Strong adhesion of polyvinylpyrrolidone-coated copper nanoparticles on various substrates fabricated from well-dispersed copper nanoparticle inks

In this study, we obtained copper nanoparticle (Cu NP) films exhibiting low resistivity and strong adhesion with respect to various substrates by drop-casting the Cu NP ink with polyvinylpyrrolidone (PVP) after being sintered at 250 °C. PVP functioned as a dispersant in the ink and as an adhesive at the interfaces between the Cu NPs and the substrates. Aggregation of the Cu NPs in the ink resulted in the creation of a porous NP film after drop-casting, and the contact area between the PVP-coated Cu NPs and the substrates was small, resulting in poor adhesion. The nuclear magnetic resonance (NMR) relaxation measurement of the Cu NP ink, which can determine the dispersibility of the undiluted Cu NPs, revealed that long dispersion time and optimal PVP concentration were required to produce a well-dispersed Cu NP ink with PVP. The well-dispersed ink resulted in dense Cu NP films and a large contact area, demonstrating strong adhesion. The ink was applied to various substrates, including glass, polyimide, polyphthalamide, liquid crystal polymer, and polytetrafluoroethylene, and these substrates, except polytetrafluoroethylene, showed strong adhesion. The weak adhesion of polytetrafluoroethylene can be attributed to the small surface energy change between the PVP-coated Cu NPs and the polytetrafluoroethylene substrate owing to the low surface energy of polytetrafluoroethylene. The well-dispersed Cu NP ink with PVP is expected to be applied to the production of adhesive Cu wiring on various substrates for printed electronics, except substrates exhibiting low surface energy such as polytetrafluoroethylene.