Patent Publication Number: US-7585046-B2

Title: Liquid-jet head unit and liquid-jet apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a liquid-jet head unit including a liquid-jet head for injecting a liquid and a liquid-jet apparatus, and particularly relates to an ink jet recording head unit including an ink jet recording head for ejecting ink as the liquid and an ink jet recording device. 
   2. Background art 
   An ink jet recording device, such as an ink jet printer or an ink jet plotter includes an ink jet recording head unit (hereinafter, referred to as a head unit) including an ink jet recording head capable of ejecting, as ink droplets, ink reserved in an ink reservoir portion of an ink cartridge or an ink tank. 
   The head unit includes: an ink jet recording head including nozzle lines, each of which is formed of nozzle orifices arranged in parallel lines; a head case fixed to ink supply ports side of the ink jet recording head; and a cover head protecting an ink-droplet ejecting surface side of the ink jet recording head. 
   Since the head case of the head unit as described above is generally formed of a resin material such as plastic, there is a problem that, due to a difference in linear expansion coefficients between the head case and a single crystal silicon substrate constituting the ink jet recording head, the head case warps due to a temperature change. Particularly when the warpage occurs in a direction, in which the nozzle orifices are arranged in parallel lines, impact positions which ink droplets impact on a recording medium such as a sheet of paper are displaced. Accordingly there is a problem that printing quality is deteriorated. 
   Additionally, since the direction, in which the lines of nozzle orifices are arranged in parallel lines, is generally a longitudinal direction of the ink jet recording head, the ink jet recording head warps in a manner that the nozzle plate side becomes convex in the longitudinal direction. As a result, there is a problem that a nozzle plate and a passage-forming substrate are separated. 
   Furthermore, although the warpage of the ink jet recording head is prevented if the head case is formed of a single crystal silicon substrate or a ceramic which has the same linear expansion coefficient as that of the material of the ink jet recording head, such a material is expensive and there arises a problem that costs are increased. 
   Note that, as a constituting member of an ink jet printer, one using a liquid crystal polymer has been proposed (for example, refer to Japanese Patent Application Laid-open No. 10-86168). 
   However, in the above patent literature, disclosed is only to mold the constituting member with high precision by reducing a mold shrinkage factor of the member in a longitudinal direction. 
   SUMMARY OF THE INVENTION 
   In consideration of the above described situations, a problem of the present invention is to provide a liquid-jet head and a liquid-jet apparatus which are respectively capable of enhancing printing quality by reducing warpage of heads thereof, and for which costs are reduced. 
   A first aspect of the present invention for solving the above problem is a liquid-jet head unit characterized by including: a liquid-jet head in which nozzle orifices for injecting ink droplets are arranged in parallel to each other; and a head case fixed to the liquid-jet head. The liquid-jet head unit is characterized in that a linear expansion coefficient of the head case in a reference direction, which is a direction in which the nozzle orifices are arranged in parallel lines, is set less than a linear expansion coefficient thereof in a direction orthogonal to the reference direction. 
   In the first aspect, the liquid-jet head unit becomes possible to reduce warpage in the direction in which the nozzle orifices are arranged in parallel lines, whereby printing quality of the head unit can be enhanced. 
   A second aspect of the present invention is the liquid-jet head unit in the first aspect, which is characterized in that: the reference direction of the head case is a longitudinal direction of the liquid-jet head. 
   In the second aspect, by reducing warpage of the liquid-jet head unit in the longitudinal direction, it is possible to reliably prevent separation between a nozzle plate on which nozzle orifices are provided, and a passage-forming substrate on which pressure generating chambers are formed. 
   A third aspect of the present invention is the liquid-jet head unit in the first or second aspect, which is characterized in that the head case is formed of a liquid crystal polymer. 
   In the third aspect, while reducing warpage of the liquid-jet head unit in the direction in which the nozzle orifices are arranged in parallel lines, it is possible to reduce a cost for the head unit. 
   A fourth aspect of the present invention is the liquid-jet head unit in any one of the first to third aspects, which is characterized in that the liquid-jet head includes a passage-forming substrate formed of a single crystal silicon substrate. On the passage-forming substrate, pressure generating chambers communicating with the respective nozzle orifices are respectively formed in divisions, and the head case is fixed to the passage-forming substrate. 
   In the fourth aspect, it is possible to prevent warpage and destruction of the passage-forming substrate formed of the single crystal silicon substrate. 
   A fifth aspect of the present invention is the liquid-jet head unit in the fourth aspect, which is characterized in that the head case is fixed to the passage-forming substrate with a protective plate, which is connected to the passage-forming substrate, interposed in between the head case and the passage-forming substrate. The protective plate is formed of a material having a linear expansion coefficient substantially equal to a linear expansion coefficient of the passage-forming substrate. 
   In the fifth aspect, it is possible to reduce warpage of the passage-forming substrate and of the protective plate and to prevent separation between the passage-forming substrate and the protective plate. Thereby, printing quality of the head unit can be enhanced. 
   A sixth aspect of the present invention is the liquid-jet head unit in any one of the first to fifth aspects, which is characterized in that the head case is molded in order that the reference direction can be an injection flow direction. 
   In the sixth aspect, it becomes possible to easily mold the head case having a predetermined linear expansion coefficient. 
   A seventh aspect of the present invention is a liquid-jet apparatus characterized by including the liquid-jet head in any one of the first to sixth aspects. 
   In the seventh aspect, it is possible to realize a liquid-jet apparatus enhanced in printing quality. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of a head unit according to Embodiment 1. 
       FIG. 2  is an assembled perspective view of the head unit according to Embodiment 1. 
       FIG. 3  is a cross-sectional view of a main part of the head unit according to Embodiment 1. 
       FIG. 4  is an exploded perspective view of a main part of the head unit according to Embodiment 1. 
       FIG. 5  is a cross-sectional view of a head case and a recording head according to Embodiment 1. 
       FIG. 6  is a schematic view of an ink jet recording device according to Embodiment 1. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinbelow, the present invention will be described in detail based on embodiments. 
   Embodiment 1 
     FIG. 1  is an exploded perspective view of an ink jet recording head unit according to Embodiment 1 of the present invention,  FIG. 2  is an assembled perspective view of the ink jet recording head, and  FIG. 3  is a cross-sectional view of a main part of the ink jet recording head. As illustrated in  FIG. 1 , a cartridge case  201 , which is a holding member constituting an ink jet recoding head unit  200  (herein after, referred to as the head unit  200 ), includes cartridge mounting portions  211  on which ink cartridges (not illustrated) are respectively mounted. For example, in this embodiment, the ink cartridges are constituted respectively of separate components filled with black ink and color ink of three colors, and the respective cartridges of the black and color ink are mounted on a cartridge case  210 . On a bottom surface of the cartridge case  210 , a plurality of ink communicating paths  212  are provided as shown in  FIG. 3 . One end of each of the communicating paths  212  opens to each of the cartridge mounting portions  211 , and the other end thereof opens to a head case described later. Furthermore, ink supply needles  213  are fixed respectively to opening portions of the respective ink communicating paths  212  of the cartridge mounting portions  211 , with filters (not illustrated) respectively interposed between the ink supply needle  213  and the opening portion. Each of the ink supply needles  213  is inserted into an ink supply port of one of the ink cartridge. Each of the filters is formed in the ink communicating paths  212  in order to remove foams and foreign materials in ink. 
   The cartridge case  210  as described above includes, on the bottom surface thereof, head cases  230  to each of which an ink jet recording head  220  is fixed on an end face thereof not facing the cartridge case  210 . Each of the ink jet recording head  220  includes a plurality of piezoelectric elements  300  and ejects ink droplets from nozzle orifices  21  by driving the piezoelectric elements  300 . In this embodiment, a plurality of the ink jet recording heads  220  for ejecting ink of each of color in the ink cartridges is provided in such a manner that the ink jet recording heads  220  correspond to the respective colors of ink, and also, a plurality of the head cases  230  are provided independently from one another in such a manner that the head cases  230  correspond to the respective ink jet recording heads  220 . 
   Here, descriptions will be given of the ink jet recording heads  220  and the head cases  230  of this embodiment which are mounted on the cartridge case  210 .  FIG. 4  is an exploded perspective view of the ink jet recording head and the head case.  FIG. 5  is a cross-sectional view of the recording head and the head case. As illustrated in the  FIGS. 4 and 5 , a passage-forming substrate  10  constituting the ink jet recording head  220  is formed of a single crystal silicon substrate whose linear expansion coefficient is 2.6 (10 −6 /° C.). Additionally, on one side surface of the passage-forming substrate  10 , there is formed an elastic film  50  formed of silicon dioxide previously obtained through thermal oxidation. On the passage-forming substrate  10 , by applying anisotropic etching thereto from the other side surface thereof, two lines of pressure generating chambers  12  divided by a plurality of compartment walls are formed in parallel to each other in a width direction thereof. Furthermore, in a region outward from each of the lines of the pressure generating chambers  12  in a longitudinal direction thereof, a communicating portion  13  is formed. By communicating with a reservoir portion  31  provided on a protective plate  30  described later, the communicating portion  13  constitutes a part of a reservoir  100  serving as a common ink chamber of the respective pressure generating chambers  12 . The communicating portion  13  is communicated with one edge portion of each of the pressure generating chambers  12  in the longitudinal direction thereof, through ink supply paths  14 . 
   Additionally, on an opening-surface side of the passage-forming substrate  10 , a nozzle plate  20 , to which nozzle orifices  21  are provided as through holes, is fixed with an adhesive agent or a thermal welding film. Each of the nozzle orifices  21  communicates with one of the respective pressure generating chambers  12  in a side thereof opposite a side where the one pressure generating chamber  12  communicates with the ink supply path  14 . That is, in this embodiment, two nozzle lines  21 , in which the nozzle orifices  21  are arranged in parallel to each other, are provided in each of the ink jet recording heads. Note that, the nozzle plate  20  is formed of a piece of glass ceramic, a single crystal silicon substrate, stainless steel or the like which has a thickness, for example, from 0.01 to 1 mm and a coefficient of linear expansion from 2.5 to 4.5 (10 −6 /° C.) under a temperature not more than 300° C. 
   On the other hand, on a side opposite the opening-surface of the passage-forming substrate  10 , on the elastic film  50 , piezoelectric elements  300  are formed by sequentially laminating a lower electrode film formed of metal, a piezoelectric layer formed of lead zirconate titanate (PZT) or the like, and an upper electrode film formed of metal. A protective plate  30 , which includes the reservoir portion  31  constituting at least a part of a reservoir  100 , is connected to the passage-forming substrate  10  on which the above described piezoelectric elements  300  are formed. This reservoir portion  31  penetrates through the protective plate  30  in a thickness direction, and is formed across in a width direction of the pressure generating chamber  12 . By communicating with the communicating portion  13  of the passage-forming substrate  10  as described above, the reservoir portion  31  constitutes the reservoir  100  serving as the common ink chamber of the respective pressure generating chambers  12 . 
   On a region of the protective plate  30  facing each of the piezoelectric elements  300 , there is provided a piezoelectric element holding portion  32  including a space, which is large only to the extent that it does not disturb movements of the piezoelectric elements  300 . As materials for the protective plate  30  as described above, glass, ceramic, a metal, plastic or the like can be cited, and it is preferable to use a material having a thermal expansion coefficient substantially equal to that of the passage-forming substrate  10 . In this embodiment, the protective plate  30  is formed of a single crystal silicon substrate, which is the same material as that of the passage-forming substrate  10 . 
   Furthermore, on the protective plate  30 , driver ICs  110  for driving the respective piezoelectric elements  300  are provided. Each terminal of the driver ICs  110  are respectively connected, through bonding wires or the like not illustrated, to lead wiring lines drawn out from an individual electrode of the respective piezoelectric elements  300 . Additionally, as shown in  FIG. 1 , the respective terminals of the driver ICs  110  are connected to an outside through an external wiring  111  formed of a flexible print cable (FPC) or the like, whereby the respective terminals are configured to receive various signals such as a print signal from the outside through the external wiring  111 . 
   Additionally, a compliance plate  40  is connected to the protective plate  30 . On the compliance plate  40 , in a region facing the reservoir  100 , an ink introducing port  44  for supplying ink to the reservoir  100  is formed in such a manner that the ink introducing port  44  penetrates the compliance plate  40  in a thickness direction thereof. On the other hand, on the compliance plate  40 , a region other than the ink introducing port  44  in the region facing the reservoir  100  is a flexible portion  43  formed thinly in a thickness direction, and the reservoir  100  is sealed by the flexible portion  43 . Compliance is given to an interior of the reservoir  100  by the flexible portion  43 . 
   As described above, the ink jet recording head  220  of this embodiment is constituted of four substrates which are the nozzle plate  20 , the passage-forming substrate  10 , the protective plate  30 , and the compliance plate  40 . A head case  230  is fixed onto the compliance plate  40  of the above described ink jet recording head  220 . In the head case  230 , ink communicating paths  231  are provided. The ink communication paths  231  supply ink from the cartridge case  210  to the respective ink introducing ports  44  in a configuration where the respective ink communication paths  231  communicate with the ink introducing ports  44  while communicating with the ink communicating paths  212  of the cartridge case  210 . On this head case  230 , a concave portion  232  is formed in a region facing each of the flexible portions  43 , whereby the flexible portions  43  can undergo flexure deformation as appropriate. Additionally, on the head case  230 , in a region facing the driver ICs  110  provided on the protective plate  30 , there is provided a driver IC holding portion  233  penetrating the head case  230  in a thickness direction thereof. The external wiring  111  is connected to the driver ICs  110  in such a manner that the external wiring  111  is inserted into and led through the driver IC holding portion  233 . 
   A linear expansion coefficient of the above described head case  230  in a reference direction, which is a direction in which nozzle orifices  21  are arranged in parallel lines, is set to be less than a linear expansion coefficient thereof in a direction orthogonal to the reference direction. Additionally, it is preferable that the linear expansion coefficient of the head case  230  in the reference direction be set to be nearly equal to each of linear expansion coefficients of the passage-forming substrate  10  formed of a single crystal silicon substrate and of the protective plate  30 , the linear expansion coefficient being 2.6 (10 −6 /° C.) in this embodiment. As a material for the above described head case  230 , a liquid crystal polymer can be used. Note that, in a case where a liquid crystal polymer is used to form the head case  230 , when the head case  230  is formed by molding, the linear expansion coefficient of the head case  230  in the reference direction can be set to be less than the linear expansion coefficient thereof in the direction orthogonal to the reference direction by setting the injection flow direction as the reference direction. 
   Here, linear expansion coefficients of representative liquid crystal polymers are shown in Table  1  presented below. Note that, in Table  1  presented below, grades of the respective liquid crystal polymers are indicated in product names manufactured by Polyplastics Co., Ltd. 
   
     
       
         
             
             
             
             
           
             
                 
               TABLE 1 
             
             
                 
                 
             
             
                 
                 
                 
               Linear expansion 
             
             
                 
               Raw material 
                 
               coefficient (at room 
             
             
                 
               and grade 
               Direction 
               temperature) 
             
             
                 
                 
             
           
          
             
                 
               VECTRA A150B 
               Reference 
               1.8 × 10 −6   
             
             
                 
                 
               direction 
             
             
                 
                 
               Direction 
               46 × 10 −6   
             
             
                 
                 
               orthogonal to 
             
             
                 
                 
               reference 
             
             
                 
                 
               direction 
             
             
                 
               VECTRA A230 
               Reference 
               2.0 × 10 −6   
             
             
                 
                 
               direction 
             
             
                 
                 
               Direction 
               48 × 10 −6   
             
             
                 
                 
               orthogonal to 
             
             
                 
                 
               reference 
             
             
                 
                 
               direction 
             
             
                 
               VECTRA B230 
               Reference 
               0 
             
             
                 
                 
               direction 
             
             
                 
                 
               Direction 
               32 × 10 −6   
             
             
                 
                 
               orthogonal to 
             
             
                 
                 
               reference 
             
             
                 
                 
               direction 
             
             
                 
               VECTRA A410 
               Reference 
                7 × 10 −6   
             
             
                 
                 
               direction 
             
             
                 
                 
               Direction 
               42 × 10 −6   
             
             
                 
                 
               orthogonal to 
             
             
                 
                 
               reference 
             
             
                 
                 
               direction 
             
             
                 
                 
             
          
         
       
     
   
   Each of the liquid crystal polymers shown in Table 1 is usable as a material for the head case  230  of the present invention. For the head case  230  of the present invention, use of any one of VECTRA A150B, VECTRA A230 and VECTRA B230 is particularly favorable. 
   As described above, it is possible to prevent warpage from occurring due to a temperature change in the reference direction of the ink jet recording head  220  which is a direction along the parallel lines of nozzle orifices  21  by setting the linear expansion-coefficient of the head case  230  in the reference direction to be less than a linear expansion coefficient thereof in a direction orthogonal to the reference direction, and also to be substantially equal to a linear expansion coefficient of the ink jet recording head  220  to which the head case  230  is fixed. The linear expansion coefficient of the ink jet recording head  220  is, in other words, each of linear expansion coefficients of the passage-forming substrate  10  and of the protective plate  30 . From this, impact positions of ink droplets are prevented from being displaced, and hence it is possible to enhance printing quality. Additionally, in order to set the linear expansion coefficient of the head case  230  to be substantially equal to each of linear expansion coefficients of the passage-forming substrate  10  and of the protective plate  30  which constitute the ink jet recording head, by using a liquid crystal polymer for the head case  230 , it is not necessary to use therefore a single crystal silicon substrate which is the same material as that of the passage-forming substrate  10  and of the protective plate  30 . Thereby, cost reduction is realized. 
   Furthermore, in this embodiment, the reference direction, in which the linear expansion coefficient of the head case  230  is small, is identical with a longitudinal direction of the ink jet recording head  220 . Thereby, the head case  230  prevents warpage of the ink jet recording head  220  in the longitudinal direction. By thus preventing the warpage of the ink jet recording head  220  in the longitudinal direction, it is possible to reliably prevent separation of adhesion between the passage-forming substrate  10  and the nozzle plate  20 . Note that, although the linear expansion coefficient of the head case  230  in the direction orthogonal to the reference direction is different from the linear expansion coefficients of the passage-forming substrate  10  and of the protective plate  30 , an influence from warpage is reduced to a minimum because the direction orthogonal to the reference direction is a non-longitudinal direction of the ink jet recording head  220 . 
   The ink jet recording head  220  of this embodiment as described above introduces ink, which has come out from the ink cartridge, from each of the ink introducing ports  44  through the ink communicating path  212  and the ink supply communicating path  231 , and fills interiors from the reservoir  100  to the nozzle orifice  21  with the ink. Afterwards, in accordance with recording signals from the driver IC  110 , a voltage is applied to the respective piezoelectric elements  300  corresponding to the pressure generating chambers  12 , whereby the elastic film  50  and the piezoelectric elements  300  undergoes flexure deformation. As a result, pressure in the respective pressure generating chambers  12  is increased, whereby ink droplets are ejected through the nozzle orifice  21 . 
   To the respective members constituting the above described ink jet recording head  220  and to the head case  230 , pin insertion holes  234  are provided in two corner portions of each of the members and of the head case  230 . The pin insertion holes  234  are used for aligning the respective members when the members are assembled. Then, while the members are being aligned relatively to each other by having pins inserted into the pin insertion holes  234 , members are joined. Thereby, the ink jet recording head  220  and the head case  230  are formed integrally. 
   Note that the above described ink jet recording head  220  is formed as the ink jet recording head  220  in the following manner. A large number of chips are formed on a silicon wafer simultaneously, and the nozzle plate  20  and the compliance plate  40  are adhered and integrated. Then, the integrated body is divided into the respective passage-forming substrates  10 , each of which is one-chip size as shown in  FIG. 1 , and then the ink jet recording head  220  is formed. 
   Four sets of the ink jet recording head  220  and the head case  230  as described above are fixed onto the above described cartridge case  210  at predetermined intervals in a direction along which the nozzle lines  21 A are arranged. That is, the eight nozzle lines  21 A are provided in the head unit  200  of this embodiment. In the case where the number of the nozzle lines  21 A formed of the nozzle orifices  21  arranged in parallel to each other is thus increased by using the plurality of ink jet recording heads  220 , it is possible to prevent reduction in yield as compared with a case where a number of the nozzle lines  21  is formed in the single ink jet recording head  220 . Additionally, by using the plurality of ink jet recording heads  220  in order to increase the number of the nozzle lines  21 , it is possible to increase an available number of the ink jet recording heads  220  formed from one silicon wafer can be increased. Thereby, waste regions of the silicon wafer are reduced, and a manufacturing cost for the ink jet recording head  220  is reduced. 
   As shown in  FIGS. 1 and 2 , the four ink jet recording heads  220 , each of which is held by the cartridge case  210  with the head case  230  interposed therebetween, are held in a manner that the four ink jet recording heads  220  are aligned relatively to each other by the cover head  240  having a box shape so as to cover the four inkjet recording heads  220 . The cover head  240  includes: an exposure opening portion  241  for exposing the nozzle orifices  21 ; and a joint portion  242 . While dividing the exposure opening portions  241 , the joint portion  242  is connected to at least both edge portions the nozzle lines  21 A of the nozzle orifices  21  arranged in parallel to each other in an ink-droplet ejecting surface of the ink jet recording heads  220 . 
   The joint portion  242  is constituted of a frame portion  243  and beam portions  244 . The frame portion  243  is provided along the perimeter of the ink-droplet ejecting surface across the plurality of ink jet recording heads  220 . Each of the beam portions  244  is provided so as to extend between adjacent ones of the ink jet recording heads  220  and divides each of the exposure opening portions  241 . The frame portion  243  and the beam portions  244  are connected to the ink-droplet ejecting surface of the ink jet recording heads  220 . Additionally, the frame portion  243  of the joint portion  242  is formed so as to cover the pin insertion holes  234  for aligning the respective members thereof when the ink jet recording head  220  is manufactured. Moreover, in the cover head  240 , a sidewall portion  245  is provided toward side surfaces of the ink-droplet ejecting surface in a manner that the sidewall portion  245  extends so as to bend across the outer peripheral portion of the ink-droplet ejecting surface. 
   As described above, the cover head  240  is configured to have the joint portion  242  adhered to the ink-droplet ejecting surface of the ink jet recording head  220 . Thereby, it is possible to reduce a step height between the ink-droplet ejecting surface and the cover head  240 , and as a result, it is possible to prevent ink from remaining on the ink-droplet ejecting surface even when a wiping or an aspirating operation is performed on the ink-droplet ejecting surface. Additionally, since regions between each of the adjacent ink jet recording heads  220  are covered with the beam portions  244 , ink cannot intrude between the adjacent ink jet recording heads  220 , whereby it is possible to prevent deterioration and destruction of the piezoelectric elements  300  and the driver ICs  110 , the deterioration and destruction being caused by ink. Moreover, since an interface between the ink-droplet ejecting surface of the ink jet recording heads  220  and the cover head  240  is adhered by use of an adhesive agent without leaving any clearance therebetween, a recorded medium is prevented from entering in a clearance therebetween, whereby it is possible to prevent deformation of the cover head  240 , and paper jams. Furthermore, by having the sidewall portion  245  cover the outer peripheral portion of the plurality of ink jet recording heads  220 , it is possible to reliably prevent ink from flowing around to side surfaces of the ink jet recording heads  220 . In addition, because the joint portion  242  connected to the ink-droplet ejecting surface of the ink jet recording heads  220  is configured to be provided to the cover head  240 , it is possible to perform the junction between the ink-droplet ejecting surface and the cover head  240  in such a manner that the respective nozzle lines  21 A of the plurality of ink recording heads  220  are aligned with high precision to the cover head  240 . 
   As a material for the cover head  240 , for example, a metal material such as stainless steal can be cited. The metal plate therefore may be formed through press working, or may be formed through molding. Additionally, by forming the cover head  240  from a conductive metal material, the cover head  240  can be connected to ground. Note that the junction between the cover head  240  and the nozzle plate  20  is not particularly limited, and the junction may be performed through adhesion using, for example, a thermosetting epoxy adhesive agent, or an ultraviolet curing adhesive agent. 
   Additionally, to the joint portion  242 , flange portions  246  each provided with a fixing hole  247  used to align and fix the cover head  240  to another member. These flange portions  246  are provided in a manner bending from the sidewall portion  245  so as to protrude in the same direction as a plane direction of the ink-droplet ejecting side. In this embodiment, as shown in  FIGS. 2 and 3 , the cover head  240  is fixed to the cartridge case  210  which is a holding member holding the ink jet recording heads  220  and the head cases  230 . In detail, as shown in  FIGS. 2 and 3 , projections  215 , which project toward the ink-droplet ejecting side and are inserted into the respective fixing holes  247  of the cover head  240 , are provided to the cartridge case  210 , and the cover head  240  is fixed to the cartridge case  210  by heating the extremities of the projections  215  to caulk the fixing holes  247  of the flange portions  246  while inserting the projections  215  into the fixing holes  247  of the cover head  240 . By allowing the respective projections  215 , which are provided to the cartridge case  210  as described above, to have an outer diameter smaller than a diameter of the respective fixing holes  247 , the cover head  240  can be fixed to the cartridge case  210  in a manner that the cover head  240  is aligned in the plane direction of the ink-droplet ejecting surface. 
   The head unit  200  as described above is mounted on an ink jet recording device.  FIG. 6  is a schematic view showing an example of the ink jet recording device. As shown in  FIG. 6 , to the head unit  200  including an ink jet recording head, cartridges  1 A and  1 B constituting ink supply means are provided in manner that the cartridges  1 A and  1 B are freely detachable from the head unit  200 . A carriage  3 , on which the head unit  200  is mounted, is provided to a carriage axis  5  fixed to a device body  4  in a manner that the carriage  3  is freely movable in an axial direction. The head units  200  are configured to eject a black-ink composition and color-ink compositions, respectively. 
   Additionally, driving force of a driving motor  6  is transferred to the carriage  3  through a plurality of gears not illustrated and a timing belt  7 , and thereby the carriage  3 , on which the head unit  200  is mounted, is moved along the carriage axis  5 . On the other hand, a platen  8  is provided along the carriage axis  5  in the device body  4 , and a recording sheet S, which is a recording medium such as a sheet of paper fed by a feeding roller not illustrated, is conveyed on the platen  8 . 
   Another Embodiment 
   Although Embodiment 1 of the present invention has been described hereinabove, the present invention is not limited to the above described embodiment. For example, although in above described Embodiment 1, the head cases  230  are fixed respectively to the plurality of ink jet recording heads  220 , the present invention is not particularly limited to this. For example, the plurality of ink jet recording heads  220  may be fixed to a single head case. 
   Additionally, although in above described Embodiment 1, the head case  230  is fixed onto the passage-forming substrate  10  of the ink jet recording head  220  with the protective plate  30  interposed therebetween, the present invention is not particularly limited to this. For example, the head case  230  may be fixed directly onto the passage-forming substrate  10 . In other words, fixing of the head case  230  to the passage-forming substrate  10  in the present invention means the fixing of the head case  230  directly, or with another member such as the protective plate  30  interposed in between, to passage-forming substrate  10 . In any case, it is possible to reduce warpage of the ink jet recording head by using the head case  230  having a predetermined linear expansion coefficient. 
   Furthermore, although the ink jet recording head  220  of a flexure vibration mode is given as an example in above described Embodiment 1, the present invention is not limited to this. It is needless to say that the present invention can be applicable to a head unit having an ink jet recording head of various structures, such as an ink jet recording head of a longitudinal vibration mode or an ink jet recording head causing ink droplets to be ejected by bubbles generated by heat generation of heat generating elements or the like. In the ink jet recording head of a longitudinal vibration mode, piezoelectric elements and electrode forming materials are alternately laminated and are caused to expand and contract in an axial direction. 
   Note that, although the head unit and the ink jet recording device each including, as a liquid-jet head, an ink jet recording head ejecting ink have been described as an example, the present invention is broadly aimed for liquid-jet head units and liquid-jet apparatuses each including a liquid-jet head in general. As other liquid-jet heads, there can be cited for example: a recording head used in image recording apparatuses such as a printer; a coloring material injection head used for producing color filters for liquid crystal displays; an electrode material injection head used for forming electrodes for organic EL displays, a FED (field emission display) or the like; and a bio-organic material injection head used for producing bio-chips.