Curable Ink Research Articles

Design and Fabrication of an Experimental Microheater Array Powder Sintering Printer

Microheater array powder sintering (MAPS) is a novel additive manufacturing process that uses an array of microheaters to selectively sinter powder particles. MAPS shows great promise as a new method of printing flexible electronics by enabling digital curing of conductive inks on a variety of substrates. For MAPS to work effectively, a microscale air gap needs to be maintained between the heater array and the conductive ink. In this article, we present an experimental MAPS printer with air gap control for printing conductive circuits. First, we discuss design aspects necessary to implement MAPS. An analysis is performed to validate that the design can maintain the desired air gap between the microheaters and the sintering layer, which consists of a silver nanoparticle ink. The printer is tested by printing conductive lines on a flexible plastic substrate with silver nanoparticle ink. Results show MAPS performs on par with or better than the existing fabrication methods for printed electronics in terms of both the print quality (conductivity of the printed line) and print speed, which shows MAPS’ great promise as a competitive new method for digital production of printed electronics.

2.5-Dimensional Inkjet Fabrication Using UV Curable Ink

In recent years, 2.5-dimentional (2.5D) fabrication for reproduction of oil paintings and decoration becomes known. UV curable ink is used for fabrication of 2.5D images because of its good stackability. However, the surface of the structures fabricated by UV curable inkjet printer is granular. Shape accuracy and surface smoothness had a trade-off relation. Therefore, we developed UV curable ink which can control wet-spreadability of the cured ink surface. Then we can switch between both stacking processes for accuracy and smoothness. The cured states and the wet-spreadability are controlled by UV irradiation energy for curing. This technology makes it possible to express the precise profile with shape accuracy and surface smoothness.

Quantitative criteria to benchmark new and existing bio-inks for cell compatibility

Recent advancements in 3D bioprinting have led to the fabrication of more complex, more precise, and larger printed tissue constructs. As the field continues to advance, it is critical to develop quantitative benchmarks to compare different bio-inks for key cell–biomaterial interactions, including (1) cell sedimentation within the ink cartridge, (2) cell viability during extrusion, and (3) cell viability after ink curing. Here we develop three simple protocols for quantitative analysis of bio-ink performance. These methods are used to benchmark the performance of two commonly used bio-inks, poly(ethylene glycol) diacrylate (PEGDA) and gelatin methacrylate (GelMA), against three formulations of a novel bio-ink, Recombinant-protein Alginate Platform for Injectable Dual-crosslinked ink (RAPID ink). RAPID inks undergo peptide-self-assembly to form weak, shear-thinning gels in the ink cartridge and undergo electrostatic crosslinking with divalent cations during curing. In the one hour cell sedimentation assay, GelMA, the RAPID inks, and PEGDA with xanthan gum prevented appreciable cell sedimentation, while PEGDA alone or PEGDA with alginate experienced significant cell settling. To quantify cell viability during printing, 3T3 fibroblasts were printed at a constant flow rate of 75 μl min−1 and immediately tested for cell membrane integrity. Less than 10% of cells were damaged using the PEGDA and GelMA bio-inks, while less than 4% of cells were damaged using the RAPID inks. Finally, to evaluate cell viability after curing, cells were exposed to ink-specific curing conditions for five minutes and tested for membrane integrity. After exposure to light with photoinitiator at ambient conditions, over 50% of cells near the edges of printed PEGDA and GelMA droplets were damaged. In contrast, fewer than 20% of cells found near the edges of RAPID inks were damaged after a 5 min exposure to curing in a 10 mM CaCl2 solution. As new bio-inks continue to be developed, these protocols offer a convenient means to quantitatively benchmark their performance against existing inks.

An investigation into the depth and time dependent behavior of UV cured 3D ink jet printed objects

Abstract

Self-Reducing Copper Precursor Inks and Photonic Additive Yield Conductive Patterns under Intense Pulsed Light

Printing conducting copper interconnections on plastic substrates is of growing interest in the field of printed electronics. Photonic curing of copper inks with intense pulsed light (IPL) is a promising process as it is very fast and thus can be incorporated in roll-to-roll production. We report on using IPL for obtaining conductive patterns from inks composed of submicron particles of copper formate, a copper precursor that has a self-reduction property. Decomposition of copper formate can be performed by IPL and is affected both by the mode of energy application and the properties of the printed precursor layer. The energy application mode was controlled by altering three pulse parameters: duration, intensity, and repetitions at 1 Hz. As the decomposition results from energy transfer via light absorption, carbon nanotubes (CNTs) were added to the ink to increase the absorbance. We show that there is a strict set of IPL parameters necessary to obtain conductive copper patterns. Finally, we show that by adding as little as 0.5 wt % single-wall CNTs to the ink the absorptance was enhanced by about 50% and the threshold energy required to obtain a conductive pattern decreased by ∼25%. These results have major implications for tailoring inks intended for IPL processing.

Focus on analytical equipment, sensors, and detectors

Focus on analytical equipment, sensors, and detectors

Fabrication of reactive pigment composite particles for blue-light curable inkjet printing of textiles

The Reactive Phthalocyanine Blue (RPB) was fabricated by two-step method, and then used to prepare blue light curable inks. After injection, RPB can participate in the copolymerization of oligomers and monomers under blue-LED irradiation.

Set‐off: Development of a Simulation Press and Analytical Approach to Study the Phenomenon

One type of mass transfer between package and food is through set‐off. This phenomenon is defined as the transfer of components from the external layer (printed surface) of a packaging material to the inner side (surface to come into contact with food) during storage of printed substrates in reels or stacks. The objective of this work was to build up the equipment for set‐off simulation and to assess the extent of benzophenone (BP) transfer. BP is a model photoinitiator used in standard ultraviolet curable inks (non‐low migration inks). For set‐off simulation, the storage conditions (time, temperature and pressure) and the ink film weight are provided by EuPIA Guidelines. Ethanol 50% (v/v) as simulant and contact condition of 40°C/10 days were used. Samples were printed and cured at different speeds. The migrated BP was determined by analysing the extracts using high‐performance liquid chromatography with diode‐array detector. Set‐off phenomenon extent was dependent on the curing. In general, the BP migrations increase as speed increased. Copyright © 2016 John Wiley & Sons, Ltd.

Disposable electrochemical paper-based devices fully fabricated by screen-printing technique

This work presents a novel method for the full fabrication of electrochemical paper-based cells by screen-printing technology. Firstly, a mixture of ultraviolet curable inks was used for patterning hydrophobic barriers into chromatography paper. Afterwards three-electrode systems were coupled for electrochemical detection by printing successively carbon and silver/silver chloride inks over the hydrophilic areas. The resulting electrochemical cells were characterized by cyclic voltammetry in different redox systems and used for amperometric detection of ferricyanide.

Application of Vinylcarbonates as Low-Toxic Monomers in Digital Inkjet Inks

During the last decade, the research on digital inks has seen a strong increase with the focus to bring this technique into new markets. In this regard, many experts predict huge market potential for ink-jet inks for printing on food packaging, textiles and garments. However, commercially available inks contain noxious substances or solvents, which limit or completely prevent their application in these specific fields. Especially, UV- curable inks that offer unique advantages such as instantaneous drying, the absence of VOCs, good adhesion on substrates and excellent film forming properties consist of precarious monomers mainly based on (meth)acrylates.[1]One remarkable drawback of (meth)acrylates is their comparably high irritancy and even cytotoxicity in their uncured state.[2] This disadvantageous behaviour can be mainly attributed to the reactivity of the acrylate double bond towards Michael Addition reactions with amino- or thiol- groups of proteins or DNA. This fact together with the incomplete curing behavior of (meth)acrylates prevents their usability for substrates which are in contact with food or the human body.Recently, several radical curable functionalities such as vinylcarbonates, vinylesters and vinylcarbamates have been introduced as interesting alternatives to (meth)acrylate based resins providing a significant lower cytotoxicity.[3,4]The focus of this work was to evaluate vinylcarbonates as reactive building blocks in UV- curable digital inks in order to overcome the health issues which are related to (meth)arylates. For that purpose, a multitude of vinylcarbonate monomers was synthesized and studied regarding their reactivity, conversion and printability.Although, the viscosity and surface tension of these monomers are appropriate for ink-jet printing, the curing speed is far too low for high speed printing processes. One possibility to circumvent this limitation is to use thiol-vinylcarbonate formulations offering reactivities and double bond conversions (DBC) similar to those of acrylates. For that purpose, a multifunctional thiol was synthesized providing low odour and also an appropriate low viscosity facilitating the formulation of pigmented ink-jet inks. These basic digital inks offer an excellent jetting behaviour (see Figure 1) together with good film forming properties and adhesion on PET. Ongoing experiments concentrate on the storage stability of this system to allow the implementation of these thiol-vinylcarbonate inks in industrial printing processes. <fig position="float" id="s119_f.1"> <label>Figure 1</label> <caption>Top left: images of the formed droplets 50 μs after actuation; top right: single droplet test; bottom: print on photo paper (Epson photo paper glossy)[5]</caption> <graphic mime-subtype="tif" xlink:href="Images\s119_f01.tif" xmlns:xlink="http://www.w3.org/1999/xlink"/> </fig&gt

Droplet spreading characteristics observed during 3D printing of aligned fiber-reinforced soft composites

The 3D printing of fiber-reinforced soft composites (FrSCs) is a hybrid process that combines conventional inkjet-based 3D printing with the directed deposition of electrospun polymer fiber mats. This paper investigates the spreading characteristics of droplets when deposited on fibrous substrates, under conditions relevant to 3D printing of aligned FrSCs. Both single and multi-droplet impingement studies are conducted on substrates with varying fiber number densities. High-speed imaging is used to study the characteristic time-scales and the spreading behavior of the droplets. The single droplet impingement studies on stationary substrates reveal that the presence of fibers promotes droplet spreading along the length of the fibers. Occasional surface energy variations in the fiber mats in the form of voids and fiber bundles are also seen to affect the droplet shape and the characteristic spreading times. In the case of a moving substrate, the droplets are seen to spread the most during in-line printing, i.e., when the direction of the printing velocity coincides with the direction of fiber alignment. They spread the least during orthogonal printing, i.e., when the direction of the printing velocity is perpendicular to the direction of fiber alignment. The printing of straight lines shows an interesting edge retraction phenomenon that gets accentuated the most in the case of in-line printing. The findings of the high-speed imaging studies have been confirmed by 3D printing comparable artifacts using UV curable inks. These studies indicate that for a given fiber mat and UV curable ink combination, the choice of the in-line or orthogonal printing strategy has implications for the overall printing time, fiber content, edge resolution and surface quality of the 3D printed FrSC part.

Evaluation of the migration of UV-ink photoinitiators from polyethylene food packaging by supercritical fluid chromatography combined with photodiode array detector and tandem mass spectrometry

UV-ink photoinitiators (PIs), which are used to initiate polymerization reaction for the curing of inks and lacquers, have become a kind of contaminant residues in printing plastic food packaging. The residual PIs in packaging may pose a potential threat to customers. In this work, migration behaviors of 13 PIs from a polyethylene (PE) packaging to food simulants according to regulation EU No 10/2011 were studied by supercritical fluid chromatography combined with photodiode array detector and tandem mass spectrometry (SFC-PDA-MS/MS). The method simultaneously analyzed 13 PIs within 4.5 min and was sensitively with low limits of detection of 0.02–2.16 μg/L, which could meet high throughput analysis for control the quality of food packaging. The migration results revealed that Irgacure 819, Darocure 1173 and TPO, which had low migration rates, should be preferably selected by plastic food packaging manufacture for food safety.

Low cost room temperature curable alumina ink for printed electronic applications

A low cost, room temperature curable alumina ink has been prepared by non-aqueous route. The ink is printed on flexible biaxially-oriented polyethylene terephthalate (BoPET) substrate as well as on photographic paper. The dielectric constant of the printed alumina on BoPET film is found to be 3.29 and 3.26 at 5 and 15 GHz respectively with a dielectric loss of the order of 10–3. The printed alumina layer (without substrate) has a dielectric constant of 4.54 and loss tangent 0.010 at 15 GHz. The temperature coefficient of dielectric constant for alumina ink with BoPET substrate and alumina ink with photographic paper are 60 and 66 ppm/°C respectively. The variation of dielectric constant and loss tangent with the thickness of the printed layer is also investigated. The results indicate that the alumina dielectric ink can be used as a potential candidate for future printed electronic applications.

Surface microstructuring to modify wettability for 3D printing of nano-filled inks

This paper investigates the effect of surface wettability on the cross-sectional profiles of printed nanofluid inks which can have a significant role on conductivity of printed lines that are used in the production of printed electronics. Glass substrates were coated with heptadecafluorodecyltrichlorosilane, nonafluorohexyltrimethoxysilane and methyltrimethoxysilane using a dipping method to enhance the wettability of the nanofluid silver ink. Inkjet printing techniques were also applied to develop micro-structural textures on the surface of the glass substrate and thereby modify the wettability of the substrate. The glass substrate, coated with heptadecafluorodecyltrichlorosilane was micro-structured using a UV curable ink to enhance the wettability for the silver nanoparticle ink. Using inkjet printing techniques to micro-structure the substrate allows modification of the wettability of the substrate whilst simultaneously printing on to the substrate. This enables the potential of increasing the performance of such printed lines, essentially permitting additional particulate material to be deposited thus increasing conductivity. The cross-sectional profile of the printed line was predicted numerically and analytically and compared to experimental data where agreement was observed. In addition, three analytical expressions for printed lines on the substrate were developed by writing the force balance equations in the x, y and z directions on a slice of printed line between z and z+dz.

Non Aqueous Synthesis of Titania Ink for Printed Electronics

A non-aqueous synthesis technique of room temperature curable titania ink, screen printed on flexible BoPET film for printed electronics applications is reported. The phase evolution of rutile titania powder, formulation of a fast curing titania ink, as well as the microstructure and dielectric properties of printed pattern are discussed. In terms of ease of synthesis, cost effectiveness and faster curing time, the developed ink is found to be advantageous over water based dielectric inks.

Study on the Combination Mechanism of the Water-Based UV Curable Ink and Paper

The bonding mechanism between water-based UV curable ink and active groups on paper’s fiber during curing process was studied in this paper. Low viscosity water-based UV-cured resin was synthesized by epoxy resins, epoxy diluent, acrylic acid and maleic anhydride in the presence of catalyst. The viscosity of the synthesis system and synthetic products were significantly reduced when epoxy diluent was added to replace parts of the epoxy resin. Epoxy diluent was very useful in reducing the viscosity of the product, but over-dose would have negative effects on the quality of the cured film. The water-based epoxy acrylate prepolymer was used as the substitution for the ink to investigate the binding mechanism between the active groups of prepolymer and fiber under UV irradiation. The prepolymer and photoinitiator were mixed and the mixture was diluted to an appropriate viscosity by a small amount of water, then printed on the paper by the method of analog printing and curred by UV curing machine. The printed paper was used to extract lignin by enzymatic/mild acidolysis. FT-IR was used to characterize the changes of the active groups in lignin. The results showed that the changes of active groups in lignin were founded in the existence of ultraviolet and photoinitiator, which consistent with the change of double bonds in prepolymer. The free radicals produced by photoinitiator in curing process not only promoted the double bonds to polymerize, but also accelerated the active groups of lignin binding. Experiments show that chemical bonds exist between them.

Optimization of UV LED-Curable Ink for Reverse-Offset Roll-to-Plate (RO-R2P) Printing

Reverse-offset roll-to-plate printing has become increasingly popular in the printing industry because of the ease with which the printing process can be manipulated to achieve a high-resolution pattern with line widths as narrow as 5 μm with precision and accuracy. The printing procedure involves three stages, and a roller is required to transfer ink from each stage. The substrates used throughout this experiment were chosen by measuring their contact angles (θ) and using them in accordance with the sequence: θ (Stage 1) >θ (roller) >θ (Stage 2) and θ (Stage 3). An ultraviolet (UV) light-emitting diode (LED)-curable ink was used during the printing process; however, the pristine solution of this ink was unsuitable for printing a final pattern on the substrate because of its viscosity. Diluting the solution of the UV LED-curable ink with 40% CH3OH resulted in reduced viscosity. The original solution had a viscosity of approximately 40.7 cP whereas that of the diluted solution was approximately 25 cP. The two solutions behaved as non-Newtonian, dilatant, shear-thickening fluids. The UV LED-curable ink solutions, both dilute and non-dilute, were successfully printed by use of an inkjet printer and three-dimensional printing methods.

Printability and Electrical Conductivity of UV Curable MWCNT Ink

Composites reinforced with multiwalled carbon nanotubes (MWCNT) in a photosensitive acrylic matrix were successfully synthesized and their printing, rheological, and electrical behavior was characterized. The shape of the reinforcement MWCNT particles was analyzed by transmission electron microscopy. The MWCNT were mixed in the acrylic polymer at increasing concentrations until the percolation threshold was determined at 2 wt.% with a conductivity of 4.26 × 10−4 S/cm. The large increase in viscosity with addition of MWCNT showed the need for a printing system capable of dispensing solutions of up to 613 × 103 cp. Lines were printed with a precision dispensing system mounted in computer controlled x–y–z stages, while an integrated ultraviolet light emission diode dot with a single wavelength of 385 nm cured seconds after the ink was dispensed. The wetting properties of the composite with respect to polyester, polyethylene terephthalate, polyimide, and paper films were analyzed with a goniometer. The relationship between the contact angle, pattern accuracy, and electrical conductivity was determined for each substrate.

Synthesis process control and property evaluation of a low-viscosity urethane acrylate oligomer for blue light curable ink of textile digital printing

A low-viscosity urethane acrylate oligomer was synthesized under optimized conditions using a specially selected low molecular weight polyether diol. The synthesis process and the reaction endpoint were monitored by Fourier transform infrared spectroscopy. The rheological properties of the synthesized urethane acrylate oligomer were evaluated by rheology measurements in both steady and dynamic modes, and the blue light induced photopolymerization behavior of the oligomer with camphorquinone and ethyl-4-dimethylaminobenzoate as photoinitiators was examined with photo-differential scanning calorimetry analysis. A blue light curable pigment ink based on the low-viscosity urethane acrylate oligomer was prepared, and jet printed on cotton fabrics using a simulating digital printing device, then photo-cured under blue light irradiation. The printed fabric samples showed fine patterns with soft fabric handle.

Detection of the inflammation biomarker C-reactive protein in serum samples: towards an optimal biosensor formula.

The development of an electrochemical immunosensor for the biomarker, C-reactive protein (CRP), is reported in this work. CRP has been used to assess inflammation and is also used in a multi-biomarker system as a predictive biomarker for cardiovascular disease risk. A gold-based working electrode sensor was developed, and the types of electrode printing inks and ink curing techniques were then optimized. The electrodes with the best performance parameters were then employed for the construction of an immunosensor for CRP by immobilizing anti-human CRP antibody on the working electrode surface. A sandwich enzyme-linked immunosorbent assay (ELISA) was then constructed after sample addition by using anti-human CRP antibody labelled with horseradish peroxidase (HRP). The signal was generated by the addition of a mediator/substrate system comprised of 3,3,5',5'-Tetramethylbenzidine dihydrochloride (TMB) and hydrogen peroxide (H2O2). Measurements were conducted using chronoamperometry at −200 mV against an integrated Ag/AgCl reference electrode. A CRP limit of detection (LOD) of 2.2 ng·mL−1 was achieved in spiked serum samples, and performance agreement was obtained with reference to a commercial ELISA kit. The developed CRP immunosensor was able to detect a diagnostically relevant range of the biomarker in serum without the need for signal amplification using nanoparticles, paving the way for future development on a cardiac panel electrochemical point-of-care diagnostic device.