Abstract:
An inkjet head includes a flow passage unit having an ink flow passage formed therein, in which ink flows, and an actuator unit secured to the flow passage unit. The actuator unit is configured to apply a discharge energy to the ink within the ink flow passage. The inkjet head also includes a driver IC configured to supply a drive signal to the actuator unit, a plurality of plates extending from the flow passage unit, and a cover member secured to the plurality of plates. The cover member, the plurality of plates, and the flow passage unit define a closed space, and the driver IC is disposed within the closed space. Moreover, the driver IC opposes at least a portion of an inside surface of one of the plurality of plates and is thermally coupled to the one of the plurality of plates, and an outside surface of the one of the plurality plates has a heat radiation property which is greater than a heat radiation property of the inside surface of the one of plurality of plates.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to inkjet heads for discharging ink onto a recording medium. 
     2. Description of Related Art 
     A known inkjet head, such as the inkjet head described in Japanese Patent Application Publication No. JP-A-2005-169839, includes a head main body for discharging the ink, a head control portion for controlling the head main body, and an upper and a lower cover for protecting the head control portion from ink splash. In the known inkjet head, the head main body includes a flow passage unit having a plurality of individual ink flow passages leading to a nozzle, and an actuator unit for changing the volume of individual ink flow passages. The head control portion includes a main board, a plurality of sub-boards electrically connected to the main board and arranged to sandwich the main board, and a driver integrated circuit (“IC”) which includes a heat sink secured to the surface of the sub-boards opposed to the main board. The sub-boards and the driver IC are electrically connected to a flexible printed circuit (“FPC”) with one end electrically connected to the actuator unit. The FPC conveys a signal outputted from the main board via the sub-boards to the driver IC, and conveys a drive signal outputted from the driver IC to the actuator unit. The actuator unit receives the drive signal, and changes the volume of some of the individual ink flow passages and applies pressure to the ink within the individual ink flow passages. In this manner, the ink is discharged from the nozzle, such that a desired image is formed on the paper. 
     Nevertheless, in the known inkjet head, because the heat sink is covered with an upper cover, the heat generated by the driver IC and the heat sink is captured within the cover. Consequently, the temperature and humidity of space within the inkjet head surrounded by the upper and lower covers increases. Moreover, an external stress is applied on the junction between the connector of the FPC and the electronic parts, and whisker may grow in the connector or the junction of the FPC. Particularly, if the joint member includes a tin based material which does not include lead, the whisker may grow. In addition, the FPC has a narrower pitch with higher wiring density and shorter terminal distance, along with the higher density of the actuator unit, whereby there is a risk that the electrical short circuit occurs due to whisker. A known method for suppressing whisker involves coating gold or adding silver, which increases costs. Further, because the ink temperature within the head main body rises, the ink discharge characteristics vary. 
     SUMMARY OF THE INVENTION 
     Therefore, a need has arisen for inkjet heads which overcome these and other shortcomings of the related art. A technical advantage of the present invention is that the closed space inkjet head is less likely to be heated by radiated heat than the known inkjet heads. 
     According to an embodiment of the present invention, an inkjet head comprises a flow passage unit having an ink flow passage formed therein, in which ink flows, and an actuator unit secured to the flow passage unit. The actuator unit is configured to apply a discharge energy to the ink within the ink flow passage. The inkjet head also comprises a driver IC configured to supply a drive signal to the actuator unit, a plurality of plates extending from the flow passage unit, and a cover member secured to the plurality of plates. The cover member, the plurality of plates, and the flow passage unit define a closed space, and the driver IC is disposed within the closed space. Moreover, the driver IC opposes at least a portion of an inside surface of one of the plurality of plates and is thermally coupled to the one of the plurality of plates, and an outside surface of the one of the plurality plates has a heat radiation property which is greater than a heat radiation property of the inside surface of the one of plurality of plates. 
     Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, the needs satisfied thereby, and the features and technical advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. 
         FIG. 1  is a perspective view of an inkjet head, according to an embodiment of the present invention. 
         FIG. 2  is a perspective view of the internal components of the inkjet head of  FIG. 1 . 
         FIG. 3  is a cross-sectional view along the line III-III of  FIG. 1 . 
         FIG. 4  is a side view of a heat sink. 
         FIG. 5  is a partial, cross-sectional perspective view of a porous film formed on the outside surface of the heat sink. 
         FIG. 6  is a longitudinal, cross-sectional view of an ink reservoir. 
         FIG. 7A  is a plan view of a flow passage unit; and  FIG. 7B  is a cross-sectional view along the line VIIB-VIIB of  FIG. 7A . 
         FIG. 8  is an enlarged, plan view of an area surrounded by the dashed line in  FIG. 7A . 
         FIG. 9  is a longitudinal, cross-sectional view along the line IX-IX of  FIG. 8 . 
         FIG. 10  is an enlarged view of an area surrounded by the dashed line in  FIG. 9 . 
         FIG. 11  is a partial, enlarged cross-sectional view near a heat sink provided on an inkjet head, according to a another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention and their features and technical advantages may be understood by referring to  FIGS. 1-11 , like numerals being used for like corresponding portions in the various drawings. 
     Referring to  FIG. 1 , an inkjet head  100  may have a elongated shape in one direction in a plan view. In this embodiment, a main scanning direction is the longitudinal direction in a plan view of the inkjet head  100 , and a subscanning direction is the direction vertical to the main scanning direction. Moreover, a lower direction is the discharge direction of the ink discharged from the inkjet head  100 , and an upper direction is the opposite direction to the lower direction. 
     The inkjet head  100  may comprise a flow passage unit  140  comprising a ink discharge port  8 , such as a nozzle, on its under surface/ink discharge face, and an ink reservoir  130  for supplying the ink to the flow passage unit  140 . Inkjet head  100  also may comprise a head cover  110  disposed on the ink reservoir  130 , and an electric circuit for controlling the inkjet head  100  may be accommodated within its internal space. Each of the ink reservoir  130  and the flow passage unit  140  may have a rectangular shape, with its long side being parallel to the main scanning direction. 
     Referring to  FIG. 2 , the ink reservoir  130  may be a laminated structure comprising three plates, in which a lower reservoir  133  on the side of the flow passage unit  140 , a reservoir base  132  and an upper reservoir  131  are laminated in this order. The reservoir base  132  may have a through hole/ink flow passage  136  formed there through, which is in fluid communication with an ink reservoir of the lower reservoir  133 . Moreover, the electric circuit may comprise a control board  170  laminated on the upper reservoir  131 . 
     The head cover  110  may have a box-like shape opened downward. The head cover  110  may be positioned on the reservoir base  132  to cover various components, such as the upper reservoir  131  on the reservoir base  132 . An ink supply valve  111  may be positioned on an upper surface of the head cover  110  to supply the ink into an ink flow passage  135  formed inside the ink reservoir  130  through the ink supply valve  111 . 
     An opening  110   a  may be formed on the side face of the head cover  110 . The opening  110   a  may be formed by cutting out the side face of the head cover  110  along the vertical direction of the head cover  110  from the lower end of the side face up to the neighborhood of the center of the side face. The opening  110   a  may have a rectangular shape, with its long side being parallel to the main scanning direction. Moreover, the short side of the opening  110   a  may be parallel to the vertical direction. On the side face of the inkjet head  100 , a heat sink  150  may be positioned inside the head cover  110 . In this embodiment, a flat protrusion  150   a  formed on the heat sink  150  is exposed via the opening  110   a  from the head cover  110 . The inkjet head  100  has a clearance between each member sealed with a seal member (not shown), such that the space surrounded by the head cover  110 , the heat sink  150 , the reservoir base  132 , and the flow passage unit  140  may be the closed space. 
     The inkjet head  100  may be applied to image recording apparatus, such as an inkjet printer. For example, when the inkjet head  100  is applied to the inkjet printer, the inkjet head  100  may be arranged, such that the main scanning direction is the direction of the length and the subscanning direction is the direction of the width in a plan view. When the paper is conveyed to the position opposite to the nozzle  8  formed on the under surface of the flow passage unit  140 , the ink is discharged from the nozzle  8 , such that the character and image are formed on the paper. The ink for use in the inkjet head  100  may be supplied from an ink cartridge provided on the inkjet printer via an ink tube connected to the ink supply valve  111 . 
     Referring to  FIG. 2 , an ink supply port  131   b  may be formed on an upper surface of the ink reservoir  130 . The ink supply port  131   b  is in fluid communication with the ink supply valve  111  provided on the upper surface of the head cover  110 . 
     The control board  170  above the upper reservoir  131  may have a rectangular shape that is elongated in the main scanning direction. The length of the control board  170  and the length of the upper reservoir  131  may be substantially the same in the subscanning direction. Various kinds of electronic components, such as an IC chip or a condenser, may be fixed on the upper surface of the control board  170 , in which a number of wirings are provided. On the control board  170 , various processors and storage units are constructed by these electronic parts and wirings. The storage unit constructed on the control board  170  stores data denoting the program for controlling the inkjet head  100  and temporary working data. The processor constructed on the control board  170  controls the operation of the inkjet head  100  based on this data. 
     Four connectors  170   a  may be fixed on the upper surface of the control board  170 . The connectors  170   a  are electrically connected to various processors and storage units constructed on the control board  170 . The four connectors  170   a  may be arranged in two rows in a staggered form in the main scanning direction. 
     One end of an FPC  162  may be connected to the side face of each connector  170   a . The FPC  162  may be a flexible sheet member formed with a plurality of wirings  162   a  inside. Moreover, a driver IC  160  may be mounted on the FPC  162  and may be electrically connected to the wirings  162   a . Referring to  FIGS. 2 and 3 , the FPC  162  is passed from the connector  170   a  along the side face of the ink reservoir  130  downward, and passed through an opening  133   a  formed on the side face of the lower reservoir  133 , such that the driver IC  160  may be disposed at the position opposite to the flat protrusion  150   a  of the heat sink  150  and sideways of the ink reservoir  130 , as shown in  FIGS. 2 and 3 . The other end of the FPC  162  is electrically connected to the actuator unit  120  secured on the upper surface of the flow passage unit  140 . 
     The driver IC  160  may be an IC chip for driving the actuator unit  120 . The driver IC  160  may have a shape which is long the main scanning direction and flat in the subscanning direction. The driver IC  160  is urged, together with the FPC  162 , to the heat sink  150  by an elastic member  161  provided on the side face of the upper reservoir  131  at the position opposite to the heat sink  150 . 
     The heat sink  150  may protrude from the upper surface at either end in the subscanning direction of the flow passage unit  140 . Referring to  FIG. 4 , each of the heat sinks may comprise aluminum metal, and may have substantially rectangular shape in which the main scanning direction is the direction of the length. The heat sink  150  may comprise a flat protrusion  150   a , a projection  155   b , and a protrusion  150   c . The flat protrusion  150   a  is formed in a portion of the heat sink  150  opposed to the side face of the upper reservoir  131  to protrude from the opening  110   a . A top end of the flat protrusion  150   a  protruding from the opening  110   a  may be flat and may have a rectangular shape which is elongated in the main scanning direction. The flat protrusion  150   a  may be formed by press working a metal sheet. In this manner, the flat protrusion  150   a  is formed on the heat sink  150 , whereby the heat sink  150  has a wider surface area and an increased rigidity. 
     The projection  150   b  projects from the lower end of the heat sink  150  downwards. For example, five projections  150   b  may be positioned along the main scanning direction. The width of the upper surface of the flow passage unit  140  may be greater than the width of the under surface of the ink reservoir  130 , and the ink reservoir  130  may be disposed in the center of the flow passage unit  140  in the subscanning direction. Consequently, an area not opposed to the under surface of the ink reservoir  130  exists near either end of the flow passage unit  140  in the subscanning direction. In this area, five concave portions  141  may be formed at the positions corresponding to the five projections  150   b . Moreover, the concave portions  141  may have a size and shape which snuggly fits with the projections  150   b  of the heat sink  150 . Because the projections  150   b  are fitted into the concave portions  141 , the heat sink  150  is spaced from the flow passage unit  140 . The protrusion  150   c  may protrude from the upper end of the heat sink  150  upwards, and may have a substantially rectangular shape in which the main scanning direction is the direction of the length. Referring to  FIG. 3 , the protrusion  150   c  contacts the inside of the side face of the head cover  110  to secure the head cover  110 . 
     A porous film  153 , which may be made a known anodizing process with dilute sulfuric acid as the electrolytic solution, may be positioned on an outside surface  151  of the heat sink  150 . Referring to  FIG. 5 , the porous film  153  may comprise a barrier layer  153   a  formed adjacent to the boundary with the outside surface  151  of the heat sink  150 , and a plurality of cells  153   c , which may form hexagonal columns, each having a micropore  153   b  formed substantially in the center thereof. In this manner, the plurality of micropores  153   b  may be formed in the porous film  153 , whereby the surface area of the outside surface of the heat sink  150  is substantially greater than the inside surface  152 . Therefore, the heat radiation characteristic on the outside surface of the heat sink  150  may be greater than the inside surface  152 , such that heat conveyed to the heat sink  150  is passed from the inside surface  152  to the outside surface  151  and radiated from the heat sink  150 . Moreover, the porous film  153  may be black, and because the micropore  153   b  is formed in the cell  153   c , the porous film  153  may be formed black by dipping the heat sink  150  in the dyestuff to fill the dyestuff in the micropore  153   b  after the porous film  153  is formed. Alternatively, pigment may be contained into the micropore  153   b , or a metallic salt bath may be applied. In another embodiment, a color other than black may be used. Because the porous film may be colored, heat conveyed to the inside surface  152  of the heat sink  150  may be radiated from the heat sink  150  in the direction from the inside surface  152  to the outside surface  151 . Moreover, because the dyestuff fills the micropore  153   b , contaminant or corrosive substance may not be absorbed through the micropore  153   b , whereby the heat sink  150  is improved in the corrosiveness, weatherability, and stainability. Further, because the porous film  153  has a greater hardness than a basis material, e.g., aluminum metal, the strength of the heat sink  150  is enhanced. 
     In this embodiment, the heat sink  150  may comprise aluminum metal such as titanium metal, magnesium metal, or their alloy, or aluminum alloy. In this case, the porous film equivalent to the porous film  153  may be formed on the heat sink, whereby the same effect may be achieved. 
     Moreover, on the inside surface  152  of the heat sink  150  opposed to the FPC  162 , an adiabatic layer  155  may have a through hole  154  formed there through, through which the inside surface  152  is exposed. Through hole  154  may be formed in an area opposed to the driver IC  160 . Using, and via the through hole  154 , the driver IC  160  may tightly contact the inside surface  152  via a heat radiation sheet  156 , e.g., the heat sink  150  and the driver IC  160  may be thermally coupled. In this manner, because the driver IC  160  tightly contacts the inside surface  152 , heat generated from the driver IC  160  migrates through the inside surface  152  to the heat sink  150 . 
     The adiabatic layer  155  may comprise a rubber sheet and may have an insulating property. Referring to  FIG. 3 , because the adiabatic layer  155  is positioned between the FPC  162  and the heat sink  150 , the FPC  162  and the heat sink  150  may not contact each other, which prevents a short circuit between the wirings  162   a . Alternatively, the adiabatic layer  155  may comprise a sponge sheet, a sheet of polyimide resin, or paint. In the case of the sponge sheet, because a plurality of air layers are provided internally, the adiabatic property is further improved. 
     Moreover, the thickness of the adiabatic layer  155  may be less than or equal to the height of the driver IC  160  in the thickness direction, e.g., the subscanning direction, of the adiabatic layer  155 . Thereby, even if the FPC  162  and the adiabatic layer  155  contact each other, the driver IC  160  and the inside surface  152  may be thermally coupled. Therefore, heat of the driver IC  160  is more likely to be conveyed to the inside surface  152 , such that the driver IC  160  may be cooled effectively. If the thickness of the adiabatic layer is greater than the height of the driver IC  160 , the distance between the driver IC  160  and the inside surface  152  is increased, when the FPC  162  and the adiabatic layer contact each other. Therefore, heat of the driver IC  162  is less likely to be conveyed to the inside surface  152 . 
     Referring to  FIG. 6 , an ink flow passage  135  may be formed inside the upper reservoir  131 . Moreover, an ink supply port  131   b  which is one opening of the ink flow passage  135  may be formed on the upper surface of the upper reservoir  131 , and an ink passage port  131   e  which is the other opening of the ink flow passage  135  may be formed on the under surface of the upper reservoir  131 . The ink supply port  131   b  may be formed adjacent to one end of the upper reservoir  131  in the main scanning direction. The ink passage port  131   e  may be formed adjacent to the center of the upper reservoir  131  in both the main scanning direction and the subscanning direction. 
     In order to form the ink flow passage  135 . The ink flow passage  135 . The ink flow passage  135  first may be directed from the ink supply port  131   b  downwards, and may be in fluid communication with an extension area  135   a  extending along the under surface of the upper reservoir  131  adjacent to the under surface of the upper reservoir  131 . A portion of the under surface of the upper reservoir  131  may comprise a flexible film  131   d . The upper surface of the film  131   d  comprises a portion of the lower wall face of the extension area  135   a . Moreover, the under surface of the film  131   d  is spaced a predetermined distance away from the reservoir base  132 , and is disposed to be displaceable corresponding to this distance. Therefore, when the film  131   d  vibrates, an impact due to a pressure wave produced in the ink filled within the ink flow passage  135  is absorbed. 
     The extension area  135   a  may be in fluid communication with the extension area  135   b . The extension area  135   b  may be formed above the extension area  135   a , and may extend parallel to an extension surface of the extension area  135   a . The extension area  135   a  and the extension area  135   b  may be segmented by a filter  131   c , and may be in fluid communication with each other via a plurality of micropores formed in the filter  131   a.    
     The ink flow passage  135  leads upwards from one end in the main scanning direction up to adjacent the upper surface of the upper reservoir  131 , and bends adjacent to the upper surface of the upper reservoir  131  in the center of the upper reservoir  131  in the main scanning direction to lead along the upper surface of the upper reservoir  131  to the center of the upper reservoir  131 . When it reaches adjacent to the center of the upper reservoir  131 , it bends downwards to lead to the under surface of the upper reservoir  131  to be in fluid communication with the ink passage port  131   e  on the under surface of the upper reservoir  131 . 
     The ink flow passage  136  may be formed inside the reservoir base  132 . One opening of the ink flow passage  136  may be formed on the upper surface of the reservoir base  132  to be in fluid communication with the ink passage port  131   e . An ink passage port  132   a , which is the other opening of the ink flow passage  136 , may be formed on the under surface of the reservoir base  132 . The ink flow passage  136  extends downwards from the ink passage port  131   e  to the ink passage port  132   a.    
     The ink flow passage  137  may be formed inside the lower reservoir  133 . One opening of the ink flow passage  137  may be formed on the upper surface of the lower reservoir  133 , and a plurality of ink passage ports  133   a , which are the other openings, may be formed on the under surface. The ink passage port  133   a  may be opposed to the flow passage unit  140  and may be in fluid communication with the ink supply port  140   a  formed on the upper surface of the flow passage unit  140 . 
     The ink flow passage  137  may comprise a first portion which extends along the main scanning direction adjacent to the center of the lower reservoir  133  in the vertical direction, a second portion which extends upwards from the first portion to the ink passage port  132   a , and a third portion which extends downwards from the first portion to each of the ink passage ports  133   a . The second portion may be formed at a position overlapping the ink flow passage  136  in a plan view, and the third portion may be formed at a position overlapping each of the ink passage ports  133   a  in a plan view. 
     In this manner, the ink supplied from the ink supply port  131   b  flows through the ink flow passages  135 - 137  formed in the ink reservoir  130  into the flow passage unit  140 . The ink passes through the filter  131   c  to reach the flow passage unit  140 , and at this time, impurities in the ink are filtered through the filter  131   c.    
     Referring to  FIG. 7A , the actuator unit  120  may be secured on the upper surface of the flow passage unit  140 . The actuator unit  120  may have a trapezoidal shape, and the actuator unit  120  may be positioned, such that a pair of parallel opposed sides may be parallel to the main scanning direction. Moreover, four actuator units  120  may be arranged in a staggered form in the main scanning direction. In the four actuator units  120 , the adjacent hypotenuses on the flow passage unit  140  may overlap partially in the subscanning direction. 
     A manifold flow passage  5 , which may be a portion of the ink flow passage, may be formed inside the flow passage unit  140 . A plurality of ink supply ports  140   a  may be formed on the upper surface of the flow passage unit  140 , and one end of the manifold flow passage  5  may be in fluid communication with each of the ink supply ports  140   a . Five ink supply ports  140   a  may be formed in each of a pair of rows, and may be formed along the longitudinal direction of the flow passage unit  140 . The ink supply ports  140   a  may be formed at positions which do not include the areas where the four actuator units  120  are positioned. 
     Referring to  FIG. 7B , the ink supply port  140   a  may be in fluid communication with the ink passage port  133   a  formed in the lower reservoir  133 . The ink may be supplied from the ink reservoir  130  to the manifold flow passage  5  via the ink supply port  140   a.    
     The lower reservoir  133  and the flow passage unit  140  may be separated except for the position at which the ink supply port  140   a  and the ink passage port  133   a  are in fluid communication. The actuator unit  120  may be positioned in the space formed between the lower reservoir  133  and the flow passage unit  140 , and may be opposed to the under surface of the lower reservoir  133 . The FPC  162  may be pasted on the upper surface of the actuator unit  120 , and the FPC  162  and the lower reservoir  133  may be separated. 
     Referring to  FIG. 8 , a plurality of sub-manifold flow passages  5   a  may branch from the manifold flow passage  5 . The sub-manifold flow passages  5   a  may extend adjacently to each other in an area opposed to each actuator unit  120  inside the flow passage unit  140 . 
     The flow passage unit  140  may comprise a pressure chamber group  9  in which a plurality of pressure chambers  10  are formed, e.g., in a matrix. The pressure chamber  10  may be a hollow area having a planar, substantially diamond shape with the rounded corner portion. The pressure chamber  10  may open on the upper surface of the flow passage unit  140 . The pressure chambers  10  may be arranged substantially over the face of the area opposed to the actuator unit  120  on the upper surface of the flow passage unit  140 . Consequently, each pressure chamber group  9  occupies the area of about same size and shape as the actuator unit  120 . Moreover, the opening of each pressure chamber  10  may be blocked by bonding the actuator unit  120  on the upper surface of the flow passage unit  140 . 
     In this embodiment, sixteen rows of pressure chambers  10  may be arranged at equal intervals in the direction of the length of the flow passage unit  140  in parallel to each other in the direction of the width. The number of pressure chambers  10  in each pressure chamber row may gradually decrease from the longer side to the shorter side which corresponds to the outer shape of the actuator unit  120 . The nozzles  8  may be similarly arranged. 
     An individual electrode  35  may be opposed to each pressure chamber  10  on the upper surface of the actuator unit  120 . The individual electrode  35  may be a size smaller than the pressure chamber  10  and may have a similar shape to the pressure chamber  10 , and may be disposed to be accommodated within the area opposed to the pressure chamber  10  on the upper surface of the actuator unit  120 . 
     The flow passage unit  140  may comprise a plurality of the nozzles  8 . The nozzles may be arranged at positions which do not include the area opposed to the sub-manifold flow passage  5   a  on the under surface of the flow passage unit  140 . Moreover, the nozzles  8  may be positioned within the area opposed to the actuator unit  120  on the under surface of the flow passage unit  140 , and the nozzles  8  within respective areas may be arranged at equal intervals along the direction of the length of the flow passage unit  140 . 
     The nozzles  8  may be formed at positions, such that the projection points of each nozzle  8  onto an imaginary line, which is parallel to the direction of the length of the flow passage unit  140  from the direction perpendicular to the imaginary line, are arranged without a break at equal intervals corresponding to the print resolution. Thereby, the inkjet head  100  may perform printing without a break at the interval corresponding to the print resolution over the substantially entire area where the nozzles  8  are position in the direction of the length of the flow passage unit  140 . 
     A number of apertures/diaphragms  12  may be positioned inside the flow passage unit  140 , and the apertures  12  may be arranged within the area opposed to the pressure chamber group  9 . The apertures  12  may extend along a direction parallel to the horizontal plane. 
     A communication pore for providing fluid communication between the aperture  12 , the pressure chamber  10 , and the nozzle  8  may be formed inside the flow passage unit  140 . Referring to  FIG. 9 , the communication pores be in fluid communication with each other to comprise the individual ink flow passages  32 . Each individual ink flow passage  32  may be in fluid with the sub-manifold flow passage  5   a . The ink supplied to the manifold flow passage  5  may be provided via the sub-manifold flow passage  5   a  to each of the individual ink flow passages  32 , and then may be discharged from the nozzle  8 . 
     The flow passage unit  140  may comprise a laminated structure comprising a cavity plate  22 , a base plate  23 , an aperture plate  24 , a supply plate  25 , the manifold plates  26 ,  27  and  28 , a cover plate  29  and a plate  30 , which may be positioned in the order from the upper surface of the flow passage unit  140 . The plates may have a plurality of communication pores formed the therethrough, and may be aligned and laminated, such that the communication pores are in fluid communication with each other to comprise the individual ink flow passages  32  and the sub-manifold flow passages  5   a . The portions comprising the individual ink flow passage  32  may be disposed in proximity with respect to each other at different positions, such that the pressure chamber  10  may be on the upper surface of the flow passage unit  140 , the sub-manifold flow passage  5   a  may be in the central portion inside, and the nozzle  8  may be on the under surface. Consequently, the sub-manifold flow passage  5   a  and the nozzle  8  may be in fluid communication via the communication pore. 
     With respect to the communication pores, the first communication pore may be the pressure chamber  10  formed on the cavity plate  22 , and the second communication pore may be the communication pore A comprising the flow passage in fluid communication from one end of the pressure chamber  10  to the sub-manifold flow passage  5   a . The communication pore A may be formed on each plate from the base plate  23 , e.g., the entrance into the pressure chamber  10 , to the supply plate  25  e.g., the exit from the sub-manifold flow passage  5   a . The communication pore A may comprise the aperture  12  formed on the aperture plate  24 . 
     The third communication pore may be a communication pore B comprising the flow passage in fluid communication from the other end of the pressure chamber  10  to the nozzle  8 . The communication pore B may be formed on each plate from the base plate  23  to the cover plate  29 . The fourth communication pore may be the nozzle  8  formed on the nozzle plate  30 , and the fifth communication pore may be the communication pore C comprising the sub-manifold flow passage  5   a . The communication pore C may be formed on the manifold plates  26 - 28 . 
     The communication pores may be in fluid communication with each other, and may comprise the individual ink flow passage  32  leading from an inflow port of the ink from the sub-manifold flow passage  5   a  to the nozzles  8 . The ink supplied to the sub-manifold flow passage  5   a  flows into the nozzle  8  via the following described path. First, the ink flows upwards from the sub-manifold flow passage  5   a  to one end of the aperture  12 . Then, the ink flows horizontally along the extending direction of the aperture  12  to the other end of the aperture  12 . The ink then flows upwards to one end of the pressure chamber  10 , and then horizontally along the extending direction of the pressure chamber  10  to the other end of the pressure chamber  10 . The ink then flows from obliquely downwards via the plates to the nozzle  8 . 
     Referring to  FIG. 10 , the actuator unit  120  may have a laminated structure in which four piezoelectric layers  41 ,  42 ,  43 , and  44  are laminated. Each of the piezoelectric layers  41  to  44  may have a thickness of about 15 mm, and the total thickness of the actuator unit  120  may be about 60 mm. Referring to  FIG. 8 , each of the piezoelectric layers  41 - 44  may extend over a plurality of pressure chambers  10 . The piezoelectric layers may comprise a ceramics material comprising lead zirconate titanate having ferroelectricity. 
     The actuator unit  120  may comprise an individual electrode  35  and a common electrode  34  comprising a metal material such as Ag—Pd. The individual electrode  35  may be positioned opposed to the pressure chamber  10  on the upper surface of the actuator unit  120 . One end of the individual electrode  35  may be drawn out of the area opposed to the pressure chamber  10  to form a land  36 . The land  36  may comprise gold, e.g., gold comprising glass frit, and may be convex and have a thickness of about 15 mm. The land  36  may be electrically connected to a plurality of wirings  162   a  of the FPC  162 . 
     When the inkjet head  100  is installed in the printer, the control portion of the control board may be electrically connected to the main control portion of the printer. The control portion of the control board  170  instructs the driver IC  160  to supply a voltage pulse corresponding to ink discharge in accordance with an instruction of the main control portion of the printer. The driver IC  160  supplies a voltage pulse corresponding to ink discharge through the FPC  162  to the individual electrode  35  in response to the instruction. 
     The common electrode  34  may be interposed over substantially the entire surface in the face direction in an area between the piezoelectric layer  41  and the piezoelectric layer  42 . For example, the common electrode  34  may extend over the pressure chambers  10  within the area opposed to the actuator unit  120 . The thickness of the common electrode  34  may be about 2 mm, and the common electrode  34  may be grounded and held at the ground potential. 
     The plurality of individual electrodes  35  and the common electrode  34  may sandwich the uppermost piezoelectric layer  41 . An area on the piezoelectric layer sandwiched between the individual electrodes  35  and the common electrode  34  may be considered an active site. In the actuator unit  120  of an embodiment, and the uppermost piezoelectric layer  41  comprises the active site, the other piezoelectric layers  42 - 44  do not comprise the active site, e.g., the actuator unit  120  may be uni-morph type actuator. 
     The volume of the pressure chamber  10  corresponding to the individual electrode  35  may be altered by selectively supplying a predetermined voltage pulse to the individual electrode  35 , such that a pressure is applied to the ink within the pressure chamber. Thereby, the ink may be discharged via the individual ink flow passage  32  from the corresponding nozzle  8 , and a desired image may be formed on the paper. 
     In the inkjet head  100 , heat of the driver IC  160  may be conveyed to the inside surface  152  of the heat sink  150  and may be radiated to the outside surface  151  from the heat sink  150 . Therefore, heat conveyed from the heated driver IC  160  to the inside surface  152  is less likely to be radiated from the inside surface  152  to the closed space. Consequently, the closed space is less likely to have a relatively high temperature or a relatively high humidity, whisker growth at the electrically connected portion between the FPC  162  and the actuator unit  140 . Moreover, a rise in the ink temperature within the ink reservoir  130  and the ink flow passage in the flow passage unit  140  can be suppressed. Therefore, the viscosity of ink is more stable, and the ink discharge is more stable. 
     Because the adiabatic layer  155  may be formed on the inside surface  152  of the heat sink  150 , if heat conveyed from the area on the inside surface  152  opposed to the driver IC  160  to the heat sink  150  is radiated from the area on the inside surface  152  not opposed to the driver IC  160 , the closed space surrounded by the head cover  110  is less likely to be heated because of the adiabatic layer  155  exists. 
     Referring to  FIG. 11  another embodiment of the present invention is substantially similar to the above embodiments of the present invention. Therefore only differences between this embodiment of the present invention and the above described embodiments are discussed with respect to this embodiment. Specifically, in this embodiment, heat sink  150  is replaced by heat sink  250 . 
     The heat sink  250  may comprise a flat protrusion  250   a  similar to the flat protrusion  150   a . The heat sink  250  may comprise a plurality of convex portions  257  protruding in the subscanning direction from the outside surface  251  of the flat protrusion  250   a . The convex portions  257  may spread in the main scanning direction on the flat protrusion. In this manner, because the plurality of convex portions  257  may be positioned on the outside surface  251  of the heat sink  250 , the surface area of the outside surface  251  of the heat sink  250  may be greater than that of the inside surface  252 . Therefore, the heat radiation characteristic on the outside surface of the heat sink  250  may be greater than on the inside surface  252 , such that heat conveyed to the inside surface  252  of the heat sink  250  is radiated in the direction from the inside surface  252  to the outside surface  251  from the heat sink  250 . 
     The heat sink  250  may comprise aluminum metal, and a porous film  253  on the outside surface  251 , similar above described embodiments. Thus, the surface area of the outside surface of the heat sink  250  may be greater than that of the inside surface  252 . Therefore, heat conveyed to the inside surface  252  is radiated in the direction from the inside surface  252  to the outside surface  251  from the heat sink  250 . In this manner, the heat radiation characteristic may be greater on the outside surface of the heat sink  250  than on the inside surface  252 , such that heat of the driver IC  160  conveyed to the heat sink  250  is less likely to be radiated to the closed space, and the closed space is less likely to be heated. 
     While the invention has been described in connection with exemplary embodiments, it will be understood by those skilled in the art that other variations and modifications of the exemplary embodiments described above may be made without departing from the scope of the invention. Other embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are considered merely as exemplary of the invention, with the true scope of the invention being indicated by the flowing claims.