JP2019120830A - Image forming device - Google Patents

Abstract

To provide an image forming device with which it is possible to suppress the scattering of a toner due to impact shock that occurs when the tip of a recording medium thrusts into a second transfer nip, as compared with a configuration in which a nip part is not changed immediately before the nip part thrusts into the recording medium and after it thrusts into the nip part.SOLUTION: The image forming device comprises: image holding means for holding a toner image while conveying it; transfer means for transferring the toner image on the image holding means to a recording medium; counter means coming in contact with the inner circumferential surface of the image holding means and facing the transfer means; and control means for controlling the nip part where the transfer means contacts the counter means across the image holding means so that the recording medium is moved closer to the upstream side in the conveyance direction after the recording medium thrusts into the nip part than immediately before the recording medium thrusts into the nip part.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus.

  An intermediate transfer belt which is stretched by a plurality of rollers and conveys a toner image on the outer peripheral surface, a secondary transfer member which secondarily transfers the toner image on the intermediate transfer belt to a recording medium, an inner peripheral surface of the intermediate transfer belt The intermediate transfer belt and the secondary transfer belt at a secondary transfer position where the secondary transfer member abuts against the secondary transfer member on the basis of sheet attribute information of the recording medium based on the sheet attribute information of the recording medium. There is known an image forming apparatus including: a changing unit configured to change a contact width formed by a member (Patent Document 1).

  A color image forming apparatus provided with pressing force application means for applying pressing force to the intermediate transfer unit in the direction opposite to the pressing direction by the secondary transfer member in accordance with the timing when the recording medium rushes into the secondary transfer portion It is also known (patent document 2)

JP, 2014-134718, A JP, 2015-102836, A

  According to the present invention, the toner is generated by an impact generated when the leading end of the recording medium contacts the nip portion immediately before the recording medium contacts the nip portion and as compared with the configuration in which the nip portion is not changed after contacting the nip portion. It is an object of the present invention to provide an image forming apparatus capable of suppressing the scattering of ink.

In order to solve the problem, an image forming apparatus according to claim 1 is
An image holding unit that holds and conveys a toner image;
A transfer unit that transfers the toner image on the image holding unit to a recording medium;
An opposing unit that is in contact with the inner circumferential surface of the image holding unit to face the transfer unit;
Before the recording medium comes into contact with the nip portion, the recording medium passes through the nip between the central portion in the conveyance direction of the recording medium of the nip portion where the transfer means abuts the opposing means across the image holding means. Control means for controlling to move to the downstream side in the transport direction as compared with after contacting the part;
It is characterized by

In order to solve the above-mentioned subject, the image forming apparatus according to claim 2 is:
An image holding unit that holds and conveys a toner image;
A transfer unit that transfers the toner image on the image holding unit to a recording medium;
An opposing unit that is in contact with the inner circumferential surface of the image holding unit to face the transfer unit;
The contact width in which a portion of the peripheral surface of the image holding means and a portion of the peripheral surface of the transfer means are in surface contact at the nip where the transfer means abuts the opposing means with the image holding means interposed therebetween And control means for controlling the recording medium to decrease before the recording medium contacts the nip as compared to after the recording medium contacts the nip.
It is characterized by

The invention according to claim 3 is the image forming apparatus according to claim 1 or 2
The control means moves the facing means downstream in the conveyance direction of the recording medium after the recording medium comes in contact with the nip portion as compared to before the contact with the nip portion.
It is characterized by

The invention according to claim 4 is the image forming apparatus according to claim 1 or 2
The control means moves the facing means upstream in the conveyance direction of the recording medium in accordance with the mass of the uppermost toner layer on the image holding means.
It is characterized by

The invention according to claim 5 is the image forming apparatus according to claim 4.
The control unit increases the moving amount of the facing unit as the mass of the toner layer of the uppermost layer on the image holding unit increases.
It is characterized by

The invention according to claim 6 is the image forming apparatus according to claim 1 or 2
The control unit increases the moving amount of the facing unit as the basis weight of the recording medium increases.
It is characterized by

The invention according to claim 7 is the image forming apparatus according to claim 1 or 2
The control means increases the moving amount of the facing means as the process speed of the image holding means increases.
It is characterized by

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects,
The toner image includes a white toner layer made of white toner or a silver toner layer made of silver toner containing an aluminum pigment.
It is characterized by

  According to the first aspect of the present invention, the leading end portion of the recording medium is compared with a configuration in which the nip portion in the conveyance direction of the recording medium is not changed before and after the recording medium enters the nip portion. It is possible to suppress the toner from being scattered by an impact generated when the toner rushes into the nip portion.

  According to the second aspect of the invention, before the recording medium enters the nip and after entering the nip at the nip, a part of the circumferential surface of the image holding means and a part of the circumferential surface of the transfer means As compared with the configuration in which the contact width at which the surface contacts the surface is not changed, the scattering of the toner due to the impact generated when the leading end portion of the recording medium rushes into the nip portion can be suppressed.

  According to the third aspect of the present invention, after the recording medium enters the nip portion, recording is performed as compared with the case where the opposing means is not moved downstream in the conveyance direction of the recording medium as compared to before entering the nip portion. After the medium rushes into the nip portion, the contact width in which a part of the peripheral surface of the image holding means and a part of the peripheral surface of the transfer means are in surface contact in the nip part can be increased.

  According to the fourth aspect of the invention, on the image holding means, the facing means is not moved to the upstream side in the conveyance direction of the recording medium according to the mass of the toner layer of the uppermost layer on the image holding means. Scattering of toner in the uppermost toner layer can be suppressed.

  According to the fifth aspect of the present invention, the toner layer of the uppermost layer is formed on the image holding means as compared with the case where the moving amount of the facing means is not increased as the mass of the toner layer of the uppermost layer is increased on the image holding means. Scattering of toner can be suppressed.

  According to the sixth aspect of the invention, the scattering of the toner can be suppressed as compared with the case where the moving amount of the facing means is not increased as the basis weight of the recording medium is increased.

  According to the seventh aspect of the present invention, the scattering of the toner can be suppressed as compared with the case where the moving amount of the facing means is not increased as the process speed of the image carrier becomes faster.

  According to the eighth aspect of the present invention, it is possible to obtain a toner image in which the shielding property is secured without being influenced by the recording medium to be the base.

FIG. 1 is a schematic cross-sectional view showing an example of a schematic configuration of an image forming apparatus according to a first embodiment. FIG. 2 is a block diagram showing a functional configuration of the image forming apparatus according to the first embodiment. FIG. 2 is a schematic cross-sectional view showing the configuration of a transfer device of the image forming apparatus according to the first embodiment. FIG. 6 is a view showing a configuration of transfer bias application and transfer nip adjustment in a secondary transfer portion of the image forming apparatus according to the first embodiment. FIG. 7 is a schematic cross-sectional view of the secondary transfer portion showing the movement of the rotation shaft of the backup roller by the movement mechanism, and FIG. FIG. 7 is a schematic cross-sectional view showing a state in which the transfer nip position is changed by moving the rotational shaft of the backup roller upstream in the transport direction by the operation of the moving mechanism. 5 is a flowchart showing a flow of control of an offset angle at the time of secondary transfer in the image forming apparatus according to the first embodiment. FIG. 8 is a schematic cross-sectional view showing a state in which the transfer nip position has changed by the rotation shaft of the backup roller moving downstream in the transport direction by the operation of the moving mechanism. FIG. 7 is a schematic cross-sectional view showing a state in which the transfer nip width has changed due to the rotation shaft of the backup roller moving upstream in the transport direction by the operation of the moving mechanism. FIG. 10 is a schematic cross-sectional view showing a state in which the transfer nip width has changed due to the rotational shaft of the backup roller moving downstream in the transport direction by the operation of the moving mechanism. 7 is a flowchart showing a flow of control of an offset angle at the time of secondary transfer in the image forming apparatus according to the second embodiment. It is a flowchart which shows the flow of control of the offset angle at the time of secondary transfer in the image forming apparatus which concerns on 3rd Embodiment. It is a figure which shows the result of the image evaluation in each condition of an Example. It is a schematic diagram which shows the image defect which this invention tends to solve. It is a schematic diagram for demonstrating the presumed cause which the image defect which this invention tends to solve generate | occur | produce. (A) is a schematic view showing a toner image containing a white toner, (b) is a schematic view showing a holding state of the toner image containing a white toner on an intermediate transfer belt.

Next, the present invention will be described in more detail by way of embodiments and specific examples with reference to the drawings, but the present invention is not limited to these embodiments and specific examples.
Moreover, in the description using the following drawings, it should be noted that the drawings are schematic, and that the ratio of each dimension is different from the actual one, and is necessary for the explanation to facilitate understanding. The illustration other than the members is appropriately omitted.
In order to facilitate the understanding of the following description, in the drawings, the front-rear direction is taken as the X-axis direction, the left-right direction as the Y-axis direction, and the vertical direction as the Z-axis direction.

First Embodiment
(1) Overall Configuration and Operation of Image Forming Apparatus (1.1) Overall Configuration of Image Forming Apparatus FIG. 1 is a schematic sectional view showing an example of a schematic configuration of an image forming apparatus 1 according to the present embodiment, and FIG. FIG. 2 is a block diagram showing a functional configuration of the device 1;
The image forming apparatus 1 includes an image forming unit 10, a sheet feeding device 20 mounted at one end of the image forming unit 10, and the other end of the image forming unit 10, and discharges the printed sheet P. A paper unit 30, an operation display unit 40, and an image processing unit 50 that generates image information from print information transmitted from a host device are configured.

  The image forming unit 10 includes a system control unit 11 (not shown), an exposure unit 12, a photosensitive unit 13, a developing unit 14, a transfer unit 15, sheet conveying units 16 a, 16 b and 16 c, a fixing unit 17, and a driving unit 18 (not And the image information received from the image processing unit 50 is formed as a toner image on a sheet P as an example of a recording medium sent from the sheet feeding device 20.

  The sheet feeding device 20 supplies the sheet P to the image forming unit 10. That is, a plurality of sheet stacking units for storing sheets P of different types (for example, material, thickness, sheet size, grain size) are provided, and the sheet P fed from any one of the plurality of sheet stacking units Are supplied to the image forming unit 10.

  The paper discharge unit 30 discharges the recording medium on which the image output has been performed by the image forming unit 10. To that end, the paper discharge unit 30 includes a paper discharge storage unit to which the recording medium after the image output is discharged. Note that the discharge unit 30 may have a function of performing post-processing such as cutting and stapling (stitching) on a sheet bundle output from the image forming unit 10.

  The operation display unit 40 is used to input various settings and instructions and to display information. That is, it corresponds to a so-called user interface, and more specifically, is configured by combining a liquid crystal display panel, various operation buttons, a touch panel, and the like.

(1.2) Configuration and Operation of Image Forming Unit In the image forming apparatus 1 having such a configuration, of the sheet feeding device 20 according to the timing of image formation, stacking of sheets designated for each printing in the print job is performed. The sheet P fed from the unit is fed to the image forming unit 10.

  The photosensitive unit 13 is provided below the exposure device 12 in parallel, and includes a photosensitive drum 31 as an image holder that is rotationally driven. The charger 32, the exposure device 12, the developing device 14, the primary transfer roller 52, and the cleaning blade 33 are disposed along the rotational direction of the photosensitive drum 31.

The developing device 14 has a developing housing 41 in which a developer is accommodated. In the developing housing 41, a developing roller 42 disposed so as to face the photosensitive drum 31 is disposed. A developer whose layer thickness is regulated is supplied to the developing roller 42, and a toner image is formed on the photosensitive drum 31.
The respective developing devices 14 are configured in substantially the same manner except for the developer contained in the developing housing 41, and each of the developing devices 14 is yellow (Y), magenta (M), cyan (C), black (K), white (W) ), Form a toner image of silver (S) as a special color.

  Above the developing device 14, a replaceable toner cartridge T containing a developer (toner including carrier) is mounted. A toner cartridge guide TG for supplying a developer from each toner cartridge T to the developing device 14 is disposed.

  The surface of the rotating photosensitive drum 31 is charged by the charger 32 and an electrostatic latent image is formed by the latent image forming light emitted from the exposure device 12. The electrostatic latent image formed on the photosensitive drum 31 is developed as a toner image by the developing roller 42.

  The transfer device 15 is formed by an intermediate transfer belt 51 as an example of an image holding unit on which each color toner image formed on the photosensitive drum 31 of each photosensitive unit 13 is transferred in multiple, and each photosensitive unit 13 A primary transfer roller 52 for sequentially transferring (primary transfer) each color toner image onto the intermediate transfer belt 51, and collectively transferring each color toner image transferred superimposed on the intermediate transfer belt 51 onto a sheet P serving as a recording medium (secondary transfer And a secondary transfer belt 53 as an example of the transfer means.

  The secondary transfer belt 53 is stretched by a secondary transfer roller 54 and a peeling roller 55, and is disposed on the back side of the intermediate transfer belt 51 as a backup roller 65 and a secondary transfer roller 54 as an example of opposing means. The sheet is nipped to form a secondary transfer portion TR.

  Each color toner image formed on the photosensitive drum 31 of each photosensitive unit 13 is subjected to an intermediate transfer by the primary transfer roller 52 to which a predetermined transfer voltage is applied from a power source (not shown) controlled by the system control device 11 Electrostatic transfer (primary transfer) is sequentially performed on the belt 51 to form a superimposed toner image on which each color toner is superimposed.

  The superimposed toner image on the intermediate transfer belt 51 is conveyed to the secondary transfer portion TR in which the secondary transfer belt 53 is disposed as the intermediate transfer belt 51 moves. When the superimposed toner image is conveyed to the secondary transfer portion TR, the sheet P is supplied from the sheet feeding device 20 to the secondary transfer portion TR in accordance with the timing. The backup roller 65 facing the secondary transfer roller 54, which is grounded via the secondary transfer belt 53, receives a predetermined transfer voltage from the power supply device or the like controlled by the system control device 11 via the feed roller 65A. As a result, the multiple toner images on the intermediate transfer belt 51 are collectively transferred onto the sheet P.

  The residual toner on the surface of the photosensitive drum 31 is removed by the cleaning blade 34 and collected in a waste toner storage portion (not shown). The surface of the photosensitive drum 31 is recharged by the charger 32.

The fixing device 17 has an endless fixing belt 17a rotating in one direction, and a pressure roller 17b in contact with the circumferential surface of the fixing belt 17a and rotating in one direction, and pressure contact of the fixing belt 17a with the pressure roller 17b The area forms a fixing area.
The sheet P to which the toner image has been transferred in the transfer device 15 is conveyed to the fixing device 17 via the sheet conveying device 16 a in a state where the toner image is not fixed. The toner image is fixed on the recording medium conveyed to the fixing device 17 by the action of pressure bonding and heating by the pair of fixing belts 17 a and the pressure roller 17 b.

The sheet P for which fixing has been completed is sent to the sheet discharge unit 30 via the sheet conveyance device 16 b.
When the image is output on both sides of the sheet P, the sheet P is reversed by the sheet conveying device 16c, and the sheet P is again sent to the secondary transfer unit TR in the image forming unit 10. Then, after the transfer of the toner image and the fixing of the transfer image are performed, the sheet is sent to the sheet discharge unit 30. The sheet P sent to the sheet discharge unit 30 is discharged to the sheet discharge storage unit after being subjected to post-processing such as cutting and stapling (stitching) as necessary.

(2) Configuration and Function of Transfer Device (2.1) Configuration of Transfer Device FIG. 3 is a schematic cross-sectional view showing the configuration of the transfer device 15 of the image forming device 1 according to the present embodiment. FIG. 14 is a view showing the configuration of transfer bias application and transfer nip adjustment in the secondary transfer portion TR, FIG. 14 is a schematic view showing an image defect to be solved by the present invention, and FIG. 15 is a generation of an image defect to be solved by the present invention FIG. 16A is a schematic view showing a toner image containing white toner, and FIG. 16B is a schematic view showing a holding state of the toner image containing white toner on the intermediate transfer belt 51. FIG.
The transfer device 15 includes an intermediate transfer belt 51, a primary transfer roller 52, a secondary transfer belt 53, a backup roller 65, a secondary transfer roller 54, and a cleaning device 56.

  The intermediate transfer belt 51 is made of a resin such as polyimide or polyamide imide containing an appropriate amount of a conductive agent such as carbon black, and is formed to have a volume resistivity of 1E + 10 to 1E + 14 Ω · cm, The film is composed of a film-like endless belt having a thickness of, for example, about 0.1 mm.

  The intermediate transfer belt 51 includes a driving roller 61 for driving the intermediate transfer belt 51 to circulate, a driven roller 62 for supporting the intermediate transfer belt 51 extending substantially linearly along the arrangement direction of the photosensitive drums 31, and the intermediate transfer belt 51. Against the tension roller 63 for preventing the meandering of the intermediate transfer belt 51 while giving a constant tension to the support roller 64 provided on the upstream side of the secondary transfer portion TR and supporting the intermediate transfer belt 51, the secondary transfer portion TR. A backup roller 65 is provided, and a cleaning backup roller 66 provided in a cleaning unit for scraping off the residual toner on the intermediate transfer belt 51 is looped and moved (see arrow A in the drawing).

The backup roller 65 is a tube of blend rubber of EPDM and NBR in which carbon is dispersed on the surface, the inside is made of EPDM rubber, the surface resistivity is 1E + 7 to 1E + 10Ω / □, and the roller diameter is 28 mm. The hardness is set to, for example, 70 degrees (Asker C).
The backup roller 65 is disposed on the back surface side of the intermediate transfer belt 51 to form a counter electrode of the secondary transfer belt 53. A metal feed roller 65A is disposed in contact with the backup roller 65. The metal feed roller 65A applies a DC voltage for forming a secondary transfer electric field at the secondary transfer portion TR.

 The primary transfer roller 52 is provided opposite to each photosensitive drum 31 with the intermediate transfer belt 51 interposed therebetween, and a voltage having a polarity opposite to the charging polarity of the toner is applied. As a result, the toner images on the respective photosensitive drums 31 are electrostatically attracted to the intermediate transfer belt 51 sequentially, and a toner image superimposed on the intermediate transfer belt 51 is formed.

The secondary transfer belt 53 is a semiconductive endless annular belt in which a conductive material such as carbon black is contained in an appropriate amount in a rubber member such as chloroprene or EPDM, and the volume resistivity is adjusted to 1E + 6 to 1E + 10 Ω · cm, for example. .
As shown in FIG. 3, the secondary transfer belt 53 is stretched around the secondary transfer roller 54 and the peeling roller 55, and is given a predetermined tension. Then, in the present embodiment, the secondary transfer belt 53 receives the driving force from the secondary transfer roller 54 and rotates at a predetermined speed (see the arrow B in the drawing).

The secondary transfer roller 54 has a conductive layer made of a foam such as silicone rubber, urethane rubber, or EPDM in which a conductive agent such as carbon black is dispersed, for example, laminated on the outer periphery of a core material that is a metal shaft. And is disposed opposite to the backup roller 65 via the secondary transfer belt 53 and the intermediate transfer belt 51.
The secondary transfer roller 54 is electrically grounded to the sheet P conveyed on the secondary transfer belt 53, and secondary-transfers the toner image held by the intermediate transfer belt 51 together with the backup roller 65. A transfer portion TR is formed.
Further, a drive motor (not shown) is connected to the secondary transfer roller 54, and is rotated by the drive motor to rotate, and further the secondary transfer belt 53 is rotated.

As shown in FIG. 3, the peeling roller 55 is located downstream of the secondary transfer roller 54 in the direction of rotation of the secondary transfer belt 53 (direction of arrow B in the drawing), and the peeling roller 55 and the secondary transfer roller 54 Thus, the belt surface for conveying the sheet P toward the downstream side is formed.
Further, the peeling roller 55 is set to have a diameter of the peeling roller 55 smaller than that of the secondary transfer roller 54 in order to peel the sheet P from the surface of the secondary transfer belt 53.

On the upstream side of the secondary transfer portion TR of the transfer device 15, a sheet guide 28 as an example of a guiding means for guiding the sheet P to the secondary transfer portion TR opposite to the toner image holding surface of the intermediate transfer belt 51 It is arranged.
The sheet guiding guide 28 includes a sheet guiding guide 28 a for guiding the upper surface (transfer surface) of the sheet P and a sheet guiding guide 28 b for guiding the lower surface (non-transfer surface) of the sheet P.
(2.2) Movement Control of Backup Roller FIG. 5A is a schematic cross-sectional view of the secondary transfer portion showing the movement of the rotation shaft of the backup roller 65 by the movement mechanism, and FIG. 5B shows a configuration example of the movement mechanism 110. FIG. 6 is a schematic cross-sectional view showing a state in which the transfer nip position is changed by moving the rotational shaft of the backup roller 65 upstream in the transport direction by the operation of the moving mechanism 110. FIG. 8 is a schematic cross-sectional view showing a state in which the transfer nip position is changed by the rotation shaft of the backup roller 65 being moved downstream in the transport direction by the operation of the moving mechanism 110. FIG. 9 is a schematic cross-sectional view showing a state in which the transfer nip width is changed by moving the rotating shaft of the backup roller 65 to the upstream side in the transport direction by the operation of the moving mechanism 110. Figure 10 is a schematic sectional view showing a state where the nip width by moving changes the rotation axis in the conveying direction downstream side of the backup roller 65 by the operation of the moving mechanism 110.

Here, the phenomenon which occurs in the secondary transfer portion TR will be described.
In the secondary transfer portion TR, the sheet P is brought into pressure contact at the transfer nip between the secondary transfer belt 53 and the backup roller 65 via the intermediate transfer belt 51 to apply a secondary transfer bias, and the toner image is formed by the formed electric field. Transfer to paper P.

Here, if the toner image formed on the intermediate transfer belt 51 is a toner image with white (W) toner or silver (S) toner, it scatters to the rear side in the transport direction at the leading end L / E side of the sheet P Image defects may occur (see FIG. 14).
When the leading edge L / E of the sheet P rushes into the secondary transfer portion TR, the sheet P strikes the transfer nip, and the tip region collides with the intermediate transfer belt 51 side (see arrow R in FIG. 15). . Due to this collision, the intermediate transfer belt 51 vibrates, and the toner held on the intermediate transfer belt 51 is scattered before the secondary transfer (see FIG. 11). In particular, since the white (W) toner and the silver (S) toner contain metal pigments, the mass is large, and the force received from the vibration of the intermediate transfer belt 51 is large, so it is presumed that such toner scattering is likely to occur. .

More specifically, when the leading end L / E of the sheet P enters the transfer nip portion NP of the secondary transfer portion TR, the sheet P is held about 15 mm upstream in the moving direction of the intermediate transfer belt 51 from the transfer nip portion NP. The toner image (see L in FIG. 11) may be scattered to the rear side in the moving direction on the intermediate transfer belt 51.
This is because, after the leading edge L / E of the sheet P rushes into the transfer nip portion NP of the secondary transfer portion TR, the sheet P is conveyed by about 15 mm and bent in a loop shape and collides with the intermediate transfer belt 51 side. It is presumed that the transfer belt 51 vibrates and the toner on the intermediate transfer belt 51 is scattered.

  In the image forming apparatus 1 according to the present embodiment, the transfer nip portion NP in which the secondary transfer belt 53 and the secondary transfer roller 54 abut on the backup roller 65 with the intermediate transfer belt 51 interposed therebetween is moved in the conveyance direction of the sheet P. A moving mechanism 110 is provided. Then, before the sheet P enters the transfer nip portion NP, the moving mechanism 110 moves the transfer nip portion NP to the upstream side in the transport direction of the sheet P as compared to after the sheet P enters the transfer nip portion NP. To control.

  Specifically, as shown in FIG. 5A (see arrow R in FIG. 5A), the moving mechanism 110 moves the transfer nip portion NP by moving the rotation shaft of the backup roller 65. .

  The moving mechanism 110 includes a transfer frame 111, a backup roller support frame 112, an eccentric cam 113, a rotary actuator 114, and a tension spring 115, as shown in FIG. 5B. The backup roller 65 is rotatably supported by the backup roller support frame 112 by a bearing.

The backup roller support frame 112 is movably supported by the stud 116 on the transfer frame 111 within the range of the major diameter of the elongated hole 117. The stud 116 protrudes through the elongated hole 117 of the transfer frame 111, and the eccentric cam 113 is in contact with the stud 116. The eccentric cam 113 is rotated by the rotary actuator 114 to move the stud 116 within the range of the major diameter of the elongated hole 117 of the transfer frame 111 to move the rotation shaft of the backup roller 65.
Thereby, the backup roller 65 moves in the transport direction of the sheet P in the secondary transfer portion TR, passes through the rotation center OA of the secondary transfer roller 54, the normal N along the vertical direction (Z direction), and the backup roller An angle (offset angle) between the rotation center OB of 65 and a line segment AB connecting the rotation center OA of the secondary transfer roller 54 is changed.

  For example, as shown in FIG. 8, when the eccentric cam 113 is rotated by the rotary actuator 114, the stud 116 moves in the range of the long hole 117, and the backup roller 65 moves its rotation axis to increase the offset angle Θ. Then, the position P1 of the transfer nip portion NP moves to the downstream side (P2) in the sheet conveyance direction (Θ1 to Θ2).

The system control apparatus 11 acquires toner information (S101), and determines whether the mass of toner used for image formation is equal to or greater than a threshold (S102). For example, when forming a toner image including white (W) toner using black paper containing carbon black as paper P, as shown in FIG. On the intermediate transfer belt 51, white (W) is held on the top layer because the white (W) toner having a large mass including the metal pigment is transferred (see FIG. 16B). The mass of the white (W) toner is 0.24 × 10 ⁻⁹ g, which is equal to or greater than the threshold.

When the mass of toner used for image formation is equal to or greater than the threshold (S102: Yes), the system control apparatus 11 rotationally drives the rotary actuator 114 (S103) to move the rotation shaft of the backup roller 65 upstream of the sheet conveyance direction. Move to the side to reduce the offset angle Θ (Θ2 to Θ1) with respect to the normal transfer (see FIG. 6). The system control device 11 increases the moving amount of the rotation shaft of the backup roller 65 as the toner mass of the toner layer which is the uppermost layer on the intermediate transfer belt 51 increases.
Thus, when the leading end L / E of the sheet P enters the transfer nip portion NP, the transfer nip portion NP is positioned on the upstream side in the sheet conveyance direction compared to that at the time of normal transfer. The tip L / E enters the transfer nip NP at a shallower angle, and deflection of the tip region is suppressed (see FIG. 6).

  Then, the system control device 11 rotates the rotary actuator 114 again (S105) at the timing (S104: Yes) at which the leading edge L / E of the sheet P has been conveyed 15 mm in the transfer nip portion NP (S105). The rotary shaft of is moved to the downstream side in the sheet conveyance direction to return to the offset angle 時 の at normal transfer (Θ 1 to Θ 2: see FIG. 8). Thereby, the transfer nip portion NP is positioned at the time of normal transfer, and the secondary transfer of the toner image onto the sheet P is performed in a state where the transfer nip width NW is increased (see FIG. 10).

In this manner, before the sheet P rushes into the transfer nip portion NP, the leading end L / E of the sheet P being conveyed is moved upstream of the transfer nip portion NP in the sheet conveyance direction as compared with that during normal transfer. After the sheet P is received and pushed into the transfer nip portion NP, the transfer nip portion NP is moved to the downstream side in the transport direction of the sheet P as compared with before the sheet P is pushed into the transfer nip portion NP.
Thereby, the leading edge L / E of the sheet P is compared with a configuration in which the transfer nip portion NP in the conveyance direction of the sheet P is not changed before the sheet P rushes into the transfer nip portion NP and after rushing into the transfer nip portion NP. It is possible to suppress the toner from being scattered by the impact generated when the toner rushes into the transfer nip portion NP.

  The operation of moving the position of the transfer nip portion NP by changing the offset angle 軸 of the secondary transfer roller 54 by moving the rotation shaft of the backup roller 65 in the sheet conveyance direction by the moving mechanism 110 has been described. As shown in FIGS. 9 and 10, by changing the offset angle Θ of the secondary transfer roller 54, part of the peripheral surface of the intermediate transfer belt 51 and part of the peripheral surface of the secondary transfer belt 53 are surfaces. The contact nip width NW decreases or increases.

  As shown in FIG. 9, the rotary actuator 114 is driven to rotate 180 degrees to move the rotation shaft of the backup roller 65 to the upstream side in the sheet conveyance direction, thereby reducing the offset angle Θ from the normal transfer (Θ2 to Θ1) Then, the transfer nip width NW decreases (see NW1 in FIG. 9). Thereby, when the leading end L / E of the sheet P enters the transfer nip portion NP, the leading end L / E of the sheet P easily enters the transfer nip portion NP, and the bending of the tip region is suppressed.

  Then, as shown in FIG. 10, the rotary actuator 114 is again driven by 180 degrees to move the rotation shaft of the backup roller 65 to the downstream side in the sheet conveyance direction to increase the offset angle 時 の during normal transfer (Θ 1 Then, the transfer nip width NW is increased (see NW2 in FIG. 10), and the secondary transfer of the toner image onto the sheet P is stably performed.

"2nd Embodiment"
FIG. 11 is a flowchart showing the flow of control of the offset angle Θ at the time of secondary transfer in the image forming apparatus 1A according to the present embodiment.
The image forming apparatus 1A according to the present embodiment is different from the image forming apparatus 1 according to the first embodiment in that the moving amount of the backup roller 65 is controlled to be larger as the basis weight of the sheet P is larger. Therefore, the same components as those of the image forming apparatus 1 according to the first embodiment are denoted by the same reference numerals.

  The system control apparatus 11 acquires toner information (S201) and also acquires sheet information (S202). Then, it is determined whether the basis weight of the sheet P to be used is equal to or more than the threshold (S203). Specifically, the threshold of the basis weight of the sheet P is set to 256 gsm, and it is determined that the sheet P having a basis weight exceeding this is a thick sheet, and the moving amount of the backup roller 65 is set to be large (S204).

  Then, it is determined whether the mass of toner used for image formation is equal to or greater than the threshold (S205). For example, when forming a toner image including white (W) toner using black paper containing carbon black as paper P, the mass of white (W) toner is 0.24 × 10 −9 g, which is equal to or higher than the threshold value. It is.

  When the mass of toner used for image formation is equal to or greater than the threshold (S205: Yes), the system control apparatus 11 rotationally drives the rotary actuator 114 (S206) to move the rotation shaft of the backup roller 65 upstream of the sheet conveyance direction. Move to the side to reduce the offset angle に 対 し て relative to normal transfer. At this time, when the basis weight of the sheet P is a thick sheet equal to or more than the threshold value, the moving amount of the backup roller 65 is controlled to be larger than that of the plain sheet to further reduce the offset angle Θ.

  Thus, even if the sheet P is a thick sheet, when the leading end L / E of the sheet P enters the transfer nip portion NP, the transfer nip portion NP is more upstream in the sheet conveyance direction than in the transfer of the plain sheet. The leading edge L / E of the sheet P enters the transfer nip portion NP at a shallower angle, and the impact at the time of the sheet entry is suppressed.

  Then, at the timing when the leading end L / E of the sheet P is conveyed by 15 mm in the transfer nip portion NP (S207: Yes), the system control device 11 rotates the rotary actuator 114 again (S208) to back up the backup roller 65. The rotary shaft of the above is moved to the downstream side in the sheet conveyance direction and returned to the offset angle .chi. At the time of normal transfer. As a result, the transfer nip portion NP is positioned at the time of normal transfer, and the secondary transfer of the toner image onto the sheet P is performed.

In this manner, before the sheet P rushes into the transfer nip portion NP, the leading edge L / E of the sheet P being conveyed is moved further upstream of the transfer nip portion NP relative to the plain sheet in the sheet conveyance direction. After the sheet P is pushed into the transfer nip portion NP, the transfer nip portion NP is moved to the downstream side in the transport direction of the sheet P compared to before the sheet P is pushed into the transfer nip portion NP.
Thus, the impact generated when the leading end L / E of the sheet P rushes into the transfer nip portion NP, as compared with the case where the moving amount of the backup roller 65 is not increased even if the basis weight of the sheet P exceeds the threshold value. Scattering of toner is suppressed.

"3rd Embodiment"
FIG. 12 is a flow chart showing the flow of control of the offset angle Θ during secondary transfer in the image forming apparatus 1B according to the present embodiment.
The image forming apparatus 1B according to the present embodiment is controlled in such a manner that the moving amount of the backup roller 65 is increased as the conveying speed of the sheet P (process speed: synonymous with the moving speed of the intermediate transfer belt 51) increases. This differs from the image forming apparatus 1 according to one embodiment. Therefore, the same components as those of the image forming apparatus 1 according to the first embodiment are denoted by the same reference numerals.

The system control apparatus 11 acquires toner information (S301) and also acquires conveyance speed information of the sheet P (S302). Then, it is determined whether the set process speed is equal to or more than a threshold (S303).
Specifically, in the image forming apparatus 1B, a plurality of process speeds are set according to conditions such as the type of the sheet P and the toner image to be formed. For example, if the sheet P is plain paper of 256 gsm or less, the process speed is set to the fastest process speed possessed by the image forming apparatus 1B, and if the toner amount of the formed toner image is large, the process speed is set to low speed. . When the process speed to be set exceeds the threshold (S303: Yes), the system control apparatus 11 sets the movement amount of the backup roller 65 to be large (S304).

  Then, it is determined whether the mass of toner used for image formation is equal to or greater than the threshold (S305). For example, when forming a toner image including white (W) toner using black paper containing carbon black as paper P, the mass of white (W) toner is 0.24 × 10 −9 g, which is equal to or higher than the threshold value. It is.

When the mass of toner used for image formation is equal to or greater than the threshold (S305: Yes), the system control apparatus 11 rotationally drives the rotary actuator 114 (S306) to move the rotation shaft of the backup roller 65 upstream of the sheet conveyance direction. Move to the side to reduce the offset angle に 対 し て relative to normal transfer. At this time, when the basis weight of the sheet P is a thick sheet equal to or more than the threshold value, the moving amount of the backup roller 65 is controlled to be larger than that of the plain sheet to further reduce the offset angle Θ.
Thus, when the leading edge L / E of the sheet P enters the transfer nip portion NP, the transfer nip portion NP is positioned more upstream in the sheet conveyance direction, and the leading edge L / E of the sheet P is transferred The sheet enters the nip portion NP at a shallower angle, and the impact upon sheet entry is suppressed.

  Then, at the timing when the leading edge L / E of the sheet P is conveyed by 15 mm in the transfer nip portion NP (S307: Yes), the system control device 11 rotates the rotary actuator 114 again (S308) to back up the backup roller 65. The rotary shaft of the above is moved to the downstream side in the sheet conveyance direction and returned to the offset angle .chi. At the time of normal transfer. As a result, the transfer nip portion NP is positioned at the time of normal transfer, and the secondary transfer of the toner image onto the sheet P is performed.

In this manner, when the process speed exceeds the threshold value, the leading edge L / E of the sheet P being conveyed is moved from the transfer nip portion NP toward the upstream side in the sheet conveyance direction before the sheet P rushes into the transfer nip portion NP. After receiving the sheet P in the moved state and moving the sheet P into the transfer nip portion NP, the transfer nip portion NP is moved to the downstream side in the conveyance direction of the sheet P compared to before the sheet P enters the transfer nip portion NP. .
As a result, compared with the case where the moving amount of the backup roller 65 is not increased even if the process speed exceeds the threshold value, the toner is scattered due to the impact generated when the leading end L / E of the sheet P enters the transfer nip portion NP. Being suppressed.

Using the image forming apparatus 1 (apparatus based on Fuji Xerox Co., Ltd. Color 1000 Press), as the sheet P, the leading edge of the image on 256 gsm A3 size metallic paper (specialty No. 314) manufactured by Goto Paper Industries Co., Ltd. From the position of 20 mm, the image defect of the toner scattering of the white band image having a width of 10 mm in the conveyance direction of the sheet P and a width of 285 mm in the direction orthogonal to the conveyance direction of the sheet P was evaluated under the following conditions.
"Condition 1"
The offset angle 固定 is fixed at 30.8 degrees "Condition 2"
The offset angle 時 の during normal transfer is fixed at 30.8 degrees, and the offset angle Θ is changed to 27 degrees before the sheet P enters the transfer nip portion NP.

The results of the image evaluation under the conditions 1 and 2 are shown in FIG.
"Condition 1"
In the white band image, remarkable toner scattering of G5 (an evaluation value obtained by relative digitizing the degree of toner scattering) was confirmed.
"Condition 2"
In the white band image, slight toner scattering of G2 (an evaluation value in which the degree of toner scattering was relatively quantified) was confirmed.

DESCRIPTION OF SYMBOLS 1, 1A, 1B ... Image formation apparatus 10 ... Image formation part 11 ... System control apparatus 12 ... Exposure apparatus 13 ... Photosensitive body unit 14 ... Development apparatus 15 ... Transfer apparatus 51: intermediate transfer belt 53: secondary transfer belt 54: secondary transfer roller 65: backup roller 17: fixing device 20: sheet feeding device 28: sheet guide guide 30 .............

Claims (8)

An image holding unit that holds and conveys a toner image;
A transfer unit that transfers the toner image on the image holding unit to a recording medium;
An opposing unit that is in contact with the inner circumferential surface of the image holding unit to face the transfer unit;
Before the recording medium comes into contact with the nip portion, the recording medium passes through the nip between the central portion in the conveyance direction of the recording medium of the nip portion where the transfer means abuts the opposing means across the image holding means. Control means for controlling to move to the upstream side in the transport direction as compared with after contacting the part;
An image forming apparatus characterized by An image holding unit that holds and conveys a toner image;
A transfer unit that transfers the toner image on the image holding unit to a recording medium;
An opposing unit that is in contact with the inner circumferential surface of the image holding unit to face the transfer unit;
The contact width in which a portion of the peripheral surface of the image holding means and a portion of the peripheral surface of the transfer means are in surface contact at the nip where the transfer means abuts the opposing means with the image holding means interposed therebetween And control means for controlling the recording medium to decrease before the recording medium contacts the nip as compared to after the recording medium contacts the nip.
An image forming apparatus characterized by The control means moves the facing means downstream in the conveyance direction of the recording medium after the recording medium comes in contact with the nip portion as compared to before the contact with the nip portion.
The image forming apparatus according to claim 1 or 2, wherein The control means moves the facing means upstream in the conveyance direction of the recording medium in accordance with the mass of the uppermost toner layer on the image holding means.
The image forming apparatus according to claim 1 or 2, wherein The control unit increases the moving amount of the facing unit as the mass of the toner layer of the uppermost layer on the image holding unit increases.
The image forming apparatus according to claim 4, The control means increases the amount of movement of the facing member as the basis weight of the recording medium increases.
The image forming apparatus according to claim 1 or 2, wherein The control means increases the moving amount of the facing member as the process speed of the image carrier increases.
The image forming apparatus according to claim 1 or 2, wherein The toner image includes a white toner layer made of white toner or a silver toner layer made of silver toner containing an aluminum pigment.
The image forming apparatus according to any one of claims 1 to 7, characterized in that:

Images