JP2007171288A - Charging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a charging device capable of providing the satisfactory cleaning performance of a cleaning member regardless of the material of the cleaning member. <P>SOLUTION: A charging roll 14 and a sponge layer 100B are abutted on each other so that the number of cells 140 of the sponge layer 100B in the circumferential direction (rotative direction; the direction of arrow 8) of the charging roll 14 within a nip area A between the cleaning roll 100 and the charging roll 14 is equal to or larger than six but equal to or smaller than twenty-one. This prevents such a problem that the pressing force of the cleaning roll 100 is insufficient and hence the cleaning of the charging roll 14 is insufficient or the pressing force of the cleaning roll 100 is excessive and hence the charging roll 14 is rubbed with soil resulting from cleaning. In addition, this ensures the satisfactory cleaning performance of the cleaning member with proper pressing force regardless of the cell density of the material of the cleaning roll 100. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a charging device provided in an image forming apparatus such as a copying machine or a printer employing an electrophotographic system.

  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. On the other hand, the contact charging method in which the conductive charging roll is directly contacted with the image carrier to charge the image carrier has significantly less generation of ozone and nitrogen oxide, and the power supply efficiency is good. Recently it has become mainstream.

  Such a charging device of the contact charging method has a disadvantage that various deposits on the image bearing member are adsorbed and easily contaminated during charging.

  On the other hand, a technique for defining the number of cells per inch on the surface of the cleaning roll to be used as in Patent Document 1 and a technique for defining the number of cells on the surface of a rectangular parallelepiped cleaning pad as in Patent Document 2 There is. Japanese Patent Application Laid-Open No. 2004-228561 has a technique for defining the amount of biting of the cleaning roll into the charging roll.

However, in these cases, due to the hardness of the material used as the cleaning member and the thickness of the cleaning member to be used, the pressing force necessary for cleaning cannot be obtained sufficiently, or conversely, the cleaning force becomes too strong. Conversely, image quality defects may be caused by rubbing.
JP-A-9-127768 Japanese Patent Laid-Open No. 10-3200 JP-A-8-62948

  In view of the above-described facts, an object of the present invention is to provide a charging device that can obtain a good cleaning performance of a cleaning member regardless of the material of the cleaning member.

  In order to achieve the above object, the invention according to claim 1 includes a charging roll for charging the image carrier, a porous elastic layer, and a support member for supporting the porous elastic layer in the charging device. And a cleaning member that contacts the charging roll and cleans the charging roll, and has a porous elastic layer along a circumferential direction of the charging roll in a nip region between the porous elastic layer and the charging roll. The porous elastic layer is in contact with the charging roll so that the number of cells is 6 or more.

  The toner and the external additive adhering to the surface of the charging roll enter the cells of the porous elastic layer, and the surface of the charging roll is cleaned. In the invention according to claim 1, the nip region between the cleaning member and the charging roll is used. The charging roll and the porous elastic layer are brought into contact with each other so that the number of cells of the porous elastic layer along the circumferential direction of the charging roll is 6 or more. That is, the minimum number of cells required for cleaning the charging roll is defined.

  As a result, the pressing force of the cleaning member is insufficient and the charging roll cannot be sufficiently cleaned, or the cleaned dirt is rubbed against the charging roll in reverse due to the excessive pressing force of the cleaning member. Therefore, regardless of the cell density of the material of the cleaning member, good cleaning performance of the cleaning member can be obtained with an appropriate pressing force. When a plurality of cleaning members are provided, the sum of the number of cells with which the porous elastic layer of each cleaning member contacts the charging roll may be 6 or more.

  According to a second aspect of the present invention, there is provided the charging device according to the first aspect, wherein the number of cells of the porous elastic layer along the circumferential direction of the charging roll in the nip region is 21 or less. The layer is in contact with the charging roll.

  If the number of cells of the porous elastic layer along the circumferential direction of the charging roll in the nip region is too large, the amount of deformation (collapse) of the cells is large and foreign matter cannot be collected. For this reason, in the invention described in claim 2, the porous elastic layer is used as the charging roll so that the number of cells of the porous elastic layer along the circumferential direction of the charging roll in the nip region is 6 or more and 21 or less. Make contact.

  According to a third aspect of the present invention, in the charging device according to the first or second aspect, the support member is in a roll shape, a plurality of porous elastic bodies are protruded on the surface, and the porous elastic body is the It is in contact with the charging roll.

  In the invention according to claim 3, the support member is formed into a roll shape, a plurality of porous elastic bodies are protruded on the surface of the support member, and the porous elastic bodies are brought into contact with the charging roll. The same location of the charging roll is cleaned a plurality of times by one cleaning, which improves the cleaning performance. Further, by projecting the porous elastic body at a plurality of locations on the support member, the sum of the number of cells with which each porous elastic body contacts the charging roll may be 6 or more. Thereby, the pressing force of the cleaning member can be reduced.

  Here, the hardness and the like can be changed for each porous elastic body, and the porous elastic body can be exchanged as a cartridge type. Since the porous elastic body is of the cartridge type, it is not necessary to replace the cleaning member every time it is replaced due to the life of the cleaning member. Therefore, it is not necessary to position the cleaning member, and the disassembly / assembly work is facilitated.

  According to a fourth aspect of the present invention, in the charging device according to the first or second aspect, an uneven portion is formed on a surface of the porous elastic layer, and the convex portion is in contact with the charging roll. And

  In the invention according to claim 4, an uneven portion is formed on the surface of the porous elastic layer, and the convex portion is brought into contact with the charging roll, whereby the sum of the number of cells in which each convex portion comes into contact with the charging roll is 6. Make more than one. Thereby, the pressing force of the cleaning member can be reduced.

  According to a fifth aspect of the present invention, in the charging device according to any one of the first to fourth aspects, the porous elastic layer has a roll shape.

  Since the present invention is configured as described above, it is possible to obtain good cleaning performance of the cleaning member with an appropriate pressing force regardless of the cell density of the material of the cleaning member.

  An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

  An image forming apparatus 10 according to this embodiment shown in FIG. 1 is a four-cycle full-color laser printer. As shown in the drawing, in the apparatus, a photosensitive drum 12 (image carrier) is located slightly above the center. ) Is rotatably arranged. As this photosensitive drum 12, for example, a drum made of a conductive cylinder having a diameter of about 47 mm and coated on a surface with a photosensitive layer made of OPC or the like is used. It is rotationally driven at a process speed of 150 mm / sec.

  The surface of the photosensitive drum 12 is charged to a predetermined potential by a charging roll 14 disposed almost directly below the photosensitive drum 12, and then exposed to a laser beam LB by an exposure device 16 disposed below the charging roll 14. Image exposure is performed, and an electrostatic latent image according to image information is formed.

  The electrostatic latent image formed on the photosensitive drum 12 has yellow (Y), magenta (M), cyan (C), and black (K) developing devices 18Y, 18M, 18C, and 18K in the circumferential direction. The toner is developed by a rotary developing device 18 disposed along the toner image to form a toner image of a predetermined color.

  At this time, charging, exposure, and development processes are repeated a predetermined number of times on the surface of the photosensitive drum 12 in accordance with the color of the image to be formed. In the developing process, the rotary developing device 18 rotates, and the corresponding color developing devices 18Y, 18M, 18C, and 18K move to a developing position facing the photosensitive drum 12.

  For example, when a full-color image is formed, the charging, exposing, and developing processes are performed on the surface of the photosensitive drum 12 in yellow (Y), magenta (M), cyan (C), and black (K) colors. The toner image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially formed on the surface of the photosensitive drum 12. When the toner image is formed, the number of rotations of the photosensitive drum 12 varies depending on the size of the image. For example, in the case of A4 size, one image is obtained by rotating the photosensitive drum 12 three times. It is formed. That is, a toner image corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K) is formed on the surface of the photosensitive drum 12 every time the photosensitive drum 12 rotates three times. Is done.

  An intermediate transfer belt 20 is wound around the outer periphery of the photosensitive drum 12 for yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive drum 12. At the primary transfer position, the images are transferred onto the intermediate transfer belt 20 by the primary transfer roll 22 while being superimposed on each other.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred in multiple onto the intermediate transfer belt 20 are recorded on a recording sheet 24 fed at a predetermined timing. The images are collectively transferred by the secondary transfer roll 26.

  On the other hand, the recording paper 24 is fed out from a paper feed cassette 28 disposed at the lower part of the image forming apparatus 10 by a pickup roll 30 and is fed in a state of being fed one by one by a feed roll 32 and a retard roll 34. The toner image is transferred to the secondary transfer position of the intermediate transfer belt 20 in synchronization with the toner image transferred onto the intermediate transfer belt 20 by the registration roll 36.

  The intermediate transfer belt 20 includes a wrap-in roll 38 that specifies the wrap position of the intermediate transfer belt 20 on the upstream side in the rotational direction of the photosensitive drum 12 and a toner image formed on the photosensitive drum 12 as an intermediate transfer belt. A primary transfer roll 22 that is transferred onto the intermediate transfer belt 20, a wrap-out roll 40 that specifies the wrap position of the intermediate transfer belt 20 on the downstream side of the wrap position, and a backup that contacts the secondary transfer roll 26 via the intermediate transfer belt 20. The roll 42, the first cleaning backup roll 46 facing the cleaning device 44 of the intermediate transfer belt 20, and the second cleaning backup roll 48 are stretched with a predetermined tension, and have a predetermined process speed (about 150 mm / sec), for example, as the photosensitive drum 12 rotates. It is driven Te.

  Here, in order to reduce the size of the image forming apparatus 10, the intermediate transfer belt 20 is configured such that a cross-sectional shape on which the intermediate transfer belt 20 is stretched is a flat and elongated substantially trapezoidal shape.

  The intermediate transfer belt 20 includes a photosensitive drum 12, a charging roll 14, an intermediate transfer belt 20, a plurality of rolls 22, 38, 40, 42, 46, and 48 that stretch the intermediate transfer belt 20, and an intermediate transfer belt. The cleaning device 44 for 20 and the cleaning device 78 for the photosensitive drum 12 described later integrally form an image forming unit 52. Therefore, the entire image forming unit 52 can be removed from the image forming apparatus 10 by opening the upper cover 54 of the image forming apparatus 10 and lifting the handle (not shown) provided on the upper part of the image forming unit 52 by hand. It has become.

  On the other hand, the cleaning device 44 for the intermediate transfer belt 20 includes a scraper 58 disposed so as to come into contact with the surface of the intermediate transfer belt 20 stretched by the first cleaning backup roll 46, and a second cleaning backup roll 48. And a cleaning brush 60 disposed so as to be in pressure contact with the surface of the stretched intermediate transfer belt 20. Residual toner and paper dust removed by the scraper 58 and the cleaning brush 60 are contained in the cleaning device 44. It has come to be collected.

  The cleaning device 44 is disposed so as to be able to swing counterclockwise in the drawing with the swing shaft 62 as the center. Until the secondary transfer of the final color toner image is completed, the intermediate transfer belt is provided. It is configured to retreat to a position separated from the surface of the surface 20 and to contact the surface of the intermediate transfer belt 20 when the secondary transfer of the final color toner image is completed.

  Further, the recording paper 24 onto which the toner image has been transferred from the intermediate transfer belt 20 is conveyed to a fixing device 64 and is heated and pressurized by the fixing device 64 to fix the toner image on the recording paper 24. Thereafter, in the case of single-sided printing, the recording paper 24 on which the toner image has been fixed is discharged as it is onto a discharge tray 68 provided at the top of the image forming apparatus 10 by a discharge roll 66.

  On the other hand, in the case of double-sided printing, the recording paper 24 on which the toner image is fixed on the first surface (front surface) by the fixing device 64 is not directly discharged onto the discharge tray 68 by the discharge roll 66 but is discharged by the discharge roll 66. With the rear end portion of the recording paper 24 being held, the discharge roller 66 is reversed, the conveyance path of the recording paper 24 is switched to the double-sided paper conveyance path 70, and the double-sided paper conveyance path 70 is disposed. In the state where the front and back of the recording paper 24 are reversed by the transport roller 72 thus transferred, the recording paper 24 is again transported to the secondary transfer position of the intermediate transfer belt 20 and the toner image is transferred to the second surface (back surface) of the recording paper 24. . Then, the toner image on the second surface (back surface) of the recording paper 24 is fixed by the fixing device 64, and the recording paper 24 is discharged onto the discharge tray 68.

  Furthermore, a manual feed tray 74 can be attached to the side surface of the image forming apparatus 10 so as to be freely opened and closed. An arbitrary size and type of recording paper 24 placed on the manual feed tray 74 is fed by a paper feed roll 76, and a secondary transfer position of the intermediate transfer belt 20 via a transport roll 73 and a registration roll 36. The image can be formed on the recording paper 24 of any size and type.

  The surface of the photosensitive drum 12 after the toner image transfer process is completed is cleaned by the cleaning blade 80 of the cleaning device 78 disposed obliquely below the photosensitive drum 12 every time the photosensitive drum 12 rotates once. Residual toner, paper dust, and the like are removed to prepare for the next image forming process.

  As shown in FIG. 2, a charging roll 14 is disposed below the photosensitive drum 12 so as to be in contact with the photosensitive drum 12. The charging roll 14 (charging member) has a conductive layer 14B formed around a conductive shaft 14A, and the shaft 14A is rotatably supported. A roll-shaped cleaning roll 100 (cleaning member) that comes into contact with the surface of the charging roll 14 is provided on the lower portion of the charging roll 14 opposite to the photosensitive drum 12. The cleaning roll 100 has a sponge layer 100B (porous elastic layer) formed around a shaft 100A, and the shaft 100A is rotatably supported.

  The cleaning roll 100 is pressed against the charging roll 14 with a predetermined load, and the sponge layer 100 </ b> B is elastically deformed along the peripheral surface of the charging roll 14 to form the nip portion 101. The photosensitive drum 12 is driven to rotate clockwise (in the direction of arrow 2) in FIG. 2 by a motor (not shown), and the charging roll 14 is driven to rotate in the direction of arrow 4 as the photosensitive drum 12 rotates. Further, the roll-shaped cleaning roll 100 is driven to rotate in the direction of the arrow 6 by the rotation of the charging roll 14.

  Further, a charging power source is connected to the charging roll 14, and only a bias in which an alternating current is superimposed on a direct current or a direct current bias is applied. On the other hand, although the bias application to the cleaning roll 100 is not particularly defined, in the present invention, the shaft 14A of the charging roll 14 and the shaft 100A of the cleaning roll 100 are rotatably supported by the same bearing (described later). ) The cleaning roll 100 is at the same potential as the charging roll 14.

  As the cleaning roll 100 is driven to rotate, dirt (foreign matter) such as toner and external additives attached to the surface of the charging roll 14 is cleaned by the cleaning roll 100. Then, when the foreign matter is taken into the foam cell of the cleaning roll 100 and the collected foreign matter aggregates to an appropriate size, the cleaning roll 100 passes the charging roll 14 to the photosensitive drum 12. It is considered that the cleaning performance is maintained and maintained by returning to the cleaning device 78 that cleans the photosensitive drum 12.

  As for the cleaning roll 100 as the cleaning member of the charging roll 14, free cutting steel, stainless steel, or the like is used as the material of the shaft 100 </ b> A. Selected in a timely manner. In addition, a non-conductive material may be processed by a general process such as a plating process and subjected to a conductive process, or may be used as it is. Further, since the cleaning roll 100 comes into contact with the charging roll 14 through the sponge layer 100B with an appropriate nip pressure, the shaft diameter having sufficient rigidity with respect to a material having a low bending strength or a shaft length. Is selected.

  The sponge layer 100B is made of a foam having a porous three-dimensional structure. The sponge layer 100B is selected from those made of a foamable resin or rubber such as polyurethane, polyethylene, polyamide, or polypropylene. The sponge layer 100B efficiently cleans foreign substances such as external additives by driven sliding rubbing with the charging roll 14, and at the same time does not damage the surface of the charging roll 14 due to rubbing of the sponge layer 100B. In order to prevent tearing and breakage, it is particularly preferable to use polyurethane that is strong in tearing and tensile strength.

  The charging roll 14 is formed by sequentially forming a conductive elastic layer and a surface layer as a charging layer 14B on a conductive shaft 14A.

  As the material of the shaft 14A, 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, and the material having no conductivity 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 14B of the charging roll 14 may be, for example, an elastic material such as rubber having elasticity, a conductive material such as carbon black or ionic conductive material for adjusting the resistance of the conductive elastic layer, or 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 14 </ b> A with a mixture in which materials usually added to rubber are 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 surface layer constituting the charging layer 14B is formed for the purpose of preventing contamination by 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.

  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.

  The conductive metal oxide particles, which are conductive particles for adjusting the resistance value, are conductive particles such as tin oxide, tin oxide doped with antimony, zinc oxide, anatase titanium oxide, and ITO. Any conductive agent using electrons as charge carriers can be used without any particular limitation. These may be used alone or in combination of two or more. Any particle size may be used as long as the present invention is not inhibited. From the viewpoint of resistance value adjustment and strength, tin oxide, antimony-doped tin oxide, and anatase-type titanium oxide are preferable. Tin oxide and antimony-doped tin oxide are preferred.

  By performing resistance control with such a conductive material, the resistance value of the surface layer does not change depending on environmental conditions, and stable characteristics can be obtained.

  Further, 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 adhesion of foreign matter to the charging roll 14. In addition, insulating particles such as alumina and silica are added to give unevenness to the surface of the charging roll 14, thereby reducing the burden at the time of rubbing against the photosensitive drum 12, and the charging roll 14 and the photosensitive drum. It is also possible to improve the mutual wear resistance.

  Next, the mounting structure of the charging roll 14 and the cleaning roll 100 will be described in detail.

  As shown in FIG. 3, in this embodiment, the charging roll 14 and the cleaning roll 100 are assembled into a single frame 120 via a pair of bearing members 110 and housed in the frame 120, and further, the photosensitive drum 12. Are also assembled into the frame 120 and unitized.

  As shown in FIGS. 4A and 4B, one bearing member 110 is formed in a flat rectangular parallelepiped shape (block shape) and has a single configuration. The bearing member 110 is formed of a synthetic resin material such as polyacetal or polycarbonate having high rigidity, high slidability, and excellent wear resistance. In order to further improve the wear resistance, the synthetic resin material may contain glass fibers, carbon fibers, or the like.

  The bearing member 110 is formed with two bearing holes 112 and 114 arranged at predetermined intervals along the longitudinal direction (vertical direction in FIG. 4). A support portion 14a provided at the end of the shaft 14A of the charging roll 14 is rotatably inserted into one bearing hole 112, and the other bearing hole 114 is provided at the end of the shaft 100A of the cleaning roll 100. The support part 100a is rotatably inserted. Further, as shown in the drawing, the inner diameter of the bearing hole 114 is made larger than the shaft diameter of the shaft 100A (support portion 100a).

  Supporting portions 14a at both ends of the shaft 14A of the charging roll 14 and support portions 100a at both ends of the shaft 100A of the cleaning roll 100 are rotatably supported by the pair of bearing members 110. When the cleaning roll 100 is pressed against the charging roll 14 with a predetermined load, as described above, the sponge layer 100B is elastically deformed along the peripheral surface of the charging roll 14 to form the nip portion 101 ( (See FIG. 2).

  As shown in FIG. 3, the frame 120 includes the pair of bearing members 110 at both ends (left and right side ends in FIG. 3) along the axial direction of the charging roll 14 and the cleaning roll 100 in the main body 122. A pair of attachment portions 124 to be attached are integrally provided.

  A guide groove 126 is formed in the attachment portion 124 along the extending direction of the attachment portion 124. The bearing member 110 is inserted into the guide groove 126 and disposed on the tip end side thereof. The bearing member 110 is guided by the guide groove 126 and extends in the extending direction of the mounting portion 124 (the direction in which it is in contact with and away from the photosensitive drum 12). It is possible to slide along.

  The outer surface sides of the pair of attachment portions 124 are thick and the front end side is extended, and a pair of bearing portions 132 that pivotally support the photosensitive drum 12 is provided at the front end portion. A bearing hole 134 is coaxially formed in the pair of bearing portions 132, and the support portion 12 a provided at the end of the shaft 12 </ b> A is rotatably inserted into each bearing hole 134. The charging roll 14 and the cleaning roll 100 are assembled to the frame 120.

  A compression coil spring 128 that urges the bearing member 110 toward the photosensitive drum 12 is provided on the base end side in the guide groove 126. The bearing member 110 is biased toward the photosensitive drum 12 by the spring force of the compression coil spring 128 (in the direction of arrow 8), and the charging roll 14 is in pressure contact with the photosensitive drum 12. Thus, when the photosensitive drum 12 rotates, the charging roll 14 is driven to rotate with the rotation of the photosensitive drum 12 to charge the photosensitive drum 12, and further, the cleaning roll 100 is driven to rotate with the rotation of the charging roll 14. Then, the charging roll 14 is cleaned.

  Next, the operation of this embodiment will be described.

  As shown in FIG. 5, in the present invention, in the nip portion 101 between the cleaning roll 100 and the charging roll 14, a nip region A (the intersection of a solid line indicating the outer periphery of the charging roll 14 and an imaginary line indicating the outer periphery of the cleaning roll 100). The charging roll 14 and the cleaning roll 100 are arranged so that the number of cells 140 of the sponge layer 100B along the circumferential direction (rotation direction; the direction of arrow 8) of the charging roll 14 is 6 or more and 21 or less between the intersections). Abut.

  The surface of the charging roll 14 is cleaned by the toner and external additives attached to the surface entering the cell 140 of the sponge layer 100B by the contact of the cleaning roll 100. When the number of cells per inch on the surface of 100 is specified or the amount of biting of the cleaning roll 100 into the charging roll 14 is specified, the hardness of the material used as the cleaning roll 100 and the thickness of the cleaning roll 100 used Therefore, there may be a case where the pressing force necessary for cleaning cannot be obtained sufficiently, or on the contrary, the pressing force becomes too strong and the cleaning stains are rubbed against each other to cause image quality defects.

  For this reason, in the present invention, by defining the minimum number of cells required for cleaning the charging roll 14, the pressing force of the cleaning roll 100 is insufficient and the charging roll 14 cannot be sufficiently cleaned, or The excessive pressing force of the cleaning roll 100 prevents a problem that the cleaned dirt is rubbed against the charging roll 14 in reverse, and an appropriate pressing force is applied regardless of the cell density of the material of the cleaning roll 100. Good cleaning performance of the cleaning member can be obtained by pressure.

  FIG. 6 shows the results of experiments conducted by changing the amount of biting so that the number of cells in the nip (Nip) in the cleaning roll 100 and the charging roll 14 changes. At this time, the outer diameter of the cleaning roll 100 was finely adjusted so that the influence of the pressing force was not included. Here, the diameter of the cleaning roll 100 is 12 mm, and the material is polyethylene. The charging roll 14 had a diameter of 14 mm, and the material used was polyamide. During the experiment, the amount of change in the finely adjusted outer diameter is ± 0.5 mm. Under this condition, the charging roll 14 soiled under the predetermined condition was cleaned, and the cleaning property was evaluated by the amount of reflected light on the surface. Specifically, the contamination level of the charging roll 14 is evaluated in five stages, and the level 2 or lower is a contamination level that causes no problem in print image quality.

  According to this, it can be seen that as the number of cells increases, the cleaning performance of the charging roll 14 is improved (the level of contamination of the charging roll 14 is improved). When the number of cells is 6 or more, the charging roll 14 The dirt level is 2 or less. Based on this result, the number of cells in the present invention is defined. When the number of cells is 8 or more, the cleaning performance is further improved. Further, when the number of cells is 21 or more, the cleaning performance deteriorates. However, when the number of cells in the nip between the cleaning roll 100 and the charging roll 14 is too large, the deformation amount (collapse) of the cell 140 is large, and the foreign matter This is because there is a case where it is not possible to collect the sample.

  By the way, when the number of cells in the nip between the cleaning roll 100 and the charging roll 14 is defined as in the present invention, even a material with a small number of cells per unit length is used as a cleaning roll depending on the contact state. Is possible.

  For example, as shown in FIG. 7, two cleaning rolls 142 are used so as to contact the charging roll 14 at two locations. FIG. 8 shows the results of experiments performed by changing the amount of biting so that the sum of the number of cells in the nip (Nip) in the two cleaning rolls 142 and the charging roll 14 changes. However, when the two cleaning rolls 142 are used to make contact with the charging roll 14 at two locations, the nip between the cleaning roll 142 and the charging roll 14 is the same as when the single cleaning roll 100 is used. If the sum of the number of cells in (Nip) is 6 or more and 21 or less, it is a stain level with no problem in print image quality.

  Here, when two cleaning rolls 142 are used, the number of cells 140 of the sponge layer 100B along the circumferential direction of the charging roll 14 in the nip regions B and C between the cleaning rolls 142 and the charging roll 14 is three. If it is more than one, it will be better. For this reason, the outer diameter of the cleaning roll 142 can be reduced. Further, by using a plurality of cleaning rolls 142, the pressing force of each cleaning roll 142 can be reduced.

  Although the cleaning roll 142 having the same size is used here, a cleaning roll having a different size may be used, and the number of cells in the nip between the cleaning roll and the charging roll 14 may be set for each cleaning roll. It may be changed to

  Further, as shown in FIG. 9, a recess 144A is provided on the surface of the resin-made support roll 144 along the axial direction of the support roll 144, and a sponge roll 146 is fitted into the recess 144A so that the surface of the support roll 144 is A convex portion (porous elastic body) 146A may be provided. Then, the convex portions 146A are brought into contact with the surface of the charging roll 14 so that the sum of the number of cells 140 of each convex portion 146A along the circumferential direction of the charging roll 14 is 6 or more and 21 or less.

  Here, each sponge roll 146 can be changed in hardness or the like, and the sponge roll 146 may be exchangeable as a cartridge type. If the sponge roll 146 is of a cartridge type, it is not necessary to replace the cleaning member 145 when replacing the cleaning member 145 due to the life of the cleaning member 145. Therefore, it is not necessary to position the cleaning member 145, and the disassembling and assembling work becomes easy.

  Furthermore, as shown in FIG. 10, not only a roll-like sponge but also a sponge member 148 having a substantially rectangular parallelepiped shape may be used. In this case, the sponge member 148 is fixed by a holder 149 provided opposite to the charging roll 14 and is disposed in a state where it cannot move. A plurality of protrusions 150 are provided on the surface of the sponge member 148, the protrusions 150 are brought into contact with the surface of the charging roll 14, and the number of cells 140 of each protrusion 150 along the circumferential direction of the charging roll 14. So that the sum is 6 or more and 21 or less.

  As mentioned above, although it demonstrated in detail by embodiment of this invention, this invention is not limited to them, Various other forms can be implemented within the scope of the present invention.

  For example, the charging roll 14 is brought into contact with the lower part of the photosensitive drum 12 and the cleaning roll 100 is brought into contact with the lower part of the charging roll 14, but the photosensitive drum 12, the charging roll 14, and the cleaning roll 100 are arranged. The positional relationship is not limited to this. For example, the present invention can be applied to a configuration in which a charging roll is brought into contact with an upper portion of the photosensitive drum and a cleaning roll is brought into contact with the upper portion of the charging roll.

  The image forming apparatus to which the present invention is applied has a four-cycle configuration in which the toner image is formed on the photosensitive drum 12 four times using the rotary developer 18 as in the above-described embodiment. It is not limited to. For example, even if the yellow, magenta, cyan, and black image forming units are arranged in parallel along the moving direction of the intermediate transfer belt, the present invention is applied to the photosensitive drum, the charging roll, and the cleaning roll of each image forming unit. Can be applied.

1 is a configuration diagram illustrating a schematic configuration of an image forming apparatus including a charging device according to an embodiment of the present invention. FIG. 2 is an enlarged view showing a configuration of a photosensitive drum, a charging roll, and a cleaning roll mounted on the image forming apparatus of FIG. 1. FIG. 3 is a partial cross-sectional side view illustrating a configuration of a charging device and a photoreceptor mounting structure according to an embodiment of the present invention. FIG. 4A is a perspective view, and FIG. 4B is a side view showing a state in which a charging roll and a cleaning roll constituting the charging device according to the embodiment of the present invention are supported by a bearing member. FIG. 3 is an enlarged cross-sectional view showing a nip state between a charging roll and a cleaning roll constituting the charging device according to the embodiment of the present invention. It is a graph which shows the number of cells in the nip of the charging roll and cleaning roll which comprise the charging device which concerns on embodiment of this invention, and the contamination level of a charging roll. It is the 1st modification of FIG. It is a graph which shows the number of cells in the nip of the charging roll and cleaning roll by the 1st modification, and the dirt level of a charging roll. It is the 2nd modification of FIG. It is the 3rd modification of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photosensitive drum (Image carrier)
14 Charging roll (charging member)
100 Cleaning roll (cleaning member)
100A shaft (support member, cleaning member)
100B Sponge layer (porous elastic layer, cleaning member)
140 cell 142 cleaning roll (cleaning member)
144 Support roll (support member, cleaning member)
145 Cleaning roll (cleaning member)
146 Sponge roll (porous elastic body)
148 Sponge member (porous elastic layer, cleaning member)
149 Holder (support member, cleaning member)
150 Protrusion (convex)

Claims (5)

A charging roll for charging the image carrier;
A cleaning member configured to include a porous elastic layer and a support member that supports the porous elastic layer, and contacts the charging roll to clean the charging roll;
With
The porous elastic layer is in contact with the charging roll so that the number of cells of the porous elastic layer along the circumferential direction of the charging roll is 6 or more in the nip region between the porous elastic layer and the charging roll. A charging device.   The porous elastic layer is in contact with the charging roll so that the number of cells of the porous elastic layer along the circumferential direction of the charging roll in the nip region is 21 or less. The charging device described.   3. The charging according to claim 1, wherein the support member is in a roll shape, a plurality of porous elastic bodies are protruded on a surface, and the porous elastic body is in contact with the charging roll. apparatus.   The charging device according to claim 1, wherein an uneven portion is formed on a surface of the porous elastic layer, and the convex portion is in contact with the charging roll.   The charging device according to claim 1, wherein the porous elastic layer has a roll shape.

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