JP2006110908A - Liquid-droplets jetting apparatus and the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid-droplets jetting apparatus enabling a high delivery-position accuracy, high-speed driving and densification to be realized. <P>SOLUTION: The liquid-droplets jetting apparatus, which delivers liquid droplets to a liquid-droplets reaching member 6 or media on the member 6 from a nozzle 30 by making a partition 90 shear-deformed with applying a driving voltage to a driving electrode 91, is equipped with a common electrode 2 countering the liquid-droplets reaching member 6 on both sides of two or more nozzles 30 and a power circuit 40 forming an electric field between the liquid-droplets reaching member 6 and the common electrode 2. After applying the driving voltage to the driving electrode 91 in the state of having formed the electric field between the liquid-droplets reaching member 6 and the common electrode 2 and delivering the liquid in a driving liquid chamber 9 as droplets from the nozzles 30 by a pressure fluctuation caused by the shear-deformation of the partition 90, the direction and rate of delivery are controlled by the electric field between the liquid-droplets reaching member 6 and the common electrode 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a droplet ejecting apparatus such as an ink jet printer that selectively ejects fine droplets onto a medium and forms an image, and a liquid ejecting method in the droplet ejecting apparatus.

  As represented by a printer, a droplet ejection technique called an ink jet method has attracted attention as a technique for forming an image or pattern on a medium. Inkjet image formation is an on-demand method that can eject the required amount of liquid droplets to the required parts, making it suitable for energy and resource savings, and further miniaturizing the device compared to electrophotography. And there are advantages such as low power consumption. In addition, since liquid materials can be ejected with the ink jet method, in recent years, not only ink is dropped on paper to form an image, but also its application to the drawing of wiring patterns of electronic components is studied. Has been.

  Specific methods for ejecting droplets in the inkjet method include a thermal method that uses the film boiling phenomenon, a laminated piezo method that uses a volume change due to the electric field of the laminated piezoelectric material, and an electrostatic force that uses charged droplets. There have been proposed a plurality of methods such as an electrostatic method for discharging and a shear deformation method using a pressure wave generated by shear deformation of a piezoelectric body.

  Among these, the electrostatic method has an advantage that the landing accuracy of the droplet on the medium is better than other methods, and in this respect, the density of images or patterns in recent years has increased. This method is suitable for high definition requirements. In other methods, the medium must be reached only at the initial velocity at which the droplets are ejected from the nozzle, and the direction may be tilted due to the influence of external factors (for example, wind) during the flight. In addition, there is an urgent need to reduce the landing position deviation caused by the ejection direction of the liquid droplets depending on the tip shape of the nozzle and the ejection angle of the liquid droplets being different for each nozzle.

  On the other hand, in the electrostatic method, an electric field is applied between the counter electrode provided on the medium and the head, and the droplet advances along the electric field direction. At this time, since the droplet itself always receives an electrostatic force in the direction of the electric field, the flight direction is easily kept constant. Therefore, the landing accuracy for each nozzle is small and the landing accuracy is improved.

  However, in the electrostatic method, the liquid in the liquid chamber is charged by the electric field as described above, and protrudes in a convex shape from the nozzle hole, and electric field concentration occurs in the protruding liquid, so that the liquid droplet is separated from the liquid. Once the liquid has protruded, the droplet discharge operation can be performed at an accelerated speed. However, when simultaneous discharge of a plurality of nozzles by a multi-nozzle is considered, the speed at which the liquid protrudes differs for each nozzle. Therefore, it must be adjusted to the slowest driving speed, and there is a limit to the driving speed.

  Further, if the charged state of the liquid in the vicinity of each nozzle is not uniform, the liquid cannot be projected in a constant convex shape, and it is difficult to make the droplet diameter uniform.

  Furthermore, in order to make a multi-nozzle by the electrostatic method, an electrode must be provided in the vicinity of each nozzle, and on / off control of several hundred volts must be performed individually, the drive circuit becomes expensive, and the drive speed is also increased. There was a limit.

  In addition, providing electrodes individually is also a main factor that causes a difference in the protruding state of the liquid for each nozzle, and there are many problems to apply to a droplet discharge device that continuously discharges from multiple nozzles at high speed. Had.

  Therefore, as a method of controlling the convex protrusion of the liquid by driving the piezoelectric body and causing the droplets to reach the medium by the electrostatic method, a pressure generating chamber equipped with a piezoelectric material is provided for each nozzle, and all There is one in which a common electrode common to the nozzle is provided in the vicinity of the nozzle (see, for example, Patent Document 1). In this configuration, in order to perform multi-nozzle control of electrostatic inkjet, a piezoelectric body corresponding to the number of nozzles is provided in the ink chamber, and the piezoelectric body is driven only for the nozzles to be ejected to raise the liquid in a convex shape. Then, droplets are ejected by the electric field between the common electrode and the medium. The voltage required to drive each piezoelectric body is several tens of volts at most, and the cost is low compared with the conventional case where individual electrodes for generating an electric field are controlled with a voltage of several hundred volts, and the discharge of the piezoelectric body is low. Good stability.

In addition, there is a piezoelectric element that can be independently driven and controlled for each ink chamber, and electrostatically ejects the convex ink that is raised from the nozzle hole by driving the piezoelectric element (for example, (See Patent Document 2). In this technique, an inexpensive single piezoelectric body may be used instead of an expensive laminated type as a piezo element. Furthermore, the nozzle density is limited to about 200 dpi in the stacked type, but this technique enables high density up to about 400 dpi.
JP-A-62-240559 JP 05-278212 A

  However, in the prior art, it has been difficult to achieve both high density and high speed driving. For example, in the configurations disclosed in Patent Documents 1 and 2, the driving frequency is estimated to be about several kHz, and the nozzle density is up to 400 dpi. Furthermore, in the configuration of Patent Document 1, it is necessary to mount a piezoelectric body for each ink chamber, and it is difficult to increase the density, and the cost is very high.

  The configuration of Patent Document 2 is relatively easy to increase in density as a manufacturing process, but only a single-layer piezo element is arranged in the ink chamber. A drive voltage of 10V is required and the device cannot be driven at high speed. Even if the piezo element can be improved so that it can be driven at high speed, there is no mechanism for attenuating the vibration that the piezo element gives to the liquid in the ink chamber, and even if the piezo element can be driven at high speed, There is a problem that the driving speed cannot be increased as a result of waiting until the residual vibration in the room naturally attenuates.

  An object of the present invention is to provide a droplet ejecting apparatus that can increase the total number of droplets that can be ejected per unit time, and that can further reduce the cost and life of the droplet ejecting apparatus. There is.

  The present invention has the following configuration as means for solving the above-described problems.

(1) A plurality of nozzle holes facing the droplet reaching member and a piezoelectric body polarized in the height direction are arranged with a plurality of gaps facing each other at the front surface in each of the plurality of nozzle holes. A plurality of partition walls, a plurality of drive liquid chambers separated from each other by each of the plurality of partition walls on the front side of each of the plurality of gaps, and drive electrodes formed on mutually facing surfaces of the plurality of partition walls; A drive circuit for applying a drive voltage to the drive electrode, a common electrode facing the droplet reaching member across the plurality of nozzle holes, and an electric field formed between the droplet reaching member and the common electrode A power supply circuit,
In a state where an electric field is formed between the droplet reaching member and the common electrode by the power supply circuit, the partition wall is shear-deformed by application of a driving voltage to the driving electrode from the driving circuit to enter the driving liquid chamber. The liquid in the driving liquid chamber is caused to protrude from the nozzle hole by the generated pressure fluctuation and then discharged as a droplet to the droplet reaching member.

  In this configuration, the pressure wave generated in the driving liquid chamber due to the shear deformation of the piezoelectric body and the electrostatic force acting on the charged droplet from the electric field formed between the common electrode arranged near the nozzle and the droplet arrival member. The energy for discharging the droplets is obtained by the attractive force.

  When both partition walls of the driving liquid chamber filled with the liquid are deformed so as to increase the volume of the driving liquid chamber, a pressure wave advances from the liquid supply direction. When the partition wall is deformed so that the volume of the driving liquid chamber is reduced at the timing when the pressure wave is superimposed in the driving liquid chamber, a larger amount of liquid projects from the nozzle hole at a high speed than the deformation of the volume of the driving liquid chamber. A discharge cycle of kHz can be realized.

  Further, by performing groove processing on the piezoelectric body using a dicing apparatus that is widely used as a semiconductor manufacturing apparatus, the driving liquid chamber can be easily formed at high density and low cost, and a discharge density of about 400 dpi can be easily realized.

  Furthermore, the driving voltage for causing shear deformation in the piezoelectric body is several V to several tens V, and a high-speed driving circuit can be easily manufactured.

  In addition, compared with a droplet ejecting apparatus that uses only shear deformation of a piezoelectric body, the droplet discharge position accuracy in the droplet reaching member is improved, the voltage applied to the partition wall can be lowered, and it is generated in the liquid chamber. Since the residual vibration is small, the standby time can be shortened, resulting in high speed driving.

  Therefore, it is possible to easily realize a high-density discharge density and a high-frequency discharge cycle at a low cost, and to improve the liquid droplet discharge position accuracy in the liquid droplet arrival member.

  (2) In the liquid ejecting apparatus according to (1), a plurality of damping liquid chambers that communicate with each other via a communication portion on the back side of each of the plurality of gaps and that are continuous with each of the plurality of driving liquid chambers. Is provided.

  In this configuration, a plurality of attenuation liquid chambers that are connected to the driving liquid chambers on the liquid supply side of the liquid chamber and communicate with each other via the communication portion are provided in each gap. Therefore, by reducing the cross-sectional area of the communication portion, the difference in cross-sectional shape between the driving fluid chamber and the damping fluid chamber is reduced, the reflection of pressure waves due to the water hammer action is reduced, and the pressure waves are reduced. While proceeding through the damping liquid chamber, the damping liquid chamber is gradually opened to the adjacent damping liquid chamber via the communication portion. As a result, the residual vibration of the pressure wave in the driving fluid chamber is reduced, and high-speed driving at about 200 kHz is possible.

  (3) A droplet ejecting method in the droplet ejecting apparatus according to (1) or (2), wherein an electric field is formed between the power supply circuit and the droplet reaching member with respect to the common electrode. A voltage is applied, and in the meantime, a driving voltage is applied to the driving electrode to shear deform the partition wall, and due to the pressure variation generated in the liquid chamber formed in the gap by the shear deformation, the common in the liquid chamber The liquid charged by the electrode is discharged as a droplet from the nozzle hole, and the discharge speed of the droplet is controlled by an electric field formed between the common electrode and the droplet reaching member. To do.

  In this configuration, the liquid filled in the driving liquid chamber is charged by the common electrode provided in the vicinity of each nozzle hole, and is discharged as a droplet in a state of being charged by the shear deformation of the partition wall. The discharge speed is controlled by the electric field between the two. Therefore, the charged liquid is raised from the nozzle hole surface by the pressure wave generated in the driving liquid chamber by the shear deformation of the partition wall, and then separated from the liquid to form a droplet. have.

  (4) A droplet ejecting method in the droplet ejecting apparatus according to (1) or (2), wherein an electric field is formed between the power supply circuit and the droplet reaching member with respect to the common electrode. A voltage is applied, and in the meantime, a driving voltage is applied to the driving electrode to shear deform the partition wall, and due to the pressure variation generated in the liquid chamber formed in the gap by the shear deformation, the common in the liquid chamber After the liquid charged by the electrode protrudes from the nozzle hole and is further discharged as a droplet from the nozzle hole by electric field concentration acting from the electric field formed between the common electrode and the droplet reaching member The droplet discharge speed is controlled by an electric field formed between the common electrode and the droplet reaching member.

  In this configuration, the liquid is protruded from the nozzle hole by shear deformation of the partition wall, and the protruding portion is formed as a droplet by electric field concentration acting on the protruding portion from the electric field between the common electrode near the nozzle hole and the droplet reaching member. The ejection speed is controlled by an electric field between the common electrode and the droplet arrival member. Therefore, the pressure wave generated by the piezoelectric body is used only for causing the liquid to protrude, and the force for separating the droplet from the protruded liquid is obtained when the charged portion of the liquid receives electrostatic attraction, so the electric field direction is Determine the initial ejection direction of the drops.

  (5) In the liquid droplet ejecting method according to (3) or (4), the common electrode and the liquid droplet are ejected from the nozzle hole until the liquid droplet reaches the liquid droplet arrival member. The potential between the droplet arrival member and the droplet arrival member is reversed at an integral multiple of the droplet ejection cycle.

  In this configuration, the potential difference between the common electrode and the droplet reaching member is inverted at an integer multiple of the discharge cycle until the droplet discharged from the nozzle hole reaches the droplet reaching member. Therefore, since the charging direction of the droplet changes every few droplets, the charging of the droplet discharged on the droplet reaching member in the vicinity is canceled.

  (6) In the liquid droplet ejecting method according to (3) or (4), the common electrode and the liquid droplet are ejected from the nozzle hole until the liquid droplet reaches the liquid droplet arrival member. It is characterized in that the potential between the droplet arrival members is reversed.

  In this configuration, the potential difference between the common electrode and the droplet reaching member is reversed before the liquid reaches the droplet reaching member after the liquid is discharged. Therefore, when a droplet is ejected from the nozzle hole, the electric field between the common electrode and the droplet reaching member acts on the droplet in the ejection direction. Before reaching the droplet arrival member, an electrostatic force in the direction opposite to the discharge direction is applied.

  According to the present invention, the following effects can be obtained.

  (1) In a droplet ejecting apparatus that can be easily densified and can be driven at a high speed, it is possible to further improve the landing position accuracy.

  (2) The residual vibration of the pressure wave in the driving liquid chamber can be reduced, and high-speed driving at about 200 kHz can be realized.

  (3) Even when ejecting a liquid with relatively low electrical conductivity, which has a low electrostatic attraction due to a small charge amount of droplets, it is less susceptible to disturbances such as wind and maintains high ejection position accuracy. can do. In addition, since suction by electrostatic attraction only needs to work during flight, the voltage to be applied to the common electrode can be lowered, and the drive frequency is a concern when the liquid charging time constant is low. Can be suppressed.

  (4) The pressure wave generated by the piezoelectric body is used only to cause the liquid to protrude, and the force for separating the liquid droplet from the protruded liquid is obtained from the electric field between the common electrode and the liquid droplet arrival member. This makes it possible to determine the initial discharge direction of droplets, and to reduce discharge position errors due to variations in the discharge direction of each nozzle hole and nozzle hole shape, thereby improving the discharge position accuracy. it can. Further, since the pressure wave in the driving liquid chamber is sufficient to cause the liquid to protrude from the nozzle hole, the amount of shear deformation of the partition wall may be very small, the amplitude of the residual vibration is reduced, and high speed driving is possible. At the same time, there is little deterioration of the piezoelectric body over time, and the cost of the drive circuit can be reduced. In particular, it is suitable for discharging a liquid with high conductivity.

  (5) By changing the charging direction of the droplet every few drops, the charging of the droplets discharged on the droplet arrival member in the vicinity is canceled, and a plurality of droplets are densely formed on the droplet arrival member. It is possible to prevent a drop in droplet discharge position accuracy due to the repulsive force between droplets charged to the same potential when discharged at the same time.

  (6) When a droplet is ejected from the nozzle hole, an electric field between the common electrode and the droplet reaching member acts on the droplet in the ejection direction. By applying an electrostatic force in the direction opposite to the discharge direction before reaching the droplet arrival member, the collision speed when reaching the droplet arrival member is suppressed while suppressing errors in the discharge direction due to disturbance during the flight of the droplet It is possible to prevent the droplets from being scattered around by reducing.

  FIG. 1 is a cross-sectional view showing a configuration of a droplet ejecting apparatus according to an embodiment of the present invention. In the droplet ejecting apparatus 200 according to this embodiment, a common electrode 2 in which a plurality of holes (electrode holes) 20 are formed in a conductive plate is formed on the front surface 1B of the piezoelectric element unit 1 that generates a pressure wave. A nozzle plate 3 made of polyimide in which (nozzle holes) 30 are formed is pasted so that the centers of the respective holes 20 and 30 are located at substantially the center of the opening of the liquid chamber 1A.

  On the back surface 1 </ b> C of the piezoelectric element portion 1, the liquid electrode 1 </ b> A of the piezoelectric element portion 1 is connected to the flexible substrate 4 for conducting the drive electrode 91 formed in the liquid chamber 1 </ b> A to the drive circuit 50 and a liquid tank (not shown). A manifold 5 for supplying a liquid therein is connected. The medium itself to which a droplet reaches or the droplet arrival member 6 that is a member for setting the medium is electrically grounded, and a rectangular pulse voltage is applied to the common electrode 2 from the power supply circuit 40.

  The liquid in the manifold 5 passes through the common liquid chamber 7 commonly connected to each liquid chamber 1A, and the damping liquid chamber 8 having a minute connecting portion 8A in part and the partition wall made of a piezoelectric material undergo shear deformation. Then, the driving liquid chambers 9 that generate pressure waves are supplied in this order. The liquid is ejected as droplets from the nozzle hole 30 of the nozzle plate 3 through the electrode hole 20 of the common electrode 2 from the driving liquid chamber 9 that has become positive pressure by pressure wave control of the driving liquid chamber 9. The ejected liquid droplets are accelerated by the electric field generated between the common electrode 2 and the liquid droplet arrival member 6 and fly toward the liquid droplet arrival member 6, and the liquid droplet arrival member 6 or the liquid droplet arrival member 6. Reach the media set above.

  The internal structure of the piezoelectric element portion 1 and the arrangement of the common electrode and the nozzle plate will be described in more detail with reference to FIG. FIG. 2A is a front view of the piezoelectric element portion, and is a diagram showing the arrangement of the end face on the droplet discharge direction side and the common electrode / nozzle plate on the end face. The piezoelectric element portion 1 is formed by applying a substantially flat cover 11 made of a ceramic material to an act substrate 10 made of a polarized piezoelectric body having a plurality of grooves engraved as a liquid chamber 1A so as to close the upper surface of the grooves. A space which is pasted using a system adhesive and has a substantially rectangular cross section formed by a groove and a cover is used as the liquid chamber 1A.

  The act substrate 10 is formed by laminating a thin plate 10B made of the same material having a thickness approximately half the depth of the driving liquid chamber 9 on a base body 10A made of a piezoelectric body polarized in the thickness direction (vertical direction on the paper surface). And the thin plate 10A have opposite polarization directions. A plurality of grooves were processed using a dicing apparatus from the direction of the thin plate 10B, and the pitch was 63 μm, the groove width was 30 μm, and the depth was 120 μm. This corresponds to a nozzle density of 400 dpi, and in our study, it is possible to narrow the pitch up to 600 dpi (pitch is 42 μm, groove width is 20 μm).

  Drive electrodes 91 are formed on both side surfaces of the partition wall 90 separating the adjacent drive liquid chambers 9. The driving electrodes 91 are electrically connected to each other in the driving liquid chamber 9 and have the same potential, and those facing each other across the partition wall 90 are insulated from each other. Voltage control can be performed for each electrode 91.

  Here, a method of generating a pressure wave for discharging a droplet from the driving liquid chamber 9B will be described. For the generation of the pressure wave, a shear deformation action generated by applying an electric field in a direction perpendicular to the polarization direction to the partition wall 90 made of a piezoelectric body polarized in the height direction (up and down direction on the paper surface) is used. Since the partition wall 90 is approximately half the height and the polarization direction is reversed, the partition wall 90 is shear-deformed into a mold.

  When an opposite phase potential is applied to the drive electrode 91A and the drive electrode 91C with respect to the drive electrode 91B, the partition wall 90AB is transformed into a> shape, the partition wall 90BC is transformed into a <shape, and the drive liquid chamber 9B is transformed into a <> shape. As a result, the driving liquid chamber 9B has a negative pressure, and a pressure wave from the common liquid chamber 7 travels into the driving liquid chamber 9B and is superimposed on the reflected wave, so that the driving liquid chamber 9B has a positive pressure. At this timing, the potentials of the drive electrode 91B, the drive electrode 91A, and the drive electrode 90C are inverted, so that the partition wall 90AB is transformed into a <mold, the partition wall 90BC is transformed into a mold, and the drive fluid chamber 9B is transformed into a <mold. In the driving liquid chamber 9B, a high pressure state is formed, and the liquid is projected from the nozzle hole 30 in a convex shape. In addition, in order for the partition wall 90 to shear and deform into a mold to generate a pressure wave, the partition wall 90 itself needs to have rigidity, and the upper and lower sides of the partition wall 90 must be fixed.

  Next, the arrangement of the common electrode 2 and the nozzle plate 3 will be described. In FIG. 2A, the third driving liquid chambers 9A to 9C from the right are in the state of the opening of the piezoelectric element portion 1, and the fourth to sixth driving liquid chambers 9D to 9F are from the piezoelectric element portion 1. The seventh to ninth drive liquid chambers 9G to 9I from the right show the state where the common electrode 2 is bonded to the front surface, and the nozzle plate 3 is bonded to the front surface of the common electrode 2.

  The common electrode 2 appearing on the front side of the fourth to sixth driving liquid chambers 9D to 9F from the right is a thin metal plate having a thickness of 70 μm, and electrode holes 20 having a diameter of 20 μm are formed at substantially the same pitch as the driving liquid chamber 9. Has been. The common electrode 2 is positioned and bonded so that the center of the electrode hole 20 coincides with the approximate center of the opening of the liquid chamber 1A. The electrode hole 20 is formed by performing various processes such as excimer laser irradiation, punching, electrical discharge machining, chemical etching including resist patterning, or electroforming using a circularly formed resist pattern on the metal thin plate to be the common electrode 2. Can be formed by a method. When these methods are used, the electrode hole 20 having a minimum diameter of about 5 μm to 20 μm can be formed. A material having high conductivity is used as the material of the common electrode 2.

  The nozzle plate 3 appearing on the front side of the seventh to ninth driving liquid chambers 9G to 9I from the right is made of polyimide having a thickness of 50 μm, and nozzle holes 30 having a diameter of 15 μm are formed at substantially the same pitch as the driving liquid chamber 9. ing. The nozzle plate 3 is positioned and bonded so that the center of the nozzle hole 30 substantially coincides with the center of the electrode hole 20. The nozzle hole 30 is generally formed in the nozzle plate 3 by excimer laser irradiation. Depending on the thickness of the polyimide, nozzle holes with a minimum diameter of about 5 μm to 10 μm can be formed. As the material for the nozzle plate, a highly insulating material is used. As the shape of the nozzle hole 30, a taper may be provided so as to spread from the front side to the back side, but it is desirable that the maximum diameter of the nozzle hole 10 is smaller than the diameter of the electrode hole 20.

  Next, the detailed structure of the damping liquid chamber shown in FIG. 1 will be described with reference to FIG. 2B is an end view of the YY portion in FIG. The major difference between the damping liquid chamber 8 and the driving liquid chamber 9 is that the damping section partition wall 80 that divides the damping liquid chamber 8 is not connected to the cover substrate 11 on the upper surface, and is a communication section that is a gap of 5 μm to 20 μm. 8A. As shown in the longitudinal sectional view of FIG. 1, the communication portion 8 </ b> A is realized by denting the surface constituting the attenuation liquid chamber of the cover substrate 11 by 5 μm to 20 μm compared to the portion constituting the driving liquid chamber. The processing depth of the recess is determined in consideration of the thickness of the paraxylene film serving as a protective film. For example, when the thickness of the paraxylene film described later is 5 μm, the recess depth is set to 15 to 30 μm. Processed. Moreover, this dent can be easily processed by sandblasting, chemical etching, or grinding using a dicing apparatus. The communication portion 8A communicates adjacent attenuation liquid chambers 8 with each other.

  Normally, it is necessary to provide a common liquid chamber, which is a large common space for supplying liquid, on the liquid supply side (back side) of the plurality of drive liquid chambers 9, and the pressure generated in each drive liquid chamber 9. When the wave travels toward the common liquid chamber, a water hammer effect is generated at the interface between the drive liquid chamber 9 and the common liquid chamber, and the reflected light travels into the drive liquid chamber 9 to travel as residual vibration. 9, which hinders high-speed driving. However, by providing the damping liquid chamber 8 on the back side of the driving fluid chamber 9, there is little difference in cross-sectional shape between the driving fluid chamber 9 and the damping fluid chamber 8, and there is little reflection due to the water hammer effect. While the pressure wave travels through the damping liquid chamber 8 to the driving liquid chamber 9, the pressure wave can be gradually opened to the adjacent damping liquid chamber 8 via the communication portion 8A. As a result, the residual vibration of the pressure wave in the damping liquid chamber 8 and the driving liquid chamber 9 can be reduced to enable high-speed driving, and high-speed driving of about 200 kHz can be realized.

  On both side surfaces of the attenuating section partition wall 80, there are provided attenuating section electrodes 81 connected to the driving electrode 91 of the driving liquid chamber 9, and the liquid chamber 1A is filled in the back side end of the piezoelectric element section 1 in FIG. The conductive resin 12 is electrically connected. In the conductive resin 12 exposed at the rear side end of the piezoelectric element portion 1, a wiring pattern formed on the flexible substrate 4 at a substantially equal pitch to the liquid chamber 1A is electrically connected via an anisotropic conductive film. Connection is fixed. The wiring pattern is conducted to a driver circuit (not shown), and the control voltage oscillated from the driver circuit propagates in this order to the flexible substrate 4, the conductive resin 12, the attenuation unit electrode 81, and the drive electrode 91. 9 is a drive voltage for forming a pressure wave.

  The electrodes 81 and 91 exposed in the liquid chamber 1A may corrode and dissolve over time due to the aqueous liquid flowing through the liquid quality 1A. Therefore, in the liquid ejecting apparatus 200 according to this embodiment, after the flexible substrate 4 is bonded to the piezoelectric element portion 1, the surface is coated with a paraxylene film. The paraxylene film is evacuated once in the chamber in which the object to be processed is stored, and the dimer that is the source of the paraxylene film is heated in the chamber to sublimate, so that the sublimated monomer diffuses into the chamber. The polymer is grown by depriving energy on the surface of the workpiece. Therefore, the paraxylene film is easy to form a uniform and stable film even in a narrow gap, and is excellent in water resistance, solvent resistance, and insulation.

  The droplet ejecting apparatus 200 having this configuration is manufactured by the following process. First, a groove serving as the liquid chamber 1A is processed in the act substrate 10 using a dicing apparatus. Next, sputtering is performed on the grooved Act substrate 10A using a copper target from the groove opening side, and copper electrodes are formed on the upper surface of the partition wall 90, the partition wall side surface, and the groove bottom surface. Next, a portion corresponding to the rear side end of the droplet ejecting apparatus 200 is filled with a silver paste using a dispenser and cured. Thereafter, the upper surface of the act substrate 10 is ground using a dicing apparatus, thereby removing the copper electrode on the upper surface of the partition wall 90 and the silver paste remaining outside the groove.

  Further, in the cover substrate 11, the dicing device is arranged so that the portion facing the damping liquid chamber 7 is recessed by about 15 μm to 30 μm as compared with the portion facing the driving liquid chamber 9 (when the thickness of the paraxylene film is 5 μm). Using the dicing apparatus, the part facing the common liquid chamber 7 was recessed by 600 μm.

  And after positioning the act board | substrate 10 and the cover board | substrate 11, it adhere | attached with the epoxy-type adhesive agent, and the piezoelectric element part 1 was formed. After performing the above-described processing in a large wafer state corresponding to a plurality of piezoelectric element portions 1 and then cutting each piezoelectric element portion 1, it can be manufactured in large quantities and at a low cost at a time. .

  After positioning the flexible substrate 4 in which the wiring pattern is formed in the piezoelectric element portion 1 thus manufactured at a substantially equal pitch to the liquid chamber 1A on the conductive resin 12 made of silver paste filled in the liquid chamber 1A, The connection is made through an anisotropic conductive film. Thereafter, a paraxylene film is formed as described above.

  Further, after the common electrode 2 is positioned on the front surface side of the piezoelectric element portion 1 so that the electrode hole 20 and the liquid chamber 1A substantially coincide with each other and bonded with an epoxy adhesive, the nozzle plate 3 is attached to the nozzle hole 30. Are positioned so that their centers substantially coincide with the centers of the electrode holes 20 of the common electrode 2 and bonded with an epoxy adhesive. Next, the manifold 5 is bonded so as to close the opening of the common liquid chamber 7 on the opposite surface side where the nozzle plate 3 of the piezoelectric element portion 1 is bonded, and the periphery is sealed so that the liquid does not leak.

  In the liquid ejecting apparatus 200 according to this embodiment, the length of the driving liquid chamber 9 in the longitudinal direction is 1.3 mm, the length of the attenuation section liquid chamber 8 is 0.8 mm, and the total length of the piezoelectric element section 1 is 3.3 mm. Was made.

  In this configuration, a pressure wave is generated in the driving liquid chamber 9 partitioned by the partition wall by shearing deformation of the partition wall made of a single-layer or two-layer piezoelectric body polarized in the height direction. Both partition walls of the driving liquid chamber 9 corresponding to the nozzle hole to which the droplet is to be discharged are deformed so that the volume of the driving liquid chamber 9 is increased, and a pressure wave advances from the liquid supply side (back side). By deforming the partition so that the volume of the driving liquid chamber 9 is reduced at the timing when the pressure wave is superimposed in the driving liquid chamber 9, the liquid is more than the amount of deformation of the volume of the driving liquid chamber 9. Can be driven at a high frequency of several tens of kHz.

  If a multilayer piezoelectric body is used, a certain level of high-speed driving is possible, but the nozzle density is up to 200 dpi. On the other hand, if a single-layer piezoelectric body is used, the nozzle density is possible up to a maximum of 400 dpi, but at a high speed. It cannot be driven.

  In addition, the partition wall is for performing groove processing on the piezoelectric body by using a dicing apparatus that is widely used as a semiconductor manufacturing apparatus. The technique can be easily performed at low cost, and the nozzle density is about 400 dpi. It can be easily realized.

  Furthermore, droplet ejection and non-ejection control is performed by driving a piezoelectric body, and the drive voltage may be several volts to several tens of volts. Thus, when considering multi-nozzle formation, it is not necessary to control individual electrodes on the order of several hundred volts as in the electrostatic method, and a high-speed drive circuit can be easily manufactured.

  Next, the droplet jetting method of the present invention will be described using examples.

<First droplet ejection method>
FIG. 3 is a schematic view of the droplet ejecting apparatus, and is a cross-sectional view taken along the line XX in FIG. Voltage controllable drive electrodes 91 that are insulated from each other are formed on both sides of the partition wall 90, and a paraxylene film 92 is on the drive electrode 91. The drive liquid chamber 9 sandwiched between the two partition walls 90 is filled with a liquid 93. The liquid 93 is also filled in the electrode holes 20 of the common electrode 2 and the nozzle holes 30 of the nozzle plate 3.

  The process of discharging one droplet from the nozzle hole 30 will be described. First, a potential difference of 100 V is always applied between the common electrode 2 and the droplet reaching member 6 so that the common electrode 2 becomes a positive electrode. Then, as shown in FIG. 3A, the liquid 93 in the vicinity of the electrode hole 20 and the nozzle hole 30 is charged to the positive electrode. Next, as described above, an electric field is applied to both side surfaces of the partition wall 90 so that the partition wall 90 is sheared and deformed in the direction of the arrow shown in FIG. When the negative pressure is widened, pressure waves proceed from both sides of the damping liquid chamber 8 side and the nozzle plate 2 side. At a certain timing, the pressure waves are superimposed, and the driving fluid chamber 9 becomes positive pressure at a certain moment.

  The partition wall 90 is shear-deformed in the direction of the arrow shown in FIG. 3B so that the direction in which the electric field is applied to the partition wall 90 is reversed at the timing when the driving liquid chamber 9 becomes positive pressure, and the volume of the driving liquid chamber 9 is reduced. Let Then, the driving liquid chamber 9 which has been in a positive pressure is pushed from both the partition walls 90 so as to reduce the volume thereof, and further becomes a positive pressure, and the liquid 93 charged from the nozzle hole 30 protrudes in a substantially columnar shape, and the surface of the discharge liquid Due to the tension action, the liquid droplets are divided in the middle to become droplets 110.

  Next, as shown in FIG. 3C, the droplet 110 charged to the positive electrode receives electrostatic attraction from the electric field that is always formed between the common electrode 2 and the droplet reaching member 6 and is accelerated while being accelerated. It reaches the reaching member 6 by flying.

  When the potential difference between the common electrode 2 and the droplet arrival member 6 is 100 V, the distance between the two is 0.5 mm, and a driving voltage of 15 V and a driving frequency of 70 kHz is applied between the partition walls 90, the continuous voltage is stable. It was confirmed that discharge was possible. Furthermore, the discharge speed of the droplet 110 was 8 mm / s or more.

The volume resistivity of the liquid used was about 4 × 10 ⁵ Ω · cm. Further, the larger the potential difference between the common electrode 2 and the droplet arrival member 6 (that is, the stronger the electric field strength), the smaller the variation in the ejection direction of the droplets 110 for each of the plurality of nozzle holes 30 and the faster the ejection speed. As a result, it was found that the landing position accuracy of the droplets 110 discharged from the plurality of nozzle holes 30 is good.

  On the other hand, when the potential difference between the common electrode 2 and the droplet reaching member 6 was 0, the landing position accuracy was the worst. Further, when a wind resistance test (a wind at a constant speed is sent in a direction perpendicular to the droplet flying direction to check the deviation of the landing position), the gap between the common electrode 2 and the droplet arrival member 6 is measured. It was found that the larger the potential difference, the smaller the deviation of the landing position from when there was no wind, and it was more resistant to wind and other disturbances.

  This is because the stronger the electric field strength in the flying region of the droplet 110, the stronger the electrostatic attractive force that the charged droplet 110 receives during the flight and the greater resistance to disturbances such as wind, and all nozzle holes This is probably because the electric field directions at 30 substantially coincide with each other, so that the influence of the variation in the ejection direction due to the difference in the shape of the nozzle hole 30 itself is reduced.

  In this droplet jetting method, the liquid is charged by the common electrode 2 provided in the vicinity of each nozzle hole 30, and the partition wall 90 is sheared and deformed by applying an electric field between the drive electrodes 91. From the common electrode 2 and the droplet reaching member 6 and discharging speed is controlled. That is, the charged liquid is caused to protrude from the nozzle hole 30 by the pressure wave generated in the driving liquid chamber 9 and is separated from the liquid to form a droplet. For this reason, since the charged droplet has an initial velocity at the same time as the droplet formation, the droplet velocity can be increased as compared with the case where the droplet is attracted only by electrostatic attraction. In particular, when discharging a liquid with relatively low electrical conductivity, the charge amount of the liquid droplet is small, so the electrostatic attractive force is small, it is susceptible to disturbances such as wind, and the discharge position accuracy is likely to deteriorate. By giving the initial velocity to the droplet, the adverse effect can be suppressed. In addition, since the droplets have an initial velocity in advance, it is sufficient that the suction by electrostatic attraction only works during flight, the voltage applied to the common electrode can be lowered, and the liquid charging time constant is low Therefore, it is possible to suppress a decrease in drive frequency that is a concern.

  Furthermore, in this droplet jetting method, since the liquid is projected by the pressure wave, the driving speed can be increased.

<Second droplet ejection method>
FIG. 4 is a schematic diagram of the droplet ejecting apparatus according to the present invention, and is a cross-sectional view taken along the line XX in FIG. Voltage controllable drive electrodes 91 that are insulated from each other are formed on both sides of the partition wall 90, and a paraxylene film 92 is on the drive electrode 91. The drive liquid chamber 9 sandwiched between the two partition walls 90 is filled with a liquid 93. The liquid 93 is also filled in the electrode holes 20 of the common electrode 2 and the nozzle holes 30 of the nozzle plate 3.

  The step of discharging one droplet from the nozzle hole 30 will be described. First, a potential difference of 400 V is applied between the common electrode 2 and the droplet reaching member 6 so that the common electrode 2 becomes a positive electrode. Then, as shown in FIG. 4A, the liquid near the electrode hole 20 and the nozzle hole 30 is charged to the positive electrode. Next, as described above, an electric field is applied to both sides of the partition wall 90 to shear the partition wall 90 in the direction of the arrow in FIG. When the negative pressure is expanded, pressure waves proceed from both sides of the damping liquid chamber 8 side and the nozzle plate 3 side. Then, the driving liquid chamber 9 instantaneously becomes positive pressure by being overlapped at a certain timing.

  At the timing when the driving liquid chamber 9 becomes positive pressure, the direction of applying an electric field to the partition wall 90 is reversed, and the partition wall 90 is sheared in the direction of the arrow in FIG. 4B so that the volume of the liquid chamber 9 decreases. Deform. Then, the driving liquid chamber 9 which has been in a positive pressure is pushed from both the partition walls 90 so as to reduce the volume thereof, and further becomes a positive pressure, and the liquid 93 charged from the nozzle hole 30 protrudes from the nozzle hole 30 into a substantially hemispherical shape. To do.

  Here, as shown in FIG. 4B, the portion protruding from the surface of the nozzle plate 3 is seen from the flat surface of the nozzle plate 3 when viewed from the electric field generated between the common electrode 2 and the droplet reaching member 6. Only a part of the charged liquid 93 protrudes, and an electric field concentration 95 is generated there. Due to this electric field concentration action, only the portion of the liquid 93 protruding from the nozzle surface receives a strong electric field and is separated by electrostatic attraction to form droplets.

Next, as shown in FIG. 4C, the droplet 110 charged to the positive electrode always receives electrostatic attraction from the electric field generated between the common electrode 2 and the droplet arrival member 6 and flies while being accelerated. As a result, the droplet reaching member 6 is reached. In this embodiment, the potential difference between the common electrode 2 and the droplet reaching member 6 is 400 V, the distance between the two is 0.5 mm, and a driving voltage of 5 V and a driving frequency of 150 kHz is applied to the driving electrode 91. It was confirmed that the droplet 110 can be discharged stably and continuously. Furthermore, the discharge speed became 8 mm / s or more. The volume resistivity of the liquid 93 was 4 × 10 ⁴ Ω · cm.

  Further, the larger the potential difference between the common electrode 2 and the droplet arrival member 6 (that is, the stronger the electric field strength), the smaller the variation in the ejection direction of the droplets 110 for each of the plurality of nozzle holes 30 and the faster the ejection speed. As a result, it was found that the landing position accuracy of the droplets 110 discharged from the plurality of nozzle holes 30 is good. On the other hand, when the potential difference between the common electrode 2 and the droplet arrival member 6 is 0, ejection was not performed. This means that the droplet 110 is not ejected only by the pressure wave in the driving liquid chamber 9. Further, when a wind resistance test (a wind at a constant speed is sent in a direction perpendicular to the droplet flying direction to check the deviation of the landing position), the gap between the common electrode 2 and the droplet arrival member 6 is measured. It was found that the larger the potential difference, the smaller the deviation of the landing position from when there was no wind, and it was more resistant to wind and other disturbances.

  This is because the stronger the electric field strength in the flying region of the droplet 110 is, the stronger the electrostatic attractive force that the charged droplet receives during the flight is, so that it is more resistant to disturbances such as wind, and all the nozzle holes 30. In this case, the electric field directions are substantially the same, and droplets are formed using the electric field concentration action, so that the initial velocity direction depends only on the electric field and is not affected by the shape difference of the nozzle hole 30 itself. .

  Note that the second discharge control has better droplet landing accuracy than the first discharge control method. However, when the potential difference between the common electrode 2 and the droplet reaching member 6 was 200 V or less, the pattern defining 110 was not discharged. The discharge limit is (potential difference between the common electrode 2 and the droplet arrival member 6) / (distance between the common electrode 2 and the droplet arrival member 6) = (electric field strength), and charging of the droplet 110. Although different values are obtained depending on the characteristics, an electric field strength of about 106 (V / m) is required to separate and discharge the droplet 110 from the liquid 93 due to electric field concentration.

  In addition, since the drive voltage may be lower than that of the discharge control 1 (15 V in the discharge control 1 and 5 V in the discharge control 2), the residual vibration of the liquid in the liquid chamber itself is small and the vibration attenuation is fast. High-speed drive is possible. In the present embodiment, it was confirmed that the liquid protrusions were stably generated up to a maximum of 200 kHz driving, and ejection was possible due to electric field concentration.

  In this droplet ejection method, the liquid is projected from the desired nozzle hole 30 using the pressure wave of the piezoelectric body, and the liquid projected through the common electrode 2 is charged. Then, the droplet is ejected by the electric field concentration action in the protruding liquid. For this reason, the pressure wave generated by the piezoelectric body is used only for causing the liquid to protrude, and the force for separating the protruding droplet is obtained by the electrostatic attraction acting on the protruding portion. Determine the discharge direction. As a result, in the multi-nozzle, it is possible to discharge droplets with high landing position accuracy with little variation in the ejection direction of each nozzle hole 30 and less influence of displacement caused by variation in the shape of the nozzle hole 30.

  Further, since the pressure wave in the driving liquid chamber 9 is sufficient to cause the liquid to protrude from the nozzle hole 30, the vibration width of the partition wall 90 may be very small, the amplitude of the residual vibration is small, and high speed driving is possible. Become.

  In addition, since the drive voltage for selectively driving the piezoelectric body may be small, the deterioration of the piezoelectric body over time is small, and the cost of the drive circuit can be reduced. In particular, this droplet jetting method is suitable for discharging a liquid with high conductivity.

<Third droplet ejection method>
In this droplet ejection method, the process of projecting the liquid in the nozzle hole 30 is the same as the first droplet ejection method or the second droplet ejection method described above, but a plurality of droplets 110 are continuously formed. When discharging, the charged potential of the droplet reaching member 6 can be canceled by inverting the potential difference between the common electrode 2 applied from the power supply circuit 40 and the droplet reaching member 6 every several drops. .

  FIG. 5A shows a state in which the common electrode 2 has a higher potential than the droplet arrival member 6. In this state, the droplet 110 has a positive charge and reaches the droplet arrival member 6 or the medium on the droplet arrival member 6. On the other hand, FIG. 5B shows a state in which the potential of the common electrode 2 is lower than that of the droplet arrival member 6. In this state, the droplet 110 has a negative charge and reaches the droplet arrival member 6 or the medium on the droplet arrival member 6.

  FIG. 6 schematically shows a driving voltage cycle for driving the piezoelectric element portion and a voltage cycle of the common electrode with respect to the droplet reaching member. As shown in FIG. 6A, a rectangular waveform drive voltage in the range of +5 V to −5 V is applied between the partition walls 90 from the drive circuit 50 at a drive frequency of 100 kHz. Here, for the sake of convenience, the potential of the drive electrode 91 in the drive liquid chamber 9 in which the droplet 110 is to be ejected is set to 0, and the voltages given to the drive electrodes 91 in the adjacent drive liquid chamber 9 are shown. One droplet can be discharged in one cycle of −5V.

  As shown in FIG. 6B, a rectangular waveform power supply voltage in the range of +400 V to −400 V is applied from the power supply circuit 40 to the common electrode 2 at a driving frequency of 25 kHz, and four cycles of the driving voltage are common electrodes. They are synchronized so as to correspond to one of the two voltage cycles.

  In this driving, the first two droplets are charged to the positive electrode and discharged, and the subsequent two droplets are charged to the negative electrode and discharged. Thus, the charging direction is different for every two droplets.

  When such a control is performed, the charging direction of the droplet 110 changes every few droplets. Therefore, when the droplet 110 reaches the reaching member 6 in proximity, the charging potential of each droplet 110 is canceled. Can do. In the case where only the droplets 110 charged to the same polarity are continuously discharged, if the next droplet 110 arrives before the charge of the previously reached droplet 110 is released, it has the same charging polarity. However, the landing position may be deviated by the Coulomb force. However, even if a plurality of droplets 110 are discharged at a high density by changing the charge polarity every few drops and canceling each other, the landing accuracy is high. Will not get worse.

<Fourth droplet ejection method>
In this droplet ejecting method, the process of projecting the liquid in the nozzle hole 30 is the same as the first droplet ejecting method or the second droplet ejecting method described above, but the nozzle hole 30 and the droplet reaching member 6 are the same. The potential difference applied between the common electrode 2 and the droplet arrival member 6 from the power supply circuit 40 is reversed while the droplet 110 is flying between the two, and immediately before the droplet 110 reaches the droplet arrival member 6. Is characterized in that the droplet flying speed is reduced.

  FIG. 7A is a schematic diagram illustrating a state immediately after the droplet 110 is discharged, and FIG. 7B is a schematic diagram illustrating a state immediately before the droplet 110 reaches the droplet reaching member 6. The droplet 110 ejected from the nozzle hole 30 by the first droplet ejecting method or the second droplet ejecting method receives an electrostatic attractive force due to an electric field as shown in FIG. It is accelerated toward the droplet reaching member 6. Next, the potential between the common electrode 2 and the droplet arrival member 6 is reversed immediately before the droplet 110 reaches the droplet arrival member 6, and the potential of the droplet arrival member 6 is set to the positive electrode potential compared to the common electrode 2. Then, as shown in FIG. 7B, the droplet 110 receives acceleration opposite to the traveling direction due to electrostatic repulsion, and the ejection speed of the droplet 110 decreases.

  By performing such control, when the droplet 110 is separated from the nozzle hole 30, variation in the ejection direction for each nozzle hole 30 is reduced by the electrostatic attractive force received from the parallel electric field. In addition, while the droplet 110 is flying, it has the effect of suppressing variation in the ejection direction due to disturbance, and the collision speed when reaching the droplet reaching member 6 is too high, causing the droplet 110 to scatter around. Can be eliminated.

It is a longitudinal cross-sectional view of the droplet ejecting apparatus according to the present invention. It is the front view of the said droplet ejecting apparatus, and the YY part end elevation in FIG. It is a schematic diagram which shows the 1st droplet ejection method in the said droplet ejecting apparatus. It is a schematic diagram which shows the 2nd droplet ejection method in the said droplet ejecting apparatus. It is a schematic diagram which shows the 3rd droplet ejection method in the said droplet ejecting apparatus. It is a figure which shows the drive voltage waveform and common voltage waveform in the said 3rd droplet ejection method. It is a schematic diagram which shows the 4th droplet ejection method in the said droplet ejecting apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric element part 1A Liquid chamber 2 Common electrode 3 Nozzle plate 4 Flexible substrate 5 Manifold 6 Droplet arrival member 7 Common liquid chamber 8 Damping liquid chamber 8A Communication part 9 Drive liquid chamber 10 Act substrate 11 Cover substrate 20 Electrode hole 30 Nozzle hole 90 Partition 91 Drive electrode 110 Droplet

Claims (6)

A plurality of nozzle holes opposed to the droplet arrival member and a plurality of gaps opposed to each other on the front surface of each of the plurality of nozzle holes are formed by a piezoelectric body polarized in the height direction. A plurality of drive liquid chambers separated from each other by each of the plurality of partition walls on the front side of each of the plurality of gaps, drive electrodes formed on mutually facing surfaces of the plurality of partition walls, and the drive A driving circuit for applying a driving voltage to the electrodes; a common electrode facing the droplet reaching member across the plurality of nozzle holes; and a power supply circuit for forming an electric field between the droplet reaching member and the common electrode And comprising
In a state where an electric field is formed between the droplet reaching member and the common electrode by the power supply circuit, the partition wall is shear-deformed by application of a driving voltage to the driving electrode from the driving circuit to enter the driving liquid chamber. A liquid droplet ejecting apparatus, wherein the liquid in the driving liquid chamber is made to protrude from the nozzle hole due to the generated pressure fluctuation and then discharged as a liquid droplet to the liquid droplet arrival member.   2. The plurality of damping liquid chambers are provided on the back side of each of the plurality of gaps through a communication portion, and a plurality of attenuation liquid chambers are provided in each of the plurality of driving liquid chambers. Droplet ejector.   3. The droplet ejecting method in the droplet ejecting apparatus according to claim 1, wherein a voltage for forming an electric field between the power supply circuit and the droplet reaching member is applied to the common electrode. During this time, a drive voltage is applied to the drive electrode to shear the partition, and the pressure variation generated in the liquid chamber formed in the gap due to the shear deformation causes charging by the common electrode in the liquid chamber. The liquid droplet is ejected from the nozzle hole as a liquid droplet, and then the liquid droplet ejection speed is controlled by an electric field formed between the common electrode and the liquid droplet arrival member. Method.   3. The droplet ejecting method in the droplet ejecting apparatus according to claim 1, wherein a voltage for forming an electric field between the power supply circuit and the droplet reaching member is applied to the common electrode. During this time, a drive voltage is applied to the drive electrode to shear the partition, and the pressure variation generated in the liquid chamber formed in the gap due to the shear deformation causes charging by the common electrode in the liquid chamber. The liquid is allowed to protrude from the nozzle hole, and is further discharged as a liquid droplet from the nozzle hole by electric field concentration acting from an electric field formed between the common electrode and the liquid droplet reaching member. The droplet ejection method is characterized in that the discharge speed of the droplet is controlled by an electric field formed between the common electrode and the droplet reaching member.   The potential between the common electrode and the droplet reaching member is an integer of the discharge period of the droplet before the droplet reaches the droplet reaching member after the droplet is discharged from the nozzle hole. 5. The liquid droplet ejecting method according to claim 3, wherein the liquid droplets are reversed at a double cycle.   The electric potential between the common electrode and the droplet reaching member is reversed before the droplet reaches the droplet reaching member after the droplet is discharged from the nozzle hole. 5. The droplet jetting method according to 3 or 4.

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