an air capacity of a clean air current blown into a shielding plate become large in both its end parts. CONSTITUTION:As for a blast (e) which has been led into a shielding plate 32 through an opening 34 from a blast duct 35, its wind velocity and air capacity become large in both its end sides of the plate 32 by a wind distributing plate 40. As a result, in both end parts of a corona discharge opening, an air curtain e2 of a blow-out system comes to have strength for inhibiting a drum wind d1 with regard to the open air flowing into a device, and a force of a curtain e1 of the center part of the plate 32 becomes slightly weak. Accordingly, even in case when an air blower 37 of a small capacity us used, an inflow of the open air is obstructed over the longitudinal area of the corona discharge opening, an invasion of a foreign matter adhering to a discharge electrode 31 is prevented, and a discharge characteristic which is stable and excellent in durability can be maintained.

Description

Detailed Description of the Invention A. Object of the Invention [Field of Industrial Application] The present invention relates to a corona discharge device, for example, a corona discharge device used to uniformly charge or eliminate static electricity on the surface of a photoreceptor in an electrophotographic device. Regarding equipment.

More specifically, a corona discharge device (so-called corotron device N) having a corona discharge electrode, a shielding plate surrounding the corona discharge electrode, and an insulating block supporting the corona discharge electrode;
The present invention also relates to an improvement of a corona discharge device (so-called scorotron device) equipped with a discharge current control member (grid).

[Conventional technology]

For convenience, an electrophotographic apparatus will be described as an example. FIG. 2 shows a very schematic structure of an electrophotographic apparatus that follows the image forming process disclosed in Japanese Patent Publication No. 42-23910 or Japanese Patent Publication No. 43-24748. Reference numeral 1 denotes a photosensitive drum as a charged body that rotates at a constant speed in the direction of arrow a. At the same time, it receives pre-exposure from two light sources, and at the same time pre-neutralizes it using a corona discharge device 3, so that the surface of the photosensitive drum is uniform. maintained at potential level. Next, corona discharge device M4
, the optical system undergoes primary charging with a polarity different from the above-mentioned pre-static charge removal, and is further subjected to secondary charging or AC corona charge removal with a polarity different from the primary charge by the corona discharge device 5, and at the same time or immediately after this, the optical system is charged. By receiving a light pattern L (slit exposure, laser beam scanning exposure, etc.) through the lens 6, an electrostatic latent image facing the exposed light pattern is sequentially formed on the photosensitive drum.Next, the entire surface is exposed by the light source 22. Receive,”-
The potential contrast of the formed latent image is enhanced. Next, the latent image is developed with a developing colored powder (hereinafter referred to as toner) in a developing device 7 to become a visible image. This visible image is sequentially transferred onto the surface of the transfer material 9 by the charging action of the corona discharge device 8. The transfer material 9 on which the image has been transferred is separated from the photosensitive drum surface, introduced into a fixing device (not shown), where the image is fixed, and then discharged outside the machine as a copy. On the other hand, the surface of the photosensitive drum 1 after the transfer is cleaned by a cleaning device 10 to remove residual toner after transfer, and thereafter the same process as described above is repeated.

Figure 3 shows a typical corona discharge device A (corotron device) used in an electrophotographic device such as the one mentioned above.
Figure (a) is a longitudinal sectional front view, (
b) Figure is a plan view, Figure (C) is a plan view of Figure (a).
C) Linear cross-sectional view, (d) Figures are the same < (d)-(d)
FIG. That is, the photosensitive drum 1 as an object to be charged
A conductive shield plate 32 (made of stainless steel, for example) having a simplified U-shape in transverse direction with the side facing the surface open as a discharge opening, insulating blocks 33 attached to both ends of the shield plate, and a conductive shield plate 32 inside the shield plate. A corona discharge wire 31 as a corona discharge electrode is positioned between the insulating blocks at both ends.

33a is a feeder provided on one side of the insulating block 33, and the corona discharge wire 31 is locked to the feeder 33a via a conductive tension spring 38 on one end thereof, and the other end is connected to the other insulating block 33. It is locked to a locking piece 33b provided on the block 33, and is always kept in tension by the tension of a spring 38.

Reference numeral 34 denotes an airflow (outside air) inflow opening formed along the length of the top plate on the side opposite to the discharge opening side of the shield plate 32. Some shield plates are designed so that the opening is provided at the boundary between the top plate and the side plate of the shield plate 32, or on the side plate side. There are some that do not specifically provide internuclear [I]. In corona discharge devices 3 and 5 in Fig. 2, which introduce light, the shield plate 32 is also opened on the side opposite to the discharge opening side for light guiding, or a window hole for light guiding is formed. Composed in form. Some have a transparent plate made of glass or the like stretched over the opening or window hole for guiding the light.

The corona discharge device A has a width dimension (
The required length dimension is designed according to the generatrix direction dimension).

The scorotron device has the above-mentioned corotron device and a grid wire 3 as a discharge current control member in the discharge opening.
9 (corona discharge device 3 and 5 in FIG. 2).

Direct current high voltage (when obtaining a positive or negative DC corona discharge) or AC high voltage (when obtaining an AC corona discharge) is applied to the corona discharge wire 31 via the feeder 33a facing the front side by a high voltage power source (not shown), or By applying a superimposed high voltage of both DC and AC, grounding the shield plate 32, or applying a bias voltage of an appropriate potential from a bias power supply, the gas (air) around the corona discharge wire 31 is brought into an ionized state. becomes. Then, the ionized front mold particles move toward the discharge opening, give kinetic energy to the gas molecules at that time, and generate a blow-out type of ion wind in the discharge amount I-1 section. 1 side and transfer material 9
The surface of the object to be charged, such as the back surface of the device, is charged or neutralized.

[Problem that the invention seeks to solve]

The ion wind blows out at each longitudinal part of the discharge opening of the shield plate 32, but the discharge amount of the ion wind 1
The wind pressure distribution along one length is the discharge amount [1] It is weaker at both ends than at the center of the length. This is because there are insulating blocks 33 and 33 supporting the corona discharge wire 31 at both ends of the shield plates 1 and 32, respectively. This is because the discharge in the portion close to the insulating block becomes weak due to the electric current.

On the other hand, as the ion wind blows out as described in L, the pressure inside the shield plate 32 becomes negative. In order to compensate for this, %c flows into the interior space of the shield plate from the air flow inlet opening 34 and the corona discharge opening of the shield plate 32 in parallel with the blowout of the ion wind. The wind pressure distribution of this inflowing outside air C along the length of the corona discharge opening is such that the wind pressure distribution of the ion wind blowing out L is strong in the center,
Since both ends are weak, the distribution is opposite to this, with the center being weak and both ends being strong.

Further, as the drum l rotates, a laminar airflow d (31st (C)φ(d)) called a drum wind is generated around the drum. Then, the drum wind d interferes with the shield plate 32 at the discharge device installation position, and a part of the drum wind d becomes a turbulent flow and flows into the space inside the shield plate from a corona discharge amount 1''. The inflow distribution of the drum wind d1 along the longitudinal length of the corona discharge opening is different from this, since the distribution of the ion wind along the longitudinal length of the corona discharge opening is strong in the center and weak in both ends. Conversely, the distribution is weak in the center (FIG. 3(C)) and strong in both ends (FIG. 3(d)).

From the above, the inflow of outside air C + drum wind from the corona discharge opening side into the interior space of the shield plate due to the rotation of the corona discharge opening is related to the longitudinal length of the corona discharge opening. There is a local inflow state at both ends, and the flow velocity is quite strong.

Therefore, external foreign matter is likely to actively creep into the shield plate 32 due to the inflow phenomenon of locally strong outside air C+todrum wind at both ends thereof.

In an electrophotographic apparatus such as the example shown in FIG. 2, scattered toner from the developing device 7 and cleaning device 10, paper dust generated from the transfer material 9, and other dust are floating in the air inside the apparatus. In particular, since it is technically difficult to completely prevent toner from leaking and scattering from both ends of the photosensitive drum of the developing device 7 and cleaning device 10, the air around both ends of the photosensitive drum 1 is particularly prone to scattering.・The atmosphere tends to contain a lot of floating toner, and the toner, transfer material paper dust, and other dust that have accumulated in those areas tend to remain on the peripheral surface of both ends of the photosensitive drum because they cannot be removed by the cleaning device. ,
Therefore, the drum air d of the photosensitive drum, especially around both ends of the drum, tends to contain detached materials such as the residual toner.

As a result, corona discharge devices are inherently prone to dirt due to dust collection caused by high-voltage electric fields;
Floating dust in the device such as paper powder, dust contained in the drum air d, toner remaining after cleaning on the peripheral surface of both ends of the photosensitive drum, etc. are caused by the above-mentioned local strong outside air C + drum NLdI inflow phenomenon at both ends of the discharge device. Actively shield plate 3
Corona discharge wire 31 is inserted into the inside of 2.
and the inner surface of the shield plate 32 becomes excessively dirty at an early stage.

Foreign matter contamination on the inner surfaces of the corona discharge wire 31 and shield plate 32 is one of the major causes of uneven discharge, and in the case of electrophotographic devices, it has a large negative effect on image quality, so cleaning must be performed frequently. There wasn't.

Here, in a type of corona discharge device that does not include the airflow inlet opening 34, the shield plate 32
The outside air C flows into the inner space of the device only on the corona discharge opening side, and the wind pressure of the outside air C flows into the opening 3 at both ends of the device.
4, the degree of contamination and the progress of contamination on the inner surfaces of the corona discharge wire 31 and shield plate 32 become even more significant.

In addition, by increasing the width of the air flow inflow amount 1'' 34, the amount of inflow of outside air C from the corona discharge opening side can be reduced to some extent, but if it is a certain width, there is no effect even if it is widened beyond that width.

Therefore, as disclosed in Japanese Utility Model Application Publication No. 57-113942, it is known to provide air inflow prevention means at both ends of the discharge opening of the discharge device. However, it was not very effective in suppressing the inflow of outside air.

Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 57-188062, conductive members are provided on the top surfaces of insulating blocks at both ends of the discharge device to increase the amount of discharge at the ends of the discharge device. Some devices suppress the inflow of outside air C from both ends of the discharge opening into the interior of the shield member by increasing the strength of the ion wind.

This has a big effect.

Furthermore, if a part of the shield member is provided with an opening for outside air inflow,
An even greater effect can be obtained. However, unnecessarily increasing the amount of discharge may cause practical problems, such as increased ozone generation and the need for a high-capacity, high-voltage power source.

Furthermore, as disclosed in Japanese Patent Publication No. 40-17229, a dedusted and dehumidified air stream is actively blown into the interior of the shield member of the discharge device to increase the discharge amount [I] by blowing out air over the entire area of There is also a device in which a curtain is formed, and the air curtain prevents outside air C and drum wind d from flowing into the interior of the shield member from the discharge opening side, thereby preventing foreign matter from contaminating the inside of the discharge device. FIG. 4 is a cross-sectional view showing a very schematic configuration of such a discharge device, and 37 is an air blower, and the air from the air blower is dedusted and dehumidified, and air flows into the air through the air duct 35. The air is actively introduced into the inner space of the shield plate 32 from the discharge opening 34, and the air is blown out from the corona discharge opening as a blowout type air curtain e1. .

This prevents the inflow of outside air C+todrum wind 1 containing dust. Reference numeral 36 designates an air baffle plate appropriately disposed within the air duct 35 in order to provide a substantially uniform strong air flow to each longitudinal portion of the corona discharge wire 31.

However, in this case, if the blower 36 has a relatively small capacity and low blowing capacity, an air curtain e will be formed.

Although the wind pressure is weak and the ion wind is strongly blown out along the length of the corona discharge opening, the inflow of the outside air C + drum wind 1 can be suppressed in the center where the inflow force of the outside air C + drum wind 1 is small. At both ends, where the inflow force of outside air C + drum wind 1 is strong, the wind pressure of the air curtain e] cannot overcome the strong inflow force of outside air C + drum wind 1, so that the dust-laden outside air C + drum wind 1 flows through the shield plate 32. It flows into the inner space and the inside of the discharge device gets dirty, so outside air C + drum wind + flows over the entire length of the discharge opening, including both ends.
In order to create an air curtain that sufficiently prevents the flow of water into the discharge device, a relatively large-capacity blower 37 is required, resulting in disadvantages such as an increase in the size of the device, increased power consumption, and increased noise. In addition, the cost increases in practice.

The present invention has a shield plate 3 as shown in the above-mentioned device shown in FIG.
This system actively blows air fIte into the inner space of No. 2 to create a blow-out air curtain e1 at the discharge opening, but even a small-capacity blower 37 can sufficiently blow outside air c+i over the entire area of the discharge opening. It is an object of the present invention to provide a device capable of suppressing the inflow of ram wind d1.

Summary: Structure of the Invention [Means for Solving the Problems] That is, the present invention provides a corona discharge device having a corona discharge electrode, a shielding plate surrounding the corona discharge electrode, and an insulating block supporting the corona discharge ttt electrode. , an opening separate from the corona discharge opening is provided in the shielding plate, and a clean airflow is blown into the shielding plate from the opening,
The gist of the present invention is to provide a corona discharge device characterized in that the wind speed and/or volume of air in the air shielding plate is configured to be larger in the vicinity of the insulating block than elsewhere.

[Effect]

Even if the blower that blows air into the shield plate has a relatively small capacity and low blowing capacity, the wind speed inside the shield plate, the wind φ, or both can be controlled elsewhere near the insulating block. By distributing the air to a larger size, a stronger air curtain is created at both ends of the corona discharge opening, that is, a corona discharge flash 1.
It is possible to form a strong air curtain that is strong enough to sufficiently suppress the strong outside air that tries to flow into the discharge device from both ends of the long side of -1. At the longitudinal center of the corona discharge opening, the amount of air blown is reduced as more air is distributed to both ends, and the air curtain that is formed is somewhat weaker, but the air originally tries to flow into the discharge device from that area. Since the wind pressure of 10 drams of outside air is weak, its inflow can be sufficiently suppressed. Therefore, the inflow of outside air + drum wind into the discharge device is effectively suppressed over the entire length of the corona discharge opening.
be done. In other words, by using a blower with a small capacity, which has advantages such as small size, low power consumption, and low noise, it is possible to sufficiently prevent foreign matter from entering the corona discharge device, and the discharge characteristics are stable for a long period of time. A corona discharge device that is maintained and has excellent durability can be obtained.

〔Example〕

FIG. 1 shows an embodiment of a corona discharge device 2tA (corotron device) according to the present invention, in which (a) is a longitudinal sectional front view, (b) and (c) are respectively ( b) - (
b) line and (C)-(C) line sectional views. Components common to those of the corona discharge device shown in FIGS. 3 and 4 will be designated by the same reference numerals and will not be described again.

40 and 40 are openings 34 for airflow inflow from the ventilation duct 35
For the air e introduced into the inner space of the shield plate 32 through
- This is an air distribution board arranged in the air duct 35 in such a position and angular orientation that the area near the area 33 is larger than other areas.

As a result, a large amount of air e is distributed to both longitudinal ends of the corona discharge opening, and the air curtain e is stronger.
2. That is, an air curtain e2 strong enough to sufficiently suppress the strong outside air C+todrum wind 1 that attempts to flow into the discharge device from both longitudinal ends of the core a discharge opening is formed. At the longitudinal center of the corona discharge opening, the amount of air blown is reduced by the amount of air e distributed to both ends, and the formed air curtain el is somewhat weaker, but it is likely that the air will originally flow into the discharge device from that area. outside air C + drum wind 1
Since the wind pressure is weak, it is actually possible to sufficiently suppress its inflow.

Therefore, even if a small-capacity blower 37 is used, it is possible to effectively prevent outside air C+todrum wind from flowing into the discharge device, that is, foreign matter from flowing over the entire length of the corona discharge opening.

It is preferable that the air e introduced into the apparatus from the air blower 37 be dust-removed by a filter means or the like and, if necessary, appropriately dehumidified.

Test Example In an electrophotographic apparatus having the configuration shown in FIG. 1, a photoreceptor having a diameter of 108 layers and having a CdS photoconductor layer was used as the photoreceptor drum L, and the process speed was set to 271 mm/sec.
Then, a constant current of ÷350 μA is applied to the primary corona discharge device W14 and a constant current of -330 JLA is applied to the secondary corona discharge device 5, so that the surface potential of the photoreceptor in the developing device 7 after full exposure is -130 V in the bright area.
, dark areas +450.

The secondary corona discharge device 5 is a known spurotron type device having an opening for image exposure.

The primary corona discharge device 4 has a stainless steel shield on the opposite side to the photosensitive drum 1 completely insulated with a Mylar film, and an outside air inlet phase opening [134] is provided over the entire discharge area.

The distance between the grounded stainless steel site shields, that is, the width of the discharge opening, is 28 mm, and in the center there is a gold-plated tungsten core with a diameter of 80 mm as the discharge electrode.
It is a corotron type device made of GM's fine discharge wire under tension. The width of the outside air inflow opening 34 of this device is 10 mm, and the length of the discharge device Wl in the longitudinal direction is 310 mm, so its area is 3. It is IXIQ-3m2. In addition, outside air inflow phase open 1'' 34 is a ventilation chamber (airflow duct 35).
A rectifying plate 36 and an air distribution plate 40 are provided inside the air conditioning plate 36 to adjust the airflow distribution. Further, an air blower 37 is connected to the chamber so that an air flow can be supplied to the chamber through a known filter for removing dust in the air.

The blower 37 uses a direct current brushless fan whose air volume and pressure characteristics can be changed depending on the input voltage, and is configured so that the magnitude of the turbulence suppression effect due to the difference in air blowing capacity can be compared.

In the electrophotographic apparatus configured as described below, continuous copying was performed at a copying speed of 40 A4 size sheets per minute with the amount of developer consumed per A4 size copy being 0.08 g. In the above, (1) For the primary corona discharge device M4, the input voltage to the blower 37 that blows air into the device (inside the shield plate 1) is set to 11.
(Power consumption: 1.3 W) to reduce the overall amount of air blown into the device 4 (maximum air volume: 0.2 m3/sin, maximum static pressure: 7.0 mm H20), ■ According to the present invention, air distribution plates 40, 40 By adjusting the air velocity along the length of the device 4, the air velocity is set to 2.4 m/sec at both ends (approximately 2C from the inside of the insulating block 33) and 0.75 m/sec at the center.
c and copying is executed (embodiment of the present invention).

■In the above ■, the input voltage to the blower 37 is the same <II
V, remove the air distribution plates 40 and 40, and make the air speed along the length of the device 4 approximately equal (Q, 9ts/5ec),
When copying is executed (Comparative Example 1).

■In the above ■, the input voltage to the air blower 37 is set to 27V (power consumption 5.3W), and the total air flow into the device 4 is approximately twice that of the cases ■ and ■ above (maximum air flow 0.4 + *3/win
, a maximum static pressure of 17.5 mmH20), and the wind speed along the length of the apparatus 4 was approximately uniform and strong at 2.2 mm/sec (Comparative Example 2).

(2) When copying is performed without operating the air blowing means, that is, without actively blowing air into the apparatus 4 (Comparative Example 3).

In each of the above cases, in order to compare the degree of contamination of the discharge electrode of device 4 over time, we counted the number of images in the halftone area where charging unevenness is easy to distinguish until image unevenness (white streaks) appears. . The results are shown in the table below.

That is, in the case of Comparative Example 3 without air blowing, unevenness occurred after 8000 sheets, whereas in the case of the Example of the present invention, the effect was greater than that of Comparative Example 3, and the same effect as that of Comparative Example 2 was obtained. obtained,
Even after 30,000 copies, good images were obtained.

*l: Measured at the airflow inflow opening 34 during non-discharge.

*2: Measured when not discharging.

Thus, in the present invention, the distribution of the airflow introduced from the outside is large at the ends of the corona discharge device and relatively small at the center, taking into consideration the distribution of ion winds, so that the discharge electrodes are prevented from becoming contaminated with the minimum amount of external airflow. It was possible to obtain a corona discharge device that achieved excellent prevention effects and maintained stable discharge characteristics without unevenness over a long period of time.

Although this embodiment shows an example in which the present invention is applied to a positively charged corotron device, the present invention is also effective to a negatively charged corona discharge device, and is applied to the scorotron charger 5, which is a secondary corona discharge device. A similar effect was obtained.

FIG. 5 shows a very schematic configuration of an apparatus that uses an amorphous silicon photoreceptor as the photoreceptor drum 11 and forms an image according to the Karun process. Around the photoreceptor charging corona discharge device 4, optical image exposure optical system 6,
A developing device 7, a corona discharge device 8 for transfer, a cleaning device IO, etc. are provided.

The amorphous silicon photoreceptor lI has a dielectric constant of about 3, whereas the dielectric constant of the CdS photoreceptor l in the device shown in FIG.
The h1ri rate is as high as about 13, and the capacitance per unit area is very large, although it depends on the film thickness. Therefore, when charging, the current directed to the photoreceptor must be controlled at the same process speed. It gets bigger by that amount.

When a photoconductor having a relatively large capacitance, such as amorphous silicon, is used, the current flowing from the discharge electrode of the corona discharge device to the photoconductor is large, and the pressure of the ion wind toward the photoconductor increases. Therefore, in order to maintain the atmospheric pressure balance in the corona discharge device, a large amount of airflow must be introduced to the side opposite to the photoreceptor.

Therefore, at the same time as the airflow flows in from the airflow inflow opening, the airflow inflow from the end portion increases significantly.

In other words, when a photoreceptor with a large capacitance is used, the occurrence of turbulent flow caused by drum wind, ion wind, and shield plate interference is significantly suppressed in the center of the corona discharge device, but at the edges. The occurrence of turbulence increases.

Therefore, in such cases, the amount of air per unit area of the outside air flow that is actively blown into the corona radiation device, or
Alternatively, the generation of turbulence can be suppressed over the entire length of the corona discharge device by making the wind speed larger at the ends and smaller at the center than in the case of the above embodiment. Also, there were no problems in actual device copying. In other words, the present invention can suppress unintentional turbulence that occurs inside the corona discharge device by skillfully combining the distribution of the ion wind generated by corona discharge and the airflow flowing in from the outside, thereby making it possible to uniformly distribute the external airflow. It can be said that this is particularly effective when the capacitance of the photoreceptor is larger than when air is blown.

Furthermore, it is clear that the present invention is effective for all corona discharge devices that require uniform static elimination from a charged fist.

C. Effects As explained above, by blowing a relatively large amount of air to the ends of the discharge electrode and less air to the center than to the ends, the effect of ionic wind associated with corona discharge can be achieved with minimal air blowing. By skillfully combining these effects, it is possible to almost completely suppress the turbulent flow that occurs near the shield inside the discharge device, preventing foreign matter from entering the discharge electrode, and providing long-term −
1. We were able to obtain a corona discharge device with excellent durability that maintains stable discharge characteristics without unevenness or leakage.

[Brief explanation of drawings]

FIGS. 1(a) to 1(c) show an embodiment of the corona discharge device according to the present invention, in which FIG. 1(a) is a longitudinal sectional front view, FIG. 1(b) and FIG. ) Figure (b) -
(b) line and (c)--(c) line sectional view, Figure 2 is a schematic diagram of the configuration of an example of an electrophotographic device, Figure 3 (a) is the same diagram of the convex metal (d
) shows an example of a conventional corona discharge device; (a)
The figure is a vertical front view, (b) is a plan view, (C) and (d) are lines (c)-(c) of (a) and (d), respectively.
)--(d), FIG. 4 is a sectional view of another example, and FIG. 5 is a schematic diagram of the configuration of another example of the electrophotographic apparatus. 1.1. 3114-5 is a photosensitive drum, 3114-5 is a corona discharge device, 37 is a blower, and 35 is a blower duct or a blower chamber.

Claims (1)

[Claims] (1) In a corona discharge device having a corona discharge electrode, a shielding plate surrounding the corona discharge electrode, and an insulating block supporting the corona discharge electrode, an opening other than the corona discharge opening is provided in the shielding plate. Clean airflow is blown into the shielding plate from the opening, and the configuration is such that the wind velocity or air volume, or both, in the blown shielding plate are greater near the insulating block than elsewhere. A corona discharge device characterized by: