JP4091864B2 - Charging device, process cartridge, and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a charging device and a process cartridge installed therein, and more particularly, a non-contact type charging roller The present invention relates to a charging device, a process cartridge, and an image forming apparatus using the printer.
[0002]
[Prior art]
Conventionally, in an image forming apparatus using an electrophotographic method, ozone and nitride oxide (NOx) generated during a charging process are limited, and mechanical wear on the surface of a photosensitive drum (image carrier) is reduced. For this purpose, many charging devices using a non-contact type charging roller are used (for example, see Patent Document 1).
[0003]
That is, by providing a minute gap between the roller portion of the charging roller and the photosensitive drum and applying a predetermined charging voltage to the charging roller, a discharge phenomenon occurs in the minute gap. Thereby, compared with a corona charging device, generation | occurrence | production of discharge products, such as ozone, can be suppressed, and the photoreceptor drum surface can be charged.
Further, the non-contact type charging roller inevitably reduces mechanical wear of the photosensitive drum and the charging roller as compared with the contact type in which the charging roller is brought into contact with the photosensitive drum.
[0004]
On the other hand, a charging device using a charging roller regardless of whether it is a non-contact type or a contact type is not as bad as a corona charging device, but a problem caused by ozone or nitrided oxide generated during the charging process is a problem. It has become. That is, the discharge product adheres to the surface of the photoconductive drum and the surface deteriorates, and an image formed on the photoconductive drum is blurred or blurred (see, for example, Patent Document 2).
[0005]
In order to solve these problems, in Patent Document 2 and the like, a technique for reducing the generation of discharge products in the discharge region by covering the outer periphery of the contact-type charging roller with a cover and adjusting the oxygen concentration in the cover. Is disclosed.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-254224 (Page 2, Fig. 1-2)
[Patent Document 2]
Japanese Patent Laid-Open No. 11-305522 (page 2-4, FIG. 1-3)
[0007]
[Problems to be solved by the invention]
In the conventional image forming apparatus described above, it is difficult to suppress the generation of discharge products while accurately maintaining the gap of the non-contact type charging roller.
Specifically, the gap of the non-contact type charging roller is formed by winding a Teflon (registered trademark) tape around the roller portion of the charging roller and pressing the charging roller toward the photosensitive drum.
On the other hand, in the charging device of Patent Document 2, the cover that covers the outer periphery of the contact-type charging roller is brought into contact with the photosensitive drum through a contact portion made of an elastic material, thereby improving the airtightness in the cover. .
[0008]
Therefore, when the cover of Patent Document 2 is used for a non-contact type charging roller, there is a possibility that the charging roller gap may not be stabilized due to the reaction force of the abutting portion installed on the cover. That is, it has been difficult to ensure the airtightness in the cover while accurately maintaining the gap of the non-contact type charging roller.
As described above, in the non-contact type charging roller, if the gap with the photosensitive drum is not stable, charging on the surface of the photosensitive drum becomes unstable, and image quality such as uneven charging is deteriorated.
[0009]
The present invention has been made to solve the above-described problems, and reduces ozone and nitride oxide generated during the charging process and increases the gap with the image carrier in the non-contact type charging roller. An object of the present invention is to provide a charging device, a process cartridge, and an image forming apparatus with high image quality that can be set with high accuracy.
[0010]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a charging device including a charging roller having a large-diameter portion at both ends for opposing the image carrier via a gap, and a case surrounding the charging roller. The case includes a case main body that covers an outer peripheral surface excluding a portion of the charging roller facing the image carrier, a bearing member that is provided at each end of the case main body and supports the charging roller, and the case main body and the image. A sealing member made of a flexible member provided in the case body for preventing air from flowing into the case from the gap of the carrier, and the bearing member is provided in the image forming apparatus body. A guide portion that engages with the projected portion, and is supported so as to be movable in a direction close to the image carrier, and has a seal member on a surface facing the non-image area of the image carrier, and The large diameter part of the charging roller Characterized in that it is biased by the pressure member in a direction for pressing the Kizo carrier.
[0011]
According to a second aspect of the present invention, there is provided the charging device according to the first aspect, wherein the flexible member has a sheet-like shape that abuts against the surface of the image carrier that is attached to the case at one end and circulates at the other end. It is a member.
[0012]
According to a third aspect of the present invention, in the charging device according to the second aspect, the sheet-like member is made of a urethane rubber material .
[0014]
A fourth aspect of the present invention is a process cartridge including the charging device according to any one of the first to third aspects .
[0015]
A fifth aspect of the present invention is an image forming apparatus including the charging device according to any one of the first to third aspects .
[0020]
In the present specification, the “process cartridge” means a developing device that develops an electrostatic latent image formed on an image carrier and a cleaning device that collects untransferred toner on the image carrier. At least one device, an image carrier, and a charging device that charges the image carrier are integrally formed into a cartridge and defined as an assembly that is detachably formed in the image forming apparatus main body.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.
[0022]
Embodiment 1 FIG.
The first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG. FIG. 1 is a configuration diagram illustrating an image forming apparatus according to the first embodiment.
In FIG. 1, 20 is a photosensitive drum as an image carrier, 22 is a charging roller for charging the surface of the photosensitive drum 20, and 22A is installed at both ends of the charging roller 22 to provide a gap with the photosensitive drum 20. 24 is a developing device for developing the electrostatic latent image formed on the photosensitive drum 20, 28 is a case main body surrounding the charging roller 22, and 39 is for collecting untransferred toner on the surface of the photosensitive drum 20. The cleaning device 45 is a registration roller that conveys the transfer material to the transfer device 48, and 48 is a transfer device that transfers the toner image formed on the photosensitive drum 20 onto the transfer material.
[0023]
Reference numeral 50 denotes an image forming apparatus main body, 51 denotes a document reading unit that places a document and reads image information of the document, and 52 irradiates the photosensitive drum 20 with laser light L based on the image information of the document reading unit 51. An optical unit, 54 is a paper feeding unit for storing a material to be transferred such as transfer paper, 55 is a paper feeding roller for feeding the material to be transferred from the paper feeding unit 54, and 57 is a toner image on the material to be transferred after the transfer process. A fixing unit 58 for fixing the image to the transfer material, and a paper discharge unit 58 for discharging the transfer material after the fixing process to the outside of the apparatus.
[0024]
The image forming apparatus configured as described above operates as follows.
First, the surface of the photosensitive drum 20 that rotates in the clockwise direction on the paper surface is charged at a portion facing the charging roller 22. Then, the surface of the photosensitive drum 20 charged by the charging roller 22 further rotates and reaches the irradiation part of the laser beam L. Then, an electrostatic latent image corresponding to image information such as a document is formed here.
[0025]
Thereafter, the surface of the photosensitive drum 20 on which the latent image is formed reaches a portion facing the developing device 24. A predetermined voltage is applied to the developing roller facing the photosensitive drum 20. Then, the toner in the developer carried on the developing roller moves and adheres to the latent image due to the potential difference between the developing roller and the latent image on the surface of the photosensitive drum 20.
Thereafter, the surface of the photosensitive drum 20 developed by the developing device 24 reaches a portion facing the transfer device 48. Then, the toner image on the photosensitive drum 20 is transferred onto the transfer material conveyed by the registration roller 45 here. At this time, a small amount of untransferred toner that is not transferred onto the transfer material remains on the photosensitive drum 20.
[0026]
Thereafter, the surface of the photosensitive drum 20 that has passed through the transfer device 48 reaches a portion facing the cleaning device 39. In the cleaning device 39, untransferred toner is collected in the cleaning device 39 by a cleaning blade that contacts the photosensitive drum 20.
Thereafter, the surface of the photosensitive drum 20 that has passed through the cleaning device 39 reaches a static elimination unit (not shown). Then, the electric potential on the surface of the photosensitive drum 20 is eliminated, and a series of image forming processes is completed.
[0027]
On the other hand, the transfer material operates as follows. First, the transfer material is fed from the paper feed unit 54 toward the transport path by the paper feed roller 55. Then, the material to be transferred that has reached the registration roller 45 is conveyed to the transfer device 48 in synchronization with the toner image created on the photosensitive drum 20, and the toner image is transferred thereto.
Then, the transfer material after the transfer process reaches the fixing portion 57 where the toner image is fixed. Finally, the material to be transferred after the fixing process passes through the paper discharge unit 58 and is discharged out of the image forming apparatus 50. Thus, a series of image forming processes is completed.
[0028]
Next, a charging device installed in the image forming apparatus will be described in detail with reference to FIGS.
FIG. 2 is a perspective view showing the charging device, and FIG. 3 is a partially enlarged sectional view showing a main part thereof. In FIG. 3, for easy understanding, the gap G between the roller portion 22a and the photosensitive drum 20 is shown larger than the actual dimensional ratio.
As shown in FIGS. 2 and 3, the charging device mainly includes a charging roller 22, sealing members 24 and 28 to 31, and a compression spring 25 (pressure member).
[0029]
Here, the charging roller 22 includes a roller portion 22a formed of a conductive material in which conductive powder is dispersed in a resin, a shaft portion 22b formed of stainless steel, and a large-diameter portion (not shown). 1 of 22A).
The large-diameter portion of the charging roller 22 is formed by winding Teflon (registered trademark) tape or the like around the surface of both ends of the roller portion 22a. That is, the large diameter portions at both ends have an outer diameter larger than the outer diameter of the roller portion 22a, and a minute gap G is formed between the roller portion 22a and the photosensitive drum 20 due to the difference in outer diameter. .
Note that the configuration of the large-diameter portion 22A is not limited to this, and for example, a configuration in which donut-shaped rollers are attached to both ends of the roller portion 22a can be employed.
[0030]
Further, the charging device sealing members 24 and 28 to 31 seal the periphery of the roller portion 22a so that air does not flow into the gap G between the charging roller 22 and the photosensitive drum 20 from the outside of the charging device. It is. Thereby, the production | generation of the discharge product in the gap G can be blunted.
The sealing member includes cases 24 and 28 that surround the roller portion 22a, and a flexible member 30 and a seal member 31 attached to the case. Further, the case includes a case main body 28 that is a main part of the case, and bearings 24 that are installed at both ends of the case main body 28. All of these members are formed of an electrically insulating material.
[0031]
With reference to FIG. 2, the case main body 28 extends in the axial direction (longitudinal direction) of the charging roller 22. And the roller part 22a and the large diameter part are accommodated in the case main body 28. FIG.
[0032]
With reference to FIG. 3, flexible members 30 are attached to the case main body 28 on the upstream side and the downstream side in the circumferential direction S of the photosensitive drum 20.
Specifically, the flexible member 30 is a thin sheet-like member made of a urethane rubber material. One end side of the flexible member 30 is attached to the case main body 28, and the other end side is an image area of the photosensitive drum 20 (a longitudinal area in which the above-described latent image and toner image are formed). Is in contact with the region (referring to a contact state following the rotation of the photosensitive drum 20).
[0033]
Here, since the flexible member 30 is soft, even if the flexible member 30 is in contact with the photosensitive drum 20, its reaction force is slight. That is, since the reaction force by the flexible member 30 is formed to be extremely smaller than the pressure applied by the compression spring 25, the gap G of the roller portion 22a determined by the large diameter portion is unstable due to the reaction force. Never become.
Furthermore, since the flexible member 30 is formed of a material having excellent adhesion to the surface of the photosensitive drum 20, airtightness in the case main body 28 is ensured.
[0034]
Further, the bearings 24 constituting the case are installed at both ends of the case main body 28.
Specifically, as shown in FIG. 4, the bearing 24 includes a recess 24a, an engagement portion 24b, a through hole 24c, and a guide portion 24d. One end of the compression spring 25 is inserted into the recess 24 a of the bearing 24. The engaging portion 24b of the bearing 24 is provided with an upright portion 24b1. Then, the engaging portion 24b having the standing portion 24b1 is engaged with the opening portion 28a of the case main body 28 having the groove portion 28a1 (the movement in the direction of the arrow in FIG. 4, and the standing portion 24b1 and the groove portion 28a1 are moved. And the case main body 28 and the bearing 24 are integrated.
[0035]
A shaft seal 29 such as a G seal is press-fitted into the through hole 24 c of the bearing 24. The shaft portion 22b of the charging roller 22 is inserted into the through holes 24c of the bearings 24 at both ends, and the charging roller 22 is rotatably supported by the bearing 24. At this time, the shaft seal 29 ensures airtightness in the case.
Further, the guide portion 24 d of the bearing 24 extends in the same direction as the pressurizing direction by the compression spring 25. Although not shown, the guide portion 24 d engages with the protrusion provided on the image forming apparatus main body 50, so that the cases 24 and 28 can slide toward the photosensitive drum 20.
[0036]
In addition, a seal member 31 is attached to the bottom of the bearing 24 and abuts against a non-image area on the surface of the photosensitive drum 20. The seal member 31 has, for example, a two-layer structure of foamed polyurethane and Teflon (registered trademark) tape (the layer on the photosensitive drum 20 side is Teflon tape). Further, the seal member 24 and the flexible member 30 are overlapped with each other in a state where the bearing 24 is engaged with the case main body 28, and a gap is not formed between the two members. Thereby, the airtightness in the cases 24 and 28 is ensured.
[0037]
In addition, referring to FIG. 2, compression springs 25 are respectively installed on bearings 24 at both ends. As a result, the charging roller 22 and the sealing members 24, 28 to 31 are integrally pressed toward the photosensitive drum 20, and the position of the charging roller 22 with respect to the photosensitive drum 20 is determined.
Although not shown, the other end of the compression spring 25 is in contact with and supported by the main body top plate of the image forming apparatus.
[0038]
With reference to FIG. 2, one shaft portion 22 b of the charging roller 22 is electrically connected to a power source 40. Then, a predetermined charging voltage is applied from the power supply unit 40 to the charging roller 22. As a result, a discharge is generated in the gap G between the roller portion 22a and the photosensitive drum 20, and the surface of the photosensitive drum 20 is uniformly charged by the discharge.
Further, the charging roller 22 is rotationally driven in the direction of arrow R in FIG. 3 by a driving unit (not shown) connected to one shaft portion 22b.
[0039]
The charging device including the charging roller 22 of FIG. 2 is configured to be detachable from the image forming apparatus main body 50.
In contrast, the photosensitive drum 20, the charging device, the developing device 24, and the cleaning device 39 may be integrated into a process cartridge. In this case, the process cartridge including the charging roller 22 of FIG. 2 is configured to be detachable from the image forming apparatus main body 50.
[0040]
As described above, in the first embodiment, the flexible member 30 is efficiently used, so that the sealing members 24 and 28 to 31 are held by the compression spring 25 while the gap G is maintained. The pressure is increased toward 20, and the inflow of air to the vicinity of the gap G is suppressed. As a result, ozone and nitride oxide generated during the charging process are reduced, and the gap G between the charging roller 22 and the photosensitive drum 20 is set with high accuracy, and high quality free from uneven charging, blurring, and blurring. Images can be provided.
Further, since the amount of oxygen in the vicinity of the gap G is reduced, film scraping on the surface of the photosensitive drum 20 due to discharge is reduced, and the life of the photosensitive drum 20 is improved.
[0041]
In the first embodiment, the gap G between the roller portion 22a and the photosensitive drum 20 is formed by providing the large diameter portion 22A at both ends of the charging roller 22.
On the other hand, the roller portion 22a is not provided with the large-diameter portion 22A, and the sealing members 24 and 28 to 31 are provided with contact portions that contact the non-image area of the photosensitive drum 20, and the contact portions The gap G between the roller portion 22a and the photosensitive drum 20 may be determined. For example, instead of the seal member 31, a contact portion made of a Teflon (registered trademark) material having low friction and a certain degree of rigidity can be installed on the bottom of the bearing 24.
[0042]
Embodiment 2. FIG.
The second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 5 is a cross-sectional view illustrating the charging device according to the second embodiment, and corresponds to FIG. 3 of the first embodiment. In the charging device of the second embodiment, the point that the upper part of the charging roller 22 is exposed and the point that the charging roller 22 and the sealing member are pressurized independently are described in the first embodiment. Is different.
[0043]
As shown in FIG. 5, unlike the first embodiment, the case main body 28 according to the second embodiment is formed so as to surround only a part of the roller portion 22a. That is, the vicinity of the gap G where air is not desired to flow in is centrally sealed, and the other regions are open.
[0044]
A flexible member 35 that is in contact with the roller portion 22 a exposed from the case body 28 is attached to the case body 28.
Specifically, the flexible member 35 is a thin sheet-like member made of a urethane rubber material. And one end side of the flexible member 35 is stuck to the case main body 28, and the other end side hits the roller part 22a. Thereby, the airtightness in the case main body 28 is ensured.
[0045]
In the second embodiment, unlike the first embodiment, the charging roller 22 and the sealing members 28, 30, and 35 are each independently pressurized toward the photosensitive drum 20.
Specifically, a compression spring 27 as a second pressure member is installed on a bearing (not shown) that supports the shaft portion 22b of the charging roller 22. As a result, a gap G corresponding to a difference in outer diameter between a large diameter portion (not shown) and the roller portion 22a is formed.
[0046]
The case body 28 is provided with a compression spring 26 as a pressure member. The pressure applied to the compression spring 26 is sufficiently small. As a result, the flexible member 30 comes into contact with the photosensitive drum 20 with an appropriate pressure, and the airtightness in the case main body 28 is ensured.
The bearing that supports the charging roller 22 is configured to be able to move independently in the pressurizing direction while ensuring sealing performance with respect to the case main body 28.
[0047]
As described above, in the second embodiment, the pressure of the sealing members 28, 30, and 35 is made independent of the pressure of the charging roller 22, so that the gap G is maintained in the state where the gap G is maintained. Air inflow is suppressed. As a result, ozone and nitride oxide generated during the charging process are reduced, and the gap G between the charging roller 22 and the photosensitive drum 20 is set with high accuracy, and high quality free from uneven charging, blurring, and blurring. Images can be provided.
Further, since the amount of oxygen in the vicinity of the gap G is reduced, film scraping on the surface of the photosensitive drum 20 due to discharge is reduced, and the life of the photosensitive drum 20 is improved.
[0048]
It should be noted that the present invention is not limited to each of the above-described embodiments, and it is obvious that each embodiment can be modified as appropriate within the scope of the technical idea of the present invention, other than suggested in each embodiment. It is. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.
[0049]
【The invention's effect】
Since the present invention is configured as described above, ozone and nitride oxide generated during the charging process can be reduced, and the gap between the non-contact charging roller and the image carrier can be set with high accuracy. An image quality charging device, a process cartridge, and an image forming apparatus can be provided. Furthermore, it is possible to provide a charging device, a process cartridge, and an image forming apparatus capable of extending the life of the image carrier.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention.
2 is a perspective view showing a charging device installed in the image forming apparatus of FIG. 1. FIG.
3 is an enlarged cross-sectional view showing a main part of the charging device of FIG. 2;
4 is an exploded view showing a sealing member in the charging device of FIG. 2;
FIG. 5 is a sectional view showing a charging device according to Embodiment 2 of the present invention.
[Explanation of symbols]
20 photosensitive drum (image carrier), 22 charging roller, 22a roller section,
22b Shaft part, 22A Large diameter part, 24 Bearing, 24a Concave part,
24b engaging part, 24b1 standing part, 24c through hole, 24d guide part,
25, 26 Compression spring (pressure member),
27 compression spring (second pressure member), 28 case body,
28a opening, 28a1 groove, 29 shaft seal,
30, 35 Flexible member, 31 Seal member, 40 Power supply part.

Claims (5)

In a charging device comprising a charging roller having a large diameter portion at both ends for opposing the image carrier via a gap, and a case surrounding the charging roller,
The case includes a case main body that covers an outer peripheral surface excluding a portion of the charging roller facing the image carrier, a bearing member that is provided at each end of the case main body and supports the charging roller, and the case main body. A sealing member made of a flexible member provided in the case main body, which prevents inflow of air into the case from the gap of the image carrier,
The bearing member is supported by a guide portion that engages with a protrusion provided in the image forming apparatus main body so as to be movable in a direction close to the image carrier, and faces the non-image area of the image carrier. Has a sealing member and is urged by a pressure member in a direction in which the large diameter portion of the charging roller is pressed against the image carrier.   2. The charging device according to claim 1, wherein the flexible member is a sheet-like member that abuts against a surface of the image carrier that is attached to the case at one end side and circulates at the other end side.   The charging device according to claim 2, wherein the sheet-like member is made of a urethane rubber material. A process cartridge comprising the charging device according to claim 1 . An image forming apparatus comprising the charging device according to claim 1 .

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