JP2005119296A - Droplet discharging method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discharge minute ink droplets at a sufficient flight speed even in the case of an ink liquid with high viscosity. <P>SOLUTION: In the droplet discharging method for discharging a liquid inside a pressure chamber as a droplet from a nozzle, by applying a drive waveform to an actuator for causing change in volume of the pressure chamber filled with the liquid, the volume of the pressure chamber is represented by V, the cross-sectional surface area of the nozzle is represented by A, the length of the nozzle is represented by 1<SB>o</SB>, the density of the liquid to be discharged is represented by ρ, the viscosity coefficient of the liquid to be discharged is represented by μ and the rate of transmission of a pressure wave transmitted through the liquid inside the pressure chamber is represented by c. These factors are set to satisfy the condition expressed by an inequality expression (1), c<SP>2</SP>/V<16π<SP>2</SP>μ<SP>2</SP>1<SB>o</SB>/(A<SP>3</SP>ρ<SP>2</SP>). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a droplet discharge method and apparatus, and more particularly, to a droplet discharge method and apparatus capable of discharging a liquid such as highly viscous ink as a fine droplet at a sufficient speed by an inkjet method.

  An ink jet type droplet discharge device records an image or the like by discharging a liquid such as ink as a droplet from a nozzle formed on a recording head toward a recording medium. There are various ink ejection methods in the ink jet ink droplet ejection device. For example, the volume of the pressure chamber is changed by deformation of piezoelectric ceramics, and ink is introduced from the ink supply path into the pressure chamber when the volume increases. In addition, there is known one that ejects ink in a pressure chamber as droplets from a nozzle when the volume of the pressure chamber decreases.

  In such an ink droplet discharge device, in order to increase the recording resolution, it is necessary to discharge a small volume of ink droplets, and various contrivances have been made for that purpose. For example, by applying a drive waveform for ejecting ink to an actuator that changes the volume of the pressure chamber, and subsequently applying an additional drive waveform, a part of the ink droplets that are ejected from the nozzle are removed from the nozzle. It is known that the ink droplets are torn off by pulling them back into the pressure chamber, and the flying ink droplets are miniaturized (see, for example, Patent Document 1).

Further, as described above, after applying a drive waveform for ejecting ink to an actuator that changes the volume of the pressure chamber, and subsequently applying an additional drive waveform for miniaturizing ink droplets, an ink is further added. A driving waveform for stabilizing the vibration state of the meniscus surface is applied so as to prevent a drop speed of ink ejected thereafter from decreasing (for example, patents). Reference 2 etc.).
JP-A-11-170515 JP 11-227203 A

  However, all of the above-described patent documents are based on the premise that the ink in the pressure chamber naturally vibrates (natural vibration) at a certain cycle. Ink droplets are ejected in a reduced size using vibration, and the one described in Patent Document 2 uses the natural vibration to cause the ink droplets at a high temperature and a low viscosity as described above. Since the ink meniscus surface is stabilized by the stabilization waveform (pulse) applied from the nozzle, both assume the natural vibration of the meniscus surface, and the ejection timing is controlled by the drive waveform using the natural vibration. In designing the drive waveform, there are time restrictions and period restrictions, and improvement has been desired.

  Generally, when the viscosity of a liquid increases, the resistance force proportional to the flow rate of the liquid increases. Accordingly, when a droplet is ejected under the same actuator driving conditions as a low-viscosity liquid even in the case of a high-viscosity ink using the conventional ink droplet ejection device as described above, The speed is reduced. Also, when the viscosity of the ink is high, the refilling of the ink after ejecting the ink droplets is delayed, and as a result, the time until the ink returns to the initial state after ejecting the ink becomes longer, so the recording (printing) speed There is a problem that decreases.

  The present invention has been made in view of such circumstances, and in the case of a high-viscosity liquid, a droplet ejection method capable of efficiently ejecting a minute droplet having a sufficient flight speed and An object is to provide an apparatus.

In order to achieve the above object, according to the first aspect of the present invention, by applying a drive waveform to an actuator for changing the volume of the pressure chamber filled with the liquid, the liquid in the pressure chamber is made a droplet from the nozzle. A droplet discharge method for discharging, wherein the volume of the pressure chamber is V, the cross-sectional area of the nozzle is A, the length of the nozzle is l ₀ , the density of the liquid to be discharged is ρ, and the viscosity coefficient of the liquid to be discharged is When the transmission speed of μ and the pressure wave transmitted through the liquid in the pressure chamber is c, these are the following inequality (1)
c ² / V <16π ² μ ² l ₀ / (A ³ ρ ² ) (1)
The droplet discharge method is characterized in that it is set so as to satisfy the condition represented by

In order to satisfy this condition, for example, the geometrical conditions A, l _{0 of} the head satisfy this equation (1) with respect to the physical property values ρ, μ, c of the liquid to be discharged. To design. By satisfying this condition, the liquid meniscus surface does not vibrate, and when applying the drive waveform, the natural vibration of the meniscus surface does not hinder, and there are no time restrictions and period restrictions. It is not necessary to consider the time for applying the drive waveform, and the drive can be performed efficiently. In particular, the present invention is particularly effective when a liquid having a liquid viscosity coefficient μ of 30 mPa · sec (30 CP) or more is ejected.

  In the droplet discharge method of the present invention, the drive waveform includes a first drive waveform for drawing the meniscus surface of the liquid of the nozzle, and a liquid column for discharging the liquid as a droplet from the nozzle. A second drive waveform for tearing off the liquid column, a third drive waveform for forming microdroplets, and a fourth for returning the meniscus surface to the initial state after the liquid column is torn off. It is characterized by having the following drive waveform.

  By forming the drive waveform in this manner, even when the liquid has a high viscosity, the liquid can be discharged as a fine droplet at a sufficient speed, and the post-discharge meniscus surface can be stabilized at an early stage.

In the droplet discharge method of the present invention, when the drive waveform has the first drive waveform, the time t from the start of the first drive waveform to the start of the second drive waveform is t. _2, wherein the absolute value of the displacement volume velocity of the first of the meniscus surface from the start of the drive waveform is greater than the time t _a up to a maximum. Further, the time t _a, the compliance of the pressure chamber C, and the inertance of the liquid channel L, and the liquid viscosity resistance in the nozzle portion and R, β = R / (2L ), γ = √ {R 2 / When (4L ² ) −1 / (LC)}, the following formula (2)
t _a = {1 / (2γ)} log {(β + γ) / (β−γ)} (2)
It is preferable to be represented by

  As a result, the drive waveform for droplet ejection is started where the acceleration of the change in the meniscus surface of the liquid is in the direction of ejection, so that efficient droplet ejection is possible.

  Further, in the droplet discharge method of the present invention, the displacement volume velocity of the liquid on the meniscus surface by the third drive waveform is an absolute value than the displacement volume velocity of the liquid on the meniscus surface by the second drive waveform. It is preferable that it is small. Furthermore, it is preferable that the displacement volume velocity of the liquid on the meniscus surface by the fourth driving waveform is larger in absolute value than the displacement volume velocity of the liquid on the meniscus surface by the third driving waveform.

  This makes it possible to discharge fine droplets with a certain droplet velocity in a high-viscosity liquid and to quickly return the meniscus surface after discharge to the initial state, thereby increasing the recording speed. Is possible.

In order to achieve the above object, the invention according to claim 7 includes a pressure chamber filled with a liquid, a nozzle for discharging the liquid provided in the pressure chamber as droplets, and a volume of the pressure chamber. A droplet discharge device comprising: an actuator to be changed; and an actuator driving means for applying a drive waveform to the actuator to change the volume of the pressure chamber to discharge a droplet from the nozzle. The volume of V, the cross-sectional area of the nozzle A, the length of the nozzle l ₀ , the density of the liquid to be ejected ρ, the viscosity coefficient of the liquid to be ejected μ, and the pressure wave transmitted through the liquid in the pressure chamber When the transmission speed is c, these are the following inequalities (1)
c ² / V <16π ² μ ² l ₀ / (A ³ ρ ² ) (1)
The droplet discharge device is characterized in that it is set so as to satisfy the condition represented by:

In order to satisfy this condition, for example, the geometrical conditions A, l _{0 of} the head satisfy this equation (1) with respect to the physical property values ρ, μ, c of the liquid to be discharged. To design. By satisfying this condition, the liquid meniscus surface does not vibrate, and the natural vibration of the meniscus surface does not hinder the application of the drive waveform, so it is necessary to consider the time for applying the drive waveform. And can be driven efficiently.

  In the droplet discharge device of the present invention, the drive waveform includes a first drive waveform for drawing the meniscus surface of the liquid of the nozzle, and a liquid column for discharging the liquid from the nozzle as droplets. A second driving waveform for tearing off the liquid column, a third driving waveform for forming micro droplets, and a fourth for returning the meniscus surface to the initial state after the liquid column is torn off. It is characterized by having the following drive waveform.

  By forming the drive waveform in this manner, even when the liquid has a high viscosity, the liquid can be discharged as a fine droplet at a sufficient speed, and the post-discharge meniscus surface can be stabilized at an early stage.

In the droplet discharge device of the present invention, when the drive waveform has the first drive waveform, the time t from the start of the first drive waveform to the start of the second drive waveform is t. _2, wherein the absolute value of the displacement volume velocity of the liquid in the meniscus surface from the start of the first driving waveform is greater than the time t _a up to a maximum. Further, the time t _a, the compliance of the pressure chamber C, and the inertance of the liquid channel L, and the liquid viscosity resistance in the nozzle portion and R, β = R / (2L ), γ = √ {R 2 / When (4L ² ) −1 / (LC)}, the following formula (2)
t _a = {1 / (2γ)} log {(β + γ) / (β−γ)} (2)
It is preferable to be represented by

  As a result, since the drive waveform for droplet ejection is started where the acceleration of the change in the meniscus surface of the liquid is in the ejection direction, efficient droplet ejection is possible.

  In the droplet discharge device of the present invention, the displacement volume velocity of the liquid on the meniscus surface by the third drive waveform is an absolute value than the displacement volume velocity of the liquid on the meniscus surface by the second drive waveform. Is preferably small. Furthermore, it is preferable that the displacement volume velocity of the liquid on the meniscus surface by the fourth driving waveform is larger in absolute value than the displacement volume velocity of the liquid on the meniscus surface by the third driving waveform.

  As described above, in the droplet discharge method and apparatus according to the present invention, even in the case of a high-viscosity liquid, the meniscus surface is set to a system that does not vibrate naturally due to the geometric conditions of the head. As a result, the degree of freedom in designing the drive waveform is widened, and it is possible to efficiently eject minute droplets having a sufficient flight speed.

  Hereinafter, a droplet discharge method and apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view of an essential part showing an outline of an embodiment of a droplet discharge apparatus according to the present invention. As shown in FIG. 1, a droplet discharge device 10 of this embodiment includes a pressure chamber 12 that stores a liquid to be discharged, and a nozzle that discharges the liquid provided at one end of the pressure chamber 12 as a droplet. 14, an actuator 16 for changing the volume of the pressure chamber 12 provided on the wall surface of the pressure chamber 12, an actuator driving means 18 for applying a driving waveform to the actuator 16 according to an image signal, and a liquid tank (not shown) And a liquid supply path 20 for supplying liquid from the liquid tank to the pressure chamber 12.

  As shown in FIG. 1, in the present embodiment, the actuator 16 as a means for generating a liquid discharge pressure for changing the volume of the pressure chamber 12 to discharge the liquid from the nozzle 14 as a droplet is the pressure chamber 12. However, the actuator 16 is not limited to such a piezoelectric element. For example, the actuator 16 is opposed to the nozzle 14. Alternatively, a piezoelectric element may be provided at the other end of the pressure chamber 12 and the volume of the pressure chamber 12 may be changed by deformation of the piezoelectric element so that the liquid is discharged from the nozzle 14 as a droplet.

  The actuator driving means 18 applies a predetermined driving waveform to the actuator 16 based on the input image signal, and moves the movable portion of the actuator 16 to move the volume of the pressure chamber 12 as will be described in detail later. The liquid is discharged from the nozzle 14 as droplets.

  Note that the liquid used in the present embodiment is a highly viscous liquid. The high-viscosity liquid does not vibrate the meniscus surface and does not have a so-called natural period, and is specifically defined by the conditions described below.

  The liquid droplet ejection apparatus according to the present embodiment ejects the liquid as fine liquid droplets at a sufficient ejection speed under the condition that the viscosity of the liquid is high and the meniscus surface does not naturally vibrate. Next, conditions for preventing the meniscus surface from vibrating will be described.

FIG. 2A is simplified to simplify the description of the pressure chamber 12 and the nozzle 14 described above, and each is represented by a cylinder. As shown in FIG. 2A, the length of the pressure chamber 12 is l ₁ , the bottom area of the pressure chamber 12 is S, the length of the nozzle 14 is l ₀ , and the bottom area of the nozzle 14 is A. Then, the volume of the pressure chamber 12 becomes V = Sl ₁ .

  Further, the compliance of the pressure chamber 12 is C, the inertance of the liquid flow path is L, the resistance due to the viscosity of the liquid at the nozzle portion is R, the density of the liquid to be discharged is ρ, the viscosity coefficient of the liquid to be discharged is μ, and the pressure chamber Let c be the transmission speed of the pressure wave that transmits. When these are used, the compliance C of the pressure chamber 12, the inertance L of the liquid flow path, and the resistance R due to the viscosity of the liquid at the nozzle portion are respectively expressed as follows.

That is,
C = Sl ₁ / ρc ² = V / ρc ² , L = ρl ₀ / A, R = 8πμl ₀ / A ² .

  Here, in order to consider the condition that the meniscus surface does not vibrate, a lumped constant model using an LCR series circuit as shown in FIG. At this time, if the current flowing through the LCR series circuit of FIG. 2B is I, the following equation of damped oscillation is obtained.

L (d ² I / dt ² ) + R (dI / dt) + (1 / C) I = 0
As is well known, the vibration period T is expressed by the following equation.

T = 4πL / √ (4L / C−R ² )
Considering this as the period of vibration of the meniscus surface of the ink, the condition that the meniscus surface does not vibrate is that T does not exist as a real number, that is, 4L / C−R ² <0.

Substituting the values shown above, C = V / ρc ² , L = ρl ₀ / A, and R = 8πμl ₀ / A ² , the following inequality (1) is obtained.

c ² / V <16π ² μ ² l ₀ / (A ³ ρ ² ) (1)
This inequality (1) is a condition for preventing the liquid meniscus surface from vibrating at all. When the formula (1) is established, as shown in FIG. 3A, the relationship between the position x of the meniscus surface and the time t, the liquid meniscus surface is simply damped without any vibration. Accordingly, at this time, the meniscus surface does not vibrate even when a stimulus is applied.

On the other hand, the following inequality (1) ′
c ² / V> 16π ² μ ² l ₀ / (A ³ ρ ² ) (1) ′
Is established, the liquid meniscus vibrates as shown in FIG. 3B, which shows the relationship between the position x of the meniscus surface and time t.

  In addition, the equation of the damped oscillation obtained by the model of the lumped constant method is solved under the above conditions, where v is the displacement volume velocity of the liquid on the meniscus surface.

That is,
L (d ² v / dt ² ) + R (dv / dt) + (1 / C) v = 0
The initial conditions are solved as v = 0 and dv / dt = −1 when t = 0.

At this time, if β = R / (2L) and γ = √ {R ² / (4L ² ) −1 / (LC)}, then v = ½exp {− (β + γ) t} −1 / 2exp {-(Β-γ) t}.

The solution v is shown as a graph in FIG. In FIG. 4A, when the value t _a of the maximum value of the displacement volume velocity v of the meniscus surface is obtained, the following equation (2) is obtained.
t _a = {1 / (2γ)} log {(β + γ) / (β−γ)} (2) Here, as a matter of course, the logarithm log is a natural logarithm. Further, when the inflection point in the graph of FIG. 4A, that is, the value t _b of the point where the rate of change (acceleration) of the displacement volume velocity of the liquid at the meniscus surface changes from increase to decrease,
t _b = {1 / (2γ)} log {(β + γ) ² / (β−γ) ² }.

  FIG. 4B shows the meniscus surface displacement x (= の vdt). As shown in FIG. 4B, the displacement x of the meniscus surface moves toward an equilibrium state without vibration as time t passes.

  The present embodiment is configured as described above, and discharges a high-viscosity liquid as a fine droplet at a sufficient discharge speed under the condition that the meniscus surface does not vibrate, represented by the inequality (1). It is. Hereinafter, a driving waveform applied to the actuator 16 by the actuator driving means 18 for such ejection will be described.

  FIG. 5 shows a comparison between the driving waveform applied to the actuator 16 and the displacement volume velocity v of the liquid on the meniscus surface. As shown in FIG. 5, the drive waveform in the present embodiment is composed of four drive waveforms: a first drive waveform W1, a second drive waveform W2, a third drive waveform W3, and a fourth drive waveform W4. , Holding units U1 and U2 for holding drive voltages, respectively, between the first drive waveform W1 and the second drive waveform W2 and between the second drive waveform W2 and the third drive waveform W3. Yes.

  The first drive waveform W1 is for sucking the liquid so as to draw the liquid meniscus surface of the nozzle 14 inward. The second drive waveform W2 is for applying a pressure to the liquid in the pressure chamber 12 to push out the liquid from the nozzle 14 in order to create a liquid column in order to discharge the liquid from the nozzle 14 as a droplet. . The third drive waveform W3 is for tearing the liquid column formed by being pushed out from the nozzle 14 to create a minute droplet. The fourth drive waveform W4 is for quickly returning the meniscus surface to the initial state after tearing.

  Hereinafter, the droplet discharge operation by the actuator driving means 18 by driving the actuator 16 using the driving waveform will be described.

The actuator 16 is first applied with the first drive waveform W1 from t = 0 to t = t ₁ . The first drive waveform W1 changes linearly from the reference voltage E ₀ to the voltage E ₁ at t = 0, and at this time, the displacement volume velocity v shown below is a constant value v ₁ . .

  In the graph of the upper drive waveform, the downward direction (the voltage decreasing side) sucks the liquid in the nozzle 14 toward the pressure chamber 12 side, and the upward direction (the voltage increasing side) conversely draws the liquid in the pressure chamber 12 from the nozzle 14. It means working like an extrusion. The graph of this drive waveform shows the change in the voltage applied to the actuator 16, but the voltage change corresponds to the change in the liquid level, and this graph shows the displacement of the liquid level at the same time. You may think that it shows.

Next, the driving voltage is kept constant (voltage E ₁ ) from time t ₁ to t ₂ (holding unit U1), and the second driving waveform W2 is applied from time t ₂ . At this time, between t _{1 and} t ₂ where the driving voltage is kept constant, the displacement volume velocity is zero because there is no displacement of the volume of the liquid.

In the example shown in FIG. 5, the first drive waveform W1 is first applied, but it is not always necessary to apply the first drive waveform W1. Without application of the first driving waveform W1, it may be suddenly applying a second driving waveform W2 from a predetermined time t _2.

From time t ₂ to time t ₃ , the second drive waveform W2 is applied, and the voltage is increased greatly linearly from E ₁ to E ₂ . As a result, the displacement volume velocity takes a large value of v ₂ , the liquid level of the liquid changes greatly, and the liquid is pushed out from the nozzle 14 to form a liquid column.

Then, a short time from time t ₃ to time t _4, keeps the voltage constant (holding unit U2). At this time, the displacement volume velocity is also zero. Then the third drive waveform W3 is applied from time t ₄ to time t _5, lowering the voltage. At this time, the displacement volume velocity is taking a negative constant value of v _3. By this third drive waveform W3, the liquid is pulled back, the liquid column is torn off, and a droplet is formed, which flies toward the recording medium.

Continuing Finally, applying a fourth driving waveform W4 from time t ₅ to t _6. The fourth drive waveform W4 decreases the voltage from E ₃ to the reference voltage E ₀ . At this time, the displacement volume velocity is negative and has a large absolute value. As a result, the liquid is further pulled back, and the liquid surface is quickly stabilized after the liquid column is torn and droplets are formed and discharged.

In the droplet discharge device 10 of the present embodiment, the actuator 16 is driven by such a drive waveform by the actuator driving means 18, and a highly viscous liquid is discharged as a fine droplet at a sufficient speed. Here, as described above, the first drive waveform W1 may not be applied. However, when the first drive waveform W1 is applied, the first drive waveform W1 is applied after the first drive waveform W1 is applied. The time t ₂ until the second drive waveform W2 is started is preferably determined as follows.

That is, as shown in FIG. 4 (a), the displacement velocity v of the liquid surface of the liquid, 0 <t <and decreased in the range of t _a, while the acceleration is negative, the t> t _a The displacement speed v starts to increase and the acceleration is positive. In addition, it is considered more efficient to apply a pressing force when the liquid surface displacement acceleration is positive to discharge the liquid as droplets.

Under the condition that the surface of the liquid at a high viscosity does not vibrate, the time t ₂ to start the application of the second drive waveform W2 for discharging the liquid as droplets, by a t _2> t _a As shown in the relationship between the meniscus surface velocity v and time t in FIG. 6A, the acceleration of the meniscus surface position is positive. Therefore, it is considered that the liquid can be efficiently discharged as droplets. As previously calculated, since a _{t a = {1 / (2γ} )} log {(β + γ) / (β-γ)}, the condition that t _2> t _a, the table with the following inequality (3) Is done.

t ₂ > {1 / (2γ)} log {(β + γ) / (β−γ)} (3)
On the other hand, in the case of t ₂ <t _a, as shown the relationship between the meniscus surface velocity v and the time t in FIG. 6 (b), the discharge of the efficient droplet for acceleration of the surface position of the meniscus is negative It becomes difficult.

Further, among these, it is considered most preferable that the acceleration of the displacement of the liquid surface of the liquid is maximum. As can be seen from the graph of FIG. 4A, in this case, the acceleration becomes maximum at the inflection point t _b . Therefore, it is more preferable that the time t ₂ from immediately after the liquid starts to be sucked until the liquid starts to be pushed out is the position t _{b of the} inflection point at which the acceleration of the displacement of the liquid surface is maximum.

That is, as previously calculated, t _b = {1 / (2γ)} log {(β + γ) ² / (β−γ) ² }, so t ₂ is set to a time determined by the following equation. Is most preferred.

t ₂ = {1 / (2γ)} log {(β + γ) ² / (β−γ) ² }
Alternatively, a time t ₂ -t ₁ from immediately after application of the first drive waveform W1 to application of the second drive waveform W2 is an inflection point at which this acceleration is maximum as shown in the following equation. it may be set to t _b.

t ₂ −t ₁ = {1 / (2γ)} log {(β + γ) ² / (β−γ) ² }
Thus, it is preferable to push out the liquid at a time later than the point t _{a at} which the displacement speed of the liquid volume becomes maximum, and further corresponds to the inflection point t _b of the displacement speed at which the displacement acceleration of the liquid volume becomes maximum. More preferably, the liquid is extruded in time.

In order to tear the liquid column formed by the application of the second drive waveform W2 next and fly as a microdroplet at a sufficient speed, the third drive waveform W3 is a graph shown in FIG. Is preferably set to be smaller in absolute value than the slope of the second drive waveform W2. That is, in the graph of the displacement volume velocity at the bottom of FIG. 5, the displacement volume velocity v ₃ corresponding to the third drive waveform W3 is less than the displacement volume velocity v ₂ corresponding to the second drive waveform W2. As shown in inequality (4), the absolute value is made small.

| V ₂ |> | v ₃ | (4)
This is because if | v ₃ | is made larger than | v ₂ |, in the case of a high-viscosity liquid, the force for pulling back the droplets that are separated from the liquid column and are about to be discharged becomes larger. This is because the flying speed of the droplets to be discharged is reduced.

  Accordingly, this makes it possible to discharge micro droplets having a certain droplet velocity in a highly viscous liquid.

Further, the relationship between the third drive waveform W3 and the fourth drive waveform W4 is such that the slope of the graph of FIG. 5 is the absolute value of the slope of the fourth drive waveform W4 than the slope of the third drive waveform W3. It is preferable to set so as to be large. That is, in the graph of the displacement volume velocity in the lower part of FIG. 5, the displacement volume velocity v ₄ corresponding to the fourth drive waveform W4 is the next to the displacement volume velocity v ₃ corresponding to the third drive waveform W3. As shown in inequality (5), the larger absolute value is preferable.

| V ₄ |> | v ₃ | (5)
As a result, it is possible to stabilize the meniscus surface of the liquid after tearing off the liquid column and ejecting the liquid as droplets, and to return to the initial state. At this time, in the case of a conventional low-viscosity liquid, the liquid surface of the liquid vibrates, so if you try to hold it down and stabilize it, it may vibrate in reverse and not stabilize. Therefore, it is necessary to determine the time for pressing the liquid in consideration of the natural vibration of the liquid surface. However, in this case, since the liquid does not vibrate with high viscosity, it is preferable to press the liquid as soon as possible.

  That is, the time between the third drive waveform W3 and the fourth drive waveform W4 should be as short as possible. As described above, according to the present embodiment, since a high-viscosity liquid is used and the condition that the liquid level of the liquid does not vibrate is set, as described above, there is no restriction on time and it is necessary to consider time. Therefore, the liquid level of the liquid can be quickly stabilized by applying the fourth drive waveform W4 that immediately suppresses the liquid. As a result, the next printing can be performed immediately and the printing speed can be increased.

In addition, the time t ₄ -t ₃ of the holding unit U2 that holds the voltage between the second drive waveform W2 and the third drive waveform W3 is as short as possible in order to form microdroplets. preferable. This is because, if this time is long, the discharged droplets become large. In some cases, this time may be set to 0 and the holding unit U2 may not be set at all.

  On the contrary, by changing the position of the drive waveform that tears the liquid column by changing the time of the holding unit U2, that is, the time to start the third drive waveform W3, is advanced or delayed. Droplet modulation may be performed by adjusting the droplet size.

In addition, it is preferable that the third drive waveform W3 is set so that the slope of the graph shown in FIG. 5 is smaller in absolute value than the slope of the second drive waveform W2. In order to enhance the tearing effect and make it easy to produce microdroplets, it is preferable that the ratio is as large as possible while satisfying the condition that the slope of the second drive waveform W2 is smaller. That is, it is preferable that the displacement volume velocity | v ₃ | corresponding to the third drive waveform W3 is as fast (large) as possible.

  As described above, according to the present embodiment, a high-viscosity liquid can be obtained by making the displacement volume velocity with respect to the driving waveform for ejecting liquid as droplets larger than the displacement volume velocity with respect to the driving waveform for tearing the liquid. Can be ejected as fine droplets having a sufficient speed.

  In addition, by increasing the displacement volume velocity corresponding to the driving waveform for setting the meniscus surface to the initial state, the displacement volume velocity corresponding to the driving waveform for tearing the liquid is increased until the meniscus surface returns to the initial state. Since the time can be shortened and the next printing can be performed immediately, the printing can be speeded up.

  Although the liquid droplet ejection method and apparatus of the present invention have been described in detail above, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the spirit of the present invention. Of course it is good.

It is principal part sectional drawing which shows the outline of one Embodiment of the droplet discharge apparatus which concerns on this invention. FIG. 2A is an explanatory diagram for simplifying the pressure chamber and the nozzle, and FIG. 2B is an LCR of a lumped constant model. It is a circuit diagram which shows a circuit. (A), (b) is a diagram which shows the relationship between the meniscus surface position x and time t, respectively. FIG. 4A is a graph showing the displacement volume velocity of the liquid obtained by solving the condition for preventing vibration, and FIG. 4B is a graph showing the displacement of the meniscus surface. It is a diagram which shows the drive waveform of the actuator in this embodiment, and the displacement volume velocity corresponding to it. (A), (b) is a diagram which shows the relationship between the meniscus surface velocity v and time t, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Droplet discharge apparatus, 12 ... Pressure chamber, 14 ... Nozzle, 16 ... Actuator, 18 ... Actuator drive means, 20 ... Liquid supply path

Claims (12)

A droplet discharge method for discharging a liquid in a pressure chamber as a droplet from a nozzle by applying a drive waveform to an actuator for changing the volume of the pressure chamber filled with the liquid,
The volume of the pressure chamber is V, the sectional area of the nozzle is A, the length of the nozzle is l ₀ , the density of the liquid to be discharged is ρ, the viscosity coefficient of the liquid to be discharged is μ, and the liquid in the pressure chamber is transmitted. When the transmission speed of the pressure wave is c, these are the following inequality (1)
c ² / V <16π ² μ ² l ₀ / (A ³ ρ ² ) (1)
A droplet discharge method characterized by being set so as to satisfy the condition represented by   The drive waveform includes a first drive waveform for drawing the meniscus surface of the liquid of the nozzle, a second drive waveform for forming a liquid column for discharging liquid from the nozzle as droplets, A third driving waveform for tearing the liquid column to form micro droplets and a fourth driving waveform for returning the meniscus surface to the initial state after the liquid column is torn off are configured. The droplet discharge method according to claim 1. When the drive waveform has the first drive waveform, a time t ₂ from the start of the first drive waveform to the start of the second drive waveform starts the first drive waveform. 3. The droplet discharge method according to claim 2, wherein _a time ta until the absolute value of the displacement volume velocity of the meniscus surface reaches a maximum is set. The time t _a is the compliance of the pressure chamber C, and the inertance of the liquid channel L, and the liquid viscosity resistance in the nozzle portion and R, β = R / (2L ), γ = √ {R 2 / (4L ² ) -1 / (LC)}, the following formula (2)
t _a = {1 / (2γ)} log {(β + γ) / (β−γ)} (2)
The droplet discharge method according to claim 3, wherein   3. The liquid displacement volume velocity at the meniscus surface by the third drive waveform is smaller in absolute value than the liquid displacement volume velocity at the meniscus surface by the second drive waveform. The droplet discharge method according to any one of -4.   The displacement volume velocity of the liquid on the meniscus surface by the fourth drive waveform is larger in absolute value than the displacement volume velocity of the liquid on the meniscus surface by the third drive waveform. The droplet discharge method according to any one of? A pressure chamber filled with liquid, a nozzle for discharging the liquid provided in the pressure chamber as droplets, an actuator for changing the volume of the pressure chamber, and a drive waveform applied to the actuator to A droplet discharge device comprising actuator driving means for changing the volume and discharging droplets from the nozzle,
The volume of the pressure chamber is V, the sectional area of the nozzle is A, the length of the nozzle is l ₀ , the density of the liquid to be discharged is ρ, the viscosity coefficient of the liquid to be discharged is μ, and the liquid in the pressure chamber is transmitted. When the transmission speed of the pressure wave is c, these are the following inequality (1)
c ² / V <16π ² μ ² l ₀ / (A ³ ρ ² ) (1)
A droplet discharge device characterized by being set to satisfy the condition represented by   The drive waveform includes a first drive waveform for drawing the meniscus surface of the liquid of the nozzle, a second drive waveform for forming a liquid column for discharging liquid from the nozzle as droplets, A third driving waveform for tearing the liquid column to form micro droplets and a fourth driving waveform for returning the meniscus surface to the initial state after the liquid column is torn off are configured. The droplet discharge device according to claim 7. When the drive waveform has the first drive waveform, a time t ₂ from the start of the first drive waveform to the start of the second drive waveform starts the first drive waveform. The liquid droplet ejection apparatus according to claim 8, wherein the time is _a time ta until the absolute value of the displacement volume velocity of the liquid on the meniscus surface becomes maximum. The time t _a is the compliance of the pressure chamber C, and the inertance of the liquid channel L, and the liquid viscosity resistance in the nozzle portion and R, β = R / (2L ), γ = √ {R 2 / (4L ² ) -1 / (LC)}, the following formula (2)
t _a = {1 / (2γ)} log {(β + γ) / (β−γ)} (2)
The droplet discharge device according to claim 9, wherein   The displacement volume velocity of the liquid on the meniscus surface by the third driving waveform is smaller in absolute value than the displacement volume velocity of the liquid on the meniscus surface by the second driving waveform. 10. The droplet discharge device according to any one of 10 to 10. 9. The liquid displacement volume velocity on the meniscus surface by the fourth drive waveform is larger in absolute value than the liquid displacement volume velocity on the meniscus surface by the third drive waveform. The liquid droplet ejection apparatus according to any one of ˜11.

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