JPH02146067A - Corona discharger - Google Patents

Abstract

PURPOSE:To prevent the advance of partly fouling of a discharge wire and to restrain the generation of ununiformity of image density by making the rising length of a both the end parts of the side plate part of a shield member longer than the central part. CONSTITUTION:A back plate part 1a that is a back face of the shield member 1 whose cross-sectional shape surrounding the discharge wire 3 is U-shaped is provided with an oblong opening part 2. The rising length of parts around both ends part 1c of the side plate part 1b is longer than at the central part. Therefore, the resistance of air inflow is increased and the inflow speed produced when a high voltage is applied to the discharge wire 3 is restrained. Then the air flow in the shield member 1 becomes smooth. Therefore, the partial adhesion of toner and dust to the discharge wire 3 is decreased and the density ununiformity of an obtained picture can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a corona discharger for charging the surface of a photoreceptor in an electrostatic recording device.

[Conventional technology]

2. Description of the Related Art A corona discharger using an elongated wire-like discharge wire as an electrode is used in an image forming section of an electrostatic recording device such as an electrophotographic copying device.

Fig. 6 is a perspective view showing the shield member of a conventional corona discharger, Fig. 7 is a central sectional view showing the conventional corona discharger, and Fig. 8 shows the shield member of Fig. 6 and the air flow around it. FIG. 2 is a perspective view and a plan view. In the figure, 11 is an elongated frame-shaped shield member made of a conductive material such as sheet metal;
la is a back plate portion of the shield member 11, llb is a side plate portion located before and after the back plate portion 11a, and 2 is an elongated hole Ω drilled in the back plate portion 11a.
The opening 3 is a discharge wire made of a tungsten wire with a thickness of several tens of micrometers, and 4 is a drum-shaped photoreceptor drum having a photoreceptor layer (for example, three As2Se layers) formed on its surface. Since members are provided at both ends 11c of the shield member 11 to stretch the discharge wire 3, air circulation is not possible. Since such a corona discharger has a simple structure, it is widely used in electrostatic recording devices such as electrophotographic copying machines. As shown in FIG. 7, the shield member 1
The discharge opening of No. 1 is brought into contact with the surface of the photoreceptor drum 4,
A high voltage (e.g. ±3KV ~
±10 KV) is applied to uniformly charge the surface of the photosensitive drum 4.

When a high voltage is applied to the discharge wire 3, a corona wind is generated, air is sucked through the opening 2, and air is blown out from between the lower part of the side plate portion 11b and the photoreceptor drum 4.

[Problem to be solved by the invention]

In the conventional corona discharger, when a high voltage is applied to the discharge wire 3 as described above, air flows due to corona wind. Since members must be provided at both ends of the shield member 11 to attach the discharge wire 3, the opening 2 cannot be made as long as the ends 11c. As a result, air is strongly sucked in from the lower part of the side plate portion, and a vortex 5 in which the wind stagnates is generated inside the shield member 11 as shown by the arrow in FIG. In such a place, the amount of corona wind from the discharge wire 3 reaching the surface of the photoreceptor drum 4 decreases, and the charge on the surface of the photoreceptor drum 4 decreases, causing density unevenness in the image and discharging in that area. The wire 3 has a larger amount of toner, dust, etc. floating in the device than other parts, reducing the discharge effect.
There has been a problem in that density unevenness increases as the number of recording operations increases.

The present invention solves these problems and almost eliminates air stagnation in the shield member 11, prevents the progress of local contamination of the discharge wire 3, and provides a corona that slightly suppresses the occurrence of image density unevenness. The purpose is to provide a discharge device.

[Failure to solve the problem]

The above purpose is to provide an elongated hole-shaped opening in the back plate portion forming the back side of a shield member having a U-shaped cross section that surrounds two discharge wires, and to Position t: This is achieved by a corona discharger characterized in that the rising length of the side plate portion is set longer at both ends than at the center.

〔Example〕

Prior to detailed description of the present invention, an outline of an example of an electrophotographic copying machine which is an electrostatic recording device to which the corona discharger of the present invention is applied will be explained.

FIG. 5 is a diagram schematically showing an example of an electrostatic recording device to which the corona discharger of the present invention is applied. Of course, the present invention is not limited to this example and can be applied to any electrostatic recording device. In the figure, a photoreceptor drum 4 is rotatably supported in the direction of the arrow, and a charging electrode 10 is placed around the photoreceptor drum 4 to uniformly charge the surface of the photoreceptor drum 4. A cell 7 that forms a latent image by forming a reflected light image from a document 9 illuminated by a lamp 8 on the surface of the photosensitive drum 4.
Otsuta lens array 22 , a developing device 23 that converts the latent image into a developed toner image, a transfer material 24 that is fed in synchronization with the rotation of the photosensitive drum 4 , a transfer that transfers the toner image onto the transfer material 24 Electrophotographic process members such as a charging electrode 25 and a cleaning device 26 for removing residual toner on the photoreceptor drum 4 are sequentially arranged around the periphery of the photoreceptor drum 4. The transfer material 24 is fed via a feed roller (not shown) in synchronization with the toner image on the photoreceptor drum 4, and the toner image is transferred and separated by a transfer charging electrode 25; then, it is fixed (not shown). It is fixed by the device and discharged outside the machine.

1 to 3 show the charging electrode 10. Transfer charging electrode 25
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view and a sectional view showing an embodiment of a corona discharger of the present invention used as a corona discharger.

1 is a perspective view showing a shield member according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line A-A in FIG. 1, FIG. 3 is a sectional view taken along the line BB in FIG. The figures are a perspective view and a plan view showing the flow of air around the shield member of the present invention when the shield member is used. In the figures, numerals 2 to 4 are the same as parts with the same numerals in FIGS. 6 and 7, and numerals 1 to 1c are the same as those in FIGS.
This portion corresponds to portions 11 to 11c in the figure. Therefore, FIG.

Description of the same parts as in FIG. 7 will be omitted. In the figure, l is a shield member, la is a back plate portion thereof, ib is a side plate portion located before and after the back plate portion 1a, and lc is its both ends. The shield member 1 has a length corresponding to the drum width of the photoreceptor drum 4, and the rising length of the portions near both ends 1c of the side plate portion 1b is longer than that of the central portion, as shown in the figure. It has become. This increases the air inflow resistance, suppresses the air inflow speed that occurs when a high voltage is applied to the discharge wire 3, and smoothes the air flow within the shield member 1, as shown in FIG. The swirl 5 did not occur, the adhesion of toner and dust on the discharge wire 3 was reduced, and the density unevenness of the image obtained by the electrostatic recording device to which this corona discharger was applied was reduced. .

In this embodiment, the rising length of the central portion of the shield member l is 9 mm, and the rising length of both end portions is 16 mm. The length of this longer rising portion varies depending on the length d of the unpierced portion of the opening 2 at both ends 1c, but the length d is, for example, 10 m.
In the case of m, it is preferably 5 to 25 mm.

The flow velocity of air in and out when using the above corona discharger,
The results of an experiment comparing density unevenness of an image obtained by an electrostatic recording device using the above corona discharger with a case using a conventional shield member will be explained.

The photoreceptor drum used in the experiment had a layer thickness of 55p as a photoreceptor.
m(1)As2Ses is used, the diameter is 100 mm, and the moving speed of the photoreceptor surface is 260 mm/sec. In the conventional shield member, the side plate portion 1b shown in FIGS. 6 and 7 has a rising length of 9 mm.

FIG. 10 is a diagram showing the flow velocity of air flowing in and out from between the side plate portion and the photosensitive drum, and FIG. 11 is a diagram showing the flow velocity of air flowing in from the opening of the back grate portion.

Taking the distance from the center of the shield members 1 and 11 on the horizontal axis,
The vertical axis represents the air flow velocity (m 2 /5 ec), and the area above the horizontal axis represents the outflow of air, and the area below the horizontal axis represents the inflow of air. The values of the conventional corona discharger are shown by white circles connected by thin lines, and the values of the corona discharger of the present invention are shown by black circles connected by thick lines.

As shown in FIG. 11, the inflow velocity from the opening 2 is almost the same as that of the conventional shield member 11, but the inflow velocity from both ends of the side plate portion 1b is as shown in FIG. It is small in the shield member l.

Further, the density distribution of an image obtained by an electrostatic recording device using the above-mentioned corona discharger was as follows. FIG. 9 is a diagram showing the image density distribution in the direction along the discharge wire, where white circles indicate the case where a conventional corona discharger is used, and black circles indicate the case where the corona discharger of the present invention is used. In this case, halftone charts with a density of 0.2 were used for both manuscripts. As shown in the figure, when the conventional corona discharger was used, the concentration at the edges was abnormally high, but when the corona discharger of the present invention was used, the concentration was almost negative up to the edges. .

〔Effect of the invention〕

According to the present invention, as explained above, since the rising length of both ends of the side plate portion of the shield member is made longer than the central portion, air retention within the shield member is almost eliminated, and the discharge wire 3 is It is now possible to provide a corona discharger that prevents the progress of local stains and suppresses the occurrence of density unevenness in images to a slight extent.

[Brief explanation of the drawing]

1 is a perspective view showing a shield member according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line A-A in FIG. 1, FIG. 3 is a cross-sectional view taken along the line B-B in FIG. 1, and FIG. The figures are a perspective view and a plan view showing the shield member of the present invention and the air flow around it. Figure 5 is a diagram schematically showing an example of an electrostatic recording device to which the corona discharger of the present invention is applied. Figure 6 is a perspective view showing the shield member of a conventional corona discharger, FIG. 7 is a central sectional view showing the conventional corona discharger, and FIG. 8 is a perspective view showing the shield member of FIG. 6 and the air flow around it. and a plan view, FIG. 9 is a diagram showing the image density distribution in the direction along the discharge wire, FIG. It is a figure which shows the flow velocity of the air which flows in from the opening part of a back plate part. 1.11... Shield member l a, lla... Back plate portion 1, b, 11b
...Side plate part 2...Opening part 3
...Discharge wire 4...Photoreceptor drum 5...
Spiral Figure 8 Figure 5

Claims (1)

[Claims] A shield member having a U-shaped cross section that surrounds the two discharge wires has an elongated hole-shaped opening in the back plate portion forming the back side, and side plates located at the front and rear of the back plate portion. A corona discharger characterized in that the rising length of the section is set longer at both ends than at the center.