JP2006159817A - Liquid droplet discharging device and driving method for liquid droplet discharging head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid droplet discharging device capable of reducing satellite to stably discharge liquid droplet. <P>SOLUTION: The liquid droplet discharging device is provided with a pressure generating chamber which expands or contracts by the action of a pressure imparting means by a drive signal and a liquid droplet discharging head containing a nozzle communicating with the pressure generating chamber, expands or contracts the pressure generating chambers by applying the drive signal to the pressure imparting means to eject liquid droplets from the nozzle. The drive signal has expansion pulses for expanding the pressure generating chamber and contraction pulses for contracting the pressure generating chamber subsequent to the expansion pulses, wherein the expansion pulses have a pulse width of 0.7 AL to 1.3 AL (AL represents half the acoustic resonant period of the pressure generating chamber), while the contraction pulses have a pulse width of 0.3 AL to 1.5 AL. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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. As one of them, for example, as disclosed in Patent Document 1, a method in which a discharge pressure of ink droplets is obtained using a piezoelectric element. There is.

  A cross-sectional view of this ink jet recording head is shown in FIG. Specifically, as shown in FIG. 12, a plurality of grooves b, b,... Are formed in a base plate a made of a piezoelectric material, and partition walls c, c,. Then, it is polarized in the depth direction of the pressure generation chamber (ink channel) d which is the internal space of the groove b, and the drive electrode e is formed in a predetermined region (for example, the upper half) of the partition wall c. A cover plate f is attached on the base plate a so as to close the upper portion of the groove b. The grooves b, b,... Are formed by cutting with a diamond blade or the like. The drive electrode e is formed by sputtering or the like.

  Then, by applying a pulse voltage corresponding to the image signal to each of the drive electrodes e, e,..., A potential difference is provided between the drive electrodes e, e,. Cause it to occur. The partition walls c, c,... Undergo shear deformation due to the piezoelectric shear strain effect generated at this time. Due to this deformation, a pressure wave is generated in the pressure generating chamber d, and the ink droplet ejection operation is performed by the pressure.

  As the shear deformation operation of each of the walls c, c,..., After an expansion pulse voltage is applied to a predetermined drive electrode e so that the partition wall c operates in a direction in which the pressure generating chamber d expands, the ink chamber d A contraction pulse voltage is applied to a predetermined drive electrode e so that the partition wall c operates in the contracting direction. As a result, a pressure wave is applied to the ink in the pressure generation chamber d, and ink droplets are ejected from the pressure generation chamber d via an ink nozzle (not shown). The expansion pulse voltage and the contraction pulse voltage are set to the same voltage value.

  Here, the pulse width of the expansion pulse voltage greatly affects the ejection force of the ink droplet, and when this pulse width matches AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber d), the ink droplet The discharge force (discharge speed) is maximized. The contraction pulse voltage is applied when the application of the expansion pulse voltage is released, that is, after the time AL has elapsed. Therefore, by setting the pulse width of the expansion pulse voltage as described above, the pressure wave accompanying the ink inflow generated when the expansion pulse voltage is applied propagates one way through the pressure generation chamber and reaches the maximum near the ink discharge portion. At the same time, it is disclosed that the most efficient discharge force can be obtained in combination with the positive pressure generated by the rapid change of the pressure generation chamber (contraction of the pressure generation chamber) due to the application of the contraction pulse voltage. Has been. (See Patent Document 1).

  In addition, as the pulse width of the contraction pulse voltage, the pressure wave after ink ejection is reduced by releasing the voltage when the positive pressure wave during ink ejection propagates back and forth in the pressure generation chamber and becomes maximum near the nozzle. It is disclosed that time 2AL is most suitable because it can be canceled efficiently. (See Patent Document 1).

Patent Document 2 also discloses that the pulse width of the contraction pulse voltage is generally equal to 2AL.
JP 2002-137390 A JP 2003-11362 A

  As in the conventional driving method, when the pulse width of the contraction pulse voltage is 2AL, the pressure wave in the pressure generating chamber is cancelled. 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. 6B shows a state of meniscus and droplet discharge at a nozzle by a conventional driving method. In FIG. 6B, 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. 6 will be given later.

  In FIG. 6B, according to the knowledge of the inventors, when the pressure wave is canceled by setting the pulse width of the contraction pulse to 2AL as in the above-described prior art, the ink column 102 has the meniscus M when the cancellation is applied. Is not separated ((5) in FIG. 6B). 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. 6B).

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

  Further, in the above driving method, when the speed of the ejected ink droplet is increased, the ejection speed of the ink column is increased, so that the ink column 102 is easily extended. Therefore, when the speed of the ink droplets ejected by the driving method as described above is increased, the ink droplets 101 become longer, so that they are likely to break up, and the satellite droplets 12 increase.

  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.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a droplet discharge device and a droplet discharge head driving method capable of reducing satellite droplets and stably discharging droplets. And

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

(Claim 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. A first expansion pulse for expanding the volume of the generation chamber; and a contraction pulse for contracting the volume of the pressure generation chamber following the first expansion pulse. The pulse width of the first expansion pulse is 0.7 AL. A droplet discharge device characterized in that it is ˜1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber), and the pulse width of the contraction pulse is 0.3 AL to 1.5 AL.

(Claim 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. A first expansion pulse for expanding the volume of the generation chamber; and a contraction pulse for contracting the volume of the pressure generation chamber following the first expansion pulse. The pulse width of the first expansion pulse is 0.7 AL. A droplet discharge device characterized in that it is ˜1.3 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber), and the pulse width of the contraction pulse is 2.5 AL to 3.5 AL.

(Claim 3)
3. The droplet discharge device according to claim 1, wherein the drive signal includes a second expansion pulse that expands a volume of the pressure generation chamber following the contraction pulse. 4.

(Claim 4)
4. When the drive voltage of the first expansion pulse is Von (V) and the drive voltage of the second expansion pulse is V2on (V), | Von | ≧ | V2on | The droplet discharge device according to 1.

(Claim 5)
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 is a first method for expanding the volume of the pressure generating chamber. An expansion pulse and a contraction pulse for contracting the volume of the pressure generation chamber following the first expansion pulse, and the pulse width of the first expansion pulse is 0.7 AL to 1.3 AL (AL is the pressure generation chamber) 1), and the pulse width of the contraction pulse is 0.3 AL to 1.5 AL.

(Claim 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 is a first method for expanding the volume of the pressure generating chamber. An expansion pulse and a contraction pulse for contracting the volume of the pressure generation chamber following the first expansion pulse, and the pulse width of the first expansion pulse is 0.7 AL to 1.3 AL (AL is the pressure generation chamber) And a contraction pulse has a pulse width of 2.5 AL to 3.5 AL.

  According to invention of Claim 1, there exist the following effects. By setting the pulse width of the first expansion pulse to 0.7 AL to 1.3 AL, which is in the vicinity of 1 AL, and subsequently applying the contraction pulse, the expansion of the pressure generating chamber at the start of application of the first expansion pulse When the negative pressure wave is reversed at 1AL and becomes a positive pressure, the positive pressure wave due to contraction is added in the form of a sum, so the discharge pressure (discharge speed) of the droplets increases and the most efficient discharge Power is obtained.

  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 the pressure wave is reversed and the pressure generating chamber becomes negative pressure after 1 AL has passed since the start of application of the contraction pulse, the action of pulling out the ejected meniscus works to narrow the extruded liquid column. work. Before and after this, the pulse width of the contraction pulse was set to 0.3 AL to 1.5 AL, and when the application of the contraction pulse was finished, the pressure generating chamber expanded and the force to pull back the meniscus further worked to further narrow the liquid column. As a result, the liquid column is separated from the meniscus at an early stage, and satellite droplets are less likely to be generated. That is, it is possible to reduce the satellite by suppressing the long tail of the liquid column.

  According to invention of Claim 2, there exist the following effects. By setting the pulse width of the first expansion pulse to 0.7 AL to 1.3 AL, which is in the vicinity of 1 AL, and subsequently applying the contraction pulse, the expansion of the pressure generating chamber at the start of application of the first expansion pulse When the negative pressure wave is reversed at 1AL and becomes a positive pressure, the positive pressure wave due to contraction is added in the form of a sum, so the discharge pressure (discharge speed) of the droplets increases and the most efficient discharge Power is obtained.

  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 the pressure wave is reversed and the pressure generation chamber becomes negative pressure after 3 AL has passed since the start of application of the contraction pulse, the action of pulling out the ejected meniscus works to narrow the extruded liquid column. work. Before and after this, the pulse width of the contraction pulse was set to 2.5 AL to 3.5 AL, and when the application of the contraction pulse was completed, the pressure generating chamber expanded and the force to pull the meniscus further worked to further narrow the liquid column. As a result, the liquid column is separated from the meniscus at an early stage, and satellite droplets are less likely to be generated. That is, it is possible to reduce the satellite by suppressing the long tail of the liquid column.

  According to invention of Claim 3, there exist the following effects. Since the second expansion pulse that expands the volume of the pressure generation chamber follows the contraction pulse, a negative pressure at the start of application of the second expansion pulse is further added, so that a pressure wave having a larger amplitude is generated. Can be generated. As a result, the effect of reducing satellite droplets can be enhanced.

  According to invention of Claim 4, there exist the following effects. From the viewpoint of satellite reduction, the pressure wave amplitude is preferably as large as possible. However, when the drive voltage of the first expansion pulse is Von (V) and the drive voltage of the second expansion pulse is V2on (V), if | Von | <| V2on |, V2on becomes excessively large. This tends to cause erroneous ejection and unstable injection. By satisfying | Von | ≧ | V2on |, it is possible to achieve both reduction of satellite drops and ejection stability.

  According to the invention described in claim 5, as in the invention described in claim 1, the most efficient ejection force can be obtained, and satellite drops can be reduced.

  According to the invention described in claim 6, as in the invention described in claim 2, the most efficient ejection force can be obtained, and satellite droplets can be reduced.

  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.

  The driving method according to the present invention includes 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 material of the cover plate 24 and the substrate 26 is not particularly limited, and may be a substrate made of an organic material. However, a substrate made of a non-piezoelectric nonmetallic material is preferable. It is preferably selected from at least one of alumina, aluminum nitride, zirconia, silicon, silicon nitride, silicon carbide, quartz, and unpolarized PZT. Examples of the organic material include organic polymers and hybrid materials of organic polymers and organic substances.

  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.

  The shear mode type recording head 2 can constitute 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.

(First embodiment)
FIG. 4A shows a driving signal for realizing the driving method according to the first embodiment of the present invention and the pressure applied to the ink in the pressure generating chamber 28 by the driving signal. FIG. 4B shows a state of meniscus and droplet discharge in the nozzle by the driving method according to the first 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 AL time, and the vertical axis represents drive voltage. 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 state shown in FIG. 3A, when the recording head 2 connects the electrodes 29A and 29C to the ground and applies a first expansion pulse (positive voltage) made of a rectangular wave to the electrode 29B, First, 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 by the first rising edge (P1) of the pulse, and both 27a and 27b cause shear 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, when the potential is returned to 0 after 1 AL time has elapsed since the first application of P1 (P2), the partition walls 27B and 27C are expanded. From the neutral position shown in FIG. 3A, high pressure is applied to the ink in the pressure generation chamber 28B.

  Subsequently, a 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 of the contraction pulse (P3), and the volume of the pressure generating chamber 28B contracts. 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.

  (3) When 1AL time has elapsed, the pressure wave of the ink in the pressure generating chamber 28B is reversed to a negative pressure, so that the arrow of FIG. Constriction occurs. At this time, 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 expands, so that a high negative pressure is applied to the ink in the pressure generating chamber 28B. It takes. As a result, the meniscus M is drawn, the rear end of the protruding ink column 102 is pulled back, and the diameter of the ink column is reduced. 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.

  (5) When 1 AL time further elapses, the pressure wave is reversed and becomes positive pressure.

  (6) When 1AL time further elapses, the pressure wave of the ink is reversed and becomes negative pressure.

  (6.5); After about 3.5 AL hours have passed since the high pressure was applied to the ink in (2) above, the negative pressure increased, and the ink column 102 protruding from the opening of the nozzle 23 was pulled strongly to draw the ink column. And then separated from the meniscus M and discharged from the nozzle 23 as droplets 101.

  Such a driving method is a driving method based on a so-called DRR (Draw-Release-Reinforce) method, and the pulse width of the first expansion pulse greatly affects the ejection force of the ink droplet, and this pulse width coincides with 1AL. Sometimes the ink droplet ejection force (ejection speed) is maximized. The contraction pulse is applied when the first expansion pulse falls (P2), that is, after the passage of 1AL. For this reason, by setting the pulse width of the first 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 is reversed to the positive pressure. At the same time, 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 contraction pulse (P3) is applied, and in combination, the most efficient discharge force is obtained. Therefore, there is an advantage that the discharge speed of the ink droplet is increased.

  Further, since the pulse width of the contraction pulse is 1AL, when the application of the contraction pulse is terminated and the voltage is returned to 0, the pressure generating chamber expands, and the negative pressure wave generated by the expansion is the first pressure wave. The pressure wave generated at the start of the application of the expansion pulse and the contraction pulse overlaps with the pressure wave of the negative pressure generated by reversing, and the force to pull back the meniscus acts to narrow the ink column, and the ink column 102 is shortened early. In the state, it separates from the meniscus M 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 contraction pulse is 1 AL in the above embodiment, it may be set within 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 the negative pressure generated at the end of the application of the contraction pulse can be strengthened with the pressure wave generated at the start of the application of the first expansion pulse and the contraction pulse, Satellites can be reduced. In particular, by setting the pulse width of the 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 contraction pulse (P4) at an early stage. 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 contraction pulse is shorter than 0.3 AL, it is considerably shorter than AL, so that the droplet discharge force is reduced and the driving efficiency is reduced (increasing driving voltage). Further, when the pulse width of the contraction pulse is 4AL, the effect of pulling back the meniscus cannot be used early, and the effect of reducing the amount of satellite becomes small.

  The pulse width of the first 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.

  In the drive signal of FIG. 4A, the ratio of the first expansion pulse drive voltage Von (V) and the contraction pulse drive voltage Voff (V) is set to | Von | / | Voff | = 2. 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.

  Further, it is more preferable that | Von | / | Voff | = 2.

(Second Embodiment)
FIG. 5A shows a drive signal for realizing the drive method according to the second embodiment of the present invention and the pressure applied to the ink in the pressure generating chamber 28 by the drive signal. FIG. 5B shows a state of meniscus and droplet discharge in the nozzle by the driving method according to the second embodiment of the present invention. The numbers in parentheses in FIGS. 5A to 5B and the following description correspond to each other in terms of time. The drive signal of the second embodiment is obtained by adding a second expansion pulse to the drive signal of the first embodiment.

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

  (1) In the state shown in FIG. 3A, when the recording head 2 connects the electrodes 29A and 29C to the ground and applies a first expansion pulse (positive voltage) made of a rectangular wave to the electrode 29B, First, 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 by the first rising edge (P1) of the pulse, and both 27a and 27b cause shear 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).

  (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 after the first P1 application (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.

  Subsequently, a 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 of the contraction pulse (P3), and the volume of the pressure generating chamber 28B contracts. Due to this contraction, a higher pressure is applied to the ink in the pressure generation chamber 28 </ b> B, and the ink column 102 protrudes from the opening of the nozzle 23.

  (3) When 1AL time has elapsed, the pressure wave of the ink in the pressure generation chamber 28B is reversed to a negative pressure, so that the arrow of FIG. Constriction occurs. At this time, 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 expands, so that a high negative pressure is applied to the ink in the pressure generating chamber 28B. It takes.

  Subsequently, a second expansion pulse (positive voltage) composed of a rectangular wave is applied. First, at the rising edge (P5) of the second expansion pulse, the volume of the ink channel 28B is expanded as shown in FIG. 3B, and a higher negative pressure is applied to the ink. As a result, the meniscus M is drawn and the rear end of the protruding ink column 102 is strongly pulled back.

  By further adding a negative pressure wave due to the expansion, a pressure wave having a larger amplitude can be generated, and the diameter of the ink column is greatly reduced.

  (5) When 1 AL time further elapses, the pressure wave is reversed and becomes positive pressure.

  (6) When 1AL time further elapses, the pressure wave of the ink is reversed and becomes negative pressure. At this time, when the potential is returned to 0 (P6) and the partition walls 27B and 27C are returned from the expanded position to the neutral position, the volume of the pressure generating chamber 28B contracts, so that a high positive pressure is applied to the ink in the pressure generating chamber 28B. To cancel the pressure wave. After that, it is separated from the meniscus M and discharged as a droplet 101 from the nozzle 23.

  In the second embodiment, since the second expansion pulse for expanding the volume of the pressure generation chamber is provided following the contraction pulse, a negative pressure at the start of application of the second expansion pulse is further added, A pressure wave having a large amplitude can be generated. When the meniscus M receives the vibration of the pressure wave, the meniscus M is separated from the meniscus M in an earlier state with the ink column 102 being short and flies as ink droplets 101. Therefore, the main droplet and the satellite droplet are hardly divided, and the amount of satellite can be further reduced.

  5A, the ratio of the drive voltage Von (V) of the first expansion pulse to the drive voltage V2on (V) of the second expansion pulse is | Von | / | V2on | = 3. Three. Thus, by setting | Von | ≧ | V2on |, it is possible to prevent erroneous ejection and instability of ejection due to excessive pressure waves in the second expansion pulse rising step (P5), and to reduce and stabilize satellite droplets. It is possible to achieve both injections.

  In the above embodiment, the pulse width of the second expansion pulse is approximately 2AL, and the time from the start of application of the contraction pulse (P3) to the end of application of the second expansion pulse (P6) is approximately 3AL. . Thus, by setting the odd multiple of AL, it is possible to cancel the pressure wave and achieve stable injection in a short cycle. This is a preferred mode for high frequency driving.

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

  FIG. 6A shows a 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. 6B shows a state of meniscus and droplet discharge in the nozzle by the conventional driving method. The numbers in parentheses in FIGS. 6A to 6B and the following description correspond to each other in terms of time.

  In FIG. 6A, the horizontal axis represents AL time, and the vertical axis represents drive voltage. L1 and the dotted line represent the drive signal, and L2 and the solid line represent the pressure.

  In FIG. 6B, 11 indicates the main droplet, 12 indicates the satellite droplet, and SL indicates the satellite length.

  (1) In such a recording head 2, when the electrodes 29A and 29C are connected to the ground and the first expansion pulse (positive voltage) is applied to the electrode 29B in the state shown in FIG. By the first rise (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 surfaces of the partition walls, as shown in FIG. ), 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 (Draw).

  (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 after the first P1 application (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.

  Subsequently, a contraction pulse (negative voltage) 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 contraction pulse (P3), and the volume of the pressure generating chamber 28B contracts. 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 has elapsed, the pressure wave of the ink in the pressure generation chamber 28B is reversed to a negative pressure, so that the neck of the protruding ink column 102 is constricted as shown by an arrow in FIG. 6B. Produce.

  (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 out of phase by 180 °, they cancel each other out, and the pressure wave attenuates early. 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.

  When the pulse width of the contraction pulse is 2AL as in the prior art, the pressure wave of the positive pressure in the pressure generation chamber and the pressure wave of the negative pressure generated at the end of the application of the contraction pulse cancel each other, and the meniscus is pulled back. Since it does not work, the subsequent separation of the ink column 102 from the meniscus M is performed in a state where the vibration of the meniscus due to the pressure wave is small, which is extremely slow. As a result, the ink pillars 102 extend, and the amount of satellites increases. SL in FIG. 6 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 three-cycle discharge operation will be further described with reference to FIG. In the example shown in FIG. 7, it is assumed that the pressure generation chamber of the recording head is composed of nine pressure generation chambers A1, B1, C1, A2, B2, C2, A3, B3, and C3. Will be described as an example. Further, FIG. 8 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.

  At the time of ink ejection, first, voltage is applied to the electrodes of the pressure generation chambers 28 of the A group (A1, A2, A3), and the electrodes of the pressure generation chambers on both sides thereof are grounded. When a first expansion pulse (positive voltage) made of a rectangular wave is applied to the A set of pressure generating chambers, the A set of partition walls to be discharged is deformed outward, and a negative pressure is generated in the pressure generating chamber 28. By this negative pressure, ink is supplied to the A set of pressure generating chambers 28.

  If this state is maintained for 1 AL, the pressure wave is reversed to a positive pressure. Therefore, when the electrode is grounded at this timing, the deformation of the partition wall is restored and high pressure is applied to the ink in the pressure generation chamber 28 of the A set. . Furthermore, when a contraction pulse (negative voltage) consisting of a rectangular wave is applied to the electrodes of each pressure generation chamber of the A group at the same timing, the partition wall is deformed inward, and a higher pressure is applied to the ink, and the ink column is pushed out from the nozzle. It is. After 1 AL time, the pressure wave is reversed and the pressure generation chamber 28 becomes negative pressure. When the electrode is grounded at this timing, the deformation of the partition wall is restored and a strong pressure wave is generated.

  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).

  When performing multi-drop ejection, ejection pulses composed of the first expansion pulse and contraction pulse are repeated for the number of ink droplets to be ejected. The drive signal generating means 100 outputs a drive signal for ejecting ink droplets continuously a plurality of times within one pixel cycle.

  Here, when ejecting ink droplets continuously from the nozzles of the same pressure generating chamber, the interval between ejection pulses (from the end of the application of the contraction pulse of the previous ejection to the start of the application of the first expansion pulse of the next ejection) Time) is preferably an odd multiple of AL. The reason is that in the driving method of the present invention, the pressure wave is not canceled, so that when the next discharge pulse is applied after the odd number AL of the previous discharge pulse, the pressure wave of the previous discharge pulse and the pressure wave due to the next discharge pulse are applied. This is because the phase is reversed and the influence of the pressure wave on the subsequent ink ejection can be minimized.

  In such a shear mode type ink jet recording head, the deformation of the partition wall 27 is caused by 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 cationically 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 a method using a trapezoidal wave, the ink droplets are ejected more efficiently, and can be driven with a lower drive voltage. In addition, the drive circuit can be designed 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. In addition, an example of a head in which ink channels that are pressure generation chambers are continuous across a partition wall has been shown. However, ink channels and dummy channels are alternately arranged so that every other ink channel is arranged. The present invention can also be applied to a dummy channel head that discharges ink from an 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.

  However, 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. As a result, since each head is a 180 dpi head, it is possible to use it as a 360 dpi recording head by shifting the nozzle pitch by ½, increasing the number of nozzles and increasing the number of nozzles. It can be.

  The channels of each row of this two-row head (nozzle pitch: 360 dpi, number of nozzles: 512) were divided into three groups based on the drive signal shown in FIG. 9, and three-cycle drive was performed under the following conditions. The ink was discharged by heating to 50 ° C. using an acrylic ultraviolet curable ink.

  The drive pulse is contracted by setting the ratio (| Von | / | Voff |) of the drive voltage Von of the first expansion pulse to the drive voltage Voff of the contraction pulse to 2 and setting the pulse width of the first expansion pulse to 1AL. The pulse width of the 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.)).

  Drive voltage ratio of the first expansion pulse and the contraction pulse: | Von | / | Voff | = 2.

  Pulse width of the first expansion pulse: 1AL.

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

  Drive cycle: 55.2 μs.

  For any one nozzle, while changing the driving voltage (Von, Voff) (fixed to | Von | / | Voff | = 2), the flying speed of the ink droplet, the satellite length, and the driving voltage are determined using the following method. evaluated.

  In addition, as for the ink droplets, 20 ink droplets were ejected continuously, and the 20th ink droplet was evaluated.

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

Drive voltage evaluation: Evaluate the drive voltage (Von) when the ink droplet velocity is 6 m / s.
(Comparative Examples 1-2)
Examples 1 to 8 were the same except that the pulse width of the contraction pulse was as shown below.

  Contraction pulse width: 0.1 AL (Comparative Example 1), 2.0 AL (Comparative Example 2).

  FIG. 10 shows the relationship between the 20th ink drop velocity and the satellite length for Examples 1 to 8 and Comparative Example 2. In Comparative Example 1, since the ink droplet speed is very slow and unstable, it is excluded.

  In FIG. 10, 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. 2. The point represented by + in the figure and the line L7 are Example 6. The point and line L8 represented by ● in the figure are Example 7. The point represented by Ж in the figure and the line L9 are implemented. Each corresponds to Example 8.

  As shown in Examples 1 to 8 in FIG. 10, the contraction pulse so that the pressure wave of negative pressure generated at the end of application of the contraction pulse and the pressure wave generated at the start of application of the first expansion pulse and contraction pulse are intensified. It has been confirmed that setting the pulse width of 1 is effective in reducing satellites. In particular, in Example 3 and Example 4 in which the pulse width was set near 1 AL, the satellite length was the shortest. In Comparative Example 2, it was confirmed that the satellite length was long because the effect of pulling back the meniscus using the pressure wave was not obtained.

  In FIG. 11, the horizontal axis represents the pulse width (AL) of the contraction pulse, and the vertical axis represents the drive voltage (V) when the ink droplet velocity is 6 m / s. As shown in Examples 2 to 5 in FIG. 11, it was confirmed that the effect of improving the driving efficiency (decreasing the driving voltage) can be obtained by setting the pulse width of the contraction pulse to 0.5 AL to 1.5 AL. . In summary, the setting of 0.5 AL to 1.5 AL is the most preferable in that both the reduction of the satellite and the reduction of the power consumption of the recording head can be realized.

  Further, the drive signals of Examples 1 to 8 are drive signals to which a second expansion pulse as shown in FIG. 5 is added (the pulse width of the second expansion pulse is 2AL and 4AL). As a result of a similar evaluation, it was confirmed that the satellite length was shortened by about 5% compared to the case without the second expansion pulse in FIG. 10, and the satellite reduction effect was increased.

  In addition, due to the canceling effect at the end of application of the second expansion pulse, the ejection stability when driving in a short cycle is improved.

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. It is sectional drawing of the state. (A)-(c) is a figure which shows operation | movement of a recording head. (A) is a figure which shows the pressure given to the ink in a pressure generation chamber by the drive signal and drive signal for implement | achieving the drive method of 1st Embodiment based on this invention, (b) is 1st Embodiment. It is a figure which shows the mode of the meniscus and droplet discharge in the nozzle by the driving method. (A) is a figure which shows the pressure given to the ink in a pressure generation chamber by the drive signal and drive signal for implement | achieving the drive method of 2nd Embodiment based on this invention, (b) is 2nd Embodiment. It is a figure which shows the mode of the meniscus and droplet discharge in the nozzle by the driving 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 illustrating 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 ink drop speed and satellite length which concern on the drive method of this invention. It is a graph which shows the experimental data which contrasted the pulse width of the contraction pulse which concerns on the drive method of this invention, and drive voltage. It is sectional drawing of the inkjet recording head for demonstrating the drive method of a prior art.

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 (6)

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 a first expansion pulse that expands the volume of the pressure generation chamber, and a contraction pulse that contracts the volume of the pressure generation chamber following the first expansion pulse;
The pulse width of the first 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 droplet discharge device, wherein the 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 a first expansion pulse that expands the volume of the pressure generation chamber, and a contraction pulse that contracts the volume of the pressure generation chamber following the first expansion pulse;
The pulse width of the first 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 droplet discharge device, wherein the contraction pulse has a pulse width of 2.5 AL to 3.5 AL. 3. The liquid droplet ejection apparatus according to claim 1, wherein the drive signal includes a second expansion pulse that expands a volume of the pressure generation chamber following the contraction pulse. 4. 4. When the drive voltage of the first expansion pulse is Von (V) and the drive voltage of the second expansion pulse is V2on (V), | Von | ≧ | V2on | The droplet discharge device according to 1. 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 a first expansion pulse that expands the volume of the pressure generation chamber, and a contraction pulse that contracts the volume of the pressure generation chamber following the first expansion pulse;
The pulse width of the first 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 contraction pulse has a pulse width of 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 a first expansion pulse that expands the volume of the pressure generation chamber, and a contraction pulse that contracts the volume of the pressure generation chamber following the first expansion pulse;
The pulse width of the first 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 contraction pulse has a pulse width of 2.5 AL to 3.5 AL.

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