JP2020042159A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of obtaining the static elimination effect of a recording material even when the charge polarity of the recording material changes downstream of a secondary transfer section.SOLUTION: The image forming apparatus includes: a static elimination plate 90 arranged downstream a secondary transfer nip N2 in the transport direction of a recording material 9 and the longitudinal direction of which is arranged parallel to the axial direction of a secondary transfer roller 56; and a control unit 110 that controls the short direction of the static elimination plate 90. The control part 110 is configured to control the transverse direction of the static elimination plate 90 to either of a first position 91 where the short side of the static elimination plate 90 is arranged toward the secondary transfer nip N2 and the second position 92 where the short side of the static elimination plate 90 is arranged in a direction different from the first position 91.SELECTED DRAWING: Figure 3

Description

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

  2. Description of the Related Art An image forming apparatus that transfers a toner image carried on an image carrier such as a photoconductor or an intermediate transfer body onto a recording material such as paper at a transfer unit is widely used. In such an image forming apparatus, the charge may excessively move to the recording material while the recording material passes through the transfer unit. In that case, it becomes difficult for the recording material after transfer to be separated from the image carrier. There is a case where a charge removing member is provided downstream of the transfer unit in order to facilitate the separation of the transferred recording material from the image carrier. By removing the charge transferred to the recording material by the charge removing member, the performance of separating the recording material from the image carrier can be improved. If some of the ions generated from the charge removing member flow into the transfer section, image disturbance may occur.

  In Patent Literature 1, a first needle-like protrusion and a second needle-like protrusion are provided as a charge removing member, and a voltage having the same polarity as that of the toner is applied to the charge removing member to apply a charge removing effect to a recording material over a wide range. Can be. When the recording material is thick paper, the first needle-like projection is moved away from the surface of the photoconductor, and when the recording material is thin paper, the first needle-like projection is swung so as to approach the surface of the photoconductor. . The first needle-like projection and the second needle-like projection swing integrally.

JP-A-10-282798

  FIG. 11 shows the relationship between the process speed at the time of image formation and the potential of the recording material downstream of the transfer section in Patent Document 1. As shown in FIG. 11, depending on the process speed, the charging polarity of the recording material was found to be positive or negative. When the charge polarity of the recording material is positive, the charge elimination effect of the recording material can be obtained by applying a voltage having the same polarity as the negative polarity toner to the charge elimination member. On the other hand, when the charge polarity of the recording material is negative, if a voltage having the same polarity as that of the negative toner is applied to the charge removing member, the charge removing effect cannot be sufficiently exhibited. At this time, a recording material having a negative charge polarity is discharged between the recording material and a member having a potential difference downstream of the transfer portion, and there is a possibility that a toner image transferred on the recording material may be disturbed.

  In addition, as shown in FIG. 12, whether the charging polarity of the recording material downstream of the transfer unit is positive or negative may change depending on the transfer bias applied to the transfer unit. According to Patent Document 1, the first needle-like projections are separated from the surface of the photoconductor when the recording material is thick paper, and the first needle-like projections are close to the surface of the photoconductor when the recording material is thin paper. Rock it. At this time, the first needle-like projection and the second needle-like projection swing integrally. For this reason, Patent Literature 1 has a problem in that the charge elimination effect of the recording material cannot be obtained according to the charging polarity of the recording material.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image forming apparatus capable of obtaining a charge eliminating effect on a recording material even if the charging polarity of the recording material changes downstream of a secondary transfer unit. Things.

  A representative configuration of the image forming apparatus according to the present invention for achieving the above object includes an image carrier on which a toner image is carried, and an endless intermediate transfer body disposed to face the image carrier. A primary transfer unit for primary transfer of a toner image from the image carrier to the intermediate transfer body, and a secondary transfer unit for secondary transfer of the toner image primarily transferred to the intermediate transfer body to a recording material A secondary transfer roller, a secondary transfer roller, and an opposing roller forming a secondary transfer nip for opposing the secondary transfer roller and nipping and conveying a recording material through the intermediate transfer member. A static elimination plate disposed downstream of the secondary transfer nip in the conveying direction of the recording material, the longitudinal direction of which is disposed parallel to the axial direction of the secondary transfer roller, and the direction of the lateral direction of the static elimination plate. And a control unit for controlling, wherein the control unit has a short side direction of the static elimination plate. A first position disposed toward the secondary transfer nip portion; and a second position in which a short direction of the charge removing plate is disposed in a direction different from the first position. It is characterized in that the direction of the short direction is controlled.

  According to the present invention, even if the charging polarity of the recording material changes downstream of the secondary transfer portion, the effect of eliminating the charge of the recording material can be obtained.

FIG. 2 is a cross-sectional view illustrating a configuration of the image forming apparatus. FIG. 2 is a cross-sectional view illustrating a configuration of an image forming unit. It is sectional drawing which shows the structure of the static elimination device of 1st Embodiment. FIG. 2 is a perspective view illustrating a configuration of a secondary transfer roller and a charge removing plate according to the first embodiment. It is the elements on larger scale of FIG. FIG. 4 is a cross-sectional view illustrating a configuration in a case where the charge removing plate according to the first embodiment is set at a first position. It is sectional drawing which shows the structure at the time of setting the static elimination plate of 1st Embodiment to a 2nd position. FIG. 6 is a diagram illustrating a relationship between an angle on a secondary transfer roller side with respect to a perpendicular of a surface of a recording material of the static elimination plate and a static elimination current when the static elimination plate is set at a second position. FIG. 6 is a cross-sectional view illustrating an angle on a secondary transfer roller side with respect to a perpendicular of a surface of a recording material of the static elimination plate when the static elimination plate is set at a second position. FIG. 7 is a diagram illustrating a relationship between a secondary transfer current flowing between a secondary transfer roller and an opposing roller when a recording material having a negative charging polarity passes through a secondary transfer nip, and a potential of the recording material. FIG. 9 is a diagram illustrating a relationship between a process speed according to the second embodiment and a potential of a recording material downstream of a secondary transfer nip in a conveyance direction of the recording material. FIG. 11 is a diagram illustrating a relationship between a secondary transfer bias and a potential of a recording material downstream of a secondary transfer nip in a conveying direction of the recording material according to a third embodiment. It is sectional drawing which shows the structure of the static elimination device of 4th Embodiment. It is sectional drawing which shows the structure of the modification of the static elimination device of 4th Embodiment. It is sectional drawing which shows the structure of the static elimination device of 5th Embodiment.

  An embodiment of the image forming apparatus according to the present invention will be specifically described with reference to the drawings. The following embodiments are examples of the best embodiments of the present invention, but the present invention is not limited to these embodiments.

[First Embodiment]
First, the configuration of a first embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS.

<Image forming apparatus>
The configuration of the image forming apparatus will be described with reference to FIGS. FIG. 1 is a sectional view illustrating a configuration of the image forming apparatus 100. FIG. 2 is a cross-sectional view illustrating a configuration of the image forming unit P. The image forming apparatus 100 shown in FIG. 1 is a laser beam printer that forms a full-color image on a recording material 9 using an electrophotographic method. As the recording material 9, a recording paper, an OHT (OverHead Transparency) sheet (a transparent sheet used for an OHP (OverHead Projector)), a cloth, or the like can be used.

  The image forming apparatus 100 has an intermediate transfer belt 51 as an endless intermediate transfer member that is disposed to face the photosensitive drum 1 as an image carrier that carries a toner image as a developer image. Along the intermediate transfer belt 51, image forming units Pa, Pb, Pc, and Pd, which are toner image forming units for yellow, magenta, cyan, and black, are arranged.

  The image forming apparatus 100 is an intermediate transfer type tandem type. The image forming units Pa, Pb, Pc, and Pd are almost the same except that the color of the toner used in each of the developing devices 4a, 4b, 4c, and 4d as the developing unit is different from yellow, magenta, cyan, and black. Be composed. For this reason, the following description may use the image forming unit P in some cases. The same applies to other image forming process means.

  In the image forming unit Pa, a yellow toner image is formed on the photosensitive drum 1 a as an image carrier, and is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 51. In the image forming section Pb, a magenta toner image is formed on the photosensitive drum 1b, and the magenta toner image is primarily transferred on the yellow toner image primarily transferred on the outer peripheral surface of the intermediate transfer belt 51. In the image forming units Pc and Pd, a cyan toner image and a black toner image are formed on the respective photosensitive drums 1c and 1d, respectively, and are also superimposed on the toner images of the respective colors that are primarily transferred on the outer peripheral surface of the intermediate transfer belt 51. The toner images of each color are sequentially primary-transferred. In the present embodiment, the photosensitive drum 1 and the intermediate transfer belt 51 are configured as an image carrier for carrying a toner image.

  The four-color toner images primarily transferred on the outer peripheral surface of the intermediate transfer belt 51 are collectively and secondarily transferred to the fed recording material 9 in the secondary transfer nip N2. The recording material 9 on which the toner image has been secondarily transferred in the secondary transfer nip portion N2 is heated and pressed by a fixing device 7 as a fixing unit, and after the toner image is fixed on the surface of the recording material 9, the image is fixed. It is discharged outside the forming apparatus 100.

  A feeding device 8 that feeds the recording material 9 feeds out the recording material 9 stored in a feeding cassette 81 by a pickup roller 82, separates the recording material 9 one by one by a separation roller 83, and feeds the recording material 9 to a conveyance roller 10. Transport. Thereafter, the skew of the recording material 9 is corrected by abutting the leading end of the recording material 9 against the stopped nip portion of the registration roller 84. The registration roller 84 receives the recording material 9 in a stopped state and waits for the recording material 9. Then, the leading end of the recording material 9 reaches the secondary transfer nip N2 at the timing when the image tip of the toner image carried on the outer peripheral surface of the intermediate transfer belt 51 reaches the secondary transfer nip N2. The recording material 9 is transported.

  The intermediate transfer unit 5 wraps an intermediate transfer belt 51 as an image carrier around a driving roller 52, support rollers 58 and 59, a tension roller 53, and an opposing roller 54, and moves the intermediate transfer belt 51 in the direction of arrow R2 in FIG. Rotate. The fixing device 7 forms a fixing nip portion N3 by pressing a pressure roller 73 against a fixing roller 72 provided with a lamp heater 71 as a center. The fixing nip portion N3 transfers the toner image transferred onto the recording material 9. The recording material 9 is fixed by heating and pressing.

  The recording material 9 on which the toner image has been fixed is discharged outside the image forming apparatus 100. The cleaning device 57 rubs the cleaning blade 57a against the outer peripheral surface of the intermediate transfer belt 51, passes through the secondary transfer nip portion N2, and remains on the outer peripheral surface of the intermediate transfer belt 51 from which the recording material 9 has been separated. The transfer residual toner and paper dust are scraped and removed.

  The image forming unit Pa shown in FIG. 2 has a charging roller 2a as a charging unit around a photosensitive drum 1a as an image carrier. Further, it has an exposing device 3a as an exposing device and a developing device 4a as a developing device. Further, it has a primary transfer roller 55a as a primary transfer portion for primarily transferring a toner image from the photosensitive drum 1 to the intermediate transfer belt 51. Further, the cleaning apparatus includes a cleaning device 6a as cleaning means.

  In the photosensitive drum 1a, an organic photoconductor layer (OPC; Organic Photo Conductor) having a negative charge polarity is formed on the outer peripheral surface of an aluminum cylinder. The photosensitive drum 1a rotates in the direction of arrow R1 in FIG. 2 at a process speed of 240 mm / sec. The charging roller 2a as a charging unit is formed by covering a surface of a metal core with a resistive elastic layer, and is pressed against the photosensitive drum 1a and is driven to rotate. The charging power source D3 applies a charging bias in which an AC voltage is superimposed on a DC voltage to the charging roller 2a. Thus, the surface of the photosensitive drum 1a is charged to a uniform negative potential.

  The exposure device 3a scans, using a rotating mirror, a laser beam L obtained by ON / OFF-modulating scanning line image data obtained by developing a yellow separation color image, and irradiates the uniformly charged surface of the photosensitive drum 1a. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 1a.

  The developing device 4a stirs the two-component developer in which the non-magnetic toner is mixed with the magnetic carrier, charges the non-magnetic toner negatively, and charges the magnetic carrier positively. The developing device 4a is provided with a developing sleeve 41a provided to face the surface of the photosensitive drum 1a. The developing sleeve 41a rotates counterclockwise in FIG. 2 which is a counter direction with respect to the direction of the arrow R1 in FIG. 2 which is the rotation direction of the photosensitive drum 1a. A fixed magnetic pole 42a is provided inside the developing sleeve 41a. The two-component developer charged by stirring is carried around the fixed magnetic pole 42a in the form of a spike on the surface of the developing sleeve 41a rotating in the counter direction with respect to the rotation direction of the photosensitive drum 1a. Rub the surface.

  The developing power source D4 applies a developing bias in which an AC voltage is superimposed on a negative DC voltage to the developing sleeve 41a. As a result, the toner in the developing device 4a is moved to an exposed portion on the surface of the photosensitive drum 1a, which has a more positive polarity than the developing sleeve 41a, and the electrostatic latent image on the surface of the photosensitive drum 1a is changed to a toner image. And reversal development.

  The primary transfer roller 55a as a primary transfer unit is pressed against the surface of the photosensitive drum 1a via the intermediate transfer belt 51. A primary transfer nip N1a is formed between the surface of the photosensitive drum 1a and the outer peripheral surface of the intermediate transfer belt 51. The primary transfer power supply D1a applies a primary transfer bias to the primary transfer roller 55a. The primary transfer power supply D1a applies a positive DC voltage of +900 V to the primary transfer roller 55a as a primary transfer bias. As a result, the negatively charged toner image carried on the surface of the photosensitive drum 1a is primarily transferred onto the outer peripheral surface of the intermediate transfer belt 51 passing through the primary transfer nip N1a.

As the primary transfer roller 55a, a semiconductive roller having a resistance value of 1 × 10 ² Ω to 1 × 10 ⁸ Ω when a voltage of 2000 V is applied was used. Specifically, an ion-conductive sponge roller formed of a blend of a nitrile rubber and an ethylene-epichlorohydrin copolymer was used.

A core metal having an outer diameter of 8 mm is provided inside the ion-conductive sponge roller, and the outer diameter of the outer periphery of the ion-conductive sponge roller is 16 mm. The primary transfer roller 55a has a resistance value of about 1 × 10 ⁶ Ω to 1 × 10 ⁸ Ω when a voltage of 2000 V is applied in an environment of a temperature of 23 ° C. and a humidity of 50% RH (Relative Humidity). is there. The cleaning device 6a rubs the cleaning blade 11a against the surface of the photosensitive drum 1a to scrape and remove transfer residual toner attached to the surface of the photosensitive drum 1a that has passed through the primary transfer nip portion N1a.

<Secondary transfer unit>
The secondary transfer unit 17 secondary-transfers the toner image primarily transferred on the outer peripheral surface of the intermediate transfer belt 51 to the recording material 9. The secondary transfer unit 17 includes a secondary transfer roller 56 and an opposing roller 54 that faces the secondary transfer roller 56 and forms a secondary transfer nip N2 for nipping and transporting the recording material 9 via the intermediate transfer belt 51. And Further, there is provided a neutralization plate 90 having conductivity, which is disposed downstream of the secondary transfer nip portion N2 in the transport direction of the recording material 9 and whose longitudinal direction is parallel to the axial direction of the secondary transfer roller 56.

  Further, the secondary transfer unit 17 includes a control unit 110 that controls the direction of a short direction orthogonal to the longitudinal direction of the charge removing plate 90. The conductive core 54 a of the opposing roller 54 of the present embodiment is connected to the ground potential G. A secondary transfer bias is applied from a secondary transfer power source D2 to the conductive core metal 56a of the secondary transfer roller 56. The secondary transfer power supply D2 is controlled by the control unit 110.

<Control unit>
The control unit 110 controls the motor 13 serving as a drive source shown in FIG. 3 to rotate the neutralization plate 90 about a rotation shaft 90a via a gear train 16 as a drive transmission unit, thereby shortening the neutralization plate 90. Control hand direction. At this time, the neutralizing plate 90 may be set at the first position 91 shown in FIG. 3 in which the short direction of the neutralizing plate 90 is arranged toward the secondary transfer nip N2. Further, the short direction of the charge removing plate 90 may be set to the second position 92 shown in FIG. The control unit 110 controls the short direction of the charge removing plate 90 to one of the first position 91 and the second position 92.

<Electric neutralizer>
Next, the configuration of the static eliminator 12 of the present embodiment will be described with reference to FIGS. FIG. 3 is a cross-sectional view illustrating the configuration of the static eliminator 12 of the present embodiment. FIG. 4 is a perspective view illustrating the configuration of the secondary transfer roller 56 and the charge eliminating plate 90 according to the present embodiment. FIG. 5 is a partially enlarged view of FIG. 4 and 5 show, by solid lines, the case where the neutralization plate 90 is located at both ends of the movable range when the neutralization plate 90 is rotated about the rotation shaft 90a and moved by the angle θ.

  As shown in FIGS. 4 and 5, the secondary transfer roller 56 as a secondary transfer member has both ends of a core bar 56 a rotatably attached to a holder 60 via bearings 61. The holder 60 is provided with a transport guide 60a upstream in the transport direction of the recording material 9 indicated by the arrow F in FIG.

  A spring member 62 is attached to each bearing 61. The secondary transfer roller 56 is pressed against the opposing roller 54 via the intermediate transfer belt 51 shown in FIG. 3 by the extension force of each spring member 62. As a result, a secondary transfer nip N2 is formed between the outer peripheral surface of the intermediate transfer belt 51 and the secondary transfer roller 56. The core metal 54a of the opposing roller 54 is connected to the ground potential G.

  The secondary transfer power source D2 applies a secondary transfer bias to the core metal 56a of the secondary transfer roller 56. As shown in FIG. 5, a secondary transfer power source D2 is electrically connected to a metal core 56a of the secondary transfer roller 56 via a metal plate spring 63. A secondary transfer bias composed of a positive DC voltage of +2.3 kV and a constant voltage controlled by the secondary transfer power source D2 is applied to the secondary transfer roller 56. Thereby, in the secondary transfer nip N2, the negatively charged toner image carried on the outer peripheral surface of the intermediate transfer belt 51 is secondarily transferred to the recording material 9 passing through the secondary transfer nip N2. .

For the intermediate transfer belt 51, a semiconductive polyimide resin having a volume resistivity ρv of 1 × 10 ⁶ Ω · m to 1 × 10 ¹¹ Ω · m was used. The outer diameter of the core metal 54a of the opposing roller 54 is 16 mm. An ethylene-propylene-diene terpolymer (EPDM; Ethylene Propylene Diene Monomer) rubber is provided on the outer periphery of the cored bar 54a.

Conductive carbon is dispersed in EPDM rubber. Thereby, the opposing roller 54 is configured as a semiconductive roller. The outer diameter of the opposing roller 54 is 20 mm. The resistance value of the opposing roller 54 is about 1 × 10 Ω to 1 × 10 ⁵ Ω when the applied voltage is 10 V in an environment where the temperature is 23 ° C. and the humidity is 50% RH.

<Discharge plate>
On the downstream side of the secondary transfer roller 56 in the conveying direction of the recording material 9 indicated by the arrow F in FIG. 3, the longitudinal direction of a charge removing plate 90 as a charge removing member for removing the charge of the recording material 9 is the center of the secondary transfer roller 56. It is provided in parallel with the axial direction of the gold 56a. The static elimination plate 90 rotates between a first position 91 and a second position 92 about a rotation shaft 90a.

  The second position 92 indicated by the broken line in FIG. 3 is located downstream of the first position 91 indicated by the solid line in FIG. 3 in the transport direction of the recording material 9 indicated by the arrow F in FIG. The non-movable portion 90b of the charge removing plate 90 is supported by being in electrical contact with a metal holding member 94. The holding member 94 is fixed to the holder 60 by screws 66.

  As shown in FIG. 3, when the charge removing plate 90 is at the first position 91, an insulating sheet 93 is disposed between the charge removing plate 90 and the secondary transfer roller 56. The insulating sheet 93 uses polyethylene terephthalate (PET), which is an insulating member having a thickness of 0.25 mm.

  The conductive charge eliminating plate 90 is connected to the ground potential G via a conductive holding member 94. On the other hand, to the conductive core metal 56a of the secondary transfer roller 56, a secondary transfer bias consisting of a positive DC voltage of +2.3 kV, which is constant-voltage controlled by the secondary transfer power source D2, is applied. Therefore, an insulating sheet 93 is disposed between the secondary transfer roller 56 and the charge removing plate 90. Accordingly, it is possible to prevent a high voltage from leaking directly between the secondary transfer roller 56 and the charge removing plate 90.

  The static elimination plate 90 is formed by processing a thin sheet of stainless steel (SUS304) having a thickness of 0.1 mm into a saw-tooth shape, and the pitch between adjacent saw teeth is 1 mm. The charge removing plate 90 is provided such that the tips of the saw teeth face the surface of the recording material 9 opposite to the surface on which the toner image is carried.

  A transport guide 64 is provided downstream of the secondary transfer nip N2 in the transport direction of the recording material 9 as indicated by the arrow F in FIG. A driven roller 65 is rotatably supported by the transport guide 64, and the driven roller 65 protrudes toward the recording material 9 from the guide surface 64 a of the transport guide 64 and the leading end 90 c of the charge removing plate 90. . As a result, while the recording material 9 conveyed in the direction of arrow F in FIG. 3 is in contact with the driven roller 65 and the driven roller 65 is driven and rotated, the recording material 9 does not come into contact with the charge eliminating plate 90.

  The non-movable portion 90 b of the charge removing plate 90 is connected to the ground potential G via the holding member 94. The static elimination plate 90 is rotated by a motor 13 as a drive source controlled by the control unit 110 and is driven by a gear train 16 as a drive transmission means. Pivotally move between. Note that, instead of the motor 13, a solenoid can be used to rotate the neutralizing plate 90 between the first position 91 and the second position 92 about the rotating shaft 90a.

<Electrification removal mechanism>
The mechanism by which the charged recording material 9 is neutralized by the charge elimination plate 90 is that an ion flux is generated between the leading end portion 90c of the charge elimination plate 90 and the charged recording material 9, and the charged recording material 9 is transferred from the charged recording material 9 to the charge elimination plate 90. The charge moves toward it. The same applies when the charge eliminating plate 90 is set to the first position 91 and when it is set to the second position 92. As shown in FIG. 12, in the secondary transfer nip portion N2, the recording material 9 is transferred in accordance with the secondary transfer bias applied when the toner image primarily transferred onto the intermediate transfer belt 51 is secondarily transferred onto the recording material 9. May change the charging polarity. According to the charging polarity of the recording material 9, the short direction of the neutralization plate 90 is pivotally moved to a first position 91 and a second position 92.

<Position of static elimination plate>
Next, the first position 91 and the second position 92 of the charge eliminating plate 90 will be described with reference to FIGS. FIG. 6 is a cross-sectional view illustrating a configuration when the static elimination plate 90 of the present embodiment is set at the first position 91. FIG. 7 is a cross-sectional view illustrating a configuration in a case where the charge removing plate 90 of the present embodiment is set at the second position 92. FIG. 8 is a diagram showing the relationship between the angle θ2 on the secondary transfer roller 56 side with respect to the perpendicular 15 of the surface of the recording material 9 of the neutralizing plate 90 and the neutralizing current when the neutralizing plate 90 is set at the second position 92. . FIG. 9 is a cross-sectional view showing the angle θ2 on the side of the secondary transfer roller 56 with respect to the perpendicular 15 of the surface of the recording material 9 of the discharging plate 90 when the discharging plate 90 is set at the second position 92.

  The static elimination plate 90 set at the second position 92 shown in FIG. 3 is arranged downstream of the static elimination plate 90 set at the first position 91 shown in FIG. As described above with reference to FIGS. 11 and 12, the charging polarity of the recording material 9 can be either positive or negative depending on the process speed of the recording material 9 and the conditions of the secondary transfer bias.

  Here, a case where the charging polarity of the recording material 9 passing through the secondary transfer nip N2 is positive is considered. In this case, in order to improve the separability of the recording material 9 from the outer peripheral surface of the intermediate transfer belt 51, the charge of the recording material 9 immediately after passing through the secondary transfer nip portion N2 is removed, and It is desirable to reduce the electrostatic attraction force of the recording material 9 to the recording material 51. In this case, the neutralizing plate 90 is rotated to the first position 91 indicated by the solid line in FIG. It is preferable that the tip 90c of the saw tooth be disposed in a direction toward the secondary transfer nip N2.

  In the present embodiment, the secondary transfer when the surface 14 extending the surface of the neutralization plate 90 intersects a straight line 200 connecting the rotation shaft centers 56b and 54b of the secondary transfer roller 56 and the opposing roller 54, respectively. The angle θ1 on the roller 56 side (secondary transfer roller side) was set to 60 °.

  When the charge eliminating plate 90 is at the first position 91 in FIG. 6, the tip 90c of the sawtooth of the charge eliminating plate 90 is arranged in a direction toward the secondary transfer nip N2. At this time, any arrangement is possible as long as the secondary transfer current flowing between the secondary transfer roller 56 and the opposing roller 54 does not flow into the charge eliminating plate 90.

  Consider a case where the short direction of the charge removing plate 90 is set to the first position 91 shown in FIG. At this time, the angle between the surface 14 that extends the surface of the charge removing plate 90 and the straight line 200 that connects the rotation axis center 56b of the secondary transfer roller 56 and the rotation axis center 54b of the opposing roller 54 is a secondary angle. The angle θ1 on the transfer roller 56 side is set in the range of the following equation (1).

[Equation 1]
40 ° ≦ θ1 ≦ 80 °

  That is, the upper limit of the angle θ1 is 80 ° and the lower limit is 40 °. When the angle θ1 exceeds the upper limit of 80 °, the tip portion 90 c of the sawtooth of the charge eliminating plate 90 approaches the secondary transfer roller 56, so that the secondary transfer current flowing through the secondary transfer roller 56 and the opposing roller 54 is applied to the charge eliminating plate 90. There is a risk of inflow.

  When the angle θ1 is smaller than the lower limit of 40 °, the tip 90c of the sawtooth of the charge removing plate 90 does not face the secondary transfer nip N2. For this reason, the discharging current flowing from the charged recording material 9 to the discharging plate 90 does not face the direction of the secondary transfer nip portion N2, and the recording material 9 causes a separation failure from the outer peripheral surface of the intermediate transfer belt 51, and the image forming apparatus 100 There is a risk that the operation will stop.

  The control unit 110 shown in FIG. 3 can acquire the charging polarity of the recording material 9 from the process speed, which is the transport speed of the recording material 9 shown in FIG. 11, and the secondary transfer bias shown in FIG. When the process speed shown in FIG. 11 is slower than 95 mm / sec or the secondary transfer bias shown in FIG. 8 is smaller than 1700 V, the control unit 110 controls the recording material 9 to be charged to a positive polarity. It is determined that there is. When the recording material 9 is positively charged, the short direction of the charge removing plate 90 is set to the first position 91 shown in FIG.

  On the other hand, the case where the charging polarity of the recording material 9 passing through the secondary transfer nip N2 is negative is considered. In this case, consideration should be given to efficiently removing the charged charges on the recording material 9. To this end, as shown by the solid line in FIG. 7, the short direction of the charge eliminating plate 90 is set to the second position 92.

  At this time, the angle between the surface 14 that extends the surface of the charge removing plate 90 and the straight line 200 that connects the rotation axis center 56b of the secondary transfer roller 56 and the rotation axis center 54b of the opposing roller 54 is a secondary angle. The angle θ2 on the transfer roller 56 side is set in a range of 30 ° or less. In addition, in FIG. 7, the auxiliary line 200 a parallel to the straight line 200 is taken into consideration due to the restriction of the drawing, and the secondary transfer roller 56 is set at an angle at which the surface 14 extending the surface of the charge removing plate 90 and the auxiliary line 200 a intersect. Side angle θ2.

The angle θ2 at this time corresponds to the angle θ2 on the side of the secondary transfer roller 56 when the surface of the charge removing plate 90 intersects the perpendicular 15 of the surface of the recording material 9 shown in FIG. When the angle θ2 exceeds 30 °, the absolute value of the charge elimination current flowing from the negatively charged recording material 9 to the charge elimination plate 90 shown in FIG. 8 is smaller than | −1.5 × 10 ⁻⁴ (A / m) | As a result, the charge removing effect of the recording material 9 decreases.

  The graph shown in FIG. 8 uses the angle θ2 shown in FIG. 9 as a parameter, connects the neutralizing plate 90 to the ground potential G, and sets the surface potential of the negatively charged recording material 9 to −3300 V. Then, an operation was performed by an electric field calculation solver (calculation software) manufactured by Canon Inc., and a static elimination current obtained as a result of the operation was used as an evaluation index.

  The angle θ2 of the surface of the recording material 9 of the static elimination plate 90 at the second position 92 with respect to the perpendicular 15 can vary depending on the type of the recording material 9 and the like. As shown in FIG. 6, the perpendicular 15 of the surface of the recording material 9 at the secondary transfer nip portion N2 coincides with the straight line 200. Therefore, in the present embodiment, as shown in FIG. 7, an auxiliary line 200a parallel to a straight line 200 connecting the rotation shaft centers 56b and 54b of the secondary transfer roller 56 and the opposing roller 54 is considered. Then, the surface 14 extending from the surface of the charge removing plate 90 at the second position 92 is considered. The angle θ2 on the side of the secondary transfer roller 56 when the surface 14 intersects the auxiliary line 200a is defined as an angle θ2 shown in FIG. The angle θ2 at this time was 5 °.

  If the angle θ2 of the neutralization plate 90 at the second position 92 shown in FIG. 9 on the side of the secondary transfer roller 56 with respect to the perpendicular 15 of the surface of the recording material 9 is 30 ° or less, as shown in FIG. The charged recording material 9 exhibits a charge eliminating effect. Here, the angle θ2 on the side of the secondary transfer roller 56 with respect to the perpendicular 15 of the surface of the recording material 9 of the charge eliminating plate 90 at the second position 92 shown in FIG. 9 is considered. At this time, the secondary transfer is performed on the auxiliary line 200a parallel to the straight line 200 connecting the secondary transfer roller 56 of the charge removing plate 90 and the respective rotation shaft centers 56b, 54b of the opposed roller 54 at the second position 92 shown in FIG. Consider the angle θ2 on the roller 56 side.

  Both angles θ2 are defined to be the same. As a result, the definition of the angle θ2 becomes clear regardless of the type of the recording material 9 and the like. The angle θ2 on the side of the secondary transfer roller 56 with respect to an auxiliary line 200a parallel to a straight line 200 connecting the secondary transfer roller 56 of the neutralization plate 90 at the second position 92 and the respective rotation shaft centers 56b, 54b of the opposed roller 54 Take into account. The angle θ2 is preferably 30 ° or less as shown in FIG. When the angle θ2 exceeds 30 °, the charge removing effect of the negatively charged recording material 9 sharply decreases. Alternatively, there is a possibility that the charge removing effect of the negatively charged recording material 9 is lost.

  FIG. 10 shows the secondary transfer current flowing between the secondary transfer roller 56 and the opposing roller 54 and the potential of the recording material 9 when the recording material 9 having a negative charging polarity passes through the secondary transfer nip N2. FIG. Graph a shown in FIG. 10 shows the secondary transfer current when the charge eliminating plate 90 is disposed only at the first position 91 in FIG. 3 regardless of the charging polarity of the recording material 9 passing through the secondary transfer nip N2, The relationship between the charging polarity and the potential of the recording material 9 having a negative polarity is shown.

  A graph b shown in FIG. 10 indicates that the charge removing plate 90 is rotated to the second position 92 when the charging polarity of the recording material 9 passing through the secondary transfer nip portion N2 is negative. Then, when the charging polarity of the recording material 9 passing through the secondary transfer nip portion N2 is positive, the charge removing plate 90 is rotated to the first position 91 in FIG. The relationship between the secondary transfer current in that case and the potential of the recording material 9 having a negative charging polarity is shown.

  Graphs a and b shown in FIG. 10 are the results of measuring the potential of the recording material 9 downstream of the secondary transfer nip N2 in the direction of conveyance of the recording material 9 as indicated by the arrow F in FIG. The vertical axis of FIG. 10 indicates the charging potential of the negative recording material 9, and the horizontal axis of FIG. 10 indicates that the negative recording material 9 is in contact with the secondary transfer roller 56 when passing through the secondary transfer nip N2. 5 shows a secondary transfer current flowing between the roller and the opposing roller 54.

  Here, when the static elimination plate 90 is arranged at the first position 91 shown in FIG. 3 when the charging polarity of the recording material 9 is negative, as shown in the graph a of FIG. I have not been able to get it efficiently. As in the present embodiment, when the charge polarity of the recording material 9 is negative, the charge removing plate 90 is disposed at the second position 92 shown in FIG. By means of the charge eliminating plate 90 arranged at 92, the charged charges on the recording material 9 can be efficiently removed.

  The control unit 110 can acquire the charging polarity of the recording material 9 from the process speed, which is the conveyance speed of the recording material 9 shown in FIG. 11, and the secondary transfer bias shown in FIG. If the process speed shown in FIG. 11 is higher than 95 mm / sec or the secondary transfer bias shown in FIG. 12 is larger than 1700 V, it is determined that the recording material 9 is charged to the negative polarity. When the recording material 9 is negatively charged, the short direction of the charge eliminating plate 90 is set to the second position 92 shown in FIG.

  As described above, the charge elimination plate 90 can efficiently remove the charge of the recording material 9 depending on whether the polarity of the recording material 9 passing through the secondary transfer nip N2 is positive or negative. When possible, the arrangement angle of the charge eliminating plate 90 is different. In the present embodiment, the arrangement angle of the charge removing plate 90 is changed according to the charging polarity of the recording material 9. This makes it possible to efficiently remove the charge on the recording material 9 according to the charge polarity of the recording material 9.

  Due to the process speed at the time of image formation shown in FIG. 11 and the secondary transfer bias shown in FIG. 12, the charging polarity of the recording material 9 downstream of the secondary transfer nip portion N2 in the direction of conveyance of the recording material 9 shown by the arrow F in FIG. Changes. Even if the charging polarity of the recording material 9 changes, the arrangement angle of the charge removing plate 90 is changed according to the charging polarity of the recording material 9. This makes it possible to efficiently remove the charged charges on the recording material 9.

  Regardless of whether the charging polarity of the recording material 9 charged in the secondary transfer process is positive or negative, recording is performed downstream of the secondary transfer nip portion N2 in the transport direction of the recording material 9 as indicated by arrow F in FIG. The arrangement angle of the charge removing plate 90 is changed according to the charging polarity of the material 9. This makes it possible to efficiently remove the charged charges on the recording material 9. This contributes to the stabilization of image quality downstream of the secondary transfer nip N2 in the direction of conveyance of the recording material 9 as indicated by the arrow F in FIG.

[Second embodiment]
Next, the configuration of an image forming apparatus according to a second embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment have the same reference numerals or the same reference numerals, even if the reference numerals are different. FIG. 11 is a diagram showing the relationship between the process speed of the present embodiment and the potential of the recording material 9 downstream of the secondary transfer nip N2 in the direction of arrow F in FIG. As shown in FIG. 11, when the process speed is 80 mm / sec, the potential of the recording material 9 is +500 V, and the charging polarity of the recording material 9 is positive.

  When the process speed is 120 mm / sec, the potential of the recording material 9 is -700 V, and the charging polarity of the recording material 9 is negative. When the process speed is 240 mm / sec, the potential of the recording material 9 is -1400 V, and the charging polarity of the recording material 9 is negative.

  That is, when the process speed is 80 mm / sec, the charging polarity of the recording material 9 is positive. At this time, the neutralizing plate 90 is set at the first position 91 shown in FIG. On the other hand, when the process speed is 120 mm / sec or 240 mm / sec, the charging polarity of the recording material 9 is negative. At this time, the neutralizing plate 90 is set at the second position 92 shown in FIG.

  That is, the control unit 110 controls the direction of the width direction of the charge removing plate 90 in accordance with the transport speed of the recording material 9. The controller 110 determines that the charging polarity of the recording material 9 is positive when the process speed shown on the horizontal axis in FIG. 11 as the conveyance speed of the recording material 9 is smaller than 95 mm / sec as the threshold. . When the recording material 9 has a positive polarity, the control unit 110 sets the short direction of the charge removing plate 90 to the first position 91 shown in FIG.

  On the other hand, when the process speed indicated by the horizontal axis in FIG. 11 as the conveyance speed of the recording material 9 is larger than the threshold value of 95 mm / sec, the control unit 110 determines that the charging polarity of the recording material 9 is negative. judge. When the recording material 9 has a negative polarity, the control unit 110 sets the direction of the width direction of the charge removing plate 90 to the second position 92 shown in FIG.

  As a result, as shown in FIG. 11, the charging polarity of the recording material 9 changes depending on the process speed. Even if the charging polarity of the recording material 9 changes, the charge eliminating plate 90 is appropriately changed to the first position 91 and the second position 92 shown in FIG. This makes it possible to efficiently remove the charge on the recording material 9 according to the charge polarity of the recording material 9. Other configurations are the same as those of the first embodiment, and the same effects can be obtained.

[Third embodiment]
Next, a configuration of an image forming apparatus according to a third embodiment of the present invention will be described with reference to FIG. In addition, the same components as those in the above-described embodiments are denoted by the same reference numerals or the same reference numerals even if the reference numerals are different, and the description is omitted. FIG. 12 is a diagram illustrating the relationship between the secondary transfer bias of the present embodiment and the potential of the recording material 9 downstream of the secondary transfer nip portion N2 in the direction of arrow F in FIG. is there.

  As shown in FIG. 12, when the secondary transfer bias applied from the secondary transfer power source D2 to the secondary transfer roller 56 is 1700V, the charging potential of the recording material 9 is 0V. When the secondary transfer bias is smaller than 1700 V, the charging polarity of the recording material 9 is positive. When the secondary transfer bias is higher than 1700 V, the charging polarity of the recording material 9 is negative.

  The control unit 110 removes electricity in accordance with a secondary transfer bias applied when the toner image primarily transferred on the outer peripheral surface of the intermediate transfer belt 51 in the secondary transfer nip N2 is secondarily transferred to the recording material 9. The short direction of the plate 90 is controlled. That is, when the secondary transfer bias shown on the horizontal axis in FIG. 12 is smaller than 1700 V as the second threshold, the control unit 110 determines that the charging polarity of the recording material 9 is positive, and The short side direction 90 is set to the first position 91 shown in FIG. On the other hand, when the secondary transfer bias shown on the horizontal axis in FIG. 12 is larger than 1700 V as the second threshold, the control unit 110 determines that the charging polarity of the recording material 9 is negative, and The short side direction 90 is set to the second position 92 shown in FIG.

  As shown in FIG. 12, the charging polarity of the recording material 9 changes depending on the difference in the secondary transfer bias. Even if the charging polarity of the recording material 9 changes, the charge eliminating plate 90 is appropriately changed to the first position 91 and the second position 92 shown in FIG. This makes it possible to efficiently remove the charge on the recording material 9 according to the charge polarity of the recording material 9. Other configurations are configured in the same manner as the above embodiments, and the same effects can be obtained.

[Fourth embodiment]
Next, a configuration of an image forming apparatus according to a fourth embodiment of the present invention will be described with reference to FIGS. In addition, the same components as those in the above-described embodiments are denoted by the same reference numerals or the same reference numerals even if the reference numerals are different, and the description is omitted. FIG. 13 is a cross-sectional view illustrating a configuration of the static eliminator 12 of the present embodiment. As shown in FIG. 13, the core metal 56a of the secondary transfer roller 56 is connected to the ground potential G, and the secondary transfer bias is applied from the secondary transfer power source D2a to the core metal 54a of the opposing roller 54 constituting the secondary transfer unit 17. Is applied.

  At this time, as the secondary transfer bias applied from the secondary transfer power source D2a to the core metal 54a of the opposing roller 54, "-1" is multiplied by the secondary transfer bias voltage value shown on the horizontal axis in FIG. A value (same value in absolute value) can be applied. A secondary transfer bias having a value obtained by multiplying the secondary transfer bias voltage value shown on the horizontal axis of FIG. 12 by “−1” is applied from the secondary transfer power source D2a shown in FIG. Then, the positive and negative potentials of the recording material shown on the vertical axis in FIG. 12 remain unchanged.

  Therefore, a secondary transfer bias having an absolute value smaller than −1700 V obtained by multiplying 1700 V of the secondary transfer bias voltage value shown on the horizontal axis of FIG. 12 by “−1” is applied to the core metal 54 a of the opposing roller 54. Then, as shown on the vertical axis in FIG. 12, the recording material 9 has a positive polarity. At this time, the charge removing plate 90 is set at the first position 91.

  On the other hand, a secondary transfer bias having an absolute value larger than −1700 V obtained by multiplying the secondary transfer bias voltage value of 1700 V shown in the horizontal axis of FIG. 12 by “−1” is applied to the core metal 54 a of the opposing roller 54. Then, as shown on the vertical axis of FIG. 12, the recording material 9 has a negative polarity. At this time, the charge removing plate 90 is set at the second position 92.

  That is, when the absolute value of the secondary transfer bias applied to the core metal 54 a of the opposing roller 54 is smaller than the second threshold value of −1700 V in absolute value, the controller 110 The direction is set to the first position 91. When the absolute value of the secondary transfer bias applied to the core metal 54a of the opposing roller 54 is larger than the second threshold value of -1700 V in absolute value, the short direction of the charge removing plate 90 is changed to the second direction. Set to two positions 92. Even if such a configuration is adopted, the same effects as those of the above-described embodiments can be obtained.

<Modification>
FIG. 14 is a cross-sectional view illustrating a configuration of a modification of the static eliminator 12 of the present embodiment. As shown in FIG. 14, a first secondary transfer bias is applied from a secondary transfer power source D2a to a core metal 54a of the opposed roller 54 constituting the secondary transfer unit 17. Further, a second secondary transfer bias is applied from the secondary transfer power source D2b to the core metal 56a of the secondary transfer roller 56 constituting the secondary transfer unit 17.

  As the first secondary transfer bias applied from the secondary transfer power source D2a to the metal core 54a of the opposing roller 54, a value of -1/2 of the secondary transfer bias voltage value shown on the horizontal axis in FIG. 12 is used. Apply. As the secondary transfer bias applied from the secondary transfer power source D2b to the metal core 56a of the secondary transfer roller 56, a value of 1/2 of the secondary transfer bias voltage value shown on the horizontal axis in FIG. 12 is used. Can be applied.

  When a secondary transfer bias of a value obtained by multiplying the secondary transfer bias voltage value shown on the horizontal axis of FIG. 12 by “−1” is applied to the core metal 54 a of the opposed roller 54, the vertical axis of FIG. The indicated positive and negative potentials of the recording material 9 remain as they are. Here, a first secondary transfer bias consisting of a negative voltage applied to the core metal 54a of the opposing roller 54 from the secondary transfer power source D2a shown in FIG. 14 is considered. Further, a second secondary transfer bias consisting of a positive voltage applied from the secondary transfer power source D2b to the core metal 56a of the secondary transfer roller 56 is considered.

  When the secondary transfer bias obtained by adding the absolute values of the first and second secondary transfer biases is smaller in absolute value than 1700 V shown on the horizontal axis of FIG. 12, the vertical axis of FIG. As shown, the recording material 9 has a positive polarity. At this time, the charge removing plate 90 is set at the first position 91.

  On the other hand, when the secondary transfer bias obtained by adding the absolute values of the first and second secondary transfer biases is larger in absolute value than 1700 V shown on the horizontal axis of FIG. 12, the vertical axis of FIG. As shown, the recording material 9 has a negative polarity. At this time, the charge removing plate 90 is set at the second position 92.

  That is, the control unit 110 considers the first secondary transfer bias applied to the core metal 54a of the opposing roller 54 and the second secondary transfer bias applied to the core metal 56a of the secondary transfer roller 56. I do. If the absolute value of the secondary transfer bias obtained by adding the absolute values of the first and second secondary transfer biases is smaller than the absolute value of 1700 V as the second threshold value, the shorting of the charge removing plate 90 is performed. The direction of the hand direction is set to the first position 91.

  When the absolute value of the secondary transfer bias obtained by adding the absolute values of the first and second secondary transfer biases is larger than 1700 V as the second threshold, The short-side direction of the charge removing plate 90 is set to the second position 92. Even with such a configuration, the same effects as those of the above-described embodiments can be obtained. Other configurations are configured in the same manner as the above embodiments, and the same effects can be obtained.

[Fifth Embodiment]
Next, a configuration of an image forming apparatus according to a fifth embodiment of the present invention will be described with reference to FIG. In addition, the same components as those in the above-described embodiments are denoted by the same reference numerals or the same reference numerals even if the reference numerals are different, and the description is omitted. FIG. 15 is a cross-sectional view illustrating a configuration of the static eliminator 12 of the present embodiment.

  As shown in FIG. 15, the non-movable portion 90b of the charge removing plate 90 is not connected to the ground potential G via the holding member 94. The control unit 110 applies a discharging bias to the discharging plate 90 by the discharging power source D5 in a state where the discharging plate 90 is set to at least one of the first position 91 and the second position 92 shown in FIG. When the static elimination plate 90 is set at the first position 91, −1000 V is applied as the static elimination bias applied to the static elimination plate 90 from the static elimination power source D 5, and the static elimination plate 90 is set to the second position 92. If so, +1000 V can be applied.

  When positively or negatively charged recording material 9 is desired to be positively neutralized in this way, positive or negative polarity is applied to neutralizing plate 90 by static elimination power source D5 so as to cancel the charging polarity of recording material 9. A static neutralization bias is applied. Even if such a configuration is adopted, the same effects as those of the above-described embodiments can be obtained. Other configurations are configured in the same manner as the above embodiments, and the same effects can be obtained.

N2 Secondary transfer nip 9 Recording material 56 Secondary transfer roller 90 Static elimination plate 91 First position 92 Second position 110 Control unit

Claims (13)

An image carrier on which the toner image is carried;
An endless intermediate transfer member arranged opposite to the image carrier,
A primary transfer unit that primarily transfers a toner image from the image carrier to the intermediate transfer body,
A secondary transfer unit for secondary transfer of the toner image primarily transferred to the intermediate transfer body to a recording material,
Has,
The secondary transfer unit,
A secondary transfer roller,
An opposing roller that forms a secondary transfer nip for opposing the secondary transfer roller and nipping and conveying the recording material via the intermediate transfer member;
A static elimination plate that is disposed downstream of the secondary transfer nip portion in the transport direction of the recording material and whose longitudinal direction is disposed parallel to the axial direction of the secondary transfer roller;
A control unit for controlling the direction of the short direction of the charge removing plate,
Has,
The control unit includes:
A first position in which the short direction of the charge removing plate is arranged toward the secondary transfer nip portion;
A second position in which the short direction of the charge removing plate is arranged in a direction different from the first position;
The image forming apparatus according to any one of claims 1 to 3, wherein the direction of the short side of the charge removing plate is controlled.   The control unit acquires the charging polarity of the recording material, and when the recording material is positively charged, sets the short direction of the charge removing plate to the first position, and sets the recording material to a negative polarity. 2. The image forming apparatus according to claim 1, wherein, when the image forming apparatus is charged, the direction of the short side of the charge removing plate is set to the second position. 3. When the short direction of the static elimination plate was set to the first position, a surface extending the surface of the static elimination plate was connected to the rotation axis center of the secondary transfer roller and the rotation axis center of the opposing roller. Of the angles at which the straight line intersects, the angle θ1 on the secondary transfer roller side is:
40 ° ≦ θ1 ≦ 80 °
The image forming apparatus according to claim 1, wherein the image forming apparatus is set in a range of:   When the short direction of the neutralization plate was set to the second position, a surface extending the surface of the neutralization plate was connected to the rotation axis center of the secondary transfer roller and the rotation axis center of the opposing roller. 4. The image forming apparatus according to claim 1, wherein an angle θ <b> 2 on the side of the secondary transfer roller among angles at which a straight line intersects is set in a range of 30 ° or less. 5. .   The apparatus according to claim 1, wherein the static elimination plate set at the second position is disposed downstream of the static elimination plate set at the first position in a recording material conveyance direction. Item 10. The image forming apparatus according to item 1.   The image forming apparatus according to claim 1, wherein the control unit controls a direction of a short side of the charge removing plate according to a conveyance speed of the recording material.   The control unit sets the short direction of the charge elimination plate to the first position when the recording material conveyance speed is lower than a threshold, and when the recording material conveyance speed is higher than the threshold, 7. The image forming apparatus according to claim 6, wherein the direction of the width direction of the charge removing plate is set to the second position.   The control unit is configured to control the width of the neutralization plate according to a secondary transfer bias applied when the toner image primarily transferred to the intermediate transfer body is secondarily transferred to a recording material in the secondary transfer nip unit. The image forming apparatus according to claim 1, wherein a direction of the direction is controlled.   When the absolute value of the secondary transfer bias is smaller than a second threshold, the control unit sets the short direction of the charge removing plate to the first position, and sets the absolute value of the secondary transfer bias. 9. The image forming apparatus according to claim 8, wherein when the value is larger than a second threshold, the short direction of the charge removing plate is set to the second position. 10.   10. The image forming apparatus according to claim 8, wherein the opposing roller is connected to a ground potential, and the secondary transfer bias is applied to the secondary transfer roller.   The image forming apparatus according to claim 8, wherein the secondary transfer roller is connected to a ground potential, and the secondary transfer bias is applied to the opposing roller.   9. The apparatus according to claim 1, wherein a first secondary transfer bias is applied to the opposing roller, and a second secondary transfer bias is applied to the secondary transfer roller. 10. Image forming device. A static elimination power supply for applying a static elimination bias to the static elimination plate,
The control unit applies a charge-eliminating bias to the charge-eliminating plate by the charge-eliminating power source in a state where the charge-eliminating plate is set at at least one of the first position and the second position. The image forming apparatus according to claim 1.