Chemistry Evaluation of Printed Inks for Harsh Environments

M. Kolel-Veetil, A. Schrand, R. Siefert, C. Neff and E. Elston
U.S. Naval Research Laboratory, United States

Keywords: advanced, manufacturing, 3D, PEEK, fuze

Using advanced manufacturing techniques, we recently examined the resiliency and radio frequency performance of two commercially available conductive inks (DuPont CB028 and KA801) printed onto a radar transparent substrate (poly ether, ether ketone; PEEK) for use in mechanically and thermally harsh environments. As CB028 was found to perform better than KA801, we have further characterized the material properties of these two inks to understand the factors that possibly lead to such enhanced performance. A careful material analysis of the two proprietary inks suggests that the differences in the nature of the binding resin and additive solvents in their matrices are likely responsible for the observed differences in performance. Such differences impact cohesive interactions among the matrix components during the curing of the inks and also interfacial interactions of the evolving cured matrix with PEEK. For example, the solvent additives used in KA801, namely, butyl carbitol acetate, dimethyl adipate and diethyl adipate have boiling points of 245oC, 227oC and 245oC, respectively, while that used in CB028, namely, dipropylene glycol methyl ether (DGME) has a boiling point of only 190oC. Such boiling point differences can affect the mobility of Ag particles during curing and also ink-substrate adhesion. Also, the Kapton polyimide resin used in KA801 can introduce greater interfacial stresses at the ink-substrate interface than the polyether resins, with PEEK-compatible –C-O-C- functional groups, present in CB028. Thus, such differences in solvent additives and resins can greatly dictate the curing profile as a function of the glass transition temperature of PEEK (~145oC) while obtaining percolation limit-driven conductive silver traces as observed in the recent evaluation, i.e. 1h at 150oC for CB028 vs. 3h at 150oC for KA801. Based on such studies, we have initiated the development of a Kevlar-based ink comprising silver nanoparticles-coated with poly-vinyl pyrrolidone (PVP). The reaction scheme for producing such PVP-coated silver nanoparticles and nanoplates is shown below. Results from the above studies will be presented.