JP2015175952A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to prevent a recording material passing through a transfer nip from being wrinkled.SOLUTION: An image forming apparatus 100 includes: toner-image forming means 7 which forms a toner image; an image carrier 10 for carrying the toner image formed by the toner-image forming means, on a surface; a transfer member 21 which is rotatably arranged around a rotation shaft 21a, and comes into direct or indirect contact with the surface of the image carrier, to form a transfer nip for transferring the toner image to a recording material; and a guide member 43 which guides the recording material in order to convey the recording material toward the transfer nip. The guide member includes a first positioning section 43A which comes into contact with the image carrier or a structure 45 holding the image carrer to position the guide member with respect to the image carrier, and a second positioning section which is held by the rotation shaft to position the guide member with respect to the transfer member.

Description

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

  2. Description of the Related Art Conventionally, there is an image forming apparatus that forms a toner image on the surface of a toner image carrier based on image information, and forms the image by transferring the toner image onto a recording sheet. As such an image forming apparatus, a sheet is conveyed from a sheet container by a conveying unit, a toner image on a toner image carrier is transferred onto the sheet at a transfer nip, and the toner image is fixed on the sheet by a fixing unit. It has been known.

  In such an image forming apparatus, before the paper conveyed toward the transfer nip enters the transfer nip, there is a possibility of colliding with the image carrier or the transfer roller that forms the transfer nip opposite the image carrier. . When the paper collides with the image carrier or the transfer roller, there is a possibility that the leading end of the paper is broken or the image carrier or the transfer roller is damaged. Further, when the paper collides, the timing at which the paper enters the paper transfer nip may be delayed.

  The sheet is conveyed toward the transfer nip so that the toner image on the image carrier is transferred to a predetermined position on the sheet. When the timing at which the sheet enters the transfer nip is delayed, the transfer position of the toner image on the sheet is changed. There arises a problem that it is displaced from a predetermined position.

  The image forming apparatus described in Patent Document 1 includes a guide plate that guides a sheet conveyed to the entrance side of the transfer nip so as to enter the transfer nip. By guiding the sheet to the transfer nip by the guide plate, it is possible to suppress the collision of the sheet as described above.

  However, due to the assembly error of the guide plate, the relative position between the image carrier and the guide member deviates from a predetermined positional relationship, and the interval between the image carrier and the guide plate is in the paper width direction, which is the direction orthogonal to the paper transport direction. In contrast, the guide plate may be assembled with an inclination relative to the image carrier. At this time, the guide plate is also inclined with respect to the transfer nip.

  For this reason, even if one end in the sheet width direction of the leading edge of the sheet guided by the guide plate passes through a path that goes straight to the transfer nip, the other end may pass through a path closer to the transfer roller than the transfer nip. In this case, one end side in the sheet width direction at the leading end of the sheet enters the transfer nip before the other end side, and a difference occurs in the sheet width direction in the sheet conveyance amount in the transfer nip, and upstream in the sheet conveying direction from the transfer nip. The paper portion on the side is distorted and wrinkles occur on the paper that has passed through the transfer nip.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing wrinkles from occurring on a recording medium that has passed through a transfer nip.

  In order to achieve the above object, the invention of claim 1 is directed to a toner image forming unit for forming a toner image, an image carrier for supporting a toner image formed by the toner image forming unit on a surface, and a rotation axis. A transfer member that is rotatably provided on the surface of the image bearing member to form a transfer nip for transferring the toner image onto the recording member, and conveys the recording member toward the transfer nip. In order to achieve this, an image forming apparatus having a guide member for guiding the recording body contacts the image carrier or a structure holding the image carrier to position the guide member relative to the image carrier. The guide member is provided with one positioning portion and a second positioning portion that is held by the rotating shaft and positions the guide member with respect to the transfer member.

  As described above, according to the present invention, there is an excellent effect that wrinkles can be suppressed from occurring on the recording medium that has passed through the transfer nip.

3 is a schematic configuration diagram of a secondary transfer unit according to Configuration Example 1. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 6 is a schematic configuration diagram of a secondary transfer unit according to Configuration Example 2. FIG. 4 is a schematic diagram of a secondary transfer unit viewed from the direction of arrow P shown in FIG. 3. The figure used for description of the generation mechanism of wrinkles generated on paper.

  FIG. 2 is a schematic configuration diagram of a printer 100 that is an image forming apparatus according to the present embodiment. The printer 100 is an image forming apparatus that employs a so-called tandem type intermediate transfer system.

  As shown in FIG. 2, image forming units 7Y, 7M, 7C, and 7Bk corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk) are arranged in parallel. In each of the image forming units 7Y, 7M, 7C, and 7Bk, four drum-shaped photoreceptors 1Y, 1M, 1C, and 1Bk are arranged as latent image carriers.

  Around the photoreceptors 1Y, 1M, 1C, and 1Bk, charging devices 4Y, 4M, 4C, and 4Bk that charge the surfaces of the photoreceptors, and development that develops a latent image formed on the photoreceptor surface using a developer containing toner. The devices 6Y, 6M, 6C, and 6M are sequentially arranged. Further, cleaning devices 2Y, 2M, 2C, and 2Bk provided with cleaning blades 3Y, 3M, 3C, and 3Bk for cleaning the surface of the photoreceptor after the toner image transfer are disposed.

  Below each of the image forming units 7Y, 7M, 7C, and 7Bk, optical writing is performed with the laser beams LY, LM, LC, and LBk to form latent images on the surfaces of the photoreceptors 1Y, 1M, 1C, and 1Bk. An exposure device 50 is provided.

  A paper feed cassette 31 is disposed below the exposure device 50 and accommodates a plurality of sheets P, which are recording bodies, in a bundle of sheets. The paper feed cassette 31 is provided with a paper feed roller 26 and is in contact with the uppermost paper P of the paper bundle accommodated in the paper feed cassette 31. Then, the uppermost sheet P is sent out toward the conveyance path 60 by being driven to rotate by a driving means (not shown).

  The paper P sent out to the transport path 60 is transported in the transport path 60 by a transport roller pair 27 provided in the transport path 60, and the leading end is between the rollers of the registration roller pair 28 disposed near the end in the paper transport direction. Is sandwiched. When the leading edge of the paper P is sandwiched between the rollers of the registration roller pair 28, both rollers rotate at an appropriate timing to feed the paper P toward a secondary transfer nip N described later.

  A guide surface 43D that guides the paper P to transport the paper P toward the secondary transfer nip N downstream of the registration roller pair 28 and in the paper transport direction of the secondary transfer nip N. A conveyance guide plate 43 having a gap between the intermediate transfer belt 10 and the intermediate transfer belt 10 is provided. The sheet P sent out by the registration roller pair 28 is guided by the guide surface 43D of the transport guide member 43 through the gap and transported toward the secondary transfer nip N.

  Above each of the image forming units 7Y, 7M, 7C, and 7Bk, a transfer device 9 having an intermediate transfer belt 10 that is an intermediate transfer member is disposed. In the transfer device 9, the intermediate transfer belt 10 is a plurality of stretching rollers, such as a driving roller 12, a tension roller 13 that is biased by a spring 14 and applies tension to the intermediate transfer belt 10, a driven roller 15, a driven roller 18, and the like. It is stretched so that it can rotate.

  By driving the driving roller 12 by a driving motor (not shown), the intermediate transfer belt 10 is driven counterclockwise in the drawing. Further, the tension roller 13, the driven roller 15, and the driven roller 18 rotate following the rotation of the intermediate transfer belt 10.

  In this embodiment, the driving speed (process speed) of the intermediate transfer belt 10 is adjusted to 200 [mm / sec]. In order to transfer the toner images formed on the photoreceptors 1Y, 1M, 1C, and 1Bk onto the intermediate transfer belt 10 at positions facing the photoreceptors 1Y, 1M, 1C, and 1Bk with the intermediate transfer belt 10 interposed therebetween. Primary transfer rollers 11Y, 11M, 11C, and 11Bk are arranged.

  The primary transfer rollers 11Y, 11M, 11C, and 11Bk are respectively pressed by springs 17Y, 17M, 17C, and 17Bk so as to contact the intermediate transfer belt 10. In this embodiment, the load is set to 1 [N] on one side.

  A predetermined transfer bias is applied to the primary transfer rollers 11Y, 11M, 11C, and 11Bk by power supplies 80Y, 80M, 80C, and 80Bk. In the present embodiment, +1800 [V] is set as the transfer bias.

  Further, the intermediate transfer belt 10 is opposed to the driving roller 12 downstream of the primary transfer rollers 11Y, 11M, 11C, and 11Bk in the intermediate transfer belt rotation direction via the intermediate transfer belt 10, and is brought into contact with the front surface of the intermediate transfer belt 10. A secondary transfer roller 21 is provided.

  The drive roller 12 that stretches the intermediate transfer belt 10 functions as a secondary transfer counter roller. The secondary transfer roller 21 and the driving roller 12 are in contact with each other via the intermediate transfer belt 10, and the surface of the intermediate transfer belt 10 and the secondary transfer roller 21 come into contact with each other, so that the intermediate transfer belt 10 and the secondary transfer roller 21 are in contact with each other. A secondary transfer nip N is formed between the transfer roller 21 and the transfer roller 21.

  Further, the surface of the intermediate transfer belt 10 and the secondary transfer roller 21 are indirectly connected to each other via a paper conveyance belt that is rotatably supported by a plurality of roller members including the secondary transfer roller 21 and carries and conveys the paper P. The secondary transfer nip N may be formed so as to be in contact with the surface.

  A belt cleaning device 51 that removes residual toner remaining on the intermediate transfer belt 10 after transfer is opposed to the tension roller 13 via the intermediate transfer belt 10 on the downstream side of the secondary transfer roller 21 in the rotation direction of the intermediate transfer belt. It is provided to do. The belt cleaning device 51 is configured to press a cleaning blade 52 made of urethane rubber against the surface of the intermediate transfer belt to block the toner and clean it.

  In the transfer device 9, the belt cleaning device 51 is disposed below the tension roller 13 to reduce the size of the transfer device 9 in the horizontal direction. The tension roller 13 has a function as a belt cleaning counter roller, and improves the adhesion between the cleaning blade 52 and the intermediate transfer belt 10.

The material of the intermediate transfer belt 10 will be described. The intermediate transfer belt 10 is composed of polyvinylidene fluoride, ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate) or the like in a single layer or a plurality of layers. Further, a conductive material such as carbon black is dispersed, the volume resistivity is 10 ⁸ [Ω · cm] to 10 ¹² [Ω · cm], and the surface resistivity is 10 ⁹ [Ω · cm] to 10 ^13. It is adjusted to be in the range of [Ω · cm].

  If necessary, a release layer may be coated on the surface of the intermediate transfer belt 10. Examples of the material used for the release layer include the following. That is, ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), polyvinylidene fluoride, PEA (perfluoroalkoxy fluororesin), FEP (tetrafluoroethylene-hexafluoropropylene copolymer) Polymers) and fluororesins such as PVF (vinyl fluoride) can be used, but are not limited thereto. The method of manufacturing the intermediate transfer belt 10 includes a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished if necessary.

  If the volume resistivity of the intermediate transfer belt 10 exceeds the above-described range, the bias required for transfer increases, which increases the power supply cost. Further, since the charging potential of the intermediate transfer belt 10 becomes high in the transfer process, the transfer paper peeling process, and the like, and self-discharge becomes difficult, it is necessary to provide a static elimination means.

  Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays quickly, which is advantageous for static elimination by self-discharge, but toner scatter occurs because the current during transfer flows in the surface direction. End up. Therefore, the volume resistivity and surface resistivity of the intermediate transfer belt 10 in this embodiment are preferably within the above ranges.

  The volume resistivity and the surface resistivity were measured using a high resistivity meter (Mitsubishi Chemical Corporation: Hiresta IP) with an HRS probe (inner electrode diameter 5.9 [mm], ring electrode inner diameter 11 [mm]). The connected one was used. Then, a voltage of 100 [V] (surface resistivity is 500 [V]) was applied to the front and back of the intermediate transfer belt 10, and measured values after 10 seconds were taken as volume resistivity and surface resistivity.

Next, the secondary transfer roller 21 will be described. The secondary transfer roller 21 is coated on a metal core such as stainless steel with an elastic body such as urethane adjusted to a resistance value in a range of 10 ⁶ [Ω] to 10 ¹⁰ [Ω] with a conductive material. Is made up of.

  Here, since the current hardly flows when the resistance value of the secondary transfer roller 21 exceeds the above range, it is necessary to apply a higher voltage in order to obtain a required transfer property, which increases the power supply cost. Invite. Further, since a high voltage is applied, a discharge occurs in the gap before and after the secondary transfer nip N, so that white spots are lost due to the discharge on the halftone image.

  On the contrary, if the resistance value of the secondary transfer roller 21 is below the above range, the transferability between the multi-color image portion (for example, three-color superimposed image) and the single-color image portion existing on the same image cannot be achieved. This is because the secondary transfer roller 21 has a low resistance value, so that a sufficient current flows to transfer the monochrome image portion at a relatively low voltage. However, it is optimal for the monochrome image portion to transfer the multiple color image portion. A voltage value higher than the voltage is required. For this reason, if the voltage is set so that the multi-color image portion can be transferred, the transfer current becomes excessive in a single-color image, and the transfer efficiency is reduced.

  The resistance value of the secondary transfer roller 21 is measured by installing the secondary transfer roller 21 on a conductive metal plate and 4.9 [N] on one side at both ends of the core metal (total of 9.8 [N] on both sides). It calculated from the value of the electric current which flows when the voltage of 1000 [V] is applied between a metal core and a metal plate in the state which applied the load of.

  Further, the secondary transfer roller 21 is brought into contact with the drive roller 12 with a load of 50 [N] via the intermediate transfer belt 10 by a spring (not shown), and rotates with the drive roller 12 via the intermediate transfer belt 10. It is the composition to do.

  A transfer bias is applied to the drive roller 12 by a power supply 81 in order to transfer the toner image on the intermediate transfer belt 10 onto the paper P. In this embodiment, constant current control is performed on the power supply 81 to apply a transfer bias to the driving roller 12, and the current setting value in this constant current control is set to −30 [μA].

  Further, the paper P is fed from the paper feed cassette 31 by the paper feed roller 26 in accordance with the timing at which the leading end of the four-color superimposed image formed by being sequentially transferred onto the intermediate transfer belt 10 reaches the secondary transfer nip N. The paper is fed and conveyed by a conveyance roller pair 27 and a registration roller pair 28.

  The four-color superimposed image transferred from the intermediate transfer belt 10 to the paper P by the secondary transfer roller 21 is guided by the secondary transfer outlet guide 41 and the fixing inlet guide 42 and conveyed to the fixing device 30. The paper P conveyed to the fixing device 30 is fixed by heat and pressure at a fixing nip formed by a fixing roller 30a having a heat source therein and a pressure roller 30b. The paper is discharged onto a paper discharge tray 70 provided on the upper surface.

  Here, in the conventional image forming apparatus, in order to suppress wrinkling on the sheet in the fixing device, the central portion in the axial direction of the fixing roller or the pressure roller is formed in an inverted crown shape having a smaller diameter than both ends. It has been known. This is due to the effect of increasing the conveyance speed of the paper at both ends from the central portion in the axial direction of the roller and stretching the paper to both ends in the width direction. Such a problem of wrinkles occurring on the paper is not limited to the fixing device, and may occur in the transfer portion as well.

  However, in order to suppress paper wrinkles, the reverse crown shape of the roller is not easily applicable to the transfer portion. That is, in the transfer unit, the paper is guided between the photoreceptor or the intermediate transfer belt and the transfer roller, and a transfer bias is applied to transfer the toner image onto the paper.

  If the transfer roller or its opposite roller is formed in a reverse crown shape, the nip width and nip pressure are non-uniform in the roller axial direction, resulting in a difference in image density between the central portion and both end portions in the axial direction. The density of the solid image at the center will be light. For this reason, it is not preferable to adopt a configuration in which the transfer roller and its opposite roller are formed in an inverted crown shape to suppress paper wrinkles.

[Configuration example 1]
FIG. 1 is a schematic configuration diagram of a secondary transfer unit according to Configuration Example 1. The driving roller 12 and the driven roller 18 that stretch the intermediate transfer belt 10 are held by a pair of frames 45 at both ends in the axial direction. A fitted portion 43B for fitting with the core metal 21a of the secondary transfer roller 21 is provided on the downstream side of the conveyance guide plate 43 having the guide surface 43D for guiding the sheet to the secondary transfer nip N in the sheet conveyance direction. ing.

  A hole 43C into which the cored bar 21a is inserted is formed in the fitted part 43B. The cored bar 21a is inserted into the hole 43C, and the fitted part 43B is fitted and held with the cored bar 21a. A conveyance guide plate 43 is attached so as to be rotatable around the cored bar 21a.

  In this configuration example, the fitted portion 43B provided on the conveyance guide plate 43 and held by the cored bar 21a of the secondary transfer roller 21 serves as a positioning portion that positions the conveyance guide plate 43 with respect to the secondary transfer roller 21. Function. Accordingly, the conveyance guide plate 43 can be positioned with high accuracy with respect to the secondary transfer roller 21, and the paper P can be accurately guided with respect to the secondary transfer nip N.

  Here, normally, the axial direction of the cored bar 21a of the secondary transfer roller 21 is the axial direction of the intermediate transfer belt 10 in contact with the secondary transfer roller 21 to form the secondary transfer nip N (the axial direction of the drive roller 12). In the same direction).

  As described above, in this configuration example, the fitted portion 43 </ b> B provided on the conveyance guide plate 43 is held by the cored bar 21 a, and the conveyance guide plate 43 is positioned with respect to the secondary transfer roller 21. Therefore, the axial direction of the fitted portion 43B of the conveyance guide plate 43 is the same as the axial direction of the cored bar 21a, so that the axial direction of the conveyance guide plate 43 is parallel to the axial direction of the intermediate transfer belt 10. Is possible.

  Further, the conveyance guide plate 43 is pressurized toward the frame 45 by a pressure spring 44. In this configuration example, the load of the pressure spring 44 that pressurizes the conveyance guide plate 43 is set to 10 [N] so that the conveyance guide plate 43 abuts against the frame 45 against the stiffness of the paper P even when the thick paper is passed. ] Is set.

  Abutting portions 43A that respectively abut against the pair of frames 45 are provided at both ends in the axial direction (both ends in the paper width direction) of the conveyance guide plate 43 on the upstream side in the paper conveyance direction. In this way, when the abutting portion 43A of the conveyance guide plate 43 abuts against the frame 45, the conveyance guide plate 43 is positioned with respect to the frame 45 holding the driving roller 12 and the driven roller 18 that stretch the intermediate transfer belt 10. Is done.

  Accordingly, the conveyance guide plate 43 can be positioned with respect to the intermediate transfer belt 10 stretched by the driving roller 12 and the driven roller 18 held by the frame 45. In this configuration example, the abutting portion 43 </ b> A that is provided on the conveyance guide plate 43 and abuts against the frame 45 functions as a positioning portion that positions the conveyance guide plate 43 with respect to the intermediate transfer belt 10.

  In addition, a part of the conveyance guide plate 43 is brought into contact with the drive roller 12 and the driven roller 18, a portion where the toner image is not formed, such as both ends in the width direction of the intermediate transfer belt 10, and the conveyance guide plate 43 with respect to the intermediate transfer belt 10. A configuration that performs the positioning may be adopted.

  Thus, in this configuration example, a part of the abutting portion 43A provided on the conveyance guide plate 43 is in contact with the intermediate transfer belt 10 or a structure (such as the frame 45) that holds the intermediate transfer belt 10, The conveyance guide plate 43 is positioned with respect to the intermediate transfer belt 10.

  Therefore, the assembly error can be reduced as compared with the case where a part such as the abutting portion 43A of the conveyance guide plate 43 is provided in contact with the intermediate transfer belt 10 or a member different from the structure, and the conveyance guide plate for the intermediate transfer belt 10 can be reduced. The positioning accuracy of 43 can be increased.

  Therefore, the intermediate transfer belt 10 and the conveyance guide plate 43 are in a predetermined positional relationship so that the axial direction of the conveyance guide plate 43 is parallel to the axial direction of the intermediate transfer belt 10. It becomes possible to position the conveyance guide plate 43 with respect to the belt 10. By positioning the conveyance guide plate 43 with respect to the intermediate transfer belt 10 in this way, it is possible to prevent the conveyance guide plate 43 from being inclined and assembled with respect to the intermediate transfer belt 10.

  Thereby, the inclination of the conveyance guide plate 43 with respect to the secondary transfer nip N is also suppressed, and the leading edge of the paper P guided by the conveyance guide plate 43 can be made to enter the secondary transfer nip N straight across the paper width direction. Therefore, a difference in the conveyance amount of the sheet P in the secondary transfer nip N in the recording body width direction is suppressed, and the sheet portion on the upstream side in the sheet conveyance direction from the secondary transfer nip N is distorted. It is possible to suppress wrinkling on the paper P that has passed through the next transfer nip N.

  When the conveyance guide plate 43 is positioned with respect to both the intermediate transfer belt 10 and the secondary transfer roller 21 as in this configuration example, a gap L between the intermediate transfer belt 10 and the conveyance guide plate 43 may cause an assembly error or a dimension. Difficult to change due to variations. Therefore, the gap L can be set to a minimum, and the gap L is set to 3 [mm] in this configuration example.

  The gap L is larger than the maximum paper thickness of the paper that can be used in the printer 100 of the present embodiment, so that the paper cannot pass between the intermediate transfer belt 10 and the transport guide plate 43. The occurrence of defects is suppressed.

  As the gap L is smaller, the leading edge of the sheet does not vary to the secondary transfer nip N, and sheet skew that may cause wrinkles in the secondary transfer nip N can be suppressed. In particular, when the leading edge of the paper due to humidity control is large, or when the transfer unit performs transfer on the back surface, which is the second surface of the paper having a large amount of curl after image formation, on the front surface, which is the first surface of the paper. The advantage of narrowing the gap L is great.

  Further, even if the paper conveyance behavior is disturbed between the registration roller pair 28 and the secondary transfer roller 21 and signs of wrinkles appear, the intermediate transfer belt 10 is reduced by narrowing the gap L. And the conveyance guide plate 43 can suppress the disturbance of the conveyance behavior.

  On the other hand, if the gap L is too small, the intermediate transfer belt 10 and the conveyance guide plate 43 may come into contact when the intermediate transfer belt 10 is partially warped or wavy. When the intermediate transfer belt 10 and the conveyance guide plate 43 come into contact with each other, there is a possibility that the toner image on the intermediate transfer belt 10 may be disturbed, or the toner attached to the conveyance guide plate 43 may contaminate the paper edge surface or the paper back surface. Therefore, in the printer 100 of this configuration example, the gap L is set to 3 [mm] in consideration of the occurrence of such a problem.

[Configuration example 2]
FIG. 3 is a schematic configuration diagram of a secondary transfer unit according to Configuration Example 2. FIG. 4 is a schematic diagram of the secondary transfer portion viewed from the direction of arrow P shown in FIG. Also in this configuration example, the conveyance guide plate 43 is positioned with respect to the frame 45 and the intermediate transfer belt 10 and the secondary transfer roller 21 by the same configuration as the configuration example 1.

  In this configuration example, as shown in FIG. 4, the conveyance guide plate 43 is shaped from the center in the sheet width direction in which the gap L between the intermediate transfer belt 10 and the conveyance guide plate 43 is perpendicular to the sheet conveyance direction. The shape is such that both ends are narrower.

  In this configuration example, the gap L1 between the both ends in the sheet width direction between the intermediate transfer belt 10 and the conveyance guide plate 43 is 3 [mm], and the gap L2 between the intermediate transfer belt 10 and the conveyance guide plate 43 in the center in the sheet width direction. It is set to 5 [mm].

The generation mechanism of wrinkles generated on the paper P will be described with reference to FIG.
As a generation mechanism of paper wrinkles, there is one caused by a difference in the conveyance speed of the paper P between both ends in the paper width direction and the center in the paper width direction. As shown in FIG. 5, when the conveyance speed in the central portion in the paper width direction is faster than both end portions in the paper width direction, a force that moves the paper P from the both end portions in the paper width direction toward the central portion in the paper width direction is generated. . Such a force for moving the paper P increases as the conveyance speed difference between the both ends in the paper width direction and the central portion in the paper width direction increases.

  The sheet conveyance speed distribution in the sheet width direction is affected by the axial outer diameter distribution of the drive roller 12 and the secondary transfer roller 21 and the deviation of the thickness of the intermediate transfer belt 10 in the belt width direction. Depending on the variation, it is possible that the distribution shown in FIG.

  Therefore, as in this configuration example, the gap L1 at both ends in the sheet width direction is narrower than the gap L2 at the center in the sheet width direction between the intermediate transfer belt 10 and the conveyance guide plate 43, so that The sheet P can be guided to a position closer to the secondary transfer nip N. Therefore, both ends of the paper P in the paper width direction first enter the secondary transfer nip N rather than the central portion of the paper P in the paper width direction.

  Therefore, even if the speed distribution is as shown in FIG. 5, due to the opening effect of the sheet P by the first secondary transfer nip entry at both ends in the sheet width direction, that is, from the center in the sheet width direction to both ends in the sheet width direction. The generation of wrinkles on the paper P can be suppressed by the action of the force that extends the paper P toward the front.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A toner image forming unit such as an image forming unit 7 that forms a toner image, an image carrier such as an intermediate transfer belt 10 that supports a toner image formed by the toner image forming unit on a surface, and a rotation shaft such as a cored bar 21a. A secondary transfer roller that is rotatably provided at the center and forms a transfer nip such as a secondary transfer nip N that directly or indirectly contacts the surface of the image carrier and transfers the toner image onto a recording medium such as paper P. In an image forming apparatus such as a printer 100 including a transfer member such as 21 and a guide member such as a conveyance guide plate 43 that guides the recording medium to convey the recording medium toward the transfer nip, an image carrier or image A first positioning portion such as an abutting portion 43A that contacts a structure such as a frame 45 that holds the carrier and positions the guide member with respect to the image carrier, and a transfer portion that is held by the rotating shaft. And a second positioning portion such as a fitted portion 43B for positioning the guide member with respect, provided on the guide member.
Here, the axial direction of the rotation axis of the transfer member is usually parallel to the axial direction of the image carrier that contacts the transfer member and forms the transfer nip.
In (Aspect A), the second positioning portion provided in the guide member is held by the rotating shaft, and the guide member is positioned with respect to the transfer member. For this reason, the axial direction of the second positioning portion of the guide member is the same as the axial direction of the rotating shaft, so that the axial direction of the guide member can be made parallel to the axial direction of the image carrier.
Further, the first positioning portion provided in the guide member comes into contact with the image carrier or the structure holding the image carrier, and the guide member is positioned with respect to the image carrier. Therefore, the assembly error can be made smaller than when the first positioning portion of the guide member is provided in contact with a member different from the image carrier or the structure, and the positioning accuracy of the guide member with respect to the image carrier can be increased. .
From this, the guide member with respect to the image carrier so that the axial direction of the guide member is parallel to the axial direction of the image carrier and the relative position between the image carrier and the guide member is in a predetermined positional relationship. Can be positioned. Accordingly, the guide member can be prevented from being inclined and assembled with respect to the image carrier, the inclination of the guide member with respect to the transfer nip can be suppressed, and the leading end of the recording member guided by the guide member can be moved in the recording member width direction. Over the transfer nip. Therefore, the occurrence of a difference in the conveyance amount of the recording medium in the transfer nip in the recording medium width direction is suppressed, and the recording medium portion on the upstream side in the recording medium conveyance direction from the transfer nip is distorted so that it passes through the transfer nip. It is possible to suppress wrinkles from occurring on the recording medium.
(Aspect B)
In (Aspect A), the gap between the image carrier and the guide member is less than or equal to a predetermined amount that can suppress disturbance in the conveyance behavior of the recording body between the image carrier and the guide member. A guide member was provided. According to this, as described in the above embodiment, the guide of the leading end of the recording medium to the transfer nip does not vary, and the skew of the recording medium that may cause wrinkles at the transfer nip can be suppressed.
(Aspect C)
In (Aspect A) or (Aspect B), the guide member is positioned relative to the transfer member. According to this, as described in the above embodiment, it is possible to accurately guide the recording medium to the transfer nip.
(Aspect D)
(Aspect C) includes a shaft member such as a cored bar 21a that rotatably supports the transfer member, and the guide member is provided to be supported by the shaft member. According to this, as described in the above embodiment, the guide member can be positioned with high accuracy with respect to the transfer member.
(Aspect E)
In (Aspect A), (Aspect B), (Aspect C), or (Aspect D), a holding member such as a frame 45 that holds the image carrier is provided, and the guide member is arranged with respect to the holding member. Position by abutting. According to this, as described in the above embodiment, the guide member can be positioned with high accuracy with respect to the image carrier held by the holding member.
(Aspect F)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D) or (Aspect E), a gap such as a gap L between the guide member and the image carrier is orthogonal to the recording medium conveyance direction. Both end portions are narrower than the center portion in the recording body width direction. According to this, as described in the above embodiment, wrinkles can be prevented from occurring on the recording body due to the action of the force that stretches the recording body from the central portion in the width direction toward both ends. .
(Aspect G)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D), (Aspect E), or (Aspect F), the gap between the image carrier and the guide member is 5 [mm] or less. . According to this, as described in the above embodiment, the guide of the recording body tip to the transfer nip does not vary, and the skew of the recording body that can cause wrinkles can be suppressed.
(Aspect H)
In the image forming apparatus, a secondary member for forming a belt member such as the intermediate transfer belt 10 and a transfer nip such as a secondary transfer nip N for transferring a toner image on the belt member onto a sheet is formed between the belt member. A transfer roller such as a transfer roller 21; a frame such as a frame 45 that holds the belt member; and a guide plate such as a conveyance guide plate 43 that guides a sheet toward the transfer nip. It has a hole such as a hole 43C inserted into a shaft such as the core metal 21a of the transfer roller and a protrusion such as an abutting portion 43A that contacts the frame.
(Aspect I)
In (Aspect H), the guide plate is rotatable about an axis such as the cored bar 21a of the transfer roller.
(Aspect J)
In (Aspect H) or (Aspect I), a spring such as a pressure spring 44 that pressurizes the guide plate toward the frame is provided.
(Aspect K)
In an image forming apparatus, an image carrier such as an intermediate transfer belt 10 that carries a toner image, and a transfer roller such as a secondary transfer roller 21 that forms a transfer nip such as a secondary transfer nip N between the image carrier. And a holding member such as a frame 45 that holds the image carrier, and a guide member such as a conveyance guide plate 43 that guides the sheet toward the transfer nip, and the guide member protrudes against the holding member. It has an abutting part such as the abutting part 43A and is rotatably supported by a shaft such as the core metal 21a of the transfer roller.
(Aspect L)
In an image forming apparatus, an image carrier such as an intermediate transfer belt 10 that carries a toner image on its surface, and a secondary transfer roller 21 that forms a transfer nip such as a secondary transfer nip N between the image carrier and the like A guide member such as a transfer guide plate 43 having a transfer roller, a holder such as a frame 45 that holds the image carrier, a guide surface 43D that guides a sheet toward the transfer nip, and the guide First alignment means such as an abutting portion 43A for aligning the surface of the image carrier and the guide surface by contacting the member and the holding body, the guide member and the core metal 21a of the transfer roller, etc. And a second alignment means such as a fitted portion 43B for aligning the transfer roller and the guide surface.
(Aspect M)
In the image forming apparatus, a belt member such as an intermediate transfer belt 10 that carries a toner image on its surface, and a transfer member such as a secondary transfer roller 21 that forms a transfer nip such as a secondary transfer nip N between the belt member. A first roller such as a driving roller 12 provided to face the transfer member at the transfer nip and supporting the belt member, and the belt member supported upstream of the first roller in the belt member traveling direction. A second roller such as a driven roller 18, a frame such as a frame 45 that supports the first roller and the second roller, and a surface of the belt member between the first roller and the second roller. And a guide member such as a conveyance guide plate 43 that guides the paper, and contacts the frame to position the guide member with respect to the belt member. A first positioning portion such as a contact part 43A, and a second positioning portion such as a fitted portion 43B for positioning said guide member relative to said transfer member, provided on the guide member.

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Cleaning apparatus 3 Cleaning blade 4 Charging apparatus 6 Developing apparatus 7 Image forming part 9 Transfer apparatus 10 Intermediate transfer belt 11 Primary transfer roller 12 Drive roller 13 Tension roller 14 Spring 15 Drive roller 17 Spring 18 Drive roller 21 Secondary transfer Roller 21a Metal core 26 Feed roller 27 Transport roller pair 28 Registration roller pair 30 Fixing device 30a Fixing roller 30b Pressure roller 31 Feed cassette 32 Discharge roller pair 41 Secondary transfer outlet guide 42 Fixing inlet guide 43 Transport guide plate 43A Abutting portion 43B Fit portion 43C Hole 43D Guide surface 44 Pressure spring 45 Frame 50 Exposure device 51 Belt cleaning device 52 Cleaning blade 60 Transport path 70 Paper discharge tray 80 Power supply 81 Power supply 100 Printer

JP 2008-303027 A

Claims (11)

Toner image forming means for forming a toner image;
An image carrier that carries the toner image formed by the toner image forming means on the surface;
A transfer member provided so as to be rotatable about a rotation axis and forming a transfer nip that directly or indirectly contacts the surface of the image carrier and transfers the toner image on the recording medium;
In an image forming apparatus comprising a guide member for guiding the recording body to convey the recording body toward the transfer nip,
A first positioning portion that contacts the image carrier or a structure that holds the image carrier and positions the guide member with respect to the image carrier; and positioning the guide member with respect to the transfer member that is held by the rotation shaft An image forming apparatus characterized in that a second positioning portion for performing the above is provided on the guide member. The image forming apparatus according to claim 1.
The guide with respect to the image carrier is adjusted so that the gap between the image carrier and the guide member is less than or equal to a predetermined amount that can suppress disturbance in the conveyance behavior of the recording body between the image carrier and the guide member. An image forming apparatus comprising a member. The image forming apparatus according to claim 1, wherein
An image forming apparatus comprising: positioning the first positioning portion against a structure holding the image carrier. The image forming apparatus according to claim 1, 2 or 3.
An image forming apparatus characterized in that a gap between the guide member and the image carrier is narrower at both ends than in a central portion in a recording body width direction which is a direction orthogonal to a recording body conveyance direction. The image forming apparatus according to claim 1, 2, 3, or 4.
An image forming apparatus, wherein a gap between the image carrier and the guide member is 5 mm or less. A belt member;
A transfer roller that forms a transfer nip for transferring the toner image on the belt member to a sheet;
A frame for holding the belt member;
A guide plate for guiding the paper toward the transfer nip,
The image forming apparatus, wherein the guide plate has a hole inserted into a shaft of the transfer roller and a protrusion that contacts the frame. The image forming apparatus according to claim 6.
The image forming apparatus, wherein the guide plate is rotatable about an axis of the transfer roller. The image forming apparatus according to claim 6 or 7,
An image forming apparatus comprising a spring that pressurizes the guide plate toward the frame. An image carrier for carrying a toner image;
A transfer roller that forms a transfer nip with the image carrier;
A holding body for holding the image carrier;
A guide member for guiding the sheet toward the transfer nip,
The image forming apparatus, wherein the guide member has an abutting portion that abuts against the holding body, and is rotatably supported by a shaft of the transfer roller. An image carrier that carries a toner image on the surface;
A transfer roller that forms a transfer nip with the image carrier;
A holding body for holding the image carrier;
A guide member having a guide surface for guiding the sheet toward the transfer nip;
First alignment means for aligning the surface of the image carrier and the guide surface by contacting the guide member and the holder;
An image forming apparatus, comprising: a second alignment unit that aligns the transfer roller and the guide surface by contacting the guide member and the shaft of the transfer roller. A belt member carrying a toner image on the surface;
A transfer member that forms a transfer nip with the belt member;
A first roller provided opposite to the transfer member at the transfer nip and supporting the belt member;
A second roller for supporting the belt member on the upstream side in the belt member traveling direction from the first roller;
A frame that supports the first roller and the second roller;
A guide member that opposes the surface of the belt member between the first roller and the second roller and guides paper;
The guide member includes a first positioning portion that contacts the frame and positions the guide member with respect to the belt member, and a second positioning portion that positions the guide member with respect to the transfer member. An image forming apparatus.

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