by Prof. Wim Deferme, University of Hasselt
Printed electronics (PE) have developed into a megatrend in packaging, food, pharmaceutical, automotive and construction industries. Their applications are multiplying as consumer interaction, instant feedback, traceability or anti-counterfeit features are seamlessly integrated in new product lines. However, PE’s production is still expensive and often based on stand-alone solutions or specific application scenarios. That is why 40 research centres and companies joined in the PAPERONICS project to investigate the future of efficient, affordable and sustainable printing of electronic components directly on paper and plastics. Today, we present the project’s results.
Figure 1: Application fields of printed electronics (modified from Quad Industries[1])
PAPERONICS was launched within the European CORNET (Collective Research Networking) framework and brought together organisations active in the field of paper, labels, cardboard, ink and printing technology, RFID tags, scavenger and encapsulation technology, software applications, design, as well as end users of packaging. The meetings took place between 2019 and early 2021.
As project’s initiators we propose a gradual shift of smart packaging functionality from external label elements to electronics fully printed on the package piece. This transition, presented in Figure 2, relies on state-of-the art components and printing technologies.
Today’s standard RFID smart packaging flow has little in common with the actual packaging industry. Only a small part of the process is performed in the packaging lines as the tags are generally supplied as labels on rolls by traditional RFID manufacturers. The future scenario would entail a complete flow performed by the packaging companies. The long-term vision is to enable the manufacturing and integration of all functional electronic components (e.g. RFID’s, sensors, signage) directly on paper or plastic packaging surface within the printing or conversion lines.
Figure 2: Vision and roadmap for smart packaging applications.
Therefore, PAPERONICS aim was to facilitate involvement of the traditional packaging industry with the supply chain of new smart applications. Figure 3 shows a schematic supply chain for smart packaging with an exemplary RFID tagged package. We claim that some steps can already be performed by the packaging manufacturer in collaboration and close feedback loop with his partners from the value chain.Figure 2: Vision and roadmap for smart packaging applications.
Figure 3: Proposed evolution of the smart packaging flow using RFID tagged package as example.
PAPERONICS chose paper as the printing substrate because of its advantages such as recyclability, thermal stability and stiffness. On the other hand, paper’s surface roughness and porosity can highly influence of printing ink’s conductivity. That said, paper has the potential to deliver low-cost, innovative applications which can serve multiple purposes within intelligent packaging[2].
Our first challenge was the selection of paper substrates from the 76 samples provided by project’s industrial partners. All substrates were screened for surface roughness and air permeability as these properties determine the final conductivity of the printed functional ink. Subsequently, two nanosilver inks were screen-printed on all substrates. The third nanosilver ink was applied by roll-to-roll screen printing and finally, the fourth nanosilver ink was tested with aerosol jet printing. Based on the measured paper properties, its thermal stability (after curing of the ink) and sheet resistance of the ink, as well as some visual and mechanical aspects, 13 substrates were selected for further research incl. morphological studies (at Fraunhofer IVV) and recyclability (Papiertechnische Stiftung-PTS) (Figure 4).
Figure 4: Sheet Resistance as function of average Surface Roughness of 5 ‘Orgacon SI-P2000’ (▲, A) and ‘Loctite ECI 1011’ square prints (●, B). Green symbols indicate the 13 paper samples that were selected for further investigation
Various printing technologies available at the facilities of IMO-IMOMEC at Hasselt University, AML at KU Leuven, PM at Chemnitz University of Technology, LabelTech, Chiyoda and VIGC were applied, incl. screen printing, aerosol jet printing, offset, rotogravure and flexo printing to investigate which inks and techniques were compatible with the fiber-based substrates. The final selection was used in the development of three demonstrators.
The first demonstrator was a customer relationship packaging in which a printed antenna (by IMO-IMOMEC) was combined with a thin-film IGZO microchip (imec) into an RFID label (operating at 13.56 MHz) – all to be integrated in durable and reusable cardboard boxes. For this demo FETRA provided paper, Agfa and Henkel supplied ink, Roartis provided the conductive adhesive and Quad Industries connected antenna and microchip to the smart label. This label was then integrated within an intelligent packaging.
A survey yielded ideas about track and trace applications, product authentication and consumer interaction. Finally, a foldable cardboard box with RFID label to be used for third-party e-logistic companies was prepared as the final demonstrator. Necessary software tools were developed in close collaboration with I4CRM allowing to follow up the package status at any time in the logistics cycle. The cardboard and the tailoring of the prototypes were delivered by Ropak. The quality of carton and the stability of different boxes was evaluated in the labs of MPR&D IMO-IMOMEC to investigate whether the final box can withstand several distribution cycles.
Figure 5: Above left: Schematic of the idea and application; Above right: Foldable box; Bottom: the integrated antenna with the RFID tag and the principle of communication
The second demonstrator was an anti-tampering packaging. Here, a printed breakage sensor was combined with an organic solar cell, electrochromic display and a supercapacitator (for extra energy storage). Smart label was again integrated in a cardboard box which showed “genuine” on the display as long as the sensor was not broken. As soon as the box opened, the current in the label was interrupted and the text disappeared from the display.
Protection against oxygen and water vapour was required for the electronic components so an encapsulation strategy was explored by coating the paper with a SiOx barrier layer and incorporating of active oxygen and water absorbers. This demo was developed by the Printing and Media Technology Group from the Chemnitz University of Technology (printed electronics and integration) and Fraunhofer-IVV (barrier coating) in collaboration with Grünperga, Agfa, Felix Schoeller Group, Saralon and Koehler Paper.
Figure 6: PAPERONICS anti-counterfeiting label in a demonstrator package with on the top left the integrated solar cells and on the top right the printed supercaps
The third demonstrator envisaged a temperature threshold indicator with a temperature sensor and an antenna, both printed on paper and then connected to each other and to an IGZO RFID microchip (prepared by imec).
Temperature tracking is critical due to the degradation mechanism of various goods (e.g. food or medicine). Demonstrator’s working principle was based on an irreversible change of electrical characteristics at a certain threshold temperature. Ideally, a material system would change its state from (semi-)conductive to insulating, or vice versa. For this specific indicator, the polymerization pathway of polyaniline has been studied to create a temperature sensitive functional print.
The structure of the temperature threshold indicator (Fig. 7) consisted of three different layers: (a) silver print of interdigitated electrodes and RFID antenna, (b) non-conductive emeraldine base coating and (c) thermo-responsive layer which released an acidic solution by exceeding the threshold temperature.
Figure 7: Layer structure of the temperature threshold indicator
The acidic solution was integrated in a thermo-responsive layer and deposited on top of the emeraldine base coating. By exceeding the threshold temperature, the acidic solution was released and shifted the indicator from insulating to (semi-)conductive. For this specific thermo-responsive layer, three material systems were investigated:
- Thermo-responsive nanocapsules
- Diffusion label based on acidic melting point
- Visco-elastic polymer
The proof-of-concept, without the thermo-responsive layer, was developed with three printing technologies, i.e. screen printing, ultrasonic spray coating (IMO-IMOMEC at UHasselt) and aerosol jet printing (AML at KU Leuven) and after connecting with the microchip (imec) validated on its functionality.
An additional aspect that was studied by another project partner, the Papiertechnische Stiftung (PTS) for all three demonstrators was recyclability. Whether smart packaging is suitable for recycling basically depends on: 1) the availability of sorting and recycling infrastructure; 2) the possibility to sort the packaging from a certain waste stream and to separate the (electronic) components; and finally 3) whether specific components or certain chemicals may prevent use after recycling. The tests that were carried out show that recycling printed antennas produced a recyclate with visual impurities. This negative effect was even more pronounced with coated paper. If a smart cardboard packaging is recycled via the general flow, this would probably have little effect due to the low ratio of electronic components (eg. RFID tag) versus the amount of fiber-based material of the cardboard box. However, regulations regarding cardboard packaging and electronics will have to be followed closely.
In conclusion, PAPERONICS has resulted in three different smart packaging applications which can encourage companies to think about similar and other applications enabled by printed electronics. Moreover, the cooperation for developing the demonstrators encouraged all involved to set up new networks and connections in order to realise new joint developments related to or sprouting from the PAPERONICS project. Our aim was to inspire companies in the paper industry that paper as a substrate can also be used in printed electronics. Hopefully, they have found the way to companies that can offer smart solutions for this.
Figure 8: Overview of potential integration of components in future-proof smart packaging applications
PAPERONICS results will be presented and discussed during a dedicated session at the Industrial Print Integration conference on 23-24 November 2021 at Dorint Kongresshotel Düsseldorf/Neuss. To register for the conference please visit www.ipi-conference.com
[1] QuadIndustries. "The building stones for smart products: printed electronics." (accessed May, 2021).
2 K. L. Yam, P. T. Takhistov, and J. Miltz, "Intelligent Packaging: Concepts and Applications," Journal of Food Science, vol. 70, no. 1, pp. R1-R10, 2005.
