JP2011150067A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deformation of an image carrier belt and image disturbance resulting from the deformation, in an image forming apparatus having a structure that brings an image carrier belt and a sheet member, disposed on a circumferential surface of a transfer roller with a recess therein, into contact with each other, and in an image forming method. <P>SOLUTION: The image forming apparatus includes: the transfer roller 4 having the recess 41 formed in the circumferential surface, a gripping portion 44 disposed in the recess 41 and gripping a transfer material S, and the sheet member 43 disposed on a circumferential surface different from the one in which the recess 41 is formed; the image carrier belt 31 for carrying an image thereon; and a control section configured such that when rotation of the transfer roller 4 is stopped, the recess 41 is made to face the image carrier belt 31, and the transfer roller 4 and image carrier belt 31 are separated, and such that when rotation of the transfer roller 4 is started and the transfer roller 4 and image carrier belt 31 are brought into contact with each other, the transfer material S is gripped by the gripping portion 44, and the transfer roller 4 and image carrier belt 31 are brought into contact with each other via the transfer material S. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method having a structure in which a sheet member disposed on a peripheral surface of a transfer roller having a concave portion and an image carrier belt are brought into contact with each other.

  As an image forming apparatus for transferring an image formed on an image carrier onto a transfer material, for example, there is one described in Patent Document 1. The apparatus described in Patent Document 1 is a so-called liquid development type image forming apparatus that visualizes an electrostatic latent image with a liquid developer containing toner particles and a carrier liquid. In this apparatus, a printing medium (transfer material) is gripped by a grip portion provided on a part of a peripheral surface of an impression cylinder roller (corresponding to a transfer roller), and the transfer material is wound around the impression roller so as to be in a drum shape. The image is transferred onto the transfer material by passing through the nip with the intermediate transfer member (image carrier). According to such a configuration, since the transfer material is passed through the nip while being mechanically gripped, there is no possibility of the transfer material sticking to the image carrier even if a strong transfer pressure is applied at the nip.

  On the other hand, in the image forming apparatus described in Patent Document 2, an image visualized by a liquid developing method is primarily transferred onto a photoconductor onto an endless belt-like image carrier belt, and an image carrier belt, a secondary transfer roller, By passing the transfer material through the nip between the two, the image on the image carrier belt is secondarily transferred to the transfer material. By applying the transfer roller having the grip portion described in Patent Document 1 as the secondary transfer roller in this apparatus, it is expected that a high transfer pressure is applied without the transfer material sticking to the image carrier belt.

Japanese translation of PCT publication No. 2006-513883 (for example, FIG. 1 and FIG. 2A) Japanese Patent Laying-Open No. 2009-036943 (for example, FIGS. 1 and 4)

  An exchangeable sheet-shaped impression cylinder paper is wound around the surface of the impression cylinder roller (transfer roller) described in Patent Document 1. Specifically, a part of the circumferential surface of the impression cylinder roller is cut out to form a recess, and one end of the impression cylinder paper is clamped and supported by an impression cylinder paper clamp provided in the recess.

  According to the experiments by the inventors of the present application, in the configuration in which the transfer roller and the image carrier belt in which the sheet-like member supported by the concave portion is wound around the peripheral surface are combined, the image carrier belt cannot be recovered. The problem that deformation may occur was revealed. Such deformation of the image carrier belt naturally causes disturbance in the image carried on the belt.

  Some embodiments according to the present invention solve the above problems in an image forming apparatus and an image forming method having a structure in which a sheet member disposed on a peripheral surface of a transfer roller having a concave portion and an image carrier belt are brought into contact with each other. Thus, the present invention provides a technique capable of preventing the deformation of the image carrier belt and the image disturbance caused by the deformation.

  In order to solve the above problems, an image forming apparatus according to the present invention is provided with a concave portion formed on a peripheral surface, a grip portion provided in the concave portion for gripping a transfer material, and a peripheral surface different from the concave portion. A transfer roller having a sheet member, an image carrier belt for carrying an image, and the transfer roller and the image carrier belt with the recess facing the image carrier belt when rotation of the transfer roller is stopped. And when the transfer roller and the image carrier belt are brought into contact with each other, the transfer material is gripped by the grip portion, and the transfer material is passed through the transfer material. The image forming apparatus includes a control unit that brings the transfer roller and the image carrier belt into contact with each other.

  According to the knowledge of the present inventors based on various experiments, it is considered that the above-described problem of deformation of the image carrier belt occurs as follows. In other words, the sheet member disposed on the peripheral surface of the transfer roller inevitably has surface irregularities (waving) in the vicinity of the switching portion between the peripheral surface of the transfer roller and the concave portion. In particular, the unevenness becomes conspicuous when the sheet member is stretched with a high tension to withstand a contact load with the image carrier belt. Thus, when the image carrier belt abuts against a sheet member having an uneven surface, the contact pressure of the sheet member against the image carrier belt varies depending on the location (contact irregularity). Here, it is virtually impossible to make the peripheral speeds of the sheet member and the image carrier belt in contact with each other completely coincide with each other, and the contact between the sheet member and the image carrier belt is not possible. The contact unevenness and the peripheral speed difference cause shear strain in the image carrier belt and cause deformation of the image carrier belt.

  In the above-described configuration of the present invention, when the sheet member on the peripheral surface of the transfer roller and the image carrier belt come into contact with each other, they do not come into direct contact but come into contact through the transfer material. Since the transfer material is interposed between the sheet member and the image carrier belt, the frictional force is greatly reduced. Therefore, the image is caused by uneven contact between the sheet member and the image carrier belt and a difference in peripheral speed. The shear stress acting on the carrier belt is reduced, and the possibility of shear strain is greatly reduced. Therefore, according to the present invention, it is possible to effectively prevent the deformation of the image carrier belt and the image disturbance resulting therefrom.

  In this invention, for example, the gripping portion includes a moving member that moves in the radial direction of the transfer roller and a support member that holds the transfer material in contact with the moving member via the transfer material, while the moving member moves. The movement unit may be configured to move the moving member in conjunction with the rotation of the transfer roller.

  In this way, by moving the moving member in conjunction with the rotation of the transfer roller to perform gripping, when the sheet member on the peripheral surface of the transfer roller comes into contact with the image carrier belt, the transfer material is surely placed between them. It is possible to intervene. If the gripping state and the release state of the gripping portion are associated with the rotation phase of the transfer roller in this way, for example, as in a known cam mechanism, it is interlocked with the rotation of the transfer roller regardless of electrical control or driving. The operation unit can be configured by a relatively simple mechanism that operates, and the apparatus configuration can be simplified.

  Further, the control unit may start rotation of the transfer roller after driving the image carrier belt, for example. When the transfer roller is stopped, the image carrier belt and the transfer roller are separated from each other. Therefore, by rotating the image carrier belt first, the rotation speed of the image carrier belt can be stabilized in advance.

  Here, for example, the control unit may start rotation of the transfer roller after the transfer material is held by the holding unit. In such a configuration, since the transfer material is gripped before the transfer roller rotates, when the transfer roller comes into contact with the image carrier belt, the transfer material can be reliably interposed therebetween. Further, for example, when a transfer material misfeed or the like occurs, it is possible to prevent the transfer roller and the image carrier belt from coming into direct contact with each other.

  On the other hand, for example, after starting the rotation of the transfer roller, the control unit grips the transfer material by the grip unit, and abuts the transfer roller that grips the transfer material by the grip unit to the image carrier belt via the transfer material. You may make it make it. In this way, since the transfer material is gripped by the gripping portion while the transfer roller rotates, the time required for starting can be shortened. In particular, this configuration can be suitably applied when the gripping unit is driven by the above-described operation unit that operates in conjunction with the rotation of the transfer roller.

  Another aspect of the image forming method according to the present invention is different from the concave portion formed on the peripheral surface, the grip portion that is disposed in the concave portion and grips the transfer material, and the concave portion in order to solve the above-described problem. The transfer roller having the sheet member disposed on the peripheral surface is opposed to the image carrier belt, and the transfer roller and the image carrier belt are separated from each other by separating the transfer roller and the image carrier belt. The image carrier belt is driven from a state in which the transfer is stopped, the transfer roller is rotated after the image carrier belt is driven, and the transfer material is gripped by the grip portion disposed on the rotated transfer roller. Then, after gripping the transfer material, the transfer roller and the image carrier belt are brought into contact with each other through the transfer material by rotation of the transfer roller.

  Another aspect of the image forming method according to the present invention is different from the concave portion formed on the peripheral surface, the grip portion that is disposed in the concave portion and grips the transfer material, and the concave portion in order to solve the above problems. The transfer roller having the sheet member disposed on the peripheral surface is opposed to the image carrier belt, and the transfer roller and the image carrier belt are separated from each other by separating the transfer roller and the image carrier belt. After the image carrier belt is driven, the transfer material is gripped by the grip portion disposed on the transfer roller and the transfer material is gripped after the image carrier belt is driven. The transfer roller is rotated, and the transfer roller and the image carrier belt are brought into contact with each other through the transfer material by the rotation of the transfer roller.

  In any of these inventions, similarly to the above-described image forming apparatus, it is possible to effectively prevent the deformation of the image carrier belt and the image disturbance resulting therefrom.

1 is a diagram illustrating a first embodiment of an image forming apparatus according to the present invention. The block diagram which shows the electric constitution of the apparatus of FIG. The perspective view which shows the whole structure of a secondary transfer roller. FIG. 4 is a partially enlarged view of the secondary transfer roller in FIG. 3. The side view which shows the state of the stretch of the elastic layer in a secondary transfer roller. The figure which shows the opening / closing mechanism of a holding part. The figure which shows the state which the secondary transfer roller has stopped. The figure which shows the 1st state during secondary transfer roller rotation. The figure which shows the 2nd state during secondary transfer roller rotation. The figure which shows the 3rd state during secondary transfer roller rotation. The figure which shows the 4th state during secondary transfer roller rotation. The figure which shows the 5th state during secondary transfer roller rotation. The figure which shows the deformation | transformation aspect of an intermediate transfer belt. FIG. 3 is a first diagram illustrating an operation sequence for supplying a carrier liquid to an intermediate transfer belt. FIG. 10 is a second diagram illustrating an operation sequence for supplying a carrier liquid to the intermediate transfer belt. The figure which shows the principal part of 2nd Embodiment of the image forming apparatus concerning this invention. The figure which shows the principal part of 3rd Embodiment of the image forming apparatus concerning this invention.

  FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the apparatus of FIG. The image forming apparatus 1 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan), and 2K (for black) that form images of different colors. The image forming apparatus 1 includes a color mode in which four color toners of yellow (Y), magenta (M), cyan (C), and black (K) are superimposed to form a color image, and only black (K) toner. And a monochrome mode for forming a monochrome image using can be selectively executed. In this image forming apparatus, when an image forming instruction is given from an external device such as a host computer to a controller 10 having a CPU, a memory, etc., the controller 10 controls each part of the apparatus to execute a predetermined image forming operation, and copy An image corresponding to the image formation command is formed on a sheet-like transfer material S such as paper, transfer paper, paper, and an OHP transparent sheet.

  Each of the image forming stations 2Y, 2M, 2C, and 2K is provided with a photosensitive drum 21 on which a toner image of each color is formed. The photosensitive drums 21 are arranged such that the rotation axis thereof is parallel or substantially parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 1), and a predetermined speed is indicated in the direction of arrow D21 in FIG. Is driven to rotate.

  Around each photosensitive drum 21, a charger 22 that is a corona charger that charges the surface of the photosensitive drum 21 to a predetermined potential and an electrostatic latent image by exposing the surface of the photosensitive drum 21 according to an image signal. An exposure unit 23 that forms an image, a developing unit 24 that visualizes the electrostatic latent image as a toner image, a first squeeze portion 25, a second squeeze portion 26, and an intermediate portion between the toner image and the transfer unit 3. A primary transfer unit that performs primary transfer onto the transfer belt 31, a cleaning unit that cleans the surface of the photosensitive drum 21 after transfer, and a cleaner blade are arranged in the order of rotation D21 of the photosensitive drum 21 (in FIG. 1, (Clockwise).

  The charger 22 does not come into contact with the surface of the photosensitive drum 21, and a conventionally well-known and commonly used corona charger can be used as the charger 22. When a scorotron charger is used as the corona charger, a positive wire current flows through the charge wire of the scorotron charger and a direct current (DC) grid charging bias is applied to the grid. When the photosensitive drum 21 is charged by corona discharge by the charger 22, the surface potential of the photosensitive drum 21 is set to a substantially uniform potential.

  The exposure unit 23 exposes the surface of the photosensitive drum 21 with a light beam in accordance with an image signal given from an external device to form an electrostatic latent image corresponding to the image signal. The exposure unit 23 can be constituted by a light beam from a semiconductor laser that is scanned by a polygon mirror, or a line head in which light emitting elements are arranged in the main scanning direction.

  Toner is applied from the developing unit 24 to the electrostatic latent image thus formed, and the electrostatic latent image is developed with the toner. In the developing unit 24 of the image forming apparatus 1, toner development is performed using a liquid developer in which toner is dispersed in a carrier liquid in an approximate weight ratio of about 20%. The liquid developer used in this embodiment is a low-concentration (1 to 2 wt%) and low-viscosity volatility that is generally used in the past, using Isopar (trademark: Exon) as a carrier liquid. It is not an ionic liquid developer but a non-volatile liquid developer having a high concentration and high viscosity and having non-volatility at room temperature. That is, the liquid developer in the present embodiment is obtained by dispersing solid particles having an average particle diameter of 1 μm in which a colorant such as a pigment is dispersed in a thermoplastic resin in a liquid solvent such as an organic solvent, silicon oil, mineral oil, or edible oil. High viscosity with a toner solid content concentration of about 20% (HAAKE RheoStress RS600 is used, and the viscoelasticity at a shear rate of 1000 (1 / S) at 25 ° C. is 30 to 300 mPa · s. Liquid developer.

  A first squeeze portion 25 is disposed on the downstream side of the developing position in the rotation direction D 21 of the photosensitive drum 21, and a second squeeze portion 26 is disposed on the downstream side of the first squeeze portion 25. The squeeze rollers 25 and 26 are respectively provided with squeeze rollers. Each squeeze roller comes into contact with the surface of the photosensitive drum 21 to remove excess carrier liquid and fog toner from the toner image. In the present embodiment, the excess carrier liquid and fog toner are removed by the two squeeze portions 25 and 26. However, the number and arrangement of the squeeze portions are not limited to this, for example, one squeeze portion. May be arranged.

  The toner image that has passed through the squeeze portions 25 and 26 is primarily transferred to the intermediate transfer belt 31 by the primary transfer unit. The intermediate transfer belt 31 is stretched around a pair of belt conveying rollers 32 and 33 that are disposed apart from each other, and is rotated in a predetermined direction D31 by roller driving by a belt driving motor M3. More specifically, the right roller 32 in FIG. 1 among these belt transport rollers 32 and 33 is a drive roller, and a belt drive motor M3 is mechanically connected to the drive roller 32. In the present embodiment, a driver 11 is provided to drive the belt drive motor M3, and a drive signal corresponding to a command pulse given from the controller 10 is output to the belt drive motor M3 for position control. As a result, the drive roller (belt transport roller) 32 rotates in the arrow direction D32 in FIG. 1 at a peripheral speed corresponding to the command pulse, and the surface of the intermediate transfer belt 31 rotates in the direction D31 at a constant speed.

  The primary transfer unit has a backup roller 271. The backup roller 271 is disposed opposite to the photosensitive drum 21 across the intermediate transfer belt 31 at the primary transfer position TR 1 to transfer the toner image on the photosensitive drum 21. Transfer to the intermediate transfer belt 31. Then, the transfer of the toner image is executed by the transfer unit of each color, so that the toner images of each color on the photosensitive drum 21 are sequentially superimposed on the intermediate transfer belt 31 to form a full color toner image.

  The toner image thus transferred to the intermediate transfer belt 31 is conveyed to the secondary transfer position TR2. At the secondary transfer position TR2, the secondary transfer roller 4 is disposed so as to face the intermediate transfer belt 31 wound around the driving roller 32 of the transfer unit 3. As shown in FIG. 2, the secondary transfer roller 4 is rotationally driven by a secondary transfer roller drive motor M4. The secondary transfer roller drive motor M4 is driven and controlled by a drive signal output from the driver 12 in response to a command pulse from the controller 10. Then, at the secondary transfer position TR2, a single-color or multi-color toner image formed on the intermediate transfer belt 31 is transferred from the gate roller 51 (a pair of rollers 51a and 51b) along the transfer path PT. Secondary transferred to S. Between the gate roller 51 and the secondary transfer position TR2, a sheet guide 52 for feeding the transfer material S to the secondary transfer position TR2 without contacting the secondary transfer roller 4 or the intermediate transfer belt 31 is disposed. ing.

  The transfer material S on which the toner image is secondarily transferred is sent from the secondary transfer roller 4 to the transport mechanism 6 along the transport path PT. In the transport mechanism 6, the first suction unit 61, the transfer material transport unit 62, and the second suction unit 63 are sequentially arranged along the transport path PT, and these cooperate to transport the transfer material S to the fixing unit 7. To do.

  In addition, in order to reliably feed the transfer material S on which the toner image has been secondarily transferred to the first suction unit 61 and to prevent image fouling, in this embodiment, the secondary transfer position TR2 and the first suction unit 61 are used. The air blowing unit 8 is arranged so as to face the secondary transfer roller 4 between the two. In the blower unit 8, the air from the opening 83 of the housing 82 generated by the operation of the airflow generator 81 is ejected as indicated by the white arrow, whereby the grip by the grip 44 of the secondary transfer roller 4. The air is blown between the intermediate transfer belt 31 and the leading end portion of the transfer material S that is released from the protrusion and protruded in a direction away from the secondary transfer roller 4 by a protrusion claw (not shown). Thus, the leading end portion of the transfer material S is fed toward the first suction portion 61. Further, when air is blown onto the transfer material S, when the rear end portion of the transfer material S is discharged from the secondary transfer position TR2, the rear end portion touches the intermediate transfer belt 31 and the like, and the image is stained. Can be prevented. In the case of the transfer material S having a small elastic restoring force and a weak waist, the air blowing by the blower unit 8 can be omitted.

  Further, a fixing unit 7 is disposed on the downstream side of the transport path PT, that is, on the side opposite to the secondary transfer roller 4 with respect to the transport mechanism 6 (the left hand side in FIG. 1), and is transferred to the transfer material S. Heat or pressure is applied to the toner image, and the toner image is fixed to the transfer material S.

  A cleaner blade 391 is in contact with the intermediate transfer belt 31 to which the toner image is secondarily transferred. More specifically, the cleaner blade 391 hits the roller 33 around which the intermediate transfer belt 31 is wound downstream of the secondary transfer position TR2 in the transport direction D31 of the intermediate transfer belt 31 via the intermediate transfer belt 31. It touches. The cleaner blade 391 removes residual deposits such as toner and carrier liquid remaining on the surface of the intermediate transfer belt 31 after the secondary transfer.

  As shown in FIG. 2, the apparatus 1 rotates the gate roller 51 in addition to the bias generation section 100 that generates a bias voltage supplied to each section of the apparatus, the secondary transfer roller 4 and the belt driving roller 32 described above. A motor 13 for driving the motor M5, a driver 13 for driving the motor M5, various drive mechanisms for driving other parts of the device, and the like, all of which are controlled by the controller 10.

  In this embodiment, the toner image is formed by a wet development method in which a toner image is formed using a liquid developer. Therefore, the secondary transfer roller 4 having a grip portion is used so that a sufficient transfer pressure can be applied to the transfer material S while preventing the transfer material S from sticking to the intermediate transfer belt 31. Hereinafter, the structure of the secondary transfer roller 4 will be described in detail with reference to FIGS. 1 and 3 to 5.

  FIG. 3 is a perspective view showing the overall configuration of the secondary transfer roller. 4 is a partially enlarged view of the secondary transfer roller of FIG. FIG. 5 is a side view showing a stretched state of the elastic layer in the secondary transfer roller. More specifically, FIG. 4A shows a fixing portion that fixes one end of the elastic layer, and FIG. 4B shows a tension portion that stretches the elastic layer. 4 and 5 show a state in which an abutting member and a gripping portion, which will be described later, are removed in order to clearly show the configuration of the fixing portion and the stretching portion.

  As shown in FIGS. 1 and 3, the secondary transfer roller 4 has a roller base 42 provided with a recess 41 formed by cutting out a part of the outer peripheral surface of a cylinder. The roller base material 42 is provided with a rotating shaft 421 extending in a direction orthogonal to the paper surface of FIG. The rotation shaft 421 is provided so as to be rotatable about an axis 4211 with respect to the support arm 40 pivotally supported by an apparatus housing (not shown). The support arm 40 is swingable about the support shaft 401 with respect to the apparatus housing, and is urged counterclockwise in FIG. 1 by urging means (not shown). Therefore, the secondary transfer roller 4 is urged in the direction of the arrow α and is pressed against the intermediate transfer belt 31 wound around the belt drive roller 32. As a result, the secondary transfer roller 4 is pressed against the intermediate transfer belt 31 with a predetermined load (for example, 60 kgf).

  Further, side plates 422 and 422 are attached to both ends of the rotating shaft 421, respectively. More specifically, each of these side plates 422 and 422 has a shape in which a notch 422a is provided on a disk-shaped metal plate. As shown in FIG. 3, the notches 422a and 422a are attached to the rotating shaft 421 while facing each other and separated by a distance slightly longer than the width of the elastic sheet. In this way, the roller base material 42 is formed which has a drum shape as a whole but has a recess 41 extending in parallel or substantially in parallel with the rotation shaft 421 on a part of the outer peripheral surface thereof.

  At both ends of the secondary transfer roller 4, support members 46 are attached to the outer surfaces of the side plates 422 so that they can rotate integrally with the roller base material 42. Further, the support member 46 is formed with a planar region 461 corresponding to the recess 41. The transfer roller side contact member 47 is attached to the flat area 461, respectively. In the abutting member 47, the base part 471 is attached to the support member 46, and the abutting part 472 extends from the base part 471 in the normal direction of the planar region 461, and the distal end portion of the abutting part 472 Extends to the opening side end of the recess 41. That is, when the contact member 47 is viewed from the direction of the rotation shaft 421, the contact member 47 closes the recess 41, and the peripheral end of the contact portion 472 is the peripheral surface of the secondary transfer roller 4 (elastic layer 43. The contact member 47 is provided so as to partially overlap with the contact member 47).

  In addition, bearings 322 (see FIG. 1) that are coaxial with the drive roller 32 and rotatable independently of the drive roller 32 are provided at both ends of the drive roller 32 around which the intermediate transfer belt 31 is wound. When the contact member 47 of the secondary transfer roller 4 faces the drive roller 32 side, the outer peripheral surface of the contact member 47 and the outer peripheral surface of the bearing 322 are in contact with each other.

  Further, an elastic sheet formed of an elastic material such as rubber or resin is wound around the outer peripheral surface of the roller base material 42, that is, the surface region excluding the region corresponding to the inside of the recess 41 on the surface of the metal plate. An elastic layer 43 is formed by the sheet. In this embodiment, the elastic sheet is not bonded to the secondary transfer roller 4 and can be exchanged in order to cope with deterioration over time such as wear and scratches on the elastic sheet (elastic layer 43). . More specifically, as shown in FIGS. 4A and 5, a sheet fixing portion 48 is provided on one inner side surface 41 a of the recess 41. The sheet fixing portion 48 has a pressing plate 481, and the pressing plate 481 is located with respect to the secondary transfer roller 4 with the pressing plate 481 and the secondary transfer roller 4 sandwiching one end 431 of the elastic sheet. Are fastened by screws 482. As a result, the one end 431 of the elastic sheet is fixed to the secondary transfer roller 4. Further, the other end portion 432 of the elastic sheet is stretched in a direction opposite to the rotation direction D4 by the sheet stretching portion 49 in a state where the central portion of the elastic sheet is wound along the outer peripheral surface of the secondary transfer roller 4. While attached to the secondary transfer roller 4.

  As shown in FIG. 3, the sheet stretching portion 49 is disposed at each end of the elastic sheet in the width direction (direction parallel to the axial direction of the rotation shaft 421). As shown in FIGS. 4 (b) and 5, in each sheet stretching portion 49, after the plate 491 attached to the end portion 432 of the elastic sheet is inserted into the slide portion of the side plate 492 and the stop plate 493 is attached. By tightening the tightening screw 494 with a predetermined torque, the elastic layer 43 is formed by winding the elastic sheet around the outer peripheral surface of the secondary transfer roller 4 without sagging. That is, one end portion 431 of the elastic sheet fixed by the sheet fixing portion 48 is the winding start side, and the opposite end portion 432 is the winding end side. The elastic layer 43 forms a nip NP so as to face the intermediate transfer belt 31 wound around the driving roller 32.

In this embodiment, the opening length (opening width) W41 of the recess 41 along the rotation direction D4 of the roller base material 42 is about 105 mm. When the elastic layer 43 formed in the region excluding the concave portion 41 on the outer peripheral surface of the secondary transfer roller 4 is in a position facing the intermediate transfer belt 31, the elastic layer 43 is pressed against the intermediate transfer belt 31 and the transfer nip NP. Is formed. The length (transfer nip width) Wnp of the transfer nip NP along the rotation direction D4 of the roller base material 42 is about 11 mm,
(Opening width W41 of the recess 41)> (transfer nip width Wnp at the transfer nip NP)
Have the relationship. Therefore, when the concave portion 41 of the secondary transfer roller 4 faces the intermediate transfer belt 31, the transfer nip temporarily disappears.

  The length of the elastic layer 43 along the rotation direction D4 of the roller base material 42 is set to about 495 mm, and this is the largest size of the transfer material S that can be used in the apparatus 1 is wound. It is something that can be done. That is, the length of the elastic layer 43 is determined to be longer than the length of the usable transfer material S that has the maximum length along the rotation direction D4 of the roller base material 42.

  In addition, a grip 44 for gripping the transfer material S is disposed in the recess 41 at a position close to the one end 431 on the winding start side of the elastic layer 43. The gripping portion 44 includes a gripper support member 441 erected on the outer peripheral surface of the roller base 42 from the inner bottom portion of the recess 41, and a gripper member 442 that is supported so as to be able to come into contact with and separate from the distal end portion of the gripper support member 441. And have. By the operation of the opening / closing mechanism 45 described below, the leading end of the gripper member 442 moves back and forth in the radial direction of the secondary transfer roller 4 and is separated from the leading end of the gripper support member 441 to prepare for gripping the transfer material S. While the gripping and releasing are performed, the transfer material S is gripped by the leading end of the gripper member 442 moving to the leading end of the gripper support member 441.

  FIG. 6 is a view showing an opening / closing mechanism of the gripping portion. In FIG. 6, in order to clearly indicate the gripping mechanism, illustrations of parts that are not related to the operation of the gripping unit, such as the contact member 47, the sheet fixing unit 48, and the sheet stretching unit 49, are omitted. This is the same also in each drawing after FIG.

  As shown in FIGS. 3 and 6, the gripper member 442 is attached to a support shaft 451 of a crank arm 452 configured to be rotatable about a support shaft 451. A cam follower 453 is provided at the tip of the crank arm 452. Although the illustration of the urging member is omitted, the gripper member 442 is urged in a direction (a counterclockwise direction centering on the support shaft 451 in FIG. 6) in which the tip end of the gripper member 442 comes into contact with the gripper support member 441. ing. That is, when no external force is applied, the tip of the gripper member 442 is urged toward the radially inner side of the secondary transfer roller 4, thereby maintaining the grip 44 in the closed state. The support shaft 451, the crank arm 452, the cam follower 453, and the like constitute an open / close mechanism 45 integrally.

  On the other hand, a cam member 50 is fixed to the inner side surface of the apparatus housing (not shown) at positions near the axial ends of the secondary transfer roller 4 and the drive roller 32. The outer peripheral surface 500 of the cam member 50 is generally along a circular arc 50a having a radius R50 centered on the rotation center 4211 of the secondary transfer roller 4, but the projecting portions 501 and 502 that partially protrude in the outer peripheral direction. It has the provided shape. The outer peripheral surface of the cam member 50 having such an outer peripheral shape and the outer peripheral surface of the cam follower 453 provided in the opening / closing mechanism 45 are intermittently brought into contact with the rotation of the secondary transfer roller 34. As the cam follower 453 moves following the outer peripheral surface shape of the cam member 50, the crank arm 452 rotates, and the tip of the gripper member 442 opens and closes with respect to the gripper support member 441.

  FIG. 7 is a diagram illustrating a state where the secondary transfer roller is stationary. More specifically, FIG. 7A is a diagram illustrating a state of the grip portion 44 when the secondary transfer roller 4 is stationary, and FIG. 7B is a partially enlarged view thereof. 7 to 12 which will be described sequentially below schematically show changes in the open / closed state of the gripping portion 44 due to the rotation of the secondary transfer roller 4 and the state of gripping / opening of the transfer material S associated therewith. It is a thing.

  As shown in FIGS. 7A and 7B, when the secondary transfer roller 4 is in a stationary state, the peripheral surface concave portion 41 faces the intermediate transfer belt 31 side, more specifically, the secondary transfer position TR2. It is in a state. At this time, at the secondary transfer position TR2, the secondary transfer roller 4 (more specifically, the elastic layer 43) and the intermediate transfer belt 31 are separated from each other, and the nip NP is not formed. Therefore, independently of the secondary transfer roller 4, the belt driving roller 32 can be rotated in the direction D32 and the intermediate transfer belt 31 can be moved in the direction D31.

  At this time, the front end portion Sh in the transfer direction of the transfer material S is positioned before the secondary transfer position TR2. In FIG. 7A, the sheet guide 52 is not shown in order to clearly show the position of the transfer material front end portion Sh. This also applies to FIGS. 8A, 9A, 10A, 11 and 12 described later.

  In a state where the secondary transfer roller 4 is stopped, the cam follower 453 of the opening / closing mechanism 45 does not contact the cam member 50 or contacts the portions other than the protruding portions 501 and 502 of the outer peripheral surface 500 thereof. For this reason, the holding part 44 is in a closed state by the action of an urging member (not shown). Note that the grip 44 may be in an open state at this time.

  FIG. 8 is a diagram illustrating a first state during rotation of the secondary transfer roller. More specifically, FIG. 8A is a diagram showing a state of the grip portion 44 immediately after the secondary transfer roller 4 starts to rotate, and FIG. 8B is a partially enlarged view thereof. When the secondary transfer roller 4 starts to rotate in the direction D4, the concave portion 41 approaches the secondary transfer position TR2, and the cam follower 453 comes into contact with the outer peripheral surface 500 of the cam member 50. As the rotation further proceeds, the cam follower 453 rides on the first protrusion 501 of the outer peripheral surface 500 of the cam member 50, whereby the crank arm 452 rotates about the support shaft 451, and the tip of the gripper member 442 becomes secondary. It moves toward the outside in the radial direction of the transfer roller 4 and starts to be separated from the gripper support member 441. When the driving of the gate roller 51 is started at this time, the transfer material S is conveyed in the direction Ds toward the grip portion 44 where the transfer material S starts to open.

  FIG. 9 is a diagram illustrating a second state during rotation of the secondary transfer roller. More specifically, FIG. 9A is a diagram showing a state of the grip portion 44 when the secondary transfer roller 4 is further rotated from the state of FIG. 8, and FIG. 9B is a partially enlarged view thereof. is there. As the rotation further proceeds, the grip 44 opens further and receives the leading end Sh of the transfer material S conveyed by the gate roller 51. That is, the transfer material front end portion Sh is inserted between the opened gripper member 442 and the gripper support member 441. At this time, the conveyance speed of the transfer material S is slightly higher than the moving speed of the gripping portion 44, and the transfer material tip portion Sh is abutted against the gripper member 442, so that the rotational phase of the secondary transfer roller 4 is increased. And the transfer material front end portion Sh can be determined accurately and reproducibly. In addition, the transfer material S bends when the leading end Sh is abutted against the grip 44, but the sheet guide 52 is provided so that it does not contact the intermediate transfer belt 31. Thus, the skew of the transfer material S can be corrected by gripping the transfer material S with the gripping portion 44 in a state where the transfer material S is bent.

  FIG. 10 is a diagram illustrating a third state during rotation of the secondary transfer roller. More specifically, FIG. 10A is a diagram showing a state of the grip portion 44 when the secondary transfer roller 4 is further rotated from the state of FIG. 9, and FIG. 10B is a partially enlarged view thereof. is there. After the transfer material S is abutted against the gripping portion 44, the outer peripheral surface 500 of the cam member 50 is shaped to gradually recede. Therefore, when the rotation of the secondary transfer roller 4 further proceeds, the gripping is performed. The opening of the part 44 becomes small. Finally, as shown in FIGS. 10 (a) and 10 (b), the transfer material S is completely gripped. In this way, the transfer material S gripping the leading end portion Sh is fed to the secondary transfer position TR2.

  FIG. 11 is a diagram illustrating a fourth state during rotation of the secondary transfer roller. More specifically, FIG. 11A is a diagram showing a state of the grip portion 44 when the secondary transfer roller 4 is further rotated from the state of FIG. 10, and FIG. 11B is a partially enlarged view thereof. is there. When the secondary transfer roller 4 further rotates, as shown in FIGS. 11A and 11B, the concave portion 41 passes the secondary transfer position TR2, and the elastic layer 43 of the secondary transfer roller 4 is transferred to the transfer material S. Through the intermediate transfer belt 31. That is, the transfer material S is sandwiched in the nip NP between the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31. Therefore, when the secondary transfer roller 4 is started from a stationary state and the nip NP is formed, the elastic layer 43 on the peripheral surface of the secondary transfer roller 4 does not contact the intermediate transfer belt 31 but the transfer material S therebetween. These abut against each other.

  The gripping portion 44 continues to grip the transfer material leading end Sh until at least the transfer material leading end Sh has passed through the nip NP. This prevents the transfer material S from sticking to the intermediate transfer belt 31.

  FIG. 12 is a diagram illustrating a fifth state during rotation of the secondary transfer roller. More specifically, FIG. 12A shows a state of the grip portion 44 when the secondary transfer roller 4 further rotates from the state of FIG. 11, and FIG. 12B shows the secondary transfer roller 4. FIG. 13 is a diagram showing a state of the gripping portion 44 when it is further rotated from the state of FIG. When the rotation further proceeds, the cam follower 453 comes into contact with the second protrusion 502 on the outer periphery of the cam member 50 as shown in FIG. When the cam follower 453 rides on the protrusion 502, the grip 44 is opened again, and the grip of the transfer material S is released. After the gripping of the transfer material front end portion Sh is released in this manner, as shown in FIG. 12B, the contact between the cam follower 453 and the cam member 50 is finished, and the gripping portion 44 is closed. The transfer material S, which has been released from gripping, is fed rearward while being urged toward the secondary transfer roller by the transport mechanism 6 and the air blowing unit 8 (see FIG. 1), and therefore falls down toward the intermediate transfer belt 31. There is no inconvenience.

  Thus, in this embodiment, as the secondary transfer roller 4 rotates, the contact state between the cam follower 453 on the secondary transfer roller 4 side and the cam member 50 on the apparatus housing side changes, and thereby the gripping portion 44 is opened and closed, and the transfer material S is gripped and released. When the secondary transfer roller 4 starts to rotate from a stationary state, the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 start to contact with the transfer material S interposed therebetween. Yes. This is to cope with the following problems that may occur when they abut directly.

  FIG. 13 is a diagram showing a deformation mode of the intermediate transfer belt. As described above, in the secondary transfer roller 4 of this embodiment, the elastic layer 43 is configured by stretching a rubber elastic sheet, for example, on the peripheral surface of the substantially cylindrical roller base material 42. As shown in FIG. 4A, the end 431 of the elastic layer 43 is pressed by the pressing plate 481, but due to the uneven distribution of the fixing position by the screw 482, the axial direction of the secondary transfer roller 4 is increased. Unevenness of the pressing force due to the pressing plate 481 is inevitable.

  For this reason, as shown in FIG. 13A, the surface of the elastic layer 43 may be wavy, particularly in the vicinity of the end 431 of the elastic layer 43 fixed by the pressing plate 481. A position in the vicinity of the end 431 in the elastic layer 43 is a position that first contacts the intermediate transfer belt 31 when the secondary transfer roller 4 in which the concave portion 41 initially faces the secondary transfer position TR2 starts to rotate. . When the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 come into contact with each other, if the surface of the elastic layer 43 has a wave, the axial direction of the secondary transfer roller 4 as shown in FIG. In addition, a portion where the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 are in contact with a portion where the elastic layer 43 is not in contact is mixed.

  Here, the moving speed (peripheral speed) of the surface of the secondary transfer roller 4, specifically the surface of the elastic layer 43, at the secondary transfer position TR 2 is completely matched with the peripheral speed of the surface of the intermediate transfer belt 31. This is practically difficult, and some difference in peripheral speed is unavoidable between the two. Therefore, in the nip NP formed by contact with the elastic layer 43, the surface of the intermediate transfer belt 31 has a portion that is in contact with the elastic layer 43 of the secondary transfer roller 4 and a portion that is not in contact. There is a slight speed difference between them. FIG. 13A illustrates a case where the peripheral speed of the secondary transfer roller 4 is higher than the peripheral speed of the intermediate transfer belt 31. In this case, the surface of the intermediate transfer belt 31 is in contact with the elastic layer 43. The part is conveyed in the circumferential direction at a relatively high speed as indicated by a dotted arrow in the figure, while the conveyance speed is smaller as indicated by the solid line arrow at a part that does not contact the elastic layer 43.

  Therefore, as shown in FIG. 13B, each position on the surface of the intermediate transfer belt 31 in the nip NP is locally pulled in a different direction, which causes shear strain in the intermediate transfer belt 31. When this shearing strain increases, the surface of the intermediate transfer belt 31 is deformed such as undulating waves and wrinkles that cannot be recovered. Deformation is also promoted by a strong pressing force by the secondary transfer roller 4. In both of the image transfer from each image forming station to the deformed intermediate transfer belt 31 and the image transfer from the intermediate transfer belt 31 to the transfer material S, it is inevitable that the image is disturbed. That is, such deformation of the intermediate transfer belt 31 causes image disturbance.

  Such deformation of the intermediate transfer belt 31 is caused when the frictional force generated between the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 is large, for example, the elastic layer 43 and the intermediate transfer belt 31 are both dry. This is conspicuous when abutting in a different state. Therefore, in this embodiment, when the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 start to contact each other, the transfer material S is interposed between them to avoid friction between the two, and the elastic layer The deformation of the intermediate transfer belt 31 due to the undulation of 43 and the peripheral speed difference from the intermediate transfer belt 31 is prevented.

  Further, as described below, it is more effective to make the liquid developer used in the image forming process in this embodiment function as a lubricant. That is, in a state where the liquid developer supplied from any one of the image forming stations 2Y, 2M, 2C, and 2K is attached to the surface of the intermediate transfer belt 31, the surface area to which the liquid developer is attached is the secondary transfer position. An operation sequence in which the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 start to come into contact with each other via the transfer material S and the liquid component when in the TR2 can be executed by the controller 10.

  Here, from the viewpoint of causing the liquid component to act as a lubricant, the liquid developer supplied to the intermediate transfer belt 31 may or may not contain a toner component. However, in order to prevent the surface of the intermediate transfer belt 31 (and the elastic layer 43 of the secondary transfer roller 4) from being soiled, it is more preferable that only the carrier liquid not containing the toner component is supplied to the intermediate transfer belt 31. . Therefore, in the following, an operation sequence for supplying only the carrier liquid containing no toner component to the intermediate transfer belt 31 out of the liquid developer stored in the image forming station will be considered.

  Here, the operation of supplying the carrier liquid from the black image forming station 2K that is closest to the secondary transfer position TR2 among the two image forming stations 2Y, 2M, 2C, and 2K will be described. The carrier liquid may be supplied from any of the forming stations, or the carrier liquid may be supplied in parallel from a plurality of image forming stations.

  14 and 15 are diagrams showing an operation sequence for supplying the carrier liquid to the intermediate transfer belt. Specifically, FIG. 14A, FIG. 14B, and FIG. 15A are diagrams schematically showing the state of each part in the process of this operation sequence. FIG. 15B is a timing chart showing this operation sequence.

  As shown in FIG. 14A, in the state where the secondary transfer roller 4 is stopped at the position where the concave portion 41 faces the secondary transfer position TR2, the carrier liquid (indicated by white circles) is first transferred from the developing unit 24 to the photosensitive member 21. ) And then primarily transferred to the intermediate transfer belt 31 as shown in FIG. 14B, and as shown in FIG. 15A, the surface of the intermediate transfer belt 31 coated with the carrier liquid When the region (application region) reaches the secondary transfer position TR2, the elastic layer 43 of the secondary transfer roller 4 and the intermediate transfer belt 31 may be brought into contact (via the transfer material S).

  More specifically, as shown in FIG. 15B, first, the intermediate transfer belt 31 and the photosensitive member 21 are rotated (time T11). Then, the charging bias Vc to the charger 22 is turned on for a certain time from time T12 to charge the photosensitive member 21 to a predetermined surface potential. The exposure from the exposure unit 23 is kept off. As a result, an electrostatic latent image corresponding to a highlight image having a density level of 0 (so-called white solid image) is formed on the surface of the photoconductor 21. Next, a predetermined developing bias Vdev is applied to the developing roller 241 provided in the developing unit 24, and the developing roller 241 is brought into contact with the photosensitive member 21. As a result, the latent image on the photosensitive member 21 is developed. Since the developed image is a solid white image, a small amount of fog toner (indicated by a black circle) adheres to the photoconductor 21, but only the carrier liquid adheres. The separation contact of the developing roller 241 with respect to the photosensitive member 21 is desirable to prevent unnecessary toner from adhering to the photosensitive member 21, but is not an essential requirement.

  The primary transfer bias Vt1 is applied to the backup roller 271 at time T13 corresponding to the timing at which the developed white solid image is conveyed to the primary transfer position TR1. As shown in FIG. 14B, the primary transfer bias Vt1 is a negative voltage having a polarity opposite to the charging polarity (positive polarity) of the toner. The fog toner on the photoconductor 21 is mainly charged with a reverse polarity (negative polarity). Therefore, by applying such a primary transfer bias Vt1 to the backup roller 271, the fog toner on the photoreceptor 21 is not transferred to the intermediate transfer belt 31, and only the carrier liquid component that is not affected by the bias is the intermediate transfer belt. 31 is applied. During this time, it is desirable to move the leading end Sh of the transfer material S to the position closest to the grip start position by rotating the gate roller 51 for a certain time.

  The secondary transfer bias Vt2 is applied to the secondary transfer roller 4 at a time T14 corresponding to the timing at which the surface area of the intermediate transfer belt 31 coated with the carrier liquid reaches the secondary transfer area TR2, and at the same time, Alternatively, the secondary transfer roller 4 starts to rotate slightly later (time T15). As a result, the transfer material front end portion Sh moves toward the grip portion 44 and is gripped when the grip portion 44 is closed. At this time, the gate roller 51 is rotated at a relatively high speed, more specifically, so that the moving speed of the transfer material S is faster than the moving speed of the grip portion 44. As described above, this is because the transfer material S is brought into contact with the grip portion 44 to perform positioning and skew correction. The gate roller 51 is switched to a low speed at the timing when gripping is almost completed (time T16), and thereafter, the moving speed of the transfer material S is made substantially equal to the moving speed of the grip portion 44.

  As a result, when the elastic layer 43 of the secondary transfer roller 4 contacts the intermediate transfer belt 31, the transfer material S is interposed therebetween, and the surface of the intermediate transfer belt 31 at the secondary transfer position TR2 is present. Is in a state where a carrier liquid is applied. Since the transfer material S and the carrier liquid act as a lubricant, the friction coefficient between the secondary transfer roller 4 and the intermediate transfer belt 31 is reduced, and the peripheral speed difference between them and the undulation of the elastic layer 43 are caused. The deformation of the intermediate transfer belt 31 is prevented. Further, by applying a negative voltage as the secondary transfer bias Vt2 to the secondary transfer roller 4, even if the fog toner adheres to the intermediate transfer belt 31, the fog toner moves to the transfer material S. This prevents the transfer material S from being soiled. The width of the application region in the moving direction D31 of the intermediate transfer belt 31 is desirably larger than the nip width Wnp (FIG. 5) in the same direction.

  Since the purpose is to prevent the deformation of the intermediate transfer belt 31 that starts to contact the elastic layer 43, at least when the elastic layer 43 and the intermediate transfer belt 31 first contact each other, the secondary transfer position is reached at that time. It is only necessary that the transfer material S exists in TR2 and the liquid component is applied to the surface of the intermediate transfer belt 31. Therefore, as shown by a solid line in FIG. 15B, a period during which the carrier liquid is moved to the intermediate transfer belt 31 by applying a bias to each part may be limited, or the bias application may be continued as shown by a broken line. The carrier liquid may be continuously applied to the intermediate transfer belt 31.

  As described above, in this embodiment, the deformation of the intermediate transfer belt 31 that occurs when the elastic layer 43 disposed on the surface and the intermediate transfer belt 31 come into contact with the rotation of the secondary transfer roller 4 is prevented. Therefore, when the secondary transfer roller 4 is started and the elastic layer 43 and the intermediate transfer belt 31 come into contact with each other to form the nip NP, the transfer material S is interposed therebetween. By doing so, when the elastic layer 43 and the intermediate transfer belt 31 are in direct contact with each other, the wave of the elastic layer 43 and the difference in peripheral speed between the secondary transfer roller 4 and the intermediate transfer belt 31 are caused by the intermediate transfer belt 31. Deformation is prevented. Thereby, the disturbance of the image carried on the intermediate transfer belt 31 is prevented.

  If a liquid developer is applied in advance to the surface area of the intermediate transfer belt 31 that first contacts the elastic layer 43, the liquid developer acts as a lubricant and reduces the friction coefficient. The effect of preventing deformation can be further enhanced.

  In addition, the liquid developer applied to the intermediate transfer belt 31 is mainly composed of a carrier liquid by reducing the toner component, so that the intermediate transfer belt 31 and the secondary transfer roller 4 are prevented from being contaminated by the toner. be able to. In addition, as a process for applying the liquid developer excluding the toner component in this way, a process for forming a highlight image having a density level of 0, that is, a so-called white solid image can be applied. A special process is not required as a process for applying to the intermediate transfer belt 31.

  In this embodiment, since the length of the peripheral surface of the secondary transfer roller 4 is larger than the length of the transfer material S, the rear end portion of the transfer material S opposite to the front end portion Sh forms the nip NP. After passing, the elastic layer 43 and the intermediate transfer belt 31 come into direct contact. However, there is almost no possibility that the intermediate transfer belt 31 is deformed at this time. This is because the waviness of the elastic sheet stretched along the peripheral surface of the secondary transfer roller 4 is a problem only in the region close to the concave portion 41 where the sheet is supported and fixed. This is because the carrier liquid is supplied from each image forming station to the intermediate transfer belt 31, and the elastic layer 43 and the intermediate transfer belt 31 do not contact each other in a completely dry state.

  In the apparatus of the first embodiment described above, by providing the opening / closing mechanism 45 that rotates in synchronization with the rotation of the secondary transfer roller 4, the grip portion 44 is automatically moved according to the rotational phase of the secondary transfer roller 4. The transfer material S is held and opened by opening and closing. For this reason, it is necessary to rotate the secondary transfer roller 4 in order to cause the grip portion 44 to grip the transfer material S. On the other hand, in the second and third embodiments of the present invention described below, an open / close mechanism that operates independently of the rotation of the secondary transfer roller 4 is provided so that the transfer can be performed even when the secondary transfer roller 4 is stopped. The material S can be gripped and released. The apparatus configurations of the second and third embodiments are the same as those of the first embodiment except for the configuration of the gripping portion and the opening / closing mechanism provided on the secondary transfer roller, and the operation and Since the operation is the same, the same components as those in the first embodiment are denoted by the same reference numerals and the description thereof is omitted.

  FIG. 16 is a view showing the main part of a second embodiment of the image forming apparatus according to the present invention. More specifically, FIG. 16 (a) is a diagram showing an opening / closing mechanism in the second embodiment, and FIG. 16 (b) is a diagram showing an operation sequence in the second embodiment. As shown in FIG. 16 (a), in the opening / closing mechanism 45a of this embodiment, a crank arm 452 connected to the gripper member 442 of the grip portion 44 and rotatable about the support shaft 451 is an elliptical or eccentric disc. It is driven by a cylindrical rotating cam member 454a and a gripper opening / closing motor 455a for driving the same. More specifically, when the cam follower 453 disposed on the crank arm 452 is in contact with the outer peripheral surface of the rotating cam member 454a and the gripper opening / closing motor 455a rotates in response to a control signal from the controller 10, a dotted line As shown, the rotating cam member 454a connected to the motor rotates around the support shaft, and the cam follower 453 moves along the outer peripheral surface thereof. As a result, the crank arm 452 rotates around the support shaft 451 to open and close the grip portion 44.

  The gripping operation of the transfer material S in this configuration is as shown in FIG. That is, the forward rotation of the gripper opening / closing motor 455a is started at time T21 in a state where the concave portion 41 faces the secondary transfer position TR2 and the secondary transfer roller 4 is stopped. Here, the rotation of the motor that rotates the rotating cam member 454a in the clockwise direction in FIG. 16A is “forward rotation”, and the rotation of the motor that rotates counterclockwise is “inversion”. By operating the gripper opening / closing motor 455a for a certain period of time, the tip of the gripper member 442 is separated from the gripper support member 441, and the gripper 44 is in an open state.

  After the grip 44 is opened, the gate roller 51 starts to rotate at time T22. As a result, the transfer material S is conveyed toward the opened gripping portion 44. In this case, since the secondary transfer roller 4 is stopped, it is not necessary to increase the transfer material conveyance speed. At time T23 after the timing when the leading end portion of the transfer material S is abutted against the grip portion 44, the rotation of the gate roller 51 is stopped and the grip portion opening / closing motor 455a is reversed. As a result, the rotating cam member 454a rotates counterclockwise, the gripping portion 44 is closed, and gripping of the transfer material S is completed (time T24).

  Thereafter, the rotation of the secondary transfer roller 4 is started at time T25 and the rotation of the gate roller 51 is restarted, whereby the secondary transfer roller 4 rotates while gripping the transfer material S by the grip portion 44. At time T26, the elastic layer 43 comes into contact with the intermediate transfer belt 31 via the transfer material S, and a nip NP (FIG. 5) is formed. Thereafter, the forward and reverse rotations of the gripper opening / closing motor 455a are executed once again, so that the transfer material leading end Sh that has passed through the nip NP is released from the gripping by the gripper 44.

  FIG. 17 is a view showing the main part of a third embodiment of the image forming apparatus according to the present invention. More specifically, FIG. 17 (a) is a diagram showing an opening / closing mechanism in the third embodiment, and FIG. 17 (b) is a diagram showing an operation sequence of the third embodiment. As shown in FIG. 17A, in this embodiment, the rear end portion of the gripper member 442b provided on the grip portion 44b opposite to the front end portion that grips the transfer material is extended, and the gripper member 442b is extended. Is rotatable around the support shaft 443b. The opening / closing mechanism 45b includes a spring 451b provided on the rear end side of the gripper member 442b and biasing the gripper member 442b in the closing direction, and a solenoid 452b provided on the front end side of the gripper member 442b. Yes. When the solenoid 452b is actuated according to the control signal from the controller 10, the tip of the gripper member 442b is pushed up against the urging force of the spring 451b, and the gripping part 44b is opened as shown by the dotted line.

  The gripping operation of the transfer material S in this configuration is as shown in FIG. That is, with the concave portion 41 facing the secondary transfer position TR2, the secondary transfer roller 4 is stopped, and at time T31, the solenoid 452b is operated to open the grip 44b. When the rotation of the gate roller 51 is started at time T32 to start the transfer of the transfer material S and the operation of the solenoid 452b is stopped at time T33, the gripping portion 44b is closed and the gripping of the transfer material S is completed.

  Thereafter, the rotation of the secondary transfer roller 4 is started and the rotation of the gate roller 51 is restarted at time T34, so that the secondary transfer roller 4 rotates while gripping the transfer material S by the grip portion 44. At time T35, the elastic layer 43 comes into contact with the intermediate transfer belt 31 via the transfer material S, and a nip NP (FIG. 5) is formed. Thereafter, by actuating the solenoid 452b for a predetermined time from time T36, the transfer material front end portion Sh that has passed through the nip NP is released from being held by the holding portion 44.

  Also with these configurations, as in the first embodiment, when the elastic layer 43 on the peripheral surface comes into contact with the intermediate transfer belt 31 by the rotation of the secondary transfer roller 4 to form the nip NP, there is a transfer material between them. S is interposed, and the elastic layer 43 and the intermediate transfer belt 31 are in direct contact with each other, so that the deformation of the intermediate transfer belt 31 and the disturbance of the image on the intermediate transfer belt 31 due to the deformation can be prevented. .

  Further, in the configuration of the first embodiment described above, since the gripping portion 44 is opened and closed in synchronization with the rotation of the secondary transfer roller 4, the secondary transfer is performed when the gripping portion 44 is switched from the open state to the closed state. A predetermined amount of rotation of the roller 4 is essential. Therefore, in order to avoid the elastic layer 43 on the circumferential surface of the secondary transfer roller 4 from coming into contact with the intermediate transfer belt 31 during the gripping operation of the transfer material S, the opening width W41 (FIG. 5) of the recess 41 is set to some extent. It is necessary to take big. On the other hand, in the configurations of the second and third embodiments, the transfer material S can be gripped without depending on the rotation of the secondary transfer roller 4, and therefore the opening width W41 of the recess 41 can be made smaller. Can do. This is an advantage in reducing the size of the apparatus.

  As described above, in each of the above embodiments, the secondary transfer roller 4 and the intermediate transfer belt 31 function as the “transfer roller” and the “image carrier belt” of the present invention, respectively. The controller 10 functions as the “control unit” of the present invention, and the elastic sheet constituting the elastic layer 43 corresponds to the “sheet member” of the present invention. Further, the gripping portion 44 functions as a “gripping portion” of the present invention, and among them, the gripper member 442 and the gripper support member 441 function as a “moving member” and a “supporting member” of the present invention, respectively. In the first embodiment, the gripping mechanism 45 and the cam member 50 function as an “operation part” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in each of the above embodiments, when the elastic layer 43 on the peripheral surface starts to contact the intermediate transfer belt 31 by the rotation of the secondary transfer roller 4, the transfer material S is interposed therebetween. . This is to prevent deformation due to shear strain of the intermediate transfer belt 31 caused by friction with the elastic layer 43. Such deformation particularly causes the elastic layer 43 and the intermediate transfer belt 31 to contact in a dry state. Sometimes it is easy to get up.

  Therefore, it is desirable to execute the above-described operation sequence at least when the apparatus is started from a state where the apparatus has been stopped for a long time. However, the transfer material is always interposed when the elastic layer 43 and the intermediate transfer belt 31 come into contact with each other. Is not essential. That is, liquid components such as carrier liquid remain on the intermediate transfer belt 31 during continuous image formation or after a short stop between a plurality of image forming jobs. Is expected to reduce friction with the elastic layer 43 as a lubricant. Therefore, in such a case, the elastic layer 43 and the intermediate transfer belt 31 may be allowed to contact directly.

  Further, for example, in each of the above embodiments, the movement of the intermediate transfer belt 31 is started prior to the rotation of the secondary transfer roller 4. However, the timing for starting the movement of the intermediate transfer belt 31 is not limited to this, and a predetermined moving speed is reached before the elastic layer 43 on the circumferential surface of the secondary transfer roller 4 starts to contact the intermediate transfer belt 31. As long as it is. However, in the operation sequence in which the carrier liquid is applied on the intermediate transfer belt 31 in advance as in the first embodiment described above, the intermediate transfer belt 31 and the photoreceptor 21 must be operated first. is there.

  Further, for example, in the first embodiment, when the carrier liquid is supplied from the image forming station 2K to the intermediate transfer belt 31, the photosensitive member 21 is sequentially turned on, the exposure is turned off, the developing bias is turned on, and the primary transfer is performed. The operation sequence is to turn on the bias. This is because, as described above, a so-called “white solid image” is formed on the photosensitive member 21 and transferred to the intermediate transfer belt 31 so that only the carrier component is applied to the intermediate transfer belt 31. Is not to be done.

  Instead, for example, a liquid developer containing a larger amount of toner components is applied to the photoconductor 21 by, for example, not charging or performing exposure, and the toner components are transferred to the intermediate transfer belt 31 at the primary transfer position TR1. Alternatively, only the carrier component may be transferred without being transferred. In order to realize this, for example, a positive voltage may be applied to the backup roller 271 as the primary transfer bias Vt1 so that the charged toner on the photoconductor 21 does not transfer to the intermediate transfer belt 31. However, since the polarity of the primary transfer bias needs to be reversed, the apparatus configuration may be complicated, and a configuration that forms a “white solid image” as in the above-described embodiment is more preferable.

  Further, the carrier liquid application to the intermediate transfer belt 31 in the first embodiment is not essential, and conversely, the carrier liquid may be applied also in the second and third embodiments. In the second and third embodiments, it is not essential to hold the transfer material S while the secondary transfer roller 4 is stopped. As in the first embodiment, the secondary transfer roller 4 is rotated. By operating each part in synchronization, the transfer material may be gripped while the secondary transfer roller 4 is rotated.

  Further, in each of the above-described embodiments, the image forming apparatus is a so-called liquid development type that uses a developer in which toner is dispersed in a liquid carrier. However, the application target of the present invention is not limited to that type. That is, regardless of the development method, as illustrated in FIG. 1, a structure in which a transfer roller having a concave portion on the peripheral surface and a sheet member disposed on a peripheral surface other than the concave portion is brought into contact with the image carrier belt. The present invention can be applied to all image forming apparatuses having the above configuration.

  2C, 2K, 2M, 2Y ... image forming station, 4 ... secondary transfer roller (transfer roller), 10 ... controller (control unit), 21 ... photoconductor drum, 24 ... developing unit, 31 ... intermediate transfer belt (image carrier) Body belt), 43 ... elastic layer (sheet member), 44, 44b ... gripping part, 45 ... opening / closing mechanism (operation part), 45a, 45b ... opening / closing mechanism, 441 ... gripper support member (support member), 442 ... gripper member (Moving member), NP ... nip, S ... transfer material

Claims (7)

A transfer roller having a recess formed in the peripheral surface, a gripping portion provided in the recess and gripping a transfer material, and a sheet member provided in the peripheral surface different from the recess;
An image carrier belt carrying an image;
When the rotation of the transfer roller stops, the concave portion is opposed to the image carrier belt to separate the transfer roller and the image carrier belt, and the transfer roller and the transfer roller are started to rotate. A control unit configured to hold the transfer material by the holding unit when the image carrier belt is brought into contact with the image carrier belt, and to bring the transfer roller into contact with the image carrier belt through the transfer material; An image forming apparatus. The grip portion includes a moving member that moves in a radial direction of the transfer roller, and a support member that contacts the moving member via the transfer material and grips the transfer material.
The image forming apparatus according to claim 1, further comprising an operation unit that moves the moving member, wherein the operation unit moves the moving member in conjunction with rotation of the transfer roller.   The image forming apparatus according to claim 1, wherein the controller starts rotation of the transfer roller after driving the image carrier belt.   The image forming apparatus according to any one of claims 1 to 3, wherein the control unit starts rotation of the transfer roller after the transfer unit grips the transfer material.   The control unit starts rotation of the transfer roller, and then grips the transfer material with the gripping unit, and transfers the transfer roller that grips the transfer material with the gripping unit to the image carrier belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is brought into contact with each other. The image carrier belt includes a concave portion formed on a peripheral surface, a grip portion disposed in the concave portion for gripping a transfer material, and a concave portion of a transfer roller having a sheet member disposed on the peripheral surface different from the concave portion. The image carrier belt is driven from a state where the transfer roller and the image carrier belt are stopped by separating the transfer roller and the image carrier belt.
Rotate the transfer roller after the image carrier belt is driven,
Grasping the transfer material with the gripping part disposed on the rotated transfer roller,
After gripping the transfer material, the transfer roller and the image carrier belt are brought into contact with each other through the transfer material by rotation of the transfer roller. The image carrier belt includes a concave portion formed on a peripheral surface, a grip portion disposed in the concave portion for gripping a transfer material, and a concave portion of a transfer roller having a sheet member disposed on the peripheral surface different from the concave portion. The image carrier belt is driven from a state where the transfer roller and the image carrier belt are stopped by separating the transfer roller and the image carrier belt.
After the image carrier belt is driven, grip the transfer material with the grip portion disposed on the transfer roller,
After gripping the transfer material, rotate the transfer roller,
An image forming method, wherein the transfer roller and the image carrier belt are brought into contact with each other through the transfer material by rotation of the transfer roller.

Images