JP6413798B2 - Liquid ejection device - Google Patents

Description

  The present invention relates to a liquid ejecting apparatus that ejects liquid from a nozzle.

  Patent Document 1 describes an ink jet head that ejects ink from nozzles. The ink jet head described in Patent Literature 1 includes a flow path unit in which an ink flow path including a plurality of nozzles and a plurality of pressure chambers is formed, and a piezoelectric actuator that applies pressure to the ink in the plurality of pressure chambers. . The piezoelectric actuator includes an ink separation layer, two piezoelectric layers, a common electrode, and a plurality of individual electrodes.

  The ink separation layer and the two piezoelectric layers are laminated on the upper surface of the flow path unit. The common electrode extends over almost the entire area between the two piezoelectric layers. The plurality of individual electrodes are arranged so as to overlap the central part of the corresponding pressure chamber. Further, the individual electrode extends to a position that does not overlap the pressure chamber on the side opposite to the nozzle in the longitudinal direction of the pressure chamber, and the tip portion serves as a connection terminal.

JP 2014-195929 A

  In the ink-jet head of Patent Document 1, as described above, the common electrode extends over almost the entire area between the two piezoelectric layers, and the individual electrode is located on the side opposite to the nozzle in the longitudinal direction of the pressure chamber so as not to overlap the pressure chamber. It extends to. Therefore, when a voltage is applied between the individual electrode and the common electrode, the pressure chamber of the portion near the end of the pressure chamber in the portion overlapping the pressure chamber of the piezoelectric layer or the pressure chamber of the portion outside the pressure chamber of the piezoelectric layer An electric field is generated in the vicinity of the ends of the electrodes, and these portions of the piezoelectric layer contract. The deformation of the piezoelectric actuator is inhibited by the contraction of these portions of the piezoelectric layer.

  An object of the present invention is to provide a liquid ejection device capable of greatly deforming a piezoelectric actuator while suppressing the inhibition of deformation of the piezoelectric actuator due to contraction of the piezoelectric layer.

According to a first aspect of the present invention, there is provided a liquid discharge apparatus including a flow path forming member having a liquid flow path including a plurality of nozzles and a plurality of pressure chambers communicating with the plurality of nozzles, and pressure applied to the liquid in the plurality of pressure chambers. A piezoelectric actuator for providing the first piezoelectric layer that covers the plurality of pressure chambers, and is disposed on one surface of the first piezoelectric layer for each of the pressure chambers. A plurality of first electrodes that overlap with the plurality of pressure chambers when viewed from a first direction perpendicular to the one surface of the one piezoelectric layer, and disposed on the other surface of the first piezoelectric layer; A second electrode overlapping the plurality of pressure chambers and the plurality of first electrodes when viewed, the pressure chamber being elongated in a second direction orthogonal to the first direction, The length in two directions is not less than 500 μm and not more than 1000 μm, The length of the third direction orthogonal to both the one direction and the second direction is 250 μm or more and 500 μm or less, and in the third direction, both ends of the first electrode are located inside the pressure chamber, In the second direction, one end of the first electrode is located inside the pressure chamber, the other end of the first electrode is located outside the pressure chamber, and the other end of the first electrode The portion including the end on the side is a tapered portion in which the length in the third direction becomes shorter as the end is approached, and the other end of the second electrode is located inside the pressure chamber. position, and the and the length between the other end of the pressure chamber is 25μm or more, and, 50 [mu] m Ri der hereinafter proximal end of the tapered portion, the other side of the second electrode Or the other side of the other side of the second electrode. It is located.
According to a second aspect of the present invention, there is provided a liquid ejection device including a flow path forming member having a liquid flow path including a plurality of nozzles and a plurality of pressure chambers communicating with the plurality of nozzles, and pressure applied to the liquid in the plurality of pressure chambers. A piezoelectric actuator for providing the first piezoelectric layer that covers the plurality of pressure chambers, and is disposed on one surface of the first piezoelectric layer for each of the pressure chambers. A plurality of first electrodes that overlap with the plurality of pressure chambers when viewed from a first direction perpendicular to the one surface of the one piezoelectric layer, and disposed on the other surface of the first piezoelectric layer; A second electrode overlapping the plurality of pressure chambers and the plurality of first electrodes when viewed, the pressure chamber being elongated in a second direction orthogonal to the first direction, The length in two directions is not less than 500 μm and not more than 1000 μm, The length of the third direction orthogonal to both the one direction and the second direction is 250 μm or more and 500 μm or less, and in the third direction, both ends of the first electrode are located inside the pressure chamber, In the second direction, one end of the first electrode is located inside the pressure chamber, the other end of the first electrode is located outside the pressure chamber, and includes the other end. The portion is a tapered portion in which the length in the third direction becomes shorter as it approaches the end, and the other end of the second electrode is located inside the pressure chamber, and the pressure A length between the other end of the chamber and the other end of the pressure chamber is 25 μm or less, and a length between the proximal end of the tapered portion and the other end of the pressure chamber is 25 μm or less; And it is located in the said one side rather than the said other end of the said 2nd electrode.

  According to the present invention, the region where at least one of the first electrode and the second electrode is not disposed is formed over the entire circumference of the end of the pressure chamber. As a result, deformation of the piezoelectric actuator during driving is less likely to be inhibited, and deformation of the piezoelectric actuator can be increased. Furthermore, when the length of the pressure chamber in the second direction is 500 μm or more and 1000 μm or less, and the length of the pressure chamber in the third direction is 250 μm or more and 500 μm or less, the second electrode in the second direction Since the length between the other end and the other end of the pressure chamber is 50 μm or less, the deformation of the piezoelectric actuator during driving can be maximized.

1 is a schematic configuration diagram of a printer according to an embodiment of the present invention. It is a top view of the inkjet head of FIG. It is a figure which shows electrode arrangement | positioning on the upper surface of a piezoelectric layer. It is a figure which shows electrode arrangement | positioning on the upper surface of a piezoelectric layer. FIG. 3 is a partially enlarged view of FIG. 2. It is the VI-VI sectional view taken on the line of FIG. It is the VII-VII sectional view taken on the line of FIG. (A) is a figure which shows a deformation | transformation of the piezoelectric actuator in the cross section of FIG. 6, (b) is a figure which shows a deformation | transformation of the piezoelectric actuator in the cross section of FIG. It is a figure which shows the relationship between length L1, L2 and the value A in the Example of this invention, (a) is a relationship when changing the thickness of a piezoelectric layer, (b) is changing the thickness of a piezoelectric layer. However, it shows the relationship when compliance is matched. It is a figure which shows the relationship between length L1, L2 and the value A in the Example of this invention, (a) is a relationship when changing the width | variety of an individual electrode, (b) is changing the length of a pressure chamber. This shows the relationship when FIG. 8 is a cross-sectional view of a piezoelectric actuator according to a first modification, where (a) a cross section corresponding to FIG. 6 and (b) a cross section corresponding to FIG. FIG. 8 is a cross-sectional view of a piezoelectric actuator of a second modification, where (a) a cross section corresponding to FIG. 6 and (b) a cross section corresponding to FIG. (A) is a figure equivalent to FIG. 5 of the modification 3, and (b) is a figure equivalent to FIG. 5 of the modification 4. (A) is a figure equivalent to FIG. 5 of the modification 5, (b) is a figure equivalent to FIG. 5 of the modification 6.

  Hereinafter, preferred embodiments of the present invention will be described.

(Printer)
As shown in FIG. 1, the printer 1 according to the present embodiment includes a carriage 2, an ink jet head 3 (“liquid ejecting apparatus” of the present invention), a paper transport roller 4, and the like. The carriage 2 is supported by two guide rails 5 extending in the scanning direction (the “second direction” in the present invention), and reciprocates in the scanning direction along the guide rails 5. In the following description, as shown in FIG. 1, the right and left sides are defined in the scanning direction. The inkjet head 3 is mounted on the carriage 2 and ejects ink from a plurality of nozzles 15 formed on the lower surface thereof. The paper transport rollers 4 are arranged on both sides of the carriage 2 in the transport direction (the “third direction” in the present invention) orthogonal to the scanning direction, and transport the recording paper P in the transport direction.

  In the printer 1, printing is performed on the recording paper P by ejecting ink from the inkjet head 3 that reciprocates in the scanning direction together with the carriage 2 while transporting the recording paper P in the transporting direction by the paper transporting roller 4. .

(Inkjet head)
Next, the inkjet head 3 will be described in detail. As shown in FIGS. 2 to 5, the inkjet head 3 includes a flow path unit 21 (“flow path forming member” of the present invention) and a piezoelectric actuator 22. In the following, as shown in FIGS. 5 and 6, the center side of the inkjet head 3 in the scanning direction may be referred to as the head center side (the “other side in the second direction” in the present invention). The outer peripheral side of the inkjet head 3 in the scanning direction may be the head outer peripheral side (“one side in the second direction” of the present invention). Moreover, the flow path unit 21 and the piezoelectric actuator 22 have the flow path unit 21 stacked below, and the direction in which both are stacked is referred to as the vertical direction.

(Flow path unit)
The flow path unit 21 is formed by stacking four plates 31 to 34. The plates 31 to 33 are made of a metal material such as stainless steel. The plate 34 is made of a synthetic resin material such as polyimide or a metal material similar to the plates 31 to 33.

  A plurality of pressure chambers 10 are formed in the plate 31. The pressure chamber 10 has a substantially rectangular planar shape with a length in the scanning direction as a longitudinal direction and a length in the scanning direction of about 500 to 1000 μm and a length in the transport direction of about 250 to 500 μm. The plurality of pressure chambers 10 are arranged in a staggered manner at equal intervals in the transport direction, and form two pressure chamber rows 9 arranged in the scanning direction. The pressure chamber 10 in the pressure chamber row 9 is transported by a length that is half the distance between the two pressure chambers 10 adjacent in the pressure chamber row 9 with respect to the pressure chamber 10 in the adjacent pressure chamber row 9. It is shifted to.

  The plate 32 is formed with substantially circular through holes 12 and 13. The plurality of through-holes 12 are arranged at positions that overlap with the end of the pressure chamber 10 on the center side of the head when viewed from the vertical direction (the “first direction” in the present invention). The plurality of through holes 13 are arranged at positions that overlap with the end portion on the outer periphery side of the head. The through hole 12 connects the pressure chamber 10 and a manifold channel 11 described later, and the through hole 13 connects the pressure chamber 10 and a through hole 14 described later.

  A manifold channel 11 and a through hole 14 are formed in the plate 33. The two manifold channels 11 are provided for the two pressure chamber rows 9 and extend in the transport direction across the entire length of the corresponding pressure chamber rows 9. In addition, the manifold channel 11 overlaps most of the pressure chambers 10 in the pressure chamber row 9 and the head outer peripheral side end portion (particularly, the periphery of the through hole 13), as viewed from the vertical direction. The two manifold channels 11 are connected at the downstream end in the transport direction. At this time, the connecting portion of the two manifold channels 11 is adjacent to the downstream end of the two pressure chamber rows 9, and for example, as shown in FIG. Overlapping in the direction. Further, a through hole 14 is formed at the outer peripheral end of the head when viewed in the vertical direction. Each through hole 14 has a substantially circular outer shape, and connects the through hole 13 and a nozzle 15 described later.

  In the plate 34, a plurality of nozzles 15 are formed in a portion overlapping with the plurality of through holes 14 when viewed in the vertical direction. The nozzle 15 overlaps the two through holes 13 and 14 at the head outer peripheral end of the pressure chamber 10 when viewed in the vertical direction. As shown in FIG. 2, the plurality of nozzles 15 are arranged in two rows in a staggered manner at a printing resolution in the transport direction.

  Ink is distributed to the two manifold channels 11 when supplied to the connection portion from the opening of the ink supply hole (ink supply port 8). The ink in the manifold channel 11 flows into the pressure chamber 10 through the through hole 12. The ink flows in the pressure chamber 10 from the center of the head toward the outer periphery of the head, and reaches the nozzle 15 through the through holes 13 and 14. When a piezoelectric actuator 22 described later is driven, the pressure chamber 10 is deformed and ink droplets are ejected from the nozzle 15.

(Piezoelectric actuator)
The piezoelectric actuator 22 is an aggregate of a plurality of unit actuators as shown in FIG. The unit actuator can be deformed independently and is arranged for each pressure chamber 10. The unit actuator is a laminated body of a diaphragm and a piezoelectric element portion laminated thereon. Among them, the piezoelectric element portion has a basic structure of a sandwich structure in which a piezoelectric layer is sandwiched between a common electrode and individual electrodes. When a voltage is applied between the two electrodes, the piezoelectric layer in between contracts spontaneously, so that the piezoelectric element part deforms into a convex shape together with the diaphragm, and changes the volume of the pressure chamber 10.

  In this embodiment, the unit actuator has a cross-sectional structure as shown in FIGS. The diaphragm is composed of an ink separation layer 41 and a piezoelectric layer 42. In the piezoelectric element portion, an individual electrode 45 (the “first electrode” of the present invention) is arranged in the center, and a piezoelectric layer and a common electrode are sequentially stacked in both the upper and lower directions. In this case, the common electrode 47 is formed on the piezoelectric layer 42 (vibrating plate). The structure of each layer will be described below.

  The ink separation layer 41 is made of a metal material such as stainless steel, and is disposed on the upper surface of the flow path unit 21 so as to cover all the pressure chambers 10. The ink separation layer 41 is for preventing the ink in the pressure chamber 10 from coming into contact with the piezoelectric layer 42 described below.

  The piezoelectric layers 42 to 44 are also plate-like members that cover all the pressure chambers 10 and are made of a piezoelectric material mainly composed of lead zirconate titanate, which is a mixed crystal of lead titanate and lead zirconate. Among these, the piezoelectric layer 42 is formed on the ink separation layer 41. As shown in FIG. 6, an electrode and a piezoelectric layer are sequentially laminated up to the outermost common electrode 46 above this. Further, the thickness of each of the piezoelectric layers 42 to 44 is, for example, about 5 to 30 μm.

  The plurality of individual electrodes 45 are disposed between the piezoelectric layer 43 (the “second piezoelectric layer” of the present invention) and the piezoelectric layer 44 (the “first piezoelectric layer” of the present invention). The plurality of individual electrodes 45 are individually provided for the plurality of pressure chambers 10, and overlap the central portion of the corresponding pressure chamber 10. In the carrying direction, both ends 45 a and 45 b of the individual electrode 45 are located inside the pressure chamber 10. That is, the upstream end 45 a is positioned downstream of the upstream end 10 a of the pressure chamber 10, and the downstream end 45 b is positioned upstream of the downstream end 10 b of the pressure chamber 10. Yes.

  In the scanning direction, the end 45 c on the head outer peripheral side of the individual electrode 45 is located inside the pressure chamber 10, and the end 45 d on the center side of the head is located outside the pressure chamber 10. That is, both ends 45c and 45d are located on the center side of the head with respect to the corresponding ends 10c and 10d of the pressure chamber 10. In addition, as shown in FIG. 3, the individual electrode 45 of this embodiment includes a tapered portion 45e whose length in the transport direction becomes shorter as the portion drawn outward from the end 10d of the pressure chamber 10 approaches the end 45d. It has become.

  As shown in FIG. 6, the common electrode 46 and the surface electrodes 49 a and 49 b are stacked on the upper surface of the piezoelectric layer 44 farthest from the pressure chamber 10, and a plurality of through holes 48 a and 48 b penetrate each pressure chamber 10. Is formed. The plurality of through holes 48 a are arranged in a zigzag pattern in two rows in the transport direction at the center of the piezoelectric layer 44. The through hole 48a is filled with a conductive material. The through hole 48a electrically connects the top surface electrode 49a and the tip portion of the tapered portion 45e of the individual electrode 45 that are vertically overlapped. Each surface electrode 48a is applied with a drive signal (a pulse signal composed of a ground potential and a drive potential) from a driver IC via a wiring (not shown).

  The tapered portion 45e is provided in the individual electrode 45, for example, by arranging the plurality of individual electrodes 45 on the center side of the head in the scanning direction as far apart as possible in the transport direction. This is to prevent a short circuit between them.

  The common electrode 46 is laminated on the upper surface of the piezoelectric layer 44, and has a plurality of overlapping portions 46a, two connection portions 46b, and a connection portion 46c. The overlapping portion 46a overlaps with the pressure chamber 10 in the vertical direction, and is aligned with another overlapping portion 46a with a gap 39 in the transport direction. As shown in FIG. 2, the plurality of overlapping portions 46a are arranged in a staggered manner at equal intervals in the transport direction, and form two overlapping portion rows arranged in the scanning direction. The arrangement form is almost the same as in the case of the plurality of pressure chambers 10. The connecting portion 46b is formed for each overlapping portion row, and connects the end portions of the overlapping portion 46a on the outer periphery side of the head. The two connection portions 46 b are both outside the pressure chamber 10. The connection portion 46c extends in the scanning direction on the upstream side in the transport direction, is adjacent to the two overlapping portion rows, and connects the ends of the two connection portions 46b. The connection portion 46c is bent at the left end in the scanning direction toward the downstream side in the transport direction to form a connection terminal 46d. A wiring member (not shown) is connected to the connection terminal 46d and is always held at the ground potential.

  Here, the overlapping portion 46 a has both ends 46 a 1 and 46 a 2 positioned outside the pressure chamber 10 in the transport direction. That is, the upstream end 46a1 is positioned upstream of the upstream end 10a of the pressure chamber 10, and the downstream end 46a2 is positioned downstream of the downstream end 10b of the pressure chamber 10. Yes. The overlapping portion 46 a is connected to the connecting portion 46 b on the outer peripheral side of the head on the outer side of the pressure chamber 10, and stops on the inner side of the pressure chamber 10 on the center side of the head. In other words, in the scanning direction, the head center side end 46a3 is located closer to the head outer peripheral side than the head center side end 10d of the pressure chamber 10. And as shown in FIG. 5, the length L1 between both is 25 micrometers or more and 50 micrometers or less.

  The common electrode 47 is laminated on the upper surface of the piezoelectric layer 42 and has two strip portions 47a and a connection portion 47b. As shown in FIG. 4, the belt-like portion 47 a is provided to overlap with the corresponding pressure chamber row 9 (plural pressure chambers 10) over the entire length, and extends in the transport direction. The connecting portion 47b extends in the scanning direction on the downstream side in the transport direction, is adjacent to the two pressure chamber rows 9, and connects the ends of the two belt-like portions 47a. The connection portion 47a is bent at the right end in the scanning direction toward the upstream side in the transport direction to form a connection terminal 47c. A plurality of through holes 48b are formed in the two piezoelectric layers 43 and 44 so as to overlap with the connection terminal 47c in the vertical direction. The connection terminal 47 c is electrically connected to the surface electrode 49 b on the upper surface of the piezoelectric layer 44 through the through hole 48 b. A wiring member (not shown) is connected to the connection terminal 47c and is always held at the ground potential.

  Here, the belt-like portion 47 a is such that the head outer peripheral end 47 a 1 is located closer to the head outer peripheral side than the head outer peripheral end 10 c of the pressure chamber 10 in the scanning direction. On the other hand, the head center side end 47 a 2 is located closer to the head outer circumference side than the head center side end 10 d of the pressure chamber 10. As shown in FIG. 5, the length L2 between the belt-like portion 47a and the end of the pressure chamber 10 on the center side of the head is 25 μm or more and 50 μm or less and shorter than the length L1.

  The portion of the piezoelectric layer 43 sandwiched between the individual electrodes 45 and the strip-shaped portion 47 a of the common electrode 47 and the portion of the piezoelectric layer 44 sandwiched between the overlapping portions 46 a of the individual electrodes 45 and the common electrode 46. Each portion is polarized in a direction from the individual electrode toward the common electrode. For this reason, when a drive signal is applied to the individual electrode 45, any portion contracts in the surface direction and deforms toward the pressure chamber 10 together with the diaphragm that does not contract spontaneously.

(Piezoelectric actuator drive method)
Next, a method for ejecting ink from the nozzle 15 by driving the piezoelectric actuator 22 will be described. In the piezoelectric actuator 22, all the individual electrodes 45 are held at the ground potential before being driven.

  When ink is ejected from a certain nozzle 15, the potential of the individual electrode 45 corresponding to that nozzle 15 is switched from the ground potential to the driving potential. When the potential of the individual electrode 45 becomes higher than that of the common electrodes 46 and 47, an electric field from the individual electrode 45 toward the common electrodes 46 and 47 is generated in the piezoelectric layers 43 and 44. Since the piezoelectric layers 43 and 44 are polarized in the direction from the individual electrode 45 to the common electrodes 46 and 47, both contract in the plane direction. On the other hand, the diaphragm (ink separation layer 41 and piezoelectric layer 42) does not spontaneously expand and contract due to an electric field. Since a strain difference is generated between the piezoelectric element portion and the diaphragm, the unit actuator is deformed in a convex manner toward the pressure chamber 10 as shown in FIG. At this time, the ink in the pressure chamber 10 is pressurized and a part of the ink is ejected from the nozzle 15 as an ink droplet.

  As described above, the piezoelectric layers 43 and 44 are deformed (contracted in this embodiment) by an electric field. If the electric field extends only in the region overlapping the central portion of the pressure chamber 10, the deformation of the piezoelectric layers 43 and 44 efficiently contributes to the volume change of the pressure chamber 10. As the electric field strength increases or the range increases, the deformation of the piezoelectric layers 43 and 44 also increases. At this time, the piezoelectric layers 43 and 44 in the vicinity of the end of the pressure chamber 10 are stretched to allow the piezoelectric layers 43 and 44 in the region overlapping the pressure chamber 10 to contract.

  The unit actuator is fixed to the plate 31 outside the pressure chamber 10. In the vicinity of the end of the pressure chamber 10, the unit actuator exhibits a cantilevered behavior with the end of the pressure chamber 10 as a fulcrum. Therefore, when the portion of the piezoelectric layers 43 and 44 that overlaps the portion near the end of the pressure chamber 10 is contracted by the electric field, the piezoelectric layers 43 and 44 in the region overlapping the central portion of the pressure chamber 10 are not easily contracted. This part of 43 and 44 tries to keep away from the pressure chamber 10. In addition, when the portion of the piezoelectric layers 43 and 44 located outside the pressure chamber 10 near the end of the pressure chamber 10 is contracted by an electric field, the portion of the piezoelectric layers 43 and 44 that overlaps the pressure chamber 10 is on the pressure chamber 10 side. It is obstructed to deform so as to be convex. In these cases, the deformation of the unit actuator is reduced accordingly. Therefore, as the distance between the overlapping portions 46a and 47a of the individual electrode 45 and the common electrodes 46 and 47 and the end of the pressure chamber 10 is large, the amount of deformation of the unit actuator increases as the distance decreases. At a certain interval, the amount of deformation becomes maximum. When the interval is further reduced, the deformation near the end of the pressure chamber 10 is affected, and the amount of deformation decreases.

  On the other hand, in the present embodiment, both ends 45a and 45b of the individual electrode 45 are located inside the pressure chamber 10 in the transport direction. In the scanning direction, the end 45 c on the head outer peripheral side of the individual electrode 45 is also located inside the pressure chamber 10. The head center side end 45 d is located closer to the head center side than the head center side end 10 d of the pressure chamber 10. However, the head central side ends 46a3 and 47a2 of the overlapping portion 46a and the belt-like portion 47a are located on the outer peripheral side of the head with respect to the end 10d of the pressure chamber 10.

  From the above, in the present embodiment, a region where at least one of the individual electrode 45 and the common electrodes 46 and 47 does not exist is formed over the entire circumference of the end of the pressure chamber 10. As a result, the electric field stops in a region overlapping the central portion of the pressure chamber 10 of the piezoelectric layers 43 and 44. Alternatively, even if the electric field reaches a region outside the region of the piezoelectric layers 43 and 44, the electric field is slightly outside the region. As a result, the contraction of the piezoelectric layers 43 and 44 at the portion where the deformation of the unit actuator is inhibited can be suppressed. Thereby, the deformation of the piezoelectric actuator 22 can be prevented from being hindered, and the deformation of the piezoelectric actuator 22 can be increased.

  Furthermore, in the present embodiment, in the scanning direction, the length L1 between the head center side end 46a3 of the overlapping portion 46a of the common electrode 46 and the head center side end 10d of the pressure chamber 10 is 50 μm or less. It has become. When the length L1 is set to 50 μm or less, as can be seen from the results of Examples described later, the deformation of the piezoelectric actuator 22 based on the contraction of the piezoelectric layer 44 can be maximized.

  Similarly, in the present embodiment, in the scanning direction, the length L2 between the head center side end 47a2 of the strip 47a of the common electrode 47 and the head center side end 10d of the pressure chamber 10 is 50 μm or less. It has become. When the length L2 is set to 50 μm or less, as can be seen from the results of Examples described later, the deformation of the piezoelectric actuator 22 based on the contraction of the piezoelectric layer 43 can be maximized.

  In the present embodiment, the length L2 between the end 47a2 on the head center side of the belt-like portion 47a and the end 10d on the head center side of the pressure chamber 10 in the scanning direction is set to the head center side of the overlapping portion 46a. This length is shorter than the length L1 between the end 46a3 of the pressure chamber 10 and the end 10d of the pressure chamber 10 on the center side of the head. Thereby, in the part which contributes to the increase in deformation of the piezoelectric actuator 22 in the piezoelectric layer 43, the area where the individual electrode 45 and the common electrodes 46 and 47 overlap increases, and the piezoelectric actuator 22 can be deformed more greatly.

  In the present embodiment, as described above, the individual electrode 45 is drawn to the upper surface of the piezoelectric layer 44 through the through hole 48 a and connected to the surface electrode 49 a disposed on the upper surface of the piezoelectric layer 44. . Here, from the viewpoint of preventing a short circuit or the like, it is preferable that the surface electrode 49a disposed on the upper surface of the piezoelectric layer 44 and the common electrode 46 are separated to some extent. In the present embodiment, the head center side end 46a3 of the overlapping portion 46a is located closer to the head outer peripheral side than the head center side end 10d of the pressure chamber 10 in the scanning direction. Therefore, the surface electrode 49a and the overlapping portion 46a can be separated greatly without extending the tapered portion 45e of the individual electrode 45 to the head center side in the scanning direction. This contributes to miniaturization of the inkjet head 3 in the scanning direction.

  Further, in the present embodiment, the plurality of individual electrodes 45 are disposed inside without being exposed on the surface of the piezoelectric actuator 22. Therefore, moisture contained in the air around the piezoelectric actuator 22 does not come into contact with the individual electrode 45 at the driving potential and is not electrolyzed.

  In the present embodiment, the overlapping portion 46a of the common electrode 46 functions as a shield, so that charged particles existing around the piezoelectric actuator 22 can be prevented from crossing the piezoelectric layer 44 from above. Thereby, electrical destruction of the piezoelectric actuator 22 can be prevented.

  Here, unlike the present embodiment, in the common electrode 46, instead of the plurality of overlapping portions 46a, a belt-like portion similar to the belt-like portion 47a may be considered. In this case, the shielding effect by the common electrode 46 as described above becomes higher.

  However, in this case, since the area where the piezoelectric layer 44 and the common electrode 46 are in contact with each other is larger than in the case of the present embodiment, the sintered piezoelectric layers 42 to 44 are larger due to the difference in linear expansion coefficient. There is a risk of warping. If a large warp occurs in the piezoelectric layers 42 to 44, when the piezoelectric actuator 22 is joined to the flow path unit 21, a gap may be formed due to the warp and ink may leak.

  Therefore, in the present embodiment, the common electrode 46 has individual overlapping portions 46 a for each pressure chamber 10. In this case, the contact area between the piezoelectric layer 44 and the common electrode 46 becomes smaller than in the above case, and warpage after firing can be made difficult to occur.

  In the present embodiment, the strip 47a of the common electrode 47 functions as a shield, thereby preventing charged particles existing in the ink or the like in the pressure chamber 10 from crossing the piezoelectric layer 43 from below. Can do. Thereby, electrical destruction of the piezoelectric actuator 22 can be prevented.

  Here, unlike the present embodiment, the common electrode 47 may have a plurality of overlapping portions similar to the plurality of overlapping portions 46a instead of the strip-shaped portion 47a. However, the shield function as described above can be enhanced if the common electrode 47 has the belt-like portion 47a as in the present embodiment. In the present embodiment, since the common electrode 47 is sandwiched between the piezoelectric layer 42 and the piezoelectric layer 43, the piezoelectric material due to the difference in the linear expansion coefficient between the piezoelectric layers 42 and 43 and the common electrode 47 during firing. The warpage of the layers 42 to 44 hardly occurs. Therefore, even if the common electrode 47 has the belt-like portion 47a and the area where the piezoelectric layers 42 and 43 and the common electrode 47 overlap is increased, the piezoelectric layers 42 to 44 are not greatly warped.

  Next, examples according to the present embodiment will be described. 9A, 9B, 10A and 10B show the relationship between the lengths L1 and L2 and the value A indicating the degree of deformation of the piezoelectric actuator 22 in various inkjet heads 3. FIG. Show. Here, the value A is a value obtained by normalizing the change amount of the volume of the pressure chamber 10 with the maximum value of the change amount, and indicates that when the value A is 1, the change amount is the maximum. In Examples 1 to 9 described below, the length L1 and the length L2 are the same length.

  FIG. 9A shows the relationship between the lengths L1 and L2 and the value A in the piezoelectric actuator 22 in which the thicknesses of the piezoelectric layers 42 to 44 are different. More specifically, in FIG. 9A, the relationship between the lengths L1 and L2 and the value A when the thickness of the piezoelectric layers 42 to 44 is 15 μm (Example 1) is indicated by a solid line. In addition, the relationship between the lengths L1 and L2 and the value A when the thickness of the piezoelectric layers 42 to 44 is 10 μm (Example 2) is indicated by a broken line. In addition, the relationship between the lengths L1 and L2 and the value A when the thickness of the piezoelectric layers 42 to 44 is 5 μm (Example 3) is indicated by a dotted line. Further, the relationship between the lengths L1 and L2 and the value A when the thickness of the piezoelectric layers 42 to 44 is 30 μm (Example 4) is indicated by a one-dot chain line. Further, when the thickness of the piezoelectric layers 42 and 43 is 30 μm and the thickness of the piezoelectric layer 43 is 5 μm (Example 5), the relationship between the lengths L1 and L2 and the value A is indicated by a two-dot chain line. . In Examples 1 to 5, the length of the pressure chamber 10 in the transport direction (hereinafter sometimes referred to as “the width of the pressure chamber 10”) is 340 μm, and the length of the pressure chamber 10 in the scanning direction (hereinafter referred to as “the width of the pressure chamber 10”). The “length of the pressure chamber 10” may be 660 μm, and the length of the individual electrode 45 in the transport direction (hereinafter, sometimes referred to as “the width of the individual electrode 45”) is 230 μm.

  FIG. 9B changes the thickness of the piezoelectric layers 42 to 44 and adjusts the compliance ratio of the inkjet head 3 (ratio of the rigidity of the driving portion of the piezoelectric actuator 22 to the rigidity of the ink in the pressure chamber 10). The relationship between the lengths L1 and L2 and the value A in the piezoelectric actuator 22 in which the width of the pressure chamber 10 is changed is shown. More specifically, in FIG. 9B, the relationship between the length L and the value A in the first and second embodiments is indicated by a solid line and a broken line, respectively. Similarly to Example 2, the thickness of the piezoelectric layers 42 to 44 is 10 μm, and the length of the pressure chamber 10 is 267 μm in order to match the compliance ratio with Example 1 (Example 6). The relationship between L1 and L2 and the value A is indicated by a dotted line.

  FIG. 10A shows the relationship between the lengths L1 and L2 and the value A in the piezoelectric actuator 22 with the individual electrodes 45 having different widths. More specifically, in FIG. 10A, the relationship between the lengths L1 and L2 and the value A in the first embodiment is indicated by a solid line. In addition, the relationship between the lengths L1 and L2 and the value A when the width of the individual electrode 45 is 200 μm (Example 7) is indicated by a broken line. In addition, the relationship between the lengths L1 and L2 and the value A when the width of the individual electrode 45 is 300 μm (Example 8) is indicated by a broken line. In Examples 7 and 8, as in Example 1, the thickness of the piezoelectric layers 42 to 44 is 15 μm, the width of the pressure chamber 10 is 340 μm, and the length of the pressure chamber 10 in the scanning direction is 660 μm.

  FIG. 10B shows the relationship between the lengths L1 and L2 and the value A in the piezoelectric actuators 22 with different lengths of the pressure chambers 10 in the scanning direction. More specifically, in FIG. 10B, the relationship between the lengths L1 and L2 and the value A in the first embodiment is indicated by a solid line. Further, the relationship between the lengths L1 and L2 and the value A when the length of the pressure chamber 10 is 860 μm (Example 9) is indicated by a broken line. In Example 9, as in Example 1, the thickness of the piezoelectric layers 42 to 44 is 15 μm, and the width of the pressure chamber 10 is 340 μm.

  Then, from the results of Examples 1 to 9 shown in FIGS. 9A, 9 </ b> B, and 10 </ b> A and 10 </ b> B, the thickness of the piezoelectric layers 42 to 44, the width of the individual electrode 45, and the size of the pressure chamber 10. Regardless of the above, it can be seen that the value A hardly fluctuates in the range where the lengths L1 and L2 are 50 μm or less, and that the value A greatly decreases when the lengths L1 and L2 exceed 50 μm. Therefore, if the lengths L1 and L2 are 50 μm or less, the deformation of the piezoelectric actuator 22 due to the contraction of the piezoelectric layer 44 can be maximized.

  Next, modified examples in which various changes are made to the present embodiment will be described.

  In the above-described embodiment, the piezoelectric actuator 22 includes the three piezoelectric layers 42 to 44, the plurality of individual electrodes 45, and the two common electrodes 46 and 47. I can't. In Modification 1, as shown in FIGS. 11A and 11B, the piezoelectric actuator 60 is obtained by removing the piezoelectric layer 42 and the common electrode 47 from the above-described piezoelectric actuator 22. In the second modification, as shown in FIGS. 12A and 12B, the piezoelectric actuator 65 switches the position of the individual electrode 45 and the position of the common electrode 46 in the piezoelectric actuator 60 of the first modification. It has become a thing. That is, the individual electrode 45 is disposed on the upper surface of the piezoelectric layer 44, and the common electrode 46 is disposed between the piezoelectric layer 43 and the piezoelectric layer 44.

  In the piezoelectric actuators 60 and 65 of the first and second modified examples, when a potential difference is generated between the individual electrode 45 and the common electrode 46, the portion sandwiched between the individual electrode 45 and the common electrode 46 of the piezoelectric layer 44 is By contracting, the portions of the ink separation layer 41 and the piezoelectric layers 43 and 44 that overlap the pressure chamber 10 are deformed so as to protrude toward the pressure chamber 10. In the first and second modifications as well, in the scanning direction, between the end 46a3 on the head center side of the overlapping portion 46a of the common electrode 46 and the end 10d on the head center side of the pressure chamber 10 in the scanning direction. By setting the length L1 to 50 μm or less, the deformation of the piezoelectric actuators 60 and 65 during driving can be maximized.

  In the above-described embodiment, the common electrode 46 has a plurality of overlapping portions 46 a individually provided for the plurality of pressure chambers 10, and the gap 39 is formed between the adjacent overlapping portions 46 a. However, it is not limited to this. The common electrode 46 has a strip-like portion continuously extending over the plurality of pressure chambers 10 forming the pressure chamber row 9, similar to the strip-like portion 47 a (see FIG. 4), instead of the plurality of overlapping portions 46 a. It may be a thing.

  In the above-described embodiment, the common electrode 47 has the belt-like portion 47a. However, the present invention is not limited to this. The common electrode 47 is provided separately for the plurality of pressure chambers 10 and overlaps with the corresponding pressure chambers 10, similar to the plurality of overlapping portions 46 a (see FIGS. 2 to 7), instead of the belt-like portions 47 a. It may have an overlapping part.

  In the above-described embodiment, the length L1 between the head center side end 46a3 of the overlapping portion 46a and the head center side end 10d of the pressure chamber 10 in the scanning direction is the head center side of the belt-like portion 47a. This is longer than the length L2 between the end 47a2 of the pressure chamber 10 and the end 10d of the pressure chamber 10 on the center side of the head, but is not limited thereto. The length L1 may be a length equal to or shorter than the length L2.

  Further, in the above-described embodiment, the tapered portion 45e is disposed only in the range located closer to the head center side than the end 10d on the head center side of the pressure chamber 10 in the scanning direction. Absent. The proximal end portion 45e1 of the tapered portion 45e may be inside the pressure chamber 10. Due to the difference in positional relationship between the base end portion 45e1 and the ends 46a3 and 47a2 of the common electrodes 46 and 47 with respect to the end 10d of the pressure chamber 10, the following two modified examples 3 and 4 and then two modified examples 5 and 6 are obtained. Illustrate. In the modified examples 3 to 6, the two ends 46a3 and 47a2 are described at the same position, but it is needless to say that the present invention is not limited to this.

  In the modified example 3, as shown in FIG. 13A, the length L1 and the length L2 are the same length and are larger than 25 μm. Further, a length L3 between the base end portion 45e1 of the tapered portion 45e and the end 10d on the head center side of the pressure chamber 10 is shorter than the lengths L1 and L2. Moreover, in the modification 4, as shown in FIG.13 (b), length L3 is longer than length L1 and L2. The remaining configuration of the modification 4 is the same as that of the modification 3.

  Here, from the results of the above-described embodiment, even when the lengths L1 and L2 are varied within a range of 50 μm or less, the deformation of the piezoelectric actuator 22 during driving does not vary so much, but varies somewhat. When the lengths L1 and L2 become a certain length of about 25 μm, which is the center of the above range, the deformation at the time of driving becomes the largest. This position is shown as an alternate long and short dash line T in FIGS.

  Of the piezoelectric layers 43 and 44, the part inside the pressure chamber 10 mainly from the straight line T contributes to the deformation of the unit actuator, and the part outside the straight line T inhibits the part. Here, when the lengths L1 and L2 are 25 μm or more, the deformation of the unit actuator is defined by the area of the individual electrode 45 that overlaps the common electrodes 46 and 47 inside the pressure chamber 10 with respect to the straight line T. If the positional relationship between the end portion 45c of the individual electrode 45 and the end portion 10c of the pressure chamber 10 does not change on the outer periphery side of the head, the base end portion 45e1 of the tapered portion 45e is related to the ends 46a3 and 47a2 of the common electrodes 46 and 47. The overlapping area is larger on the head center side than on the head outer periphery side. That is, in the positional relationship between the base end portion 45e1 and the ends 46a3 and 47a2, the former is more deformed in the unit actuator.

  Therefore, when the lengths L1 and L2 are 25 μm or more, the length L3 between the base end portion 45e and the end 10d on the head center side of the pressure chamber 10 is preferably equal to or less than the lengths L1 and L2.

  Moreover, in the modification 5, as shown to Fig.14 (a), length L1 and length L2 become the same length, and are shorter than 25 micrometers. Further, the length L3 between the base end portion 45e1 of the tapered portion 45e and the end 10d on the head center side of the pressure chamber 10 is longer than the lengths L1 and L2 and shorter than 25 μm. Moreover, in the modification 6, as shown in FIG.14 (b), length L3 is longer than 25 micrometers in length. The remaining configuration of the modification 6 is the same as that of the modification 5.

  When the lengths L1 and L2 are less than 25 μm, the base end portion 45e1 overlaps the pressure chambers 10 of the piezoelectric layers 43 and 44 when the base end portion 45e1 is closer to the center of the head than the straight line T as shown in FIG. In the portion located on both sides of the straight line T, the tapered portion 45e and the common electrodes 46 and 47 overlap. Therefore, as shown in FIG. 14A, the individual electrodes 45 in the portions of the piezoelectric layers 43 and 44 that contribute to the increased deformation of the piezoelectric actuator 22 as compared with the case where the length L3 is 25 μm or less. The area where the common electrodes 46 and 47 overlap is reduced, and the deformation of the piezoelectric actuator 22 is reduced.

  On the other hand, when the lengths L1 and L2 are less than 25 μm, if the base end portion 45e1 is located closer to the head center side than the head center side ends 46a3 and 47a2 of the overlapping portion 46a and the belt-like portion 47a, the piezoelectric layer In the portions 43 and 44 that inhibit the deformation of the piezoelectric actuator 22, the common electrodes 46 and 47 overlap only with portions other than the tapered portion 45 e of the individual electrode 45. That is, the area where the individual electrode 45 and the common electrodes 46 and 47 overlap is increased in the portion of the piezoelectric layers 43 and 44 that inhibits deformation of the piezoelectric actuator 22. As a result, in this case, the degree of inhibition of deformation of the piezoelectric actuator 22 during driving is greater than in the fifth and sixth modifications.

  From the above, from the viewpoint of increasing the deformation of the piezoelectric actuator 22, when the lengths L1 and L2 are 25 μm or less, the base end portion 45e1 of the tapered portion 45e and the head center side of the pressure chamber 10 in the scanning direction. It is preferable that the length L3 between the two ends is not less than the lengths L1 and L2 and not more than 25 μm.

  Moreover, although the example which applied this invention to the inkjet head which discharges an ink from a nozzle was demonstrated above, it is not restricted to this. The present invention can also be applied to a liquid ejecting apparatus other than an ink jet head that ejects liquid other than ink.

DESCRIPTION OF SYMBOLS 3 Inkjet head 10 Pressure chamber 15 Nozzle 21 Flow path unit 22, 60, 65 Piezoelectric actuator 42-44 Piezoelectric layer 45 Individual electrode 45c Tapered part 46, 47 Common electrode 46a Overlapping part 46b Connection part 47a Band-shaped part

Claims (9)

A flow path forming member having a liquid flow path including a plurality of nozzles and a plurality of pressure chambers communicating with the plurality of nozzles;
A piezoelectric actuator for applying pressure to the liquid in the plurality of pressure chambers,
The piezoelectric actuator is
A first piezoelectric layer covering the plurality of pressure chambers;
A plurality of first electrodes disposed on one surface of the first piezoelectric layer for each pressure chamber and overlapping the plurality of pressure chambers when viewed from a first direction perpendicular to the one surface of the first piezoelectric layer. When,
A second electrode disposed on the other surface of the first piezoelectric layer and overlapping the plurality of pressure chambers and the plurality of first electrodes when viewed from the first direction;
The pressure chamber is long in a second direction orthogonal to the first direction, the length in the second direction is not less than 500 μm and not more than 1000 μm, and is orthogonal to both the first direction and the second direction. The length in the third direction is 250 μm or more and 500 μm or less,
In the third direction, both ends of the first electrode are located inside the pressure chamber,
In the second direction,
One end of the first electrode is located inside the pressure chamber, the other end of the first electrode is located outside the pressure chamber, and includes the other end of the first electrode. The portion is a tapered portion in which the length in the third direction becomes shorter as it approaches the end ,
The other end of the second electrode is positioned inside the pressure chamber, the length between the other end of the pressure chamber is at 25μm or more, and state, and are less 50 [mu] m,
A liquid , wherein a base end portion of the tapered portion overlaps with the other end of the second electrode, or is located on the other side of the other end of the second electrode. Discharge device. A flow path forming member having a liquid flow path including a plurality of nozzles and a plurality of pressure chambers communicating with the plurality of nozzles;
A piezoelectric actuator for applying pressure to the liquid in the plurality of pressure chambers,
The piezoelectric actuator is
A first piezoelectric layer covering the plurality of pressure chambers;
A plurality of first electrodes disposed on one surface of the first piezoelectric layer for each pressure chamber and overlapping the plurality of pressure chambers when viewed from a first direction perpendicular to the one surface of the first piezoelectric layer. When,
A second electrode disposed on the other surface of the first piezoelectric layer and overlapping the plurality of pressure chambers and the plurality of first electrodes when viewed from the first direction;
The pressure chamber is long in a second direction orthogonal to the first direction, the length in the second direction is not less than 500 μm and not more than 1000 μm, and is orthogonal to both the first direction and the second direction. The length in the third direction is 250 μm or more and 500 μm or less,
In the third direction, both ends of the first electrode are located inside the pressure chamber,
In the second direction,
One end of the first electrode is located inside the pressure chamber, the other end of the first electrode is located outside the pressure chamber, and the portion including the other end is the end of the first electrode. As it gets closer to the taper, the length in the third direction becomes shorter ,
The other end of the second electrode is located inside the pressure chamber, and a length between the second electrode and the other end of the pressure chamber is 25 μm or less ;
A length between the proximal end portion of the tapered portion and the other end of the pressure chamber is 25 μm or less, and is located on the one side with respect to the other end of the second electrode. liquid discharge apparatus characterized in that it. The plurality of pressure chambers are arranged along the third direction,
The second electrode is
Provided for each of the pressure chambers, and a plurality of overlapping portions overlapping the previous SL plurality of pressure chambers as viewed from the first direction,
A connecting portion for connecting the plurality of overlapping portions,
In the third direction, both ends of the overlapping portion are located outside the pressure chamber and have a gap between the adjacent overlapping portions,
In the second direction, the one end of the overlapping portion is located outside the pressure chamber,
The connecting portion extends in the third direction, of the plurality of overlapping portions, according to claim 1 or, wherein the connecting portions between which is located outside the pressure chamber of the one side in the second direction 3. The liquid ejection device according to 2. Wherein the plurality of first electrodes, a liquid ejecting apparatus according to any one of claims 1 to 3, characterized in that it is arranged on the surface of the pressure chamber side of the first piezoelectric layer. The piezoelectric actuator is
A second piezoelectric layer disposed with the plurality of first electrodes together with the first piezoelectric layer;
A third electrode disposed between the plurality of first electrodes and the second piezoelectric layer, the third electrode overlapping the plurality of pressure chambers and the plurality of first electrodes when viewed from the first direction; ,
In the second direction, the other end of the third electrode is positioned inside the pressure chamber, and a length between the other end of the pressure chamber and the other end is 50 μm or less. liquid ejecting apparatus according to any one of claims 1 to 4. In the second direction,
The portion including the other end of the first electrode is a tapered portion in which the length in the third direction becomes shorter as it approaches the end,
A length between the other end of the third electrode and the other end of the pressure chamber is 25 μm or more;
The base end portion of the tapered portion overlaps with the other end of the third electrode or is positioned on the other side of the other end of the third electrode. Item 6. The liquid ejection device according to Item 5 . In the second direction,
The portion including the other end of the first electrode is a tapered portion in which the length in the third direction becomes shorter as the end is approached,
A length between the other end of the third electrode and the other end of the pressure chamber is 25 μm or less;
The base end portion of the tapered portion has a length between the other end of the pressure chamber of 25 μm or less, and is closer to the one side than the other end of the third electrode. The liquid ejecting apparatus according to claim 5 , wherein the liquid ejecting apparatus is located. The plurality of pressure chambers are arranged along the third direction,
The second piezoelectric layer is disposed closer to the pressure chamber than the first piezoelectric layer,
The third electrode is
The belt-shaped portion that overlaps with the plurality of pressure chambers and the plurality of first electrodes when viewed from the first direction and extends continuously across the plurality of pressure chambers in the third direction. Item 8. The liquid ejection device according to any one of Items 5 to 7 . In the second direction, wherein said other end of the third electrodes, according to claim 8, wherein the than the other end of the second electrode, characterized in that close to the other end of the pressure chamber The liquid discharge apparatus according to 1.