Inkjet Printhead Research Articles

Fabrication of 3D Temperature Sensor Using Magnetostrictive Inkjet Printhead

Abstract Recently, the three-dimensional (3D) printing technique has attracted much attention for creating objects of arbitrary shape and manufacturing. For the first time, in this work, we present the fabrication of an inkjet printed low-cost 3D temperature sensor on a 3D-shaped thermoplastic substrate suitable for packaging, flexible electronics, and other printed applications. The design, fabrication, and testing of a 3D printed temperature sensor are presented. The sensor pattern is designed using a computer-aided design program and fabricated by drop-on-demand inkjet printing using a magnetostrictive inkjet printhead at room temperature. The sensor pattern is printed using commercially available conductive silver nanoparticle ink. A moving speed of 90 mm/min is chosen to print the sensor pattern. The inkjet printed temperature sensor is demonstrated, and it is characterized by good electrical properties, exhibiting good sensitivity and linearity. The results indicate that 3D inkjet printing technology may have great potential for applications in sensor fabrication.

Patterns of Knowledge Flow: Cycles of Divergence and Convergence in Printers

This paper considers technological trajectories as a series of problem-solving activities, manifesting the pattern of divergence-convergence knowledge flow. We propose that technological trajectories diverge when new knowledge is able to solve the problem of most concern. Relatedly, technological trajectories converge when existing knowledge becomes obsolescent in the face of new problems. To illustrate our ideas, we choose to study the technological evolution of the thermal inkjet print head, using key-route search and the patent assignee cross-citation network. The thermal inkjet print head experienced three cycles of divergence-convergence knowledge flow, each of which is characterized by the problem of most concern and referred solution. To enhance the rigor of our analysis, we also draw on archival data to examine in more detail the identified main paths as well as the assignee cross-citation network.

Inkjet jet failures detection and droplets speed monitoring using piezo self-sensing

The jetting reliability of the inkjet printhead is a key factor for successful usage of the printer. It is known that the monitoring method using self-sensing signal can detect jetting failures to ensure jetting reliability. However, a monitoring technique using self-sensing signal to identify different failure types with the ability to calculate the droplet speed has not been reported so far. In order to identify failure type accurately, different self-sensing signal features are investigated in the present study, including the improper driving voltage, fluid viscosity and the backpressure control. Furthermore, the self-sensing signal is applied to extract the characteristic parameters and explore the droplet speed monitoring pattern. In order to evaluate the effectiveness of the proposed detection method, a monitoring system consisting of the self-sensing signal acquisition module and the monitoring software interface is also developed in the present study. Experimental results indicate that the monitoring system recognizes jetting failures accurately. It is found that during the normal operation of the printhead, the average error for the single nozzle and the multi-nozzle is 5.03 % and 7.37 %, respectively.

An in-situ crosslinking binder for binder jet additive manufacturing

Additive Manufacturing (AM) of metals is a potentially disruptive technology that could significantly change the industrial supply chain. There are a limited number of AM methods capable of creating metal parts, and one method showing significant potential is Binder Jet AM (Binder Jetting). Binder Jetting utilizes an inkjet print head to deposit a binder fluid onto a powder bed and bind together powder particles into a desired geometry. This study investigates a new binder system consisting of a difunctional monomer, triethylene glycol dimethacrylate (TEG-DMA). TEG-DMA exhibits excellent printability with an Ohnesorge’s number of .258 making the Z number 3.876. During the thermal curing process, the difunctional monomer polymerizes and crosslinks at the onset temperature of 138 °C, becoming a solid dimethacrylate network. When the binder is utilized within the stainless-steel powder bed at 200 °C, it forms a network incorporating the stainless-steel particles, binding the powder into any specified geometry. Crosslinking the monomer within the stainless-steel 420 powder bed imparts a flexural strength of 1.0–3.3 MPa to the green part depending on the volume of monomer in the part. After sintering, the final stainless-steel parts results in a void fraction close to 60 % and carbon content below 0.4 %.

Jetting behavior in drop-on-demand printing: Laboratory experiments and numerical simulations

The formation and evolution of micron-sized droplets of a Newtonian liquid generated on demand in an industrial inkjet printhead are studied experimentally and simulated numerically. The shapes and positions of droplets during droplet formation are observed using a high-speed camera and compared with their numerically obtained analogs. Both the experiments and the simulations use practical length scales for inkjet printing. The results show how fluid properties, specifically viscosity and surface tension, affect the drop formation, ligament length, and breakoff time. We identify the parameter space of fluid properties for producing single drops at a prescribed speed and show this is not simply a restriction on the Ohnesorge number, but that there is an additional restriction on the Reynolds number that is distinct from the Reynolds number limit associated with the prevention of splashing. This phase diagram provides more precise guidance on the space of fluid parameters for jetting single droplets in drop-on-demand inkjet printers.

PDMS‐based hot embossing method of fabricating SU‐8 photoresist conical nozzle for inkjet print‐head

This work reports a PDMS-based hot embossing technique. The proposed method enables rapid, low-cost and mass-produced fabrication of SU-8 photoresist conical nozzle for inkjet print-head with soft PDMS moulds. The hydrophobic time for SU-8 master mould treated by trimethyldichlorosilane (TMCS) was determined. And the optimised thickness of SU-8 photoresist before hot embossing was 58.5 ± 1.55 μm corresponding to 3750 r/min of spin coating speed. The imprinting parameters were investigated. The highest replication precision was obtained in the embossed SU-8 conical nozzle processed by an embossing pressure of 2.57 MPa, an embossing temperature of 80°C, and an embossing time of 6 min. Finally, this work presents the fabrication of the SU-8 conical nozzle plate with the large aperture of 40.01 ± 1.24 μm, small aperture of 27.12 ± 1.07 μm, and the nozzle height of 50 ± 1.26 μm.

Effect of driving waveform on size and velocity of generated droplets of nanosilver ink (Smartink)

The quality of generated droplets in direct-write inkjet printing strongly depends on the shape of waveform voltages that control the piezoelectric actuators of the inkjet print head. The goal of this study is to investigate the optimal waveform voltage that influences the size and the velocity of ejected droplets to increase the performance of inkjet printing process. In this paper, Jetlab® 4xl inkjet printer with single nozzle of diameter 60 μm is used to control the behavior of Smartink (nanosilver ink) droplets at different jetting parameters. The velocity of droplets is measured at different dwell voltages and dwell times and the relationships between the size of the droplets and dwell time and dwell voltage are investigated. Also, a new method is developed by using Python programming to measure the size of the generated droplets and recognize whether the droplet has a spherical or an elliptical shape, and the result is compared with Aphelion imaging software. Finally, lines are printed at three optimum waveform voltages on PEEK and glass substrates.

Secondary Tail Formation and Breakup in Piezoacoustic Inkjet Printing: Femtoliter Droplets Captured in Flight

The role of meniscus motion and ink viscosity in the formation of a secondary tail and its breakup are studied experimentally during the picoliter-droplet formation process of a MEMS piezoacoustic inkjet print head using laser-induced 8-ns single-flash stroboscopic imaging with a temporal resolution of 100 ns. It is found that the formation of the secondary tail is driven by meniscus motion and that the secondary tail forms reproducibly between the primary tail and the meniscus in the final microseconds before pinchoff. We demonstrate that the stability of the secondary tail can be controlled through the motion of the meniscus after the primary tail has formed. A 4 times increase in stretching rate results in a 2.2 times increase in the secondary-tail length and a 3 times higher number of femtoliter satellites. Furthermore, as expected for Rayleigh breakup, a 43% increase in ink viscosity is found to increase the secondary-tail length by 50%. Finally, it is found that, during inkjet printing, the secondary tail cascades into tertiary and quaternary tails. We show that the formation of higher-order tails is irreproducible and therefore driven by noise. The formation of thicker secondary and thinner higher-order tails results in a bimodal satellite size distribution, where the secondary satellites with a volume greater than or equal to $4\phantom{\rule{0.2em}{0ex}}\mathrm{fL}$ are located closer to the primary-tail droplet, while satellites with a volume less than $4\phantom{\rule{0.2em}{0ex}}\mathrm{fL}$ are located closer to the nozzle. The main findings of the present work, that the stability of the secondary tail decreases with a decrease in stretching rate and ink viscosity, can be employed in the inkjet-printing community for waveform design to minimize internal contamination of inkjet printers.

Analysis of drop-on-demand piezo inkjet performance

For a particular printing ink and drop-on-demand piezoelectric inkjet printhead, piezoelectric voltage and temperature of the ink were varied to change the inkjet performance, and the jetting velocity of the inkjet was analyzed under various conditions. The ink was cooled by using a Peltier module, which was attached to the nozzle plate as a heat sink. The inkjet drops were captured by the shadowgraphic method using a high-speed camera. The positions and velocities of these drops were then estimated after image processing. The drop state was distinguished by dimensionless numbers, such as the Weber and Z numbers, to decide whether it was stable for ejection and printing. Increasing the piezoelectric voltage increased the ejection velocity but with an associated generation of satellite drops. Cooling the ink increased the viscosity, which in turn decreased the drop velocity while diminishing the satellite drops. Therefore, it was shown that the cooled ink enabled stabilized inkjet ejection.

3D printing of ceramics and graphene circuits-on-ceramics by thermal bubble inkjet technology and high temperature sintering

Alumina ceramics and graphene circuits-on-ceramics were 3D printed using inkjet technology. Water-based binders for ceramics and graphene oxide inks were prepared and jetted through thermal inkjet printhead. To increase the density of the 3D printed ceramics, two steps sintering and one step infiltration were performed. The sintering temperature dependent structure properties of the printed ceramics were systematically studied. The 3D printed α-Al2O3 ceramic sintered at 1600 °C for 2 h has achieved maximum density of 95.2%, volume shrinkage rate of 32%, Vickers hardness of 291.6 Hv, surface roughness of 3.7 μm, and maximum compression strength and flexural strength of 89 MPa and 49.4 MPa, respectively. The average adhesion of reduced graphene oxide (rGO) to 3D printed α-Al2O3 ceramic is 7.5 N/m. The printed graphene circuits-on-ceramics has achieved conductivity of 5.34 × 102 S m−1 after annealing at 600 °C in nitrogen atmosphere.

Design and Characteristic Analysis of a MEMS Piezo-Driven Recirculating Inkjet Printhead Using Lumped Element Modeling.

The recirculation of ink in an inkjet printhead system keeps the ink temperature and viscosity constant, and leads to the development of a high-performance device. Herein, we propose a recirculating piezo-driven micro-electro-mechanical system (MEMS)-based inkjet printhead that has a pressure chamber, a nozzle, and double restrictors. The design and characteristic analysis are performed using a two-port lumped element model (LEM) to investigate the effect of design parameters on the system responses. Using LEM, the jetting pressure at the pressure chamber, velocity at the nozzle inlet, meniscus pressure, and Helmholtz resonance frequency are predicted and the comparative analysis of the jetting pressure and velocity between LEM and the finite element method (FEM) simulation is conducted to validate our proposed LEM method. Furthermore, the effect of a change in major design parameters on the jetting pressure, velocity, and Helmholtz resonance frequency is analyzed. On the basis of this analysis, the optimized device dimensions are finalized. From our analysis, it is also concluded that the restrictor is more sensitive than the pressure chamber in terms of their variations in depth. As the cross-talk effect can occur due to an array of hundreds or thousands of nozzles, we investigated the effect of a single activated nozzle on the non-activated neighboring nozzles, as well as the effect of multi-activated nozzles on a single central nozzle using our proposed LEM.

Simulation & modelling of dilute solutions in drop-on-demand inkjet printing: a review

This review is about the most important matters for advancing inkjet printing with a focus on piezoelectric droplet on demand (DOD) inkjet thin-film devices. The Nano material compounds can be incorporated into a polymeric matrix and deposited by piezoelectric inkjet printing. Current problems in advanced printers are discussed as embodied in liquid filament breakup along with satellite droplet formation and reduction in droplet sizes. Various model that predicts the printability of dilute, mono disperse polymer solutions in drop-on-demand “DOD” inkjet printing have been discussed. For satellite droplets, it is exhibited which liquid filament break-up treatment can be predicted via using a combination of two pi-numbers, including the Weber number. The layer was printed over other printed layers including electrodes composed of the conductive polymers and also several polymers. It has been discussed, some polymer materials are suitable for deposition and curing at low to moderate temperatures and atmospheric pressure, allowing for the use of polymers or paper as supportive substrates for the devices, and greatly facilitating the fabrication process. Furthermore, through this review, it has been discussed scaling analyses for designing and operating of inkjet heads. Because of droplet sizes from inkjet nozzles are typically on the order of nozzle dimensions, a numerical simulation is shown for explaining how to reduce droplet sizes through employing a novel input waveform impressed on the inkjet-head liquid inflow without changing the nozzle geometries. Regardless of their any less performance, inkjet printer head as a technique for the mentioned devices presents many advantages, the most notable of which are quickly fabricating and patterning, substrate flexibilities, avoidance of material wastage via applying “DoD” technologies.

A robust ink deposition system for binder jetting and material jetting

The adaptation of inkjet technology for additive manufacturing (AM) enabled the highest standards of print speed and print resolution in the industry. However, inkjet printheads impose strict limitations on ink properties. Ink compositions ex volatility, rehydration, surface tension, chemical stability, abrasiveness, and electrical properties that deviate from printhead specifications shorten its service life. Frequent and complex maintenance procedures are necessary, but replacement is the only solution to declining print quality, accruing heavy maintenance costs. This is especially limiting for AM as part quality and properties are closely dependent on ink composition. We propose an ink deposition system designed for robustness by implementing modular and dedicated components. The system deposits ink in a continuous jet. We find optimal process parameters and evaluate system performance in comparison to inkjet and material extrusion (ME). The system produces line widths between 0.3-0.5mm, indicating print resolution capabilities are comparable to commercial ME systems.

Design and fabrication of composite vibrating plate used for piezoelectric inkjet print head

A piezoelectric vibrating plate is an important component of the piezoelectric inkjet print head, it determines the ejection performance of the piezoelectric inkjet print head. Based on the design model of the vibrating plate and the lead zirconate titanate piezoelectric film in the inkjet print head, the approximate expression of the equivalent load and deflection of the vibrating plate were established. The Cu/SiO2 vibration plate structure of the piezoelectric inkjet print head was fabricated based on MEMS process. The laser Doppler test was performed on the vibrating plate to obtain the amplitude of the Cu/SiO2 vibrating plate. The test results are in good agreement with the theoretical predictions based on the mechanical analysis.

Shortwave infrared imaging setup to study entrained air bubble dynamics in a MEMS-based piezo-acoustic inkjet printhead

Piezo-acoustic inkjet printing is the method of choice for high-frequency and high-precision drop-on-demand inkjet printing. However, the method has its limitations due to bubble entrainment into the nozzle, leading to jetting instabilities. In this work, entrained air bubbles were visualized in a micrometer scale ink channel inside a silicon chip of a MEMS-based piezo-acoustic inkjet printhead. As silicon is semi-transparent for optical imaging with shortwave infrared (SWIR) light, a highly sensitive SWIR imaging setup was developed which exploited the optical window of silicon at 1550 nm. Infrared recordings of entrained bubbles are presented, showing rich phenomena of acoustically driven bubble dynamics inside the printhead.Graphic abstract

High-precision three-dimensional inkjet technology for live cell bioprinting.

In recent years, bioprinting has emerged as a promising technology for the construction of three-dimensional (3D) tissues to be used in regenerative medicine or in vitro screening applications. In the present study, we present the development of an inkjet-based bioprinting system to arrange multiple cells and materials precisely into structurally organized constructs. A novel inkjet printhead has been specially designed for live cell ejection. Droplet formation is powered by piezoelectric membrane vibrations coupled with mixing movements to prevent cell sedimentation at the nozzle. Stable drop-on-demand dispensing and cell viability were validated over an adequately long time to allow the fabrication of 3D tissues. Reliable control of cell number and spatial positioning was demonstrated using two separate suspensions with different cell types printed sequentially. Finally, a process for constructing stratified Mille-Feuille-like 3D structures is proposed by alternately superimposing cell suspensions and hydrogel layers with a controlled vertical resolution. The results show that inkjet technology is effective for both two-dimensional patterning and 3D multilayering and has the potential to facilitate the achievement of live cell bioprinting with an unprecedented level of precision.

1-D and 2-D Magnetostrictive Actuators

The magnetostrictive inkjet printhead (MagJet), an example of the 1-D magnetostrictive actuator (MA), consists of one MA, a nozzle, a chamber, and a fluid inlet. The mathematical estimation tells that the droplets are not likely to be made due to the inverse of Ohnesorge number less than one. The experimental results, however, show that the MagJet ejects the high viscosity fluid up to 1000 cP at room temperature. The magnetostrictive motor (MagMotor), an example of the 2-D MA, is composed of one Terfenol-D rod, one toroidal coil, one solenoid coil, a stator, a rotor, and housing. The experimental results show that the MagMotor rotates successfully up to 60 rpm, and about an arbitrary axis.

Comparison of Linear and 4-Arm Star Poly(vinyl pyrrolidone) for Aqueous Binder Jetting Additive Manufacturing of Personalized Dosage Tablets

Fabrication of personalized dosage oral pharmaceuticals using additive manufacturing (AM) provides patients with customizable, locally manufactured, and cost-efficient tablets, while reducing the probability of side effects. Binder jetting AM has potential for fabrication of customized dosage tablets, but the resulting products lack in strength due to solely relying on the binder to produce structural integrity. The selection of polymeric binders is also limited due to viscosity restraints, which limits molecular weight and concentration. To investigate and ameliorate these limitations, this article reports a comprehensive study of linear and 4-arm star poly(vinyl pyrrolidone) (PVP) over a range of molecular weights as polymeric binders for binder jetting AM and their effect on physical tablet properties. Formulation of varying molecular weights and concentrations of linear and 4-arm star PVP in deionized water and subsequent jetting revealed relationships between the critical overlap concentrations (C*) and jettability on binder jetting systems with thermal inkjet printheads. After printing with a commercially available ZCorp Spectrum Z510 printer with an HP11 printhead with a lactose and powdered sugar powder bed, subsequent measurement of compressive strength, compressive modulus, and porosity revealed structure-property relationships between molecular weight, polymer concentration, and linear and 4-arm star architectures with physical properties of binder jetted tablets. This study elucidated that the dominating factor to increase compressive strength of a tablet is dependent on the weight percent of the polymer in the binder, which filled interstitial voids between powder particles. Because 4-arm star polymers have lower solution viscosities compared to linear analogues at the same molecular weights, they were jettable at higher concentrations, thus producing the strongest tablets at a compressive strength of 1.2 MPa. Finally, the inclusion of an active pharmaceutical ingredient (API), acetaminophen, revealed maintenance of the tablet physical properties across 5-50 total wt % API in each tablet.

Adjoint-based shape optimization of the microchannels in an inkjet printhead

In drop-on-demand inkjet printheads, ink is pumped steadily through small channels, each of which contains an actuator and a nozzle. When an actuator pulses, a droplet is forced through the nozzle, after which acoustic oscillations reverberate within the channel. Manufacturers would like to damp the residual reverberations, without increasing the pressure drop required to drive the steady flow. In this paper we use gradient-based optimization to show that this can be achieved by constricting the channel where the acoustic velocity is largest and enlarging the channel where the acoustic velocity is smallest. This increases the viscothermal dissipation of the acoustics without changing the viscous dissipation of the steady flow. We separate the compressible Navier–Stokes equations into equations for a steady flow with no oscillations and equations for oscillations with no steady flow. We define two objective functions: the viscous dissipation of the steady flow and the dissipation of the oscillations. We then derive the adjoints for both sets of equations, and obtain expressions for the gradient of each objective function with respect to boundary deformations in Hadamard form. We combine these with a gradient-based optimization algorithm, incorporating constraints such as the shapes of the actuator and nozzle. This algorithm quickly converges to a design that has the same viscous dissipation for the steady flow but a 50 % larger decay rate for the oscillating flow. We show that this design is nearly optimal. It is a shape that inkjet manufacturers, using physical insight and trial and error, have probably not yet considered. We also show how the adjoint fields provide physical insight into the mechanisms affecting each objective function. The main requirements of this method are that the steady flow Mach number and oscillating flow Mach number are small, and that dissipation is dominated by thermoviscous mechanisms. These requirements are often satisfied in microfluidics, so the method in this paper could be applied to many other applications.

Real time observation of binder jetting printing process using high-speed X-ray imaging

A high-speed synchrotron X-ray imaging technique was used to investigate the binder jetting additive manufacturing (AM) process. A commercial binder jetting printer with droplet-on-demand ink-jet print-head was used to print single lines on powder beds. The printing process was recorded in real time using high-speed X-ray imaging. The ink-jet droplets showed distinct elongated shape with spherical head, long tail, and three to five trailing satellite droplets. Significant drift was observed between the impact points of main droplet and satellite droplets. The impact of the droplet on the powder bed caused movement and ejection of the powder particles. The depth of disturbance in the powder bed from movement and ejection was defined as interaction depth, which is found to be dependent on the size, shape, and material of the powder particles. For smaller powder particles (diameter less than 10 μm), three consecutive binder droplets were observed to coalesce to form large agglomerates. The observations reported here will facilitate the understanding of underlying physics that govern the binder jetting processes, which will then help in improving the quality of parts manufactured using this AM process.