JP2011033761A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which hardly causes leakage of current between a pre-transfer guide and transfer material and can form an image of high quality as a result. <P>SOLUTION: The pre-transfer guide 24 includes a pre-transfer guide body 25 comprising insulating resin member and a conductive sheet 26 which is made to adhere to an inclined leading end portion of the pre-transfer guide body 25 by a conductive double-sided tape 27. The conductive sheet 26 is provided so as to project downstream of the pre-transfer guide body 25 in the conveying direction of paper P. The double-sided tape using aluminum foil base material and conductive adhesive is used as the conductive double-sided tape 27. Furthermore, the image forming apparatus satisfies h≤i, wherein h represents the distance from the distal end of the conductive sheet 26 to an exit of a secondary transfer nip portion N; and i represents the length of a minimum margin at a tail end of the paper P. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

  As a conventional image forming apparatus, formed between an image carrier (photosensitive drum), a biased transfer member (transfer roller) disposed opposite to the image carrier, and the image carrier and the transfer member. There is a pre-transfer guide for guiding a sheet to the transferred transfer nip (Patent Document 1). The pre-transfer guide includes a pre-transfer guide plate on the transfer member side and a pre-transfer guide plate on the image carrier side. As a material for these pre-transfer guide plates, a resin member whose resistance is adjusted by adding carbon is used, and this pre-transfer guide is grounded. The pre-transfer guide plate on the image carrier side is provided with a sheet-like semiconductive member. The pre-transfer guide plate on the transfer member side is in contact with the pre-transfer guide plate on the image carrier side via the semiconductive member.

JP 2006-195193 A

  However, in this configuration, if the pre-transfer guide plate on the transfer member side is too close to the transfer member, there is a problem in that leakage occurs between the pre-transfer guide plate and the transfer member. In addition, if the pre-transfer guide plate on the transfer member side is arranged at a position away from the transfer member, the trailing edge of the sheet falls in the transfer nip tangential direction at the moment when it passes through the pre-transfer guide plate. And there was a problem of missing transfer.

  Therefore, a main object of the present invention is to provide an image forming apparatus that is unlikely to leak between the pre-transfer guide and the transfer member and that can form a high-quality image.

  According to the first aspect of the present invention, an image carrier, a transfer member disposed opposite to the image carrier and applied with a bias, and a transfer nip formed between the image carrier and the transfer member are provided with paper. An image forming apparatus provided with a pre-transfer guide for guiding, wherein the pre-transfer guide protrudes downstream of the pre-transfer guide main body made of an insulating resin member and the pre-transfer guide main body in the sheet conveying direction. An image forming apparatus comprising: a conductive member provided.

  According to the first aspect of the present invention, since the pre-transfer guide body is made of an insulating resin member, current leakage is unlikely to occur between the pre-transfer guide and the biased transfer member. On the other hand, the sheet is guided to the transfer nip portion by the conductive member protruding to the downstream side in the sheet conveyance direction of the guide body before transfer.

  In general, when the pre-transfer guide made entirely of an insulating resin member is brought close to the transfer nip portion, a part of the toner on the image carrier moves to the pre-transfer guide due to static electricity of the pre-transfer guide itself. Adhere to. Since the pre-transfer guide is in sliding contact with the back surface of the paper, the back surface of the paper is soiled by the toner adhering to the pre-transfer guide. However, as in the present invention, by projecting the conductive member downstream of the guide body before transfer in the paper conveyance direction, the toner on the image carrier becomes difficult to move to the conductive member, and the toner adheres to the conductive member. It becomes difficult to do. Therefore, contamination of the back side of the paper due to toner is suppressed. On the other hand, since the pre-transfer guide body made of an insulating resin member is far away from the transfer member, even if the pre-transfer guide body itself has static electricity, a part of the toner on the image carrier is pre-transfer guide. It is difficult to move to the main body, and the toner does not easily adhere to the pre-transfer guide main body.

  A second aspect of the invention is an image forming apparatus according to the first aspect of the invention, wherein the conductive member is a conductive sheet.

  In the invention of claim 2, since the conductive member is in the form of a sheet, the conductive member can be brought closest to the transfer nip portion, and the sheet can be smoothly guided to the vicinity of the transfer nip portion by the conductive member. Further, even when the rear end of the sheet passes through the pre-transfer guide, it is difficult to fall in the transfer nip tangential direction. Therefore, it is possible to prevent the occurrence of transfer defects such as horizontal stripes and transfer omission in the formed image of the paper.

  The invention according to claim 3 is an invention dependent on the invention according to claim 1 or claim 2, wherein the distance from the leading end of the conductive member to the exit of the transfer nip portion is h, and the minimum margin length of the trailing edge of the sheet An image forming apparatus, wherein h ≦ i, where i is i.

  In the invention of claim 3, since h ≦ i, where h is the distance from the leading edge of the conductive member to the exit of the transfer nip portion and i is the minimum margin length of the trailing edge of the paper, an image is formed on the paper. During this time, the trailing edge of the sheet does not move away from the guide before transfer, and the trailing edge of the sheet can be supported by the guide before transfer. Accordingly, it is possible to reliably prevent transfer failure at the trailing edge of the sheet.

  According to the present invention, since the guide body before transfer is made of an insulating resin member, current leakage hardly occurs between the guide before transfer and the transfer member to which a bias is applied. Further, by projecting the conductive member to the downstream side of the pre-transfer guide body in the paper conveyance direction, the toner on the image carrier becomes difficult to move to the pre-transfer guide (conductive member), and the toner adheres to the pre-transfer guide. It becomes difficult. Accordingly, it is possible to suppress the stain on the back side of the paper due to the toner. As a result, a leak hardly occurs between the pre-transfer guide and the transfer member, and high-quality image formation can be performed.

  The above-described object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

1 is a schematic configuration diagram illustrating an image forming apparatus according to the present invention. It is a principal part expansion schematic block diagram of the guide vicinity before transfer.

  FIG. 1 is a schematic configuration diagram showing an intermediate transfer tandem type color image forming apparatus. The endless intermediate transfer belt 8 is supported by a primary transfer roller 6a, 6b, 6c, 6d, a driven roller 10, a drive roller 11, a tension roller 20 and a backup roller 22 so as to be rotatable in the clockwise direction. The drive roller 11 is paired with the secondary transfer roller 9 with the intermediate transfer belt 8 interposed therebetween. A cleaning device 18 for removing toner remaining on the intermediate transfer belt 8 is disposed on the outer peripheral surface of the intermediate transfer belt 8.

  Below the intermediate transfer belt 8, image forming units for magenta, cyan, yellow, and black are arranged in a row at substantially constant intervals. The photosensitive drums 1a, 1b, 1c, and 1d for magenta, cyan, yellow, and black are driven counterclockwise at a predetermined speed by a driving unit. Near the outer periphery of each of the photosensitive drums 1a, 1b, 1c, and 1d, chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a, 1b, 1c, and 1d, and developing devices 3a, 3b, 3c, and 3d, rubbing members 5a, 5b, 5c and 5d are provided for removing the toner remaining on the photosensitive drums 1a, 1b, 1c and 1d.

  Laser light L emitted from the laser scanning unit 4 is irradiated onto the photosensitive drums 1a, 1b, 1c, and 1d to form an electrostatic latent image. On the downstream side of the laser scanning unit 4, developing devices 3a, 3b, 3c, 3d are arranged. The developing devices 3a, 3b, 3c, and 3d are for applying magenta, cyan, yellow, and black toners to the photosensitive drums 1a, 1b, 1c, and 1d, respectively.

  The electrostatic latent image on the photosensitive drum 1a is developed by the developing device 3a and visualized as a magenta toner image. The visualized magenta toner image on the photosensitive drum 1a is primarily transferred onto the intermediate transfer belt 8 by applying a voltage having a polarity opposite to that of the toner to the primary transfer roller 6a. When the magenta toner image for one page is primarily transferred onto the intermediate transfer belt 8, the intermediate transfer belt 8 further rotates, and the above process is sequentially performed for each color of cyan, yellow, and black. A toner image is formed to overlap.

  A paper feed cassette 16 capable of stacking and storing a large number of frequently used standard paper sheets is disposed at the lower part of the image forming apparatus, and special paper (OHP) that is used less frequently is disposed on the side surface of the image forming apparatus. A manual feed tray (manual paper feeder) 36 on which sheets, postcards, cardboard, etc.) can be stacked is provided.

  When printing on standard paper, the pickup roller 12 feeds paper from the paper feed cassette 16. The sheet is suddenly changed in direction and conveyed to a main conveyance path 31 extending in a substantially vertical direction along the left side of the image forming apparatus. The paper passes through the conveying roller pair 32 and is once waited in front of the secondary transfer roller 9 by the registration roller pair 44, and then guided by the pre-transfer guide 24 and superimposed on the intermediate transfer belt 8. The combined color toner image of magenta, cyan, yellow, and black is secondarily transferred by the secondary transfer roller 9 to which a voltage having a polarity opposite to that of the toner is applied, and is carried into the fixing device 13. The sheet to which the composite color toner image has been transferred is fixed by the fixing device 13, discharged as a color print by the discharge roller pair 15 and stacked on the discharge tray 17.

  On the other hand, when printing on special paper (OHP sheet, postcard, cardboard, etc.), the pickup roller 37 feeds the paper from the manual feed tray 36. The sheet is conveyed along the bypass conveyance path 35. The bypass conveyance path 35 is extended in a substantially horizontal direction so as not to suddenly change the direction in consideration of the fact that a variety of sheets are likely to cause a paper feed failure, and joins the main conveyance path 31 from the middle. Thus, a shared portion is provided between the main transport path 31 and the main transport path 31. The sheet passes through a pair of conveying rollers (bypass roller pair) 40, 41, 42 and an intermediate roller pair 43, and is temporarily held by the registration roller pair 44 before the secondary transfer roller 9 and then guided by the pre-transfer guide 24. Then, the combined color toner image of magenta, cyan, yellow, and black superimposed on the intermediate transfer belt 8 is secondarily transferred by the secondary transfer roller 9 and carried into the fixing device 13. The sheet to which the composite color toner image has been transferred is fixed by the fixing device 13, discharged as a color print by the discharge roller pair 15 and stacked on the discharge tray 17.

  Next, the pre-transfer guide 24 will be described with reference to FIG. The pre-transfer guide 24 includes a pre-transfer guide main body 25 made of an insulating resin member, and a conductive sheet 26 bonded to the inclined front end portion of the pre-transfer guide main body 25 with a conductive double-sided tape 27. The conductive sheet 26 is provided so as to protrude to the downstream side in the transport direction of the paper P of the guide body 25 before transfer. As the conductive double-sided tape 27, a double-sided tape using an aluminum foil base material and a conductive adhesive (in the case of this embodiment, # 8530AD manufactured by DIC Corporation) is used. By disposing the aluminum foil base material of the conductive double-sided tape 27 between the pre-transfer guide body 25 and the conductive sheet 26, the potential of the entire conductive sheet 26 can be made uniform uniformly.

  The pre-transfer guide 24 having the above configuration suppresses the occurrence of current leakage between the pre-transfer guide 24 and the biased secondary transfer roller 9 because the pre-transfer guide body 25 is made of an insulating resin member. Can do. On the other hand, the sheet P is guided to the secondary transfer nip portion N constituted by the intermediate transfer belt 8 and the secondary transfer roller 9 by the conductive sheet 26 protruding to the downstream side of the pre-transfer guide body 25 in the sheet conveyance direction. The

By protruding the conductive sheet 26 to the downstream side of the pre-transfer guide body 25 in the paper conveyance direction, the toner on the intermediate transfer belt 8 is less likely to move to the conductive sheet 26 and the toner is less likely to adhere to the conductive sheet 26. . Therefore, even when the conductive sheet 26 is in sliding contact with the back surface of the paper P, the back surface of the paper due to the toner adhering to the pre-transfer guide 26 can be suppressed. Specifically, it is preferable to use, for example, a transparent conductive PET resin having a surface resistance of 1 × 10 ¹³ Ω / □ or less as the conductive sheet 26. As a result, even when the conductive sheet 26 is brought close to the intermediate transfer belt 8, the conductive sheet 26 can be prevented from being charged, and the toner on the intermediate transfer belt 8 becomes difficult to move to the conductive sheet 26. It is possible to prevent a problem that the back surface of P is stained. Note that the electrostatic charge generated in the conductive sheet 26 disappears by natural discharge.

  On the other hand, since the pre-transfer guide body 25 made of an insulating resin member is far away from the secondary transfer roller 9, even if the pre-transfer guide body 25 itself has static electricity, the toner on the intermediate transfer belt 8 remains. It is difficult to move to the pre-transfer guide body 25 and the toner hardly adheres to the pre-transfer guide body 25.

  Further, since the conductive sheet 26 is thin, the conductive sheet 26 can be closest to the secondary transfer nip N, and the conductive sheet 26 can smoothly guide the paper P to the vicinity of the secondary transfer nip N. it can. Further, even when the trailing edge of the paper P passes through the pre-transfer guide 24, it is difficult to fall in the tangential direction of the secondary transfer nip. Accordingly, it is possible to prevent the occurrence of transfer defects such as horizontal stripes and transfer omission in the formed image on the paper P.

  Specifically, the thickness of the conductive sheet 26 is preferably set to 80 to 300 μm. By setting the thickness of the conductive sheet 26 to 300 μm or less, the conductive sheet 26 can be brought closest to the secondary transfer nip portion N, and the sheet P is placed near the entrance of the secondary transfer nip portion N by the conductive sheet 26. Can be guided smoothly. On the other hand, if the thickness of the conductive sheet 26 is too thin, the mechanical strength of the conductive sheet 26 cannot withstand the weight of the paper P, the conductive sheet 26 bends, and the conductive sheet 26 is formed on the secondary transfer roller 9. There is a worry to touch. However, by setting the thickness of the conductive sheet 26 to 80 μm or more, the mechanical strength that can sufficiently support the paper P can be secured, and the conductive sheet 26 does not bend. There is no worry that the conductive sheet 26 comes into contact.

  In the case of the present embodiment, when the distance from the leading edge of the conductive sheet 26 to the outlet of the secondary transfer nip portion N is h and the minimum trailing edge margin length of the paper P is i, h ≦ i. Is set. For example, the distance h is about 3 mm, and the rear end minimum margin length i is about 4 mm. As a result, while the image is formed on the paper P, the trailing edge of the paper P is not separated from the pre-transfer guide 24 (conductive sheet 26), and the pre-transfer guide 24 (conductive sheet 26) prevents the paper P from being separated. Can support the rear end. Accordingly, it is possible to reliably prevent transfer failure at the trailing edge of the paper P.

  Further, by creating the main body of the pre-transfer guide 24 with an insulating resin member, the pre-transfer guide 24 can be produced at a lower cost than when the entire pre-transfer guide 24 is formed with a conductive member.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is carried out within the range of the summary.

8 Intermediate transfer belt (image carrier)
9 Secondary transfer roller 24 Pre-transfer guide 25 Pre-transfer guide body 26 Conductive sheet (conductive member)
N Secondary transfer nip

Claims (3)

An image carrier, a biased transfer member disposed opposite to the image carrier, and a transfer for guiding a sheet to a transfer nip formed between the image carrier and the transfer member; An image forming apparatus comprising a front guide,
The pre-transfer guide includes a pre-transfer guide main body made of an insulating resin member, and a conductive member provided so as to protrude downstream of the pre-transfer guide main body in the sheet conveyance direction. , Image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the conductive member is a conductive sheet.   3. The distance from the leading edge of the conductive member to the exit of the transfer nip portion is h, and the minimum margin length at the trailing edge of the sheet is i, and h ≦ i. The image forming apparatus described in 1.

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