JPH06258921A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent damage from occurring even in the image non-formation part of a photosensitive drum, etc., serving as an image carrier and to prevent image quality from being impaired by providing a means for removing the negative electrification of the paper non-passage part of the organic photosensitive body and a means for removing the positive electrification of a transfer drum. CONSTITUTION:A transfer control means 50 restricts transfer effect for the transfer film 15A of the transfer drum 15, for example which corresponds to the paper non-passage part of the photosensitive drum, by actuating a drive means 51 in response to a paper size signal from a paper size detector, thereby actuating a shutter 53 to the position where a part of the opening of the transfer shield 17A of a transfer corotron 17 is covered. This shutter 53 is actuated only when paper with a size smaller than the maximum image formation area is used, that is, only when the image non-formation area exists. Therefore, by using the transfer control means 50, positive charges injected to the transfer film 15A in the image non-formation area are eliminated, and it is prevented from being electrified to the positive polarity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a fax machine,
The present invention relates to removal of an image quality defect in an image forming apparatus using an electrophotographic system such as a printer.

[0002]

2. Description of the Related Art FIG. 1 of the accompanying drawings is a block diagram showing an example of a conventional electrophotographic copying machine. The present invention is preferably applied to this type of copying machine. As shown in FIG. 1, this type of copying machine includes an automatic document feeder 1, an image input unit 2, an image output unit 3, and a transfer material feeding unit 4. Color manuscripts
It is placed on the platen glass 5 by the automatic document feeder 1. The image input unit 2 includes an imaging unit 6, a wire 7 for driving the imaging unit 6, a drive pulley 9, and the like. In the case of four color full color using the line sensor and color filter in the imaging unit 6, the color original is B (blue), G which is the primary color of light.
Each of (green) and R (red) is read and converted into a digital image signal, and the signals are the toner primary colors Y (yellow), C (cyan), M (magenta), and K (black).
In addition, in order to improve reproducibility of color, gradation, accuracy, etc., various data processing is performed to convert the color gradation toner signal into an ON / OFF binary signal, and an image output unit Three
Output to.

The image output section 3 has a scanner 10 and a photosensitive drum 11, and a charger 12 for uniformly charging the photosensitive drum 11 and an electrostatic latent image are provided around the photosensitive drum 11. A developing device 13 for developing a toner image, a transfer device 14 for transferring a toner image onto a transfer material, and a cleaning device (cleaner) 16 for collecting residual toner that has not been transferred are arranged.
Is driven to rotate by an electric motor as shown by an arrow.

In the laser output unit 10a of the scanner 10, for example, a yellow image signal from the image input unit 2 is converted into an optical signal, and the photoconductor is passed through the polygon mirror 10b, the f / o lens 10c and the reflection lens 10d. Drum 1
A latent image corresponding to the original image is formed on the image 1. When this yellow latent image is transferred to the transfer material through development, the photosensitive drum 11 is charged by the charger 12 after the residual toner is removed by the cleaner 16, and the laser output unit 1
0a outputs a magenta image signal. Hereinafter, latent images of cyan and black image signals are sequentially formed.

The developing device 13 is a yellow developing device 13.
Y, magenta developing device 13M, cyan developing device 13C,
The black developing device 13K is provided, and each developing device is arranged around the rotating shaft. Then, for example, when a yellow toner image is formed, development is performed by the yellow developing device 13Y at the position of FIG. 1, and when a magenta toner image is formed, the developing device 13 is rotated to rotate the photosensitive drum. The magenta developing unit 13M is arranged at a position in contact with 11. Cyan and black are operated in the same manner.

A transfer material carrier made of a dielectric sheet is stretched around the outer periphery of the transfer drum 15 constituting the transfer device 14, and the transfer drum 15 is connected to a dedicated drive motor or the photosensitive drum 11 by a gear. And is driven to rotate as shown by the arrow. Around the transfer drum 15, a transfer charger 17, a toner charge control static eliminator 19, and a peeling claw 2 are provided.
0, a static eliminator 21, a cleaner 22, a pressing roll 23, and a suction charger 25 are arranged. The transfer material conveyed from the transfer material supply unit 4 via the paper feed roller 4a and the paper feed guide 4b is attracted to the dielectric sheet by corona discharge of the attraction charger 25. The transfer drum 15 is synchronized with the photosensitive drum 11, and, for example, a toner image developed in yellow is transferred onto a transfer material by a transfer charger 17, and the transfer drum 15 rotates to sequentially transfer other colors. Is transcribed.

When the transfer drum is rotated four times and the transfer of the four colors is completed, AC is discharged by the separating discharger 18 provided inside and outside the transfer drum 15, the transfer material is separated by the peeling claw, and the transfer belt is conveyed. The toner image is sent to the fixing device 29 by 27 and the toner image is melted and fixed by the heat and pressure roller 30, and the copy cycle ends.

Conventionally, as shown in the enlarged view of FIG. 4, the cleaner 16 has a rubber-like elastic cleaning blade 33 abutted against the photosensitive member 11 from the advantages of the structure, cost, space and the like. Many of them are in contact with each other to clean the residual toner. However, the cleaning blade alone cannot completely clean the toner, the fibers of the paper, and the filler that remain on the photoconductor in a large amount.
Cleaning brush 3 on the upstream side of the cleaning blade
2, the toner is first disturbed by the cleaning brush to remove the fibers and the filler of the paper, and then the residual toner is removed by the cleaning blade. Further, the cleaner 16 is also provided with a film sheet 31 for preventing toner from spilling from the cleaner.

[0009]

When an organic photoconductor (hereinafter referred to as OPC) is used as a photoconductor in the conventional full-color copying machine as described above, the charge transport layer (hereinafter referred to as CTL) on the photoconductor surface is used. There were cases where fine scratches were made in the circumferential direction of the photoconductor. FIG. 2 shows a photoconductor having such a scratch, and a fine scratch 11A on the surface of the photoconductor 11 is measured by using a surface roughness meter in the direction of the arrow in FIG. As a result, the results shown in FIG. 3 were obtained. Such fine scratches on the photoconductor result in scattering of the exposure light for forming the latent image and disturbance of the latent image, resulting in image quality failure of printing out on a copy. The following may be considered as a mechanism for forming such scratches on the surface of the OPC.

OPC is negatively charged by the charging means. A latent image (image portion: charge eliminating area, BKG: non-charge eliminating area) is formed on the OPC by exposure. The negatively charged toner is developed on the latent image (charge elimination area) by the developing means. This developed image is transferred to a recording paper or an intermediate transfer member that is attracted by a static electricity onto a transfer drum that is positively charged.

At this time, in a non-image forming area which can be formed when a recording paper smaller than the maximum image forming area on the image carrier is used,
The strongly negatively charged image carrier and the strongly positively charged transfer drum are in direct contact with each other at the transfer portion by electrostatic force. FIG. 4 shows the photosensitive drum 1 in this way.
1 shows details of a portion where the transfer drum 1 and the transfer drum 15 are in contact with each other. As shown in FIG.
The transfer film 15A on the outer periphery of 5 is a transfer baffle 17A.
The photoconductor drum 11 is contacted at the transfer corotron 17 having the. FIG. 5 further shows the photosensitive drum 11.
5A is an enlarged view of a contact portion between the transfer film 15A and the transfer film 15A. As shown in FIG. 5, in the portion where the photoconductor and the transfer drum are in direct contact with each other, the residual developer or dust 40 Consider the case where

When the inclusions 40 are present, the inclusions 40 are strongly pressed against the photoconductor 11. When the inclusion is strongly pressed against the CTL of the photoconductor 11, a small recess 41 is formed in the CTL by the inclusion, as shown in FIG. When the portion of the recess 41 enters the cleaner 16, the cleaning blade 33 and the brush 32 fill the developer in the recess 41. The developer embedded in the recess 41 serves as a nucleus to grow a scratch. Conventionally, the CTL of the photoreceptor is worn by the developer remaining near the cleaning edge of the cleaning blade. FIG. 7 shows the surface portion of the CTL of the photoconductor drum. When the scratch core 41A is present, the shaded area on the both sides of the core is due to the residual developer near the blade edge. More shaving, resulting in uneven wear on the CTL. FIG. 8 is a sectional view taken along the line AA of FIG.

When such nonuniformity exceeds a certain limit, the exposure light is scattered and the latent image is disturbed, which is printed out and the image quality is disturbed. Such an image quality defect remarkably occurs in a portion that is a sheet passing portion when a large-sized transfer material passes and a non-sheet passing portion when a small-size transfer material passes.

An object of the present invention is to provide an image forming apparatus which solves the above-mentioned problems of the prior art.

[0015]

According to the present invention, an image bearing member, a charging unit for charging the image bearing member, and the image bearing member charged by the charging unit are exposed to form a latent image. Latent image forming means, developing means for developing the latent image formed on the image carrier by the latent image forming means, and the developed image on the image carrier developed by the developing means is transferred to a recording paper. In the image forming apparatus, the image forming apparatus is provided with a transfer member that comes into contact with the image carrier, a transfer unit that performs the transfer, and a cleaner having a cleaning blade that removes the residual developer on the image carrier. First means for removing or reducing charging by the charging means in a non-sheet passing area on the image carrier when a recording paper smaller than the maximum image forming area on the carrier is used; Maximum image area And a second means for preventing or reducing the charging by the transfer means to the portion of the transfer member corresponding to the non-paper passing area on said image bearing member which occurs when using the remote small recording paper.

[0016]

Considering the mechanism of the scratch generation on the CTL of the photoconductor as described above, the cause of forming the nucleus of the scratch is that OPC which is strongly negatively charged and strongly positively charged in the transfer portion. It can be said that there is electrostatic adhesion between the transfer drums. If this adhesive force is removed, the occurrence of drum scratches can be suppressed. In the present invention, the means for removing the negative charge of the OPC in the non-sheet passing portion, the means for removing the positive charge of the transfer drum, or the means for preventing strong charging are used between the both in the transfer portion. I try to remove the electrostatic adhesion.

[0017]

The invention will now be described in more detail with reference to the accompanying drawings, in particular with reference to FIGS. 9 to 15.

FIG. 9 is a schematic view showing the arrangement of an image forming apparatus as an embodiment of the present invention. 9, the same parts as those of the conventional image forming apparatus shown in FIG. 1 are designated by the same reference numerals, and the description thereof will not be repeated. In the embodiment of FIG. 9, according to the present invention, the means for removing the charge on the non-sheet passing portion on the photosensitive drum 11 is a scanning beam (ROS beam) for forming a latent image on the photosensitive drum, that is, A scanning laser beam from the scanner 10 is used. Further, a transfer limiting unit 50 is arranged with respect to the transfer corotron 17 as a unit for limiting the positive charging on the transfer drum 15 corresponding to the non-sheet passing portion on the photosensitive drum 11.

FIG. 10 shows, on the surface of the photoconductor drum 11, for example, a region which is a non-sheet passing portion in the case of transferring onto an A4 size recording sheet by hatching.
According to this embodiment of the present invention, using a suitable paper size detector, detecting the size of the recording paper used,
At that time, the non-sheet passing portion on the photosensitive drum 11 is determined, the scanner 10 is operated, and the area of the non-sheet passing portion of the photosensitive drum 11 is exposed by the scanning beam. In this case, the amount of toner developed by the scanning beam can be controlled by the intensity of the scanning beam.
It is set to 0.1 to 0.2 mg / cm ² .

11 and 12 are schematic views for explaining the construction and operation of an example of the transfer limiting means used in the present invention. FIG. 11 shows a non-actuated state of the transfer limiting means. The transfer limiting means 50 is attached to the transfer corotron 17 having the transfer shield 17A and the transfer baffle 17B arranged on the photosensitive drum 11 at the transfer portion. It is arranged. The transfer limiting unit 50 is selectively moved to a position where the driving unit 51, the driving arm 52 connected to the driving unit 51, and the driving arm 52 are attached to cover a predetermined area of the opening of the transfer shield 17A of the transfer corotron 17. And a shutter 53 made of an insulating film such as Mylar.

The transfer restricting means 50 operates the driving means 51 in response to a signal indicating the paper size from a paper size detector (not shown), so that the transfer restricting means 50 shown in FIG.
As shown in FIG. 10, the shutter 53 is operated to a position that covers a part of the opening of the transfer shield 17A of the transfer corotron 17, and for example, the non-sheet passing of the photoconductor drum as shown by hatching in FIG. The transfer effect of the transfer drum 15 corresponding to a part to the transfer film 15A is limited. However, the shutter 53 is operated only when a sheet smaller than the maximum image forming area is used, that is, only when there is a non-image forming area. By such a transfer limiting means 50, the effect of transferring only the non-image forming area is limited. According to this transfer limiting means, there is no positive charge injected into the transfer film in the non-image forming area, so that the transfer film is not positively charged. Usually, the shutter 53 should have a width smaller than the width of the non-image forming area.

FIG. 13 is a view similar to FIG. 9 showing the structure of an image forming apparatus according to another embodiment of the present invention. In this embodiment, instead of using the scanning beam for forming a latent image to expose the non-image portion in the embodiment of FIG. 9, the exposure is performed on the downstream side of the developing means 13 and in the transfer portion. This is performed by the light emitting diode 60 arranged on the upstream side. The light emitting diode 60 is adapted to expose the non-image portion only when a transfer material of a small size is sent in response to a signal indicating the paper size from the paper size detector. The transfer limiting means 50 is similar to that described with reference to FIGS. 11 and 12, and will not be described again.

FIG. 14 is a view similar to FIG. 9 showing an image forming apparatus as still another embodiment of the present invention. This embodiment has almost the same configuration as that of the embodiment of FIG. 9, and the transfer film 15A in the embodiment of FIG. 9 is used as an intermediate transfer member 15B, and the toner image on this intermediate transfer member 15B is transferred to the transfer unit 1.
7C and 17D are used to transfer to a transfer material. Other than that, since it is the same as the embodiment of FIG. 9,
I won't explain it again.

FIG. 15 is a view similar to FIG. 13 showing an image forming apparatus as still another embodiment of the present invention.
This embodiment has almost the same configuration as the embodiment of FIG.
The transfer film 15A in the embodiment of FIG. 13 is used as an intermediate transfer body 15B, and the toner image on this intermediate transfer body 15B is
The transfer means 17C and 17D are adapted to transfer to a transfer material. Otherwise, it is the same as the embodiment of FIG. 13 and will not be described repeatedly.

Using the copying machine having the structure shown in FIG. 9, under the following conditions, A3 and A4 papers were used as transfer materials at the same ratio, and the shorter edge of the paper was made perpendicular to the paper feeding direction. I ran a running test. Photosensitive drum: OPC with a diameter of 84 mm 160 mm / sec Blade: Urethane 70 Hs, thickness 2.0 mm, free length 10
mm, bite amount 1.2 mm Development system: reversal development Environment: 10 degrees Celsius, relative humidity 30% As a result, the number of copies that causes image defects due to drum scratches in the non-image area has the constitution of the present invention. It is three times as large as that of the case without it.

[0026]

EFFECTS OF THE INVENTION Even in a non-image portion such as a photoconductor drum which is an image carrier, no scratch is generated, and it is possible to prevent image quality trouble.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of a conventional electrophotographic copying machine.

FIG. 2 is a schematic view showing a state of scratches on a photoconductor of the copying machine as shown in FIG.

FIG. 3 is a diagram showing a measurement example of scratches on the photoconductor of FIG.

4 is a diagram showing in detail a portion where a photosensitive drum and a transfer drum are in contact with each other in the copying machine of FIG.

5A and 5B are views for explaining a mechanism in which a photoconductor drum is scratched in the copying machine of FIG.

6A and 6B are views for explaining a mechanism in which a photoconductor drum is scratched in the copying machine of FIG.

7A and 7B are views for explaining a mechanism in which a photoconductor drum is scratched in the copying machine of FIG.

FIG. 8 is a diagram for explaining a mechanism in which a photoconductor drum is scratched in the copying machine of FIG.

FIG. 9 is a schematic diagram showing a configuration of an image forming apparatus as an embodiment of the present invention.

FIG. 10 is a diagram illustrating a relationship between an image portion and a non-image portion on the surface of the photosensitive drum.

FIG. 11 is a schematic diagram for explaining the configuration and operation of an example of a transfer limiting unit used in the present invention.

FIG. 12 is a schematic diagram for explaining the configuration and operation of an example of a transfer limiting unit used in the present invention.

FIG. 13 is a view similar to FIG. 9 showing another embodiment of the present invention.

FIG. 14 is a view similar to FIG. 9 showing still another embodiment of the present invention.

FIG. 15 is a view showing still another embodiment of the present invention.
It is a figure similar to.

[Explanation of symbols]

 10 Scanner 11 Photoreceptor Drum 13 Developing Device 15 Transfer Drum 16 Cleaner 17 Transfer Corotron 50 Transfer Limiting Means 51 Driving Means 52 Driving Arm 53 Shutter 60 Light Emitting Diode

Claims (5)

[Claims] 1. An image carrier, a charging unit for charging the image carrier, a latent image forming unit for exposing the image carrier charged by the charging unit to form a latent image, and the latent image. Developing means for developing the latent image formed on the image carrier by the forming means, and transfer for contacting the latent image formed on the image carrier by the developing means and transferring the developed image on the image carrier to recording paper. In an image forming apparatus including a member, a transfer unit for performing the transfer, and a cleaner having a cleaning blade for removing the residual developer on the image carrier, a maximum image forming area on the image carrier is more than that. First means for removing or reducing charging by the charging means in a non-sheet passing area on the image carrier when a small recording paper is used, and recording paper smaller than the maximum image forming area on the image carrier When using An image forming apparatus comprising: second means for preventing or reducing electrification by the transfer means to a portion of the transfer member corresponding to a non-sheet passing area on the image carrier. 2. The first means exposes a non-sheet passing area on the image carrier after the charging of the image carrier by the charging means and before the development by the developing means. The image forming apparatus according to claim 1, which is an exposing unit. 3. The exposure means for exposing the non-sheet passing area on the image carrier after the development by the developing means and before the transfer by the transfer means. 1. The image forming apparatus according to 1. 4. The image forming apparatus according to claim 2, wherein the second means is a transfer limiting means that eliminates the effect of the transfer means on the exposed area by the exposure means. 5. The image forming apparatus according to claim 4, wherein the transfer unit is a corotron, and the transfer limiting unit is a shutter for the corotron.