JP5867072B2 - Droplet ejection device and method for driving droplet ejection device - Google Patents

Description

  The present invention relates to a droplet ejection device and a driving method of the droplet ejection device, and more particularly, a droplet ejection device and a liquid that can stably eject low-viscosity ink without being affected by ejection of adjacent nozzles. The present invention relates to a driving method of a droplet ejection device.

  A droplet ejection device with a recording head that ejects ink in a channel, which is a pressure generation chamber, as fine ink droplets from a nozzle, records a desired inkjet image by landing the ink droplets on a recording medium such as recording paper. Widely used as an inkjet recording apparatus to be formed. In the field of such an ink jet recording apparatus, there is a growing need for industrial use ink jet inks, and the ejection of inks having various physical properties is desired. In particular, in recent years, interest in water-based inks containing water as a main solvent has been very high due to environmental considerations. Water-based inks often have low ink viscosity due to the physical properties of water.

However, a low-viscosity ink having a viscosity of less than 5.0 × 10 ⁻³ Pa · sec (Pascal second) has a small viscosity resistance inside the channel of the recording head, and therefore the vibration of the meniscus in the nozzle becomes large. As a result, when the actuator is driven to eject the ink in the channel from the nozzle, there may be a problem that air is trapped inside the nozzle during the ejection.

  In particular, such a problem is caused by using a partition shared by adjacent channels as an actuator and driving the partitions corresponding to the channels arranged side by side in a time-sharing manner, thereby sequentially ejecting ink in each channel from the nozzles. This is more noticeable when a shear mode type recording head is used.

  That is, in such a shear mode type recording head, ink droplets cannot be ejected simultaneously in adjacent channels. Therefore, when ink in one channel is ejected from a nozzle, the adjacent channel is ejected simultaneously. However, in reality, pressure is generated also in the ink in the adjacent channel due to the influence of the partition wall of the channel being deformed to eject the ink droplet, and the meniscus in the nozzle adjacent to the ejection channel is pushed out. There's a problem. When the amount of meniscus extrusion is large, air is entrained when the meniscus is drawn back into the nozzle, and subsequent stable injection becomes impossible.

  This meniscus extrusion is not a problem when ink droplets are subsequently ejected from a channel adjacent to a channel for ejecting ink droplets, because it is canceled by the ink droplet ejection operation. This is more noticeable when the channel adjacent to the ejection channel is a channel that does not eject ink droplets. In particular, in the drive pattern in which the injection channel and the non-injection channel are arranged every other channel, the non-injection channel is affected by the driving pressure of the adjacent injection channels, and thus the stable injection with such a drive pattern is most achieved. difficult.

In FIG. 9, using two types of ink, viscosity 3.8 × 10 ⁻³ Pa · sec (= 3.8 cp) and viscosity 5.7 × 10 ⁻³ Pa · sec (= 5.7 cp). 4 shows the time change of the meniscus push-out amount in the nozzle in the non-injection channel when each of the shear mode type recording heads is driven for 3 cycles (drive every other channel).

  As shown in FIG. 5, in the 3-cycle drive, every other channel 31 is divided into three groups of A group, B group, and C group with every other channel 31 as a group. This is one of the driving methods of the driven shear mode type recording head. In FIG. 9, even-numbered channels among the channels 31 are driven as ink ejection channels in the order of A group → B group → C group (A cycle → B cycle → C cycle). Focusing on a specific non-injection channel (odd channel), the meniscus extrusion amount changes with time. Here, since the even channel is the emission channel, the odd channel itself in the A set channel is a non-injection channel, but the adjacent B set and C set channels are both even channels and become injection channels. Therefore, it is easily affected by this injection channel.

  As can be seen from the figure, the lower the ink viscosity, the greater the meniscus extrusion amount. As the meniscus push-out amount increases, the risk of entraining air when the meniscus returns into the nozzle increases. In actual printing, not all channels are driven all the time, and a non-ejecting channel sandwiched between emissive channels as described above may occur depending on print data even in 3-cycle driving. The problem of air entrainment due to increased meniscus extrusion in the nozzle in the injection channel is not negligible.

  Conventionally, Patent Document 1 discloses that a channel for performing ejection and a dummy channel for which ejection is not performed are alternately provided in order to reduce the influence of ejection on a channel adjacent to a channel that ejects ink. However, with this method, it is difficult to increase the channel density (nozzle density), and it is difficult to improve print productivity and achieve high image quality.

Patent Document 2 discloses that the voltage ratio between the first pulse and the second pulse is set to 1.2 or more and 5.0 or less in order to stabilize the meniscus during high-speed driving. However, this technique focuses on suppressing meniscus vibration in the nozzle after the ink is ejected from the nozzle, and in particular, using a low-viscosity ink having a viscosity of less than 5.0 × 10 ⁻³ Pa · sec. The influence of the meniscus of the adjacent channel when driven is not considered. In this technique, as described above, when time-sharing drive is performed with a three-cycle drive with a shear mode type recording head, there is no solution to the problem that air is entrained by the extrusion of a non-injection meniscus adjacent to the injection channel. could not.

JP 2000-15802 A JP 2001-310461 A

  The present invention has been made in view of the above circumstances, and ink droplets are formed by time-division driving using a low-viscosity ink from a shear mode type recording head that shears and deforms a partition shared by adjacent channels as an actuator. A droplet ejection apparatus and a droplet capable of stably ejecting ink droplets from a recording head by stabilizing the vibration of a meniscus of a non-ejecting nozzle adjacent to the nozzle performing ejection when performing ejection It is an object to provide a method for driving an injection device.

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

  The above problems are solved by the following inventions.

1.
It is composed of a plurality of nozzles for ejecting ink droplets, a plurality of channels connected in parallel to the nozzles, and a partition made of a piezoelectric material shared by the adjacent channels, and is sheared by application of a drive signal. A recording head having an actuator for ejecting ink in the channel from the nozzle by changing the volume of the channel;
Drive signal generating means for generating the drive signal including a plurality of drive pulses for driving the actuator;
All of the channels are divided into two or more sets so that the channels separated from each other with one or more of the channels are combined into one set, and the drive signal is applied to each set A droplet ejection device that drives and controls the recording head so as to sequentially perform ink ejection operations in a time-sharing manner,
The ink has a viscosity of less than 5.0 × 10 ⁻³ Pa · sec,
The plurality of driving pulses for ejecting an ink droplet from the nozzle once expands the volume of the channel and returns the volume of the channel to a first pulse composed of a rectangular wave that returns to the original volume after a predetermined time. deflated, it consists of a second pulse composed of a rectangular wave to return to the original volume after a predetermined time,
The droplet ejection apparatus according to claim 1, wherein a ratio of the voltage Von of the first pulse and the voltage Voff of the second pulse is 0.5 ≦ | Von / Voff | ≦ 0.8.
2.
The pulse width of the first pulse is not less than 0.7 AL and not more than 1.3 AL, and the ratio of the pulse width PWon of the first pulse to the pulse width PWoff of the second pulse is 0.45 ≦ | 2. The droplet ejection apparatus according to 1 above, wherein PWon / PWoff | ≦ 0.55.
3.
It is composed of a plurality of nozzles for ejecting ink droplets, a plurality of channels connected in parallel to the nozzles, and a partition made of a piezoelectric material shared by the adjacent channels, and is sheared by application of a drive signal. A recording head having an actuator for ejecting ink in the channel from the nozzle by changing the volume of the channel;
Drive signal generating means for generating the drive signal including a plurality of drive pulses for driving the actuator;
All of the channels are divided into two or more sets so that the channels separated from each other with one or more of the channels are combined into one set, and the drive signal is applied to each set Then, a driving method of a droplet ejecting apparatus that drives and controls the recording head so that ink ejection operations are sequentially performed in a time-sharing manner,
The ink has a viscosity of less than 5.0 × 10 ⁻³ Pa · sec,
The plurality of driving pulses for ejecting an ink droplet from the nozzle once expands the volume of the channel and returns the volume of the channel to a first pulse composed of a rectangular wave that returns to the original volume after a predetermined time. deflated, it consists of a second pulse composed of a rectangular wave to return to the original volume after a predetermined time,
A method for driving a droplet ejecting apparatus, wherein a ratio of a first pulse voltage Von and a second pulse voltage Voff is 0.5 ≦ | Von / Voff | ≦ 0.8.
4).
The pulse width of the first pulse is not less than 0.7 AL and not more than 1.3 AL, and the ratio of the pulse width PWon of the first pulse to the pulse width PWoff of the second pulse is 0.45 ≦ | 4. The droplet ejection apparatus driving method according to 3 above, wherein PWon / PWoff | ≦ 0.55.

  According to the present invention, when ejecting ink droplets by time-division driving using a low-viscosity ink from a shear mode type recording head that shears and deforms a partition shared by adjacent channels as an actuator, a nozzle that performs ejection A droplet ejection apparatus capable of stably ejecting ink droplets from a recording head by stabilizing the vibration of a non-ejecting nozzle meniscus adjacent to the recording head and a method for driving the droplet ejection apparatus are provided. it can.

The figure which shows schematic structure of the inkjet recording device which is an application example of the droplet ejection apparatus which concerns on this invention 2A and 2B are diagrams illustrating an example of a recording head constituting the droplet ejection apparatus according to the present invention, in which FIG. 1A is a perspective view showing an outer appearance in cross section, and FIG. The figure which shows an example of the drive signal in this invention The figure explaining the operation | movement at the time of the ink ejection of a recording head Diagram explaining 3-cycle drive Timing chart of drive signal at 3 cycle drive Timing chart of drive signal at 3 cycle drive Graph showing meniscus push-out amount during 3-cycle drive (drive every other channel) when │Von / Voff│ is varied A graph showing the meniscus push-out amount during three-cycle driving (driving every other channel) with different ink viscosities

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

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

  In the inkjet recording apparatus 1, the recording medium 10 is sandwiched between the transport roller pair 22 of the transport mechanism 2 and further transported in the Y direction (sub-scanning direction) by the transport roller 21 that is rotationally driven by the transport motor 23. It has become.

  The recording head 3 is provided between the conveyance roller 21 and the conveyance roller pair 22 so as to face the recording surface 10 a of the recording medium 10. This recording head 3 is shown in the drawing X 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 10. The flexible cable 6 is mounted on a carriage 5 provided so as to be capable of reciprocating along the −X ′ direction (main scanning direction) with the nozzle surface facing the recording surface 10 a of the recording medium 10. Via the drive signal generator 100 (see FIG. 4), which is a drive signal generator provided in the drive circuit.

  The recording head 3 scans and moves the recording surface 10a of the recording medium 10 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. A desired inkjet image is recorded.

  2A and 2B are views showing an example of the recording head 3 constituting the droplet ejection apparatus according to the present invention, wherein FIG. 2A is a perspective view showing the appearance in cross section, and FIG. 2B is a cross-sectional view seen from the side.

  In the recording head 3, 30 is a channel substrate. On the channel substrate 30, a large number of narrow groove-like channels 31 and partition walls 32 are arranged in parallel so as to be alternately arranged. A cover substrate 33 is provided on the upper surface of the channel substrate 30 so as to block all the channels 31 above. A nozzle plate 34 is bonded to the end surfaces of the channel substrate 30 and the cover substrate 33, and a nozzle surface is formed by the surface of the nozzle plate 34. One end of each channel 31 communicates with the outside through a nozzle 34 a formed on the nozzle plate 34.

  The other end of each channel 31 gradually becomes a shallow groove with respect to the channel substrate 30, and communicates with a common flow path 33 a common to each channel 31 formed in the cover substrate 33. The common flow path 33 a is further closed by a plate 35, and ink is supplied from the ink supply pipe 35 b into the common flow path 33 a and each channel 31 through an ink supply port 35 a formed in the plate 35.

  Each partition wall 32 is made of a piezoelectric material such as PZT which is an electric / mechanical conversion means, and functions as an actuator of the present invention. Here, the upper wall portion 32a and the lower wall portion 32b are both formed of a polarized piezoelectric material, and the polarization direction is indicated by the upper wall portion 32a and the lower wall portion 32b (indicated by arrows in FIG. 2B). However, the portion formed by the polarized piezoelectric material may be only the portion indicated by reference numeral 32 a, and may be at least a part of the partition wall 32. The partition walls 32 are arranged in parallel with the channels 31. Accordingly, one partition 32 is shared by the adjacent channels 31 and 31.

  In each channel 31, drive electrodes (not shown in FIG. 2) are formed from the wall surfaces of both partition walls 32 to the bottom surface of the channel 31, and both drive electrodes sandwiching the partition walls 32 are described later. When a drive signal having a predetermined voltage is applied from the drive signal generation unit 100 provided in the drive circuit, the partition wall 32 undergoes shear deformation at the joint surface between the upper wall portion 32a and the lower wall portion 32b. A pressure wave is generated by changing the volume in the channel 31 due to the shear deformation of the partition wall 32, and pressure for ejecting from the nozzle 34a is applied to the ink in the channel 31. Therefore, in this recording head 3, the inside of the channel 31 surrounded by the channel substrate 30, the cover substrate 33, and the nozzle plate 34 constitutes a pressure generating chamber, and the ink in the channel 31 is ejected from the nozzle 34a by the shear deformation of the partition wall 32. This is a shear mode type recording head.

In the present invention, the ink in the channel 31 of the recording head 3 is a low-viscosity ink having a viscosity of less than 5.0 × 10 ⁻³ Pa · sec. The viscosity of the ink is normally a viscosity at normal temperature (25 ° C.), but it is known that the viscosity of the ink is temperature-dependent. In some cases, a temperature device is provided to increase the ink temperature and lower the viscosity. In this case, the viscosity of the ink is a viscosity measured at the set temperature at which the ink to be ejected is heated.

  A drive signal generation unit 100 provided in a drive circuit electrically connected to the recording head 3 via the flexible cable 6 generates a drive signal including a plurality of drive pulses for ejecting ink droplets. .

  An example of the drive signal used in the present invention is shown in FIG.

  The drive signal shown in FIG. 3 is obtained by expanding the volume of the channel within the drive cycle T, the first pulse Pa consisting of a square wave of a positive voltage (+ Von) returning to the original volume after a certain time, and the volume of the channel. And a second pulse Pb composed of a square wave of a negative voltage (−Voff) that is contracted and returned to the original volume after a certain time.

  Note that a certain time, which is a duration for expanding or contracting the volume of the channel, is represented by AL (Acoustic Length). AL is 1/2 of the acoustic resonance period of the pressure wave in the channel. AL measures the velocity of the ink droplet ejected when a rectangular wave drive pulse is applied to the drive electrode, and changes the rectangular wave pulse width while keeping the rectangular wave voltage value constant. It is obtained as the pulse width that maximizes the flight speed.

  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, a rectangular wave refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½, preferably within ¼ of AL.

  In particular, in the shear mode type recording head 3, ink droplets are ejected from the nozzles 34 a using the resonance of pressure waves generated in the channel 31, so that ink droplets can be ejected more efficiently by using rectangular waves. it can.

  Further, since the shear mode type recording head 3 has a fast meniscus response to the application of a drive signal composed of a rectangular wave, the drive voltage can be kept low. In general, since a voltage is always applied to the recording head 3 regardless of whether it is ejected or not, a low driving voltage is important for suppressing the heat generation of the head and ejecting ink droplets stably.

  Furthermore, since the rectangular wave can be easily generated by using a simple digital circuit, there is an advantage that the circuit configuration can be simplified as compared with the case of using a trapezoidal wave having a gradient wave.

  Next, an ink ejection operation when the recording head 3 is driven using the drive signal shown in FIG. 3 will be described with reference to FIG. FIG. 4 shows a part of a cross section obtained by cutting the recording head 3 in a direction orthogonal to the length direction of the channel 31.

  FIG. 4 shows three adjacent channels (31A, 31B, 31C) which are a part of a large number of channels 31. One end of the channel 31 is connected to a nozzle 34a formed on the nozzle plate 34 shown in FIG. 2, and the other end is connected to an ink tank (not shown) via an ink supply port 35a. Drive electrodes 36A, 36B, and 36C connected to the bottom surface of the channel 31 are formed in close contact with the surface of the partition wall 32 that faces each channel 31. The drive electrodes 36A, 36B, and 36C are electrically connected to the drive signal generator 100.

  When the drive signal shown in FIG. 3 is applied to the drive electrodes 36A, 36B, and 36C formed in close contact with the surfaces of the partition walls 32A, 32B, 32C, and 32D by the control of the drive signal generation unit 100, the following operations are exemplified. Thus, an ink droplet is ejected from the nozzle 34a.

  First, when no drive signal is applied to any of the drive electrodes 36A, 36B, 36C, none of the partition walls 36A, 36B, 36C is deformed. In the state shown in FIG. 4A, when the drive electrodes 36A and 36C are grounded and the drive signal shown in FIG. 3 is applied to the drive electrode 36B, the piezoelectric material constituting the partition walls 32B and 32C is formed by the first pulse Pa. An electric field in a direction perpendicular to the polarization direction is generated. As a result, each of the partition walls 32B and 32C is deformed at the joint surfaces of the partition walls 32a and 32b, and the partition walls 32B and 32C are deformed toward each other as shown in FIG. Inflates. As a result, a negative pressure is generated in the channel 31B, and the ink flows (Draw).

  Since the pressure in the channel 31B is reversed every 1AL, if this state is maintained for 1AL, the pressure is reversed to a positive pressure. When grounded at this timing, the partition walls 32B and 32C are moved from the expanded position shown in FIG. Returning to the neutral position shown in FIG. 4A, high pressure is applied to the ink in the channel 31B (Release).

  Then, when the second pulse Pb is continuously applied to the drive electrode 36B without any interval from the fall of the first pulse Pa, as shown in FIG. 4C, the partitions 32B and 32C are By deforming in opposite directions, the volume of the channel 32B is contracted. Since the second pulse Pb is applied at the timing when the pressure in the channel 31B is reversed to the positive pressure after the application of the first pulse Pa, the positive pressure wave due to the contraction of the volume of the channel 32B is added. Thus, the ejection pressure (ejection speed) of the ink droplet is increased, and the most efficient ejection power can be obtained. As a result, the drive voltage can be lowered, so that power consumption can be reduced.

  By applying the second pulse Pb, the channel 31B contracts, so that a higher pressure is applied to the ink filling the channel 31B (Reinforce), and the ink column is pushed out from the nozzle. After 2AL from the application of the second pulse Pb, when the potential of the second pulse Pb is returned to 0, the channel 31B returns to the neutral position in FIG.

  In the above description, the pulse width PWon of the first pulse Pa is 1 AL, but the pulse width PWon of the first pulse Pa in the present invention is in the range of 0.7 AL or more and 1.3 AL or less in the vicinity of 1 AL. I just need it. Further, if the ratio of PWon to PWoff (PWon / PWoff) is 0.45 ≦ | PWon / PWoff | ≦ 0.55, the meniscus surface after injection can be stabilized efficiently.

  Thus, when driving the recording head 3 having a plurality of channels 31 separated by the partition walls 32 at least partially made of a piezoelectric material, when the partition walls 32 of one channel 31 perform the ejection operation, they are adjacent to the recording head 3. Therefore, in general, among the plurality of channels 31, the channels 31 that are separated from each other by sandwiching one or more channels 31 are combined into one set, and all the channels 31 are Drive control is performed so that the ink ejection operation is sequentially performed in a time-division manner by being divided into two or more groups and applying a drive signal from the drive signal generation unit 100 for each group. In particular, when all the channels 31 are driven to output a solid image, a so-called three-cycle driving method is performed in which the channels 31 are selected every two channels and emitted in three phases.

  The injection operation by such 3-cycle driving will be further described with reference to FIG. In the example shown in FIG. 5, the recording head is described as having nine channels 31 of A1, B1, C1, A2, B2, C2, A3, B3, and C3. Here, the nozzle is not shown. In addition, FIG. 6 shows a timing chart of drive signals applied to drive the respective channels 31 of A, B, and C at this time.

  First, the drive signals shown in FIG. 3 are applied to the drive electrodes of each channel of the A group (A1, A2, A3), and the drive electrodes of the adjacent channels are grounded. Then, only the two partitions of the A group of channels to which the ink droplets are to be ejected undergoes shear deformation as described with reference to FIG. 4, and the ink droplets are ejected from the nozzles of the A group of the respective channels 31 (A cycle).

  Next, a drive signal shown in FIG. 3 is applied to the drive electrodes of each channel of the B group (B1, B2, B3), and the drive electrodes of the adjacent channels are grounded. Then, only both partition walls of the B group channels to be ejected with ink droplets are shear-deformed as described with reference to FIG. 4, and ink droplets are ejected from the nozzles of each of the B group channels (B cycle).

  Further, a drive signal shown in FIG. 3 is applied to the drive electrodes of each channel of the C group (C1, C2, C3), and the drive electrodes of the adjacent channels are grounded. Then, only both partition walls of the C set channels to which ink droplets are to be ejected are subjected to shear deformation as described with reference to FIG. 4, and ink droplets are ejected from the nozzles of each channel of the C set (C cycle).

  The above description is an example in which ink droplets are ejected from all the channels 31 of each group, for example, when printing a solid image. However, depending on the print data, for example, FIG. ) May be a non-injection channel. If the adjacent C31 and B2 channels 31 are injection channels, an increase in the meniscus extrusion amount in the nozzle of the A2 channel 31 is a problem. Become.

  In such a shear mode type recording head 3, the partition wall 32 is deformed by a voltage difference applied to drive electrodes provided on both sides of the partition wall 32 so as to sandwich the partition wall 32. Therefore, in the case of the drive signal shown in FIG. 3, instead of applying the second pulse Pb having a negative voltage (−Voff) to the drive electrode in the channel 31 for ejecting ink droplets, as shown in FIG. The same operation is performed by grounding the drive electrode in the channel 31 for ejecting droplets and applying the second pulse Pb as a positive voltage (+ Voff) pulse to the drive electrode in the adjacent channel 31. be able to.

  For example, when the A group of channels 31 is an emission channel, the first pulse Pa (+ Von) is applied to the drive electrode in each of the A group of channels 31 and then continues to the falling edge of the first pulse Pa. At the same time, the drive electrodes in the A set of channels 31 are grounded, and at the same time, the second pulse Pb (+ Voff) is applied to the drive electrodes in the adjacent B set and C set of the channel 31 sharing the partition walls with the A set of channels 31. May be applied respectively. This method is a preferable mode because it can be driven only by a positive voltage.

  In the present invention, the ratio (Von / Voff) between the voltage Von of the first pulse Pa and the voltage Voff of the second pulse Pb satisfies the relationship of 0.5 ≦ | Von / Voff | ≦ 0.8. is important.

  Thus, by setting | Von / Voff | to 0.8 or less, the amount of meniscus extrusion from the nozzle is reduced, and the risk of entraining air can be reduced. The reason for this is considered to be that the drawing amount (Draw) of the drive channel for ejecting ink droplets is relatively reduced, and the meniscus extrusion amount of the adjacent channel by Draw is reduced.

FIG. 8 pays attention to a specific non-driven channel in the set A when three-cycle driving (driving every other channel) is performed using an ink having a viscosity of 3.8 × 10 ⁻³ Pa · sec. The time change of the extrusion amount of the meniscus is shown. Here, as in the case of FIG. 9, when even-numbered channels of each channel are driven in the order of A group → B group → C group (A cycle → B cycle → C cycle) as an ejection channel for performing ink ejection. , A set of specific non-injection channels (odd channels). As a result, when the adjacent B sets of even-numbered channels (even-numbered channels) are driven for injection, the meniscus extrusion amount when | Von / Voff | = 0.67 compared to when | Von / Voff | = 2. It can be seen that is reduced.

  Also, by setting | Von / Voff | to 0.5 or more, it is possible to reduce heat generation and IC load due to a decrease in drive efficiency.

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

  The ratio of the voltage Von of the first pulse to the voltage Voff of the second pulse in the drive signal shown in FIG. 3 is used by using the following two types of ink in the shear mode type recording head shown in FIG. | Von / Voff |) was changed to evaluate the upper limit of the stable speed and the amount of satellite generated when three-cycle driving was performed.

  The recording head has 256 nozzles, the nozzle diameter is 30 μm, AL = 5.6 μs, the pulse width PWon of the first pulse of the drive signal is 5.6 μs (1 AL), and the pulse width of the second pulse PWoff = It was set to 11.2 μs (2AL), and the driving cycle T was set to 28 μs (5AL).

  The upper limit of the stable speed is that at each voltage ratio of | Von / Voff |, the voltage is increased without changing | Von / Voff | Is the maximum flight speed (m / s) that can be injected immediately before. In addition to normal all channel drive, this stable speed upper limit is only for even-numbered channels (2 (B cycle channel), 4 (A cycle channel), 6 (C cycle channel), 8 (B cycle channel) ...) Switching between driving and odd-numbered channel (1 (A cycle channel), 3 (C cycle channel), 5 (B cycle channel), 7 (A cycle channel) ...) only every fixed time (1 sec) Measured with drive pattern (switch drive), the lower speed was applied in both evaluations.

  It is to be noted that the larger the upper limit of the stable speed, the wider the ink droplet flying speed range is preferable. Since lack of injection leads to significant image quality deterioration, it is preferable that there is a difference of at least about 1.5 m / s between the actually used speed and the upper limit of the stable speed. Here, it is assumed that an image is formed by ejecting ink droplets at a flying speed of 6 m / s, and that the upper limit of the stable speed is 7.5 m / s or more can be used without problems (present invention). ing.

  The amount of satellite generation is determined by visually checking the image quality when 10 ink droplets are ejected onto the recording paper and the evaluation image including the switching drive as described above is drawn. It was.

The evaluation criteria are shown below.
Small: 0 to 1 out of 10 judges that satellite splash is conspicuous Medium: 2 to 4 out of 10 judges that satellite splash is conspicuous Multi: More than 5 out of 10 judges that satellite splash is conspicuous

<Ink type>
Ink 1: Viscosity 3.8 × 10 ⁻³ Pa · sec
Surface tension 38 × 10 ⁻³ N · m ⁻¹
Ink 2: Viscosity 4.3 × 10 ⁻³ Pa · sec
Surface tension 56 × 10 ⁻³ N · m ⁻¹

Table 1 shows the measurement results when ink 1 was used, and Table 2 shows the measurement results when ink 2 was used.

  As is apparent from Tables 1 and 2, in both inks 1 and 2, the upper limit of the stable speed is 7.5 m / in the range of 0.5 ≦ | Von / Voff | ≦ 0.8 (Examples 1 to 6). It can be seen that a favorable result is obtained that is greater than or equal to s and the amount of satellite generated is small.

  In Comparative Examples 2, 3, 5, and 6 where the value of | Von / Voff | is greater than 0.8, the upper limit of the stable speed is low. This is because ejection failure occurs when the droplet velocity is increased during switching driving because of large meniscus vibration.

  On the other hand, even if the value of | Von / Voff | is less than 0.5 as in Comparative Examples 1 and 4, the upper limit of the stable speed decreases. This is because the lower the | Von / Voff |, the smaller the pull-in of ink in the first pulse, which is an expansion pulse, and the lower the drive efficiency. That is, if the driving efficiency is low, more voltage is required for high-speed injection, but the upper limit of the stable speed is limited due to the rated value of the driving IC and the problem of heat generation. This problem occurs remarkably when the value of | Von / Voff | is less than 0.5.

  Also, when the value of | Von / Voff | is less than 0.5, the amount of satellite generation increases in both inks 1 and 2. When the value of | Von / Voff | is decreased, the pulse voltage Voff is relatively increased. This means that the cancellation of the pressure wave becomes large, and therefore, the collision of pressure when the ink droplet is torn off becomes large and the generation amount of satellites increases.

  From the above results, preferable ink flying characteristics can be obtained in the range of 0.5 ≦ | Von / Voff | ≦ 0.8, but particularly preferable ink droplet flying characteristics are obtained when | Von / Voff | = 0.67. It is done.

(Reference example)
For reference, the same recording head and driving method as those described above were employed, and the upper limit of the stable speed was measured in the same manner as described above, using the inks 3 and 4 described below. The measurement results are shown in Table 3.

Ink 3: Viscosity 5.7 × 10 ⁻³ Pa · sec, surface tension 41 × 10 ⁻³ N · m ⁻¹
Ink 4: Viscosity 7.2 × 10 ⁻³ Pa · sec, surface tension 39 × 10 ⁻³ N · m ⁻¹

  The inks 3 and 4 are derived from the high viscosity and do not cause significant instability in the switching drive. Therefore, the stable injection upper limit is almost the same regardless of the value of | Von / Voff |.

As a result, the ejection instability at the time of switching driving is remarkable when the ink viscosity is less than 5.0 × 10 ⁻³ Pa · sec. To solve this problem, the voltage Von of the first pulse and the second pulse It can be seen that it is effective to set the ratio of the voltage Voff to 0.5 ≦ | Von / Voff | ≦ 0.8.

1: Inkjet recording device 2: Conveying mechanism 21: Conveying roller 22: Conveying roller pair 23: Conveying motor 3: Recording head 30: Channel substrate 31, 31A, 31B, 31C: Channel 32, 32A, 32B, 32C, 32D: Partition wall 32a: Upper wall part 32b: Lower wall part 33: Cover substrate 33a: Common flow path 34: Nozzle plate 34a: Nozzle 35: Plate 35a: Ink supply port 35b: Ink supply pipes 36A, 36B, 36C: Drive electrode 4: Guide Rail 5: Carriage 6: Flexible cable 10: Recording medium 10a: Recording surface 100: Drive signal generator Pa: First pulse Pb: Second pulse

Claims (4)

It is composed of a plurality of nozzles for ejecting ink droplets, a plurality of channels connected in parallel to the nozzles, and a partition made of a piezoelectric material shared by the adjacent channels, and is sheared by application of a drive signal. A recording head having an actuator for ejecting ink in the channel from the nozzle by changing the volume of the channel;
Drive signal generating means for generating the drive signal including a plurality of drive pulses for driving the actuator;
All of the channels are divided into two or more sets so that the channels separated from each other with one or more of the channels are combined into one set, and the drive signal is applied to each set A droplet ejection device that drives and controls the recording head so as to sequentially perform ink ejection operations in a time-sharing manner,
The ink has a viscosity of less than 5.0 × 10 ⁻³ Pa · sec,
The plurality of driving pulses for ejecting an ink droplet from the nozzle once expands the volume of the channel and returns the volume of the channel to a first pulse composed of a rectangular wave that returns to the original volume after a predetermined time. deflated, it consists of a second pulse composed of a rectangular wave to return to the original volume after a predetermined time,
The droplet ejection apparatus according to claim 1, wherein a ratio of the voltage Von of the first pulse and the voltage Voff of the second pulse is 0.5 ≦ | Von / Voff | ≦ 0.8. The pulse width of the first pulse is not less than 0.7 AL and not more than 1.3 AL, and the ratio of the pulse width PWon of the first pulse to the pulse width PWoff of the second pulse is 0.45 ≦ | 2. The droplet ejection apparatus according to claim 1, wherein PWon / PWoff | ≦ 0.55. It is composed of a plurality of nozzles for ejecting ink droplets, a plurality of channels connected in parallel to the nozzles, and a partition made of a piezoelectric material shared by the adjacent channels, and is sheared by application of a drive signal. A recording head having an actuator for ejecting ink in the channel from the nozzle by changing the volume of the channel;
Drive signal generating means for generating the drive signal including a plurality of drive pulses for driving the actuator;
All of the channels are divided into two or more sets so that the channels separated from each other with one or more of the channels are combined into one set, and the drive signal is applied to each set Then, a driving method of a droplet ejecting apparatus that drives and controls the recording head so that ink ejection operations are sequentially performed in a time-sharing manner,
The ink has a viscosity of less than 5.0 × 10 ⁻³ Pa · sec,
The plurality of driving pulses for ejecting an ink droplet from the nozzle once expands the volume of the channel and returns the volume of the channel to a first pulse composed of a rectangular wave that returns to the original volume after a predetermined time. deflated, it consists of a second pulse composed of a rectangular wave to return to the original volume after a predetermined time,
A method for driving a droplet ejecting apparatus, wherein a ratio of a first pulse voltage Von and a second pulse voltage Voff is 0.5 ≦ | Von / Voff | ≦ 0.8. The pulse width of the first pulse is not less than 0.7 AL and not more than 1.3 AL, and the ratio of the pulse width PWon of the first pulse to the pulse width PWoff of the second pulse is 0.45 ≦ | 4. The method for driving a droplet ejection device according to claim 3, wherein PWon / PWoff | ≦ 0.55.

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