Effect of driving waveform on size and velocity of generated droplets of nanosilver ink (Smartink) (original) (raw)
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Micromachines
Experimental and numerical analysis of the drop-on-demand inkjet was conducted to determine the jetting characteristics and meniscus motion under the control of the ink supply pressure. A single transparent nozzle inkjet head driven by a piezoelectric actuator was used to eject droplets. To control ink supply pressure, the pressure of the air in the reservoir was regulated by a dual valve pressure controller. The inkjet performance and the motion of the meniscus were evaluated by visualization and numerical simulation. A two-dimensional axisymmetric numerical simulation with the dynamic mesh method was performed to simulate the inkjet dynamics, including the actual deformation of the piezoelectric actuator. Numerical simulation showed good agreement with the experimental results of droplet velocity and volume with an accuracy of 87.1%. Both the experimental and simulation results showed that the drop volume and velocity were linearly proportional to the voltage change. For the speci...
Pressure response and droplet ejection of a piezoelectric inkjet printhead
International Journal of Mechanical Sciences, 1999
The present study aims to investigate the pressure rise in the ink flow channel and the ink droplet formation process of a piezoelectric printhead after an electrical pulse is applied to the printhead. The ink flow channel is modeled as a straight circular pipe followed by a convergent nozzle. Both numerical analysis and experimental observations are performed in this study. In the numerical analysis, a characteristic method is used to solve the one-dimensional wave equation to obtain the transient pressure and velocity variations in the flow channel of the printhead. In this analysis, the channel is assumed to have a non-uniform cross section. In addition, a flow visualization system was set up to observe the ink droplet injection process. After the piezoelectric material is driven by the input electric pulse, the ink droplet images are immediately captured by a charge-couple device (CCD) camera converted to a digital image via a frame grabber, and stored in a computer. The results obtained from the experimental observations are also compared with the numerical prediction. The effects of electric pulse shape and voltage on the ink injection length and the ejected droplet weight are also presented.
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Acta Mechanica Sinica, 2020
In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations. Two different types of waveforms, namely the unipolar and bipolar actuations, are investigated for three fluids with different physical properties. We focus on two key parameters, which are the dwell time and the velocity amplitude. For the unipolar driving, the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger. The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume. The ejection velocity decreases significantly for large liquid viscosity, while the influences of viscosity on the ejected liquid volume are much weaker. Four different droplet morphologies and the corresponding parameter ranges are identified. The droplet radius can be successfully reduced to about 40% of the nozzle exit radius. For the bipolar waveforms, same droplet morphologies are observed but with shifted boundaries in the phase space. The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.
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Inkjet printing technology uses the low-cost direct deposition manufacturing technique for printing and is applicable in various fields including optics, ceramics, three-dimensional printing in biomedicine, and conductive circuitry. This study reviews the classifications and applications of inkjet printing technologies, with a focus on recent publications. The different design approaches, applications, and research progress of several inkjet printing techniques are reviewed. Among them, the piezoelectric inkjet printing technology is the main focus owing to its reliability and handling of a diverse range of inks. A piezo-driven inkjet printhead is activated by applying a voltage waveform to a piezoelectric membrane. The waveform ensures the formation of the designed droplet and a stable jet. A survey of various drivingvoltage waveforms is conducted, which can serve as a reference to the research community that uses piezodriven inkjet printheads. The challenges of printing quality, stability, and speed and their solutions as published in recent studies are reviewed. Technologies for producing high-viscosity inkjets are explored, and the applications of inkjet printing technology in textile, displays, and wearable devices are discussed.
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Piezoelectric Drop‐On‐Demand Inkjet Printing of High‐Viscosity Inks
Advanced Engineering Materials, 2021
Inkjet printing (IJP) has been adopted as a material deposition technology in different fields, such as, electronics, [1] biology, [2] and biomedicine, [3] being a fully recognized flexible, scalable, and cost-effective technique. [4,5] In contrast to more traditional manufacturing techniques, IJP is a solutionbased maskless additive technique, allowing minimum material waste combined with extreme precision in controlling the deposition of active material droplets in the picoliter range. [6-9] There are two main IJP modes of operation: the continuous inkjet printing (CIJ) and the drop-on-demand (DOD) system. [10] Despite CIJ being widely exploited in graphical applications, such as coding and marking, the great advantage of a DOD system over CIJ is the possibility to print smaller features (i.e. %20-50 μm vs %100 μm of CIJ) and that the ink droplet is ejected only when is needed, eliminating most of the complex structural parts present in CIJ. [11] Finally, CIJ systems involve a recycling system that can potentially cause the contamination of the ink itself. [12,13] Current DOD ink-printing technology works through various methods, such as thermal, electrostatic, piezoelectric (PZT), acoustic, and laser-assisted. [14-16] The active material is processed as a solution, i.e., ink, requiring specific physical properties to be framed in very restricted ranges of values to guarantee ink printability. [17] For example, the upper limit of viscosity for IJP is 20-40 mPa s. [18] This represents one of the major drawbacks of the DOD system, which shows severe limitations in ink printability. A possible solution to reduce the viscosity is to increase the temperature. Despite being a very intuitive and simple method, some issues may arise when dealing with temperature-sensitive inks as their properties can be degraded beyond a certain temperature value. The need for low-viscosity inks poses many limitations because inks generally require high dilution to be processed. This translates to a reduction of the functional material content, resulting in the necessity of printing more layers to reach a certain target thickness. However, printing many layers can affect and lower the final resolution of the printed pattern. In addition to this issue, the necessity of keeping low the concentration of the functional material is a potential limiting factor for the formulation of inks capable of limiting the well-known coffee ring effect (CRE). The CRE is an extremely common defect defined as the progressive accumulation of nonvolatile material toward the edges, with a consequent depletion from the inner
Micromachines
After a piezoelectric inkjet printhead jets the first droplet, the actuating membrane still vibrates, creating residual vibrations in the ink channel, which can degrade the inkjet printhead performance. For suppressing these vibrations, an optimized actuating voltage waveform with two pulses must be obtained, of which the first pulse is used for jetting and the second pulse is used to suppress the residual vibrations. In this study, the pressure history within the ink channel of a recirculating piezoelectric inkjet printhead was first acquired using lumped element modeling. Then, for suppressing residual vibrations, a bipolar voltage waveform was optimized via analysis of the tuning time (tt ), dwell time (td2), rising time (tr2), falling time (tf2), and voltage amplitude of the second pulse. Two voltage waveforms, Waveform 01 and Waveform 02, were optimized thereafter. In Waveform 01, tt=2 μs, td2=2 μs, and tr2 and tf2=1 μs were finalized as the optimal parameters; in the case of a...
Journal of Manufacturing Processes, 2020
Ink properties play a critical role in different printing techniques. However, it is not straightforward to correlate ink properties to the printing results. In this study, several parameters were identified and analyzed to evaluate the droplet behavior in electrohydrodynamic inkjet printing. More specifically, the effects of metallic nanoparticle sizes in the ink formulation were explored through the analysis of droplet impact behaviors. These parameters include droplet wetting diameter, height, initial impact velocity, and contact angle. With the assistance of machine vision, a high-speed camera captured a sequence of images, which were analyzed to extract the aforementioned parameters. Under fields of gravitational force with/without electric force, four phases of ink droplet behaviors were identified. Our data suggest that with an electric force field, particle size dominates the droplet behavior in respect to contact angle and wetting diameter. The increase of particle size decreased the droplet wetting diameter with an electric field, while increased the droplet wetting diameter without the electric field applied. Larger droplet size resulted in higher bouncing frequency and lower droplet height. Furthermore, under both gravitational and electrical fields, the droplet with medium particle size (average diameter of 276 nm) had a higher impact velocity than that with small (average diameter of 140 nm) and big (average diameter of 1517 nm) particle sizes. This study contributes to fundamental understanding of particle size effects. The results will help optimize ink formulations when designing new ink materials for electrohydrodynamic inkjet printing.
The dynamics of the piezo inkjet printhead operation☆
Physics Reports, 2010
The operation of a piezo inkjet printhead involves a chain of processes in many physical domains at different length scales. The final goal is the formation of droplets of all kinds of fluids with any desired volume, velocity, and a reliability as high as possible. The physics behind the chain of processes comprise the two-way coupling from the electrical to the mechanical domain through the piezoelectric actuator, where an electrical signal is transformed into a mechanical deformation of the printhead structure. The next two steps are the coupling to the acoustic domain inside the ink channels, and the coupling to the fluid dynamic domain, i.e. the drop formation process. The dynamics of the printhead structure are coupled via the acoustics to the drop formation process in the nozzle. Furthermore, wetting of the nozzle plate and air bubbles can have a negative influence on the printhead performance. The five topics (actuation, channel acoustics, drop formation, wetting, and air bubbles) are reviewed in this paper. This research connects the product developments for many emerging new industrial applications of the inkjet technology to the fundamental physical phenomena underlying the printhead operation.
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A hybrid design tool combining one-dimensional (1D) lumped parameter model and three-dimensional (3D) computational fluid dynamics (CFD) approach has been developed and applied to industrial inkjet head design for the application of direct writing on printed circuit boards (PCB). Lumped element modeling technique is applied to simplify the composite Inkjet print head system and the calculation of lumped parameters such as compliance, resistance and inertance is explained theoretically. Performance of 1D analysis shows that it is useful for the evaluation of a proposed design of inkjet head. Time sequence of droplet generation is verified by the comparison between 3D analysis result and photographic images acquired by stroboscopic technique. The developed model helps to understand the drop formation process and influence of flow part on the jetting performance.