JP5459695B2 - Inkjet recording apparatus and inkjet recording method - Google Patents

Description

  The present invention relates to an ink jet recording apparatus and a recording method, and more particularly to an ink jet recording apparatus and a recording method in which a plurality of pressure chambers adjacent to each other are mounted and an image is recorded at a high speed while increasing an appropriate amount of liquid.

  In an ink jet recording method that records an image by ejecting minute ink droplets from a nozzle and landing on a recording medium, it is important to ensure the uniformity of the image that the ink droplets land on the target position of the recording medium. It is.

  In recent years, in order to record higher quality images, nozzle density and ink droplet size have been reduced.

  On the other hand, in order to increase productivity, it is also required to increase the recording speed. For this purpose, the drive frequency is increased and the number of nozzles is increased.

  Bender type, piston type, shear mode type, shared wall type, etc. are known as the type of recording head, but it is possible to discharge liquids of various viscosities, and the shear mode type is advantageous when considering high density. It is considered to be.

  However, when the drive frequency is increased to increase the recording speed, that is, when the ink droplet is ejected with a short time interval, the time until the next ejection is short, and therefore the pressure wave attenuation in the pressure chamber is difficult to proceed. I found it to happen.

  Since the share mode type head shares the partition wall of the channel serving as the pressure chamber with the adjacent channel and cannot discharge simultaneously from the adjacent channels on both sides, every pair of A, B, and C every 3 channels. Driving is performed by a set of three-cycle driving in which the driving is divided into channel groups. At that time, this phenomenon occurs remarkably.

  For example, when the A, B, and C channels are arranged in order, they are small in the B channel that is adjacent to them, that is, the B channel to be discharged next, due to deformation caused by the driving of A, but cannot be ignored. This is because extra pressure is generated.

  Moreover, the shorter the time interval, the less the pressure wave decays. As a result, the discharge of the next channel cannot be performed well, and the angle direction due to the tail bending of the droplet is shifted, and landing errors are likely to occur. It was.

  That is, when ink droplets are ejected from the nozzle at a predetermined driving frequency, the interval between dots formed by the ink droplets from the first droplet is ideally always constant as shown in FIG. Is. However, when ink droplets are ejected at a high driving frequency, as shown in FIG. 11 (b), the droplets are bent at the time of ejection and the angular direction is deviated as shown in FIG. There is a case where the image is distorted due to landing at a position deviated from the position to land, or the nozzle is not ejected at all due to ejection.

  When the same head is driven at a lower driving frequency, it becomes possible to discharge stably, so it is considered that the same head is generated depending on the driving frequency and the way of attenuation of the pressure wave generated at that time. In other words, lowering the drive frequency to allow sufficient time for attenuation, or reducing the droplet velocity during discharge and suppressing pressure waves to make it easier to attenuate, sacrifices productivity at low speed. How to make it possible.

  However, this method reduces the recording speed and makes it difficult to shorten the recording time, making it impossible to satisfy the demands for speeding up image recording and improving productivity.

  On the other hand, in order to discharge at a high speed and stably with high accuracy, the appropriate amount of liquid is less than the target, and the amount of liquid to be discharged is small. It is known that the influence of waves is reduced and the spread of droplets upon landing is small, so that the landing accuracy can somehow achieve a lower limit level that can withstand market demands.

  In other words, it is difficult to obtain high-definition images that do not reduce the appropriate amount of liquid, are high-speed to meet market demands, are highly productive due to synergistic effects, and have no problems in ejection accuracy such as tail bending. I found out.

  Japanese Patent Application Laid-Open No. 2004-260260 discloses a technique for discharging at a driving frequency of 15 kHz or more using a water-soluble organic solvent ink with a nozzle opening diameter of 30 μm or less. However, a tail bend occurs at a high speed, for example, 20 kHz or more. It did not endure practical use.

  As a technique using the meniscus position, there is Patent Document 2. However, only a technique for ejecting small droplets when a predetermined amount of meniscus is drawn is disclosed, which is not a technique for high-speed driving, but can improve landing accuracy in high-frequency driving for high speed. It was not possible.

Patent Document 3 discloses a technique for controlling the volume of ink droplets to be ejected by defining the meniscus of a pressure chamber adjacent to the pressure chamber to which a driving signal is applied, This technology has not solved the problem of tail bending in high-speed driving, and has not been put to practical use.
JP 2002-264333 A JP 2003-165220 A JP 2006-76260 A

  Therefore, the present invention enables continuous and stable discharge from the same nozzle, discharges at a high speed without reducing the discharge speed, and records a high-definition image at a high speed, and also increases an appropriate amount of liquid. It is an object of the present invention to provide an ink jet recording apparatus and a recording method which have the conflicting characteristics of being capable of being manufactured and having high productivity due to the synergistic effect.

  The above problems are solved by the following inventions.

1. An ink jet recording apparatus having a recording head having a plurality of pressure chambers communicating with a nozzle having an opening for ejecting ink and having an electromechanical conversion means for changing the volume of the pressure chamber by application of a drive signal ,
A drive signal having a Draw pulse for expanding the volume of the pressure chamber , and a Release pulse for returning the volume of the pressure chamber after the Draw pulse and ejecting ink from the nozzle at a drive frequency of 20 kHz or more. When ejecting by applying to the recording head, the pushing amount of the meniscus position of the nozzle at the time of applying the Draw pulse is larger than 0 and not more than 30% of the diameter of the opening,
Satisfy the following equation, where Va is the amount of liquid ejected to the outside of the nozzle at the time of applying the Draw pulse, and Vt is the amount of one ejected liquid droplet: An ink jet recording apparatus.
0 <Va ≦ Vt / 4

2. 2. The ink jet recording apparatus of item 1 , wherein 1/2 of the acoustic resonance period of the pressure chamber is 1 μsec or more and 3 μsec or less.

3 . 3. The ink jet recording apparatus according to 1 or 2 , wherein the drive signal includes a cancel pulse for canceling reverberation of a pressure wave, and the Draw pulse is applied first.

4). Wherein the nozzle is an ink jet recording apparatus according to any one of the 1 to 3, characterized in that it has a tapered portion which is a cross-sectional area gradually increases from the ink discharge side to the pressure chamber side.

5 . 5. The inkjet recording apparatus as described in 4 above, wherein the taper portion has a taper angle of 6 degrees or more.

6 . 6. The ink jet recording apparatus according to 4 or 5 , wherein the tapered portion has two different taper angles.

7 . 7. The ink jet recording apparatus according to any one of 1 to 6 , wherein the ink has a viscosity of 5 mPa · s or more.

8). A plurality of pressure chambers communicating with a nozzle having an opening for ejecting ink are adjacent to each other, and an inkjet recording method using a recording head including an electromechanical conversion unit that changes the volume of the pressure chamber by applying a drive signal ,
A drive signal having a Draw pulse for expanding the volume of the pressure chamber , and a Release pulse for returning the volume of the pressure chamber after the Draw pulse and ejecting ink from the nozzle at a drive frequency of 20 kHz or more. When ejecting by applying to the recording head, the pushing amount of the meniscus position of the nozzle at the time of applying the Draw pulse is larger than 0 and not more than 30% of the diameter of the opening,
Satisfy the following equation, where Va is the amount of liquid ejected to the outside of the nozzle at the time of applying the Draw pulse, and Vt is the amount of one ejected liquid droplet: An inkjet recording method characterized by the above.
0 <Va ≦ Vt / 4

9 . 9. The ink jet recording method according to item 8 , wherein 1/2 of the acoustic resonance period of the pressure chamber is 1 μsec or more and 3 μsec or less.

10 . 10. The ink jet recording method according to 8 or 9 , wherein the drive signal includes a cancel pulse for canceling reverberation of a pressure wave, and the Draw pulse is applied first.

11. Wherein the nozzle is an ink jet recording method according to any one of the 8 to 10 characterized in that it has a tapered portion which is a cross-sectional area gradually increases from the ink discharge side to the pressure chamber side.

12 . 12. The ink jet recording method as described in 11 above, wherein a taper angle of the taper portion is 6 degrees or more.

13 . 13. The ink jet recording method as described in 11 or 12 , wherein the tapered portion has two different taper angles.

14 . 14. The ink jet recording method according to any one of 8 to 13 , wherein the viscosity of the ink is 5 mPa · s or more.

  According to the present invention, it is possible to discharge continuously and stably from the same nozzle, discharge at a high speed without reducing the discharge speed, and record a high-definition image at a high speed, and also increase an appropriate amount of liquid. In addition, it is possible to provide an ink jet recording apparatus and a recording method having the conflicting characteristics of high productivity due to the synergistic effect.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The description in this column does not limit the technical scope of the claims or the meaning of terms. Further, the assertive description in the following embodiments of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.
<Inkjet recording apparatus>
FIG. 1 is a diagram illustrating a schematic configuration of an ink jet recording apparatus. In the ink jet recording apparatus 1, the recording medium P is sandwiched between the transport roller pair 32 of the transport mechanism 3 and further transported in the Y direction in the figure by the transport roller 31 that is rotationally driven by the transport 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. A carriage 5 provided so as to be capable of reciprocating along the XX ′ direction (main scanning direction) is mounted so that the nozzle surface of the recording head 2 faces the recording surface PS of the recording medium P. The drive signal generator 100 is electrically connected via a flex cable 6 to a drive signal generator 100 (see FIG. 3) as a drive signal generator provided with a circuit for generating an ejection signal, which will be described later.

  The recording head 2 moves the recording surface PS of the recording medium P in the direction XX ′ in the drawing as the carriage 5 moves, and ejects ink droplets toward the recording medium P in this moving process, thereby A desired inkjet image is recorded on the recording surface PS of the medium P.

  In the figure, reference numerals 7 and 8 denote ink receivers, which are arranged on both sides of the recording medium P, respectively. When the recording head 2 is positioned on the ink receivers 7 and 8 (whether stopped or moving), a small amount of ink droplets are purged toward the ink receivers 7 and 8. . Further, when the recording head 2 has been stopped for a long time at the home position, although not shown in FIG. 1, the nozzle surface of the recording head 2 is covered by a cap.

  Furthermore, in the present invention, any recording medium can be used as the recording medium P as long as a dot image can be recorded by the ink droplets ejected from the recording head 2, and various kinds of paper are used in addition to the above-described plain paper. can do. In addition, a synthetic resin film, a synthetic resin sheet, or a cloth can also be used.

  The recording medium P is not limited to a long one that is continuously drawn out from the roll body, and may be one that has been cut into a predetermined size in advance.

  Further, as the ink droplet ejection method of the recording head 2, an electro-mechanical conversion method (for example, a share mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal ink jet type, bubble jet (registered trademark)). Type), electrostatic attraction method (for example, electric field control type, slit jet type, etc.), discharge method (for example, spark jet type, etc.) and the like can be given as specific examples. Preferably, a discharge method such as an electrostatic suction method may be added as long as the effects of the present invention are not impaired.

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

  In FIG. 2, 21 is an ink tube, 22 is a nozzle forming member, 23 is a nozzle, 23K is an opening for ejecting ink, 24 is a cover plate, 25 is an ink supply port, 26 is a substrate, and 27 is a partition wall. A channel (hereinafter also referred to as a pressure chamber) 28 serving as a pressure chamber is formed by the partition wall 27, the cover plate 24, and the substrate 26.

  As shown in detail in FIG. 3 in particular, the recording head 2 includes a plurality of partition walls 27A, 27B, and 27C made of a piezoelectric material such as PZT as an electro / mechanical conversion means between the cover plate 24 and the substrate 26. 2 shows a share mode type recording head in which a large number of channels 28 separated from each other are arranged in parallel. In such a recording head 2, the partition wall 27 is deformed to generate a pressure change in the channel 28.

  Although three chambers (28A, 28B, 28C) which are a part of many channels 28 are shown in FIG. 3, the number of channels 28 is not limited. 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, 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, 29C are drive signal generating means. A drive signal generator 100 is connected.

  Here, each partition wall 27 is constituted by two piezoelectric materials 27a and 27b having different polarization directions as indicated by arrows in FIG. 3, but the piezoelectric material may be only a portion 27a, for example. 27 may be present in at least a part of 27.

  The piezoelectric material used for the piezoelectric materials 27a and 27b is not particularly limited as long as it deforms when a voltage is applied, and a known material may be used, and a substrate made of an organic material may be used. A substrate made of a piezoelectric non-metallic material is preferable, and a substrate made of a piezoelectric non-metallic material such as a ceramic substrate formed through a process such as molding or firing, or a substrate formed through a coating or lamination process, etc. There is. Examples of the organic material include organic polymers and hybrid materials of organic polymers and inorganic materials.

As the ceramic substrate, there are PZT (PbZrO ₃ -PbTiO ₃ ) and third component added PZT. As the third component, Pb (Mg _1/3 Nb _2/3 ) O ₃ , Pb (Mn _1/3 Sb _{2 / 3} ) O ₃ , Pb (Co _1/3 Nb _2/3 ) O ₃ or the like, and further formed using BaTiO ₃ , ZnO, LiNbO ₃ , LiTaO ₃ or the like.

  Moreover, as a board | substrate formed through the process of application | coating or lamination, it can form by the sol-gel method, laminated substrate coating, etc., for example.

  On the upper surface of the piezoelectric material 27a, the cover plate 24 is bonded via an adhesive so as to cover the deep grooves 28a over the entire channels 28, and into the channels 28 on the shallow grooves 28b of the channels 28. Ink inlet 77 is formed.

  After the cover plate 24 is bonded, the single nozzle forming member 22 provided with the nozzle 23 is bonded through an adhesive.

  The material of the cover plate 24 and the substrate 26 is not particularly limited, and may be a substrate made of an organic material. However, a substrate made of a non-piezoelectric nonmetallic material is preferable. It is preferably selected from at least one of alumina, aluminum nitride, zirconia, silicon, silicon nitride, silicon carbide, quartz, and unpolarized PZT. Examples of the organic material include organic polymers and hybrid materials of organic polymers and organic substances.

  Further, as the material of the nozzle forming member 23, a synthetic resin such as polyimide resin, polyethylene terephthalate resin, liquid crystal polymer, aromatic polyamide resin, polyethylene naphthalate resin, polysulfone resin, or a metal material such as stainless steel can be used. .

  A metal electrode 29 is formed in each channel 28 from both side surfaces to the bottom surface, and the metal electrode 29 extends to the rear side surface of the piezoelectric material 27a through the shallow groove portion 28b. The flexible cable 6 is bonded to each metal electrode 29 via an anisotropic conductive film 78 on the rear side surface. By applying a drive signal to each metal electrode 29 from the drive signal generating means 100, the side wall 27 is applied. The ink in the channel 28 is discharged from the opening 23K of the nozzle 23 formed in the nozzle plate 22 by the pressure at the time of deformation.

  As the metal used for the metal electrode 29, platinum, gold, silver, copper, aluminum, palladium, nickel, tantalum, and titanium can be used. In particular, from the viewpoint of electrical characteristics and workability, gold, aluminum, copper Nickel is preferable and is formed by plating, vapor deposition, or sputtering.

  Next, in the ink jet recording apparatus 1, a driving method that is a feature of the present invention will be described with reference to FIGS. 3, 4, and 5. Here, as an example, a method of applying drive signals to the three channels A, B, and C to eject ink, the drive signals in FIGS. 4 and 5A and the droplet shape in FIG. This will be described with reference to the meniscus position.

  The numbers in parentheses in FIGS. 5A and 5B correspond to each other in time. In FIG. 5A, the horizontal axis represents AL time, and the vertical axis represents drive voltage. FIG. 5B shows the nozzle 23, the nozzle opening 23 </ b> K, the ink column 102, the ink droplet 11, and the meniscus M.

  When a drive signal as shown in FIG. 4 is applied to the electrodes 29A, 29B, and 29C formed in close contact with the surfaces of the partition walls 27 by the control of the drive signal generator 100, ink droplets are ejected from the nozzles 23 by the operation exemplified below. The ink is discharged from the opening 23K. In FIG. 3, the nozzle is omitted.

  Since the share mode type recording head 2 shares the partition wall 27 of the channel 28 with the adjacent channel 28, it cannot eject simultaneously from the adjacent channel 28 on both sides. For this reason, it is preferable to perform a three-cycle drive in which every two channels 28 are divided into three sets of channel groups A, B, and C. In addition, a set of cycle driving such as 4, 5,... Can be performed within a range that does not impair the effects of the present invention.

  First, when no drive signal is applied to any of the electrodes 29A, 29B, and 29C, none of the partition walls 27A, 27B, and 27C is deformed, but the electrodes 29A and 29C are grounded in the state shown in FIG. At the same time, when a drive signal is applied to the electrode 29B from the drive signal generator 100, an electric field in a direction perpendicular to the polarization direction of the piezoelectric material constituting the partition walls 27B and 27C is generated, and both the partition walls 27B and 27C As shown in FIG. 3B, the partition walls 27B and 27C are deformed toward each other, expanding the volume of the channel 28B and generating a negative pressure in the channel 28B. It flows in (this is hereinafter referred to as “Draw pulse”).

  Further, after maintaining this state for 1 AL time, when the potential is returned to 0 (AL is a half of the acoustic resonance period of the channel and will be described in detail later), the partition walls 27B and 27C are shown in FIG. ) To the neutral position shown in FIG. 3A, and high pressure is applied to the ink in the channel 28B (Release).

  As a result, the meniscus in the nozzle 23 due to a part of the ink filling the channel 28 </ b> B changes in the direction in which it is pushed out of the nozzle 23. When the positive pressure becomes so large that the ink droplet is ejected from the nozzle 23, a semicircle is formed in the droplet ejection direction at the meniscus position where the ink droplet shown in (1) of FIG. At the same time as forming the surface of the spherical droplet, the nozzle 23 is discharged so as to match the direction of the velocity vector in the discharge direction.

  Subsequently, after maintaining for 1 AL time, the potential is reversed, and as shown in FIG. 3 (c), the partition walls 27B and 27C are deformed in the opposite directions to contract the volume of the channel 28B. The pressure wave is generated and the remaining pressure wave is canceled (Cancel). After maintaining this state for 1 AL time, the potential is returned to 0, the partition walls 27B and 27C are returned from the contracted position to the neutral position, and the remaining pressure wave is canceled. (Cancel).

  In this way, after applying a Draw pulse that first expands the volume of the pressure chamber, a droplet depicting a clean free surface by a series of driving methods in which a Release pulse and two Cancel pulses are applied at 1 AL intervals. By suppressing the reverberation of the pressure chamber after ejection, the next ink droplet can also have the same meniscus position, so that a good ejection cycle can be stably performed.

  One embodiment of the present invention is a basic driving method of the recording head that is driven in the share mode as described above, and draw (channel enlargement) → release (return) → cancel (channel shrinkage). ) → Cancel (return) operation has been described as an example of a so-called DRC drive signal.

  As an actual example, for example, A1, B1, C1, A2, B2, and C2 are set consecutively. In this case, in three cycles, the C1 channel is surrounded by the partition walls 27A and 27B, while the A2 channel is surrounded by the partition walls 27B and 27C. It is assumed that the channel is surrounded by.

  In order to adjust the amount of extrusion at the meniscus position of the present invention and to control and increase the appropriate amount of liquid, it is necessary to deform the partition walls 27B and 27C outward when discharging from the A2 channel. Before that, the partition wall 27B is deformed to the right side (A2 channel side), and the deformation amount can be adjusted by controlling the voltage. Further, the maintenance or control of the push-out position generated by the deformation can be adjusted by changing the time interval until the next A2 channel 27B undergoes the deformation operation.

  Preferably, for example, when discharging from A2, the pressure generated by deformation by the drive signal of C1 is changed to control the meniscus position of the A2 channel, and the timing of the end of the drive signal of the C1 channel and A2 It is preferable to adjust the time interval of applying the Draw pulse of the drive signal.

  The drive signal used for the C1 channel is not particularly limited, but in particular, the last pulse of the drive signal contracts for the C1 channel, that is, the partition wall 27B is deformed to the left (C1 channel side) into a "<" character (right side). In order to cancel the reverberation pressure of the discharge of the C1 channel itself while changing the voltage of the signal that returns to the neutral state after returning to the (A2 channel side), and canceling, as shown in FIG. It is preferable to select and apply the timing at which the interval between the pulse and the Cancel pulse becomes 1AL.

  It is particularly preferable that the driving signals of C1, A2, B2, C2, and the channel are continuous and the same while satisfying this requirement.

  Preferably, in the above-mentioned DRC drive signal, the magnitude of the cancellation potential is preferably 0.6 to 1.0 with respect to Draw in terms of speed stability.

  Furthermore, within the range that does not impair the effects of the present invention, it is possible to use a later-described DRR drive signal in combination with a cancel pulse.

  What is important is to adjust the meniscus position according to the present invention by appropriately adjusting these. On the other hand, FIG. 6A shows the amount of meniscus extrusion within a nozzle having a diameter of 25 μm when the driving signal shown in FIG. 4 (also shown in FIG. 6B) is repeatedly applied at a driving frequency of 20 kHz or more. The state of is shown. A dotted line in FIG. 6B indicates that the illustrated driving signal is repeatedly applied. Note that the time axes in FIGS. 6A and 6B are the same.

  As shown in FIG. 6, the meniscus position expands at the timing of applying the Draw pulse, and the amount of extrusion at the meniscus position of the nozzle of the present invention is about 5 μm, which is 30% or less of the diameter of the nozzle opening. I understand.

  Here, the diameter of the opening of the nozzle in the present invention means the diameter of the opening at the tip of the ink ejection side of the nozzle, and is the diameter when the section of the opening is circular. The diameter when the cross section is non-circular such as a rectangle, an ellipse, or an ellipse is the diameter when the cross section is replaced with an equal circle.

  Thus, as a result of intensive studies, in order to increase the productivity of the present invention at high speed, the meniscus extrusion amount is within the scope of the present invention. It turns out that three reverberation reductions must be achieved simultaneously. As a result of intensive studies, the present invention has been achieved.

  As described above, in the present invention, the pushing amount of the meniscus position of the nozzle when the Draw pulse is applied when the drive signal is applied and discharged is larger than 0, and is 30% or less of the diameter of the nozzle opening, preferably 20 % Or less, more preferably 5% to 20% is preferable because the speed during discharge is easily increased. When the amount of extrusion is 0 or less, that is, in the retracted state, the time until ejection becomes a time lag that cannot be ignored in high-speed driving, and is not included in the present invention because it cannot be ejected stably at high speed.

  Here, the push-out amount is a value of the position of the meniscus from the nozzle tip observed when a Draw pulse is applied (immediately before application) with a drive signal. The extrusion amount of the meniscus from the nozzle can be measured by strobe synchronization using a digital microscope “VH-6300” manufactured by KEYENCE, for example. As shown in FIG. 12, the amount of extrusion is a value obtained by measuring the amount of protrusion of the meniscus M from the nozzle tip at the approximate center of the nozzle in a direction substantially perpendicular to the nozzle forming member.

In the present invention, when an appropriate amount of liquid corresponding to the overflow amount pushed out of the nozzle at the time of applying the Draw pulse is Va, and an appropriate amount of discharged liquid including the overflow amount is Vt, the following equation is used. Is preferably satisfied.
0 <Va ≦ Vt / 4
Va and Vt can be obtained by experiments, simulations, or the like.

Va in the shear mode type head of the present embodiment is obtained by the following definition. The appropriate amount of one drop of liquid when discharged at a driving frequency of 20 kHz or higher continuously with 3 cycle drive of A, B, C channels is Vt. For example, only A channel of A, B, C is driven. Then, Va = Vt−V1 when an appropriate amount of liquid when one drop is discharged is V1.
Is required.

  From high definition recording, Va is more preferably Vt / 16 or more and Vt / 8 or less. When the overflow amount is 0 or less, that is, in the pulled-in state, the time until ejection becomes a time lag that cannot be ignored in high-speed driving, and is not included in the present invention because it cannot be ejected stably at high speed.

  The meniscus position of the present invention can be adjusted as appropriate by changing the surface tension of the ink, inertia, driving frequency, AL of the pressure chamber itself, resistance of the nozzle, and ease of attenuation of pressure in the pressure chamber.

  If the diameter of the nozzle opening is increased, the meniscus position can be easily adjusted to 30% or less. However, if the diameter is increased too much, the resistance of the nozzle decreases, but the reverberation of the pressure wave after discharge becomes difficult to attenuate, and the total stability is improved. The property is lowered by continuous discharge. Therefore, the diameter of the nozzle opening is preferably 10 to 30 μm.

  The length of the nozzle in the ink ejection direction increases the nozzle resistance, so it is preferably longer than 30 μm from the attenuation of the pressure wave. However, if the length is too long, the AL becomes longer and the pushing amount of the meniscus position when the drive frequency is high. 80% or less is preferable.

  In addition, the nozzle preferably has a tapered portion whose cross-sectional area gradually increases from the ink ejection side to the pressure chamber side as shown in FIG. 2, and the nozzle resistance is reduced by reducing the taper angle of the tapered portion. It can be designed to 30% or less by greatly increasing the pressure wave attenuation at the same time.

  However, by setting the taper angle to 6 degrees or more, the drive voltage can be lowered and heat generation in the total amount of the recording head is reduced. Therefore, the taper angle is preferably 6 degrees to 10 degrees.

  Similarly, by using a tapered portion having two different taper angles, such as a funnel type, the nozzle resistance can be lowered and adjusted to increase the amount of extrusion. Any taper angle is preferably 6 degrees or more.

  The amount of meniscus extrusion can be adjusted by combining the diameter of the nozzle opening, the taper angle, and the funnel shape as appropriate. It is preferable to use a nozzle having two different taper angles, such as a funnel type, because the drive voltage can be lowered as a result, and heat generation in the total amount of the recording head is reduced.

  On the other hand, even if the channel length of the pressure chamber (L in FIG. 2) is increased, the resistance increases, so that the meniscus position can be adjusted, but AL also changes, so the channel length is 1 mm to 2 mm. However, it is preferable that the amount of extrusion can be adjusted stably and appropriately to 30% or less even in high frequency driving.

  Further, even if the channel cross-sectional area (the product of D in FIG. 2 and W in FIG. 3) is reduced, the resistance increases, so that the amount of extrusion can be adjusted. Since there is no effect, the height (D in FIG. 2) is preferably 150 to 350 μm and the width (W in FIG. 3) is preferably 70 to 90 μm from the drive voltage. However, since the inertia decreases as the cross-sectional area decreases, it is necessary to appropriately adjust these parameters so that the meniscus position of the present invention is within 30%.

  The surface tension of the ink is preferably 20 to 40 dyn / cm, more preferably 20 dyn / cm or more, and the meniscus position is easily stabilized. If it exceeds 40 dyn / cm, fine droplets and splashes after ejection are likely to occur during high-speed ejection in high-frequency driving, and the appropriate amount of liquid may be difficult to stabilize.

  By setting the ink viscosity to 5 mPa · s or more, generation of splash (micro droplets) at the time of ejection is suppressed, and high-definition printing is preferable.

  A share mode type recording head is preferable because it can produce a head having a large number of nozzles, which is advantageous in terms of productivity.

  The drive frequency is preferably 25 kHz or more from the viewpoint of productivity and 40 kHz or less in order to stably maintain the meniscus position at 30% or less. If it exceeds 40 kHz, the meniscus position may be difficult to control continuously.

  AL which is ½ of the acoustic resonance period of the pressure chamber of the recording head is preferably 1 μsec or more and 3 μsec or less, more preferably 2 μsec or less, and high productivity is preferable because high speed driving is possible.

  Here, AL (Acoustic Length) is 1/2 of the acoustic resonance period of the channel. This AL measures the velocity of ink droplets ejected by applying a rectangular wave voltage pulse to a partition wall 27 made of a piezoelectric material, which is an electrical / mechanical conversion means, and makes the rectangular wave voltage value constant. Is obtained as a pulse width that maximizes the flying speed of the ink droplets. The pulse width is defined as the time between 10% rise and 10% fall of the voltage. 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, preferably ¼ of AL.

  As a drive signal, that is, it is preferable that ink is ejected at intervals of 5 AL in a 3-cycle drive.

  Since the voltage rises and falls sharply in the rectangular wave, it seems that the pressure fluctuation of the ink is larger than the trapezoidal wave in which the rectangular wave is inclined. In practice, however, the recording head 2 shown in this embodiment has the channel 28. Is a shear mode type recording head that creates pressure for ejecting ink droplets from the nozzles 23 by shear deformation of the partition walls 27, and therefore, resonance of the generated pressure waves. The displacement of the partition wall 27 that undergoes shear deformation is only in the order of nanometers, and the deformation of the channel 28 is smaller than that of a recording head that deforms the diaphragm with a laminated piezoelectric element that operates in an expansion / contraction mode. It is as small as 1/10 to 1/100. For this reason, even if the partition wall 27 is suddenly displaced using a rectangular wave, the meniscus does not vibrate as much as the above-described laminated type, and it takes time to suck in air or stabilize the meniscus vibration. No problem.

  In addition, when the rectangular wave is used, the voltage rises and falls more steeply than the trapezoidal wave, so that the length of the drive signal can be as short as half or less.

  Further, 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 the trapezoidal wave having the inclined wave.

  In order for the appropriate amount Va corresponding to the overflow amount of the present invention to satisfy the above equation, the viscosity of the ink, inertia, drive frequency, AL of the pressure chamber itself, the nozzle By changing the resistance and the pressure in the pressure chamber, it can be appropriately adjusted in the same manner as the adjustment of the extrusion amount described above.

  On the other hand, the first example of the prior art is shown in FIGS. Unlike the present invention, DRC driving is performed in a state where the meniscus position exceeds 30% (in FIG. 8, the amount of extrusion when a Draw pulse is applied is about 11 μm, and the nozzle opening diameter is about 44% of 25 μm in diameter). In this case, since the inertia of the appropriate amount of ink liquid at the time of Draw is large and the nozzle resistance is large, it is impossible to create an appropriate droplet shape for discharging the droplet, so it is possible to match the velocity vector necessary for discharging It cannot be performed, and it cannot be ejected simply because the liquid droplets overflow from the nozzle. Naturally, continuous discharge cannot be performed due to the overflowed liquid droplets.

  Further, a second example of the prior art in which the meniscus is not pushed out will be described with reference to FIGS.

  When a drive signal so-called DRR (Draw-Release-Reinforce) method as shown in FIG. 9A is applied, the partition walls 27B and 27C are directed outward as shown in FIG. As a result, the volume of the channel 28B is enlarged and a negative pressure is generated in the channel 28B, so that the ink flows (Draw). Further, after maintaining this state for 1 AL time, the potential is returned to 0 to 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). Subsequently, when a drive signal is applied so as to deform in the reverse direction as shown in FIG. 3C and the volume of the channel 28B is contracted, a positive pressure is generated in the channel 28B (Reinforce).

  As a result, the meniscus in the nozzle 23 due to a part of the ink in the channel is pushed out from the nozzle 23 and ink droplets are ejected from the nozzle 23. After maintaining this state for 2 AL hours, the potential is returned to 0, the partition walls 27B and 27C are returned from the contracted position to the neutral position, and the remaining pressure wave is canceled (Cancel).

  FIGS. 9B and 9C show a case where the drive frequency is made lower than 20 kHz and very slow with the DRR drive signal of FIG. 9A. However, unlike FIG. 5 in the above-described embodiment, the meniscus position is pulled in at the time of Draw, and the inertia of the ink is small. For this reason, the tail length of the liquid droplet until the liquid droplet is formed becomes longer, and the reverberation remains because the timing is further shifted. As a result, the meniscus after ejection is not formed and the liquid becomes dull, and the next ink is continuously stable. Therefore, the effect of the present invention cannot be obtained.

  Incidentally, as described herein, the height of the surface in a situation where it overflows and adheres to the nozzle surface is not included in the extrusion amount of the present invention. Similarly, it is not included in the overflow amount.

  On the other hand, the drive frequency which is not the present invention is 15 kHz.

  As shown in FIGS. 9B and 9C, the ink can be discharged at a high speed, but it is not discharged at a high speed. Of course, the high speed productivity of the present invention cannot be achieved and it is not useful.

Example 1
The recording head, print specifications, and ink used are described below. Share mode type recording head shown in FIG. 2 (channel length 1.5 mm, AL = 3 μsec, taper angle 6 degrees, nozzle pitch: 180 dpi, number of nozzles: 256, nozzle opening diameter: 25 μm, ink droplet amount: 4 pl) The nozzle rows of each head are shifted by ½ pitch from each other, and are bonded so that they are arranged in a staggered manner. Each head is a 180 dpi head. A recording head of 360 dpi was manufactured by shifting the position by 2. Evaluation was performed by 3 cycle driving.

  The ink used was an acrylic ultraviolet curable ink having a viscosity of 10 mPa · s (measured value at 50 ° C.) and a surface tension of 28 dyn / cm (measured value at 25 ° C.). The drive signal was the DRC drive signal shown in FIG. 5, and the drive frequency was 22 kHz.

Recording head moving speed: 105 cm / sec
Gap spacing between recording medium and nozzle surface: 1.0 mm
Reference ink drop initial velocity: 6 m / sec
The evaluation items were productivity, which is the upper limit of the discharge accuracy and the speed at which stable discharge is possible.
<Discharge accuracy>
While moving the recording head in the main scanning direction, ink droplets were ejected to a stationary recording medium under the condition that the ejection interval (driving frequency when image data was thinned out) and the amount of ink droplets were changed. The interval between dots on the recording medium in the main scanning direction was examined over time. Since the regular dot interval can be obtained from the moving speed and the driving frequency of the recording head, the deviation from the steady state was examined.

Judgment criteria are as follows. Δ is not practically problematic, but ○ is preferable.
○: Dot interval is 1.25 times or less of steady state Δ: Dot interval exceeds 1.25 times of steady state and less than 1.75 times ×: Dot interval is 1.75 times or more of steady state or ejection is not possible <Productivity>
The initial velocity of ink droplets was 6 m / sec, and the drive frequency was increased to evaluate the maximum drive frequency at which stable ejection, no splashing, and no nozzle shortage occurred. Δ is not practically problematic, but ○ is preferable.
○: Can be discharged even at 25 kHz or higher. Δ: Can be discharged at 20 to 25 kHz. X: Can be discharged even when the frequency is lower than 20 kHz or higher.

  Further, the amount of extrusion at the meniscus position of the nozzle was measured by the method described above, and the ratio to the diameter of the nozzle opening was evaluated.

(Comparative Example 1 )
The same head as in Example 1 was prepared except that the diameter of the nozzle opening was 27 μm, and evaluation was performed in the same manner as in Example 1.

(Comparative Example 2 )
Evaluation was performed in the same manner as in Example 1 except that the driving frequency was 16 kHz with the same head as in Example 1.

  The above results are shown in Table 1.

(Example 2)
A head was prepared in the same manner as in Example 1 except that AL was 2.5 μsec and the diameter of the nozzle opening was 22 μm. Evaluation was performed in the same manner as in Example 1 except that the driving frequency was 27 kHz.

(Example 3)
The same head as in Example 1 was manufactured except that AL was 2.5 μsec, and evaluation was performed in the same manner as in Example 1 except that the drive frequency was 27 kHz.

(Comparative Example 3)
The same head as in Example 1 was prepared except that AL was 2.5 μsec and the diameter of the nozzle opening was 28 μm, and evaluation was performed in the same manner as in Example 1 except that the driving frequency was 27 kHz.

  The above results are shown in Table 2.

Example 4
The same head as in Example 1 was prepared except that AL was 2.5 μsec, and evaluation was performed in the same manner as in Example 1 except that the drive frequency was 30 kHz.

  The results are shown in Table 3.

(Example 5)
The same head as in Example 1 was prepared except that the nozzle of the recording head had a taper of 7 degrees, and evaluation was made in the same manner as in Example 1 except that the drive frequency was driven at 27 kHz.

(Example 6)
Except that the nozzle of the recording head is a two-stage funnel type having a taper angle of 5 degrees on the ink discharge side and a taper angle of 45 degrees on the pressure chamber side, the same head as in Example 1 was produced and the drive frequency was 27 kHz. Evaluation was performed in the same manner as in Example 1.

  The results of Example 3 with a taper angle of 6 degrees are also shown in Table 3.

  However, the driving voltage was 20 V in Example 3 and 24 V in Example 5, and Example 3 was preferred. In addition, when the funnel type was used as in Example 6, the driving voltage was particularly preferable at 18V.

(Example 7)
The same head as in Example 1 was manufactured except that AL was 2.5 μsec, the driving frequency was driven at 24 kHz, and evaluation was performed in the same manner as in Example 1 except that the following evaluation items were added.

Va is measured when Va is the appropriate amount of liquid equivalent to the amount pushed out of the nozzle at the time of applying the Draw pulse, and Vt is the appropriate amount of liquid discharged, and the ratio of Va to Vt is calculated. Examined. Moreover, the splash was evaluated according to the following evaluation criteria.
<Evaluation of splash>
The characters were printed with Y, M, C, and K at the maximum density to visually evaluate whether or not the spray was clean. Δ is not practically problematic, but ○ is preferable.
○: Not visible visually.
Δ: Slightly visible.
X: Conspicuous visually (Example 8)
A head was manufactured in the same manner as in Example 7 except that the diameter of the nozzle opening was 23 μm, and was evaluated in the same manner as in Example 7.

Example 9
The same head as in Example 7 was prepared except that the diameter of the nozzle opening was 27 μm, and evaluation was performed in the same manner as in Example 7 except that the drive frequency was 21 kHz.

  In Examples 7 to 9, the drive frequency was adjusted and evaluated so that the amount of extrusion was almost the same even when the diameter of the nozzle opening was changed.

  The results are shown in Table 5.

  It can be seen that Examples 7 and 9 that satisfy the relationship of 0 <Va ≦ Vt / 4 have less splashing than Example 8 that does not satisfy the relationship.

  From the above Tables 1 to 5, it can be seen that the examples of the present invention are superior in ejection accuracy and productivity as compared with the comparative examples.

  Example 2 and Example 5 in which the ratio of the amount of extrusion at the meniscus position of the nozzle to the diameter of the nozzle opening is in the range of 20% or less are higher than the other examples in which the ratio exceeds 20% and is 30% or less. I understand that it is expensive.

Diagram showing inkjet recording apparatus 2A and 2B are diagrams illustrating an example of a recording head, where FIG. 1A is a perspective view illustrating a partial cross section, and FIG. Diagram showing operation during ink ejection The figure which shows the DRC drive method of this invention The figure which shows the DRC drive method and meniscus position of this invention The figure which shows the DRC drive method and meniscus extrusion amount of this invention The figure which shows the conventional DRC drive method and meniscus position The figure which shows the conventional DRC drive method and meniscus extrusion amount The figure which shows the conventional DRR drive method and meniscus position The figure which shows the conventional DRR drive method and meniscus extrusion amount (A) is a figure which shows the ideal dot space | interval formed with each ink drop, (b) is a figure which shows a dot space | interval when discharge stability is inferior. Diagram showing meniscus extrusion amount

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 2 Recording head 3 Conveyance mechanism 4 Guide rail 5 Carriage 6 Flexi cable 7, 8 Ink receptacle 21 Ink tube 22 Nozzle formation member 23 Nozzle 24 Cover plate 25 Ink supply port 26 Substrate 27 Partition 28 Channel 31 Conveyance roller 32 Conveying roller pair 33 Conveying motor 100 Drive signal generator P Recording medium PS Recording surface

Claims (14)

An ink jet recording apparatus having a recording head having a plurality of pressure chambers communicating with a nozzle having an opening for ejecting ink and having an electromechanical conversion means for changing the volume of the pressure chamber by application of a drive signal ,
A drive signal having a Draw pulse for expanding the volume of the pressure chamber , and a Release pulse for returning the volume of the pressure chamber after the Draw pulse and ejecting ink from the nozzle at a drive frequency of 20 kHz or more. When ejecting by applying to the recording head, the pushing amount of the meniscus position of the nozzle at the time of applying the Draw pulse is larger than 0 and not more than 30% of the diameter of the opening,
Satisfy the following equation, where Va is the amount of liquid ejected to the outside of the nozzle at the time of applying the Draw pulse, and Vt is the amount of one ejected liquid droplet: An ink jet recording apparatus.
0 <Va ≦ Vt / 4   2. The ink jet recording apparatus according to claim 1, wherein a half of an acoustic resonance period of the pressure chamber is 1 μsec or more and 3 μsec or less.   The inkjet recording apparatus according to claim 1, wherein the drive signal includes a cancel pulse for canceling reverberation of a pressure wave, and the Draw pulse is applied first.   4. The inkjet recording apparatus according to claim 1, wherein the nozzle has a tapered portion whose cross-sectional area gradually increases from the ink discharge side toward the pressure chamber side. 5.   The inkjet recording apparatus according to claim 4, wherein a taper angle of the tapered portion is 6 degrees or more.   6. The ink jet recording apparatus according to claim 4, wherein the tapered portion has two different taper angles.   The ink jet recording apparatus according to claim 1, wherein the ink has a viscosity of 5 mPa · s or more. A plurality of pressure chambers communicating with a nozzle having an opening for ejecting ink are adjacent to each other, and an inkjet recording method using a recording head including an electromechanical conversion unit that changes the volume of the pressure chamber by applying a drive signal ,
A drive signal having a Draw pulse for expanding the volume of the pressure chamber , and a Release pulse for returning the volume of the pressure chamber after the Draw pulse and ejecting ink from the nozzle at a drive frequency of 20 kHz or more. When ejecting by applying to the recording head, the pushing amount of the meniscus position of the nozzle at the time of applying the Draw pulse is larger than 0 and not more than 30% of the diameter of the opening,
Satisfy the following equation, where Va is the amount of liquid ejected to the outside of the nozzle at the time of applying the Draw pulse, and Vt is the amount of one ejected liquid droplet: An inkjet recording method characterized by the above.
0 <Va ≦ Vt / 4   9. The ink jet recording method according to claim 8, wherein 1/2 of the acoustic resonance period of the pressure chamber is 1 μsec or more and 3 μsec or less.   10. The ink jet recording method according to claim 8, wherein the drive signal includes a cancel pulse for canceling reverberation of a pressure wave, and the Draw pulse is applied first.   11. The ink jet recording method according to claim 8, wherein the nozzle has a tapered portion whose cross-sectional area gradually increases from the ink discharge side toward the pressure chamber side.   The inkjet recording method according to claim 11, wherein a taper angle of the tapered portion is 6 degrees or more.   The inkjet recording method according to claim 11, wherein the tapered portion has two different taper angles.   The inkjet recording method according to claim 8, wherein the ink has a viscosity of 5 mPa · s or more.

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