JP4779578B2 - Droplet discharge apparatus and droplet discharge head driving method - Google Patents

Description

  The present invention relates to a droplet discharge device that discharges droplets from a nozzle and a method for driving a droplet discharge head.

  A droplet discharge head that discharges droplets from a nozzle, such as an ink jet recording head (hereinafter sometimes simply referred to as a recording head) for recording an image using minute ink droplets, applies pressure to the pressure generating chamber. As a result, droplets are ejected from the nozzle and landed on a recording medium such as recording paper.

  There are various pressure applying means for applying pressure to the pressure generating chamber, but here, the partition of the pressure generating chamber, which is disclosed in Patent Document 1, is constituted by a piezoelectric element that is a pressure applying means, and this piezoelectric element is deformed. Thus, a recording head when ink droplets are ejected from the nozzles will be briefly described with reference to FIG.

  As shown in FIG. 12, the shear mode type recording head 600 includes a bottom wall 601, a top wall 602, and a shear mode actuator wall 603 therebetween. The actuator wall 603 is composed of a lower wall 607 bonded to the bottom wall 601 and polarized in the direction of arrow 611 and an upper wall 605 bonded to the top wall 602 and polarized in the direction of arrow 609. A pair of actuator walls 603 form an ink flow path 613 as a pressure generation chamber therebetween, and a space 615 narrower than the ink flow path 613 is formed between the next pair of actuator walls 603. Yes. This space 615 is a dummy channel, and no ink is ejected from this channel. This is a so-called dummy channel type head.

  A nozzle plate 617 having nozzles 618 is fixed to one end of each ink flow path 613, and electrodes 619 and 621 are provided as metallization layers on both side surfaces of each actuator wall 603. Each electrode 619 and 621 is covered with an insulating layer (not shown) for insulating from ink. The electrode 621 facing the space 615 is connected to the ground 623, and the electrode 619 provided in the ink flow path 613 is connected to a silicon chip 625 that provides an actuator driving circuit.

  By the way, in order to record an inkjet image at a high speed, it is necessary to eject ink droplets in a fast cycle by driving the recording head 600 at high frequency. Then, it is necessary to eject ink droplets quickly and stably from the same nozzle.

  In view of this, it is conceivable to reduce the pressure fluctuation in the ink flow path 613, which is the pressure generation chamber, by applying a cancel pulse after the ejection pulse for ejecting ink as disclosed in Patent Document 1. ing.

  That is, a cancel pulse that generates a pressure wave whose phase is opposite to that of the pressure fluctuation in the ink flow path 613 is applied after a certain time from ink ejection. As shown in FIG. 13, a cancel pulse D whose pulse width is AL and whose phase is opposite to that of the ejection pulse is applied to the electrode 619 of the ink flow path 613 after AL time from the fall of the ejection pulse C. Here, AL is 1/2 of the acoustic resonance period of the pressure generating chamber.

Further, the voltage value is set according to the amplitude of the pressure fluctuation so as to just cancel the fluctuation (for example, 0.6 times the ejection pulse). By giving this cancel pulse, the actuator wall 603 is deformed in the opposite direction to that during ink ejection, and a pressure wave having a phase opposite to that of the pressure fluctuation is given to cancel the pressure fluctuation. As a result, the ink ejection speed does not change when the frequency of the voltage pulse is changed, and the print quality is improved. This enables ink droplets to be ejected quickly and stably from the same nozzle after ejecting ink droplets, and ink droplets can be ejected in a fast cycle by driving the recording head at high frequency. become.
JP 2003-276200 A

  As in the conventional driving method, the pressure wave in the pressure generating chamber is canceled by applying a cancel pulse. Accordingly, the meniscus vibration due to the pressure wave in the pressure generation chamber is greatly attenuated at this point, and thereafter, the next ink droplet ejection operation can be started.

  FIG. 5B shows the state of meniscus and droplet discharge at the nozzle by the conventional driving method. In FIG. 5B, 23 indicates a nozzle, 102 indicates an ink column, 101 indicates an ink droplet, 11 indicates a main droplet, 12 indicates a satellite droplet, and M indicates a meniscus. A detailed description of FIG. 5 will be given later.

  In FIG. 5B, according to the knowledge of the inventors, when the pressure wave is canceled by applying a cancel pulse as in the above-described prior art, the ink column 102 is separated from the meniscus M at the time when the cancel is applied. ((3) and (5) in FIG. 5B). In this state, if the ink column 102 extends in a direction away from the nozzle 23, the ink column 102 is only affected by the surface tension of the ink, so that the ink column 102 is very badly cut and pulled to the speed of the main droplet portion. As a result, the ink column extends for a long time. Thereafter, the length of the separated ink droplet 101 is also increased, and the speed difference between the head and the tail is increased. As a result, when the surface tension to be combined is overcome in the course of flight, the ink droplet 101 has a predetermined volume and ejection speed, and a smaller volume and ejection speed than the main droplet 11. It was found that the satellite drops 12 were easily separated and the satellite drops 12 increased. (See (9) and (10) in FIG. 5B).

  Such a phenomenon appears more prominently when ink having low surface tension or ink having high viscosity is ejected.

  Such satellite droplets 12 land with a deviation from the landing position of the main droplet 11, thereby causing a problem of lowering the image quality.

  Further, in the above-described ink jet recording head, if there is a deposit near the nozzle on the discharge side surface of the nozzle forming member, the ejected ink contacts the deposit and flies in a bent direction or is dragged by the deposit. In some cases, the ink stops flying and ink drips near the nozzles. There is a problem that the satellite droplet 12 floats in the vicinity of the recording head and adheres to the vicinity of the nozzle on the ejection side surface, thereby causing the above-described ejection failure.

  Further, when the amount of the satellite droplets 12 increases, the mist in the apparatus increases as a result, the problem of contamination in the apparatus, and in the worst case, the mist adheres to the electrical contact portion, causing a malfunction of the recording apparatus. Is derived.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a droplet discharge device and a droplet discharge head that can be driven at high frequency, can reduce satellite droplets, and can stably discharge droplets. An object of the present invention is to provide a driving method.

  The object of the present invention is achieved by the following configurations.

1.
A droplet applying head having a pressure applying unit that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying unit, and a nozzle that communicates with the pressure generating chamber, and a driving signal are generated. A droplet discharge device that expands or contracts the volume of the pressure generation chamber by applying the drive signal to the pressure applying unit, and discharges the droplet from the nozzle. An expansion pulse that expands the volume of the generation chamber, a first contraction pulse that contracts the volume of the pressure generation chamber following the expansion pulse, and a second contraction that contracts the volume of the pressure generation chamber after the first contraction pulse The expansion pulse has a pulse width of 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber), and the pulse width of the first contraction pulse is 0 .3A Droplet discharge device, characterized in that the ～1.5AL.

2.
A droplet applying head having a pressure applying unit that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying unit, and a nozzle that communicates with the pressure generating chamber, and a driving signal are generated. A droplet discharge device that expands or contracts the volume of the pressure generation chamber by applying the drive signal to the pressure applying unit, and discharges the droplet from the nozzle. An expansion pulse that expands the volume of the generation chamber, a first contraction pulse that contracts the volume of the pressure generation chamber following the expansion pulse, and a second contraction that contracts the volume of the pressure generation chamber after the first contraction pulse The expansion pulse has a pulse width of 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generation chamber), and the pulse width of the first contraction pulse is 2 .5A Droplet discharge device, characterized in that the ～3.5AL.

3.
The drive signal has a pulse width of the first contraction pulse of 0.3 AL to 1.0 AL, and an interval between the end of the expansion pulse and the start of the second contraction pulse is 0.7 AL to 1.. 2. The droplet discharge device according to 1, wherein the distance is 3 AL or more, and an interval between the end of the first contraction pulse and the start of the second contraction pulse is 0.3 AL or more.

4).
When the drive voltage of the first contraction pulse is Voff (V) and the drive voltage of the second contraction pulse is V2off (V), | Voff | = | V2off | The droplet discharge device according to any one of the above.

5.
The drive signal is a drive signal that has a plurality of sets of the expansion pulse, the first contraction pulse, and the second contraction pulse in the same drive cycle, and discharges a droplet a plurality of times in succession. Any one of 1-4 characterized by these. The droplet discharge apparatus of any one of 1-4.

6).
Driving signal to the pressure applying means of the droplet discharge head having pressure applying means that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber. Is applied to expand or contract the volume of the pressure generating chamber, and discharge a droplet from the nozzle. The driving signal includes an expansion pulse that expands the volume of the pressure generating chamber. A first contraction pulse that contracts the volume of the pressure generation chamber following the expansion pulse, and a second contraction pulse that contracts the volume of the pressure generation chamber after the first contraction pulse, and the pulse of the expansion pulse The width is 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber), and the pulse width of the first contraction pulse is 0.3 AL to 1.5 AL. Features and Droplet method of driving the ejection head that.

7).
Driving signal to the pressure applying means of the droplet discharge head having pressure applying means that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber. Is applied to expand or contract the volume of the pressure generating chamber, and discharge a droplet from the nozzle. The driving signal includes an expansion pulse that expands the volume of the pressure generating chamber. A first contraction pulse that contracts the volume of the pressure generation chamber following the expansion pulse, and a second contraction pulse that contracts the volume of the pressure generation chamber after the first contraction pulse, and the pulse of the expansion pulse The width is 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber), and the pulse width of the first contraction pulse is 2.5 AL to 3.5 AL. Features and Droplet method of driving the ejection head that.

  According to invention of Claim 1, there exist the following effects. By setting the pulse width of the expansion pulse to 0.7 AL to 1.3 AL, which is in the vicinity of 1 AL, and subsequently applying the first contraction pulse, the negative pressure due to expansion of the pressure generating chamber at the start of application of the expansion pulse When the wave reverses at 1AL and becomes a positive pressure, a positive pressure wave due to contraction is added in a combined form, increasing the droplet discharge pressure (discharge speed) and obtaining the most efficient discharge force It is done. As a result, the driving voltage can be lowered, so that the power consumption of the pressure applying means can be reduced.

  When 1AL elapses from this state, the pressure wave reverses and the pressure generating chamber becomes negative pressure, and when 1AL elapses further, the pressure wave reverses and the pressure generating chamber becomes positive pressure. Thereafter, the pressure wave is attenuated while the pressure is reversed every time 1 AL is passed. When 1 AL has passed from the start of application of the first contraction pulse and the pressure wave is reversed and the pressure generating chamber becomes negative pressure, the force that pulls out the discharged meniscus acts to narrow the extruded liquid column. The action to work. Before and after this, the pulse width of the first contraction pulse is set to 0.3 AL to 1.5 AL, and when the application of the contraction pulse is completed, the pressure generating chamber expands, and the force to pull back the meniscus further acts to further increase the liquid column. The liquid column is separated from the meniscus at an early stage, and satellite droplets are hardly generated. That is, it is possible to reduce the satellite by suppressing the long tail of the liquid column.

  Furthermore, by having the second contraction pulse after the first contraction pulse, the pressure wave can be canceled by the second contraction pulse. As a result, after the liquid droplets are discharged, the liquid droplets can be discharged quickly and stably from the same nozzle, and the liquid droplets are discharged at a fast cycle by driving the liquid droplet discharge head at high frequency. Is possible.

  According to invention of Claim 2, there exist the following effects. By setting the pulse width of the expansion pulse to 0.7 AL to 1.3 AL, which is in the vicinity of 1 AL, and subsequently applying the first contraction pulse, the negative pressure due to expansion of the pressure generating chamber at the start of application of the expansion pulse When the wave reverses at 1AL and becomes a positive pressure, a positive pressure wave due to contraction is added in a combined form, increasing the droplet discharge pressure (discharge speed) and obtaining the most efficient discharge force It is done. As a result, the driving voltage can be lowered, so that the power consumption of the pressure applying means can be reduced.

  When 1AL elapses from this state, the pressure wave reverses and the pressure generating chamber becomes negative pressure, and when 1AL elapses further, the pressure wave reverses and the pressure generating chamber becomes positive pressure. Thereafter, the pressure wave is attenuated while the pressure wave is inverted every time 1 AL elapses. When 3AL elapses from the start of application of the first contraction pulse and the pressure wave is reversed and the pressure generating chamber becomes negative pressure, the force of pulling out the discharged meniscus acts to narrow the extruded liquid column. The action to work. Before and after this, the pulse width of the first contraction pulse is set to 2.5 AL to 3.5 AL, and when the application of the contraction pulse is finished, the pressure generating chamber expands, and the force to pull back the meniscus further acts to further increase the liquid column. The liquid column is separated from the meniscus at an early stage, and satellite droplets are hardly generated. That is, it is possible to reduce the satellite by suppressing the long tail of the liquid column.

  Furthermore, by having the second contraction pulse after the first contraction pulse, the pressure wave can be canceled by the second contraction pulse. As a result, after the liquid droplets are discharged, the liquid droplets can be discharged quickly and stably from the same nozzle, and the liquid droplets are discharged at a fast cycle by driving the liquid droplet discharge head at high frequency. Is possible.

  According to invention of Claim 3, there exist the following effects. By setting the pulse width of the first contraction pulse to 0.3 AL to 1.0 AL, the interval between the end of the expansion pulse and the start of the second contraction pulse is 0.7 AL to 1.. 3AL can be set. As a result, a positive pressure wave from the start of the second contraction pulse is added when the positive pressure wave generated at the end of the expansion pulse and the start of the first contraction pulse is reversed to a negative pressure after 1 AL. Thus, the effect of canceling the pressure wave can be enhanced, and driving at a higher frequency can be realized.

  Furthermore, by setting the interval between the end of the first contraction pulse and the start of the second contraction pulse to be 0.3 AL or more, the satellite reduction effect and the cancellation effect by the second contraction pulse can be enhanced.

  According to invention of Claim 4, there exist the following effects. When the driving voltage of the first contraction pulse is Voff (V) and the driving voltage of the second contraction pulse is V2off (V), | Voff | = | V2off | Can be generated. Therefore, the power supply cost can be reduced.

  According to the fifth aspect of the present invention, the drive signal is a drive signal for ejecting droplets continuously a plurality of times within the same drive cycle, and therefore, the drive signal is shot against one dot on the medium on which the droplets land. The number of droplets can be controlled in multiple stages.

  According to the sixth aspect of the invention, similarly to the first aspect of the invention, high-frequency driving is possible, satellite droplets are reduced, and droplets can be stably ejected.

  According to the invention described in claim 7, as in the invention described in claim 2, high-frequency driving is possible, satellite droplets are reduced, and droplets can be ejected stably.

Although the example of embodiment regarding this invention is shown below, the aspect of this invention is not limited to these.
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an ink jet recording apparatus to which a liquid droplet ejection apparatus according to the present invention is applied. In the inkjet recording apparatus 1, the recording medium P is sandwiched between the conveyance roller pair 32 of the conveyance mechanism 3 and further conveyed in the Y direction in the figure by a conveyance roller 31 that is rotationally driven by a conveyance motor 33.

  The recording head 2 is provided between the conveying roller 31 and the conveying roller pair 32 so as to face the recording surface PS of the recording medium P. The recording head 2 is shown substantially orthogonal to the conveyance direction (sub-scanning direction) of the recording medium P by a driving means (not shown) along the guide rail 4 spanning the width direction of the recording medium P. The flexure cable 6 is mounted on a carriage 5 provided so as to be capable of reciprocating along the XX ′ direction (main scanning direction) so that the nozzle surface side faces the recording surface PS of the recording medium P. Is electrically connected to drive signal generating means 100 (see FIG. 3) provided with a circuit for generating a drive signal.

  The recording head 2 records a desired inkjet image by moving the recording surface PS of the recording medium P in the direction XX ′ in the drawing as the carriage 5 moves, and ejecting ink droplets in this moving process. It has become.

  In the figure, reference numeral 7 denotes an ink receiver, and the recording head 2 is provided at a standby position such as a home position during non-recording. When the recording head 2 is in this standby position, a small amount of ink droplets are discarded toward the ink receiver 7. When the recording head 2 has stopped operating for a long time at this standby position, although not shown, the nozzle surface of the recording head 2 is covered by a cap. Reference numeral 8 denotes an ink receiver provided at a position opposite to the ink receiver 7 with the recording medium P in between. When recording in both reciprocating directions, the same operation is performed when switching from forward to backward movement. Accept discarded ink drops.

  A driving method according to the present invention is a droplet including a nozzle opening for discharging a droplet, a pressure generating chamber communicating with the nozzle opening, and a pressure applying means for changing the pressure in the pressure generating chamber. Any liquid discharge head can be used as long as it is a discharge head, and any liquid can be filled in the pressure generating chamber. In the following description, a shear mode (shear mode) is a droplet discharge head that includes pressure applying means that changes pressure by expanding or contracting the volume in the pressure generating chamber and uses ink as the liquid that fills the pressure generating chamber. ) Type ink jet recording head 2 will be described.

  In the shear mode type recording head, the partition wall of the pressure generating chamber is constituted by a piezoelectric element as pressure applying means, and ink droplets are ejected from the nozzle by deforming the piezoelectric element.

  2A and 2B are diagrams showing a schematic configuration of a shear mode type ink jet recording head which is an embodiment of a droplet discharge head, in which FIG. 2A is a perspective view showing a partial cross-section, and FIG. 2B includes an ink supply unit. FIG.

  In the following description, since the configuration related to the pressure generation chamber is common to all the pressure generation chambers, the alphabetic suffixes indicating the configuration related to the individual pressure generation chambers may be omitted and may be collectively described.

  3A to 3C are diagrams showing the operation.

  2 and 3, 100 is a drive signal generating means, 2 is a recording head, 21 is an ink tube, 22 is a nozzle forming member, 23 is a nozzle, 24 is a cover plate, 25 is an ink supply port, 26 is a substrate, and 27 is a substrate. The partition, L is the length of the pressure generating chamber, D is the depth of the pressure generating chamber, and W is the width of the pressure generating chamber. A pressure generation chamber 28 that is an ink channel is formed by the partition wall 27, the cover plate 24, and the substrate 26.

  As shown in FIG. 3, the recording head 2 is separated between a cover plate 24 and a substrate 26 by a plurality of partition walls 27A, 27B, 27C, and 27D made of a piezoelectric material such as PZT that is an electromechanical conversion means. This is a shear mode type recording head in which a large number of pressure generating chambers 28 are arranged in parallel. In FIG. 3, three (28A, 28B, 28C) which are a part of many pressure generation chambers 28 are shown. One end (hereinafter sometimes referred to as a nozzle end) of the pressure generating chamber 28 is connected to a nozzle 23 formed on the nozzle forming member 22, and the other end (hereinafter also referred to as a manifold end) is an ink supply port. 25, the ink tube 21 is connected to an ink tank (not shown). Electrodes 29A, 29B, and 29C are formed in close contact with the surface of the partition wall 27 in each pressure generating chamber 28 from above the partition walls 27 to the bottom surface of the substrate 26. The electrodes 29A, 29B, and 29C generate drive signals. Connected to means 100.

  Next, a manufacturing method and constituent materials of the recording head 2 will be described.

  Two piezoelectric materials 27a and 27b having different polarization directions are bonded to each other on the substrate 26 via an adhesive, and a plurality of grooves serving as the pressure generating chambers 28 are formed from the upper piezoelectric material 27a by a diamond blade or the like. All are cut in parallel with the same shape. As a result, the adjacent pressure generation chambers 28 are partitioned by the side walls 27 polarized in the direction of the arrow. Further, the pressure generation chamber 28 is gradually increased from the deep groove portion 28a on the outlet side (left side in FIG. 2) of the pressure generation chamber 28 to the inlet side (right side in FIG. 2) of the pressure generation chamber 28 from the deep groove portion 28a. And a shallow groove portion 28b that becomes shallow.

  Here, each partition wall 27 is constituted by two piezoelectric materials 27a and 27b having different polarization directions as indicated by arrows in FIG. 3, but the piezoelectric material may be only a portion 27a, for example. 27 may be present in at least a part of 27.

  The piezoelectric material used for the piezoelectric materials 27a and 27b is not particularly limited as long as it deforms when a voltage is applied, and a known material may be used, and a substrate made of an organic material may be used. A substrate made of a piezoelectric non-metallic material is preferable, and a substrate made of a piezoelectric non-metallic material such as a ceramic substrate formed through a process such as molding or firing, or a substrate formed through a coating or lamination process, etc. There is. Examples of the organic material include organic polymers and hybrid materials of organic polymers and inorganic materials.

Ceramic substrates include PZT (PbZrO ₃ —PbTiO ₃ ) and third component added PZT. The third component includes Pb (Mg _1/3 Nb _2/3 ) O ₃ , Pb (Mn _1/3 Sb _{2 / 3} ) O ₃ , Pb (Co _1/3 Nb _2/3 ) O _{3, and the} like, and further, BaTiO ₃ , ZnO, LiNbO ₃ , LiTaO _{3, and the} like can be used.

  Moreover, as a board | substrate formed through the process of application | coating or lamination, it can form by the sol-gel method, laminated substrate coating, etc., for example.

  On the upper surface of the piezoelectric material 27a, the cover plate 24 is bonded via an adhesive so as to cover the deep groove 28a over the entire pressure generating chamber 28, and on the shallow groove 28b of each pressure generating chamber 28, An ink inflow port 77 into the pressure generating chamber 28 is formed.

  After the cover plate 24 is bonded, the single nozzle forming member 22 provided with the nozzle 23 is bonded through an adhesive.

  The materials of the cover plate 24 and the substrate 26 are not particularly limited, and may be a substrate made of an organic material. However, from the viewpoint of high thermal conductivity and prevention of crosstalk between channels due to electric field distortion, non-piezoelectric non-reflection is possible. A substrate made of a metal material is preferable, and the substrate made of this non-piezoelectric nonmetal material is selected from at least one of alumina, aluminum nitride, zirconia, silicon, silicon nitride, silicon carbide, quartz, and unpolarized PZT. Is preferred. Examples of the organic material include organic polymers and hybrid materials of organic polymers and inorganic materials.

  Further, as the material of the nozzle forming member 23, a synthetic resin such as polyimide resin, polyethylene terephthalate resin, liquid crystal polymer, aromatic polyamide resin, polyethylene naphthalate resin, polysulfone resin, or a metal material such as stainless steel can be used. .

  In each pressure generating chamber 28, a metal electrode 29 is formed from both side surfaces to the bottom surface, and the metal electrode 29 extends to the rear side surface of the piezoelectric material 27a through the shallow groove portion 28b. The flexible cable 6 is bonded to each metal electrode 29 via an anisotropic conductive film 78 on the rear side surface. By applying a drive signal to each metal electrode 29 from the drive signal generating means 100, the side wall 27 is applied. The ink in the pressure generating chamber 28 is ejected from the nozzles 23 formed on the nozzle plate 22 by the deformation pressure.

  As the metal used for the metal electrode 29, platinum, gold, silver, copper, aluminum, palladium, nickel, tantalum, and titanium can be used. In particular, from the viewpoint of electrical characteristics and workability, gold, aluminum, copper Nickel is preferable and is formed by plating, vapor deposition, or sputtering.

  Since the shear mode type recording head 2 can form the main part of the head only by forming the pressure generating chamber 28 in the piezoelectric materials 27a and 27b and forming the metal electrode 29 on the side wall 27 as described above. Since the manufacturing is simple and a large number of pressure generating chambers 28 can be arranged at a high density, this is a preferable mode for recording high-definition images.

  Next, the discharge operation will be described.

  When a drive signal is applied from the drive signal generating means 100 to the electrodes 29A, 29B, 29C formed in close contact with the surfaces of the partition walls 27, ink droplets are ejected from the nozzles 23 by the operation exemplified below. In FIG. 3, the nozzle is omitted.

  In the recording head 2, as described above, positive and negative pressure is applied to the ink in the pressure generating chamber 28 by deformation of the partition wall 27, and the partition wall 27 constitutes a pressure applying unit.

(Driving method of embodiment)
FIG. 4A shows a drive signal for realizing the drive method according to the embodiment of the present invention and the pressure applied to the ink in the pressure generating chamber 28 by the drive signal. FIG. 4B shows a state of meniscus and droplet discharge in the nozzle by the driving method according to the embodiment of the present invention. The numbers in parentheses in FIGS. 4A to 4B and the following description correspond to each other in terms of time.

  In FIG. 4A, the horizontal axis represents the AL time, and the vertical axis represents the relative values of the drive voltage and pressure. L1 and the dotted line represent the drive signal, and L2 and the solid line represent the pressure.

  In FIG. 4B, 102 indicates an ink column, 101 indicates an ink droplet, and M indicates a meniscus.

  In this specification, the “ink column” means that the front end protrudes from the opening of the nozzle 23, but the rear end is connected to the meniscus M in the nozzle 23 and is not yet separated from the meniscus M. The ink refers to ink, and the “ink droplet” refers to ink in a state where the rear end is completely separated from the meniscus in the nozzle 23.

  (1) In the recording head 2, when the electrodes 29A and 29C are connected to the ground and an expansion pulse (positive voltage) made of a rectangular wave is applied to the electrode 29B in the state shown in FIG. Due to the first rise (P1) from the beginning of the pulse, an electric field in a direction perpendicular to the polarization direction of the piezoelectric materials 27a and 27b constituting the partition walls 27B and 27C is generated, and both 27a and 27b cause slippage deformation on the bonding surfaces of the partition walls, As shown in FIG. 3B, the partition wall 27B and the partition wall 27C are deformed outward from each other, and the volume of the pressure generating chamber 28B is expanded. As a result, a negative pressure is generated in the ink in the pressure generating chamber 28B, and the ink flows (Draw).

  In addition, AL (Acoustic Length) is 1/2 of the acoustic resonance period of the pressure generation chamber as described above. This AL measured the speed of ink droplets ejected by applying a rectangular wave pulse to the partition wall 27, which is an electrical / mechanical conversion means, and changed the rectangular wave pulse width while keeping the rectangular wave voltage value constant. Sometimes it is determined as the pulse width that maximizes the flying speed of the ink droplets. The AL of the recording head 2 of the present embodiment is 2.4 (μs), but this value is determined depending on the head structure, ink density, and the like.

  A pulse is a rectangular wave having a constant voltage peak value. When 0V is 0% and a peak voltage is 100%, the pulse width is the start of rising or falling of the voltage from 0V. Is defined as the time between 10% of 10% and 10% of the start of falling from the peak voltage or 10% of rising. Furthermore, the rectangular wave here refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½ of AL, preferably within ¼. .

  (2) Since the pressure wave in the pressure generation chamber 28B repeats reversal every 1 AL time, if the potential is returned to 0 after 1 AL time has elapsed since the first P1 application (the time when the application of P2 has ended is an expansion pulse) The partition walls 27B and 27C return from the expanded position to the neutral position shown in FIG. 3A, and high pressure is applied to the ink in the pressure generating chamber 28B.

  Subsequently, a first contraction pulse (negative voltage) composed of a rectangular wave is applied. First, as shown in FIG. 3C, the partition walls 27B and 27C are deformed in opposite directions due to the fall (P3) from the beginning of the pulse, and the volume of the pressure generating chamber 28B is contracted. By this contraction, a higher pressure is applied to the ink in the pressure generation chamber 28B (Reinforce), and the ink column 102 is projected from the opening of the nozzle 23.

  (2.5) When 0.5 AL time has elapsed, the pressure wave in the pressure generating chamber 28B is reversed to negative pressure. At this time, when the potential is returned to 0 (the end of the application of P4 is the end of the first contraction pulse) and the partition walls 27B and 27C are returned from the contracted position to the neutral position, the volume of the pressure generating chamber 28B is increased. By expanding, negative pressure is applied to the ink in the pressure generating chamber 28B. As a result, the meniscus M is pulled in, the rear end of the protruding ink column 102 is pulled back, the diameter of the ink column is reduced, and it is difficult to extend. Further, the pressure wave generated by the negative pressure due to the expansion and the pressure wave of the inverted negative pressure have the same phase and overlap and strengthen each other, so that a pressure wave having a large amplitude is generated in the pressure generating chamber 28B.

  (3) When 0.5 AL time elapses, the negative pressure of the ink becomes maximum, so that the neck of the protruding ink column 102 is constricted as shown by an arrow in FIG. 4B. At this time, a second contraction pulse (negative voltage) composed of a rectangular wave is applied. First, due to the fall (P5) from the beginning of the pulse, as shown in FIG. 3C, the partition walls 27B and 27C are deformed in opposite directions, and the volume of the pressure generating chamber 28B is contracted. The pressure wave due to the positive pressure of the contraction and the pressure wave of the negative pressure cancel each other out, and the pressure wave is weakened.

  (5) When 1 AL time further passes, the positive pressure becomes maximum. At this time, when the potential is returned to 0 (the end of the application of P6 is the end of the second contraction pulse) and the partition walls 27B and 27C are returned from the contracted position to the neutral position, the volume of the pressure generating chamber 28B is increased. By expanding, negative pressure is applied to the ink in the pressure generating chamber 28B. The pressure wave caused by the negative pressure of the expansion and the pressure wave of the positive pressure cancel each other and cancel each other, and the pressure is attenuated early and effectively disappears.

  (6.5); After about 3.5 AL hours have passed since the high pressure was applied to the ink in (2) above, the ink column 102 protruding from the opening of the nozzle 23 is separated from the meniscus M, and the nozzle 101 is formed as a droplet 101. 23 is discharged.

  Such a driving method is a driving method based on a so-called DRRC (Draw-Release-Reinforce-Cansel) method, and the pulse width of the expansion pulse greatly affects the ejection force of the ink droplet, and when this pulse width matches 1AL. In addition, the ink droplet ejection force (ejection speed) is maximized. The first contraction pulse is applied when the expansion pulse falls (P2), that is, after the passage of 1AL. For this reason, by setting the pulse width of the expansion pulse to 1AL as described above, the negative pressure wave generated at the rise (P1) of the expansion pulse propagates through the pressure generation chamber and reverses to the positive pressure. The positive pressure generated by the contraction of the pressure generating chamber due to the fall of the expansion pulse (P2) and the fall of the first contraction pulse (P3) is added, and these together give the most efficient discharge force. As a result, the driving voltage can be lowered, so that the power consumption of the pressure applying means can be reduced.

  Further, since the pulse width of the first contraction pulse is set to 0.5 AL, when the application of the first contraction pulse is finished and the potential is returned to 0, the pressure generating chamber expands, and the negative pressure generated by this expansion occurs. The pressure wave of pressure overlaps and strengthens the pressure wave of negative pressure generated by reversing the pressure wave generated at the beginning of the expansion pulse and the first contraction pulse, and a strong negative pressure is generated in the pressure generation chamber 28B. A wave is generated. The force wave pulling back the meniscus is exerted by this strong negative pressure wave to narrow the ink column, and at an early stage, the ink column 102 is separated from the meniscus M in a short state and flies as ink droplets 101. Therefore, the main droplet and the satellite droplet are less likely to be split, and the amount of satellite can be reduced.

  Although the pulse width of the first contraction pulse is 0.5 AL in the above embodiment, it may be set in the range of 0.3 AL to 1.5 AL or 2.5 AL to 3.5 AL time. By setting within this range, the pressure wave of negative pressure generated at the end of the contraction pulse can be strengthened with the pressure wave generated at the start of the expansion pulse and the first contraction pulse. Can be reduced. In particular, by setting the pulse width of the first contraction pulse to 0.3 AL to 1.5 AL, it is possible to generate a large negative pressure at the end of application of the first contraction pulse (P4) at an early stage. At an early stage, the ink column 102 can be separated from the meniscus M in a short state and fly as ink droplets 101, thereby reducing the amount of satellites.

  If the pulse width of the first contraction pulse is shorter than 0.3 AL, it is much shorter than AL, so that the droplet discharge force is reduced and the driving efficiency is lowered (increasing driving voltage). Further, if the pulse width of the first contraction pulse is longer than 3.5 AL, the effect of pulling back the meniscus cannot be used early, and the effect of reducing the amount of satellite is reduced.

  The pulse width of the expansion pulse is 1AL in the above embodiment, but may be set within a range of 0.7AL to 1.3AL. Outside this range, the ejection efficiency due to pressure waves decreases and the drive voltage increases significantly.

  Further, since the interval between the end of the expansion pulse and the start of the second contraction pulse is set to 1AL, the positive pressure wave generated at the end of the expansion pulse and the start of the first contraction pulse becomes a negative pressure after 1AL. By adding a positive pressure wave due to the start of the second contraction pulse at the time of reversal, the effect of canceling the pressure wave is enhanced, and higher frequency driving can be realized. The interval between the end of the expansion pulse and the start of the second contraction pulse may be set to 0.7AL to 1.3AL, which is in the vicinity of 1AL, but 1AL is most preferable.

  By setting the pulse width of the first contraction pulse to 0.3 AL to 1.0 AL, the interval between the end of the expansion pulse and the start of the second contraction pulse is 0.7 AL to 1.. 3AL can be set. Furthermore, by setting the interval between the end of the first contraction pulse and the start of the second contraction pulse to be 0.3 AL or more, the satellite reduction effect and the cancellation effect by the second contraction pulse can be enhanced. The interval between the end of the first contraction pulse and the start of the second contraction pulse is preferably 1.0 AL or less in order to further enhance the canceling effect of the second contraction pulse.

  The pulse width of the second contraction pulse is preferably set to 0.7 AL to 1.3 AL in the vicinity of 1 AL, and more preferably 1 AL as in the above embodiment. This is because the canceling effect is enhanced by the negative pressure wave generated at the end of the second contraction pulse.

  In the drive signal of FIG. 4A, when the drive voltage of the first contraction pulse is Voff (V) and the drive voltage of the second contraction pulse is V2off (V), | Voff | = | V2off | Therefore, both pulses can be generated by one power source. Therefore, the power supply cost can be reduced.

  Further, the ratio of the drive voltage Von (V) of the expansion pulse and the drive voltage Voff (V) of the first contraction pulse is set to | Von | / | Voff | = 1 / 0.7. Thus, the relationship | Von |> | Voff | has an effect of promoting the supply of ink into the pressure generating chamber, and is particularly preferable when high-frequency driving is performed with high-viscosity ink.

  Note that the reference voltage of the voltage Von and the voltage Voff is not always zero. The voltage Von and the voltage Voff are respectively differential voltages.

  As described above, ink droplets fly to form an image, but in order to form a gradation image and a high-density image in detail, the pressure in the same pixel cycle (within the same drive cycle) according to the print data. A series of drive pulses (expansion pulse, first contraction pulse, and second contraction pulse) are applied to the applying unit a plurality of times to cause a plurality of ink droplets to fly, and the plurality of ink droplets land on the recording paper. One pixel (dot) can also be formed at the time of landing by combining before landing, that is, during flight, or after landing (combining as a dot). As a result, it is possible to form a high-quality image by enlarging the dots filling the pixels or by forming a plurality of ink droplets on one pixel to form gradation and high density pixels.

  When the plurality of ink droplets are combined to form one pixel, the plurality of individual ink droplets are referred to as sub-drop SD, and the combination is referred to as super drop.

  In order to form a super drop by fusing a plurality of sub-drops SD or combining them at a landing position (which may be combined as dots), basically the second sub-drop SD 1 is faster than the first sub-drop SD 1 to fly. It is difficult to unite if the sub-drop SD2 is not flying faster. Therefore, it is necessary to sequentially increase the speed to the third sub-drop SD3... SDn.

  For this purpose, it is necessary to appropriately cancel the pressure wave for each SD discharge. If the cancel amount is insufficient, the speed varies among SDs, and a plurality of SD (ink droplets) forming one pixel lands away from each other, and the pixels are disturbed or stable ejection cannot be performed due to fluctuations in the meniscus position. Occurs. By using the driving method of the present invention, the pressure wave can be canceled almost completely, so that the super drop can be formed stably without causing such a problem.

(Prior art driving method)
Next, for comparison, a case in which a conventional driving method is applied will be described.

  FIG. 5A shows the driving signal for realizing the driving method according to the prior art and the pressure applied to the ink in the pressure generating chamber 28 by the driving signal.

  FIG. 5B shows a state of meniscus and droplet discharge in the nozzle by the conventional driving method. The numbers in parentheses in FIGS. 5A to 5B and the following description correspond to each other in terms of time.

  In FIG. 5A, the horizontal axis represents the AL time, and the vertical axis represents the relative values of the drive voltage and pressure. L1 and the dotted line represent the drive signal, and L2 and the solid line represent the pressure.

  In FIG. 5B, 11 indicates a main droplet, 12 indicates a satellite droplet, and SL indicates a satellite length.

  (1) In such a recording head 2, when the electrodes 29A and 29C are connected to the ground and an ejection pulse (positive voltage) is applied to the electrode 29B in the state shown in FIG. Due to (P1), an electric field in a direction perpendicular to the polarization direction of the piezoelectric materials 27a and 27b constituting the partition walls 27B and 27C is generated, and both 27a and 27b are deformed in the joint surface of the partition walls, as shown in FIG. As described above, the partition wall 27B and the partition wall 27C are deformed toward each other, and the volume of the pressure generating chamber 28B is expanded. As a result, a negative pressure is generated in the ink in the pressure generating chamber 28B, and the ink flows.

  (2) Since the pressure wave in the pressure generation chamber 28B repeats reversal every 1 AL time elapses, when the potential is returned to 0 after 1 AL time elapses from the first application of P1 (P2), the partition walls 27B and 27C expand. From the position, the ink returns to the neutral position shown in FIG. 3A, and high pressure is applied to the ink in the pressure generating chamber 28B. By this contraction, a higher pressure is applied to the ink, and the ink column 102 is projected from the opening of the nozzle 23.

  (3) When 1 AL time elapses, the negative pressure becomes maximum, and therefore, the base of the protruding ink column 102 is constricted as shown by an arrow in FIG. Here, a cancel pulse (negative voltage. The absolute value of the voltage is 1/2 of the positive voltage of the ejection pulse) is applied. First, as shown in FIG. 3C, the partition walls 27B and 27C are deformed in opposite directions due to the fall of the cancel pulse (P3), and the volume of the pressure generating chamber 28B contracts. Since the pressure wave due to the positive pressure of the contraction and the pressure wave of the negative pressure are 180 degrees out of phase, they cancel each other out, and the pressure wave is attenuated early. At this time, the ink column 102 is not separated from the meniscus M.

  (5) When 1 AL time further elapses, the pressure wave reverses and becomes positive pressure. Therefore, when the potential is returned to 0 (P4) and the partition walls 27B and 27C are returned from the contracted position to the neutral position, the volume of the pressure generating chamber 28B is increased. As the ink expands, the meniscus M is drawn, and the rear end of the protruding ink column 102 is pulled back. Since the pressure wave due to the negative pressure of the expansion and the pressure wave of the positive pressure are almost equal in amplitude and out of phase by 180 °, they cancel each other out, and the pressure wave is attenuated early and effectively disappears. become. At this time, the ink column 102 is not separated from the meniscus M.

  (6), (7) Thereafter, the ink column 102 continues to grow in a state where there is almost no meniscus vibration due to the pressure wave.

  (8) Due to the surface tension of the ink, the ink pillars 102 naturally fly as ink droplets 101 that are separated from the meniscus M and have a long tail.

  (9) (10) The ink droplet 101 is separated into the main droplet 11 and the satellite droplet 12.

  In the prior art driving method, the action of pulling back the meniscus at an early stage does not work, so that the subsequent separation of the ink column 102 from the meniscus M is performed in a state where there is almost no meniscus vibration due to the pressure wave, which is extremely slow. . As a result, the ink pillars 102 extend, and the amount of satellites increases. SL in FIG. 5 is the satellite length, and the satellite amount increases as this length increases.

  Next, time-division driving, which is an example of the driving method according to the embodiment of the present invention, will be described.

  When the recording head 2 having a plurality of pressure generation chambers 28 separated by the partition walls 27 at least partially made of a piezoelectric material as described above is driven, when the partition walls of one pressure generation chamber 28 perform a discharge operation. Since the adjacent pressure generation chambers 28 are affected, the pressure generation chambers 28 that are separated from each other with one or more pressure generation chambers 28 are usually combined into one set. In this manner, the drive control is performed so that the ink is divided into two or more groups and the ink ejection operation is sequentially performed for each group in a time division manner. For example, a so-called three-cycle discharge method is performed in which every two total pressure generation chambers 28 are selected and discharged in three phases.

  Such a 3-cycle discharge operation will be further described with reference to FIG. In the example shown in FIG. 6, the recording head has a pressure generating chamber composed of nine pressure generating chambers A1, B1, C1, A2, B2, C2, A3, B3, and C3. An example in which five ink droplets are ejected will be described. Further, FIG. 7 shows a timing chart of drive signals applied to the electrodes of the pressure generation chambers 28 of each set of A, B, and C at this time. Here, an example in which five sub-drops can be discharged within the same pixel period (within the same drive period) based on the drive signal of FIG. 4 is shown. In order to discharge the sub-drop SD1, an expansion pulse with a pulse width of AL, followed by a first contraction pulse with a pulse width of 0.5AL, followed by a rest period of zero voltage with a length of 0.5AL, followed by a pulse width Is applied with a second contraction pulse of 1AL, followed by a drive pulse consisting of a zero-voltage pause of length AL. Similarly, in order to discharge the sub-drops SD2 to SD5, drive pulses having the same configuration are respectively applied. The period of the drive pulse is 4AL as shown in the figure. Then, by providing a period of zero voltage having a length of 3AL after the driving pulse of SD5, a period for forming a super drop by five drops of SD1 to SD5 is set to 23AL.

  When a super drop is formed by a drive pulse shown in FIG. 7 and is caused to fly, the sub-drops SD1 to SD5 can be stably combined during the flight or on the recording medium.

  When ink is ejected, first, a series of driving pulse voltages for ejecting the SD1 to SD5 are applied to the electrodes of the pressure generating chambers 28 of the A group (A1, A2, A3), and the electrodes of the pressure generating chambers on both sides thereof are grounded. The ink droplets of SD1 to SD5 are ejected from the A set of nozzles.

  Subsequently, the operation is performed in the same manner as described above for each pressure generating chamber 28 of the B group (B1, B2, B3) and further to each pressure generating chamber 28 of the C group (C1, C2, C3).

  The above is a case of a solid image (full drive), but actually, the number of ink droplets to be ejected among SD1 to SD5 is changed according to the print data of each pixel.

  In such a shear mode type ink jet recording head, the deformation of the partition wall 27 occurs due to a voltage difference applied to the electrodes provided on both sides of the wall. Therefore, instead of applying a negative voltage to the electrode of the pressure generating chamber for discharging ink, FIG. As shown, the same operation can be achieved by grounding the electrode of the pressure generating chamber for discharging ink and applying a positive voltage to the electrodes of the pressure generating chambers on both sides thereof. According to this latter method, since it can be driven only by a positive voltage, it is a preferable aspect in terms of power supply cost.

  Note that the driving method of the present invention exhibits a remarkable effect when the viscosity of the ink at the ink temperature at the time of ejection is 5 cp or more and 15 cp or less. Such ink has a high viscosity and a high fluid resistance, so that the ink column is difficult to separate from the meniscus. Therefore, the ink column is easily elongated for a long time, and satellites are easily generated.

  Further, if the viscosity is too high, the ink cannot be smoothly ejected from the nozzles, and the drive voltage increases. Therefore, the ink viscosity is preferably 15 cp or less.

  The viscosity can be measured using a vibration viscometer Model VM-1A-L (Yamaichi Electronics Co., Ltd.). Further, the density was measured using a density meter Model DA-110 (Kyoto Electronics), and the reading value of the vibration viscometer was divided by the density to obtain the viscosity.

  Further, the driving method of the present invention exhibits a remarkable effect when the surface tension of the ink at 25 ° C. is 20 dyne / cm or more and 30 dyne / cm or less. This is because such an ink having a low surface tension makes it difficult to separate the ink column from the meniscus, as in the case of the high-viscosity ink, and satellites are easily generated.

  If the surface tension of the ink is too low, the wettability with respect to the nozzle forming member 22 increases, so that the ink tends to adhere to the vicinity of the nozzle 23 on the ejection side surface, and the ink ejection is easily affected. If there is a deposit in the vicinity of the nozzle 23 on the ejection surface, the ejected ink will fly in a curved direction in contact with the deposit. For this reason, the surface tension of the ink is preferably 20 dyne / cm or more.

  The surface tension can be measured using a surface tension meter CBVP type A-3 (Kyowa Kagaku Co., Ltd.).

  Examples of such ink include oil-based ink and ultraviolet curable ink. The oil-based ink refers to an ink containing 80% by mass or more of a saturated hydrocarbon having 15 to 18 carbon atoms, a monohydric alcohol having 15 to 18 carbon atoms, or a derivative thereof as a solvent. Oil-based inks have the advantage that images with good water resistance can be obtained.

  As the ultraviolet curable ink, a cation polymerizable ink and a radical polymerizable ink can be used singly, but they can be mixed and used as a hybrid ink.

  The ultraviolet curable ink preferably contains an epoxy compound, an epoxidized oil, an oxetane compound, an aprotic solvent, a radical polymerizable monomer, a coloring material, other additives, and the like as described below as constituent components.

  As the cationic polymerizable compound, an epoxy compound, an epoxidized oil, an oxetane compound, or the like can be used. Moreover, a radically polymerizable monomer can be used as the radically polymerizable compound. As the radical polymerizable monomer, various (meth) acrylate monomers can be used. For example, isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isomyristyl acrylate, isostearyl acrylate, 2-ethylhexyl-diglycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid , Butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2 Hydroxy-3-phenoxypropyl acrylate, 2-acryloylethyl succinic acid, 2-acryloylethyl phthalic acid, 2-acryloylethyl-2-hydroxyethyl-phthalic acid, lactone-modified flexible acrylate, t- Monofunctional monomers such as butylcyclohexyl acrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6- Hexanediol diacrylate, 1,9-nonanediol diacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecane diacrylate, bis Bifunctional monomers such as EO adduct diacrylate of Enol A, PO adduct diacrylate of bisphenol A, neopentyl glycol diacrylate hydroxypivalate, polytetramethylene glycol diacrylate, trimethylolpropane triacrylate, EO-modified trimethylolpropane Triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerin propoxytriacrylate, cowprolactone-modified trimethylolpropane triacrylate, pentaerythritol ethoxytetraacrylate, caprolactam-modified dipenta Three officials such as erythritol hexaacrylate And a polyfunctional monomer having a capacity higher than that of the polymer.

  When UV curable ink is used for image recording, the UV curable ink is cured if irradiated with UV after image recording, so that the image can be maintained without disappearing for a long period of time, and the image quality by the ink jet printer can be improved. it can. Further, when ultraviolet curable ink is used for image recording, even if the recording medium is not a recording medium with good ink absorption (for example, paper), the recording medium has no ink absorption or a recording medium with low ink absorption. Even image recording can be performed.

  In particular, in the case of ultraviolet curable ink, it is particularly important to reduce satellites, since it becomes difficult to remove the ultraviolet rays after being attached to the vicinity of the nozzles and then irradiated with ultraviolet leakage light and cured.

  In the above embodiment, the pressure applying means (partition wall S) is constituted by a piezoelectric element. The driving method of the present invention is preferable because the control for expanding the volume of the pressure generating chamber can be easily performed when the pressure applying means is constituted by a piezoelectric element.

  In the above embodiment, a rectangular-wave drive pulse having a sufficiently short rise time and fall time as compared with AL is applied to the piezoelectric element. By using the rectangular wave, it is possible to perform driving using the acoustic resonance of the pressure wave more effectively. Compared with the method using a trapezoidal wave, the efficiency of ejecting ink droplets is good, and it is possible to drive with a low driving voltage and to design a driving circuit with a simple digital circuit. In addition, the pulse width can be easily set.

  In the above embodiment, a shear mode type piezoelectric element that deforms in a shear mode by applying an electric field is used as the pressure applying means. The shear mode type piezoelectric element is preferable because a rectangular-wave drive pulse can be used more effectively, the drive voltage is lowered, and more efficient drive is possible. Further, although an example of a head in which ink channels as pressure generation chambers are continuous across a partition wall is shown, ink channels and dummy channels as disclosed in the prior art are alternately arranged so that the ink channel is 1 The present invention can also be applied to a dummy channel type head which is arranged every other unit and which ejects ink from the ink channel. In this case, even if the partition wall of the ink channel is shear-deformed, the ink channel is easily driven without affecting other adjacent ink channels.

  Furthermore, since this shear mode head forms an ink channel serving as an ink groove in the piezoelectric element, when the piezoelectric element generates heat by driving, this heat is transmitted to the ink and the ink is heated. When the ink temperature rises due to heating, the viscosity decreases and the discharge speed increases, causing the landing position to deviate from the target position and causing a significant decrease in image quality. In the driving method of the present invention, as shown in the embodiments described later, the power consumption is reduced by lowering the driving voltage compared to the driving method of the prior art. Change can be reduced.

  The present invention is not limited to these, and other types of piezoelectric elements such as a single plate type piezoelectric actuator and a longitudinal vibration type stacked piezoelectric element may be used as the piezoelectric element. Also, other pressure applying means such as an electromechanical conversion element using electrostatic force or magnetic force, or an electrothermal conversion element for applying pressure using a boiling phenomenon may be used.

  In the above description, an application example of an ink jet recording apparatus is shown as a liquid droplet ejection apparatus, and an ink jet recording head for performing image recording is used as a liquid droplet ejection head. However, the present invention is not limited to this. Rather, a nozzle for discharging droplets, a pressure generation chamber communicating with the nozzle, and a pressure applying means for changing the pressure in the pressure generation chamber, and the liquid in the pressure generation chamber as droplets from the nozzle The present invention can be widely applied as a droplet discharge device for discharging and a method for driving a droplet discharge head. In particular, it is effective in industrial applications that require high-definition printing with no satellite adhesion, such as liquid crystal color filter manufacturing applications.

(Examples 1-8)
Two share mode type recording heads (nozzle pitch: 180 dpi, number of nozzles: 256, nozzle diameter: 23 μm, AL: 2.4 μs, ink droplet amount: 4 pl) shown in FIG. 2 are prepared. They were attached so that they were shifted by 1/2 pitch from each other and arranged in a staggered manner. Accordingly, since each of the heads is a 180 dpi head, the nozzle pitch can be shifted by ½, so that it can be used as a 360 dpi recording head, the number of nozzles can be increased, and a high density recording head can be used. It can be.

  A drive signal (expansion pulse width: 1AL, first) that ejects five sub-drops of SD1 to SD5 shown in FIG. 7 through the channels of each row of the two-row head (nozzle pitch: 360 dpi, number of nozzles: 512). The pulse width of the contraction pulse: 0.5 AL and the pulse width of the second contraction pulse: 1 AL) were divided into three groups, and three-cycle driving was performed.

  The ink was discharged using an acrylic ultraviolet curable ink heated to 50 ° C. by a heater.

  For the drive pulse, the ratio (| Von | / | Voff |) of the drive voltage Von of the expansion pulse to the drive voltage Voff of the first contraction pulse is set to 1 / 0.7, the pulse width of the expansion pulse is set to 1AL, The pulse width of the first contraction pulse was changed in the following eight ways.

  conditions.

  Ink: Acrylic ultraviolet curable ink (viscosity 10 cp (measured value at 50 ° C.), surface tension 28 dyne / cm (measured value at 25 ° C.)).

  Pulse width of first contraction pulse: 0.3AL (Example 1), 0.5AL (Example 2), 1.0AL (Example 3), 1.25AL (Example 4), 1.5AL (Implementation) Example 5), 2.5AL (Example 6), 3.0AL (Example 7), 3.5AL (Example 8).

  For any one nozzle, while changing the drive voltage (Von, Voff) (| Von | / | Voff | is fixed to 1 / 0.7), the relationship between the flying speed of the ink droplet and the satellite length and the drive voltage ( The relationship between Von) and the flying speed of ink droplets was evaluated using the following method.

  Measurement of flying speed and satellite length: The ink droplet speed and satellite length SL were measured when the SD1 ink droplet flew about 1 mm from the nozzle opening by strobe measurement using a CCD camera. The satellite amount increases as the satellite length SL increases.

  Measurement of flying speed and driving voltage: The first SD1 ink and the fifth SD5 ink were measured by the strobe measurement using a CCD camera under the condition of the pulse width of the first contraction pulse = 0.5 AL (Example 2). Measure the ink drop velocity when the drop flies about 1mm from the nozzle opening.

  Measurement of ink droplet speed change due to driving heat generation: Under the condition of the pulse width of the first contraction pulse = 0.5 AL (Example 2), a driving voltage at which SD1 is 6 m / s, 2 rows of heads are set at 25.5 KHz. The full drive (solid print data) was continuously performed at the drive frequency of, and the change (increase) in drive time and ink droplet speed was examined. The heater sets the electric power so that the initial value is 50 ° C., and does not perform feedback control after driving. When the temperature of the ink rises due to driving heat generation, the ink viscosity decreases and the ink droplet speed increases. Accordingly, a small speed change indicates that the drive heat generation is small because the power consumption of the drive pulse is small.

In the case of this head, the optimum value of the speed difference between SD1 and SD5 is 6m when the SD period is 4AL and the gap between the recording medium and the nozzle is 2mm as the condition that each SD1 and SD5 land at the same position. For SD / s, SD5 is 7 m / s.
(Comparative Example 1)
The driving pulses SD1 to SD5 in FIG. 7 are the same as those in the embodiment except that each of the driving pulses SD1 to SD5 is replaced with the driving pulse of the conventional example shown in FIG.
(Comparative Examples 2 to 5)
The first contraction pulse was the same as the example except that the pulse width was as shown below.

  Pulse width of the first contraction pulse: four types of 0.1AL (Comparative Example 2), 1.6AL (Comparative Example 3), 2.0AL (Comparative Example 4), and 2.4AL (Comparative Example 5).

  FIG. 9 shows the relationship between the speed of the ink droplet of SD1 and the satellite length when only SD1 is ejected for the example and the comparative example. In Comparative Example 2, since the ink droplet speed is very slow and unstable, it is excluded.

  In FIG. 9, the horizontal axis represents the ink droplet velocity (m / s), and the vertical axis represents the satellite length (μm). The points and lines L1 represented by 中 in the figure are Example 1, the points and lines L2 represented by ○ in the figure are Example 2, and the points and lines L3 represented by ▲ in the figure are Example 3. In the figure, the point represented by ▪ and the line L4 are Example 4, the point represented by Δ in the figure and the line L5 are Example 5, and the point represented by-and the line L6 in the figure are comparative examples. 1. The point represented by X in the figure and the line L7 are Comparative Example 3, the point represented by ◆ in the figure and the line L8 are Comparative Example 4, the point represented by □ in the figure and the line L9 are compared. Example 5, point and line L10 represented by + in the figure are Example 6, point and line L11 represented by ● in the figure are Example 7, point and line L12 represented by Ж in the figure are Each corresponds to Example 8.

  The driving method of the example of FIG. 9 has a satellite length that is significantly shorter than the driving method of the comparative example, and it has been confirmed that the driving method of the present invention is effective in reducing satellites.

  FIG. 10 shows the drive voltage Von (V) and the ink droplet speed (m / s) in the drive signal of Example 2, the horizontal axis represents the drive voltage Von (V), and the vertical axis represents the ink droplet. Expresses speed (m / s). ◇ and line SD1 in the figure are data for SD1 when SD1 to SD5 are continuously ejected, and ▪ and line SD5 in the figure are data for SD5.

  From FIG. 10, the speed increase width of SD5 with respect to the speed of SD1 is as small as 1 m / s or less, and it was confirmed that the light was emitted stably and was canceled appropriately. Further, the speed could be stably discharged up to 11 m / s.

  In FIG. 10, data when the drive pulse of Comparative Example 1 is used is not shown, but it is almost the same as the data of Example 2 above.

  From the results of FIGS. 9 and 10, it was confirmed that the driving method of the example can obtain a canceled state equivalent to the driving method of the comparative example, and the satellite can be significantly reduced.

  In FIG. 11, the horizontal axis represents the drive time (s), and the vertical axis represents the change in ink droplet speed due to drive heat generation (the amount of increase from 6 m / s). A point and a line H1 represented by ◆ in the figure correspond to Comparative Example 1, and a point and a line H2 represented by ■ in the figure correspond to Example 2, respectively. The drive voltage Von at which the speed of the ink droplet of SD1 is 6 m / s is 21.9 V in the comparative example and 16.4 V in the example, and the drive voltage is lower by about 25% in the example.

  From FIG. 11, it was confirmed that the speed change was smaller in the driving method of the example than in the driving method of the comparative example. The heater for heating the ink sets electric power so that the initial value is 50 ° C., and does not perform feedback control after driving. Accordingly, a small speed change indicates that the drive heat generation is small because the power consumption of the drive pulse is small. It has been confirmed that the driving method of the present invention can reduce power consumption and suppress the heat generation during driving, as compared with the driving method of the comparative example.

It is a figure which shows schematic structure of an inkjet recording device. It is a figure which shows schematic structure of the shear mode (shear mode) type inkjet recording head which is one aspect | mode of a droplet discharge head, (a) is a perspective view which shows a partial cross section, (b) is provided with the ink supply part. FIG. (A)-(c) is a figure which shows operation | movement of a recording head. (A) is a diagram showing a driving signal for realizing the driving method of the embodiment according to the present invention and a pressure applied to the ink in the pressure generating chamber by the driving signal, and (b) is a driving of the embodiment according to the present invention. It is a figure which shows the mode of the meniscus and droplet discharge in the nozzle by a method. (A) is a diagram showing a driving signal for realizing the conventional driving method and a pressure applied to the ink in the pressure generating chamber by the driving signal, and (b) is a diagram of meniscus and droplet discharge in the nozzle by the conventional driving method. It is a figure which shows a mode. (A)-(c) is explanatory drawing of the time division operation | movement of a recording head. It is a timing chart of the drive signal applied to the electrode of the pressure generation chamber of each set of A, B, and C. It is a timing chart of a drive signal at the time of using only a positive voltage. It is a graph which shows the experimental data which contrasted the speed of the ink drop which concerns on the drive method of this invention, and the length of the satellite. It is a graph which shows the experimental data which contrasted the drive voltage and the speed of an ink drop which concern on the drive method of this invention. It is a graph which shows the experimental data which contrasted the speed change of the ink droplet by the drive time and drive heat_generation | fever by the drive method of this invention. It is a figure which shows the inkjet recording head of a prior art example. It is a figure which shows the drive method of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording apparatus 2 Recording head 21 Ink tube 22 Nozzle formation member 23 Nozzle 24 Cover plate 25 Ink supply port 26 Substrate 27 Partition 28 Pressure generating chamber 3 Conveying mechanism 31 Conveying roller 32 Conveying roller pair 33 Conveying motor 4 Guide rail 5 Carriage 6 Flexi cable 7, 8 Ink receiver 100 Drive signal generating means P Recording medium PS Recording surface 101 Ink droplet 102 Ink column 11 Main droplet 12 Satellite droplet M Ink meniscus SL Satellite length

Claims (7)

A droplet applying head having a pressure applying unit that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying unit, and a nozzle that communicates with the pressure generating chamber, and a driving signal are generated. A droplet discharge device that includes a drive signal generating unit, expands or contracts the volume of the pressure generation chamber by applying a drive signal to the pressure applying unit, and discharges a droplet from the nozzle;
The drive signal includes an expansion pulse for expanding the volume of the pressure generation chamber, a first contraction pulse for contracting the volume of the pressure generation chamber following the expansion pulse, and contracting the volume of the pressure generation chamber after the first contraction pulse. A second contraction pulse to cause
The pulse width of the expansion pulse is 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber),
The droplet discharge device, wherein the first contraction pulse has a pulse width of 0.3 AL to 1.5 AL. A droplet applying head having a pressure applying unit that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying unit, and a nozzle that communicates with the pressure generating chamber, and a driving signal are generated. A droplet discharge device that includes a drive signal generating unit, expands or contracts the volume of the pressure generation chamber by applying a drive signal to the pressure applying unit, and discharges a droplet from the nozzle;
The drive signal includes an expansion pulse for expanding the volume of the pressure generation chamber, a first contraction pulse for contracting the volume of the pressure generation chamber following the expansion pulse, and contracting the volume of the pressure generation chamber after the first contraction pulse. A second contraction pulse to cause
The pulse width of the expansion pulse is 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber),
The droplet discharge device, wherein the first contraction pulse has a pulse width of 2.5 AL to 3.5 AL. The drive signal has a pulse width of the first contraction pulse of 0.3 AL to 1.0 AL, and an interval between the end of the expansion pulse and the start of the second contraction pulse is 0.7 AL to 1.. 3AL,
2. The droplet discharge device according to claim 1, wherein an interval between the end of the first contraction pulse and the start of the second contraction pulse is 0.3 AL or more. 2. When the driving voltage of the first contraction pulse is Voff (V) and the driving voltage of the second contraction pulse is V2off (V), | Voff | = | V2off | The droplet discharge device according to any one of? The drive signal is a drive signal that has a plurality of sets of the expansion pulse, the first contraction pulse, and the second contraction pulse in the same drive cycle, and discharges a droplet a plurality of times in succession. The liquid droplet ejection apparatus according to claim 1, wherein: Driving signal to the pressure applying means of the droplet discharge head having pressure applying means that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber. Is a liquid droplet ejection head driving method for expanding or contracting the volume of the pressure generating chamber to eject liquid droplets from a nozzle,
The drive signal includes an expansion pulse for expanding the volume of the pressure generation chamber, a first contraction pulse for contracting the volume of the pressure generation chamber following the expansion pulse, and contracting the volume of the pressure generation chamber after the first contraction pulse. A second contraction pulse to cause
The pulse width of the expansion pulse is 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber),
A method for driving a droplet discharge head, wherein the pulse width of the first contraction pulse is 0.3 AL to 1.5 AL. Driving signal to the pressure applying means of the droplet discharge head having pressure applying means that operates by applying a driving signal, a pressure generating chamber whose volume expands or contracts by the operation of the pressure applying means, and a nozzle that communicates with the pressure generating chamber. Is a liquid droplet ejection head driving method for expanding or contracting the volume of the pressure generating chamber to eject liquid droplets from a nozzle,
The drive signal includes an expansion pulse for expanding the volume of the pressure generation chamber, a first contraction pulse for contracting the volume of the pressure generation chamber following the expansion pulse, and contracting the volume of the pressure generation chamber after the first contraction pulse. A second contraction pulse to cause
The pulse width of the expansion pulse is 0.7 AL to 1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber),
A method for driving a droplet discharge head, wherein the pulse width of the first contraction pulse is 2.5 AL to 3.5 AL.

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