Abstract:
A liquid jet head includes a head portion having a supply flow path configured to allow liquid supplied from the outside to flow therethrough, a pressure chamber that communicates with the supply flow path, a driver element that drives the pressure chamber, and a nozzle that communicates with the pressure chamber for ejecting liquid droplets. A circuit portion supplies a drive waveform to the driver element. A cooling portion has a cooling flow path configured to allow the liquid to flow therethrough, and the cooling portion is coupled and fixed to the circuit portion to absorb heat energy dissipated by the circuit portion. The supply flow path and the cooling flow path communicate with each other so that the same liquid flows through both paths thereby eliminating the need for a dedicated cooling liquid system and achieving size and cost reduction.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a liquid jet head which jets liquid droplets onto a recording medium to perform recording and a liquid jet apparatus. 
     2. Related Art 
     In recent years, there has been used a liquid jet head of an ink jet system which ejects ink droplets onto, for example, recording paper to record characters or figures thereon, or ejects a liquid material onto the surface of an element substrate to form a functional thin film thereon. In this ink jet system, liquid such as ink and a liquid material is guided from a liquid tank into a channel through a supply tube, and pressure is applied to the liquid filled in the channel to thereby eject the liquid as liquid droplets from a nozzle which communicates with the channel. In the ejection of liquid droplets, characters or figures are recorded, or a functional thin film having a predetermined shape or a three-dimensional structure is formed by moving the liquid jet head or a recording medium. 
     A liquid jet head of an ink jet system includes a pressure chamber to which liquid such as ink is introduced, a driver element which drives the pressure chamber, a drive circuit portion which generates a drive waveform and supplies the drive waveform to the driver element, a nozzle which communicates with the pressure chamber and ejects liquid inside the pressure chamber therefrom, and the like. In the driver element, there is used a system that generates pressure waves in liquid filled in the pressure chamber using a piezoelectric effect of a piezoelectric body and ejects liquid droplets by the pressure waves or a system that heats a heat generator provided in the pressure chamber to generate air bubbles in liquid filled in the pressure chamber and ejects liquid droplets by pressure waves generated along with the generation of the air bubbles. When driving the pressure chamber, the driver element itself generates heat and the drive circuit portion which generates a drive waveform also generates heat. 
     JP 2006-212795 A describes a configuration that performs cooling of a head portion in which a driver element using a piezoelectric body is formed and cooling of a drive circuit portion which generates a drive waveform.  FIG. 8  is a perspective view of an ink jet printer head  105  described in JP 2006-212795 A.  FIGS. 9A and 9B  are explanatory diagrams of a temperature control base  151  for the ink jet printer head  105  described in JP 2006-212795 A. The ink jet printer head  105  is fixed onto the temperature control base  151  to cool a part of the inkjet printer head  105  required to be cooled. The ink jet printer head  105  mainly includes an ink ejecting portion  121  and a drive waveform generating portion  122 . The ink ejecting portion  121  includes a PZT substrate  124  which is covered with a top plate  125  and a nozzle plate  126  which is fixed to the tip part of the ink ejecting portion  121 . The PZT substrate  124  has a plurality of grooves (not illustrated) which are covered with the top plate  125  to constitute pressure chambers. Ink is supplied to the pressure chambers through an ink supply tube  127 . The drive waveform generating portion  122  includes a circuit board  128  which is coupled to the ink ejecting portion  121 . The circuit board  128  includes a first board  128   a  which is directly fixed to the ink ejecting portion  121  and a second board  128   b  which is coupled to the first board  128   a  and provided with a connector  130 . A driver IC is disposed on the lower face of the first board  128   a . When the driver IC generates a drive waveform and the generated drive waveform is applied to drive electrodes (not illustrated) which are formed on supports located on opposite sides of each of the pressure chambers, the supports are deformed by a piezoelectric effect and the volume of each of the grooves thereby changes. As a result, the ink filled in the pressure chambers is ejected from nozzles  123 . As this point, the driver IC and the PZT substrate  124  generate heat. 
     The temperature control base  151  includes a first base  152  and a second base  153  which are coupled to each other through an adhesive layer  154 . The temperature control base  151  is fixed to the lower part of the ink jet printer head  105 . A structure base  151   a  is attached to the lower part of the temperature control base  151 . The first base  152  is fixed to the ink ejecting portion  121  and cools the PZT substrate  124  of the ink ejecting portion  121 . The second base  153  is fixed to the drive waveform generating portion  122  and heats the driver IC. The first base  152  is provided with a liquid circulation tube inside thereof. The liquid circulation tube of the first base  152  is coupled to two first coupling portions  155 . The second base  153  is provided with a liquid circulation tube inside thereof. The liquid circulation tube of the second base  153  is coupled to two second coupling portions  156 . Cooling liquid is circulated through the first coupling portions  155  and the second coupling portions  156  to thereby release heat to the outside. Water or oil is used as the cooling liquid. 
     JP 2005-279952 A describes a configuration that prevents deterioration of recording quality caused by a difference in temperature of ejection ink depending on nozzle installation locations. When a difference in temperature of ejection ink is generated depending on nozzle installation locations, the ejection characteristics change according to the difference in temperature of ink. Accordingly, the recording quality on a recording medium is deteriorated. Thus, an IC chip which generates a drive waveform for driving a head portion is coupled to a heat release member, and the heat release member is routed up to the vicinity of an ink supply member of the head portion. As a result, heat generated by the IC chip is transmitted through the heat release member and then released near the ink supply member. Ink in the ink supply member is heated by the released heat, thereby reducing temperature variations between various locations of ink. 
     The ink jet printer head  105  described in JP 2006-212795 A is capable of independently cooling the PZT substrate  124  and the circuit board  128 . However, it is necessary to connect the ink supply tube  127  for supplying ink to the head portion, two outgoing and return cooling tubes for cooling the PZT substrate  124 , and two outgoing and return cooling tubes for cooling the circuit board  128  to the ink jet printer head  105 . Thus, it is necessary to connect five liquid circulation tubes in total between the head portion and the control portion. Therefore, many components are required, and assembly thereof becomes complicated. JP 2005-279952 A describes the configuration which uses heat generated by the IC chip for driving the head portion. However, JP 2005-279952 A fails to describe a configuration and a method for efficiently cooling the IC drive chip. 
     SUMMARY 
     A liquid jet head according to the present invention includes: a head portion including a supply flow path configured to allow liquid supplied from the outside to flow therethrough, a pressure chamber communicating with the supply flow path, a driver element configured to drive the pressure chamber, and a nozzle communicating with the pressure chamber, the head portion being configured to eject liquid droplets through the nozzle; a circuit portion configured to supply a drive waveform to the driver element; and a cooling portion including a cooling flow path configured to allow the liquid to flow therethrough, the cooling portion being coupled and fixed to the circuit portion, wherein the liquid flows through the supply flow path and through the cooling flow path in parallel. 
     The liquid jet head further includes a supply port configured to allow the liquid supplied from the outside to flow in therethrough and a discharge port configured to discharge the liquid to the outside therethrough. The liquid flowing into the supply port is divided to flow into the supply flow path and the cooling flow path, and the liquid flowing out of the supply flow path and the liquid flowing out of the cooling flow path join together and the joined liquid is discharged to the outside through the discharge port. 
     The supply flow path includes a first supply flow path and a second supply flow path. The liquid flowing into the supply port is divided to flow into the first supply flow path, the second supply flow path, and the cooling flow path. The liquid flowing out of the first supply flow path, the liquid flowing out of the second supply flow path, and the liquid flowing out of the cooling flow path join together and the joined liquid is discharged to the outside through the discharge port. 
     The liquid jet head further includes a branch point at which the liquid is divided to flow into the first supply flow path and the second supply flow path. A flow path resistance between the branch point and the first supply flow path is equal to a flow path resistance between the branch point and the second supply flow path. 
     The liquid jet head further includes a junction point at which the liquid flowing out of the first supply flow path and the liquid flowing out of the second supply flow path join together. A flow path resistance between the junction point and the first supply flow path is equal to a flow path resistance between the junction point and the second supply flow path. 
     The circuit portion includes a driver IC configured to generate the drive waveform and a circuit board on which the driver IC is mounted. The cooling portion includes a cooling substrate having the cooling flow path formed inside thereof. The circuit board and the cooling substrate are coupled and fixed to each other with substrate surfaces facing each other. 
     The circuit board and the cooling substrate are coupled and fixed to each other with a heat release sheet interposed therebetween. 
     The circuit board includes a first circuit board and a second circuit board. The first circuit board is coupled and fixed to one substrate surface of the cooling substrate. The second circuit board is coupled and fixed to the other substrate surface of the cooling substrate. 
     The cooling flow path has a cross-sectional shape in which the width in a direction parallel to the substrate surfaces of the cooling substrate is wider than the width in a direction perpendicular to the substrate surfaces of the cooling substrate. 
     The cooling flow path meanders within a plane parallel to the substrate surfaces of the cooling substrate. 
     The driver IC is disposed corresponding to the cooling flow path. 
     The cooling flow path is divided into a plurality of flow paths on an upstream side and the plurality of flow paths join together on a downstream side. 
     A liquid jet apparatus of the present invention includes the liquid jet head described above, a movement mechanism configured to relatively move the liquid jet head and a recording medium, a liquid supply tube configured to supply the liquid to the liquid jet head, and a liquid tank configured to supply the liquid to the liquid supply tube. 
     EFFECT OF INVENTION 
     The liquid jet head according to the present invention includes: a head portion including a supply flow path configured to allow liquid supplied from the outside to flow therethrough, a pressure chamber communicating with the supply flow path, a driver element configured to drive the pressure chamber, and a nozzle communicating with the pressure chamber, the head portion being configured to eject liquid droplets through the nozzle; a circuit portion configured to supply a drive waveform to the driver element; and a cooling portion including a cooling flow path configured to allow the liquid to flow therethrough, the cooling portion being coupled and fixed to the circuit portion, wherein the liquid flows through the supply flow path and through the cooling flow path in parallel. Accordingly, it is possible to efficiently cool the circuit portion without using cooling liquid other than the liquid for ejection and to simplify the connection with an apparatus in which the liquid jet head is installed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic view of a liquid jet head according to a first embodiment of the present invention; 
         FIG. 2  is a schematic perspective view of a liquid jet head according to a second embodiment of the present invention; 
         FIGS. 3A to 3C  are explanatory diagrams of the liquid jet head according to the second embodiment of the present invention; 
         FIGS. 4A and 4B  are explanatory diagrams of a liquid jet head according to a third embodiment of the present invention; 
         FIG. 5  is a schematic cross-sectional view for explaining inner flow paths of a liquid jet head according to a fourth embodiment of the present invention; 
         FIG. 6  is a schematic front view of a cooling portion used in a liquid jet head according to a fifth embodiment of the present invention; 
         FIG. 7  is a schematic perspective view of a liquid jet apparatus according to a sixth embodiment of the present invention; 
         FIG. 8  is a perspective view of a conventionally known ink jet printer head; and 
         FIGS. 9A and 9B  are explanatory diagrams of a temperature control base for the conventionally known ink jet printer head. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       FIG. 1  is a schematic view of a liquid jet head  1  according to a first embodiment of the present invention. The first embodiment shows a basic configuration of the present invention. As illustrated in  FIG. 1 , the liquid jet head  1  is provided with a head portion  2  which ejects liquid droplets from a nozzle  6 , a circuit portion  7  which supplies a drive waveform to the head portion  2 , and a cooling portion  10  which is coupled and fixed to the circuit portion  7 . The head portion  2  includes a supply flow path  3  which allows part of the liquid supplied from the outside to flow therein, to flow through the inside thereof, and to flow out to the outside therefrom, a pressure chamber  4  which communicates with the supply flow path  3 , a driver element  5  which drives the pressure chamber  4 , and the nozzle  6  which communicates with the pressure chamber  4 . The circuit portion  7  generates a drive waveform for driving the driver element  5  of the head portion  2 . The cooling portion  10  includes a cooling flow path  11  which allows part of the rest part or the entire rest part of the liquid supplied from the outside to flow therein, to flow through the inside thereof, and to flow out to the outside therefrom. Thus, the liquid flows through the supply flow path  3  and through the cooling flow path  11  in parallel. 
     For example, the pressure chamber  4  is surrounded by left and right side walls  4   c  and  4   d  each of which is made of a piezoelectric material such as PZT ceramics and upper and lower side walls  4   e  and  4   f  each of which is made of a piezoelectric material or a non-piezoelectric material. The pressure chamber  4  communicates with the supply flow path  3  and the nozzle  6 . The driver element  5  includes the left and right side walls  4   c  and  4   d  made of a piezoelectric material and drive electrodes  5   a  and  5   b  which are disposed on opposite side surfaces of each of the side walls  4   c  and  4   d . The side walls  4   c  and  4   d  on each of which the drive electrodes  5   a  and  5   b  are disposed are previously polarized upward and downward from a position located at half the height thereof. The circuit portion  7  includes a driver IC  8  which generates a drive waveform for driving the driver element  5 . Application of a drive waveform between the drive electrodes  5   a  which face the pressure chamber  4  and the respective drive electrodes  5   b  which are located opposite to the pressure chamber  4  causes thickness-shear deformation of the two side walls  4   c  and  4   d , thereby changing the volume of the pressure chamber  4 . Accordingly, liquid filled in the pressure chamber  4  is ejected from the nozzle  6 . When the liquid in the pressure chamber  4  has been consumed, liquid is supplied through the supply flow path  3 . A piezoelectric material such as PZT ceramics or another insulating material may be used as the upper and lower side walls  4   e  and  4   f.    
     The driver IC  8  generates heat when the drive waveform is supplied to the driver element  5 . The heat generated by the driver IC  8  of the circuit portion  7  is transmitted to the cooling flow path  11  of the cooling portion  10  so as to be transmitted to liquid flowing through the cooling flow path  11 , and then released to the outside. Thus, the liquid supplied from the outside flows through the cooling flow path  11  and through the supply flow path  3  in parallel. Therefore, it is possible to control the pressure of liquid flowing through the supply flow path  3  with higher accuracy than when the liquid flows through the cooling flow path  11  of the cooling portion  10  and through the supply flow path  3  of the head portion  2  in series. Specifically, it becomes easy to control a meniscus formed on an opening of the nozzle  6 . Further, the liquid is used for both cooling and ejection. Thus, it is possible to simplify the configuration of an apparatus in which the liquid jet head  1  is installed. That is, it is not necessary to use liquid dedicated for cooling and to provide a tube and a liquid feed or suction pump dedicated for cooling. In addition, since liquid flows through the supply flow path  3 , it is possible to stabilize the temperature of the head portion  2 . 
     The drive electrodes  5   a  and  5   b  may be formed up to half the height of the side walls  4   c  and  4   d  of the pressure chamber  4 , and the side walls  4   c  and  4   d  may be previously uniformly polarized upward or downward. Further, another driver element that differs from the driver element  5  of the present embodiment may be used. For example, a driver element which is composed of a heat generator may be disposed inside the pressure chamber  4 , the heat generator may be heated to generate air bubbles in liquid inside the pressure chamber  4 , and liquid droplets may be ejected by pressure waves generated along with the generation of the air bubbles. Further, as the driver element  5 , a piezoelectric body polarized in the thickness direction may be disposed outside the side walls  4   c  and  4   d , and the side walls  4   c  and  4   d  may be deformed by driving the piezoelectric body to change the volume of the pressure chamber  4 . In the present embodiment, the supply flow path  3  of the head portion  2  allows part of the liquid supplied from the outside to flow therein, to flow through the inside thereof, and to flow out to the outside therefrom. Instead of this, the supply flow path  3  of the head portion  2  may allow part of the liquid supplied from the outside to flow therein, and supply the liquid flowed therein to the pressure chamber  4  without allowing the liquid to flow out to the outside therefrom. That is, the supply flow path  3  of the head portion  2  is used only for circulation of liquid to be ejected. 
     Second Embodiment 
       FIG. 2  is a schematic perspective view of a liquid jet head  1  according to a second embodiment of the present invention.  FIGS. 3A to 3C  are explanatory diagrams of the liquid jet head  1  according to the second embodiment of the present invention.  FIG. 3A  is a schematic front view of the liquid jet head  1  illustrating a cooling portion  10  viewed from the front side.  FIG. 3B  is a schematic side view of the liquid jet head  1  illustrating the cooling portion  10  and a circuit portion  7  viewed from the lateral side.  FIG. 3C  is a schematic cross-sectional view of a head portion  2  in a direction perpendicular to a reference direction K. Identical elements or elements having identical functions will be designated by the same reference numerals. 
     As illustrated in  FIGS. 2 and 3A to 3C , the liquid jet head  1  is provided with the head portion  2  which ejects liquid droplets downward, a base member  18  to which the head portion  2  is fixed, a supply port  13  and a discharge port  14  each of which is disposed on the base member  18  on the opposite side of the head portion  2 , the cooling portion  10  which is fixed to the supply port  13  and the discharge port  14  and stands on the opposite side of the head portion  2 , and the circuit portion  7  which is coupled and fixed to the cooling portion  10 . The circuit portion  7  includes a driver IC  8  which generates a drive waveform, a circuit board  9  on which the driver IC  8  is mounted, connectors  9   a  and  9   b  which input and output data such as a drive signal, an electrode terminal (not illustrated) for outputting the drive waveform. The cooling portion  10  includes a cooling substrate  12  which has a cooling flow path  11  formed inside thereof. The circuit board  9  and the cooling substrate  12  are coupled and fixed to each other with a heat release sheet  15  which is composed of a thermally conductive silicone paste or sheet interposed therebetween as well as with substrate surfaces facing each other. Specifically, the cooling substrate  12 , the heat release sheet  15 , and the circuit board  9  are formed in this order from the left side of  FIG. 3B . The heat release sheet  15  is in contact with a surface of the circuit board  9 , the surface being located opposite to a surface on which the connector  9   a  and the like are disposed. Further, a surface of the heat release sheet  15 , the surface being located opposite to the surface that is in contact with the circuit board  9 , is in contact with the cooling substrate  12 . The cooling substrate  12  is fixed to the supply port  13  and the discharge port  14  with a space from the base member  18 . Leaving a space between the base member  18  and the cooling substrate  12  prevents heat from the cooling substrate  12  from being transmitted to the head portion  2 . The supply port  13  includes a connection portion  13   a . The liquid supplied from the outside flows in through the connection portion  13   a . The discharge port  14  includes a connection portion  14   a . The liquid is discharged to the outside through the connection portion  14   a.    
     As illustrated in  FIG. 3C , the head portion  2  is provided with an actuator substrate  2   a , a cover plate  2   b  which is bonded to the upper surface of the actuator substrate  2   a , a flow path member  2   d  which is bonded to the upper surface of the cover plate  2   b , and a nozzle plate  2   c  which is bonded to the lower surface of the actuator substrate  2   a . The actuator substrate  2   a  is composed of, for example, a piezoelectric substrate made of PZT ceramics. The actuator substrate  2   a  is provided with pressure chambers  4   a  and  4   b  each of which is elongated in the direction perpendicular to the reference direction K. The left and right pressure chambers  4   a  and  4   b  are arranged in parallel to each other and displaced by a half pitch with respect to each other in the reference direction K. Side walls which define each of the pressure chambers  4   a  and  4   b  function as a driver element together with drive electrodes (not illustrated) which are formed on the respective side walls and drive each of the pressure chambers  4   a  and  4   b . The cover plate  2   b  is provided with a liquid chamber  2   e  which communicates with the right end of each of the pressure chambers  4   a  and the left end of each of the pressure chambers  4   b , a liquid chamber  2   f  which communicates with the left end of each of the pressure chambers  4   a , and a liquid chamber  2   g  which communicates with the right end of each of the pressure chambers  4   b . An electrode terminal (not illustrated) which is electrically connected to the driver element is formed on the upper surface or the lower surface of the actuator substrate  2   a  or the upper surface of the cover plate  2   b , and electrically connected to an electrode terminal (not illustrated) of the circuit board  9  through a flexible circuit board (not illustrated). In this manner, the drive waveform generated by the driver IC  8  can be transmitted to the driver element. 
     The flow path member  2   d  is provided with a communication flow path  2   h  which allows the central liquid chamber  2   e  to communicate with an inner flow path R of the supply port  13  and a communication flow path  2   i  which allows the left liquid chamber  2   f  and the right liquid chamber  2   g  to communicate with an inner flow path S of the discharge port  14 . Thus, liquid flowing from the supply port  13  flows through a supply flow path  3  which includes the communication flow path  2   h , the liquid chamber  2   e , the pressure chambers  4   a ,  4   b , the liquid chambers  2   f ,  2   g , and the communication flow path  2   i  inside the head portion  2 , and flows out to the discharge port  14 . The communication flow path  2   h  and the communication flow path  2   i  are respectively formed on first and second ends in the reference direction K and spaced from each other in the reference direction K. The liquid chamber  2   e  communicates with the communication flow path  2   h  on the first end in the reference direction K and extends over the plurality of pressure chambers  4   a ,  4   b  in the sheet direction of the  FIG. 3C  (the direction along which the plurality of pressure chambers  4   a ,  4   b  are arrayed). The liquid chamber  2   f  communicates with the communication flow path  2   i  on the second end in the reference direction K  2  and extends over the plurality of pressure chambers  4   a  in the sheet direction of  FIG. 3C . The liquid chamber  2   g  communicates with the communication flow path  2   i  on the second end in the reference direction K and extends over the plurality of pressure chambers  4   b  in the sheet direction of  FIG. 3C . 
     The nozzle plate  2   c  is provided with left nozzles  6   a  which communicate with the respective left pressure chambers  4   a  and right nozzles  6   b  which communicate with the respective right pressure chambers  4   b . That is, the nozzle plate  2   c  has two right and left nozzle arrays. The supply port  13  divides the liquid supplied from the outside to flow into the supply flow path  3  and the cooling flow path  11 . The discharge port  14  allows liquid flowing out of the supply flow path  3  and liquid flowing out of the cooling flow path  11  to join together and discharges the joined liquid to the outside therefrom. 
     A good thermal conductor such as aluminum is preferably used as the cooling substrate  12 . The cooling flow path  11  meanders within a plane parallel to the substrate surfaces of the cooling substrate  12 . Accordingly, the contact area between the liquid and the cooling substrate  12  increases, thereby making it possible to improve the cooling efficiency. Further, when the cooling flow path  11  is a single smoothly meandering flow path, air bubbles are not likely to be mixed when liquid is filled into the flow path. In addition, it becomes easy to discharge the filled liquid. The cooling flow path  11  preferably has a cross-sectional shape in which the width in a direction parallel to the substrate surfaces of the cooling substrate  12  is wider than the width in a direction perpendicular to the substrate surfaces of the cooling substrate  12 . This prevents an increase in the volume of the cooling substrate  12  and also increases the contact area between the liquid and the cooling substrate  12 . Accordingly, it is possible to improve the cooling efficiency. A top plate and a bottom plate of the cooling flow path  11  which constitute the cooling substrate  12  preferably have a predetermined thickness, for example, a thickness of 0.5 mm or more to improve the thermal conductivity. 
     The driver IC  8  is preferably disposed corresponding to the cooling flow path  11 . That is, the driver IC  8  is disposed to overlap the cooling flow path  11  in the normal direction of the cooling substrate  12 . Accordingly, it is possible to promptly transmit the heat generated by the driver IC  8  to the liquid in the cooling flow path  11 . The overlapping area between the cooling flow path  11  and the driver IC  8  is preferably as wide as possible. A thermal conductor which is in contact with the outer surface of the driver IC  8  may be fixed to the cooling substrate  12  to cool the driver IC  8  from both sides thereof. 
     In this manner, part of the liquid supplied from the outside is circulated through the supply flow path  3  of the head portion  2 , and part of the rest part or the entire rest part of the liquid supplied from the outside is circulated through the cooling flow path  11  of the cooling portion  10 . Thus, it is possible to efficiently cool the circuit portion  7  without using cooling liquid other than the liquid for ejection. Further, the liquid is used for both cooling and ejection. Thus, it is possible to simplify the configuration of an apparatus in which the liquid jet head  1  is installed. Further, the circuit board  9  and the cooling portion  10  stand on the opposite side of the liquid droplet ejecting direction. Thus, the installation area of the liquid jet head  1  is reduced, and it is therefore possible to arrange many liquid jet heads  1  with high density. 
     Third Embodiment 
       FIGS. 4A and 4B  are explanatory diagrams of a liquid jet head  1  according to a third embodiment of the present invention.  FIG. 4A  is a schematic side view of the liquid jet head  1 .  FIG. 4B  is a schematic cross-sectional view of a head portion  2  in a direction perpendicular to a reference direction K. The third embodiment differs from the second embodiment mainly in that a first circuit portion  7   x  and a second circuit portion  7   y  are coupled and fixed to a cooling portion  10 , and the head portion  2  is provided with a first supply flow path  3   x  and a second supply flow path  3   y . Identical elements or elements having identical functions will be designated by the same reference numerals. 
     As illustrated in  FIGS. 4A and 4B , the liquid jet head  1  is provided with the head portion  2  which ejects liquid droplets downward, a base member  18  to which the head portion  2  is fixed, a supply port  13  and a discharge port  14  each of which is disposed on the base member  18  on the opposite side of the head portion  2 , a cooling portion  10  which is fixed to the supply port  13  and the discharge port  14  and stands on the opposite side of the head portion  2 , and the first circuit portion  7   x  and the second circuit portion  7   y  which are coupled and fixed to the cooling portion  10 . 
     The cooling portion  10  includes a cooling substrate  12  which has a cooling flow path  11  formed inside thereof. As with the second embodiment, the cooling flow path  11  meanders within a plane parallel to the substrate surfaces of the cooling substrate  12 . The circuit portion  7  is provided with the first circuit portion  7   x  and the second circuit portion  7   y . The first circuit portion  7   x  is provided with a first driver IC  8   x  which generates a drive waveform, a first circuit board  9   x  on which the first driver IC  8   x  is mounted, and a connector  9   a  which is disposed on the upper end of the first circuit board  9   x . The second circuit portion  7   y  is provided with a second driver IC  8   y  which generates a driver waveform, a second circuit board  9   y  on which the second driver IC  8   y  is mounted, and a connector  9   a  which is disposed on the upper end of the second circuit board  9   y . The first circuit board  9   x  is coupled and fixed to one of the substrate surfaces of the cooling substrate  12  with a heat release sheet  15   a  interposed therebetween. The second circuit board  9   y  is coupled and fixed to the other substrate surface of the cooling substrate  12  with a heat release sheet  15   b  interposed therebetween. 
     The head portion  2  has a structure having two head portions  2  of the second embodiment coupled to each other, wherein four pressure chambers  4   a ,  4   b ,  4   a , and  4   b  are arranged in the direction perpendicular to the reference direction K and four pressure chamber arrays are arrayed in the reference direction K. The pressure chambers  4  in the respective arrays are displaced by a one-quarter pitch in the reference direction K. The head portion  2  includes, for example, a first head portion  2   x  having the same structure as the head portion  2  of the second embodiment and a second head portion  2   y  having the same structure as the first head portion  2   x  which are displaced by a one-quarter pitch in the reference direction K. 
     Alternatively, four pressure chambers  4  may be arranged in the direction perpendicular to the reference direction K on a single actuator substrate  2   a , and four pressure chamber arrays may be arrayed in the reference direction K. In this case, a single cover plate  2   b  is disposed on the upper surface of the actuator substrate  2   a , and a single nozzle plate  2   c  provided with four nozzle arrays is disposed on the lower surface of the actuator substrate  2   a . Further, a flow path member  2   d  is disposed on the upper surface of the cover plate  2   b . The actuator substrate  2   a , the cover plate  2   b , the nozzle plate  2   c , and the flow path member  2   d  are integrally configured. The supply flow path  3  includes the first supply flow path  3   x  and the second supply flow path  3   y . The first supply flow path  3   x  communicates with two of the pressure chamber arrays. The second supply flow path  3   y  communicates with the other two pressure chamber arrays. Flexible circuit boards (not illustrated) are disposed between the first circuit board  9   x  and the actuator substrate  2   a  and between the second circuit board  9   y  and the actuator substrate  2   a  so that drive waveforms generated by the first driver IC  8   x  and the second driver IC  8   y  can be supplied to the actuator substrate  2   a.    
     The cooling substrate  12  of the cooling portion  10  is held by the supply port  13  and the discharge port  14  with a space from the base member  18 . The supply port  13  includes a connection portion  13   a  through which liquid supplied from the outside flows in and divides the liquid to flow into the first supply flow path  3   x , the second supply flow path  3   y , and the cooling flow path  11 . The discharge port  14  includes a connection portion  14   a  through which the liquid is discharged to the outside, and allows liquid flowing out of the first supply flow path  3   x , liquid flowing out of the second supply flow path  3   y , and liquid flowing out of the cooling flow path  11  to join together and discharges the joined liquid to the outside therefrom. 
     The supply port  13  includes a branch point Pb at which the liquid is divided to flow into the first supply flow path  3   x  and the second supply flow path  3   y  and a branch point Pb′ at which the liquid is divided to flow into the cooling flow path  11 , the branch point Pb′ being located between the branch point Pb and the first supply flow path  3   x . Similarly, the discharge port  14  includes a junction point Pg (not illustrated) at which the liquid flowing out of the first supply flow path  3   x  and the liquid flowing out of the second supply flow path  3   y  join together and a junction point Pg′ (not illustrated) at which the liquid flowing out of the cooling flow path  11  joins the liquid flowing out of the first supply flow path  3   x , the junction point Pg′ being located between the junction point Pg and the first supply flow path  3   x . A flow path resistance between the branch point Pb of the supply port  13  and the first supply flow path  3   x  differs from a flow path resistance between the branch point Pb and the second supply flow path  3   y . The liquid is divided to flow into the cooling flow path  11  at the branch point Pb′. Similarly, a flow path resistance between the junction point Pg of the discharge port  14  and the first supply flow path  3   x  differs from a flow path resistance between the junction point Pg and the second supply flow path  3   y . The liquid from the cooling flow path  11  joins the liquid from the first supply flow path  3   x  at the junction point Pg′. Thus, there is generated a difference in pressure between the liquid supplied to the first supply flow path  3   x  and the liquid supplied to the second supply flow path  3   y . In view of this, an inner flow path R of the supply port  13  and an inner flow path S of the discharge port  14  should be designed so as to allow the pressure difference not to affect the ejection characteristics. 
     Although the branch point Pb and the junction point Pg are respectively located in the inner flow path R of the supply port  13  and the inner flow path S of the discharge port  14 , the present invention is not limited to this configuration. The branch point Pb or the junction point Pg may be located in the cooling flow path  11 , or may also be located inside the head portion  2 . 
     Fourth Embodiment 
       FIG. 5  is a schematic cross-sectional view for explaining inner flow paths of a liquid jet head  1  according to a fourth embodiment of the present invention. The fourth embodiment differs from the third embodiment in the configurations of inner flow paths R, Rx, and Ry of a supply port  13  and inner flow paths S, Sx, and Sy of a discharge port  14 . The other configurations are the same as those of the third embodiment. Thus, hereinbelow, the differences from the third embodiment will be described, and description of the other configurations will be omitted. Identical elements or elements having identical functions will be designated by the same reference numerals. 
     As illustrated in  FIG. 5 , a head portion  2  is disposed on the lower part of a base member  18 . The supply port  13  and the discharge port  14  are disposed on the upper part of the base member  18 . A cooling portion  10  is held by the supply port  13  and the discharge port  14  with a space from the base member  18 . The supply port  13  includes a connection portion  13   a  through which liquid supplied from the outside flows in. Similarly, the discharge port  14  includes a connection portion  14   a  through which the liquid is discharged to the outside. 
     The inner flow path R which allows liquid supplied from the outside to flow to the cooling substrate  12  is formed inside the supply port  13 . A point at which the inner flow path R and a cooling flow path  11  communicate with each other constitutes a branch point Pb′. The liquid is divided to flow into the cooling flow path  11  and a flow path leading to the head portion  2  at the branch point Pb′. A branch point Pb is located on the flow path leading to the head portion  2 . The flow path leading to the head portion  2  is divided into the inner flow path Rx which communicates with a first supply flow path  3   x  and the inner flow path Ry which communicates with a second supply flow path  3   y  at the branch point Pb. Similarly, the inner flow path S which allows the liquid to flow to the outside from the cooling substrate  12  is formed inside the discharge port  14 . A point at which the cooling flow path  11  and the inner flow path S communicate with each other constitutes a junction point Pg′. Liquid flowing from the cooling flow path  11  and liquid flowing from a flow path leading from the head portion  2  join together at the junction point Pg′. A junction point Pg is located on the flow path leading from the head portion  2 . The inner flow path Sx which communicates with the first supply flow path  3   x  and the inner flow path Sy which communicates with the second supply flow path  3   y  join together at the junction point Pg. Thus, the liquid supplied to the supply port  13  is divided to flow into the first supply flow path  3   x , the second supply flow path  3   y , and the cooling flow path  11 . Similarly, the liquid flowing out of the first supply flow path  3   x , the liquid flowing out of the second supply flow path  3   y , and the liquid flowing out of the cooling flow path  11  join together, and the joined liquid is discharged through the discharge port  14 . 
     A flow path resistance in the inner flow path Rx between the branch point Pb and the first supply flow path  3   x  is equal to a flow path resistance in the inner flow path Ry between the branch point Pb and the second supply flow path  3   y . Similarly, a flow path resistance in the inner flow path Sx between the junction point Pg and the first supply flow path  3   x  is equal to a flow path resistance in the inner flow path Sy between the junction point Pg and the second supply flow path  3   y . This decreases a difference in pressure between a pressure chamber communicating with the first supply flow path  3   x  and a pressure chamber communicating with the second supply flow path  3   y . Thus, it is possible to equalize the ejection characteristics between ejection operations from the respective pressure chambers. The branch point Pb and the junction point Pg may be respectively located inside the supply port  13  and the discharge port  14  to make the flow path resistance in the inner flow path Rx equal to the flow path resistance in the inner flow path Ry and to make the flow path resistance in the inner flow path Sx equal to the flow path resistance in the inner flow path Sy. 
     Although the branch points Pb, Pb′ and the junction point Pg, Pg′ are located inside the cooling substrate  12  in the present embodiment, the present invention is not limited to this configuration. For example, the liquid flowing from the connection portion  13   a  may be directly guided to the head portion  2 , and an inner flow path R having a branch point Pb on the head portion  2  and an inner flow path S having a junction point Pg on the head portion  2  may be formed to make the flow path resistance between the branch point Pb and the first supply flow path  3   x  equal to the flow path resistance between the branch point Pb and the second supply flow path  3   y  and to make the flow path resistance between the junction point Pg and the first supply flow path  3   x  equal to the flow path resistance between the junction point Pg and the second supply flow path  3   y.    
     Fifth Embodiment 
       FIG. 6  is a schematic front view of a cooling portion  10  used in a liquid jet head  1  according to a fifth embodiment of the present invention. The cooling portion  10  of the fifth embodiment differs from the cooling portions  10  of the first to fourth embodiments in that a cooling flow path  11  is divided into a plurality of flow paths. The other configurations are the same as those of the other embodiments. Identical elements or elements having identical functions will be designated by the same reference numerals. 
     As illustrated in  FIG. 6 , the cooling flow path  11  is divided into a plurality of flow paths  11   a  on the upstream side. The flow paths  11   a  join together on the downstream side. Accordingly, it is possible to suppress an increase in the flow path resistance to increase the flow path area, and to thereby improve the cooling efficiency. 
     Sixth Embodiment 
       FIG. 7  is a schematic perspective view of a liquid jet apparatus  30  according to a sixth embodiment of the present invention. The liquid jet apparatus  30  is provided with a movement mechanism  40  which reciprocates liquid jet heads  1 ,  1 ′, flow path portions  35 ,  35 ′ which supply liquid to the liquid jet heads  1 ,  1 ′ and discharge liquid from the liquid jet heads  1 ,  1 ′, and liquid pumps  33 ,  33 ′ and liquid tanks  34 ,  34 ′ which communicate with the flow path portions  35 ,  35 ′. As the liquid pumps  33 ,  33 ′, either or both of supply pumps which supply liquid to the flow path portions  35 ,  35 ′ and discharge pumps which discharge liquid to components other than the flow path portions  35 ,  35 ′ may be provided to circulate liquid. Further, a pressure sensor or a flow sensor (not illustrated) may be provided to control the flow rate of liquid. As each of the liquid jet heads  1 ,  1 ′, any one of the liquid jet heads  1  of the first to fifth embodiments may be used. That is, the liquid jet head  1  is provided with the head portion  2  which ejects liquid droplets, the circuit portion  7  which supplies a drive waveform to the driver element of the head portion  2 , and the cooling portion  10  which is coupled and fixed to the circuit portion  7 . The cooling portion  10  performs cooling using the liquid for ejection. Thus, it is not necessary to connect the liquid jet heads  1 ,  1 ′ to a flow path portion dedicated for cooling. Further, it is not necessary to provide a liquid pump dedicated for cooling the liquid jet heads  1 ,  1 ′. 
     The liquid jet apparatus  30  is provided with a pair of conveyance units  41 ,  42  which conveys a recording medium  44  such as paper in a main scanning direction, the liquid jet heads  1 ,  1 ′ each of which jets liquid onto the recording medium  44 , a carriage unit  43  on which the liquid jet head  1 ,  1 ′ are placed, the liquid pumps  33 ,  33 ′ which supply liquid stored in the liquid tanks  34 ,  34 ′ to the flow path portions  35 ,  35 ′ by pressing, and the movement mechanism  40  which moves the liquid jet heads  1 ,  1 ′ in a sub-scanning direction that is perpendicular to the main scanning direction. A control unit (not illustrated) controls the liquid jet heads  1 ,  1 ′, the movement mechanism  40 , and the conveyance units  41 ,  42  to drive. 
     Each of the conveyance units  41 ,  42  extends in the sub-scanning direction, and includes a grid roller and a pinch roller which rotate with the roller surfaces thereof making contact with each other. The grid roller and the pinch roller are rotated around the respective shafts by a motor (not illustrated) to thereby convey the recording medium  44  which is sandwiched between the rollers in the main scanning direction. The movement mechanism  40  is provided with a pair of guide rails  36 ,  37  each of which extends in the sub-scanning direction, the carriage unit  43  which is slidable along the pair of guide rails  36 ,  37 , an endless belt  38  to which the carriage unit  43  is coupled to move the carriage unit  43  in the sub-scanning direction, and a motor  39  which revolves the endless belt  38  through a pulley (not illustrated). 
     The plurality of liquid jet heads  1 ,  1 ′ are placed on the carriage unit  43 . The liquid jet heads  1 ,  1 ′ eject, for example, four colors of liquid droplets: yellow, magenta, cyan, and black. Each of the liquid tanks  34 ,  34 ′ stores therein liquid of the corresponding color, and supplies the stored liquid to each of the liquid jet heads  1 ,  1 ′ through each of the liquid pumps  33 ,  33 ′ and each of the flow path portions  35 ,  35 ′. Each of the liquid jet heads  1 ,  1 ′ jets liquid droplets of the corresponding color in response to the drive waveform. Any patterns can be recorded on the recording medium  44  by controlling the timing of jetting liquid from the liquid jet heads  1 ,  1 ′, the rotation of the motor  39  which drives the carriage unit  43 , and the conveyance speed of the recording medium  44 . 
     The liquid jet head  1  according to the present invention does not use liquid dedicated for cooling other than the liquid for liquid droplet ejection in the head portion  2 . Thus, it is not necessary to dispose a tube for cooling liquid between the liquid jet heads  1 ,  1 ′ and the liquid pumps  33 ,  33 ′. This makes the placement of the liquid jet head  1  easy and also simplifies the configuration of the liquid jet apparatus  30 . In the liquid jet apparatus  30  of the present embodiment, the movement mechanism  40  moves the carriage unit  43  and the recording medium  44  to perform recording. However, instead of this, the liquid jet apparatus may have a configuration in which a carriage unit is fixed, and a movement mechanism two-dimensionally moves a recording medium to perform recording. That is, the movement mechanism may have any configuration as long as it relatively moves the liquid jet head and a recording medium.