JPH0619626B2 - Corona discharge device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Purpose of the invention [Industrial field of application] The present invention relates to a corona discharge device for use in a corona discharge device, for example, an electrophotographic device, for uniformly charging or discharging the surface of a photoreceptor. Regarding the device.

More specifically, a corona discharge device (a so-called corotron device) having a corona discharge electrode, a shield plate surrounding the corona discharge electrode, and an insulating block supporting the corona discharge electrode,
Alternatively, it also relates to improvement of a corona discharge device (so-called scorotron device) provided 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 the electrophotographic apparatus according to the image forming process disclosed in Japanese Patent Publication No. Sho 42-23910 or Japanese Patent Publication No. Sho 43-24748. 1 is a photosensitive drum as the member to be charged which rotates at a constant speed in the direction of arrow a, before neutralization is performed in the light source 2 ₁ receives the pre-exposure by the corona discharge device 3 simultaneously, the photosensitive drum surface is uniform It is kept at the potential level. Next, the corona discharge device 4 receives a primary charge having a polarity different from that of the above-mentioned precharge, and the corona discharge device 5 further receives a secondary charge having a polarity different from that of the primary charge or a charge removal by an AC corona. Immediately after that, by receiving the light pattern irradiation L (slit exposure, laser beam scanning exposure, etc.) through the lens 6 of the optical system, electrostatic latent images facing the exposure light pattern are sequentially formed on the photosensitive drum. Then subjected to entire surface exposure with the light source 2 _2, the potential contrast of the latent image the formation is enhanced. Then, the latent image is developed with developing colored powder (hereinafter referred to as toner) in the developing device 7 to be visualized. This visible image is sequentially transferred to the surface of the transfer material 9 by the charging action of the corona discharge device 8. The transfer material 9 that has received the image transfer is separated from the surface of the photosensitive drum, is introduced into a fixing device (not shown), undergoes image fixing, and is discharged outside the machine as a copy. On the other hand, the surface of the photosensitive drum 1 after transfer is cleaned by removing the transfer residual toner by the cleaning device 10, and thereafter, the same process as above is repeated.

FIG. 3 shows a general corona discharge device A (corotron device) used by incorporating it in the electrophotographic device as described above.
(A) is a vertical front view, (b) is a plan view, (c) is a sectional view taken along line (c)-(c) of (a), and (d) is Is a sectional view taken along line (d)-(d). That is, a conductive shield plate 32 (for example, made of stainless steel) having a substantially U-shaped cross section whose side facing the surface of the photosensitive drum 1 serving as a member to be charged is opened as a discharge opening, and insulations attached to both ends of the shield plate. And a corona discharge wire 31 as a corona discharge electrode, which is located inside the shield plate and stretched between the insulating blocks at both ends.

33a is an electron supply provided on the insulating block 33 on one side, and the corona discharge wire 31 has one end thereof locked to the electricity supply 33a via a conductive tension spring 38 and the other end insulated from the other. It is locked to a locking piece 33b provided on the block 33, and is always kept in a tensioned state by the pulling force of the spring 38.

Reference numeral 34 is an air flow (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. In some cases, the opening is designed to be provided at the boundary between the top plate and the side plate of the shield plate 32, or at the side plate side. In some cases, the opening is not particularly provided. For introducing light such as the corona discharger 3 and 5 in FIG. 2, the side opposite to the discharge opening side of the shield plate 32 is opened for guiding light, or a light guiding window hole is formed. Configured into a form. In some cases, a light-transmitting plate such as glass is stretched over the opening or window for guiding the light.

The corona discharger A is designed to have a required length dimension corresponding to the width dimension (dimension in the generatrix direction) of the photosensitive drum that is the member to be charged.

In addition to the above-mentioned scorotron device, the scorotron device has a grid wire 3 as a discharge current control member in the discharge opening.
9 (corona discharge device 3, 5 in FIG. 2).

Thus, a direct current high voltage (when positive or negative DC corona discharge is obtained) or an alternating high voltage (when AC corona discharge is obtained) by a voltage power source (not shown) on the corona discharge wire 31 via the power supply 33a. Alternatively, 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 source,
The gas (air) around the corona discharge wire 31 is ionized and ionized. Then, the ionized charged particles move toward the discharge opening, give kinetic energy to the gas molecules at that time, and generate an ionic wind b of a blowing system at the discharge opening, and the ionic wind b causes the surface of the photosensitive drum 1 or the transfer. The surface of the material to be charged such as the back surface of the material 9 is charged or discharged.

[Problems to be solved by the invention]

The blowout of the ionic wind b occurs at each longitudinal portion of the discharge opening of the shield plate 32, but the wind pressure distribution of the ionic wind along the longitudinal length of the discharge opening is weaker at both end sides than at the central portion of the longitudinal length of the discharge opening. This is an insulating block 33 that supports the corona discharge wires 31 on both ends of the shield plate 32.
This is because the presence of 33 makes the discharge weak in the portion close to the insulating block.

On the other hand, the inner pressure of the shield plate 32 becomes negative due to the blowing of the ion wind b. In order to compensate for this, the outside air c flows into the inside of the shield plate from the airflow inflow opening 34 of the shield plate 32 and each longitudinal portion of the corona discharge opening in parallel with the blowing of the ion wind b. The wind pressure distribution of the inflowing outside air c along the longitudinal direction of the corona discharge opening is the center of the wind pressure distribution of the blown-out ion wind b.
Since it is strong and both ends are weak, the distribution is central-weak and both ends is strong on the contrary.

Along with the rotation of the drum 1, a laminar air flow d (FIG. 3 (c). (D)) called a drum wind is generated around the drum.
Then, the drum wind d interferes with the shield plate 32 at the position where the discharge device is arranged, and a part d ₁ thereof becomes a turbulent flow and flows into the inner space of the shield plate from the corona discharge opening.
The distribution of the inflow amount of the drum wind d ₁ along the length of the corona discharge opening is as described above, because the blowout distribution of the ion wind b along the length of the corona discharge opening is strong at the central portion and weak at both end portions. Contrary to the central part-weak (Fig. 3 (c)),
The distribution is on both ends side-strong ((d) in the figure).

From the above, with the corona discharge and the rotation of the drum 1, the inflow of the outside air c + the drum wind d ₁ from the corona discharge opening side into the inside of the shield plate is substantially related to the length of the corona discharge opening. At both ends, there is a local inflow, and the flow velocity is quite strong.

Therefore, external foreign matter is likely to be positively sunk into the shield plate 32 due to the locally strong inflow phenomenon of the outside air c + the drum wind d ₁ on both end sides.

Regarding the electrophotographic apparatus as shown in FIG. 2, scattered toner from the developing device 7 and the cleaning device 10, paper dust generated from the transfer material 9, and other dust are floating in the air inside the apparatus. In particular, it is technically difficult to completely prevent toner leakage and scattering from the ends of the developing device 7 and the cleaning device 10 on both sides of the photosensitive drum. Therefore, the air around both ends of the photosensitive drum 1 is particularly scattered.・ It tends to create an atmosphere containing a large amount of floating toner. Further, toner, transfer material, paper powder, and other dust attached to the peripheral portions of both ends of the photosensitive drum 1 easily remain without being completely removed by the greening device,
Therefore, in the drum wind d of the photosensitive drum, especially in the drum wind around the both ends of the drum, the removed substances such as the above-mentioned removed residual toner are likely to be included.

As a result, the corona discharge device tends to get dirty due to the dust collection phenomenon due to the high voltage electric field.
Floating dust inside the device such as paper dust, dust contained in the drum wind d, cleaning residual toner on the peripheral surfaces of both ends of the photosensitive drum, etc. locally flow in strong outside air c + drum wind d ₁ at both ends of the discharge device. Shield plate 32 positively due to the phenomenon
The inner surfaces of the corona discharge wire 31 and the shield plate 32 are excessively soiled at an early stage due to being stuck inside. Foreign matter stains on the inner surfaces of the corona discharge wire 31 and the shield plate 32 are one of the major causes of uneven discharge, and in the case of an electrophotographic apparatus, the image quality is greatly adversely affected. Therefore, cleaning work must be performed frequently. There wasn't.

Here, in the corona discharge device of the type that does not have the airflow inflow opening 34, the outside air c flows into the inner space of the shield plate 32 due to the corona discharge only on the corona discharge opening side, and the outside air on both end sides of the device is discharged. The inflow wind pressure of c is opening 34
Since it becomes stronger than the type with
The degree of contamination / progress of contamination on the inner surfaces of the corona discharge wire 31 and the shield plate 32 becomes more remarkable.

Further, by increasing the width of the airflow inflow opening 34, the inflow amount of the outside air c from the corona discharge opening side is reduced to some extent, but if the airflow inflow opening 34 has a certain width, there is no effect in expanding it.

Therefore, for example, as disclosed in Japanese Utility Model Laid-Open No. 57-93942, it is known to provide air inflow prevention means at both ends of the discharge opening of the discharge device, but the inflow of outside air into the discharge device is essential. However, the effect of suppressing the inflow of outside air was small.

Further, as disclosed in Japanese Patent Laid-Open No. 57-188062,
A conductive member is provided on the top surface of the insulating block at both ends of the discharge device to increase the amount of discharge at the end of the discharge device and to strengthen the ionic wind at the end so that the inside of the shield member is empty from both ends of the discharge opening. There are also things that suppress the inflow of outside air c into the. This has a great effect, and if a part of the shield member is provided with an opening for inflowing outside air, a larger effect can be obtained. However, unnecessarily increasing the discharge amount may cause practical problems such as an increase in ozone generation and a high-capacity high-voltage power supply.

Further, as disclosed in Japanese Patent Publication No. 40-17229,
The dedusted and dehumidified airflow is positively blown into the inside of the shield member of the discharge device to create an air curtain of a blowing system over the entire discharge opening, and the air curtain moves from the discharge opening side to the inside of the shield member. There is also _{one in which} the inflow of the outside air c and the drum wind d ₁ is suppressed to prevent the foreign matter from being contaminated in the discharge device. FIG. 4 is a cross-sectional view showing a very schematic structure of such a discharge device, and 37 is a blower, in which the air blown from the blower is dedusted and dehumidified and flows into the airflow through a blower duct 35. The air is positively introduced into the inner space of the shield plate 32 from the use opening 34, and the blown air is blown out from the corona discharge opening as an air curtain e ₁ of a blowing system. The air curtain e ₁ prevents the inflow of dust-containing outside air c + drum wind d ₁ from the discharge opening side into the inside of the shield member. Reference numeral 36 denotes an air rectifying plate appropriately arranged in the air blowing duct 35 in order to give 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 a low blowing capacity, the wind pressure of the air curtain e ₁ formed is weak,
At a length of the corona discharge opening, strong balloon ion wind b, also the inflow of the external air c + drum style d ₁ at the center inlet force is small external air c + drum wind d ₁ are obtained by suppressing, outside air c + At both ends where the flow of the drum wind d ₁ is strong, the wind pressure of the air curtain e ₁ cannot overcome the strong flow of the outside air c + the drum wind d ₁ , so that the outside air c containing dust + the drum wind d ₁ of the shield plate 32. It flows into the inner space and the inside of the discharge device becomes dirty. Therefore, in order to generate the air curtain e ₁ sufficient to suppress the inflow of the outside air c + the drum wind d ₁ into the discharge device over the entire length of the discharge opening including both ends, the blower 37 having a relatively large capacity is required. In addition to the harmful effects of increasing the size of the device, increasing the power consumption, and increasing the noise, the cost increases in practice.

The present invention, like the device shown in FIG.
2 is a system in which the airflow e is positively blown into the inner air to generate an air curtain e ₁ of a blowing system at the discharge opening. However, even with a small-capacity blower 37, the entire area of the discharge opening is sufficiently exposed to the outside air. An object of the present invention is to provide a device capable of suppressing the inflow of c + drum wind d ₁ .

(B) Structure of the Invention [Means for Solving the Problems] That is, the present invention relates to a corona discharge electrode, a shield that surrounds the corona discharge electrode and has a ventilation opening provided over the longitudinal direction of the corona discharge electrode, and the corona discharge electrode. In an corona discharge device having an insulating block that supports, and a blowing unit that blows a clean air flow into the shield from the blowing opening, in an air flow blown to the blowing opening by the blowing unit. The gist of a corona discharge device is characterized in that the wind speed is set to be higher than other places in the vicinity of the insulating block.

[Operation] Even if the blower that blows air into the shield plate has a relatively small capacity and low blower capacity, the wind speed in the shield plate for that blower is set to be higher than other places in the vicinity of the insulating block. By distributing the air to the corona discharge opening, the air curtain of a strong blowing system at both longitudinal end portions of the corona discharge opening, that is, strong outside air + drum wind that tends to flow into the discharge device from both longitudinal end portions of the corona discharge opening is sufficiently suppressed. A strong enough air curtain can be formed. At the longitudinal center of the corona discharge opening, the amount of air that is distributed to both ends is reduced, and the air curtain that is formed becomes somewhat weak, but from that part it tends to flow into the discharge device. Since the wind pressure of outside air + drum wind is weak, the inflow can be sufficiently suppressed. Therefore, the inflow of the outside air and the wind of the drum into the discharge device is well suppressed over the entire length of the corona discharge opening. In other words, it is possible to sufficiently prevent foreign matter from entering the corona discharge device by using a small-capacity blower, which has advantages of small size, low power consumption, low noise, etc. It is possible to obtain a corona discharge device having excellent durability that is maintained.

〔Example〕

FIG. 1 shows an embodiment of a corona discharge device A (corotron device) according to the present invention. (A) is a vertical sectional front view,
Figures (b) and (c) are respectively (b)-(b) line and (c)-in Figure (a).
(c) A sectional view taken along the line. The same members as those of the corona discharge device of FIGS.

40, 40 are openings 34 for inflowing air from the air duct 35.
The position and angle of the airflow e introduced into the inner space of the shield plate 32 through the shield plate 32 in the inner space of the shield plate 32 in the vicinity of the insulating blocks 33, 33 on both end sides is higher than that in other places. Is the air distribution plate disposed in the air duct 35.

As a result, a large amount of blast e is distributed to both ends of the corona discharge opening in the longitudinal direction, and the air curtain e of the blowing system is stronger by that much.
₂ , that is, a strong air curtain e ₂ is formed which is sufficient to sufficiently suppress the strong outside air c + the drum wind d ₁ which is about to flow into the discharge device from both longitudinal ends of the corona discharge opening. At the longitudinal center of the corona discharge opening, the amount of air blown to both ends is reduced, and the amount of air blow is reduced, and the formed air curtain e ₁ becomes somewhat weaker, but it originally flows into the discharge device. Outside air c + drum style d ₁
Since the wind pressure is weak, it can effectively suppress the inflow.
Therefore, even if a small-capacity blower 37 is used, the inflow of the outside air c + the drum wind d ₁ into the discharge device, that is, the inflow of foreign matter can be favorably prevented over the entire length of the corona discharge opening.

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

Test Example In the electrophotographic apparatus having the structure shown in FIG. 1, a photosensitive body having a diameter of 108 mm having CdS as a photoconductive layer is used as the photosensitive drum 1, the process speed is 271 mm / sec, and the primary corona discharge device 4 is used. + 350μA, -6 for secondary corona discharge device 5
A constant current of 30 μA was applied, and the surface potential of the photosensitive member in the developing device 7 after the entire surface exposure was set to be −150 V for the light portion and +450 for the dark portion.

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

In the primary corona discharge device 4, a stainless steel shield on the side opposite to the side facing the photosensitive drum 1 is entirely insulated with a mylar film, and an outside air inflow opening 34 is provided in the entire discharge area.

The space between the grounded stainless steel side shields, that is, the width of the discharge opening, is 26 mm, and a corotron type device in which a discharge fine wire with a diameter of 60 μm with a gold plating on a tungsten core is tightened as a discharge electrode in the center thereof. . Since the width of the outside air inflow opening 34 of this device is 10 mm and the length of the discharge device in the longitudinal direction is 310 mm, its area is
It is 3.1 × 10 ⁻³ m ² . Further, the outside air inflow opening 34 is connected to the air blowing chamber (air blowing duct 35), and inside thereof, a flow regulating plate 36 and a air distribution plate 40 are provided for adjusting the air flow distribution. 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 DC brushless fan capable of changing the air flow rate and air pressure characteristics depending on the input voltage, and is configured to compare the magnitude of the turbulent flow suppression effect due to the difference in the blowing capacity.

In the electrophotographic apparatus configured as described above, the amount of developer consumed per copy of A4 size is 0.06 g
Continuous copying was performed at a copying speed of 40 sheets. Thus, in the above, for the primary corona discharge device 4, the input voltage to the blower 37 that blows air into the device (shield plate) is 11V.
(Power consumption 1.3W) to reduce the total air flow into device 4 (maximum air flow 0.2m ³ / min, maximum static pressure 7.0mm
H ₂ O), and by adjusting the air distribution plates 40, 40 according to the present invention, the blast wind speed along the length in the device 4 is 2.4 m / sec on both end sides (range of about 2 cm from the inside of the insulating block 33). When copying is executed by setting the central portion to 0.75 m / sec (Example of the present invention).

In the above, the input voltage to the blower 37 is also 11V.
Then, the air distribution plates 40, 40 were removed to make the air flow velocity along the length inside the apparatus 4 substantially uniform (0.9 m / sec), and copying was performed (Comparative Example 1).

In the above, the input voltage to the blower 37 is set to 27 V (power consumption 5.3 W), and the total blown amount into the device 4 is
About twice (maximum air volume 0.4m ³ / min, maximum static pressure 17.5)
mmH ₂ O), and the copying was carried out with the blowing air velocity along the length inside the device 4 set to a substantially uniform and strong 2.2 m / sec (Comparative Example 2).

A case where copying is performed without operating the air blowing unit, that is, without actively blowing air into the device 4 (Comparative Example 3).

In each of the above cases, in order to compare the degree of fouling of the discharge electrode of the apparatus 4 over time, the number of sheets until the image unevenness (white streak) appears in the image of the halftone portion where uneven charging is easily discriminated is counted. . The results are shown in the table below.

That is, in the case of Comparative Example 3 without air blowing, unevenness occurred in 8000 sheets, whereas in the case of the example of the present invention, the effect was larger than that of Comparative Example 3, and the same effect as Comparative Example 2 was obtained. A good image was obtained even after 30,000 sheets had passed.

Thus, according to the present invention, the distribution of the air flow introduced from the outside in consideration of the distribution of the ionic wind is large at the end of the corona discharge device and relatively small at the center, so that the discharge electrode is contaminated with the minimum external air flow. It was possible to obtain a corona discharge device capable of obtaining an excellent prevention effect and maintaining stable discharge characteristics without unevenness for a long period of time.

In the present embodiment, an example in which the present invention is applied to a positively charged corotron device is shown, but the present invention is also effective for a negatively charged corona discharge device, for example, applied to a scorotron charger 5 which is a secondary corona discharge device. Even if the same effect was obtained.

Figure 5 is an amorphous silicon photosensitive member as the photosensitive drum 1 _1, Carlson shows a very schematic structure of an apparatus for image formation according to the process, the photosensitive member 1 ₁ of the photosensitive member charging corona discharge device 4 around, Optical image exposure optical system 6,
A developing device 7, a transfer corona discharge device 8, a cleaning device 10 and the like are provided.

The amorphous silicon photoconductor ₁₁ has a large dielectric constant of about 13 while the dielectric constant of the CdS photoconductor 1 in the apparatus shown in FIG. 2 is about 3, and it depends on the film thickness. The electrostatic capacity becomes very large, and therefore, when charging is performed, the current to the photoconductor becomes larger when the process speed is the same.

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 wind pressure of the ionic wind toward the photoconductor is high. Therefore, in order to maintain the equilibrium of the atmospheric pressure in the corona discharge device, a large amount of airflow must flow into the side opposite to the side facing the photoconductor. Therefore, at the same time that the airflow flows in from the airflow inflow opening, the airflow inflow from the end portion remarkably increases.

That is, when a photoconductor having a large electrostatic capacity is used, in the central portion of the corona discharge device, the generation of turbulent flow caused by the interference of the drum wind, the ion wind, and the shield plate is significantly suppressed, but at the end portion. The occurrence of turbulence increases.

Therefore, in such a case, the wind speed of the outside airflow that is positively blown into the corona discharge device is set to be larger at the end portion and smaller at the central portion than in the above embodiment, so that the corona discharge device is made smaller. Generation of turbulence is suppressed over the entire length. There was no problem in the actual copying of the device. That is, the present invention, the ionic wind by corona discharge,
By skillfully combining the distribution with the air flow introduced from the outside, it is possible to suppress the involuntary turbulence that occurs in the corona discharge device. Can be said to be particularly effective when is large.

Further, it is clear that the present invention is effective for all corona discharge devices that require uniform charging and discharging.

C, Effect As described above, by blowing a relatively large amount of air at the end of the discharge electrode and a smaller amount of air toward the center than at the end, the effect and blast of ionic wind associated with corona discharge is achieved with a minimum of air blowing. By combining these effects skillfully, it is possible to almost completely suppress the turbulent flow that occurs near the shield in the discharge device, prevent foreign substances adhering to the discharge electrode from entering, and stabilize for a long period without unevenness or leakage. It was possible to obtain a corona discharge device having excellent durability and maintaining excellent discharge characteristics.

[Brief description of drawings]

1 (a) to 1 (c) show an embodiment of a corona discharge device according to the present invention, in which (a) is a vertical sectional front view, (b) and (c) are respectively (a). (B)-(b) line and (c)-(c) line sectional view of FIG. 2, FIG. 2 is a schematic configuration diagram of an example of an electrophotographic apparatus, FIG.
(a) to (d) show an example of a conventional corona discharge device, (a) is a longitudinal front view, (b) is a plan view, (c) and (d) are respectively ( (a) diagram (c)-(c) line and (d)-(d) line sectional view, FIG. 4 is a sectional view of another example, and FIG. 5 is a schematic configuration diagram of another example of the electrophotographic apparatus. is there. 1 - _{1 1} a photosensitive drum, 3 · 4 · 5 · 8 · A corona discharge device 37 is blower 35 is blower duct or blower chamber.

Claims (1)

[Claims] 1. A corona discharge electrode, a shield that surrounds the corona discharge electrode and is provided in the longitudinal direction of the corona discharge electrode, and has an opening for blowing, an insulating block that supports the corona discharge electrode, and the opening for blowing air. In a corona discharge device having a blowing means for blowing a clean air flow in the shield, the wind velocity of the air flow blown to the blowing opening by the blowing means is higher than that in other places in the vicinity of the insulating block. A corona discharge device characterized in that