Ink System Research Articles

Comparing low-temperature thermal and plasma sintering processes of a tailored silver particle-free ink

Silver particle-free inks are under rapid development due to their unique properties. Currently, most of the developed silver particle-free inks contain multiple components. In addition to the necessary solvents and silver precursors, these inks also contain complexing agents, reducing agents, and various additives. While such complex compositions assure good stability and printability of the inks, they hamper the sintering process as excess time and energy are often required to remove residues from various compositions to ensure high conductivities of the printed structures. Thus, a simple ink system is expected. On the other hand, plasma sintering shows its sintering potential in treating silver particle-free inks, but is only employed for the sintering of silver nitrate or silver acetate-based inks. Consequently, developing new particle-free ink systems with simple compositions and exploring the potential of plasma sintering is very meaningful. In this work, a clear and transparent silver particle-free ink was formulated, which can be treated both by low-pressure argon plasma sintering and low-temperature thermal sintering (120–160 °C). The roles of 2-amino-2-methyl-1-propanol (AMP) in the ink formulation were investigated in detail, which not only acts as the solvent but also as the complexing agent for silver oxalate to lower the sintering temperature of the ink. The electrical performance of the formulated ink was examined for both sintering processes for different conditions. The thermal sintering resulted in a resistivity value of 24.3 μΩ·cm on glass substrates after treatment at 160 °C for 60 min, while the plasma sintering yielded a resistivity value of 29 μΩ·cm at 500 W for 30 min. Compared to thermal sintering, plasma sintering achieved a similar electrical performance, but with a more nonuniform film structure. The power, sintering time, and the pressure of argon are key factors responsible for the conductivity of the produced films. Nevertheless, both resistivity values do meet the minimal electrical requirements of most electronic applications.

3D Coaxial Printing Tough and Elastic Hydrogels for Tissue Engineering Using a Catechol Functionalized Ink System.

3D printing is now popular in tissue engineering as it provides a facile route to the fabrication of scaffolds with/without living cells with a predesigned geometry. The properties of the ink constituents are critical for printing structures to meet both mechanical and biological requirements. Despite recent advances in ink development, it remains a challenge to print biopolymer based tough and elastic hydrogels. These hydrogels are in great demand as they can mimic the biomechanics of soft tissues such as skin, muscle, and cartilage. In this study, a catechol functionalized ink system is developed for 3D coaxial printing tough and elastic hydrogels. The ink is based on biopolymers including catechol modified hyaluronic acid (HACA) and alginate. A novel crosslinking strategy is proposed, involving simple ionic crosslinking, catechol mediated crosslinking, and Michael addition that are all induced under mild conditions. The HACA and alginate form a double network with high fracture toughness and elasticity, while proteins such as gelatin can be integrated with the HACA/alginate hydrogel during printing to improve cell interactions. The printed constructs demonstrate high cytocompatibility and support the differentiation of myoblasts into aligned myotubes. The catechol functionalized ink can be further modified to target various applications in soft tissue engineering.

Ink Engineering of Inkjet Printing Perovskite.

Inkjet printing method is one of the most effective ways for fabricating large-area perovskite solar cells (PSCs). However, because ink crystallizes rapidly during printing, the printed perovskite film is discontinuous with increasing defects. It severely restricts the application of the inkjet printing technology to the fabrication of perovskite photovoltaic devices. Here, we designed a new mixed-cation perovskite ink system that can controllably retard the crystallization rate of perovskite. In this new ink system, the printing solvent is composed of n-methyl pyrrolidone (NMP) and dimethyl formamide (DMF), and PbX2 is replaced by PbX2-DMSO (X = Br, I) complex as a printing precursor to create a high-quality perovskite layer. Accordingly, the printed Cs0.05MA0.14FA0.81PbI2.55Br0.45 perovskite film exhibited high homogeneity with a large grain size (over 500 nm). Besides, the printed perovskite film possessed lower defects with improved carrier lifetime compared to the control sample. Combining these advantages, the printed PSC delivers decent power conversion efficiencies (PCEs) of 19.6% (0.04 cm2) and 17.9% (1.01 cm2). The large-area device can still retain its original efficiency of 89% when stored in air with humidity less than 20% for 1000 h.

The use of natural (Pinus pinaster) resin in the production of printing ink and the printability effect

AbstractAlkyd resins are generally used in the production of printing inks. All industries look for alternative raw materials in the production of ink with the growing inclination toward using natural products. Resins forming the vehicle of the ink to be obtained from natural resources will provide benefits for the environment, nature, and living creatures. The aim of the study was to promote the use of natural resin in the ink system. Natural Pinus pinaster resin was added into vegetable and mineral oil‐based solvents in pure form with alkyd resin in different amounts and ink varnishes of different combinations were prepared. Then, printing inks were produced from these varnishes in pure and hybrid form. Following the assessment of the rheological properties of the inks prepared, printing tests were conducted to assess the printing quality parameters. Ideal mixing ratios of the natural resins in the ink were determined for printability. The environmental importance and advantages of the use of natural resins were discussed. Recommendations were given in line with the results to encourage widespread use of natural resins in near future.

Functional Metal Oxide Ink Systems for Drop-on-Demand Printed Thin-Film Transistors.

Drop-on-demand printing is a noncontact direct patterning and rapid manufacturing printing technology which shows considerable potential in future display manufacturing. Metal oxides are an important kind of functional material in thin-film transistors, which are the core component of active matrix display technology, and thus printing a high-quality metal oxide functional layer is of great importance. In this feature article, we focused on the current progress in one of the foundations of drop-on-demand printing technology-the ink system. We explained the basic principles of a metal oxide ink system for printed electronics and summarized the applications of several kinds of ink systems in thin film transistor printing. Meanwhile, we also summed up problems that printed thin film transistors are facing as well as the corresponding solutions from the aspect of ink systems.

Invisible Inks for Secrecy and Anticounterfeiting: From Single to Double-encryption by Hydrochromic Molecules.

Secret information recorded by traditional single-encrypted invisible inks is easily cracked because the inks can switch only between "NONE" and "TRUTH". Developing double-encrypted systems makes the information reversibly switchable between "FALSE" and "TRUTH", which is helpful to ensure the safety of the secret information during transport. Here, we prepared heat-developed invisible inks by hydrochromic molecules donor-acceptor Stenhouse adducts (DASAs) and oxazolidines (OXs) and promoted the invisible inks from single to double encryption. DASAs coordinate with water molecules and form stable colorless cyclic DASA·xH2O molecules, which lose coordinated water molecules after heating and switch to colored linear DASAs. In contrast, OXs are colored with water and are colorless after heating. Single-encrypted secrecy was realized by DASA invisible inks. The information is invisible under the encrypted state and becomes bright purple after heating. Vapor treating re-encrypted the information in ∼5 min. Furthermore, the single-encryption was promoted to double-encryption by a DASA/OX invisible inks system. Heating and vapor treating switch the information between the "FALSE" and "TRUTH" reversibly. The DASA/OX invisible ink system is applied for secrecy of texts, graphic images, and quick response (QR) codes.

Effect of microwave-salt synergetic pre-treatment on the 3D printing performance of SPI-strawberry ink system

This study investigated the effect of microwave pre-treatment on the 3D printing performance and self-supporting behavior of soybean protein isolate (SPI)-strawberry ink system. The results indicated that salt and microwave treatment greatly improved the printing accuracy and self-supporting performance of the ink system. Salted sample treated with 70 W microwave obtained the best shape accuracy, the smallest transverse relaxation time and the highest hardness (676.33 g), gumminess (216.73 g), springiness (0.28 g) and cohesiveness (0.22 g). Low power microwave treated samples illustrated regular changes in terms of e-nose and chroma. As the microwave power increased, the L*, a*, b* values dropped, the E-nose response rose first and then decreased. The low power microwave enables ink printability at low power. And it could save energy and increase the acceptability of the final product. Moreover, the addition of salt promoted the formability and stability of 3D printed products. Based on the results, we conclude that the low power microwave-salt synergy pre-treatment has a positive effect on the printing performance and self-supporting behavior of the SPI-strawberry system.

Polymerizable Ceramic Ink System for Thin Inkjet-Printed Dielectric Layers.

An innovative ceramic ink system for thin inkjet-printed dielectric layers is presented, with which it is possible to avoid undesired drying effects. This system contains surface-modified Ba0.6Sr0.4TiO3 (BST) particles, a cross-linking agent, and a thermal radical initiator. The polymerization starts immediately after the ink drop contacts the heated substrate and therefore leads to very homogeneous topographies. Since an organic/inorganic composite ink is used, no sintering is needed after printing and thus printing on flexible substrates is possible. A comparison of the printing and drying behavior between modified and nonmodified BST with the described ink system is performed. The successful surface modification is confirmed via X-ray photoelectron spectroscopy (XPS). Topographies of different printed structures are compared by white light interferometry, the occurring polymerization is confirmed by measurements with an oscillatory rheometer, layer thicknesses are determined by scanning electron microscopy (SEM) images, and the capacitance of a printed capacitor is measured via impedance spectroscopy. It is successfully shown that the developed ink system enables the production of thin ceramic layers (<1 μm) with very homogeneous topographies since undesired drying effects can be avoided. The printed dielectric layers on flexible substrates have a high ceramic content and a high permittivity of 40.

Conversión digital de texto entre sistemas Braille y Letra en tinta

Writing is a communication way available to preserve information, ideas and knowledge, to be transmitted between different social groups and through the step of time of a generation towards its successors. To use the system of Letter in ink, it is required that the person can use the sight to recognize the lines and strokes that form the letters and can obtain knowledge; for blind people, they need to use another sense, in this case touch, to carry out the reading of information through the Braille system. Nowadays, there is a large amount of information in digital format, managed by informatics systems, where sight in needed to read that information. The development of this conversion system will allow blind people to be integrated into the world of digital information, so that they can access text files, represent them in Braille system and have the ability to read them without any problem; in addition, it will allow these people to express their own ideas, emotions and knowledge by writing them in the system they already know end be converted to the Letter in Ink system so that later, it can be placed on the Internet and used by anyone worldwide

Polymer-Doped Ink System for Threshold Voltage Modulation in Printed Metal Oxide Thin Film Transistors.

A polymer-doped ink system was applied to a printed InO x thin film transistor (TFT), and enhancement mode devices were obtained with an appropriate polymer doping amount. As the polymer doping concentration (PDC) increases, the threshold voltage of thin film transistor shifts positively, while the mobility and subthreshold slope show only an insignificant degradation. The microanalysis shows that the polymer doping can generate traps and defects in the oxide lattice, thus shifting the threshold voltage positively and degrading the mobility and subthreshold slope. Meanwhile, the doping can also facilitate the formation of an oxide lattice in the local region, which counterbalances the effect of doping on the mobility and subthreshold slope. The InO x, the TFT shows good electrical performance at an optimal PDC of 0.3 wt %, with a mobility of 4.2 cm2 V-1 s-1, a threshold voltage of 0.7 V, an on/off ratio of 106, and a subthreshold slope of 0.30 V/dec.

3D inkjet printing of biomaterials with strength reliability and cytocompatibility: Quantitative process strategy for Ti-6Al-4V

Among additive manufacturing (AM) techniques, laser or electron beam based processes have been widely investigated for metallic implants. Despite the potential in manufacturing of patient-specific biomedical implants, 3D inkjet powder printing (3DIJPP, a variant of AM) of biomaterials is still in its infancy, as little is known quantitatively about the transient process physics and dynamics. An equally important challenge has been the ink formulation to manufacture biomaterials with reliable mechanical properties and desired biocompatibility. We have developed, for the very first time, the theoretical foundation and experimental formulation of a unique process strategy involving the ‘on-demand’ delivery of a novel in situ polymerisable acrylic ink system to print a model biomaterial, Ti-6Al-4V. The post-ejection in-flight dynamics of ink droplets have been captured in situ by employing high speed stroboscopic shadowgraphy, to quantitatively estimate the dimensionless numbers of fluid physics for ‘printability’ assessment. Washburn model was adapted extensively to quantify the capillary ink infiltration time in porous powder bed of finite thickness. On the other hand, particle tracking mode in diffusing wave spectroscopy (DWS) was exploited to analyse the timescale for effective binding of powder particles during in situ polymerisation. The clinically relevant combination of 3D porous architecture with 98.4% interconnectivity among 10–40 μm pores together with modest combination of elastic modulus (4 GPa) and strength reliability (Weibull modulus ∼8.1) establish the potential of inkjet printed Ti-6Al-4V as cortical bone analogue. A better cell attachment, viability, cytoskeletal spreading with pronounced proliferation of murine fibroblasts and pre-osteoblasts on 3DIJPP Ti-6Al-4V, when benchmarked against the metallurgically processed (commercial) or selective laser melted (SLM) Ti-6Al-4V, has been demonstrated, in vitro. The enhanced cellular activities on the 3DIJPP Ti-6Al-4V was explained in terms of an interplay among the elastic stiffness, surface roughness and wettability against the same benchmarking. It is conceived that the quantitative understanding of the integrated process physics and dynamics to print Ti-6Al-4V with reliable mechanical properties together with better cytocompatibility can lead to a paradigm shift in adapting the scalable 3DIJPP for manufacturing of metallic biomaterials.

A Simple, Low Cost Ink System for Drop-on-Demand Printing High Performance Metal Oxide Dielectric Film at Low Temperature

We have successfully developed an ink system containing inexpensive raw materials through a simple process and have printed ZrO x dielectric film at a relatively low annealing temperature of 250 °C. The ZrO x dielectric film afforded a leakage current density of 5.4 × 10-6 A/cm2 at 1 MV/cm and a dielectric constant of 10 and shows a promising future for flexible electronics. The ink system shows a temperature-induced gelation behavior, and a gel network is formed when the temperature rises. A high concentration of oxide precursors is obtained near the network area through the absorption function of polymer groups, and thus oxide structure can be formed at a relatively low temperature due to the shorter diffusion path of precursor polymerization. The microstructure of the printed ZrO x film was investigated by high resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS), and the effect of annealing temperature on film structure was studied.

Nickel Based RTD Fabricated via Additive Screen Printing Process for Flexible Electronics

A novel nickel (Ni)-based resistance temperature detector (RTD) was successfully developed for temperature monitoring applications. The RTD was fabricated by depositing Ni ink on a flexible polyimide substrate using the screen printing process. Thermogravimetric analysis was performed to study the thermal behavior of the Ni ink, and it was observed that the Ni ink can withstand up to 200 °C before the decomposition of the binder in the ink system. Scanning electron microscopy and white light interferometry were used to analyze the surface morphology of the printed Ni. X-ray diffractometry was used to obtain structural information, phase, and crystallite size of the deposited Ni nanoparticles. Energy dispersive X-ray spectroscopy was used to obtain semi-quantitative information of the elements present in the fabricated RTD. The capability of the RTD to detect temperatures varying from -60 °C to 180 °C, in steps of 20 °C, was investigated at a constant relative humidity of 20%RH. The results of the RTD demonstrated a linear response with resistive changes as high as 113% at 180 °C when compared with its base resistance at -60 °C. An average TCR of 0.44%/°C was calculated for the printed RTD with a response time of <;10 s. The obtained results demonstrated the feasibility of employing Ni on flexible substrates for the development of flexible temperature sensors.

A Modularized and Switchable Component for Flexible Passive Device: Terahertz Photonic Crystals with Fine‐Tuning

AbstractIn this work, tunable terahertz photonic crystals (PCs) used as modularized and switchable components in flexible passive device are designed and prepared. Flexible woodpile structures created by the direct‐writing technology with a composite ink system composed of barium strontium titanate nanoparticles and polydimethylsiloxane are immersed in 5CB liquid crystals (LCs), where the orientation of LC molecule is modulated by the external magnetic field. Each of these can work in terahertz wavelength with specific position and depth of the dips in the transmittance spectra due to different geometries as well as having the ability of fine‐tuning. Experiments show that the photonic gaps of these PCs can cover from 0.2 to 0.3 THz, as well as about 7.5% fine tunability of photonic gap appearing with the orientation change of the magnetic field. More interestingly, the dips of photonic gaps keep the same position but become deeper with the increase of layer, an ability to realize another dimensional switchover. This work demonstrates that efficient terahertz PCs with different geometry parameters could be dynamically tuned by the orientation of magnetic field and it can open a universal approach to shrinking the size of device and rapid manufacturing in a large throughput.

Control of the Surface Morphology of Ceramic/Polymer Composite Inks for Inkjet Printing

The use of organic/inorganic composite inks in the Drop on Demand inkjet printing technology is a promising as well as demanding approach for the fabrication of composite thick films. Therefore, a versatile ceramic/polymer composite ink system for inkjet printing is developed in this study, containing Ba0.6Sr0.4TiO3 (BST) and poly(methyl methacrylate) (PMMA). When developing such inks suitable for a one‐step fabrication, the major challenge is to fulfill the requirements of the inkjet printing technology and to obtain homogeneous surface morphologies after drying. Thus, possible influencing factors like the solvent composition, the solids content, and the ratio of ceramic to polymer are investigated to obtain a detailed knowledge for the general ink development. The fluid mechanical properties, viscosity, density, and surface tension are characterized. The main focus of this study lies on the drying behavior of the different inks, with the interactions of the ceramic particles, and the dissolved polymer molecules being highlighted. Furthermore, the drying behavior depending on the ink composition is shown. This study provides new insights into the possibility of using composite inks for the inkjet printing process and the fabrication of printed composite thick films in a single process step.

Morphology Modulation of Direct Inkjet Printing by Incorporating Polymers and Surfactants into a Sol–Gel Ink System

Many methods have been reported to prevent the nonuniformity of inkjet printing structures. Most of them depend on the balance of the capillary flow in the printing pattern during the evaporation of the solvent. However, as the relation of evaporation and capillary flow can obviously vary among different ink systems, it is difficult for a method to fit most of the situations. Therefore, it would be a promising way to eliminate any capillary flow before solvent evaporation so that morphology of the printing structure will not be affected by the evaporation behavior of the ink system. In this paper, a novel method of direct inkjet printing of a uniform metal oxide structure is reported. We introduce a polymer polyacrylamide and a surfactant FSO into a sol-gel ink system, and the new ink system can gel from the printing pattern edge to center as temperature increases because of the cross-linking of the polymer chains. By that means, transport of solute molecules and solvent molecules is limited. Meanwhile, the surfactant can ensure that the solute in the central liquid phase deposits uniformly by enhancing the Marangoni flow during the gelation process. The ZrO2 film with uniform morphology was fabricated by drying and annealing the gelating film and afforded a leakage current density of 7.48 × 10-7 A cm-2 at 1 MV and a breakdown field of 1.9 MV cm-1 at an annealing temperature of 250 °C.

Experimental realization of Mie-resonance terahertz absorber by self-assembly method.

Mie-resonance terahertz absorbers by self-assembly method are designed and demonstrated in experiments and simulations. A monolayer of zirconium dioxide (ZrO2) microspheres fixed on a copper film with designed grids that were manufactured by direct writing with a composite ink system composed of polydimethylsiloxane (PDMS). More importantly, different spacing and array configurations were created economically and efficiently, showing visual performance. Magnetic resonance leads to near-unity absorption at about 0.4 THz in the samples. This work demonstrates efficient terahertz absorbers and highlights a novel direct writing fabrication method that can be extended to produce other optical devices for applications.

Characterization and optimization of an inkjet-printed smart textile UV-sensor cured with UV-LED light

For the development of niche products like smart textiles and other functional high-end products, resource-saving production processes are needed. Niche products only require small batches, which makes their production with traditional textile production techniques time-consuming and costly. To achieve a profitable production, as well as to further foster innovation, flexible and integrated production techniques are a requirement. Both digital inkjet printing and UV-light curing contribute to a flexible, resource-efficient, energy-saving and therewith economic production of smart textiles. In this article, a smart textile UV-sensor is printed using a piezoelectric drop-on-demand printhead and cured with a UV-LED lamp. The UVcurable ink system is based on free radical polymerization and the integrated UVsensing material is a photochromic dye, Reversacol Ruby Red. The combination of two photoactive compounds, for which UV-light is both the curer and the activator, challenges two processes: polymer crosslinking of the resin and color performance of the photochromic dye.Differential scanning calorimetry (DSC) is used to characterize the curing efficiency of the prints. Color measurements are made to determine the influence of degree of polymer crosslinking on the developed color intensities, as well as coloration and decoloration rates of the photochromic prints. Optimized functionality of the textile UV-sensor is found using different belt speeds and lamp intensities during the curing process.

Direct Writing of Flexible Barium Titanate/Polydimethylsiloxane 3D Photonic Crystals with Mechanically Tunable Terahertz Properties

Mechanically flexible 3D terahertz photonic crystals (3D‐TPCs) are created by the direct‐writing technology with a composite ink system composed of polydimethylsiloxane (PDMS) and barium titanate (BaTiO3) nanoparticles. The direct‐writing technology allows an easy creation of complex 3D structures with designed geometry, while the refractive indices of the composite ink can be modulated by varying the content of BaTiO3 nanoparticles. Thus, 3D‐TPCs with different terahertz properties are obtained by the direct‐writing technology. More interestingly, these 3D‐TPCs demonstrate a unique tunable terahertz property under external force field due to their mechanical flexibility from the PDMS matrix of the composite ink. Thus, their terahertz property is responsive to external force fields reversibly, which can find novel applications in terahertz technology and other related technological applications.

高精彩スクリーンインキシステムの紹介

高精彩スクリーンインキシステムはスクリーン印刷でありながら，100 μmの細線を116 μm以内のダレ幅で印刷できる高精度かつ印刷安定性に優れたシステムである。