Environmentally Friendly Printable Piezoelectric Inks and Their Application in the Development of All-Printed Touch Screens

Piezoelectric inks have been developed based on poly(vinylidene fluoride-co-trifluoroethylene), PVDF-TrFE, dissolved in the environmentally friendly solvent N,N0-dimethylpropyleneurea (DMPU). The inks were prepared for different printing techniques, including doctor-blading, spray-printing, and screen-printing, representing therefore a relevant step for the additive manufacturing of sensors, actuators, and touch screens, among others. The rheological properties of the inks demonstrate that DMPU is a good solvent for this polymer and allows one to obtain dense piezoelectric films with the different printing techniques, showing also similar physicochemical and electrical properties. The highest piezoelectric coefficient |d33| = 19 pC/N is obtained for films processed by screen-printing, the piezoelectric coefficient being stable over more than 6 weeks. The corresponding PVDF-TrFE films were applied in the development of a touch screen by additive manufacturing, with two screen-printed silver electrodes in the form of an array of touch buttons. The all-printed piezoelectric touch screen allows easy fabrication and, therefore, improved integration into a variety of substrates, including flexible ones.