By Dr. Kasha Ghaffarzadeh, CEO, TechBlick
Printed electronics are everywhere and can be found in applications as diverse as a smart diaper to a precision missile. This article will highlight some application and technology development examples for roll-to-roll (R2R) printed electronics and the end-use markets they serve, including healthcare, packaging, photovoltaics, displays, and beyond. The common thread here is R2R printing of electronics regardless of printing technique, e.g., screen, flexo, gravure, slot-die, etc. The applications reviewed herein are presented randomly and follow no particular order of importance. The images and examples below are extracted from 2021 presentations offered by this firm, which is a global information resource for printed, flexible, hybrid, and in-mold electronics.
Editor’s Note: For an expanded version of this article, see www.convertingquarterly.com and search for the headline.
Medical sensors
To begin, many medical sensors are already printed. For example, glucose test strips are printed, often R2R. But given that they are a declining market thanks to the rise of continuous glucose monitoring (CGM), we will not review them further here.
Large volumes of medical sensors are regularly screen-printed roll-to-roll. For example, EKG electrodes are R2R-produced in significant quantities, e.g., >1 million units/year. An incontinence sensor is commercially R2R screen-printed using conductive carbon on a stretchable non-woven material. It is an advancement of the art of functional R2R screen-printing to be able to print using stretchable inks onto such thin and even stretchable substrates without creasing or improper stretching and without shrinking during the ink-curing steps.
Rotary screen-printing also is the basis of more advanced wearable medical sensors: smart skin patches. Figure 1 shows such a such product, involving rotary screen-printing of stretchable conductive inks, dielectric inks, silver chloride inks, and more. These smart electronic skin patches are the basis of a wearable-sensor platform enabling the measurement of vital signs. The patches can start with measuring heart rate and respiration and move on to other physiological parameters.
FIGURE 1. Schematic of a wearable medical sensor (Source: Quad Industries)
Another interesting recent commercial success story in R2R printed electronics is in a grade-I medical product developed by InnovationLab GmbH (iL) for Dr. Jean Bausch GmbH & Co. KG. This digital articulating paper for digitally measuring the topography of teeth uses 60-μm thin sensors R2R-printed with piezoresistive and silver inks, enabling digital measurement of 256 pressure levels.
The pilot R2R machine at iL can print five layers in-line on a 330-mm web with lengths up to 17 meters. Furthermore, the machine integrates various curing (hot-air, IR, UV, hot embossing) as well as converting (laminating, slitting, die & kiss-cutting) modules. While this system can run up to 160 serial mpm, the actual device is not produced at this speed. The production machines, by iL’s partner Heidelberger Druckmaschinen AG, can handle 440-mm webs at much higher speeds thanks to a long (25-meter) drying section.
Smart pharma packaging
The primary task of smart pharmaceutical packaging is to improve a patient’s medication adherence. Jones Healthcare Packaging has been actively developing this technology since 2013 and is now commercializing with real samples being tested by patients. The initial development was based on a narrow-web, pilot R2R printer (see Figure 2) using silver/carbon inks on a PET substrate. The current product is flexographically printed using carbon inks on paper substrates. The printed carbon circuitry is shown in the middle image of Figure 2. Now a first-generation product, in the future, functional electronics as well as printed displays could be integrated into the smart packaging itself.
FIGURE 2. Jones Healthcare Packaging’s smart pharmaceutical packaging aims to improve a patient’s medication adherence. (Source: Jones Healthcare presented at TechBlick March 2021)
Photovoltaics
Organic photovoltaics (OPV) have been in commercial development for 20 years or more. Many may recall the heady days of Konarka (est. 2001), which went bankrupt in 2012 after having raised some $170 million. Technology development continued without pause despite this setback. Now, both R2R-printed and R2R-evaporated approaches are reaching a high level of technological maturity.
The Brazilian firm Sunew has taken steps to scale up production. Its line consists of 5 print stations, each laying down one layer in the OPV stack. There are 32 print lines across the 500-mm-wide web, and the length can be up to 1.5 km. Sunew can maintain thickness uniformity of +/-2% across the web width. Note that a major challenge in scaleup from lab results is the control of interlayer interfaces and the morphology of the donor-acceptor active layer. Note that other firms such as Armor (R2R coating) and Heliatek (R2R-evaporated tandem cell) also scaling up the process in speed and width.
Of course, many these days actively pursue perovskite photovoltaics (PePV), which have shown the fastest learning curve of all PV technologies. These materials also can be printed. For example, Energy Material Corp (EMC) is scaling up fully in-line, unwind-to-rewind, R2R production of PePV. Figure 3 shows the ongoing transition from pilot to large-scale production, highlighting the ambitious scale of the operation. The production line will involve R2R printing on 1.5-meter-wide webs of 100-µm thick flexible glass at web speeds approaching 30 mpm. The ambition is to have a R2R-printed PePV factory able to produce 20 million sq meters/yr.
The transparent conductive layer includes a R2R metal mesh printed using R2R flexography that employs Kodak technology. The metal-mesh film (left image in Figure 3) is printed on 100-µm Corning glass at 60 mpm. The linewidths are proprietary, but the Kodak process can print sub-10-µm linewidths reliably at high web speeds.
FIGURE 3. Perovskite photovoltaics [Source: Kodak (left) and EMC (right)]
Displays
R2R printing for electrochromic displays also has moved toward mass production. The Ynvisible production line, based on R2R screen-printing turns out multilayer displays consisting of a silver layer, counter electrode, electrolyte, symbol layer, electrochromic layer, and a graphic layer – all sandwiched by a top and bottom moisture-barrier substrate. To reduce production costs, converting and testing take place in-line R2R, which is an important step forward.
These printed electrochromic displays are suited for simple segmented displays targeted at high-volume IoT applications. The displays are <300 µm thick and can be bent to a radius of 10 mm. Furthermore, there are very low power (1µW/cm2) as they can retain their state for 15 min or longer before requiring a refresh. Powered at 1.5-3.0V, the displays can be driven using simple microelectronics; this means that they could be powered by printed batteries and printed OPVs. In the latest developments, a graphical layer can be added to give a sense of color so the displays are on brand.
R2R printing is and can be used in other types of more complex displays. In quantum dot (QD)-LCD displays, the enhancement QD film in a commercial product is R2R slot-die coated.
Conclusion
In summary, we demonstrate that R2R printed electronics really are everywhere with numerous and growing end-use applications across many markets. It is a vibrant and fast-evolving landscape of new technology, ecosystems and material & production processes.
Editor’s Note: Part 2 of this article continues the discussion of breakthrough developments in displays, as well as progress in fine-line R2R printing, RFID printing, automotive applications, and flexible hybrid electronics.
Kasha Ghaffarzadeh, CEO of TechBlick (Frankfurt, Germany), holds a Master’s degree and Ph.D. from the University of Cambridge and University College London, respectively. During his Ph.D., he worked with Samsung (SAIT) to produce and characterize state-of-the-art, amorphous metal-oxide TFTs. Kasha spent more than a decade leading a global analysts team focused on emerging technologies at IDTechEx. He now oversees the curation of TechBlick's world-class year-around program of learning, training, and networking agenda for its 1,000+ global members. Kasha and his team scout the technology landscape and the global ecosystem to curate presentation agendas. He is a regular presenter at conferences in his areas of expertise, delivering keynotes as well as masterclasses. His work was published in leading academic journals such as Nature, receiving more than 1,000 citations. Kasha can be reached at +49-17-661-70413, email: khasha@techblick.com, www.techblick.com
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