JP2007017560A - Charging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging device with a simple constitution where the inflow of smoke toner and the storage of an external addition agent on a grid electrode are suppressed, and a satisfactory image can be obtained. <P>SOLUTION: The charging device 2 is provided with: a corona discharge electrode 21; a shield case 22; and a grid electrode 23. Further, the side face on the side of a development apparatus 4 of the shield case 22 is provided with a casing member 25 arranged with a prescribed cap so as to cover the side face; and a seal member for clogging the gap between the casing member 25 and a photoreceptor drum 1. Then, an external addition agent or the like stuck to the surface of the photoreceptor drum 1 are clogged by the seal member 25, and are taken into an external addition agent recovery duct 26 by a free fall and an air stream. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a charging device used in an electrophotographic image forming apparatus. More specifically, the present invention relates to a charging device that uniformly charges the surface of an image carrier using a corona discharge member.

  Conventionally, as a charging device for uniformly charging an image carrier (for example, a photosensitive drum) of an image forming apparatus, there is one using a corona discharge member. As shown in FIG. 6, a general charging device using a corona discharge member includes a corona discharge electrode 21 arranged in parallel in the axial direction of the photosensitive drum 1, and the corona discharge electrode 21 facing the photosensitive drum 1. A shield case 22 surrounding three sides excluding the surface to be shielded, and a grid electrode 23 disposed on the opening surface of the shield case 22.

  Since the charging device 20 using such corona discharge is not in contact with the photosensitive drum 1, it may inhale the smoke toner of the adjacent developing device 4. When this fuming toner accumulates on the grid electrode 23 of the charging device 20, the photosensitive drum 1 cannot be sufficiently charged at the accumulated location, which causes a charging failure.

Therefore, in order to remove the fumed toner, for example, in Patent Document 1, a duct for sucking the fumed toner is arranged around the charging device, and an appropriate air flow is formed by a fan or the like to remove the fumed toner. A forming apparatus is disclosed.
Japanese Patent No. 3067406

  However, the conventional charging device described above has the following problems. In other words, even if the duct is arranged, there is a gap between the duct and the photosensitive drum, so that the fumed toner cannot be sufficiently collected. In addition, a large fan capable of forming an air flow from the entire axial length of the charging device is required. For this reason, the entire image forming apparatus is increased in size.

  Therefore, as shown in FIG. 7, it is conceivable that a seal member 24 is attached to the side surface of the shield case 22 on the developing device 4 side to prevent the inflow of fumed toner. By closing the gap between the shield case 22 of the charging device 20 and the photosensitive drum 1 in this way, it is possible to suppress the inflow of fumed toner with a compact configuration.

  However, the addition of the seal member 24 causes a new problem. That is, the toner and the external additive that have passed through the cleaning member 6 positioned on the upstream side of the charging device 20 are blocked by the seal member 24 and accumulated. In particular, an external additive having a small diameter is likely to pass through the cleaning member 6 and is easily accumulated inside the charging device 20 by the seal member 24. When the external additive or the like falls on the grid electrode 23, the external additive or the like is charged up by corona discharge. Therefore, the surface potential of the photosensitive drum 1 is locally increased, and image noise such as a white belt is generated.

  The present invention has been made to solve the problems of the conventional charging device described above. That is, an object of the present invention is to provide a charging device that can obtain a good image with a simple configuration, suppressing inflow of fuming toner and accumulation of external additives on the grid electrode. .

  A charging device for solving this problem is a charging device for charging an image carrier by corona discharge, a discharge electrode, a grid electrode positioned between the discharge electrode and the image carrier, and a discharge electrode. A shield case facing the image carrier with the grid electrode in between, and a portion facing the image carrier opening, and a shield case located on the downstream side surface in the rotation direction of the image carrier, and the shield A casing portion that forms a space where an opposing portion to the image carrier is opened between the downstream side surface of the case, and a seal portion that is attached to the casing portion and seals a gap between the image carrier and the casing portion. It is characterized by having.

  The charging device of the present invention is a charging device that uniformly charges the surface of an image carrier by corona discharge, and includes a discharge electrode, a grid electrode, and a shield case. Further, the charging device has a casing portion on the downstream side surface of the shield case, and a space is formed between the casing portion and the downstream side surface of the shield case so that the portion facing the image carrier opens. . That is, the charging device has a first region (charging region) surrounded by the shield case and a second region (vacant space) located on the downstream side of the first region. Further, the casing portion is provided with a seal portion that seals the gap with the image carrier, so that the intrusion of the fuming toner can be prevented.

  In the charging device of the present invention, external additives and the like are accumulated inside the charging device by the seal portion attached to the casing portion. The accumulated external additives and the like are located downstream of the shield case and fall into a space formed by the casing portion. That is, the external additive or the like is accommodated in a space formed by the casing portion and does not fall on the grid electrode. Therefore, the occurrence of image noise such as a white belt is suppressed.

  Further, it is better that the casing portion of the charging device of the present invention can be connected to an exhaust means for forming an air flow in a space inside the charging device. That is, it is better if a recovery duct for transporting the stored external additive or the like in the empty space can be formed. Thereby, the external additive etc. accumulate | stored in a void can be appropriately discharged | emitted out of an apparatus.

  Alternatively, it is better to provide a vent hole in the wall surface of the shielding case of the charging device so as to communicate with the space formed by the casing portion. That is, an exhaust passage for removing discharge products such as ozone is formed in the shield case. Therefore, by providing the shield case with a vent that communicates with the void formed by the casing portion, an air flow can be formed in the void using the air flow in the shield case. Thereby, the external additive etc. accumulate | stored in a void can be appropriately discharged | emitted out of an apparatus. Further, since the exhaust means for discharging the external additive can also be used as the exhaust means for forming an air flow in the shield case, the apparatus can be downsized and the number of parts can be reduced.

  The charging device is attached to a side surface covered with the casing portion of the shield case, and has a second seal portion that is not in contact with the image carrier and seals a part of a gap between the image carrier and the shield case. It is better if it is. That is, when an air flow is formed in the void by the casing portion, external additives or the like blocked by the seal portion may scatter in the void. Therefore, by providing the second seal portion, it is possible to prevent intrusion of the external additive or the like that scatters. Therefore, generation of image noise such as a white belt can be more reliably suppressed. Since the second seal portion is not in contact with the photoreceptor, accumulation of external additives and the like does not occur.

  According to the present invention, the space for accommodating the external additive or the like is disposed at a position downstream of the grid electrode in the rotation direction of the image carrier. Then, by disposing the seal portion at the tip, the external additive or the like is prevented from dropping onto the grid electrode. Therefore, with a simple configuration, it is possible to suppress the inflow of fuming toner and the accumulation of external additives or the like on the grid electrode and obtain a good image.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best mode for embodying the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, the photosensitive drum is uniformly charged, and the present invention is applied to a charging device using a corona discharge member.

[First embodiment]
FIG. 1 shows an overall schematic configuration of an image forming apparatus 100 including the charging device 2 of the first embodiment. That is, the image forming apparatus 100 has a photosensitive drum 1 that carries a toner image as shown in FIG. The photosensitive drum 1 is an OPC photosensitive member having a negatively charged polarity, and rotates at a constant speed in the direction of an arrow in FIG. Further, around the photosensitive drum 1, a charging device 2, a developing device 4, a transfer device 5, and a cleaning member 6 are sequentially arranged along the rotation direction. An electrostatic latent image is formed between the charging device 2 and the developing device 4 by the laser light from the exposure device 3.

  The charging device 2 is a non-contact charging device including a corona discharge electrode 21 and uniformly charges the surface of the rotating photosensitive drum 1 within a range of −450V to −500V. In this embodiment, a rectangular wave voltage obtained by switching a DC voltage is applied to the corona discharge electrode 21 of the charging device 2. In this embodiment, a rectangular wave voltage is supplied to the charging device 2, but the waveform of the applied bias is not limited to this. That is, the applied bias may have any waveform as long as the surface potential of the photosensitive drum 1 can be set to a predetermined value. For example, it may be a DC voltage or an AC voltage, or may be an oscillating voltage obtained by superimposing the AC voltage on the DC voltage. Also, a pulse voltage or other waveform voltage may be used. Details of the charging device 2 will be described later.

  The developing device 4 applies toner to the latent image. The developing device 4 may be a contact type or a non-contact type. Further, the developing method may be a two-component developing method including toner and a carrier, or a one-component developing method not including a carrier. In this embodiment, negatively charged toner is used. However, positively charged toner may be used as long as the toner image can be developed.

  In the image forming apparatus 100 configured as described above, first, the surface of the photosensitive drum 1 is charged to a predetermined potential by the negative polarity bias to the charging device 2. Next, a laser beam corresponding to a signal input from a host device such as a personal computer is emitted from the exposure device 3 to the exposure portion on the photosensitive drum 1, and the surface of the photosensitive drum 1 is scanned and exposed. A latent image of the first page is formed.

  Next, the developing device 4 performs development with negative polarity toner, and a toner image of the first page is formed on the photosensitive drum 1. Next, the transfer device 5 applies a bias (for example, 800 V to 1000 V in this embodiment) having a polarity opposite to that of the toner from the back surface of the transfer material, and the toner image of the first page is transferred onto the transfer material. That is, the toner on the photosensitive drum 1 is transferred to the transfer member by the positive polarity bias of the transfer device 5.

  The toner that has not been transferred to the transfer material remains on the photosensitive drum 1 and reaches the cleaning device 6. The cleaning device 6 is located between the transfer device 5 and the charging device 2, is disposed in contact with the photosensitive drum 1, and collects toner remaining on the photosensitive drum 1. At this time, an external additive (for example, strontium titanate) adhering to the toner acts as a lubricant for preventing abrasion of the edge of the cleaning device 6.

  Next, the charging device 2 will be described in detail. As shown in FIG. 1, the charging device 2 of the present embodiment includes a corona discharge electrode 21, a shield case 22 that surrounds the corona discharge electrode 21 from three sides except the surface facing the photosensitive drum 1, and a corona discharge electrode 21. And the photosensitive drum 1 and a grid electrode 23 located on the opening of the shield case 22. Further, the corona discharge electrode 21 and the shield case 22 are connected to different power sources, and a voltage is appropriately applied.

  The corona discharge electrode 21 is a sawtooth discharge electrode plate and is disposed along the axial direction of the photosensitive drum 1. The corona discharge electrode 21 is not limited to a sawtooth discharge electrode plate, and may be, for example, a discharge wire or a pin electrode.

  Further, both end portions of the shield case 22 in the axial direction are open ends. As shown in FIG. 2, the charging device 2 has an intake duct 27 connected to one end, an exhaust duct 28 connected to the other end, and a fan 29 installed downstream of the exhaust duct 28. . Therefore, an air flow that flows in the longitudinal direction of the shield case 22 is generated in the shield case 22 as indicated by an arrow in FIG. That is, an exhaust passage for removing discharge products such as ozone is formed in the charging device 2. Note that a filter for appropriately treating the discharge products is disposed in front of the fan 29 in the exhaust flow path.

  Further, on the side surface of the charging device 2 on the developing device 4 side, as shown in FIG. 1, a casing member 25 disposed with a predetermined gap so as to cover the side surface of the shield case 22, and the casing member 25 and the photosensitive member. A seal member 24 for closing the gap with the drum 1 is provided.

  In the charging device 2, since the side surface of the shield case 22 on the developing device 4 side is covered with the casing member 25, a space (hereinafter referred to as “external additive”) is formed between the shield case 22 and the casing member 25. A recovery duct 26 ") is formed. That is, the external additive recovery duct 26 is provided downstream of the grid electrode 23 in the rotation direction of the photosensitive drum 1.

  The wall surface of the shield case 22 covered with the casing member 25 is provided with a vent 221 for ventilating the charging area in the shield case 22 and the external additive recovery duct 26. That is, the external additive recovery duct 26 is connected to an exhaust passage for exhausting discharge products via the vent 221. The vent 221 may be opened continuously in the longitudinal direction of the shield case 22 or may be opened at two locations near the intake duct 27 and near the exhaust duct 28. . Due to the vent 221, an air flow that flows in the axial direction of the photosensitive drum 1 is generated in the external additive recovery duct 26 in the same manner as an exhaust flow path for exhausting discharge products.

  Further, as shown in FIG. 3, a seal member 24 is attached to the side surface of the casing member 25 along the axial direction of the casing member 25. The seal member 24 is held in a state where one side is fixed to the casing member 25 and the other side is in contact with the photosensitive drum 2. As a result, the gap between the casing member 25 and the photosensitive drum 1 is sealed, and the inflow of smoke toner from the developing unit 4 is suppressed. The sealing member 24 is formed, for example, of polyurethane in a sheet shape having a thickness of about 100 to 200 μm. It should be noted that the material is not limited to polyurethane, and any material having appropriate elasticity may be used. Further, the seal member 24 may be formed of a foam.

  Further, since the seal member 24 is held in contact with the photosensitive drum 2, external additives and toner (hereinafter referred to as “external additive etc.”) adhering to the photosensitive drum 1 are casing members. It is blocked inside 25. The external additive or the like blocked by the seal member 24 is taken into the external additive recovery duct 26 by free fall or air flow. That is, the fall on the grid electrode 23 is avoided. The external additive or the like taken into the external additive recovery duct 26 is conveyed toward the exhaust duct 28 in the longitudinal direction by the air flow, and is discharged out of the charging device 2 through the exhaust duct 28. Thereby, accumulation of the external additive on the grid electrode 23 is avoided, and charging unevenness due to charge-up of the external additive is suppressed.

  The intake duct 27 and the exhaust duct 28 are connected to a region outside the region facing the image forming region as shown in FIG. Thereby, it is possible to suppress the external additive from dropping due to the air flow formed in the charging device 2 during image formation.

  Next, the evaluation result of the charging device according to the embodiment will be described. In this evaluation, “magicolor2340DL” (hereinafter referred to as “evaluation machine”) manufactured by Konica Minolta Co., Ltd., which is a full-color 4-cycle copy machine, is used. ) And a conventional charging device (FIG. 7) were applied for evaluation. The results are shown in FIG. In FIG. 4, the recovery duct “Yes” is the charging device of this embodiment, and “No” is the charging device of the conventional form.

  In this evaluation, a test image with a printing rate of 15% was printed in an environment with an air temperature of 10 ° C., and the presence or absence of white bands was confirmed every 500 sheets. Then, it was judged as good (◯) when no white band occurred, and judged as poor (×) when a white band occurred.

  As a result of this evaluation, in the charging device of this embodiment, no white belt was generated even after printing 4500 sheets. On the other hand, in the charging device of the conventional form, a white belt was generated after printing 1500 sheets. From this evaluation result, it was found that the provision of an external additive recovery duct suppresses the generation of white belt images due to charge-up of external additives and the like, and the long-term image quality is improved.

  As described above in detail, in the charging device 100 of this embodiment, the casing that accommodates the corona discharge electrode 21 and covers the side surface on the downstream side surface of the shield case 22 that faces the photosensitive drum 1 with the grid electrode 23 interposed therebetween. The member 25 is provided. By this casing member 25, a space (external additive recovery duct 26) is formed at the downstream side of the grid electrode 23 where the portion facing the photosensitive drum 1 opens. Then, a sealing member 24 for preventing intrusion of fuming toner is fixed to the casing member 25. The external additive or the like accumulated inside the charging device 100 by the seal member 24 falls into the external additive recovery duct 26 and is stored. That is, it does not fall on the grid electrode 23. Therefore, in the charging device 100 of the present embodiment, the occurrence of image noise such as a white belt is suppressed while the intrusion of the fuming toner is suppressed. Therefore, a charging device capable of suppressing the inflow of fuming toner and the accumulation of the external additive on the grid electrode and obtaining a good image has been realized.

  In the charging device 100 of this embodiment, a vent hole to the external additive recovery duct 26 is provided on the side surface of the shield case 22. An air flow is generated in the external additive recovery duct 26 by the vent, and the external additive and the like accumulated in the external additive recovery duct 26 can be appropriately discharged. Further, since the means for generating the air flow is also used as the exhaust means (exhaust duct 28, etc.) for removing discharge products such as ozone, the apparatus can be downsized and the number of parts can be reduced. .

[Second form]
FIG. 5 shows an overall schematic configuration of the image forming apparatus 200 including the charging device 220 of the second embodiment. That is, in the image forming apparatus 200, the charging device 220, the developing device 4, the transfer device 5, and the cleaning member 6 are sequentially arranged around the photosensitive drum 1 along the rotation direction. The charging device 220 of this embodiment includes a corona discharge electrode 21, a shield case 22, a grid electrode 23, and a casing member 25.

  In addition to the outer seal member 241 that seals the gap between the casing member 25 and the photosensitive drum 1, the charging device 220 is an inner seal member that seals the gap between the shield case 22 on the developing device 4 side and the photosensitive drum 1. 242 is provided. Further, the outer seal member 241 attached to the casing member 25 is disposed so as to contact the photosensitive drum 1, but the inner seal member 242 attached to the shield case 22 is not contacted with the photosensitive drum 1. Arranged. Therefore, the toner and the external additive adhering to the photosensitive drum 1 pass on the inner seal member 242 and are blocked by the outer seal member 241.

  By disposing the inner sheet member 242 between the grid electrode 23 and the outer sheet member 241 in this way, the external additive blocked by the outer sheet member 241 is applied to the grid electrode 23 by airflow or vibration. Prevent falling. Thereby, generation | occurrence | production of image noise, such as a white belt, can be suppressed more reliably. Further, the external additive can be recovered more smoothly by the external additive recovery duct 26.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the image carrier is not limited to the photosensitive drum, and may be, for example, an intermediate transfer member (belt, drum, roller, or the like) or a paper carrier (belt or the like). Further, as the image forming apparatus using the charging device of the present embodiment, any device that uses a corona discharge charger such as a copying machine, a printer, a FAX, or a complex machine of these may be used.

  Further, although a roller-shaped photosensitive drum is used as the image carrier, a belt-shaped photosensitive belt may be used. The exposure apparatus may be a laser or LED. The transfer device may use a transfer charger in addition to the transfer roller. Alternatively, in addition to a method of directly transferring a toner image from a photosensitive member to a sheet, a method of providing an intermediate transfer member and performing transfer in two or more stages may be used. In addition to the cleaning blade, the cleaning device may be a cleaning brush or a cleaning roller.

  In the charging device of the embodiment, the casing member 25 outside the shield case 22 may be integrated with the shield case 22 or may be a separate body. That is, in the charging device of the present invention, a space for accommodating the external additive may be formed in the region on the downstream side of the shield case 22. Therefore, whether or not the casing member 25 for forming the external additive recovery duct 26 is integral with the shield case 22 does not matter.

  In addition to the inventions described in the claims, the embodiments of the present invention described above include inventions as shown in the following supplementary notes.

[Appendix 1] In a charging device for charging an image carrier by corona discharge,
A discharge electrode;
A grid electrode positioned between the discharge electrode and the image carrier;
A housing member containing the discharge electrode and having an opening facing the image carrier;
A seal member attached to a downstream side surface of the housing member in the rotation direction of the image carrier, and sealing a gap between the image carrier and the housing member;
The housing member has an internal space in the first region that accommodates the discharge electrode and faces the image carrier with the grid electrode interposed therebetween, and is located downstream of the first region in the rotation direction of the image carrier. A charging device having an inner wall partitioned into a second region located.

[Appendix 2] In the charging device described in Appendix 1,
The charging device according to claim 1, wherein the housing member is connectable to exhaust means for forming an air flow in the second region.

[Appendix 3] In the charging device described in Appendix 1,
The charging device according to claim 1, wherein a vent hole that ventilates between the first region and the second region is provided on an inner wall of the housing member.

[Appendix 4] In the charging device described in any one of Appendix 1 to Appendix 3,
A charging device, comprising: a second seal member attached to an inner wall of the housing member, wherein the second seal member seals a part of a gap between the image carrier and the inner wall and is not in contact with the image carrier.

It is a figure which shows schematic structure of the image forming apparatus containing the charging device concerning a 1st form. It is sectional drawing which looked at the charging device concerning a 1st form from the side. It is the schematic which looked at the charging device concerning a 1st form from the side. It is a figure which shows the test result of the charging device concerning a 1st form. It is a figure which shows schematic structure of the image forming apparatus containing the charging device concerning a 2nd form. It is FIG. (1) which shows schematic structure of the image forming apparatus containing the charging device concerning the conventional form. FIG. 6 is a diagram (part 2) illustrating a schematic configuration of an image forming apparatus including a charging device according to a conventional form.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging device (charging device)
21 Corona discharge electrode (discharge electrode)
22 Shield Case (Shield Case)
23 Grid electrode (grid electrode)
24 Seal member (seal part)
241 Outside seal member (seal part)
242 Inner seal member (second seal part)
25 Casing member (casing part)
26 External additive recovery duct (vacant)
27 Intake duct 28 Exhaust duct (exhaust means)
29 Fan (exhaust means)
DESCRIPTION OF SYMBOLS 3 Exposure apparatus 4 Developing apparatus 5 Transfer apparatus 6 Cleaning apparatus 100 Image forming apparatus

Claims (4)

In a charging device for charging an image carrier by corona discharge,
A discharge electrode;
A grid electrode positioned between the discharge electrode and the image carrier;
A shield case containing the discharge electrode, facing the image carrier across the grid electrode, and having an opening opposite the image carrier;
A casing portion that is located on the downstream side surface of the shield case in the rotational direction of the image carrier, and that forms a space between the downstream side surface of the shield case and the portion facing the image carrier;
A charging device comprising a seal portion attached to the casing portion and sealing a gap between the image carrier and the casing portion. The charging device according to claim 1,
The charging device according to claim 1, wherein the casing portion is connectable to an exhaust means for forming an air flow in the space. The charging device according to claim 1,
The charging device according to claim 1, wherein a vent hole communicating with a space formed by the casing portion is provided on a wall surface of the shield case. In the charging device according to any one of claims 1 to 3,
A second seal portion is provided on a side surface covered with the casing portion of the shield case, and is in non-contact with the image carrier and seals a part of a gap between the image carrier and the shield case. The charging device.

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