JP2007225725A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-reliability image forming apparatus capable of ensuring the improved stability of the entire apparatus and retaining high-quality image formation over a long period of time. <P>SOLUTION: In an image forming unit 13K, in which because of the effect of monochrome/color ratio in image formation, a charging roll 16 is more likely to be soiled than the respective charging rolls of image-forming units 13Y, 13M, and 13C used for the formation of a color image, a cleaning system whose cleaning performance is higher than that of each of the image forming units for the formation of a color image is used as a cleaning member for the charging roll 16. Since each charging roll 16 can be cleaned satisfactorily, while the differences between the soil levels of the charging rolls 16 are restricted, the stability of the entire apparatus is improved and the reliability is enhanced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer that employs an electrophotographic method, and more particularly, a contact charging method that charges the surface of an image carrier while rotating in contact with the rotationally driven image carrier. The present invention relates to an image forming apparatus having a charging roll and a cleaning member for the charging roll.

  In recent years, as a charging device for an image forming apparatus such as a copying machine or a printer using an electrophotographic method, in order to suppress ozone emission, reduce the size of the apparatus, and reduce the high-voltage power supply cost, a conventional scorotron or the like can be used. Instead of the non-contact type charger, a roller charger (BCR) that is in contact with or close to the image carrier is used.

  In such a contact charging type charging device, since the charging roll is always in contact with the image carrier, there is a problem that the surface of the charging roll is liable to be contaminated by foreign matter. The surface of the image carrier on which the image forming operation is repeatedly performed passes through a cleaning process for removing foreign matter such as residual toner after transfer on the downstream side of the transfer process, and then enters the charging process area. Even after the process, a part of the toner and an external additive of the toner, such as finer particles than the toner, remain on the image carrier without being cleaned and adhere to the surface of the charging roll. The foreign matter adhering to the surface of the charging roll causes unevenness in the surface resistance value of the charging roll, resulting in abnormal discharge or unstable discharge, which deteriorates charging uniformity.

  Therefore, in order to improve such a problem, a cleaner made of a plate-like brush or sponge is brought into contact with the surface of the charging roll, or a cleaning roll made of a roll-like sponge or the like is rotated (for example, Patent Document 1), and a technique for cleaning the surface of the charging roll has been proposed.

  However, in a high-speed type image forming apparatus including a plurality of image forming units and a tandem type color image forming apparatus, the state of each image forming unit varies depending on the use state of the apparatus. When using a charging roll cleaning system with the same type of cleaning member) or exactly the same conditions (various parameters on the cleaning member are the same), the contamination level of each charging roll is particularly high under the conditions such as black-and-white / color ratio and arrangement in the device. There is a problem in that the occurrence of image defects differs depending on the image forming unit.

On the other hand, for example, in a tandem type image forming apparatus including a plurality of image forming units, it is particularly considered that most of the paper dust on the intermediate transfer member is transferred to the photosensitive drum located upstream in the rotation direction. However, a technique has been proposed in which the cleaning member is provided only on the upstream charging roll that is easily affected by paper dust contamination, thereby reducing the cost (see, for example, Patent Document 2).
JP-A-8-62948 JP 2004-4749 A

  However, as described above, if even one of the plurality of image forming units on the downstream side is not cleaned, the image forming unit has passed through the upstream photoconductor cleaner (cleaning blade). Contamination due to the external additive causes the charging uniformity of the charging roll to deteriorate at an early stage and generate an image defect, so that the stability and reliability of the entire apparatus becomes a problem. For this reason, this technique cannot be used particularly for an image forming apparatus in which a plurality of image forming units are integrally formed.

  In view of the above facts, an object of the present invention is to provide a highly reliable image forming apparatus capable of improving the stability of the entire apparatus and maintaining high-quality image formation over a long period of time.

  In order to achieve the above object, the invention described in claim 1 includes a plurality of image forming units each including an image carrier, a charging roll that charges the image carrier, and a cleaning member that cleans the charging roll. The image forming apparatus is characterized in that the cleaning method using the cleaning member is different in at least one image forming unit from other image forming units.

  In the present invention, with respect to the cleaning member of each charging roll provided in the plurality of image forming units, at least one image forming unit cleans the other image forming units with the cleaning member according to the contamination level of each image forming unit. By using different methods (types of cleaning members), each of the charging rolls can be cleaned satisfactorily while suppressing the difference in contamination level between the charging rolls. Thereby, the stability of the entire apparatus is improved and high reliability can be obtained.

  Note that the cleaning method is an elastic roll method in which the cleaning member is formed in a roll shape with an elastic material and is rotated and brought into contact with the charging roll for cleaning, and the cleaning member is formed in a roll shape with a brush material and charged. The brush roll system is a brush roll for rotating and contacting the roll, the cleaning pad is formed of an elastic material in a pad shape, the elastic pad system is an elastic pad for cleaning by contacting the charging roll, and the cleaning member A brush pad method or the like formed into a pad shape with a brush material and cleaned by contacting with a charging roll can be used. By appropriately selecting these cleaning methods according to the contamination level of each image forming unit, an image forming apparatus with improved stability and high reliability can be realized.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a transfer image carrier to which each image formed by the plurality of image forming units is transferred, and the plurality of image forming units includes In at least one image forming unit arranged to transfer the images to the transfer image carrier in a predetermined order and transferring an image after the second of the plurality of image forming units, the cleaning member is the charging roll. It is characterized by the fact that it is an elastic roll that rotates and comes into contact with the cleaning roller.

  When the plurality of image forming units are arranged to transfer the formed images to a transfer image carrier such as an intermediate transfer member in a predetermined order, the image forming unit that transfers the image after the second transfer When the image that has already been transferred enters the image carrier, the charging roll easily becomes dirty.

  On the other hand, in the present invention, at least one image forming unit that transfers an image after the second of the plurality of image forming units has a high cleaning performance by using an elastic roll that rotates and contacts the charging roll. Thus, each of the image forming units can be cleaned satisfactorily while suppressing the difference in the contamination level of the charging roll of each image forming unit.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the at least one image forming unit forms a black image.

  In the image forming unit that forms a black image, the charging roll is more easily stained than the image forming unit that forms a color image due to the influence of the monochrome / color ratio in image formation.

  On the other hand, in the present invention, the image forming unit that forms a black image among the plurality of image forming units has a cleaning performance of the cleaning member of the charging roll with respect to, for example, another image forming unit that forms a color image. By using a high cleaning method, specifically, by using a cleaning member having high cleaning performance such as an elastic roll that rotates and contacts the charging roll, the contamination level of the charging roll of each image forming unit can be reduced. Each can be satisfactorily cleaned while suppressing the difference.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, in the at least one image forming unit of the other image forming units, the cleaning member is the It is characterized in that it can be brought into and out of contact with the charging roll.

  In the present invention, among the plurality of image forming units, for example, in the at least one image forming unit having a high contamination level of the charging roll, a cleaning method having a relatively high cleaning performance is used for the cleaning member of the charging roll, and contamination of the charging roll is performed. In the other image forming unit having a low level, in the configuration in which a cleaning method having a relatively low cleaning performance is used as the cleaning member for the charging roll, and in at least one of the other image forming units, The cleaning member that can be brought into and out of contact with the charging roll can be switched between a cleaning operation state at the time of contact and a non-cleaning operation state at the time of separation. As a result, it is possible to adjust the level of deterioration of the cleaning performance relative to the cleaning member that cannot be contacted / separated, and it is possible to better suppress the difference in the contamination level of the charging rolls of the image forming units.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus further includes a fixing unit that fixes the image formed by the image forming unit and transferred to a recording medium, and includes a plurality of image forming units. At least the image forming unit disposed closest to the fixing unit is characterized in that the cleaning member is an elastic roll that rotates and contacts the charging roll.

  In the image forming unit disposed in the vicinity of the fixing unit that fixes the image formed by the image forming unit and transferred to the recording medium, the temperature is likely to rise due to the conduction heat from the fixing unit during the fixing process, so that the image forming unit adheres to the charging roll. Contaminants such as external additives are easily fixed.

  On the other hand, in the present invention, at least the image forming unit disposed closest to the fixing unit among the plurality of image forming units provides high cleaning performance using an elastic roll that rotates and contacts the charging roll. Accordingly, it is possible to satisfactorily suppress the difference in the contamination level of the charging rolls included in each image forming unit while preventing the adhesion of the contaminants to the charging roll.

  According to a sixth aspect of the present invention, there is provided an image forming apparatus including a plurality of image forming units each including an image carrier, a charging roll that charges the image carrier, and a cleaning member that cleans the charging roll. One image forming unit is characterized in that the cleaning conditions by the cleaning member are different from those of the other image forming units.

  In the present invention, with respect to the cleaning member of each charging roll provided in the plurality of image forming units, at least one image forming unit cleans the other image forming units with the cleaning member according to the contamination level of each image forming unit. By varying the conditions (various parameters of the cleaning member), each of the charging rolls can be cleaned well while suppressing the difference in contamination level. Thereby, the stability of the entire apparatus is improved and high reliability can be obtained.

  As for the above cleaning conditions, the amount of biting of the cleaning member with respect to the charging roll, the nip width of the cleaning member with respect to the charging roll, the density of the cleaning member, the thickness of the cleaning member in contact with the charging roll, the hardness of the cleaning member, the cleaning member These materials can be used. The cleaning member may be an elastic roll that is formed into a roll shape with an elastic material and cleaned by rotating contact with the charging roll, a brush roll that is formed in a roll shape with a brush material and cleaned by rotating contact with the charging roll, and an elastic material. An elastic pad that is formed in a pad shape and is cleaned by contact with the charging roll, and a brush pad that is formed in a pad shape with a brush material and is cleaned by contact with the charging roll can be used. In this case, the outer diameter can be used as the cleaning condition, and in the case of a brush roll or brush pad, the brush fiber length can be used as the cleaning condition. By appropriately selecting these cleaning conditions according to the contamination level of each image forming unit, an image forming apparatus with improved stability and high reliability can be realized.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the image forming apparatus further comprises contact / separation means for contacting and separating the cleaning member with respect to the charging roll, and the contact and separation of the cleaning member are repeated at a predetermined interval. It is characterized by doing.

  In the present invention, among the plurality of image forming units, for example, in the at least one image forming unit having a high contamination level of the charging roll, cleaning conditions with relatively high cleaning performance are used for the cleaning member of the charging roll, and contamination of the charging roll is performed. In the other image forming unit having a low level, a configuration in which a cleaning condition having a relatively low cleaning performance is used for the cleaning member of the charging roll, or conversely, for example, the at least one image forming unit having a low contamination level of the charging roll, for example. Then, a cleaning condition with a relatively low cleaning performance is used for the cleaning member for the charging roll, and a cleaning condition with a relatively high cleaning performance is used for the cleaning member for the charging roll in the other image forming unit having a high contamination level of the charging roll. In such a configuration, further contact and separation By a cleaning member which is capable separable to the charging roller by the step, performed repeatedly at a separable predetermined intervals (time, number of prints, etc.). As a result, the cleaning operation state at the time of contact and the non-cleaning operation state at the time of separation can be switched, and the relative cleaning performance difference of each cleaning member can be adjusted, and the contamination level of the charging roll possessed by each image forming unit Difference can be suppressed more favorably.

  In addition, if the cleaning member is in contact with and separated from the charging roll (cleaning / non-cleaning) repeatedly according to the degree of contamination of the charging roll at predetermined intervals such as time and the number of prints, the contact and separation always in contact with each other. Compared to an impossible configuration, excessive contact more than necessary is avoided, and the durability of the charging roll can be improved while satisfying the required cleaning performance.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the different cleaning condition is an interval of a cleaning operation of the cleaning member.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the different cleaning condition is a cleaning operation time of the cleaning member.

  According to a tenth aspect of the present invention, in the image forming apparatus according to the seventh aspect, the different cleaning condition is whether or not the cleaning member is in contact with or separated from the charging roll.

  In the configuration in which the cleaning member is brought into contact with and separated from the charging roll, as in the inventions according to claims 8 to 10, the different cleaning conditions include the cleaning operation interval of the cleaning member and the cleaning operation of the cleaning member. The time and the presence / absence of the contact / separation operation of the cleaning member with respect to the charging roll can be determined. By appropriately setting these cleaning conditions according to the contamination level of each image forming unit, the difference in the contamination level of the charging roll of each image forming unit can be further suppressed, and the stability of the image forming apparatus can be suppressed. Improvement and high reliability can be achieved.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the sixth to tenth aspects, at least one image forming portion having different cleaning conditions by the cleaning member forms a black image. It is characterized by being a part.

  In the present invention, the image forming unit that forms the black image, which is the at least one image forming unit among the plurality of image forming units, cleans the charging roll with respect to other image forming units that form color images, for example. A cleaning condition with high cleaning performance is used for the member. Accordingly, each of the image forming units can be cleaned satisfactorily while suppressing the difference in the contamination level of the charging rolls included in each image forming unit.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to the eleventh aspect, the image forming unit that forms the black image has a plurality of rotational speeds of the image carrier during image formation.

  In the present invention, the image forming unit that forms a black image, which is the at least one image forming unit among the plurality of image forming units, has a plurality of rotational speeds of the image carrier during image formation. When forming a black and white image in which only the image forming unit that forms the black image operates, the image carrier can be rotated at a higher speed than when a color image is formed. Thereby, the productivity of monochrome image formation can be improved.

  Further, during the black-and-white image formation, the charging roll for charging the image carrier rotates at a high speed as the image carrier rotates, and is cleaned well by the cleaning member. As a result, an image forming unit that forms a black image in which the charging roll is more easily stained than an image forming unit that forms a color image due to the influence of the black / white / color ratio in image formation, and an image forming unit that forms a color image Thus, the difference in the contamination level of each charging roll can be suppressed.

  A thirteenth aspect of the present invention is the image forming apparatus according to any one of the sixth to twelfth aspects, further comprising a fixing unit that fixes the image formed by the image forming unit and transferred to a recording medium. And the image forming unit disposed closest to the fixing unit among the plurality of image forming units has a plurality of rotational speeds of the image carrier during image formation.

  In the present invention, the image forming unit disposed closest to the fixing unit among the plurality of image forming units has a plurality of rotation speeds of the image carrier during image formation. For example, the image forming unit is closest to the fixing unit. When forming an image by operating a plurality of image forming units at the time of forming a single color (for example, a specific color such as red, green, blue, brown, white, or black) in which only the arranged image forming unit operates As a result, the image carrier can be rotated at a higher speed. Thereby, the productivity of monochromatic image formation can be improved.

  Further, at the time of this monochromatic image formation, the charging roll for charging the image carrier rotates at a high speed as the image carrier rotates, and is well cleaned by the cleaning member. This prevents the contamination from adhering to the charging roll in the image forming unit disposed closest to the fixing unit, which is likely to increase in temperature due to the heat of conduction from the fixing unit. The difference in the contamination level of each charging roll between the image forming units separated from the means can be suppressed. Furthermore, an image forming unit that forms a monochromatic image in which the charging roll is more easily soiled than an image forming unit that forms a color image due to the influence of a single color (specific color, black, etc.) / Color ratio in image formation, and a color image A difference in contamination level of each charging roll between the image forming unit to be formed can be suppressed.

  According to a fourteenth aspect of the present invention, there is provided the image forming apparatus according to any one of the sixth to twelfth aspects, further comprising a fixing unit that fixes the image formed by the image forming unit and transferred to a recording medium. The at least one image forming unit having a different cleaning condition by the cleaning member is an image forming unit disposed closest to the fixing unit.

  In the present invention, at least one image forming unit that changes the cleaning condition by the cleaning member is an image forming unit that is disposed closest to the fixing unit among the plurality of image forming units. Cleaning conditions with relatively high cleaning performance are used for these cleaning members, and cleaning conditions with relatively low cleaning performance are used for the cleaning members of the charging rolls in other image forming units. This prevents the contamination from adhering to the charging roll in the image forming unit disposed closest to the fixing unit, which is likely to increase in temperature due to the heat of conduction from the fixing unit. The difference in the contamination level of each charging roll between the image forming units separated from the means can be suppressed.

  In the image forming apparatus of the present invention, the stability of the entire apparatus is improved, and high reliability capable of maintaining high-quality image formation over a long period of time is obtained.

  An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected and demonstrated to the structure which has the same function through all drawings, and the description is abbreviate | omitted depending on the case.

(First embodiment)
FIG. 1 shows a tandem type digital color printer 100 as an image forming apparatus according to the first embodiment of the present invention, and FIG. 2 shows an image forming apparatus according to the first embodiment of the present invention. A tandem type digital color copying machine 101 is shown.

  As shown in FIGS. 1 and 2, the digital color printer 100 and the copying machine 101 of this embodiment include a main body 1. In the case of the digital color copying machine 101, as shown in FIG. An automatic document feeder (ADF) 3 that automatically feeds the document 2 in a state where the documents 2 are separated one by one, and a document reading device 4 that reads an image of the document 2 conveyed by the automatic document feeder 3 are disposed at the top. Has been.

  The document reader 4 illuminates a document 2 placed on a platen glass 5 with a light source 6, and a reflected light image from the document 2 includes a full-rate mirror 7, half-rate mirrors 8 and 9, and an imaging lens 10. Scanning exposure is performed on the image reading element 11 composed of a CCD or the like via the reduction optical system, and the color material reflected light image of the document 2 is read by the image reading element 11 at a predetermined dot density (for example, 16 dots / mm). It is configured.

  The color material reflected light image of the document 2 read by the document reading device 4 is, for example, IPS (Image) as document reflectance data of three colors of red (R), green (G), and blue (B) (each 8 bits). IPS 12 performs predetermined images such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, etc. on the reflectance data of the document 2. Processing is performed. The IPS 12 is also configured to perform predetermined image processing on image data sent from a personal computer or the like.

  The image data that has been subjected to the predetermined image processing by the IPS 12 is processed by the IPS 12 in four color reproduction color materials of yellow (Y), magenta (M), cyan (C), and black (K) (8 bits each). It is converted into tone data and sent to the ROS (Raser Output Scanner) 14 of the image forming units 13Y, 13M, 13C, and 13K for each color of yellow (Y), magenta (M), cyan (C), and black (K). In the ROS 14 as the image exposure apparatus, image exposure with the laser beam LB is performed in accordance with document reproduction color material gradation data of a predetermined color.

  In addition, in the main body 1, four image forming units 13Y, 13M, 13C, and 13K of yellow (Y), magenta (M), cyan (C), and black (K) are spaced apart in the horizontal direction. Are arranged in parallel.

  These four image forming units 13Y, 13M, 13C, and 13K are configured in the same manner except for a cleaning member for the charging roll 16 described later, and are rotationally driven at a predetermined speed (for example, 200 mm / s). A photosensitive drum 15 as an image carrier, a charging roll 16 as a charging device for uniformly charging the surface of the photosensitive drum 15, a cleaning member for cleaning the charging roll 16, and a predetermined surface on the surface of the photosensitive drum 15. ROS 14 as an image exposure unit that exposes an image corresponding to each color to form an electrostatic latent image, and a developing unit that develops the electrostatic latent image formed on the photosensitive drum 15 with toner of a predetermined color. The developing device 17 and a cleaning device 18 for cleaning the surface of the photosensitive drum 15 are provided. These photosensitive drums 15 and the respective image forming members disposed around the photosensitive drum 15 are unitized as one unit, and are configured to be detachable from the main body 1 so that they can be individually replaced.

  As shown in FIGS. 1 and 2, the ROS 14 is configured in common to the four image forming units 13Y, 13M, 13C, and 13K, and four semiconductor lasers (not shown) are used as original reproduction color material gradation data for each color. According to the gradation data, laser light LB-Y, LB-M, LB-C, and LB-K are emitted from these semiconductor lasers. The ROS 14 may be configured individually for each of a plurality of image forming units.

  Laser beams LB-Y, LB-M, LB-C, and LB-K emitted from the semiconductor laser are applied to the polygon mirror 19 through an f-θ lens (not shown) and deflected and scanned. The laser beams LB-Y, LB-M, LB-C, and LB-K deflected and scanned by the polygon mirror 19 pass through an imaging lens (not shown) and a plurality of mirrors to an exposure point on the photosensitive drum 15. Then, scanning exposure is performed obliquely from below.

  As shown in FIG. 1, the ROS 14 is configured to scan and expose an image on the photosensitive drum 15 from below, so that the ROS 14 includes four image forming units 13Y, 13M, 13C, and 13K that are located above the developing unit 17 and the like. There is a risk that toner or the like may fall and be contaminated. Therefore, the ROS 14 is hermetically sealed by a frame 20 having a rectangular parallelepiped shape, and four laser beams LB-Y, LB-M, LB-C, and LB-K are formed on the upper portion of the frame 20 for image formation. In order to perform exposure on the photosensitive drums 15 of the units 13Y, 13M, 13C, and 13K, shield members 21Y, 21M, 21C, and 21K made of transparent glass are provided.

  Further, the image data of each color of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially input from the IPS 12 to the ROS 14 and emitted from the ROS 14 according to the image data. The surface of the corresponding photosensitive drum 15 is scanned and exposed by the laser beams LB-Y, LB-M, LB-C, and LB-K to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drum 15 are respectively developed in yellow (Y), magenta (M), cyan (C), and black (K) colors by developing units 17Y, 17M, 17C, and 17K. The toner image is developed.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K On the intermediate transfer belt 25 of the transfer unit 22 arranged over the forming units 13Y, 13M, 13C, and 13K, the images are transferred in multiple by the four primary transfer rolls 26Y, 26M, 26C, and 26K. These primary transfer rolls 26Y, 26M, 26C, and 26K are disposed on the back side of the intermediate transfer belt 25 corresponding to the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K. Further, a transfer bias power source (not shown) is connected to the primary transfer rolls 26Y, 26M, 26C, and 26K, and a transfer bias having a polarity opposite to a predetermined toner polarity (positive polarity in this embodiment) is set at a predetermined timing. Applied.

  As shown in FIG. 1, the intermediate transfer belt 25 is wound around a drive roll 27, a tension roll 24, and a backup roll 28 with a constant tension, and has a dedicated speed (not shown) excellent in constant speed. The drive roll 27 is rotationally driven by a drive motor and is circulated at a predetermined speed in the direction of the arrow. Further, as the intermediate transfer belt 25, for example, a belt whose resistance is adjusted with a belt material (rubber or resin) that does not cause charge-up is used.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 25 in a multiple manner are shown in FIG. The recording sheet 30 is secondarily transferred onto a recording sheet 30 as a recording medium by a secondary transfer roll 29 that is in pressure contact with the backup roll 28 disposed on the recording sheet 30 as a recording medium, and the toner images of these colors are transferred. Is conveyed to the fixing device 31 positioned above. The secondary transfer roll 29 is in pressure contact with the side of the backup roll 28, and secondarily transfers the toner images of the respective colors onto the recording paper 30 that is conveyed upward from below in the vertical direction. The recording paper 30 onto which the toner images of each color have been transferred is subjected to a fixing process by heating and pressing by a fixing device 31, conveyed by a discharge roll 32, and placed on a discharge tray 33 provided on the upper part of the main body 1. Discharged.

  The recording paper 30 is supplied from a paper feeding device 34 disposed in the lower part of the main body 1. In this embodiment, the recording paper 30 of a predetermined size is used for a nudger roll 35 and a paper separating and conveying sheet. The feed rolls 36 are once transported to a registration roll 38 provided in the paper transport path 37 in a state of being separated one by one and stopped. The sheet conveyance path 37 extends in the main body 1 from the lower part to the upper part in a substantially vertical direction, and the recording sheet 30 supplied from the sheet feeding device 34 to the sheet conveyance path 37 rotates at a predetermined timing. Is sent to the secondary transfer position of the intermediate transfer belt 25 by the resist roll 38.

  In the digital color printer 100 and the copying machine 101 of the present embodiment, when full-color double-sided copying is performed, the recording paper 30 with the image fixed on one side is discharged as it is onto the discharge tray 33 by the discharge roll 32. Instead, the conveyance direction is switched by a switching gate (not shown), and the sheet is conveyed to the duplex conveyance unit 40 via the sheet conveyance roll pair 39. In the double-sided conveyance unit 40, the recording paper 30 is conveyed again to the registration roll 38 in a state where the recording paper 30 is turned upside down by a conveyance roll pair (not shown) provided along the conveyance path 41. After the image is transferred and fixed to the back surface of the paper, it is discharged onto the discharge tray 33.

  In addition, toner cartridges 44Y and 44M that supply toner of a predetermined color to the developing device 17 of each color of yellow (Y), magenta (M), cyan (C), and black (K) are disposed in the upper portion of the main body 1. , 44C, 44K are disposed.

  FIG. 3 shows the image forming unit mounted in the digital color printer 100 and the copying machine 101.

  As shown in FIG. 3, each color image forming unit 13 (13Y, 13M, 13C, 13K) is provided with the above-described photosensitive drum 15, and the surface of each photosensitive drum 15 is uniformly provided by a charging roll 16. Is charged. After this charging, the surface of the photosensitive drum 15 is scanned and exposed with an image forming laser beam LB emitted from the ROS 14 according to image data, and an electrostatic latent image corresponding to each color is formed. The electrostatic latent image formed on the photoconductor drum 15 is yellow, magenta, cyan, and black by the developing rolls 17a of the developing units 17 of the image forming units 13Y, 13M, 13C, and 13K. The visible toner images are developed with the toners of the toner, and the visible toner images are sequentially transferred in multiple onto the intermediate transfer belt 25 by the charging of the primary transfer roll 26.

  Further, residual toner and the like are removed from the surface of the photosensitive drum 15 after the toner image transfer process is completed by the cleaning device 18 to prepare for the next image forming process. The cleaning device 18 includes a cleaning blade 42 and removes residual toner and the like on the photosensitive drum 15 by the cleaning blade 42. In addition, residual toner, paper dust, and the like are removed from the surface of the intermediate transfer belt 25 after the transfer of the toner image by the cleaning device 43 shown in FIGS. 1 and 2 to prepare for the next image forming process. The cleaning device 43 includes a cleaning brush 43a and a cleaning blade 43b. The cleaning brush 43a and the blade 42 remove residual toner, paper dust, and the like on the intermediate transfer belt 25.

  The image forming units 13Y, 13M, 13C, and 13K are provided with a cleaning member that cleans the roll surface of each charging roll 16. As shown in FIG. 21, in this embodiment, each charging roll 16 of the image forming units 13Y, 13M, and 13C holds a large number of brush fibers 59B shown in FIG. A brush pad (fixed brush cleaner) 59 formed and configured is used. The charging roll 16 of the image forming unit 13K has a roll-like sponge on the peripheral surface of the shaft 90A shown in FIG. A sponge roll 90 formed by forming the layer 90B is used.

  Here, the charging roll (BCR) 16 and the sponge roll 90 of this embodiment will be described.

  As described above, the charging roll 16 is disposed in contact with the surface of the photosensitive drum 15, and charges the surface of the photosensitive drum 15 by applying a DC voltage or an AC voltage to the DC voltage. Further, the shape is a roll shape in which a resistance elastic layer constituting the charging layer 16B is provided around the core constituting the shaft 16A, and the resistance elastic layer is formed from the outside and the elastic layer supporting them. A configuration in which the layers are divided in order is also possible. Furthermore, a protective layer can be provided on the outside of the resistance layer as needed to impart durability and contamination resistance to the charging roll 16.

  Hereinafter, the case where an elastic layer, a resistance layer, and a protective layer are provided on the core material will be described in more detail.

  The core material is conductive and generally used is iron, copper, brass, stainless steel, aluminum, nickel, or the like. Also, a material other than metal can be used as long as it has conductivity and appropriate rigidity. For example, a resin molded product in which conductive particles are dispersed, ceramics, or the like can be used. In addition to the roll shape, a hollow pipe shape can also be used.

  The elastic layer is made of a material having conductivity or semiconductivity, and generally is a material in which conductive particles or semiconducting particles are dispersed in a resin material or a rubber material. Polyester resin, acrylic resin, melamine resin, epoxy resin, urethane resin, silicon resin, urea resin, polyamide resin, etc. are used as the resin material, and ethylene-propylene rubber, polybutadiene, natural rubber are used as the rubber material. Polyisobutylene, chloroprene rubber, silicon rubber, urethane rubber, epichlorohydrin rubber, fluorosilicone rubber, ethylene oxide rubber, or a foamed material obtained by foaming them is used.

  Conductive particles or semiconductive particles include carbon black, zinc, aluminum, copper, iron, nickel, chromium, titanium and other metals, ZnO-Al2O3, SnO2-Sb2O3, In2O3-SnO2, ZnO-TiO2, MgO-Al2O3, Metal oxides such as FeO-TiO2, TiO2, SnO2, Sb2O3, In2O3, ZnO, MgO and ionic compounds such as quaternary ammonium salts can be used. These materials can be used alone or in combination of two or more. May be used. Furthermore, you may mix the 1 type (s) or 2 or more types of organic fillers, such as inorganic fillers, such as a talc, an alumina, and a silica, and the fine powder of a fluororesin or a silicon rubber, as needed.

  As the material of the resistance layer and the protective layer, conductive particles or semiconductive particles are dispersed in a binder resin to control the resistance. The resistivity is 10 ^ 3 to 10 ^ 14 Ωcm, preferably 10 ^ 5 10 ^ 12Ωcm, more preferably 10 ^ 7-10 ^ 12Ωcm. Moreover, as a film thickness, 0.01-1000 micrometers, Preferably it is 0.1-500 micrometers, More preferably, 0.5-100 micrometers is good. As binder resin, acrylic resin, cellulose resin, polyamide resin, methoxymethylated nylon, ethoxymethylated nylon, polyurethane resin, polycarbonate resin, polyester resin, polyethylene resin, polyvinyl resin, polyarylate resin, polythiophene resin, PFA, FEP, A polyolefin resin such as PET, a styrene butadiene resin, a melamine resin, an epoxy resin, a urethane resin, a silicon resin, a urea resin, or the like is used.

  As the conductive particles or the semiconductive particles, one or more of ionic compounds such as carbon black, metal, metal oxide, and quaternary ammonium salt exhibiting ionic conductivity, which are the same as those of the elastic layer, may be used. Mixed. If necessary, antioxidants such as hindered phenols and hindered amines, inorganic fillers such as clay, kaolin, talc, silica and alumina, organic fillers such as fine powder of fluororesin and silicon resin, silicone oil, etc. 1 type (s) or 2 or more types, such as a lubricant, can be added. Further, a surfactant, a charge control agent and the like are added as necessary.

  As a means for forming these layers, a blade coating method, a Meyer bar coating method, a spray coating method, a dip coating method, a bead coating method, an air knife coating method, a curtain coating method, or the like can be used.

  The sponge roll 90 is formed of a core material constituting the shaft 90A and a porous elastic layer constituting a sponge layer 90B formed on the peripheral surface of the core material, and contacts the surface of the charging roll 16 as described above. Arranged.

  As the material of the core material, a material that supports the porous elastic layer and has a rigidity that can maintain a contact state with an appropriate pressure contact force to the charging roll 16 is used. Generally, iron, copper, brass, In addition to metals such as stainless steel, aluminum, and nickel, resin molded products, ceramics, and the like in which conductive particles are dispersed, and inorganic fillers are dispersed. In addition to the roll shape, a hollow pipe shape can also be used.

  The porous elastic layer is a roll-like sponge formed at a predetermined cell density. For example, ether-based urethane foam, polyethylene foam, polyolefin foam, melamine foam, micropolymer, or the like can be used.

  Taking a polyurethane foam as an example, the production method will be briefly described. It is produced using a polyol, isocyanate, water, a catalyst (amine catalyst, metal catalyst, etc.) and a foam stabilizer (surfactant). Additives such as are used. When these raw materials are mixed and stirred, a chemical reaction occurs, and a urethane resin foam can be obtained.

  The sponge roll 90 is pressed against the charging roll 16 with a predetermined load, and the sponge layer 90B is elastically deformed along the peripheral surface of the charging roll 16 to form a nip portion. When the photosensitive drum 15 is driven to rotate, the charging roll 16 is driven to rotate as the photosensitive drum 15 rotates, and further, the sponge roll 90 is driven to rotate as the charging roll 16 rotates.

  Due to the rotational contact of the sponge roll 90, dirt (foreign matter) such as toner and external additives attached to the surface of the charging roll 16 is cleaned by the sponge roll 90. When the foreign matter is taken into the cell of the foam (sponge layer 90B) of the sponge roll 90 and the foreign matter collected in the cell is aggregated to an appropriate size, the sponge roll 90 passes through the charging roll 16. By returning to the photosensitive drum 15 and being collected by the cleaning device 18 that cleans the photosensitive drum 15, the maintenance of the cleaning performance is continued.

  In the digital color printer 100 and the copying machine 101 of the present embodiment configured as described above, the sponge roll with excellent long-term cleaning performance is provided by the image forming unit 13K disposed on the most downstream side in the moving direction of the intermediate transfer belt 25. By using 90, almost the same life could be achieved in all the image forming units.

  For comparison, when the brush pad 59 is used for the charging rolls 16 of all of the image forming units 13Y, 13M, 13C, and 13K, the black image forming unit 13K has streaky charging roll stains in the other color image forming units. This occurred earlier than the previous image, resulting in image quality defects. This is because if the image forming unit 13K is closest to the fixing device 31 and the external additive attached to the surface of the charging roll is not always removed, new problems such as sticking are likely to occur. Since the forming unit 13K forms an image in both the black and white and color modes, it is more likely that the external additive adheres than the other image forming units 13Y, 13M, and 13C.

  As described above, in the digital color printer 100 and the copying machine 101 according to the present embodiment, the image forming units 13Y, 13M, 13C, and 13K are used for the cleaning members of the charging rolls 16 included in the image forming units 13Y, 13M, 13C, and 13K. In the image forming unit 13K, the cleaning method using the cleaning member is different from that of the image forming units 13Y, 13M, and 13C in accordance with the contamination level of each of the image forming units 13K. Can be cleaned. Therefore, the stability of the entire apparatus is improved and high reliability can be obtained.

  In addition, in the image forming unit 13K that forms a black image, the charging roll 16 is more easily soiled than the image forming units 13Y, 13M, and 13C that form a color image due to the influence of the black / white / color ratio in image formation. In the image forming unit 13K of the embodiment, a sponge roll 90 having relatively high cleaning performance is used for cleaning by rotating contact with the charging roll 16, and in the image forming units 13Y, 13M, and 13C, cleaning is performed by sliding on the charging roll 16. By using the brush pad 59 having a relatively low cleaning performance, each of the image forming units can be cleaned satisfactorily while suppressing the difference in the contamination level of the charging roll 16 of each image forming unit.

  Further, in the image forming unit 13 </ b> K arranged close to the fixing device 31, the temperature easily rises due to conduction heat from the fixing device 31 during the fixing process, and thus contaminants such as external additives attached to the charging roll 16 are easily fixed. However, also in this case, the image forming unit 13K of the present embodiment uses a cleaning method with a relatively high cleaning performance for the charging roll 16, so that the contaminants adhere to the charging roll 16. It is possible to satisfactorily suppress the difference in the contamination level of the charging roll of each image forming unit.

(Second Embodiment)
In the second embodiment, in the tandem digital color printer 100 and the copying machine 101 of the first embodiment, as shown in FIG. 21, the image forming units 13Y, 13M, and 13C include the brush pad 59 described above. 9 and 17, the image forming unit 13 </ b> K is provided with a sponge roll 90 as in the first embodiment. I use it.

  Here, the charging device 50 of the present embodiment and the contact / separation means 62 that contacts and separates the cleaning member 54 (brush pad 59) with respect to the charging roll 16 included in the charging device 50 will be described.

  As shown in FIG. 4, the charging device 50 of this embodiment includes the above-described charging roll 16 and a housing member 51 that substantially covers one side surface and the lower end surface of the charging roll 16. As shown in FIG. 5, the housing member 51 is provided integrally with a side wall portion 52 covering one side surface of the charging roll 16 and both ends in the longitudinal direction of the side wall portion 52, and the metal shaft 16 </ b> A of the charging roll 16. And a cleaning member 54 that also serves as a bottom wall that covers the lower end surface of the charging roll 16. Note that a bearing member 55 that rotatably supports the metal shaft 16A of the charging roll 16 is attached to the bearing portion 53 here so as to be movable in a direction in which it is in contact with and away from the photosensitive drum 15. The bearing member 55 is urged in a direction approaching the photosensitive drum 15 by a coil spring 56 attached to the bearing portion 53.

  As shown in FIG. 6, the cleaning member 54 includes a flat plate portion 57 positioned on the lower side of the charging roll 16 and a side wall portion 58 standing upright from the left end of the flat plate portion 57. As shown in FIG. 7, a brush pad 59 is fixed to the upper surface 57a formed in a substantially chevron shape by means such as adhesion using a double-sided tape. As shown in FIGS. 5 and 7, the cleaning member 54 is attached to the bearing portion 53 of the housing member 51 so as to be rotatable around the shaft portion 60. The stopper 60a provided in the portion engages with the bearing portion 53, so that the stopper 60a stops in a state substantially orthogonal to the side wall portion 52 as shown in FIG. Further, as shown in FIG. 8, the cleaning member 54 rotates in the counterclockwise direction, and the front end portion 54 a in the width direction comes into contact with a stopper 61 provided on the lower end portion of the inner surface of the side wall portion 52. Is configured to stop.

  Further, in the main body 1 of the digital color printer 100 and the copying machine 101 of the present embodiment, as shown in FIGS. 9 and 10, a cleaning member 54 is rotated and is provided on the cleaning member 54 so as to be one of the cleaning members 54. A contact / separation means 62 is provided for contacting or separating the brush pad 59 constituting the part with the surface of the charging roll 16 at a predetermined timing.

  As shown in FIGS. 10 and 12, the contact / separation means 62 is disposed below the housing member 51 of the charging device 50 in each of the yellow, magenta, and cyan image forming units 13Y, 13M, and 13C. A cam-like member 63 is provided to drive the cleaning member 54 in a direction in which the cleaning member 54 contacts and separates from the surface of the charging roll 16.

  As shown in FIG. 13, the cam-like member 63 includes a shaft portion 64 formed in an elongated rod shape having a substantially circular cross section, and a narrow flat plate integrally formed along the longitudinal direction on the upper surface of the shaft portion 64. It is comprised by the part 65 and the mylar film (brand name) 66 which is a thin synthetic resin film-like member as an elastic member fixed on the flat plate part 65 by adhesion | attachment by a double-sided tape. As the mylar film 66, for example, a film having a thickness of 125 μm is used. The Mylar film 66 has a different thickness, and the Mylar film 66 is elastically deformed by changing the length of the free end. It is possible to adjust the pressing force to be brought into contact with.

  As shown in FIGS. 14 and 15, the cam-like member 63 is formed on a synthetic resin frame member 67 disposed below each of the image forming units 13Y, 13M, and 13C, with both ends of the shaft portion 64 as the center. It is rotatably attached and is configured to be rotated along the arrow direction by an arm portion 68 provided at one end of the cam-like member 63 in the axial direction. Then, as shown in FIG. 10, the cam-like member 63 rotates the cam-like member 63 by the arm portion 68 to push up the back surface of the cleaning member 54 by the mylar film 66, and the cleaning member 54 is moved to the position shown in FIG. The brush pad 59 provided on the cleaning member 54 is configured to contact the surface of the charging roll 16 by rotating in the counterclockwise direction. The mylar film 66 is easily elastically deformed (especially the central portion in the longitudinal direction) when the cleaning member 54 is rotated, and prevents the cleaning member 54 from rotating insufficiently. As shown in FIG. 11, a plurality of ribs 69 project from the center of the back surface of 54.

  In addition, the main body 1 of the digital color printer 100 and the copying machine 101 of the present embodiment has yellow (Y), magenta (M), and cyan (C) colors as shown in FIGS. 12 and 14 to 16. The image forming units 13Y, 13M, and 13C are provided with shutter members 70 that open and close the optical path of the image exposure apparatus (ROS14). As shown in FIG. 15, the shutter member 70 is rotated around a shaft portion 71 shown in FIG. 14 on a synthetic resin frame member 67 disposed below the image forming units 13Y, 13M, and 13C. It is movably attached and is configured to be opened and closed along the arrow direction by an arm member 72 made of a synthetic resin plate-like elastic member or the like provided at one end in the axial direction. The shutter member 70 is normally urged clockwise (closed direction) by an urging member 73 made of a coil spring or the like as shown in FIG. With the film-like member 74 in contact with the housing of the developing device 17, the optical path of the image exposure device (ROS) 14 is shielded, and dust such as toner falling from above adheres to the image exposure device 14. Is to prevent.

  Further, as shown in FIGS. 10 to 12, the main body 1 of the digital color printer 100 and the copying machine 101 of the present embodiment includes image forming units for each color of yellow (Y), magenta (M), and cyan (C). A drive mechanism 74 for contact / separation means 62 is disposed on the front side of 13Y, 13M, and 13C.

  The drive mechanism 74 includes a drive motor 75 including a pulse motor as a drive source on the front side of the image forming units 13Y, 13M, and 13C and on the side of the cyan image forming unit 13C. The drive gear 76 of the drive motor 75 is engaged with a fan-shaped gear 80 provided integrally with the lower end portion of the arm member 79 via two stages of reduction gears 77 and 78. The arm member 79 can swing along the direction of the arrow by rotating the drive motor 75 by a predetermined amount.

  Further, as shown in FIG. 12 and the like, an operating rod 81 made of a sheet metal formed in a state of being bent into a predetermined shape is connected to the distal end portion of the arm member 79. As shown in FIGS. 16 and 17, the actuating rod 81 is provided with a horizontal plate portion 83 connected to the arm member 79 by a first notch portion 82, and a state inclined obliquely downward from the horizontal plate portion 83. A short inclined plate portion 84, a connecting plate portion 85 provided horizontally at the end of the inclined plate portion 84, and a short operating plate portion 86 provided obliquely upward from the connecting plate portion 85. One set is formed continuously over the other two image forming units. Further, each horizontal plate portion 83 of the operating rod 81 is provided with a second notch portion 87 for driving the shutter member 70 at a predetermined position. As shown in FIG. 10 and the like, the arm member 79 is configured to directly push the arm portion 68 of the cam-like member 63 provided in the cyan image forming unit 13C by a projection 79a.

  As shown in FIG. 16 and the like, the actuating rod 81 is moved by a predetermined amount in the left direction in the figure, by the edge of the second notch 87 provided in each horizontal plate 83. The shutter member 70 is rotated counterclockwise via an operating plate-like member 72 provided at the end of the shutter member 70 to open the exposure portion. Further, as shown in FIG. 16 and the like, when the operating rod 81 moves by a predetermined amount in the right direction in the drawing, the operating rod 81 is moved by the edge of the second cutout portion 87 provided in each horizontal plate portion 83. The latching state of the plate member 72 for operation provided at the end of the shutter member 70 is released, and the shutter member 70 is rotated clockwise by the biasing force of the spring 73 to close the exposure unit. Has been.

  Further, as shown in FIG. 16 and the like, the actuating rod 81 is provided at the axial end of the cam-like member 63 when the actuating rod 81 moves further by a predetermined amount in the right direction in the figure. The arm portion 68 is pushed to rotate the cam-like member 63 by a predetermined amount in the counterclockwise direction. As a result, the cleaning member 54 of the charging roll 16 is rotated by the mylar film 66 of the cam-like member 63, and the brush pad 59 provided on the cleaning member 54 contacts the surface of the charging roll 16 as shown in FIG. Get in touch.

  In the present embodiment, the control means for changing the operation such as the cleaning operation time (contact time to the surface of the charging roll 16) and the cleaning interval (interval) by the cleaning member 54 according to the print mode, the number of prints, and the like. It has.

  As shown in FIG. 10, the digital color printer 100 and the copier 101 are provided with a control circuit 110 as a control means including a CPU or the like for controlling the operation of the entire apparatus, and the control circuit 110 includes the ROS 14 described above. Or a contact / separation circuit 112 that operates the drive motor 75 at a predetermined timing and contacts the cleaning member 54 with the surface of the charging roll 16 at a predetermined timing, a contact time, and an interval according to a print mode, etc. A process speed variable circuit 114 that changes the process speed according to the mode is connected.

  With the above configuration, the present embodiment can provide the same effects as those of the first embodiment. Further, in the image forming unit 13K where the contamination level of the charging roll 16 is high, a cleaning method (sponge roll 90) having a relatively high cleaning performance is used, and in the image forming units 13Y, 13M and 13C where the contamination level of the charging roll 16 is low, In a configuration using a cleaning method (brush pad 59) having a relatively low cleaning performance, the image forming units 13Y, 13M, and 13C perform cleaning at the time of contact by the brush pad 59 that can be brought into and out of contact with the charging roll 16. Since the operation state and the non-cleaning operation state at the time of separation can be switched, it is possible to adjust the level of deterioration of the cleaning performance relative to the sponge roll 90 in which the image forming unit 13K cannot be contacted / separated. Contamination of the charging roll 16 of the forming unit It can be better suppress different bell. In addition, by retracting the brush pad 59 of the image forming units 13Y, 13M, and 13C in the monochrome mode for forming a monochrome image, it is possible to avoid contact between the charging roll 16 and the brush pad 59 during non-image formation. In addition, the reliability of the color image forming units 13Y, 13M, and 13C is further improved.

(Third embodiment)
As shown in FIG. 19, in the image forming apparatus 200 according to the third embodiment, the outer diameter of the photosensitive drum 15 of the image forming unit 13K is larger than that of the image forming units 13Y, 13M, and 13C. The mode productivity is further improved. In this embodiment, as shown in FIG. 21, as a cleaning member for cleaning the charging roll 16 of the image forming unit 13K, a large number of brush fibers 92B shown in FIG. 18C are radially formed on the peripheral surface of the shaft 92A. The brush roll 92 formed and configured is used, and the above-described sponge roll 90 is used for each charging roll 16 of the image forming units 13Y, 13M, and 13C.

  As a result, the image forming apparatus 200 according to the present embodiment is faster than the digital color printer 100 and the copying machine 101 according to the first and second embodiments, and even when the ratio of the monochrome mode is larger than the color mode. By using different types of cleaning members (cleaning methods) for the color image forming units 13Y, 13M, and 13C and the image forming unit 13K, stable image formation can be performed over a long period of time. Further, it was confirmed that the same effect was obtained in the configuration in which two brush rolls 92 were provided on the charging roll 16 of the image forming unit 13K.

(Fourth embodiment)
As shown in FIG. 20, in the image forming apparatus 201 according to the present embodiment, four color image forming units 13Y, 13M, 13C, and 13K are accommodated in one cartridge 202, and a CRU (Customer replaceable Unit) is replaced. In this case, all the image forming units are simultaneously performed. Further, retransfer toner (toner whose polarity is reversed to a plus by the transfer roll and adheres again on the photosensitive drum 15) by the transfer system is most likely to enter the M-color image forming unit 13M. The charging roll 16 is most easily contaminated, and the other image forming units 13Y, 13C, and 13K have a problem that the CRU must be replaced even when no image defect occurs.

  Therefore, in the image forming apparatus 201 of the present embodiment, as shown in FIG. 21, the sponge roll 90 is used for the charging roll 16 of the image forming unit 13M, and the other image forming units 13Y, 13C, and 13K are used. By using the brush roll 92 for each of the charging rolls 16, contamination of the image forming unit is all reduced, and it is possible to maintain a state in which no image quality defect has occurred until the set CRU lifetime. Therefore, even in the image forming apparatus 201 having such a unit in which the four color image forming units are integrated, variation in the contamination level of each image forming unit can be minimized, and the life can be further extended. realizable. Thus, high reliability comes to be obtained by improving the stability of the whole apparatus.

  In the first to fourth embodiments described above, the cleaning method is a brush pad method in which the cleaning member is formed into a pad shape with the brush fibers 59B and is brought into contact with the charging roll 16 for cleaning. The cleaning member is a sponge layer 90B (elastic material) formed in a roll shape, and is a sponge roll 90 (elastic roll method) in which the charging roller 16 is rotated and brought into contact with the cleaning roller, and the cleaning member is a brush fiber 92B. Although the example of the brush roll system in which the brush roll 92 is formed in a roll shape and rotates and contacts the charging roll 16 for cleaning has been described as an example, it is also formed in a pad shape as shown in FIG. The sponge layer 94B is held by the holding member 94A, and the sponge pad 94 is configured. That the sponge pad system (elastic pad system) or the like can be used.

  Hereinafter, the fifth to tenth embodiments will be described. In the fifth to tenth embodiments, the image forming unit of the tandem digital color printer 100 and the copying machine 101 described in the first embodiment is used. The same type of cleaning member (method) is used for each of the 13Y, 13M, 13C, and 13K charging rolls 16, and the cleaning conditions of the cleaning member are varied.

(Fifth embodiment)
In the fifth embodiment, in the digital color printer 100 and the copying machine 101 described above, the same type of brush pad 59 is provided on each charging roll 16 of the image forming units 13Y, 13M, 13C, and 13K. However, as shown in FIG. 22, the biting amount of the brush pad 59 with respect to the charging roll 16 is 0.5 mm in the image forming units 13Y, 13M, and 13C, and is 0.75 mm in the image forming unit 13K. The charging roll 16 has a diameter of 12 mm, the brush pad uses a 48T nylon yarn and 44T conductive polyester mixed woven brush pad, has a width of 6 mm, a fiber length of 3 mm, and the same configuration except for the amount of biting.

  As described above, the cleaning method is the same for each image forming unit, and the cleaning conditions are different. That is, the image forming unit 13K performs image formation in both the monochrome mode and color, and thus other image forming units 13Y. , 13M, 13C, and the charging roll 16 is more dirty. However, by setting the cleaning performance higher than that of the image forming units 13Y, 13M, 13C, a sufficient cleaning effect can be obtained. Become.

  However, in this configuration, the encroaching amount of the brush roll 92 is increased in the image forming unit 13K, so that the damage to the charging roll 16 is larger than that in the image forming units 13Y, 13M, and 13C, and the charging roll surface layer is peeled off at 60 kpv. The image defect by was confirmed. At this time, no image defect was observed in the image forming units 13Y, 13M, and 13C.

  Therefore, when only the CRU of the image forming unit 13K is replaced with a new one and the other image forming units 13Y, 13M, and 13C are further used as they are, the image forming units 13Y, 13M, and 13C are slightly different from each other, but at around 60 kpv. A streaky charging roll stain occurred. In this way, almost the same life was obtained in all the image forming units 13Y, 13M, 13C, and 13K, and a long life could be achieved.

  For comparison, when the brush roll 92 is set and used with the same biting amount of 0.5 mm as the target value for all colors, streaky charging roll stains are observed in the other color image forming units in the black image forming unit 13K. Compared with that, it occurred earlier (30 kpv), resulting in image quality defects. Also in this case, in the image forming unit 13K closest to the fixing device 31 described above, if the charging roll is not always cleaned, the external additive attached to the roll surface tends to adhere, or black and white and color. In the image forming unit 13K that performs image formation in both modes, it is mentioned that external additives are more likely to adhere than the other image forming units 13Y, 13M, and 13C. In this case as well, when only the CRU of the image forming unit 13K is replaced with a new one and the operation is continued, the image forming units 13Y, 13M, and 13C slightly differ from each other, but streaky charging roll stains occur at around 60 kpv.

  Further, for comparison, when the brush roll 92 is set to the same value of 0.75 mm with the target value of 0.75 mm for all colors, the image forming unit 13Y, 13M, and 13C has an early image defect due to peeling of the charging roll surface layer. (Around 40 kpv).

  The reason why the surface layer peeling life is 40 kpv shorter than 60 kpv in the image forming unit 13K is that the image forming units 13Y, 13M, and 13C are more attached to the charging roll 16 than the image forming unit 13K due to the difference in image forming frequency. This is because the surface of the charging roll surface layer is exposed more and is easily scraped off by the brush.

  Similarly, other conditions for improving the cleaning ability of the cleaning member of the charging roll 16, specifically, as shown in FIG. 22, increase in the density and hardness of the brush and pad, increase in nip width and pad width, In some cases, such as shortening of the fiber length, it is applied only to the K-color image forming unit 13K to increase the cleaning capability, so that almost the same life is obtained in all the image forming units 13Y, 13M, 13C, and 13K by the same effect as described above. Can be achieved.

(Sixth embodiment)
In the sixth embodiment, the brush pads 59 of all the image forming units 13Y, 13M, 13C, and 13K are brought into contact with the charging roll 16 by using the contact / separation means 62 (retract mechanism) described in the second embodiment. The cleaning operation is performed at a predetermined interval and a contact time. As a result, the life against the peeling of the surface layer of the charging roll is extended, and a substantially long life (approximately 80 kpv) can be achieved in all the image forming units 13Y, 13M, 13C, and 13K.

(Seventh embodiment)
In the seventh embodiment, as in the comparative example of the fifth embodiment, the contact load (pressing force) of the cleaning member is the same for all the image forming units 13Y, 13M, 13C, and 13K. As shown, the cleaning interval is shortened only for the image forming unit 13K. Also by this, it is possible to obtain an effect that the lifetimes are averaged equally (60 kpv) in all the image forming units 13Y, 13M, 13C, and 13K.

(Eighth embodiment)
In the eighth embodiment, as shown in FIG. 22, in the image forming units 13Y, 13M, and 13C, the amount of biting of the sponge roll 90 (EP70: made by Inoac, sponge thickness 2 mm) into each charging roll 16 is set to 0. 5 mm and 0.75 mm in the image forming unit 13K. The charging roll 16 is φ12 mm, the urethane sponge is φ10 mm, and the configuration is the same except for the amount of biting.

  As described above, since the image forming unit 13K forms an image in both the monochrome mode and the color mode, the printing frequency is higher than that of the other image forming units 13Y, 13M, and 13C. Since the contamination level of the charging roll 16 increases as the printing frequency increases, the image forming unit 13K is set to have higher cleaning performance than the image forming units 13Y, 13M, and 13C. As a result, sufficient cleaning performance was obtained even in the image forming unit 13K.

  However, in this case as well, the image formation unit 13K increases damage to the charging roll 16 as compared with the image forming units 13Y, 13M, and 13C, and an image defect due to peeling of the charging roll surface layer appears at 80 kpv. Such image defects did not appear for the image forming units 13Y, 13M, and 13C. Thus, although there was a difference in maintainability, since the image forming unit 13K is frequently used, the replacement frequency is also high, and the maintainability required for the K color is satisfactory.

(Ninth embodiment)
In the ninth embodiment, as shown in FIG. 22, in the image forming units 13Y, 13M, and 13C, a sponge roll having a relatively low 0.5 mm compressive load of around 50 gf is used instead of the eighth embodiment. 90 (RR26: manufactured by Inoac, sponge thickness 2 mm), and the amount of biting is 0.75 mm. The image forming unit 13K is made of the same urethane sponge as in the eighth embodiment and uses a relatively hard material compared to the urethane sponge having a 0.5 mm compression load of about 80 gf to 100 gf, and has a bite amount of 0.75 mm. .

  As a result of using these conditions, sufficient cleanability was obtained for each color by changing the material and hardness even when the amount of biting was the same, as in the fifth embodiment. In terms of maintainability, the same result was obtained by reducing the bite amount of a relatively hard material even if the bite amount was the same.

(Tenth embodiment)
In the tenth embodiment, as shown in FIG. 22, for the image forming units 13Y, 13M, and 13C, the charging roll 16 has an outer diameter of φ12 mm, the sponge roll 90 has an outer diameter of φ10 mm (sponge thickness 2 mm), and the amount of biting is reduced. For the image forming unit 13K, the charging roll 16 has an outer diameter of φ12 mm, the sponge roll 90 has an outer diameter of φ12 mm (sponge thickness of 3 mm), and the biting amount is 0.5 mm.

  As a result of using these conditions, the amount of biting in the image forming unit 13K is the same as that of the image forming units 13Y, 13M, and 13C, but the contact area (nip width) between the charging roll 16 and the sponge roll 90 is increased, and image formation is performed. A sufficient cleaning performance was obtained even with the unit 13K. Further, since the amount of biting in the image forming unit 13K is not different from that of the image forming units 13Y, 13M, and 13C of other colors, the damage is the same and the maintainability is the same in all colors.

  However, by increasing the diameter of the sponge roll 90, it is necessary to secure an installation space around the charging roll of the CRU in the image forming unit 13K. However, in the case of the image forming unit 13K, the space is easier to secure than the image forming units 13Y, 13M, and 13C because the image forming unit 13K is disposed in a relatively wide space on the most downstream side in the moving direction of the intermediate transfer belt. Problems such as a limited shape can be avoided.

  As described above, due to the configuration unique to the apparatus such as being close to the fixing device 31 and being easily affected by heat, the degree of progress of the charging roll 16 stains differs between the image forming units 13Y, 13M, 13C, and 13K. However, by appropriately selecting the cleaning method described in the first to fourth embodiments and the cleaning conditions described in the fifth to tenth embodiments for each image forming unit, or By appropriately combining these cleaning methods and conditions, it is possible to achieve a long life while aligning the life of all the image forming units 13Y, 13M, 13C, and 13K.

  The present invention has been described in detail with reference to the first to tenth embodiments. However, the present invention is not limited to these embodiments, and various other modes can be implemented within the scope of the present invention. is there.

1 is a configuration diagram showing a digital color printer as an image forming apparatus according to a first embodiment of the present invention. 1 is a configuration diagram showing a digital color copying machine as an image forming apparatus according to a first embodiment of the present invention. 1 is a configuration diagram illustrating an image forming unit of an image forming apparatus according to a first embodiment of the present invention. FIG. 6 is a perspective view showing a charging roll of an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a perspective view illustrating a charging roll housing of an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a perspective view illustrating a cleaning member of an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a perspective view illustrating a cleaning member of an image forming apparatus according to a second embodiment of the present invention. FIG. 6 is a perspective view illustrating a charging roll housing of an image forming apparatus according to a second embodiment of the present invention. It is a perspective view which shows the principal part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a block diagram which shows schematic structure of the retract mechanism which concerns on the 2nd Embodiment of this invention. It is a front view which shows the principal part of the retract mechanism which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the principal part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the cam-shaped member of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the principal part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the principal part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the principal part of the image forming apparatus which concerns on the 2nd Embodiment of this invention. It is a perspective view which shows the action | operation rod which concerns on the 2nd Embodiment of this invention. (A)-(B) is a front view showing a plurality of types of cleaning members used in the image forming apparatus of the present invention. It is a block diagram which shows schematic structure of the image forming apparatus which concerns on the 3rd Embodiment of this invention. It is a block diagram which shows schematic structure of the image forming apparatus which concerns on the 4th Embodiment of this invention. FIG. 6 is a table showing cleaning methods for image forming units of respective colors in the image forming apparatuses according to the first to fourth embodiments of the present invention. In the image forming apparatus according to the fifth to tenth embodiments of the present invention, it is a table showing the cleaning conditions for each color image forming unit.

Explanation of symbols

13Y Image forming unit (image forming unit)
13M image forming unit (image forming unit)
13C image forming unit (image forming unit)
13K image forming unit (image forming unit)
15 Photosensitive drum (image carrier)
16 Charging roll 16A Shaft 16B Charging layer 25 Intermediate transfer belt (transfer image carrier)
30 Recording paper (recording medium)
31 Fixing device (fixing means)
54 Cleaning member 59 Brush pad (cleaning member)
59B Brush fiber 59A Holding member 62 Contacting / separating means 90 Sponge roll (cleaning member)
90A Shaft 90B Sponge layer 92 Brush roll (cleaning member)
92A Shaft 92B Brush fiber 94 Sponge pad (cleaning member)
94A Holding member 94B Sponge layer 100 Digital color printer (image forming apparatus)
101 Digital color copier (image forming device)
200 Image forming apparatus 201 Image forming apparatus

Claims (14)

In an image forming apparatus comprising a plurality of image forming units each having an image carrier, a charging roll that charges the image carrier, and a cleaning member that cleans the charging roll.
The image forming apparatus according to claim 1, wherein the cleaning method of the at least one image forming unit is different from that of the other image forming units. The image forming unit further includes a transfer image carrier to which each image formed by the plurality of image forming units is transferred, and the plurality of image forming units are arranged to transfer the images to the transfer image carrier in a predetermined order,
The at least one image forming unit that transfers an image after the second of the plurality of image forming units is characterized in that the cleaning member is an elastic roll that rotates and contacts the charging roll. Item 2. The image forming apparatus according to Item 1.   The image forming apparatus according to claim 1, wherein the at least one image forming unit forms a black image.   The at least one image forming unit among the other image forming units is configured such that the cleaning member can be brought into contact with and separated from the charging roll. The image forming apparatus according to Item. A fixing unit for fixing the image formed by the image forming unit and transferred to the recording medium;
The at least one of the plurality of image forming units disposed closest to the fixing unit is an elastic roll in which the cleaning member rotates and contacts the charging roll for cleaning. The image forming apparatus according to 1. In an image forming apparatus comprising a plurality of image forming units each having an image carrier, a charging roll that charges the image carrier, and a cleaning member that cleans the charging roll.
The image forming apparatus according to claim 1, wherein the cleaning condition of the cleaning member is different in at least one image forming unit from other image forming units.   The image forming apparatus according to claim 6, further comprising a contact / separation unit configured to contact and separate the cleaning member with respect to the charging roll, and repeatedly performing contact and separation of the cleaning member at a predetermined interval.   The image forming apparatus according to claim 7, wherein the different cleaning condition is an interval of a cleaning operation of the cleaning member.   9. The image forming apparatus according to claim 7, wherein the different cleaning condition is a cleaning operation time of the cleaning member.   The image forming apparatus according to claim 7, wherein the different cleaning condition is whether or not the cleaning member is in contact with or separated from the charging roll.   11. The image forming apparatus according to claim 6, wherein at least one image forming unit having different cleaning conditions by the cleaning member is an image forming unit that forms a black image.   The image forming apparatus according to claim 11, wherein the image forming unit that forms the black image has a plurality of rotational speeds of the image carrier during image formation. A fixing unit for fixing the image formed by the image forming unit and transferred to the recording medium;
13. The image forming unit disposed closest to the fixing unit among the plurality of image forming units has a plurality of rotational speeds of the image carrier at the time of image formation. The image forming apparatus according to claim 1. A fixing unit for fixing the image formed by the image forming unit and transferred to the recording medium;
13. The image according to claim 6, wherein the at least one image forming unit having different cleaning conditions by the cleaning member is an image forming unit disposed closest to the fixing unit. Forming equipment.

Images