JP2011245822A - Inkjet recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a printing quality by making small variation of a liquid amount and an ejection speed in high-speed printing.SOLUTION: A driving waveform consists of a first contraction pulse which contracts the volume of a pressure chamber, an expansion pulse which expands the volume of the pressure chamber following the first contraction pulse, and a second contraction pulse which contracts the volume of the pressure chamber after rest following the expansion pulse. The inkjet recording apparatus emits the ink by impressing a driving signal with the driving waveform to a recording head. The inkjet recording apparatus satisfies the following relationship when pressures of peak from the first negative pressure of a pressure wave applied to the ink to peak of the third negative pressure are made M1, M2 and M3, and pressures of peak from the first positive pressure to peak of the third positive pressure are made P0, P1, P2 and P3. 1.0<|M1|/|M2|≤3.0. 0.05≤|P0|/|P1|≤0.25. 0.05≤|M3|/|P1|≤0.25. 0.05≤|P3|/|P1|≤0.25.

Description

  The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus capable of stable ejection in a one-pass printer using an independent head.

  In order to make a head capable of drawing a high-definition image, the share mode structure is advantageous because it can easily increase the nozzle density.

  The share mode type head shares the partition wall of the channel that becomes the pressure chamber with the adjacent channel, and cannot discharge from the adjacent channels on both sides simultaneously. Drive with a set of three cycle drives that are divided into channel groups or drive with an independent drive set in which air channels (also referred to as air chambers) and ink channels (also referred to as pressure chambers) are arranged alternately. .

  In recent years, one-pass inkjet printing (an inkjet head having a nozzle row with a printing width length, or a recording head unit having a nozzle row with a printing width length integrated with a plurality of inkjet heads shorter than the printing width length, and Therefore, there is a demand for speeding up by a method of printing by moving the recording medium relatively once.

  When applying a share mode type head to one-pass, especially one-pass ink jets with independent air-driven heads that are not affected by adjacent channels. Widely used in printers.

  Furthermore, a head for a one-pass printer with an increased amount of droplets has been desired for high speed and wide format printing.

  However, when used in one-pass independent drive, unlike the three-cycle drive (A1-B1-C1-A2-B2-C2), adjacent crosstalk that occurs in the three-cycle drive (B and C channels when focusing on the A channel) Since there is no vibration of crosstalk caused by driving, refilling by so-called pumping action (accelerating action of ink introduction by expansion / reduction of the pressure chamber) (ink ejects ink from the nozzle, then ink flows into the pressure chamber from the ink supply port) There is no promotion effect. For this reason, it takes a long time for the meniscus to return from the time of discharge once to the next discharge, and it is difficult to increase the speed. In addition, the larger the liquid droplet head to which the amount of liquid to be ejected is, the more the delay in refilling becomes so remarkable that a stable liquid amount cannot be produced. In particular, since the reverberation of the pressure wave before the second drop is least, the liquid amount of the second drop is reduced.

  That is, it is necessary to give the same effect as the pumping action obtained at the time of adjacent driving by the driving waveform. However, in order to obtain pumping, it is necessary to give reverberation for a certain period of time after discharge, but after the meniscus fully recovers to until the next discharge, it is necessary that there is almost no reverberation.

  In Patent Document 1, when expanding and contracting an ink chamber in order to reduce reverberation, a technique is provided in which a certain predetermined pause time is provided to reduce crosstalk between ink chambers and to partially cancel the reverberation. There is.

  However, this technology was applied to one-pass independent drive ejection, but with this, the refill could not catch up at all, the ejection speed of the second drop insufficiently refilled was abnormally high, and the next second drop was left behind. In contrast, it was found that the liquid volume increased and the discharge speed slowed down, and the liquid volume fluctuations in the odd and even numbers were large, so that the independent drive could not withstand practical use at all.

  Patent Document 2 discloses a driving technique in which a meniscus pushing pulse signal is vibrated while maintaining 2 (N + 1) times AL to prevent decap, and then the channel is enlarged and returned to its original state. Due to the 1AL of the pause time between 2 (N + 1) times and the main drive signal following it, the oscillated meniscus fluctuates, so the speed component fluctuates greatly, and the discharge speed also increases in frequency. Fluctuated and could not withstand use.

  In addition, as a similar technique, and in Patent Document 3, as a technique for discharging a droplet amount into a minute droplet of about 4 pl or less for high resolution, the time of the expansion pulse signal and the rest time following it are set. A technique for achieving 0.8 to 1.2 AL is disclosed. However, with this technology, the reverberation of a pressure wave that is too large to obtain a pumping effect in an independent drive is caused to act too much, and a sufficient refill is exhibited at a certain frequency. The meniscus was vibrated greatly even at the timing of discharge, and the liquid amount was largely insufficient because the stability greatly varied with frequency. Further, in the head having a shape with a large amount of discharged liquid, the meniscus becomes further unstable, and the object of the present invention cannot be achieved.

Japanese Patent Laid-Open No. 2002-19103 Japanese Patent Laying-Open No. 2005-212411 JP 2004-82425 A

  The object of the present invention is to promote refilling, so that even when printing at high speed, a stable liquid volume is discharged, and the influence of the driving frequency is suppressed, so that the liquid volume and the injection speed can be obtained in various discharge modes. Is to provide an inkjet recording apparatus and a recording method capable of improving the print quality by reducing the fluctuations of the image and capable of highly reliable recording. It is an object to provide an ink jet recording apparatus and a recording method capable of stably discharging even when the size is increased.

  The object of the present invention has been achieved by the following means.

1. A recording head having pressure generating means that operates by applying a driving signal, a pressure chamber whose volume expands or contracts by the operation of the pressure generating means, and a nozzle that communicates with the pressure chamber, and generates the driving signal An ink jet that expands or contracts the volume of the pressure chamber by applying the drive signal from the drive signal generating means to the pressure generating means and ejects ink droplets from the nozzles. In the recording device,
The drive signal is composed of a periodic series of drive waveforms for generating one ink droplet, and the drive waveform follows at least a first contraction pulse for contracting the volume of the pressure chamber and the first contraction pulse. An expansion pulse that expands the volume of the pressure chamber, and a second contraction pulse that contracts the volume of the pressure chamber after a pause following the expansion pulse,
The relative value P of the pressure generated in the ink in the pressure chamber with respect to time t is obtained from the following equations 1 and 2.
The relative value of the pressure of the first negative pressure peak generated by the expansion pulse is M1,
The relative value of the pressure of the second negative pressure peak following the first negative pressure peak is M2,
The relative value of the pressure of the third negative pressure peak following the second negative pressure peak is M3,
The relative value of the pressure of the positive pressure peak generated before the first negative pressure peak is P0,
The relative value of the pressure of the first positive pressure peak following the first negative pressure peak is P1,
The relative value of the pressure of the second positive pressure peak following the first positive pressure peak is P2,
The relative value of the pressure of the third positive pressure peak following the second positive pressure peak is P3,
In the ink jet recording apparatus, the relative value of the pressure of each peak satisfies the relations of expressions 3 to 6.

Formula 1 Si = Ri × Exp (− (t−ei) / τ) × Sin [2π × fr × (t−ei)]
Formula 2

(P: Relative value of pressure in the pressure chamber, t: time, ei: time when the i-th edge of the drive waveform is generated, τ: attenuation constant obtained in the injection experiment, Ri: i-th edge of the drive waveform Voltage change, Si: relative value of pressure component generated by i-th edge of drive waveform)
(Fr = 1 / (2AL), AL: 1/2 of the acoustic resonance period of the pressure generating chamber)
Formula 3 1.0 <| M1 | / | M2 | ≦ 3.0
Formula 4 0.05 ≦ | P0 | / | P1 | ≦ 0.25
Formula 5 0.05 ≦ | M3 | / | P1 | ≦ 0.25
Formula 6 0.05 ≦ | P3 | / | P1 | ≦ 0.25.

  The inventor first studied diligently a reverberation pattern necessary for obtaining a pumping action. Contrary to expectations, it has been found that sufficient pumping action can be obtained by creating a large negative pressure during the initial meniscus retraction. In addition to the pumping action, the influence of such reverberation also affects the vibration of the ink meniscus in the nozzle. If the relationship between the first and second negative pressures is | M1 |> | M2 If it is |, it was found that the pumping effect is greater than the meniscus vibration. As a result, it was found that | M1 |> | M2 | is a necessary condition. Further, if | M1 | / | M2 | ≦ 3.0, it is possible to drive at a low voltage while suppressing an applied voltage.

  In addition, the reverberation needs to be reduced by the next discharge while obtaining the pumping action, and analysis is performed by paying attention to M3 and P3, and these | M3 | and | P3 | As described above, it was found that when the ratio was 1/4 or less | P1 |

  Further, the pumping action can be obtained by setting 0.05 ≦ | M3 | / | P1 | as shown in Equation 5 and 0.05 ≦ | P3 | / | P1 | as shown in Equation 6.

  As a result of continuous discharge using these techniques, it was found that the amount of liquid in the second drop was still reduced and could not be put to practical use.

  This is considered to be because the reverberation of the second drop is the smallest compared to the continuous case, and the pumping effect cannot be obtained. Although the meniscus does not vibrate greatly, a very small amount of extrusion pressure is applied to push out the meniscus by a minute amount. Later, as described above, when the pressure wave peak pressures M1 to M3, P0, P1, and P3 were combined, fluctuations in the liquid volume of the second drop were no problem.

  Here, when | P0 | is equal to or smaller than 1/4 | P1 | as shown in Expression 4, the speed fluctuation at the next discharge is within 10% and the liquid volume fluctuation is within 5%, and the light can be continuously and stably emitted. , 0.05 ≦ | P0 | / | P1 |, the pumping action is obtained. As described above, the present invention can be achieved by sequentially analyzing and improving the problems and their causes, and cannot be achieved by a known technique by independent driving.

  2. The recording head alternately provides a number of pressure chambers provided with the nozzles for ejecting the ink droplets and a number of air chambers into which ink is not introduced. 2. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is adjacent to a partition having the pressure generating means that is deformed in response to the pressure generating means and is a shear mode type recording head in which the pressure generating means is a piezoelectric material. .

  3. The drive signal includes a time t1 for the expansion pulse for expanding the volume of the pressure chamber, a time t2 for a predetermined rest period, and a second time for contracting the volume of the pressure chamber to eject ink. 3. The ink jet recording apparatus according to 1 or 2, wherein t <b> 1 and t <b> 2 are both 0.7 or more and less than 1 AL when the time of the contraction pulse of 2 is t <b> 3.

  4). 4. The ink jet recording apparatus according to any one of items 1 to 3, wherein a time t0 of the first contraction pulse is in a range of 0.2 to 0.5 AL.

  5. In the recording head, the shape of the pressure chamber is a rectangular parallelepiped, and one surface of the rectangular parallelepiped has an ink supply port through which ink flows from the common ink chamber to the pressure chamber, and faces the surface having the ink supply port. 5. The ink jet recording apparatus according to any one of 2 to 4, wherein a nozzle is provided on the surface of the rectangular parallelepiped.

  According to the present invention, an independent recording head that is often used in a one-pass printer or the like provides an ink jet recording apparatus that is excellent in refill characteristics and droplet velocity stability and can be stably ejected even when printed at high speed. did it.

It is a schematic diagram which shows the structure of a line type inkjet recording device. FIG. 4 is a diagram illustrating an example of arrangement of recording heads of a recording head unit. FIG. 4 is a diagram illustrating a relationship between an outer shape of a recording head, a discharge width, and a staggered arrangement. It is a figure which shows a recording head. FIG. 6 is a diagram illustrating an operation of a share mode type recording head during ink ejection. Drive waveform for obtaining the attenuation constant τ. The pressure wave of the present invention. The pressure wave of Example 1. The pressure wave of the comparative example 1. The pressure wave of the comparative example 2. The pressure wave of the comparative example 3. The pressure wave of the comparative example 4. The pressure wave of Comparative Example 5 The pressure wave of the comparative example 6. The pressure wave of Comparative Example 7 The pressure wave of the comparative example 8. The pressure wave of Example 2. The pressure wave of Example 3. The pressure wave of Example 4. The pressure wave of Example 5. The pressure wave of Example 6. The pressure wave of Example 7. The pressure wave of the comparative example 9. The pressure wave of Comparative Example 10

  Hereinafter, although the present invention is explained in detail using a drawing, the present invention is not limited to this.

  FIG. 1 is a schematic diagram showing a configuration of a line-type ink jet recording apparatus 1.

  As shown in FIG. 1, a long recording medium 10 wound in a roll shape is unwound from an unwinding roll 10 </ b> A in the direction of arrow X by a driving unit (not shown) and conveyed. The long recording medium 10 is conveyed while being wound around and supported by a back roll 20. Ink is ejected from the recording head unit 30 toward the recording medium 10 to form an image based on the image data. The recording head unit 30 has a plurality of recording heads 31 corresponding to the ejection width in the recording medium width direction. The recording head 31 may be configured to be movable in the recording medium width direction, and may eject ink toward the recording medium 10 while moving in the recording medium width direction.

  Ink is supplied to each recording head 31 through a plurality of ink tubes 43 from an intermediate tank 40 that adjusts the ink back pressure of the recording head 31. In this description, the ink tube 43 in the figure is a plurality of ink tubes. Ink supply to the intermediate tank 40 is performed by a liquid feed pump P provided in the middle of the supply pipe 51 from the storage tank 50 for storing ink. The recording medium 10 on which an image is formed by the recording head unit 30 is dried by the drying unit 90 and taken up by the take-up roll 10B.

  FIG. 2 is a diagram illustrating an arrangement example of the recording head 31 of the recording head unit 30.

  The recording head unit 30 shown in FIG. 2 is an example in which all the recording heads 31 are arranged at the same height with respect to the intermediate tank 40 (see FIG. 1) that temporarily stores ink. Since the discharge width that can be discharged by one recording head is narrower than the outer dimensions of the recording head, a plurality of recording heads are arranged in a staggered manner in the recording medium conveyance direction in order to discharge without gaps. In the example shown in FIG. 2, a plurality of recording heads corresponding to the ejection width are arranged in two rows in a staggered manner in the recording medium width direction.

  FIG. 3 is a diagram illustrating the relationship between the outer shape, the ejection width, and the staggered arrangement of the recording head 31. The number of recording heads 31 and the number of rows in a staggered arrangement are appropriately set according to the ejection width of the recording heads 31 and the like, and are not limited to this example.

  FIG. 4 is a diagram showing the recording head 31. FIG. 4A is a perspective view showing a partial cross section of the head chip 310 of the shear mode type recording head 31, in which nozzles are provided every other channel, and ink is introduced into the pressure chambers where the nozzles are provided. However, the channel in which the nozzle is not provided has no ink supply port, and becomes an air channel into which ink is not introduced. In general, a chip having 256 or more pressure chambers is preferable, but FIG. 4A omits a number of channels for the sake of clarity. FIG. 4B is a cross-sectional view seen from the channel arrangement direction.

  In FIG. 4, 43 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, 27 is a partition wall, L is the length of a pressure chamber, and D is a pressure chamber. , W (see FIG. 5) is the width of the pressure chamber. A pressure chamber 28 is formed by the partition wall 27, the cover plate 24, and the substrate 26.

  FIG. 5 is a diagram illustrating the operation of the share mode type recording head 31 during ink ejection.

  As shown in FIG. 5, the recording head 31 includes a pressure chamber separated between a cover plate 24 and a substrate 26 by a plurality of partition walls 27A, 27B, 27C, and 27D made of a piezoelectric material such as PZT that is a pressure generating means. Many 28 are arranged in parallel. In FIG. 5, three (28A, 28B, 28C) which are a part of many pressure chambers 28 are shown. An end of the pressure chamber 28 on the nozzle side (hereinafter sometimes referred to as a nozzle end) is connected to a nozzle 23 formed on the nozzle forming member 22, and the other end (hereinafter also referred to as a manifold end) is ink. The ink tube 43 is connected to an ink tank (not shown) through the supply port 25. 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 surface of the partition walls 27 in each pressure chamber 28, as shown in FIGS. 4B and 5A. As shown, the electrodes 29 </ b> A, 29 </ b> B, 29 </ b> C are connected to the drive signal generating unit 100 via the anisotropic conductive film 78 and the flexible cable 6.

  Here, each partition wall 27 is constituted by two piezoelectric materials 27a and 27b having different polarization directions as indicated by arrows in FIG. 5, but the piezoelectric material may be only the portion indicated by reference numeral 27a. 27 may be present in at least a part of 27. In this manner, the piezoelectric material constituting the partition wall 27 serves as pressure generating means, and applies pressure to the ink in the pressure chamber.

  The drive signal generation means 100 is supplied from the drive signal generation circuit (not shown) for generating a series of drive signals including a plurality of drive pulses for each pixel period and from the drive signal generation circuit for each pressure chamber. It comprises a drive pulse selection circuit (not shown) that selects a drive pulse from the drive signal according to the image data of each pixel and supplies it to each pressure chamber, and serves as pressure generating means according to the image data of each pixel. A driving pulse which is a driving signal for driving the partition wall 27 is supplied.

  When the image data is received, the control unit (not shown) controls the recording medium conveying means, and the drive signal generating circuit includes at least a pulse for expanding the volume of the pressure chamber 28 and a pulse for contracting the volume of the pressure chamber. A drive signal having a drive pulse is generated. Further, the control unit outputs information on the drive pulse to be selected to the drive pulse selection circuit based on the image data. Then, the drive pulse selection circuit selects a drive pulse based on the information and supplies it to the partition wall 27. As a result, ink droplets are ejected from the nozzles 23 of the recording head 31 within one pixel period.

  In the ink jet recording apparatus according to the present embodiment, when the partition wall 27 is driven, a drive signal from the drive signal generating unit 100 is applied to the first contraction pulse for contracting the volume of the pressure chamber 28 and the first contraction pulse. Subsequently, the driving waveform has a combination of a first expansion pulse for expanding the volume of the pressure chamber 28 and a second contraction pulse for contracting the volume of the pressure chamber 28 after the expansion pulse following the expansion pulse. At a constant drive cycle.

(Attenuation constant)
The attenuation constant was obtained as follows.

  A drive signal using the drive waveform of FIG. 6 was applied, and an emission test was performed with a single channel (for example, when the chip has 256 pressure chambers, the drive signal is not applied to 255 channels). The drive signal consists of a periodic series of the drive waveforms. In FIG. 6, the vertical axis represents the voltage applied to the electrode of the pressure chamber, the upper direction is the positive voltage direction, and the lower direction is the negative voltage direction. The horizontal axis is time. In FIG. 6, the pressure chamber is expanded by applying a pulse of voltage Von, and the pressure chamber is contracted by applying a pulse of voltage Voff. Both pulse widths are 1AL, and the pause time between both pulses is also 1AL. The drive signal is formed by repeating the drive waveform with a constant drive cycle at intervals. Von and Voff are changed under the condition that the droplet velocity is 6 m / s when the drive cycle is 10 AL, and the drive cycle is changed from 6 · AL to 10 · AL in 0.5 · AL increments. The variation in speed was measured.

  As a result, most stable against changes in the driving cycle (injection speed X when the driving cycle is 10 AL, and injection when the driving cycle is changed from 6 AL to 10 AL in increments of 0.5 AL. When the speed is Yj (j = 1 to 9), the maximum value of | Yj−X | is minimum) | Von |: | Voff | That is, the pressure wave was considered to be the most attenuated when the voltage ratio was m: n.

  Next, from Equations 1 and 2, the voltage ratio is m: n, the damping constant τ is changed, the relationship between the time t and the relative value P of the pressure is obtained, and the damping constant τ with the best pressure wave cancellation is obtained. Asked.

  The best cancellation of the pressure wave is that the pressure after the second negative pressure peak (pressure trough) becomes zero.

  Since the attenuation constant τ does not depend on the drive waveform, the same τ can be used even when other drive waveforms are used.

  AL (Acoustic Length) is 1/2 of the acoustic resonance period of the ink channel. This AL measured the speed of ink droplets ejected by applying a rectangular wave pulse to the partition wall 27, which is an electrical / mechanical conversion means, and changed the rectangular wave pulse width while keeping the rectangular wave voltage value constant. Sometimes it is determined as the pulse width that maximizes the flying speed of the ink droplets. This value is determined depending on the structure of the head, the density of the ink, and the like.

(Drive signal)
The drive signal of the present invention will be described using the drive waveform shown in FIG. The drive signal consists of a periodic series of the drive waveforms. In the drive waveform of FIG. 7, the vertical axis is the voltage applied to the electrode of the pressure chamber, the upward direction is the positive voltage direction, and the downward direction is the negative voltage direction. The horizontal axis is time.

  When a positive voltage is applied to the electrode, the pressure chamber expands from the state of FIG. 5A where no voltage is applied, as shown in FIG. 5B, and a negative pressure component is generated in the ink. Conversely, when a negative voltage is applied, the pressure chamber contracts as shown in FIG. 5C, and a positive pressure component is generated in the ink.

  The drive waveforms constituting the drive signal are, in order, a first contraction pulse (voltage Voff, contraction pulse with a pulse width t0), an expansion pulse (voltage Von, an expansion pulse with a pulse width t1), and a pause (voltage 0 V, time t2). And a second contraction pulse (voltage Voff, contraction pulse at time t3).

  A time t1 of a pulse signal for expanding the volume of the ink chamber, a predetermined time t2 following that, and a pulse signal for contracting the volume of the ink chamber to actually eject the actuator by deforming it. When time t3 is set, it is preferable that t1 and t2 are both 0.7 or more and less than 1AL. It is preferable that the drive waveform for providing a pause time is less likely to be pulled back when the meniscus is broken and is easily restored, and the resonance period is shifted from there to increase the reverberation, thereby promoting refilling.

  The time t0 of the pulse signal for contracting the ink chamber for pushing out the meniscus in the nozzle to the extent that it does not vibrate before the pulse signal t1 for expanding the volume of the ink chamber is in the range of 0.2 to 0.5 AL. preferable. By setting t0 within this range, the speed and liquid volume fluctuation of the second drop are reduced.

  Here, the pulse is a rectangular wave having a constant voltage peak value, and when 0V is 0% and the peak voltage is 100%, the pulse width is the start or fall of the voltage from 0V of the voltage. It is defined as the time between the beginning 10% and the beginning of falling from the peak value voltage or 10% of the beginning of rising. Furthermore, the rectangular wave here refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within 1/10, preferably within 1/20 of AL. .

(pressure)
When the voltage applied to the piezoelectric element changes, the piezoelectric element is deformed, and the pressure applied to the ink in the pressure chamber changes. The voltage change occurs at the beginning and end of the pulse.

  In FIG. 7, the voltage change is caused by edge 1 (voltage drop from 0 V to Voff) due to the first contraction pulse, edge 2 (voltage rise from Voff to Von) due to the first contraction pulse and expansion pulse, and expansion pulse. It occurs at edge 3 (voltage drop from Von to 0 V), edge 4 (voltage drop from 0 V to Voff), and edge 5 (voltage rise from Voff to 0 V) of the second contraction pulse. The generation time of edge i is represented by ei. That is, the generation times of the edges 1 to 5 are t = e1 to t = e5. Here, e1 = 0.

  At each edge i, a pressure component proportional to the voltage fluctuation Ri applied to the piezoelectric element acts on the ink. By Equation 1, the relative values S1 to S5 of the pressure component acting on the ink at the edges 1 to 5 are obtained.

  That is, the following may be used as the voltage fluctuation.

R1 = Voff (voltage drop from 0V to Voff at t = e1)
R2 = Von-Voff (voltage rise from Voff to Von at t = e2)
R3 = -Von (voltage drop from Von to 0V at t = e3)
R4 = Voff (voltage drop from 0 to Voff at t = e4)
R5 = -Voff (voltage rise from Voff to 0V at t = e5)
However, Von is a positive value and Voff is a negative value.

  The relative value P of the ink pressure can be obtained by Equation 2 as a sum of S1 to S5.

  That is, a change in the positive pressure direction occurs at the edges 1, 3, 4, a change in the negative pressure direction occurs at the edges 2, 5, and the pressure wave components generated at the respective edges are added together to generate Is formed. Therefore, the pressure wave P is calculated by adding up the components of the pressure wave generated at each edge.

According to the present invention, the relative value of the first negative pressure peak generated by the expansion pulse is expressed as M1,
The relative value of the pressure of the second negative pressure peak following the first negative pressure peak is M2,
The relative value of the pressure of the third negative pressure peak following the second negative pressure peak is M3,
The relative value of the pressure of the positive pressure peak generated before the first negative pressure peak is P0,
The relative value of the pressure of the first positive pressure peak following the first negative pressure peak is P1,
The relative value of the pressure of the second positive pressure peak following the first positive pressure peak is P2,
The relative value of the pressure of the third positive pressure peak following the second positive pressure peak is P3,
In this case, the relative value of the pressure of each peak satisfies the relationship of the above formulas 3-6.

Formula 3 1.0 <| M1 | / | M2 | ≦ 3.0
Formula 4 0.05 ≦ | P0 | / | P1 | ≦ 0.25
Formula 5 0.05 ≦ | M3 | / | P1 | ≦ 0.25
Formula 6 0.05 ≦ | P3 | / | P1 | ≦ 0.25.

  The negative pressure peak is a point on the pressure wave where the pressure wave P is minimum, and the positive pressure peak is a point on the pressure wave where the pressure wave P is maximum.

  As an example, P0, M1, P1, M2, P2, M3, and P3 are shown on the pressure wave of FIG. 8 using the drive waveform according to the present invention.

[Examples 1-6 and Comparative Examples 1-8]
The experimental conditions are shown below. First, a head for discharging 30 pl was created.

Recording head: Share mode type head shown in FIG. 4 (number of nozzles: 256, nozzle diameter: 39 μm, D = 300 μm, L = 4.5 mm)
AL: 7.6 μs
Ink: Solvent ink (viscosity 10 mPa · s, surface tension 30 mN / m (25 ° C.))
Attenuation constant: 27 μs
Driving time: continuous 300 seconds Under the above conditions, driving signals having various driving waveforms having the pulse widths t0, t1, t3 and the pause time t2 shown in Table 1 were given, and Examples 1-6 and Comparative Examples 1-7 The discharge experiment was conducted. In Comparative Example 8, as shown in Table 2, the drive signal was applied with a drive waveform in which the order of the expansion pulse and the pause was opposite to the drive waveform of the present invention. In the above table, the time of the process in which no pulse or pause exists is 0. The drive pulse width is shown in AL units.

  The pressure wave P calculated | required by Formula 1 and Formula 2 was shown to FIGS. The unit of time t on the horizontal axis is μs (μsec). At time t, e1 was set to 0.

  Below, the correspondence of an Example, a comparative example, and a figure is shown.

Example 1 FIG.
Example 2 FIG.
Example 3 FIG.
Example 4 FIG.
Example 5 FIG.
Example 6 FIG.
Comparative Example 1 FIG.
Comparative Example 2 FIG.
Comparative Example 3 FIG.
Comparative Example 4 FIG.
Comparative Example 5 FIG.
Comparative Example 6 FIG.
Comparative Example 7 FIG.
Comparative Example 8 FIG.
Table 3 shows the result of calculation based on the pressure wave P whether or not the conditions of formulas 3 to 6 are satisfied.

(Evaluation of fluid volume fluctuation)
The fluctuation of the liquid amount was determined as a reference droplet amount L1 by measuring the initial droplet amount when a driving signal having a driving period of 10 AL having the driving waveform shown in Table 1 was applied. On the other hand, continuous ejection was performed at a driving frequency of 17 kHz, the total droplet amount was measured, and the average droplet amount L2 was obtained.

  The droplet amount was determined as the droplet amount per droplet from the collected ink droplet amount and the number of droplets.

Liquid volume fluctuation = (L2-L1) / L1
As the evaluation criteria for the liquid volume fluctuation, the absolute value of the liquid volume fluctuation was ○ within 5%, Δ when the liquid volume was 5-15%, and x exceeding 15%.

(Evaluation of speed stability)
Velocity stability is an index indicating a small fluctuation in the flying speed of each droplet, which is continuously ejected from each nozzle.

  The driving cycle is 7AL (driving frequency is 18.8 kHz), and, as in the evaluation of liquid volume fluctuation, high-speed video shooting is performed, and when the first injection speed in the continuous driving is 6 m / sec, The change in the speed of the second shot, which is easily affected, was evaluated.

  The absolute value of the difference between the speed of the first shot of 6 m / sec and the speed of the second shot (m / sec) is within 5%, when the speed is 5 to 15%, over the range of 15% X.

(Evaluation of high-speed stability)
High-speed stability is an index that represents a small amount of non-ejection when a large number of droplets are emitted per unit time by shortening the driving cycle.

  The high-speed stability is the number of non-ejections with respect to the total number of ejections (256 nozzles × 150,000 times) when ejection (150,000 times) is performed at the driving cycle 7AL (driving frequency is 18.8 kHz) under the above experimental conditions. The ratio of was calculated. The evaluation criteria were ◎ when the number of non-ejections was 0%, ◯ when less than 1%, △ when less than 1% to less than 5%, and x when more than 5%.

(Comprehensive evaluation)
Even if there is one, there is a x and it cannot be used. △ also when there is △. Those with three circles were marked with ◎, others with circles.

  The evaluation results are shown in Table 3.

  From Table 3, it can be seen that the ink jet recording apparatus using the drive waveform of the present invention is excellent in liquid volume fluctuation, speed stability, and high speed stability, and particularly in liquid volume fluctuation and speed stability.

[Example 7, Comparative Examples 9 and 10]
The experiment was conducted using the following head and ink.

Recording head: Share mode type head shown in FIG. 4 (number of nozzles: 256, nozzle diameter: 28 μm, D = 300 μm, L = 2.5 mm)
Droplet volume: 14 pl
AL: 5.0 μs
Ink: Water-based ink (viscosity 5.7 mPa · s, surface tension 58 mN / m (25 ° C.))
Attenuation constant: 13 μs
Drive cycle: 15 kHz
Driving time: continuous 300 seconds Under the above conditions, driving signals having various driving waveforms shown in Table 4 were given, and an ejection experiment was performed. In Table 4, the time of the process in which there is no pulse or pause is 0. The pulse widths t0, t1, t3 and the rest time t2 are shown in AL units.

  The pressure wave P calculated | required by Formula 1 and Formula 2 was shown to FIGS. The unit of time t on the horizontal axis in FIGS. 22 to 24 is μs (μ seconds).

  Below, the correspondence of an Example, a comparative example, and a figure is shown.

Example 7 FIG.
Comparative Example 9 FIG.
Comparative Example 10 FIG.
Table 5 shows the results calculated from the pressure wave P to determine whether the conditions of Formulas 3 to 6 are satisfied.

  Evaluation was performed in the same manner as in Examples 1 to 6 and Comparative Examples 1 to 8, and the results are shown in Table 5.

  From Table 5, it can be seen that the ink jet recording apparatus using the drive waveform of the present invention is excellent in liquid volume fluctuation, speed stability and high speed stability, and in particular, liquid volume fluctuation and speed stability are excellent.

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 10 Recording medium 20 Back roll 23 Nozzle 24 Cover plate 25 Ink supply port 26 Substrate 27 Partition 28 Pressure chamber 30 Recording head unit 31 Recording head 40 Intermediate tank 43 Ink tube 50 Storage tank 51 Supply pipe 90 Drying unit 100 Drive Signal generation means

Claims (5)

A recording head having pressure generating means that operates by applying a driving signal, a pressure chamber whose volume expands or contracts by the operation of the pressure generating means, and a nozzle that communicates with the pressure chamber, and generates the driving signal An ink jet that expands or contracts the volume of the pressure chamber by applying the drive signal from the drive signal generating means to the pressure generating means and ejects ink droplets from the nozzles. In the recording device,
The drive signal is composed of a periodic series of drive waveforms for generating one ink droplet, and the drive waveform follows at least a first contraction pulse for contracting the volume of the pressure chamber and the first contraction pulse. An expansion pulse that expands the volume of the pressure chamber, and a second contraction pulse that contracts the volume of the pressure chamber after a pause following the expansion pulse,
The relative value P of the pressure generated in the ink in the pressure chamber with respect to time t is obtained from the following equations 1 and 2.
The relative value of the pressure of the first negative pressure peak generated by the expansion pulse is M1,
The relative value of the pressure of the second negative pressure peak following the first negative pressure peak is M2,
The relative value of the pressure of the third negative pressure peak following the second negative pressure peak is M3,
The relative value of the pressure of the positive pressure peak generated before the first negative pressure peak is P0,
The relative value of the pressure of the first positive pressure peak following the first negative pressure peak is P1,
The relative value of the pressure of the second positive pressure peak following the first positive pressure peak is P2,
The relative value of the pressure of the third positive pressure peak following the second positive pressure peak is P3,
In the ink jet recording apparatus, the relative value of the pressure of each peak satisfies the relations of expressions 3 to 6.
Formula 1 Si = Ri × Exp (− (t−ei) / τ) × Sin [2π × fr × (t−ei)]
Formula 2

(P: Relative value of pressure in the pressure chamber, t: time, ei: time when the i-th edge of the drive waveform is generated, τ: attenuation constant obtained in the injection experiment, Ri: i-th edge of the drive waveform Voltage change, Si: relative value of pressure component generated by i-th edge of drive waveform)
(Fr = 1 / (2AL), AL: 1/2 of the acoustic resonance period of the pressure generating chamber)
Formula 3 1.0 <| M1 | / | M2 | ≦ 3.0
Formula 4 0.05 ≦ | P0 | / | P1 | ≦ 0.25
Formula 5 0.05 ≦ | M3 | / | P1 | ≦ 0.25
Formula 6 0.05 ≦ | P3 | / | P1 | ≦ 0.25   The recording head alternately provides a number of pressure chambers provided with the nozzles for ejecting the ink droplets and a number of air chambers into which ink is not introduced. 2. The ink jet recording according to claim 1, wherein the ink jet recording is a shear mode type recording head which is adjacent to each other through a partition having the pressure generating means which is deformed in response to the pressure generating means and the pressure generating means is a piezoelectric material. apparatus.   The drive signal includes a time t1 for the expansion pulse for expanding the volume of the pressure chamber, a time t2 for a predetermined rest period, and a time for contracting the volume of the pressure chamber to eject ink. 3. The ink jet recording apparatus according to claim 1, wherein t <b> 1 and t <b> 2 are both 0.7 or more and less than 1 AL when the time of the contraction pulse of 2 is t <b> 3.   The inkjet recording apparatus according to any one of claims 1 to 3, wherein a time t0 of the first contraction pulse is in a range of 0.2 to 0.5 AL.   In the recording head, the shape of the pressure chamber is a rectangular parallelepiped, and one surface of the rectangular parallelepiped has an ink supply port through which ink flows from the common ink chamber to the pressure chamber, and faces the surface having the ink supply port. The inkjet recording apparatus according to claim 2, further comprising a nozzle on a surface of the rectangular parallelepiped.

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