Patent Publication Number: US-2023134366-A1

Title: Head Unit and Liquid Ejecting Apparatus

Description:
The present application is based on, and claims priority from JP Application Serial Number 2021-180016, filed Nov. 4, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a head unit that ejects a liquid and a liquid ejecting apparatus, and more particularly, to a head unit that ejects ink as the liquid and an ink jet recording apparatus. 
     2. Related Art 
     A liquid ejecting apparatus represented by an ink jet recording apparatus, such as an ink jet printer or a plotter, includes a head unit capable of ejecting a liquid such as ink that is stored in an ink tank, an ink cartridge, or the like. 
     Disclosed is a configuration of a head unit including a cover constituting a casing, and a flow passage member and a wiring substrate accommodated in the casing, in which a supply protrusion and a discharge protrusion, which are flow passage coupling portions to which the external flow passage member is coupled, are disposed outside the cover (see, for example, JP-A-2021-53882). 
     Moreover, disclosed is a configuration in which an opening portion as an intake port of air and an opening portion as an exhaust port of the air are provided in the casing, and the air flows into the cover from the intake port to the exhaust port to cool a wiring member in the casing (see, for example, JP-A-2020-62763). 
     However, when a positional relationship between the intake port and the exhaust port formed in the casing and the flow passage coupling portion is not sufficiently considered, the flow passage coupling portion is heated by heat of a substrate or the air that flows in the casing and that has absorbed the heat of the substrate, thus heating the liquid flowing in the flow passage coupling portion, which results in a reduction of viscosity of the liquid. The liquid having the reduced viscosity is ejected from a nozzle, which may result in ejection defects such as deterioration in ejection characteristics. 
     SUMMARY 
     According to an aspect of the present disclosure, there is provided a head unit configured to eject a liquid, the head unit including: a circuit substrate for driving the head unit; a casing including a cover for defining an accommodation space that accommodates the circuit substrate; and a flow passage member of which a part is disposed in the casing, including a flow passage coupling portion for coupling with a flow passage member outside the head unit, in which the cover has an intake port for sucking air from an outside of the cover to the accommodation space and an exhaust port for exhausting the air passing through the accommodation space, and the flow passage coupling portion is disposed outside the casing and disposed closer to the intake port than to the exhaust port. 
     According to another aspect of the present disclosure, there is provided a liquid ejecting apparatus including: the head unit according to the above-described aspect; and a liquid storage portion storing the liquid supplied to the head unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a plan view illustrating a schematic configuration of a recording apparatus according to a first embodiment. 
         FIG.  2    is an exploded perspective view of a schematic configuration of a head unit according to the first embodiment. 
         FIG.  3    is an exploded perspective view of a schematic configuration of the head unit according to the first embodiment. 
         FIG.  4    is a sectional view of a main portion of the head unit according to the first embodiment. 
         FIG.  5    is a sectional view of a main portion of the head unit according to the first embodiment. 
         FIG.  6    is a bottom view of the head unit according to the first embodiment. 
         FIG.  7    is an exploded perspective view of a schematic configuration of a liquid ejecting head according to the first embodiment. 
         FIG.  8    is a sectional view of a main portion of a head unit according to a second embodiment. 
         FIG.  9    is a sectional view of a main portion of a head unit according to a third embodiment. 
         FIG.  10    is a sectional view of a main portion of a head unit according to a fourth embodiment. 
         FIG.  11    is a sectional view of a main portion of the head unit according to the fourth embodiment. 
         FIG.  12    is a sectional view of a main portion of a head unit according to a fifth embodiment. 
         FIG.  13    is a sectional view of a main portion of a modification of the head unit according to the fifth embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, the present disclosure will be described based on embodiments. However, the following description shows an aspect of the present disclosure, and it is possible to make changes in an arbitrary manner within the scope of the present disclosure. In each drawing, members with the same reference numerals are the same members and description thereof will be appropriately omitted. In the drawings, X, Y, and Z represents three spatial axes orthogonal to one another. In the present specification, directions along these axes are defined as an X direction, a Y direction, and a Z direction, respectively. A direction of arrow in the drawings is described as a positive (+) direction, and a direction opposite to the arrow is described as a negative (−) direction. Further, the three spatial axes that do not limit the positive direction and the negative direction will be described as the X axis, the Y axis, and the Z axis, respectively. 
     First Embodiment 
       FIG.  1    is a plan view illustrating a schematic configuration of an ink jet recording apparatus  1 , which is an example of a liquid ejecting apparatus, according to a first embodiment of the present disclosure. In the present embodiment, a +X direction is an example of a “first direction”, and a +Y direction is an example of a “second direction”. 
     An ink jet recording apparatus  1 , which is an example of a “liquid ejecting apparatus” of the present embodiment is a printing apparatus that performs printing (as known as a recording operation) of an image or the like by ejecting and landing ink, which is a type of the liquid, onto a medium S for printing and arranging dots formed on the medium S. As the medium S, any material such as a resin film or cloth can be used in addition to a recording sheet. In addition, the ink jet recording apparatus  1  in the present embodiment is a so-called line recording apparatus that performs printing by ejecting and landing the ink onto the medium S from a head unit  2  while transporting the medium S, in a state in which the head unit  2  is fixed to an apparatus main body  6  during printing. 
     As illustrated in  FIG.  1   , the ink jet recording apparatus  1  includes the head unit  2 , a liquid storage portion  3 , a control unit  4 , a transport mechanism  5 , and the apparatus main body  6 . 
     The head unit  2  has a nozzle for ejecting ink supplied from the liquid storage portion  3  toward the +Z direction. The head unit  2  is a so-called line head that ejects and lands the ink onto the medium S while transporting the medium S, in a state in which the head unit  2  is fixed to the apparatus main body  6  during printing. Details of the head unit  2  will be described later. 
     The liquid storage portion  3  separately stores a plurality of types of ink (for example, a plurality of colors) ejected from the head unit  2 . The ink of the liquid storage portion  3  is supplied to the head unit  2  through the tube  3   a . Examples of the liquid storage portion  3  include an ink cartridge that can be attached to and detached from the apparatus main body  6 , a bag-like ink pack that is formed of a flexible film, and an ink tank that can be refilled with the ink. For example, the liquid storage portion  3  stores inks having a plurality of different colors or types. 
     The control unit  4  includes, for example, a control device such as a central processing unit (CPU) or a field programmable gate array (FPGA), and a storage device such as a semiconductor memory. The control unit  4  generally controls respective components of the ink jet recording apparatus  1 , that is, the head unit  2 , the transport mechanism  5 , and the like by executing a program stored in the storage device by the control device. 
     The transport mechanism  5  has a transport roller  5   a  that is controlled by the control unit  4  and transports the medium S in a direction along the Y axis. That is, the transport mechanism  5  transports the medium S in the direction along the Y axis by rotation of the transport roller  5   a . The transport mechanism  5  transporting the medium S is not limited to include the transport roller  5   a , and may be a transport roller transporting the medium S by a belt or a drum. 
       FIGS.  2  and  3    are exploded perspective views illustrating a schematic configuration of the head unit  2  in the present embodiment.  FIG.  4    is a sectional view of a main portion of the head unit  2  in a direction perpendicular to the Y axis.  FIG.  5    is a sectional view of the main portion taken along line V-V in  FIG.  4   . 
     As illustrated in  FIGS.  2  to  5   , the head unit  2  includes a flow passage member  10  having the ink supplied from the liquid storage portion  3 , a liquid ejecting portion  30  having a plurality of liquid ejecting heads  100  that eject the ink supplied from the flow passage member  10 , a circuit substrate  40  for driving the head unit  2 , a unit base  20  supporting the liquid ejecting portion  30  and the flow passage member  10 , and a cover  50  accommodating the flow passage member  10  and the circuit substrate  40  between the cover  50  and the unit base  20 . In the head unit  2 , the circuit substrate  40 , the flow passage member  10 , the unit base  20 , and the liquid ejecting portion  30  are sequentially stacked toward the +Z direction, and the cover  50  is disposed so as to accommodate the flow passage member  10  and the circuit substrate  40  in the −Z direction of the liquid ejecting portion  30 . The flow passage member  10 , the unit base  20 , the liquid ejecting portion  30 , the circuit substrate  40 , and the cover  50  are fixed to each other with an adhesive (not illustrated), screws, or the like. 
     The flow passage member  10  has a plurality of first introduction ports S 1  according to the number of types of ink supplied to the head unit  2  and a plurality of discharge ports D according to the number of types of ink and the number of a plurality of liquid ejecting heads  100 .  FIGS.  2  and  3    illustrate that the flow passage member  10  has four first introduction ports S 1  and  24  discharge ports D. 
     The flow passage member  10  includes a flow passage member main body  11  and the flow passage coupling portion  12 . The flow passage member main body  11  has a rectangular shape whose direction along the X axis when viewed in the +Z direction is a longitudinal direction and whose direction along the Y axis is a transverse direction. That is, the flow passage member main body  11  extends along the X axis. The flow passage coupling portion  12  protrudes from an end portion of the flow passage member main body  11  in the −X direction toward the −Z direction. The flow passage member main body  11  and the flow passage coupling portion  12  are integrally formed. 
     The plurality of first introduction ports S 1  are provided in the flow passage coupling portion  12 . 
     Specifically, the plurality of first introduction port S 1  is located on a side surface of the flow passage coupling portion  12  in the +Y direction. A tube  3   a  coupled to the liquid storage portion  3  is coupled to the flow passage coupling portion  12  where the first introduction port S 1  is opened. That is, the tube  3   a  is an example of an “external flow passage member” coupled to the flow passage coupling portion  12 . 
     The discharge port D is located on a surface of the flow passage member main body  11  on the +Z direction side. In the flow passage member  10 , a flow passage communicating between any one of the first introduction ports S 1  and at least one of the discharge ports D is formed. That is, one end of the flow passage that is provided inside the flow passage member  10  is the first introduction port S 1 , and the other end is the discharge port D. 
     In the present embodiment, the flow passage member  10  includes only the flow passage member main body  11  and the flow passage coupling portion  12 . In addition, the flow passage member  10  may not include a flexible tube such as the tube  3   a . That is, the flow passage member  10  may be formed of only a rigid body. When a flow passage needle or a flow passage pipe as the rigid body is provided on an end portion of the tube  3   a  on a side coupled to the flow passage member  10 , the tube  3   a  and the flow passage coupling portion  12  may be airtightly coupled to each other by press-fitting the flow passage needle or the flow passage pipe into the first introduction port S 1  of the flow passage coupling portion  12 . In this case, the first introduction port S 1  may include a flexible sealing member therein in order to airtightly couple the flow passage needle or the flow passage pipe. Further, the flow passage coupling portion  12  may be a flow passage needle or a flow passage pipe that protrudes from the flow passage member main body  11  to the −Z direction and having the first introduction port S 1  formed on a tip thereof. 
     The liquid ejecting portion  30  has a plurality of liquid ejecting heads  100 , and in the present embodiment, six liquid ejecting heads  100 . The plurality of liquid ejecting heads  100  are located on the unit base  20  in the +Z direction and fixed to the unit base  20  with an adhesive (not illustrated), screws, or the like. In the present embodiment, the plurality of liquid ejecting heads  100  are fixed into a head accommodating portion  21  having a recessed shape opening to a surface of the unit base  20  in the +Z direction. That is, the plurality of liquid ejecting heads  100  are fixed to a bottom surface of the head accommodating portion  21 , that is, to a surface defining the head accommodating portion  21  in the −Z direction. The head accommodating portion  21  in the present embodiment has a size for accommodating six liquid ejecting heads  100 . The unit base  20  has a plurality of opening portions corresponding to the plurality of discharge ports D formed therein. In addition, a plurality of second introduction ports S 2  are provided on each liquid ejecting head  100  in the −Z direction. The plurality of second introduction ports S 2  are coupled to the plurality of discharge ports D of the flow passage member  10 , respectively, through the plurality of opening portions formed in the unit base  20 . That is, the liquid ejecting portion  30  has the plurality of second introduction ports S 2  each corresponding to the plurality of discharge ports D of the flow passage member  10 . 
     Moreover, a first accommodating portion  22  having a recessed shape opening to the surface in the −Z direction is provided on the unit base  20  in the −Z direction. The flow passage member  10  is accommodated in the first accommodating portion  22 . 
     In the present embodiment, six liquid ejecting heads  100  are provided on one head unit  2 . However, the number of the liquid ejecting heads  100  provided on one head unit  2  is not particularly limited thereto. One head unit  2  may include only one liquid ejecting head  100 , or may include two or more liquid ejecting heads  100 . 
     Moreover, a flange portion  23  is provided on end portions of the unit base  20  in the +X direction and in the −X direction. In the head unit  2 , the flange portion  23  is fastened and fixed to the apparatus main body  6  by a fixing member such as screws or the like. That is, a fixing region where the head unit  2  is fixed to the apparatus main body  6  is a flange portion  23 . 
     Here, a flow of the ink until the ink stored in the liquid storage portion  3  is supplied to the liquid ejecting head  100  of the head unit  2  will be described. The ink stored in the liquid storage portion  3  is supplied to the first introduction port S 1  of the flow passage member  10  through the tube  3   a . The ink supplied to the first introduction port S 1  is distributed by a flow passage (not illustrated) provided inside the flow passage member main body  11 , and the ink is then supplied to the second introduction port S 2  of each of six liquid ejecting heads  100  of the liquid ejecting portion  30  through the discharge port D. That is, the flow passage member  10  functions as a distribution flow passage member that distributes and supplies the ink supplied from the first introduction port S 1  to the head unit  2  to each of the plurality of liquid ejecting heads  100  of the head unit  2 . 
     In the present embodiment, the flow passage member  10  is the distribution flow passage member. However, the flow passage member  10  may be provided with a recovery flow passage for discharging the ink, which has not been ejected from the liquid ejecting head  100 , to the outside of the head unit  2 . Specifically, a merging flow passage is formed in the flow passage member main body  11  to merge and recover the ink which has not been ejected from the plurality of liquid ejecting heads  100 , and a discharge port is formed in the flow passage coupling portion  12  to discharge the ink flowing through the merging flow passage to the outside of the head unit  2 . The discharge port may be formed as a part of the flow passage member main body  11 . By using the flow passage coupling portion  12  for supplying the ink, the discharge port may be provided separately from the flow passage coupling portion  12 , and may be formed in the flow passage coupling portion for recovery, stacked on the flow passage member main body  11 . 
     Here, an example of an arrangement of the plurality of liquid ejecting heads  100  in the head unit  2  will be described.  FIG.  6    is a bottom view of the head unit  2  when viewed in the −Z direction. 
     As illustrated in  FIG.  6   , the plurality of the liquid ejecting heads  100  of the head unit  2  each have six head chips  140  (see  FIG.  7   ) arranged side by side along the +X direction. In addition, each head chip  140  has a plurality of nozzles N for ejecting the supplied ink onto the medium S. The plurality of nozzles N of each head chip  140  are arranged side by side along a row direction RD in a direction perpendicular to the Z axis and in an XY plane defined by the X axis and the Y axis. The row direction RD is a direction to be inclined to both the X axis and the Y axis. In the following description, a row in which the plurality of nozzles N are arranged side by side along the row direction RD may be referred to as a nozzle row. The number of head chips  140  included in each of the plurality of liquid ejecting heads  100  is not limited to six. 
     Next, an example of a structure of the liquid ejecting head  100  will be described.  FIG.  7    is an exploded perspective view of a schematic configuration of the liquid ejecting head  100 . 
     Each liquid ejecting head  100  includes a filter portion  110 , a wiring substrate  120 , a holder  130 , six head chips  140 , and a fixing plate  150 . The liquid ejecting head  100  is formed by sequentially superposing the filter portion  110 , the wiring substrate  120 , the holder  130 , and the fixing plate  150  toward the +Z direction, and has the head chip  140  accommodated between the holder  130  and the fixing plate  150 . 
     The filter portion  110  has a substantially parallel quadrilateral shape in which when viewed in the +Z direction, two sides facing each other extend along the +X direction, and other two sides facing each other extend along the row direction RD. The filter portion  110  includes four flow passage filters  111  and four second introduction ports S 2 . Four second introduction ports S 2  are located in the filter portion  110  in the −Z direction, and provided corresponding to the four flow passage filters  111  that are located in the filter portion  110 . The flow passage filter  111  collects foreign substances such as air bubbles and dust contained in the ink supplied from the second introduction port S 2 . 
     The wiring substrate  120  is located on the filter portion  110  in the +Z direction, and has a substantially parallel quadrilateral shape in which when viewed in the +Z direction, two sides facing each other in the +Z direction extend along the X axis and two sides facing each other extend along the row direction RD. A wiring member  141  led out from each head chip  140  to the −Z direction is electrically coupled to the wiring substrate  120 . Further, coupling wirings  121  are coupled to both end portions of the wiring substrate  120 , respectively, in the row direction RD. The coupling wiring  121  includes a flexible wiring substrate and a flexible wiring such as a flexible flat cable (FFC) and a flexible printed circuit (FPC). The two coupling wirings  121  electrically couple the circuit substrate  40  and the wiring substrate  120  through both sides of the filter portion  110  in the +Y direction and the −Y direction. 
     The holder  130  is located on the wiring substrate  120  in the +Z direction side, and has a substantially parallel quadrilateral shape in which when viewed in the +Z direction, two sides facing each other in the +Z direction extend along the X axis and two sides facing each other extend along the row direction RD. In addition, the holder  130  has a holding portion  131  having a groove-like space formed in the +Z direction. The holding portion  131  is continuously provided on a surface of the holder  130  in the +Z direction over the +X direction, so that the holding portion  131  is provided opening to the both side surfaces in the +X direction and the −X direction. The six head chips  140  are arranged in the holding portion  131  of the holder  130  along the +X direction and fixed with an adhesive or the like. In the present embodiment, the six head chips  140  are accommodated in one holding portion  131 . However, the present embodiment is not limited thereto, and a plurality of holding portions  131  capable of separately accommodating each head chip  140  may be provided. 
     Moreover, four third introduction ports S 3  are provided at four corners of the holder  130  in the −Z direction. Each of the third introduction ports S 3  is coupled to the flow passage of the filter portion  110 . Accordingly, the ink supplied from the second introduction port S 2  of the filter portion  110  is supplied to the third introduction port S 3  of the holder  130 . The ink supplied to the third introduction port S 3  is distributed to the six head chips  140  through the flow passage in the holder  130 , and then supplied to the six head chips  140 . 
     The head chip  140  has the nozzle N for ejecting the ink to the +Z direction side. In the present embodiment, two nozzle rows in which the nozzles N are arranged in the row direction RD are arranged in one head chip  140  along the X axis. In addition, the head chip  140  has a fourth introduction port S 4  on the −Z direction side. The ink from the holder  130  is supplied to the head chip  140  through the fourth introduction port S 4 . Further, in each head chip  140 , a flow passage including a pressure chamber that communicates with the nozzles N and the fourth introduction port S 4 , and a pressure generation unit that causes pressure change in the ink in the pressure chamber are provided. As the pressure generation unit, for example, a unit that ejects ink droplets from the nozzle N by changing a volume of the flow passage due to deformation of a piezoelectric actuator having a piezoelectric material for exhibiting an electromechanical conversion function and by causing pressure change in the ink in the flow passage, can be used. Further, as the pressure generation unit in addition to this, a unit that has a heat generating element disposed in the flow passage and ejects the ink droplets from the nozzle N by bubbles generated by heat of the heat generating element, a so-called electrostatic actuator that ejects the ink droplets from the nozzles N by generating an electrostatic force between a vibration plate and an electrode and deforming the vibration plate by the electrostatic force, or the like can be used. A nozzle surface where the nozzle N of the head chip  140  is opened constitutes a part of the ejection surface  2   a.    
     The wiring member  141  coupled to an internal pressure generation unit (not illustrated) is derived from a surface of each head chip  140  on the −Z direction side. As the wiring member  141 , a flexible sheet-like wiring substrate, for example, a flexible substrate such as a chip on film (COF) substrate and a flexible wiring such as the FFC or the FPC can be used. For example, a switching element for driving the pressure generation unit may or may not be mounted on the wiring member  141 . 
     The holder  130  is provided with a wiring insertion hole  132  opening to a bottom surface of the holding portion  131 , that is, a surface of the holding portion  131  in the −Z direction, and a surface on a side of the wiring substrate  120 . The wiring member  141  of the head chip  140  held by the holding portion  131  is derived from the holder  130  in the −Z direction through the wiring insertion hole  132 . A plurality of wiring members  141  derived from the holder  130  in the −Z direction are electrically coupled to the wiring substrate  120 . 
     The fixing plate  150  is located on the +Z direction side of the holder  130 . The fixing plate  150  is formed by bending a plate member such as a metal, so that an opening of the holding portion  131  is closed on side surfaces of the holder  130  in the +Y direction and the −Y direction side. In addition, the fixing plate  150  is provided with an exposure opening portion  151 , which is a through-hole for exposing the nozzle N of each head chip  140 . In the present embodiment, the exposure opening portion  151  is provided so as to be opened independently for each head chip  140 . That is, the head unit  2  in the present embodiment has the six head chips  140 , and thus the fixing plate  150  is provided with six independent exposure opening portions  151 . The fixing plate  150  is bonded to the holder  130  and the plurality of head chips  140  via an adhesive. A surface of the fixing plate  150  in the +Z direction constitutes a part of the ejection surface  2   a . That is, the ejection surface  2   a  of the head unit  2  in the present embodiment includes a nozzle surface where the nozzle N of the head chip  140  exposed by the exposure opening portion  151  is opened, and a surface opposite to the nozzle N of the fixing plate  150 , in other words, a surface of the fixing plate  150  on a side where the exposure opening portion  151  is opened. That is, the ejection surface  2   a  of the head unit  2  includes a nozzle surface facing the medium S, where the nozzle N is opened, and a surface of the fixing plate  150  located on the medium S closer to the nozzle surface. Further, the ejection surface  2   a  includes a surface including a nozzle surface facing the medium S, where the nozzle N is opened, and includes a surface where the ink adheres due to the ejection of the ink among the surfaces of the head unit  2  facing the medium S. Furthermore, the ejection surface  2   a  includes a surface wiped by a wiping member such as elastomer or cloth (not illustrated). The ejection surface  2   a  may be formed by only the nozzle surface where the nozzle N is opened. Further, the nozzle N is a flow passage including an opening that forms a meniscus of the ink ejected by pressure change in the pressure chamber caused by driving the pressure generation unit. 
     On the other hand, the circuit substrate  40  of the head unit  2  is located on the flow passage member  10  on the −Z direction side, as illustrated in  FIGS.  2  to  5   . The circuit substrate  40  is a plate-like member having a substantially rectangular shape in which when viewed in the +Z direction, two sides facing each other extend along the +X direction and the other two sides facing each other extend along the +Y direction, and the circuit substrate  40  is a so-called a rigid substrate. In addition, the circuit substrate  40  is disposed in a direction in which a thickness direction is perpendicular to the ejection surface  2   a , that is, in a direction in which the thickness direction is the same as the +Z direction. The circuit substrate  40  is disposed in the direction in which the thickness direction is the same as the +Z direction, such that it is possible to prevent an increase in size of the head unit  2  in the +Z direction and to achieve a reduction in size of the head unit  2 . 
     The circuit substrate  40  is formed with a drive signal generation circuit (not illustrated) that outputs a drive signal for driving the pressure generation unit of the liquid ejecting head  100 . The drive signal generation circuit includes wiring (not illustrated) and electronic components. Examples of the electronic components constituting drive signal generation circuit include a capacitor, a transistor, and an integrated circuit. In addition, the circuit substrate is provided with two connectors  41 , which are examples of the electronic component, on a surface thereof in the −Z direction. The control unit  4  is coupled to the connector  41  through wiring (not illustrated), and a power supply voltage of the head unit  2 , a positional information signal representing a transport position of the medium S, image information, and the like are input from the control unit  4 . The circuit substrate  40  generates the drive signal for driving the pressure generation unit or a control signal for supplying the drive signal, such as a timing signal, from the power supply voltage, the positional information signal, and the image signal received through the connector  41 , and outputs the generated drive signal or control signal to each liquid ejecting head  100 . 
     Moreover, a heat sink  42  for dissipating heat generated in the electronic components (not illustrated) is attached to a surface of the circuit substrate  40  on the −Z direction side. That is, in an accommodation space formed by a first accommodating portion  22  and a second accommodating portion  51  to be described later, the circuit substrate  40  is disposed between the flow passage member main body  11 , which is a part of the flow passage member  10 , and the heat sink  42 . As such, the heat sink  42  is provided on the circuit substrate  40 , such that it is possible to improve a cooling effect of the electronic components of the circuit substrate  40 . Further, because the circuit substrate  40  is disposed between the heat sink  42  and the flow passage member main body  11 , heat of the heat sink  42  is hardly conducted to the flow passage member main body  11 , and it is thus possible to prevent the ink in the flow passage member main body  11  from being heated. That is, the circuit substrate  40  is disposed in a casing, which will be described later in detail, so that the accommodation space, which will be described later in detail, is defined into a space where the flow passage member main body  11  is disposed and a space where the heat sink  42  is disposed. 
     The circuit substrate  40  is provided with the drive signal generation circuit, thus easily generating heat as compared with a relay substrate that relays coupling between wirings. Therefore, the circuit substrate  40  generates heat by ejecting the ink to the head unit  2 , such that cooling is required for the circuit substrate  40  to prevent the drive signal generation circuit from running away or being destroyed by the heat. Of course, in the present embodiment, the circuit substrate  40  is provided with the drive signal generation circuit. However, the present embodiment is not particularly limited thereto, and the circuit substrate  40  may not be formed with the drive signal generation circuit and may be formed with the wiring or the like. 
     Moreover, the coupling wirings  121  of the plurality of liquid ejecting heads  100  are electrically coupled to the circuit substrate  40 . Specifically, the coupling wirings  121  of the liquid ejecting head  100  pass through the outside of the flow passage member  10  in the +Y direction and the −Y direction and are electrically coupled to a surface of the circuit substrate  40  in the +Z direction. Further, the circuit substrate  40  is a common substrate to which the coupling wirings  121  of the six liquid ejecting heads  100  are commonly coupled. Of course, the circuit substrate  40  may be divided into two or more. Further, a plurality of circuit substrates  40  may be stacked along the Z axis. 
     The cover  50  has the second accommodating portion  51  opening in the +Z direction. The second accommodating portion  51  is defined by a first wall portion  51   a  provided in the −X direction, a second wall portion  51   b  provided in the +X direction, a third wall portion  51   c  provided in the −Y direction, a fourth wall portion  51   d  provided in the +Y direction, and a ceiling portion  51   e  provided in the −Z direction. Further, the cover  50  has an extension portion  52  extending in the −X direction from the first wall portion  51   a . By fixing the cover  50  to a surface of the unit base  20  in the −Z direction, the “accommodation space” formed by the first accommodating portion  22  and the second accommodating portion  51  is defined between the unit base  20  and the cover  50 . The circuit substrate  40  is accommodated in the accommodation space, in the present embodiment, in the second accommodating portion  51 . That is, the cover  50  and the unit base  20  in the present embodiment are a “casing” for defining the accommodation space. In addition, the flow passage member main body  11 , which is a part of the flow passage member  10  is accommodated in the first accommodating portion  22  of the accommodation space. The flow passage coupling portion  12  of the flow passage member  10  is provided outside the accommodation space. 
     The flow passage coupling portion  12  and the first wall portion  51   a  are disposed at a position where they face each other at an interval. Further, the flow passage coupling portion  12  is disposed at a position overlapping with the accommodation space with respect to a direction perpendicular to the ejection surface  2   a , that is, the +Z direction in the present embodiment. Here, the “flow passage coupling portion  12  is disposed at a position overlapping with the accommodation space with respect to the +Z direction” means that the flow passage coupling portion  12  and the second accommodating portion  51  forming the accommodation space overlap with each other in an in-plane direction of the XY plane defined by the X axis and the Y axis perpendicular to the +Z direction, and in the present embodiment, means that at least a part of the flow passage coupling portion  12  overlaps with the second accommodating portion  51  when viewed in the +X direction. In the present embodiment, the flow passage coupling portion  12  is disposed at a position that completely overlaps with the second accommodating portion  51  when viewed in the +X direction, but only a part of the flow passage coupling portion  12  may overlap with the second accommodating portion  51  when viewed in the +X direction. The flow passage coupling portion  12  is disposed in the accommodation space with respect to the +Z direction, in the present embodiment, at a position overlapping with the second accommodating portion  51 , such that it is possible to prevent the increase in size of the head unit  2  in the +Z direction, as compared with case in which the flow passage coupling portion  12  is disposed at a position not overlapping with the accommodation space with respect to the +Z direction. 
     Moreover, the cover  50  is provided with an intake port  53  and an exhaust port  54  for communicating between the second accommodating portion  51  and the outside. 
     The intake port  53  is an opening for sucking the air from the outside to the inside of the second accommodating portion  51 . The intake port  53  is disposed closer to the flow passage coupling portion  12  than to the exhaust port  54 . Specifically, the intake port  53  in the present embodiment penetrates the first wall portion  51   a  over the X axis. That is, the intake port  53  in the present embodiment is provided at a position facing the flow passage coupling portion  12 . Therefore, the intake port  53  and the flow passage coupling portion  12  are disposed at an interval from each other in the +X direction. The intake port  53  is preferably open in a relatively wide area, and in the present embodiment, the intake port  53  is opened over the substantially entire surface of the first wall portion  51   a.    
     The exhaust port  54  is an opening for exhausting the air inside the second accommodating portion  51  to the outside. The exhaust port  54  is disposed farther from the flow passage coupling portion  12  than the intake port  53 . Specifically, the exhaust port  54  penetrates an end portion side of the fourth wall portion  51   d  in the −X direction over the Y axis. That is, the circuit substrate  40  is disposed so that a direction along the +X direction is the longitudinal direction, the intake port  53  is provided on one end side of the second accommodating portion  51  in the +X direction, in the present embodiment, on the end portion of the second accommodating portion  51  in the −X direction, and the exhaust port  54  is provided on the other end side of the second accommodating portion  51  in the +X direction, in the present embodiment, on an end portion side of the second accommodating portion  51  in the +X direction. 
     The flow passage coupling portion  12  is disposed at a position facing the intake port  53  at an interval from the intake port  53  of the cover  50  in the −X direction. That is, the intake port  53  is provided in an end portion of the second accommodating portion  51  in the −X direction. On the other hand, the exhaust port  54  is provided on an end portion side of the second accommodating portion  51  in the −X direction, which is a side opposite to the flow passage coupling portion  12  of the second accommodating portion  51 . Therefore, the flow passage coupling portion  12  is disposed closer to the intake port  53  than to the exhaust port  54 . The “flow passage coupling portion  12  is disposed closer to the intake port  53  than to the discharge port  54 ” means that a distance L 1  between the flow passage coupling portion  12  and the intake port  53  in a direction along the X axis is shorter than a distance L 2  between the flow passage coupling portion  12  and the exhaust port  54 , when viewed in the +Z direction. That is, the distance L 1  and the distance L 2  satisfy a relationship of L 1 &lt;L 2 . 
     In the present embodiment, the intake port  53  has a rectangular shape when viewed in the +X direction. In addition, the exhaust port  54  has a rectangular shape when viewed in the −Y direction. Of course, the shape of the opening of the intake port  53  and the exhaust port  54  is not particularly limited thereto, and may be a circular shape, an elliptical shape, a polygonal shape, and the like. 
     The exhaust port  54  of the cover  50  is provided with an exhaust fan  55  for blowing the air inside the second accommodating portion  51  to the outside. The exhaust fan  55  is an “air blowing mechanism” in which the air inside the second accommodating portion  51  is blown to the outside of the second accommodating portion  51  to generate a negative pressure inside the second accommodating portion  51  relative to the outside and sends the air inside the second accommodating portion  51  from the outside of the second accommodating portion  51  through the intake port  53 . The air blowing mechanism is not particularly limited thereto, and may be provided with a suction fan, on the intake port  53 , which blows the air from the outside toward the inside of the second accommodating portion  51 , or may be provided with both the suction fan and the exhaust fan. Further, the air blowing mechanism is not particularly limited to the suction fan and the exhaust fan, and may be a pressure-feeding pump feeding the external air from the intake port  53  into the second accommodating portion  51  or a suction pump sucking the air inside the second accommodating portion  51  from the exhaust port  54  to the outside. 
     By operating the exhaust fan  55  provided on the exhaust port  54 , the air inside the second accommodating portion  51  is exhausted from the exhaust port  54  to the outside of the second accommodating portion  51 . As such, the air inside the second accommodating portion  51  is exhausted from the exhaust port  54 , thus generating a negative pressure inside the second accommodating portion  51  relative to the outside (for example, atmospheric pressure) and sucking the air outside the second accommodating portion  51  to the inside through the intake port  53 . That is, the operation of the exhaust fan  55  causes the air to flow from the intake port  53  toward the exhaust port  54  along the +X direction in the second accommodating portion  51 . That is, the air outside the second accommodating portion  51  is sucked inside the second accommodating portion  51  from the intake port  53 , and the air sucked in the second accommodating portion  51  moves along the +X direction, thereby cooling the circuit substrate  40  and the heat sink  42 . The air heated by cooling the circuit substrate  40  and the heat sink  42  in the second accommodating portion  51  is exhausted from the exhaust port  54  to the outside of the second accommodating portion  51 . 
     That is, the air sucked from the intake port  53  flows inside the second accommodating portion  51  along the +X direction, and the flow passage coupling portion  12 , the intake port  53 , and the exhaust port  54  are sequentially arranged in the +X direction. 
     In the second accommodating portion  51 , the air taken in from the intake port  53  flows toward the exhaust port  54  along the +X direction. Therefore, the circuit substrate  40  and the heat sink  42  are easily cooled on a side of the intake port  53  and hardly cooled on a side of the exhaust port  54  in comparison to the side of the intake port  53 . This is because the air taken in from the intake port  53  is heated by cooling the side of the intake port  53  in the circuit substrate  40  and the heat sink  42 , and the heated air heats the side of the exhaust port  54  in the circuit substrate  40  and the heat sink  42 . That is, temperatures of the circuit substrate  40  and the heat sink  42  cooled by the air flowing in the second accommodating portion  51  are high on the +X direction side along the X axis and gradually decrease toward the −X direction. Therefore, by disposing the flow passage coupling portion  12  at a position closer to the intake port  53  than to the exhaust port  54 , a part having the relatively low temperatures of the circuit substrate  40  and the heat sink  42  is disposed close to the flow passage coupling portion  12 , and the ink passing through the flow passage coupling portion  12  is hardly heated by heat of the circuit substrate  40  and the heat sink  42 . On the other hand, for example, when the flow passage coupling portion  12  is disposed at a position closer to the exhaust port  54  than to the intake port  53 , a part having the relatively high temperatures of the circuit substrate  40  and the heat sink  42  is disposed close to the flow passage coupling portion  12 , and the ink passing through the inside of the flow passage coupling portion  12  may be heated by heat of the circuit substrate  40  and the heat sink  42 . When the ink in the flow passage coupling portion  12  is heated, problems, such as a decrease in the viscosity of the ink, deterioration of ejection characteristics of the ink ejected from the liquid ejecting head  100 , and occurrence of ejection defects of the ink, occurs. In the present embodiment, the ink in the flow passage coupling portion  12  is hardly heated by the circuit substrate  40  and the heat sink  42 , such that it is possible to prevent the decrease in the viscosity of the ink supplied to the liquid ejecting head  100 , to prevent the deterioration of ejection characteristics of the ink ejected from the liquid ejecting head  100 , and to prevent occurrence of ejection defects of the ink. 
     In the present embodiment, the flow passage coupling portion  12  as described above is located at a position facing the intake port  53 , and the exhaust port  54  does not face the flow passage coupling portion  12 . That is, the air sucked from the intake port  53  moves from the intake port  53  toward the exhaust port  54  in the +X direction, and the flow passage coupling portion  12 , the intake port  53 , and the exhaust port  54  are sequentially arranged in the +X direction. As such, by sequentially arranging the flow passage coupling portion  12 , the intake port  53 , and the exhaust port  54  in the +X direction, the flow passage coupling portion  12  is disposed at a position away from the second accommodating portion  51  of the accommodation space provided with the intake port  53  and the exhaust port  54  and at a position relatively far from the exhaust port  54 . Therefore, the heat in the second accommodating portion  51  can be prevented from being conducted to the flow passage coupling portion  12  via the cover  50 . Particularly, a part having a relatively high temperature on the side of the exhaust port  54  in the second accommodating portion  51  is relatively far from the flow passage coupling portion  12 , such that it is possible to prevent the flow passage coupling portion  12  from being heated. Accordingly, the ink in the flow passage coupling portion  12  can be further prevented from being heated by the heat in the second accommodating portion  51 . Further, since the exhaust port  54  is provided at a position not facing the flow passage coupling portion  12 , it is possible to prevent the heated air exhausted from the exhaust port  54  from being blown to the flow passage coupling portion  12  and prevent the heating of the flow passage coupling portion  12 . 
     Here, the distance L 1  between the flow passage coupling portion  12  and the intake port  53  is preferably equal to or more than a maximum width W of the intake port  53 . That is, the distance L 1  and the maximum width W satisfy a relationship of L 1 ≥W. The distance L 1  between the flow passage coupling portion  12  and the intake port  53  is a minimum dimension between the flow passage coupling portion  12  and the intake port  53  in the +X direction. Moreover, the maximum width W of the intake port  53  means a maximum width W, which is a diagonal dimension of the intake port  53  illustrated in  FIG.  2   , because the intake port  53  in the present embodiment has a rectangular shape. By setting the distance L 1  between the flow passage coupling portion  12  and the intake port  53  to the maximum width W or more of the intake port  53 , it is possible to prevent a gap between the flow passage coupling portion  12  and the intake port  53  from inhibiting the suction of the air from the intake port  53 , to efficiently suck the air from the intake port  53 , and to efficiently cool the circuit substrate  40  and the heat sink  42 . Further, by setting the distance L 1  between the flow passage coupling portion  12  and the intake port  53  to the maximum width W or more of the intake port  53 , it is possible to prevent the flow passage coupling portion  12  from being heated by radiant heat of the circuit substrate  40  and the heat sink  42  in the second accommodating portion  51 . Therefore, the ink introduced from the first introduction port S 1  can be prevented from being heated inside the flow passage coupling portion  12  by the circuit substrate  40  and the heat sink  42 . 
     The air sucked from the intake port  53  flows into the second accommodating portion  51  along the +X direction, and the air is exhausted from the exhaust port  54  in the +Y direction different from the +X direction, which is a direction in which the air flows in the second accommodating portion  51 . As such, the exhaust port  54  is provided in the cover  50  so as to exhaust the air in the +Y direction, the exhaust fan  55  coupled to the exhaust port  54  or an exhaust duct  56  coupled to the exhaust fan  55 , which will be described in detail, can thus be disposed on the head unit  2  in the +Y direction. Therefore, the head unit  2  can be reduced in size in the +X direction, as compared with a case in which the exhaust fan  55  or the exhaust duct  56  is provided on the cover  50  on the +X direction side. Further, since the exhaust fan  55  or the exhaust duct  56  does not have to be disposed on the cover  50  in the +X direction, it is possible to prevent deterioration in workability when the head unit  2  is fixed to the apparatus main body  6  without covering the flange portion  23  of the unit base  20  by the exhaust fan  55  or the exhaust duct  56  in order to fix the head unit  2  to the apparatus main body  6 . 
     In the present embodiment, the circuit substrate  40  is disposed in the longitudinal direction along the +X direction, the intake port  53  is provided on the end portion of the second accommodating portion  51  on the −X direction side, which is one end portion side of the second accommodating portion  51  in the +X direction, and the exhaust port  54  is provided on the end portion side of the second accommodating portion  51  in the +X direction, which is the other end portion side of the second accommodating portion  51  in the +X direction. Therefore, it is possible to form a flow of the air along the longitudinal direction of the circuit substrate  40  in the second accommodating portion  51 , and to efficiently cool the circuit substrate  40  and the heat sink  42  with the air by increasing a distance at which the air flowing in the second accommodating portion  51  comes into contact with the circuit substrate  40  and the heat sink  42 . 
     In the present embodiment, the intake port  53  is disposed at the position facing the flow passage coupling portion  12 . That is, the intake port  53  is provided in the first wall portion  51   a . The intake port  53  is provided in the first wall portion  51   a , such that it is possible to achieve a reduction in size of the head unit  2  and the ink jet recording apparatus  1  in a direction along the Y axis, as compared with a case in which the intake port  53  is provided in the third wall portion  51   c  or the fourth wall portion  51   d . That is, when the intake port  53  is provided at a position not facing the flow passage coupling portion  12 , for example, in the third wall portion  51   c  or the fourth wall portion  51   d , another member cannot be provided at a position to close the intake port  53 . Therefore, the intake port  53  needs to be disposed with a gap between the third wall portion  51   c  or the fourth wall portion  51   d  and another member, thus resulting in an increase in size of the ink jet recording apparatus  1  along the Y axis. Similarly, when the flow passage coupling portion  12  is provided at a position protruding in the +Y direction or the −Y direction from the cover  50  of the head unit  2  so that the intake port  53  does not face the flow passage coupling portion  12 , the head unit  2  is increased in size along the Y axis. In the present embodiment, the flow passage coupling portion  12  and the intake port  53  are disposed facing each other, the flow passage coupling portion  12  is thus not required to be disposed at a position protruding in the +Y direction or the −Y direction from the cover  50 , and the head unit  2  and the ink jet recording apparatus  1  can be reduced in size in the direction along the Y axis. 
     In the present embodiment, the first introduction port S 1  of the flow passage coupling portion  12  is provided opening to the side surface in the +Y direction. That is, the first introduction port S 1  of the flow passage coupling portion  12  is provided at a position not facing the intake port  53 . Therefore, when the tube  3   a  is coupled to the first introduction port S 1 , it is not required to couple the tube  3   a  at a narrow place between the flow passage coupling portion  12  and the intake port  53 , such that it is possible to easily perform a coupling work. Also, the tube  3   a  hardly closes the intake port  53 , such that it is possible to prevent the suction of the air from the intake port  53  from being inhibited by the tube  3   a.    
     In the present embodiment, as illustrated in  FIG.  1   , one end of the exhaust duct  56  is coupled to the exhaust fan  55 . The other end of the exhaust duct  56  is provided outside the ink jet recording apparatus  1 , that is, opening to an outer surface of the apparatus main body  6 . Therefore, the air exhausted from the inside of the second accommodating portion  51  to the outside by the exhaust fan  55  is exhausted to the outside of the ink jet recording apparatus  1  through the exhaust duct  56 . When the exhaust duct  56  is provided, a position of the exhaust fan  55  is not particularly limited, and the exhaust fan  55  may be provided inside the exhaust duct  56  by coupling one end of the exhaust duct  56  to the exhaust port  54 . Further, the exhaust fan  55  may be provided on the other end side of the exhaust duct  56 , that is, an outer surface side of the apparatus main body  6 . The exhaust duct  56  is provided, such that the exhaust fan  55  can exhaust the air in the second accommodating portion  51  to the outside of the ink jet recording apparatus  1 . Therefore, it is possible to prevent the heated air exhausted from the exhaust port  54  from being sucked from the intake port  53 . That is, by providing the exhaust duct  56 , the air heated by cooling the circuit substrate  40  and the heat sink  42  in the second accommodating portion  51  is exhausted to the outside of the ink jet recording apparatus  1 , and the heated air exhausted from the exhaust port  54  is hardly sucked from the intake port  53  to the inside of the second accommodating portion  51 . Accordingly, the air heated in the second accommodating portion  51  can be prevented from being sucked again from the intake port  53  to efficiently cool the circuit substrate  40  and the heat sink  42  in the second accommodating portion  51  with the air that is not heated. 
     The cover  50  is formed of a resin material or a metal material. In the present embodiment, the cover  50  is formed of the resin material, such that it is possible to achieve reduction in weight and costs. 
     Moreover, the extension portion  52  of the cover  50  is provided with an opening portion  52   a  for exposing the connector  41  of the circuit substrate  40  to the outside in the −Z direction. External wiring (not illustrated) from the control unit  4  is coupled to the connector  41  through the opening portion  52   a.    
     As described above, in the present embodiment, the head unit  2  configured to eject the ink as a liquid includes a circuit substrate  40  for driving the head unit  2 , and the casing including the cover  50  for defining the first accommodating portion  22  and the second accommodating portion  51 , which is the accommodation space accommodating the circuit substrate  40 . In addition, the head unit  2  includes the flow passage member  10  of which a part is disposed in the casing, including the flow passage coupling portion  12  for coupling to the tube  3   a , which is the flow passage member outside the head unit  2 . Further, the cover  50  has the intake port  53  for sucking the air from the outside of the cover  50  to the second accommodating portion  51 , and the exhaust port  54  for exhausting the air passing through the second accommodating portion  51 . The flow passage coupling portion  12  is disposed outside the casing and disposed closer to the intake port  53  than to the exhaust port  54 . 
     Since the air taken in from the intake port  53  flows toward the exhaust port  54 , the circuit substrate  40  is easily cooled on the side of the intake port  53  and hardly cooled on the side of the exhaust port  54  in comparison to the side of the intake port  53 . Therefore, by disposing the flow passage coupling portion  12  close to the intake port  53 , the heat of the circuit substrate  40  is hardly conducted to the flow passage coupling portion  12 , and the ink in the flow passage coupling portion  12  is hardly heated, as compared with a configuration in which the flow passage coupling portion  12  is disposed close to the exhaust port  54 . As such, since the ink in the flow passage coupling portion  12  is hardly heated by the circuit substrate  40 , it is possible to prevent the decrease in the viscosity of the ink supplied from the flow passage coupling portion  12  to the liquid ejecting head  100 , to prevent the deterioration of ejection characteristics of the ink ejected from the liquid ejecting head  100 , and to prevent occurrence of ejection defects of the ink. 
     In the head unit  2  of the present embodiment, it is preferable that the intake port  53  faces the flow passage coupling portion  12 . As such, the intake port  53  and the flow passage coupling portion  12  face each other, such that it is possible to achieve the reduction in size of the head unit  2  in the direction along the Y axis. That is, when the intake port  53  is provided at a position not facing the flow passage coupling portion  12 , for example, in the third wall portion  51   c  or the fourth wall portion  51   d , other members cannot be provided at a position to close the intake port  53 . 
     Therefore, the intake port  53  needs to be disposed with a gap between the third wall portion  51   c  or the fourth wall portion  51   d  and another member, thus resulting in an increase in size of the ink jet recording apparatus  1  along the Y axis. Similarly, when the flow passage coupling portion  12  is provided at a position protruding in the +Y direction or the −Y direction from the cover  50  of the head unit  2  so that the intake port  53  does not face the flow passage coupling portion  12 , the head unit  2  is increased in size along the Y axis. In the present embodiment, the flow passage coupling portion  12  and the intake port  53  are disposed facing each other, the flow passage coupling portion  12  is not thus required to be disposed at a position protruding in the +Y direction or the −Y direction from the cover  50 , and the head unit  2  and the ink jet recording apparatus  1  can be reduced in size in the direction along the Y axis. 
     In the head unit  2  of the present embodiment, the distance L 1  between the intake port  53  and the flow passage coupling portion  12  is preferably equal to or more than the maximum width W of the intake port  53 . By sufficiently separating the flow passage coupling portion  12  and the intake port  53  from each other, it is possible to prevent the flow passage coupling portion  12  from inhibiting the suction of the air from the intake port  53 , and it is possible to prevent the flow passage coupling portion  12  from being heated by radiant heat of the circuit substrate  40  in the second accommodating portion  51 . 
     In the head unit  2  of the present embodiment, it is preferable that the first introduction port S 1 , which is an opening of the flow passage formed in the flow passage coupling portion  12 , does not face the intake port  53 . The first introduction port S 1  is provided at a position where the first introduction port S 1  does not face the intake port  53 , such that the tube  3   a  is not required to be coupled to the first introduction port S 1  at a narrow place between the flow passage coupling portion  12  and the intake port  53 , and it is possible to easily perform the coupling work. Further, the tube  3   a  hardly closes the intake port  53 , such that it is possible to prevent the suction of the air from the intake port  53  from being inhibited by the tube  3   a.    
     In the head unit  2  of the present embodiment, it is preferable that the exhaust port  54  does not face the flow passage coupling portion  12 . As such, the exhaust port  54  does not face the flow passage coupling portion  12 , it is thus possible to prevent the heated air exhausted from the exhaust port  54  from being blown toward the flow passage coupling portion  12  and prevent the flow passage coupling portion  12  from being heated. 
     In the head unit  2  of the present embodiment, the air sucked from the intake port  53  moves from the intake port  53  toward the exhaust port  54  in the +X direction, which is the first direction, and the flow passage coupling portion  12 , the intake port  53 , and the exhaust port  54  are sequentially arranged in the +X direction. As such, by sequentially arranging the flow passage coupling portion  12 , the intake port  53 , and the exhaust port  54  in the +X direction, the flow passage coupling portion  12  is disposed at a position away from the second accommodating portion  51  and at a relatively far position from the exhaust port  54 . Therefore, the heat in the second accommodating portion  51  can be prevented from being conducted to the flow passage coupling portion  12  via the cover  50 . Particularly, a part having a relatively high temperature on the side of the exhaust port  54  in the second accommodating portion  51  is relatively far from the flow passage coupling portion  12 , such that it is possible to prevent the flow passage coupling portion  12  from being heated. 
     In the head unit  2  of the present embodiment, it is preferable that the circuit substrate  40  is provided in the +X direction, which is the first direction, as a longitudinal direction, the intake port  53  is provided on one end side of the second accommodating portion  51  in the +X direction, which is a space from the intake port  53  to the exhaust port  54  in the accommodation space, and the exhaust port  54  is provided on the other end side of the second accommodating portion  51  in the +X direction. Since the air moves along the +X direction in the second accommodating portion  51  from the intake port  53  to the exhaust port  54 , the circuit substrate  40  can have a large area coming into contact with the air flowing in the second accommodating portion  51  by making the longitudinal direction of the circuit substrate  40  coincide with the +X direction. Therefore, the circuit substrate  40  can be efficiently cooled. 
     In the head unit  2  of the present embodiment, it is preferable that the exhaust port  54  exhausts the air in the +Y direction, which is the second direction, different from the +X direction, which is the first direction. Accordingly, the exhaust port  54  is provided so as to exhaust the air to the +Y direction. Thus, the air blowing mechanism such as the exhaust fan  55  or the suction pump can be disposed in the +Y direction, rather than providing the exhaust port  54  so as to exhaust the air to the +X direction. Therefore, the head unit  2  can be reduced in size in the +X direction. Moreover, in the head unit  2 , the flange portions  23 , which are fixing regions for fixing the apparatus main body  6  with screws or the like, are provided on both sides of the unit base  20  in the +X direction and the −X direction. Therefore, when the air blowing mechanism is provided on the exhaust port  54 , the flange portions  23  are not covered by the air blowing mechanism, such that it is possible to prevent workability from deteriorating when the head unit  2  is fixed to the apparatus main body  6 . 
     In the head unit  2  of the present embodiment, it is preferable that the head unit  2  is a line head in which the plurality of liquid ejecting heads  100  are arranged in the +X direction, which is the first direction, and the circuit substrate  40  is a circuit substrate  40  common to the plurality of liquid ejecting heads  100 . 
     In the head unit  2  of the present embodiment, it is preferable that the head unit  2  has the ejection surface  2   a  on which the plurality of nozzles N configured to eject the ink as the liquid are formed, and the flow passage coupling portion  12  overlaps with the accommodation space with respect to the +Z direction, which is a direction perpendicular to the ejection surface  2   a . Accordingly, the flow passage coupling portion  12  and the accommodation space are disposed at a position where the flow passage coupling portion  12  and the accommodation space overlap with each other with respect to the +Z direction, such that it is possible to prevent an increase in size of the head unit  2  in the +Z direction and to achieve a reduction in size of the head unit  2 . 
     In the head unit  2  of the present embodiment, it is preferable that the thickness direction of the circuit substrate  40  is the same as the +Z direction, which is the direction perpendicular to the ejection surface  2   a . The circuit substrate  40  is disposed in the direction in which the thickness direction is the same as the +Z direction, such that it is possible to prevent the cover  50  from being increased in size in the +Z direction in order to form a large second accommodating portion  51  accommodating the circuit substrate  40  in the +Z direction, and it is possible to achieve the reduction in size of the head unit  2  in the +Z direction. 
     It is preferable that the head unit  2  of the present embodiment further includes the heat sink  42  for dissipating the heat of the circuit substrate  40 , disposed on the second accommodating portion  51 , which is the accommodation space. The flow passage member main body  11 , which is a part of the flow passage member  10 , is disposed in the first accommodating portion  22 , which is the accommodation space, and the circuit substrate  40  is disposed between the flow passage member main body  11  disposed in the first accommodating portion  22 , which is the accommodation space, and the heat sink  42 . The heat sink  42  is provided on the circuit substrate  40 , such that it is possible to improve a cooling effect of the electronic components of the circuit substrate  40 . Further, because the circuit substrate  40  is disposed between the heat sink  42  and the flow passage member main body  11 , heat of the heat sink  42  is hardly conducted to the flow passage member main body  11 , and it is thus possible to prevent the ink in the flow passage member main body  11  from being heated. 
     It is preferable that in the head unit  2  of the present embodiment, the exhaust fan  55 , which is the air blowing mechanism, introduces the air from the outside of the cover  50  through the intake port  53 . By providing the air blowing mechanism represented by the exhaust fan  55  as such, the air for cooling the circuit substrate  40  can be taken into the accommodation space from the intake port  53  and exhaust the air from the exhaust port  54  to the outside. 
     The ink jet recording apparatus  1 , which is an example of the liquid ejecting apparatus of the present embodiment, includes the head unit  2  described above, and the liquid storage portion  3  storing the ink, which is a liquid supplied to the head unit  2 . The circuit substrate  40  can prevent the flow passage coupling portion  12  from being heated, such that it is possible to realize a liquid ejecting apparatus that prevents deterioration in ink ejection characteristics and prevents ink ejection defects. 
     Second Embodiment 
       FIG.  8    is a sectional view of a main portion of a head unit  2  according to a second embodiment of the present disclosure. The same reference numerals will be given to the same members as in the embodiment in the drawings, and a redundant description thereof will be omitted. 
     As illustrated in  FIG.  8   , in the head unit  2  of the present embodiment, the intake port  53  is provided on an end portion of the fourth wall portion  51   d  of the cover  50  on the −X direction side. That is, the exhaust port  54  is provided on an end portion of the fourth wall portion  51   d  on the +X direction side. That is, both the intake port  53  and the exhaust port  54  are disposed at a position not facing the flow passage coupling portion  12 . Further, the flow passage coupling portion  12  is disposed at a position away from the first wall portion  51   a  in the −X direction. Therefore, the flow passage coupling portion  12  is disposed closer to the intake port  53  than to the exhaust port  54 . A distance L 3  between the flow passage coupling portion  12  and the intake port  53  is shorter than the distance L 2  between the flow passage coupling portion  12  and the exhaust port  54  in a direction along the X axis. That is, the distance L 3  and the distance L 2  satisfy a relationship of L 3 &lt;L 2 . 
     Other configurations of the head unit  2  are the same as those in the embodiments described above, and thus duplicate descriptions thereof will be omitted. 
     In such a head unit  2  of the present embodiment, by disposing the flow passage coupling portion  12  close to the intake port  53 , the heat of the circuit substrate  40  is hardly conducted to the flow passage coupling portion  12 , and the ink in the flow passage coupling portion  12  is hardly heated, as compared with a configuration in which the flow passage coupling portion  12  is disposed close to the exhaust port. As such, since the ink in the flow passage coupling portion  12  is hardly heated by the circuit substrate  40 , it is possible to prevent the decrease in the viscosity of the ink supplied from the flow passage coupling portion  12  to the liquid ejecting head  100 , to prevent the deterioration of ejection characteristics of the ink ejected from the liquid ejecting head  100 , and to prevent occurrence of ejection defects of the ink. 
     Third Embodiment 
       FIG.  9    is a sectional view of a main portion of a head unit  2  according to a third embodiment of the present disclosure. The same reference numerals will be given to the same members as in the embodiment in the drawings, and a redundant description thereof will be omitted. 
     As illustrated in  FIG.  9   , in the head unit  2  of the present embodiment, the intake port  53  is provided on an end portion of the ceiling portion  51   e  of the cover  50  on the −X direction side. In addition, the exhaust port  54  is provided in the second wall portion  51   b . That is, both the intake port  53  and the exhaust port  54  are disposed at a position not facing the flow passage coupling portion  12 . Further, the flow passage coupling portion  12  is disposed at a position away from the first wall portion  51   a  in the −X direction. Therefore, the flow passage coupling portion  12  is disposed closer to the intake port  53  than to the exhaust port  54 . A distance L 4  between the flow passage coupling portion  12  and the intake port  53  is shorter than a distance L 5  between the flow passage coupling portion  12  and the exhaust port  54  in a direction along the X axis. That is, the distance L 4  and the distance L 5  satisfy a relationship of L 4 &lt;L 5 . 
     In the present embodiment, the circuit substrate  40  is disposed in a direction in which the thickness direction is the same as the +Y direction. That is, the circuit substrate  40  and the heat sink  42  are arranged along the +Y direction. 
     Other configurations of the head unit  2  are the same as those in the embodiments described above, and thus duplicate descriptions thereof will be omitted. 
     In such a head unit  2  of the present embodiment, by disposing the flow passage coupling portion  12  close to the intake port  53 , the heat of the circuit substrate  40  is hardly conducted to the flow passage coupling portion  12 , and the ink in the flow passage coupling portion  12  is hardly heated, as compared with a configuration in which the flow passage coupling portion  12  is disposed close to the exhaust port. As such, since the ink in the flow passage coupling portion  12  is hardly heated by the circuit substrate  40 , it is possible to prevent the decrease in the viscosity of the ink supplied from the flow passage coupling portion  12  to the liquid ejecting head  100 , to prevent the deterioration of ejection characteristics of the ink ejected from the liquid ejecting head  100 , and to prevent occurrence of ejection defects of the ink. 
     Fourth Embodiment 
       FIG.  10    is a sectional view of a main portion of a head unit  2  according to a fourth embodiment of the present disclosure.  FIG.  11    is a sectional view of the main portion taken along line XI-XI in  FIG.  10   . The same reference numerals will be given to the same members as in the embodiment in the drawings, and a redundant description thereof will be omitted. 
     As illustrated in  FIGS.  11  and  12   , the flow passage member  10  constituting the head unit  2  of the present embodiment includes a flow passage member main body  11  and two flow passage coupling portions  12 . The two flow passage coupling portions  12  are provided on end portions of the flow passage member main body  11  in the −X direction and the +X direction, respectively. In the present embodiment, one flow passage coupling portion  12  provided in the −X direction is referred to as a first flow passage coupling portion  12 A, and the other flow passage coupling portion  12  provided in the +X direction is referred to as a second flow passage coupling portion  12 B. Hereinafter, the first flow passage coupling portion  12 A and the second flow passage coupling portion  12 B are collectively referred to as the flow passage coupling portion  12 , unless otherwise distinguished. A plurality of first introduction ports S 1  are provided on each of side surfaces of the flow passage coupling portion  12  in the +Y direction. In the present embodiment, four first introduction ports S 1  are provided in each of the flow passage coupling portions  12 , that is, a total of eight first introduction portions S 1  are provided. Of course, the number of the first introduction ports S 1  are not limited thereto, and when four first introduction ports S 1  are provided as in the first embodiment, two first introduction ports S 1  may be provided in each of two flow passage coupling portion  12 , or the different number of the first introduction ports S 1  may be provided in each of the two flow passage coupling portion  12 . The first introduction port S 1  may be provided in one flow passage coupling portion  12 , and a discharge port of the recovery flow passage may be provided in the other flow passage coupling portion  12  in order to discharge the ink, which has not been ejected from the liquid ejecting head  100 , to the outside of the head unit  2 . In addition, the first flow passage coupling portion  12 A is disposed in the −X direction from the first wall portion  51   a  at an interval with the first wall portion  51   a . In addition, the second flow passage coupling portion  12 B is disposed in the +X direction from the second wall portion  51   b  at an interval with the second wall portion  51   b.    
     The cover  50  is provided with two intake ports  53  and one exhaust port  54 . The intake ports  53  are provided in the end portions of the fourth wall portion  51   d  on the +X direction side and −X direction side, respectively. In the present embodiment, one intake port  53  provided in the −X direction is referred to as a first intake port  53 A, and the other intake port  53  provided in the +X direction is referred to as a second intake port  53 B. Hereinafter, the first intake port  53 A and the second intake port  53 B are collectively referred to as the intake port  53 , unless otherwise distinguished. The flow passage coupling portion  12  is disposed closer to the intake port  53  than to the exhaust port  54 . That is, the first flow passage coupling portion  12 A is disposed closer to the first intake port  53 A than to the exhaust port  54 . A distance L 6  between the first flow passage coupling portion  12 A and the first intake port  53 A is shorter than a distance L 7  between the first flow passage coupling portion  12 A and the exhaust port  54  in the direction along the X axis. That is, the distance L 6  and the distance L 7  satisfy a relationship of L 6 &lt;L 7 . Further, the second flow passage coupling portion  12 B is disposed closer to the second intake port  53 B than to the exhaust port  54 . A distance L 8  between the second flow passage coupling portion  12 B and the second intake port  53 B is shorter than a distance L 9  between the second flow passage coupling portion  12 B and the exhaust port  54  in the direction along the X axis. That is, the distance L 8  and the distance L 9  satisfy a relationship of L 8 &lt;L 9 . That is, each of the two flow passage coupling portions  12  are disposed closer to any one of two intake ports  53  than to the exhaust port  54 . 
     Other configurations of the head unit  2  are the same as those in the embodiments described above, and thus duplicate descriptions thereof will be omitted. 
     In such a head unit  2  of the present embodiment, by disposing the flow passage coupling portion  12  close to the intake port  53 , the heat of the circuit substrate  40  is hardly conducted to the flow passage coupling portion  12 , and the ink in the flow passage coupling portion  12  is hardly heated, as compared with a configuration in which the flow passage coupling portion  12  is disposed close to the exhaust port. As such, since the ink in the flow passage coupling portion  12  is hardly heated by the circuit substrate  40 , it is possible to prevent the decrease in the viscosity of the ink supplied from the flow passage coupling portion  12  to the liquid ejecting head  100 , to prevent the deterioration of ejection characteristics of the ink ejected from the liquid ejecting head  100 , and to prevent occurrence of ejection defects of the ink. 
     Fifth Embodiment 
       FIG.  12    is a sectional view of a main portion of a head unit  2  according to a fifth embodiment of the present disclosure. The same reference numerals will be given to the same members as in the embodiment in the drawings, and a redundant description thereof will be omitted. 
     As illustrated in  FIG.  12   , the same intake port  53  and exhaust port  54  described in the first embodiment are provided in the cover  50  of the head unit  2  in the present embodiment. 
     A filter  60  is provided on the first wall portion  51   a  where the intake port  53  of the cover  50  is opened. When the air is sucked from the intake port  53 , the filter  60  captures foreign matters such as mist generated by ejection of the ink or paper dust and dust generated during transport of the medium S to prevent the foreign matters from being sucked into the second accommodating portion  51 . As such a filter  60 , for example, a sheet-like filter with a plurality of micropores formed by finely weaving a metal, a single plate-like member such as a metal plate or a resin plate formed with a plurality of through-holes, non-woven fabric, or the like can be used. In the present embodiment, the filter  60  is provided so as to have a size to cover the entire opening of the intake port  53 . Instead of the filter  60 , a gas-liquid separation membrane that allows gas to pass therethrough but does not allow the liquid to pass therethrough may be provided on the first wall portion  51   a  where the intake port  53  of the cover  50  is opened. Even with this configuration, it is possible to prevent mist and the like from being sucked into the second accommodating portion  51 . 
     Other configurations of the head unit  2  are the same as those in the embodiments described above, and thus duplicate descriptions thereof will be omitted. 
     As described above, in the head unit  2  of the present embodiment, the cover  50  includes the filter  60  provided on the intake port  53 . By providing the filter  60  on the intake port  53  as such, it is possible to prevent the foreign matters such as mist of the ink or paper dust from entering into the second accommodating portion  51  from the intake port  53 . Therefore, the foreign matters adhere to the circuit substrate  40 , such that it is possible to prevent short circuit of electronic components or wiring, and it is possible to deteriorate a cooling effect of the heat sink  42  due to the foreign matter. Further, the flow passage coupling portion  12  is provided at a position facing the intake port  53 . Therefore, by providing the filter  60 , the filter  60  can capture the ink leaked when the tube  3   a  is attached to and detached from the flow passage coupling portion  12  and prevent the ink from entering into the second accommodating portion  51  from the intake port  53 . 
       FIG.  13    is a diagram illustrating a modification of a head unit  2  according to the fifth embodiment of the present disclosure. As illustrated in  FIG.  13   , the filter  60  includes a first part  61  covering the intake port  53  on the −Z direction side, and a second part  62  bent at 90 degrees to the first part and protruding like eaves in the −X direction. 
     In the ink jet recording apparatus  1 , when the medium S is transported to the head unit  2  on the −Z direction side, the foreign matters such as paper dust and dust generated during transportation of the medium S fall on the head unit  2  from the −Z direction. Therefore, the second part  62  of the filter  60  is provided on the filter  60 , such that the second part  62  can receive the foreign matters. Further, the first part  61  is provided on the filter  60 , such that the first part  61  can catch the foreign matters so as not to suck the foreign matters received by the second part  62  into the second accommodating portion  51  from the intake port  53 . 
     Accordingly, it is possible to efficiently prevent the foreign matters from entering into second accommodating portion  51  from the intake port  53 . 
     The filter  60  does not cover the intake port  53  on the +Z direction side. Therefore, the filter  60  can prevent reduction of a suction force of the air sucked from the intake port  53  and efficiently cool the inside of the second accommodating portion  51  by the air. 
     The filter  60  may be attached to and detached from the cover  50 . Accordingly, the filter  60  can be easily replaced, and maintenance can be improved. 
     Further, a mechanism for removing the foreign matters adhering to the filter  60  may be provided. For example, a wiping mechanism wiping the filter  60  may be provided. Further, by providing a mechanism for periodically sending out the filter  60  wound in a roll shape, the intake port  53  may be covered with a region of the filter  60  to which the foreign matters do not adhere. Such a mechanism is provided, the filter  60  can thus be used for a long period of time, and the maintenance can be improved because it is not required to frequently replace the filter  60 . As a drive source such as the mechanism wiping the filter  60  or the sending-out mechanism, a drive source or the like provided in the ink jet recording apparatus  1  for moving the head unit  2  along the Z axis can be used, thereby reducing costs. Of course, when the intake port  53  communicates with the outside of the ink jet recording apparatus  1  through a suction duct, the filter  60  can capture dust and the like outside the ink jet recording apparatus  1 . In addition, when the intake port  53  communicates with the outside of the ink jet recording apparatus  1  through the suction duct, the filter  60  may be provided in the middle of an intake duct, on an outer surface of the ink jet recording apparatus  1 , or the like. 
     Other Embodiments 
     As described above, the embodiments of the present disclosure have been described, but the basic configurations of the present disclosure are not limited to the embodiments described above. 
     For example, in the embodiments described above, the first introduction port S 1  is opened on the side surface of the flow passage coupling portion  12  in the +Y direction. However, the present embodiment is not limited thereto, and the first introduction port S 1  may be opened on a surface of the flow passage coupling portion  12  in the −Z direction. Of course, the first introduction port S 1  may be provided on a surface of the flow passage coupling portion  12  in the −Y direction or a surface of the flow passage coupling portion  12  in the −X direction. 
     The ink jet recording apparatus  1  in the embodiments described above is a line recording apparatus that performs printing in a state in which the head unit  2  is fixed to the apparatus main body  6 . However, the ink jet recording apparatus  1  is not particularly limited thereto, and may be a so-called serial recording apparatus that performs printing while the head unit  2  moves in a direction intersecting the +Y direction, which is a transport direction of the medium S, for example, in the +X direction and the −X direction. 
     In the embodiments described above, the circuit substrate  40  is provided with the heat sink  42 , but is not particularly limited thereto, and may not be provided with the heat sink  42 . That is, the circuit substrate  40  may be accommodated in the second accommodating portion  51  and directly cooled by the air. Further, the circuit substrate  40  may include a plurality of substrates. For example, the circuit substrate  40  may have a substrate provided with the drive signal generation circuit and a relay substrate relaying the coupling between the substrate and coupling wiring or external wiring. Of course, the circuit substrate  40  may have a plurality of substrates stacked along the Z axis, or may be divided into two or more substrates along the +X direction. 
     In the embodiments described above, the configuration has been described in which the intake port  53  sucks the air inside the ink jet recording apparatus  1 . However, the present embodiment is not limited thereto, and the intake port  53  may suck the air outside the ink jet recording apparatus  1  into the second accommodating portion  51  through the suction duct, by opening the other end of the intake duct whose one end is coupled to the intake port  53  to the outside of the ink jet recording apparatus  1 , that is, to the outer surface of the apparatus main body  6 . 
     Furthermore, the present disclosure is intended for a wide range of the head unit. For example, the present disclosure can be also applied to head units using recording heads such as various ink jet recording heads used in image recording apparatuses such as printers, coloring material ejecting heads used in manufacturing color filters for liquid crystal displays, and the like, electrode material ejecting heads used for electrode formation such as organic electroluminescent (EL) displays, field emission displays (FEDs), bio-organic matter ejecting heads used in biochip manufacturing, and the like. Although the ink jet recording apparatus  1  has been described as an example of the liquid ejecting apparatus, a liquid ejecting apparatus with the head unit using other liquid ejecting heads described above can be also used.