Digital Roll-to-Product Manufacturing of Flexible Printed Smart Systems
The digital roll-to-product manufacturing of flexible printed smart systems requires comprehensive know-how, technology expertise and a suitable production line with all the appropriate manufacturing techniques. In this respect, Fraunhofer ENAS carries out extensive research and development to demonstrate for the industry a top-notch technology concept based on an approved pilot production line for the manufacturing of components of printed smart systems: printed conductive paths, antenna systems, and sensors. Particular attention is paid to the combination of digital, material-efficient printing processes and high speed sintering techniques.
The installed pilot line microFLEX™ (Fig. 1) consists (from left to right) of an unwinder, a screen printing unit (spgprints®), a digital inkjet module (Fujifilm Dimatix SAMBA™ head technology), a UV-LED array, an IR curing unit (Heraeus), a digital intense pulsed light (IPL) photonic sintering device (Novacentrix® Ltd.) and a rewinder.
One of the major competences of the department Printed Functionalities is the processing (printing and sintering) of functional inks (e.g. based on metal particles and polymers). These inks require a special, often technologically complex treatment after printing to achieve the desired functionality like electrical conductivity, semi-conductivity, or insulation.
High-speed functionalization/sintering of inks
Functional inks consist of several ingredients: e.g. metal nano particles to generate conductivity, additives (e.g. polymers) to stabilize the ink, and solvent mixtures to tune the viscosity to the chosen printing technology. For the targeted functionality of electrical conductivity the metal nanoparticles are essential, while all other ingredients are solely determined by the printing process itself but they usually decrease or even prevent the conductivity. Therefore, these ingredients have to be removed from the printed layer. Thermal or IR treatment can eliminate most of the solvents. To get rid of the remaining polymers more sophisticated technologies like IPL are necessary. These technologies help to fuse the isolated nanoparticles to solid metal layers by sintering which are electrically conductive.
Our solution is the combination of near infrared (NIR) and intense pulsed light (IPL) photonic sintering technology in one roll-to-product manufacturing line to interlink the isolated metal nanoparticles. By this combination of sintering technologies a defined energy is applied to the printed pattern on a micro to millisecond timescale. This ensures a heat up and melting of particles generating a conductive pattern.
The short time scale for this sintering process allows a high-speed production of flexible printed smart systems with a throughput of 1 m²/min.
Ongoing research and development
Driven by our customer needs, research and development is focused on:
Smart systems applications on flexible and temperature sensitive substrates like polyethylene terephthalate – PET: The challenge is the PET substrate temperature limitation of only 110 °C which requires new methods for sintering of printed patterns which must be done at temperatures of up to 1000 °C (functional ink dependent).
The printability of new functional inks: The challenge is the adjustment of printing process parameters in respect of ink parameters like viscosity, particle sizes, binders as well as the adhesion on the substrate.
Sintering techniques for new functional inks and different kinds of flexible substrates: The challenge is to obtain specified functional layers with reliable adhesion to the substrate.