Patent Publication Number: US-7213911-B2

Title: Ink-jet head

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink-jet head that conducts recordings by ejecting ink onto a recording medium. 
     2. Description of Related Art 
     An ink-jet head ejects ink by means of, applying pressure to ink using a piezoelectric element, applying thermal energy to ink using a heater, and the like. 
     According to one of techniques that adopt the latter method, an ink passage formed on a substrate has therein a heating element which generates heat upon driving of a driver IC, and thermal energy thus generated is applied to ink contained in the ink passage (see Japanese Patent No. 2803840). A heat sink having a plurality of fins is provided opposite to the ink passage across the substrate. Since the heat sink dissipates heat, members of the head such as the driver IC, and ink contained in the ink passage are prevented from excessively rising in temperature. As a result, a stable ink ejection can be obtained. 
     In the above-described technique, however, an ink-jet head disadvantageously incurs a size increase of itself, because the fins constituting the heat sink protrude substantially throughout one face of the substrate. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an ink-jet head capable of dissipating heat of a driver IC and at the same time reducing a size of itself. 
     According to an aspect of the present invention, there is provided an ink-jet head comprising a passage unit, an actuator unit, an ink supply unit, a flexible substrate, and a driver IC. The passage unit includes a plurality of nozzles that eject ink, and a plurality of pressure chambers connected to the respective nozzles. The actuator unit is fixed to one surface of the passage unit in order to change the volume of the pressure chambers. The ink supply unit is fixed to the passage unit and supplies ink to the passage unit. The flexible substrate is connected to the actuator unit and has a signal wire formed thereon for feeding electric power to the actuator unit. The driver IC is connected to the flexible substrate in order to drive the actuator unit. The driver IC is held on the ink supply unit. 
     According to the above-described structure, heat of the driver IC can be dissipated, because the ink supply unit having a relatively large heat capacity is disposed in contact with the driver IC. Since, like this, the ink supply unit is employed for dissipating heat of the driver IC, a heat sink, etc., is not specially required and therefore the head can be downsized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the accompanying drawings in which: 
         FIG. 1  illustrates a general structure of an exemplified ink-jet printer that includes ink-jet heads according to an embodiment of the present invention; 
         FIG. 2  is a bottom view of the ink-jet heads of  FIG. 1  that are arranged in parallel; 
         FIG. 3  is a perspective view of a head main body of the ink-jet head of  FIG. 1 ; 
         FIG. 4  is a sectional view taken along a line IV—IV of  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of an ink supply unit illustrated in  FIGS. 3 and 4 , 
         FIG. 6  is a local sectional view of a passage unit illustrated in  FIGS. 3 and 4 ; and 
         FIG. 7  is a sectional view, which corresponds to  FIG. 4 , of an exemplified modification of the ink-jet head of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  illustrates an exemplified ink-jet printer that includes ink-jet heads according to an embodiment of the present invention. An ink-jet printer  1  illustrated in  FIG. 1  is a color ink-jet printer comprising four ink-jet heads  2 . The ink-jet printer  1  comprises a paper feed unit  11  (on a lefthand in  FIG. 1 ) and a paper discharge unit  12  (on a righthand in  FIG. 1 ). Within the printer  1 , formed is a paper conveyance path extending from the paper feed unit  11  to the paper discharge unit  12 . 
     A pair of paper feed rollers  5   a  and  5   b  are disposed immediately downstream of the paper feed unit  11  so that a paper as a medium is conveyed from left to right in  FIG. 1 . Two belt rollers  6  and  7 , a looped conveyor belt  8 , and a substantially rectangular parallelepiped belt guide  38  are disposed in a middle of the paper conveyance path. The conveyor belt  8  is wrapped around the belt rollers  6  and  7  to be stretched between them. The belt guide  38  is disposed within a region enclosed by the conveyor belt  8 . The belt guide  38  and the conveyor belt  8  have substantially the same width. The belt guide  38  is in contact with an inner surface of the conveyor belt  8  at an upper part thereof, and thereby supports the conveyor belt  8 . 
     An outer surface of the conveyor belt  8  is formed of a silicone rubber. A paper fed through the pair of paper feed rollers  5   a  and  5   b  is held onto the conveyor belt  8  by adhesive power, and in this condition conveyed downstream, i.e., rightward in  FIG. 1  as one belt roller  6  is driven in clockwise rotation in  FIG. 1  (i.e., rotation in a direction of an arrow  90 ). 
     Pressing members  9   a  and  9   b  are provided at positions for feeding a paper onto the conveyor belt  8  and discharging a paper from the conveyor belt  8 , respectively. The pressing members  9   a  and  9   b  serve to press a paper onto the conveyor belt  8  in order to prevent a separation of a paper from the conveyor belt  8 . The paper is surely held onto the conveyor belt  8  by the adhesive power. 
     A peeling plate  10  is provided immediately downstream (i.e., on a right side in  FIG. 1 ) of the conveyor belt  8 . The peeling plate  10  peels off a paper, which is held onto the conveyor belt  8 , from the conveyor belt  8  so that the paper can be transferred to the righthand paper discharge unit  12 . 
     Each of the four ink-jet heads  2  has, at its lower end, a head main body  2   a . Each head main body  2   a  has a rectangular section. The head main bodies  2   a  are arranged adjacent to one another with a longitudinal axis of each head main body  2   a  being perpendicular to a paper conveyance direction, i.e., perpendicular to the drawing sheet of  FIG. 1 . That is, this printer  1  is a line type printer. A bottom face of each head main body  2   a  confronts the paper conveyance path. In the bottom faces of the respective head main bodies  2   a , formed are a large number of small-diameter nozzles (see  FIG. 2 ). The four head main bodies  2   a  eject from their nozzles  13  ink of magenta, yellow, cyan, and black, respectively. 
     The ink-jet heads  2  are, by means of holders  18 , mounted on a suitable member provided in the printer  1 . The holders  18  are fixed, with an adhesive or screws, etc., to a later-described ink supply unit  40  that occupies an upper portion of the head main bodies  2   a.    
     The ink-jet heads  2  are disposed such that a narrow clearance may be formed between lower faces of the head main bodies  2   a  and a conveyance face of the conveyor belt  8 . The paper conveyance path is formed within this clearance. With this construction, while a paper, which is being conveyed by the conveyor belt  8 , passes immediately below the four head main bodies  2   a  in order, the respective color inks are ejected through the corresponding nozzles  13  (see  FIG. 2 ) toward an upper face, i.e., a print face, of the paper to thereby form a desired color image on the paper. 
     Next, a description will be given to a construction of the head main body  2   a  of the ink-jet head  2 . As illustrated in  FIG. 4 , the head main body  2   a  includes an ink supply unit  40 , a passage unit  20 , and actuator units  19 . 
     The ink supply unit  40  supplies ink into the passage unit  20 , and has a layered structure of three substantially rectangular plates  41 ,  42 , and  43  (a first plate  41 , a second plate  42 , and a third plate  43  from the top), as illustrated in  FIGS. 3 and 4 . The passage unit  20  has, as illustrated in  FIG. 6 , a layered structure of nine thin metal plates  21 ,  22 ,  23 ,  24 ,  25 ,  26 ,  27 ,  28 , and  29 . The passage unit  20  includes the above-mentioned large number of nozzles  13  and a plurality of pressure chambers  34  connected to the respective nozzles  13 . The actuator unit  19  is a thin sheet-like member for changing the volume of the pressure chambers  34 . As illustrated in  FIGS. 2 and 5 , the actuator unit  19  has a substantially trapezoidal shape in a plan view. 
     It can be seen from  FIGS. 2 and 5  that a plurality of actuator units  19  are arranged on and bonded to an upper face of the passage unit  20  in a zigzag pattern along a lengthwise direction of the passage unit  20 . Each actuator unit  19  is disposed with its parallel opposed sides, i.e., upper and lower sides, extending along the lengthwise direction of the passage unit  20 . Oblique sides of the neighboring actuator units  19  overlap each other in a widthwise direction of the passage unit  20 . In a lower face of the passage unit  20 , an area corresponding to a region where each actuator unit  19  is bonded is formed as an ink ejection region. 
     In regions of the upper face of the passage unit  20  where no actuator unit  21  is bonded, formed are a plurality of circular inlet ports  20   a  (see  FIGS. 2 ,  4 , and  5 ). As illustrated in  FIGS. 2 and 5 , the inlet ports  20   a  include ones disposed at diagonal positions near both lengthwise ends of the passage unit  20 , and ones disposed in pairs in a zigzag pattern along shorter sides of the parallel opposed sides of the respective actuator unit  19 . 
     As illustrated in  FIG. 4 , the ink supply unit  40  is bonded to such regions of the upper face of the passage unit  20  as to include and surround the inlet ports  20   a . In the remaining region thereof including the region where the actuator units  19  are bonded, the ink supply unit  40  is spaced from the passage unit  20 . On the upper face of the passage unit  20 , the actuator units  19  are disposed out of the regions where the ink supply unit  40  is bonded. Thus, the actuator units  19  are in no contact with the ink supply unit  40  and at a predetermined distance therefrom. 
     Subsequently, there will be described constructions of the aforementioned three elements that constitute the head main body  2   a.    
     First, the ink supply unit  40  will be described. 
     Among the three plates forming the ink supply unit  40 , the first and second plates  41  and  42  are made of a metal such as stainless steels, and the third plate  43  is formed as a layered structure of a metal plate  43   a  such as stainless steels and a resin plate  43   c  such as polyimide. The third plate  43  is so disposed that the metal plate  43   a  may confront the passage unit  20 .  FIGS. 3 ,  4 , and  5  show that the first plate  41  has a larger thickness than those of the other two plates  42  and  43 . 
     As illustrated in  FIG. 5 , at a widthwise center near one lengthwise end of the first plate  41 , formed by etching, etc., is an ink introduction port  41   a  penetrating through the plate  41  in its thickness direction. Ink is introduced into the ink introduction port  41   a  from an ink supply source (not illustrated) via a tube, etc. 
     In the second plate  42 , a hole to constitute an ink reservoir  42   a  for storing ink is formed by press working, etc. The hole to constitute the ink reservoir  42   a  extends along a lengthwise direction of the second plate  42 . Further, a plurality of notches  42   c  each having a substantially semicylindrical shape are serially formed at sidewalls of the hole that constitutes the ink reservoir  42   a.    
     Ink outlet ports  43   b  are formed at such portions of the metal plate  43   a  of the third plate  43  as to correspond to inlet ports  20   a  formed in the passage unit  20 . Each of the ink outlet ports  43   b  has the same shape as that of the inlet port  20   a , and penetrates through the metal plate  43   a  in its thickness direction. These portions where the ink outlet ports  43   b  are formed correspond also to the notches  42   c  formed in the second plate  42 . 
     Ink filters  43   f  are formed at such portions of the resin plate  43   c  of the third plate  43  as to correspond to the inlet ports  20   a  formed in the passage unit  20 , i.e., as to correspond to the aforementioned ink outlet ports  43   b . Each of the ink filters  43   f  has the same outline as those of the inlet port  20   a  and the ink outlet port  43   b.    
     The ink outlet ports  43   b  can be formed by etching the metal plate  43   a . Then, the filters  43   f  can easily be formed by performing excimer laser machining on the resin plate  43   c  so that a large number of small-diameter pores (16 to 24 micrometers) are formed to neighbor one another in a concentrated manner at the portions of the resin plate  43   c  corresponding to the ink outlet ports  43   b . Adopting the above-described method for forming a filter, there can be obtained the filter  43   f  in which pores are stabilized in shape and size, and at the same time a manufacture cost of the filter  43   f  can be reduced. 
     Further, a part of the metal plate  43   a  of the third plate  43  has been cut off by etching, etc., and remaining are only areas including the ink outlet ports  43   b , which are indicated by dotted lines in  FIG. 5 . Thus, a concavity  43   g  appears in the third plate  43  on a side facing the passage unit  20 . The concavity  43   g  serves as a space  44  (see  FIG. 4 ) in which the actuator units  19 , illustrated in  FIG. 5  on the surface of the passage unit  20  with alternate long and two short dashes lines, are to be arranged. 
     Protrusions  43   h  protruding toward a passage unit  20  side are formed at areas of the metal plate  43   a  corresponding to outsides of long sides of the actuator units  19 , i.e., at areas outside alternate long and short dash lines in  FIG. 5  (see  FIG. 4 ). Each of the protrusion  43   h  has such a height that a later-detailed flexible printed circuit (FPC)  4  may extend out of the space  44 . These protrusions  43   h  close the space  44 . 
     The number of processing steps can be reduced by simultaneously performing two etchings on the metal plate  43   a , i.e., the etching for forming the concavity  43   g  and the etching for forming the ink outlet ports  43   b.    
     The above-described first plate  41 , the second plate  42 , and the third plate  43  are put in layers, so that the ink supply unit  40  is formed therein with an ink branching passage that branches ink from the ink introduction port  41   a  into the ink outlet ports  43   b.    
     The ink reservoir  42   a  temporarily reserves therein ink, which then flows through the notches  42   c  into the filters  43   f , and then reaches the ink outlet ports  43   b . In this embodiment, ink does not incur so much change in passage resistance before and after the ink passes through the filters  43   f , i.e., while the ink flows out of the notches  42   c  into the ink outlet ports  43   b . This allows the ink to flow smoothly, without the bubbles being generated when the ink passes the filters  43   f.    
     The ink supply unit  40  is bonded to the passage unit  20  such that the notches  42   c  and the corresponding inlet ports  20   a  may communicate with each other. Thus, ink reserved within the ink reservoir  42   a  of the ink supply unit  40  can be introduced through the inlet ports  20   a  into the passage unit  20 . The plurality of inlet ports  20   a  are arranged at a distance from one another along the lengthwise direction of the passage unit  20 . Therefore, even when the head  2  is elongated, ink reserved in the ink reservoir  42   a  can stably be supplied to the passage unit  20  with its passage resistance restrained. 
     Next, a construction of the passage unit  20  will be described in detail. 
     As illustrated in  FIG. 6 , the nine metal plates constituting the passage unit  20  are hereinbelow referred to as, from the top, a first plate  21 , a second plate  22 , a third plate  23 , a fourth plate  24 , a fifth plate  25 , a sixth plate  26 , a seventh plate  27 , a eighth plate  28 , and a ninth plate  29 . Each of the plates  21  to  29  has holes or openings formed therein by etchings including half-etchings, laser machinings, or press workings, etc. 
     A manifold channel  30  is formed in the fifth to seventh plates  25  to  27  in such a manner as to extend over these three plates. The manifold channel  30  communicates with the above-described inlet ports  20   a  (see  FIGS. 2 ,  4 , and  5 ) via a non-illustrated path. The forth plate  24  has connection holes  31  formed therein, and the connection holes  31  communicate with corresponding apertures  32  that are formed in the third plate  23 . 
     Each of the apertures  32  functions as a throttle for adjusting a passage resistance, and communicates, via each of communication holes  33  formed in the second plate  22 , with one end of each pressure chamber  34  formed in the first plate  21 . The pressure chambers  34 , which are formed in one-to-one correspondence with the respective nozzles  13 , serve to apply pressure to ink upon driving of the actuator units  19  fixed onto the upper face of the passage unit  20 . The other end of each pressure chamber  34  communicates, via each of nozzle connection holes  35  formed throughout the second to eighth plates  22  to  28 , with a corresponding tapered nozzle  13  formed in the ninth plate  29 . 
     The manifold channel  30  communicates with the pressure chambers  34  through the apertures  32 . The manifold channel  30  temporarily reserves therein ink that has been introduced from the inlet ports  20   a , and distributes the ink among the respective pressure chambers  34 . 
     In the head main body  2   a , ink supplied from the ink supply source (not illustrated) is firstly introduced through the ink introduction port  41   a  into the ink reservoir  42   a , where the ink is reserved for a time (see  FIGS. 4 and 5 ). The ink reserved in the ink reservoir  42   a  subsequently passes through the notches  42   c , and then through the filters  43   f . At this time, foreign matters mixed in the ink are removed by the filters  43   f . The ink, after passing through the filters  43   f , reaches the ink outlet ports  43   b . The ink is then led from the ink outlet ports  43   b  into the inlet ports  20   a  of the passage unit  20 , and further into the manifold channel  30 . The ink in the manifold channel  30  is supplied to the respective pressure chambers  34  through the connection holes  31 , the apertures  32 , and the communication holes  33  (see  FIG. 6 ). Then, upon driving of the actuator unit  19 , pressure is applied to the ink in the respective pressure chambers  34  so that the ink is ejected from the corresponding nozzles  13  through the nozzle connection holes  35 . 
     A construction of the actuator unit  19  will then be described in detail. 
     The actuator unit  19  is formed of a layered structure of a plurality of piezoelectric sheets made of, e.g., a lead zirconate titanate (PZT)-base ceramic material. Thin film electrodes made of., e.g., an Ag—Pd-base metallic material are interposed between the piezoelectric sheets, so that active portions are formed at regions facing respective pressure chambers  34 . When the electrodes disposed between the piezoelectric sheets cause a potential difference from one another, the respective active portions deform into a convex shape toward the pressure chamber  34  side. As a result, the corresponding pressure chambers  34  are reduced in volume, so that pressure is applied to the ink contained in the pressure chambers  34 . 
     An FPC  4  is bonded onto an upper face of each actuator unit  19  (see  FIG. 6 ). Signal wires for feeding electric power to the actuator unit  19  are formed on the FPC  4 . As illustrated in  FIG. 4 , the FPCs  4  are bent on sides of the head main body  2   a  to extend upward therefrom. Silicon-base sealing members  36  are disposed at side portions of the head main body  2   a  corresponding to openings through which the FPCs  4  extend outward. The sealing members  36  safeguard the FPCs  4  as well as seal the space  44  in order to prevent ink, etc., from entering the space  44 . 
     As illustrated in  FIG. 3 , the head main body  2   a  has four driver ICs  52  aligned thereon along its lengthwise direction. Each FPC  4  extending out of the inside of the head main body  2   a  is connected to an upper face of the corresponding driver IC  52 , and thus the driver IC  52  is held between the ink supply unit  40  and the FPC  4 . The FPC  4  is connected to the driver IC  52 , and moreover connected to a substrate (not illustrated) that is fixed to the holder  18  (see  FIG. 1 ) and has an MCU (Micro Controller Unit), etc., mounted thereon. 
     The driver IC  52  generates drive pulses for driving the actuator unit  19 , and the drive pulses are supplied via the FPC  4  to the actuator unit  19 , thereby causing deformations of the aforementioned active portions. This potential control is performed on the respective pressure chambers  34  independently of one another. 
     As described above, the ink-jet head  2  of this embodiment can dissipate heat of the driver ICs  52 , because the ink supply unit  40  having a relatively large heat capacity is disposed in contact with the driver ICs  52 . Since, like this, the ink supply unit  40  is employed for dissipating heat of the driver ICs  52 , a heat sink, etc., is not specially required and therefore the head  2  can be downsized. 
     In addition, as illustrated in  FIG. 3 , the driver ICs are held between the ink supply unit  40  and the corresponding FPCs  4 . Accordingly, on the ink supply unit  40 , the driver ICs can be held in a stable manner, and at the same time the FPCs  4  can be connected to the driver ICs  52  in a stable manner. 
     Moreover, since the first plate  41 , which is closest to the driver ICs  52  among the plate forming the ink supply unit  40 , is made of a metal, heat of the driver ICs  52  can be dissipated efficiently. 
     The ink supply unit  40  has the layered structure of the three plates  41 ,  42 , and  43 , among which the first plate  41  closest to the driver ICs  52  has a larger thickness than those of the other plates. The first plate  41  having such a larger thickness and therefore having a relatively large heat capacity enables more efficient dissipation of the heat of the driver ICs  52 . 
     The passage unit  20  is fixed to the ink supply unit  40  on a side opposite to the driver IC  52 , and the resin plate  43   c  of the ink supply unit  40  is disposed near the passage unit  20 . The resin plate  43   c  disposed in this manner can prevent a further heat transfer to the passage unit  20 , which otherwise follows a heat transfer from the driver ICs  52  to the ink supply unit  40 . This can relieve the problem of a temperature rise of the passage unit  20  and therefore a temperature rise of ink contained in the passage unit  20 . 
     The driver ICs  52  are in contact with a plate of the ink supply unit  40  other than the resin plate  43   c , i.e., in contact with the first plate  41  made of a metal. Such an ink supply unit  40  of this embodiment has a larger heat capacity and thus heat of the driver ICs can be dissipated more efficiently, as compared with another structure in which the resin plate  43   c  is contactable with the driver ICs  52 . More specifically, the heat generated by the driver ICs  52  is transferred firstly to the first sheet  41  made of a metal and then to the second sheet  42  made of a metal, too. Through this process the heat is dissipated. 
     Further, since the ink supply unit  40  includes therein the ink filters  43   f , foreign matters such as dust and dirt contained in ink can be removed within the ink supply unit  40  in advance prior to introduction into the passage unit  20 . Consequently, there is less need to provide filters inside ink passages (see  FIG. 6 ) of the passage unit  20 . When no filter is provided in the passage unit  20  as in this embodiment, the plates  21  to  29  constituting the passage unit  20  can be aligned with one another with relative ease. Therefore, the ink-jet head  2  can readily be manufactured, so as to realize an improved manufacture yield and reduced manufacture cost. 
     Still further, the ink supply unit  40  includes the resin plate  43   c  having the filters  43   c  formed therein, and the metal plate  43   a  bonded to one face of the resin plate  43   c . Such a double-layered structure of the metal plate and the resin plate can not only facilitate a formation of the filters  43   f  but also keep good strength of the resin plate  43   c . In addition, the third plate  43  made up of the resin plate  43   c  and the metal plate  43   a  can be laminated with the second plate  42  with more ease. 
     Here, a further modification of the ink-jet head according to the present invention will be described with reference to  FIG. 7 . 
       FIG. 7 , which corresponds to  FIG. 4 , shows a sectioned head main body  102   a  of an ink-jet head according to this modification. The head main body  102   a  of this modification differs from the above-described embodiment mainly in a construction of the ink supply unit and in a position of the driver IC. The other members of the head such as the passage unit  20 , etc., are the same as those of the aforementioned embodiment, and therefore they will be denoted by the common reference numerals and descriptions thereof are omitted. 
     An ink supply unit  80  includes a first plate  81 , a second plate  42 , and a third plate  43 . The first plate  81  has a different configuration from that of the aforementioned embodiment. The second and third plates  42  and  43  are the same as those of the aforementioned embodiment. 
     The first plate  81  comprises a base  82  and two plate-like protrusions  83  and  84 . The base  82  has substantially the same shape as that of the first plate  41  in the aforementioned embodiment, and an ink introduction port  41   a  is formed in the base  82 . Each of the two plate-like protrusions  83  and  84  protrudes vertically upward from an upper face of the base  82 : at each widthwise end of the base  82 . Thus, the ink supply unit  80  has a U-shaped section. 
     Eight ribs  85  are formed on an outer surface of each of the protrusions  83  and  84 . The eight ribs  85  protrude perpendicularly to the outer surface, i.e., in a horizontal direction. One set of four ribs  85  is provided at a predetermined distance from the other set of four ribs  85  in a vertical direction. Between these two sets of four ribs  65 , disposed are a driver IC  52  and a thermal conductive member  88  such as a sponge. The thermal conductive member  88  is connected to the outer surface of each protrusion  83 ,  84 , and the driver IC  52  is connected to an outer surface of the thermal conductive member  88 . An FPC  4 , which is bent at a side of the head main body  2   a  and extends upward therefrom, is connected to an outer surface of the driver IC  52 . 
     Like this, the ink-jet head of this embodiment can more efficiently dissipate heat of the driver ICs  52 , because the thermal conductive members  88  are interposed between the driver ICs  52  and the ink supply unit  80 . More specifically, heat of the driver ICs  52  is transferred firstly to the thermal conductive members  88  and then to the protrusions  83  and  84  of the ink supply unit  80 . Through this process the heat is dissipated. 
     In addition, the ink supply unit  80  has the protrusions  83  and  84 , on which the driver ICs  52  are held. By providing the protrusions  83  and  84  in this manner, the ink supply unit  80  obtains an increased surface area and thus a larger heat capacity. Therefore, heat of the driver ICs  52  can efficiently be dissipated still more. Moreover, the heat of the driver ICs  52  is, prior to being transferred to the base  82 , dissipated in the protrusions  83  and  84  to some extent. Accordingly, a relatively less quantity of heat is transferred to the base  82 , and the second and third plates  42  and  43  located below. This can still better relieve the problem of a temperature rise of the passage unit  20  located further below, and therefore a temperature rise of ink contained in the passage unit  20 . 
     In this modification, particularly, the two protrusions  83  and  84  protrude vertically upward from the widthwise ends of the ink supply unit  80 , so that the ink supply unit  80  has the U-shaped section. The ink supply unit  80  having such a U-shaped configuration can provide the same effects as mentioned above, i.e., improved dissipation of the heat of the driver ICs  52  and prevention of temperature rise of the passage unit  20 . 
     The driver ICs  52  are held between the protrusions  83 ,  84  and the FPCs  4 . As a result, on the ink supply unit  80 , the driver ICs  52  can be held in a stable manner, and at the same time the FPCs  4  can be connected to the driver ICs  52  in a stable manner, as stated in the aforementioned embodiment, too. 
     The formation of the ribs  85  on the protrusions  83  and  84  further increases the surface area of the ink supply unit  80 . Due to this increased surface area, dissipation of heat of the drive ICs  52  improves still more. 
     The number of the protrusions is not limited to two, but one protrusion, and three or more protrusions can be employed. The formation of the protrusions need not always result in the ink supply unit having the U-shaped section. In addition, the protrusions can do without the ribs  85 . 
     The thermal conductive member  88  can be omitted from the above modification. 
     In the aforementioned embodiment and modification, a material for the resin sheet  43   c  is not limited to polyimides, and, e.g., polyester, vinyl chloride and the like are also adoptable. Moreover, a material for the metal sheet  43   a  is not limited to stainless steels, and nickel alloys such as  42  alloy or invar are also adoptable. A material for the first plate  41  or  81  and the second plate  42  is not limited to stainless steels, either, and nickel alloys such as  42  alloy or invar are also adoptable. 
     It is not always required that the third plate  43  has the double-layered structure of the resin plate  43   c  and the metal plate  43   a . The ink filters  43   f  can be omitted from the ink supply unit  40  or  80 . Further, the resin member such as the resin plate  43   c  can also be omitted from the ink supply unit  40  or  80 . 
     In the aforementioned embodiments the first plate  41  is not necessarily thicker than the other plates  42  and  43 . The three plates  41  to  43  may have the same thickness, for example. 
     Although the ink supply unit  40  in the aforementioned embodiment has the layered structure of three plates, a layered structure of two plates or four or more plates may also be acceptable. The ink supply unit is not limited to a layered structure of a plurality of plates, and may be configured as a single member. 
     It is not always necessary that a part of the supply unit  40  or  81  closest to the driver IC  52  is made of a metal. 
     The driver IC  52  may not be held between the ink supply unit  40  or  80  and the FPC  4 , as long as the driver IC  52  is held on the ink supply unit  40  or  80 . 
     The ink passage formed within the ink supply unit and the passage unit may variously be changed. For example, it is possible to form two or more ink introduction ports  41   a , or to shape the ink introduction port  41   a  into square or ellipse. Regions where the filters  43   f  are formed may be changed in accordance with a shape of the ink introduction port  43   b.    
     The number of heads to be included in the printer is not limited to four, and the printer is not limited to a color printer. 
     The present invention is applicable not only to a line-type ink-jet printer that performs printing while conveying a paper relative to the fixed head main body  2   a  as in the aforementioned embodiment, but also to a serial-type ink-jet printer that performs printing while, for example, conveying a paper and at the same time reciprocating the head main body  2   a  perpendicularly to a paper conveyance direction. 
     The application of the present invention is not limited to a printer. The present invention is also applicable, for example, to ink-jet type facsimile machines or copying machines. 
     While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.