Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/04581—Control methods or devices therefor, e.g. driver circuits, control circuits controlling heads based on piezoelectric elements
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/04508—Control methods or devices therefor, e.g. driver circuits, control circuits aiming at correcting other parameters
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/04516—Control methods or devices therefor, e.g. driver circuits, control circuits preventing formation of satellite drops
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/015—Ink jet characterised by the jet generation process
  • B41J2/04—Ink jet characterised by the jet generation process generating single droplets or particles on demand
  • B41J2/045—Ink jet characterised by the jet generation process generating single droplets or particles on demand by pressure, e.g. electromechanical transducers
  • B41J2/04501—Control methods or devices therefor, e.g. driver circuits, control circuits
  • B41J2/04588—Control methods or devices therefor, e.g. driver circuits, control circuits using a specific waveform
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/14—Structure thereof only for on-demand ink jet heads
  • B41J2/14201—Structure of print heads with piezoelectric elements
  • B41J2/14209—Structure of print heads with piezoelectric elements of finger type, chamber walls consisting integrally of piezoelectric material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/14—Structure thereof only for on-demand ink jet heads
  • B41J2/14201—Structure of print heads with piezoelectric elements
  • B41J2/14233—Structure of print heads with piezoelectric elements of film type, deformed by bending and disposed on a diaphragm
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/14—Structure thereof only for on-demand ink jet heads
  • B41J2002/14419—Manifold
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/005—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by bringing liquid or particles selectively into contact with a printing material
  • B41J2/01—Ink jet
  • B41J2/135—Nozzles
  • B41J2/14—Structure thereof only for on-demand ink jet heads
  • B41J2002/14491—Electrical connection
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2202/00—Embodiments of or processes related to ink-jet or thermal heads
  • B41J2202/01—Embodiments of or processes related to ink-jet heads
  • B41J2202/12—Embodiments of or processes related to ink-jet heads with ink circulating through the whole print head

Definitions

• the present invention relates to a droplet ejection head and a drive control method.
• a droplet ejection head records an image by ejecting droplets, such as ink droplets, from nozzles and landing the droplets on a target recording medium.
• minute droplets called satellites may be generated in addition to droplets to be ejected.
• an image includes a film and a planar structure.
• the satellites adhere to the recording medium or the surroundings, such as the droplet ejection head, the satellites may decrease the quality of a formed image or affect normal droplet ejection of the droplet ejection head.
• Patent literature 1 discloses a technique for suppressing satellites by devising drive waveforms of a multi-drop type inkjet recording apparatus that unites a plurality of discharged droplets and lands the united droplets on the same position (pixel) of a target.
• a droplet ejection apparatus ejects and lands droplets on a recording medium in a state where the nozzle surface and the recording medium are not in contact with each other and are close to each other. Therefore, the distance between the nozzle surface and the recording medium needs to be accurately adjusted. When the distance is increased, the satellites give a greater influence on image quality and are likely to decrease image quality.
• An object of the present invention is to provide a droplet ejection head and a drive control method capable of performing an image recording operation more flexibly while suppressing a decrease in image quality.
• the present invention is a liquid ejection head including: a liquid channel that passes liquid and includes a pressure chamber, the pressure chamber storing the liquid and applying a pressure fluctuation; and a nozzle that communicates with the liquid channel and ejects a droplet of the liquid to which the pressure fluctuation has been applied, wherein a refill Q factor related to oscillation of a liquid surface in the nozzle is 1.17 or greater when a viscosity of the liquid is 5.7 mPa ⁇ s, a liquid density is 1,080 kg/m 3 , a speed of sound in the liquid is 1,521 m/s, and a surface tension is 42 mN/m.
• FIG. 1A and FIG. 1B are diagrams illustrating an ink channel of an inkjet head 1 according to the present embodiment.
• FIG. 1A is a cross-sectional view of the ink channel.
• ink liquid flows from an ink tank into individual channels F (liquid channels) that communicate with individual nozzles N via a common ink channel or a manifold.
• the inflow ink is supplied to the nozzle N through the individual channel F.
• the individual channel F includes a pressure chamber P.
• the pressure chamber P is a part that applies pressure fluctuation to the ink in the pressure chamber P by the deformation of the pressure chamber P.
• the pressure chamber P is wider than the other parts of the individual channel F to have an appropriate volume.
• the pressure chamber P temporarily stores the ink.
• the pressure chamber P has, for example, a circular shape or a rectangular shape with rounded corners in plan view but is not particularly limited thereto.
• An oscillation plate and a piezoelectric element are positioned along the upper surface of the pressure chamber P having such a plan view shape. When a voltage having a voltage pattern corresponding to a pressure fluctuation pattern to the ink is applied to the piezoelectric element, the piezoelectric element is deformed, so that the pressure chamber P is deformed.
• the nozzle N may have a tapered shape (truncated cone shape) the diameter of which becomes smaller toward the ink ejection port (nozzle opening) at the tip end, although not particularly limited.
• the nozzle opening In plan view (bottom view), the nozzle opening has a circular shape having a diameter of D0.
• the nozzle diameter (diameter) at the x is expressed as D(x).
• D(x) is greater than or equal to D0 and is a linear function that changes depending on x. D0 is determined according to the resolution of a image to be recorded, the ink droplet amount to be ejected, and so forth.
• the droplet amount ejected by one time of ink ejection on a pixel namely the droplet amount per dot
• the droplet amount herein is the total of the multi drops in one cycle.
• the other part of the individual channel F basically has a prism shape or a cylinder shape of a uniform thickness.
• the individual channel F extends in the laminated substrates.
• the size of the individual channel F which is expressed by a cross-sectional area, a cross-sectional shape, and a length, is generally determined for each of the substrates.
• the nozzle N is at the nozzle substrate 11.
• the nozzle substrate 11 is made of metal or resin, for example, but is not limited thereto.
• the pressure chamber P is positioned in the pressure chamber substrate 14.
• the channel substrate 12, the intermediate substrate 13, and so forth are positioned between the nozzle substrate 11 and the pressure chamber substrate 14. These are glass (silicon dioxide) substrates and/or metal substrates of SUS or 42 alloy, for example.
• a downstream individual channel L extends in the channel substrate 12 and the intermediate substrate 13 and connects the pressure chamber P to the nozzle N.
• the spacer substrate 15 is positioned on the upper side of the pressure chamber substrate 14.
• the spacer substrate 15 has a hollow portion, and the hollow portion includes the pressure chamber P in a plan view position.
• the oscillation plate 51 is located at the boundary between the spacer substrate 15 and the pressure chamber P.
• the piezoelectric element 52 interposed between electrodes is positioned in the cavity portion on the upper surface side of the oscillation plate 51.
• the oscillation plate 51 may be a conductive metal member and may serve as one of the electrodes sandwiching the piezoelectric element 52.
• the piezoelectric element 52 is not particularly limited but is lead zirconate titanate (PZT), for example.
• the wiring substrate 16 is positioned on the upper side of the spacer substrate 15.
• the electrodes sandwiching the piezoelectric element 52 are connected to the wiring of the wiring substrate 16 via bumps or the like.
• the upper surface of the wiring substrate 16 is connected to a drive substrate.
• the drive substrate inputs a drive voltage signal related to a voltage to be applied to the piezoelectric element 52.
• the drive substrate is not particularly limited but may be a flexible printed circuit (FPC), for example.
• FPC flexible printed circuit
• the upstream individual channel U is connected to a manifold, a common ink channel, and so forth that store and send out ink supplied to the nozzles N.
• the substrates may be bonded to each other with an adhesive or the like.
• a parameter of the oscillation is expressed by a combination of electrical elements of resistor elements, capacitor elements (capacitors), and inductive elements (coils).
• the upstream individual channel U, the downstream individual channel L, and the nozzle N are connected in series with the pressure chamber P interposed therebetween.
• the upstream individual channel U and the downstream individual channel L may be further divided into channels of the respective substrates and displayed.
• a combined resistance of the multiple resistor elements, a combined inertance of the multiple inductive elements, and so forth may be obtained.
• the oscillation of the ink liquid surface (meniscus) in the nozzle N is important for properly ejecting ink, in particular for suppressing satellites.
• a once-applied pressure fluctuation remains while being attenuated for a certain period according to oscillation characteristics. If the damped oscillation remains at an appropriate magnitude after ink ejection, satellites are suppressed. On the other hand, if the damped oscillation remains excessively, the remaining oscillation is added to the oscillation for the next cycle of ink ejection. This may affect continuous ejection.
• oscillation characteristics related to the oscillation of the liquid surface are variables corresponding to the structure of the individual channel F and the characteristics (e.g., viscosity) of the ink.
• the shape and the position of the liquid surface are maintained by the surface tension of the ink. That is, the surface tension influences the restoring force of the liquid surface after ink ejection. Therefore, it can be said that stable ink ejection is enabled by an inkjet head that has individual channels F configured to have appropriate oscillation characteristics according to characteristics of ink to be ejected.
• a Q factor is known as a parameter related to the oscillation (damping thereof).
• the Q factor is a dimensionless quantity parameter that becomes smaller as the energy loss in one cycle of oscillation in energy of the system is greater.
• the Q factor is too small, the energy loss is large; the oscillation quickly converges; and further, the pressure fluctuation itself related to the original ink ejection is suppressed.
• the Q factor is too large, the energy loss is small, and the oscillation remains for a long time for one drive pulse.
• the Q factor related to the liquid surface oscillation is referred to as a refill Q factor.
• the value Q of the refill Q factor is obtained as follows for the individual channel F.
• Q ⁇ ⁇ Ln / Rn
• Ln is the combined inertance of the m inductors Lm included in the above equivalent circuit. That is, in a case where the inductors Lm are connected in series, the following is applied.
• Rn is the combined resistance of the k resistances Rk included in the equivalent circuit. That is, when the resistances Rk are connected in series, the following is applied.
• Cn is the compliance of the ink liquid surface.
• ⁇ is the surface tension of the ink and determined according to the ink.
• A 128 ⁇ / ⁇ .
• H is the viscosity of the ink
• ⁇ is the density of the ink
• d is the radius of the cylinder
• 1 is the length of the cylinder.
• a and “b” are the lengths of two sides of the cross section of the prism channel, and “w” is the length of the prism channel.
• the resistance value R and the inertance L of the part are analytically obtained as follows.
• R 128 ⁇ ⁇ / 3 ⁇ ⁇ w / ⁇ 2 ⁇ ⁇ 1 ⁇ ⁇ 1 ⁇ 3 ⁇ ⁇ 2 ⁇ 3
• L 4 ⁇ ⁇ / ⁇ ⁇ w / ⁇ 2 ⁇ ⁇ 1 ⁇ ⁇ 1 ⁇ 1 ⁇ ⁇ 2 ⁇ 1
• ⁇ 1 and ⁇ 2 are the base diameter and the top diameter of the truncated cone, respectively.
• the resistance value R and the inertance L of a portion having a complicated shape, such as the pressure chamber P, can be obtained using numerical simulation.
• the resistance values R and the inertances L of the respective parts arranged in series are combined to obtain a combined resistance Rn and a combined inertance Ln of the individual channel F.
• the refill Q factor of the individual channel F is obtained from the parameters (a, b, w, ⁇ 1, ⁇ 2, and D0) related to the shape of the individual channel F and the parameters ( ⁇ , ⁇ , and ⁇ ) related to the characteristics of the ink.
• a channel resistance or the like may occur at the bent portion of the ink channel and so forth. Since such a channel resistance is smaller than the above in a general individual channel F, it is not considered here. However, such a channel resistance can be taken into consideration to obtain the refill Q factor.
• the type of the ink namely the characteristics of the ink can be determined independently of the inkjet head.
• many inkjet heads, particularly industrial inkjet heads generally have their corresponding inks to be used. Therefore, it is sufficient that the properties of the corresponding ink be considered.
• the range of an appropriate refill Q factor is determined by causing the inkjet head to eject ink while changing the refill Q factor of the inkjet head and examining the ejection characteristics.
• FIG. 2A and FIG. 2B are diagrams illustrating a driving operation for ejecting ink.
• FIG. 2A illustrates the flow of a drive signal.
• the head drive section 5 performs an operation of deforming the piezoelectric element 52 under the control of the signal controller 41 of the head drive controller 4.
• the signal controller 41 includes a processor, such as a central processing unit (CPU), and performs control operation related to image recording operation.
• the signal controller 41 may be a general-purpose CPU of the inkjet recording apparatus or may be a dedicated CPU different from the general-purpose CPU. In this case, the signal controller 41 may be located together with the drive circuit 50 on the drive board.
• the head drive section 5 includes the drive circuit 50 on the drive board and the piezoelectric element 52.
• the drive circuit 50 outputs a drive voltage signal having an appropriate waveform (drive waveform) to the piezoelectric element 52, the piezoelectric element 52 deforms such that pressure fluctuation for ejecting ink is generated on the ink.
• the drive circuit 50 includes a signal generation section 53.
• the signal generation section 53 converts the digital waveform into an appropriate analog waveform, amplifies power (voltage and current), and outputs the analog waveform under the control of the signal controller 41.
• the output drive voltage signal is selectively output to the piezoelectric element 52 corresponding to the nozzle N to eject ink, based on image data.
• FIG. 2B is a diagram illustrating an example of the drive waveform.
• ink ejection is done by a one-drop method or a multi-drop method.
• one droplet is ejected by one drive pulse.
• the multi-drop method uses such a drive waveform that applies multiple drive pulses to unite multiple droplets ejected from the nozzle N and causes the united droplet to land at the same pixel position.
• the inkjet head 1 may be configured to use both methods or may be mainly specialized for either of the methods.
• the drive waveform of the multi-drop method will be described.
• three drive pulses per pixel are output at an interval of twice the acoustic length (AL).
• the AL is half the resonance period (acoustic resonance period) of pressure oscillation that occurs on the ink in the pressure chamber P.
• Three drive pulses are output in synchronization with the resonance period, so that the respective ink surface oscillations are utilized to efficiently eject the ink.
• the resonance period is determined according to the ink ejection frequency required for the inkjet head.
• a specific resonant frequency is 10 to 250 ⁇ s, for example.
• the currently common range thereof is 70 ⁇ s or less.
• the interval between rises of the drive pulses namely the time between rising start timings of the adjacent drive pulses may be slightly deviated from 2AL.
• the interval is set to about 1.8AL or greater and 2.3AL or less.
• the duration of each drive pulse namely the time between the timing at which the voltage starts rising to the timing at which the drive voltage ends is 1.2AL, which is slightly longer than the AL. Accordingly, the oscillation of the liquid surface caused by the preceding drive pulse is suppressed from remaining excessively.
• the width of the drive pulse greatly deviates from 1.0AL, pressure fluctuation is not appropriately applied to the ink. Therefore, it is preferable that the width of the drive pulse be in the range of about 0.8AL to 1.3AL.
• the drive pulse is, for example, a rectangular wave, but may be a trapezoidal wave. In the case of the trapezoidal wave, the ratio between the voltage change period and the period of the constant drive voltage may be determined as appropriate.
• the voltage amplitude V1 of the third pulse is greater than the voltage amplitude V2 of the first and second pulses.
• the ink droplet that is ejected last certainly catches up with and unites with the preceding ink droplets. It is preferable that the absolute values of the voltage amplitudes V1 and V2 be great, namely that the droplet speed be high, within a range of not causing abnormal ink ejection.
• the satellites are suppressed, and the ink is stably ejected.
• how much influence of the satellites on image quality is suppressed ultimately depends on the structure of the inkjet head 1, the properties of ink, and the like. It is possible to judge how much appropriate ink ejection is performed with little degradation in image quality, based on the image quality of an image formed by the ink ejection.
• FIG. 3A to FIG. 3C are diagrams illustrating image quality determination.
• FIG. 3A and FIG. 3B are examples of images to be formed and used for image quality determination.
• FIG. 3A shows a one-dimensional barcode (code 1)
• FIG. 3B shows a two-dimensional code (code 2).
• code 1 code 1
• code 2 code 2
• ISO15416 JIS X 0520
• ISO15415 JIS X 0521
• FIG. 3C shows partial contents of ISO15415.
• the inspection contents include the error ratio in a region where positions of white cells and black cells are fixed, such as the contrast between white cells and black cells, imbalance, finder pattern, quiet zone, alignment pattern, and timing pattern, reading abnormality, distortion amount of the two-dimensional code itself, variations in size of each cell (relative uniformity), and the utilization rate of an error correction code (data restoration code) used in reading of stains and losses.
• Each of the items is evaluated by a numerical value of 0.0 to 4.0 (revised edition in 2016) or by five stages by alphabets of A to D and F (edition in 2000). Among the evaluations of the respective items, the stage of the lowest evaluation is determined to be the overall judgement.
• FIG. 4 is a table showing the combined inertance Ln, the combined resistance Rn, and the compliance Cn of an equivalent circuit corresponding to each refill Q factor when inspection is performed according to the inspection standards of the above code 1 and code 2.
• the respective refill Q factors are obtained based on the above (Expression 8) or the like.
• the shape of the individual channel F may be changed so as to decrease the combined resistance Rn or increase the combined inertance Ln as described above, for example.
• FIG. 5A is a table showing the inspection result of the code 1 according to the inspection standards.
• FIG. 5B is a table showing the inspection result of the code 2 according to the inspection standards.
• These inspection results were obtained by performing tests using inkjet heads having different structural parameters related to the refill Q factor while changing the distance from the ink ejection face to the ink landing surface (image recording surface).
• the distance namely the head/media gap, is hereinafter referred to as a gap.
• the overall evaluation of C or better is regarded as OK. Even if the overall evaluation is D or worse, the image quality may not necessarily be NG. However, to stably obtain an image (image quality) having appropriate quality, it is preferable that the overall evaluation be C or better.
• the ink used for image recording in this inspection has a viscosity of 5.7 mPa ⁇ s, a concentration (liquid concentration) of 1080 kg/m 3 , a speed of sound in the ink of 1,521 m/s, and a surface tension of 42 mN/m.
• the recorded code 1 and code 2 were read by a code reader "SR-1000" of Keyence Corporation (registered trademark). The code reader outputs the overall evaluation.
• the refill Q factor when the refill Q factor was 2.44 and the gap was 15 mm, an appropriate quality was not obtained.
• the refill Q factor was 2.32 or less, an image having satisfactory quality was obtained even when the gap was 15 mm. That is, from the viewpoint of a decrease in image quality related to satellites, it is preferable that the refill Q factor be 1.17 or greater, and it is further preferable that the refill Q factor be 1.85 or greater. In addition, it is further preferable that the refill Q factor be 2.32 or less.
• FIG. 6 is a diagram illustrating the relation between the refill Q factor and the maximum droplet speed at which ink can be stably ejected by the multi-drop method.
• the maximum droplet speed at which ink can be stably ejected is the speed at the distance of 0. 5 mm from the ink ejection face. It is shown that the maximum droplet speed is positively correlated with the refill Q factor. When the refill Q factor is 1.31 or greater, the maximum droplet speed is 5 m/s or greater. On the other hand, when the refill Q factor is less than 1.31, the maximum droplet speed is 5 m/s or less, which is unsatisfactory for practical use. It is considered that, if the refill Q factor is low in the multi-drop method, ink supply to the nozzle N cannot keep up with the high-speed injection where the interval between drive pulses is short and the AL is small. As a result, the ejection may become unstable.
• the refill Q factor is 1.31 or greater in addition to the above range of the refill Q factor.
• the refill Q factor be 1.31 or greater.
• the droplet speed be 7 m/s or greater at the point of the gap of 5 mm. It is therefore preferable that such an inkjet head 1 have the refill Q factor of 1.38 or greater.
• the inkjet head 1 have the above-described refill Q factor that allows an appropriate droplet speed, regardless of the ink ejection method.
• FIG. 7 is a diagram showing the influence of the reverberation oscillation of the meniscus caused by the first ink ejection among two ink ejections on the droplet speed of the second ink ejection.
• FIG. 7 shows the difference between the ink droplet speed at the first ejection and the ink droplet speed at the second ejection with respect to the drive cycle related to the two ink ejections.
• the lines correspond to six different types of refill Q factors, respectively.
• the drive cycle is indicated, based on the AL.
• the refill Q factor is 2.12 or less. Since the droplet speed is to be about 5 m/s or greater as described above, the difference of 1 m/s is 20% or less of the droplet speed.
• the influence of such a difference in the droplet speed on the image quality may be acceptable, although the influence also depends on the gap size, the conveyance speed of the recording medium, and the like. Therefore, in addition to the above-described range of the refill Q factor, it is preferable that the refill Q factor be 2.12 or less.
• FIG. 8 is a diagram showing another example of the drive voltage waveform related to ink ejection.
• an ink ejection waveform or a drive voltage waveform be used that is less likely to cause satellites and that can stably and continuously eject ink, in particular in the multi-drop method.
• a pulse waveform having a voltage amplitude V3 greater than the voltage amplitude V1 of the last pulse waveform is added after the last pulse waveform of FIG. 2B at an interval of 4.0AL, which is twice the normal interval.
• the duration (pulse length) of the pulse waveform added to the last is 1.0AL.
• the pulse length of the pulse waveform having the voltage amplitude V1 which is no longer the last pulse waveform, is set to 1.3AL, which is the same as the pulse length of the previous pulse waveform. According to such drive voltage waveforms, ink ejection can be more stably continued in the multi-drop method.
• FIG. 9A, FIG. 9B , FIG. 10A, FIG. 10B , FIG. 11A, and FIG. 11B are diagrams illustrating other examples of the ink channel.
• the specific structure of the ink channel may be different from the structure illustrated in the above-described embodiment.
• a common ink channel Sc is positioned in the channel substrate 12a between the nozzle substrate 11a and the pressure chamber substrate 14a.
• FIG. 9B is a diagram illustrating an equivalent circuit of this ink channel.
• the corresponding resistance value R, inertance L, and so forth are applied to each of the structural portions of the individual channel U, the pressure chamber P, the downstream individual channel L, and the nozzle N.
• the inkjet head 1b may be configured to apply pressure fluctuation using the piezoelectric element 52 that deforms in a shear mode.
• the ink having flowed into the individual channel Fb is supplied to the nozzle N through the upstream individual channel U, the pressure chamber P of the pressure chamber substrate 14b, and the downstream individual channel L of the intermediate substrate 13b.
• the piezoelectric element is positioned on a side surface of the pressure chamber P.
• the piezoelectric element deforms in a direction along the individual supply channel S in a shear mode and applies pressure fluctuation to ink in the individual channel Fb of the pressure chamber substrate 14b.
• the refilling Q factor can be obtained according to the parameters of the respective structural portions illustrated in FIG. 10B .
• FIG. 11A shows another example of the ink channel of an inkjet head 1c.
• the ink flowing into the upstream individual channel U from the common ink channel Sc is ejected from the nozzle N of the nozzle substrate 11c through the pressure chamber P of the pressure chamber substrate 14c and the downstream individual channel L of the intermediate substrate 13c.
• the ink may be separated into the individual discharge channels E1 and E2 in the channel substrate 12c and the intermediate substrate 13c.
• the ink that has passed through the common discharge channels Ec1 and Ec2 may be returned to the ink tank.
• the inkjet head 1c having such circulation channels can swiftly discharge entrained air bubbles, dust, and so forth and allows separation of components of stagnated ink in the individual supplying channels S including the upstream individual channel U, the pressure chamber P, and the downstream individual channel L. Therefore, the inkjet head 1c can perform image recording operation more stably.
• the equivalent circuit corresponding to the nozzle N, the individual supply channel S, and the individual discharge channels E1, E2 included in the individual channel Fc can also be taken into consideration for such a inkjet head 1c.
• the individual discharge channels E1 and E2 are positioned in parallel with the individual supply channel S in the individual channel Fc.
• the refill Q factor is obtained using the parameters of the resistance elements, the capacitors, and the inductive elements of the circuit configuration and the characteristics of the ink.
• the application of the individual discharge channels E1, E2 and the common discharge channels Ec1, Ec2 is not limited to the individual channel Fc that deforms in the shear mode and applies pressure fluctuation to the ink. These may be applied to the individual channels F and Fa and so forth that deform in the above-described slack mode to apply pressure fluctuation to ink.
• the inkjet head 1 of the present embodiment includes: the individual channel F that passes liquid (ink) and includes the pressure chamber P that stores ink and applies pressure fluctuation; and the nozzle N that communicates with the individual channel F and ejects droplets of the ink to which the pressure fluctuation is applied.
• the inkjet head 1 is configured such that the refill Q factor related to oscillation of the liquid surface in the nozzle N is 1.17 or greater when the viscosity of liquid is 5.7 mPa ⁇ s, the liquid density is 1080 kg/m 3 , the speed of sound in liquid is 1521 m/s, and the surface tension is 42 mN/m.
• the inkjet head 1 having such a structure can eject ink while reducing the influence of satellites on image quality, even when the distance between the nozzle opening and the recording medium is increased to about 5 mm, which is greater than a conventional distance of about 1 mm.
• the inkjet head 1 can suppress deterioration in image quality of images to be recorded.
• the inkjet head 1 can be used for various image recording operations more flexibly than in the related art.
• the structure of the inkjet head 1 is determined, based on the characteristics of liquid as a reference. Therefore, when the characteristics of liquid differ, the actual refill Q factor also changes.
• the inkjet head 1 of the present disclosure it is possible to somewhat obtain the effect of reducing the influence of the satellites on image quality while widening the gap between the nozzle opening and the recording medium in the range of the generally used ink.
• the refill Q factor is 1.38 or greater.
• the ink can more appropriately fly the gap of about 5 mm at a high speed.
• the inkjet head 1 can more stably and flexibly eject ink for a wide gap.
• the refill Q factor is 1.85 or greater.
• the distance between the nozzle opening and the recording medium can be further increased to about 15 mm. Therefore, according to the inkjet head 1, it is possible to stably perform recording operation without trouble while suppressing a decrease in image quality, even on a three-dimensional recording medium having unevenness.
• the inkjet head 1 is configured such that the refill Q factor is 2.32 or less under the same configuration and ink conditions described above.
• the inkjet head 1 can stably perform image recording operation with a wide gap while suppressing a decrease in image quality, no matter whether the multi-drop method or the one-drop method is used.
• the inkjet head 1 can flexibly record images on a wide variety of recording media.
• the refill Q factor is 2.12 or less.
• the refill Q factor is 2.12 or less.
• multiple drive pulses are applied to eject droplets toward the same pixel position by the multi-drop method.
• the drive waveform of the multi-drop method is set such that the width of each of the drive pulses is 0.8 or greater and 1.3 or less of the AL, and the interval between rises of the drive pulses is 1.8 or greater and 2.3 or less of the AL. With such a drive pulse width, it is possible to certainly unite liquid droplets in the multi-drop method, to suppress the influence of satellites on image quality, and to stably land an appropriate droplet amount at a desired position.
• the last drive pulse among the multiple drive pulses may rise at an interval of 4.0 AL or greater from the rise of the drive pulse that is immediately before the last drive pulse.
• influences of drive pulses are superposed on a later drive pulse, so that satellites tend to occur between ejected droplets.
• the interval between the last two drive pulses is greater than usual to suppress remaining satellites in the end. Therefore, most of the ejected ink can be united and land on the recording medium.
• the drive waveform may be determined such that the droplet speed at the position of 0.5 mm from the opening end of the nozzle N is 7 m/s or greater.
• the flying speed is low, and particularly when the gap is wide, ink flies for a longer time.
• the ink may receive a greater influence of outside air flow and so forth during flight.
• the droplet speed is about 7 m/s or greater, the ejected ink can more stably land on an appropriate position, and images having appropriate image quality can be formed.
• the drive waveform may be determined such that the droplet amount to be ejected per dot is equal to or greater than 10 pL.
• the droplet amount is small, and particularly when the droplet flies a wide gap, the droplet is likely to greatly decelerate by air resistance.
• the drive control method can suppress a decrease in image quality when the inkjet head 1 of the present embodiment lands ink on the recording medium with a wide gap.
• the drive waveform in the multi-drop method described above is an example. Drive signals having other drive waveforms may be generated and output. Furthermore, although trapezoidal drive pulses are combined in the above embodiment as an example, the present invention is not limited to this.
• the drive pulses may be rectangular wave pulses. In the above description, although the drive pulses change from a reference voltage to the positive side only, the present invention is not limited thereto. The drive pulses may change only to the negative side, or a drive pulse that changes to both the positive and negative sides may be combined.
• the nozzle N may not have a tapered shape.
• the nozzle N may have a short cylindrical shape or the like.
• other shapes of the ink channel may be appropriately determined.
• the combined resistance and the inertance of each part may be obtained analytically or by numerical simulation, depending on the shape.
• the required combined resistance, inertance, and the like may not correspond to only the shape of the ink channel. That is, when a filter or the like is disposed, the combined resistance, the inertance, and so forth may be calculated in consideration of these.
• the signal controller 41, the signal generation section 53, and so forth may be configured as desired. Any configuration may be adopted as long as appropriate drive signals are generated and an output destination is selected according to image data.
• the present invention can be used for a droplet ejection head and a drive control method.

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• 2024
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