JP2010096825A - Charging device, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scorotron charging device which maintains stable electrostatic charge performance, even with a lapse of time, and has a long lifetime and superior charging uniformity. <P>SOLUTION: A contact part 241C of a feed screw 241 with an electrode plate 245 is located on an outer circumference of the feed screw; the contact part 241C is smaller than the electrode plate 245 in width; then level difference parts 241D are formed on both sides of the contact part 241C. When a cleaning device not illustrated moves back and forth, the contact part 241C moves in a direction B by an amount equivalent to thrust backlash by thrust force generated in the feed screw 241; and toner and discharge product accumulated in the contact part 241C drop to the level difference parts 241D. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a scorotron charging device used in an image forming apparatus such as a copying machine, a printer, and a facsimile machine, a process cartridge including the charging device, and an image forming apparatus.

JP 2002-268339 A JP 2007-233281 A Japanese Patent No. 3549731 Japanese Patent Laid-Open No. 08-190255

  In image forming apparatuses such as electrophotographic copying machines, printers, facsimiles, etc., as a means for uniformly charging the surface of the photoconductor, a charge wire and a charge wire that are arranged in the shield case at a predetermined interval on the surface of the photoconductor In addition, a scorotron charging device including a grid electrode disposed closer to the photosensitive member is known. By applying a high voltage to the charge wire, corona discharge can be generated, and the surface of the photoreceptor can be charged with substantially the same potential as the grid electrode. In order to maintain stable charging performance over time, a cleaning member is often provided for cleaning an electrode movable in the stretching direction of the charge wire. In many cases, the cleaning member is moved using a feed screw or a screw. The feed screw has the same potential as that of the ground or the casing or the grid electrode, and the material of the feed screw is generally metallic.

  As described above, the scorotron charging device is contaminated with toner, discharge products, paper dust and the like over time. Due to this contamination, the uniformity of charging cannot be ensured, and the photoreceptor potential is partially lowered at the contaminated portion, resulting in unevenness in the output image. For this reason, many scorotron charging devices are provided with a cleaning mechanism for cleaning charge wires and grid electrodes. Generally, the charging device is a maintenance part, and is replaced after a certain number of outputs. However, it is very economical and environmentally important to extend the life of the charging device by removing contamination by this cleaning device. .

  Cleaning is performed while the slider holding the cleaning member meshes with the feed screw, and the feed screw rotates and moves in the stretch direction of the charge wire. At this time, the electrode plate for short-circuiting with the casing in contact with the feed screw is configured to rub against the feed screw during the cleaning operation. In particular, over time, after discharge products and toner enter the gap between the feed screw and the electrode plate and are rubbed by the cleaning operation, the conduction between the feed screw and the electrode plate tends to be unstable or insulated. If the continuity is unstable or insulated, it affects the formation of the electric field around the charge wire, so the ion flow to the photoconductor becomes unstable or weakens, making it impossible to charge the photoconductor uniformly. There is a problem that the image becomes uneven.

  In order to reduce the size and cost of the apparatus, a small DC brush motor is often used for driving the feed screw. Increasing the contact force stabilizes continuity, but the drive torque of the feed screw increases, cleaning operation time increases, malfunction of the cleaning device occurs, and abnormal noise is generated. It is difficult. In addition, when the lead screw is metallic, discharge products and toner enter the meshing portion of the lead screw and the slider with time, the friction resistance between the slider and the lead screw is increased, and the drive torque of the lead screw is increased. The cleaning operation time may increase or the cleaning device may malfunction. Although there is a possibility that the problem can be solved by using a stepping motor or a DC brushless motor as the drive motor, there is a problem that the size of the apparatus is increased and the cost is increased.

  An object of the present invention is to solve the above-mentioned problems in the conventional scorotron charging device, to provide a scorotron charging device that maintains stable charging performance over time, has a long life, and is excellent in charging uniformity. It is another object of the present invention to provide a process cartridge and an image forming apparatus that include the scorotron charging device and that do not cause image unevenness over time and have a long life.

  According to the present invention, the above-described problem is achieved by using a shield case having a discharge opening, a discharge electrode disposed in the shield case, a grid electrode stretched in the discharge opening, and a feed screw. A scorotron comprising: a cleaning member provided so as to be movable in the longitudinal direction of the discharge electrode, and cleaning the discharge electrode by rubbing the discharge electrode; and an electrode plate for short-circuiting the shield case and the feed screw In the charging device, a contact portion of the feed screw with the electrode plate is on an outer periphery of the feed screw, the contact portion is smaller than a width of the electrode plate, and a step is formed on both sides of the contact portion. Is solved.

The contact portion of the feed screw is preferably provided so as to be inclined with respect to the axial direction of the feed screw.
The feed screw is preferably made of a conductive resin.

The base resin of the conductive resin is preferably a polyacetal.
In addition, according to the present invention, there is provided a process cartridge including at least an image carrier and a charging unit for charging the surface of the carrier, and configured to be detachable from the image forming apparatus main body. This can be solved by a process cartridge equipped with the scorotron charging device according to any one of claims 1 to 4.

  Further, according to the present invention, there is provided an image forming apparatus comprising the scorotron charging device according to any one of claims 1 to 4 as a charging unit that includes an image carrier and charges a surface of the image carrier. Solved by the device.

  Further, according to the present invention, the above problem is solved by an image forming apparatus comprising the process cartridge according to claim 5.

  According to the scorotron charging device of the present invention, the contact portion of the feed screw with the electrode plate is on the outer periphery of the feed screw, the contact portion is smaller than the width of the electrode plate, and steps are formed on both sides of the contact portion. As a result, there is a gap between the electrode plate, toner and discharge products can be prevented from accumulating at the contact point, and stable charging performance can be maintained over time, and charging can be performed with a long service life. It is possible to provide a scorotron charging device excellent in the above.

  According to the configuration of the second aspect, since the contact portion of the feed screw with the electrode plate is inclined with respect to the axial direction of the feed screw, the position of contact with the electrode plate changes when the feed screw rotates. In addition, it is possible to provide a scorotron charging device that does not collect toner and discharge products at the contact point, maintains stable charging performance over time, has a long life, and is excellent in charging uniformity.

  According to the structure of the third aspect, since the material of the feed screw is conductive resin, the slidability with the holding member (slider) of the feed screw is improved, the drive torque of the feed screw is increased, the cleaning operation time is increased, or the cleaning is performed. It is possible to prevent malfunction of the apparatus.

  According to the fourth aspect of the present invention, since the base resin of the conductive resin is polyacetal, it is possible to improve the slidability with the holding member (slider) of the feed screw and to prevent the electrode plate from being worn. Therefore, it is possible to provide a scorotron charging device that maintains stable charging performance over time, has a long life, and is excellent in charging uniformity.

  According to the process cartridge of claim 5, the image forming apparatus of claim 6, and the image forming apparatus of claim 7, by mounting the scorotron charging device having a long life and excellent charging uniformity, image unevenness can be caused even with time. A process cartridge and an image forming apparatus that do not occur and have a long life can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing the entire configuration of a full-color copying machine which is an example of an image forming apparatus including a scorotron charging device according to the present invention. A full-color copying machine 100 shown in FIG. 1 includes an image forming unit 300, a paper feeding unit 200, a document reading unit 400, and a document conveying unit 500. The image forming unit 300 includes an image forming unit 10, an exposure device 3, a transfer device 5, and a fixing device 7.

  The image forming unit 10 includes four process cartridges 10 (Y, M, C, and K) that form yellow (Y), cyan (C), magenta (M), and black (K) toner images in parallel. . At the center of each process cartridge 10 (Y, M, C, K), there are provided photoreceptors 1Y, 1C, 1M, 1K, respectively, around which charging device 2, developing device 4, cleaning device 6 (FIG. 2). For example).

  The exposure device 3 converts data read by the document reading unit 400 or an image signal sent from the outside such as a PC (not shown), scans the laser beam with a polygon motor, and sensitizes based on the image signal read through the mirror. An electrostatic latent image is formed on the body 1.

  The transfer device 5 is configured to include an endless belt-shaped intermediate transfer belt 50 that sequentially superimposes and holds toner images formed on the respective photoreceptors 1, and color toner formed on the intermediate transfer belt 50. An image is transferred onto a recording sheet. In the intermediate transfer belt 50, a base layer is made of a material that is difficult to stretch, such as a fluororesin or a canvas, and an elastic layer is provided thereon. The elastic layer is made of, for example, fluororubber or acrylonitrile-butadiene copolymer rubber. The surface of the elastic layer is, for example, coated with a fluorine-based resin and covered with a smooth coat layer. Then, it is wound around the support roller and can be rotated and conveyed clockwise. Further, an intermediate transfer belt cleaning device 53 for removing residual toner remaining on the intermediate transfer belt 50 after image transfer is provided.

In addition, the recording paper may be conveyed by a transfer conveyance belt, and the toner image formed on each photoconductor 1 may be directly transferred to the recording paper.
A primary transfer unit 51 is provided at a position facing the photoreceptor 1 with the intermediate transfer belt 50 interposed therebetween. The primary transfer unit 51 is connected to a power source (not shown), and a voltage is applied when the toner image on the photoreceptor 1 is transferred to the intermediate transfer belt 50, so that an electric field is formed between the photoreceptor 1 and the intermediate transfer belt 50. The toner image is electrostatically transferred. On the other hand, a secondary transfer device 52 is provided with the intermediate transfer belt 50 interposed therebetween. The secondary transfer device 52 is configured as a transfer roller in the illustrated example, and transfers the image on the intermediate transfer belt 50 to a sheet.

  A registration roller pair 54 is disposed on the upstream side of the secondary transfer device 52, and a conveyance belt 55 that conveys the sheet to the fixing device 7 is disposed on the downstream side of the secondary transfer device 52. The fixing device 7 is composed of a heating roller having a halogen heater or the like inside, a fixing belt stretched around the fixing roller, and a pressure roller. Heat and pressure are applied to fix the toner image. In addition, a pair of rollers or a pair of belts may be used.

  In addition, the image forming apparatus 100 includes a double-side reversing unit 9, a paper discharge tray 8, and the like. Further, the paper feed unit 200 disposed at the lowermost part of the apparatus main body is provided with four paper feed stages, and a paper feed tray 201 and a paper feed device 202 are provided for each paper feed stage.

FIG. 2 is an enlarged view of the process cartridge 10 of FIG.
The photoconductor 1 can be made of amorphous metal having photoconductivity, amorphous metal such as amorphous selenium, or organic compound such as bisazo pigment or phthalocyanine pigment. In consideration of environmental problems and post-treatment after use, a photoreceptor using an organic compound is preferable.

  The charging device 2 is a scorotron charging device and includes a charge wire 21, a shield case 22, a grid electrode 23, and a power source (not shown) connected to the charge wire 21 and the grid electrode 23. A high voltage is applied to each of the charge wire 21 and the grid electrode 23 to generate a corona discharge between the photoconductor 1 and the charge wire 21 to uniformly charge the surface of the photoconductor 1. The grid electrode 23 is arranged in a shape along the curvature of the photoreceptor 1 in order to improve the potential controllability. In addition, a charge cleaning device 24 is disposed in order to maintain stable charging performance over time.

  An exhaust duct 11 is provided so as to cover the charging device 2 and the charging cleaning device 24. The exhaust duct 11 communicates with an exhaust duct on the back of the image forming apparatus 100 and is discharged out of the apparatus through an ozone treatment filter.

  The developing device 4 includes a developer carrier 41 that carries a developer and supplies the developer 1 to the photosensitive member 1, a toner supply screw 42, and the like. The developer carrier 41 includes a hollow cylindrical developer carrier 41 that is rotatably supported, and a magnet roll that is fixed inside the developer carrier 41 coaxially therewith. The developer is magnetically attracted to the outer peripheral surface of the carrier 41 and conveyed. The developer carrier 41 is made of a non-magnetic member that is electrically conductive, and is connected to a power source (not shown) for applying a developing bias. A voltage is applied from the power source between the developer carrying member 41 and the photosensitive member 1, and an electric field is formed in the developing region.

  The cleaning device 6 includes a cleaning blade 61, a cleaning brush roller 62, and a waste toner discharge screw 63, and removes transfer residual toner remaining on the photosensitive member 1 after the primary transfer to prepare for image formation again.

The charging device 2, the developing device 4, the cleaning device 6, and the photosensitive member 1 are an integrated process cartridge, and can be integrally replaced from the image forming apparatus 100.
FIG. 3 shows an enlarged view of a portion of the charging device 2 provided with the charging cleaning device 24. FIG. 4 is a perspective view thereof. FIG. 5 is a perspective view showing the state of FIG. 4 viewed from below. The scorotron charging device 2 will be described with reference to these drawings.

  An end block 25 made of an insulating resin is fixed before and after the shield case 22, the charge wire 21 and the grid electrode 23 are fixed to the end block 25, and the grid electrode 23 is stretched in a curved shape. In this embodiment, the grid electrode 23 is disposed at a distance of 2 mm from the photoreceptor 1.

  The electrostatic cleaning device 24 includes a feed screw 241, a slider 242, a grid cleaner pad 243 A, a wire cleaner pad 243 B, and a drive gear 244. The grid cleaner pad 243A and the wire cleaner pad 242B come into contact with the grid electrode 23 and the charge wire 21 for cleaning. The material of the grid cleaner pad 243A is made of foamed PUR. The base material of the charge wire cleaner pad 243B is foamed PUR, and the surface layer is an abrasive-containing layer in order to improve cleanability. The electrode plates 245 have the same potential by short-circuiting the shield case 22 and the feed screw 241. The material of the feed screw 241 is a conductive resin using polyacetal as a base resin. The electrode plate 245 is made of a copper leaf spring material.

Next, the step portion of the feed screw 241 will be described with reference to FIGS.
The feed screw 241 has a screw portion 241A in the range in which the slider moves, and a shaft portion 241B in the other range, and step portions 241D are provided at both ends of the electrode plate contact portion 241C. At this time, the outer diameter Ds5 of the stepped portion is smaller than the outer diameter Ds4 of the electrode plate contact portion and the outer diameter Ds1 of the shaft portion, and the electrode plate 245 contacts the electrode plate contact portion 241C with force F. Is done. When the cleaning device reciprocates, the electrode plate contact portion 241C (outer diameter Ds4) moves in the B direction (front and back) by the thrust backlash by the thrust force generated in the feed screw 241. The width Hs2 of the stepped portion is larger than the electrode plate abutting width Hs1, and the toner and discharge products accumulated in the electrode plate abutting portion 241C with the passage of time are caused by the thrust movement in the B direction by the reciprocating operation of the cleaning device. It is the structure which falls to level | step-difference part 241D. Further, since the width Hs1 of the electrode plate contact portion 241C is smaller than the width He of the electrode plate 245, the contact pressure is sufficiently ensured, and the feed screw 241 and the shield case 21 are reliably connected (short circuit). Has been. Since the feed screw 241 is made of a conductive resin based on polyacetal that is resistant to frictional loads, the electrode plate contact portion 241C will not be worn even if the cleaning operation is repeated. Further, even if toner or a discharge product adheres between the slider 242 and the feed screw 241, because of the resin, the frictional property is high and the driving torque does not increase.

FIG. 8 is a view showing another example of the feed screw 241.
As shown in this figure, the step portion 241D may be provided by making the outer diameter Ds4 of the electrode plate contact portion 241C larger than the outer diameter Ds1 of the shaft. In this case, the outer diameter Ds1 of the shaft and the outer diameter Ds5 of the stepped portion may be the same. In this case, the same effect as in FIG. 7 can be obtained.

FIG. 9 is a view showing still another example of the feed screw 241.
As shown in this figure, the electrode plate contact portion 241C may be provided to be inclined with respect to the axial direction by an acute angle θ. It is desirable that θ is larger than tan ^ -1 (Ds4 / He). In this case, when the feed screw rotates during cleaning, the contact of the electrode plate changes, so that the toner and discharge products accumulated in the electrode plate contact portion 241C are more likely to fall to the step portion 241D. Equivalent effect or better.

Further, as shown in FIG. 10, the tip of the electrode plate contact portion may have an arc cross section or a curved shape.
Even if these are arbitrarily combined, the same effect can be obtained.

Table 1 below shows the results of evaluation experiments over time (after passing 100,000 sheets) using the charging device of the present invention.

  In this experiment, the material of the feed screw of the electrification cleaning device 24 is a conductive resin based on stainless steel SUS303 or polyacetal, and at the initial stage with and without the step, after lapse of time (after passing 100,000 sheets of A4 horizontal conversion) The conductive state between the electrode plate and the feed screw, the driving torque of the cleaning device, and the image unevenness level (1 × 1 dot) were evaluated. Note that the image unevenness level is less than 4 as X (NG: unacceptable unevenness level). The cleaning device was operated at a timing of once every 5,000 sheets. The small drive torque is almost equal to the rated torque of the drive motor, and the large drive torque is almost equal to the maximum torque of the drive motor.

The dimensions and settings of the apparatus during the experiment were as follows.
[Feed screw]
Shaft portion outer diameter Ds1: Φ3.5 [mm], screw portion length Ls: 350 [mm], screw pitch P: 3 [mm], screw portion outer diameter Ds2: Φ5 [mm], screw portion Valley diameter Ds3: Φ3.8 [mm], electrode plate contact portion width Hs1: 1 [mm], electrode plate contact portion outer diameter Ds4: Φ3.5 [mm], electrode plate contact portion angle θ = 45 ° , Rotation speed n: 200 [rpm]
[Step part]
Step part outer diameter Ds5: Φ2.5 [mm], Step part width Hs2: 3 [mm]
[Electrode plate]
Electrode plate width He: 4 [mm], thickness t: 0.2 [mm], electrode plate biting amount d: 2 [mm], electrode plate contact force F: 0. 5 [N]

  In Experiment 1, since the conduction between the feed screw 241 and the casing (shield case 22) is reliable in the initial stage, the image unevenness level is 5 and there is no problem. However, as time passes, foreign matter such as toner enters the contact portion of the electrode plate 245 and the conduction becomes unstable, so that the electric field around the charge wire is affected, charging unevenness occurs on the photoreceptor, and the image unevenness level is 2. And NG. In addition, the driving torque of the cleaning device increases with time. This is because the sliding resistance with the slider 242 is increased by foreign matters such as toner in the thread portion of the feed screw 241. Since a DC brush motor is used to drive the cleaning device in order to reduce the size of the device, an increase in driving torque results in a decrease in the number of rotations of the motor and a cleaning operation time increases. Since the printing operation cannot be performed during the cleaning operation, an increase in the cleaning operation time leads to an increase in the waiting time of the user.

  In Experiment 2, since the conduction between the feed screw 241 and the casing is reliable both initially and over time, the image unevenness level is 5 and there is no problem. However, the driving torque of the cleaning device increases with time. This leads to an increase in the waiting time of the user as in Experiment 1.

  In Experiment 3, since the conduction between the feed screw 241 and the casing is reliable in the initial stage, the image unevenness level is 5 and there is no problem. However, over time, as in Experiment 1, foreign matter such as toner enters the contact portion of the electrode plate 245 and becomes unstable, which affects the electric field around the charge wire and causes uneven charging on the photoreceptor. The image unevenness level is 2. Even over time, since the feed screw 241 and the slider 242 are made of resin, the sliding performance is high and the sliding resistance is kept low. There is no increase in torque. For this reason, the waiting time during the cleaning operation of the user is almost the same as the initial time.

  In Experiment 4, since the conduction between the feed screw 241 and the casing is reliable both initially and over time, the image unevenness level is 5 and there is no problem. Further, as in Experiment 3, since there is no increase in driving torque, the waiting time of the user is almost the same as the initial time.

  In this way, by providing a step at both ends of the electrode plate contact portion of the feed screw of the charging device cleaning device, the feed screw is made of a conductive resin having a base resin of polyacetal, so that it has a long life and high image quality. A scorotron charging device with low waiting time can be provided. In addition, the process cartridge and the image forming apparatus provided with the scorotron charging device can obtain stable charging performance over time, so that good image formation can be maintained without causing image unevenness over time. It becomes.

  As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this. For example, the diameter of the feed screw, the width of the electrode plate, the width of the contact portion of the feed screw with the electrode plate, etc. are arbitrary and can be set as appropriate. Moreover, the magnitude | size of a level | step difference can also be set suitably. The configuration of the charging device such as the number of charge wires can be changed within the scope of the present invention. Appropriate materials can be used for the structure and material of the cleaning member.

  Any device can be mounted on the process cartridge, and a configuration not including a developing device is also possible. The image carrier (photosensitive member) is not limited to a drum shape, and a belt-like image carrier can also be used.

  The configuration of the image forming unit of the image forming apparatus is also arbitrary, and the arrangement order of the color image forming units in the tandem system is arbitrary. In addition to the tandem type, a configuration in which a plurality of developing devices are arranged around a single photosensitive member, or a configuration using a revolver type developing device is also possible. The present invention can also be applied to a full color machine using three color toners, a multicolor machine using two color toners, or a monochrome apparatus. Of course, the image forming apparatus is not limited to a copying machine, but may be a printer, a facsimile machine, or a multifunction machine having a plurality of functions.

1 is a cross-sectional view illustrating an overall configuration of a full-color copying machine that is an example of an image forming apparatus including a scorotron charging device according to the present invention. It is a block diagram showing a process cartridge of the copying machine. It is an enlarged view of a charging device provided with a cleaning device. It is a perspective view of the charging device. It is a perspective view which shows the state which looked at FIG. 4 from the downward direction. It is the elements on larger scale which show in detail the level | step-difference part of the feed screw of a charging device. It is a side view of the level | step-difference part of a feed screw. It is a side view of the level | step-difference part which shows another example of a feed screw. It is a side view of the level | step-difference part which shows another example of a feed screw. It is a side view of the level | step-difference part of the feed screw which made the front-end | tip of the electrode plate contact part the circular arc shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charging device 4 Developing device 6 Cleaning device 10 Image forming unit 11 Exhaust duct 21 Charge wire 22 Shield case 23 Grid electrode 24 Charging cleaning device 25 End block 100 Full color copying machine 241 Feed screw 241B
242 Slider 245 Electrode plate 241C Electrode plate contact portion 241D Step portion

Claims (7)

A shield case having a discharge opening, a discharge electrode arranged in the shield case, a grid electrode stretched in the discharge opening, and a movable screw can be moved and moved in the longitudinal direction of the discharge electrode A scorotron charging device comprising: a cleaning member that is disposed on the discharge electrode to clean the discharge electrode by rubbing the discharge electrode; and an electrode plate for short-circuiting the shield case and the feed screw.
The contact portion of the feed screw with the electrode plate is on the outer periphery of the feed screw, the contact portion is smaller than the width of the electrode plate, and steps are formed on both sides of the contact portion. Characteristic scorotron charging device.   The scorotron charging device according to claim 1, wherein the contact portion of the feed screw is provided to be inclined with respect to an axial direction of the feed screw.   The scorotron charging device according to claim 1, wherein a material of the feed screw is a conductive resin.   The scorotron charging device according to claim 3, wherein the base resin of the conductive resin is polyacetal. A process cartridge comprising at least an image carrier and charging means for charging the surface of the carrier, and configured to be detachable from the image forming apparatus main body;
A process cartridge comprising the scorotron charging device according to claim 1 as the charging means.   An image forming apparatus comprising the scorotron charging device according to claim 1, comprising an image carrier and charging means for charging the surface of the image carrier.   An image forming apparatus comprising the process cartridge according to claim 5.

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