JP4432426B2 - Driving method of droplet discharge head - Google Patents

Description

  The present invention relates to a method for driving a droplet discharge head that discharges droplets from a nozzle, and more particularly to a method for driving a droplet discharge head capable of high-frequency driving.

  In a liquid droplet ejection head that ejects liquid droplets from a nozzle, such as an inkjet recording head for recording an image using minute ink droplets, the liquid droplets are ejected from the nozzle by applying pressure to the pressure generating chamber. Land on a recording medium such as recording paper.

  There are various means for applying pressure to the pressure generating chamber. Here, a liquid droplet discharge head in the case where the partition of the pressure generating chamber is constituted by a piezoelectric element and ink droplets are discharged from the nozzle by deforming the piezoelectric element. Will be briefly described with reference to FIGS.

  FIG. 1 is a diagram showing a schematic configuration of a shear mode (share mode) type ink jet recording head (hereinafter simply referred to as a recording head), which is an embodiment of a droplet discharge head, and FIG. FIG. 4B is a cross-sectional view showing a state in which an ink supply unit is provided. FIG. 2 is a diagram illustrating the operation, FIG. 3 is a diagram illustrating a droplet discharge operation, and FIG. 4 is a diagram illustrating a drive waveform.

  In FIG. 1, 1 is an ink tube, 2 is a nozzle forming member, 3 is a nozzle, S is a partition, 6 is a cover plate, 7 is an ink supply port, and 8 is a substrate. As shown in FIG. 2, an ink channel A that is a pressure generation chamber is formed by the partition wall S, the cover plate 6, and the substrate 8.

  FIG. 1B shows a cross-sectional view of one ink channel A having one nozzle 3, but the recording head H operating in an actual shear mode is shown in FIG. 2A. In addition, a plurality of partition walls S, that is, a plurality of ink channels A1, A2,... An separated by S1 + 1 are formed between the cover plate 6 and the substrate 8. One end of the ink channels A1, A2,... An (hereinafter sometimes referred to as nozzle end) communicates with the nozzle 3 formed on the nozzle forming member 2, and the other end (hereinafter sometimes referred to as manifold end). ) Is connected to an ink tank (not shown) by a supply port 7 and an ink tube 1 constituting an ink supply unit, and a meniscus is formed in the nozzle 3 by ink.

  Each of the partition walls S1, S2,... Is composed of partition walls Sa (S1a, S2a,...) And Sb (S1b, S2b,...) Made of two piezoelectric materials having different polarization directions as indicated by arrows in FIG. The partition wall S1 is provided with electrodes Q1 and Q2 formed in close contact, and the partition wall S2 is provided with electrodes Q3 and Q4 formed in close contact. Similarly, electrodes are formed in close contact with the partition walls, and the electrodes Q1, Q2,... Are electrically connected to a drive pulse generating circuit.

  In the state shown in FIG. 2 (a), for example, when the recording head H connects the electrodes Q1 and Q4 to the ground and applies a driving pulse consisting of the rectangular wave shown in FIG. 4 to the electrodes Q2 and Q3, first, Due to the first rise (P1) of the drive pulse, an electric field in a direction perpendicular to the polarization direction of the piezoelectric material constituting the partition walls S1 and S2 is generated, and the partition walls S1a and S1b are deformed at the joint surfaces of the partition walls, and the partition wall S2a. , S2b is similarly deformed in the opposite direction, and as shown in FIG. 2B, the partition walls S1a, S1b and the partition walls S2a, S2b are deformed outwardly to expand the volume of the ink channel A1. As a result, a negative pressure is generated in the ink in the ink channel A1, and the ink flows. At the same time, the pressure starts to increase from the manifold end and the nozzle end, and the acoustic wave is transmitted toward the center of the ink channel. Thereafter, the acoustic wave reaches the opposite end, and the inside of the ink channel becomes positive pressure.

  When the potential is returned to 0 after a predetermined time has elapsed from the application of the first drive pulse (P2), the partition walls S1 and S2 return from the enlarged position to the neutral position shown in FIG. 2A, and high pressure is applied to the ink.

  Subsequently, as shown in FIG. 2C, when the drive pulse is applied to deform the partition walls S1a, S1b and S2a, S2b in opposite directions (P3), and the volume of the ink channel A1 is reduced, the ink is reduced. A positive pressure is generated in channel A1. As a result, the meniscus in the nozzle 3 due to a part of the ink filling the ink channel A1 changes in the direction pushed out from the nozzle 3, and the ink column 100 protrudes from the nozzle 3 (see FIG. 3A).

  After maintaining this state for a predetermined time, when the potential is returned to 0 (P4) and the partition walls S1 and S2 are returned from the contracted position to the neutral position, the volume of the ink channel A1 is expanded and the meniscus is drawn and protruded. Since the rear end of the ink column 100 is pulled back, the ink column 100 separates from the meniscus and flies as a droplet 101 (see FIG. 3B).

  In this recording head H, as described above, positive and negative pressure is applied to the ink in the ink channel A by deformation of the partition wall S, and this partition wall S constitutes a pressure applying unit.

  By the way, in the above, regarding the time for reducing the volume of the ink channel A1 and maintaining the state in which the ink column 100 protrudes from the nozzle 3, it is described in Patent Document 1 that 2AL time is optimal. Has been. “AL” is ½ of the acoustic resonance period of the ink channel A1.

  Patent Document 2 also discloses that the above time is generally 2AL time.

JP 2002-137390 A JP 2003-11362 A

  In the case of the recording head H, as described above, after the volume of the ink channel A1 is reduced and the ink column 100 is protruded from the nozzle 3, the partition walls S1 and S2 are returned from the reduced position to the neutral position, thereby returning the ink channel A1. When the volume of is increased, the residual pressure wave in the ink channel A1 is canceled. Therefore, the behavior of the meniscus due to the residual pressure wave in the ink channel A1 is temporarily stopped at this point, and thereafter, the next ink droplet ejection operation can be started.

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

  However, the duration of maintaining the state in which the volume of the ink channel A1 is reduced and the ink column 100 protrudes from the nozzle 3 as described above is set to 2AL time as in the prior art, and then the residual pressure wave is canceled. Even when the droplet 101 is ejected, the operation of ejecting the subsequent droplet becomes unstable and it becomes difficult to perform high-frequency driving, particularly when ink having high viscosity and low surface tension is used. According to the knowledge of the present inventor, the volume of the ink channel A1 is reduced and the state in which the ink column 100 protrudes from the nozzle 3 is continued for 2 AL hours, and then the residual pressure wave is canceled. The meniscus in the nozzle 3 is located on the far side opposite to the droplet discharge direction from the front end surface on the droplet discharge side in the opening of the nozzle 3, and this causes instability of the next droplet discharge. It has been found that this is an obstacle to high frequency driving.

  Therefore, an object of the present invention is to provide a driving method of a droplet discharge head that enables high-frequency driving and can perform stable discharge.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

  According to the first aspect of the present invention, an opening of a nozzle for discharging droplets, a pressure generation chamber capable of storing liquid therein and communicating with the opening of the nozzle, and a volume in the pressure generation chamber are enlarged or reduced. A method of driving a droplet discharge head including a pressure applying unit that changes a pressure to be applied, the first step of expanding the volume of the pressure generating chamber by the pressure applying unit, and after the first step, The second step of reducing the volume of the pressure generating chamber by the pressure applying means and causing the liquid in the pressure generating chamber to protrude from the opening of the nozzle, and the second step of 3.5 to 4.4 AL (AL Is continued from the acoustic resonance period of the pressure generating chamber for 1/2) time, and then the volume of the pressure generating chamber is expanded by the pressure applying means, thereby protruding from the opening of the nozzle in the second step. The A third step of separating that liquid droplets, a method for driving a droplet discharge head characterized in that it comprises a.

  According to a second aspect of the present invention, in the method of driving a droplet discharge head according to the first aspect, the second step is continued for 4 AL hours.

  According to a third aspect of the present invention, the volume of the pressure generating chamber when reduced by the second step is smaller than the volume before the pressure generating chamber is expanded by the first step, and the first step 3. The volume of the pressure generating chamber when expanded by the step 3 is substantially the same as the volume before the pressure generating chamber is expanded by the first step. This is a driving method of the described droplet discharge head.

  According to a fourth aspect of the present invention, the pressure applying means is driven such that the volume in the pressure generating chamber is changed by applying a voltage, and different pressures are applied to the pressure generating chamber by applying different voltages. When the voltage applied to the pressure applying means in the first step is a (V), and the voltage applied to the pressure applying means in the third step is b (V), 4. The method of driving a droplet discharge head according to claim 1, wherein | a |> | b |.

  According to a fifth aspect of the present invention, in the method of driving a droplet discharge head according to the fourth aspect, the voltage a and the voltage b are | a | / | b | = 2.

  A sixth aspect of the present invention is the method of driving a droplet discharge head according to any one of the first to fifth aspects, wherein the pressure applying means is a piezoelectric element.

  The invention according to claim 7 is the method of driving a droplet discharge head according to claim 6, wherein the piezoelectric element is deformed in a shear mode by applying an electric field.

  The invention according to claim 8 is characterized in that the duration of the first step is 0.8 to 1.2 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber). The method for driving a droplet discharge head according to any one of 1 to 7.

  The invention according to claim 9 is characterized in that the duration of the first step is 1AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber). This is a driving method of the described droplet discharge head.

  A tenth aspect of the present invention is the method of driving a droplet discharge head according to any one of the first to ninth aspects, wherein the viscosity of the liquid is 5 cp or more and 15 cp or less.

  The invention according to claim 11 is the method of driving a droplet discharge head according to any one of claims 1 to 10, wherein the surface tension of the liquid is 20 dyne / cm or more and 30 dyne / cm or less. .

  According to a twelfth aspect of the present invention, in the method of driving a droplet discharge head according to any one of the first to eleventh aspects, the liquid is ink.

  According to a thirteenth aspect of the present invention, the drive waveform applied to the pressure applying means to change the volume in the pressure generating chamber is a rectangular wave. This is a method for driving a droplet discharge head.

  According to the present invention, high-frequency driving is possible and stable ejection can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  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 the liquid filled in the pressure generation chamber may be any liquid. A shear mode type ink jet recording shown in FIGS. 1 and 2, which is a droplet discharge head that includes pressure applying means for changing the pressure by enlarging or reducing the volume, and using ink as the liquid filled in the pressure generating chamber. This will be described using the head H.

  FIG. 5A shows an example of a drive waveform for realizing the drive method according to the present invention, and FIG. 5B shows the pressure applied to the ink in the ink channel A by the drive waveform. FIG. 6 shows a state of meniscus and droplet discharge in the nozzle by the driving method according to the present invention. The numbers in parentheses in FIGS. 5 and 6 and the following description correspond to each other in time.

  In the present specification, the “ink column” means an ink whose front end protrudes from the opening of the nozzle 3 but whose rear end is connected to the meniscus in the nozzle 3 and has not yet been separated from the meniscus. The term “droplet” refers to ink in a state where the rear end is completely separated from the meniscus in the nozzle 3.

  (1); First, the partition wall S is expanded from the neutral state of FIG. 2A as shown in FIG. 2B to expand the volume of the ink channel A (Draw), and the ink is introduced into the ink channel A. (First step). When the driving waveform does not change, the pressure in the ink channel A repeats reversal every 1 AL time. Therefore, if this duration is continued for 1 AL time, the drawn meniscus M is moved to the droplet discharge side at the opening of the nozzle 3. (Hereinafter, the droplet discharge side tip surface of the opening of the nozzle 3 is referred to as the “return position” of the meniscus M), and the ink pressure is reversed to a positive pressure. When the expanded ink channel A is returned to the original neutral state (Release), high pressure is applied to the ink in the ink channel A. The ink pressure in the nozzle 3 changes with a slight delay from the change in the drive waveform, and the change in the meniscus M further delays a little.

  Note that “AL” is ½ of the acoustic resonance period of the ink channel, as described above. The duration is defined as 10% of the start of voltage rise or fall to the start of the next step. This AL measures the speed of the ink droplet ejected by applying a rectangular wave voltage pulse to the partition wall S, and changes the duration of the rectangular wave while keeping the rectangular wave voltage value constant. It is calculated as the time when the flight speed is maximized. Further, the rectangular wave is a waveform in which both the rise time and fall time between 10% and 90% of the voltage are preferably within ½ of AL, more preferably within ¼. is there.

  (2); Subsequently, as shown in FIG. 2C, the volume of the ink channel A is reduced, a higher pressure is applied to the ink (Reinforce), and the ink column 10 protrudes from the opening of the nozzle 3 (second step). ).

  (3): When 1 AL time has elapsed, the pressure of the ink is reversed and becomes a negative pressure, so that the neck of the protruding ink column 10 is constricted as shown by an arrow in FIG.

  (4); When 0.5 AL time has passed, the negative pressure becomes maximum, the meniscus M is drawn into the deepest position in the direction opposite to the opening of the nozzle 3, and the meniscus M appears clearly.

  (5); When 0.5 AL time further elapses, the pressure is reversed to become positive pressure, and the meniscus M moves toward the return position. However, as can be seen from FIG. 6, at this time, the meniscus M is still located on the far back side opposite to the droplet discharge direction from the return position.

  (6); When a further time elapses, the meniscus M returns to the return position. The meniscus M drawn deeply into the nozzle 3 starts to move rapidly toward the return position when the capillary force of the ink and the positive ink pressure are combined. When the meniscus M returns to the return position, the ink column 10 is not yet separated from the meniscus M, and the tail portion 10 b is connected to the meniscus M.

  (7); After 4 AL hours have elapsed since the high pressure was applied to the ink in (2) above, the partition wall S is returned to the neutral position as shown in FIG. 2 (a), and the volume of the ink channel A is reduced from the previously reduced state. By enlarging and retracting the meniscus M from the opening of the nozzle 3 in the direction opposite to the liquid droplet ejection direction, the ink column 10 protruding from the opening of the nozzle 3 is separated from the meniscus M by the second step, and the liquid The droplets 11 are discharged from the nozzle 3 (third step).

  Here, a DRR (Draw-Release-Reinforce) method driving waveform (hereinafter also referred to as a DRR waveform) consisting of a rectangular wave is used, and the third step is executed after 4 AL hours have elapsed from the second step. However, the residual pressure wave in the ink channel A is canceled by enlarging the volume of the ink channel A in the third step. At this time, the meniscus M has substantially returned to the return position, so that the next drive can be started quickly, and the drive frequency can be increased. In the case where the duration time for causing the ink column to protrude is 2 AL time as in the prior art, the residual pressure wave is canceled considerably before (rear side) the meniscus M from the return position. The return to the return position is performed only by the capillary force, and is extremely slow and it is difficult to increase the drive frequency.

  Also, if the duration of the second step is set to 3AL or near 5AL, the residual pressure wave cannot be canceled and the emission becomes unstable, and if it is set to 6AL or more, the drive waveform time becomes longer and the drive frequency is increased. Can not.

  The duration of the second step is most preferably 4AL as described above, but is preferably 3.5 to 4.4AL hours.

  Here, the point of time when the ink column 10 is substantially restored refers to a state in which the position of the meniscus M after the ink column 10 protrudes is substantially located at the return position or protrudes from the opening of the nozzle 3. The term “substantially positioned” means that the distance d between the meniscus M and the return position is 1/2 or less, preferably 1/4 or less of the nozzle radius, as shown in FIG. Rather than projecting from the opening of the nozzle 3, it is preferable to be positioned substantially at the return position in that the drive frequency can be further increased. The opening shape of the nozzle 3 is not limited to a perfect circle but may be an ellipse or the like. That is.

  In such driving, the volume of the ink channel A when reduced by the second step is smaller than the volume before the ink channel A is enlarged by the first step, and is enlarged by the third step. The volume of the ink channel A at this time is substantially the same as the volume before the ink channel A is expanded by the first step. The driving waveform for driving in this way can be a simple waveform as shown in FIG. Moreover, in the final third step, the partition wall S returns to the initial state, and at this time, the residual pressure wave in the ink channel A is canceled, so the residual pressure wave to the meniscus M after substantially returning to the return position. There is no influence of this, and high-speed driving is possible.

  Further, as shown in the drive waveform of FIG. 5A, the voltage a (V) applied to the ink channel A in the first step and the voltage b (V) applied to the ink channel A in the third step. Is a relationship of | a |> | b |, the meniscus M is quickly restored, which is more preferable for high-speed driving. Moreover, it is preferable at the point of discharge stability. The reference voltage of the voltage a and the voltage b is not always 0. The voltage a and the voltage b are differential voltages.

  The voltage a and voltage b are more preferably | a | / | b | = 2, which makes it possible to achieve both high-speed driving and ejection stability.

  If the duration of the first step is 1AL as in the present embodiment, the negative pressure wave due to the volume expansion of the pressure generation chamber applied in the first step is inverted at 1AL, and becomes a positive pressure wave. In this case, since the positive pressure wave due to the volume reduction in the second step is added in a combined form, the ink discharge pressure is most preferably increased. However, the duration of the first step is 0.8-1. 2 AL hours are preferred.

  By the way, the capillary penetration speed of the ink is expressed as {2 · (capillary radius) · (surface tension) · cos (contact angle)} / {8 · (viscosity) · (tube length)}. Largely affected by tension. For example, when an ink having a surface tension of 40 dyne / cm and a viscosity of 2 cp is compared with an ink having a surface tension of 28 dyne / cm and a viscosity of 10 cp, with the same capillary radius and the same tube length, the latter ink has a capillary penetration rate 1 / It will drop to 10.

  Accordingly, the return timing of the meniscus M to the return position differs depending on the difference in ink viscosity, and the return of the meniscus M is delayed in the case of ink having a high viscosity, whereas the return of the meniscus M is accelerated in the case of ink having a low viscosity. Similarly, the return timing of the meniscus M to the return position differs depending on the difference in the surface tension of the ink, so that the return of the meniscus M is delayed with an ink with a low surface tension, and conversely with an ink with a high surface tension. The return of M is faster.

  As described above, when the return timing of the meniscus M to the return position varies depending on the difference in ink viscosity and surface tension, the meniscus M is not changed even if the second step is continued for 4 AL hours and then the third step is performed. Is assumed to have not yet substantially returned to the return position. However, since the meniscus M returns to the vicinity of the return position after being continued for 4 AL hours, it is located on the far side opposite to the droplet discharge direction from the return position as in the case of 2AL of the prior art. High frequency driving is possible compared to the state.

  The driving method of the present invention exhibits a remarkable effect when the viscosity of the ink is 5 cp or more and 15 cp or less. This is because such an ink has a high viscosity and is less likely to be disturbed by the residual pressure during the meniscus recovery process, and the droplets are difficult to separate from the meniscus.

 Ink with such a high viscosity has a slow return speed of the meniscus M to the return position, so in the 2AL of the prior art, the residual pressure wave is canceled far behind the droplet discharge direction than the return position. Therefore, the drive frequency is not increased at all, and setting 3.5 to 4.4 AL according to the present invention is canceled when returning to the vicinity of the return position, so that a more remarkable effect is exhibited.

  In addition, the driving method of the present invention exhibits a remarkable effect even when the surface tension of the ink is 20 dyne / cm or more and 30 dyne / cm or less. This is because such an ink has a low surface tension, and similarly, it is difficult for the droplets to be separated from the meniscus.

 Further, such ink with low surface tension has a slow return speed of the meniscus M to the return position, so in the conventional 2AL, a residual pressure wave is generated on the far side opposite to the droplet discharge direction rather than the return position. Since it is canceled, the drive frequency is not raised at all, and setting 3.5 to 4.4 AL of the present invention is canceled when returning to the vicinity of the return position, so that a more remarkable effect is exhibited.

  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 timing of lowering the pressure in the pressure generating chamber can be easily controlled when the pressure applying means is constituted by a piezoelectric element.

  In the above embodiment, a rectangular driving waveform is applied to the piezoelectric element. By using the rectangular wave, it becomes easy to set the timing when starting the third process at the timing when the meniscus M returns to the return position, and a strong negative pressure is generated by the third process, so that the droplets can be easily formed. It is preferable because it can be separated.

  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 the rectangular waveform driving waveform shown in FIG. 6A can be used more effectively, the driving voltage is lowered, and more efficient driving is possible. 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 inkjet recording head for performing image recording is used as the droplet discharge head. However, the present invention is not limited to this, and the nozzle opening for discharging droplets communicates with the nozzle opening. The invention can be similarly applied as long as it includes a pressure generating chamber and a pressure applying means for changing the pressure in the pressure generating chamber.

(Examples 1-3)
Using a recording head in a shear mode with a nozzle pitch of 180 dpi and an output droplet amount of 14 pl, the DRR waveform has a Draw to Reinforce voltage ratio (| a | / | b |) of 2/1 and Draw (first step ) Was set to 1 AL, and the drive was performed by changing the duration (R time) of Reinforce (second step) as shown in Table 1 to discharge droplets. The position of the meniscus at that time, the ejection stability of the droplet, and the high-speed driving performance were observed.

  Meniscus position measurement: The position of the meniscus in the nozzle was estimated by observing the movement of the meniscus pushed out from the nozzle opening immediately after droplet discharge by strobe measurement using a CCD camera, and confirmed by simulation.

Ink used: Oil-based ink (10 cp, 28 dyne / cm)
Drive voltage: 20V
AL = 4.5μs

The emission stability was evaluated according to the following criteria.
(Double-circle): It ejected stably to droplet speed 10m / s.
○: The liquid was stably emitted up to a droplet speed of 8 m / s.
(Triangle | delta): Although there was some fluctuation | variation of the droplet velocity at the droplet velocity of 8 m / s, it ejected | emitted without generating an ejection | missing defect.
×: Unstable and lack of emission.

Moreover, the high-speed drivability was evaluated according to the following criteria.
○: Stable light is emitted at a driving cycle of 30 μs.
Δ: Slightly unstable emission, but no emission failure occurs.
X: Outgoing light is unstable and shortage occurs.

(Comparative Examples 1-4)
Example 2 was the same as Examples 1 to 3 except that the duration (R time) of the second step was as shown in Table 1.

  The results of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1.

  If the duration of the second step is short and the meniscus is canceled when the meniscus is close to the return position, the subsequent meniscus return is quicker, so that high frequency driving can be handled.

  In Comparative Example 1, even if high frequency driving is performed, ink filling is not in time, and emission is unstable.

  In Comparative Examples 2 and 3, the meniscus returns, but the cancellation timing does not correspond to the residual pressure wave, and there is a problem in the stability of emission.

  Furthermore, in Comparative Example 4, although the emission is stable, the duration (R time) of the second process is too long, and the entire driving cycle becomes long, so that high frequency driving is not supported.

  In Example 2, the residual pressure wave was effectively canceled and more stable emission was obtained.

  From the above, it was found that 4AL is a more preferable condition for the duration time (R time) of the second step.

(Examples 4 to 7)
In Example 2, the drop ejection stability and the high-speed driving performance when the voltage ratio (| a | / | b |) of Draw and Reinforce was changed as shown in Table 2 were evaluated.

The emission stability was evaluated according to the following criteria.
(Double-circle): It radiate | emits stably to droplet speed 10m / s.
○: Stable emission up to a droplet velocity of 8 m / s.
Δ: When ejecting at a droplet velocity of 8 m / s, there is some fluctuation of the droplet velocity, but the droplet is ejected without generating ejection failure.

Moreover, the high-speed drivability was evaluated according to the following criteria.
○: Stable light is emitted at a driving cycle of 30 μs.
Δ: Slightly unstable emission, but no emission failure occurs.
X: Outgoing light is unstable and shortage occurs.

  The results are shown in Table 2.

  In Example 6, the residual pressure wave was canceled more effectively, and more stable emission was obtained even when the droplet velocity was slow.

  In Example 4, meniscus recovery was slow, ink filling was not in time when driving at high frequency, and unstable emission was observed.

  From the above results, it was found that | a | / | b | = 2/1 is a preferable condition for obtaining more stable and high-speed emission.

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. Sectional view (A)-(b) is a figure which shows the operation | movement of a recording head. (A) (b) is explanatory drawing which shows the mode of the droplet discharge by the conventional drive method The figure which shows the drive waveform in the conventional drive method (A) is a figure which shows the drive waveform for implement | achieving the drive method which concerns on this invention, (b) is a figure which shows the pressure provided to the ink in an ink channel by a drive waveform. The figure which shows the mode of the meniscus and droplet discharge in the nozzle by the drive method which concerns on this invention The figure explaining the positional relationship between the nozzle opening and the meniscus

Explanation of symbols

1: Ink tube 2: Nozzle forming member 3: Nozzle 6: Cover plate 7: Ink supply port 8: Substrate 10, 101: Ink column 10a, 101a: Main droplet 10b, 101b: Tail 101c: Secondary droplet 200: Recording medium H: recording head A, A1,...: Ink channel S, S1,...: Partition wall (electrical / mechanical conversion means)
Q, Q1, ...: Electrode M: Ink meniscus

Claims (13)

A nozzle opening for discharging droplets, a pressure generating chamber capable of storing liquid therein and communicating with the nozzle opening, and a pressure applying means for changing a pressure for expanding or reducing a volume in the pressure generating chamber A method for driving a droplet discharge head comprising:
A first step of expanding the volume of the pressure generating chamber by the pressure applying means;
After the first step, a second step of reducing the volume of the pressure generating chamber by the pressure applying means and causing the liquid in the pressure generating chamber to protrude from the opening of the nozzle;
After the second step is continued for 3.5 to 4.4 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber) time, the volume of the pressure generating chamber is expanded by the pressure applying means. A third step of separating the liquid protruding from the opening of the nozzle in the second step as a droplet;
A method for driving a droplet discharge head, comprising:   2. The method of driving a droplet discharge head according to claim 1, wherein the second step is continued for 4 AL hours.   The volume of the pressure generating chamber when reduced by the second step is smaller than the volume before the pressure generating chamber is expanded by the first step, and when the volume is expanded by the third step. 3. The droplet discharge head drive according to claim 1, wherein the volume of the pressure generating chamber is substantially the same as a volume before the pressure generating chamber is expanded by the first step. Method.   The pressure applying means is configured to change the volume in the pressure generating chamber by applying a voltage, and is configured to be able to apply different pressures to the pressure generating chamber by applying different voltages. When the voltage applied to the pressure applying means in the first step is a (V) and the voltage applied to the pressure applying means in the third step is b (V), | a |> | b | 4. The method of driving a droplet discharge head according to claim 1, 2, or 3.   5. The method of driving a droplet discharge head according to claim 4, wherein the voltage a and the voltage b are | a | / | b | = 2.   6. The method of driving a droplet discharge head according to claim 1, wherein the pressure applying unit is a piezoelectric element.   The method of driving a droplet discharge head according to claim 6, wherein the piezoelectric element is deformed in a shear mode by applying an electric field.   The duration of the first step is 0.8 to 1.2 AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber). A method for driving a droplet discharge head.   8. The liquid droplet ejection head drive according to claim 1, wherein the duration of the first step is 1AL (AL is 1/2 of the acoustic resonance period of the pressure generating chamber). Method.   The method of driving a droplet discharge head according to claim 1, wherein the liquid has a viscosity of 5 cp to 15 cp.   The method for driving a droplet discharge head according to claim 1, wherein the liquid has a surface tension of 20 dyne / cm or more and 30 dyne / cm or less.   The method of driving a droplet discharge head according to claim 1, wherein the liquid is ink.   The driving method of the droplet discharge head according to claim 1, wherein a driving waveform applied to the pressure applying unit in order to change the volume in the pressure generating chamber is a rectangular wave.

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