JP2008015027A - Charging device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain an air flow from being generated in a space between a charging roll and a cover in the rotating direction of the charging roll. <P>SOLUTION: Above the charging roll 24 for charging the surface of a photoreceptor drum 12, the cover 42 is disposed so as to cover the upper part of the charging roll 24. The cover 42 has an entrance 44 for use as an air inlet on the upstream side of the charging roll 24 in the rotating direction, and an exit 46 for use as an air outlet on the downstream side thereof. The cover 42 is formed such that a distance between an internal wall 42A on the entrance 44 side and the charging roll 24 is longer than a distance between the internal wall 42A on the exit 46 side and the charging roll 24. Consequently, the inflow resistance of air flowing from the entrance 44 is made lower than the outlet resistance of air let out from the exit 46. This makes air less likely to escape from the exit 46. Accordingly, an air flow from the entrance 44 to the exit is restrained. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a charging device including a charging roll that charges the surface of an image carrier such as a photoconductor, and an image forming apparatus such as a copying machine and a printer including the charging device.

  Conventionally, as a charging device for an image forming apparatus such as a copying machine or a printer adopting an electrophotographic method, a device using a corona discharge phenomenon such as a scorotron charger has been widely used, but a charging device using a corona discharge phenomenon is used. In this case, the generation of ozone and nitrogen oxides that have a negative effect on the human body and the global environment is a problem. In contrast, the contact charging method in which a conductive charging roll or the like is in direct contact with the photosensitive member to charge the photosensitive member generates less ozone and nitrogen oxides and is more power efficient. It has become mainstream.

  In such a contact charging method, the charging roll is brought into pressure contact with the surface of the photoconductor, and is rotated by the rotation of the photoconductor. Further, a cover is provided around the charging roll in order to suppress a leak and hold a cleaning member for cleaning the charging roll (see, for example, Patent Document 1).

  In recent years, with the increase in the speed of image forming apparatuses, it has become necessary to rotate the charging roll at a higher speed, and there is a problem that a toner cloud is generated in the image forming apparatus due to an air flow generated by the rotation of the charging roll at a high speed. is there. In addition, when a cover is provided around the charging roll, the space between the cover and the charging roll serves as an air duct, and an air flow that blows out from the outlet of the cover on the downstream side in the rotation direction of the charging roll is generated. Dirt tends to float in the image forming apparatus due to the blown airflow. In addition, since the airflow to be sucked in at the inlet side of the cover on the upstream side in the rotation direction of the charging roll, if the toner cloud such as a developing device is easily contaminated on the inlet side, the toner cloud is more sucked. It will be. For this reason, not only the dirt in the image forming apparatus is further accelerated, but also the charging roll is easily dirty by sucking the dirt into the cover, which becomes a factor of shortening the life of the charging roll.

On the other hand, a configuration is disclosed in which an airflow generation device that sucks air in the vicinity of the charging roll is provided in order to suppress dirt and the like from adhering to the surface of the charging roll (see, for example, Patent Document 2). However, when the airflow generation device is provided, there is a problem that the configuration is complicated, the device is enlarged, and the cost is increased.
Japanese Patent Laid-Open No. 2004-101610 JP-A-11-161120

  The present invention has been made in view of the above problems, and a charging device capable of suppressing dirt from adhering to the surface of the charging roll due to the air flow in the rotation direction of the charging roll, and preventing dirt from floating in the image forming apparatus, and An object is to provide an image forming apparatus.

  In order to solve the above-described problem, a charging device according to the first aspect of the present invention includes a charging roll that charges the surface of an image carrier that is rotationally driven, and a cover that covers the charging roll. By rotating the charging roll, the inflow resistance of air flowing from the upstream side in the rotation direction of the charging roll between the charging roll and the cover is made smaller than the discharge resistance discharged from the downstream side.

  According to the first aspect of the present invention, the cover for covering the charging roll is provided, and the inflow resistance of the air flowing from the upstream side in the rotation direction of the charging roll between the charging roll and the cover is discharged from the downstream side. It is smaller than the discharge resistance. A laminar flow is generated between the charging roll and the cover in the rotational direction of the charging roll, and air flows from the upstream side and easily flows to the downstream side, but the inflow resistance of the air flowing from the upstream side is discharged from the downstream side. By making it smaller than the discharge resistance, the generation of airflow from the upstream side to the downstream side is suppressed. As a result, it is possible to prevent the toner cloud or the like from entering the cover and soiling the charging roll, and to prevent dirt from floating in the image forming apparatus due to airflow.

  According to a second aspect of the present invention, in the charging device according to the first aspect, an air inflow port constituted by the charging roll and the cover is provided as an air exhaust port constituted by the charging roll and the cover. It is characterized by being larger than the exit.

  According to the second aspect of the present invention, the air inlet formed by the charging roll and the cover is made larger than the air outlet formed by the charging roll and the cover. The inflow resistance of air flowing in from the side inlet becomes smaller than the discharge resistance discharged from the downstream outlet. As a result, air hardly flows on the discharge port side, and the occurrence of airflow along the rotation direction of the charging roll is suppressed.

  According to a third aspect of the present invention, in the charging device according to the first aspect, a protrusion is provided on the inner wall of the cover on the discharge port side.

  According to the invention described in claim 3, since the protrusion is provided on the inner wall of the cover on the discharge port side, the inflow resistance of the air flowing in from the inflow port on the upstream side in the rotation direction of the charging roll is discharged from the discharge port on the downstream side. It becomes smaller than the discharge resistance. This makes it difficult for air to flow at the protrusions, and the occurrence of airflow along the rotation direction of the charging roll is suppressed.

  According to a fourth aspect of the present invention, in the charging device according to the first aspect, a cleaning member for cleaning the charging roll in the cover is provided on the discharge port side.

  According to the fourth aspect of the present invention, since the cleaning member for cleaning the charging roll in the cover is provided on the discharge port side, the inflow resistance of the air flowing in from the inflow port on the upstream side in the rotation direction of the charging roll is reduced on the downstream side. It becomes smaller than the discharge resistance discharged from the discharge port. Thereby, it becomes difficult for air to flow in the vicinity of the cleaning member, and generation of airflow along the rotation direction of the charging roll is suppressed.

  The invention according to claim 5 comprises a charging roll for charging the surface of the image carrier to be rotated and a cover for covering the charging roll from above, and the longitudinal direction of the charging roll is provided on the top of the cover. It is characterized in that an opening is formed.

  According to the fifth aspect of the present invention, the cover for covering the charging roll from above is provided, and the opening is formed in the longitudinal direction of the charging roll at the top of the cover. Between the charging roll and the cover, a laminar flow is generated in the rotation direction of the charging roll, and air flows from the upstream side and easily flows downstream, but an opening is formed in the longitudinal direction of the charging roll at the top of the cover. By doing so, the air that has flowed in from the upstream side is discharged from the opening to the outside of the cover, and the occurrence of airflow from the upstream side to the downstream side is suppressed. As a result, it is possible to prevent the toner cloud or the like from entering the cover and soiling the charging roll, and to prevent dirt from floating in the image forming apparatus due to airflow.

  According to a sixth aspect of the present invention, in the charging device according to the fifth aspect, the longitudinal length of the opening is longer than the longitudinal length of the charging roll.

  According to the invention described in claim 6, since the length in the longitudinal direction of the opening is longer than the length in the longitudinal direction of the charging roll, the air flow becomes non-uniform along the longitudinal direction of the charging roll. Is suppressed, and the occurrence of uneven dirt on the charging roll is suppressed.

  According to a seventh aspect of the present invention, in the charging device according to the fifth or sixth aspect, a filter is provided in the opening.

  According to the seventh aspect of the present invention, since the filter is provided in the opening, the dirt contained in the air in the cover is captured by the filter, and the air from which the dirt has been removed is discharged to the outside of the cover. For this reason, it is suppressed that the dirt contained in the air floats in the image forming apparatus.

  According to an eighth aspect of the invention, in the charging device according to the fifth or sixth aspect, a check valve having a flow from the inside to the outside of the cover is provided in the opening. .

  According to the invention described in claim 8, since the check valve having the flow from the inside to the outside of the cover is provided in the opening, the air in the cover is discharged from the opening to the outside of the cover, and the outside of the cover Air is prevented from entering the inside of the cover through the opening. For this reason, the occurrence of airflow from the upstream side toward the downstream side along the rotation direction of the charging roll in the cover is further suppressed.

  The invention according to claim 9 comprises a charging roll for charging the surface of the image carrier that is rotationally driven, and a cover that covers the charging roll from below, and a longitudinal direction of the charging roll is provided at the bottom of the cover. It is characterized in that an opening is formed.

  According to the ninth aspect of the present invention, the cover for covering the charging roll from below is provided, and the opening is formed in the longitudinal direction of the charging roll at the bottom of the cover. A laminar flow is generated between the charging roll and the cover in the rotation direction of the charging roll, and air flows from the upstream side and tends to flow downstream, but an opening is formed in the longitudinal direction of the charging roll at the bottom of the cover. By doing so, the air that has flowed in from the upstream side is discharged from the opening to the outside of the cover, and the occurrence of airflow from the upstream side to the downstream side is suppressed. The opening is provided at the bottom of the cover, and when the air in the cover is discharged from the opening to the outside, foreign matter in the air falls in the direction of gravity. As a result, it is possible to prevent the toner cloud or the like from entering the cover and soiling the charging roll, and to prevent dirt from floating in the image forming apparatus due to airflow.

  According to a tenth aspect of the present invention, in the charging device according to the ninth aspect of the present invention, there is provided an accommodating portion that accommodates the foreign matter blown out from the opening to the lower portion of the cover.

  According to the invention described in claim 10, the foreign matter blown out from the opening to the lower portion of the cover falls in the direction of gravity and is accommodated in the accommodating portion. For this reason, it is further suppressed that dirt in the air diffuses outside the cover.

  According to an eleventh aspect of the present invention, in the charging device according to any one of the fifth to tenth aspects, the opening holds the image holding member passing through a contact point between the image holding member and the charging roll. It is characterized in that it is provided on the side away from the developing device for forming a toner image on the surface of the image carrier with respect to the normal of the body.

  According to the eleventh aspect of the invention, the opening is provided on the side away from the developing device with respect to the normal of the image carrier passing through the contact point between the image carrier and the charging roll. The toner cloud generated in the vicinity of the apparatus is prevented from entering the inside of the cover from the opening.

  An image forming apparatus according to a twelfth aspect of the present invention is formed on the image carrier that is rotationally driven, the charging device according to any one of the first to eleventh aspects, and the image carrier. And a developing device for developing the electrostatic latent image to form a toner image.

  According to the twelfth aspect of the present invention, since the charging device according to any one of the first to eleventh aspects is provided, the rotation direction of the charging roll is between the cover and the charging roll. The generation of airflow from the upstream side to the downstream side along the line is suppressed. As a result, it is possible to prevent the toner cloud or the like from entering the cover and soiling the charging roll, and to prevent dirt from floating in the image forming apparatus due to airflow.

  ADVANTAGE OF THE INVENTION According to this invention, generation | occurrence | production of the airflow which goes to a downstream from an upstream along the rotation direction of a charging roll can be suppressed between a cover and a charging roll. Therefore, it is possible to suppress the toner cloud or the like generated near the developing device from entering the cover and soiling the charging roll, and it is possible to suppress the dirt from floating in the image forming apparatus due to airflow.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an image forming apparatus 100 including a charging device according to the first embodiment of the present invention.

  The image forming apparatus 100 performs image processing based on color image information sent from an image data input device such as a personal computer (not shown), and forms a color image on a recording sheet P by an electrophotographic method.

  The image forming apparatus 100 includes image forming units 10Y, 10M, 10C, and 10K that form toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). In the following, when it is necessary to distinguish YMCK, description will be made by adding any of Y, M, C, and K after the reference. When YMCK does not need to be distinguished, Y, M, C, K is omitted.

  The image forming units 10Y, 10M, 10C, and 10K are arranged so that the image forming units 10Y, 10M, 10C, and 10K move in the traveling direction of the endless intermediate transfer belt 30 that is stretched by the backup roll 34 and the plurality of stretch rolls 32. They are arranged in series in the order of 10K. In addition, the intermediate transfer belt 30 is provided with a primary transfer roll 16Y disposed opposite to the photosensitive drums 12Y, 12M, 12C, and 12K as image carriers of the image forming units 10Y, 10M, 10C, and 10K. It is inserted between 16M, 16C and 16K.

  Next, the configuration of each of the image forming units 10Y, 10M, 10C, and 10K and the image forming operation will be described using the image forming unit 10Y that forms a yellow toner image as a representative.

  The surface of the photosensitive drum 12Y is uniformly charged by the charging roll 24Y. Next, image exposure corresponding to the yellow image is performed by the exposure device 14Y, and an electrostatic latent image corresponding to the yellow image is formed on the surface of the photosensitive drum 12Y.

  The electrostatic latent image corresponding to the yellow image is developed by the toner carried on the developing roll 18Y to which the developing bias of the developing device 15Y is applied, and becomes a yellow toner image. The yellow toner image is primarily transferred onto the intermediate transfer belt 30 by the pressing force of the primary transfer roll 16Y and the electrostatic attraction force by the transfer bias applied to the primary transfer roll 16Y.

  In this primary transfer, the entire yellow toner image is not transferred to the intermediate transfer belt 30, and a part of the yellow toner image remains on the photosensitive drum 12Y as transfer residual yellow toner. Further, an external additive of toner is also attached to the surface of the photosensitive drum 12Y. After the primary transfer, the photosensitive drum 12Y passes through a position facing the cleaning device 20Y, and transfer residual toner and the like on the surface of the photosensitive drum 12Y are removed. Thereafter, the surface of the photosensitive drum 12Y is charged again by the charging roll 24Y for the next image forming cycle.

  As shown in FIG. 1, in the image forming apparatus 100, the image forming process similar to the above is performed at each image forming unit 10Y at a timing in consideration of the relative position difference between the image forming units 10Y, 10M, 10C, and 10K. , 10M, 10C, and 10K, and Y, M, C, and K color toner images are sequentially superimposed on the intermediate transfer belt 30 to form a multiple toner image.

  Then, electrostatic attraction of the secondary transfer roll 36 to which the transfer bias is applied to the recording paper P conveyed to the secondary transfer position where the secondary transfer roll 36 and the intermediate transfer belt 30 face each other at a predetermined timing. The multiple toner images are collectively transferred from the intermediate transfer belt 30 to the recording paper P by the force.

  The recording paper P to which the multiple toner images have been transferred is separated from the intermediate transfer belt 30, and then conveyed to the fixing device 31, where it is fixed to the recording paper P by heat and pressure, thereby forming a full color image.

  The transfer residual toner on the intermediate transfer belt 30 that has not been transferred to the recording paper P is collected by the intermediate transfer belt cleaner 33.

  In the image forming apparatus 100, as shown in FIG. 2, a charging device 40 is disposed on the upper part of the photosensitive drum 12. The charging device 40 includes a charging roll 24 that comes into contact with the surface of the photosensitive drum 12, and a cover 42 that covers the periphery of the charging roll 24 on the side opposite to the photosensitive drum 12.

  The charging roll 24 has a charging layer 24B formed around a conductive shaft 24A. A predetermined high voltage is applied to the shaft 24A from a power source (not shown). A motor (not shown) is connected to the support shaft of the photosensitive drum 12, and the photosensitive drum 12 is driven to rotate clockwise (in the direction of arrow 2) in FIG. Further, the charging roll 24 rotates in the direction of the arrow 4 following the rotation of the photosensitive drum 12.

  The cover 42 is formed longer than the entire length of the charging roll 24 in the longitudinal direction, and the wall portion of the cover 42 is bent in an inverted U shape so as to surround the peripheral surface of the charging roll 24. Between the cover 42 and the charging roll 24, an inlet 44 as an air inlet is provided on the upstream side with respect to the rotation direction of the charging roll 24, and an outlet 46 as an air outlet is provided on the downstream side. Yes. At this time, with respect to the normal line 48 of the photosensitive drum 12 passing through the contact point between the photosensitive drum 12 and the charging roll 24, the inlet 44 is on the side closer to the developing roll 18, and the outlet 46 is on the side away from the developing roll 18. Is provided.

  The cover 42 is formed such that the distance between the inner wall 42A of the cover 42 on the inlet 44 side and the charging roll 24 is longer than the distance between the inner wall 42A of the cover 42 on the outlet 46 side and the charging roll 24. For example, the distance between the inner wall 42A on the inlet 44 side and the charging roll 24 is set to be approximately 2.5 mm longer than the distance between the inner wall 42A on the outlet 46 side and the charging roll 24. As a result, the inflow resistance of air flowing from the inlet 44 on the upstream side in the rotation direction of the charging roll 24 between the charging roll 24 and the cover 42 due to the rotation of the charging roll 24 is discharged from the outlet 46 on the downstream side. Smaller.

  Next, details of the charging roll 24 will be described.

  In this charging roll 24, a conductive elastic layer and a surface layer are sequentially formed as a charging layer 24B on a conductive shaft 24A.

  The diameter of the charging roll 24 is 7 mm to 15 mm, more preferably 8 mm to 14 mm, and the thickness of the charging layer 24B is preferably 2 mm to 4 mm. If the diameter is 15 mm or more, the number of times of contact with the external additive per location on the peripheral surface is reduced, and the number of discharges is reduced. This is disadvantageous from the viewpoint of miniaturization, although it has excellent long-term stability against dirt and charging performance. . If the diameter is 7 mm or less, the image forming apparatus 100 can be downsized, which is advantageous. However, the number of times of contact with the external additive per peripheral surface increases and the number of discharges increases, which is disadvantageous for long-term stability. It becomes.

  The charging roll 24 is not limited to the following configuration as long as it has a predetermined charging performance.

  As the material of the shaft 24A, free-cutting steel, stainless steel or the like is used. The material and the surface treatment method are appropriately selected according to the application such as slidability, and the non-conductive material is generally plated. It may be processed by an appropriate process and a conductive process may be performed.

  The conductive elastic layer constituting the charging layer 24B of the charging roll 24 may be, for example, an elastic material such as rubber having elasticity, a conductive material such as carbon black or ion conductive material for adjusting the resistance of the conductive elastic layer, and the like. Accordingly, materials that can be usually added to rubber, such as softeners, plasticizers, curing agents, vulcanizing agents, vulcanization accelerators, anti-aging agents, and fillers such as silica and calcium carbonate, may be added. It is formed by coating the peripheral surface of the conductive shaft 24A with a mixture in which a material usually added to rubber is added. As a conductive agent for the purpose of adjusting the resistance value, a material in which a material that conducts electricity using electrons and / or ions as a charge carrier, such as carbon black or an ionic conductive agent blended in a matrix material, is used. it can. The elastic material may be a foam.

  The elastic material constituting the conductive elastic layer is formed, for example, by dispersing a conductive agent in a rubber material. Rubber materials include isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, urethane rubber, silicone rubber, fluorine rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide. -Allyl glycidyl ether copolymer rubber, ethylene-propylene-diene terpolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber, natural rubber and the like, and blended rubbers thereof. Among these, silicone rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, acrylonitrile-butadiene copolymer rubber, and blended rubbers thereof are preferably used. These rubber materials may be foamed or non-foamed.

  As the conductive agent, an electronic conductive agent or an ionic conductive agent is used. Examples of electronic conductive agents include carbon blacks such as ketjen black and acetylene black; pyrolytic carbon, graphite; various conductive metals or alloys such as aluminum, copper, nickel, and stainless steel; tin oxide, indium oxide, titanium oxide Examples thereof include fine powders such as various conductive metal oxides such as tin oxide-antimony oxide solid solution and tin oxide-indium oxide solid solution; Examples of ionic conductive agents include perchlorates and chlorates such as tetraethylammonium and lauryltrimethylammonium; alkali metals such as lithium and magnesium; perchlorates and chlorates of alkaline earth metals Can be mentioned.

  The surface layer constituting the charging layer 24B is formed for the purpose of preventing contamination due to foreign matters such as toner, and the surface layer material may be any of resin, rubber, etc. It is not limited. Polyester, polyimide, copolymer nylon, silicone resin, acrylic resin, polyvinyl butyral, ethylene tetrafluoroethylene copolymer, melamine resin, fluoro rubber, epoxy resin, polycarbonate, polyvinyl alcohol, cellulose, polyvinylidene chloride, polyvinyl chloride, polyethylene And ethylene vinyl acetate copolymer. Of these, polyvinylidene fluoride, a tetrafluoroethylene copolymer, polyester, polyimide, and copolymer nylon are preferably used from the viewpoint of contamination of the external additive.

  The surface layer can contain a conductive material to adjust the resistance value. The conductive material preferably has a particle size of 3 μm or less. In addition, as a conductive agent for the purpose of adjusting the resistance value, it electrically conducts electrons and / or ions as charge carriers, such as carbon black, conductive metal oxide particles, or ionic conductive agent blended in the matrix material. What disperse | distributed material etc. can be used.

  In addition, a fluorine-based or silicone-based resin is used for the surface layer. In particular, it is preferably composed of a fluorine-modified acrylate polymer. Further, fine particles may be added to the surface layer. As a result, the surface layer becomes hydrophobic and acts to prevent the foreign matter from adhering to the charging roll 24. In addition, insulating particles such as alumina and silica are added to provide irregularities on the surface of the charging roll 24, thereby reducing the burden at the time of rubbing against the photosensitive drum 12, and the charging roll 24 and the photosensitive drum. It is also possible to improve the mutual wear resistance.

  In the image forming apparatus 100 configured as described above, the distance between the inner wall 42A on the inlet 44 side and the charging roll 24 is set longer than the distance between the inner wall 42A on the outlet 46 side of the cover 42 and the charging roll 24. The inflow resistance of the air flowing from the inlet 44 on the upstream side in the rotation direction of the charging roll 24 is smaller than the discharge resistance discharged from the outlet 46 on the downstream side.

  In general, a laminar flow 50 is generated between the charging roll 24 and the cover 42 in the rotation direction of the charging roll 24, and air easily enters from the inlet to the outlet. By making the distance between the inner wall 42 </ b> A and the charging roll 24 shorter than the inlet 44 side, air entering from the inlet 44 is difficult to escape to the outlet 46. For this reason, a flow 52 is generated in which the air that has entered from the inlet 44 turns back inside the cover 42 and is discharged from the inlet 44, and the airflow that enters from the inlet 44 along the rotation direction of the charging roll 24 toward the outlet 46 is reduced. .

  Further, since the inlet 44 is provided on the side close to the developing roll 18, it is possible to prevent toner cloud or the like generated near the developing roll 18 from flowing into the outlet 44 and being discharged from the outlet 46. Therefore, it is possible to suppress the toner cloud and the like from entering the cover 42 and soiling the charging roll 24, and it is possible to suppress the dirt from floating in the image forming apparatus 100 due to the air flow from the inlet 44 to the outlet 46.

  Next, a charging device according to a second embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the member same as 1st Embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 3, in the charging device 60, the distance between the inner wall 62 </ b> A on the inlet 44 side of the cover 62 and the charging roll 24 and the distance between the inner wall 62 </ b> A on the outlet 46 side of the cover 62 and the charging roll 24 are substantially the same. However, a plurality of projections 64 projecting toward the charging roll 24 are provided on the inner wall 62A on the outlet 46 side. The plurality of protrusions 64 are formed so as to protrude in a direction substantially perpendicular to the axial direction of the surface of the charging roll 24.

  In such a charging device 60, a plurality of protrusions 64 projecting toward the charging roll 24 are formed on the inner wall 62 </ b> A on the outlet 46 side of the cover 62, and the air flowing from the inlet 44 upstream in the rotation direction of the charging roll 24 is formed. The inflow resistance is smaller than the discharge resistance discharged from the downstream outlet 46.

  In general, a laminar flow 50 is generated between the charging roll 24 and the cover 62 in the rotation direction of the charging roll 24 and air easily enters from the inlet to the outlet, but in this embodiment, the laminar flow 50 enters from the inlet 44. The air is blocked by the plurality of protrusions 64, so that it is difficult to escape to the outlet 46. For this reason, a flow 52 is generated in which the air that has entered from the inlet 44 turns back inside the cover 62 and is discharged from the inlet 44, and the air flow that enters from the inlet 44 toward the outlet 46 along the rotation direction of the charging roll 24 is reduced. .

  Further, since the inlet 44 is provided on the side close to the developing roll 18, it is possible to prevent toner cloud or the like generated near the developing roll 18 from flowing into the outlet 44 and being discharged from the outlet 46. For this reason, it is possible to suppress the toner cloud and the like from entering the cover 62 and soiling the charging roll 24, and it is possible to suppress the dirt from floating in the image forming apparatus 100 due to the air flow from the inlet 44 to the outlet 46.

  Next, an image forming apparatus according to a third embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the member same as 1st Embodiment and 2nd Embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 4, in the charging device 70, the distance between the inner wall 72A on the inlet 44 side of the cover 72 and the charging roll 24 and the distance between the inner wall 72A on the outlet 46 side of the cover 72 and the charging roll 24 are substantially the same. However, a cleaning roll 74 that is in contact with the surface of the charging roll 24 is provided at a position close to the outlet 46 side. The cleaning roll 74 is disposed on the far side from the inlet 44 side of the portion of the cover 72 bent in an inverted U shape. By providing the cleaning roll 74, the inflow resistance of air flowing from the inlet 44 on the upstream side in the rotation direction of the charging roll 24 becomes smaller than the discharge resistance discharged from the outlet 46 on the downstream side.

  The cleaning roll 74 has a roll-like sponge layer 74B formed on the peripheral surface of the shaft 74A. The shaft 74A is rotatably supported by bearings at both ends (not shown). The cleaning roll 74 rotates in the direction of the arrow following the rotation of the charging roll 24.

  As the material of the shaft 74A, free-cutting steel, stainless steel or the like is used, and the material and the surface treatment method are appropriately selected according to the use such as slidability. It may be processed by a general process and subjected to a conductive process, and may be used as it is. Further, since the cleaning roll 74 is brought into contact with the charging roll 24 through the sponge layer 74B at an appropriate nip pressure, the shaft diameter having sufficient rigidity with respect to a material having a strength that does not bend at the time of the nip or a shaft length is sufficient. Selected.

  The sponge layer 74B is made of a foam having a porous three-dimensional structure, and has cavities and irregularities (hereinafter referred to as cells) inside and on the surface, and has elasticity. This sponge layer 74B is selected from those made of foamed resin or rubber such as polyurethane, polyethylene, polyamide, olefin, melamine or polypropylene, NBR, EPDM, natural rubber and styrene butadiene rubber, chloroprene, silicone, nitrile, etc. Is done. Thereby, sponge layer 74B which has many cells can be manufactured cheaply. The sponge layer 74B efficiently cleans foreign substances such as external additives by driven sliding rubbing with the charging roll 24, and at the same time, the surface of the charging roll 24 is not scratched by rubbing of the sponge layer 74B. In order to prevent tearing and breakage, it is particularly preferable to use polyurethane that is strong in tearing and tensile strength.

  The number of cells in the sponge layer 74B is preferably 40 to 80 cells / 25 mm, and more preferably 45 to 75 cells / 25 mm. By setting the number of cells as described above, foreign substances such as toner and external additives can be easily taken into the cells, and foreign substances such as external additives taken in can be easily transferred to the charging roll 24 and the photosensitive drum 12. . When the number of cells is more than 80/25 mm, the cell diameter is small, so the uptake of the external additive is reduced. Conversely, when the number of cells is less than 40/25 mm, the cell diameter becomes too large and the incorporated external additive. It becomes difficult to harden to an appropriate size for transferring the toner to the charging roll 24.

  In such a charging device 70, the cleaning roll 74 is provided at a position close to the outlet 46 side of the cover 72, and the inflow resistance of the air flowing from the inlet 44 on the upstream side in the rotation direction of the charging roll 24 is reduced by the outlet on the downstream side. It becomes smaller than the discharge resistance discharged from 46.

  In general, a laminar flow 50 is generated between the charging roll 24 and the cover 62 in the rotation direction of the charging roll 24 and air easily enters from the inlet to the outlet, but in this embodiment, the laminar flow 50 enters from the inlet 44. When the air is blocked by the cleaning roll 74, it becomes difficult to escape to the outlet 46. For this reason, a flow 52 is generated in which the air that has entered from the inlet 44 is folded back in the cover 72 and is discharged from the inlet 44, and the air flow that enters from the inlet 44 to the outlet 46 along the rotation direction of the charging roll 24 is reduced. .

  Further, since the inlet 44 is provided on the side close to the developing roll 18, it is possible to prevent toner cloud or the like generated near the developing roll 18 from flowing into the outlet 44 and being discharged from the outlet 46. For this reason, it is possible to prevent the toner cloud or the like from entering the cover 72 and soiling the charging roll 24, and to prevent the dirt from floating in the image forming apparatus 100 due to the air flow from the inlet 44 to the outlet 46.

  Next, an image forming apparatus according to a fourth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the member same as 1st-3rd embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 5, the charging device 110 includes a cover 112 on the opposite side of the charging roll 24 from the photosensitive drum 12 so as to cover the upper side of the charging roll 24, and the wall portion of the cover 112 includes a charging roll. It is bent in an inverted U shape so as to surround the circumferential surface of 24. In the opposite part of the cover 112 and the charging roll 24, an inlet 114 as an air inflow port on the upstream side with respect to the rotation direction of the charging roll 24 (direction of arrow 4), and an air discharge port on the downstream side. An outlet 116 is provided.

  In this charging device 110, the distance between the inner wall 112A on the inlet 114 side of the cover 112 and the charging roll 24 and the distance between the inner wall 112A on the outlet 116 side of the cover 112 and the charging roll 24 are substantially the same. An opening 118 having a substantially uniform width in the longitudinal direction of the charging roll 24 is provided at the top of the cover 112 in the middle of the outlet 116. The opening 118 is provided in the upper part of the charging roll 24 and is formed longer than the length of the charging roll 24 in the longitudinal direction.

  In such a charging device 110, an opening 118 is provided in the middle of the inlet 114 and the outlet 116 of the cover 112, and a flow 120 in which air is blown out of the cover 112 from the opening 118 is generated. In general, a laminar flow 50 is generated in the rotation direction of the charging roll 24 at the facing portion between the charging roll 24 and the cover 112, and air easily flows from the inlet to the outlet. By providing the opening 118 in the middle of the inlet 114 and the outlet 116, the air that has entered from the inlet 114 is blown out of the cover 112 from the opening 118. As a result, the air flow entering from the inlet 114 toward the outlet 116 along the rotation direction of the charging roll 24 is reduced.

  Further, since the inlet 114 is provided on the side close to the developing roll 18, it is possible to prevent toner cloud or the like generated near the developing roll 18 from flowing into the outlet 114 and being discharged from the outlet 116. For this reason, it is possible to suppress the toner cloud or the like from entering the cover 112 and soiling the charging roll 24, and it is possible to suppress the dirt from floating in the image forming apparatus 100 due to the air flow from the inlet 114 to the outlet 116.

  Further, since the length in the longitudinal direction of the opening 118 is longer than the length in the longitudinal direction of the charging roll 24, it is possible to prevent the air flow from becoming non-uniform along the longitudinal direction of the charging roll 24. For this reason, it is possible to suppress the occurrence of uneven dirt on the surface of the charging roll 24.

  Next, an image forming apparatus according to a fifth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the member same as 1st-4th embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 6, the charging device 130 has a filter 132 attached to an opening 118 formed at the top of the cover 112 in the middle of the inlet 114 and the outlet 116. As the filter 132, for example, an activated carbon filter, a resin fiber filter such as polyester or polypropylene, a glass fiber filter, or the like is used.

  In such a charging device 130, an opening 118 is provided in the middle of the inlet 114 and the outlet 116 of the cover 112, and a flow 120 is generated in which air is blown out of the cover 112 from the opening 118. Since the filter 132 is attached to the opening 118, dirt such as foreign matters contained in the air in the cover 112 is captured by the filter 132, and the air from which the dirt has been removed is blown out to the outside of the cover 112. . For this reason, it is possible to prevent dirt from floating in the image forming apparatus 100.

  Next, an image forming apparatus according to a sixth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the member same as 1st-5th embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 7, the charging device 140 includes a check valve 142 having a flow from the inside to the outside of the cover 112 in an opening 118 formed at the top of the cover 112 in the middle of the inlet 114 and the outlet 116. It is attached. The check valve 142 is curved outwardly of the opening 118 and has an opening / closing hole 142A formed in the center thereof. When a predetermined air pressure is applied, the check valve 142 passes from the inside of the cover 112 to the outside through the opening / closing hole 142A. It is configured so that air flows and air does not flow in the reverse direction.

  In such a charging device 140, since the check valve 142 is provided in the opening 118, a flow 120 is generated in which air in the cover 112 is blown outside through the opening / closing hole 142 </ b> A of the check valve 142. Outside air is prevented from entering the cover 112 through the opening 118. For this reason, it can further suppress that the air flow which goes to the exit 116 from the entrance 114 along the rotation direction of the charging roll 24 within the cover 112 generate | occur | produces.

  Next, an image forming apparatus according to a seventh embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the member same as 1st-6th embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 8, the charging device 150 is provided with an opening 154 at the top of the cover 152 in the middle of the inlet 114 and the outlet 116. The opening 154 is formed on the side away from the developing roll 18 with respect to the normal line 48 of the photosensitive drum 12 passing through the contact point between the photosensitive drum 12 and the charging roll 24.

  In such a charging device 150, since the opening 154 is provided on the side away from the developing roll 18 with respect to the normal line 48, air outside the cover 152 enters the cover 152 from the opening 154, Flows 156 and 157 flowing toward the developing roll 18 are generated. For this reason, the toner cloud generated in the vicinity of the developing roll 18 can be prevented from flowing into the cover 152 from the outside of the cover 152 through the opening 154. Further, since the generation of airflow from the inlet 114 toward the outlet 116 along the rotation direction of the charging roll 24 can be suppressed, toner cloud or the like can be prevented from entering the cover 152 and contaminating the charging roll 24, and from the inlet 114. It is possible to prevent dirt from floating in the image forming apparatus 100 due to the air flow toward the outlet 116.

  Next, an image forming apparatus according to an eighth embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the member same as 1st-7th embodiment, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 9, the photosensitive drum 160 rotates clockwise (in the direction of the arrow 162), and a charging device 170 is provided below the photosensitive drum 160. The charging device 170 is provided with a charging roll 166, which is rotated in the direction of the arrow 164 following the rotation of the photosensitive drum 160. The charging device 170 includes a cover 172 that covers the lower side of the charging roll 166 on the opposite side of the charging roll 166 from the photosensitive drum 160. The cover 172 has a substantially U-shaped cross section. The cover 172 is provided with an inlet 174 as an air inflow port on the upstream side and an outlet 176 as an air discharge port on the downstream side with respect to the rotation direction of the charging roll 166 (the direction of the arrow 164). .

  The cover 172 is provided with an opening 178 at the bottom part in the middle of the inlet 174 and the outlet 176 and in the gravity drop direction with respect to the charging roll 166. The opening 178 has a substantially uniform width in the longitudinal direction of the charging roll 166, and is formed longer than the entire length of the charging roll 166 in the longitudinal direction. In addition, an accommodation member 180 that accommodates foreign matters such as toner and external additives is provided below the opening 178. The housing member 180 is a tray whose cross section is bent into a substantially U shape, and is configured to capture the fallen foreign matter.

  In such a charging device 170, a flow 182 is generated in which air that has entered the cover 172 from the inlet 174 is blown out from the lower opening 178. The opening 178 is provided at the lower part of the charging roll 166, and when air in the cover 172 is blown out from the opening 178, dirt such as foreign matters in the air falls on the housing member 180 in the gravity direction. Or it is sprayed and dirt, such as a foreign material, is accommodated in the inside of the accommodating member 180. FIG. For this reason, it is possible to further suppress the contamination such as foreign matter in the air from floating in the image forming apparatus outside the cover 172.

  In the above embodiment, except for FIG. 4, only the charging roll is provided in the cover of the charging device. However, the present invention is not limited to this configuration. A cleaning member such as a brush, a pad, or an elastic roll for cleaning the charging roll may be provided in the cover.

  The image forming apparatus 100 shown in FIG. 1 has a configuration in which image forming units 10Y, 10M, 10C, and 10K of yellow, magenta, cyan, and black are arranged in parallel along the moving direction of the intermediate transfer belt 30. The configuration is not limited to this. For example, the charging device of the present invention can be applied even to a configuration in which a toner image is formed on a photosensitive drum repeatedly by four cycles using a rotary developing device having four color developing devices. is there.

1 is a schematic configuration diagram illustrating an image forming apparatus including a charging device according to a first embodiment of the present invention. It is a block diagram which shows the charging device shown in FIG. It is a block diagram which shows the charging device of 2nd Embodiment of this invention. It is a block diagram which shows the charging device of 3rd Embodiment of this invention. It is a block diagram which shows the charging device of 4th Embodiment of this invention. It is a block diagram which shows the charging device of 5th Embodiment of this invention. It is a block diagram which shows the charging device of 6th Embodiment of this invention. It is a block diagram which shows the charging device of 7th Embodiment of this invention. It is a block diagram which shows the charging device of 8th Embodiment of this invention.

Explanation of symbols

10Y, 10M, 10C, 10K Image forming units 12Y, 12M, 12C, 12K Photosensitive drum (image carrier)
15Y developing device 18 developing roll 24 charging roll 24A shaft 24B charging layer 40 charging device 42 cover 42A inner wall 44 inlet (inlet)
46 Exit (discharge port)
60 Charging Device 62 Cover 62A Inner Wall 64 Protrusion 70 Charging Device 72 Cover 72A Inner Wall 74 Cleaning Roll 74A Shaft 74B Sponge Layer 100 Image Forming Device 110 Charging Device 112 Cover 112A Inner Wall 114 Entrance (Inlet)
116 Exit (discharge port)
118 Opening portion 130 Charging device 132 Filter 140 Charging device 142 Check valve 150 Charging device 152 Cover 154 Opening portion 160 Photosensitive drum (image holding member)
166 Charging roll 170 Charging device 172 Cover 174 Entrance (inlet)
176 Exit (discharge port)
178 Opening 180 Housing member

Claims (12)

A charging roll for charging the surface of the image carrier to be rotated;
A cover for covering the charging roll,
Charging characterized in that, due to rotation of the charging roll, the inflow resistance of air flowing from the upstream side in the rotation direction of the charging roll between the charging roll and the cover is made smaller than the discharge resistance discharged from the downstream side. apparatus.   The charging device according to claim 1, wherein an air inlet configured by the charging roll and the cover is made larger than an air outlet configured by the charging roll and the cover.   The charging device according to claim 1, wherein a protrusion is provided on an inner wall of the cover on the discharge port side.   The charging device according to claim 1, wherein a cleaning member for cleaning the charging roll in the cover is provided on the discharge port side. A charging roll for charging the surface of the image carrier to be rotated;
A cover for covering the charging roll from above,
A charging device, wherein an opening is formed in a longitudinal direction of the charging roll at a top of the cover.   The charging device according to claim 5, wherein a length of the opening in a longitudinal direction is longer than a length of the charging roll in a longitudinal direction.   The charging device according to claim 5, wherein a filter is provided in the opening.   The charging device according to claim 5 or 6, wherein a check valve having a flow from the inside to the outside of the cover is provided in the opening. A charging roll for charging the surface of the image carrier to be rotated;
A cover for covering the charging roll from below,
A charging device, wherein an opening is formed in a longitudinal direction of the charging roll at a bottom portion of the cover.   The charging device according to claim 9, further comprising a housing portion that houses foreign matter blown out from the opening to a lower portion of the cover.   The opening is provided on a side away from a developing device that forms a toner image on the surface of the image carrier with respect to a normal line of the image carrier passing through a contact point between the image carrier and the charging roll. The charging device according to any one of claims 5 to 10, wherein the charging device is provided. An image carrier that is rotationally driven;
A charging device according to any one of claims 1 to 11,
A developing device for developing a latent electrostatic image formed on the image carrier to form a toner image;
An image forming apparatus comprising:

Images