Liquid jetting apparatus, piezoelectric actuator, and method for producing the liquid jetting apparatus

A liquid jetting apparatus includes a channel unit in which a liquid channel including a nozzle for jetting a liquid is formed, and a piezoelectric actuator provided on the channel unit and configured to apply jetting energy to the liquid inside the liquid channel. The piezoelectric actuator has a piezoelectric element and a wiring substrate in which a first electrode and a wire electrically connected to the first electrode are formed and which is joined to one surface of the piezoelectric element. The first electrode is configured to make contact with the piezoelectric element.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. 2012-191112, filed on Aug. 31, 2012 and Japanese Patent Application No. 2012-191114, filed on Aug. 31, 2012, the disclosure of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid jetting apparatus, a piezoelectric actuator, and a method for producing the liquid jetting apparatus.

2. Description of the Related Art

Conventionally, as a configuration of piezoelectric actuators used for various purposes, there has been known such configuration in which a wiring substrate is connected to a surface electrode of a piezoelectric element to supply a signal for driving the piezoelectric element.

Conventionally, there have been known piezoelectric actuators provided for an ink-jet head to jet liquid droplets. Such ink-jet head is provided with a channel unit (channel structure) in which ink channels including a plurality of nozzles are formed, and a piezoelectric actuator provided for the channel unit. Further, the piezoelectric actuator has a piezoelectric layer, and a plurality of individual electrodes formed on a surface of the piezoelectric layer to correspond to the plurality of nozzles, respectively.

A flexible wiring substrate (COF) is connected to the plurality of individual electrodes of the above piezoelectric actuator. A driver IC is mounted on the wiring substrate, and a plurality of wires connected with the driver IC are formed in the wiring substrate. Further, the wiring substrate is provided with a plurality of contact points (substrate-side contact points) corresponding to the plurality of individual electrodes respectively, and these plurality of contact points are connected to the driver IC via the aforementioned wires. Then, the plurality of individual electrodes on the surface of the piezoelectric layer are connected to the plurality of contact points of the wiring substrate, respectively, by bumps of conductive resin including a metallic material and a thermosetting resin. By virtue of this, a drive voltage is applied to each of the plurality of individual electrodes from the driver IC mounted on the wiring substrate.

In a conventional piezoelectric actuator, the electrodes (the individual electrodes) are formed on the surface of the piezoelectric layer, the contact points (the substrate-side contact points) are formed on the wiring substrate, and it is configured such that the individual electrodes of the piezoelectric layer and the contact points of the wiring substrate are connected by the bumps of conductive resin. Therefore, the connection structure between the wiring substrate and the piezoelectric layer (piezoelectric element) is complicated. Further, it is necessary to not only form the electrodes on the piezoelectric layer but also form the contact points on the wiring substrate. This accordingly increases the number of production processes, thereby suffering disadvantage in terms of cost.

SUMMARY OF THE INVENTION

An object of the present invention is to simplify the connection structure between the piezoelectric element and the wiring substrate.

According to a first aspect of the present invention, there is provided a liquid jetting apparatus for jetting a liquid, the apparatus including: a channel unit in which a liquid channel including a nozzle for jetting the liquid is formed; and a piezoelectric actuator which is provided on the channel unit and which applies jetting energy to the liquid inside the liquid channel, wherein the piezoelectric actuator includes: a piezoelectric element; and a wiring substrate in which a first electrode and a wire electrically connected to the first electrode are formed and which is joined to one surface of the piezoelectric element, and wherein the first electrode makes contact with the piezoelectric element.

According to the liquid jetting apparatus of the first aspect of the present invention, the first electrode is formed on the wiring substrate joined to the piezoelectric element, and the first electrode is in contact with the piezoelectric element. That is, because it is configured to connect the piezoelectric element with the wiring substrate via the first electrode alone, the connection structure is simplified between the piezoelectric element and the wiring substrate. Further, since it is not necessary to form any electrode on the piezoelectric element and form any contact point on the wiring substrate as in the conventional manner, it is also possible to simplify the production process.

According to a second aspect of the present invention, there is provided a piezoelectric actuator including: a piezoelectric element; and a wiring substrate in which a first electrode and a wire electrically connected to the first electrode are formed and which is joined to one surface of the piezoelectric element, wherein the first electrode makes contact with the piezoelectric element.

According to a third aspect of the present invention, there is provided a method for producing a liquid jetting apparatus including: a channel unit in which a liquid channel including a nozzle for jetting the liquid is formed; and a piezoelectric actuator which includes a piezoelectric element and a wiring substrate joined to one surface of the piezoelectric element, and which is provided on the channel unit to apply jetting energy to the liquid inside the liquid channel, the method including: a groove formation step for forming a plurality of first grooves on a joint surface of the wiring substrate with respect to the piezoelectric element; and an electrode formation step for forming a first electrode on the joint surface and joining the joint surface of the wiring substrate to the piezoelectric element by filling the first grooves with a liquid conductive material.

In the liquid jetting apparatus obtained according to the production method of the third aspect of the present invention, because the first electrode formed on the wiring substrate is in contact with the piezoelectric element, the connection structure is simplified between the piezoelectric element and the wiring substrate. Further, since it is not necessary to form any electrode on the piezoelectric element and form any contact point on the wiring substrate as in the conventional manner, the production process is also simplified. Further, by using the permeation action by the capillary force to fill the plurality of first grooves with the liquid conductive material after forming the plurality of first grooves in the joint surface of the wiring substrate with the piezoelectric element, it is possible to form the first electrode in a simple manner. Further, the first electrode formed in this manner has a high adhesion and thus is less liable to detachment from the wiring substrate, because its contact area with the wiring substrate becomes larger, compared with the case of forming the same in a flat surface by a printing method or the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, a first embodiment of the present invention will be explained. First, referring toFIG. 1, a schematic construction of an ink jet printer1will be explained. Further, in the following explanations, the front side of the page ofFIG. 1is defined to be the upper side while the back side of the page is defined to be the lower side, and the directional terms “upper” and “lower” are used as appropriate. As shown inFIG. 1, the ink jet printer1includes a platen2, a carriage3, an inkjet head4, a transport mechanism5, etc.

A sheet of recording paper100, which is a recording medium, is placed on the upper surface of the platen2. Further, above the platen2, two guide rails10and11are provided to extend parallel to a left-right direction (a scanning direction) ofFIG. 1. The carriage3is configured to be movable reciprocatingly in the scanning direction along the two guide rails10and11in an area facing the platen2. Further, the carriage3is connected to an endless belt14wound around two pulleys12and13. When a carriage drive motor15drives the endless belt14to put the endless belt14into motion, the carriage3moves in the scanning direction along with the motion of the endless belt14.

The ink-jet head4(a liquid jetting apparatus) is installed on the carriage3, and moves along with the carriage3in the scanning direction. A plurality of nozzles16are formed on the lower surface of the ink jet head4(the surface on the back side of the page ofFIG. 1). Further, as shown inFIG. 1, a holder9is provided in a printer main body la of the ink jet printer1. Four ink cartridges17containing four color inks (black, yellow, cyan and magenta), respectively, are installed in the holder9. The ink jet head4mounted on the carriage3is connected to the holder9through four tubes (not shown). The four color inks in the four ink cartridges17are supplied respectively to the ink jet head4through the four tubes. The ink jet head4causes the plurality of nozzles16to jet the inks supplied from the ink cartridges17to the recording paper100placed on the platen2.

The transport mechanism5has two transport rollers18and19arranged to interpose the platen2in a transport direction, and these two transport rollers18and19are driven to rotate by an unshown motor. The transport mechanism5causes the two transport rollers18and19to transport the recording paper100placed on the platen2in the transport direction.

The ink jet printer1causes the inks to be jetted from the ink-jet head4moving reciprocatingly along with the carriage3in the scanning direction (the left-right direction ofFIG. 1) to the recording paper100placed on the platen2. At the same time, the two transport rollers18and19transport the recording paper100in the transport direction (downward inFIG. 1). By the above operation, images, characters and the like are recorded on the recording paper100.

Next, the ink jet head4will be explained. Further, in order to simplify the figures,FIGS. 2 and 3show a COF50, which is shown byFIGS. 4 and 5in detail, in a simplified manner with a two-dot chain line. Further,FIG. 5also shows a driver IC (seeFIG. 2), which is not shown inFIG. 3. As shown inFIGS. 2 to 4, the ink jet head4includes a channel unit20, and a piezoelectric actuator21.

As shown inFIG. 4, the channel unit20has a structure of stacking five plates30to34in which many channel formation holes are formed respectively. By letting the many channel formation holes communicate with each other when these five plates30to34are stacked, such ink channels are formed in the channel unit20as will be described below. While the five plates30to34are not limited to any particular material, they are formed of a metallic material such as stainless steel, nickel alloy steel, or the like in the first embodiment. Further, inFIGS. 4 and 5, the symbol “I” shows the ink filling the inside of the ink channels.

As shown inFIG. 2, in the upper surface of the channel unit20(the upper surface of the vibration plate30which is the plate positioned at the uppermost layer), four ink supply holes26which are to be connected to the four ink cartridges17(seeFIG. 1) respectively are formed. Inside the channel unit20, four manifolds25are formed to extend respectively in the transport direction. The four manifolds25are connected respectively to the four ink supply holes26, and supplied with the four color inks (black, yellow, cyan and magenta) contained in the four ink cartridges17, respectively.

As shown inFIGS. 2 to 5, the channel unit20has the plurality of nozzles16, and a plurality of pressure chambers24which are communicated with the plurality of nozzles16, respectively. The plurality of nozzles16are formed on the lower surface (the nozzle plate34) of the channel unit20. Each of the plurality of pressure chambers24has such a planar shape as is approximately elliptic and long in the scanning direction, and is covered by the vibration plate30positioned at the uppermost layer among the five plates30to34. As shown inFIG. 2, the plurality of nozzles16and the plurality of pressure chambers24are arranged in four rows corresponding to the four manifolds25, respectively, which are supplied with the four color inks.

As shown inFIG. 4, each of the plurality of pressure chambers24communicates with the corresponding manifold25via a throttle channel28extending in the longitudinal direction of the pressure chamber24. Further, each of the pressure chambers24communicates with one of the nozzles16. By virtue of this, as shown inFIG. 4, a plurality of individual ink channels27are formed in the channel unit20to branch from each of the manifolds25through the throttle channels28and pressure chambers24to the nozzles16.

Next, the piezoelectric actuator21will be explained. The piezoelectric actuator21is arranged on the upper surface of the vibration plate30of the channel unit20. As shown inFIGS. 2 to 5, the piezoelectric actuator21has a plurality of piezoelectric elements40, and a wiring substrate41connected to the plurality of piezoelectric elements40.

Each of the plurality of piezoelectric elements40is made of a piezoelectric material which is composed primarily of ferroelectric lead zirconium titanate (PZT), and is a solid solution of lead titanate and lead zirconate. Each of the plurality of piezoelectric elements40has a planar shape of an approximate ellipse which is one-size smaller than the pressure chamber24. Further, the piezoelectric elements40are polarized in their thickness direction. The plurality of piezoelectric elements40are arranged in an area of the upper surface of the vibration plate30to face the central portions of the plurality of pressure chambers24, respectively. Further, as is understood fromFIG. 5, the plurality of piezoelectric elements40are arranged to separate from each other.

While the wiring substrate41, which will be described later, is joined to the upper surfaces of the respective piezoelectric elements40(the surfaces on the opposite side to the vibration plate30), a first electrode42is provided between each of the piezoelectric elements40and the wiring substrate41. That is, the first electrodes42are arranged in contact with both the upper surfaces of the piezoelectric elements40and the lower surface of the wiring substrate41. As shown inFIG. 3, each of the first electrodes42has a planar shape of an approximate ellipse which is one-size smaller than that of the pressure chambers24similar to the piezoelectric elements40, and is arranged to face the approximately central portion of the corresponding pressure chamber24. A drive voltage is applied to each of the first electrodes42from a driver IC45mounted on the wiring substrate41. The first electrodes42will be described later in detail.

A second electrode43is arranged on the lower surface of each of the piezoelectric element40so that the second electrode43faces one of the first electrodes42while sandwiching the piezoelectric element40between the first electrode42and the second electrode43. As shown inFIGS. 4 and 5, an insulation film44made of a synthetic resin material or the like is formed on and across almost the entire upper surface of the metallic vibration plate30. By this insulation film44, insulation is secured between the second electrodes43of the lower surfaces of the piezoelectric elements40and the metallic vibration plate30. As viewed from above, each of the second electrodes43has a planar shape a little smaller than the piezoelectric elements40. In more detail as shown inFIG. 4, each of the second electrodes43is formed to be smaller than the piezoelectric elements40with respect to the longitudinal direction of the piezoelectric elements40(the extending direction of aftermentioned filling grooves52), without exposing their lateral portions (the lateral portions on the left and right inFIG. 4) in the longitudinal direction of the piezoelectric elements40(that is, the second electrodes43do not face such portions of the wiring substrate41where the aftermentioned filling grooves52extend out from the piezoelectric elements40). On the other hand, as shown inFIG. 5, each of the second electrodes43is almost as long as the piezoelectric elements40in a short direction of the piezoelectric elements40, partially exposing their lateral portions in the short direction of the piezoelectric elements40(the lateral portions on the left and right inFIG. 5).

Further, as shown inFIG. 5, the portions of the second electrodes43exposed from the piezoelectric elements40are connected to a conductive pattern46formed on the insulation film44. Thus, by this conductive pattern46, the plurality of second electrodes43of the piezoelectric elements40are electrically conducted to one another. Further, the conductive pattern46is electrically connected, by solder or the like, to a ground wire (not shown) formed in the wiring substrate41. By virtue of the above configuration, the second electrodes43of the piezoelectric elements40are all constantly maintained at the ground potential.

If the drive voltage is applied from the driver IC45to the first electrode42of a certain piezoelectric element40, then a potential difference occurs between this first electrode42and the second electrode43at the ground potential. Hence, an electric field acts on the piezoelectric element40in the thickness direction. Because the direction of the electric field is parallel to the polarization direction of the piezoelectric element40, the piezoelectric element40extends in the thickness direction while contracting in the planar direction. Due to the contraction of the piezoelectric element40, the vibration plate30covering the corresponding pressure chamber24bends to be convex toward the pressure chamber24, thereby causing a decrease in the volume of the pressure chamber24. At this time, a pressure (jetting energy) is applied to the ink inside the pressure chamber24, thereby jetting liquid droplets of the ink from the corresponding nozzle16.

Next, the wiring substrate41will be explained. The wiring substrate41is a flexible substrate made of a synthetic resin material such as polyimide or the like. The wiring substrate41has the driver IC45, and a plurality of wires47connected to the driver IC45. As shown inFIGS. 2 to 5, the wiring substrate41is arranged to cover the plurality of piezoelectric elements40of the piezoelectric actuator21, and joined to the upper surfaces of the plurality of piezoelectric elements40.

The driver IC45is connected to an unshown control substrate controlling the operation of the ink jet head4. Further, the driver IC45is connected to the first electrodes42of the plurality of piezoelectric elements40via the plurality of wires47, respectively. Based on a command from the control substrate, the driver IC45individually applies the drive voltage to the plurality of piezoelectric elements40so as to jet the inks from desired nozzles16.

As described earlier, it is configured that the plurality of first electrodes42are provided respectively between the upper surfaces of the plurality of piezoelectric elements40and the lower surface of the wiring substrate41to be joined to the plurality of piezoelectric elements40(hereinbelow, also referred to as joint surface), and thereby only the first electrodes42are in contact with both the wiring substrate41and the piezoelectric elements40. This configuration differs from the conventional configuration in which the electrodes formed on the piezoelectric elements40are connected to the contact points formed on the wiring substrate41via the bumps, and simplifies the connection structure between the piezoelectric elements40and wiring substrate41. Further, since it is not necessary to form the electrodes on the piezoelectric elements, form the contact points on the wiring substrate, and join the electrodes and the contact points thereafter as in the conventional manner, it is also possible to simplify the production process.

Further, as shown inFIGS. 4 and 5, a recess50is formed on the upper surface of the wiring substrate41at a portion51which is to be joined to one of the piezoelectric elements40(a portion which is to be in contact with the first electrodes42), and thus these joint portions51are formed to be thinner than the other portions of the wiring substrate41. In this manner, because the wiring substrate41is locally thin at the portions51at which the wiring substrate41is joined to the piezoelectric elements40, when the drive voltage is applied, the wiring substrate41is less likely to inhibit deformation of the piezoelectric elements40.

Next, a detailed explanation will be given about a structure of the first electrodes42and the wires47which are in electrical conduction with the first electrodes42. In order to make it easy to understand a positional relation between the wiring substrate41and the piezoelectric elements40,FIGS. 6A and 6Bshow the piezoelectric elements40with two-dot chain lines. As shown inFIGS. 4,5and6B, the plurality of filling grooves52(an example of first grooves) are formed in each area, of the lower surface (the joint surface) of the wiring substrate41, facing one of the piezoelectric elements40. Each of the plurality of filling grooves52has a very narrow width as long as a few micrometers (μm) or so. As shown inFIG. 6B, the plurality of filling grooves52includes a first filling groove52aextending in the short direction of the approximately elliptic piezoelectric element40, and a plurality of second filling grooves52beach communicating with the first filling groove52aand extending in the longitudinal direction of the piezoelectric element40. The first filling groove52acommunicates with a through hole54penetrating through the wiring substrate41in its thickness direction. As shown inFIG. 6B, the through hole54is formed at a position deviated from the center of the piezoelectric element40in the longitudinal direction of the piezoelectric element40. Further, as shown inFIGS. 4,6A and6B, each area53, of the lower surface of the wiring substrate41, formed with the filling grooves52extends out beyond the corresponding piezoelectric element40on both sides in its longitudinal direction. Then, the plurality of second filling grooves52bextend respectively from the first filling groove52a, which is the communication portion with the through hole54, toward portions53a, of the wiring substrate41, which extend out from the piezoelectric element40.

As shown inFIGS. 4,6A and6B, a plurality of supply grooves55are formed on the upper surface of the wiring substrate41(the surface on a side opposite to the joint surface with the piezoelectric elements40) to correspond to the plurality of piezoelectric elements40respectively. The supply groove55(an example of second groove) corresponding to any one of the piezoelectric elements40includes a first supply groove55aformed on the bottom surface of the recess50, and a second supply groove55bformed on an area of the wiring substrate41at which the recess50is not formed. The first supply groove55acommunicates with the aforementioned through hole54. The second supply groove55bcommunicates with the first supply groove55avia a vertical groove55cformed on a lateral side of the recess50. The second supply groove55bextends on the upper surface of the wiring substrate41from the communication portion with the vertical groove55cto the area at which the driver IC45is placed. Further, in the end portion of the second supply groove55bon the side of the piezoelectric element40(the vertical groove55c), a liquid receiving portion55dis formed with a locally greater groove width (and groove depth). Further, each of the first supply groove55a, the second supply groove55b, the liquid receiving portion55dand the vertical groove55cconstituting one of the supply grooves55has a considerably greater groove width and groove depth (i.e., a greater sectional area of the groove orthogonal to the length direction), compared with the aforementioned filling groove52in communication with the supply groove55. For example, the groove width of the aforementioned filling groove52is a few micrometers (μm), whereas the groove width of the second supply groove55bis tens of micrometers (μm).

With the wiring substrate41having the above configuration of grooves, if a liquid conductive ink (conductive material) is supplied to each of the supply grooves55, due to the action of capillary force, the conductive ink flows from each of the supply grooves55into the plurality of filling grooves52having smaller groove width (groove sectional area) than the supply grooves55. Further, if the sectional area of the filling grooves52is smaller, a greater capillary force acts on the conductive ink, thereby making it easier for the conductive ink to permeate the filling grooves52. In this manner, by filling the plurality of filling grooves52and supply grooves55with the conductive ink, there are formed the first electrodes42, and the wires47in respective conduction with the first electrodes42. Further, inFIGS. 4,5,6A and6B, the state of filling the filling grooves52and supply grooves55with the conductive material (conductive ink) is indicated by hatching those grooves.

Hereinbelow, referring toFIGS. 7A to 7C, a specific method will be explained for forming the first electrodes42described above.

First, press working, laser processing, or the like is carried out to form the plurality of recesses50at the portions51of the wiring substrate41to be joined to the plurality of piezoelectric elements40respectively. Then, for each of the portions51of the wiring substrate41, as shown inFIG. 7A, the plurality of filling grooves52(first filling grooves52aand second filling grooves52b) are formed on the lower surface of the wiring substrate41at the portion51to be joined to one of the piezoelectric elements40. Here, each of the areas53, of the wiring substrate41, at which the plurality of filling grooves52are formed is made to be greater than the upper surface of the corresponding piezoelectric element40in its longitudinal direction. Further, the through hole54is formed in the wiring substrate41to communicate with the first filling grooves52a. Further, the supply groove55(first supply groove55a, second supply groove55b, vertical groove55c, and liquid receiving portion55d) is formed on the surface of the wiring substrate41on the side opposite to the joint surface with the piezoelectric elements40. Further, it is possible to form these grooves by laser processing.

Next, as shown inFIG. 7B, the wiring substrate41is arranged on the plurality of piezoelectric elements40so that the wiring substrate40makes contact with the upper surfaces of the plurality of piezoelectric elements40. Here, the wiring substrate41is arranged such that each of the areas53of the wiring substrate41, at which the plurality of filling grooves52are formed, may extend out beyond the piezoelectric element40on both sides in the longitudinal direction. Further, the wiring substrate41is maintained in the state of making contact with the plurality of piezoelectric elements40not to be out of alignment with respect to the plurality of piezoelectric elements40, by pressing the wiring substrate41from above, or by using an adhesive or another appropriate fixation means to temporarily fix the wiring substrate41, etc.

Next, as shown inFIG. 7C, an inkjet head60for jetting a conductive ink61is placed above the wiring substrate41. Then, the conductive ink61is jetted from the ink jet head60to the liquid receiving portion55dof the supply groove55corresponding to each of the piezoelectric elements40. As the conductive ink, compounds of a thermosetting resin, such as unsaturated polyester resin, two-component polyolefin resin, epoxy resin, etc., and particles of a metal such as Ag or the like can be adopted. Due to the permeation action by the capillary force, the conductive ink61supplied to the liquid receiving portion55dflows from the first supply groove55ainto the plurality of filling grooves52having small groove widths (groove sectional areas) via the through hole54. Further, the plurality of filling grooves52are open to the atmosphere in the portions extending out from the piezoelectric elements40. By virtue of this, the plurality of filling grooves52are filled throughout with the conductive ink61to form the first electrode42between the wiring substrate41and the piezoelectric element40. Further, by filling not only the first supply groove55abut also the second supply groove55bwith the conductive ink61, the wire47is formed on the upper surface of the wiring substrate41to connect the first electrode42and the driver IC45. Thereafter, by hardening the infilled conductive ink, the wiring substrate41is joined to the plurality of piezoelectric elements40. For example, if the conductive ink61composed primarily of a thermosetting resin is used, a heating process is carried out after filling the filling grooves52and the supply groove55with the conductive ink61.

In this manner, according to the first embodiment, by making use of the permeation action by the capillary force to fill the plurality of filling grooves52formed in the wiring substrate41with the liquid conductive ink61, it is possible to simply form the first electrodes42in contact with both the wiring substrate41and the piezoelectric elements40. Further, there is also such an advantage that the first electrodes42formed by filling the plurality of filling grooves52with the conductive ink61, have a high adhesion and thus are less liable to be detached from the piezoelectric elements40, because the electrode material has a greater contact area with the wiring substrate41compared with the case of forming the same in a flat surface with little asperity or irregularity by a printing method or the like.

Further, as shown inFIG. 7C, after arranging the wiring substrate41so that the wiring substrate41makes contact with the piezoelectric elements40to form minute interspaces between the filling grooves52of the wiring substrate41and the upper surfaces of the piezoelectric elements40, these interspaces are filled with the conductive ink61. In this case, compared with the state in which the filling grooves52are open before the wiring substrate41makes contact with the piezoelectric elements40, greater capillary force acts on the conductive ink61. Therefore it becomes easier to fill the plurality of filling grooves52throughout with the conductive ink61. Further, by hardening the liquid conductive ink61which remains in the state of making contact with both the wiring substrate41and the piezoelectric elements40, the formed first electrodes42also have a high adhesion to the piezoelectric elements40. Therefore, compared with such a case as attaching the wiring substrate41formed with the first electrodes42to the piezoelectric elements40, the first electrodes42are less liable to be detached from the piezoelectric elements40.

Further, as shown inFIGS. 4,6A and6B, parts of the areas53, at which the plurality of filling grooves52of the wiring substrate41are formed, extend out from the piezoelectric elements40on both sides in the longitudinal direction, and these extending-out portions53aare not joined to the upper surface of the piezoelectric element40. That is, at the extending-out portions53a, the plurality of filling grooves52are open to the atmosphere. Therefore, when the conductive ink61is supplied from the supply groove55to the plurality of filling grooves52, the air inside the plurality of filling grooves52is let out from the above extending-out portions53ato the outside. Therefore, it becomes possible to fill the plurality of filling grooves52throughout with the conductive material. Further, the plurality of filling grooves52extend from the communication portion with the through hole54on the side of the supply groove55toward the portions53aextending out from the piezoelectric element40. Therefore, the conductive ink61, which has flowed into the plurality of filling grooves52from the supply groove55, flows toward the portions53aextending out from the piezoelectric element40, that is, the portions of the filling grooves52in communication with the atmosphere. Hence, it becomes even easier for the air to move out of the filling grooves52.

However, if parts of the areas53, at which the plurality of filling grooves52of the wiring substrate41are formed, extend out from the piezoelectric elements40, it is conceivable that the conductive ink61drips down from these extending-out portions53a. To address this problem, as shown inFIG. 4in the first embodiment, the insulation film44is formed in the area, of the metallic vibration plate30of the channel unit20, facing the extending-out portions53aextending out of the piezoelectric elements40. Therefore, even if the conductive ink61drips down from the extending-out portions53a, short circuit is still reliably prevented between the first electrodes42and the metallic vibration plate30. Further, in each of the piezoelectric elements40, while the second electrode43facing the first electrode42is exposed at lateral portions in the latitudinal direction of the piezoelectric element40(seeFIG. 5), as shown inFIG. 4, the second electrode43is not exposed at lateral portions in the longitudinal direction of the piezoelectric element40(the lateral portions on the sides at which the filling grooves52extend out from the piezoelectric element40). Therefore, even if the conductive ink61drips down from the filling grooves52along the lateral sides of the piezoelectric elements40, short circuit is still prevented between the first electrodes42and the second electrodes43.

In the first embodiment, the supply grooves55each of which has greater groove width than each of the plurality of filling grooves52are formed on the surface of the wiring substrate41on the side opposite to the joint surface of the wiring substrate41. Then, by jetting the conductive ink61from the ink jet head60toward the supply grooves55having greater groove width, the conductive ink61permeates the plurality of filling grooves52from the supply grooves55due to the action of capillary force. By virtue of this, it is easy for the conductive material to fill the plurality of filling grooves52having smaller groove width. Further, by also filling the supply grooves55with the conductive ink61, it is possible to form the wires47in conduction with the first electrodes42at the same time.

Further, because each of the supply grooves55includes the liquid receiving portion55dhaving locally greater groove width, by jetting the conductive ink61into these liquid receiving portions55d, it is easy to supply the conductive ink61to the supply grooves55. Further, each of the liquid receiving portions55dis positioned in the end portion of one of the supply groove55on a side at which the supply groove55communicates with the plurality of filling grooves52. In this manner, by landing the conductive ink61on the end portion of each of the supply grooves55near the filling grooves52, it becomes easy for the conductive ink to permeate the plurality of filling grooves52having smaller groove width.

Next, referring toFIGS. 11 to 15E, a second embodiment will be explained. Note that, however, the same reference numerals are used to refer to the components with identical or similar configurations to those of the first embodiment, any explanation for which will be omitted as appropriate.

In the second embodiment as shown inFIG. 12, a piezoelectric layer140is arranged over the upper surface of the vibration plate30to commonly cover the plurality of pressure chambers24. Further, in the second embodiment, the portions of the piezoelectric layer140facing the plurality of pressure chambers24respectively correspond to the piezoelectric elements of the present invention. Further, each of the second electrodes43has a planar shape of an approximate ellipse in the same way as the first electrodes42.

As shown inFIG. 11, a through hole46is formed in a portion of the piezoelectric layer140overlapping with one end portion of each of the second electrodes43in the longitudinal direction. Each of the through holes46is filled with a conductive material and, further, on the upper surface of the piezoelectric layer140, pullout electrodes49are formed in conduction with the conductive material inside the through holes46. By virtue of this, the second electrodes43formed beneath the lower surface of the piezoelectric layer140are configured to be in conduction with the pullout electrodes49formed on the upper surface of the piezoelectric layer140. Further, because each of the pullout electrodes49is connected with an aftermentioned ground wire48formed on the wiring substrate41, each of the second electrodes43is constantly maintained at the ground potential. It is possible to form the second electrodes43and the pullout electrodes49in conduction with the second electrodes43by a publicly known method such as screen printing, sputtering, or the like.

Next, a detailed explanation will be given about structures of the first electrodes42, and the wires47in conduction with the first electrodes42.

As shown inFIGS. 11,13A and13B, for each of portions of the wiring substrate41corresponding to the pressure chambers24respectively, the plurality of filling grooves52are in communication with, at their end portions on one side, the corresponding through hole54penetrating through the wiring substrate41in the thickness direction. Further, the plurality of supply grooves155are formed in the upper surface of the wiring substrate41(the surface on the side opposite to the joint surface with the piezoelectric layer140) to correspond to the plurality of first electrodes42, respectively. Each of the supply grooves155(an example of second groove) corresponding to one of the first electrodes42communicates with the corresponding through hole54via a vertical groove155aformed on a lateral side of the recess50. On the other hand, the supply groove155extends on the upper surface of the wiring substrate41to the area on which the driver IC45is placed. Further, in the vicinity of the end portion of the supply groove155on the side of the filling grooves52, a liquid receiving portion155bhaving a locally greater groove width (and groove depth) is formed. Further, compared with the aforementioned filling groove52, the supply groove155(including the liquid receiving portion155b) has a considerably greater groove width and groove depth (i.e., a greater sectional area of the groove orthogonal to the length direction). For example, the groove width of the aforementioned filling groove52is a few micrometers (μm), whereas the groove width of the supply groove155is tens of micrometers (μm).

Further, for each of portions of the wiring substrate41corresponding to the pressure chambers24respectively, the plurality of filling grooves52are connected to an atmosphere communication groove56formed on the joint surface of the wiring substrate41at the end portion on a side opposite to the through hole54. The atmosphere communication groove56extends from the communication portion with the plurality of filling grooves52in the longitudinal direction of the pressure chamber24. As shown inFIG. 14, the atmosphere communication groove56has two types of ribs56aand56bwhich project from the lateral sides of the groove in mutually opposite directions. These two types of ribs56aand56bare arranged alternately along the length direction of the groove. By virtue of this, the atmosphere communication groove56has a complicated internal shape (labyrinth form), thereby increasing the fluid-flow resistance when a fluid passes through the atmosphere communication groove56.

Further, the atmosphere communication groove56, and is connected to an atmosphere communication hole57penetrating through the wiring substrate41in the thickness direction to open to both upper and lower surfaces. By virtue of this, even if the wiring substrate41contacts with the upper surface of the piezoelectric layer140and the plurality of filling grooves52are closed up by the piezoelectric layer140, the plurality of filling grooves52still communicate with the atmosphere via the atmosphere communication groove56and atmosphere communication hole57. That is, in the second embodiment, an atmosphere communication passage58, through which the plurality of filling grooves52communicate with the atmosphere, is constituted by the atmosphere communication groove56and atmosphere communication hole57.

If a liquid conductive ink (conductive material) is supplied to each of the supply grooves155in a state that the piezoelectric layer140is in contact with the wiring substrate41having the above configuration of grooves, the conductive ink flows from each of the supply grooves155into the plurality of filling grooves52having smaller groove width (groove section area) than the supply grooves155due to the action of capillary force. Further, if the sectional area of the filling grooves52is smaller, a greater capillary force acts on the conductive ink, thereby making it easier for the conductive ink to permeate the filling grooves52. Further, because the plurality of filling grooves52communicate with the atmosphere communication passage58, when the filling grooves52are filled with the conductive ink61, the air inside the plurality of filling grooves52is let out from the atmosphere communication passage58to the outside. InFIGS. 11,12,13A and13B, the state in which the filling grooves52and supply grooves155are filled with the conductive material (conductive ink) is indicated by hatching those grooves.

In this manner, by filling the plurality of filling grooves52on the lower surface of the wiring substrate41with the conductive ink61, the first electrodes42are formed between the wiring substrate41and the piezoelectric layer140. Further, by filling the supply grooves155on the upper surface of the wiring substrate41with the conductive ink61, the wires47in conduction with the first electrodes42are formed.

Further, in the second embodiment as shown inFIGS. 11,13A and13B, the atmosphere communication passage58connected to the plurality of filling grooves52is provided in an area of the wiring substrate41outside the pressure chambers24. However, as shown inFIG. 11, the atmosphere communication passage58is arranged to overlap with the throttle channel28extending from the pressure chamber24in its longitudinal direction. Therefore, it is not necessary to widen the intervals for arranging the pressure chambers24on the side of the channel unit20in order to form the atmosphere communication passages58in the wiring substrate41, and the channel unit20does not become large in size either.

Further, although the atmosphere communication passage58may also be left as it is after filling the plurality of filling grooves52with the conductive ink, in the second embodiment, the atmosphere communication hole57(especially the atmosphere communication groove56penetrating through the wiring substrate41) is used for ground connection of the second electrode43. The atmosphere communication hole57vertically penetrating through the wiring substrate41is open to both the upper and lower surfaces of the wiring substrate41. A supply groove59connected to the atmosphere communication hole57is formed on the upper surface of the wiring substrate41. Then, by filling the atmosphere communication hole57with the conductive material (conductive ink) from the supply groove59, the conductive material inside the atmosphere communication hole57is electrically connected to the pullout electrode49of the second electrode43pulled out to the one surface of the piezoelectric layer140. Further, by filling the supply groove59with the conductive material, the ground wire48is formed on the upper surface of the wiring substrate41. By using the atmosphere communication hole57penetrating through the wiring substrate41, it is possible to connect the pullout electrode49of the second electrode43to the ground wire48formed on the upper surface of the wiring substrate41.

Hereinbelow, a specific method will be explained for forming the first electrode42described above.FIGS. 15A to 15Eare views for explaining a process of forming each of the first electrodes42.

First, press working, laser processing, or the like is carried out to form a plurality of recesses50at a plurality of portions51of the wiring substrate41corresponding to the plurality of pressure chambers24respectively. Then, for each of the portions51of the wiring substrate41, as shown inFIG. 15A, the plurality of filling grooves52are formed on the lower surface of the wiring substrate41. Further, the through hole54is formed in the wiring substrate41to communicate with the plurality of filling grooves52. Further, the supply groove155(including the vertical groove155aand liquid receiving portion155b) and the supply groove59are formed on a surface of the wiring substrate41on a side opposite to the joint surface with the piezoelectric layer140. Further, it is possible to form these grooves by laser processing.

As shown inFIG. 15A, the atmosphere communication groove56is formed on the lower surface of the wiring substrate41to communicate with the plurality of filling grooves52. Further, the atmosphere communication hole57is formed to penetrate through the wiring substrate41and to communicate with the atmosphere communication groove56. In the same way as the above groove formation process, it is possible to form the atmosphere communication groove56and atmosphere communication hole57by laser processing.

Next, as shown inFIG. 15B, the wiring substrate41is arranged to contact with the upper surface of the piezoelectric layer140. Further, the wiring substrate41is maintained in the state of making contact with the piezoelectric layer140not to be out of alignment with respect to the piezoelectric layer140, by pressing the wiring substrate41from above, or by using an adhesive or another appropriate fixation means to temporarily fix the wiring substrate41, etc.

Next, as shown inFIG. 15C, the ink-jet head60for jetting the conductive ink61is placed above the wiring substrate41. Then, the conductive ink61is jetted from the ink jet head60to the liquid receiving portion155bof the supply groove155. As the conductive ink, compounds of a thermosetting resin, such as unsaturated polyester resin, two-component polyolefin resin, epoxy resin, etc. and particles of a metal such as Ag or the like can be adopted. Due to the permeation action by the capillary force, the conductive ink61supplied to the liquid receiving portion155bflows from the supply groove155into the plurality of filling grooves52having small groove widths (groove sectional areas) via the through hole54, so as to form the first electrode42between the wiring substrate41and the piezoelectric layer140. Further, by filling the supply groove155with the conductive ink61, the wire47is formed on the upper surface of the wiring substrate41to connect the first electrode42and the driver IC45.

Here, since the plurality of filling grooves52are in communication with the atmosphere communication groove56, when the plurality of filling grooves52are filled with the conductive ink61, the air inside the filling grooves52moves out from the atmosphere communication groove56to the upside via the atmosphere communication hole57. Therefore, the plurality of filling grooves52are filled throughout with the conductive ink61. Further, as shown inFIG. 14, since the atmosphere communication groove56has a complicated labyrinth form with the two types of ribs aligned alternately, even if a part of the conductive ink61filling the filling grooves52flows out into the atmosphere communication groove56, the conductive ink61will not fill the atmosphere communication groove56entirely, thereby preventing the conductive ink61from flowing to the outside.

After forming the first electrode42, as shown inFIG. 15D, the conductive ink61is jetted from the ink jet head60into the supply groove59. Then, as shown inFIG. 15E, the atmosphere communication hole57is filled with the conductive ink61from the supply groove59, and the conductive ink61filled in the atmosphere communication hole57makes contact with and is electrically connected to the pullout electrodes49formed on the upper surface of the piezoelectric layer140. Further, by filling the supply groove59with the conductive ink61, the ground wire48is formed on the upper surface of the wiring substrate41. By using the atmosphere communication holes57, it is possible to connect the pullout electrode49of the second electrodes43formed on the upper surface of the piezoelectric layer140to the ground wire48formed on the upper surface of the wiring substrate41. Further, as described above, because the atmosphere communication groove56is formed into the labyrinth form between the atmosphere communication hole57and the plurality of filling grooves52which form the first electrode42, the conductive ink61filled in the atmosphere communication hole57is prevented from reaching the plurality of filling grooves52to be conducted with the first electrode42.

Thereafter, by hardening the infilled conductive ink61, the wiring substrate41is joined to the piezoelectric layer140. For example, if the conductive ink61composed primarily of a thermosetting resin is used, a heating process is carried out after filling the filling grooves52, the supply groove155, the atmosphere communication hole57and the supply groove59with the conductive ink61.

If the wiring substrate41is in contact with the piezoelectric layer140, the plurality of filling grooves52of the wiring substrate41are closed up by this piezoelectric layer140. In the second embodiment, however, the atmosphere communication passage58, through which the plurality of filling grooves52communicate with the atmosphere, is formed in the wiring substrate41to let. Therefore, when the plurality of filling grooves52are filled with the conductive ink61in the state that the wiring substrate41makes contact with the piezoelectric layer140, it becomes easy for the air inside the plurality of filling grooves52to move from the atmosphere communication passage58to the outside. Accordingly, it becomes easier to fill the plurality of filling grooves52throughout with the conductive ink61. Further, as shown inFIGS. 13A and 13B, the plurality of filling grooves52extend from the communication portion with the through hole54on the side of the supply groove155toward the communication portion with the atmosphere communication passage58. Therefore, the conductive ink61, which has flowed into the plurality of filling grooves52from the supply groove155, flows toward the atmosphere communication passage58. Hence, it becomes even easier for the air to move out of the filling grooves52.

Next, explanations will be given about a few modifications which apply various changes to the first and second embodiments. Note that, however, the same reference numerals are used to refer to the components with identical or similar configurations to those of the above embodiments, any explanation for which will be omitted as appropriate.

The pattern of the filling grooves52for forming the first electrode42is not limited to the patterns of the first and second embodiments. For example, the plurality of filling grooves52may intersect each other to form a netlike pattern as shown inFIG. 8orFIG. 16.

Further, in the first embodiment, a part of the area53, at which the filling grooves52of the wiring substrate41are formed, extend out beyond the piezoelectric elements40in the longitudinal direction (seeFIGS. 4 and 6B). However, the filling grooves52may alternatively extend out in the latitudinal direction of the piezoelectric elements40. Further, the filling grooves52may also extend out through the entire circumference of the piezoelectric elements40.

Alternatively, as shown inFIG. 9, the size of the area53, at which the filling grooves52of the wiring substrate41are formed, may be the same as or smaller than that of the piezoelectric elements40, and thus the filling grooves52may not extend out from the piezoelectric elements40. Even if the wiring substrate41is in contact with each of the piezoelectric elements40, there is still some interspace between the wiring substrate41and each of the piezoelectric elements40. Therefore, even if the filling grooves52do not extend out from the piezoelectric elements40, it is still possible to drain the air inside the filling grooves52to the outside along with the filling of the conductive ink61. Further, with such a configuration as shown inFIG. 9, because the filling grooves52do not extend out from the piezoelectric elements40, differing from the configuration of the first embodiment, there is no occurrence of the problem that the conductive ink filling the filling grooves52drips down.

In the first embodiment, as shown inFIG. 5, the plurality of piezoelectric elements40corresponding to the plurality of pressure chambers24respectively are separated from each other. In contrast to this, as shown inFIG. 10, the piezoelectric actuator21may alternatively be configured to have a piezoelectric layer70arranged in a planar manner over the plurality of pressure chambers24so that the plurality of piezoelectric elements40corresponding to the plurality of pressure chambers24are integrated into one body.

It is also possible to appropriately change the configuration of the supply grooves55,155of the first and second embodiments for filling the filling grooves52with the conductive ink61. For example, it is possible to appropriately change the position and shape of the liquid receiving portions55d,155bon which the conductive ink61jetted from the ink jet head60is landed. Further, if the second supply groove55bhas a sufficiently large groove width to such an extent as is able to land the conductive ink61jetted from the ink jet head60, it is also possible to omit the liquid receiving portions55d. Further, it is not necessary to form the supply grooves55,155on the surface of the wiring substrate41on the side opposite to the joint surface with the piezoelectric elements40, but it is possible to appropriately determine the arrangement of the supply grooves55,155according to how the wires47are laid out from the first electrodes42. For example, even if the supply grooves55,155are formed on the joint surface of the wiring substrate41, it is sufficiently possible to jet the conductive ink61from the inkjet head60into the supply grooves55,155so that the conductive ink61jetted from the ink jet head60does not land on the piezoelectric elements40, by forming the supply grooves55,155to extend to a position sufficiently away from the piezoelectric elements40.

The method for filling the filling grooves52with the liquid conductive material is not limited to the method by jetting the conductive ink61from the inkjet head60. For example, it is also possible to adopt a method of injecting a predetermined quantity of the liquid conductive material with a dispenser provided with a needle for liquid injection.

In the first and second embodiments, the wiring substrate41and the piezoelectric elements40(piezoelectric layer140) are joined together by hardening the conductive ink having filled the filling grooves52. However, the wiring substrate41and the piezoelectric elements40(piezoelectric layer140) may also be joined together by another process different from that of filling with the conductive ink (forming the first electrodes), for example, by using another adhesive different from the conductive ink.

In the first and second embodiments, in a state that the wiring substrate41makes contact with the piezoelectric elements40(piezoelectric layer140), the filling grooves52, which are closed up by the piezoelectric elements40, are filled with the liquid conductive material (conductive ink). However, the filling grooves52of the wiring substrate41may be filled with the liquid conductive material and the conductive material may be hardened to form the first electrodes42on the wiring substrate41, and then, the wiring substrate41may be joined to the piezoelectric elements40while making the first electrodes42contact with the piezoelectric elements40.

Although the plurality of filling grooves52are formed on the joint surface of the wiring substrate41in the first and second embodiments, the plurality of filling grooves52may alternatively be formed on the upper surface of each of the piezoelectric elements40to be joined to the wiring substrate41, and then the plurality of filling grooves52may be filled with the liquid conductive material to form the first electrodes42.

The first electrodes42are not limited to being formed by filling the filling grooves52formed in the wiring substrate41(or in the piezoelectric elements40) with the liquid conductive material as described above. For example, each of the first electrodes42may be formed on the joint surface of one of the wiring substrate41and the corresponding piezoelectric element40by a publicly known method such as screen printing, sputtering or the like, and then the joint surface is joined to, while letting each of the first electrodes42contact with, the other of the wiring substrate41and the corresponding piezoelectric element40. In this modification, the first electrodes42are also arranged between the wiring substrate41and each of the piezoelectric elements40being in contact with the wiring substrate41and each of the piezoelectric elements40, and this simplifies the configuration of connecting the both. Further, because it is not necessary to form electrodes on both the wiring substrate41and the piezoelectric elements40, the production process can also be simplified.

The atmosphere communication passage58in communication with the plurality of filling grooves52is not limited to the configuration of the second embodiment. For example, the atmosphere communication passage58does not need to open at the upper surface of the wiring substrate41(the surface on the side opposite to the joint surface). As shown inFIG. 17, instead of the atmosphere communication hole57opening to the upper surface of the wiring substrate41, the atmosphere communication groove56connected to the plurality of filling grooves52may extend to the end (edge) of the wiring substrate41along the lower surface of the wiring substrate41, and open at the end (edge).

While the atmosphere communication passage58(the atmosphere communication grooves56) of the second embodiment preferably has a high fluid-flow resistance such that the liquid conductive material filling the plurality of filling grooves52may not flow out, they are not limited to the shape and the like shown inFIG. 14. As shown inFIG. 18for example, it is also possible to form each of the atmosphere communication passages58with a plurality of ribs56cprojecting only from one lateral side of the atmosphere communication groove56. Further, without any ribs, it is still possible to increase the fluid-flow resistance in the atmosphere communication grooves56by some other technique such as narrowing the groove width, increasing the length, forming a serpentine shape and increasing the number of curved portions, or the like.

While each of the embodiments and modifications explained above is an example of applying the present invention to an ink jet head which is a liquid jetting apparatus, the piezoelectric actuator of the present invention is not limited to being used for the purpose of applying pressure to a liquid. For example, it may also be used for the purpose of causing a solid matter to undergo displacement, vibration, etc.