JPH11202594A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably control an image forming body to specified potential, to smooth the electrification potential so as to uniformize an uneven latent image and to eliminate color blotting by making the numerical aperture of a control electrode opposed to plural saw-toothed electrode plate rows smaller on a downstream side than on an upstream side in the rotating direction of the image forming body. SOLUTION: A scorotron electrifier is constituted by attaching control grids 115 and 116 being the control electrode to supporting members 121 and 122 corresponding to the saw-toothed electrode plates 111 and 112. The control grid 116 provided to be opposed to the electrode plate 112 is provided so that the numerical aperture of the grid 116 may be made rougher (larger or higher) than that of the grid 115 provided to be opposed to the electrode plate 111 and arranged on an upstream side in the rotating direction of a photoreceptor drum 10 with respect to the grid 115. By making the numerical aperture rougher on the upstream side, the radiation efficiency of corona discharge from the electrode plate 112 is enhanced and the electrification potential of the drum 10 to be electrified is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, etc., which is provided with a plurality of charging means, image exposing means and developing means each using a sawtooth electrode plate around an image forming body. The present invention relates to an electrophotographic color image forming apparatus which forms a color image by superposing toner images during one rotation of an image forming body in a set.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a multi-color image, a single color image formed on each image forming body is provided with the same number of image forming bodies, charging means, developing means and the like as the number of colors required for image formation. Color image forming apparatus that forms a color image by superimposing the toner image on a transfer material, or a color image forming apparatus that rotates the image forming body a plurality of times and repeats charging, image exposure, and development for each color to form a color image Alternatively, there is known a color image forming apparatus which forms a color image by sequentially performing charging, image exposure, and development for each color within one rotation of the image forming body.

However, each of the above image forming apparatuses is provided with the same number of image forming bodies, charging means, developing means, etc. as the number of colors required for image formation, and superposes a single color toner image formed on each image forming body on a transfer material. A color image forming apparatus that forms a color image together has a drawback that the volume of the apparatus is increased due to the necessity of transporting a plurality of image forming bodies and a transfer material. A color image forming apparatus that forms a color image by repeating charging, image exposure, and development has a limitation that although the volume is reduced, the size of the formed image is limited to the surface area of the image forming body or less. .

In this regard, a color image forming apparatus which forms a color image by sequentially performing charging, image exposure and development for each color within one rotation of the image forming body has no restriction on the size of the image and has a high speed image. There are advantages such as enabling formation. Further, an apparatus in which a light-transmitting substrate is used as a substrate of an image forming body and an image exposing means is arranged inside the image forming body to reduce the size of the apparatus has been proposed, for example, in Japanese Patent Application Laid-Open No. 5-307307. .

On the other hand, corona discharge type charging means used in image forming apparatuses such as copiers, printers, and faxes are roughly classified into a wire discharge type and a pin discharge type (pin electrode type, sawtooth electrode type, etc.). You. The latter has been used in electrophotographic copying machines, printers and the like in recent years because of its small size and low ozone generation. In particular, a saw-tooth electrode plate in which a plurality of saw-tooth electrodes are provided on one thin plate-like member as a discharge electrode is US
P. 4,725,732, and using a sawtooth electrode,
Japanese Unexamined Patent Publication No. Hei 5
No. 2314.

[0006]

However, when a serrated electrode plate is used as the charging means of the color image forming apparatus proposed above, the serrated electrode plate is small, generates low ozone, and provides stable discharge. However, since the directivity is strong, the corona discharge from the local and narrow sawtooth-shaped electrode results in a narrow charging capability, which makes it difficult to control the potential to a predetermined value. In the case of superimposed color image formation,
In order to prevent color bleeding of the color toner image, it is necessary to smooth the charging potential in order to equalize a latent image having irregularities.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems and stably controls an image forming body to a predetermined potential by a charging means using a saw-toothed electrode plate, and smoothes the charging potential in superimposed color image formation. Accordingly, it is an object of the present invention to provide a color image forming apparatus which forms a superimposed color toner image without color fringing by making a latent image having irregularities uniform.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to dispose a plurality of charging means, image exposing means and developing means on a peripheral surface of an image forming body so that charging, image exposing and image forming operations are performed during one rotation of the image forming body. In a color image forming apparatus that repeats development and forms a color toner image by superimposing a plurality of toner images on the peripheral surface of the image forming body, the charging device includes a plurality of saw-tooth electrode plate arrays and control electrodes as the charging unit, This is achieved by a color image forming apparatus, wherein an aperture ratio of a control electrode opposed to the plurality of sawtooth electrode rows is smaller on the downstream side than on the upstream side in the rotation direction of the image forming body.

[0009]

Embodiments of the present invention will be described below. The description of the present application does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. Further, in the following description, the image exposure means is provided inside the image forming body, but the means provided outside the image forming body is also included in the present invention.

An image forming process and each mechanism of a color image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of an embodiment of the color image forming apparatus of the present invention, FIG. 2 is a cross-sectional configuration diagram of a charging unit using a sawtooth electrode plate, and FIG.
FIG. 3 is a diagram showing components of the charging unit of FIG. 2 and how to assemble the same.

Referring to FIG. 1, a photosensitive drum 10, which is an image forming member, has a light-transmitting member formed on the outer periphery of a cylindrical base formed of a light-transmitting member such as glass or light-transmitting acrylic resin. Conductive layer, a-Si layer or organic photosensitive layer (OPC)
And the like. Photoconductor drum 1
In the case of 0, the photosensitive drum 10 is rotated clockwise as indicated by an arrow in FIG. 1 in a state where the light-transmitting conductive layer is grounded by power from a drive source (not shown).

The light transmittance of the light-transmitting substrate of the photosensitive drum in the present embodiment does not need to be 100%, but may be such that a certain amount of light is absorbed when the exposure beam is transmitted. The point is that any suitable contrast can be provided. As a material of the light-transmitting substrate, an acrylic resin, particularly one obtained by polymerization using a methyl methacrylate monomer is preferably used because of its excellent light-transmitting properties, strength, accuracy, surface properties, and the like, and other general optical members. Various translucent resins such as acryl, fluorine, polyester, polycarbonate, polyethylene terephthalate and the like used for the above can be used. Further, as long as it has a light-transmitting property with respect to the exposure light, it may be colored. Examples of the light-transmitting conductive layer include indium tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, Ni,
A light-transmissive metal thin film made of Al or the like is used. As a film forming method, a vacuum deposition method, an active reaction deposition method, various sputtering methods, various CVD methods, a dip coating method, a spray coating method, and the like are used. You. The photoconductor layer includes an amorphous silicon (a-Si) alloy photosensitive layer, an amorphous selenium alloy photosensitive layer, and various organic photosensitive layers (OP
C) can be used.

Reference numeral 16 denotes a pre-charge light eliminator as light elimination means for removing the optical memory.
After the optical memory is removed by the static elimination or by a corona eliminator (not shown), for example, the first yellow (Y) scorotron charger 11 performs uniform charging.

Scorotron charger 1 as charging means
1. An exposure unit 12 as an image exposure unit and a developing unit 13 as a developing unit are used in an image forming process of each color of yellow (Y), magenta (M), cyan (C) and black (K). In the present embodiment, FIG.
With respect to the rotation direction of the photosensitive drum 10 indicated by the arrow,
Y, M, C, and K are arranged in this order.

In this embodiment, yellow (Y),
As the charging means for magenta (M), cyan (C) and black (K), a scorotron charger 11 provided with a plurality of, for example, two rows of sawtooth electrode plates 111 and 112 as corona discharge electrodes is used.

As will be described later, a scorotron charger 11 as a charging means for each color is provided with two rows of sawtooth electrode plates 11.
1, 112 and a U-shaped side plate (unsigned) serving as a shield member are attached. Further, support members (unsigned) for attaching the side plate are provided corresponding to the respective sawtooth electrode plates 111, 112. Control grids 11 as control electrodes arranged with different aperture ratios
5, 116 are attached. A control grid 115 disposed opposite to the saw-tooth electrode plate 111 has a saw-tooth electrode plate 112 on the downstream side in the rotation direction of the photosensitive drum 10.
The control grid 116 disposed opposite to is arranged on the upstream side.

A scorotron charger 11 for each color is mounted facing the photosensitive drum 10 in a direction perpendicular to the moving direction of the photosensitive drum 10 (perpendicular to the plane of FIG. 1). The scorotron charger 11 includes a corona discharge electrode for performing a corona discharge having the same polarity as the toner (in this embodiment, a negative polarity), and a photosensitive drum 10.
The above-mentioned organic photoconductor layer performs a charging operation (negative charging in the present embodiment) with a control electrode maintained at a predetermined potential to apply a uniform potential (for example, −700 V) to the photoconductor drum 10. give.

The exposure unit 12 serving as an image exposing means for each color is arranged such that the exposure position on the photoreceptor drum 10 is on the downstream side in the rotation direction of the photoreceptor drum 10 with respect to the charging means for each color. It is arranged inside the body drum 10.
The exposure unit 12 for each color includes a linear exposure element (not shown) in which a plurality of LEDs (light emitting diodes) as light emitting elements of image exposure light are arranged in an array in parallel with the axis of the photosensitive drum 10. A selfoc lens (not shown) as an equal-magnification imaging element is configured as an exposure unit attached to a holder. Exposure unit 1 for each of these colors
2 is attached to a columnar holding member 20 and housed inside the base of the photoconductor drum 10. As an exposure element,
In addition, a linear element in which a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) are arranged in an array is used.

The exposure unit 12 performs image processing, which will be described in detail later, based on image data of each color sent from a separate computer (not shown) and stored in a memory. Image exposure is performed on the body drum 10 to form a latent image on the photosensitive drum 10. The emission wavelength of the light emitting element used in this embodiment is usually Y, M, C
It is preferable that the toner having a high light transmittance in the range of 680 to 900 nm is used. However, since the image exposure is performed from the back surface, the wavelength may be shorter than the wavelength which does not sufficiently transmit the color toner.

The developing device 13 as a developing means for each color includes
For example, each has a thickness of 0.5 mm to 1 mm and an outer diameter of 15 to
25 mm cylindrical developing sleeve 13 a which is a developer carrier formed of a nonmagnetic stainless steel or aluminum material
And a developing casing (no symbol), and contains therein a two-component (or one-component) developer of yellow (Y), magenta (M), cyan (C) or black (K). . The developing sleeve 13a contains a fixed magnet (not shown) in which N and S magnetic poles are alternately arranged, and is stirred and mixed by a stirring screw (no sign), and is conveyed from a stirring unit by a supply roller (no sign). And the supplied two-component developer to the developing unit. At this time, the layer thickness of the two-component developer on the peripheral surface of the developing sleeve 13a is 3 to 10 in diameter.
The developing roller 13a is regulated by a thin layer forming rod (not shown) as a thin layer forming member which is made of a metallic material having a circular cross section of a magnetic material having a thickness of 1 mm and is uniformly pressed against the peripheral surface of the developing sleeve 13a with a predetermined load. The two-component developer having passed through the developing unit is scraped by a plate-shaped elastic member (for example, SUS, urethane rubber, or the like) provided with one end of the long side of the belt in parallel contact with the developing sleeve 13a. Developing sleeve 13a
Removed from the top, transported to the stirring unit by the supply roller,
The mixture is stirred and mixed by a stirring screw so as to have a predetermined toner concentration.

In the developing section, the developing sleeve 13a is kept out of contact with the photosensitive drum 10 by a contact roller (not shown) with a gap of a predetermined value, for example, 100 μm to 1000 μm. DC voltage (for example, -600 V) of the same polarity as toner (minus polarity in this embodiment) or a superimposed voltage of DC and AC is applied to the developing sleeve 13a as a developing bias. By doing so, non-contact reversal development is performed on the exposed portion of the photoconductor drum 10. At this time, the precision of the development interval needs to be about 20 μm or less in order to prevent image unevenness.

As described above, the developing unit 13 applies the electrostatic latent image on the photosensitive drum 10 formed by the charging by the scorotron charger 11 and the image exposure by the exposure unit 12 in a non-contact state. The reversal development is performed with toner having the same polarity as the charging polarity of the drum 10 (in the present embodiment, the photosensitive drum is negatively charged, and the toner has a negative polarity).

At the start of image recording, a photosensitive member driving motor (not shown) is rotated to rotate the photosensitive drum 10 clockwise in FIG. 1 and, at the same time, the optical memory is removed by the static eliminator 16 before charging. First color scorotron charger 1
1 (Y), the photosensitive drum 10 is uniformly charged, and the application of a potential to the photosensitive drum 10 is started by the charging action of the Y scorotron charger 11.

After a potential is applied to the photosensitive drum 10, exposure is started by a first color signal, that is, an electric signal corresponding to the Y image signal in the Y exposure unit 12, and the surface of the photosensitive drum 10 is exposed by rotational scanning of the drum. An electrostatic latent image corresponding to the Y image of the original image is formed on the layer.

The latent image is reversal-developed by the Y developing unit 13 in a state where the developer on the developing sleeve 13a is not in contact with the developer, and a yellow (Y) toner image is formed according to the rotation of the photosensitive drum 10.

Next, the photosensitive drum 10 is further provided with a potential on the yellow (Y) toner image by the charging action of the magenta (M) scorotron charger 11 for the second color, and Exposure is performed by an electrical signal corresponding to the color signal of No. 2, that is, the M image signal, and the magenta (M) toner is formed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. Images are formed superimposed.

By the same process, the cyan (C) scorotron charger 11 for the third color, the exposure unit 1 for C,
The cyan (C) toner image corresponding to the third color signal is further generated by the second and C developing devices 13, and the fourth color (S) black (K) scorotron charger 11, the exposure unit 12 and the developing device 13 form the fourth toner image. Are sequentially superimposed, and a color toner image is formed on the peripheral surface within one rotation of the photosensitive drum 10.

Exposure unit 1 for Y, M, C and K
Exposure of the organic photosensitive layer of the photosensitive drum 10 by 2 is performed from the inside of the drum through the transparent substrate described above. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence from the previously formed toner image, and the same exposure as the image corresponding to the first color signal is performed. It is possible to form an electrostatic latent image, which is preferable, but exposure may be performed from outside the photosensitive drum 10.

On the other hand, the recording paper P, which is a transfer material, is fed from a paper feed cassette 15 which is a transfer material storage means to a feed roller 1.
The sheet is fed by a feed roller 5a, fed by a feed roller (no symbol), and transported to a timing roller 15b.

The recording paper P is synchronized with the color toner image carried on the photoreceptor drum 10 by driving the timing roller 15b, and the paper charger 1 serving as a paper charging means is synchronized.
Due to the electrification of 4C, it is attracted to the conveyor belt 14D and fed to the transfer area. The recording paper P, which has been closely transported by the transport belt 14D, is rotated around the photosensitive drum 10 by a transfer unit 14A as a transfer unit to which a voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied in a transfer area. The color toner images on the surface are collectively transferred to the recording paper P.

The recording paper P on which the color toner image has been transferred is
The charge is removed by a paper separation AC charge remover 14B as a transfer material separating means, separated from the transport belt 14D, and transported to a fixing device 17 as a fixing means. Then, by applying heat and pressure between a fixing roller 17a having a heater (not shown) therein and a pressure roller 17b, the toner adhered on the recording paper P is fixed and the recording paper P is discharged. The paper is sent by the printer 18 and discharged to a tray at the top of the apparatus.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is cleaned by a cleaning blade 19a provided in a cleaning device 19 as cleaning means. The photoreceptor drum 10 from which the residual toner has been removed is removed from the optical memory by the charge removal of the pre-charging light remover 16 for removing the optical memory due to the repetition of charging and exposure, and then uniformly charged by the Y scorotron charger 11. Upon receiving the charge, the process proceeds to the next image forming cycle.

According to FIG. 2 or FIG.
The sawtooth electrode plate 111 which is a corona discharge electrode having the sawtooth electrode 111a in the groove 121a is bonded to the sawtooth electrode plate 112 which is a corona discharge electrode having the sawtooth electrode 112a in the groove 122a of the support member 122, for example. It is attached with the agent. Two rows of support members 121 and 122 provided with sawtooth electrode plates 111 and 112 are attached in parallel to a Y-shaped side plate 113 as a shield member, and the sawtooth electrode plates are further attached to the support members 121 and 122. 11
Control grids 115 and 116, which are control electrodes, are attached to the scorotron chargers 11 and 112 respectively.

Serrated electrode plate 11 as corona discharge electrode
1 has a plurality of saw-tooth electrodes 111a provided with tip portions 111b at a constant pitch L, and a saw-tooth electrode plate 112 as a corona discharge electrode has a tip portion 112b having a constant pitch L.
(Not shown) having a plurality of saw-toothed electrodes 112a,
Each of these is an electrode plate for corona discharge that is arranged orthogonally to the moving direction of the photosensitive drum 10 as an image forming body, as indicated by the arrow in FIG.

The sawtooth electrode plates 111 and 112 are, for example,
It is made by etching a stainless steel plate having a thickness of 0.1 mm, and the curvature of the tips 111b and 112b of the sawtooth electrodes 111a and 112a is R = 40 μm or less. The control grids 115 and 116 have, for example, a plate thickness of 0.
It is made by etching a 1 mm stainless steel plate and has a mesh width of 1 mm. The side plate 113 serving as a shield member is formed by, for example, a drawing member made of aluminum. The support members 121 and 122 are made of an insulating resin, for example, an ABS resin.

The control grid 116 provided opposite to the sawtooth electrode plate 112 preferably has an opening ratio of the control grid 116 of 60 to 90%, and the opening of the control grid 115 provided opposite the sawtooth electrode plate 111. It is provided coarser (larger or higher) than the ratio, and is disposed on the upstream side in the rotation direction of the photosensitive drum 10 with respect to the control grid 115.
By increasing the aperture ratio on the upstream side, the sawtooth electrode plate 11
The discharge efficiency of the corona discharge from 2 is increased, and the charged potential of the photosensitive drum 10 to be charged is increased.

The control grid 115 mounted opposite to the sawtooth electrode plate 111 preferably has an aperture ratio of the control grid 115 of 40 to 70%.
The control grid 116 is provided so as to be smaller (smaller or lower) than the aperture ratio of the control grid 116 provided opposite to the control grid 2, and is disposed downstream of the control grid 116 in the rotation direction of the photosensitive drum 10. By reducing the aperture ratio on the downstream side, the discharge efficiency of corona discharge from the sawtooth electrode plate 112 is reduced, but the potential controllability of the charged photosensitive drum 10 is increased, and the potential is increased and charged on the upstream side. The uniformed charged potential is achieved.

A high voltage of -5 to -6 kV is applied to the sawtooth electrode plates 111 and 112 from the constant current power supply E1 as a common power supply, and the constant voltage power supply ES1 is applied to the control grid 116 on the upstream side.
The constant voltage of -600 V is applied to the control grid 11 on the downstream side.
5 is supplied with a constant voltage of -700 V from the constant voltage power supply ES2, and the photosensitive drum 10 has unevenness in potential on the upstream side due to insufficient controllability, but the potential is raised to about -600V. Charged and -70 downstream
The uniform charging of 0 V is performed, and the discharge efficiency of corona discharge is improved, and the charging is made uniform by improving the potential controllability. Note that the same voltage -700 V as that on the downstream side may be applied to the control grid 116 on the upstream side.

Further, in the formation of a color image by the color image forming apparatus, in order to remove the optical memory of the photosensitive drum 10, before charging the first color, for example, Y in the above-described embodiment, light before charging as light discharging means is used. Although the optical memory is removed by the static eliminator 16, the optical memory is removed, but the static elimination is incomplete or light fatigued, so that the first color is unstable and easily has a low charging potential. The use of a sawtooth electrode plate is small and generates low ozone, and stable discharge can be obtained, but the directivity is strong and corona discharge from a narrow and narrow sawtooth electrode. And it is difficult to control to a predetermined potential. From this, the charging potential of the first color is unstable and it is difficult to ride, so the Y scorotron charger 1 of the first color 1
The aperture ratio of the control grids 115 and 116 as the first control electrode is set to the control grid 11 of the scorotron charger 11 as the M, C and K control electrodes of the second to fourth colors.
70-90%, 50-
It is set as high as 70%.
Charging is performed by the Y scorotron charger 11 having the rows of sawtooth electrode plates 111 and 112, and the pre-charging light neutralizer 1 is charged.
6 makes it possible to raise the charged potential of the photosensitive drum 10 which is photo-destaticized and hardly charged to the same potential as the charged potentials of M, C and K of the second to fourth colors. Since the first color has no toner or potential irregularities, the potential can be easily smoothed (uniform) even if the aperture ratio is increased.

As described above, the image forming body is also stably controlled to a predetermined potential by the charging means using the sawtooth electrode plate, and the charged potential in the formation of the superimposed color image is smoothed, so that the latent image having irregularities is formed. And a superimposed color toner image without color bleeding is formed.

In the description of the above embodiment, control electrodes having different aperture ratios are provided opposite to a plurality of corona discharge electrodes (in the case of the above embodiment, a corona formed of two rows of sawtooth electrode plates). Although two control electrodes are provided opposite to the discharge electrode), it is also possible to use a single control electrode provided with different aperture ratios facing the corona discharge electrodes formed of the respective sawtooth electrode plates.

[0042]

According to the present invention, the image forming body is stably controlled to a predetermined potential by the charging means using the sawtooth electrode plate, and the charging potential in the superimposed color image formation is smoothed. Therefore, the latent image having unevenness is made uniform to form a superimposed color toner image without color fringing.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of an embodiment of a color image forming apparatus of the present invention.

FIG. 2 is a cross-sectional configuration diagram of a charging unit using a sawtooth electrode plate.

FIG. 3 is a view showing constituent members of a charging unit of FIG. 2 and an assembling method thereof.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 photoconductor drum 11 scorotron charger 12 exposure unit 13 developing device 16 pre-charging light neutralizer 111,112 sawtooth electrode plate 111a, 112a sawtooth electrode 113 side plate 115,116 control grid

Claims (4)

[Claims] A plurality of charging means, an image exposing means, and a developing means provided on a peripheral surface of the image forming body, and charging, image exposing, and developing are repeated during one rotation of the image forming body; A color image forming apparatus that forms a color toner image by superimposing a plurality of toner images on a peripheral surface of the color image forming apparatus, comprising: a plurality of sawtooth electrode plate rows and a control electrode as the charging unit; Wherein the aperture ratio of the control electrode facing the image forming member is smaller on the downstream side than on the upstream side in the rotation direction of the image forming body. 2. The color image forming apparatus according to claim 1, wherein the aperture ratio is 60% to 90% on the upstream side. 3. The color image forming apparatus according to claim 1, wherein the aperture ratio is 40 to 70% on the downstream side. 4. The control device according to claim 1, wherein the aperture ratio of the control electrode of the charging unit disposed at the most upstream position in the rotation direction of the image forming body is higher than the aperture ratio of the control electrode of the charging unit disposed on the downstream side. The color image forming apparatus according to claim 1.