JPH1165386A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reducing the fluctuation of potential on a photoreceptor surface before entering into the charging process, and to make the photoreceptor surface possible to be uniformly charged. SOLUTION: This device is provided with a cleaning roller 26 so as to coming into contact with the surface of the photoreceptor 12 after transferring. On the cleaning roller 26, the voltage of relatively large potential in polarity opposite to the charge polarity of the photoreceptor 12 (first specified voltage), or the voltage of the potential smaller than the first specific voltage in polarity of the photoreceptor 12 (second specified voltage), is selectively applied. In a word, when the image area where an electrostatic latent image is formed, or the non-image area where the secondary charge is performed by an electrostatic charger 14 is shifted to the cleaning roller 26, the first specified voltage is applied on the cleaning roller 26, and when the residual non-image area where the primary charge is performed by the electrostatic charger 14 is shifted to the cleaning roller 26, the secondary specified voltage is applied, with respect to the cleaning roller 26.

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,
In particular, the present invention relates to an image forming apparatus which is applied to, for example, a copying machine or a printer using an electrophotographic system, and collects untransferred toner remaining on a photoconductor simultaneously with development.

[0002]

2. Description of the Related Art One example of this type of conventional image forming apparatus is as follows.
Japanese Patent Application Laid-Open No. 64-64 filed on Feb. 27, 1988
No. 5,089,009 [G03G 2/00]. According to this conventional technique, untransferred toner remaining on a photoreceptor after transfer by a transfer unit is recovered simultaneously with development by a potential difference between the photoreceptor and a developing device (developing roller), and a voltage having a polarity opposite to that of the toner is reduced. The applied memory removing member disturbs the toner pattern remaining on the photoconductor, thereby preventing an image before one rotation of the photoconductor (pre-process) from appearing as a memory.

[0003]

In order to uniformly charge the photosensitive member in the next charging step after the transfer, it is necessary to minimize the potential variation on the photosensitive member surface before the charging step. However, the surface potential of the photoreceptor after transfer is very unstable, for example, -200 V to +400 V in the image area, and +800 V to +1000 V in the non-image area. That is, depending on the image pattern and the output style (single or continuous), the photoconductor potential before the next charging step is -20.
It changes within the range of 0 V to +1000 V, and it is almost impossible to uniformly charge the surface of the photosensitive member in the charging step by the conventional technique in which only a predetermined voltage is applied to the memory removing member.

Further, when the photoreceptor is formed of a negatively chargeable photoconductive member, talc (talc) contained in the transfer material causes the toner, which should be charged to the negative electrode, to be charged to the positive electrode. There is also a problem that image deterioration occurs. SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an image forming apparatus capable of uniformly charging the photosensitive member by reducing the surface potential variation of the photosensitive member before the charging step.

Another object of the present invention is to provide an image forming apparatus capable of preventing image deterioration due to reverse charging of toner.

[0006]

According to the present invention, there is provided a photosensitive member having an electrostatic latent image formed on a surface thereof, a charging means for uniformly charging the surface of the photosensitive member, and an electrostatic latent image formed by exposing the charged photosensitive member to light. Exposure means for forming an image, a container for containing a non-magnetic one-component developer, a developing means for developing an electrostatic latent image into a developer image by the developer, and a polarity opposite to the charging polarity of the photoreceptor Transfer means for transferring a developer image to a transfer material by a transfer bias voltage,
When the static elimination roller rotatably contacts the photoconductor after transfer, and the image area on the photoconductor where the electrostatic latent image is formed and some non-image areas on the photoconductor except the image area are displaced by the static elimination roller. The first charge roller having the opposite polarity to the charge polarity of the photosensitive member
A first application unit for applying a predetermined voltage, and a second predetermined voltage having a polarity opposite to a charging polarity of the photoconductor is applied to the charge eliminating roller when a non-image area on the photosensitive member excluding a part is displaced by the charge eliminating roller. An image forming apparatus including a second applying unit.

[0007]

[Function] By contacting the surface of the photoreceptor after transfer,
A static elimination roller is provided. Then, a first predetermined voltage having a polarity (negative polarity) opposite to the charging polarity of the photoconductor is applied to the charge removing roller.
A predetermined voltage is selectively applied. That is, an image area on the photoreceptor where an electrostatic latent image is formed and static electricity needs to be reliably removed, or a non-image area where the secondary charging is performed by the charging unit and the potential is increased (a part of the non-image area) Is displaced to the charge eliminating roller, a first predetermined voltage (eg, -400 V) having a polarity (negative polarity) opposite to the charging polarity is applied to the charge eliminating roller.
Is applied, and when the other non-image area is displaced by the charge eliminating roller, a second predetermined voltage (−200 V) having a potential lower than the first predetermined voltage is applied to the charge eliminating roller, and the surface of the photoconductor before the charging step is applied. To reduce the variation in potential.

Further, if the photoreceptor is made of a positively chargeable photoconductive member, there is no danger that the toner will be reversely charged by paper dust generated by the transfer of the transfer material and image fog or the like will occur.

[0009]

According to the present invention, the potential variation on the surface of the photoreceptor before entering the next charging step can be suppressed, so that simultaneous development and cleaning with stable image quality can be performed. Moreover, by using a positively chargeable photosensitive member, it is possible to prevent talc (talc) contained in the transfer material (recording paper) from charging the toner in the developing device to the opposite polarity and deteriorating the image. be able to.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus 10 according to this embodiment shown in FIG.
Includes an image carrier, which includes a photoreceptor 12 rotating in the direction of the arrow. The photoreceptor 12 is a positively chargeable organic photoconductor (OP).
C) is applied to a conductive substrate made of an aluminum tube or the like. In this embodiment, a drum-shaped photoconductor is used, but a belt-shaped or plate-shaped photoconductor may be used.

Above the photoreceptor 12, a charger (charging means) 14 is arranged. The charger 14 is a scorotron type charger having a grid electrode (not shown).
The surface of the photoconductor 12 is uniformly charged by the charger 14 whose charging potential is defined by the Zener diode 16. The developing light image formed by the exposure device 18 is incident on the charged photoconductor 12 via a mirror (not shown) or the like, and an electrostatic latent image is formed on the photoconductor 12. Further, on the right side of the photoconductor 12, a developing device 20 as a developing unit is provided. The developing device 20 comes into contact with the surface of the photoconductor 12 and contacts the photoconductor 12 with a developer (hereinafter, referred to as “toner”). ) Is provided. A toner hopper (container) 20b for storing a non-magnetic one-component toner is provided in association with the developing roller 20a, and the toner is supplied to the developing roller 20a by a supply roller 20c in the toner hopper 20b. further,
In the toner hopper 20b, a developing blade 20 that contacts the surface of the developing roller 20a to reduce the thickness of the toner carried on the developing roller 20a and frictionally charges the toner.
d is provided. A bias voltage having a predetermined potential is applied to the developing roller 20a and the supply roller 20c.

Below the photosensitive member 12, a transfer device 22 as a transfer means is disposed, and the transfer device 22 transfers the photosensitive member 12 to a transfer material 24 such as paper conveyed by a paper feeding device (not shown). The upper toner image is electrostatically attracted. That is, a bias voltage having a polarity opposite to the charging polarity of the photoconductor 12 (negative pole in this embodiment) is applied to the transfer unit 22, and the photoconductor 1 is charged.
The toner on 2 is electrically transferred to the transfer material 24. As described above, when the area on the photoconductor 12 where the electrostatic latent image is formed, that is, the image area, is displaced to the transfer unit 22, the transfer unit 22
Is applied with a bias voltage having a polarity (negative polarity) opposite to the charging polarity of the photoconductor 12, but when the non-image area other than the image area is displaced to the transfer unit 22, the transfer unit 22 A bias voltage of the same polarity, that is, a positive polarity, is applied. Thus, the toner attached to the transfer device (transfer roller) 22 can be transferred to the photoconductor 12 side.

On the left side of the photosensitive member 12, the photosensitive member 1
A cleaning roller (static elimination roller) 26, which is rotatably in contact with the surface of the cleaning roller 2 and is made of a conductive member, is provided with a first predetermined voltage and a second predetermined voltage from power supply devices 28a and 28b. And a voltage. That is, the image area on the photoconductor 12 where the electrostatic latent image is formed and the photoconductor 1 excluding the image area
When a part of the non-image area on the second roller 2 is displaced by the cleaning roller 26, the cleaning roller 26 applies a first predetermined voltage (for example,- 400 V) is applied, and when the other non-image area is displaced by the cleaning roller 26, a second predetermined voltage (for example, -200 V) having a potential lower than the first predetermined voltage is applied to the cleaning roller 26.
Is applied.

That is, the photosensitive member 12 after passing through the transfer device 22
2, the surface potential is -200 to +400 V in the image area (B) where the electrostatic latent image is formed, while the surface potential in the non-image area (A) where the electrostatic latent image is not formed as shown in FIG. +8
A variation of 00 to +1000 V occurs. This is because, for example, the non-image area (paper length) immediately before the image area is 124.
In the case of 2 mm, 94.2 mm immediately before the image area (photoconductor 1
(Circumference) is the area where the primary charging was performed by the charger 14, whereas the previous (remaining) 30 mm was secondary-charged by the charger 14, and of course, the potential in that area was changed to other areas. It rises compared to the area. Further, the potential of the region where the bias voltage having the same polarity as the charging polarity of the photoconductor 12 is applied by the transfer unit 22 is also increased as compared with the region where the bias voltage is not applied.

As described above, the potential is varied depending on the location even in the non-image area. When the image area is included, the potential on the surface of the photosensitive member 12 after the transfer is -200 to + 1000V.
Therefore, it was very difficult to obtain a uniform charging potential in the charging step by the charger 14. If the surface potential of the photoreceptor 12 after the transfer has the above-described variation, the charging potential after passing through the charger 14 is 200 at a maximum.
There is a problem that a potential difference of V is generated, which leads to image deterioration.

Therefore, in this embodiment, the secondary charging is performed by the charger 14 and the potential is increased by being located in the image area where the static elimination is required to be surely performed or the image area in the rotation direction of the photosensitive member 12 and upstream of the image area. When the non-image area (a part of the non-image area) is displaced by the cleaning roller 26, a high potential voltage (first predetermined voltage) having a polarity opposite to the photoconductor polarity (negative pole in this embodiment) is applied, On the other hand, when the non-image area having a relatively low potential, which has been primary-charged by the charger 14, is displaced to the cleaning roller 26, a voltage having a potential lower than the first predetermined voltage (second predetermined voltage) is applied to the cleaning roller 26. Thus, the variation in the surface potential of the photoconductor 12 before entering the next charging step is reduced. Thereby, as shown in FIG. 3, a potential change (variation) on the surface of the photoconductor 12 after passing through the charger 14.
Can be suppressed to a maximum of about 50 V, so that a uniform electrostatic latent image can be formed in the next exposure step.

Next, the above operation will be described with reference to the flowchart of FIG. In step S1 of FIG.
The photoconductor 12 is driven, the charger 14 is turned on,
In step S3, the cleaning roller 26
A voltage of 00V is applied. In the following step S5, a bias voltage (for example, +600 V) having the same polarity as the charging polarity of the photoconductor 12 is applied to the transfer device 22, and the developing device 20 is turned on in step S7. Then, in the next step S9, it is determined whether or not a predetermined period has elapsed since the activation of the charger 14, and if "YES" is determined there, in a step S11, the cleaning roller 26 is determined.
Is applied with a voltage of -200V. That is, step S
In 9, it is determined whether or not the non-image area primary charged by the charger 14 has been displaced to the cleaning 26. If it is determined that the non-image area has been displaced, the first predetermined voltage ( −400
A second predetermined voltage having a potential (−200 V) lower than V) is applied.

Subsequently, in step S13, the exposure device 18 is turned on to form an electrostatic latent image on the photosensitive member 12, and in step S15, a negative bias voltage is applied to the transfer device 22 to perform normal transfer. Enter the process. Next step S
In step S17, it is determined whether a predetermined period has elapsed since the activation of the charger 14 again. When the predetermined period has elapsed, the cleaning roller 26 is determined in step S19.
A voltage having a potential (−400 V) higher than the second predetermined voltage is applied to the second voltage. That is, in step S17, it is determined whether any of the non-image area secondary charged by the charger 14 or the image area requiring static elimination is displaced to the cleaning roller 26, and the area where the potential is rising is determined. In addition, a voltage having a relatively large potential having a polarity opposite to the charging polarity is applied to a region requiring static elimination.

When exposure of image data corresponding to one page to be formed is completed, the exposing device 16 is disabled in step S21, and then a positive bias voltage is applied to the transfer device 22 in step S23. And step S
At 25, it is determined whether a print request has been made. If "YES" is determined in the step S25, that is, if there is image data of another page to be formed, the process returns to the step S9 and the above-described electrophotographic process is repeated, but "NO" is determined in the step S25. Then, in step S27, the charging device 16 and the developing device 20 are disabled, and in step S29, the photosensitive member 12 is stopped, and all operations are ended.

FIG. 5 shows the control timing of each process in accordance with the flowchart of FIG. 4. Referring to the flowcharts of FIGS. 6 and 7, the untransferred toner and paper The operation until is collected will be described. 6 and 7, ● represents toner, and ○ represents paper dust of the transfer material 24 generated during conveyance. FIG.
7 to 7, photoconductor 12 is charged to, for example, +800 V by charger 14, and then exposed to light 1
Exposure of the original image by 8 forms an electrostatic latent image on photoconductor 12. This electrostatic latent image is developed with a developing roller 20a which receives a developing bias voltage (for example, +400 V). The toner image formed on the photoconductor 12 is transferred to a transfer material 24 by a transfer unit 22 to which a bias voltage of, for example, -1000 V is applied. As described above, when the non-image area is displaced to the transfer unit 22, a bias voltage of about +600 V is applied to the transfer unit 22, and the toner attached to the transfer unit 22 is removed.

The toner remaining on the photoconductor 12 without being transferred to the transfer material 24 and the toner transferred to the photoconductor 12 due to the background electric field between the photoconductor 12 and the transfer device 22 pass through the cleaning roller 26, It is recharged together with the photoreceptor 12 by the charger 14, and the charged potential is raised to + 800V. Then, the toner on the photoreceptor 12 is electrically attracted to the developing device 20 and is supplied to the toner hopper 2.
0b. Further, the paper dust generated by the transfer of the transfer material 24 and attached to the surface of the photoconductor 12 is charged by the charger 14 and the charged potential is raised to + 800V. Like the toner, the positively-charged paper powder is attracted to the developing unit 20 in terms of potential, but is gradually negatively charged due to frictional contact. Therefore, the powder is collected by the supply roller 20c to which a voltage of +500 V is applied.

In this embodiment, the image area where the electrostatic latent image is formed or the non-image area (partial non-image area) immediately before the image area where the secondary charging is performed is displaced by the cleaning roller 26. At this time, a voltage (first predetermined voltage) having a polarity opposite to the charging polarity of the photoreceptor 12 is applied, and the non-image area (non-image area except for a part) which has been primarily charged by the charger 14 is cleaned. When the roller is displaced, a second predetermined voltage having a potential lower than the first predetermined voltage is applied to the cleaning roller to suppress a potential variation on the surface of the photoconductor 12 before the next charging by the charger. As a result, the charging potential was made uniform,
Development simultaneous cleaning with stable image quality can be performed.

Further, as in the above embodiment, the photosensitive member 12
If a positively chargeable photoconductive member is used, there is no possibility that the toner is reversely charged by paper dust and image fogging or the like occurs.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2 is a graph showing a potential change on the surface of a photoconductor when there is no charge removal step.

FIG. 3 is a graph showing a potential change on the surface of a photoconductor when a charge removing step is performed according to the embodiment of FIG.

FIG. 4 is a flowchart showing an example of the operation of the embodiment in FIG. 1;

FIG. 5 is a chart showing the control timing of the embodiment in FIG. 1;

FIG. 6 is an explanatory diagram illustrating a process until the toner on the photoconductor is collected in a developing device.

FIG. 7 is an explanatory diagram showing a process until paper dust on a photoreceptor is collected by a supply roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 12 ... Photoconductor 14 ... Charger 18 ... Exposure device 20 ... Developing device 20a ... Developing roller 20b ... Toner hopper 20c ... Supply roller 22 ... Transfer device 24 ... Transfer material 26 ... Cleaning roller

Claims (4)

[Claims] A photosensitive member having a surface on which an electrostatic latent image is formed; charging means for uniformly charging the surface of the photosensitive member; and exposing the charged photosensitive member to form the electrostatic latent image. Exposure means, development means including a container for housing a non-magnetic one-component developer, and developing the electrostatic latent image into a developer image by the developer, transfer of a polarity opposite to the charging polarity of the photoconductor Transfer means for transferring the developer image to a transfer material by a bias voltage, a charge removing roller rotatably contacting the transferred photoconductor, an image area on the photoconductor on which the electrostatic latent image is formed, and the image First application means for applying a first predetermined voltage having a polarity opposite to a charging polarity of the photoconductor to the charge eliminating roller when a part of the non-image area on the photosensitive member excluding an area is displaced to the charge eliminating roller; And the non-image area on the photoreceptor excluding the part When There displaced to the discharging roller comprises a second application means for applying a second predetermined voltage to the charging polarity opposite to the polarity of the photosensitive member to the discharging roller, the image forming apparatus. 2. The image forming apparatus according to claim 1, wherein said non-image area is a section on which secondary charging has been performed by said charging means. 3. The image forming apparatus according to claim 1, wherein said first predetermined voltage is a potential higher than said second predetermined voltage. 4. The image forming apparatus according to claim 1, wherein said photosensitive member includes a positively chargeable photoconductive member.