Continuous Inkjet Printing Research Articles

선택적 영역 코팅을 위한 양방향 연속 잉크젯 프린팅

The continuous inkjet (CIJ) printing method has fewer nozzle clogging issues and faster jetting speed compared to the drop-on-demand (DOD) inkjet method, and it can be relatively cost-effective to implement. Additionally, it has relatively wider printing capability, which allows for coating or marking printing on curved substrates. Nevertheless, commercially available CIJ equipment is still limited to narrow printing width of about 10 mm, because most continuous inkjet devices employ a unidirectional printing method. In this study, we conducted research on a bidirectional printing method that can expand the printing width, enabling continuous inkjet to be utilized in a broader range of applications. Bidirectional printing requires bidirectional charging, which can cause problems when the polarity of the ink changes. We address and visualize these issues and propose a printing method that can overcome them. We expect that the proposed method will have suitable applicability for coating selective areas.

Analysis of the Ink-Stream Break-Up Phenomenon in Continuous Inkjet Printing.

The ink-stream break-up phenomenon in continuous inkjet printers has been studied herein. A numerical model has been developed to reproduce and analyze the non-monotonic behavior of ink-stream break-up length (BUL) against the amplitude of piezo-actuator oscillation. That is, when the amplitude is increased, the BUL initially decreases to a local minimum point, then increases to a local maximum point, and finally decreases again. The developed model is split into two stages, first being the emergence of periodic "initial indentation" on ink stream caused by piezo-oscillation and the second being the growth of indentation. Finally, the calculated results of BUL against oscillation amplitude is compared with experimental data. We confirmed that the model well reproduces the characteristic of BUL and clarified the emergence mechanism of its local minimum and maximum points.

Continuous inkjet printing and machine learning identify unknown liquid viscosities

Approach much faster, more comprehensive than measuring individual liquids using conventional rheometers

Rheological identification of jetted fluid using machine learning

The understanding of flowing properties of fluids and the knowledge of the related rheological properties are crucial from both a research and industrial point of view. To determine the complex rheological properties of fluids, many devices have thus been developed, the so-called rheometers. The main objective of the present paper is to identify the rheological properties of a fluid jetted using continuous inkjet (CIJ) printing process by comparing the morphology of the aforementioned jetted fluid to a dataset of known (rheologically speaking) fluid jet morphologies and properties of a fluid by the viscosity, the surface tension, and the density of fluids using large datasets and a CIJ printing process. When ejecting a fluid, the CIJ ejection process competes among several forces: inertial, viscous, surface tension, and elasticity, which affect the morphology of the resulting jet. Also, under certain conditions, the morphology of the jet is unique and directly related to the rheological properties of the fluid. We want to use this uniqueness to identify the fluid among a large dataset of known fluid jet morphologies to be compared with, to obtain its rheological properties. Using a large numerically generated dataset of Newtonian fluid jets, we show in this article that the identification of the viscosity using neural network is not only feasible but also proves to be very accurate with an average error of less than 1% for a large range of viscosities.

Improved Continuous Inkjet for Selective Area Coating Using High‐Viscosity Insulating Inks

While drop‐on‐demand (DOD) inkjet has been broadening its applications, especially in manufacturing sectors such as printed electronics, continuous inkjet (CIJ) has been limited to use in conventional graphics and marking areas. So far, there have been few attempts to use functional materials in CIJ printing despite the advantages of its high‐speed printing capability and relatively low implementation costs. Herein, the performance of CIJ in terms of printable ink viscosity, print area, and printing speed is significantly improved. For demonstration, selective area printing methods using insulation inks are presented. The selective area coating is very difficult to implement since charged droplets becoming closer together can increase undesirable charge repulsion effects among them. To reduce the charge interaction among the charged droplets and maximize the printing efficiency, a new voltage driving scheme for selective area coating applications is proposed.

Reversal and Inversion of Capillary Jet Breakup at Large Excitation Amplitudes

The evolution of the capillary breakup of a liquid jet under large excitation amplitudes in a parameter regime relevant to inkjet printing is analysed using three-dimensional numerical simulations. The results exhibit a reversal of the breakup length of the jet occurring when the velocity scales associated with the excitation of the jet and surface tension are comparable, and an inversion of the breakup from front-pinching to back-pinching at sufficiently large excitation amplitudes. Both phenomena are shown to be associated with the formation of vortex rings and a local flow obstruction inside the jet, which modify the evolution of the jet by locally reducing or even reversing the growth of the capillary instability. Hence, this study provides a mechanism for the well-known breakup reversal and breakup inversion, which are both prominent phenomena in inkjet printing. An empirical similarity model for the reversal breakup length is proposed, which is shown to be valid throughout the considered range of characteristic parameters. Hence, even though the fluid dynamics observed in capillary jet breakup with large excitation amplitudes are complex, the presented findings allow an accurate prediction of the behaviour of jets in many practically relevant situations, especially continuous inkjet printing.

Deflecting the Issue: The Origin of Nanoscale Material Build-up in Continuous Inkjet Printing

Continuous Inkjet (CIJ) printing relies on steering charged droplets accurately to the surface with electric fields. A vital component is the set of deflecting electrodes within the printhead that create these fields. Unwanted deposition of ink on the electrodes, known as build-up, is a concern for operators because it modifies the applied electric field, affects long-term reliability and requires manual intervention, but is not widely reported or explored. Here we report a laser-based high-speed visualisation technique to observe build-up and show it stems from small satellite droplets that break off from the main printed drops. We characterise the material build-up and reveal its nanoscale particulate nature. Combining the tracking with characterisation allows us to quantify the charge-to-mass ratio of these droplets. This study provides a route to understand the build-up phenomenon and will enable optimisation of the printing conditions and printing reliability.

Deflecting the Issue: The Origin of Nanoscale Material Build-up in Continuous Inkjet Printing

Abstract Continuous inkjet printing relies on steering charged droplets accurately to the surface by using electric fields. A vital component is the set of deflecting electrodes within the printhead, which create these fields. Unwanted deposition of ink on the electrodes, known as build-up, is a concern for operators because this modifies the applied electric field, affects long-term reliability, and requires manual intervention. However, this has not been widely reported or explored. Here, the authors report a laser-based high-speed visualization technique to observe build-up and show that it stems from small satellite droplets that break off from the main printed drops. They characterize the material build-up and reveal its nanoscale particulate nature. Combining the tracking with characterization allows quantifying the charge-to-mass ratio of these droplets. This study provides a route to understanding the build-up phenomenon, and it will enable optimization of printing conditions and printing reliability.

Effects of drive amplitude on continuous jet break-up

We develop a one-dimensional model of jet breakup in continuous inkjet printing to explore the nonlinear behavior caused by finite-amplitude modulations in the driving velocity, where jet stability deviates from classic (linear) “Rayleigh” behavior. At low driving amplitudes and high Weber numbers, the spatial instability produces drops that pinch-off downstream of the connecting filament, leading to the production of small satellite droplets between the main drops. On the other hand, we identify a range of driving amplitudes where pinching becomes “inverted,” occurring upstream of the filament connecting the main drops, rather than downstream. This inverted breakup is preferable in printing, as it increases the likelihood of satellite drops merging with the main drops. We find that this behavior can be controlled by the addition of a second harmonic to the driving signal. This model is in quantitative agreement with a full axisymmetric simulation, which incorporates nozzle geometry.

Edible solid foams as porous substrates for inkjet-printable pharmaceuticals

The aim of this study was to investigate new porous flexible substrates, i.e., solid foams that would serve as a carrier with a high ink absorption potential for inkjet printable pharmaceuticals. Propranolol hydrochloride was used as a model active pharmaceutical ingredient (API). Pharmaceutically approved and edible cellulose derivatives and gums together with different additives were evaluated as a base for the substrate. Different methods for preparation of a solid foam such as freeze-drying, vacuum oven drying and drying at room temperature were explored. Only freeze-drying of the polymeric solutions resulted in the desired porous and flexible, but mechanically stable, soft sponge-like substrates with hydroxypropyl methylcellulose (HPMC)-based solid foams being the most suitable for the use in continuous inkjet printing. The plasticized HPMC foams had a superior absorption capacity and fast penetration speed for the different solvents due to the open cell pore structure and higher porosity as compared to nonplasticized additive-free foams, although, the latter were less hygroscopic. The produced solid foams were well suited for inkjet printing of high volumes of API-containing ink. The inkjet-printed API was immediately released from the dosage forms upon contact with the dissolution medium. This work demonstrates that the fabricated solid foams, based on plasticized HPMC, show a great potential as porous carriers in the fabrication of high dose dosage forms by inkjet printing.

Contact angle control of sessile drops on a tensioned web

In this study, the influence of the change of tension applied to flexible and thin web substrate on the contact angle of sessile drop in roll-to-roll system was investigated. Graphene oxide and deionized water solutions were used in the experiments. Tension was changed to 29, 49, and 69 N, and the casting distance of the micropipette and the material was set to 10, 20, and 40 mm, and the droplet volume was set to 10, 20, and 30 μL, respectively. Statistical analysis of three variables and analysis of the variance methodology showed that the casting distance was most significant for the contact angle change, and the most interesting tension variable was also affected. The change in tension caused the maximum contact angle to change by 5.5°. The tension was not uniform in the width direction. When the droplet was applied in the same direction in the width direction, it was confirmed that the tension unevenness had great influence on the contact angle up to 11°. Finally, the casting distance, which has a large effect on the contact angle, was calibrated in the width direction to reduce the width direction contact angle deviation to 1%. This study can be applied to fine patterning research using continuous inkjet printing and aerosol jet printing, which are roll-to-roll processes based on droplet handling.

Influence of the Nozzle Shape on the Breakup Behavior of Continuous Ink Jets

In this work, the influence of nozzle shape on microfluidic ink jet breakup is investigated. First, an industrial ink used in continuous inkjet (CIJ) printing devices is selected. Ink rheological properties are measured to ensure an apparent Newtonian behavior and a constant surface tension. Then, breakup lengths and shapes are observed on a wide range of disturbance amplitude for four different nozzles. Later on, ink breakup behaviors are compared to the linear theory. Finally, these results are discussed using numerical simulations to highlight the influence of the velocity profiles at the nozzle outlet. Using such computations, a simple approach is derived to accurately predict the breakup length for industrial CIJ nozzles.

Combined Inkjet Printing and Infrared Sintering of Silver Nanoparticles using a Swathe-by-Swathe and Layer-by-Layer Approach for 3-Dimensional Structures.

Despite the advancement of additive manufacturing (AM)/3-dimensional (3D) printing, single-step fabrication of multifunctional parts using AM is limited. With the view of enabling multifunctional AM (MFAM), in this study, sintering of metal nanoparticles was performed to obtain conductivity for continuous line inkjet printing of electronics. This was achieved using a bespoke three-dimensional (3D) inkjet-printing machine, JETx, capable of printing a range of materials and utilizing different post processing procedures to print multilayered 3D structures in a single manufacturing step. Multiple layers of silver were printed from an ink containing silver nanoparticles (AgNPs) and infrared sintered using a swathe-by-swathe (SS) and layer-by-layer sintering (LS) regime. The differences in the heat profile for the SS and LS was observed to influence the coalescence of the AgNPs. Void percentage of both SS and LS samples was higher toward the top layer than the bottom layer due to relatively less IR exposure in the top than the bottom. The results depicted a homogeneous microstructure for LS of AgNPs and showed less deformation compared to the SS. Electrical resistivity of the LS tracks (13.6 ± 1 μΩ cm) was lower than the SS tracks (22.5 ± 1 μΩ cm). This study recommends the use of LS method to sinter the AgNPs to obtain a conductive track in 25% less time than SS method for MFAM.

Influence of Z number and Pulse Voltage on Drop-on-Demand (DOD) Inkjet Printability

Inkjet printing has been applied in manufacturing structural and functional materials for decades. There are two kind of methods known as continuous inkjet (CIJ) printing and drop-on-demand (DOD) inkjet printing.[1] In DOD inkjet printing, drops are generated only when a drop needed by producing a pressure pulse in a chamber filled with inks. And before drop generation, the inkjet printing head will be moved to the desired location to locate the drop in a precise position. DOD inkjet printing is a method that directly places materials on demand, which saves the required raw materials and reduces the printing steps. As a consequence, DOD inkjet printing saves more time with lower waste consumption during production than CIJ printing and the equipment has a smaller footprint.DOD inkjet printing can be divided into two methods by which the pressure pulse is generated followed by drop ejection: thermal DOD inkjet printing and piezoelectric DOD inkjet printing. In piezoelectric DOD inkjet printing, the pressure pulse is produced by the mechanical actuation of the chamber walls.[2] When a voltage is applied, the piezoelectric material changes shape, which generates a pressure pulse in the fluid forcing a droplet of ink from the nozzle. It is important to know the inkjet printable range to generate accurate and repeatable drops. Fromm had defined ink printability in drop on demand (DOD) printing using a dimensionless Z number which related to the physical properties of the inks.[3] However, it is still not agreed whether there is a precise Z number range for inkjet printability and not known whether the range varies using different actuating pulses.The goal of our study is to find out the detail relationship between the ink properties and Drop-on-Demand inkjet printing printability and explore whether the printable Z number range change with actuating pulses and different kind of printheads.Here we investigate the influence of Z number and pulse voltage on printability using two inkjet printheads (10 pl Dimatix and 80 μm MicroFab). We have used 10 model inks made from solvent mixtures of ethylene glycol, diethylene glycol and distilled water. A range of actuating pulse voltages has also been studied. We found that the printable Z number range changes with the pulse voltages applied on inkjet printing. When increasing pulse voltage to print the same ink, it becomes printable under low pulse voltage and flying slow in the air and then printing well until at a certain voltage satellites forms and more satellites form when further increasing the pulse voltage. We also found that the printable voltage range is slightly different among inks with Z < 8. Under higher pulse voltages, it is possible to get single droplets with Z < 4, but inks with Z < 4 are printed out with some satellites. However, accurate and stable drops without satellites could be formed using inks of Z < 4 under lower voltages and it is not printable for inks of Z < 4 when printed under lower pulse voltages. These results could give an explanation of the different Z number range shown in different researches published when they using different printheads and pulse voltages.

Supramolecular approach to new inkjet printing inks.

Electronically complementary, low molecular weight polymers that self-assemble through tunable π-π stacking interactions to form extended supramolecular polymer networks have been developed for inkjet printing applications and successfully deposited using three different printing techniques. Sequential overprinting of the complementary components results in supramolecular network formation through complexation of π-electron rich pyrenyl or perylenyl chain-ends in one component with π-electron deficient naphthalene diimide residues in a chain-folding polyimide. The complementary π-π stacked polymer blends generate strongly colored materials as a result of charge-transfer absorption bands in the visible spectrum, potentially negating the need for pigments or dyes in the ink formulation. Indeed, the final color of the deposited material can be tailored by varying the end-groups of the π-electron rich polymer component. Piezoelectric printing techniques were employed in a proof of concept study to allow characterization of the materials deposited, and a thermal inkjet printer adapted with imaging software enabled in situ analysis of the ink drops as they formed and of their physical properties. Finally, continuous inkjet printing allowed greater volumes of material to be deposited, on a variety of different substrate surfaces, and demonstrated the utility and versatility of this novel type of ink for industrial applications.

Polymer degradation during continuous ink-jet printing

Abstract Results are reported for the first time on the possibility and cause of polymer degradation in a full commercial inkjet printer. The behaviour of three linear poly(methyl methacrylate) (PMMA) samples, having M w 90, 310 and 468 kDa respectively, in a continuous inkjet (CIJ) Domino A-Series+ printer is investigated and compared with earlier reported results for two experimental drop on demand (DOD) printers, a Dimatix DMP-2800 and a Microfab single nozzle glass capillary. Despite all three printheads having equivalent strain rate at the nozzle tip ( e ) no degradation is observed within the CIJ head alone whereas single pass degradation is observed in both DOD printheads. This can be attributed to a consequence of a number of factors including the slightly greater nozzle diameter, and different nozzle geometry, which includes cone angle and nozzle cylinder length, for CIJ, the different mode of drop generation or the higher polymer concentration investigated. It should also be noted that the flow through the CIJ nozzle is continuous, where it is pulsed in the case of DOD. The calculated maximum strain rates are similar, but in DOD it is being periodically ramped up and switched off. The main source of polymer degradation in CIJ printing through a CIJ Domino A-Series+ printer is found to be the continuous recycling of ink through the pump resulting in mechano-chemical polymer degradation. Molecular weight degradation proceeds by random scission, and is obtained at the lower shear rates experience as a consequence of the longer residence time due to mechano-chemical damage in the pump. These results have significance in the total design of inkjet systems for the delivery of high molecular weight polymers and materials sensitive to mechano-chemical degradation and highlight the need for careful consideration when moving from laboratory based print tools to full scale application.

The Effect of Substrate on Continuous Electrohydrodynamic Printing

In this paper, the behavior of ejected jet is studied at three different substrates (conductive, semiconductor and dielectric) in continuous electrohydrodynamic inkjet printing mode. Because the polarization charges will accumulate at the surface of the substrate in a short nozzle-to-collector distance, one can observe that the different flight behavior in the space. Results show that the substrate has little effect on the threshold voltage and the relaxation time of the substrate can be used to indicate the behavior of the jet. When the lifetime of the jet is larger than the relaxation time of the substrate, the jet can be deposited on the substrate regularly. Based on this guideline, a designed parallel lines and grid pattern are fabricated with several micrometers on a silicon substrate. These show that the designed pattern could be fabricated in a controllable jet. In the future, this method is able to be utilized to fabricate the mirco/nano-devices.

Modeling fluid–structure interaction in a direct write manufacturing process

This paper investigates the fluid–structure interaction (FSI) within a direct write manufacturing process. The interaction of three fields namely: electrostatic, structural, and fluidic in a continuous inkjet (CIJ) print head used for direct write manufacturing is captured with a multiphysics model. A FSI algorithm was used to capture the interaction of the piezoelectric (PZT) disc with different fluid media. The effects of input parameters such as fluid pressure, frequency, and voltage on the PZT disc displacement were studied. Further, their effects on the transient pattern of the PZT displacement are explained with respect to fluid type. The multiphysics model developed was validated by an ultra-high speed photography experimental setup. The outcome of this research concludes that fluids with higher viscosities display increased PZT disc displacements. Substantial rise in PZT disc displacements were observed with a proportional increase in the frequency of excitation. An increase in the density of the fluid resulted in higher PZT disc displacements. Thus, fluid density and rheology play an important role in the dampening behavior of the PZT disc as captured by the multiphysics model. For a particular fluid type, a minimal level of PZT displacement threshold is required for drop breakup from the fluid stream. Based on the findings of this research the input process parameters can be controlled to optimize microdrop formations that are critical toward direct write manufacturing.

Study on the equal pressure distributed hydrokinetics of the supplying ink for continuous inkjet printing system

Supplying uniform pressure ink in continuous inkjet printing system is the key factor for forming uniform and constant speed ink droplets, it is related to the final imaging effects, this research has seldom been reported in these years. This paper studied on the hydrokinetics and uniform distributed mechanics of supplying ink pressure for the continuous inkjet printing system based on the theoretical calculation, CFD (Computational Fluid Dynamics) and the advanced testing equipment. According to the analysis of laminar flow characteristics and the other jetting flow dynamics factors of the ink, a new type of equipment for supplying ink was designed in this paper, including the structure of the transition pipe and nozzle. The shape of the equipment is rectangular, where the flow section is gradually tapered. This supplying ink equipment can make the ink droplets distribute under the equal pressure on the cross direction. This study educed the optimally hydrokinetics parameters for the continuous inkjet printing. The experiments showed that this new supplying ink equipment could make the ink droplets distribute under the equal pressure and uniform velocity on the cross direction, so it greatly improved the imaging effects for the continuous inkjet printing system.

Computational fluid dynamics analysis of a direct write manufacturing process

This paper investigates the microdroplet generation mechanism in a direct write manufacturing process. A continuous inkjet (CIJ) method is utilised to deposit conductive nano particulate materials which can be used for building functionally gradient micro-sized features and devices. The spatial and temporal complexity of this process requires a computational modelling methodology to complement its experimental development. A CFD model is developed that is further validated using an ultra-high speed photography experimental setup. Input parameters such as fluid pressure, excitation frequency and voltage of the piezoelectric disc within the CIJ print head are varied to obtain trends for droplet volume and velocity. The dynamic pressure fluctuations due to acoustic waves generated during the piezoelectric disc excitation are studied. The effect of excitation parameters on satellite droplet formations is explained. These findings can be useful for the fabrication of freeform miniaturised devices in three dimensional spaces.