Inkjet Technology Research Articles

Engineering and scaling-up ceramic tiles with humidity self-regulation functionality

The humidity regulation in the interior spaces of buildings by means of passive solutions that do not require energy consumption is a topic of great interest due to the current needs for comfort and energy efficiency. This paper addresses the engineering of humidity regulating ceramic tiles that incorporate a functional coating formulated from gibbsite together with other common raw materials whose moisture regulating capacity has been demonstrated previously. A multi-layer coating tile system has been proposed, consisting of the following elements: an engobe layer, the functional coating with the regulating capacity, a decoration by inkjet technology and a protective topcoat glaze.This system has been analysed with moisture adsorption–desorption tests. The moisture regulation capacity and the effect of the coating thickness on this property have been determined, allowing to optimise the functionality.Finally, an analysis of the humidity regulation has been performed on the basis of demonstrators or small-sized cubicles that simulate the conditions of final use in rooms of buildings. The results show the different behaviour of the demonstrator with functional tiles in relation to conventional tiles, with an indoor ambient humidity that remains in the comfort zone for longer periods of time.

Highly reflective engobes for ink-jet printed coloured porcelain stoneware tiles (CO-2:L05)

Ink-jet decoration is a technology suitable for designing ceramic tiles with solar reflectance (SR) properties. SR is the ratio between the solar energy reflected by a surface and the total incident energy. If incorporated into the cities' building envelope, solar reflective tiles mitigate the Urban Heat Island (UHI) phenomenon, which makes urban centres hotter than rural areas. Even if many efforts have been conducted to develop solar reflective surfaces, little research has been conducted for the development of coloured tiles suitable to be fabricated by ink-jet technology, where the inks tend to counteract the effect of the reflective engobes. To overcome such an issue, the fabrication of solar reflective ink-jet decorated tiles using a reflective engobe was investigated. The engobe was prepared using an industrial CZAS (CaO–ZrO2–Al2O3–SiO2) frit and a ZrSiO4 pigment. The engobe prepared with such frit presented a high SR value (0.918 ± 0.002) and was able to develop ink-jet printed coloured tiles (cool colors) using both white and red porcelain stoneware supports. Overall, it was found that using high engobe thicknesses, white porcelain stoneware supports, and light colour inks allows the fabrication of cool color ink-jet printed tiles. Most of those tiles present solar reflective properties higher than those reported in previous works, even for dark inks that usually tend to counteract the effect of solar reflective engobes.

Process Development for Printed Copper With Surface Mount Devices on Inkjet Metallization

Abstract Printed electronics is a fastest growing and emerging technology that have shown much potential in several industries including automotive, wearables, healthcare, and aerospace. Its applications can be found not only in flexible but also in large area electronics. The technology provides an effective and convenient method to additively deposit conductive and insulating materials on any type of substrate. Despite its status, it is not without its challenges. Inkjet technology has gained much attention due to its low cost, low-material consumption, and capability for mass manufacturing. The preferred conductive metal of choice has been mostly silver due to its excellent electrical properties and ease in sintering. However, silver comes to be expensive than its counterpart copper. Since copper is prone to oxidation, much focus has been given toward photonic sintering that involves sudden burst of pulsed light at certain energy to sinter the copper nanoparticles. With this technique, only the printed material gets sintered in a matter of seconds without having a great impact on its substrate. With all the knowledge, there is still a large gap in the process side with copper where it is important to look how the print process affects the electrical and mechanical properties of copper. With the process developed, the resistivity of printed copper was found to be five times the bulk copper. In regards to adhesion to the polyimide film, mechanical shear load to failure was found to be within 15–20 gF. To demonstrate the complete process, commercial-off-the-shelf components are also mounted on the additively printed pads. Statistically, control charting technique is implemented to understand any process variation over long duration of prints.

Direct Inkjet 3D Printing Microwires with Small Feature Size by Freezing, Sublimation, and Evaporation Induced Colloidal Nanoparticles Self‐Assembly Mechanism

AbstractThe feature size (FS) of inkjet printing is limited by nozzle size and drop spreading, which limits the realization of small optoelectronics devices and 3D microstructures. Some methods can realize small FS, but sacrifice advantages of inkjet technology. For instance, dewetting can reduce FS with all the advantages of inkjet technology kept, but is hard to print wires due to Rayleigh–Plateau instability. To solve these problems, in this paper, freezing and sublimation are introduced to direct inkjet printing wire processes. After optimizing the glycerol amount and adding tert‐butyl alcohol (TBA) in water‐based nanoparticle inks, condensed microwires of PS colloidal nanoparticles, graphene oxide (GO) nanosheets, and silver nanowires (AgNws) with small FS can be printed, respectively, by freezing, sublimation, and evaporation induced nanoparticle self‐assembly (FSE‐INS) mechanism. Using printhead with the nozzle size of 21 µm, the minimum feature size is only ≈2 µm for GO nanosheet samples. The FSE‐INS mechanism shows particle‐dimension dependent structure properties, introduces an additional particle manipulation freedom perpendicular to the substrate with sacrificial vertical solid surfaces, and exhibits great potential to realize small and novel devices and 3D structures, without sacrificing the advantages of inkjet technology.

Fabrication of flexible carbon heaters and silver interdigitated electrodes using ink-jet printing technology for electro-chemical gas sensor applications

PurposeThe purpose of this paper is to deal with an identification of a novel ink-jet printing sensor fabrication technology for fabricating flexible carbon heaters of macro and micro sizes, carbon interdigitated (IDT) electrodes and silver IDT electrodes. The technology involved in the proposed ink-jet printing method and materials used for the formulation of homemade nano-conductive inks (digital inks) are discussed in detail. The ink-jet printed flexible carbon heaters of different sizes (macro and micro) and carbon IDT electrodes and flexible silver IDT electrodes can be used as the flexible sensing layers in electrochemical gas sensors for sensitive and selective gas sensing applications. The characterization of ink-jet printed carbon heaters on Kapton substrate and its results are discussed. Similarly, the results of formulation of silver nano-conductive ink and printing of silver IDT electrodes on Kapton and its characterization are reported here for the first time.Design/methodology/approachFlexible carbon heaters of different sizes (macro and micro), carbon micro-IDT electrodes and silver IDT electrodes patterns were developed using AutoCAD 2D and printed on the Kapton (polyimide sheet) flexible substrate using the home-made nano-conductive inks with the help of EpsonT60 commercial piezo-head-based drop-on demand technology printer with standard printing options.FindingsThe proposed novel method is able to print heater patterns and IDT electrode patterns of approximately 12 µm and approximately 1 µm thickness, respectively, on flexible substrate using the home-made nano-conductive inks of carbon and silver by using a commercial low-cost printer. The home-made nano-conductive inks can be re-used for multiple prints up to six months shelf life. The resistance of the carbon heater was measured as 88 O under normal atmospheric condition. The novel flexible carbon heater was tested for its functionality and found to be satisfactory. The resistance of the silver IDT flexible electrodes was measured as 9.5 O which is better than the earlier works carried out in this paper.Research limitations/implicationsThe main challenge is associated with cleaning of printing ink ejection system in the existing commercial printers. The customization of the existing printer in the near future can minimize the printing challenges.Practical implicationsThe novel ink-jet printing technology proposed in this work is cost-effective, capable of achieving bulk production of flexible sensor elements, and consumes the least device fabrication time and high material yielding. The printing can be done with commercial piezo-head-based ink-jet printers with custom-prepared nano-conductive inks. There is a huge market potential for this paper.Originality/valueBoth the carbon heaters and silver IDT electrodes were printed on Kapton flexible substrate by using the commercial printer for the first time. The paper is promising the revolution in flexible low-cost sensor fabrication for mass production, and it is an alternate for thin film and thick sensor fabrication methods. The future of sensor fabrication technology will be the ink-jet printing method. In this paper, the research developments of flexible carbon heaters and flexible silver IDT electrodes for the time are reported. The characterization of carbon heaters and silver IDT electrodes were carried out and confirmed that the results are favourable for gas sensor applications.

Development of a P1-filling process to increase the cell performance in the copper indium gallium Selenide photovoltaics by implementation of the inkjet technology

In this paper, the suitability of integrating a digital manufacturing tool i.e. inkjet technology is exemplified to increase the electrical performance of thin-film based Copper Indium Gallium Selenide (CIGS) photovoltaic (PV) modules. Typically, the series connection within the PV module is established conventionally by three adjacent scribing lines at different deposition stages (patterning P1, P2 and P3). The total width of these three scribes is typically in the order of several 100's of microns and is electrically inactive, so these regions are lost areas for current generation (up to 5% “dead area”). To reduce the line width of the first scribe (P1) without compromising on the electrical parameters, we have concentrated on accurately filling of the interconnect P1-trenches with insulating material using inkjet technology, as initial step to realize the concept for dead area reduction by developing a P1-filling process (< 80 μm printed filling width) for laser structured/patterned trenches of ~50 μm width. With the right combination of carefully selected material interface, inkjet printhead, deposition settings, pattern digitalization & other parameters, we are able to develop an industry relevant micro-filling process. And, show an increase in the performance of PV cells, as compared to the reference modules. The results lay the foundation for direct up-scaling to industrial-size substrate areas and open up the possibility to realize all kinds of advanced interconnect schemes for the next generation thin-film CIGS PV modules. • Digital manufacturing of P1-filling for the thin-film photovoltaics in conjunction with laser process. • Approach towards reduction of dead-area in photovoltaics. • Inkjet printing of functional material within μm range channels/trench (< 80 μm). • Increase in photovoltaic performance (fill factor & module efficiency). • P1-filling process developed under ambient condition, without any inert atmosphere.

33‐3: Invited Paper: Research and Applications of Inkjet Printing for OLED Mass Production

OLEDs (organic light‐emitting diode) are one of the prevalent display technologies and their penetration in the consumer electronic market is fast growing. As a reliable and cost‐effective deposition technique for polymeric planarization layers, inkjet printing has been successfully applied to the mass production of flexible OLED displays. In this paper, we present the concept that for today's common ranges of process layer thickness, the quality and consistency of the deposited polymeric film can be agnostic to the selection of drop volumes. However, printer flexibility in terms of drop size and printhead support is critical to meeting the full range of current and future processes adopting the proven inkjet printing process. Applications utilizing the state‐of‐the‐art Kateeva inkjet printing systems are presented to demonstrate our study and for the reader to be able to assess if inkjet technology could be advantageous for a particular OLED application.

InkFiltration: Using Inkjet Printers for Acoustic Data Exfiltration from Air-Gapped Networks

Printers have become ubiquitous in modern office spaces, and their placement in these spaces been guided more by accessibility than security. Due to the proximity of printers to places with potentially high-stakes information, the possible misuse of these devices is concerning. We present a previously unexplored covert channel that effectively uses the sound generated by printers with inkjet technology to exfiltrate arbitrary sensitive data (unrelated to the apparent content of the document being printed) from an air-gapped network. We also discuss a series of defense techniques that can make these devices invulnerable to covert manipulation.The proposed covert channel works by malware installed on a computer with access to a printer, injecting certain imperceptible patterns into all documents that applications on the computer send to the printer. These patterns can control the printing process without visibly altering the original content of a document, and generate acoustic signals that a nearby acoustic recording device, such as a smartphone, can capture and decode. To prove and analyze the capabilities of this new covert channel, we carried out tests considering different types of document layouts and distances between the printer and recording device. We achieved a bit error ratio less than 5% and an average bit rate of approximately 0.5 bps across all tested printers at distances up to 4 m, which is sufficient to extract tiny bits of information.

3D-printed nails for aesthetic silicone prostheses.

The nail is a crucially important part that needs to be closely reproduced in aesthetic silicone prostheses. The traditional method of producing prosthetic nails is a laborious process often fraught with errors and rejects. In this article, additive manufacturing or 3D printing intervention was sought to make this process less time-consuming and more exacting. With a focus on finger prosthesis, the process involves reverse engineering a patient's hand using a 3D scanner to obtain a digital blue print for referencing. 3D models of the nail shapes were created using CAD software. Colors sampling is obtained using image processing software from 2D digital images. Using specifically the inkjet technology from Stratasys, batches of nails of different sizes and colors were printed, which were then used for manual adhesion to silicone finger prostheses. This article has demonstrated that 3D printing is able to produce nails of comparable quality with those produced by traditional methods in size, shape, curvature, and thickness. More consistent thickness, better size, and shape-matching using 3D files also minimize rejects and grinding time when finishing a prosthesis, leading to significant time savings. However, 3D-printed nails fall short in color match, surface texture, and life-likeness. Traditionally produced nails that are made using a more translucent grade of acrylic than that used in the 3D-printed nails are better able to reproduce the life-like coloration of the translucent human nail. The limitations encountered with 3D printing as applied to prosthetic nails production relate to camera settings, digital image color capture and display, differences in color system used in the printer and monitor, ambient lighting, and suitability of acrylic grade used with the proprietary 3D printing system for material translucency or opacity.

Development of high-frequency and high-viscosity piezoelectric DOD print head and its jet performance

The demand for print heads with a wide range of jet viscosity and high jet frequency became evident with the development of micro-drop inkjet technology. In this paper, a new high-frequency and high-viscosity piezoelectric drop-on-demand (DOD) print head structure was proposed and manufactured. Furthermore, its reliability was confirmed via hydrodynamic and thermodynamic simulation analyses. The print head jetting performance was tested through the print head jetting performance test platform, and the effects of various waveform driving parameters on the performance were observed. The influences of dwell time, voltage amplitude, and drive frequency were considered. The results have shown that the print head jetting viscosity ranges up to 8.2 cps at room temperature, with the highest value being 98.17 cps obtained after regulating the solution viscosity and the temperature field. Moreover, the stable ejection droplet driving frequency was up to 15 kHz, confirming the good jetting stability.

Photoinduced birefringence pattern based on selective induction of photoreactivity with inkjet technology

A random copolymethacrylate containing benzoic acid and benzaldehyde side groups (P1), and a diblock copolymer of P1 and a polymer with heptadecafluorodecyl side groups (P2) were synthesized by means of reversible addition-fragmentation chain transfer (RAFT) polymerization. The linearly polarized (LP) UV light exposure initiated the thermally stimulated photoinduced reorientation of P1(P2)/4-methoxyaniline (AN) films due to the axis-selective photoisomerization of in situ formed N-benzylideneaniline (NBA) groups. A photoinduced birefringent pattern was achieved by sublimation or inkjet coating with AN on the P1(P2) film, which formed NBA moieties in the desired region. Clear birefringent pattern was attained when using P2 because the fluorine-containing block improved the NBA formation at the AN-coated region.

Enhancing Droplet Quality of Edible Ink in Single and Multi-Drop Methods by Optimization the Waveform Design of DoD Inkjet Printer

The multi-drop method with a good droplet quality is a big challenge in inkjet technology. In this study, optimization of Drop on Demand (DoD) inkjet printer waveform design was conducted. The effectiveness of the waveform design, so-called W waveform, from previous study as a preliminary vibration for the multi-drop ejection method was investigated. The unmodified W waveform was proven not to be an effective waveform for lower viscosity of liquid, especially when compared by the standard waveform obtained from a print-head manufacturer. Edible ink with a viscosity below the optimum range for print-head specifications was employed as the operating liquid. The preliminary vibration W waveform was modified to improve the droplet quality of the edible ink. It was proven that a 40% adjusted voltage of the rear wave of the W waveform was effective as the optimum waveform design for edible ink. The droplet quality of the multi-drop ejection method for grey-scale technology was improved by optimizing the W waveform design.

Improving the Throughput of Inkjet Superflash Freezing by Dense Cell Printing

Cryopreservation is widely used for the stable and long-term storage of cells in various fields. To inhibit ice crystal generation, at least one cryoprotective agent (CPA) must be added. We previously reported a CPA-free cryopreservation method based on inkjet technology. To achieve vitrification of cells, tiny droplets containing cells are deposited at intervals of 200 μm on the liquid nitrogen-cooled substrate, which confines the number of cells in a single operation. In this study, we aim to increase the number of droplets containing cells on the substrate by reducing the intervals between the droplets. To inhibit an influence on the cell viability, the temperature rise of formerly deposited droplets and the decrease in the cooling rate were analyzed and evaluated. The temperature of the neighboring droplet did not exceed the glass transition temperature, over which recrystallization ultrarapidly occurs, even when the droplet interval was 75 μm. On the other hand, the cooling rate at the intervals of 125 μm was slightly below the critical cooling rate of the cell. Therefore, the intervals between the droplets should be above 150 μm. We also experimentally confirmed that the cell viability at the intervals of 150 μm was the same and the viability at the intervals of 75 μm decreased by approximately 40% compared to the one at the intervals of 200 μm. Both the results suggest that CPA-free cryopreservation achieves by depositing 70pL droplets at intervals above 150 μm.

Optimization of a resin with carbon nanotubes ink for printing by Inkjet technologies

The main aim of this research is the development of a nanoreinforced thermosetting resin based ink to be used in injection printers for additive manufacturing processes.&nbsp; (inkjet tecnhnologies). Firstly, printing conditions have been optimized for the nanoreinforced epoxy resin at different MWCNT contents. Afterwards these inks have been used to print 2D circuits based on joined parallel straight lines. These printed materials were tested to evaluate their mechanical and electrical properties. MWCNT reinforced epoxy resin inks developed resulted in successful injection to produce the 2D circuits repetitively. The dispersion of the MWCNTs in the epoxy resin is adequate and the circuits containing 0.3 wt.% of nanoreinforcement were electrically conductive. Mechanical properties were similar for both materials.

Characterization of Additively Produced RF-Structures on Low-Cost PCB Materials Based on Inkjet Technology for Industrial Applications up to 80 GHz

Usually, the printed circuit board industry has to use special subtractive manufacturing methods, if small line and space dimensions down to 50 μm are desired. This drastically raises production effort and costs. In this paper a method is shown, how the inkjet technology can be used to produce passive RF structures with minimum line and space dimensions of 25 μm. For the first time, this is possible over complete panels of low-cost PCB substrates, which have a relatively high surface roughness compared to ceramic or glass carriers. To ensure process reliability, printed lines must also be plated with an additional electroless copper layer to overcome the surface roughness with conductive layers and to lower insertion loss in the two-digit GHz range. Additionally, a surface impedance model is developed, which allows broadband first time right simulations. Finally, additively produced, passive RF filters are compared to their subtractive counterparts to show their benefits regarding production costs and electrical performance up to 80 GHz.

Drop-on-demand (DOD) inkjet dynamics of printing viscoelastic conductive ink

Emerging applications of drop-on-demand (DOD) inkjet printing, such as printed electronics and bioprinting, are leading to an ever-increasing development of diverse functional inks with complex chemical and rheological properties, especially viscoelastic polymers. Forming droplets with desirable velocity and volume as well as excellent reliability is of great importance for successful printing. In this study, the dynamics and performance of droplet formation during DOD inkjet printing of viscoelastic ink were investigated by employing the piezoelectric inkjet technology to print a conductive polymer ink under various excitation waveform parameters. Four distinct droplet formation regimes were identified, namely, no droplet formation, a single droplet, one satellite droplet, and multiple satellite droplets. A process dynamics-related dimensionless number (Wj) was proposed to construct an operating phase diagram on droplet formation and quantify the transition of droplet formation regimes. The effects of bipolar waveform parameters on droplet formation were systematically examined in terms of Wj, droplet velocity, and droplet diameter. Moreover, the printing of conductive microlines and micropatterns was precisely controlled under well-formed droplets. This study could support fully understanding the droplet formation dynamics during DOD inkjet printing of viscoelastic inks to guide generating desirable droplets of functional ink and improve the performance and function of inkjet-printed devices.

Novel Piezo Inkjet Technology and Printhead Capable of Jetting Extreme Viscosity Fluids for Additive Manufacturing

A novel operation mode for piezo inkjet printheads has been invented to close the gap of current commercial printheads in meeting the requirements for advanced additive manufacturing. Subsequently, a printhead using the new technology has been developed along with the necessary sub-systems for integration in a printer. The new inkjet technology brings a combination of advantages, the most relevant being the capability to jet extremely high viscosity fluids, combined with very high productivity per nozzle, very wide drop size control and the capability to jet fluids with high particle load and large particle sizes.

Integrated Fabrication of Novel Inkjet-Printed Silver Nanoparticle Sensors on Carbon Fiber Reinforced Nylon Composites.

Inkjet-printing technology enables the contactless deposition of functional materials such as conductive inks on surfaces, hence reducing contamination and the risk of substrate damage. In printed electronics, inkjet technology offers the significant advantage of controlling the volume of material deposited, and therefore the fine-tuning of the printed geometry, which is crucial for the performance of the final printed electronics. Inkjet printing of functional inks can be used to produce sensors to detect failure of mechanical structures such as carbon fiber reinforced composite (CFRC) components, instead of using attached sensors, which are subject to delamination. Here, silver nanoparticle-based strain sensors were embedded directly in an insulated carbon-fiber laminate by using inkjet printing to achieve an optimized conductive and adhesive geometry, forming a piezoresistive strain sensor. Following the inkjet-printing optimization process, the sensor conductivity and adhesion performance were evaluated. Finally, the sensor was quantified by using a bending rig which applied a pre-determined strain, with the response indicating an accurate sensitivity as the resistance increased with an increased strain. The ability to embed the sensor directly on the CFRC prevents the use of interfacial adhesives which is the main source of failure due to delamination.

Marangoni Flow Manipulated Concentric Assembly of Cellulose Nanocrystals.

Tunable assembly of cellulose nanocrystals (CNCs) is important for a variety of emerging applications in optics, sensing, and security. Most exploited assembly and optical property of CNCs are cholesteric assembly and corresponding circular dichroism. However, it still remains challenge to obtain homogenous and high-resolution cholesteric assembly. Distinct assembly and optical property of CNCs are highly demanded for advanced photonic materials with novel functions. Herein, a facile and programmable approach for assembling CNCs into a novel concentric alignment using capillary flow and Marangoni effect, which is in strike contrast to conventional cholesteric assembly, is demonstrated. The concentric assembly, as quantitatively evidenced by polarized synchrotron radiation Fourier transform infrared imaging, demonstrates Maltese cross optical pattern with good uniformity and high resolution. Furthermore, this Maltese cross can be readily regulated to "on/off" states by temperature. By combining with 3D inkjet technology, a functional binary system composed of "on"/"off" CNCs optical patterns with high spatial resolution, fast printing speed, good repeatability, and precisely controllable optical property is established for information encryption and decryption. This concentric assembly of CNCs and corresponding tunable optical property emerge as a promising candidate for information security, anticounterfeiting technology, and advanced optics.

Morphologies and dynamics of micro-droplet impact onto an idealised scratch

As inkjet technology develops to produce smaller droplets, substrate features such as accidental scratches or manufacturing defects can potentially affect the outcome of printing, particularly for printed electronics where continuous tracks are required. Here, the deposition of micro-droplets onto a scratch of commensurate size is studied. The scratch is considered as a groove of rectangular cross-section, with rectangular side ridges representing material displaced from the substrate, and seven equilibrium morphologies are identified as a result of inertial spreading, contact-line pinning, imbibition into the scratch and capillary flow. A regime map is constructed in terms of scratch depth and width, and theoretical estimates of the regime boundaries are developed by adapting droplet spreading laws for flat surfaces to account for liquid entering the scratches. Good agreement is seen with numerical results obtained using a graphical processing unit-accelerated three-dimensional multiphase lattice Boltzmann model validated against published experiments, and the influences of Reynolds number, Weber number and advancing and receding contact angles are explored. Negative and positive implications of the results for printing applications are discussed and illustrated via multiple-droplet simulations of printing across and along scratches.