Patent Publication Number: US-11390087-B2

Title: Liquid ejection head

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2019-107713 filed on Jun. 10, 2019, the content of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Aspects of the disclosure relate to a liquid ejection head that ejects liquid such as ink and that is included in a liquid ejection apparatus. 
     BACKGROUND 
     Some known liquid ejection apparatus is configured to eject ink toward a medium such as a recording sheet from a liquid ejection head (hereinafter, simply referred to as the “head”) to form an image on the medium. Such a head may include a heater that is configured to heat a supply channel structure that allows liquid to flow therethrough. 
     For example, some known head includes a channel structure, a supply channel structure, and heaters. The channel structure includes ejection channels that lead ink toward nozzles. The supply channel structure includes supply channels that allow ink to flow therefrom to the ejection channels. The heaters are configured to heat the supply channel structure. In such a known head, heaters and temperature sensors are fixed to an outer periphery of the supply channel structure using an adhesive. 
     In order to eject relatively high viscosity ink from nozzles effectively, ink may need to be heated to be at a temperature slightly higher than a room temperature (e.g., approximately 40 degrees Celsius) to cause ink to have a suitable viscosity. The known head is configured to apply heat to the supply channel structure using the heaters to heat ink in the supply channel structure. 
     SUMMARY 
     In the known head, the heaters may be fixed to the outer periphery, that is, a side surface, of the supply channel structure using an adhesive. Nevertheless, it may be difficult to attach the heaters to the side surface of the supply channel structure in fabrication of the head. Thus, the procedure for fabricating such a head may include complicated steps. 
     Accordingly, aspects of the disclosure provide a liquid ejection head that may include a heater for heating a supply channel structure, wherein the liquid ejection head may be fabricated without a complicated step. 
     In one or more aspects of the disclosure, a liquid ejection head may include a supply channel structure and a heater. The supply channel structure may have a supply channel configured to allow liquid to flow therefrom to ejection channels that may be configured to lead liquid to nozzles aligned in a first direction. The heater may be configured to heat liquid. Assuming that a side of the liquid ejection head, in which the nozzles are provided, is defined as a lower side of the liquid ejection head, the heater may be disposed above the supply channel structure. 
     According to this configuration, the heater may be disposed above the supply channel structure. Attaching a heater in such a manner may be easier than attaching a heater to a side surface of a supply channel structure, thereby avoiding complication of the fabrication procedure. Such a configuration may enable the heater to heat the supply channel via the upper surface of the supply channel structure, thereby heating liquid more effectively as compared with a head including a heater disposed on a side surface of a supply channel structure. 
     With such a configuration, the one or more aspects of the disclosure may thus provide a liquid ejection head that may include a heater for heating a supply channel structure, wherein the liquid ejection head may be fabricated without a complicated step. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view illustrating a general configuration of a liquid ejection head (hereinafter, simply referred to as the “head”) according to a first illustrative embodiment of the disclosure. 
         FIG. 2  is a schematic partial perspective view illustrating a configuration of an upper portion of the head of  FIG. 1  according to the first illustrative embodiment of the disclosure. 
         FIG. 3A  is a schematic sectional view of a supply channel structure and a thermal conductor of the head of  FIG. 1  in a plane with respect to a first direction according to the first illustrative embodiment of the disclosure, wherein a dimension of an opening of the supply channel structure and a dimension of an opening of the heat transfer portion are compared in the first direction. 
         FIG. 3B  is a schematic sectional view of the supply channel structure and the thermal conductor of the head of  FIG. 1  in a plane with respect to a direction perpendicular to the first direction according to the first illustrative embodiment of the disclosure, wherein a dimension of the opening of the supply channel structure and a dimension of the opening of the heat transfer portion are compared in the direction perpendicular to the first direction. 
         FIG. 4  is a schematic partial perspective view illustrating another configuration of the upper portion of the head of  FIG. 1  according to the first illustrative embodiment of the disclosure. 
         FIG. 5  is a schematic partial sectional view illustrating a configuration of a head according to a modification of the first illustrative embodiment of the disclosure. 
         FIG. 6  is a schematic partial sectional view illustrating a specific configuration of the head of  FIG. 5  according to the modification of the first illustrative embodiment of the disclosure. 
         FIG. 7  is a schematic sectional view illustrating a general configuration of a head according to a second illustrative embodiment of the disclosure. 
         FIG. 8  is a schematic partial perspective view illustrating a configuration of an upper portion of the head of  FIG. 7  according to the second illustrative embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, illustrative embodiments of the disclosure will be described with reference to the accompanying drawings. As used throughout this disclosure and the drawings, the same or similar elements will be indicated by common reference numerals or letters. Therefore, one of the same or similar elements may be described in detail, and description for the others may be omitted. 
     First Illustrative Embodiment 
     Configuration of Liquid Ejection Head 
     Referring to  FIGS. 1 and 2 , a liquid ejection head  10  (hereinafter, simply referred to as the “head”) according to a first illustrative embodiment will be described as one of examples of a head according to the disclosure. As illustrated in  FIG. 1 , the head  10  includes a channel structure  11 , supply channel structures  12 A, an actuator substrate  13 , support substrates  14 A, a nozzle substrate  15 , thermal conductors  16 , dampers  21 , an elastic layer  23 , piezoelectric elements  26 , heaters  31 A, a wiring substrate  34 , and a drive IC  35 . 
     The channel structure  11  may have a flat plate like shape. The channel structure  11  may have longer sides and shorter sides. A direction in which the longer sides of the channel structure  11  extend may be referred to as a longitudinal direction. The channel structure  11  is fixed to the supply channel structures  12 A. The channel structure  11  has one surface and another surface opposite to each other. The actuator substrate  13  and the support substrates  14 A are disposed between the channel structure  11  and the set of the supply channel structures  12 A and are fixed to the one surface of the channel structure  11 . The nozzle substrate  15  and the dampers  21  are fixed to the other surface of the channel structure  11 . Each supply channel structure  12 A has one surface and another surface opposite to each other. The other surface faces toward the channel structure  11 . The thermal conductors  16  are disposed on the one surfaces of the respective supply channel structures  12 A. The heaters  31 A are disposed overlapping the respective thermal conductors  16 . 
       FIG. 1  illustrates a cross section of the head  10  in a direction orthogonal to the longitudinal direction. The longitudinal direction may be defined as a length direction. A direction orthogonal to the longitudinal direction may be defined as a transverse direction. A direction orthogonal to the length direction and the transverse direction may be defined as an up-down direction. With reference to the directions,  FIG. 1  illustrates a cross section of the head  10  in a plane extending both in the transverse direction and in the up-down direction. In  FIG. 1 , the head  10  is thus elongated in the transverse direction. In  FIG. 1 , the channel structure  11  is disposed below the supply channel structures  12 A. In other words, the supply channel structures  12 A are disposed above the channel structure  11 . In the description below, directions of “up” and “down” may be defined with reference to the positional relationship between the channel structure  11  and the supply channel structures  12 A. 
     In the head  10  illustrated in  FIG. 1 , the nozzle substrate  15  and the dampers  21  are joined to the lower surface of the channel structure  11 , and the actuator substrate  13  and the support substrates  14 A are joined to the upper surface of the channel structure  11  together with the supply channel structures  12 A. The head  10  may basically have a symmetric structure with respect to the cross section of the head  10  in the transverse direction. Therefore, a configuration of one of the halves of the head  10  will be described and description for the other half will be omitted. 
     For describing the positional relationship in the head  10 , the longitudinal direction, that is, the length direction, may be defined as a first direction regarded as a reference direction. The transverse direction may correspond to a right-left direction. The right-left direction may be defined as a second direction. The up-down direction may be defined as a third direction. The first direction is indicated by a double-headed arrow d 1  in  FIG. 2 . The second direction is indicated by a double-headed arrow d 2  in  FIGS. 1 and 2 . The third direction is indicated by a double-headed arrow d 3  in  FIGS. 1 and 2 . For directions, basically the longitudinal direction may be used. In the description below, when not distinguishing the directions of “up”, “down”, “right”, and “left”, the transverse direction may be used. When distinguishing the directions of “up”, “down”, “right”, and “left”, the up-down direction or the right-left direction may be used. 
     The nozzle substrate  15  is disposed at the lower surface of the head  10 . The nozzle substrate  15  has a plurality of nozzles  25  arranged along the longitudinal direction (e.g., the direction of the arrow d 1  in  FIG. 2 ). In the illustrative embodiment, the nozzles  25  are arranged in two nozzle rows in the nozzle substrate  15 . Nevertheless, the number of nozzle rows is not limited to the specific example. A spacing (or pitch) between nozzles  25  in each nozzle row is not limited specifically. Any spacing may be adopted as long as the spacing corresponds to a density of dots to be formed on a recording sheet when the head  10  ejects liquid droplets (i.e., when the head  10  performs printing). 
     The nozzle substrate  15  is disposed at a middle portion of the lower surface of the head  10  in the right-left direction (e.g., the direction of the arrow d 2  in  FIG. 1 ). The dampers  21  are disposed at end portions of the lower surface of the head  10  in the right-left direction. The channel structure  11  has openings that may serve as ejection channels  42  that lead ink (e.g., liquid) toward the nozzles  25 . The dampers  21  are disposed at the lower surface of the channel structure  11  to close the openings of the channel structure  11  to define the ejection channels  42 . 
     The actuator substrate  13  is laminated on a middle portion of the upper surface of the channel structure  11  in the right-left direction. The elastic layer  23  is laminated on an upper surface of the actuator substrate  13 . The support substrates (e.g., protection substrates)  14 A are laminated on an upper surface of the elastic layer  23 . Each support substrate  14 A has a cavity  24 . The cavities  24  may be recesses defined in lower surfaces of the respective support substrates  14 A. The elastic layer  23  is disposed at the lower surfaces of the support substrates  14 A to close the cavities  24 . The piezoelectric elements  26  are disposed in the cavities  24 . In other words, each support substrate  14 A has a recess at a portion corresponding to corresponding ones of the piezoelectric elements  26 . Each recess may have an appropriate size that may allow driving of the corresponding piezoelectric elements  26 . The recesses may serve as the cavities  24 . The piezoelectric elements  26  are disposed on the upper surface of the elastic layer  23 . Thus, the piezoelectric elements  26  are disposed at a lower portion of a corresponding closed cavity  24 . 
     The actuator substrate  13  has pressure chambers  43  that may be through holes. The pressure chambers  43  are disposed vertically below the corresponding cavities  24 , that is, the respective corresponding piezoelectric elements  26 . The elastic layer  23  defines upper surfaces of the respective pressure chambers  43 . The channel structure  11  defines lower surfaces of the respective pressure chambers  43 . The pressure chambers  43  are thus closed by the elastic layer  23  and the channel structure  11 . The ejection channels  42  of the channel structure  11  are in communication with the respective corresponding pressure chambers  43 . The channel structure  11  further includes nozzle communication channels  44  (e.g., descenders) that may be through holes. The nozzle communication channels  44  are in communication with the respective corresponding nozzles  25 . The nozzle communication channels  44  are also in communication with the respective corresponding pressure chambers  43 . As illustrated in  FIG. 1 , a pressure chamber  43  is in communication with a corresponding ejection channel  42  via one end portion of the lower surface of the pressure chamber  43  in the right-left direction. The pressure chamber  43  is also in communication with a nozzle communication channel  44  via the other end portion of the lower surface of the pressure chamber  43  in the right-left direction. 
     The pressure chambers  43  of the actuator substrate  13  are in fluid communication with the respective corresponding nozzles  25  defined in the nozzle substrate  15 . In the first illustrative embodiment, the nozzles  25  of the nozzle substrate  15  are arranged in two rows along the longitudinal direction (e.g., the direction of the arrow d 1  in  FIG. 2 ). Thus, the pressure chambers  43  of the actuator substrate  13  are also arranged in two rows along the longitudinal direction to correspond to the respective corresponding nozzles of the nozzle rows. The piezoelectric elements  26  are disposed on the elastic layer  23  in a one-to-one correspondence with the pressure chambers  43 . The piezoelectric elements  26  are thus arranged in two rows along the longitudinal direction to correspond to the nozzle rows and the respective pressure chambers  43 . 
     As illustrated in  FIG. 1 , the supply channel structures  12 A are disposed over the channel structure  11 , the actuator substrate  13  disposed on the upper surface of the channel structure  11 , and the support substrates  14 A. Each supply channel structure  12 A includes a supply channel  41  (e.g., a manifold) that is configured to allow ink (e.g., liquid) to flow therefrom to corresponding ejection channels  42  of the channel structure  11 . The supply channels  41  are elongated in the up-down direction in the transverse cross section in  FIG. 1 . Each supply channel  41  is in communication with corresponding ones of the ejection channels  42  via its lower end. The supply channels  41  are connected to an ink cartridge (or ink tank). The supply channels  41  may be supplied with ink from the ink cartridge. 
     The head  10  has a hollow  22  including a first space  22   a  and a second space  22   b . The supply channel structures  12 A are spaced from each other in the right-left direction to define the first space  22   a  therebetween. The support substrates  14 A are spaced from each other in the right-left direction to define the second space  22   b  therebetween. The first space  22   a  and the second space  22   b  are elongated along the longitudinal direction. The upper surface of the actuator substrate  13  is partially exposed through the second space  22   b.    
     The supply channel structures  12 A are separated from each other to define the first space  22   a  therebetween to allow the second space  22   b  to be exposed. With this arrangement, the supply channel structures  12 A partially cover the channel structure  11 , the actuator substrate  13 , and the support substrates  14 A. Such a configuration may thus allow the upper surface of the actuator substrate  13  to be partially exposed through the hollow  22  consisting of the first space  22   a  and the second space  22   b.    
     An electrode trace extends on the upper surface of the actuator substrate  13  from each piezoelectric element  26 . The electrode traces of the piezoelectric elements  26  are disposed in the second space  22   b . The electrode traces of the piezoelectric elements  26  are connected to the wiring substrate  34 . The drive IC  35  for driving the piezoelectric elements  26  is mounted on the wiring substrate  34 . At least a portion of the wiring substrate  34  and the drive IC  35  are disposed in the hollow  22 . 
     Each piezoelectric element  26  is configured to cause ink ejection from a corresponding nozzle  25 . In response to driving of a piezoelectric element  26  by the drive IC  35 , a corresponding portion of a vibration plate including the elastic layer  23  is warped to protrude toward a pressure chamber  43 . This may cause ink (e.g., liquid) flow from the pressure chamber  43  to a corresponding nozzle  25  via a nozzle communication channel  44 , thereby causing ejection of ink (e.g., liquid) from the corresponding nozzle  25 . That is, the channel structure  11 , the actuator substrate  13 , the elastic layer  23 , and the piezoelectric elements  26  constitute an actuator unit. 
     The heaters  31 A are disposed at an upper portion of the head  10 . The heaters  31 A are configured to heat ink (or any liquid to be ejected from the head  10 ). According to the disclosure, a side of the head, in which the nozzles  25  are provided, may be defined as a lower side of the head. Thus, the head according to the disclosure has the nozzles  25  at the lower portion thereof. The heaters  31 A are disposed at the upper portion of the head. The channel structure  11  that is in fluid communication with the nozzles  25  is disposed at the lower portion of the head  10 . The supply channel structures  12 A fixed to the channel structure  11  are disposed above the channel structure  11 . Thus, the heaters  31 A are disposed above the respective supply channel structures  12 A. 
     In the head according to the disclosure, the heaters may be disposed above the respective supply channel structures  12 A. In the first illustrative embodiment, as illustrated in  FIGS. 1 and 2 , the supply channel structures  12 A are disposed on opposite sides of the hollow  22  (e.g., the first space  22   a ) in the longitudinal direction. That is, one of the supply channel structures  12 A is disposed on one side with respect to the right-left direction and the other of the supply channel structures  12   a  is disposed on the other side with respect to the right-left direction. The supply channel structures  12 A include the supply channels  41  (e.g., the manifolds), respectively, defined therein. The heaters  31 A are disposed above the respective supply channel structures  12 A in order to heat ink in the supply channels  41 . 
     Hereinafter, one of the halves of the head  10  will be described. In the description below, plural same components have the same or similar configuration and function in the same or similar manner to each other. Therefore, one of the plural same components will be described in detail, and a description for the others will be omitted. In the first illustrative embodiment, the thermal conductor  16  is disposed on the upper surface of the supply channel structure  12 A and the heater  31 A is disposed on an upper surface of the thermal conductor  16 . Nevertheless, in other embodiments, for example, the heater  31 A may be disposed on the upper surface of the supply channel structure  12 A. While the thermal conductor  16  may have a plate like shape that may be substantially the same shape as the upper surface of the supply channel structure  12 A, the thermal conductor  16  may need to be made of material having a higher thermal conductivity than material used for the supply channel structure  12 A. 
     As illustrated in  FIGS. 1 and 2 , the thermal conductor  16  has an opening  16   a  that is in fluid communication with the supply channel  41 . As illustrated in  FIG. 2 , the opening  16   a  is elongated in the longitudinal direction of the supply channel structure  12 A (e.g., the head  10 ). One or more temperature sensors such as thermistors may be disposed at a side surface of the head  10 . 
     In the head  10  having the above configuration, the supply channel  41  (e.g., the manifold) of the supply channel structure  12 A may be supplied with ink from the ink cartridge. The supply channel  41  is in communication with the ejection channels  42  of the channel structure  11 . The ejection channels  42  are in communication with respective corresponding ones of the pressure chambers  43  arranged in the longitudinal direction. The nozzle communication channels  44  of the channel structure  11  and the nozzles  25  of the nozzle substrate  15  are arranged in the longitudinal direction. The pressure chambers  43  are in communication with the respective corresponding nozzles  25  of the nozzle substrate  15  via the respective corresponding nozzle communication channels  44 . Such a configuration may thus allow ink supplied to the supply channel  41  to flow therefrom to the pressure chambers  43  via the ejection channels  42 . 
     The piezoelectric elements  26  are disposed at the upper surfaces of the respective corresponding pressure chambers  43 . The vibration plate including the elastic layer  23  is disposed to extend over the upper surfaces of the pressure chambers  43 . With such a configuration, as a piezoelectric element  26  is driven, ink flows from a pressure chamber  43  to a nozzle  25  via a nozzle communication channel  44 , thereby causing ejection of ink to the outside of the head  10 . While ink flows from the pressure chamber  43  to the nozzle, the heater  31 A heats the supply channel structure  12 A from the upper surface side, thereby heating the supply channel  41  (e.g., the manifold) via the upper surface of the supply channel structure  12 A. The heater  31 A is configured to be driven by control of a controller. More specifically, for example, the controller controls driving of the heater  31 A based on at least temperature measured by the temperature sensor. 
     The configuration of the head  10  is not limited to the specific example such as the head  10  including the channel structure  11 , the supply channel structures  12 A, the actuator substrate  13 , the support substrates  14 A, the nozzle substrate  15 , the thermal conductors  16 , the dampers  21 , the elastic layer  23 , the piezoelectric elements  26 , and the heaters  31 A. In other embodiments, a head having any known configuration may be adopted. 
     The channel structure  11  may be a substrate made of, for example, inorganic material. In the first illustrative embodiment, for example, the channel structure  11  may be a silicon substrate. The ejection channels  42  and the nozzle communication channels  44  of the channel structure  11  may be formed by known anisotropic etching or half etching. The supply channel structure  12 A may be made of, for example, known resin material. In the first illustrative embodiment, for example, the supply channel structure  12 A may be made of ABS resin. In another example, the supply channel structure  12 A may be made of inorganic material instead of resin material. Examples of the inorganic material include alumina (Al 2 O 3 ). 
     The actuator substrate  13  may be a substrate made of, for example, inorganic material. In the first illustrative embodiment, for example, the actuator substrate  13  may be a silicon substrate. The actuator substrate  13  has a plurality of pressure chambers  43  formed by, for example, anisotropic etching. The pressure chambers  43  correspond to the respective corresponding nozzles  25  defined in the nozzle substrate  15 . 
     The piezoelectric elements  26  are placed in the cavities  24  of the support substrates  14 A and are thus protected by the support substrates  14 A. That is, the support substrates  14 A may be protection substrates for the piezoelectric elements  26 . A material used for the support substrate  14 A is not limited specifically. Examples of the material used for the support substrate  14 A include inorganic materials such as glasses, ceramic materials, silicon monocrystal substrates, and metals, or organic materials such as known resin materials. The nozzle substrate  15  may be, for example, a silicon substrate made of inorganic material. The nozzles  25  arranged in rows (e.g., nozzle rows) may be formed in the nozzle substrate  15  by, for example, dry etching. 
     The thermal conductor  16  may be made of material having a relatively good thermal conductivity. More specifically, for example, the thermal conductor  16  may preferably be made of material having a higher thermal conductivity than the material used for the supply channel structure  12 A. The material used for the supply channel structure  12 A includes, for example, oxide-based inorganic material such as resin material or alumina. The material used for the thermal conductor  16  includes, for example, metal such as stainless steel (SUS), which may have a higher thermal conductivity than resin material and alumina. Using such metal as the material for the thermal conductor  16  may enable reasonable fabrication of the thermal conductor  16 . 
     The damper  21  may be a film made of resin material (e.g., a damper film). For example, the damper  21  may be made of PPS resin. The elastic layer  23  may be made of elastic material. In the first illustrative embodiment, the elastic layer  23  may be, for example, a silicon dioxide layer having a thickness of approximately 1 μm. An insulating layer made of an insulating material is provided on the elastic layer  23 . Examples of the insulating material include zirconium oxide. Nevertheless, the insulating material used for the insulating layer is not limited to the specific example. The piezoelectric elements  26  are disposed on the lamination of the elastic layer  23  and the insulating layer in a one-to-one correspondence with the pressure chambers  43 . 
     The configuration of the piezoelectric elements  26  is not limited specifically. In the first illustrative embodiment, for example, the piezoelectric elements  26  have a configuration such that a lower electrode layer, a piezoelectric layer, and an upper electrode layer are laminated one above another on the lamination of the elastic layer  23  and the insulating layer and a pattern is provided by a known patterning method to correspond to the respective pressure chambers  43 . The upper and lower electrode layers may be made of, for example, known metal. The piezoelectric layer may be made of, for example, known piezoelectric material including lead zirconate titanate (PZT). One of the upper and lower electrode layers may serve as a common electrode and the other may serve as individual electrodes. The elastic layer  23 , the insulating layer, and the lower electrode layer may serve as a vibration plate configured to vibrate when the piezoelectric elements  26  are driven. 
     Electrode traces extend from the respective individual electrodes (e.g., the upper electrode layer or the lower electrode layer) on the insulating layer. The electrode traces are connected to the wiring substrate  34 . A configuration of the wiring substrate  34  is not limited specifically. In the first illustrative embodiment, the wiring substrate  34  may be a known Chip on Film (“COF”) substrate. The configuration of the drive IC  35  is not limited specifically. An integrated circuit or a drive element known in the field of liquid ejection head may be suitable. The drive IC  35  is configured to apply a drive signal (e.g., a drive voltage) to a particular portion between the upper electrode layer and the lower electrode layer of a particular piezoelectric element  26  to deform the piezoelectric element  26 . This may thus cause the vibration plate including the lower electrode, the insulating layer, and the elastic layer  23  to vibrate. 
     The type of the temperature sensor such as a thermistor is not limited specifically. Any thermistor known in the field of liquid ejection head may be suitable. The configuration of the heater  31 A is not limited specifically. Any heater known in the field of liquid ejection head may be suitable. In the first illustrative embodiment, for example, a known film heater or a known ceramic heater may be used as the heater  31 A. The configuration of the controller is not limited specifically. For example, a microcomputer, a CPU of a microcontroller, or any controller having a known configuration including various storages may be used. 
     The fabrication method of the head  10  is not limited specifically. The head  10  may be fabricated using a known method in which the members such as the channel structure  11 , the supply channel structures  12 A, the actuator substrate  13 , the support substrates  14 A, the nozzle substrate  15 , the dampers  21 , the elastic layer  23 , and the piezoelectric elements  26  may be fixed or joined to each other. The laminating order in which the members of the head  10  are fixed or joined to each other is not limited specifically. For example, the channel structure  11 , the dampers  21 , and the nozzle substrate  15  may be joined to fabricate a channel unit. The actuator substrate  13 , the elastic layer  23 , the piezoelectric elements  26 , and the support substrates  14 A may be joined to fabricate an actuator unit. Then, the channel unit and the actuator unit may be fixed to each other to fabricate the head  10 . 
     The method for fixing or joining the members and/or the units to each other is not limited specifically. In one example, a known adhesive may be used. In another example, the members and/or the units may be fixed or joined to each other without using an adhesive. In this disclosure, in a case where the channel structure  11  and the supply channel structures  12 A are fixed to each other using an adhesive, the adhesive may preferably have a higher thermal conductivity than the material used for the supply channel structures  12 A. 
     In a case where the supply channel structures  12 A are made of resin material, an adhesive having a higher thermal conductivity than the resin material used for the supply channel structures  12 A may be used. More specifically, for example, in a case where the supply channel structures  12 A are made of ABS resin material, an epoxy adhesive may be suitable. As compared with a silicone adhesive that may be one of typical adhesives, an epoxy adhesive tends to have a higher thermal conductivity than ABS resin. Thus, using such an epoxy adhesive may effectively reduce an occurrence of great difference in linear expansion coefficient between the channel structure  11  and the supply channel structures  12 A at their joint surfaces. Consequently, the joint condition of the channel structure  11  and the supply channel structures  12 A may be maintained in an appropriate condition. 
     Configuration of Heater and Thermal Conductor 
     Referring to  FIGS. 1, 2, 3A, 3B, and 4 , an example of the heater  31 A and an example of the thermal conductor  16  of the head  10  will be described in detail. 
     The head according to the disclosure may include at least one heater that may serve as a liquid heating portion configured to heat ink (e.g., liquid). In the head according to the disclosure, the liquid heating portion may be disposed above the supply channel structure  12 A. In the first illustrative embodiment, as illustrated in  FIG. 1 , the heater  31 A is disposed on the upper surface of the thermal conductor  16  disposed on the upper surface of the supply channel structure  12 A. That is, the heater  31 A is disposed above the supply channel structure  12 A. The thermal conductor  16  disposed between the upper surface of the supply channel structure  12 A and the heater  31 A may increase heat transferability from the heater  31 A to the supply channel structure  12 A. 
     The thermal conductor  16  may have a plate like shape that may cover the upper surface of the supply channel structure  12 A. Nevertheless, the thermal conductor  16  may preferably have a shape that may cover another portion the supply channel structure  12 A in addition to the upper surface of the supply channel structure  12 A. As illustrated in  FIG. 3A , the supply channel structure  12 A has an opening  41   a  in its upper surface. The opening  41   a  is in communication with the supply channel  41 . The opening  16   a  of the thermal conductor  16  may preferably have a smaller dimension than a dimension of the opening  41   a  of the supply channel structure  12 A in the longitudinal direction (e.g., the first direction). As illustrated in  FIGS. 1, 3A, and 3B , the thermal conductor  16  may preferably cover at least a portion of an inner circumferential surface of the opening  41   a  and/or a portion of a side surface of the supply channel structure  12 A in addition to the upper surface of the supply channel structure  12 A. 
     As illustrated in  FIGS. 3A and 3B , the opening  41   a  of the supply channel structure  12 A is in fluid communication with the supply channel  41  at the upper surface of the supply channel structure  12 A and is elongated in the longitudinal direction. The opening  16   a  of the thermal conductor  16  is in fluid communication with the opening  41   a  of the supply channel structure  12 A and is elongated in the longitudinal direction as with the opening  41   a.    
     As illustrated in  FIG. 3A , it is assumed that a dimension of the opening  41   a  in the longitudinal direction (e.g., a length) is L 1  and a dimension of the opening  16   a  in the longitudinal direction (e.g., a length) is L 2 . In such a case, it is preferable that L 1 &gt;L 2 . Values of the length L 1  and the length L 2  are not limited specifically. The length L 1  and the length L 2  may be assigned respective appropriate values in accordance with the specific configuration of the head  10 . For example, the length L 1  may be assigned a value of between 25 mm and 30 mm and length L 2  may be assigned a value of between 20 mm and 25 mm while the relationship of L 1 &gt;L 2  is satisfied. 
     With this configuration, an area of the opening  16   a  of the thermal conductor  16  is smaller than an area of the opening  41   a  of the supply channel structure  12 A. Thus, as illustrated in  FIG. 3A , the inner circumference of the thermal conductor  16  protrudes inward to be positioned partially over the opening  41   a  of the supply channel structure  12 A. Such a configuration may thus enable the thermal conductor  16  to be contacted directly to ink in the supply channel  41  and increase a contact area between the thermal conductor  16  and ink. Consequently, ink may be effectively heated via the thermal conductor  16 . 
     As illustrated in  FIG. 3B  (and  FIG. 1 ), a dimension of the opening  16   a  in a direction perpendicular to the longitudinal direction (e.g., the first direction) may preferably be smaller than a dimension of the opening  41   a  in the direction perpendicular to the longitudinal direction. The direction perpendicular to the longitudinal direction may correspond to the right-left direction (e.g., the second direction). As illustrated in  FIG. 3B , it is assumed that a dimension of the opening  41   a  in the right-left direction (e.g., a width) is W 1  and a dimension of the opening  16   a  in the right-left direction (e.g., a width) is W 2 . In such a case, it is preferable that W 1 &gt;W 2 . 
     Values of the width W 1  and the width W 2  are not limited specifically. The width W 1  and the width W 2  may be assigned respective appropriate values in accordance with the specific configuration of the head  10 . For example, the width W 1  may be assigned a value of between 2 mm and 3 mm and the width W 2  may be assigned a value of between 1 mm and 2 mm while the relationship of W 1 &gt;W 2  is satisfied. With this configuration, the area of the opening  16   a  of the thermal conductor  16  is smaller than the area of the opening  41   a  of the supply channel structure  12 A. Such a configuration may thus enable the thermal conductor  16  to be contacted directly to ink in the supply channel  41 . Consequently, ink may be effectively heated via the thermal conductor  16 . 
     As illustrated in  FIGS. 1 and 3B , the thermal conductor  16  may cover the upper surface of the supply channel structure  12 A and at least a portion of the inner circumference of the supply channel  41 . More specifically, for example, the thermal conductor  16  further includes an inner wall portion  16   b . The inner wall portion  16   b  extends from the opening  16   a  of the thermal conductor  16  to the inside of the supply channel  41  through the opening  41   a  of the supply channel structure  12 A. Such a configuration may thus enable increase of a heat transfer area of the thermal conductor  16  for transferring heat generated by the heater  31 A and a particular portion of the thermal conductor  16  to be contacted directly to ink in the supply channel  41 . Consequently, ink may be effectively heated via the thermal conductor  16 . 
     In the example configuration illustrated in  FIGS. 1 and 3B , the inner wall portion  16   b  may extend from one of the sides of an inner circumference defining the opening  16   a  in the right-left direction. Nevertheless, in other embodiments, for example, the inner wall portion  16   b  may extend each side of the inner circumference defining the opening  16   a  in the right-left direction. In another example, the inner wall portion  16   b  may extend continuously or intermittently along the opening  16   a  in the longitudinal direction. 
     As illustrated in  FIG. 3A , the thermal conductor  16  may cover the upper surface and at least a particular portion of a side surface of the supply channel structure  12 A. In  FIG. 3A , the thermal conductor  16  further includes an outer wall portion  16   c  extending from its each end in the longitudinal direction. The outer wall portions  16   c  extend from the respective ends of the upper surface of the heat transfer portion  16  to cover upper portions of the side surfaces of the supply channel structure  12 A. Such a configuration of the thermal conductor  16  may enable further increase of the heat transfer area of the thermal conductor  16  for transferring heat generated by the heater  31 A. Consequently, ink in the supply channel  41  may be effectively heated via the thermal conductor  16 . 
     In the example configuration illustrated in  FIG. 3A , the outer wall portion  16   c  may extend from each end of the heat transfer portion  16  in the right-left direction. Nevertheless, in other embodiments, for example, the outer wall portion  16   c  may extend from one of the ends of the heat transfer portion  16  in the longitudinal direction or may extend from one or each of the ends of the heat transfer portion  16  in the right-left direction. In a case where the outer wall portion  16   c  extends from one or each end of the thermal conductor  16  in the right-left direction, the outer wall portion  16   c  may extend continuously or intermittently along the thermal conductor  16  in the longitudinal direction. 
     The heater  31 A may have a shape that may cover the entirety of the upper surface of the supply channel structure  12 A. Nevertheless, as illustrated in  FIG. 2 , the heater  31 A may preferably cover a particular portion other than a central portion of the upper surface of the supply channel structure  12 A. As described above, the supply channel structure  12 A has the opening  41   a  at the central portion of the upper surface thereof. In a case where the thermal conductor  16  is disposed between the heater  31 A and the supply channel structure  12 A, the thermal conductor  16  has the opening  16   a  at its central portion. Thus, the heater  31 A may have a hollow rectangular shape corresponding to the shape of the upper surface of the supply channel structure  12 A, thereby covering the particular portion other than the central portion of the upper surface of the supply channel structure  12 A. Thus, the heater  31 A may heat the upper surface of the supply channel structure  12 A intensively. 
     In the example illustrated in  FIG. 2 , a single heater  31 A may be used for covering the particular portion other than the central portion of the upper surface of the supply channel structure  12 A. Nevertheless, in other embodiments, for example, as illustrated in  FIG. 4 , a heater  31 B that may be a combined heater including a plurality of heaters may be used instead of the heater  31 A. For example, the heater  31 B includes a plurality of, for example, two wide heaters  37   a  and a plurality of, for example, two narrow heaters  37   b . The wide heaters  37   a  are disposed at respective end portions of the supply channel structure  12 A in the longitudinal direction. The narrow heaters  37   b  are disposed between the wide heaters  37   a  in the longitudinal direction and extend in parallel to each other. The wide heaters  37   a  and the narrow heaters  37   b  surround the opening  16   a.    
     Each wide heater  37   a  has longer sides and shorter sides. Each wide heater  37   a  is disposed such that its longer sides extend along the right-left direction (e.g., the second direction). Each narrow heater  37   b  has longer sides and shorter sides. Each narrow heater  37   b  is disposed such that its longer sides extend along the longitudinal direction (e.g., the first direction). Thus, as with the heater  31 A, the heater  31 B may have a hollow rectangular shape corresponding to the shape of the upper surface of the supply channel structure  12 A, thereby heating the particular portion other than the central portion of the upper surface of the supply channel structure  12 A. The configuration of the heater  31 B is not limited to the specific example of  FIG. 4 . In other embodiments, for example, the heater  31 B may include three or less or five or more heaters. 
     Modifications 
     The head according to the disclosure may include the supply channel structures  12 A and at least one heater. The heater may be disposed above one of the supply channel structures  12 A. In the first illustrative embodiment, examples of the heater disposed above the supply channel structure  12 A include the heater  31 A that may be a single heater and the heater  31 B that may a combined heater include a plurality of heaters. The heaters  31 A and  31 B may be disposed at the topmost portion of the head  10 . Nevertheless, the configuration of the head according to the disclosure is not limited to the specific examples. Another member may be disposed above the heater  31 A or  31 B. 
     For example, as illustrated in  FIG. 5 , a head  10 A includes second thermal conductors  17 . The second thermal conductors  17  are disposed above the respective heaters  31 A. Both of the second thermal conductors  17  may have the same configuration to each other, and therefore, one of the second thermal conductors  17  will be described. The second thermal conductor  17  may be made of the same material (e.g., metal such as stainless steel) as the material used for the thermal conductor  16  (e.g., a first thermal conductor) disposed below the heater  31 A. The head  10 A illustrated in  FIG. 5  has a similar configuration to the head  10  illustrated in  FIG. 1  except that the head  10 A includes the second thermal conductors  17 . Therefore, a detailed description of the head  10 A is omitted. 
     In this modification, the head  10 A includes the second thermal conductor  17  that is disposed above the heater  31 A and made of the same material as the material used for the thermal conductor  16 . That is, the heater  31 A that may be a film heater is sandwiched between the thermal conductors  16  and  17  that may be made of the same material. Such a configuration may thus reduce an occurrence of distortion in the head  10 A due to difference in thermal expansion coefficient between the heater  31 A and the thermal conductors  16  and  17  during heating by the heater  31 A. 
     A manner of fixing the second thermal conductor  17  to the upper surface of the heater  31 A is not limited specifically. For example, as illustrated in  FIG. 6 , in the head  10 A, the heater  31 A is disposed on the thermal conductor  16  at an area other than an inner peripheral area of the thermal conductor  16 . An adhesive layer  45  is provided on the inner peripheral area of the thermal conductor  16  and the entirety of the upper surface of the heater  31 A to join the second thermal conductor  17  to the thermal conductor  16 . 
     As illustrated in  FIG. 6 , the heater  31 A disposed on the upper surface of the supply channel structure  12 A recedes relative to the thermal conductor  16  by a distance D. Such an area may be referred to as an offset area. The offset area may provide an additional portion for applying adhesive around the heater  31 A. Thus, the adhesive layer  45  may be formed on the offset area as well as the upper surface of the heater  31 A. Thus, the thermal conductors  16  and  17  may be fixed to each other by adhesive. Consequently, the condition in which the heater  31 A is sandwiched between the thermal conductors  16  and  17  may be maintained in an appropriate condition. 
     In the example illustrated in  FIG. 6 , the offset area may be provided at an inner peripheral edge portion of the upper surface of the thermal conductor  16  adjacent to the opening  16   a . Nevertheless, in other embodiments, for example, an offset area may be provided at an outer peripheral edge portion or at both of the inner and outer peripheral edge portions of the upper surface of the thermal conductor  16 . In a case where the heater  31 B including the plurality of heaters is used, spaces between the heaters may serve as offset areas. A value of the distance D is not limited specifically. The distance D may be an offset amount of the offset area. The distance D may be assigned an appropriate value in accordance with the specific configuration of the head  10 A. For example, the distance D may be assigned a value of 1 mm or greater. 
     In a case where a particular member is disposed above the heater  31 A, the following adhesion method may be adopted. A position of the particular member is fixed using a jig while a portion for applying adhesive is left and the particular member is placed above the heater  31 A leaving a gap (e.g., a space) therebetween. Then, an adhesive layer is formed at the portion for applying adhesive to maintain the position of the particular member. That is, the particular member and the heater  31 A may be adhered to each other in the air. With this procedure, the particular member may be fixed to the thermal conductor  16  while a gap is left between the upper surface of the heater  31 A and a lower surface of the particular member. 
     In the head according to the disclosure, the heater  31 A may be disposed above the supply channel structure  12 A (or on the upper surface of the supply channel structure  12 A). When necessary, the head may include another heater disposed at another portion of the supply channel structure  12 A. For example, as with the known head, the head  10 ,  10 A may include a further heater disposed on a side surface of the supply channel structure  12 A. In a case where the further heater is disposed on the side surface of the supply channel structure  12 A in addition to the upper surface of the supply channel structure  12 A, the supply channel  41  may be heated from two sides via the upper surface and side surface of the supply channel structure  12 A. Thus, ink in the supply channel  41  may be heated appropriately. 
     Second Illustrative Embodiment 
     In the head  10  according to the first illustrative embodiment, the heater  31 A is disposed on the upper surface of the thermal conductor  16 . Nevertheless, the head according to the disclosure is not limited to the specific example. In the head according to the disclosure, a heater may be disposed on an upper surface of a supply channel structure. Referring to  FIGS. 7 and 8 , an example of such a configuration will be described. 
     In a second illustrative embodiment, as illustrated in  FIG. 7 , a head  110  has a similar configuration to the head  10 . Nevertheless, the head  110  includes a supply channel structure  12 B, a support substrate  14 B, and a heater  31 C instead of the supply channel structures  12 A, the support substrates  14 A, and the heaters  31 A. The supply channel structure  12 B has a shape that may cover the entirety of an upper surface of the support substrate  14 B that may be a protection substrate. The heater  31 C is disposed on an upper surface of the supply channel structure  12 B and extends over substantially the entirety of the upper surface of the supply channel structure  12 B. As with the support substrates  14 A of the first illustrative embodiment, the support substrate  14 B has cavities  24 . Each cavity  24  may be a recess defined in a lower surface of the support substrate  14 B. An elastic layer  23  is disposed at the lower surface of the support substrate  14 B to close the cavities  24 . Piezoelectric elements  26  are disposed in the cavities  24 . 
     In the first illustrative embodiment, the head  10  includes two support substrates  14 A and has the second space  22   b  between the support substrates  14 A in the right-left direction. Nevertheless, in the second illustrative embodiment, the head  110  includes a single support substrate  14 B and thus might not have such a space. In the first illustrative embodiment, the head  10  further includes two supply channel structures  12 A and has the first space  22   a  between the supply channel structures  12 A in the right-left direction. The first space  22   a  and the second space  22   b  constitute the hollow  22 . Such a configuration may thus allow the upper surface of the actuator substrate  13  to be partially exposed through the hollow  22 . The wiring substrate  34  is connected to the exposed portion of the actuator substrate  13 . The drive IC  35  is disposed at the wiring substrate  34 . 
     Nevertheless, in the second illustrative embodiment, any portion of the actuator substrate  13  might not be allowed to be exposed. Thus, the head  110  includes through electrodes instead of the wiring substrate  34 . The through electrodes penetrate the support substrate  14 B. Each through electrode has one end connected to an electrode trace of a corresponding piezoelectric element  26  on the actuator substrate  13 , and the other end connected to a corresponding drive IC  35 . As illustrated in  FIG. 7 , the drive ICs  35  are disposed on the upper surface of the support substrate  14 B (vertically above the respective cavities  24 ). The drive ICs  35  are configured to drive the piezoelectric elements  26 . 
     In the second illustrative embodiment, although the head  110  does not have a hollow  22 , the drive ICs  35  may be disposed on the upper surface of the support substrate  14 B. Thus, the supply channel structure  12 B may have a shape that may cover the entirety of the upper surface of the support substrate  14 B and the heater  31 C may be disposed on the upper surface of the supply channel structure  12 B such that the heater  31 C extends over substantially the entirety of the upper surface of the supply channel structure  12 B. Such a configuration may thus enable the supply channel structure  12 B to have a shape that may cover the entirety of the upper surface of the support substrate  14 B. Thus, the supply channel structure  12 B may provide a sufficient area for placing the heater  31 C on its upper surface. 
     The entirety of the upper surface of the supply channel structure  12 B may be heated by the single heater  31 C, thereby effectively reducing an occurrence of temperature differences between the supply channels  41  when heated by the heater  31 C, inconsistencies in density caused by temperature differences, and liquid ejection deficiency. As illustrated in  FIG. 7 , the drive ICs  35  disposed on the upper surface of the support substrate  14 B and the portion of the supply channel structure  12 B covering the support substrate  14 B define a clearance therebetween. Such a clearance may thus insulate heat generated by the heater  31 C disposed on the upper surface of the supply channel structure  12 B. 
     The supply channel structure  12 B may be made of resin material or inorganic material as with the supply channel structure  12 A of the first illustrative embodiment. Nevertheless, in a case where the heater  31 C is disposed on the upper surface of the supply channel structure  12 B (e.g., the second illustrative embodiment), the supply channel structure  12 B may preferably be made of inorganic material such as metal. The supply channel structure  12 B made of inorganic material such as metal having a relatively high thermal conductivity may transfer heat generated by the heater  31 C more effectively, thereby heating liquid in the supply channel  41  more effectively. 
     The entirety of the supply channel structure  12 B might not necessarily be made of inorganic material such as metal. For example, a portion constituting the upper surface of the supply channel structure  12 B (e.g., an upper portion of the supply channel structure  12 B) may be made of inorganic material and the other portion of the supply channel structure  12 B may be made of resin material or inorganic material other than metal. In a case where at least the upper portion of the supply channel structure  12 B is made of inorganic material having a relatively high thermal conductivity and the heater  31 C is disposed on the upper surface of the supply channel structure  12 B, the heater  31 C may heat the upper surface of the supply channel structure  12 B directly, thereby heating the supply channel  41  appropriately. 
     The material used for the portion constituting the upper surface of the supply channel structure  12 B might not necessarily be made of inorganic material such as metal and is not limited specifically as long as the material has a relatively good thermal conductivity. More specifically, for example, the thermal conductivity of the material may have a higher thermal conductivity than the material used for the dampers  21 . The dampers  21  may be resin films. In a case where the material used for the portion constituting the upper surface of the supply channel structure  12 B has a higher thermal conductivity than the material used for the dampers  21 , a relative thermal conductivity of the supply channel structure  12 B may be increased. Consequently, heat generated by the heater  31 C disposed at the upper surface of the supply channel structure  12 B may be transferred to the supply channel  41  more effectively. 
     In the second illustrative embodiment, as illustrated in  FIG. 8 , the head  110  further includes a flexible printed circuit board (“FPC”)  36 . The FPC  36  is electrically connected to the drive ICs  35 . Input lines  33  are electrically connected to the heater  31 C. As described above, the drive ICs  35  are disposed on the support substrate  14 B and the head  110  might not have a hollow  22 . Thus, the FPC  36  is not allowed to be routed to extend upward as with the head  10  of the first illustrative embodiment. The supply channel structure  12 B has an opening  38  penetrating its one-side wall in the longitudinal direction. The FPC  36  extends out of the supply channel structure  12 B from the drive ICs  35  toward the one side of the head  110  with respect to the longitudinal direction through the opening  38 . Therefore, the heater  31 C may preferably be disposed on the upper surface of the supply channel structure  12 B such that the input lines  33  extending from the heater  31 C extend toward the same side toward which the FPC  36  extends. 
     If the input lines  33  and the FPC  36  extend toward different sides of the head  110 , a space for placing the input lines  33  and a space for placing the FPC  36  may be needed on respective sides of the head  110 . In the second illustrative embodiment, as described above, the input lines  33  and the FPC  36  are routed to extend toward the same direction (e.g., toward the one side of the head  110  with respect to the longitudinal direction). In such a case, for example, as illustrated in  FIG. 8 , the input lines  33  of the heater  31 C extend from the upper portion of the head  110  toward the one side of the head  110  and the FPC  36  extends from the lower portion of the head  110  toward the one side of the head  110  with respect to the longitudinal direction. That is, a space on one of the sides of the head  110  may be used as a common space for placing the input lines  33  and the FPC  36 . As compared with a case where the input lines  33  and the FPC  36  extend toward different sides of the head  110 , such a configuration may thus reduce interference of electrical components between the input lines  33  and other structures and between and the FPC  36  and other structures. Consequently, the head  110  may be compact in size. According to one or more aspects of the disclosure, a head may include a supply channel structure and a heater. The supply channel structure may have a supply channel configured to allow liquid to flow therefrom to ejection channels that may be configured to lead liquid to nozzles aligned in a first direction. The heater may be configured to heat liquid. Assuming that a side of the head, in which the nozzles may be provided, may be defined as a lower side of the liquid ejection head, the heater may be disposed above the supply channel structure. The heater may be disposed on the upper surface of the supply channel structure or on an upper surface of a first heat transfer portion. According to such a configuration, the heater may be disposed above the supply channel structure. Attaching the heater in such a manner may be easier than attaching a heater to a side surface of the supply channel structure, thereby avoiding complication of the fabrication procedure. Such a configuration may enable the heater to heat the supply channel via the upper surface of the supply channel structure, thereby heating liquid more effectively as compared with a head including a heater disposed on a side surface of a supply channel structure. 
     While the disclosure has been described in detail with reference to the specific embodiments thereof, these are merely examples, and various changes, arrangements and modifications may be applied therein without departing from the spirit and scope of the disclosure. The particular elements and features disclosed in the illustrative embodiments and the modifications or variations may be combined with each other in other ways without departing from the spirit and scope of the disclosure. 
     The disclosure may be suitable for liquid ejection heads of liquid ejection apparatuses configured to eject liquid such as ink.