Drop formation mechanisms in piezo-acoustic inkjet (original) (raw)
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Velocity profile inside a piezo-acoustic inkjet droplet: experimental and theoretical results
2011
Inkjet printing deposits droplets with a well-controlled narrow size distribution. This paper aims at improving experimental and numerical methods for the optimization of drop formation. We introduce a method to extract the one-dimensional velocity profile inside a single droplet during drop formation. We use a novel experimental approach to capture two detailed images of the very same droplet with a small time delay. The one-dimensional velocity within the droplet is resolved by accurately determining the volume distribution of the droplet. We compare the obtained velocity profiles to a numerical simulation based on the slender jet approximation of the Navier-Stokes equation and we find very good agreement.
Velocity profile inside a piezo-acoustic inkjet droplet: Experimental and numerical comparison
2013
Inkjet printing deposits droplets with a well-controlled narrow size distribution. This paper aims at improving experimental and numerical methods for the optimization of drop formation. We introduce a method to extract the one-dimensional velocity profile inside a single droplet during drop formation. We use a novel experimental approach to capture two detailed images of the very same droplet with a small time delay. The one-dimensional velocity within the droplet is resolved by accurately determining the volume distribution of the droplet. We compare the obtained velocity profiles to a numerical simulation based on the slender jet approximation of the Navier-Stokes equation and we find very good agreement.
Applied Physics A, 2016
For drop-on-demand inkjet technology, the capacity to reduce the inkjet droplet size without changing the size of the nozzle orifice would beneficially impact coating, processing, and maintenance attributes. To examine droplet sizes emanating from prescribed nozzle orifices, this manuscript applies numerical simulation based on computational fluid dynamics and an in-depth assessment of relevant parameters associated with producing liquid droplets, and then compares the outcomes with published data. For a given liquid, six distinct flow regimes were determined to affect droplet sizes, the critical characterization of which could be effectively assessed by using two non-dimensional parameters, including the Weber number, We, and a newly defined, non-dimensional temporal frequency number, X. The use of the regimes enables the specification of operational conditions to control and minimize droplet sizes to less than 20 % of the nozzle orifice diameter and up to 150 times smaller droplet volumes from nozzle orifices. As a consequence, a new method is proposed that would be useful for lowering droplet sizes while maintaining desired droplet quality for deposition on and coating of surfaces. List of symbols Roman symbols D Print-head inlet diameter (m) f Temporal jetting frequency (1/s)
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
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.
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.
Analysis of the Droplet Ejection for Piezoelectric-driven Industrial Inkjet Head
2006
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.
Physical Review Applied, 2014
Inkjet printing deposits droplets with a well-controlled narrow size distribution. This paper aims at improving experimental and numerical methods for the optimization of drop formation. We introduce a method to extract the one-dimensional velocity profile inside a single droplet during drop formation. We use a novel experimental approach to capture two detailed images of the very same droplet with a small time delay. The one-dimensional velocity within the droplet is resolved by accurately determining the volume distribution of the droplet. We compare the obtained velocity profiles to a numerical simulation based on the slender jet approximation of the Navier-Stokes equation and we find very good agreement.