Abstract:
Disclosed is an ink jet head exhibiting good assemblability while protecting an electrode portion. An ink jet head ( 10 ) comprising a head chip ( 2 ) including drive walls ( 22 ) and channels ( 23 ) juxtaposed alternately with a drive electrode ( 25 ) being formed on the drive wall ( 22 ), and a nozzle plate ( 24 ) wherein a connection electrode is formed on the rear surface of the head chip ( 2 ), a wiring board ( 3 ) on which an electrode portion ( 32 ) is formed is bonded to project from the head chip ( 2 ), and ink in the channel ( 23 ) is ejected by causing shear deformation of the drive wall ( 22 ) is further provided with a holding member ( 5 ) disposed at a position covering the electrode portion ( 32 ) and holding a portion ( 31 ) of the wiring board ( 3 ) projecting from the head chip ( 2 ), and an electrode portion protection member ( 4 ) bonded between the holding member ( 5 ) and the electrode portion ( 32 ) using adhesive and having a thickness in the range of 0.01-0.5 mm at a part covering the electrode portion ( 32 ).

Description:
This application is the United States national phase application of International Application PCT/JP2009/052761 filed Feb. 18, 2009. 
     TECHNICAL FIELD 
     The present invention relates to an ink jet head, and specifically to an ink jet head having a structure for protecting an electrical connecting section in a head chip. 
     BACKGROUND TECHNOLOGY 
     Regarding an ink jet head installed in an ink jet printer, an ink jet head is conventionally known where a piezoelectric element is provided to each nozzle for ejecting ink, and by making shear deformation of this piezoelectric element an ink is ejected from the each nozzle. 
     As one type of head chip to be used in this kind of ink jet head, a head chip in which drive walls and channels are juxtaposed alternately is commonly known. 
     In this type of head chip a drive electrode is formed for each channel, and a connection electrode for connecting with the drive electrode is formed on an upper surface of the head chip. On the upper surface of the head chip, a wiring board which is formed with an electrode portion corresponding to the connection electrode is bonded such that the connection electrode and the electrode portion are electrically connected (for example, refer to Patent Document 1). 
     By making the head chip to have this type of structure, an ink jet head can be realized that is easy for manufacturing process, easy for connecting the drive electrode with an external wiring, and compact to lower the cost.
     Patent Document 1: Unexamined Japanese Patent Application Publication No. 2006-82396.   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In this type of the head chip, since the electrode portion formed at the wiring board tends to be easily peeled off or broken away, it is necessary to take a measure for preventing a stress on the electrode portion. 
     In particular, in cases where the electrode portion is formed on the wiring board made of a ceramic by aluminum evaporation and the like, strength of bonding between the electrode portion and the wiring board body is weak such that the electrode portion may be peeled off by a small deformation, thus the electrode portion needs to be protected. 
     However in cases of adopting the head chip of the above described structure, since the distance between the electrode portion and other member adjacent to the electrode portion is extremely small, if it is tried to make the gap between the electrode portion and the other member in order to prevent the stress being applied to the electrode portion, an assembling work may become very difficult. 
     Further, in a case of trying to coat a filling material for protecting the electrode portion, the problem arises that it is very difficult to coat the filling material thinly and without generating pinholes and the like in a small gap between the electrode portion and the other member. 
     In view of the above described points, objectives of the present invention is to provide an ink jet head of easy assembling in addition to protecting the electrode portion of the wiring board. 
     Means to Solve the Problems 
     In order to solve the above described problems, an ink jet head described in claim  1  is provided with: a head chip including a drive wall and a channel juxtaposed alternately, an outlet and an inlet of the channel arranged respectively at a front surface and a rear surface of the chip, and a drive electrode formed on the drive wall; a nozzle plate provided with a nozzle for ejecting ink, at a corresponding position to the channel on the front surface of the head chip; a connection electrode to electrically connect to the drive electrode, formed on the rear surface of the head chip; and wiring board on which an electrode portion is formed for applying a voltage from a drive circuit to the drive electrode via the connection electrode, the wiring board being bonded to project from the head chip in a direction perpendicular to a channel array direction; wherein the ink jet head ejects the ink in the channel from the nozzle by applying the voltage to the drive electrode and causing a shear deformation on the drive wall, 
     the ink jet head characterizing in further comprising a holding member disposed at a position covering the electrode portion and holds a portion of the wiring board projecting from the head chip; and an electrode portion protection member bonded between the holding member and the electrode portion by using adhesive, and having a thickness in the range of 0.01-0.5 mm at a part covering the electrode portion. 
     The ink jet head described in claim  2  is the ink jet head described in claim  1 , wherein the electrode portion protection member is made of polytetrafluoroethylene or polyolefin. 
     The ink jet head described in claim  3  is the ink jet head described in claim  1  or  2 , wherein the drive wall is made of a ceramic comprising leadzilconatetitanate. 
     The ink jet head described in claim  4  is the ink jet head described in any one of claims  1 - 3 , wherein the adhesive is an epoxy type adhesive. 
     The ink jet head described in claim  4  is the ink jet head described in any one of claims  1 - 4 , further including a cap member disposed in a periphery of an ink ejection surface of the nozzle plate, wherein the holding member is provided between the cap member and the electrode portion. 
     Effect of the Invention 
     According to the invention described in claim  1 ,  3 ,  4 , or  5 , in an ink jet head having a very small gap between the electrode portion and the other member adjacent to the electrode portion, by disposing the electrode portion protection member in the gap between the electrode portion and the other member adjacent to the electrode portion, the electrode portion protection member may be peeled off instead of the electrode portion in case of a stress being applied to the electrode portion. Due to this, the broken away of the electrode portion is protected, and generation of disconnection in wiring can be prevented. Namely, the electrode portion can be protected. 
     According to the invention described in claim  2 , since the electrode potion protection member is made of polytetrafluoroethylene or polyolefin, an adhesion force of the electrode potion protection member is weak. Therefore, the electrode portion protection member may be firstly peeled off instead of the electrode portion in case of a stress being applied to the electrode portion. Due to this, the separation of the electrode portion is protected, and breakage of wiring can be prevented. Namely, the electrode portion can be protected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing a total structure of the ink jet head relating to the present embodiment. 
         FIG. 2  is an exploded perspective view of the inkjet head shown in  FIG. 1 . 
         FIG. 3  is a section view of the inkjet head shown in  FIG. 1 . 
         FIG. 4  is an exploded perspective view showing a structure of main part of the inkjet head shown in  FIG. 1 . 
         FIG. 5  is an exploded perspective view of the head chip relating to the present embodiment. 
       EXPLANATION OF SIGNS 
       
           
           
             
                 1 : flexible substrate 
                 11 : bending portion 
                 2 : head chip 
                 21 : substrate 
                 22 : drive wall 
                 23 : channel 
                 24 : nozzle plate 
                 25 : drive electrode 
                 3 : wiring board 
                 31 : projection portion 
                 32 : electrode portion 
                 33 : opening 
                 4 : electrode portion protection member 
                 41 : opening 
                 5 : holding member 
                 51 : opening 
                 52 : bottom plate 
                 53 : side wall 
                 6 : radiator plate 
                 7 : cap member 
                 71 : opening 
                 8 : manifold 
                 81 : flow path connection section 
                 10 : ink jet head 
                 20 : chassis 
             
           
         
      
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, embodiments of the ink jet head relating to the present embodiment will be described, however the scope of invention is not restricted with illustrated examples. 
       FIG. 1  shows a perspective view showing an external appearance of the ink jet head relating to the present embodiment,  FIG. 2  is an exploded perspective view of the inkjet head shown in  FIG. 1  and  FIG. 3  is a section view of the inkjet head taken on line III-III of  FIG. 1 .  FIG. 4  is an exploded perspective view showing a structure of main part of the ink jet head shown in  FIG. 1 . Wherein, XYZ axis common to all the above figures is shown in each figure. As shown in  FIG. 1  through  FIG. 3 , ink jet head  10  has a chassis  20  open in upper and bottom surfaces. As shown in  FIG. 3 , inside of chassis  20  assembled and arranged are flexible substrates  1 ,  1 , head chip  2 , wiring board  3 , electrode portion protection member  4 , holding member  5 , radiator plate  6 , cap member  7 , manifold  8 , etc., and cap member is provided on the bottom surface of chassis  20 . 
     Among them, flexible substrates  1 ,  1  are formed of plane substrates as shown in  FIG. 2 , and arranged with a prescribed distance with each other. On each of flexible substrates  1 ,  1  an unillustrated drive circuit and the like are mounted. Further, on the lower end portions of the flexible substrates  1 ,  1 , bent portions  11 ,  11  are provided to be faced as oppositely bent, and on the upper surface of the bent portions  11 ,  11 , wiring board  3  (described later) is provided. And, in a space formed with a pair of flexible substrates  1 ,  1  and an upper surface of wiring board  3 , manifold  8  (to be described later) is provided. Further, the upper end portions of flexible substrates  1 ,  1 , are projected upward from the upper surface of chassis  20 . 
     Head chip  2  has a structure where drive wall  22  and channel  23  are alternately arranged between two substrates  21 ,  21  as shown in  FIG. 5 . On the bottom surface (front surface) of head chip  2 , provided is nozzle plate  24  in which an ink ejection hole is arranged at a position corresponding to each channel  23 . 
     Here, drive wall  22  is formed of a piezoelectric element which generates a deformation by applying a voltage. Commonly known materials can be utilized as a piezoelectric material, while lead zirconate titanate (PZT) is preferable. 
     On an inner wall of each channel  23  drive electrode  25 , which being a metal layer independent for each channel  23 , is formed, and drive electrode  25  is electrically connected to an unillustrated connecting electrode formed on the upper surface of head chip  2  (a surface facing to wiring board  3 ) for each channel  23 . 
     Further, on the upper surface (rear surface) of head chip  2 , wiring board  3 , which being connected to the above described flexible substrate  1 ,  1 , is bonded. 
     Wiring board  3  is formed with larger longitudinal and width sizes compared to those of head chip  2 , and has projection portion  31  which is protruded from head chip  2  in a bonded state with head chip  2 . 
     On lower surface of wiring board  3  (the surface facing to head chip  2 ), electrode portions  32  are formed with the same number and same pitch as the connecting electrodes. Electrode portion  32  is connected to the connecting electrode when wiring board  3  is attached to head chip  2 . Thus, electrode portion  32  is connected to drive electrode  25  through the connection electrode. 
     Further, on wiring board  3 , a rectangular opening  33  is formed being elongated in the longitudinal direction (X direction). Opening  33  is formed to be a size such that every opening of channel  23  is able to be exposed. While, since opening  33  is made to have a smaller surface area than the surface area of head chip  2 , in the case of attaching wiring board  3  onto head chip  2 , head chip  2  is surely prevented from passing through wiring board  3 . Therefore, in the case of bonding wiring board  3  onto head chip  2 , wiring board  3  does not block off the opening of channel  23  while contacting substrates  21 ,  21 . 
     Wiring board  3  is formed of plastics or glass and the like having low coefficient of thermal expansion. As wiring board  3 , ceramics such as non-polarized PZT or AIN can be used. Further, in order to prevent the generation of deformation in head chip  2  caused by difference of thermal expansion, materials having the difference of thermal expansion coefficient of ±1 ppm or less can be preferably utilized wiring board  3 . 
     At the position where electrode portion  32  is formed on projection portion  31 , bending portions  11 ,  11  are attached, thus electrode portion  32  of wiring board  3  and the drive circuit of flexible substrates  1 ,  1  are electrically connected. Thus, signals from the drive circuit of flexible substrates  1 ,  1  are enabled to be applied onto drive electrode  25  on the inner wall of each channel  23  in head chip  2  through bending portions  11 ,  11  and electrode portion  32  of flexible substrates  1 ,  1 . 
     Further, in the under side of projection portion  31 , electrode portion protection member  4  is provided as shown in  FIG. 4 . 
     Electrode portion protection member  4  has opening  41  with the same size as head chip  2 , and head chip  2  is inserted in opening  41 . In this case, the upper surface of electrode portion protection member  4  covers electrode section  32  of wiring board  3  via bending portions  11 ,  11 . By this configuration, stress on electrode section  32  is eased. Electrode portion protection member  4  is adhered to wiring board  3  by the use of epoxy-type adhesive. 
     As a material for electrode portion protection member  4 , resins with low adhesive property may be used, while the use of polytetrafluoroethylene (PTFE) or polyolefin is preferable. By utilizing the material with low adhesive property as electrode portion protection member  4 , in cases where stress of heat shock and the like is induced on electrode portion  32 , electrode portion protection member  4  is made to be peeled off instead of electrode portion  32 . 
     Electrode portion protection member  4 , has a thickness raging within 0.01 to 0.5 mm at a portion of covering electrode portion  32 . Namely, either the maximum or minimum values of the thickness of electrode portion protection member  4  at the portion of covering electrode portion  32  is designed to be within the above range. In the present embodiment, electrode portion protection member  4  having approximately uniform thickness within the above range is utilized. 
     Further, under the electrode portion protection member  4 , holding member  5  to hold projection portion  31  of wiring board  3  bonded onto head chip  2  is provided. 
     Holding member  5  is configured to have bottom plate  52  formed with a rectangular opening  51 , and side wall  53  raising from both sides of bottom plate  52  toward electrode portion protection member  4 . Bottom plate  52  has a width approximately same as wiring board  3 , and opening  51  is formed to be approximately same as nozzle plate  24 . 
     Head chip  2  is set in opening  51 , while wiring board  3  is placed on the upper surface of bottom plate  52  of holding member  5 . Therefore, flexible substrate  1 ,  1  is also arranged inside of holding member  5  and, flexible substrates  1 ,  1  and side wall  53  of holding member  5  is made approximately in parallel. 
     Further, under holding member  5 , tabular radiator plate  6  is provided. 
     Radiator plate has opening  61  having the same size as nozzle plate  24 , and head chip  2  is set in the opening  61  such that an upper surface of radiator plate  6  contacts a bottom surface of holding member  5 . 
     Under radiator plate  6 , cap member  7  is provided. 
     Cap member  7  is a rectangular plane plate and provided under side of cassis  20 . 
     In cap member  7 , opening  71  which has the same size with nozzle plate  24  is provided. Nozzle plate  24  is set in opening  7  such that an ink ejection surface of nozzle plate  24  and a bottom surface of cap member  7  are arranged in a same plane. In this way, since cap member  7  is arranged in the periphery of ink ejection surface of muzzle plate  24 , breakage of the ink ejection surface of nozzle plate  24 , which may be caused by contact with other member, can be prevented and head chip  2  is configured to be protected. 
     Although it is explained in the above description that an ink ejection surface of nozzle plate  24  and a bottom surface of cap member  7  are arranged in a same plane, “arranged in a same plane” does not necessary mean an exactly same plane, but may be arranged for example, such that the ink ejection surface of the nozzle plate  24  is arranged at a depressed position compared to the lower surface of cap member  7 , or a concave depression is formed in the periphery of nozzle plate according to the size of opening  71 . 
     Further, the surface of cap member  7  is made water-shedding, and prevents the ink adhesion on the surface due to ink splash in case of ejecting ink from head chip  2 . 
     Further, cap member  7  may function as a suction lip to tightly contact with a suction cap in a case of maintenance work of head chip  2 . 
     The maintenance work is for example a suction removal work that is conducted in cases where an ejection hole is clogged due to thickening or solidification of ink caused by evaporation of ink solvent in the ejection hole at the time of image formation by utilizing high viscosity ink, or the ejection hole is clogged due to generation of air bubble of dirt in an ink flow path connecting to the ejection hole. 
     At this time, the suction cap contacts cap member  7  in the periphery of head chip  2  so as to cover the lower and surface of head chip  2  where ink ejection hole being arranged, and a suction pump connected to the suction cap sucks the ink and the like remained in the ejection hole of nozzle plate  24  in head chip  2 . 
     Manifold  8  is made in box shape having open bottom surface, being disposed in the space formed with a pair of flexible substrates  1 ,  1  and the upper surface of wiring board  3 , and keeping the ink inside. 
     At right and left two positions on the upper surface of manifold  8 , flow path connection sections  81 ,  81  is dispose as shown in  FIG. 2 , and to unillustrated ink supply pipes are connected to flow path connection section  81 . 
     Further, as shown in  FIG. 3 , manifold  8  is formed to be coincide with the periphery of projection portion  31  of upper surface in wiring board  3 , thus an ink room common to all channel  23  is formed. 
     Meanwhile, it is possible to interpose a heater and the like, between cap member  7  and nozzle plate  24 , for heating the ink according to need. 
     Although in the present embodiment explained is that electrode protection member  4  is fixed to wiring board  3  via flexible substrates  1 ,  1 , electrode protection member  4  may be directly fixed to the exposed area of electrode portion  32  in the wiring board  3 . Further electrode protection member  4  only needs to be fixed at a position covering electrode portion  32 , for example may be adhered on the upper surface of bottom plate  52  of holding member  5 . 
     Further, holding member  5 , radiator plate  6 , and cap member  7  may be unified to form a holding member. In this case the holding member functions as a radiator plate and a cap member. 
     Further, without providing radiator plate  6 , holding member  5  and cap member  7  may be unified to form a holding member. In this case the holding member functions as a cap member. 
     Next, operations of the present embodiment will be explained. 
     In the ink jet head  10  structured as described above, by attaching wiring board  3  on the upper surface of head chip  2 , drive electrode  25  and electrode portion  32  of wiring board  3  are electrically connected for each channel  23  of head chip  2 . 
     When signals relating to ink ejection are sent to ink jet head  10 , the signals transfer from the wiring of flexible substrates  1 ,  1  through electrode portion  32  of wiring board  3 , to the connection electrode of head chip  2  and arrive to drive electrode  25 . Thus, drive wall  22  formed of piezoelectric element is shear deformed to apply pressure to the ink in channel  23 , and the ink is ejected from the nozzle formed in nozzle plate  24 . 
     Next, effect of the present embodiment will be explained. 
     In ink jet head of the present embodiment, by providing electrode protection member  4  having weaker adhesion property than electrode portion  32  between electrode portion  32  connected with bending portion  11 ,  11  of flexible substrates  1 ,  1  and the member disposed under the bottom face of electrode portion  32 , in cases where heat shock is imposed for example, electrode portion  32  is kept without being peeled off since electrode protection member  4  is firstly peeled off. 
     As described above, by providing electrode protection member  4  between electrode portion  32  and the member disposed under the bottom face of electrode portion  32 , and by firstly peeling off electrode protection member  4  in the case where stress is applied to electrode portion  32 , the peeling off of electrode portion  32  can be prevented and generation of disconnection can be prevented. Thus, electrode portion can be protected. 
     Further, by providing electrode protection member  4 , in the case of coating adhesive, the adhesive can be evenly coated due to the surface contact between electrode protection member  4  and bending portion  11 , which leads to improve working efficiency. 
     EXAMPLE 
     The present invention will be described by using examples. However, the present invention shall not be restricted by the examples. 
     Examples 1-5 
     As shown in Table 1 below, electrode protection members made of PTFE having thickness of 0.05 mm-0.5 mm are mounted on the above described ink jet head  10  in which the distance between the cap member and the wiring board is arranged to be 1 mm or 2 mm. And, the ink jet head was subjected to three cycle heat shock tests of heating and cooling within the temperature range of −20° C. to 80° C. After the heat shock test, conditions of wiring connection were checked and evaluated as described below. 
     &lt;&lt;Evaluation&gt;&gt; 
     A: There is no generation of disconnection in the electrode portion. 
     B: There are slight generations of disconnections in the electrode portion. 
     C: There are generations of disconnections in the electrode portion. 
     Comparative Examples 1-3 
     As shown in Table 1 below, electrode protection member made of PTFE having thickness of 0.8 mm or 1.0 mm are mounted on the above described ink jet head  10  in which the distance between the cap member and the wiring board is arranged to be 2 mm or 3 mm. And, the ink jet head was subjected to the same heat shock tests as the above, and similarly evaluated. 
     Examples 6-8 
     As shown in Table 1 below, electrode protection member made of polyethylene (PE) having thickness of 0.1 mm, 0.2 mm or 0.5 mm are mounted on the above described ink jet head  10  in which the distance between the cap member and the wiring board is arranged to be 1 mm. And, the ink jet head was subjected to the same heat shock tests as the above, and similarly evaluated. 
     Comparative Examples 4 and 5 
     As shown in Table 1 below, electrode protection member made of polyethylene (PE) having thickness of 0.1 mm is mounted on the above described ink jet head  10  in which the distance between the cap member and the wiring board is arranged to be 1 mm or 2 mm. And, the ink jet head was subjected to the same heat shock tests as the above, and similarly evaluated. Wherein, in Comparative Example 4, holding member  5  and radiator plate  6  are not provided. 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 Distance 
                   
               
               
                   
                   
                 b/w cap 
               
               
                   
                 Electrode 
                 member and 
               
               
                   
                 protection member 
                 wiring board 
               
             
          
           
               
                   
                 Material 
                 Thickness [mm] 
                 [mm] 
                 Evaluation 
               
               
                   
                   
               
             
          
           
               
                 Example 1 
                 PTFE 
                 0.05 
                 1 
                 A 
               
               
                 Example 2 
                 PTFE 
                 0.1 
                 1 
                 A 
               
               
                 Example 3 
                 PTFE 
                 0.2 
                 1 
                 A 
               
               
                 Example 4 
                 PTFE 
                 0.5 
                 1 
                 A 
               
               
                 Example 5 
                 PTFE 
                 0.5 
                 2 
                 A 
               
               
                 Comp. Example 1 
                 PTFE 
                 0.8 
                 2 
                 B 
               
               
                 Comp. Example 2 
                 PTFE 
                 1.0 
                 2 
                 C 
               
               
                 Comp. Example 3 
                 PTFE 
                 1.0 
                 3 
                 B 
               
               
                 Example 6 
                 PE 
                 0.1 
                 1 
                 A 
               
               
                 Example 7 
                 PE 
                 0.2 
                 1 
                 A 
               
               
                 Example 8 
                 PE 
                 0.5 
                 1 
                 A 
               
               
                 Comp. Example 4 
                 PE 
                 1.0 
                 1 
                 C 
               
               
                 Comp. Example 5 
                 PE 
                 1.0 
                 2 
                 C 
               
               
                   
               
               
                 Note: 
               
               
                 Comp. Example means Comparative Example. 
               
             
          
         
       
     
     From the above result, generation of disconnection in the electrode portion was not observed in cases of providing the electrode protection member having thickness of 0.05 mm-0.5 mm, and generation of disconnection was confirmed in cases of providing the electrode protection member having thickness of 0.8 mm or 1.0 mm. 
     The electrode protection member having thickness of less than 0.05 mm is presumed to be effective, however in cases where the thickness of the electrode protection member is less than 0.01 mm, forming of the member may become difficult, and the thickness of the electrode protection member is preferable in the range 0.01 mm-0.5 mm from a view point of practical usage. 
     Other than the above, the present invention is appropriately changeable, being not restricted the above described embodiments.