Patent Publication Number: US-8523333-B2

Title: Thin plate stacked structure and ink-jet recording head provided with the same

Description:
RELATED APPLICATIONS 
     This is a divisional patent application of U.S. application Ser. No. 11/087,297 filed Mar. 22, 2005, now U.S. Pat. No. 7,311,272 which is a divisional patent application of U.S. application Ser. No. 10/446,465 filed May 27, 2003, now U.S. Pat. No. 6,955,420, the entire disclosure of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a structure obtained by adhering and fixing, in a stacked form, a plurality of thin plate-shaped parts to be used, for example, for an ink-jet printer head and an electronic part. 
     2. Description of the Related Art 
     Examples of the ink-jet printer head of the on-demand type are described, for example, in Japanese Patent Application Laid-open No. 62-111758 corresponding to U.S. Pat. Nos. 4,680,595 and 4,730,197, Japanese Patent Application Laid-open No. 10-119263, and Japanese Patent Application Laid-open No. 2002-96478 corresponding to U.S. Patent Application Publication No. US2002/0036678 A1. As described in these patent documents, a structure is disclosed, in which a jetting pressure-generating member such as a driving piezoelectric element is secured, corresponding to each of portions of a plurality of pressure chambers, to a back surface of a cavity unit composed of a plurality of operating plates retained in an integrated manner by the aid of an adhesive in a stacked state. 
     The respective operating plates of the cavity unit include a nozzle plate which is provided with a plurality of nozzles, a base plate which is provided with pressure chambers corresponding to the respective nozzles, and a manifold plate which has ink chambers (manifolds) connected to an ink supply source and connected to the pressure chambers. Each of the plates is a thin metal plate having a thickness of about 200 μm or less. 
     Japanese Patent Application Laid-open No. 2002-96478 discloses the process in which the adhesive is applied to wide width surfaces of the base plate, the spacer plate, and the manifold plate of the cavity unit respectively to overlap and join the plates to one another. In this arrangement, release grooves, which are provided for the adhesive applied on the adhesion surface at positions disposed outer circumferentially as compared with ink flow passages such as the ink manifold, are formed on the wide width surface of each of the plates. Further, air release holes, which are provided to release the air in the plate thickness direction, are formed penetratingly through each of the plates opposed to the release grooves. 
     In the case of the patent document described above, as shown in  FIG. 19 , ink flow passages  202 , through which the ink flows in the direction from the pressure chambers to the nozzles, are bored in arrays in the long side direction at substantially central portions with respect to the short sides of the plate  201  (illustrated plate is the spacer plate). Ink flow passages  203 , through which the ink flows in the direction from the manifold chambers to the pressure chambers, are also bored in arrays in the long side direction at both left and right side portions with respect to the short sides of the plate  201 . A plurality of release grooves  204  are formed in parallel to the long side direction of the plate  210  to surround the outer sides of the ink flow passages  202 ,  203 . A large number of release grooves  205  are also formed in parallel to the short sides of each of the plates  201 . Accordingly, the effect to release the adhesive is enhanced, and the adhesive is prevented from any inflow into the ink flow passages  202 ,  203 . 
     However, the stack (cavity unit), which is constructed by laminating the respective plates, receives the pressure exerted from the actuator which is joined on the back surface side thereof, and the respective pressure chambers are expanded and contracted in the long side direction of the plate  201 . The pressure chambers are formed in the base plate of the stack, and hence the base plate is also expanded and contracted. The base plate is adhered to the other plates in the stack. Therefore, when the base plate is expanded and contracted, the bending moment tends to be received so that the axis of the cavity unit (plate  201 ) in the long side direction is bent in the plate thickness direction. Therefore, when the large number of release grooves  205 , which are parallel to the short side direction of the plate  201 , are formed, the cross sections of the portions of the release grooves  205  parallel to the short side of the plate  201  are decreased. In particular, the plate thickness is thinned, and hence the bending rigidity is decreased with respect to the bending moment in the direction as described above. When the actuator is repeatedly operated, the following first problem has arisen due to the fatigue phenomenon caused by the stress concentration brought about by the stress exerted repeatedly on the portion of the groove parallel to the short side. That is, any crack appears in the plate  201  during the use for a long period of time, the adhesive surface between the respective plates is exfoliated, and any leakage of the ink is apt to occur. 
     The air release holes are provided in order that the air (bubble), which is caught up in the applied adhesive or by the overlay surfaces of the adjoining plates when the plurality of plates are stacked, pressed, and joined by the aid of the adhesive, is discharged to the outside of the cavity unit via the release grooves. Any excessive amount of the applied adhesive can be also discharged to the outside of the cavity unit via the release grooves and the air release holes during the process in which the overlay surfaces are mutually pressed. Further, the release grooves are not open to the outer circumferential edges of the respective plates. Therefore, when the layer of the applied adhesive is also used as the seal layer, it is possible to avoid the leakage of the ink to the outside of the cavity unit, for example, from the ink flow passages. 
     However, the following second problem has arisen. That is, when the viscosity of the adhesive is low, then the adhesive overflows to the outside from the through-holes of the plate disposed at the uppermost layer during the operation for pressing and joining the plates, and the adhesive consequently adheres to the pressing and joining apparatus. Therefore, in order to clean and treat the overflow adhesive, it is necessary to frequently perform the maintenance operation for conducting any extra cleaning operation. In other cases, extra time and labor are required, for example, such that the pressing and joining apparatus is laid with a sheet to prevent the adhesion of the adhesive when the pressing and joining operation is performed. 
     The first and second problems may also arise during the assembling of an electronic part constructed by staking a thin plate formed with a minute pattern onto another thin plate. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a stacked and adhered (fixed) structure of thin plate-shaped parts in which the problems involved in the conventional technique as described above have been dissolved, and an ink-jet recording head provided with the same. 
     According to a first aspect of the present invention, there is provided a thin plate stacked structure comprising a plurality of thin plates which are stacked with an adhesive, the plurality of thin plates including at least one liquid flow passage thin plate provided with a liquid flow passage having a predetermined pattern formed on at least one surface, the stacked structure further comprising:
         a release groove which is formed on the liquid flow passage thin plate and which releases the adhesive;   an air release hole which is bored through a thin plate stack stacked on the liquid flow passage thin plate, which is communicated with the release groove, and which penetrates in a stacking direction; and   an opening which is formed on the thin plate disposed at an outermost layer of the thin plate stack and which allows the air release hole to be open to the outside, wherein:   the air release hole has a diameter which is larger than a width of the release groove and which is larger than the opening disposed at the outermost layer.       

     In the stack according to the present invention, the air release hole is formed to be larger than the width of the release groove, and the air release hole is formed to be larger than the opening disposed on the outermost layer. Accordingly, the cavity volume (capacity) of the air release hole is increased. Therefore, any excessive adhesive is accumulated in the air release hole, and it is possible to greatly decrease the amount of the adhesive outflowing to the outside of the cavity unit. Therefore, it is possible to suppress the adhesion of the adhesive to the pressing and joining apparatus, which would be otherwise caused by the outflow to the outside from the air release hole of the thin plate-shaped part disposed at the outermost layer. It is possible to avoid any extra cleaning operation which would be otherwise performed to clean and treat the outflow adhesive. Further, it is also possible to decrease the frequency of exchange of the installation of the sheet to the pressing and joining apparatus in order to avoid any adhesion of the adhesive thereto when the operation for pressing and joining the thin plates is performed. 
     According to a second aspect of the present invention, there is provided a thin plate stacked structure comprising a plurality of thin plates which are stacked with an adhesive, the plurality of thin plates including at least one liquid flow passage thin plate provided with a liquid flow passage having a predetermined pattern formed on at least one surface, the stacked structure further comprising:
         a release groove which is formed on the liquid flow passage thin plate and which releases the adhesive;   an air release hole which is bored through a thin plate stack stacked on the liquid flow passage thin plate, which is communicated with the release groove, and which penetrates in a stacking direction; and   an opening which is formed on the thin plate disposed at an outermost layer of the thin plate stack and which allows the air release hole to be open to the outside, wherein:   at least one portion of the release groove, which is disposed in the vicinity of the air release hole, has a width which is wider than those of other portions of the release groove to form an adhesive pool.       

     In the stacked structure according to the second aspect, any excessive adhesive, which appears on the intermediate layer during the adhesion with the adhesive, is accumulated in the adhesive pool having an enlarged volume. Accordingly, it is possible to greatly decrease the amount of the adhesive outflowing to the outside of the stacked structure. Therefore, it is possible to avoid the cleaning operation for the outflow or protruding adhesive. 
     In the stacked structure according to each of the first and second aspects of the present invention, the release groove may be formed outside the liquid flow passage on the liquid flow passage thin plate. Further, a hole for defining the air release hole may be formed through each of the thin plates for constructing the stack. Further, the liquid flow passage having the predetermined pattern may be composed of a plurality of through-holes arranged in a certain direction. 
     According to another aspect of the present invention, there is also provided an ink-jet recording head comprising a cavity plate which is composed of the stacked structure according to the first or second aspect of the present invention, and an actuator, wherein the cavity plate has a plurality of nozzles, and the liquid flow passage is an ink flow passage for allowing an ink to pass from an ink supply source to the nozzles. A large amount of the adhesive does not protrude from the uppermost layer during the operation for stacking the thin plates of the ink-jet recording head. Therefore, the production is carried out with ease, and the cost is low. 
     The holes, which are formed through the respective thin plates for constructing the stack, may be arranged coaxially or in an offset manner in the stacking direction. The adhesive, which is applied to the overlay surface of the thin plate, is moved to the adjoining thin plate during the pressing and joining operation from the release groove (via the enlarged adhesive pool) via the air release hole penetrating in the vertical direction of each of the thin plates. When the holes, which are formed through the respective thin plates, are arranged coaxially or in the offset manner in the stacking direction, the adhesive is moved in a zigzag manner. Accordingly, the adhesive having a small viscosity hardly arrives at the outermost layer. Therefore, it is possible to decrease the amount of protrusion of the adhesive to the outside of the stack. 
     According to a third aspect of the present invention, there is provided a thin plate stacked structure comprising a plurality of thin plates which are stacked with an adhesive, the plurality of thin plates including at least one pattern-formed thin plate provided with a hole or a recess having a predetermined pattern formed on at least one surface to extend in a predetermined direction; the stacked structure further comprising a release groove which is formed on the at least one surface of the pattern-formed thin plate and which releases the adhesive, wherein the release groove includes a groove which extends while being inclined with respect to the predetermined direction. In the stacked structure according to the present invention, even when the bending moment acts in a predetermined direction, for example, in a direction perpendicular to the long side direction of the thin plate to bend each of the thin plates in the plate thickness direction, the rigidity is scarcely decreased in relation to the bending moment, because the portion of the release groove (portion having a small plate thickness) appears only a part of a cross section perpendicular to the predetermined direction as viewed in the cross section perpendicular to the predetermined direction. Therefore, the stacked structure having a high strength is provided even when the thickness is thin. In the stacked structure according to the present invention, the release groove may be formed to circumscribe at least a part of the predetermined pattern. The recess or the hole may be a flow passage for a liquid including, for example, an ink. 
     In the stacked structure according to the third aspect of the present invention, the release groove may further include a groove which extends in the predetermined direction and which is communicated with the groove which extends while being inclined with respect to the predetermined direction. Any excessive adhesive, which is applied to the surface of the thin plate, can be released via the two types of the release grooves, while the rigidity in relation to the bending moment can be maintained to be high as well. 
     An air release hole, which is communicated with the release groove and which penetrates in a thickness direction of the thin plate, may be bored on the at least one surface of the pattern-formed thin plate. The air, which is caught up in the adhesive or by the overlay surface (wide width surface) of the thin plate, behaves as bubbles to move together with the adhesive existing on the overlay surface, in the release groove in the lateral direction, and in the air release hole in the vertical direction, and thus the air is successfully discharged to the outside of the thin plate. As a result, it is possible to form stable adhesive/seal layers by means of the layers of the adhesive formed in a layered form on the overlay surfaces (wide width surfaces) of the adjoining thin plates. Further, the air release hole is not open at the end of each of the thin plates unlike the conventional technique. Therefore, the liquid leakage is reliably avoided, which would be otherwise caused at such portions. In the stacked structure according to the third aspect of the present invention, the release groove may be formed in a meandering form as viewed in plan view. 
     According to still another aspect, there is provided an ink-jet recording head comprising a cavity plate which is composed of the stacked structure of the present invention according to the third aspect, and an actuator, wherein the cavity plate has a plurality of nozzles, and the hole or the recess is an ink flow passage for allowing an ink to pass from an ink supply source to the nozzles. Therefore, it is possible to reliably prevent such an accident that the ink is leaked to the outside from the ink flow passage formed in the cavity plate for the ink-jet printer head, and thus it is possible to secure the performance necessary for the ink-jet printer head. When the cavity plate includes a base plate having a plurality of pressure chambers arranged in the predetermined direction, the rigidity in relation to the bending moment is decreased due to the array of the plurality of pressure chambers. However, when the groove, which extends while being inclined with respect to the predetermined direction, is formed to traverse at least two of the pressure chambers, it is possible to minimize the decrease of the rigidity and the flexure of the base plate caused by the presence of the groove. 
     According to a fourth aspect of the present invention, there is provided a thin plate stacked structure comprising a plurality of thin plates which are stacked and adhered with an adhesive, the plurality of thin plates including at least one thin plate provided with a liquid flow passage having a predetermined pattern formed on at least one surface of the at least one thin plate, wherein:
         a plurality of anchor holes are bored penetratingly in a thickness direction of the at least one thin plate.       

     In the thin plate stacked structure according to the fourth aspect, the anchor holes of one plate are not connected to one another in the in-plane direction of the plate. Accordingly, the rigidity against the bending moment is not greatly decreased (lowered) locally. It is possible to obtain the stacked and adhered structure of the thin plate-shaped parts having the high degree of strength even though the thickness is thin. Further, a part of the adhesive disposed between the stacked plates enters the anchor holes, and the adhesive is adhered to at least portions of the circumferential surfaces of the anchor holes so that the force is allowed to act to fasten the both plate (referred to as “anchoring effect”). Therefore, it is possible to effect the powerful joining function as compared with the joining force brought about by the adhesive based on only the areas of the stacking surfaces at which the plates are opposed to one another. 
     In the thin plate stacked structure according to the fourth aspect of the present invention, the anchor holes may be disposed in a zigzag arrangement as viewed in plan view of a plate. 
     In the thin plate stacked structure according to the fourth aspect of the present invention, the at least one thin plate is adjoining stacked thin plates each of which has the anchor holes, the anchor holes may be arranged so that portions of the anchor holes are communicated with each other in a stacking direction at adjoining stacked portions of the thin plates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exploded perspective view illustrating a piezoelectric ink-jet printer head according to an embodiment of the present invention. 
         FIG. 2  shows an exploded perspective view illustrating a cavity unit. 
         FIG. 3  shows a magnified exploded perspective view illustrating portions of the cavity unit. 
         FIG. 4  shows a magnified exploded perspective view illustrating portions of the cavity unit which is arranged while directing nozzles upwardly. 
         FIG. 5  shows a plan view illustrating a spacer plate. 
         FIG. 6  shows a magnified sectional view illustrating the piezoelectric ink-jet printer head taken along a line VI-VI indicated by arrows shown in  FIG. 1 . 
         FIG. 7A  shows a sectional view illustrating, for example, release grooves and air release holes depicting a state of application of an adhesive prior to the stacking, and  FIG. 7B  shows a sectional view illustrating a stacked and adhered state of the respective plates. 
         FIG. 8  shows a perspective view illustrating the stacking of lead frames according to the present invention. 
         FIG. 9  shows an exploded perspective view illustrating the release grooves and the air release holes of the respective plates which are arranged while directing nozzles upwardly. 
         FIG. 10A  shows a sectional view illustrating, for example, release grooves and air release holes depicting a state of application of an adhesive prior to the stacking, and  FIG. 10B  shows a sectional view illustrating a stacked and adhered state of the respective plates. 
         FIG. 11  shows a magnified perspective view illustrating major parts depicting, for example, release grooves, enlarged adhesive pools, and air release holes according to a second embodiment. 
         FIG. 12A  shows a sectional view illustrating, for example, release grooves and air release holes depicting a state of application of an adhesive prior to the stacking in the second embodiment, and  FIG. 12B  shows a sectional view illustrating a stacked and adhered state of the respective plates. 
         FIG. 13  shows a plan view illustrating release grooves according to a third embodiment. 
         FIG. 14  shows a plan view illustrating release grooves according to a fourth embodiment. 
         FIG. 15  shows a plan view illustrating major parts of release grooves depicting a state of stacking in the fourth embodiment. 
         FIG. 16  shows a plan view illustrating anchor holes according to a fifth embodiment. 
         FIG. 17A  shows a sectional view illustrating, for example, anchor holes depicting a state of application of an adhesive prior to the stacking in the fifth embodiment,  FIG. 17B  shows a sectional view illustrating respective plates depicting a stacked and adhered state, and  FIG. 17C  shows a plan view illustrating major parts depicting an arrangement of the anchor holes in a stacked condition. 
         FIG. 18A  shows a sectional view illustrating thin plates depicting a state of application of an adhesive prior to the stacking,  FIG. 18B  shows a sectional view illustrating respective plates in a stacked and adhered condition, and  FIG. 18C  shows a sectional view illustrating, for example, anchor holes in other modified embodiment. 
         FIG. 19  shows a plan view illustrating a state of release grooves for the adhesive in the case of an exemplary conventional technique. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     An embodiment of the present invention will be explained below with reference to the drawings.  FIGS. 1 to 7  show a piezoelectric ink-jet printer head according to a first embodiment of the present invention. In  FIG. 1 , a flexible flat cable  40  is overlapped and joined with an adhesive to effect the connection to an external apparatus on an upper surface of a plate type piezoelectric actuator  20  which is joined to a cavity unit  9  made of metal plates. The ink is jetted downwardly from nozzles  15  which are open on the lower surface side of the lowermost layer of the cavity unit  9 . 
     The cavity unit  9  is constructed as shown in  FIGS. 2 to 6 . That is, the cavity unit  9  has such a structure that five thin plates, i.e., a nozzle plate  10 , two manifold plates  11 ,  12 , a spacer plate  13 , and a base plate  14  are overlapped, joined, and stacked with an adhesive respectively. In this embodiment, each of the plates  11 ,  12 ,  13 ,  14  is made of a 42% nickel alloy steel plate having a thickness of about 50 μm to 150 μm except for the nozzle plate  10  made of a synthetic resin. The nozzles  15  for jetting the ink, each of which has a minute diameter (about 25 μm in this embodiment), are provided on the nozzle plate  10  in two arrays of the zigzag arrangement in the first direction (long side direction) of the nozzle plate  10 . That is, the large number of nozzles  15  are bored in the zigzag arrangement at spacing distances of minute pitches P along two parallel reference lines  10   a ,  10   b  which extend in the first direction of the nozzle plate  10 . Manifolds  12   a ,  12   b,  which serve as fluid passages for supplying the ink to respective pressure chambers  16  as described later on after storing the ink supplied from an external ink supply source, are formed as bores of the two manifold plates  11 ,  12  so that the manifolds  12   a ,  12   b  extend along the both sides of the arrays of the nozzles  15 . However, the manifolds  12   b , which are formed on the manifold plate  11  disposed on the lower side opposed to the nozzle plate  10 , are formed as recesses so that the manifolds  12   b  are open on only the upper side of the manifold plate  12  (see  FIGS. 3 and 4 ). The manifolds  12   a ,  12   b  are structured such that they are tightly closed by stacking the spacer plate  13  on the manifold plate  12  disposed on the upper side.  FIG. 4  shows, with partial cutout, a perspective view illustrating parts of the nozzle plate  10 , the manifold plates  11 ,  12 , the spacer plate  13 , and the base plate  14  respectively in a state in which back surfaces (lower surfaces) of portions corresponding to the right ends as shown in  FIG. 3  are directed upwardly. 
     A large number of pressure chambers  16 , each of which has a thin width and which extend in the second direction (short side direction) perpendicular to the center line extending along the long side (in the first direction described above), are bored through the base plate  14 . Longitudinal reference lines  14   a ,  14   b  are established to extend in parallel on the both left and right sides with the center line intervening therebetween. On this assumption, tip flow passages  16   a  of the pressure chambers  16 , which are disposed on the left side of the center line, are positioned on the longitudinal reference line  14   a  disposed on the right side, while tip flow passages  16   a  of the pressure chambers  16 , which are disposed on the right side of the longitudinal center line, are positioned on the longitudinal reference line  14   b  disposed on the left side. Further, the tip flow passages  16   a  of the left and right pressure chambers  16  are alternately arranged. Therefore, the pressure chambers  16 , which are disposed on the both left and right sides, are arranged alternately every other one to extend in the mutually opposite directions. 
     The tip flow passages  16   a  of the respective pressure chambers  16  are communicated with the nozzles  15  disposed in the zigzag arrangement on the nozzle plate  10  via communication holes  17 ,  17 ,  17  having minute diameters to serve as ink flow passages (liquid passages) which are bored in the zigzag arrangement as well through the spacer plate  13  and the both manifold plates  11 ,  12 . On the other hand, second ends of the respective pressure chambers  16  are connected to second end flow passages  16   b  having large diameters via slender throttle sections  16   d  which serve as ink flow passages having small cross-sectional areas. The second end flow passages  16   b  are communicated with the manifolds  12   a ,  12   b  of the both manifold plates  11 ,  12  via through-holes  18  which serve as liquid passages bored through both left and right side portions of the spacer plate  13 . As shown in  FIGS. 3 and 4 , the second end flow passages  16   b  and the slender throttle sections  16   d  are formed as recesses so that they are open on only the lower surface side of the base plate  14 . The diameter of the second end flow passage  16   b  is formed to be substantially the same as the diameter of the through-hole  18 . The cross section of the throttle section  16   d  is smaller than that of the pressure chamber  16  in order to restrict the flow of the ink directed from the pressure chamber  16  to the manifold  12   a ,  12   b  when the piezoelectric actuator  20  is driven. 
     Interconnecting sections  16   c , which have thicknesses about the half of the plate thickness of the base plate  14 , are provided at intermediate portions of the respective pressure chambers  16  in the longitudinal direction. Accordingly, the side walls of the large number of juxtaposed pressure chambers  16  are prevented from the decrease in rigidity. 
     Supply holes  19   b , which are bored through first end portions of the spacer plate  13 , are communicated with the manifolds  12   a . Further, the supply holes  19   b  are also communicated with supply holes  19   a  which are bored through first end portions of the base plate  14  disposed at the uppermost layer. A filter  29  is stretched on the upper surfaces of the supply holes  19   a  in order to remove the dust contained in the ink to be supplied from an ink tank provided thereover. 
     The situation, in which the plates  11 ,  12 ,  13 ,  14  are stacked, is shown in  FIGS. 4 and 5 . In this case, a plurality of release grooves  34 , which are provided to release the adhesive  39 , are formed as recesses to extend in directions not perpendicular to the long side direction of the plates at portions disposed outside the outer circumferences of the pressure chambers  16 , the communication passages  17 , the through-holes  18 , and the supply holes  19   a ,  19   b  to serve as the liquid flow passages as described above at least on first surfaces (wide width surfaces) of the respective plates. Another type of release grooves  35  are formed along the long sides. The both release grooves  34 ,  35  are communicated with each other at their connecting portions. Further, the release grooves  34 ,  35  are formed to extend in mutually inclined directions. 
     Next, an explanation will be made about a method for assembling the cavity unit  9 . As shown in  FIG. 8 , four lead frames  100   a  to  100   d  are stacked, adhered, and fixed. The manifold plates  11 ,  12 , the spacer plates  13 , and the base plates  14 , which are the thin plate-shaped parts formed with predetermined patterns, are arranged and juxtaposed to one another at constant spacing distances on the respective lead frames  100   a  to  100   d . That is, the lead frame  100   d , which is disposed at the lowermost layer, is formed so that the base plates  14  as described in the embodiment are arranged at the constant spacing distances. Left and right slender frame bars  102 ,  102  are connected to one another by tie bars  104  disposed at appropriate spacing distances. Similarly, the spacer plates  13  are formed at the same spacing distances as those described above on the lead frame  100   c  disposed at the second layer from the bottom. The manifold plates  12  are formed at the same spacing distances as those described above on the lead frame  100   b  disposed at the third layer from the bottom. The second manifold plates  11  are formed at the same spacing distances as those described above on the lead frame  100   a  disposed at the uppermost layer. Feeding holes  103   a ,  103   b  and positioning holes  105  are appropriately formed at constant spacing distances through the frame bars  102  of the respective lead frames  100   a  to  100   d . The respective plates  11 ,  12 ,  13 ,  14  are connected to the frame bars  102  by the aid of interconnecting tabs  106  having minute widths. 
     When the lead frames are stacked, as shown in  FIG. 4 , the lead frames are stacked so that the parts are disposed upside down as compared with the state of use of the cavity unit  9  (state in which the ink nozzles are open on the lower surface side). In this situation, as shown in  FIG. 4 , they are arranged so that the release grooves  34 ,  35  for the adhesive, which are formed on the respective first surfaces of the base plate  14  disposed at the lowermost layer, the spacer plate  13  disposed at the second layer from the bottom, and the manifold plate  12 , are directed upwardly.  FIG. 5  shows a plan view illustrating the arrangement of the release grooves  34 ,  35  formed on the spacer plate  13 , depicting an example in which release grooves  137  for the adhesive having annular configurations as viewed in the plan view are formed as recesses at the outer circumferences of the supply holes  19   b.    
     Air release holes  36 ,  36 ,  36  are bored at upper and lower identical positions of the release grooves  34 ,  35  and the flat surfaces of the respective plates opposed thereto so that the air release holes  36 ,  36 ,  36  are communicated with the release grooves and the air release holes  36 ,  36 ,  36  penetrate through the plate thicknesses of the respective plates  13 ,  12 ,  11  to make the communication in the vertical direction. Further, at least one of the air release holes  36  formed for the manifold plate  11  disposed at the uppermost layer or the base plate  14  disposed at the lowermost layer is open to the outside. Preferably, the air release hole  36 , which is formed for the base plate  14  disposed at the lowermost layer, is a recess which has about a half thickness of the plate thickness and which is not communicated with the lower surface side (see  FIGS. 7A and 7B ). 
     The adhesive  39  is previously applied to plate-stacking surfaces of the lead frames  100   a  to  100   d . One of the methods for applying the adhesive  39  is as follows. That is, the adhesive  39  is previously applied in thin thickness onto a flat surface of an unillustrated jig, and the plate-stacking surface of each of the lead frames  100   a  to  100   d  is placed and overlaid on the applied surface. Accordingly, it is possible to transfer the adhesive  39 , for example, to the flat land surface other than the recesses of, for example, the release grooves  34 ,  35 , the pressure chambers  16 , the second end flow passages  16   b , the throttle sections  16   d , and the air release holes  36  of the base plate  14 . The adhesive  39  may be transferred by making the pressing abutment of the plate-stacking surface against a roller surface to which the adhesive  39  has been applied. 
     Subsequently, pins are inserted into the positioning holes  105  to adhere and fix the lead frames  100   a  to  100   d  by allowing the pressing force or the interposing force to act on the lead frame  100   d  disposed at the lowermost layer and the lead frame  100   a  disposed at the uppermost layer. 
     When the plurality of lead frames, to which the adhesive  39  has been transferred, are pressed as described above to adhere and fix the wide width surfaces of the respective plates  11 ,  12 ,  13 ,  14 , any excessive adhesive  39  inflows into the release grooves  34 ,  35 . Subsequently, as shown in  FIG. 7B , the air release holes  36  are filled with the excessive adhesive  39 . During this process, the air, which is caught up in the adhesive  39  and the overlay surfaces (wide width surfaces) of the adjoining plates  11 ,  12 ,  13 ,  14 , behaves as bubbles which are moved together with the adhesive  39  in the release grooves  34 ,  35  in the lateral direction and the air release holes  36  in the vertical direction and which are discharged to the outside of the plates. As a result, it is possible to form stable adhesive/seal layers by means of the adhesive  39  formed in layered configurations without containing any bubble on the overlay surfaces (wide width surfaces) of the adjoining plates  11 ,  12 ,  13 ,  14 . 
     The interconnecting tabs  106  are cut from the lead frames  100   a  to  100   d  having been adhered and fixed as described above, and the integrated cavity units  9  are removed. Each of the cavity units  9  is constructed as follows. That is, the ink inflows into the manifolds  12   a ,  12   b  from the supply holes  19   a ,  19   b  bored through the first ends of the base plate  14  and the spacer plate  13 . The ink passes from the manifolds  12   a  via the respective through-holes  18 , and the ink is distributed into the respective pressure chambers  16 . After that, the ink passes from the respective pressure chambers  16  via the communication holes  17 ,  17 ,  17 , and the ink arrives at the nozzles  15  corresponding to the pressure chambers  16 . 
     On the other hand, as shown in  FIGS. 1 and 6 , the piezoelectric actuator  20  has such a structure that a plurality of piezoelectric sheets  21  are stacked. In the same manner as disclosed in Japanese Patent Application Laid-open No. 4-341853 corresponding to U.S. Pat. No. 5,402,159, thin width individual electrodes (not shown), which are disposed at respective positions corresponding to the respective pressure chambers  16  of the cavity unit  9 , are formed in arrays in the first direction (long side direction) on the upper surfaces (wide width surfaces) of the piezoelectric sheet disposed at the lowermost level and the piezoelectric sheets having odd numbers as counted upwardly therefrom, of the respective piezoelectric sheets  21  each having a thickness of about 30 μm. The respective individual electrodes extend to positions in the vicinity of the end edges of the long sides of the respective piezoelectric sheets in the second direction perpendicular to the first direction. Common electrodes (not shown), which are common to the plurality of pressure chambers  16 , are formed on the upper surfaces (wide width surfaces) of the piezoelectric sheets disposed at the even number levels as counted from the bottom. Those provided on the upper surface of a top sheet disposed at the uppermost level along the end edges of the long sides thereof are surface electrodes  30  which are electrically connected to the respective individual electrodes, and surface electrodes  31  which are electrically connected to the common electrodes (see  FIG. 1 ). 
     An adhesive sheet  41 , which is composed of an ink-impermeable synthetic resin material to serve as an adhesive layer, is previously stuck to the entire lower surface (wide width surface opposed to the pressure chambers  16 ) of the plate type piezoelectric actuator  20  constructed as described above. Subsequently, the piezoelectric actuator  20  is adhered and fixed to the cavity unit  9  while allowing the respective individual electrodes to correspond to the respective pressure chambers  16  of the cavity unit  9  respectively (see  FIG. 6 ). The flexible flat cable  40  is overlaid and pressed onto the upper surface of the piezoelectric actuator  20 . Accordingly, various wiring patterns (not shown) of the flexible flat cable  40  are electrically connected to the respective surface electrodes  30 ,  31 . 
     In this arrangement, when the voltage is applied between the common electrode and an arbitrary individual electrode of the respective individual electrodes of the piezoelectric actuator  20 , the strain in the stacking direction, which is based on the piezoelectric effect, is generated at the portion of the individual electrode of the piezoelectric sheet  21  to which the voltage is applied as described above. The internal volume of the pressure chamber  16  corresponding to each of the individual electrodes is reduced by the strain. Accordingly, the ink contained in the pressure chamber  16  is jetted in a liquid droplet form from the nozzle  15  to perform the predetermined printing (see  FIG. 6 ). 
     The release grooves  34 ,  35  for the adhesive of the respective plates  11  to  14  of the cavity unit  9  extend in the directions which are not perpendicular to the long sides of the respective plates. Therefore, even when any bending moment acts on the-cavity unit  9  in the direction perpendicular to the long side direction to bend the respective plates in the plate thickness direction by the pressing force exerted by the actuator  20 , the rigidity against the bending moment is not greatly decreased locally, because the portions corresponding to the release grooves  34 ,  35  (portions having small plate thicknesses) appear only parts of the short sides of the respective plates as viewed in cross sections taken in parallel to the short sides of the respective plates. Therefore, it is possible to obtain the cavity unit  9  having a large strength even though it has a thin thickness. In particular, when the release groove  34  is formed to traverse the plurality of pressure chambers  16  arranged in the base plate  14 , then it is possible to decrease the flexure of the base plate  14  which would be otherwise caused by the presence of the plurality of pressure chambers  16 , and it is possible to avoid the decrease of the rigidity which would be otherwise caused by the bending moment described above, as compared with a case in which the release grooves  34  are formed in the short side direction. 
     Second Embodiment 
     A second embodiment of the piezoelectric ink-jet printer head according to the present invention will be explained below. The head and a method for producing the same are approximately the same as those described in the first embodiment except that the air release hole and the release groove of the cavity unit differ in structure as explained below. In the cavity unit, as shown in  FIGS. 9 ,  10 A, and  10 B, thin width release grooves  34 ,  35  for the adhesive are formed as recesses on first surfaces of the mutually opposing surfaces of the plates which are disposed adjacently in the vertical direction. In  FIG. 9 , the release grooves  34 ,  35  for the adhesive, which are formed on the first surfaces of the base plate  14  disposed at the lowermost layer, the spacer plate  13  disposed at the second layer from the bottom, and the manifold plate  12  disposed at the third layer from the bottom, are arranged so that they are directed upwardly. 
     Air release holes  37 ,  38  are bored at positions to make the communication with the release grooves  34 ,  35 , the positions being vertically identical positions of the flat surfaces of the respective plates  12 ,  13  to be stacked so that they are communicated with each other in the vertical direction while making the penetration through the plate thicknesses of the respective plates  12 ,  13 . The manifold plate  11  disposed at the uppermost layer (or base plate  14  when the base plate  14  is disposed at the uppermost layer) is formed with openings  136  to make the penetration through the plate thickness at positions to make the communication with the air release holes  37 ,  38 . The openings  136  are open to the outside. Air release holes  136   a , which are formed on the base plate  14  disposed at the lowermost layer, are recesses which have approximately the same depths (about the half of the plate thickness) as those of the release grooves  34  ( 35 ) and which are not communicated with the lower surface side (see  FIGS. 10A and 10B ). 
     The diameters D 2  of the air release holes  37 ,  38  formed for the plates  12 ,  13  disposed at the intermediate layers except for the plate  11  disposed at the uppermost layer and the plate  14  disposed at the lowermost layer are formed to be larger than at least the diameter D 1  of the openings  136  formed for the plate  11  disposed at the uppermost layer. Further, the diameters D 2  of the air release holes  37 ,  38  are formed to be larger than the widths of the release grooves  34 ,  35 . Owing to the diameter D 2 , when the adhesive  41  is moved along the overlay surfaces of the respective plates  11  to  14  during the stacking process, then the air release holes  37 ,  38  having the large diameters formed for the intermediate layers secure the release routes for the air (bubbles) contained in the adhesive  41  in a mixed manner, and the air release holes  37 ,  38  create adhesive pools to prevent the adhesive  41  from any leakage to the outer circumferential edges of the respective plates (see  FIG. 10B ). 
     As shown in  FIG. 8 , when the lead frames are stacked, the adhesive  41  is previously applied to plate-stacking surfaces of the lead frames  100   a  to  100   d . One of the methods for applying the adhesive  41  is as follows. That is, the adhesive  41  is previously applied in thin thickness onto a flat surface of a jig, and the plate-stacking surface of each of the lead frames  100   a  to  100   d  is placed and overlaid on the applied surface. Accordingly, it is possible to transfer the adhesive  41 , for example, to the flat land surface other than the recesses of, for example, the release grooves  34 ,  35 , the pressure chambers  16 , the second end flow passages  16   b , the throttle sections  16   d , and the air release holes  136   a  of the base plate  14 . The adhesive  41  may be transferred by making the pressing abutment of the plate-stacking surface against a roller surface to which the adhesive  41  has been applied. 
     Subsequently, pins are inserted into the positioning holes  105  to press, adhere, and fix the lead frames  100   a  to  100   d  by allowing the pressing force or the interposing force to act on the lead frame  100   d  disposed at the lowermost layer and the lead frame  100   a  disposed at the uppermost layer. 
     When the plurality of lead frames, to which the adhesive  41  has been transferred, are pressed as described above to adhere and fix the wide width surfaces of the respective plates  11 ,  12 ,  13 ,  14 , any excessive adhesive  41  inflows into the release grooves  34 ,  35 . Subsequently, as shown in  FIG. 10B , the air release holes  136   a ,  37 ,  38  are filled with the excessive adhesive  41 . During this process, the air, which is caught up in the adhesive  41  or by the overlay surfaces (wide width surfaces) of the adjoining plates  11 ,  12 ,  13 ,  14 , behaves as bubbles which are moved together with the adhesive  41  in the release grooves  34 ,  35  in the lateral direction and the air release holes  136   a ,  37 ,  38  in the vertical direction and which are discharged to the outside of the plates from the openings  136 . As a result, it is possible to form stable adhesive/seal layers by means of the adhesive  41  formed in layered configurations without containing any bubble on the overlay surfaces (wide width surfaces) of the adjoining plates  11 ,  12 ,  13 ,  14 . Further, the diameters D 2  of the air release holes  37 ,  38  of the intermediate layers are larger than those of the openings  136 , namely the cavity volume (capacity) of the air release hole is large. Therefore, the excessive adhesive  41  is accumulated in the air release holes  37 ,  38 , and it is possible to greatly decrease the amount of the adhesive  41  which outflows from the openings  136  to the outside of the cavity unit  9 . Further, the adhesive intends to stay at the boundary wall surface between the opening  136  and the air release hole  38  on account of the capillary phenomenon, because the diameter D 2  of the air release hole  37 ,  38  is larger than the diameter Dl of the opening  136 . Therefore, the adhesive hardly goes out of the opening  136 . 
     The air release grooves  136   a  of the plate  14  disposed at the lowermost layer may be formed to have large diameters. However, the air release grooves  136   a  of the plate  14  disposed at the lowermost layer may have the same diameter as the width of the release groove  35 , because the adhesive inflows from the release grooves  35  into the air release holes  38  having the large diameters. 
     Therefore, the adhesive scarcely overflows to the outside from the openings  136  of the plate disposed at the uppermost layer, and the adhesive hardly adheres to the pressing and joining apparatus. It is also possible to decrease the number of times of the execution of the maintenance operation which would be otherwise performed such that any excessive cleaning operation is conducted in order to clean and treat the adhesive. Further, the following effect is also obtained. That is, it is possible to decrease the frequency of exchange of the installation of the sheet to avoid the adhesion of the adhesive with respect to the pressing and joining apparatus when the pressing and joining operation is performed. 
     After that, when the air release holes  136  are sealed with a seal material such as an adhesive at the upper surface of the manifold plate  11  disposed at the uppermost layer, it is possible to reliably effect the closure with the seal material, because the upper surface of the manifold plate  11  is the smooth wide width surface, and the sealing is effected on this surface. As a result, it is possible to reliably avoid the leakage of the ink to the outside of the cavity unit  9  from the ink flow passages of the respective plates  11 ,  12 ,  13 ,  14  including, for example, the common ink chambers  12   a ,  12   b , the communication holes  17 , the ink flow passages  18 , and the respective pressure chambers  16  as well as the tip flow passages  16   a  and the second end flow passages  16   b.    
     In the capillary phenomenon in which the (liquid) adhesive  41  having the low viscosity passes through the narrow gap such as those between the overlay surfaces of the plates (including, for example, the base plate  14  in this case and in the following cases as well), the adhesive  41  is preferentially attracted to portions having small cross-sectional areas with the large capillary force prior to portions having large cross-sectional areas. Therefore, when the cross-sectional areas of the release grooves  34 ,  35  are established to be smaller than the respective cross-sectional areas of the ink flow passages  18 , the communication holes  17 , and the throttle sections  16   d  to make the communication to the pressure chambers  16  from the second end flow passages  16   b  as the ink flow passages, then the adhesive  41 , which is disposed on the overlay surface of the plate, behaves such that the adhesive  41  is introduced via the release grooves  34 ,  35  into the air release holes  37 ,  38  of the intermediate layers having the large cavity volume (capacity) prior to the respective ink flow passages, and thus it is possible to prevent the ink flow passages from being closed by the adhesive  41 . 
     In another embodiment shown in  FIGS. 11 ,  12 A, and  12 B, an enlarged adhesive pool  42 , which is formed so that the width, i.e., the area is enlarged as viewed in a plan view, is formed at a part of the release groove  35  disposed in the vicinity of each of the air release holes  37 ,  38 . The enlarged adhesive pool  42  is formed as a recess by means of the half etching by a thickness of about the half of the plate thickness of each of the plates  12  to  14 . It is preferable that the diameter of the air release hole is the same as the width of the enlarged adhesive pool  42 . However, the former may be smaller than the latter. Any excessive adhesive  41 , which is located on the intermediate layers during the joining with the adhesive  41 , is pooled or accumulated in the enlarged adhesive pools  42 . Therefore, it is possible to greatly decrease the amount of the adhesive  41  which would otherwise outflow to the outside of the cavity unit  9 . The following effect is obtained. That is, it is possible to decrease the frequency of the maintenance operation in the same manner as described above. 
     In a modified embodiment of the foregoing embodiment, the positions of the air release holes  37 ,  38 , and the opening  136  of the vertically adjoining plates are laterally deviated so that their axes are not coincident with each other (they are deviated so that the axes of the upper and lower air release holes, which extend in the stacking direction of the plates, are in discord). For example, as in the embodiment shown in  FIGS. 11 ,  12 A, and  12 B, the air release hole  38  of the upper layer plate  13  is formed at the position to overlap with a part of the enlarged adhesive pool  42  of the lowermost layer plate  14  as viewed in the plan view, the air release hole  37  of the upper layer plate  12  is formed at the position to overlap with a part of the enlarged adhesive pool  42  of the plate  13  as viewed in the plan view, and the opening  136  of the upper layer plate  11  is formed at the position to overlap with a part of the enlarged adhesive pool  42  of the plate  12  as viewed in the plan view. In this arrangement, it is established that at least the axes of the vertically adjoining air release holes are laterally deviated from each other so that they are not coincident with each other. 
     When the positions of the upper and lower air release holes are laterally deviated as described above, the adhesive  41 , which is applied to the overlay surfaces of the plates  11  to  14 , is accumulated in the enlarged adhesive pools  42  as a result of the inflow thereinto from the release grooves  34 ,  35  during the pressing and joining process, and then the adhesive  41  is moved toward the plate disposed at the upper layer via the air release holes penetrating in the vertical direction of the respective plates. Thus, the adhesive  41  is moved along with the zigzag routes. Therefore, the adhesive  41  having the small viscosity does not suddenly arrive at the upper layer plate. The adhesive  42  is reliably captured in the air release holes  37  ( 38 ) having the large diameters and the enlarged adhesive pools  42  of the respective layers. It is possible to decrease the amount of protrusion of the adhesive  41  to the outside of the cavity unit  9 . 
     The interconnecting tabs  106  are cut from the lead frames  100   a  to  100   d  (see  FIG. 8 ) having been adhered and fixed as described above, and the integrated cavity units  9  are removed. After that, the nozzle plate  10  is fixed with the adhesive as well. The cavity unit  9  is constructed as follows. That is, the ink inflows into the common ink chambers  12   a ,  12   b  from the supply holes  19   a ,  19   b  bored through the first ends of the base plate  14  and the spacer plate  13 . The ink passes from the common ink chambers  12   a  via the respective ink flow passages  18 , and the ink is distributed into the respective pressure chambers  16 . After that, the ink passes from the respective pressure chambers  16  via the communication holes  17 ,  17 ,  17 , and the ink arrives at the nozzles  15  corresponding to the pressure chambers  16 . 
     The piezoelectric actuator  20  is assembled and attached to the cavity plate in the same manner as explained in the first embodiment. 
     Third Embodiment 
     A third embodiment of the present invention will be explained below with reference to  FIG. 13 .  FIG. 13  shows shapes of release grooves  142  as viewed in plan view according to a third embodiment. In this embodiment, the respective release grooves  142  are formed by means of the half etching to have a meandering form as viewed in plan view on one surface of each of plates  11  to  14 .  FIG. 13  shows a case in which the plurality of meandering release grooves  142  are formed to have long dimensions along the long side on one surface of the spacer plate  13 . Air release holes  43 , which penetrate in the plate thickness direction of the spacer plate  13 , are provided at appropriate positions of the release grooves  142 . The other constitutive components of the spacer plate  13  are the same as those in the first embodiment. Therefore, the same constitutive components are designated by the same reference numerals, any detailed explanation of which is omitted. 
     Few portions of the release grooves  142  according to the third embodiment are parallel to the long side direction and the short side direction of the respective plates. Therefore, even when any bending moment acts on a cavity unit  9  obtained by stacking the plurality of plates  11  to  14 , for example, so that an intermediate portion in the long side direction is greatly bent, the rigidity against the bending moment is not greatly decreased (lowered) locally. Thus, it is possible to obtain the cavity unit  9  having a high degree of strength even though the thickness is thin. 
     Fourth Embodiment 
     A fourth embodiment of the present invention will be explained below with reference to the drawings.  FIGS. 14 and 15  show shapes of release grooves  44  according to a fourth embodiment as viewed in plan view. The respective release grooves  44  are formed so that they extend in inclined directions with respect to the long side direction and the short side direction of each of plates (directions not perpendicular thereto) as viewed in plan view on one surface of each of the plates  11  to  14 . The respective release grooves  44  are formed by means of the half etching.  FIG. 14  shows a case in which the plurality of release grooves  44  are formed on one surface of the spacer plate  13  so that the directions of inclination of the release grooves  44  are alternately changed oppositely in the longitudinal direction, i.e., in a separated and inverted V-shaped form as viewed in plan view. Although not shown, air release holes, which penetrate in the plate thickness direction of the plate, may be provided at appropriate positions of the respective release grooves  44 . Further, as shown in  FIG. 15 , it is desirable that the release grooves  44  are formed at deviated positions so that the release grooves  44 , which are formed on the adjoining stacked plates, are not superimposed completely as viewed in plan view when the plurality of plates are stacked. The other constitutive components of the spacer plate  13  are the same as those in the first embodiment. Therefore, the same constitutive components are designated by the same reference numerals, any detailed explanation of which is omitted. 
     No portions of the release grooves  44  according to the fourth embodiment are parallel to the long side direction and the short side direction of the respective plates in the directions in which the release grooves  44  extend. Further, the release grooves  44  are not parallel to only one direction as a whole as well. Therefore, even when any bending moment acts on a cavity unit  9  obtained by stacking the plurality of plates  11  to  14 , for example, so that an intermediate portion in the long side direction is greatly bent, the rigidity against the bending moment is not greatly decreased (lowered) locally. Thus, it is possible to obtain the cavity unit  9  having a high degree of strength even though the thickness is thin. 
     Fifth Embodiment 
     A fifth embodiment of the present invention will be explained below with reference to the drawings.  FIGS. 16 ,  17 A to  17 C show the fifth embodiment in which a plurality of anchor holes  45  are bored penetratingly in the plate thickness direction of each of plates. The shape of each of the anchor holes  45  is circular as viewed in plan view.  FIG. 16  shows the large number of anchor holes  45  which are arranged for the spacer plate  13  in the zigzag arrangement as viewed in plan view. As shown in  FIG. 17C , it is desirable that the anchor holes  45  are formed at deviated positions at which the anchor holes  45  formed through the adjoining stacked plates are not superimposed completely as viewed in plan view when the plurality of plates are stacked. 
     The other constitutive components of the spacer plate  13  are the same as those in the first embodiment. Therefore, the same constitutive components are designated by the same reference numerals, any detailed explanation of which is omitted. 
     In the fifth embodiment, an adhesive  41  is previously applied to one surface of each of the plates  11  and  12  as shown in  FIG. 17A , and then the pressure is applied while adjusting the positions of the plurality of plates  11  to  13  stacked in the vertical direction to stack and join the plates  11  to  13  by the aid of the adhesive  41  thereby as shown in  FIG. 17B . Accordingly, the excessive adhesive  41  enters the respective anchor holes  45 , and the adhesive  41  is adhered to at least portions  45   a  of the circumferential surfaces of the anchor holes  45  so that the force is allowed to act to fasten the both plates (referred to as “anchoring effect”). Therefore, it is possible to effect the powerful joining function as compared with the joining force brought about by the adhesive based on only the areas of the stacking surfaces at which the plates are opposed to one another. Further, the anchor holes  45  penetrate in the plate thickness direction of each of the plates. Therefore, the air release function is also provided such that the air, which stays on the stacking surfaces and in the anchor holes  45 , can be released to the outside via the anchor holes  45  when the respective plates are joined to one another with the adhesive  41 . Additionally, an effect is obtained such that the air release function is facilitated when portions of the anchor holes  45  are arranged to make the communication in the stacking direction at the adjoining stacked portions of the plates. 
     The large number of anchor holes  45  are disposed in the zigzag arrangement as viewed in plan view when the anchor holes  45  are bored through one plate. Accordingly, it is possible to increase the spacing distances between the mutually adjoining anchor holes  45  as compared with a case in which identical numbers of anchor holes  45  are arranged linearly in the long side direction and the short side direction of the plate. Thus, it is possible to minimize the decrease (lowering) of the rigidity with respect to the bending of the cavity unit  9 . Further, the rigidity against the bending moment is not greatly decreased (lowered) locally, because the mutually adjoining anchor holes  45  of one plate are not connected to one another in the in-plane direction of the plate. It is possible to obtain the cavity unit  9  having a high degree of strength even though the thickness is thin. 
       FIGS. 18A and 18B  show a modified embodiment of the anchor holes  45 . For example, when the plates  11  and  12  are stacked and joined; the anchor holes  45  may be formed to have such diameters that large diameter portions  45   b  are formed on one surface side of the plate, and small diameter portions  45   c  are formed on the other surface side of the plate. Owing to the adhesive  41  entered the large diameter portions  45   b , it is possible to further increase the joining area, and thus it is possible to enhance the anchoring effect. Alternatively, as shown in  FIG. 18C , the anchor holes  47  may be formed and bored so that positions at which the anchor holes  47  are open on one surface of the plate P are deviated from positions at which they are open on the other surface. Further alternatively, the shape of the anchor hole  45 ,  47  as viewed in plan view is not limited to the shape of circular hole. It is possible to adopt arbitrary shapes including, for example, elliptic shapes, oblong circular shapes such as oval shapes, and rectangular shapes. It is preferable that the respective anchor holes  45 ,  47  are bored through the plate made of metal by means of the etching. 
     When a large number of anchor holes  45  having circular shapes are bored, then the distance L to the adjoining anchor hole  45  may be made larger than the diameter D of the anchor hole  45  (D&lt;L), or the distance L may be made larger than the plate thickness T of the plate P (T&lt;L). Accordingly, it is possible to minimize the decrease (lowering) of the bending rigidity of the cavity unit  9  to be as small as possible. 
     The present invention has been applied to the assembling of the ink-jet head in the respective embodiments described above. However, the present invention is also applicable to the assembling of electronic parts. In this case, the present invention is most appropriate to a structure obtained by stacking and fixing a plurality of thin plate-shaped parts such as a plurality of lead frames including at least one thin plate-shaped part in which a liquid flow passage is formed in a predetermined pattern on at least one surface.