Printing Behavior Research Articles

Effect of Moisture on Shape Memory Polyurethane Polymers for Extrusion-Based Additive Manufacturing.

Extrusion-based additive manufacturing (EBAM) or 3D printing is used to produce customized prototyped parts. The majority of the polymers used with EBAM show moisture sensitivity. However, moisture effects become more pronounced in polymers used for critical applications, such as biomedical stents, sensors, and actuators. The effects of moisture on the manufacturing process and the long-term performance of Shape Memory Polyurethane (SMPU) have not been fully investigated in the literature. This study focuses primarily on block-copolymer SMPUs that have two different hard/soft (h/s) segment ratios. It investigates the effect of moisture on the various properties via studying: (i) the effect of moisture trapping within these polymers and the consequences when manufacturing; (ii) and the effect on end product performance of plasticization by moisture. Results indicate that higher h/s SMPU shows higher microphase separation, which leads to an increase of moisture trapping within the polymer. Understanding moisture trapping is critical for EBAM parts due to an increase in void content and a decrease in printing quality. The results also indicate a stronger plasticizing effect on polymers with lower h/s ratio but with a more forgiving printing behavior compared to the higher h/s ratio.

Effect of rheological properties of potato, rice and corn starches on their hot-extrusion 3D printing behaviors

In this study, the relationship between rheological properties and printability of three types of starch (potato, rice and corn starch) for hot-extrusion 3D printing (HE-3DP) were systematically investigated. Each starch sample showed a shear-thinning behavior, self-supporting property, as well as the feature of a substantial decrease at higher strains and a recovery at lower strains in storage modulus (G′), which indicated the suitability of starch for HE-3DP. Besides, the flow stress (τf), yield stress (τy), and G′ increased with a higher starch concentration. We found that starch suspensions with concentrations of 15–25% (w/w) heated to 70–85 °C possessed preferable values of τf (140–722 Pa), τy (32–455 Pa), and G' (1150–6909 Pa) for HE-3DP, which endowed them with excellent extrusion processability and sufficient mechanical integrity to achieve high resolutions (0.804–1.024 mm line width). Overall, our results provided useful information to produce individualized starch-based food by HE-3DP.

Investigation on characteristics of 3D printing using Nostoc sphaeroides biomass.

Gel-like constructs can be produced using an extrusion-based 3D food printing (3D-FP) technique. Nostoc sphaeroides biomass is a natural gel material. Considering its good nutrition and rheological properties, these algae were chosen in this study as supply material (ink) for 3D-FP. With this gel material, the extrusion-based 3D printing system was set as a model, and the printing behavior was investigated. Furthermore, the 3D-FP mechanisms were explained through low-field nuclear magnetic resonance and rheological measurements. Results indicated that although fresh biomass gel was printable, non-uniformity and instability occurred during printing. Blanched inks showed non-smooth printing behavior, which was associated with a decrease in elasticity and viscosity. Printability was improved by increasing the rehydration time to 24 h when rehydrated powder was used. Increasing the rehydration time increased the water-binding degree. Pre-gelatinized potato starch was added to the mixture at ratios ranging from 1 to 100 g kg-1 . The best printing outcome was observed at 40 g kg-1 potato starch. We emphasize that elasticity and viscosity balance is an essential parameter to achieve printability. The strategies adopted in this work provide new insights into the development of personalized food regarding texture and nutritional additive content. © 2018 Society of Chemical Industry.

Optimizing piezoelectric inkjet printing of silica sols for biosensor production

The inkjet printing of biocompatible silica sols has gained popularity, both for biosensor production and development of holographic devices. However, there still remain significant issues related to premature clogging of inkjet printheads when printing aqueous silica sols. To better understand the causes of clogging of piezoelectric inkjet nozzles, printing studies were coupled with studies of colloidal stability along with silica deposition on surfaces, both under normal flow and piezoelectrically driven oscillating flow through an inkjet cartridge. Our studies show that clogging most likely results from deposition of silica colloids onto the internal surfaces of the printhead, followed by displacement of micron-sized pieces of the deposited material upon piezoelectric deformation of the printhead surface, which then block the nozzles of the printhead. Based on this result, we formulated a low-pH sol derived from sodium silicate and evaluated its colloidal stability, binding to silica surfaces and resistance to clogging of inkjet nozzles under normal and voltage-driven oscillating flow. We show that silica sols with a pH of 3.1 provide optimal printing behavior while allowing reproducible printing of spatially controlled silica patterns on paper to produce enzyme-based biosensing devices.

Pro-environmental Printing Behaviour as an Indicator to Reduce Paper Cost at Work

Today we are facing environmental hitches such as deforestation and global warming, due to which atmospheric CO2 level has increased by 25% since 1850. It is human activities that have created these problems; hence, the resolutions to these encounters lie in behavioral change. Thus, it is only by empowering people that the environment can be protected. This study aims to explore reduction of printing at elementary schools by enhancing pro-environmental printing behavior. Literature review is presented in the following themes – demographic, impact of printing on the environment and pro-environmental printing behavior. An observation method is applied in this study and data is obtained from 108 teachers from seven elementary schools at three different regions in Northwest Friesland, The Netherlands by using digital print data and printers’ observation. The main findings illustrate that pro-environmental behaviour has a positive effect on the printing behavior. This research reveals that the experimental group printed 45% to 51% less during intervention. Therefore by extending pro environmental behaviour, financial and environmental costs can be minimized. This reading recommends directors of the schools to enhance pro-environmental printing behaviour among teachers to reduce both financial and environmental costs measured as use of paper.

Dual extrusion 3D printing of mashed potatoes/strawberry juice gel

Currently most of food printers apply one printhead to extrude a single or a mixture of multiple materials. Such a printhead cannot control the materials distribution in a drop-on-demand way, while a multi-extruder printer enables the fabrication of highly attractive multi-material constructs with higher geometric complexity. In this study, the effects of extruder offset and retraction on the printing behavior were firstly optimized, followed by the preliminary tests of two methods of dual extrusion 3D printing. Method A is to create a multi-part model and assign each of them to one extruder. Method B is to create a single part model and assign different roles to each extruder. Some constructs with different inside shape were created using Method A. Product hardness and gumminess increased linearly with mashed potatoes (MP) percentage but showed no correlation with inside shape. Porous samples with special texture were printed using Method B by varying infill levels. Total printing time, firmness, hardness and gumminess increased with infill levels, and a clear discrimination was observed by principle component analysis (PCA). This suggested that dual extrusion 3D printing enables the fabrication of attractive multi-material constructs and has a potential to tailor textural properties of samples through varying infill percentage.

Continuous hydrothermal flow synthesis of Gd‐doped CeO2 (GDC) nanoparticles for inkjet printing of SOFC electrolytes

AbstractGdxCe1‐xO2‐δ (GDC) nanoparticles were synthesized, using continuous hydrothermal flow synthesis. By varying the synthesis conditions, particle size and morphology could be tailored. Here, particle sizes between 6 and 40 nm with polyhedral or octahedral shape could be obtained. Gd0.2Ce0.8O2‐δ nanoparticles were further processed into inks for inkjet printing. Despite the small particle size/large surface area, inks with excellent printing behavior were formulated. For proof‐of‐concept, thin GDC layers were printed on a) green NiO‐GDC substrates, and on b) presintered NiO‐YSZ substrates. While no dense layers could be obtained on the green NiO‐GDC substrates, GDC nanoparticles printed on NiO‐YSZ substrates formed a dense continuous layer after firing at 1300°C.

Graphene Oxide: An All-in-One Processing Additive for 3D Printing.

Many 3D printing technologies are based on the development of inks and pastes to build objects through droplet or filament deposition (the latter also known as continuous extrusion, robocasting, or direct ink writing). Controlling and tuning rheological behavior is key for successful manufacturing using these techniques. Different formulations have been proposed, but the search continues for approaches that are clean, flexible, robust and that can be adapted to a wide range of materials. Here, we show how graphene oxide (GO) enables the formulation of water-based pastes to print a wide variety of materials (polymers, ceramics, and steel) using robocasting. This work combines flow and oscillatory rheology to provide further insights into the rheological behavior of suspensions combining GO with other materials. Graphene oxide can be used to manipulate the viscoelastic response, enabling the formulation of pastes with excellent printing behavior that combine shear thinning flow and a fast recovery of their elastic properties. These inks do not contain other additives, only GO and the material of interest. As a proof of concept, we demonstrate the 3D printing of additive-free graphene oxide structures as well as polymers, ceramics, and steel. Due to its amphiphilic nature and 2D structure, graphene oxide plays multiple roles, behaving as a dispersant, viscosifier, and binder. It stabilizes suspensions of different powders, modifies the flow and viscoelasticity of materials with different chemistries, particle sizes and shapes, and binds the particles together, providing green strength for manual handling. This approach enables printing complex 3D ceramic structures using robocasting with similar properties to alternative formulations, thus demonstrating the potential of using 2D colloids in materials manufacturing.

Impact of rheological properties of mashed potatoes on 3D printing

Rheological properties of the mashed potatoes (MP) with addition of potato starch (PS) and their 3D printing behavior were investigated. Both flow ramp and dynamic oscillation frequency experiments were used to characterize the rheological properties of the mixtures. The correlation between the formulation and processability during 3D printing was established. MP with 0% PS possessed low yield stress (τ0) (195.90 Pa) and printed objects deformed in sagged afterwards. Whereas, addition of 2% PS displayed excellent extrudability and printability, i.e., shear-thinning behavior, consistency index (K) of 118.44 (Pa•sn), τ0 of 312.16 Pa and proper elastic modulus (G′). At such condition, the printed objects possessed smooth shape, good resolution, and could withstand the shape over time. Although MP with addition of 4% PS represented good shape retention due to proper τ0 (370.33 Pa) and G′, the poor extrudability made it difficult to print due to high K (214.27 Pa•sn) and viscosity.

Stencil Printing Optimization using a Hybrid of Support Vector Regression and Mixed-integer Linear Programming

This research proposes an optimization approach to enhance the stencil printing process (SPP) in surface mount printed circuit board (PCB) assembly. Stencil printing behavior is affected by many variables including stencil design, solder paste composition, squeegee speed and pressure, and other environmental conditions. In this research, support vector regression (SVR) model is trained to capture the complex relationships among these variables, based on historical data. A mixed-integer linear programming (MILP) model is proposed to minimize the total absolute predicted deviation of average volume transfer from target. The optimal printing settings are retrieved for different sample problems with low computational cost.

Promoting Pro-environmental Printing Behavior: The Role of ICT Barriers and Sustainable Values

This study aims to explore how to reduce printing at elementary schools through strengthening both the effective use of ICT and pro-environmental values. Literature review is presented in themes – ICT barriers (fears, knowledge, skills and time), demographic, printing behavior and sustainable values (egoistic, hedonic, prosocial & biospheric). A quantitative method is applied in this study, data is obtained from 108 teachers from seven elementary schools at three different regions in Northwest Friesland, The Netherlands by using a questionnaire. The value scale by De Groot and Steg (2008) is applied for sustainable values while for ICT barriers and printing behavior, questions are developed by the author and validated by Cronbach. The main findings illustrate that lower ICT fears and higher biospheric values have a positive effect on the pro-environmental printing behavior. To minimize teachers' ICT fears and printing, directors of the schools should train teachers in the use of ICT and enhance their biospheric values. This study is one of the first to explore ICT barriers with the combination of pro-environmental values orientation contributing pragmatic evidence to reducing financial and environmental costs.

Digital fabrication of organic solar cells by Inkjet printing using non-halogenated solvents

Inkjet printing offers versatility and flexibility for the sequential deposition of functional layers for the production of large area organic photovoltaics (OPV). Four layers of an OPV cell are inkjet printed, comprising an ITO-free semi-transparent front electrode (a metal current collecting grid, inkjet printed PEDOT:PSS and ZnO nanoparticle layers), and the photo-active layer combined with PEDOT:PSS as hole transport layer. To render the process R2R compatible, large area printing is performed using a 3.5cm wide printhead and non-halogenated ink formulations only. Similar performance is achieved for the inkjet printed cells as for cells with only spin coated layers and ITO. For the P3HT/PCBM bulk-heterojunction, a mixture of non-halogenated solvents ensured good solubility, proper printing behavior and a blend morphology that yields similar performance to a layer spin-coated from chlorinated solvents. The potential of inkjet printing for large area OPV was demonstrated by the fabrication of a module with 92cm2 active area, which showed an efficiency of 0.98%. Losses due to front and back electrode resistances are modeled and used to explain the recorded I-V curve. Combining these functional layers with inkjet printed electrodes lays out the roadmap toward fully roll-to-roll compatible digital fabrication of OPV.

Tuning the viscosity of halogen free bulk heterojunction inks for inkjet printed organic solar cells

For the solution processing of organic photovoltaics on an industrial scale, the exclusion of halogenated solvents is a necessity. However, the limited solubility of most semiconducting polymer/fullerene blends in non-halogenated solvents results in ink formulations with low viscosities which poses limitations to the use of roll-to-roll compatible deposition processes, such as inkjet printing. We propose to add polystyrene as a rheological modifier to increase the viscosity of bulk heterojunction (BHJ) non-halogenated inks. The printing and performance of P3HT/PCBM photoactive layer inks are characterized as a function of polystyrene concentration and three different molecular weights. Addition of 1wt% polystyrene provided a near two-fold gain in viscosity, with the largest viscosity gains coming from the polymer with the highest molecular weight. However, this coincided with greater viscoelastic behavior, which reduced the jetting performance of the inks. Differences in solvent compatibility of the polystyrene/P3HT/PCBM ternary blend resulted in phase separation upon layer drying, whereby polystyrene segregated to the layer-air interface to form an isolated domain or network like topology. Nevertheless, a 1.7-fold increase in dynamic viscosity was obtained for devices with printed BHJ layers containing polystyrene at the expense of a 20% reduction in OPV performance. The improved viscosity and good printing behavior achieved with small additions of polystyrene demonstrates its potential to overcome the limited viscosity resulting from typical non-halogenated ink formulations for semiconducting polymers. These results offer a step forward to the industrialization of inkjet printing as an effective deposition technique for functional layers of organic electronics.

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.

Fabrication of a flexible Ag-grid transparent electrode using ac based electrohydrodynamic Jet printing

In the dc voltage-applied electrohydrodynamic (EHD) jet printing of metal nanoparticles, the residual charge of droplets deposited on a substrate changes the electrostatic field distribution and interrupts the subsequent printing behaviour, especially for insulating substrates that have slow charge decay rates. In this paper, a sinusoidal ac voltage was used in the EHD jet printing process to switch the charge polarity of droplets containing Ag nanoparticles, thereby neutralizing the charge on a polyethylene terephthalate (PET) substrate. Printed Ag lines with a width of 10 µm were invisible to the naked eye. After sintering lines with 500 µm of line pitch at 180 °C, a grid-type transparent electrode (TE) with a sheet resistance of ∼7 Ω sq−1 and a dc to optical conductivity ratio of ∼300 at ∼84.2% optical transmittance was obtained, values that were superior to previously reported results. In order to evaluate the durability of the TE under bending stresses, the sheet resistance was measured as the number of bending cycles was increased. The sheet resistance of the Ag grid electrode increased only slightly, by less than 20% from its original value, even after 500 cycles. To the best of our knowledge, this is the first time that Ag (invisible) grid TEs have been fabricated on PET substrates by ac voltage applied EHD jet printing.

Drop-on-demand E-jet printing of continuous interconnects with AC-pulse modulation on highly insulating substrates

In this paper, we present a novel AC-pulse modulated electrohydrodynamic (EHD) jet printing technology that enables high resolution fabrication of electrical features and interconnects using the silver nanoink on highly insulating substrates. In traditional EHD jet printing, the remained charge of the printed droplets changes the electrostatic field distribution and interrupts the follow-on printing behavior, especially for highly insulating substrates having a slow charge decay rate. In this paper, a modulated AC-pulsed voltage was used for the EHD jet printing process that can alternate the charge polarity of the consequent droplets to neutralize the residue charge on the substrate. The effect of the residue charge is minimized, which enables high resolution printing of continuous patterns. With three printing parameters (e.g. pulse frequency, voltage, and duration), the EHD jet printing speed and droplet size can be controlled independently. We demonstrated that AC-pulse modulated EHD jet printing can overcome the charge accumulation challenge on highly insulating substrates, and investigated the variables of fabrication process to achieve reliable jet printing of conductive silver tracks.

Printing PPEs: Fundamental Structure-Property Relationships.

A series of differentially alkyl- and alkoxy-substituted poly(para-pheneyleneethynylene)s of different molecular weight were prepared and their rheological properties investigated. It was found that the side chain structure of the PPEs of roughly equal molecular weight and degree of polymerization has a significant influence on the rheology and printing behavior of the PPEs. Introduction of branched alkoxy or alkyl substituents improve the printing behavior of the PPEs dramatically.

High-resolution ac-pulse modulated electrohydrodynamic jet printing on highly insulating substrates

This paper presents a new high-resolution ac-pulse modulated electrohydrodynamic (EHD)-jet printing technology on highly insulating substrates for drop-on-demand fabrication of electrical features and interconnects using silver nanoink. In traditional EHD-jet printing, the remained charge of the printed droplets changes the electrostatic field distribution and interrupts the follow-on printing behavior, especially for highly insulating substrates which have slow charge decay rates. The residue charge makes the control of EHD-jet printing very challenging for high-resolution continuous features. In this paper, by using modulated ac-pulsed voltage, the EHD-jet printing process switches the charge polarity of the consequent droplets to neutralize the charge on the substrate. The effect of the residue charge is minimized, which enables high-resolution printing of continuous patterns. Moreover, by modulating the pulse frequency, voltage, and duration, the EHD-jet printing behavior can be controlled with respect to printing speed/frequency and droplet size. Printing frequency is directly controlled by the pulse frequency, and the droplet dimension is controlled by the voltage and the duration of the pulse. We demonstrated that ac-pulse modulated EHD-jet printing can overcome the long-predicated charge accumulation problem on highly insulating substrates, and potentially be applied to many flexible electronics applications.

Only reasoned action? An interorganizational study of energy-saving behaviors in office buildings

Substantial energy savings can be achieved by reducing energy use in office buildings. The reported study used a Theory of Planned Behavior (TPB) model extended with perceived habit to explain office energy-saving behaviors. One aim was to examine if organizational contextual variability independently predicted office energy-saving behaviors over and above TPB variables and self-reported habit. Another aim was to examine the relative predictive value of TPB variables and habit for energy-saving behaviors between organizational contexts. Survey data on energy-saving behaviors, TPB variables, and habit and number of office mates were collected from office workers of four organizations in the Netherlands. The results indicate that intention was the strongest direct predictor of the behaviors printing smaller and not printing e-mails, whereas habit was the strongest predictor of the behaviors switching off lights and switching off monitors. Of the social-cognitive factors, attitude was the strongest predictor of intentions overall. The effect of perceived norm varied widely between behaviors and subgroups. Number of office mates had a direct, unmediated effect on the behavior switching off lights and a mediated effect via attitude and perceived control. The effect of organizational contextual variability on behavior was entirely mediated through the psychosocial factors for the two ‘printing behaviors’, but only partially for the two ‘switching behaviors’. The relative predictive value of habit and intention differed between organizations. The findings suggest that organizational contextual variability has unconscious influences on some office energy-saving behaviors. Interventions should take variation in the relative importance of cognitive factors and habit between behaviors, and to a lesser extent between organizational contexts, into account.

Direct Writing of Gallium‐Indium Alloy for Stretchable Electronics

In this paper, a direct writing method for gallium‐indium alloys is presented. The relationships between nozzle inner diameter, standoff distance, flow rate, and the resulting trace geometry are demonstrated. The interaction between the gallium oxide layer and the substrate is critically important in understanding the printing behavior of the liquid metal. The difference between receding and advancing contact angles demonstrates that the adhesion of the oxide layer to the substrate surface is stronger than the wetting of the surface by the gallium‐indium alloy. This further demonstrates why free‐standing structures such as the traces described herein can be realized. In addition to the basic characterization of the direct writing process, a design algorithm that is generalizable to a range of trace geometries is developed. This method is applied to the fabrication of an elastomer‐encapsulated strain gauge that displays an approximately linear behavior through 50% strain with a gauge factor of 1.5.