JP2012224004A - Liquid droplet injection device, and method for driving liquid droplet injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid droplet injection device providing excellent injection stability even in a case of ink of high dry thickening property by achieving efficient ink agitation avoiding heat generation during waiting time of the recording operation of a recording head.SOLUTION: The liquid droplet injection device includes: a drive signal-forming means; and a recording head injecting liquid droplets toward a recording medium from a nozzle provided according to a plurality of channels by driving an actuator that varies the volume of the channels on the basis of drive signals. The drive signal-forming means creates injection pulse that injects the liquid droplets and fine vibration pulse that finely vibrates meniscus in the nozzle in the degree of not injecting the liquid droplets from the nozzle, the fine vibration pulse includes a rectangular wave whose pulse width that, after varying the volume of the channels, returns the channel volume to the original volume, is 1AL (AL is 1/2 of acoustic resonance frequency), is composed of a plurality of pulses whose pulse interval of the rectangular wave is (n+0.5)×AL (n is an integer 1 or higher), and the fine vibration pulse is applied during waiting time of the recording operation of a recording head.

Description

  The present invention relates to a droplet ejecting apparatus and a driving method of the droplet ejecting apparatus, and more specifically, by causing a meniscus in a nozzle to vibrate slightly to the extent that a droplet is not ejected from the nozzle when waiting for a recording operation. The present invention relates to a droplet ejecting apparatus that can eject stably and a driving method of the droplet ejecting apparatus.

  In an ink jet recording apparatus that records an image on a recording medium by ejecting ink droplets from the nozzles of the recording head, efforts have been made to increase the printing speed in order to increase print productivity. In order to increase the printing speed, it is necessary to increase the drying speed of the printed image. Therefore, ink having high volatility and drying property is often used.

  In addition, water-based inkjet inks that can be directly printed on non-absorbent media such as polyvinyl chloride sheets have been developed as inkjet inks for industrial use. Many of these inks are added with resin fine particles that are not dissolved in the ink as a binder resin, and are fixed to the medium by drying and thickening the ink.

  However, in such a droplet ejection device that uses ink having a high drying viscosity, the meniscus dries quickly, so that when the ink droplets are not ejected for a relatively long time, such as when waiting for a recording operation, Slow injection and nozzle clogging occur, making it difficult to achieve stable injection.

  In order to suppress the drying and thickening of the meniscus, there has been conventionally known a method in which the meniscus is slightly vibrated and the thickened ink on the nozzle surface is stirred with the ink in the channel.

  In Patent Document 1, when the ink non-ejection state continues for a predetermined time or when a predetermined time elapses after the recording head moves to the maintenance position, the volume of the channel is increased and the pressure in the channel becomes negative → positive → A method is disclosed in which a minute vibration pulse that allows cancellation of residual pressure vibration by returning the volume of the channel when it becomes negative is given at a time interval shorter than a predetermined time during which a non-ejection state does not occur.

  Further, Patent Document 2 gives fine vibration to a non-ejecting nozzle during image recording, and when the recording head is positioned at a home position that is waiting for a recording operation, ink thickened toward the ink receiver is applied. A method for forcibly throwing out is disclosed.

JP 2008-230144 A JP 2004-262237 A

  In a droplet ejecting apparatus that uses ink for fixing by dry thickening, the meniscus thickens faster than normal ink, and therefore, ink agitation must be frequently performed even during slight ejection pauses. In particular, when the recording head is in a standby state such as when the recording head is at the home position, the ink ejection is stopped for a relatively long time, so that the ink must be frequently stirred.

  However, on the other hand, the amount of heat generated by the recording head depends on the number of times the micro-vibration pulse is applied and the voltage. Therefore, frequent ink agitation causes heat generation of the recording head, which in turn causes ink thickening. For this reason, when stirring ink with high drying viscosity, it is necessary to efficiently stir the ink with a small number of pulses to avoid the generation of heat.

  According to the method disclosed in Patent Document 1, although a certain degree of emission stability is obtained, the fine vibration pulse is restored when the pressure in the channel changes from negative to positive and then becomes negative again. When the ink is applied for a relatively long time and ink with higher drying viscosity is ejected, there is a problem that efficient nozzle agitation cannot be performed.

  In particular, the recording head uses a common drive wall between adjacent channels, and by applying a voltage to the drive electrodes formed in close contact with both sides of the drive wall, the drive wall is shear-deformed into a U-shape, thereby causing the inside of the channel. In the case of a shear mode type recording head that applies pressure for ejection to ink, the same micro-vibration pulse cannot be simultaneously applied to adjacent channels. At this time, even if the fine vibration pulse as disclosed in Patent Document 1 is used, the adjacent fine vibration pulse cannot be used efficiently, so that there is a case where the stirring cannot catch up with the ink having high drying viscosity. Therefore, the problem that efficient nozzle stirring cannot be performed still cannot be solved.

  In the method disclosed in Patent Document 2, a fine vibration pulse is not applied during standby of the recording operation, and another method of preventing thickening due to ejection is employed. However, since this is forcibly ejecting ink, in the case of ink with high drying thickening viscosity, the ink in the meniscus must continue to be spit out at a short time interval that does not dry, There is a problem that a lot of ink is wasted.

  The present invention has been made under the circumstances described above, and realizes efficient ink agitation that avoids the generation of heat when the recording head waits for the recording operation, and has excellent ejection even in the case of ink having high dry viscosity. It is an object of the present invention to provide a droplet ejection device capable of obtaining stability and a driving method for the droplet ejection device.

  The other subject of this invention becomes clear from the following description.

  The above problems are solved by the following inventions.

The invention according to claim 1 is a drive signal generation means for generating a drive signal;
Droplet ejection having a recording head that ejects droplets toward a recording medium from nozzles provided corresponding to the plurality of channels by driving an actuator that changes the volume of the channel based on the drive signal A device,
The drive signal generating means generates an ejection pulse for ejecting a droplet and a micro-vibration pulse for causing the meniscus in the nozzle to vibrate so as not to eject the droplet from the nozzle,
The micro-vibration pulse includes a rectangular wave having a pulse width of 1AL (AL is 1/2 of the acoustic resonance frequency of the channel) for returning to the original volume after changing the channel volume, and the pulse interval of the rectangular wave is ( n + 0.5) × AL (n is an integer of 1 or more), and is composed of a plurality of pulses.
The liquid droplet ejection apparatus is characterized in that the micro-vibration pulse is applied when the recording head waits for a recording operation.

  According to a second aspect of the present invention, the ejection pulse expands the volume of the channel and returns to the original volume after 1 AL, and the volume of the channel is contracted to return to the original volume after a certain time. Von | ≧ | Voff |, where Von is the voltage of the first pulse and Voff is the voltage of the second pulse. 2. The droplet ejection device according to claim 1, wherein | Vs | ≦ | Voff |

  According to a third aspect of the present invention, the drive signal generation means includes a plurality of the channels of the recording head that are separated from each other with one or more of the channels as a set. 3. The liquid according to claim 1, wherein the channel is divided into two or more groups, and the micro-vibration pulse is sequentially applied to each group in a time-division manner while waiting for a recording operation of the recording head. It is a droplet ejection device.

The invention according to claim 4 is a shuttle type recording head that performs recording by ejecting liquid droplets in the process of scanning and moving over the width direction of the recording medium,
4. The liquid droplet ejection apparatus according to claim 1, wherein the recording head waits for a recording operation outside the recording medium in the width direction and when the scanning movement of the recording head is stopped. It is.

According to a fifth aspect of the present invention, the recording head is a line type that performs recording by ejecting liquid droplets toward the recording medium that is stretched across the width direction of the recording medium and conveyed in a certain direction. Recording head,
4. The droplet ejecting apparatus according to claim 1, wherein the recording head waits for a recording operation when the recording medium is stopped.

According to the sixth aspect of the present invention, the actuator that changes the volume of the channel is driven based on the drive signal generated by the drive signal generating means, so that the nozzles provided corresponding to the plurality of channels are transferred to the recording medium. A droplet ejection apparatus driving method having a recording head for ejecting droplets toward
As the pulse generated by the drive signal generating means, an ejection pulse for ejecting a droplet and a fine vibration pulse for causing the meniscus in the nozzle to vibrate so as not to eject the droplet from the nozzle are generated,
The micro-vibration pulse includes a rectangular wave having a pulse width of 1AL (AL is 1/2 of the acoustic resonance frequency of the channel) for returning to the original volume after changing the channel volume, and the pulse interval of the rectangular wave is ( n + 0.5) × AL (n is an integer of 1 or more), and is composed of a plurality of pulses.
The method of driving a droplet ejection apparatus, wherein the micro-vibration pulse is applied when the recording head waits for a recording operation.

  According to a seventh aspect of the present invention, the ejection pulse expands the volume of the channel and returns the original volume after 1 AL to the original volume, and contracts the volume of the channel and returns to the original volume after a predetermined time. Von | ≧ | Voff |, where Von is the voltage of the first pulse and Voff is the voltage of the second pulse. 7. The droplet ejection apparatus driving method according to claim 6, wherein | Vs | ≦ | Voff |

  According to an eighth aspect of the present invention, among the plurality of channels of the recording head, the channels separated from each other with one or more of the channels interposed therebetween are grouped together to form two or more of the plurality of channels. 8. The droplet ejection apparatus driving method according to claim 6, wherein the fine vibration pulses are sequentially applied in a time-sharing manner for each set when waiting for a recording operation of the recording head. is there.

The invention according to claim 9 is a shuttle type recording head that performs recording by ejecting liquid droplets in the process of scanning and moving over the width direction of the recording medium,
9. The droplet ejection apparatus according to claim 6, 7 or 8, wherein the recording operation waiting time of the recording head is outside the recording medium in the width direction and when the scanning movement of the recording head is stopped. This is a driving method.

According to a tenth aspect of the present invention, the recording head is a line type in which recording is performed by ejecting droplets toward the recording medium that is stretched across the width direction of the recording medium and conveyed in a certain direction. Recording head,
9. The droplet ejection apparatus driving method according to claim 6, 7 or 8, wherein the recording head waits for a recording operation when the recording medium is stopped.

  According to the present invention, a droplet capable of achieving efficient ink agitation avoiding the generation of heat while waiting for a recording operation of the recording head, and obtaining excellent ejection stability even in the case of ink with high dry viscosity. An ejection device and a driving method of a droplet ejection device can be provided.

The figure which shows schematic structure of the inkjet recording device which is an example of the droplet ejection apparatus which concerns on this invention 2A and 2B are diagrams illustrating an example of a recording head, in which FIG. The figure which shows the action | operation at the time of the ink ejection of the recording head shown in FIG. FIG. 3 is a diagram for explaining a three-cycle ejection operation of the recording head shown in FIG. Diagram showing an example of ejection pulse of recording head The figure which shows another example of the ejection pulse of a recording head Diagram showing an example of micro vibration pulse Diagram explaining the relationship between micro vibration pulse and pressure in channel The figure which shows another example of a micro vibration pulse

  FIG. 1 is a diagram showing a schematic configuration of an ink jet recording apparatus which is an example of a droplet ejection apparatus according to the present invention.

  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 flexible 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 a drive signal generator 100 (see FIG. 3) provided with a circuit for generating an ejection pulse and a fine vibration pulse, which will be described later.

  The recording head 2 scans and moves the recording surface PS of the recording medium P in the XX ′ direction as the carriage 5 moves in the main scanning direction, and ejects ink droplets from the nozzles during the scanning movement. Thus, a desired inkjet image is recorded.

  In the ink jet recording apparatus 1, as described later, when the recording head 2 is in the image recording standby position, the ink thickened at the nozzle openings is vibrated slightly. When the recording head 2 has stopped operating for a long time at the image recording standby position, although not shown, the nozzle surface of the recording head 2 is covered with a cap for protection.

  In the present invention, the standby state for the recording operation means that all the nozzles of the recording head are in a state where the ejection of droplets based on the droplet ejection data such as image data is suspended. For example, in the case of the shuttle type recording head 2 that records an image by ejecting liquid droplets in the process of scanning and moving over the width direction of the recording medium P as in the present embodiment, the recording head 2 is placed on the recording medium P. This is when the scanning movement of the recording head 2 is stopped outside the recording medium P in the width direction. Specifically, the case where the recording head 2 is stopped at the home position or the maintenance position can be exemplified.

  Although not shown in the drawings, in the present invention, the recording head is stretched over the width direction of the recording medium, and a recording operation is performed in one pass by ejecting droplets toward the recording medium conveyed in a certain direction. The present invention can also be applied to a droplet ejecting apparatus having a line-type recording head. In the case of such a line type recording head, the waiting time for the recording operation is when the conveyance of the recording medium is stopped. Specifically, it can be exemplified when the recording head or the transport mechanism is in a maintenance state where the operation is stopped.

  2 and 3 are diagrams illustrating an example of the recording head 2, in which FIG. 2A is a schematic perspective view, FIG. 2B is a cross-sectional view, and FIG. 3 is a diagram illustrating an operation during ink ejection.

  In the figure, 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 partition wall. A channel 28 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 by a plurality of partition walls 27A, 27B, 27C, and 27D made of a piezoelectric material such as PZT, which is an electro-mechanical conversion means, between the cover plate 24 and the substrate 26. 2 shows a shear mode (share mode) type recording head in which a large number of formed channels 28 are arranged side by side. In this recording head 2, the partition functions as an actuator.

  In FIG. 3, three (28A, 28B, 28C) which are a part of many channels 28 are shown. One end of the channel 28 (hereinafter sometimes referred to as a nozzle end) is connected to the nozzle 23 formed on the nozzle forming member 22, and the other end (hereinafter sometimes referred to as a manifold end) is connected to the ink supply port 25. Then, the ink tube 21 is connected to an ink tank (not shown). Electrodes 29A, 29B, and 29C connected from above the partition walls 27 to the bottom surface of the substrate 26 are formed in close contact with the surfaces of the partition walls 27 in the channels 28. The electrodes 29A, 29B, and 29C are connected to the drive signal generator 100. Is electrically connected.

  The drive signal generation unit 100 is drive signal generation means of the present invention, and is supplied from the drive signal generation circuit for generating a series of drive signals including a plurality of drive pulses and for each channel. A drive pulse selection circuit that selects a drive pulse from the drive signal according to the data of each pixel and supplies it to each channel, and drives the partition wall 27 as an electro-mechanical conversion means according to the data of each pixel. A driving pulse is supplied. In addition to such an ejection pulse, the drive pulse generated by the drive signal generation unit 100 includes a micro-vibration pulse that causes the meniscus in the nozzle to vibrate so as not to eject a droplet from the nozzle in order to perform nozzle agitation. Also included.

  In the recording head 2, each partition wall 27 is composed of two piezoelectric materials 27a and 27b having different polarization directions as indicated by arrows in FIG. 3, but the piezoelectric material is only a portion indicated by reference numeral 27a, for example. It suffices if it is at least part of the partition wall 27.

  When an ejection pulse is applied to the electrodes 29A, 29B, and 29C formed in close contact with the surface of each partition wall 27 by the control of the drive signal generator 100, an ink droplet is ejected from the nozzle 23 by the operation exemplified below. In FIG. 3, the nozzle is omitted.

  First, when no emission pulse is applied to any of the electrodes 29A, 29B, and 29C, none of the partition walls 27A, 27B, and 27C is deformed. In the state shown in FIG. 3A, when the electrodes 29A and 29C are grounded and an injection pulse is applied to the electrode 29B, an electric field in a direction perpendicular to the polarization direction of the piezoelectric material constituting the partition walls 27B and 27C is generated. As a result, each of the partition walls 27B and 27C is deformed at the joint surfaces of the partition walls 27a and 27b, and the partition walls 27B and 27C are deformed outward as shown in FIG. And a negative pressure is generated in the channel 28B, and ink flows (Draw).

  When the potential is returned to 0 from this state, the partition walls 27B and 27C return from the expanded position shown in FIG. 3B to the neutral position shown in FIG. 3A, and high pressure is applied to the ink in the channel 28B ( Release).

  Next, as shown in FIG. 3C, when the injection pulse is applied to deform the partition walls 27B and 27C in the opposite directions to reduce the volume of the channel 28B, a positive pressure is generated in the channel 28B ( Reinforce).

  As a result, the ink meniscus in the nozzle due to a part of the ink filling the channel 28B changes in the direction pushed out from the nozzle. When the positive pressure becomes so large that the ink droplet is ejected from the nozzle, the ink droplet is ejected from the nozzle. The other channels operate in the same manner as described above by applying the ejection pulse. Such an ink droplet ejection method is called a DRR driving method, which is a typical driving method for a share mode type recording head.

  Thus, when driving the recording head 2 having a plurality of channels 28 separated by the partition walls 27 which are at least partially made of a piezoelectric material, when the partition wall of one channel performs the ejection operation, the adjacent channel is affected. In general, among the plurality of channels 28, the channels 28 that are separated from each other with one or more channels 28 sandwiched together are combined into one set, and the plurality of channels are combined into two or more sets. The drive control is performed so that the ink droplet ejection operation is sequentially performed in a time division manner for each set. For example, when all the channels 28 are driven and a solid image is output, a so-called three-cycle injection method is performed in which the channels 28 are selected every two channels and injected in three phases.

  Such a three-cycle injection operation will be further described with reference to FIG. In the example shown in FIG. 4, the recording head is described as having nine channels 28 of A1, B1, C1, A2, B2, C2, A3, B3, and C3. Further, FIG. 5 shows a timing chart of pulse waveforms applied to the respective channels 28 of A, B, and C at this time.

  When ink droplets are ejected, first, a voltage is applied to the electrodes of each channel of the A group (A1, A2, A3), and the electrodes of the adjacent channels are grounded. For example, when an ejection pulse composed of a square wave of a positive voltage + Von having a 1AL width is applied to the A group of channels, the partition walls of the A group of channels to be ejected are deformed outward, and negative pressure is generated in the channel 28. By this negative pressure, ink flows from the ink tank into the A set of channels 28 (Draw).

  If this state is maintained for 1 AL, the pressure is reversed to a positive pressure. Therefore, when the electrode is grounded at this timing, the deformation of the partition wall is restored, and a high pressure is applied to the ink in the A set of channels 28 (Release). Further, when a rectangular wave of negative voltage −Voff is applied to the electrodes of each channel of the A group at the same timing, the partition wall is deformed inward, and a higher pressure is applied to the ink (Reinforce), and the ink column is pushed out from the nozzle. After 1AL, the pressure reverses and the inside of the channel 28 becomes negative pressure. When 1AL further passes, the pressure in the channel 28 reverses and becomes positive pressure. When the electrode is grounded at this timing (after 2AL has passed) The deformation of the partition wall is restored and the remaining pressure wave can be canceled.

  Here, the voltage of this injection pulse is | Von | ≧ | Voff |.

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

  In addition, AL (Acoustic Length) is 1/2 of the acoustic resonance period of the channel as described above. This AL measures the speed of ink droplets ejected by applying a rectangular wave voltage pulse to the partition wall 27 which is an electrical / mechanical conversion means, and changes the pulse width of the rectangular wave while keeping the rectangular wave voltage value constant. The pulse width at which the flying speed of the ink droplet is maximized. 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 10% of the voltage from 0V and the peak voltage. It is defined as the time between 10% of the falling edge. 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. .

  In such a shear mode type recording head, the deformation of the partition wall 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 channel for ejecting ink droplets, as shown in FIG. In addition, the same operation can be performed by grounding the electrode of the channel that ejects ink droplets and applying a positive voltage to the electrodes of the adjacent channels. This latter method is preferable because it can be driven only by a positive voltage.

  Next, with reference to FIG. 7, in the share mode type recording head 2, an operation for giving a slight vibration to the meniscus when the recording head 2 is in the image recording standby position will be described.

  Similarly to the ink droplet ejection operation, the operation for giving a slight vibration to the meniscus is a group of channels separated from each other by sandwiching one or more channels among the plurality of channels of the recording head 2. In this way, a plurality of channels can be divided into two or more groups, and when the recording head 2 waits for a recording operation, the fine vibration pulses can be sequentially applied to each group in a time division manner. Here again, a description will be given of the case where the channel is divided into three groups A to C and the three-cycle operation is performed as described above. Here, it is assumed that only a positive voltage is used as the drive waveform voltage, and the micro-vibration pulse is applied in the order of A set → B set → C set.

  In the example shown in FIG. 7, when the recording head 2 is waiting for the recording operation, first, a micro-vibration pulse composed of a rectangular wave with a positive voltage of 1 AL width is applied to the electrodes of the A group of channels. The voltage | Vs | of the fine vibration pulse is a voltage equal to or lower than the injection pulse voltage | Voff |. As a result, the channel of the A group expands in volume and becomes negative pressure, and turns to positive pressure after 1 AL. After the passage of 1AL, the electrodes of the B group and C group channels are grounded to restore the volume of the A group channel. However, since the pulse voltage | Vs | is equal to or lower than the ejection pulse voltage | Voff | Drops do not fire.

  Thereafter, during (n + 0.5) AL, the electrodes of all the channels of the A group to the C group are grounded (n is an integer of 1 or more). As a result, the meniscus in the nozzles of the A group of channels is given a slight vibration so as to be pushed out to the extent that ink droplets are not ejected from the nozzles, and only the partition on one side of each channel of the B and C groups is displaced, A micro-vibration with half the intensity of the A set of channels is given.

  Similarly, when the fine vibration pulse is applied to the B group after (n + 0.5) AL after the application of the fine vibration pulse to the A group channel is completed, a positive 1 AL width is applied to the electrode of the B group channel. A micro-vibration pulse composed of a rectangular wave of voltage is applied at a voltage equal to or lower than | Voff | of the ejection pulse voltage, and the channel electrodes of the A group and the C group are grounded, and thereafter, during (n + 0.5) AL, Ground the electrode of the channel. The application of the micro-vibration pulse of the C sets of channels is similarly performed.

  In the present invention, the micro-vibration pulse that causes micro-vibration to such an extent that the ink droplets are not ejected from the nozzles is generated in the drive signal generator 100 shown in FIG. 3 as in the case of applying the ejection pulses. The micro-vibration pulse in the present invention includes a rectangular wave, includes a rectangular wave having a pulse width of 1AL, and includes a plurality of pulses having a pulse interval of (n + 0.5) × AL (n is an integer of 1 or more). It is characterized by that. In the case of the recording head 2 having a common partition wall in adjacent channels as in this embodiment, the fine vibration pulse is applied with a shift of (n + 0.5) × AL between adjacent channels.

  In the present invention, the meniscus can be greatly shaken at a low voltage (| Voff | or less) by using a rectangular wave having a pulse width of 1 AL as with the emission pulse as the fine vibration pulse.

  Further, setting the pulse interval of the fine vibration pulse to (n + 0.5) × AL means that the next fine vibration pulse is applied at the timing when the direction of the pressure wave generated in the channel changes. Thereby, it is possible to minimize the influence of the reverberation of the previously applied fine vibration pulse and to apply the next fine vibration pulse.

  Thereby, it is not necessary to cancel the pressure wave with the fine vibration pulse itself, so that the meniscus can be efficiently shaken with a small number of pulses. For this reason, it is possible to prevent heat generation and to prevent the phenomenon that the ink liquid is unexpectedly ejected by repeating the strengthening of the pressure wave when the fine vibration pulse is continuously applied.

  In addition, since the fine vibration pulses are sequentially applied to each of the channels A to C in a time-sharing manner, for example, when the fine vibration pulse is applied to the channels A, the channels A and B are also set to the channels A and C. However, it is possible to obtain an effect of efficiently shaking the meniscus of all the channels. In addition, since the micro-vibration pulse is not applied to each channel of the B group and the C group, heat generation of the recording head 2 can be suppressed.

  FIG. 8 shows the pressure wave in the channel when the pulse interval is (n + 0.5) × AL in three-cycle driving. By applying a fine vibration pulse composed of a square wave of 1AL at an interval of (n + 0.5) × AL (n is an integer of 1 or more), the next fine vibration pulse is generated at the timing when the direction of the pressure wave in the channel changes. It is shown that the influence of the reverberation of the fine vibration pulse is suppressed.

  The value of n is preferably 3-8. The meniscus can be vibrated most efficiently with an integer value in this range, and heat generation can be suppressed. In addition, the present inventor has confirmed through experiments that almost the same effect can be obtained even if there is an error of about ± 0.05 from the integer value.

  FIG. 8 shows an example in which n = 6, that is, the interval between each micro-vibration pulse is uniform at 6.5 AL. However, the interval between each micro-vibration pulse may not be uniform. For example, in the following equation, if m = 6, the pulse interval between the fine vibration pulse of A-cycle and the subsequent fine vibration pulse of B-cycle is (m + 1 + 0.5) × AL (= 7.5AL), and The pulse interval between the B-cycle micro-vibration pulse and the subsequent C-cycle micro-vibration pulse is (m-1 + 0.5) × AL (= 5.5 AL), and further the C-cycle micro-vibration pulse. If the pulse interval is a length of (natural number +0.5) × AL, such as (m + 0.5) × AL (= 6.5 AL), The same action is shown, and the next fine vibration pulse is applied at the timing when the direction of the pressure wave in the channel changes, and the influence of the reverberation of the fine vibration pulse is suppressed.

  Further, since the pulse interval of (n + 0.5) × AL is not affected by the previous micro-vibration pulse, even if the pulse interval is changed (the value of n is changed), the amount of meniscus extrusion does not change. Therefore, it is possible to easily control the magnitude of the micro-vibration by adjusting the voltage, and there is an advantage that it is easy to set an optimum pulse interval that differs depending on the ink.

  The voltage | Vs | of the micro-vibration pulse is such that | Vs | ≦ | Voff | is satisfied when the ejection pulse is | Von | ≧ | Voff | However, if it is too low with respect to | Voff |, nozzle agitation may be insufficient depending on the ink. From the viewpoint of enabling more efficient nozzle agitation, it is preferable to set an optimum value according to the physical properties of the ink and the dimensions of the head.

  The application of the fine vibration pulse in the present invention is not limited to the above-described three-cycle driving, and for example, as shown in FIG. 9, driving divided into odd-numbered nozzles and even-numbered nozzles (two-cycle driving) can be performed. This drive is preferably applied to ink that tends to dry and thicken more, but because the number of pulses per hour increases, adjustments such as setting a longer pulse interval (setting a larger value for n) are necessary. It is. From the viewpoint of heat generation, it is desirable to set the pulse interval as long as possible and the drive voltage as low as possible in any drive.

  The present invention can be particularly preferably applied to a case where a liquid with high dry thickening is ejected as droplets from a nozzle. Examples of liquids with high drying thickening include those in which the droplet velocity is reduced by about 50% when ejected from the same nozzle after leaving (resting) for 20 seconds after ejection of the droplet.

Such a liquid with high dry thickening is not particularly limited in the present invention, but examples thereof include a liquid (ink) containing at least the following four components a to d.
a. Pigment coated with water-insoluble resin b. Ink-soluble resin having a solid content of 2% to 10% c. A water-soluble organic solvent selected from glycol ethers or 1,2-alkanediols d. Silicone or fluorine surfactant

  Hereinafter, each component will be described.

(A. Pigment coated with water-insoluble resin)
The water-insoluble resin is a resin that is insoluble in water in a weakly acidic to weakly basic range, and is preferably a resin having a solubility in an aqueous solution of pH 4 to 10 of less than 2%.

  Such resins include acrylic, styrene-acrylic, acrylonitrile-acrylic, vinyl acetate, vinyl acetate-acrylic, vinyl acetate-vinyl chloride, polyurethane, silicon-acrylic, acrylic silicon, polyester Examples thereof include epoxy resins and epoxy resins. Moreover, resin containing a hydrophobic monomer and a hydrophilic monomer can be used as the resin.

  Examples of hydrophobic monomers include acrylic acid esters (such as n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate), methacrylic acid esters (such as ethyl methacrylate, butyl methacrylate, glycidyl methacrylate), styrene. Etc.

  Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid can preferably be those neutralized with a base after polymerization.

  Organic and inorganic pigments can be used as the pigment. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Examples include cyclic pigments, dye lakes such as basic dye lakes, and acid dye lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments, and inorganic pigments such as carbon black.

  Specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the orange or yellow pigment include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. And CI Pigment Yellow 138.

  Examples of pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

(B. Ink-soluble resin)
The ink-soluble resin is contained in the ink in a solid content of 2% to 10%. The ink-soluble resin is a resin having a solubility of at least about 10% with respect to the ink vehicle.

  Examples of such resins include acrylic resins, styrene-acrylic resins, acrylonitrile-acrylic resins, vinyl acetate-acrylic resins, polyurethane resins, and polyester resins.

  As the ink-soluble resin, a resin containing a hydrophobic monomer and a hydrophilic monomer can be used.

  Examples of hydrophobic monomers include acrylic acid esters (such as n-butyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate), methacrylic acid esters (such as ethyl methacrylate, butyl methacrylate, glycidyl methacrylate), styrene. Etc.

  Examples of the hydrophilic monomer include acrylic acid, methacrylic acid, acrylamide and the like, and those having an acidic group such as acrylic acid can preferably be those neutralized with a base after polymerization.

(C. Water-soluble organic solvent)
The ink contains at least a water-soluble organic solvent selected from glycol ether or 1,2-alkanediol.

  Specific examples of the glycol ether include ethylene glycol monoethyl, ethylene glycol monobutyl, diethylene glycol monobutyl, triethylene glycol monobutyl, propylene glycol monopropyl, dipropylene glycol monomethyl, and tripropylene glycol monomethyl.

  Examples of the 1,2-alkanediol include 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and the like.

  In addition to glycol ether or 1,2-alkanediol, a solvent can be added to such an ink.

  Specifically, alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, Propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N- Ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenedi Amine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocyclic rings (For example, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxides (for example, dimethyl sulfoxide) and the like.

(D. Surfactant)
As the surfactant, a silicone-based or fluorine-based surfactant is used. Among the fluorosurfactants, certain types are traded under the trade name Megafac F from Dainippon Ink & Chemicals, Inc., and surflon from Asahi Glass Co., Minnesota Mining and Under the trade name Fluorad FC from Manufacturing Company, under the trade name Monflor from Imperial Chemical Industry, and Zonyls from EI Dupont Nemeras & Company. It is commercially available under the trade name and also under the trade name Licowet VPF from Farbeberke Hoechst. Examples of nonionic fluorosurfactants include Megafax 144D manufactured by Dainippon Ink and Surflon S-141 and 145 manufactured by Asahi Glass Co., and amphoteric fluorosurfactants. Examples of the agent include Surflon S-131 and 132 manufactured by Asahi Glass Co., Ltd.

  In the above-described liquid droplet ejection apparatus, the recording head actuator is exemplified by deforming the partition wall in the shear mode by applying an electric field to the partition wall made of a piezoelectric material between adjacent channels. Any configuration may be used as long as it provides a function of changing the volume of the channel. As shown in the present embodiment, when the piezoelectric material is deformed in the shear mode, the rectangular wave described above can be used more effectively, the drive voltage is reduced, and the drive is more efficient. Is preferable because it becomes possible.

  In the above description, the application example of the ink jet recording apparatus is shown as the liquid droplet ejecting apparatus. However, the present invention is not limited to this, and the liquid droplet ejecting the liquid in the channel as a liquid droplet from the nozzle. The present invention is widely applicable as a driving method for an ejection device and a droplet ejection device.

  Hereinafter, the effect of the present invention will be illustrated based on examples.

(Production of water-insoluble resin)
50 g of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducing tube, a reflux condenser, a thermometer and a stirring device, and heated to 75 ° C. while bubbling nitrogen. Thereto, a mixture of 80 g of n-butyl methacrylate, 5 g of butyl acrylate, 5 g of 2-hydroxyethyl methacrylate, 10 g of acrylic acid and 50 g of methyl ethyl ketone, and 500 mg of initiator (AIBN) was dropped from a dropping funnel over 3 hours. It heated and refluxed for 6 hours after dripping. After being allowed to cool, methyl ethyl ketone was added to volatilize to obtain a solution of water-insoluble resin D having a solid concentration of 50% by mass.

(Preparation of pigment coated with water-insoluble resin (hereinafter referred to as pigment dispersion))
A 100% g of a 50% solution of water-insoluble resin D in methyl ethyl ketone was neutralized with 100% of a salt-forming group by adding a predetermined amount of a 20% aqueous sodium hydroxide solution as a neutralizing agent. I. Pigment Blue 15: 3 and 50 g were added little by little, and then kneaded in a bead mill for 2 hours. 400 g of ion-exchanged water was added to the obtained kneaded product and stirred, and then heated under reduced pressure to distill off methyl ethyl ketone. Furthermore, ion-exchanged water was added to obtain a pigment dispersion P having a solid content concentration of 15%.

(Preparation of ink-soluble resin)
50 g of methyl ethyl ketone was added to a flask equipped with a dropping funnel, a nitrogen introducing tube, a reflux condenser, a thermometer and a stirring device, and heated to 75 ° C. while bubbling nitrogen. Thereto, a mixture of 80 g of n-butyl methacrylate, 5 g of butyl acrylate, 5 g of 2-hydroxyethyl methacrylate, 10 g of acrylic acid and 50 g of methyl ethyl ketone, and 500 mg of initiator (AIBN) was dropped from a dropping funnel over 3 hours. It heated and refluxed for 6 hours after dripping. After allowing to cool, the mixture was heated under reduced pressure to remove methyl ethyl ketone. In 450 ml of ion-exchanged water, dimethylaminoethanol corresponding to 1.05 mol of acrylic acid added as a monomer was dissolved, and the polymer residue was dissolved therein. An aqueous solution of an ink-soluble resin R having a solid content concentration of 20% was prepared with ion-exchanged water.

(Preparation of water-based inkjet ink)
4 parts by weight of pigment dispersion P, 4 parts by weight of ink-soluble resin R, 10 parts by weight of diethylene glycol monobutyl ether and diethylene glycol as solvents, and 0.5 part by weight of KF-351A manufactured by Shin-Etsu Chemical Co., Ltd. as surfactants And 71.5 parts by mass of ion exchange water were added and mixed. After preparation, the mixture was filtered with a 5 μm filter to obtain an aqueous inkjet ink C.

  When the water-based inkjet ink C was left for 20 seconds after being ejected and then ejected from the same nozzle again, the droplet speed was reduced to 50%.

(Evaluation of invention effect)
Each channel of the share mode type recording head (nozzle number 256, AL: 5.0 μs) shown in FIG. 1 is filled with water-based inkjet ink C, each channel is divided into three groups, and from a rectangular wave as shown in FIG. The micro-vibration pulse signal is used to sequentially apply micro-vibration to the meniscus of each channel in three cycles.

  The pulse width and pulse interval of the micro-vibration pulse are varied as shown in Table 1, and each drop is ejected with the DRR waveform shown in FIG. We observed the change in the initial speed at the time, and verified the improvement effect of decap (decrease in injection speed and nozzle clogging). The droplet velocity was measured by stroboscopic synchronization using a digital microscope “VH-100” manufactured by KEYENCE.

Condition ink: water-based inkjet ink C (viscosity: 10 cp, surface tension: 26 mN / m, 25 ° C.)
Applied voltage: Injection pulse: Von = + 16V, Voff = + 8V
Slight vibration pulse: Vs = + 8V

Evaluation (temperature rise)
After applying a minute vibration pulse for 3 minutes, the temperature change of the head was measured and evaluated according to the following criteria.
A: Temperature rise is less than 0.5 ° C. ○: Temperature rise is 0.5 ° C. or more and less than 1 ° C. Δ: Temperature rise is 1 ° C. or more and less than 1.5 ° C. ×: Temperature rise is 1.5 ° C. or more, 2 Less than 0 ° C XX: Temperature increase is 2.0 ° C or more

(Decap characteristics improvement effect)
After applying a minute vibration pulse for 3 minutes, ejection was performed with an ejection pulse having a DRR waveform, and the velocity of the first droplet was measured. Under the same conditions, the initial droplet velocity and the velocity when ejected soon after refreshing were compared, and evaluated by the rate of decrease in the initial droplet velocity according to the following criteria.
◎: Decrease rate of less than 10% ○: Decrease rate of 10% or more, less than 20% △: Decrease rate of 20% or more, less than 50% X: Decrease rate of 50% or more

  As shown in Table 1, when the pulse interval of the micro-vibration pulse is set to an even number AL (Comparative Examples 1, 3, 5, and 7), the micro-vibration pressure waves strengthen each other, resulting in erroneous ejection of liquid droplets. End up. On the other hand, if the pulse interval is set to an odd number AL, the pressure wave is canceled, so that the decap improvement effect is reduced (Comparative Examples 4, 6, and 8) or even if a certain degree of decap improvement effect is seen, heat generation occurs. Becomes larger (Comparative Example 2). When the pulse interval is increased, the heat generation tends to be improved, but the decap improvement effect tends to decrease.

  However, in the present invention (Examples 1 to 6) in which the pulse interval of the fine vibration pulse is set to (n + 0.5) × AL, the fine vibration pulse can be applied at a short interval timing without being affected by the pressure wave. It is possible to increase the decap improvement effect without causing erroneous injection, and heat generation is hardly a problem.

  When the pulse width of the fine vibration pulse is 2AL (Comparative Example 9), even if the pulse interval is set so as to satisfy (n + 0.5) × AL (n = 3), a remarkable decap improvement effect is obtained. Moreover, the problem of heat generation could not be improved.

1: Inkjet recording device 2: Recording head 21: Ink tube 22: Nozzle forming member 23: Nozzle 24: Cover plate 25: Ink supply port 26: Substrate 27, 24A, 27B, 27C: Partition wall 27a, 27b: Piezoelectric material 28, 28A, 28B, 28C: Channels 29A, 29B, 29C: Electrodes 3: Conveying mechanism 31: Conveying roller 32: Conveying roller pair 33: Conveying motor 4: Guide rail 5: Carriage 6: Flexi cable 100: Drive signal generator P: Recording medium PS: Recording surface

Claims (10)

Drive signal generating means for generating a drive signal;
Droplet ejection having a recording head that ejects droplets toward a recording medium from nozzles provided corresponding to the plurality of channels by driving an actuator that changes the volume of the channel based on the drive signal A device,
The drive signal generating means generates an ejection pulse for ejecting a droplet and a micro-vibration pulse for causing the meniscus in the nozzle to vibrate so as not to eject the droplet from the nozzle,
The micro-vibration pulse includes a rectangular wave having a pulse width of 1AL (AL is 1/2 of the acoustic resonance frequency of the channel) for returning to the original volume after changing the channel volume, and the pulse interval of the rectangular wave is ( n + 0.5) × AL (n is an integer of 1 or more), and is composed of a plurality of pulses.
The droplet ejection apparatus, wherein the micro-vibration pulse is applied when the recording head waits for a recording operation.   The ejection pulse includes a first pulse consisting of a rectangular wave that expands the volume of the channel and restores the original volume after 1 AL, and a second pulse that consists of a rectangular wave that contracts the volume of the channel and restores the original volume after a certain time. When the voltage of the first pulse is Von and the voltage of the second pulse is Voff, | Von | ≧ | Voff |, and when the voltage of the micro-vibration pulse is Vs, | Vs 2. The droplet ejection apparatus according to claim 1, wherein | ≦ | Voff |.   The drive signal generation means includes a plurality of the channels of the recording head, the channels separated from each other with one or more of the channels sandwiched in one group, and the two or more channels are combined into one set. 3. The droplet ejection apparatus according to claim 1, wherein the liquid droplet ejecting apparatus is divided into groups, and the fine vibration pulses are sequentially applied to each group in a time division manner while waiting for a recording operation of the recording head. The recording head is a shuttle type recording head that performs recording by ejecting liquid droplets in the process of scanning and moving over the width direction of the recording medium,
4. The liquid droplet ejection apparatus according to claim 1, wherein the recording head waits for a recording operation outside the recording medium in the width direction and when the scanning movement of the recording head is stopped. . The recording head is a line-type recording head that performs recording by ejecting droplets toward the recording medium that is spanned across the width direction of the recording medium and conveyed in a certain direction,
4. The liquid droplet ejection apparatus according to claim 1, wherein the recording head waits for a recording operation when the recording medium is stopped. Recording in which droplets are ejected from a nozzle provided corresponding to the plurality of channels toward a recording medium by driving an actuator that changes the volume of the channel based on the driving signal generated by the driving signal generating means. A method for driving a droplet ejection apparatus having a head,
As the pulse generated by the drive signal generating means, an ejection pulse for ejecting a droplet and a fine vibration pulse for causing the meniscus in the nozzle to vibrate so as not to eject the droplet from the nozzle are generated,
The micro-vibration pulse includes a rectangular wave having a pulse width of 1AL (AL is 1/2 of the acoustic resonance frequency of the channel) for returning to the original volume after changing the channel volume, and the pulse interval of the rectangular wave is ( n + 0.5) × AL (n is an integer of 1 or more), and is composed of a plurality of pulses.
A method for driving a droplet ejecting apparatus, wherein the micro-vibration pulse is applied when a recording operation of the recording head is on standby.   The ejection pulse includes a first pulse consisting of a rectangular wave that expands the volume of the channel and restores the original volume after 1 AL, and a second pulse that consists of a rectangular wave that contracts the volume of the channel and restores the original volume after a certain time. When the voltage of the first pulse is Von and the voltage of the second pulse is Voff, | Von | ≧ | Voff |, and when the voltage of the micro-vibration pulse is Vs, | Vs The driving method of the droplet ejecting apparatus according to claim 6, wherein | ≦ | Voff |.   Of the plurality of channels of the recording head, the channels that are separated from each other with one or more channels sandwiched together are grouped into one group, and the plurality of channels are divided into two or more groups, and the recording 8. The method of driving a droplet ejecting apparatus according to claim 6, wherein the micro-vibration pulse is sequentially applied in a time-sharing manner for each set when the recording operation of the head is on standby. The recording head is a shuttle type recording head that performs recording by ejecting liquid droplets in the process of scanning and moving over the width direction of the recording medium,
9. The droplet ejection apparatus according to claim 6, 7 or 8, wherein the recording operation waiting time of the recording head is outside the recording medium in the width direction and when the scanning movement of the recording head is stopped. Driving method. The recording head is a line-type recording head that performs recording by ejecting droplets toward the recording medium that is spanned across the width direction of the recording medium and conveyed in a certain direction,
9. The method of driving a droplet ejection apparatus according to claim 6, 7 or 8, wherein the recording operation waiting time of the recording head is when conveyance of the recording medium is stopped.

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