JPH0117146B2 - - Google Patents

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a corona discharge device for electrophotography.

(Prior Art) In one type of electrophotographic multiple device, reflected light from an original to be copied is projected onto a uniformly charged photoreceptor to form an electrostatic latent image, and this latent image is treated with a developing agent. A copy is obtained by developing and converting the powder image into a powder image, and then fixing this powder image as it is on a photoreceptor. In another type of electrophotographic copying apparatus, a copy is obtained by transferring the powder image formed on the photoreceptor onto plain paper and fixing the transferred image. In the latter case, the surface of the photoreceptor after transfer is usually cleaned to remove developer, particularly toner, remaining on the surface, and the photoreceptor can be used repeatedly.

Among these series of copying processes, charging, transfer,
In the cleaning step, a corona discharge device is used, and FIGS. 1a and 1b show a corona discharge device conventionally used for this purpose.
The corona discharge device 1 includes insulating blocks 12a, 1 at the end of the elongated conductive shield 11 having a U-shaped cross section.
2b is fixed, and both of these insulating blocks 12a,
A discharge wire 14 is stretched between the wires 12b and 12b with set screws 13a and 13b. The discharge wire 14 is two parallel wires held at the same potential and connected to the conductive rod 1.
5 to a high voltage power supply 2 (see FIG. 1b). The insulating blocks 12a, 12b are covered with covers 12c, 12d made of an insulating material, leaving an effective discharge length in order to prevent lightning strikes. In addition, the covers 12c and 12d are connected to the insulation block 1.
Together with 2a and 12b, it is useful for reducing the gap between the discharge device and the photoreceptor 3, preventing air from flowing into the discharge device from the outside, and preventing wind disturbance inside the conductive shield 11. As is clear from FIG. 1b, the conductive shield 11 is grounded,
The photoreceptor 3 is placed opposite to the lower opening 11a of the conductive shield 11. The photoreceptor 3 is also normally grounded.

When corona discharge occurs, dielectric breakdown occurs in the air around the discharge wire 14, and the air in this area becomes ionized. Ions generated by this ionization move toward opposing electrodes such as the conductive shield 11 and the photoreceptor 3 according to their polarity, and charge the surface of the photoreceptor 3 having an insulating layer. At this time, the ions generated by ionization are drifted by the electric field and collide with the gas molecules of the air present in the conductive shield 11, and as a result, the gas molecules move as shown by arrow A in Figure 1b. Create a type of wind to move in a direction. Although this wind does not contain ions, it is called ``ionic wind'' because it is generated by ions. This ionic wind contains a considerable amount of ozone and nascent oxygen. When the ion wind flows out from the conductive shield opening 11a as a result of the discharge, outside air flows in from the portion with less discharge, that is, from the vicinity of both ends of the discharge device 1, in order to maintain the balance of the atmospheric pressure inside the conductive shield. The distribution of ion wind and incoming air during corona discharge is shown in Figure 1c. The direction of the arrow in the figure represents the direction of the wind, and the length represents the speed of the wind.

It is known that when the photoreceptor 3 is exposed to ion wind, the photoreceptor permanently deteriorates and its sensitivity decreases, resulting in fogging of copied images and uneven image quality. Japanese Patent Publication No. 51-10785 discloses a corona discharge device to solve this problem, which uses a corona discharge electrode and a corona discharge electrode so that more corona current flows toward the conductive shield than toward the photoreceptor during discharge. A configuration has been proposed in which the relative position of the conductive shield and the photoreceptor is determined, and at least one ion wind discharge opening is provided at a suitable location in the conductive shield. With this configuration, more of the ion wind generated during discharge can be led out of the discharge device without hitting the photoreceptor, and permanent deterioration of the photoreceptor and decrease in sensitivity due to the ion wind can be reduced. Copy images of uniform image quality with less fog can be obtained.

However, when incorporating the requirements of a corona discharge device into a copying machine, it was found that it is difficult to always uniformly discharge an ion wind without hitting the photoreceptor using only the above proposal. This is the current that flows through the surface of the conductive shield facing the photoreceptor.
This is because it depends on the magnitude of i _b and the current i _p flowing through the photoreceptor. There is no problem when i _b ≫ i _p , but i _b is necessary for stabilizing the discharge and is not directly related to the charging of the photoreceptor. Since a large value of i _b has the disadvantage that more ozone is generated, it is desirable to make i _b as small as possible. Therefore, it was found that when i _b is decreased, the ion wind tends to flow in the longitudinal center of the discharge device so as to hit the photoreceptor.

(Objects and Structure of the Invention) The present invention eliminates such drawbacks and provides an even more excellent corona discharge device.In particular, the present invention focuses on the ionic wind that is generated more in the central portion of the corona discharge device in the longitudinal direction. The purpose is to improve and uniformly absorb and discharge ion wind by suppressing the generation of ion wind. In addition, an insulating member is provided at the longitudinal center of the discharge device.

With this configuration, near the center in the longitudinal direction of the discharge device, the component of the combined vector sum of the corona discharge current that goes toward the ion discharge port side, which is not the photoreceptor side, becomes large, and as a result, the gas is more strongly absorbed than near both ends. can be easily discharged from this discharge port, and generation of ion wind can be made almost uniform in the longitudinal direction.

(Example) The present invention will be explained below based on the drawings.

FIG. 2 shows an embodiment of the corona discharge device according to the present invention, and in these figures, the same reference numerals as in FIG. 1 indicate the same components.

The conductive shield 11 is made of a conductive material such as aluminum and has a U-shape, and consists of a back plate 11b facing the photoreceptor 3, and two parallel side plates 11c, 11c not facing the photoreceptor 3. Back plate 11 of conductive shield 11
An opening 11d for discharging the ion wind is formed at the connection portion between the side plate 11b and each side plate 11c. There are insulating blocks 1 at both ends of the conductive shield 11.
2a and 12b are fixed, and two corona discharge wires 14 are stretched in parallel between these two blocks by set screws 13a and 13b. The attachment portion of the discharge wire 14 to the insulating block is covered with insulating covers 12c and 12d. Conductive shield 1
1, an insulating plate 16 made of an insulating material such as synthetic resin is attached to the outside of the side plates 11c, 11c with adhesive or the like, and a guard made of a conductive material is further outside of this insulating plate 16. A plate 17 is attached by an appropriate method such as screws. While the conductive shield 11 is grounded, this guard plate 17 is not grounded. When a part of the corona current reaches the guard plate 17 through an opening (not shown), it generates a voltage, absorbs floating dust by applying static electricity, and discharges the discharge wire 1.
4. Works to prevent floating dust from adhering to 4.

The insulating plate 16 is connected to the side plates 11c and 11c of the conductive shield 11 as shown in FIGS. 2a and 2b.
It extends downward from the bottom edge of the side plate 1.
A stepped portion is formed at the lower end of 1c. An insulating member 18 is fixed on the insulating plate 16 by adhesive or other method over a length l at the longitudinal center of the discharge device 1. This situation is well illustrated in Figures 2a and b. This insulating member 18 is made of a material that can withstand high voltage, and the preferred material is almost any synthetic resin including acrylic resin. The insulating member 18 is provided at the center in the longitudinal direction of the discharge device 1 symmetrically with the discharge wire 14 sandwiched therebetween, and its length l is equal to the effective discharge length of the device (the length of the corona discharge wire that contributes to the charging of the photoreceptor). ) Can be arbitrarily selected within the range of 30% to 80% of L. Although this range is not critical, it has been experimentally confirmed that the effect of the insulating member is no longer recognized if it deviates significantly from this range. As an example, for discharge device 1 with effective discharge length L = 250 mm, l = 142
cm insulation members were used. The width of the insulating member 18 is approximately determined by the overall dimensions of the corona discharge device, in particular the distance of the corona discharge wire 14 from the back plate 11b and the photoreceptor 3. That is, the corona discharge device of the present invention basically positions the corona discharge wire 14, the conductive shield 11, and the photoconductor 3 so that more corona current flows toward the conductive shield 11 than toward the photoconductor 3 during discharge. A relationship must be established, and the width of the insulating member 18 must be determined after satisfying such a positional relationship. From the above point of view, it is preferable to provide the corona discharge wire 14 at the same level as the lowest end of the side plate 11c, and this has been confirmed experimentally.

Now, in the corona discharge device having the above configuration, when a high voltage is applied to the discharge wire 14 to generate a corona discharge, the photoreceptor 3 is charged and an ionic wind is generated. Looking at the discharge between the discharge wire 14 and the side plate 11c, FIG.
In the region R, the discharge effect of the ion wind is promoted because the insulating member 18 is affected by the discharge suppressing effect, but in the region S, there is no discharge suppressing effect because the insulating member is not provided.
Therefore, the ion wind discharge effect becomes relatively uniform when viewed in the longitudinal direction of the discharge device. Therefore, according to the configuration of the present invention, it is possible to make the generation of ion wind almost uniform over the longitudinal direction of the device. Residual ozone and other active gases have no adverse effect on the photoreceptor.

In the above embodiment, the insulating member 18 used to insulate a part of the side plate 11c of the conductive shield 11 is a plate-like member made of synthetic resin, a film such as Mylar tape, or a highly insulating paint. But that's fine. The insulating member 18 may have uniform insulating properties over the length l, but
If the insulation resistance increases continuously or discontinuously by changing the thickness from both ends to the center continuously or discontinuously, the amount of ion wind generated can be suppressed continuously or stepwise. This is even more preferable.

As a result of making and comparing black and white copies using the corona discharge device made according to the embodiment shown in FIG. Density unevenness was observed, especially in the center of the image, a decrease in contrast and fog were observed, as well as decolorization in the center of the photoreceptor (photoreceptors using zinc oxide usually have a reddish-purple color due to sensitizing dyes such as rose bengal). However, when exposed to large amounts of ionic wind, the pigment is destroyed and turns yellow.) These phenomena are clearly the result of the central part of the photoreceptor being exposed to more ion wind than the peripheral part.

(Effects of the Invention) In this way, in the present invention, the positional relationship between the discharge wire, the photoconductor, the insulating member, and the backplate is selected so that more corona discharge current flows toward the backplate than toward the photoconductor. Moreover, since an insulating member is provided in the center of the side plate of the conductive shield, it is possible to prevent most of the ion wind from hitting the photoreceptor, and to promote suction and discharge of the ion wind in the center, so that it spreads throughout the length. The amount of ion wind generated can be made almost uniform throughout. As a result, it is possible not only to reduce the adverse effects such as deterioration and deterioration of the photoreceptor caused by the ion wind, but also to make the photoreceptor uniform across the width of the photoreceptor, thereby improving the quality of the copied image.

[Brief explanation of drawings]

Figure 1a of the accompanying drawings is a perspective view of a conventional corona discharge device, Figure 1b is a schematic sectional view taken along the line X-X of Figure 1a and viewed in the direction of the arrow, and Figure 1c. is a diagram showing the wind conditions during corona discharge by the same device,
FIG. 2a is a perspective view of the corona discharge device according to the present invention, FIG. 2b is an enlarged perspective view taken along the Y-Y line of FIG. Figure a is a bottom view of the device shown in figure a; DESCRIPTION OF SYMBOLS 1... Corona discharge device, 11... Conductive shield, 11a... Opening, 11b... Back plate, 11c... Side plate, 11d... Opening, 12a, 12b... Insulating block, 12c,
12d... Cover, 13a, 13b... Set screw, 14... Discharge wire, 15... Conductive rod, 2...
…High voltage power supply.

Claims (1)

[Claims] 1. At least three sides of the corona discharge electrode are covered with grounded conductive shields, and an ion wind outlet is provided in the longitudinal direction of the photoreceptor of one of the front conductive shields, and the conductive shield of the corona discharge electrode and In an electrophotographic corona discharge device that charges a photoreceptor disposed on the opposite side by corona discharge, the conductive shield is integrated with the outer surface of two conductive shields that do not face the photoreceptor, each extending toward the photoreceptor. an insulating plate and a guard plate are provided on the outside thereof, and an insulating member is provided at a longitudinally central portion of the inner surface of the insulating plate and at a position between the corona discharge electrode and the photoreceptor. A corona discharge device characterized by: 2. The corona discharge device according to claim 1, wherein the thickness of the insulating member increases from both ends to the center. 3. The corona discharge device according to claim 1, wherein the installation level of the discharge electrode is the uppermost position of an insulating member provided on the conductive shield.