Patent Publication Number: US-11046072-B2

Title: Printing apparatus

Description:
The present application is based on, and claims priority from JP Application Serial Number 2019-092553, filed May 16, 2019, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The invention relates to a printing apparatus that performs printing by ejecting liquid. 
     2. Related Art 
     In a printing apparatus that performs printing by ejecting liquid such as ink to a printing medium, mist is generated when the liquid is ejected by a print head, and the mist floats in the apparatus. 
     JP-A-2016-198926 discloses a configuration in which a wall part is provided between a heat sink that makes contact with a circuit board for driving a print head and a range in which an ejection port and a supply port of air flow are formed in a cover frame that holds the circuit board for the purpose of reducing adhesion of mist included in the airflow to the circuit board (see JP-A-2016-198926). 
     Other than the configuration with the positional relationship between the circuit board, the heat sink, the supply port, and the like disclosed in the JP-A-2016-198926, a configuration for further improving protection of the circuit board from mist in the printing apparatus is desired. In addition, the circuit board to be protected from the mist is not limited to the circuit board for driving the print head. 
     SUMMARY 
     A printing apparatus includes a support unit configured to support a printing medium, a print head disposed at a position opposite the support unit, the print head being configured to eject liquid to the printing medium, a circuit unit disposed downstream of the print head in a transport path of the printing medium at a position opposite the support unit, and a sliding mechanism configured to support the circuit unit such that the circuit unit is movable in a first direction in which the circuit unit approaches the support unit and a second direction that is opposite the first direction, wherein the circuit unit includes a circuit board, a cover surrounding an opposing face is opposite the support unit, the cover being configured to house the circuit board inside the cover, a first airflow inlet formed in a first surface of the cover, and a first duct that is formed in the first surface and in communication with the first airflow inlet, the sliding mechanism includes a fixed frame fixed inside the printing apparatus and configured to support the circuit unit, a second airflow inlet formed in the fixed frame, the second airflow inlet being formed at a position that is opposite the first airflow inlet when the circuit unit is located at a first position where the circuit unit is close to the support unit, and a second duct that is formed in the fixed frame and in communication with the second airflow inlet, and when the circuit unit is located at the first position, the first duct and the second duct are engaged with each other such that a third duct is formed to cause the first airflow inlet and the second airflow inlet communicate with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating a configuration of a printing apparatus. 
         FIG. 2  is an exploded perspective view of an UV irradiator and a sliding mechanism. 
         FIG. 3  is a diagram illustrating a positional relationship between the slide mechanism and the UV irradiator located at a first position. 
         FIG. 4  is a perspective view illustrating a first duct. 
         FIG. 5  is a perspective view illustrating airflow second duct. 
         FIG. 6A  is a diagram illustrating the first duct and the second duct in the state where the UV irradiator is not located at the first position, and  FIG. 6B  is a diagram illustrating the first duct and the second duct in the state where the UV irradiator is located at the first position. 
         FIG. 7  is a cross-sectional view of a partial range including the UV irradiator. 
         FIG. 8  is a diagram illustrating airflow rate where a wall part is provided on an outer side of the sliding mechanism. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present disclosure will be described below with reference to the accompanying drawings. The drawings are merely examples for describing the present embodiment. Since the drawings are examples, shapes and ratios may be inaccurate, may contradict with each other, or may be partially omitted. 
     1. Schematic Configuration of Printing Apparatus 
       FIG. 1  is a schematic view illustrating a configuration of a printing apparatus  1 . The printing apparatus  1  may be referred to as an ink-jet printer, a liquid ejection apparatus, an image recording apparatus, and the like. In the drawings, an XYZ orthogonal coordinate system with X, Y and Z directions is illustrated for understanding of the arrangement relationship of the parts of the apparatus. In  FIG. 1 , the direction from left to right is the X direction, the direction from the far side (rear side) to the near side (front side) is the Y direction, and the vertical upward direction is the Z direction. As illustrated in  FIG. 1 , the printing apparatus  1  includes a feeding shaft  20  and a winding shaft  40 , and a single sheet S in a roll shape wound around the feeding shaft  20  and the winding shaft  40  is pulled therebetween along a transport path Pc. 
     The sheet S is a printing medium. Printing on the sheet S is performed while the sheet S is transported in a transport direction Ds from the feeding shaft  20  toward the winding shaft  40 . The transport direction Ds is the direction along the transport path Pc. In the example illustrated in  FIG. 1 , the transport path Pc is formed in a combination of a plurality of straight lines and curved lines, and accordingly the transport direction Ds differs among positions in the transport path Pc. Types of the sheet S are broadly categorized into a paper type and a film type. Specific examples of the paper type include a high-quality paper, cast paper, art paper and coated paper, and specific examples of the film type include synthetic paper, polyethylene terephthalate (PET) and polypropylene (PP). 
     The printing apparatus  1  generally includes a feeding unit  2  that feeds the sheet S from the feeding shaft  20 , a processing unit  3  that performs printing on the sheet S fed from the feeding unit  2 , and a winding unit  4  that winds, around the winding shaft  40 , the sheet S on which printing has been performed by the processing unit  3 . The feeding unit  2 , the processing unit  3 , and the winding unit  4  arranged in the X direction are housed in a housing  10  of the printing apparatus  1 . In the transport path Pc, the feeding unit  2  is located upstream of the processing unit  3  and the winding unit  4 . In addition, in the transport path Pc, the winding unit  4  is located downstream of the feeding unit  2  and the processing unit  3 . In the following description, upstream and downstream in the transport path Pc are simply referred to as upstream and downstream. 
     The feeding unit  2  includes the feeding shaft  20  around which an end of the sheet S is wound, and a driven roller  21  on which the sheet S drawn out from the feeding shaft  20  is wound. When the feeding shaft  20  is rotated clockwise in  FIG. 1 , the sheet S wound around the feeding shaft  20  is fed to the processing unit  3  through the driven roller  21 . While supporting the sheet S fed from the feeding unit  2  by means of the rotary drum  30 , the processing unit  3  performs printing an image on the sheet S by appropriately performing a process using a processing unit PU disposed along the outer circumferential surface of the rotary drum  30 . In the processing unit  3 , a front driving roller  31  and a rear driving roller  32  are provided near both ends of the rotary drum  30  in the X direction. The sheet S transported from the front driving roller  31  to the rear driving roller  32  is supported by the rotary drum  30 . 
     The front driving roller  31  rotates clockwise in  FIG. 1  to thereby transport downstream the sheet S fed from the feeding unit  2 . A nip roller  31   n  is provided for the front driving roller  31 . The nip roller  31   n  makes contact with the sheet S to thereby sandwich the sheet S between the nip roller  31   n  and the front driving roller  31 . Thus, a frictional force between the front driving roller  31  and the sheet S is ensured and the sheet S is reliably transported by the front driving roller  31 . 
     The rotary drum  30  is a cylindrical drum having a central axis parallel to the Y direction. In the example of  FIG. 1 , the rotary drum  30  corresponds to a “support unit” that supports the printing medium. The support unit that supports the printing medium is also referred to as a platen. The rotary drum  30  includes a rotary shaft  300  extending in the axis direction through the central line of the cylindrical shape of the rotary drum  30 . The rotary shaft  300  is rotatably supported by a support mechanism (not illustrated), and the rotary drum  30  rotates about the rotary shaft  300 . On the outer circumferential surface of the rotary drum  30 , the sheet S transported from the front driving roller  31  to the rear driving roller  32  is wound. The rotary drum  30  supports the sheet S while being driven into rotation in the transport direction Ds of the sheet S by receiving a frictional force between the rotary drum  30  and the sheet S. 
     The processing unit  3  is provided with driven rollers  33  and  34  that fold back the sheet S at both ends of the region of the sheet S that is wound on the rotary drum  30 . The driven roller  33  folds back the sheet S by winding the sheet S between the front driving roller  31  and the rotary drum  30 . On the other hand, the driven roller  34  folds back the sheet S by winding the sheet S between the rotary drum  30  and the rear driving roller  32 . In this manner, by folding back the sheet S at respective positions upstream and downstream of the rotary drum  30 , a long range in which the sheet S is wound on the rotary drum  30  can be ensured. 
     The rear driving roller  32  winds the sheet S that is transported from the rotary drum  30  through the driven roller  34 . In addition, the rear driving roller  32  rotates clockwise in  FIG. 1  to thereby transport the sheet S to the winding unit  4 . A nip roller  32   n  is provided for the rear driving roller  32 . The nip roller  32   n  makes contact with the sheet S to thereby sandwich the sheet S between the nip roller  32   n  and the rear driving roller  32 . Thus, a frictional force between the rear driving roller  32  and the sheet S is ensured and the sheet S is reliably transported by the rear driving roller  32 . 
     The processing unit PU includes a plurality of print heads  6  and a plurality of UV irradiators  37 . Reference signs  6   a,    6   b,    6   c,    6   d,    6   e  and  6   f  are appropriately used for distinction of the individual print heads  6 . Likewise, reference signs  37   a,    37   b,  and  37   c  are appropriately used for distinction of the individual UV irradiators  37 . The processing unit PU also includes a carriage  36 . The carriage  36  includes the print heads  6   a,    6   b,    6   c,    6   d,    6   e  and  6   f  and the UV irradiators  37   a  and  37   b.    
     The plurality of print heads  6  and the plurality of UV irradiators  37  are disposed along the outer circumference of the rotary drum  30  in such a manner as to face the outer circumferential surface of the rotary drum  30 . In  FIG. 1 , the print heads  6   a,    6   b,    6   c,    6   d,    6   e  and  6   f  and the UV irradiators  37   a,    37   b  and  37   c  are radially disposed with respect to the rotary shaft  300  of the rotary drum  30 . For example, the print heads  6   a,    6   b,    6   c,    6   d,    6   e  and  6   f  correspond to white (W), cyan (C), magenta (L), yellow (Y), black (K), and clear (CL), respectively, and can eject inks of respective colors by an ink-jet method. The print head  6  includes a plurality of nozzles (not illustrated) at opposing faces facing the outer circumferential surface of the rotary drum  30 , and ejects the ink in the form of liquid from the nozzles. The print head  6  may be referred to as an ink-jet head, a liquid ejection head, or the like. A color image is printed on the sheet S supported by the rotary drum  30  by ejecting the ink by the print heads  6 . 
     Each print head uses an ultraviolet (UV) ink that is cured when irradiated with an ultraviolet ray. The UV ink is referred also to as a photo-curable ink. The UV irradiator  37  is provided for the purpose of curing and fixing the ink to the sheet S. The UV irradiator  37  applies an ultraviolet ray from the opposing face facing the outer circumferential surface of the rotary drum  30 . In the example of  FIG. 1 , the UV irradiator  37   a  is disposed between the print head  6   a  and the print head  6   b,  and the UV irradiator  37   b  is disposed between the print head  6   e  and the print head  6   f.  Thus, the W ink ejected from the print head  6   a  to the sheet S is cured by receiving an ultraviolet ray from the UV irradiator  37   a  before the C, M, Y, K and CL inks are overlaid. The C, M, Y and K inks ejected from the print heads  6   b,    6   c,    6   d  and  6   e  to the sheet S are cured by receiving an ultraviolet ray from the UV irradiator  37   b  before the CL ink is overlaid. 
     In the example of  FIG. 1 , a guide rail  35  extending parallel to the Y direction is disposed at a predetermined position on the left and right of the carriage  36 , and the carriage  36  is mounted across the two guide rails  35 . Thus, the print heads  6   a,    6   b,    6   c,    6   d,    6   e  and  6   f  and the UV irradiators  37   a  and  37   b  mounted on the carriage  36  can be moved parallel to the Y direction by the carriage  36 . 
     In the processing unit  3 , the UV irradiator  37   c  is disposed downstream of the print head  6   f.  Thus, the CL ink ejected from the print head  6   f  to the sheet S is cured by receiving an ultraviolet ray from the UV irradiator  37   c.  The UV irradiator  37   c  is not mounted on the carriage  36 . The UV irradiator  37   c  corresponds to a “first irradiator” and the UV irradiators  37   a  and  37   b  different from the UV irradiator  37   c  correspond to a “second irradiator”. The UV irradiator  37   c  is an example of a “circuit unit”. 
     The sheet S on which printing has been performed by the processing unit  3  is transported to the winding unit  4  by the rear driving roller  32 . The winding unit  4  includes a driven roller  41  that winds the sheet S between the winding shaft  40  and the rear driving roller  32  in addition to the winding shaft  40  around which the end of the sheet S is wound. When the winding shaft  40  rotates clockwise in  FIG. 1 , the sheet S transported from the rear driving roller  32  is wound around the winding shaft  40  through the driven roller  41 . 
     The number and arrangement of rollers that are provided within the transport path Pc for transporting the sheet S are not limited to those of the configuration illustrated in  FIG. 1 . Also, the color of the ink used for printing by the processing unit  3  is not limited to the above-described color. 
     2. Description of UV Irradiator and Sliding Mechanism 
     Next, the UV irradiator  37   c  and configurations relating to the UV irradiator  37   c  will be described. 
       FIG. 2  is an exploded perspective view illustrating a configuration of the UV irradiator  37   c  and a slide mechanism that slidably supports the UV irradiator  37   c  as viewed from the front side (the near side in the drawing). 
       FIG. 3  illustrates a positional relationship between the slide mechanism and the UV irradiator  37   c  located at the first position. 
     The UV irradiator  37   c  includes an opposing face  50  that faces the rotary drum  30 . A light source  51  for applying an ultraviolet ray is provided in the opposing face  50 . The light source  51  is an LED, for example. The surface of the UV irradiator  37   c  is covered with the cover  52  in part or in its entirety except for the opposing face  50 . In other words, the cover  52  is a housing of the UV irradiator  37   c  that is coupled with the opposing face  50  and is disposed to surround the opposing face  50 . 
     In  FIG. 2 , some of the configurations inside the cover  52  are indicated by a dashed line. As illustrated in  FIG. 2 , a circuit board  53  is housed in the cover  52 . The circuit board  53  is a substrate for driving the light source  51 , and a circuit composed of various types of electronic components required for driving the light source  51  is installed in the circuit board  53 . In the UV irradiator  37   c,  each surface of the cover  52  corresponds to a side surface of the opposing face  50 . Of the side surfaces, surfaces  54  and  56  that are opposite in the Y direction are referred to as a first surface  54  and a second surface  56 . In the example of  FIG. 2 , the first surface  54  is the front surface of the cover  52 , and the second surface  56  is the rear surface of the cover  52 . 
     For the purpose of cooling the circuit board  53  that generates heat in driving of the light source  51 , the cover  52  includes a airflow inlet  55  and a airflow outlet  57  as through holes. The airflow inlet  55  is formed in the first surface  54 , and the airflow outlet  57  is formed in the second surface  56 . Air flowing into the cover  52  from the airflow inlet  55  cools the circuit board  53 . Air inside the cover  52  flows out of the cover  52  from the airflow outlet  57 . Although the illustration is omitted in  FIG. 2 , an air intake fan  58  configured to introduce cooling air into the cover  52  is provided in association with the airflow inlet  55 , and an exhaust fan  59  configured to eject air out of the cover  52  is provided in association with the airflow outlet  57 . See  FIGS. 3, 7 and 8  for the intake fan  58  and the exhaust fan  59 . 
     In the following description, the airflow inlet  55  is referred to as “first airflow inlet  55 ” for distinction from a airflow inlet  82  described below. 
     The UV irradiator  37   c  is mounted on a movable frame  60 . The movable frame  60  is formed by, for example, bend in airflow sheet metal or the like. The movable frame  60  includes a bottom part  61  that supports the UV irradiator  37   c  from below, and a first frame wall  62  and a second frame wall  63  extending upright from the end of the bottom part  61 . In the state where the UV irradiator  37   c  is mounted on the movable frame  60 , the first frame wall  62  is located forward of the first surface  54  of the cover  52  so as to face the first surface  54 . In addition, in the state where the UV irradiator  37   c  is mounted on the movable frame  60 , the second frame wall  63  is located rearward of the second face  56  of the cover  52  so as to face the second surface  56 . 
     As illustrated in  FIG. 2 , the first frame wall  62  includes a protrusion  64  protruding outward, and the second frame wall  63  includes a protrusion  65  protruding outward. More specifically, the protrusion  64  is a portion protruding forward from the first frame wall  62 , and the protrusion  65  is a portion protruding rearward from the second frame wall  63 . The UV irradiator  37   c  is fixed to the movable frame  60  in the state where the UV irradiator  37   c  is mounted on the movable frame  60  having the above-mentioned configuration. 
     In  FIG. 2 , reference signs  70  and  71  represent slide rails elongated in a direction parallel to a first direction D 1  and a second direction D 2 . The first direction D 1  is the direction in which the UV irradiator  37   c  approaches the rotary drum  30 , and the second direction D 2  is the direction opposite to the first direction D 1 . In the illustrated example, the first direction D 1  and the second direction D 2  are parallel to the X direction. Note that the first direction D 1  and the second direction D 2  may be inclined with respect to the X direction. 
     A slide rail  70  is a rail fixed to a first fixed frame  80  in the state where a recess faces the first frame wall  62  of the movable frame  60 . A slide rail  71  is a rail fixed to a second fixed frame  81  in the state where a recess faces the second frame wall  63  of the movable frame  60 . In  FIG. 2 , the slide rail  70  hidden by the first fixed frame  80  is indicated by a dashed line. 
       FIG. 2  illustrates a portion of the first fixed frame  80  and the second fixed frame  81 . The first fixed frame  80  and the second fixed frame  81  are collectively referred to as a fixed frame. The slide rails  70  and  71  may be understood as a part of the fixed frame. The fixed frame is formed of, for example, a sheet metal or the like, and is fixed inside the housing  10  of the printing apparatus  1 . More specifically, the first fixed frame  80  is located forward of the first frame wall  62  of the movable frame  60  and faces the first surface  54  and the first frame wall  62 . The second fixed frame  81  is located rearward of the second frame wall  63  of the movable frame  60  and faces the second surface  56  and the second frame wall  63 . The first fixed frame  80  and the second fixed frame  81  may be members separate from each other or may be partially coupled with each other. 
     The protrusion  64  of the first frame wall  62  fits into the recess of the slide rail  70 , and the protrusion  65  of the second frame wall  63  fits into the recess of the slide rail  71 . Thus, the movable frame  60  on which the UV irradiator  37   c  is mounted is allowed to move in the first direction D 1  and the second direction D 2  while being regulated by the slide rails  70  and  71 . 
     In the following description, movement of the movable frame  60  on which the UV irradiator  37   c  is mounted is simply referred to as movement of the UV irradiator  37   c.  The movement of the UV irradiator  37   c  may be achieved by power of a motor or the like, or may be achieved by hand of a user. When the UV irradiator  37   c  moves in the first direction D 1 , the opposing face  50  comes close to the rotary drum  30 . The position of the UV irradiator  37   c  when the UV irradiator  37   c  comes close to the rotary drum  30  such that the gap between the opposing face  50  and the rotary drum  30  is a predetermined distance is referred to as “first position”. The UV irradiator  37   c  illustrated in  FIG. 1  may be understood as being located at a first position. In addition, the UV irradiator  37   c  illustrated in  FIG. 3  is located also at the first position. 
     At the first position, the UV irradiator  37   c  drives the light source  51  and emits an ultraviolet ray from the light source  51 . The UV irradiator  37   c  does not move beyond the first position in the first direction D 1 . Although not illustrated in the drawings, a stopper may be provided in the movable frame  60 , the slide rails  70  and  71 , and the like to prevent the movement of the UV irradiator  37   c  beyond the first position in the first direction D 1 . By moving the UV irradiator  37   c  located at the first position in the second direction D 2 , the UV irradiator  37   c  may be separated away from the rotary drum  30 . For example, the UV irradiator  37   c  is moved in the second direction D 2  for maintenance of the UV irradiator  37   c  and/or for an operation of passing the sheet S through the transport path Pc. 
     The movable frame  60  including the protrusions  64  and  65  and the fixed frame including the slide rails  70  and  71  constitute a “slide mechanism” that movably supports the circuit unit in the first direction D 1 , which is a direction toward the support unit and a second direction D 2 , which is the direction opposite to the first direction D 1 . Note that the arrangement of the protrusion and the recess constituting the sliding mechanism for supporting the circuit unit as a movable body may be an arrangement opposite to the above-described configuration. Specifically, a configuration corresponding to the slide rail as a recess may be provided in the movable body or the movable frame, and a protrusion that fits into the recess may be provided in the fixed frame. 
       FIG. 3  illustrates a portion of the first fixed frame  80 , and the movable frame  60  and the UV irradiator  37   c  located rearward of the first fixed frame  80  as viewed from the front side. In  FIG. 3 , the movable frame  60  and UV irradiator  37   c  hidden by the first fixed frame  80  are indicated by a two-dot chain line and a dashed line, respectively. In addition, in  FIG. 3 , illustration of the slide rail  70  of the first fixed frame  80  is omitted. 
     The airflow inlet  82  serving airflow a through-hole is formed in the first fixed frame  80 . In the following description, the airflow inlet  82  is referred to as “second airflow inlet  82 ”. As shown in  FIG. 3 , the second airflow inlet  82  is formed in the first fixed frame  80  at a position that faces the first airflow inlet  55  when the UV irradiator  37   c  is located at the first position. 
     3. Description of Duct 
     Next, a duct provided in association with the first airflow inlet  55  will be described. The cover  52  of the UV irradiator  37   c  includes a first duct  90  that communicates with the first airflow inlet  55 . The fixed frame of the slide mechanism includes a second duct  100  that communicates with the second airflow inlet  82 . 
       FIG. 4  is a perspective view illustrating the first duct  90  as viewed from the front side. The first duct  90  includes a flange  91 , and walls  92 ,  93 ,  94  and  95  extending upright from the flange  91 . The first duct  90  is formed of, for example, a sheet metal or the like. The flange  91  is a surface that is parallel or substantially parallel to the first surface  54  of the cover  52  and is attached to the first surface  54 . A hole that communicates with the first airflow inlet  55  is formed in a center portion of the flange  91 , and the walls  92 ,  93 ,  94  and  95  surround the periphery of the hole. Of the walls  92 ,  93 ,  94  and  95 , the wall  92  and the wall  93  face each other, and the wall  94  and the wall  95  face each other. The wall  92  is closer to the rotary drum  30  than the wall  93  in the first direction D 1 . Of the walls  92 ,  93 ,  94  and  95 , the wall  94  is located on the upper side and the wall  95  is located on the lower side. For convenience sake, the wall  92  is referred to as a first duct left wall  92 , the wall  93  as a first duct right wall  93 , the wall  94  as a first duct upper wall  94 , and the wall  95  as a first duct lower wall  95 . 
     As illustrated in  FIG. 4 , the first duct right wall  93  has a higher degree of projection from the flange  91 , i.e., a greater height from the flange  91 , than other walls of the first duct  90 , namely, the first duct left wall  92 , the first duct upper wall  94 , and the first duct lower wall  95 . Such a first duct  90  may be a member attached as described above at a position that communicates with the first airflow inlet  55  of the cover  52  of the UV irradiator  37   c,  or may be a portion of the cover  52  that is integrally formed with the cover  52  at a position that communicates with the first airflow inlet  55 . Naturally, the first duct  90  is movable together with the UV irradiator  37   c  in the first direction D 1  and/or the second direction D 2 . 
       FIG. 5  is a perspective view illustrating the second duct  100  as viewed from the rear side. The second duct  100  includes a flange  101 , and walls  102 ,  103 ,  104  and  105  extending upright from the flange  101 . The second duct  100  is formed of, for example, a sheet metal or the like. The flange  101  is a surface that is parallel to or substantially parallel to the surface of the first fixed frame  80 , and is attached to the surface of the first fixed frame  80  that faces the first surface  54  of the cover  52 . A hole that communicates with the second airflow inlet  82  is formed in a center portion of the flange  101 , and the walls  102 ,  103 ,  104  and  105  surround the periphery of the hole. Of the walls  102 ,  103 ,  104  and  105 , the wall  102  and the wall  103  face each other, and the wall  104  and the wall  105  face each other. The wall  120  is located closer to the rotary drum  30  than the wall  103  in the first direction D 1 . Of the walls  102 ,  103 ,  104  and  105 , the wall  104  is located on the upper side and the wall  105  is located on the lower side. For convenience sake, the wall  102  is referred to as a second duct left wall  102 , the wall  103  as a second duct right wall  103 , the wall  104  as a second duct upper wall  104 , and wall  105  as a second duct lower wall  105 . 
     As illustrated in  FIG. 5 , the second duct right wall  103  has a lower degree of projection from the flange  101 , i.e., a smaller height from the flange  101 , than other walls of the second duct  100 , namely, the second duct left wall  102 , the second duct upper wall  104 , and the second duct lower wall  105 . Such a second duct  100  may be a member attached as described above at a position that communicates with the second airflow inlet  82  of the first fixed frame  80 , or may be a portion of the first fixed frame  80  that is integrally formed with the first fixed frame  80  at a position that communicates with the second airflow inlet  82 . 
       FIGS. 6A and 6B  illustrate shapes of the first duct  90  and the second duct  100  as viewed from the front side. Note that  FIG. 6A  illustrates a state where the UV irradiator  37   c  is located at a remote position than the first position in the second direction D 2 , and  FIG. 6B  illustrates a state where the UV irradiator  37   c  is located at the first position. In  FIGS. 6A and 6B , the first duct left wall  92 , the first duct right wall  93 , the first duct upper wall  94  and the first duct lower wall  95  of the first duct  90 , and the second duct left wall  102 , the second duct right wall  103 , the second duct upper wall  104  and the second duct lower wall  105  of the second duct  100  are provided with certain thicknesses for illustration. In addition, in  FIGS. 6A and 6B , illustration of the flange  91  of the first duct  90  and the flange  101  of the second duct  100  is omitted. 
     As illustrated in  FIG. 6A , in the state where the UV irradiator  37   c  is not located at the first position, the first duct  90  and the second duct  100  are not in communication with each other. As illustrated in  FIG. 6B , the first duct  90  and the second duct  100  communicate with each other when the UV irradiator  37   c  moves in the first direction D 1  from the state illustrated in  FIG. 6A  and reaches the first position. Specifically, as the UV irradiator  37   c  moves in the first direction D 1 , a portion of the first duct  90  is housed inside the second duct  100 , and thus the first duct  90  and the second duct  100  are engaged with each other. The term “engage” means fitting each other, which includes, for example, coupling, overlapping, and contacting. 
     In the first duct  90  illustrated in  FIG. 4 , the hatched portion is a “first engagement part” that engages with the second duct  100  of the first duct  90 . In other words, a tip end portion  92   a  of the outer surface of the first duct left wall  92 , a tip end portion  93   a  of the inner surface of the first duct right wall  93 , and a tip end portion  94   a  of the outer surface of the first duct upper wall  94  correspond to the first engagement part. In addition, although not illustrated in  FIG. 4 , the tip end portion of the outer surface of the first duct lower wall  95  also corresponds to the first engagement part. 
     In the second duct  100  illustrated in  FIG. 5 , the hatched portion is a “second engagement part” that engages with the first duct  90  of the second duct  100 . In other words, a tip end portion  102   a  of the inner surface of the second duct left wall  102 , a tip end portion  103   a  of the outer surface of the second duct right wall  103 , and a tip end portion  105   a  of the inner surface of the second duct lower wall  105  correspond to the second engagement part. In addition, although not illustrated in  FIG. 5 , the tip end portion of the inner surface of the second duct upper wall  104  also corresponds to the second engagement part. 
     The state where the tip end portion  92   a  of the outer surface of the first duct left wall  92  overlaps the tip end portion  102   a  of the inner surface of the second duct left wall  102 , the tip end portion  94   a  of the outer surface of the first duct upper wall  94  overlaps the tip end portion of the inner surface of the second duct upper wall  104 , and the tip end portion of the outer surface of the first duct lower wall  95  overlaps the tip end portion  105   a  of the inner surface of the second duct lower wall  105  is the state where a portion of the first duct  90  is housed inside the second duct  100 . The first duct  90  is formed in such a size that a portion of the first duct  90  is housed inside the second duct  100 . 
     As described above, in the second duct  100 , the second duct right wall  103  has a lower height from the flange  101  than the second duct left wall  102 , the second duct upper wall  104 , and the second duct lower wall  105 . As such, when the UV irradiator  37   c  moves in the first direction D 1 , the first duct  90  is partially housed inside the second duct  100  without hitting the second duct right wall  103  at the first duct left wall  92 . In addition, as described above, in the first duct  90 , the first duct right wall  93  has a higher height from the flange  91  than the first duct left wall  92 , the first duct upper wall  94 , and the first duct lower wall  95 . Thus, in the state where a portion of the first duct  90  is housed inside the second duct  100 , the tip end portion  93   a  of the inner surface of the first duct right wall  93  overlaps the tip end portion  103   a  of the outer surface of the second duct right wall  103 . 
     When the first duct  90  and the second duct  100  engage with each other in the above-described manner, the first airflow inlet  55  and the second airflow inlet  82  communicate with each other. The first duct  90  and the second duct  100  in the state where the first airflow inlet  55  and the second airflow inlet  82  are in communication with each other are collectively referred to as a third duct  120 . 
     As illustrated in  FIGS. 4, 5, 6A and 6B , the shape of the opening of the first duct  90  and the shape of the opening of the second duct  100  are shapes tapered toward the first direction D 1 . Thus, with the tapered shapes of the openings of the first duct  90  and the second duct  100 , a portion of the first duct  90  can be smoothly housed inside the second duct  100  as the UV irradiator  37   c  moves in the first direction D 1 . 
     It is also possible to adopt a configuration including a cushioning member at least at one of the first engagement part of the first duct  90  and the second engagement part of the second duct  100 . In  FIGS. 6A and 6B , the grey colored member is a sponge  110  as an example of a cushioning member. In the example of  FIGS. 6A and 6B , the sponge  110  is bonded to the first engagement part of the first duct  90 . Thus, as illustrated in  FIG. 6B , when the first duct  90  and the second duct  100  are engaged with each other, the sponge  110  is interposed between the first duct  90  and the second duct  100 . Naturally, the sponge  110  may be bonded to the second engagement part of the second duct  100 . The sponge  110  fill a gap between the first duct  90  and the second duct  100  forming the third duct  120 . In addition, when a portion of the first duct  90  is housed inside the second duct  100  as the UV irradiator  37   c  moves in the first direction D 1 , the sponge  110  eases the impact exerted on the first duct  90  and the second duct  100 . 
       FIG. 7  is a cross-sectional view, through the first airflow inlet  55  and the second airflow inlet  82 , of a partial range including the UV irradiator  37   c  of the printing apparatus  1  as viewed from above. In  FIG. 7 , the cross section of each member is hatched except for of the cross section of the sponge  110 . Note that, while the convex portion  64  and the slide rail  70  are present between the first frame wall  62  of the movable frame  60  and the first fixed frame  80  of the fixed frame, illustration of the protrusion  64  and the slide rail  70  is omitted in  FIG. 7 . 
       FIG. 7  illustrates a state where the UV irradiator  37   c  is located at the first position. In other words, the first duct  90  and the second duct  100  illustrated in  FIG. 7  form the third duct  120  and communicate between the first airflow inlet  55  and the second airflow inlet  82 . According to  FIG. 7 , the first duct  90  and the second duct  100  are engaged with each other at a position between the first frame wall  62  and the first fixed frame  80  in the Y direction. In addition, according to  FIG. 7 , a portion of the first duct  90  is housed inside the second duct  100 . 
     When the third duct  120  is formed and the first airflow inlet  55  and the second airflow inlet  82  communicate with each other, air outside the first fixed frame  80  whose amount of floating mist is very small flows into the cover  52  through the third duct  120  and the first airflow inlet  55  from the second airflow inlet  82 . Then, the third duct  120  can prevent inflow of mist floating in the printing apparatus  1  into the first airflow inlet  55  from the gap between the first fixed frame  80  and the first frame wall  62  of the movable frame  60  and/or the gap between the first frame wall  62  and the first surface  54  of the cover  52 . 
     With reference to  FIGS. 6A and 6B , the sponge  110  between the first duct left wall  92  of the first duct  90  and the second duct left wall  102  of the second duct  100  illustrated in  FIG. 7  is the sponge  110  bonded to the first duct left wall  92 . In addition, with reference to  FIGS. 6A and 6B , the sponge  110  between the first duct right wall  93  of the first duct  90  and the second duct right wall  103  of the second duct  100  illustrated in  FIG. 7  is the sponge  110  bonded to the first duct right wall  93 . 
       FIG. 8  illustrates a configuration of a region around the first fixed frame  80  serving airflow the sliding mechanism as viewed from the same direction as  FIG. 3 . As illustrated in  FIG. 8 , the present embodiment may have a configuration in which wall parts  130  and  131  extending upright from an outer surface  80   a  of the first fixed frame  80  close at least a portion of the periphery of the second airflow inlet  82 . The wall parts  130  and  131  are plate-like members. The outer surface  80   a  is a surface of the first fixed frame  80 , and is a rear surface of a surface that faces the first surface  54  of the surface of the cover  52 . The surface of the first fixed frame  80  that faces the first surface  54  of the cover  52  may be referred to as an inner surface of the first fixed frame  80 . The second duct  100  protrudes from the inner surface of the first fixed frame  80  toward the cover  52 . 
     In the example illustrated in  FIG. 8 , a drum cooling device  140  for cooling the rotary drum  30  is disposed at a predetermined position that is closer to the rotary drum  30  than the second airflow inlet  82  in the first direction D 1 . In such a configuration, the wall part  130  is disposed at a position above the second airflow inlet  82  in such a manner that the end facing toward the first direction D 1  reaches the drum cooling device  140 . In addition, the wall part  131  is disposed at a predetermined position farther from the rotary drum  30  than the second airflow inlet  82  in the second direction D 2  in such a manner that the wall part  131  extends downward and is in contact with the end of the wall part  130  facing toward the second direction D 2 . 
     The tip ends of the wall parts  130  and  131  extending upright from the outer surface  80   a  of the first fixed frame  80  are in contact with an inner surface  11   a  of the housing  10  of the printing apparatus  1 , for example.  FIG. 7  illustrates a state where the tip end of the wall part  131  is in contact with the inner surface  11   a  of the front wall  11  of the housing  10 . Although the wall part  130  is not illustrated in  FIG. 7 , the tip end of wall part  130  is also in contact with the inner surface  11   a  of front wall  11  as with the tip end of wall part  131 . The tip ends of the wall parts  130  and  131  may be a cushioning member, such as the sponge  110  described above, and may be configured such that the cushioning member makes contact with the inner surface  11   a  of the front wall  11 . Such wall parts  130  and  131  can reduce inflow, into the second airflow inlet  82 , of mist generated from the print head  6 . 
     4. Summary 
     As described above, according to the present embodiment, the printing apparatus  1  includes a support unit configured to support a printing medium, the print head  6  disposed at a position opposite the support unit, the print head  6  being configured to eject liquid to the printing medium, the circuit unit disposed downstream of the print head  6  in the transport path Pc of the printing medium at a position opposite the support unit, and the sliding mechanism configured to support the circuit unit such that the circuit unit is movable in the first direction D 1  in which the circuit unit approaches the support unit and the second direction D 2  that is opposite the first direction D 1 . The circuit unit includes the circuit board  53 , the cover  52  surrounding the opposing face  50  is opposite the support unit, the cover  52  being configured to house the circuit board  53  inside the cover  52 , the first airflow inlet  55  formed in the first surface  54  of the cover  52 , and the first duct  90  formed in the first surface  54  in communication with the first airflow inlet  55 . The sliding mechanism includes the fixed frame fixed inside the printing apparatus  1  and configured to support the circuit unit, the second airflow inlet  82  formed in the fixed frame, the second airflow inlet  82  being formed at a position that is opposite the first airflow inlet  55  when the circuit unit is located at a first position where the circuit unit is close to the support unit, and the second duct  100  formed in the fixed frame and in communication with the second airflow inlet  82 . When the circuit unit is located at the first position, the first duct  90  and the second duct  100  are engaged with each other such that the third duct  120  is formed, the third duct  120  being configured to communicate between the first airflow inlet  55  and the second airflow inlet  82 . 
     With the above-described configuration, when the circuit unit is moved to the first position, the first duct  90  and the second duct  100  engage with each other and form the third duct  120  that connects between the first airflow inlet  55  and the second airflow inlet  82 . With the third duct  120  thus formed, it is possible to reduce inflow, into the cover  52  from the first airflow inlet  55 , mist that is generated through ejection of liquid by the print head  6  in the printing apparatus  1 . By reducing the inflow of the mist into the cover  52 , attachment of the mist to the circuit board  53  can be reduced and the circuit board  53  can be protected. 
     In addition, in the present embodiment, the first duct  90  and the second duct  100  may engage with each other when a portion of the first duct  90  is housed inside the second duct  100 . 
     With the above-described configuration, it is possible to form the third duct  120 , with which mist does not easily pass through the connecting portions between the first duct  90  and the second duct  100 . 
     In addition, in the present embodiment, the shape of the opening of the first duct  90  and the shape of the opening of the second duct  100  may be tapered toward the first direction D 1 . 
     With the above-described configuration, when the circuit unit moves in the first direction D 1 , a portion of the first duct  90  can be smoothly housed inside the second duct  100 . 
     Note that the configuration in which a portion of the first duct  90  is housed inside the second duct  100  is merely an example. For example, a configuration may be adopted in which the opening size of the first duct  90  is greater than the opening size of the second duct  100 , and a portion of the second duct  100  is housed inside the first duct  90 . In addition, in the case where a portion of the second duct  100  is housed inside the first duct  90 , the shape of the opening of the first duct  90  and the shape of the opening of the second duct  100  may be tapered toward the second direction D 2 . 
     In addition, in the present embodiment, a cushioning member may be provided at least at one of the first engagement part of the first duct  90  and the second engagement part of the second duct  100 , the first engagement part being configured to engage with the second duct  100 , the second engagement part being configured to engage with the first duct  90 . 
     With the above-described configuration, the gap between the first duct  90  and the second duct  100  is filled with the cushioning member, and it is thus possible to more reliably prevent the entry of mist from the connecting portions between the first duct  90  and the second duct  100 . Additionally, when the first duct  90  and the second duct  100  engage with each other, the cushioning member can ease the impact exerted on the first duct  90  and the second duct  100 . 
     In addition, in the present embodiment, the wall parts  130  and  131 , which close at least a part of the periphery of the second airflow inlet  82 , may extend upright from the back surface (the outer surface  80   a ) of the surface of the fixed frame that faces the first surface  54 . 
     With the above-described configuration, the inflow of mist into the cover  52  through the second airflow inlet  82  can be reduced. 
     In addition, in the present embodiment, the tip ends of the wall parts  130  and  131  may be in contact with the inner surface  11   a  of the housing  10  of the printing apparatus  1 . 
     With the above-described configuration, the inflow of mist into the cover  52  through the second airflow inlet  82  can be more sufficiently reduced. 
     In addition, in the present embodiment, the circuit unit may be an irradiator configured to emit, at the first position, an ultraviolet ray from the opposing face  50  to the printing medium on which the liquid was ejected by the print head  6 . 
     With to the above-described configuration, the circuit board  53  inside the cover  52  can be protected from the mist for the UV irradiator  37   c  that is located at a position downstream of the print head  6 , i.e., a position where the mist generated by the print head  6  is easily received from the airflow inlet, and is movable in the first direction D 1  and the second direction D 2 . 
     Referring to  FIG. 1 , the UV irradiator  37   c  that is the most downstream UV irradiator  37 , i.e., the first irradiator, is relatively far from the adjacent print head  6  along the transport path Pc and has a wider space in comparison with the UV irradiators  37   a  and  37   b,  which are the second irradiators. As such, a larger amount of mist is likely to float and remain in the region near the UV irradiator  37   c,  and the UV irradiator  37   c  entails a higher risk of failure of the circuit board due to the influence of mist in comparison with other UV irradiators  37 . That is, in the printing apparatus  1 , a first irradiator, a second irradiator that is an irradiator different from the first irradiator, a first print head that is the print head  6 , and a second print head that is the print head  6  different from the first print head are disposed along the transport path Pc, and the distance between the first irradiator and the print head  6  adjacent to the first irradiator is greater than the distance between the second irradiator and the print head  6  adjacent to the second irradiator. In the present embodiment, regarding the first irradiator disposed in the above-described manner, the circuit board inside the first irradiator is protected from the mist by applying the features in which the third duct  120  is formed by the first duct  90  and the second duct  100 . Note that each of the first print head and the second print head does not represent a specific print head  6 , and the first print head and the second print head merely mean the presence of a plurality of print heads  6 . When any one of the plurality of print heads  6  is referred to as the first print head, the print head  6  different from the one print head  6  corresponds to the second print head. 
     5. Description for Other Points 
     The present embodiment is not limited to the configuration including a plurality of the print heads  6  and a plurality of the UV irradiators  37 . For example, the present embodiment is applicable to the printing apparatus  1  including one print head  6  and one UV irradiator  37  that is disposed downstream of the print head  6 . 
     The circuit unit that cools the circuit board housed inside the cover with an external air flow while protecting it from mist is not limited to the UV irradiator  37 . For example, on the assumption that a plurality of the print heads  6  are present and that one print head  6  is disposed downstream of another print head  6 , the present embodiment is applicable to the one print head  6  as the circuit unit. 
     The support unit that supports the printing medium is not limited to the rotary drum  30 . For example, the support unit may have a configuration in which a flat supporting surface is provided and a process such as printing is performed on a printing medium supported by the flat supporting surface. 
     Naturally, the positional relationship of the components in the present embodiment is not limited to the illustrated configuration. For example, the positional relationship between the feeding unit  2  and the winding unit  4  sandwiching the processing unit  3  may be opposite to the positional relationship illustrated in  FIG. 1 . In addition, various modifications may be made to the positional relationship between the airflow outlet and the airflow inlet in the cover of the circuit unit. For example, the positional relationship between the airflow outlet  57  and the first airflow inlet  55  in the cover  52  may be opposite to the positional relationship illustrated in  FIGS. 2 and 7 . In this case, the third duct  120  and the second airflow inlet  82  of the fixed frame are formed on the rear side of the cover  52 .