- The Influence of Ink Rheology on Flexographic Printing Instabilities (Miles Morgan – WCPC)
- Pore Network Structure and Surface Design: capturing the power of pore-fluid interaction for our future in printed functionality (Prof. Dr. Patrick Gane – Omya International AG)
- Study of the Influence of Calcium Carbonate in Polymers during the Additive Manufacturing Process (Fabio Ippolito – Omya International AG)
- Optimisation of Screen Printed Transparent Electrodes (Sarah-Jane Potts – WCPC)
- Importance of ink rheology for high resolution screen printing (John Lau – WCPC)
- Industrial Coatings: The story of watching Paint Dry (Emily Radley – WCPC)
- The effect of graphite and carbon black ratios on conductive ink performance (Chris Phillips, Awadh Al-Ahmadi, Sarah-Jane Potts)
- Printed Batteries – from primary to secondary (Dr Martin Krebs – VARTA Microbattery GmbH)
- Performance of Printed Batteries (Michael Wendler, Tim Claypole, Erich Steiner, Martin Krebs)
- Evaluation of the corrosion resistance of screen printed metallic current collectors for printed thin film batteries with aqueous alkaline electrolytes (Patrick Rassek – HdM Stuttgart/WCPC)
- The application of active and intelligent packaging to detect spoilt high value food products and extend the life of food products (Caitlin McCall – WCPC)
- Printed Sensor on Chip Technology (Ben Clifford – WCPC)
- Scaling Physics of Printable Thin Film Solar Cells & Large Area Optoelectronics (Paul Meredith – Sêr Cymru Chair in Sustainable Advanced Materials)
- Up-scaling of combined planarizing and insulating layers on rough steel substrates for large area solar cells (Tatyana Korochkina and David Gethin – WCPC)
- The effect of plasma functionalisation on the dispersion and print quality of graphene nanoplatelet based inks (Andrew Claypole – WCPC)
- Custom electronics for printed electronic devices (Dr Tim Mortensen – WCPC)
Uniformity is crucial in the printing of electronic devices to ensure optimum functional performance. Understanding the causes of non-uniformity in flexographic printing is therefore of great interest in the pursuit of low-cost, high volume printed electronics. However, this challenge is compounded by the rheological complexity of printable fluids for printed electronics. Several causes of non-uniformity originate in the surface instabilities that occur during the printing process, particularly at the nip, during substrate-plate separation. The present work seeks to understand the influence of ink rheology on print uniformity by formulating, characterising and printing model inks with a desire to link rheology, uniformity and functional print performance.
Prof. Dr. Patrick Gane – Omya International AG
At some stage in the production and conversion of paper, board and packaging, fluid (gas or liquid) will inevitably be introduced to or extracted from a porous medium. This may be in the formation of the fibre base product, during the application of a coating, printing, gluing, fluid permeation or lamination, barrier formation etc. It is, thus, vital not only to understand the individual process technologies but to formulate the mechanistic interactions involved in a sufficiently formalistic way, so as to apply the physics of fluid flow, pore capillarity, percolation and permeability, and to parameterise the physical chemistry controlling fluid-surface contact. The future of functional printing, in particular, depends on our ability to design and control the multitude of interactions between fluids and porous media.
We all recognise that the printing and packaging industry is facing many challenges, and thereby enjoying a raft of new opportunities ranging from the need to provide sustainable products, reduced transported weight and storage volume, together with the demand for increased product protection, longevity and the unending question of cost, as well increasing the attractiveness for the end consumer, including advanced optical effects. Based on the fundamentals of liquid-pore interaction, examples will be given how functional printing can be enhanced and supported by pore network structure design. Further new opportunities in providing tools for testing and vector delivery of novel pharmaceutical actives, for medical diagnostics, for agricultural micronutrient and crop protection treatments, and other analytical systems, based on microfluidics, will be illustrated, in turn providing greater dosage control, improved quality of analysis and spatial resolution, enhanced component identification and, importantly, reduced volumes of test analyte. Inclusion of micro and nanofibrillated cellulose in future nanocomposite coating designs adds an additional dimension in achievable material properties.
Capturing the benefits of current multifaceted research in the areas discussed in this address will help to unlock our future in creating major benefits in functionality derived from the behaviour of the basic material phases in our world – liquid/gas and solid/space – manifest in fluid-porous media interactions.
Fabio Ippolito – Omya International AG
There are various Additive Manufacturing processes available to produce a 3D layered products.
The selective laser sintering (SLS) process is one of the most established and widely used Additive Manufacturing approaches. It is a layer manufacturing process in which the layers of predefined geometry are made out of a powder bed by fusing them together using a laser beam.
With the evolution of various techniques for prototyping through to the production of actual end-use parts, there is a growing need to develop a much greater variety of materials suitable for the 3D printing environment, and to increase and/or change the properties of the end-product, including functionality, without high increase in production costs. Several aspects need to be considered during the development of a new compound, which is suitable for the selective laser sintering process.
In this study, the influence of an inorganic filler material in a polymer is investigated and its usage as a functional filler during the additive manufacturing process will be determined. Investigations such as the influence of the particle size of the filler material on the resultant compound properties, the surface modification of the inorganic particles and its effect in the compound, the different fabrication techniques for the composite production and their influence on the processability in 3D printing, etc. will be carried out.
This presentation will give an overview on the challenges and approaches for such an investigation as well as the first results on the manipulation of the properties of the produced compounds.
Screen Printing is a very versatile and popular process, currently responsible for producing around 98% of printed electronics. Including, printed circuit boards, printed electroluminescent devices and photovoltaics. Currently, transparent conductive inks are being developed as a cheaper alternative top electrode in solar cells. Screen printable inks offer a promising solution due to the simplicity and low cost of screen printing. This study investigates the printability of a transparent, conductive, silver nanowire based screen printing ink is assessed to find the optimal drying and curing techniques for this ink including air drying, infrared drying and photonic curing as well as combinations of the methods.
The topographic 3d profiles of the prints were analysed using the Veeco NT9300 Wide Area White Light Interferometer with the 15x lens to analyse the print quality as well as record the average print heights and roughness’s. The microstructures of the printed silver nanowires were analysed using the Zeis EVO Scanning Electron Microscope (SEM) and the JEOL 7800 FEG SEM to visualise and assess the orientation and dispersion of the printed silver nanowires. Additionally, the electrical characterisation of the prints was assessed using resistivity measurements conducted with a 4-point probe. Several drying induced defects were observed throughout the results including raised edges due to Marangoni effect, irregular edges, ghost lines around the edges, bubbles in the deposit due to gas evolution. The print with the least defects, adequate surface roughness and lowest resistivity was dried using the conveyor infrared dryer.
Printed electronic devices such as electroluminescent displays, organic light emitting diodes, and photovoltaic devices, all require transparent, electronically conductive materials for their electrodes. In situations where flexible devices are desired, transparent electrodes produced from Indium doped Tin Oxide (ITO) coated polymer films have been a popular choice. Due to material scarcity, cost and the desire for greater device performance, alternatives to ITO could prove beneficial. One viable approach is to produce an electrode by combining highly transparent substrates with a fine printed grid of opaque, highly conductive metallic ink. This provides a great opportunity to fine tune the optical and electronic performance of the resulting electrode for specific applications.
The target for this project; printing a network of sub 30 micron, highly conductive fine tracks onto flexible substrates of over a meter squared in size could is technologically challenging process. In this study the printability of ultra-fine features through very high thread count mesh will be equated with the rheological properties of the ink. This work will bring together ASADA’s expertise of high resolution mesh screens combined with the advanced rheological characterisation expertise of the Welsh Centre for Printing and Coating.
Polyester melamine coatings are highly susceptible to changes in curing conditions that can lead to surface defects. The first part of this study has focused on quantitatively characterizing these differences by investigating the effect of changes in dwell time and oven temperatures on cure levels using microhardness and infra-red (FT-IR) spectroscopy.
The coatings investigated are made up of polyester with a melamine cross-linker. Melamine cross-linking can be measured using FT-IR spectroscopy as the transetherification reaction which occurs causes the loss of a methoxy group, by varying temperature and dwell time, a relationship between a higher peak metal temperature (PMT) and a higher cross-link density can be established. Notably, this shows how microhardness demonstrates a positive correlation between increased cross-link density and increased curing as demonstrated by an increase in hardness.
Using this technique, the second part of this work has investigated the effect these changes have on stress whitening. Stress whitening is a common aesthetic defect which has been a long standing issue when bending pre-coated metal to form products for the industrial market.
Conductive inks based on graphite and carbon black are used in a host of applications including energy storage, energy harvesting, electrochemical sensors and printed heaters. This requires accurate control of electrical properties tailored to the application; ink formulation is a fundamental element of this. Data on how formulation relates to properties has tended to apply to only single types of conductor at any time, with data on mixed types of carbon only empirical thus far. Therefore screen printable carbon inks with differing graphite, carbon black and vinyl polymer content were formulated and printed to establish the effect on rheology, deposition and conductivity. The study found that at a high total carbon loading ink, optimal conductivity (0.029 Ω∙cm) was achieved at a graphite to carbon black ratio of 2.6 to 1. For a lower total carbon loading, this ratio was reduced to 1.8 to 1. Formulation affected viscosity and hence ink transfer and also surface roughness due to retention of features from the screen printing mesh and the inherent roughness of the carbon components, as well as the ability of features such as fine lines to be reproduced consistently.
Dr Martin Krebs – VARTA Microbattery GmbH
Today State-of-the-Art printed batteries PB’s are primary cells. The preferred electrochemical system is Zinc-Carbon. It consists of a Zinc metal anode and a Manganese dioxide cathode with a near-neutral electrolyte consisting of Zinc and Ammonium chloride. This system provide reliable, easy to print, cheap and environmental friendly batteries. The use is in so-called “disposable” applications were cheap printed products are used for a certain, short period of time and then disposed of.
Especially for higher value applications like sensors it may be useful to have rechargeable batteries. That concerns Smart Object where high value chips are integrated and which can be used repeatedly. So a higher turn-over and benefit for the environment can be generated.
In this talk possible electrochemical systems for rechargeable PB’s will be introduced and discussed. The most important parameters are material costs, processing and life time. Also different cell design will be shown and discussed. A special aspect will be the principle of reversibility of the electrodes and how that can be achieved.
Finally an outlook will be given on potential applications.
Michael Wendler, Professor Tim Claypole MBE, Erich Steiner, Martin Krebs
Batteries as primary and secondary sources of portable electrical power, have been in use for many years. Advanced electronic devices depend on availability of batteries. Especially for use in smart objects, like autonomous sensor systems, medical strips or RFID/NFC tags, thin and flexible energy storage devices are in great demand. The major development in this field within the past years has been the development of printed batteries. This category of batteries may be composed of different cell chemistries, with unique performance characteristics. The common feature is the use of printing processes in the production process. Differentiation comes from variation of the main cell configurations, stacked or coplanar, as well as the variation of the electrode shape.
The main objectives of battery research and development are to increase the useable power and energy of a battery system for a specific application. But, beside the electrical performance, at least as important are considerations related to cost, physical design, safety, environmental sustainability and reliability. These six factors are strongly dependent on the requirements of the application.
To determine battery performance, the capacity (the amount of charge [Q]), the open-circuit potential (OCP) and the cell impedances are dominant factors. Further parameters are discharge current, discharge time, ambient temperature as well as cut-off voltage at which the discharge process is stopped.
In this work, the galvanostatic discharge at constant current (CC) and electrochemical impedance spectroscopy (EIS) are used to investigate the performance of screen printed primary Zn/MnO2 and secondary Ni/MH batteries. The battery designs under test are coplanar (only Zn/MnO2) and stacked cell configurations.
The performance of screen printed primary Zn/MnO2 batteries will be demonstrated by means of a battery-powered NFC temperature logger, as an application example.
Patrick Rassek – HdM Stuttgart/WCPC
Aqueous electrolyte solutions made of dissolved potassium hydroxide (KOH) are predominantly used in alkaline primary and secondary electrochemical battery systems like nickel-metal hydride or manganese dioxide zinc. The benefits of aqueous KOH electrolytes with concentrations in the range of 35% to 52% are characterized by the high ionic conductivity along with a decreased internal resistance of the batteries and a reduced hydrogen gassing rate compared to battery systems containing acidic electrolytes (e.g. ZnCl2).
When used in printed thin film batteries, aqueous or gelled KOH electrolyte solutions consequently damage the printed metallic current collectors in short periods by corrosive and capacity consuming reactions if not covered by additional electrochemically inert protective coatings. The result of these corrosive reactions is a delamination of the current collectors from the mainly used plastic type substrates with an accompanied malfunction of the printed batteries.
In this study commercially available silver, carbon and graphene screen printing inks with different particle sizes, morphologies and loadings of solids content are evaluated with respect to corrosion resistance by printing battery current collectors and protective layers made of various material combinations and different layer thicknesses. Qualified material combinations with a preferably high corrosion resistance to the KOH electrolyte are identified by performing cyclic voltammetry (CV) experiments in a three-electrode set-up simulating charge and discharge cycles of printed batteries. It shall be investigated, whether the material characteristics or the printed layer thickness of the protective layers has the main impact on the corrosion resistance of screen printed current collectors.
The results of this study can be seen as a further step in improving the performance and life cycle of printed alkaline batteries. The extended corrosion resistance of current collectors is essential for an economical production of printed batteries with longer operating lives.
‘Each year there are millions of tons of waste causing detrimental environmental impacts. Major global leaders are taking on more social responsibility in conserving the planets resources and in turn there is an increasing demand for advances in the prevention and detection of spoilt food and the use of biodegradable or recyclable materials. Additionally, spoilt food can have serious health implications for the consumer.
The development of intelligent and active packaging will enable food to last longer, products tracked throughout the manufacturing and distribution processes, and will aid in the detection of the quality of food to minimise the likelihood of illness.
The overall aim of this project is to design a recyclable or biodegradable packaging system that has the ability to contain a food, ensure that the food is monitored and through use of intelligent and active packaging, extend the product life. Specifically, this project will look at the use of an integrated printed antenna and microbial detection system to communicate with an RFID reader. The packaging systems must be fully printable, with methods reported, and repeatable results are achievable. The system will be miniaturised, yet achieve a high efficiency to match current system as a minimum requirement. The integration of multiple technologies to give the packaging multi-detection capability including moisture control, oxygen control, pH level control, RFID tracking, security checking, and temperature monitoring will be key in this project. The sensors shall cover a small area, have a wide operating temperature range and high efficiency. The printed antennas combined with a silicon chip will transmit the signal from the sensor to an RFID reader. Compatibility, miniaturisation and the distance at which the antenna can be read from will be key considerations with regards to the antenna development. Current testing has been done with silver inks using Flexographic printing. Further work will look at the compatibility of the chip and antenna, and then aiming to miniaturise the chip.’
This presentation will discuss the development of an aerosol jet printed sensing platform integrating elements of silicon and printed electronics. To demonstrate the technology, thin film humidity sensors have been fabricated over the top surface and sides of pre-packaged integrated circuits using a combination of direct-write aerosol jet deposition and drop-casting. The resistive based sensor consists of an aerosol jet deposited interdigitated nano-particle silver electrode structure overlaid with a thin film of Nafion® acting as a humidity sensitive layer. The fabricated sensor displayed a strong response to changes in relative humidity over the tested range (40% RH to 80% RH) and showed a low level of hysteresis whilst undergoing cyclic testing. The successful fabrication of relative humidity sensors over the surface and pins of a packaged integrated circuit demonstrates a new level of integration between printed and silicon based electronics − leading to Printed-Sensor-on-Chip devices. Whilst demonstrated for humidity, the proposed concept is envisaged to work as a platform for a wide range of applications, from bio-sensing to temperature or gas monitoring.
Paul Meredith – Sêr Cymru Chair in Sustainable Advanced Materials
Department of Physics, Swansea University, Singleton Park Swansea SA2 8PP
Organic solar cells and organohalide perovskite solar cells share several common electro-optical operating principles . Both families of devices operate within the thin film, low finesse cavity limit and there are also commonalities in electrodes and ancillary layer materials and structures . It is therefore not surprising that organic and organohalide perovskite solar cells are subject to the same scaling physics considerations, i.e. the physical mechanisms that come into play in retaining performance and efficiency in large area devices, particularly those deposited by printing or other solution processing methods. A simple example of such physics is the limitation in the size of ‘maximum carrier collection path length’ which is dominated by the sheet resistance of the transparent conducting electrode and shown to be ~ 1-2 cm for commonly used 15 ohm/sq indium tin oxide . This phenomenon has meant that the majority of large area organic solar cells are invariably serially interconnected thin strips.
In my talk I will review these scaling physics considerations and explain their basic origin in terms of electro-optics and transport phenomena in both organic and organohalide perovskite solar cells. I will explore how the limitations of scaling physics can potentially be overcome and demonstrate so-called large area ‘monolithic architectures’ which retain their fill factor and hence power conversion efficiency up to 5 cm x 5 cm. Addressing the scaling physics in next generation thin film solar cells is an essential part of endeavors to create viable modules and hence progress low cost manufacturing and ultimately commercialization of printed solar cells. In addition, the same scaling physics comes into play when considering other optoelectronic platforms such as photodetectors and large area lighting.
 Lin et al. Nature Photonics, 9, 106-112 (2015);
 Armin et al. ACS Photonics, 1(3), 173-181 (2014);
 Jin et al. Advanced Energy Materials, 2(11), 1338-1342 (2012).
The versatility of printing technologies and their intrinsic ability to outperform other techniques in large-area deposition gives scope to revolutionize the building integrated photovoltaic (BIPV) manufacturing field. Printing methods are commonly used in conventional silicon-based PVs to cover part of the production process. Screen printing techniques, for example, are applied to deposit electrical contacts on the silicon wafer. However, it is with the advent of third generation PVs that printing/coating techniques have been extensively used in almost all of the manufacturing processes. In particular, printing technology has received significant attention in recent years as a means of realizing large area PVs. Printing offers the promise of allowing the delivery of PVs with low fabrication cost per unit area and is also highly compatible with large area steel substrates. Among all the third generation PVs the thin-film solar cells (TFSC) such as chalcopyrite (CIGS), amorphous silicon (a-Si:H) and organic (OPV) show great potential for BIPVs. In order to greatly accelerate their applications and commercialization in BIPVs large-area functionalised steel substrates are needed.
Printing and coating techniques, such as bar coating and screen printing, were developed for an effective scale-up of the technology. The latter also enables the manufacture of solar modules on semi-rigid/flexible substrates, an option beneficial for many applications and for roll-to-roll production. In this study functionalised steels were fabricated by large scale printing and coating methods in ambient environment (humility ∼50%, temperature ∼20 °C), which produced steel/intermediate layer (IL) lengths as long as 30 cm and 50 m. Furthermore, two different functional layers such as SiOx and solvent resistant dielectric were successfully used to fabricate demonstrators on four “rough” steel substrates and showed good/moderate performance with TFSC. Results of extensive characterisation of two ILs printed onto four steel substrates, such as AISI430 stainless steel, and DX51D bare cold rolled low carbon steel as well as DX51D hot-dip galvanized with Zn or Al which was cold rolled to achieve the desired final thickness, are reported. We have highlighted critical challenges in achieving smooth insulating IL on large scale. This study provides low-cost, large-scale techniques to fabricate large-area functionalised steels with great potential applications in BIPVs.
Graphene has been an area of high interest in recent years due to its well documented thermal, mechanical and electrical properties. Graphene nanoplatelets consist of between 5-100 layers of graphene and could provide a cost-effective alternative to single layer graphene. These graphene nanoplatelets are typically 50nm thick and up to 5um long and this high aspect ratio gives the platelets a very high specific surface area which when coupled with carbon’s relative inert nature give the platelets a high tendency to agglomerate due to van der Waals forces. This can lead to the formation of doublets or higher multiplets which increase viscosity as they trap matrix material increasing the diversion of flow within the suspension. Therefore, the ability to disperse these materials is of high importance if they are to be utilized in a mass manufacture process such as printing. One way of improving the dispersion of these platelets is to modify the surface of these nanoparticles, adding chemical groups to the surface to create a charge of long enough range to overcome the short-range van der Waals forces, or to add chemical groups that have a high chemical affinity for the polymer, allowing the polymer to fully wet onto the surface of the particles helping to hold them far enough apart to overcome the van der Waals attraction. In plasma functionalisation particles are passed through a high energy plasma, within a vacuum, which bombards the surface removing any contamination and creating sites for new functional groups to attach. By changing the plasma process gas, you can add different chemical groups to the surface of the GNPs and this paper looks to use rheological measurements and print analysis to examine the effect that the addition of different functional groups has upon the dispersion and subsequent performance of inks incorporating graphene nanoplatelets.
As printed electronic devices become increasingly capable it becomes crucial to create affordable and robust connections between substrate and the power sources and control electronics required for them to operate. Many of these devices are connected to conventional electronics and the interface between the substrate and the printed circuit board (PCB) can be a stumbling block in operation.
We’ve worked on a number of solutions for allowing printed circuits to be connected either temporarily for testing purposes, or permanently in the creation of complete devices. This presentation will showcase a number of connection methods and highlight key design considerations when creating a hybrid printed and conventional electronic devices.