Given that they either involve a string of process steps or large quantities of sometimes expensive raw materials, the standard processes for manufacturing flexible touchscreens are considered costly and laborious. Using photochemical metalization and printing (gravure printing, inkjet printing) of transparent conductive oxides (TCOs), the INM has therefore developed new processes that save a great deal of time and money. Visitors can discover the results for themselves at HANNOVER MESSE 2019.
"Most processes for conductor paths are subtractive. Metal is first applied over the entire surface and the excess metal is removed in further process steps," explains Peter W. de Oliveira, head of the InnovationCenter at the INM. "These classic processes, such as sputtering in a high vacuum and subsequent lithography, consume large amounts of silver. Our additive processes go the other way round, with conductor tracks being printed or deposited only where they are needed. Expensive high-vacuum technology isn’t required, which saves time and money," de Oliveira continues.
In another innovative printing process, the INM researchers use nanoparticle inks containing TCOs, such as indium tin oxide (ITO), for inkjet or gravure printing. "We use the TCOs to produce nanoparticles with special properties," says de Oliveira, adding: "The TCO ink is then produced by adding a solvent and a special binder. Not only does the binder ensure that the TCO nanoparticles adhere well to the film, it also increases the flexibility of the TCO coating - which ensures the conductivity is maintained when the films are bent. This makes it possible to produce highly flexible transparent conductor structures, for touch sensors or displays for example, in one simple printing process."