Rheological properties and screen printability of UV curable conductive ink for flexible and washable E-textiles

As a critical component for the realization of flexible electronics, multifunctional electronic textiles (e-textiles) still struggle to achieve controllable printing accuracy, excellent flexibility, decent washability and simple manufacturing. The printing process of conductive ink plays an important role in manufacturing e-textiles and meanwhile is also the main source of printing defects. In this work, we report the preparation of fully flexible and washable textile-based conductive circuits with screen-printing method based on novel-developed UV-curing conductive ink that contains low temperature and fast cure features. This work systematically investigated the correlation between ink formulation, rheological properties, screen printability on fabric substrates, and the electrical properties of the e-textile made thereafter. The rheological behaviors, including the thixotropic behavior and oscillatory stress sweep of the conductive inks was found depending heavily on the polymer to diluent ratio in the formulation. Subsequently, the rheological response of the inks during screen printing showed determining influence to their printability on textile, that the proper control of ink base viscosity, recovery time and storage/ loss modulus is key to ensure the uniformity of printed conductive lines and therefore the electrical conductivity of fabricated e-textiles. A formulation with 24 wt% polymer and 10.8 wt% diluent meets all these stringent requirements. The conductive lines with 1.0 mm width showed exceptionally low resistivity of 2.06 × 10−5 Ω cm Moreover, the conductive lines presented excellent bending tolerance, and there was no significant change in the sample electrical resistance during 10 cycles of washing and drying processes. It is believed that these novel findings and the promising results of the prepared product will provide the basic guideline to the ink formulation design and applications for screen-printing electronics textiles.