JP6299487B2 - Image forming apparatus - Google Patents

Description

The present invention relates to an image forming apparatus, and more particularly to a technique for separating the sheets after the toner over image has been transferred from the photosensitive drum from the photosensitive drum.

  For example, a monochrome image forming apparatus employs a transfer technology that transports paper to the nip between the photoconductive drum and transfer roller and moves the toner image formed on the surface of the photoconductive drum to the paper with an electric field applied to the transfer roller. Has been.

  In the image forming apparatus having the above configuration, when the paper conveyance becomes unstable and fluctuates between the transfer of the toner image to the paper and the fixing, the paper and the toner are only electrically attracted to the paper. The toner image on the paper is disturbed. For this reason, a grounded sheet metal is disposed between the transfer and fixing, and the sheet is electrostatically adsorbed to be along the sheet conveying surface, thereby stabilizing the sheet conveying behavior.

  However, if such a sheet metal is arranged in a large area with respect to the paper, the cost increases accordingly. In addition, in order to apply an electrostatic attractive force to the paper, it is necessary to bring the sheet metal position as close as possible to the paper transport. However, if the paper is moved too close, the transport load will increase and the transfer-fixing interval will increase. When the sheet is bent, the sheet is rubbed against the guide surface of the sheet conveyance guide provided with the sheet metal, and there is a concern that the toner may be scattered due to frictional charging.

  In addition, after the toner image is transferred to the paper in the nip portion, the paper sticks to the photosensitive drum, the separation of the paper from the photosensitive drum is poor, and the paper is conveyed while being attracted to the photosensitive drum. Paper jams and wrinkles, and toner scattering due to peeling discharge between the paper and the photosensitive drum may occur.

  Therefore, in order to discharge the paper charged by the transfer electric field and electrostatically attracted to the photosensitive drum (the entire paper is electrically ± 0) and separated from the photosensitive drum, the discharging needle is placed at the transfer nip outlet. The structure provided in the proximity | contact position of is known. Patent Document 1 listed below discloses a technique that simplifies the structure by integrating such a static elimination needle with a conveying sheet metal.

JP 2002-328552 A

  The conveyance sheet metal disclosed in the above-mentioned patent document 1 has a small cost suppressing effect because it cannot stabilize the sheet conveyance unless it is arranged in a wide area between transfer and fixing. Moreover, depending on the conveyance sheet metal disclosed in Patent Document 1, there is a possibility that the above other concerns cannot be solved. Even if the above-mentioned static elimination needle is arranged, thin paper or the like is weak in paper, and when the electrostatic action becomes almost dominant, it is conveyed while adsorbing to the photosensitive drum from the leading edge of the paper, and the static elimination from the needle is performed. The discharge may not reach and cannot be separated from the photosensitive drum. Here, as long as at least the leading edge of the thin paper can be separated from the photosensitive drum, the portion behind the leading edge of the paper approaches the needle and the discharge discharge easily reaches, and even the thin paper can be stably separated from the photosensitive drum. Therefore, it is necessary to further improve the separation at the leading edge of the paper.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the separation of the front end of the paper from the photosensitive drum and the paper conveyance between transfer and fixing at a relatively low cost.

An image forming apparatus according to an aspect of the present invention includes an image carrier,
A charging unit to which a charging bias having the same polarity as the toner is applied and charging the surface of the image carrier to the same polarity as the toner;
An electrostatic latent image forming unit that forms an electrostatic latent image on the surface of the image carrier charged by the charging unit;
Toner same polarity of the developing bias is applied, a developing roller for developing a toner over image on the electrostatic latent image on the surface of the image bearing member,
A transfer roller that forms a transfer nip with the image carrier, a transfer bias of toner reverse polarity is applied, and the toner image formed on the surface of the image carrier in the transfer nip is transferred to a sheet;
A paper transport unit provided in a transport path for transporting paper, and transports paper to and from the transfer nip;
The sheet is disposed downstream of the transfer roller in the sheet conveyance direction by the sheet conveyance unit, has an elongated shape in the sheet width direction orthogonal to the sheet conveyance direction, and the sheet conveyed from the transfer nip is toner. A paper guide unit supported from the back side of the image transfer surface, which is elongated in the paper width direction, and has an upstream end in the paper transport direction formed into a plurality of needles and is formed downstream in the paper transport direction. The sheet metal is disposed so as to approach the sheet conveyance path through which the sheet is conveyed in the conveyance path, and protrudes from the surface of the sheet metal, and comes into contact with the sheet conveyed from the transfer nip. A paper guide portion having a rib for guiding the paper without bringing the paper into contact with the sheet metal;
A neutralizer that applies a neutralizing bias to neutralize the leading edge of the sheet separated from the image carrier to the sheet metal, and
The ribs are formed to extend in the paper transport direction;
The length of the sheet metal in the paper transport direction is shorter than the length of the rib in the paper transport direction,
A portion formed as a plurality of needle shapes at the upstream end of the sheet metal in the sheet conveying direction is a discharging needle that discharges and discharges the charge charged at the leading edge of the sheet separated from the surface of the image carrier. The sheet metal part other than the needle is a conveyance sheet metal that attracts the discharged paper to the paper guide part,
The static elimination needle has a posture that makes an angle close to the horizontal with the sheet conveyed from the transfer nip.

  According to the present invention, it is possible to improve the separation of the leading edge of the paper from the image carrier and the paper conveyance between the transfer and fixing at low cost.

1 is a left side sectional view showing a structure of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram schematically illustrating how a sheet is discharged from a transfer nip, and illustrates a state immediately after the sheet is discharged from a transfer nip. FIG. 3 is a diagram schematically illustrating how a sheet is discharged from a transfer nip, and illustrates how a sheet discharged from a transfer nip is further conveyed downstream in the sheet conveying direction from the state illustrated in FIG. 2. FIG. 4 is a diagram schematically illustrating a state in which a sheet is discharged from a transfer nip, and illustrates a state in which the sheet is conveyed further to the downstream side of the sheet conveyance than FIG. 3. It is a perspective view of a paper guide part.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a left side sectional view showing the structure of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus 1 according to an embodiment of the present disclosure is, for example, a printer. In the present embodiment, the side (the right side in FIG. 1) on which a manual feed tray 65 to be described later is disposed is the front side of the image forming apparatus 1.

  The image forming apparatus 1 includes a housing M, an image forming unit that forms a predetermined image on a sheet P based on predetermined image information, and a sheet P on which an image is formed while feeding the sheet P to the image forming unit. And a paper supply / discharge section for discharging the paper.

  As shown in FIG. 1, the image forming unit includes a photosensitive drum 2, a charging unit 10, a laser scanner unit 4, a developing device 16, a toner cartridge 5, a toner supply device 6, a transfer roller 8, A fixing device 9 and a drum cleaning unit 11 are provided. The paper supply / discharge unit includes a paper supply cassette 52, a manual feed tray 65, a registration roller pair 80, and a conveyance path L for paper P.

  The photosensitive drum 2 is made of a cylindrical member and functions as an image carrier. The photosensitive drum 2 is disposed in the housing M in such a manner that it can rotate around a rotation axis perpendicular to FIG. An electrostatic latent image is formed on the surface of the photosensitive drum 2.

  The charging unit 10 is disposed above the photosensitive drum 2. The charging unit 10 is applied with a charging bias having the same polarity as the toner (for example, plus polarity), and uniformly charges the surface of the photosensitive drum 2 in a positive (plus polarity) manner.

  The laser scanner unit 4 is disposed above the photosensitive drum 2 and spaced from the photosensitive drum 2. The laser scanner unit 4 includes a laser light source (not shown), a polygon mirror, a polygon mirror driving motor, and the like.

  The laser scanner unit 4 scans and exposes the surface of the photosensitive drum 2 based on image information output from an external device such as a PC (personal computer). By performing scanning exposure with the laser scanner unit 4, electric charges charged on the surface of the photosensitive drum 2 are removed. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 2. The laser scanner unit 4 corresponds to an electrostatic latent image forming unit in claims.

The developing device 16 is disposed in front of the photosensitive drum 2 (on the right side in FIG. 1). Developing device 16, a single color to the electrostatic latent image formed on the photosensitive drum 2 (usually black) to develop the toner over image. The developing device 16 includes a developing roller 17 that can be disposed to face the photosensitive drum 2 and a stirring spiral 18 for stirring the toner. Developing roller 17, the toner the same polarity (e.g., positive polarity) developing bias is applied to develop the toner over image on an electrostatic latent image on the surface of the photosensitive drum 2.

  The toner cartridge 5 stores toner supplied to the developing device 16.

  The toner supply device 6 supplies the toner contained in the toner cartridge 5 to the developing device 16.

  The drum cleaning unit 11 is disposed behind the photosensitive drum 2 (on the left side in FIG. 1). The drum cleaning unit 11 removes toner and deposits remaining on the surface of the photosensitive drum 2, and transports the removed toner and the like to a predetermined recovery mechanism for recovery.

Transfer roller 8 functions as a transfer device for transferring the toner over image developed on the surface of the photosensitive drum 2 to the sheet P. The transfer roller 8, the voltage application means (not shown), a transfer bias of the toner opposite polarity for transferring the toner over image developed on the photosensitive drum 2 to the sheet P (e.g., negative polarity) is applied.

The transfer roller 8 is brought into contact with and separated from the photosensitive drum 2. Specifically, the transfer roller 8 is configured to be movable between a contact position where the transfer roller 8 is in contact with the photosensitive drum 2 and a separation position where the transfer roller 8 is separated from the photosensitive drum 2. In particular, the transfer roller 8, when transferring the toner over image developed on the photosensitive drum 2 to the sheet P is moved to the contact position, in other cases are moved to the separated position.

Sheet P is sandwiched between the photosensitive drum 2 and the transfer roller 8 pressed against the surface (the side where toner over image is developed) of the photosensitive drum 2. Thus the transfer nip N is formed, toner over image developed on the photosensitive drum 2 is transferred to the paper P.

The fixing device 9, the toner constituting the toner over image transferred on the sheet P is melted, thereby fixing the sheet P. The fixing device 9 includes a heating roller 9a and a pressure roller 9b pressed against the heating roller 9a. A heating roller 9a and a pressure roller 9b is toner over image is conveyed so as to sandwich the sheet P that has been transferred. By transporting the paper P so as to be sandwiched between the heating roller 9a and the pressure roller 9b, the toner transferred onto the paper P is melted and fixed.

  The paper feed cassette 52 is disposed at the bottom of the housing M. The paper feed cassette 52 is arranged on the front side (right side in FIG. 1) of the housing M so as to be able to be pulled out in the horizontal direction. The paper feed cassette 52 includes a placement plate 60 on which the paper P is placed. The paper feed cassette 52 stores the paper P in a state where the paper P is stacked on the placement plate 60. The cassette paper feed unit 51 is disposed at the paper feed side end (the right side end in FIG. 1) of the paper feed cassette 52. The cassette paper feeding unit 51 sends out the paper P stored in the paper feeding cassette 52 to the transport path L.

  The cassette paper feeding unit 51 includes a multi-feed prevention mechanism including a forward feed roller 61 that takes out the paper P placed on the placement plate 60 and a roller pair 63 that feeds the paper P to the transport path L one by one.

  A transport path L for transporting the paper P is formed between the cassette paper feed unit 51 or the manual paper feed unit 64 and the paper discharge unit 50. The conveyance path L is transferred from the first conveyance path L1 from the cassette paper feeding unit 51 to the first merge part P1, the second conveyance path L2 from the first merge part P1 to the registration roller pair 80, and the transfer from the registration roller pair 80. A third conveyance path L3 to the roller 8, a fourth conveyance path L4 from the transfer roller 8 to the fixing device 9, a fifth conveyance path L5 from the fixing device 9 to the branching portion P3, and a discharge portion from the branching portion P3. The sixth transport path L6 up to 50 and the seventh transport path L7 from the manual feed tray 65 to the first junction P1.

  The first merging portion P1 is a merging portion between the first conveying path L1 that conveys the paper P from the cassette paper feeding portion 51 and the seventh conveying path L7 that conveys the paper P from the manual feed tray 65.

  A second junction P2 is disposed in the middle of the second transport path L2. Furthermore, the conveyance path L has a return conveyance path Lb from the branching part P3 to the second joining part P2. The second junction P2 is a junction between the second conveyance path L2 and the return conveyance path Lb.

  A registration roller pair 80 is arranged on the upstream side (right side in FIG. 1) of the transfer direction of the paper P in the transfer roller 8.

  The return conveyance path Lb is a conveyance path that is provided to make the opposite surface (non-printing surface) to the surface of the photosensitive drum 2 opposite to the surface already printed when performing double-sided printing on the paper P.

  A manual paper feed unit 64 is provided on the front side of the housing M (on the right side in FIG. 1) and above the paper feed cassette 52. The manual paper feed unit 64 includes a manual tray 65 that is a paper placement unit, and a paper feed roller 66 that is a paper feed roller.

  On the opening side of the paper discharge unit 50, a paper discharge stacking unit M1 is formed. The paper discharge stacking unit M1 is formed on the upper surface (outer surface) of the housing M. The paper discharge stacking portion M1 is a portion formed by the upper surface of the housing M being depressed downward. The bottom surface of the paper discharge stacking unit M1 constitutes a part of the top surface of the housing M. In the paper discharge stacking unit M1, the paper P discharged from the paper discharge unit 50 and having a predetermined image transferred thereon is stacked and stacked.

  Each part of the transport path L is provided with a transport roller 81 for transporting the paper in the transport path L. These transport rollers 81 and a drive source such as a motor (not shown) that supplies rotational driving force to the transport rollers 81 constitute a paper transport unit.

It will now be described mechanism for transporting the to separate the leading edge of the sheet P toner over image is transferred from the photosensitive drum 2 to the sheet P to the fixing device 9 in the transfer nip N. 2 to 4 are views schematically showing how the paper P is discharged from the transfer nip N, and is an enlarged view of the vicinity of the transfer nip N in FIG. FIG. 5 is a perspective view of the paper guide unit 12.

  As shown in FIG. 2, in the image forming apparatus 1 according to the present embodiment, a paper guide unit 12 is disposed downstream of the transfer nip N in the paper transport direction. The sheet guide unit 12 supports the sheet P conveyed from the transfer nip N to the downstream side in the sheet conveyance direction from the back surface of the toner image transfer surface, and guides the sheet conveyance direction.

  As shown in FIG. 5, the paper guide unit 12 is an elongated shape that extends in the width direction of the paper P (the depth direction in FIG. 2) that is orthogonal to the paper transport direction by the paper transport unit, and has a substantially rectangular shape. It is a member. The sheet guide unit 12 projects to a position closer to the sheet metal 13 with respect to the sheet metal 13 that is elongated in the width direction of the sheet P and the sheet P conveyed from the transfer nip N, and guides the sheet P. Ribs 14 to be provided. The ribs 14 are formed having a width direction in the paper transport direction. In addition, a plurality of ribs 14 are arranged in parallel in the longitudinal direction of the sheet guide portion 12 at a predetermined interval. The protruding length of the rib 14 is, for example, 1 mm or more.

  The sheet metal 13 is exposed on the surface of the sheet guide portion 12. As will be described later, a neutralization bias is applied to the sheet metal 13 from the neutralizer 15 (FIG. 2). When the paper P conveyed from the transfer nip N comes into direct contact with the sheet metal 13 to which the neutralizing bias is applied, peeling discharge occurs at the time of collision, and unfixed toner on the surface of the paper P is scattered, or the transfer current leaks. However, if the plurality of ribs 14 protrude from the surface of the sheet metal 13 as described above, the ribs 14 come into contact with the conveyed paper P. The For this reason, since the paper P does not contact the sheet metal 13, toner scattering and image defects can be prevented, and an increase in the heavy paper transport load can be suppressed.

  As shown in FIG. 5, the end of the sheet metal 13 on the upstream side in the sheet conveying direction is formed into a plurality of needles. The needle functions as a static elimination needle 131 that neutralizes and discharges the electric charge charged at the tip of the paper P separated from the surface of the photosensitive drum 2. On the other hand, the portion other than the needle functions as a transport sheet metal that stabilizes the transport of the paper by attracting the discharged paper P to the paper guide unit 12.

  The sheet metal 13 is disposed on the downstream side of the sheet conveyance of the transfer nip N at an inclination angle such that the surface approaches the sheet P as it goes in the downstream direction of sheet conveyance (FIG. 4). That is, the sheet metal 13 is disposed in such a posture that the surface thereof approaches a paper transport path through which the paper P is transported in the paper transport path L1 as the surface thereof moves in the downstream direction of the paper transport. However, the length of the sheet metal 13 in the sheet conveyance direction is configured to be shorter than the length of the rib 14 in the sheet conveyance direction. Thereby, each part of the sheet metal 13 does not come into contact with the sheet P conveyed from the transfer nip N, including the end on the downstream side in the sheet conveying direction.

  In general, the static elimination needle is disposed at an angle close to perpendicular to the paper P conveyed from the transfer nip N, but in this embodiment, the static elimination needle 131, that is, the end of the sheet metal 13 on the upstream side of the paper conveyance. The plurality of needles formed in the section are arranged in an attitude that makes an angle close to the horizontal with the sheet P conveyed from the transfer nip N. Accordingly, the sheet metal 13 and the sheet guide portion 12 can be disposed at a position where they do not easily interfere with the transfer roller 8, and the tip of the static elimination needle 131 can be disposed closer to the exit of the transfer nip N. With such an arrangement, the separation of the paper P attached to the surface of the photosensitive drum 2 during transfer of the toner image in the transfer nip N when the front end portion is separated from the surface of the photosensitive drum 2 is improved. Is possible. In addition, according to the paper guide unit 12 according to the present embodiment, it is possible to ensure the effect of improving the separability even if the length of the sheet metal 13 in the paper conveyance direction is set to be relatively short. As a result, the width of the sheet metal 13 in the sheet conveyance direction, that is, the area of the sheet metal 13 can be reduced, so that the cost can be reduced.

  Returning to FIG. 2, the separation of the front end of the paper P from the photosensitive drum 2 and the subsequent conveyance will be described. The static elimination needle 131 that is the tip of the needle formed at the upstream end of the sheet metal 13 in the sheet conveyance direction is, for example, 8 mm downstream from the transfer nip N in the sheet conveyance direction, and the sheet separated from the photosensitive drum 2. It is assumed that the P toner image transfer surface is disposed 3 mm away from the back surface. Further, it is assumed that the paper linear velocity from 2 mm before and 3 mm after the leading edge of the paper P passes through the transfer nip N is 100 mm / s.

  FIG. 2 shows a state immediately after the sheet P is discharged from the transfer nip N. The transferred paper P is discharged from the transfer nip N while being charged by the photosensitive drum 2 while the toner image transfer surface is charged with the same polarity as the toner and the back surface is charged with the reverse polarity of the toner. For this reason, the sheet P as a whole is often charged to the opposite polarity of the toner by the peeling discharge. The static eliminator 15 applies a static elimination bias to the sheet metal 13 during the period from −20 msec to +30 msec when the leading edge of the paper P enters the transfer nip N. For example, the static elimination bias is obtained by superimposing an AC bias having an amplitude of 1.5 kV, a duty ratio of 50%, and a frequency of 2.5 kHz on a +300 V DC bias.

  As described above, when the leading end of the sheet P approaches the upstream end of the sheet metal 13 in the sheet conveying direction, the charge of the same polarity as the toner is applied to the sheet metal 13, so that the charge charged at the leading end of the sheet P is changed. As a result, the electrostatic attraction force is reduced and the paper P is easily separated from the photosensitive drum 2.

  FIG. 3 shows a state in which the paper P discharged from the transfer nip N is further conveyed downstream from the state shown in FIG. The static eliminator 15 connected to the sheet metal 13 applies a neutralization bias to the sheet metal 13. The static eliminator 15 includes a switch 151 that switches whether to apply a static elimination bias to the sheet metal 13, a power source 152 for applying the bias, and a control unit 153 that controls a switch switching operation of the switch 151. In the present embodiment, the switch 151 switches between a state in which the sheet metal 13 is connected to the power source 152 and a state in which the sheet metal 13 is grounded.

  The static eliminator 15 is, for example, when the control unit 153 has the leading end of the conveyed paper P in the vicinity of the transfer nip N and is approaching the static elimination needle 131 at the upstream end of the sheet metal 13 in the paper conveyance direction. The switch 151 is brought into a state where the sheet metal 13 is connected to the power source 152. Then, for example, after the leading edge of the paper P has passed through the transfer nip N, the control unit 153 neutralizes the voltage applied to the sheet metal 13 to the switch 151 at the timing when the leading edge of the paper P has passed through the transfer nip N by 3 mm or more. Switch from bias to ground potential. That is, the control unit 153 switches the switch 151 from the broken line state shown in FIG. 3 to the solid line state.

  As the charge elimination bias, a charging bias in the charging unit 10 or a developing bias in the developing device 16 can be used. This eliminates the need for a high voltage circuit for generating a static elimination bias, thereby reducing the cost. In this embodiment, FIGS. 2 to 4 show a mode in which the charge removal bias is obtained from the development bias application unit.

  FIG. 4 shows how the paper P is transported further downstream than FIG. As a result of the switch switching control, as shown in FIG. 4, an electric field that attracts the paper P to the paper guide portion 12 side acts on the back surface of the toner image transfer surface of the paper P, and the paper P discharged from the transfer nip N. Approaches the grounded sheet metal 13 as it proceeds downstream in the paper transport direction. The sheet P is attracted to the grounded sheet metal 13 and is stably conveyed along the ribs 14 of the sheet guide unit 12. The control unit 153 causes the switch 151 to ground the sheet metal 13 until the rear end of the sheet P passes over the sheet metal 13. Then, when the next sheet P reaches the upstream end of the sheet metal 13 in the sheet conveyance direction, the control unit 153 switches the switch 151 and applies a neutralization bias having the same polarity as the toner to the sheet metal 13 again.

  During continuous printing, if the subsequent sheet P reaches the end of the sheet metal 13 on the upstream side of the sheet conveyance before the preceding sheet P passes over the sheet metal 13, the discharge bias is applied to the sheet metal 13. There is a possibility that toner scattering and current leakage may occur in the rear end portion of the paper P. For this reason, the length of the sheet metal 13 in the sheet conveyance direction is preferably shorter than a predetermined interval between the sheets P to be conveyed. For example, when the interval between the sheets is set to 50 mm, the length of the sheet metal 13 in the sheet conveyance direction is less than 50 mm. Thereby, in continuous printing, toner scattering and image defects at the rear end portion of the paper P can be prevented.

  As described above, according to this embodiment, it is possible to improve the separation of the leading edge of the paper P of the photosensitive drum 2 and the paper conveyance between transfer and fixing at low cost.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above embodiment, a printer is used as an embodiment of the image forming apparatus according to the present invention. However, this is only an example, and other image forming apparatuses such as a copying machine, a facsimile machine, and a multifunction machine are used. It may be a device.

  Moreover, in the said embodiment, the structure and process which were shown by the said embodiment using FIG. 1 thru | or FIG. 5 are only one Embodiment of this invention, and are not the meaning which limits this invention to the said structure and process.

1 Image forming apparatus 2 Photosensitive drum (image carrier)
4 Laser scanner unit (electrostatic latent image forming part)
8 Transfer roller 10 Charging unit 17 Development roller 12 Paper guide unit 13 Sheet metal 14 Rib 15 Static eliminator 151 Switch 152 Power supply 153 Control unit 81 Conveying roller N Transfer nip P Paper

Claims (4)

An image carrier;
A charging unit to which a charging bias having the same polarity as the toner is applied and charging the surface of the image carrier to the same polarity as the toner;
An electrostatic latent image forming unit that forms an electrostatic latent image on the surface of the image carrier charged by the charging unit;
Toner same polarity of the developing bias is applied, a developing roller for developing a toner over image on the electrostatic latent image on the surface of the image bearing member,
A transfer roller that forms a transfer nip with the image carrier, a transfer bias of toner reverse polarity is applied, and the toner image formed on the surface of the image carrier in the transfer nip is transferred to a sheet;
A paper transport unit provided in a transport path for transporting paper, and transports paper to and from the transfer nip;
The sheet is disposed downstream of the transfer roller in the sheet conveyance direction by the sheet conveyance unit, has an elongated shape in the sheet width direction orthogonal to the sheet conveyance direction, and the sheet conveyed from the transfer nip is toner. A paper guide unit supported from the back side of the image transfer surface, which is elongated in the paper width direction, and has an upstream end in the paper transport direction formed into a plurality of needles and is formed downstream in the paper transport direction. The sheet metal is disposed so as to approach the sheet conveyance path through which the sheet is conveyed in the conveyance path, and protrudes from the surface of the sheet metal, and comes into contact with the sheet conveyed from the transfer nip. A paper guide portion having a rib for guiding the paper without bringing the paper into contact with the sheet metal;
A neutralizer that applies a neutralizing bias to neutralize the leading edge of the sheet separated from the image carrier to the sheet metal, and
The ribs are formed to extend in the paper transport direction;
The length of the sheet metal in the paper transport direction is shorter than the length of the rib in the paper transport direction,
A portion formed as a plurality of needle shapes at the upstream end of the sheet metal in the sheet conveying direction is a discharging needle that discharges and discharges the charge charged at the leading edge of the sheet separated from the surface of the image carrier. The sheet metal part other than the needle is a conveyance sheet metal that attracts the discharged paper to the paper guide part,
The image forming apparatus is configured such that the static elimination needle has an angle close to a horizontal angle with a sheet conveyed from the transfer nip.   The static eliminator applies the static elimination bias to the sheet metal when the leading edge of the sheet reaches the upstream end of the sheet metal in the sheet conveying direction, and the leading edge of the sheet is upstream of the sheet metal in the sheet conveying direction. The image forming apparatus according to claim 1, wherein the sheet metal is grounded after passing through the end portion.   The image forming apparatus according to claim 1, wherein the static eliminator uses the charging bias or the developing bias as the static elimination bias. Length in the sheet conveying direction of the sheet metal, to one of the transfer short claim than between the sheets of paper against the Stevenage flops are continuously conveyed sheet conveyance direction downstream side 1 to claim 3 The image forming apparatus described.