Patent Publication Number: US-11022928-B2

Title: Cleaning device and image forming apparatus

Description:
INCORPORATION BY REFERENCE 
     This application is based on Japanese Patent Application No. 2019-101701 filed with the Japanese Patent Office on May 30, 2019 and Japanese Patent Application No. 2019-175380 filed with the Japanese Patent Office on Sep. 26, 2019, the contents of which are incorporated by reference. 
     BACKGROUND 
     Field of the Invention 
     The present disclosure relates to a cleaning device which cleans a sheet conveyance member, such as a conveyance roller and a conveyance belt that conveys a sheet, and to an image forming apparatus including the cleaning device. 
     Related Art 
     The image forming apparatus, such as a printer, includes a sheet conveyance unit which conveys a sheet to an image forming unit that executes image forming processing. The sheet conveyance unit includes, for example, a pair of resist rollers each having a length corresponding to a width of the sheet to be conveyed. The pair of resist rollers forms a nip portion through which the sheet travels. When a distal end portion of the sheet is brought into contact with the nip portion in a state where the rotation of the pair of resist rollers is stopped, skewing of the sheet is straightened. Afterward, when the pair of resist rollers rotates, the sheet is conveyed into the nip portion and then is fed out from there at proper timing matching timing of image forming at the image forming position. 
     Another example of the sheet conveyance unit is a sheet conveyance unit including a plurality of support rollers and a conveyance belt supported in an extended manner between the plurality of support rollers. The sheet conveyance unit having such a configuration drives the conveyance belt at predetermined timing, thereby conveying the sheet placed on the conveyance belt to the image forming unit. 
     There is a case where a surface of the sheet conveyance member, such as the resist roller and the conveyance belt, is soiled because of sheet conveyance. Soiling of the surface of the sheet conveyance member may create a problem, such as an image to be printed on the sheet being stained with foreign matter. A conventional technique has been disclosed as a configuration in which a web of a strip shape is brought into contact with one resist roller out of a pair of resist rollers. A predetermined amount of the web is fed out periodically from a feed-out roller, and this predetermined amount of the web fed out is taken up by a take-up roller. Between the feed-out roller and the take-up roller, the web comes in contact with an outer peripheral surface of the one resist roller, and wipes paper dust away from the outer peripheral surface to clean the outer peripheral surface. 
     SUMMARY 
     A cleaning device according to an aspect of the present disclosure includes: a sheet conveyance roller that conveys a sheet in an image forming apparatus that executes image forming processing, using a recording member; and a cleaning unit that cleans a surface of the sheet conveyance roller. 
     The cleaning unit includes: a cleaning member configured to come in contact with the surface of the sheet conveyance roller; and a pressing roller that presses the cleaning member against the surface of the sheet conveyance roller. The pressing roller includes a low Young&#39;s modulus area formed at least on a part of the pressing roller in a radial direction, the low Young&#39;s modulus area having a Young&#39;s modulus lower than a Young&#39;s modulus of the sheet conveyance roller. When the surface of the sheet conveyance roller is cleaned, the pressing roller is pressed against the sheet conveyance roller so as to elastically deform in the radial direction in a state where the cleaning member is sandwiched between the pressing roller and the sheet conveyance roller. 
     A cleaning device according to another aspect of the present disclosure includes a sheet conveyance belt supported in an extended manner between a plurality of support rollers. The cleaning unit includes: a cleaning member configured to come in contact with the surface of the sheet conveyance belt; and a pressing roller that presses the cleaning member against one support roller out of the plurality of support rollers. The pressing roller includes a low Young&#39;s modulus area formed at least on a part of the pressing roller in a radial direction, the low Young&#39;s modulus area having a Young&#39;s modulus lower than a Young&#39;s modulus of the one support roller. When the surface of the sheet conveyance belt is cleaned, the pressing roller is pressed against the one support roller so as to elastically deform in the radial direction in a state where the cleaning member and the sheet conveyance belt are sandwiched between the pressing roller and the one support roller. 
     An image forming apparatus according to still another aspect of the present disclosure includes: an image forming unit that executes image forming processing, using a recording material; a sheet conveyance unit that conveys a sheet to the image forming unit, the sheet conveyance unit including a sheet conveyance member that comes in contact with the sheet; and the above cleaning device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a cross-sectional view showing a structure of a resist roller unit, a cleaning unit, and their surroundings; 
         FIG. 3  is a perspective view showing an external structure of the cleaning unit; 
         FIG. 4  is a perspective view showing an external structure of the cleaning unit; 
         FIG. 5  is a perspective view showing an external structure of the cleaning unit; 
         FIG. 6  is a cross-sectional view taken along line VI-VI in  FIG. 5 ; 
         FIG. 7  shows the resist roller unit and the cleaning unit in a state where the cleaning unit is at a mounting and removing position; 
         FIG. 8  is a partial cross-sectional view showing the resist roller unit and the cleaning unit in a state where the cleaning unit is slightly pushed up in a right diagonal direction, from the mounting and removing position; 
         FIG. 9  is a partial cross-sectional view showing the resist roller unit and the cleaning unit in a state where the cleaning unit is at a cleaning position; 
         FIG. 10  is a schematic view showing a resist upper roller, a resist lower roller, a pressing roller, and a web; 
         FIG. 11  is a schematic view showing a part where the resist lower roller and the web are in contact with each other; 
         FIG. 12  shows the resist lower roller; 
         FIG. 13  shows the pressing roller; and 
         FIG. 14  is a schematic view showing a structure of a sheet conveyance unit and the cleaning unit in an image forming apparatus according to a second embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will hereinafter be described with reference to the drawings. The embodiments to be described below are examples of the present disclosure, and the present disclosure, except its essential configurations, is not limited in any form by the following embodiments. 
     First Embodiment 
     &lt;Overall Configuration of Image Forming Apparatus&gt; 
       FIG. 1  depicts an internal structure of an image forming apparatus  1  according a first embodiment of the present disclosure. The image forming apparatus  1  shown in  FIG. 1  is an ink jet recording apparatus which forms (records) an image on a sheet S by ejecting droplets of water-based ink (recording material). The image forming apparatus  1  includes an apparatus body  10 , a paper supply unit  20 , a resist roller unit (sheet conveyance unit)  30 , a belt conveyance unit  40 , an image forming unit  50 , and a curl correction unit  60 . 
     The apparatus body  10  is a box-shaped housing that houses various devices for forming an image on the sheet S. In the apparatus body  10 , a first conveyance path  11 , a second conveyance path  12 , and a third conveyance path  13  which form a conveyance path of the sheet S are formed. 
     The paper supply unit  20  supplies the sheet S to the first conveyance path  11 . The paper supply unit  20  includes a paper supply cassette  21  and a paper supply roller  22 . The paper supply cassette  21  is detachably mounted on the apparatus body  10  and sheets S are stored in the paper supply cassette  21 . The paper supply roller  22  feeds out sheets S stored in the paper supply cassette  21  one by one, by picking a sheet S on an uppermost layer of a bundle of sheets S and sending the sheet S out to a first conveyance path  11 . 
     The sheet S supplied to the first conveyance path  11  is conveyed by a pair of first conveyance rollers  111  provided on the first conveyance path  11 , to a resist roller unit  30  disposed on a downstream side of the first conveyance path  11 . A paper supply tray  24  is disposed on a right side surface of the apparatus body  10 , and sheets S can be manually placed on an upper surface of the paper supply tray  24 . The sheets S placed on the paper supply tray  24  are fed out toward the resist roller unit  30  by the paper supply roller  23 . 
     The resist roller unit  30  is a device that conveys the sheet S, which is fed to the resist roller unit  30  through the first conveyance path  11  or the paper supply roller  23 , toward a conveyance belt  41  of the belt conveyance unit  40  in a sheet conveyance direction A 1 . Details of the resist roller unit  30  are described later. 
     When a distal end of the sheet S conveyed by the resist roller unit  30  comes in contact with an outer peripheral surface  411  of the conveyance belt  41 , the sheet S is then conveyed by the conveyance belt  41 , which is being driven, in a sheet conveyance direction A 2  in a state where the sheet S is held on the outer peripheral surface  411 . The sheet conveyance direction A 2  is a direction in which the sheet S is conveyed from the right side to the left side in a left-right direction. 
     The belt conveyance unit  40  is disposed under the image forming unit  50  so as to face line heads  51 . The belt conveyance unit  40  conveys the sheet S, which is conveyed by the resist roller unit  30 , in the sheet conveyance direction A 2  toward the curl correction unit  60  such that the sheet S passes under the image forming unit  50 . The belt conveyance unit  40  has the conveyance belt  41  and a suction unit  43 . 
     The conveyance belt  41  is an endless belt having a width in a front-rear direction (direction orthogonal to the paper surface in  FIG. 1 ) and extending in a left-right direction. The conveyance belt  41  is disposed so as to face the image forming unit  50 , and conveys the sheet S in the sheet conveyance direction A 2  on an outer peripheral surface  411 . More specifically, in a predetermined conveyance area facing the line heads  51  of the image forming unit  50 , the conveyance belt  41  conveys the sheet S held on its outer peripheral surface  411 , in the sheet conveyance direction A 2 . An image forming position, at which the line heads  51  of the image forming unit  50  carry out image forming processing, is set on an orbital movement path of the conveyance belt  41 . 
     The conveyance belt  41  is supported in an extended manner between and by the first support roller  421 , the second support roller  422 , the third support roller  423 , and the pair of fourth support rollers  424 . Inside the conveyance belt  41  supported in an extended manner as described above, the suction unit  43  is disposed so as to face an inner peripheral surface  412 . The first support roller  421  is a drive roller extending in the front-rear direction that is a width direction of the conveyance belt  41 . In the sheet conveyance direction A 2 , the first support roller  421  is disposed downstream to the suction unit  43 . The first support roller  421  is rotatably driven by a drive motor (not shown), and allows the conveyance belt  41  to orbit in a predetermined orbital direction. As a result of an orbital movement of the conveyance belt  41 , the sheet S held on the outer peripheral surface  411  of the conveyance belt  41  is conveyed in the sheet conveyance direction A 2 . 
     The second support roller  422  is a belt speed detection roller extending in the front-rear direction. In the sheet conveyance direction A 2 , the second support roller  422  is disposed upstream to the suction unit  43 . The second support roller  422  is disposed such that the second support roller  422  cooperates with the first support roller  421  to maintain the planarity of an area of the outer peripheral surface  411  of the conveyance belt  41 , the area facing the line heads  51 , and the planarity of an area of the inner peripheral surface  412  of the conveyance belt  41 , the area facing the suction unit  43 . On the outer peripheral surface  411  of the conveyance belt  41 , an area facing the line heads  51  and located between the first support roller  421  and the second support roller  422  serves as the above predetermined conveyance area where the sheet S held on the outer peripheral surface  411  is conveyed. The second support roller  422  is driven to rotate in a movement interlocked with the orbiting of the conveyance belt  41 . The second support roller  422  is fitted with a pulse plate (not shown). This pulse plate rotates integrally with the second support roller  422 . By measuring a rotating speed of the pulse plate, a rotating speed of the conveyance belt  41  is detected. 
     The third support roller  423  is a tension roller extending in the front-rear direction, and gives the conveyance belt  41  a tensile force to prevent the conveyance belt  41  from slacking. The third support roller  423  is driven to rotate in a movement interlocked with the orbiting of the conveyance belt  41 . Each of the pair of fourth support rollers  424  is a guide roller extending in the front-rear direction, and guides the conveyance belt  41  to cause it to pass under the suction unit  43 . The pair of fourth support rollers  424  is driven to rotate in a movement interlocked with the orbiting of the conveyance belt  41 . The conveyance belt  41  has a plurality of suction holes penetrating the conveyance belt  41  in its thickness direction from the outer peripheral surface  411  to the inner peripheral surface  412 . 
     The suction unit  43  is disposed so as to face the image forming unit  50  with the conveyance belt  41  interposed between the suction unit  43  and the image forming unit  50 . The suction unit  43  brings the sheet S, which is held on the outer peripheral surface  411  of the conveyance belt  41 , into close contact with the outer peripheral surface  411  of the conveyance belt  41  by generating a negative pressure between the sheet S and the conveyance belt  41 . The suction unit  43  includes a belt guide member  431 , a suction housing  432 , a suction device  433 , and an exhaust duct  434 . 
     The belt guide member  431  is disposed so as to face an area of the inner peripheral surface  412  of the conveyance belt  41 , the area being located between the first support roller  421  and a second support roller  422 . The belt guide member  431  is a plate-like member having a width substantially equal to a length of the conveyance belt  41  in its width direction (front-rear direction). The belt guide member  431  forms an upper surface portion of the suction housing  432 , and has a shape that is substantially equal to a shape of the suction housing  432  when seen from above. The belt guide member  431  guides the orbital movement of the conveyance belt  41  in an interlocking manner with the rotation of the first support roller  421  between the first support roller  421  and the second support roller  422 . 
     The belt guide member  431  has a plurality of groove portions formed on a belt guide surface facing the inner peripheral surface  412  of the conveyance belt  41 . The groove portions are formed so as to correspond respectively to the suction holes of the conveyance belt  41 . The belt guide member  431  further has through-holes formed so as to correspond respectively to the groove portions. Each through-hole is a hole that in each groove portion, penetrates the belt guide member  431  in its thickness direction. Each through-hole thus communicates with each suction hole of the conveyance belt  41  across each groove portion. 
     The suction unit  43  configured in the above manner generates a suction force by sucking air from a space above the conveyance belt  41  through the groove portions and through-holes of the belt guide member  431  and the suction holes of the conveyance belt  41 . Due to such a suction force, an airflow (suction air) toward the suction unit  43  is generated in the space above the conveyance belt  41 . When the sheet S is conveyed onto the conveyance belt  41  by the resist roller unit  30  and covers a part of the outer peripheral surface  411  of the conveyance belt  41 , a suction force (negative pressure) acts on the sheet S, and the sheet S is brought into close contact with the outer peripheral surface  411  of the conveyance belt  41 . 
     The suction housing  432  is a box-shaped housing having an upper opening, and the suction housing  432  is disposed below the conveyance belt  41  such that the upper opening is covered by the belt guide member  431 . The suction housing  432  defines a suction space  432 A in cooperation with the belt guide member  431 . This means that a space enclosed with the suction housing  432  and the belt guide member  431  serves as the suction space  432 A. This suction space  432 A communicate with the suction holes of the conveyance belt  41  through the groove portions and through-holes of the belt guide member  431 . 
     An opening portion  432 B is formed in a bottom wall portion of the suction housing  432 , and the suction device  433  is disposed corresponding to the opening portion  432 B. The exhaust duct  434  is connected to the suction device  433 . The exhaust duct  434  is connected to an exhaust port (not shown) formed in the apparatus body  10 . 
     The image forming unit  50  is disposed above the belt conveyance unit  40 . Specifically, above the belt conveyance unit  40 , the image forming unit  50  is disposed so as to face the outer peripheral surface  411  of the conveyance belt  41 . The image forming unit  50  forms an image by applying image forming processing to the sheet S which is conveyed in the sheet conveyance direction A 2  in a state where the sheet S is held on the outer peripheral surface  411  of the conveyance belt  41 . In the present embodiment, an image forming method of the image forming unit  50  is an ink jet method, according to which an image is formed on the sheet S by ejecting droplets of water-based ink (recording material). 
     The image forming unit  50  includes line heads  51  ( 51 Bk,  51 C,  51 M,  51 Y). The line head  51 Bk ejects black ink droplets, the line head  51 C ejects cyan ink droplets, the line head  51 M ejects magenta ink droplets, and the line head  51 Y ejects yellow ink droplets. The line heads  51 Bk,  51 C,  51 M, and  51 Y are arranged adjacent to each other from an upstream side to a downstream side in the sheet conveyance direction A 1 . Each of the line heads  51 Bk,  51 C,  51 M, and  51 Y ejects ink droplets on the sheet S conveyed in the sheet conveyance direction A 2  in a state where the sheet S is held on the outer peripheral surface  411  of the conveyance belt  41 , thereby forming an image on the sheet S. As a result, an image is formed on the sheet S. 
     The sheet S on which the image is formed is conveyed by the conveyance belt  41 , and is guided by a discharge guide unit  44  to enter the curl correction unit  60 . The curl correction unit  60  is disposed downstream of the conveyance belt  41  in the sheet conveyance direction A 2  with the discharge guide unit  44  sandwiched therebetween. The curl correction unit  60  corrects the curl of the sheet S on which the image is formed while conveying the sheet S to the downstream side. 
     The sheet S whose curl has been corrected by the curl correction unit  60  is fed out to the second conveyance path  12 . The second conveyance path  12  extends along a left side surface of the apparatus body  10 . The sheet S fed out to the second conveyance path  12  is conveyed by a pair of second conveyance rollers  121  disposed on the second conveyance path  12  toward a paper discharge port  12 A formed on a left side of the apparatus body  10 , and the sheet S is discharged onto a paper discharge unit  14  from the paper discharge port  12 A. 
     In a case where both-side printing is applied to the sheet S, meanwhile, the sheet S, whose front surface has been subjected to the image forming processing, is fed out from the second conveyance path  12  toward a sheet reversing unit  15 . The sheet reversing unit  15  is a conveyance path branching out from a midpoint of the second conveyance path  12 , serving as a part where the sheet S is reversed in surface position and conveyance direction (switchback). The sheet S reversed by the sheet reversing unit  15  to have its front and back surfaces switched to each other is fed out to a third conveyance path  13 , on which the sheet S is conveyed in a reverse direction by a pair of third conveyance rollers  131  disposed on the third conveyance path  13 . Subsequently, the sheet S travels through the resist roller unit  30  and is re-supplied onto the outer peripheral surface  411  of the conveyance belt  41  in a state where the sheet S is reversed to have its front and back surfaces switched to each other. The re-supplied sheet S is conveyed by the conveyance belt  41  as the image forming processing is applied to the back surface of the sheet S by the image forming unit  50 . The sheet S on which both-side printing has been completed passes through the second conveyance path  12 , and is discharged onto the paper discharge unit  14  from the paper discharge port  12 A. 
     &lt;Structure of Resist Roller Unit and its Surroundings&gt; 
       FIG. 2  shows a structure of the resist roller unit  30  and its surroundings. As shown in  FIG. 2 , the resist roller unit  30  has a resist housing  30 H, and a pair of resist rollers consisting of a resist upper roller  31  and a resist lower roller  32  (sheet conveyance roller). The resist housing  30 H is mounted on the apparatus body  10 , and rotatably supports the resist upper roller  31  and the resist lower roller  32 . In the resist housing  30 H, the sheet S is conveyed into a nip portion formed between the pair of resist rollers consisting of the resist upper roller  31  and the resist lower roller  32 . The resist roller unit  30  has a roller drive unit (not shown) that drives the resist upper roller  31  and the resist lower roller  32  to rotate. 
     The resist upper roller  31  is a metal roller made of, for example, an aluminum alloy. The resist lower roller  32  is constructed by coating an outer peripheral surface of a roller base material made of a solid, hard rubber layer, with a highly water-repellent tube. A structure of the resist lower roller  32  will be described in detail later with reference to  FIG. 12 . The resist lower roller  32  forms the nip portion between the resist lower roller  32  and the resist upper roller  31 , the nip portion allowing the sheet S to travel therethrough, and conveys the sheet S toward the image forming unit  50  at timing matching timing of the image forming processing. 
     As shown in  FIG. 2 , a virtual straight line L connecting the center of the resist upper roller  31  and the center of the resist lower roller  32  is inclined at an acute angle (e.g., 10 degrees) with respect to a vertical direction. In other words, the resist lower roller  32  is disposed at the position displaced upstream in a conveyance direction of the sheet S with respect to the resist upper roller  31 . 
     When the above both-side printing is carried out, the sheet S having been subjected to single-side printing is reversed to have its front and back surfaces switched to each other, and is conveyed into the nip portion of the pair of resist rollers. As a result, the resist lower roller  32  comes in contact with a printed surface of the sheet S. At this time, undried ink adheres to a surface of the resist lower roller  32  in some cases. Such a case leads to a problem that ink adhering to the resist lower roller  32  is transferred to another incoming sheet S when it travels through the pair of resist rollers. Another concern is that the resist lower roller  32  disposed on the lower side out of the pair of resist rollers is a roller that allows foreign matter, such as paper dust, to adhere thereto easily. 
     In view of the above circumstances, the image forming apparatus  1  according to the present embodiment is provided with a cleaning unit  70  (cleaning device) and with a movement mechanism  75 . The cleaning unit  70  can clean a surface of the resist lower roller  32 . The cleaning unit  70 , of which a detailed structure will be described later, includes a web driven roller  71 , a pressing roller  72 , a web drive roller  73 , a cleaning housing  70 H that pivotally supports these rollers  71  to  73 , and a web W. 
     The web W is a strip-shaped member forming a contact surface that comes in contact with the surface of the resist lower roller  32  to clean up the surface. The web W is made of a fabric material, such as nonwoven fabric, and is rolled in advance into a web roll WR, which is fitted on the exterior of the web driven roller  71 . The web W is fed out by fixed amount from the web roll WR fitted on the web driven roller  71 , travels the pressing roller  72  past, and is rolled up around the web drive roller  73 . The web W is supported in an extended manner between the web driven roller  71 , the pressing roller  72 , and the web drive roller  73  so as to have no slackness. 
     The movement mechanism  75  ( FIG. 2 ) is a mechanism that allows the cleaning unit  70  to be moved between a cleaning position ( FIG. 2 ) and a mounting and removing position ( FIG. 7 ) below the cleaning position. At the cleaning position, the movement mechanism  75  allows the web W of a cleaning part  70 A to come in contact with the resist lower roller  32 . At the mounting and removing position, the movement mechanism  75  allows the cleaning part  70 A to be disposed below the resist lower roller  32  in a separated manner and allows the cleaning unit  70  to be mounted and removed on and from the apparatus body  10 . The movement mechanism  75  can cause the cleaning unit  70  to stay at a separation position located at a midpoint between the cleaning position and the mounting and removing position. At the separation position, the cleaning part  70 A is disposed below the resist lower roller  32  in a separated manner as the cleaning unit  70  is disconnected from a web feed-out mechanism. 
     The movement mechanism  75  has a cleaning unit rotating unit  45  and a unit driving unit  80  that cause the cleaning unit  70  to rotate such that the cleaning unit  70  changes its orientation between the cleaning position and the mounting and removing position. The cleaning unit rotating unit  45  includes a rotary shaft  451  supported on the conveyance unit frame  40 H holding the belt conveyance unit  40 , and a pair of front and rear rotary levers  452  fitted respectively to front and rear parts of the rotary shaft  451 . 
     The unit driving unit  80  includes a drive motor (not shown), and generates a drive force for rotating the rotary shaft  451  around its center axis. Being driven by rotation of the drive motor, the rotary shaft  451  is caused to rotate by a predetermined angle. To the drive motor of the unit driving unit  80 , a controller  90  is connected. The drive motor is rotatably driven according to a control signal from the controller  90 . The controller  90  is configured such that in a computer system including a CPU, ROM, RAM and the like, the controller  90  executes a predetermined operation program. 
     The rotary levers  452  have pin receiving portions  452 P ( FIG. 8 ) formed respectively thereon. The pin receiving portions  452 P receive unit fulcrum pins  70 P protruding in the front-rear direction from front and rear parts of the cleaning unit  70 , respectively, and rotatably support the unit fulcrum pins  70 P. The cleaning unit  70  is controlled in orientation to take its respective orientations at three positions, i.e., the cleaning position, the separation position, and the mounting and removing position, according to angels of rotation of the rotary shaft  451  rotated by the unit driving unit  80 . A state shown in  FIG. 2  is a state where the cleaning unit  70  is at the cleaning position at which the pressing roller  72  is in contact with the resist lower roller  32  with the web W sandwiched between the pressing roller  72  and the resist lower roller  32 . 
     When the cleaning unit  70  is at the separation position, the pressing roller  72  is disposed below in a separated manner so that the web W is separated from the resist lower roller  32 . When the cleaning unit  70  is at the mounting and removing position, the pressing roller  72  is disposed further below in a separated manner. 
     &lt;Detailed Structure of Cleaning Unit&gt; 
       FIGS. 3 to 5  are perspective views of an external structure of the cleaning unit, showing the external structure of the cleaning unit seen in different directions.  FIG. 6  is a cross-sectional view taken along line VI-VI in  FIG. 5 . The cleaning unit  70  includes the cleaning part  70 A and the cleaning housing  70 H. The cleaning part  70 A has a contact surface WA extending along an axial direction of the resist lower roller  32 . The cleaning part  70 A is disposed such that the contact surface WA comes in contact from below with the surface of the resist lower roller  32 , and the contact surface WA wipes out the surface of the resist lower roller  32  to clean up the surface. 
     The cleaning housing  70 H supports the cleaning part  70 A. The cleaning housing  70 H has a front wall  701  and a rear wall  702 , a connection wall  703 , the pair of unit fulcrum pins  70 P, a sheet member  704 , and a pair of guide rollers  705 . The front wall  701 , the rear wall  702 , and the connection wall  703  of the cleaning housing  70 H are made of a metal material (magnetic material). 
     The front wall  701  and the rear wall  702  are disposed so as to face each other in the front-rear direction (the axial direction of the resist lower roller  32 ), and support the cleaning part  70 A. The connection wall  703  connects the front wall  701  to the rear wall  702  along the front-rear direction. The connection wall  703  has a side wall  703 A making up an upper right side surface of the cleaning housing  70 H, and a bottom wall  703 B making up a bottom surface of the cleaning housing  70 H (see  FIG. 6 ). 
     The pair of unit fulcrum pins  70 P protrude in the front-rear direction from an outer surface of the front wall  701  and the same of the rear wall  702 , respectively. The unit fulcrum pins  70 P are disposed on a left lower portion of the front wall  701  and the same of the rear wall  702 , respectively. Each unit fulcrum pin  70 P has a circular cylindrical shape in two stages where an outer diameter of the unit fulcrum pin  70 P decreases from a base portion toward a distal end portion. 
     The sheet member  704  is a film-like member making up a left side surface of the cleaning housing  70 H, and is fixed to the bottom wall  703 B ( FIG. 6 ). The sheet member  704  prevents foreign matter, such as paper dust and ink pigment, collected by the cleaning unit  70  from scattering in the apparatus body  10 . 
     Above the unit fulcrum pins  70 P, the pair of guide rollers  705  are supported by the front wall  701  and the rear wall  702 , respectively, and each include an outer peripheral surface rotatable around a center axis parallel to the front-rear direction. The guide rollers  705  are disposed on right upper portions of the front wall  701  and the rear wall  702  respectively. The pair of guide rollers  705  has a function of guiding the cleaning unit  70  when the cleaning unit  70  moves to the cleaning position, the separation position, and the mounting and removing position described above. 
     The cleaning part  70 A includes the web W, and the web driven roller  71  (feed-out roller), the pressing roller  72 , and the web drive roller  73  (take-up roller) that are supported rotatably by the front wall  701  and the rear wall  702 . The web W is a strip-shaped member forming the above contact surface WA, which comes in contact with the surface of the resist lower roller  32  to clean up the surface. A feed-out distal end of the web W is put over an outer peripheral surface of the pressing roller  72  and then is fixed to an outer peripheral surface of the web drive roller  73 . 
     As described above, the web W of a strip shape is reeled out from the web roll WR fitted on the web driven roller  71 . The web roll WR is arranged such that an amount of the remaining web W can be visually recognized from the outside of the cleaning unit  70  through an opening portion formed between the side wall  703 A and the bottom wall  703 B. This prevents a case where the cleaning unit  70  having been removed from the apparatus body  10  during use of the image forming apparatus  1  because of having a little amount of the remaining web W to be used is mounted erroneously on the apparatus body  10 . 
     The pressing roller  72  is in contact with a back surface of the web W and presses a front surface of the web W against the resist lower roller  32 . On a movement path of the web W, the pressing roller  72  lies at a midpoint between the web driven roller  71  and the web drive roller  73 . The pressing roller  72  is an elastic roller constructed by fitting an elastic material on a peripheral surface of a shaft. A structure of the pressing roller  72  will be described in detail with reference to  FIG. 13 . When the cleaning unit  70  is disposed at the above cleaning position ( FIG. 2 ), the pressing roller  72  is brought into contact with the resist lower roller  32  with the web W sandwiched between the pressing roller  72  and the resist lower roller  32 . At this time, a center of the pressing roller  72  is on the straight line L. The above contact surface WA is a contact portion where the web W comes in contact with the resist lower roller  32 , the contact portion being a part of a nip portion formed between the pressing roller  72  and the resist lower roller  32  so as to be on the straight line L, and is a strip-shaped portion extending in the front-rear direction. 
     The web driven roller  71  is a roller that can be driven to rotate around an axis of a driven roller shaft  71 S. The web driven roller  71  feeds out the web W so as to cause a part of the web W that comes in contact with the resist lower roller  32  to shift. The web drive roller  73  takes up the web W having been fed out from the web driven roller  71 . The web drive roller  73  is a roller that rotates around an axis of a drive roller shaft  73 S, which is supplied with a rotational drive force from a drive system. 
     The cleaning unit  70  has a unit input gear  711  (see  FIG. 4 ), an interlocking gear  711 T, a transmission gear  712 , and a drive roller gear  713  (see  FIG. 6 ), which make up the above drive system. The unit input gear  711  is rotatably supported at a lower right end portion of the front wall  701 . An input gear shaft  711 S of the unit input gear  711  penetrates the front wall  701  and extends to the inside (back side) of the front wall  701 . The interlocking gear  711 T is fixed to the input gear shaft  711 S, and rotates integrally with the unit input gear  711 . The transmission gear  712  is rotatably supported inside the front wall  701 , and is engaged with the interlocking gear  711 T and with the drive roller gear  713 . The drive roller gear  713  is a gear fixed to one end portion of the web drive roller  73 . 
     The web W is fed out by a predetermined amount from the web roll WR at predetermined timing, by the web feed-out mechanism. This process is not described in detail. The web feed-out mechanism has a function of giving the drive roller shaft  73 S a rotational drive force to feed out the web W. The web feed-out mechanism includes a solenoid that serves as a driving source, and a drive transmission system that coverts an extending and retracting motion of an extendable and retractable shaft of the solenoid into a torque and that transmits the torque to the unit input gear  711 . 
     &lt;Forms of Movement of Cleaning Unit&gt; 
     As described above, the cleaning unit  70  of the image forming apparatus  1  according to the present embodiment can be moved among the cleaning position, the separation position, and the mounting and removing position. Forms of movement of the cleaning unit  70  to respective positions will be described with reference to  FIGS. 7 to 9 .  FIG. 7  shows the cleaning unit  70  and its surroundings in a state where the cleaning unit  70  is at the mounting and removing position. FIG.  8  is a partial cross-sectional view showing the resist roller unit  30  and the cleaning unit  70  in a state where the cleaning unit  70  is slightly pushed up in an upper diagonal direction, from the mounting and removing position, and  FIG. 9  is a partial cross-sectional view showing the resist roller unit  30  and the cleaning unit  70  in a state where the cleaning unit  70  is at the cleaning position. 
     As shown in  FIG. 8 , the unit fulcrum pins  70 P of the cleaning unit  70  are engaged with the pin receiving portions  452 P formed on parts of rotary levers  452  that are close to their distal ends, respectively. As a result of the rotary shaft  451  being rotatably driven by the drive motor (not shown) included in the unit driving unit  80 , the distal ends of the rotary levers  452  rotate counterclockwise. The cleaning unit  70  is thus pushed up in the right diagonal direction in a movement interlocked with the rotation of the rotary levers  452 . When the rotary shaft  451  is driven to rotate in reverse, the rotary levers  452  rotate clockwise, which causes the cleaning unit  70  to move down leftward. 
     The unit fulcrum pins  70 P of the cleaning unit  70  are disposed below and left to a center of gravity of the cleaning unit  70 . As a result, when the cleaning unit  70  is pushed up, the cleaning unit  70  takes an orientation where an upper part of the cleaning unit  70  tilts rightward. 
     As shown in  FIG. 7 , guide frames  101  are provided in a part that is between the resist roller unit  30  and the unit driving unit  80  and that is above the cleaning unit  70  in the right diagonal direction. On respective left side portions of the guide frames  101 , guide surfaces  101 R are formed as sloped surfaces. The guide surfaces  101 R are guide surfaces for guiding the pair of guide rollers  705 , which are disposed on a right upper corner of the cleaning unit  70 , to guide surfaces  102 R formed on a lower part of the resist frame  102 . 
     When the cleaning unit  70  at the mounting and removing position ( FIG. 2 ) is pushed up by the rotation of the rotary levers  454 , the cleaning unit  70  tilts rightward because of the above-described positional difference between the unit fulcrum pins  70 P and the center of gravity. This brings the pair of guide rollers  705  into contact with the guide surfaces  101 R, along which the guide rollers  705  are guided. Then, when the rotary levers  454  rotate further, the pair of guide rollers  705 , which have been guided along the guide surfaces  101 R and the guide surfaces  102 R, are pushed into positioning portions  102 S of the resist frame  102  (see  FIG. 9 ). At a point of time at which the pair of guide rollers  705  are pushed into the positioning portions  102 S, the cleaning unit  70  is disposed at the cleaning position and is stopped from moving relative to the resist roller unit  30 . 
     The separation position of the cleaning unit  70  refers to an intermediate position of the cleaning unit  70 , the intermediate position being located between the position of the cleaning unit  70  shown in  FIG. 8  and the same shown in  FIG. 9 . The separation position can be set properly as any given position at which the web W is separated from the resist lower roller  32 . 
     &lt;Cleaning Process by Cleaning Unit&gt; 
     A cleaning process of cleaning the surface of the resist lower roller  32  by the cleaning unit  70  will be described with reference to  FIGS. 10 and 11 .  FIG. 10  is a schematic view showing the resist lower roller  32 , the pressing roller  72 , and the web W in a state where the cleaning unit  70  is at the cleaning position.  FIG. 11  is an enlarged view of a part A shown in  FIG. 10 . 
     As shown in  FIG. 10 , when the sheet S carrying an image formed on its one surface is reversed to switch its front and back surfaces to each other and is conveyed into the resist roller unit  30 , ink INK adheres to a surface  32   f  of the resist lower roller  32  in some cases. When the cleaning unit  70  is at the cleaning position, the pressing roller  72  is pressed against the resist lower roller  32  such that a part of an outer peripheral portion of the pressing roller  72  elastically deform inwardly in a radial direction in a state where the web W is sandwiched between the pressing roller  72  and the resist lower roller  32 . In the present embodiment, for example, the pressing roller  72  is pressed at a pressure of 10 to 15 gf/mm 2  (9.81 e+7 to 1.478e+8 Pa), against the resist lower roller  32 . 
     As shown in  FIG. 11 , rotation of the resist lower roller  32  results in a relative movement of the web W to a roller surface  32   f  of the resist lower roller  32 . In the present embodiment, the resist lower roller  32  is rotated in the above-described state where the part of the outer peripheral portion of the pressing roller  72  is elastically deformed in the radial direction. As a result, a state of contact of the web W with the surface  32   f  of the resist lower roller  32  is not line contact (line contact in a direction orthogonal to the paper surface in  FIG. 11 ) but becomes surface contact having a nip width WNP. 
     In this manner, as a result of the relative movement of the web W to the roller surface  32   f , the ink INK adhering to the roller surface  32   f  reaches a nip entrance EN of a cleaning nip N formed between the pressing roller  72  and the resist lower roller  32 , where the web W is pressed by the pressing roller  72  to come in contact with the resist lower roller  32 . The ink INK is then blocked at the nip entrance EN, thus forming an ink puddle there. Afterward, most of the ink INK adhering to the roller surface  32   f  is absorbed by the web W in a contact area between the roller surface  32   f  and the web W. 
     However, a tiny portion of the ink INK adhering to the roller surface  32   f  passes through the cleaning nip N, that is, the contact area between roller surface  32   f  and the web W, thus coming out of a cleaning nip exit EX, as a portion of the ink INK staying on the roller surface  32   f  Specifically, there may be a case where the ink INK, due to its surface tension, infiltrates into a tiny gap between the pressing roller  72  and the web W and slips through the cleaning nip N. The ink INK that is not absorbed by the web W at the cleaning nip N to stay on the roller surface  32   f  in the above manner dries and solidifies as time goes by, and, consequently, a pigment or the like included in the ink INK sticks firmly to the roller surface  32   f.    
     Such ink INK sticking firmly to the roller surface  32   f  is also wiped away certainly by the web W when the web W is brought into contact with the sticking ink INK as a result of the rotation of the resist lower roller  32 . Specifically, as shown in  FIG. 11 , at the time of cleaning the roller surface  32   f , the part of the outer peripheral portion of the pressing roller  72  is caused to deform elastically in the radial direction to form the nip width WNP relatively long in a roller rotation direction. A state of contact of the web W with the roller surface  32   f  is thus made surface contact state, in which the firmly sticking ink INK can be wiped away by the web W frictionally sliding over the roller surface  32   f.    
     When a cleaning process as described above is completed, the web drive roller  73  is rotatably driven (see  FIG. 6 ) to feed out the web W. This creates a state where at the next round of the cleaning process, a new part of the surface of the web W is allowed to come in contact with the resist lower roller  32 . 
     &lt;Structure of Resist Lower Roller and of Pressing Roller&gt; 
     A structure of the resist lower roller  32  and of the pressing roller  72  will then be described in detail.  FIG. 12  is a cross-sectional view of the resist lower roller  32 , and  FIG. 13  is a cross-sectional view of the pressing roller  72 . 
     As shown in  FIG. 12 , the resist lower roller  32  includes a first core portion  321 , a first outer peripheral portion  322  covering an outer periphery of the first core portion  321 , and an outer skin layer  323  covering a surface of the first outer peripheral portion  322 . The first core portion  321 , as in the case of the resist upper roller  31 , is composed of, for example, a shaft made of a metal, such as an aluminum alloy. 
     The first outer peripheral portion  322  is formed of a solid rubber layer. For example, a rubber, such as ethylene-propylene diene (EPDM) rubber, can be used as a material making up the rubber layer. The first outer peripheral portion  322  of the resist lower roller  32  is required to have rigidity that hardly allows the resist lower roller  32  to deform in the radial direction so that the resist lower roller  32  can nip the sheet S along with the resist upper roller  31  and convey the sheet S at an accurate linear velocity. It is preferable, for this reason, that a Young&#39;s modulus E 1  of the first outer peripheral portion  322  be set as a Young&#39;s modulus within a range of about 4.3 MPa or more and about 6.27 MPa or less. 
     The outer skin layer  323  is formed of a highly water-repellent, thin-walled tube made of, for example, a tetrafluoroethylene-perfluoroalkoxy ethylene copolymer resin (PFA). Providing the resist lower roller  32  with such an outer skin layer  323  enhances smoothness of a peripheral surface of the resist lower roller  32 . As a result, the web W easily absorbs the ink INK adhering or firmly sticking to the peripheral surface of the resist lower roller  32 . 
     As shown in  FIG. 13 , the pressing roller  72  is an elastic roller that includes a second core portion  72 S serving as a rotating shaft of the pressing roller  72 , and a second outer peripheral portion  72 A covering an outer periphery of the second core portion  72 S. The pressing roller  72  elastically deforms to dent inwardly in the radial direction when pressing the web W against the surface  32   f  of the resist lower roller  32 . 
     The second core portion  72 S is a metal shaft, and may be provided as, for example, a shaft made of an iron solid material. Similar to the above first outer peripheral portion  322  of the resist lower roller  32 , the second outer peripheral portion  72 A is made of, for example, a rubber, such as ethylene-propylene diene (EPDM) rubber. As shown in an enlarged view of  FIG. 13 , however, the second outer peripheral portion  72 A of the pressing roller  72  is made of a foamed rubber (sponge) containing a number of pores  72 B. In other words, the second outer peripheral portion  72 A making up a part of the pressing roller  72  is made of an elastic material having an air bubble ratio higher than an air bubble ratio of the first outer peripheral portion  322  of the resist lower roller  32 . 
     Having the second outer peripheral portion  72 A made of the foamed rubber in this manner, the pressing roller  72  works as a roller including a low Young&#39;s modulus area formed at least on its part in the radial direction. A Young&#39;s modulus E 2  of the second outer peripheral portion  72 A is set as a Young&#39;s modulus that is 1/1000 or more and 1/10 or less, more preferably, 1/100 or more and 1/10 or less of a Young&#39;s modulus E 1  of the first outer peripheral portion  322  of the resist lower roller  32 . A specific value for the Young&#39;s modulus E 2  of the second outer peripheral portion  72 A of the pressing roller  72  can be selected from, for example, values ranging from 0.04 MPa to 0.6 MPa (inclusive). 
     &lt;Effects&gt; 
     The cleaning unit  70  (cleaning device) according to the first embodiment is a cleaning mechanism that cleans the roller surface  32   f  (surface) of the resist lower roller (sheet conveyance roller)  32  included in the resist roller unit  30  (sheet conveyance unit) that conveys the sheet S to the image forming unit  50 . The image forming unit  50  executes the image forming processing, using the ink INK (recording member). The cleaning unit  70  has the web W (cleaning member) that can come in contact with the roller surface  32   f  of the resist lower roller  32 , and the pressing roller  72  that presses the web W against the roller surface  32   f  of the resist lower roller  32 . The pressing roller  72  includes the low Young&#39;s modulus area (second outer peripheral portion  72 A) formed at least on a part of the pressing roller  72  in the radial direction, the low Young&#39;s modulus area having the Young&#39;s modulus lower than the Young&#39;s modulus of the resist lower roller  32 . When the roller surface  32   f  of the resist lower roller  32  is cleaned, the pressing roller  72  is pressed against the resist lower roller  32  so as to elastically deform in the radial direction in a state where the web W is sandwiched between the pressing roller  72  and the resist lower roller  32 . 
     As a result of setting the Young&#39;s modulus E 2  of the pressing roller  72  (second outer peripheral portion  72 A) lower than the Young&#39;s modulus E 1  of the resist lower roller  32  (first outer peripheral portion  322 ), when the roller surface  32   f  is cleaned, the pressing roller  72  pressed against the resist lower roller  32  elastically deforms to dent inwardly in the radial direction. As a result, at cleaning of the roller surface  32   f , a state of contact of the web W with the resist lower roller  32  is not line contact but becomes surface contact having the large nip width WNP. The pressing roller  72  is pressed against the surface  32   f  of the resist lower roller  32  by a predetermined pressing force (e.g., 10 to 15 gf/mm 2 ). This brings the web W into contact with the surface  32   f  such that a high frictional force acts between the web W and the surface  32   f  Even if the ink INK sticks firmly to the roller surface  32   f  of the resist lower roller  32 , therefore, the sticking ink INK can be wiped away by the web W frictionally sliding over the roller surface  32   f.    
     The present embodiment is to meet a requirement that elastic deformation of the resist lower roller  32  be prevented as much as possible to allow the sheet S to be conveyed accurately at a predetermined linear velocity. In view of this requirement, the Young&#39;s modulus E 1  of the resist lower roller  32  is not made relatively low but the Young&#39;s modulus E 2  of the pressing roller  72  is made relatively low. 
     In the present embodiment, the resist lower roller  32  is configured to include the first core portion  321  and the first outer peripheral portion  322 , and the pressing roller  72  is configured to include the second core portion  72 S and the second outer peripheral portion  72 A. The Young&#39;s modulus E 2  of the outer peripheral portion  72 A of the pressing roller  72  is set lower than the Young&#39;s modulus E 1  of the first outer peripheral portion  322  of the resist lower roller  32 . As the first core portion  321  and the second core portion  72 S pivotally and firmly support the resist lower roller  32  and the pressing roller  72 , respectively, therefore, the second outer peripheral portion  72 A of the pressing roller  72  is caused to elastically deform when the pressing roller  72  is pressed. 
     The second outer peripheral portion  72 A is configured to have the air bubble ratio higher than the air bubble ratio of the first outer peripheral portion  322 . Setting a difference in air bubble ratio in this manner allows a wider range of material selection, and allows the second outer peripheral portion  72 A of the pressing roller  72  to elastically deform in the radial direction when the roller surface  32   f  is cleaned. In the present embodiment, the first outer peripheral portion  322  has a solid structure. The resist lower roller  32 , however, may be made into a structure having a few pores. It is necessary, however, that the first outer peripheral portion  322  of the resist lower roller  32  have an air bubble ratio set lower than the air bubble ratio of the second outer peripheral portion  72 A of the pressing roller  72 . The second outer peripheral portion  722  and the first outer peripheral portion  322  are made of the same material (EPDM), except for a difference in air bubble ratio. Obviously, however, the second outer peripheral portion  722  and the first outer peripheral portion  322  may be made respectively of different materials. 
     In the cleaning unit  70  according to the present embodiment, E 2 /E 1  is set in a range of 1/1000 or more and 1/10 or less, more preferably, in a range of 1/100 or more and 1/10 or less. As a result, when the pressing roller  72  is pressed (to clean the roller surface  320 , the second outer peripheral portion  72 A of the pressing roller  72  is certainly caused to elastically deform as deformation of the first outer peripheral portion  322  of the resist lower roller  32  is inhibited, and the pressing force that presses the web W against the resist lower roller  32  is kept high. 
     The image forming apparatus  1  according to the present embodiment has been described as the image forming apparatus that includes the sheet reversing unit  15  to offer the both-side printing function. In the image forming apparatus  1  having the both-side printing function, the ink INK used in the preceding image forming processing tends to adhere to the roller surface  32   f  of the resist lower roller  32  and, as time goes by, firmly sticks to the roller surface  32   f  in some cases. In such a case, the cleaning unit  70  having the above configuration causes the web W to certainly remove the ink INK firmly sticking to the roller surface  32   f  of the resist lower roller  32  by frictionally sliding over the roller surface  32   f.    
     Second Embodiment 
       FIG. 14  shows a sheet conveying unit (sheet conveyance unit)  39  that is a constituent element of an image forming apparatus according to a second embodiment of the present disclosure and that makes the image forming apparatus according to the second embodiment different from the image forming apparatus according to the first embodiment. The image forming apparatus according to the present embodiment is the same in configuration as the image forming apparatus  1  according to the first embodiment, except for the sheet conveying unit  39  shown in  FIG. 14 . 
     In the first embodiment, the resist roller unit  30  is described as an example of the sheet conveyance unit that conveys the sheet S to the belt conveyance unit  40 . In the second embodiment, on the other hand, the sheet conveying unit  39  is adopted as another example of the sheet conveyance unit, the sheet conveying unit  39  including a plurality of support rollers (first to fourth support rollers  33  to  36 ), a feed-out belt  37 , and a suction unit  38 . 
     As shown in  FIG. 14 , the first support roller  33  and the fourth support roller  36  are disposed to be separated from each other across a distance in the left-right direction. The first support roller  33  and the fourth support roller  36  each extend in the front-rear direction (the direction orthogonal to the paper surface in  FIG. 14 ). In the present embodiment, for example, the first support roller  33  is a drive roller and the fourth support roller  36  is a belt speed detection roller. 
     The second support roller  34  is disposed below the first support roller  33  in a right diagonal direction. The third support roller  35  is disposed below the fourth support roller  36 , and is disposed right with respect to the second support roller  34  with a predetermined distance formed between the second support roller  34  and the third support roller  35 . 
     The feed-out belt  37  is supported in an extended manner between the four support rollers  33  to  36  so as to have no slackness. Being driven by the rotation of the first support roller  33 , the feed-out belt  37  orbits in a direction indicated by arrows B. Inside an orbital path of the feed-out belt  37 , the suction unit  38  having the same configuration as the configuration of the suction unit  43  according to the first embodiment is provided. The feed-out belt  37  has a plurality of holes penetrating the feed-out belt  37  in its thickness direction, which holes will not be described in detail. Through these holes, the sheet S placed on a belt surface (outer peripheral surface)  37   f  of the feed-out belt  37  is sucked in a direction indicated by arrows C. 
     In a state where the cleaning unit according to the present embodiment is disposed at the cleaning position, the pressing roller  72  presses the third support roller  35  (one support roller), with the web W and the feed-out belt  37  being sandwiched between the pressing roller  72  and the third support roller  35 . This brings the belt surface  37   f  of the feed-out belt  37  into contact with the web W. 
     The third support roller  35 , similar to the resist lower roller  32  according to the first embodiment, includes a third core portion  351 , and a third outer peripheral portion  352  covering an outer periphery of the third core portion  351 . This third outer peripheral portion  352  is made of a solid rubber, such as an EPDM rubber. Similar to the pressing roller  72  of the first embodiment, the pressing roller  72  of the second embodiment is an elastic roller that includes the second core portion  72 S (fourth core portion), and the second outer peripheral portion  72 A (fourth outer peripheral portion) covering an outer periphery of the second core portion  72 S. The second outer peripheral portion  72 A is a low Young&#39;s modulus area made of a foamed rubber (sponge) containing a number of pores  72 B, showing a Young&#39;s modulus lower than a Young&#39;s modulus of the third support roller  35  against which the second outer peripheral portion  72 A is pressed when the belt surface  37   f  is cleaned. 
     Specifically, when a Young&#39;s modulus of the third outer peripheral portion  352  of the support roller  35  is E 1  and a Young&#39;s modulus of the second outer peripheral portion  72 A of the pressing roller  72  is E 2 , E 2 /E 1  is set in a range of 1/1000 or more and 1/10 or less (more preferably, in a range of 1/100 or more and 1/10 or less). Because of such a difference in Young&#39;s modulus, when the belt surface  37   f  is cleaned, the pressing roller  72  elastically deform such that a part of its outer peripheral portion  72 A dents inwardly in the radial direction, which brings the web W into surface contact with the belt surface  37   f  of the feed-out belt  37  (part indicated by an arrow D). 
     According to the second embodiment, the Young&#39;s modulus E 2  of the second outer peripheral portion  72 A of the pressing roller  72  is set lower than the Young&#39;s modulus E 1  of the third support roller  35 . When the belt surface  37   f  of the feed-out belt  37  (sheet conveyance belt) is cleaned, the pressing roller  72  is pressed against the third support roller  35  so as to elastically deform in the radial direction in a state where the web W and the feed-out belt  37  are sandwiched between the pressing roller  72  and the third support roller  35 . 
     As a result of setting the Young&#39;s modulus E 2  of the pressing roller  72  (second outer peripheral portion  72 A) lower than the Young&#39;s modulus E 1  of the third support roller  35  (third outer peripheral portion  352 ), when the belt surface  37   f  is cleaned, the pressing roller  72  pressed against the third support roller  35  elastically deforms to dent inwardly in the radial direction. As a result, at cleaning of the belt surface  37   f , a state of contact of the web W with the feed-out belt  37  is not line contact but becomes surface contact having a large contact width. The pressing roller  72  is pressed against the belt surface  37   f  of the feed-out belt  37  by a predetermined pressing force (e.g., 10 to 15 gf/mm 2 ). This brings the web W into contact with the belt surface  37   f  such that a high frictional force acts between the web W and the belt surface  37   f . In this configuration, even if the ink INK adheres to the belt surface  37   f  of the feed-out belt  37  and sticks firmly to the belt surface  37   f  as time goes by, the firmly sticking ink INK can be wiped away by the web W. 
     If not the Young&#39;s modulus E 2  of the pressing roller  72  but the Young&#39;s modulus E 1  of the third support roller  35  is made relatively low, the third support roller  35  elastically deforms when the pressing roller  72  is pressed against the support roller  35  at cleaning of the belt surface  37   f  This may lead to slackening of the feed-out belt  37 . In another case, applying a tensile force to the feed-out belt  37  causes the third support roller  35  to deform elastically. This case may also lead to slackening of the feed-out belt  37 . In this manner, when not the Young&#39;s modulus of the pressing roller  72  but the Young&#39;s modulus of the third support roller  35  is made relatively low, the ink INK firmly sticking to the belt surface  37   f  of the feed-out belt  37  is not wiped away effectively by the web W frictionally sliding over the belt surface  37   f , and accurately conveying the sheet S in the sheet conveyance process becomes difficult. For these reasons, according to the second embodiment, the Young&#39;s modulus E 2  of the pressing roller  72  is made relatively low. 
     [Modifications] 
     The embodiments of the present disclosure have been described above. The present disclosure is, however, not limited to these embodiments but may be embodied as the following modified embodiments. 
     (1) In the above first and second embodiments, the water-based ink is adopted as an example of the recording material. The present disclosure, however, is not limited by this. For example, non-water-based ink or toner may also be adopted as the recording material. When toner is adopted as the recording material, however, the toner adheres to the surface of the sheet conveyance member, cools and solidifies, and sticks firmly to the surface of the sheet conveyance member in some cases, as the water-based ink does. In such a case, by adopting the cleaning unit  70  having the configuration of the first embodiment or the second embodiment, the same effect as described above can be achieved. 
     (2) In the first and second embodiments, the web W is reeled out from the web roll WR and is taken up by the web drive roller  73 . The present disclosure, however, is not limited by this. For example, a configuration may be adopted according to which a web of a strip sheet shape is brought into contact with the sheet conveyance member and is replaced with another web at predetermined timing. 
     (3) In the first and second embodiments, the image forming apparatus  1  including the sheet reversing unit  15  is adopted. According to the present disclosure, however, an image forming apparatus not including the sheet reversing unit may also be adopted. Such an image forming apparatus not including the sheet reversing unit may be configured to allow an operation that the user reverses the sheet carrying an image formed on its one surface and places the reversed sheet on a hand-feeding tray (paper supply tray) to form an image on the other surface. In this case, the recording material may stick firmly to the sheet conveyance member, as does in the above case. In such a case, however, a cleaning device, such as the above cleaning unit  70 , certainly removes the recording material sticking firmly to the sheet conveyance member, through the frictional sliding of the web W. 
     (4) The first embodiment has been described above as an example in which the resist lower roller  32  includes the first core portion  321  and the first outer peripheral portion  322 , while the pressing roller  72  includes the second core portion  72 S and the second outer peripheral portion  72 A. The second embodiment, on the other hand, has been described above as an example in which the third support roller  35  includes the third core portion  351  and the third outer peripheral portion  352 . Each of the sheet conveyance roller, the support roller, and the pressing roller may be a roller of an integral structure made of a single material. 
     Although the present disclosure has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present disclosure hereinafter defined, they should be construed as being included therein.