The idea of printing circuits on a flexible carrier material such as film or paper is nothing new - but it does offer certain advantages. For a start, a process like this is usually economical and practical but, more importantly, it enables users to create extraordinary designs with curved lighting or input elements. All the same, implementing this idea in a practical and reliable process requires special materials that won't be damaged during the printing process and will continue to exhibit good conductivity even when their substrate is undergoing flexing. Researchers at the Leibniz Institute for New Materials (INM) have therefore developed hybrid inks that can be used in a printer or pen to create circuits on film or paper and are also ready to use immediately on drying - without requiring any further sintering. The developers themselves are on hand at HANNOVER MESSE 2017 to take visitors through their results in detail and showcase a whole range of options.
The special properties of the hybrid inks can be attributed to the complementary benefits of polymers and metallic nanoparticles. Gold or silver nanoparticles are coated with organic, conductive polymers and are then suspended in mixtures of water and alcohol. "Metal nanoparticles with ligands are already being used to print electronic circuits," explains materials scientist Professor Tobias Kraus. These shells mostly had to be removed by a sintering process because, although they control the arrangement of the nanoparticles, they impede conductivity. According to the experts, this is difficult when working with carrier materials that are sensitive to temperature such as paper or polymer films since these would be damaged during the sintering process. "Our new hybrid inks are conductive in the as-dried state, are mechanically flexible, and do not require sintering", explains Professor Kraus.