Application Of Inkjet Printing Research Articles

Building Functional Prototypes Using Conductive Inkjet Printing

The recently developed conductive inkjet printing process enables conductive circuits to be created quickly, cheaply, and easily using a consumer-grade inkjet printer. In its basic form, the technique supports a single layer of wiring on a flexible substrate. This can be a valuable tool for pervasive computing research because it allows simple electronic circuits and devices to be built and iterated quickly, in an analogous manner to the use of 3D printers for prototyping mechanical structures. It is possible to rapidly create touch- and proximity-sensitive surfaces, to cut and fold the printed conductive patterns, and to augment them with off-the-shelf electronic components and custom-made subcircuits. The authors present the possibilities enabled by conductive inkjet printing, bringing together their previously published results and presenting their latest insights and findings. They consider these printing and fabrication techniques as a suite of tools for researchers and practitioners who wish to fabricate a variety of functional device prototypes. They aim to enable others to understand the strengths, weaknesses, and applicability of conductive inkjet printing across a range of pervasive computing applications. This article is part of a special issue on printing and fabrication.

Fabrication of patterned thermoplastic microphases between composite plies by inkjet printing

We report on the pioneering application of inkjet printing in depositing patterned thermoplastic microphases between composite plies and the beneficial effect of the printed thermoplastic on the interlaminar fracture toughness of carbon fibre-reinforced polymer laminates. Double-cantilever beam test and short-beam shear test were employed to investigate the mechanical performances of the engineered composites. The results from this work revealed that by printing thermoplastic poly(ethylene glycol) and poly(methyl methacrylate) between the carbon fibre-reinforced polymer plies, mode I interlaminar fracture toughness (GIc) is noticeably enhanced, whilst the shear strength has also been preserved. Scanning electron microscopy was used to investigate the fracture surfaces generated during the double-cantilever beam test. The microscopic addition of the thermoplastic polymers (approximately 0.015 wt%) did not increase the weight of the composites significantly, which compares favourably to other conventional toughening methods.

UV-curable encapsulation of surface—Modified organic pigments for inkjet printing of textiles

Aqueous dispersions of nano-scale organic pigments were prepared through ball milling and ultra-sonication in presence of dispersing agents. The well dispersed pigment was encapsulated into UV-curable resin via miniemulsion technique. Effects of molecular structure of organic pigments, type of dispersing agent and time of ball milling were investigated. Results showed that C.I. Pigment Green 7 had better dispersion stability with time compared with other pigments. Ultracentrifuge sedimentation test, shelf life stability, thermal gravimetric analysis (TGA) and transmission electron microscope (TEM) provided supporting evidences for the encapsulation of C.I. Pigment Green 7 into polyester tetra acrylate/1,6-hexandiol dimethacrylate. Zeta potential results proved that UV-curable encapsulation of C.I. Pigment Green 7 intensifies the charge on the surface of the pigment and significantly increases the dispersion stability. This method of modifying organic pigments to be used as pigmented UV-curable inkjet inks was found to be durable and effective in preliminary application in inkjet printing of textiles.

Inkjet printing of weakly elastic polymer solutions

Fluid assessment methods, requiring small volumes and avoiding the need for jetting, are particularly useful in the design of functional fluids for inkjet printing applications. With the increasing use of complex (rather than Newtonian) fluids for manufacturing, single frequency fluid characterisation cannot reliably predict good jetting behaviour, owing to the range of shearing and extensional flow rates involved. However, the scope of inkjet fluid assessments (beyond achievement of a nominal viscosity within the print head design specification) is usually focused on the final application rather than the jetting processes. The experimental demonstration of the clear insufficiency of such approaches shows that fluid jetting can readily discriminate between fluids assessed as having similar LVE characterisation (within a factor of 2) for typical commercial rheometer measurements at shearing rates reaching 104rads−1.Jetting behaviour of weakly elastic dilute linear polystyrene solutions, for molecular weights of 110–488kDa, recorded using high speed video was compared with recent results from numerical modelling and capillary thinning studies of the same solutions.The jetting images show behaviour ranging from near-Newtonian to “beads-on-a-string”. The inkjet printing behaviour does not correlate simply with the measured extensional relaxation times or Zimm times, but may be consistent with non-linear extensibility L and the production of fully extended polymer molecules in the thinning jet ligament.Fluid test methods allowing a more complete characterisation of NLVE parameters are needed to assess inkjet printing feasibility prior to directly jetting complex fluids. At the present time, directly jetting such fluids may prove to be the only alternative.

Controllable synthesis and characterization of poly(aniline‐co‐pyrrole) using anionic spherical polyelectrolyte brushes as dopant and template

A poly(aniline‐co‐pyrrole), using anionic spherical polyelectrolyte brushes (ASPB) as dopant and template, was synthesized by chemical oxidation polymerization. The composites were characterized by scanning electron microscopy (SEM), Fourier‐transform infrared spectrometry (FTIR), X‐ray diffraction (XRD), and electrical studies. The SEM images confirmed that the composites had a spherical‐like structure, with a size of ca. 170 nm. The FTIR spectra showed the intermolecular interaction between poly(aniline‐co‐pyrrole) and ASPB. The XRD analysis revealed that the interplanar distance of the copolymers increased from 0.373 nm to 0.391 nm. The electrical conductivity of the poly(aniline‐co‐pyrrole)/ASPB nanocomposites at room temperature was 8.3 S cm−1, higher than that of the conducting copolymers (2.1 S cm−1). These conductive nanocomposites have nanoparticle size, controllable morphology, and the potential for application in inkjet electronic printing. POLYM. COMPOS., 35:1858–1863, 2014. © 2014 Society of Plastics Engineers

Alternating Current Electrohydrodynamic Printing of Microdroplets

This paper discusses the technology of orderly printing of microdroplets by means of electrohydrodynamic print (EHDP) with alternating current (AC). The AC electric field induces charges to reciprocate in the electrohydrodynamic charged jet and generates periodic alternation of electric field force, which facilitates the breakup of charged jets and injection of microdroplets. Microdroplets with a diameter of 100~300 μm can be printed with a frequency of 5~25 Hz via AC EHDP. Effects of process parameters on the microdroplet injection behaviors were investigated. A higher frequency of applied AC voltage led to a higher deposition frequency, but smaller diameters of printed droplets. Deposition frequency and droplet diameters increased with the increase of duty cycle and solution supply rate. AC pulse voltage has provided a novel way to study the control technology in EHDP, which would accelerate the application of inkjet printing in the field of micro/nanosystem production.

DoD Inkjet Printing of Weakly Elastic Polymer Solutions

Fluid assessment devices, such as high frequency rheometers and torsion resonators, filament stretching and thinning systems, and oscillating DoD drops, requiring small volumes and avoiding the need for jetting, are particularly useful in the design of functional fluids for inkjet printing applications. With the increasing use of complex (rather than Newtonian) fluids for manufacturing, single frequency fluid characterisation cannot reliably predict good jetting behaviour, owing to the range of shearing and extensional flow rates involved. However, the scope of inkjet fluid assessments (beyond achievement of a nominal viscosity within the print head design specification) is usually focused on the final application rather than the jetting processes. The experimental demonstration of the clear insufficiency of such approaches shows that fluid jetting can readily discriminate between fluids assessed as having similar LVE characterisation (within a factor of 2) for typical commercial rheometry measurements at shearing rates reaching 104 rad s-1.Jetting behaviour of weakly elastic dilute linear polystyrene solutions, for molecular weights of 110-488 kDa, recorded using high speed video was compared with recent results from numerical modelling and capillary thinning studies of the same solutions.The jetting images show behaviour ranging from near-Newtonian to “beads-on-a-string”. The inkjet printing behaviour does not correlate simply with the measured extensional relaxation times or Zimm times, but may be consistent with non-linear extensibility L and the production of fully extended polymer molecules in the thinning jet ligament.Fluid test methods allowing a more complete characterisation of NLVE parameters are needed to assess inkjet printing feasibility prior to directly jetting complex fluids. At the present time, directly jetting such fluids may prove to be the only alternative.

Demonstration of inkjet-printed silver nanoparticle microstrip lines on alumina for RF power modules

The paper shows the application of direct inkjet printing on alumina for fast-prototyping of high frequency circuits, adopting inks based on polymer–silver nanocomposite. Modeling, design, fabrication and experimental characterization of different microwave testing structures is presented and discussed. The integration of soldered surface mount devices and ground connections through wrap-around is successfully exploited. A 4W power amplifier operating in the 0.7–1GHz band (35% fractional bandwidth), is designed, fabricated and characterized, demonstrating the feasibility of the adopted approach.

Jetting of Complex Fluids

Recent results from a number of UK academic inkjet research studies advance the understanding of complex fluid jetting behavior and may be of interest to the wider digital fabrication community for the enhancement of inkjet printing applications.

Behavior of printable formulations of loperamide and caffeine on different substrates—Effect of print density in inkjet printing

The primary goal of the current work was to study the applicability of precision inkjet printing in fabrication of personalized doses of active pharmaceutical ingredients (APIs). Loperamide hydrochloride (LOP) and caffeine (CAF) were used as model compounds. Different doses of the drugs in a single dosage unit were produced, using a drop-on-demand inkjet printer by varying printing parameters such as the distance between jetted droplets (drop spacing) and the physical dimensions of the printed dosage forms. The behavior of the formulated printable inks for both APIs was investigated on the model substrates, using different analytical tools. The obtained results showed that printed LOP did not recrystallize on any substrates studied, whereas at least partial recrystallization of printed CAF was observed on all carrier surfaces. Flexible doses of both APIs were easily obtained by adjusting the drop spacing of the depositing inks, and the results were relevant with regards to the theoretical content. Adapting the dose by varying physical dimensions of single dosage units was less successful than the approach in which drop spacing was altered. In conclusion, controlled printing technology, by means of adjusting the distance between jetted droplets, offers a means to fabricate dosage forms with individualized doses.

Inkjet Printing of Back Electrodes for Inverted Polymer Solar Cells

AbstractEvaporation is the most commonly used deposition method in the processing of back electrodes in polymer solar cells used in scientific studies. However, vacuum‐based methods such as evaporation are uneconomical in the upscaling of polymer solar cells as they are throughput limiting steps in an otherwise fast roll‐to‐roll production line. In this paper, the applicability of inkjet printing in the ambient processing of back electrodes in inverted polymer solar cells with the structure ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag is investigated. Furthermore, the limitation of screen printing, the commonly employed method in the ambient processing of back electrode, is demonstrated and discussed. Both inkjet printing and screen printing of back electrodes are studied for their impact on the photovoltaic properties of the polymer solar cells measured under 1000 Wm−2 AM1.5. Each ambient processing technique is compared with evaporation in the processing of back electrode. Laser beam induced current (LBIC) imaging is used to investigate the impact of the processing techniques on the current collection in the devices. We report that inkjet printing of back electrode delivers devices having photovoltaic performance comparable to devices with evaporated back electrodes. We further confirm that inkjet printing represent an efficient alternative to screen printing.

Inkjet printed (bio)chemical sensing devices

Inkjet printing has evolved from an office printing application to become an important tool in industrial mass fabrication. In parallel, this technology is increasingly used in research laboratories around the world for the fabrication of entire (bio)chemical sensing devices or single functional elements of such devices. Regularly stated characteristics of inkjet printing making it attractive to replace an alternative material deposition method are low cost, simplicity, high resolution, speed, reproducibility, flexibility, non-contact, and low amount of waste generated. With this review, we give an overview over areas of (bio)chemical sensing device development profiting from inkjet printing applications. A variety of printable functional sensor elements are introduced by examples, and the advantages and challenges of the inkjet method are pointed out. It is demonstrated that inkjet printing is already a routine tool for the fabrication of some (bio)chemical sensing devices, but also that novel applications are being continuously developed. Finally, some inherent limitations of the method and challenges for the further exploitation of this technology are pointed out.

Development of Printing Method to Produce High-glossy Images with UV Inkjet Printer

While UV-curable inkjet printers have come into wide use, these printing systems have a few problems to be solved. We took notice that the printed images showed relatively low gloss. The decrease in gloss is known to be caused by the fact that UV-curable ink changes into solid before leveling off under irradiation of UV light. We have been trying to develop the new application of UV-curable inkjet printing to obtain high glossy images on the surface of various articles. We had already presented a prototype as one of such trials at ICJ2012, the annual conference of the Imaging Society of Japan in 2012. The process was called DVT which was the decompression transfer printing process with a UV-curable inkjet printer and a vacuum chamber. The DVT had some problems such as low image quality and troublesome process with manual operation. The first improved process which was called DVT-I was proposed at ICJ2013 held in Tokyo last June. However there still remained a few problems, so that we have continued our study and then developed an automated machine in this study. High image gloss has been obtained by excluding air bubbles during the decompression process. Thus we have been able to create products with high quality and glossy images on the surface of various articles.

Imaging Models for Robust Single-pass Printing using SAMBA™ Piezo Drop-on-Demand Silicon MEMS (Si-MEMS) Inkjet Printheads

SAMBA™ inkjet printheads offer a high nozzle packing density of 1200 nozzles per inch, flexibility to print with multiple drop sizes, and wide ink latitude making them attractive candidates for a variety of inkjet printing applications. In this paper, we offer insight into how these features can be utilized to enable imaging models that provide high image resolution and print speed as well as increased robustness to missing jets, a key element required in single pass printing. We show that SAMBA printheads can be designed to operate in multiple imaging modes and we use simulation and experimental data to analyze their performance. We evaluate multiple imaging models enabled by SAMBA 1200 printheads and compare them for their image quality capability, image artifacts caused by transient jets, and productivity potential for single pass printing. We show that Samba 1200 imaging models combined with over-addressing and grayscale printing offer superior image quality and improved robustness to streaks without compromising on productivity.

Inkjet Printing Technology for OPV Applications

Large-scale production of organic photovoltaics (OPVs) at low cost is, still, a future concept thought to promote the market share of solar energy. Working towards the roll-to-roll production of OPVs, different compatible deposition techniques are investigated. Inkjet printing is a promising candidate, as it allows the contact-free deposition of patterned functional materials with high flexibility. In this article, we further extend the application of inkjet printing for roll-to-roll production of OPVs. Inkjet-printed high-conducting PEDOT:PSS is compatible with indium tin oxide-free devices, by combination with an Ag grid to form the anode. A P3HT/PCBM layer is inkjet printed on top using non-chlorinated halogen-free solvents only, and large-area homogeneous layers with surface areas up to 3 cm by 3 cm were obtained. The device thus manufactured showed performance comparable to a reference device with spin-coated layers for which chlorobenzene was used as solvent for the photoactive layer. This is an essential step forward in the knowledge on materials and process conditions using inkjet printing for OPVs and working towards the full roll-to-roll production of OPVs without loss of performance.

Application of Inkjet Printing to Fabricate Controllable Pt Catalyst Patterns for Low Temperature Catalytic Combustion

Different platinum catalysts patterns such as dots array and films were successfully fabricated by directly inkjet printing of catalyst precursor inks on the substrate. It offers a feasible way for platinum catalyst deposition by precise control of catalyst loading, deposition position, and morphology. The effects on drying behavior of printed catalyst droplet on the catalytic performance of low temperature methanol catalytic combustion were investigated. The results show that the conversion of methanol over printed Platinum patterns in the catalytic combustion is approximately 85% at 100°C.

Inkjet Printed Fractal-Connected Electrodes with Silver Nanoparticle Ink

The development of a simple and reliable method for nanoparticles-based ink in an aqueous solution is still a challenge for its inkjet printing application. Herein, we demonstrate the inkjet printing of fractal-aggregated silver (Ag) electrode lines on substrates. Spherical, monodisperse Ag nanoparticles have been synthesized using silver nitrate as a precursor, ethylene glycol as a reducing agent, and polyvinyl pyrrollidone as a capping agent. As-synthesized pure Ag nanoparticles were well dispersed in water-ethylene glycol mixture, which was directly used as an ink for inkjet printing. Using this ink, the Ag electrodes of fractal-connected lines were printed on Si/SiO2, glass, and polymer substrates. The fractal-connected Ag lines were attributed to the diffusion-limited aggregation of Ag nanoparticles and the effect of annealing on conductivity was also examined.

Chemical solution deposition using ink-jet printing for YBCO coated conductors

This paper reports the successful application of ink-jet printing to the deposition of both continuous coatings and multi-filamentary structures of YBCO. Stable inks have been prepared using both the established TFA-MOD route and novel fluorine-free precursors with appropriate rheological properties for ink-jet printing. Continuous and well textured coatings with lengths exceeding 100 m and a thickness of 0.5 µm have been deposited by electromagnetic ink-jet printing from TFA precursors on LZO-buffered Ni–W substrates and samples have achieved a Jc around 1.5 MA cm−2 (self-field, 77 K). On single crystal substrates, continuous coatings and multi-filamentary structures have been deposited using piezoelectric ink-jet printing both from TFA- and water-based precursors, achieving Jc values up to 3 MA cm−2.

Inkjet Printing of Sol–Gel Synthesized Hydrated Tungsten Oxide Nanoparticles for Flexible Electrochromic Devices

Tungsten oxide nanoparticles were synthesized via a sol-gel route using metallic tungsten as precursor, and were printed on a flexible electrode using inkjet printing in order to build solid-state electrochromic cells. Several spectroscopic techniques were used to characterize and compare tungsten oxide particles obtained from different origins. FTIR, Raman and X-ray diffraction spectroscopic measurements showed that the sol-gel synthesis described here produces nanoparticles mainly in an amorphous state with hexagonal crystalline domains and allowed the analysis of the hydration extent of those nanoparticles. The size was measured combining dynamic light scattering, sedimentation, and microscopic techniques (AFM), showing a consistent size of about 200 nm. The tungsten oxide nanoparticles were used to produce an ink formulation for application in inkjet printing. Solid-state electrochromic devices were assembled at room temperature, without sintering the tungsten oxide printed films, showing excellent contrast between on/off states. Electrochemical characterization of those films is described using cyclic voltammetry. The devices were then tested through spectroelectrochemistry by Visible/NIR absorption spectroscopy (400-2200 nm range), showing a dual spectroscopic response depending on the applied voltage. This phenomenon is attributed to the presence of two different crystalline states in accordance with results obtained from the spectroscopic characterization of the nanoparticles. The electrochromic cells had a good cycling stability showing high reversibility and a cyclability up to more than 50,000 cycles with a degradation of 25%.

Synthesis of ZnO Nanoparticles and Their Ink-Jetting Behavior

Zinc oxide (ZnO) nanoparticles were synthesized by ultrasonically-assisted solution process without using any surfactants. The as-synthesized spherical ZnO nanoparticles with diameter of 20 +/- 5 nm possessed crystalline nature with wurtzite hexagonal phase and showed a blue-shifted near band-edge ultra-violet absorption at -340 nm due to quantum confinement effect of ZnO nanoparticles. The as-synthesized ZnO nanoparticles were further formulated as an ink for ink-jet printing application. Jetting and writing of various line patterns on Si and ITO substrates were demonstrated using the as-formulated ZnO ink. UV-treated substrates showed an improvement in the fixation of ink on substrate due to decreased contact angle with controlled surface wettability.