Flexible pigment-nanocellulose substrate for printed electronics with good thermal tolerance

In printed electronics, most of the components and structures are printed on substrates made of synthetic materials, such as plastics, ceramics or silicon. Here we present a micro/nanocomposite substrate, which consists of inorganic pigment fillers and nano-fibrillar cellulose (NFC) and demonstrate the feasibility of the substrate for printed electronics applications. The composite structure can contain up to 90% pigment filler being still mechanically stable and flexible. Heat and pressure are used to make the surfaces smooth and glossy with a plastic-like feel. The resulting surfaces are smoother than the smoothest paper surface in the market (photo paper), and the dimensional stability as a function of moisture is significantly better than for traditional paper. The composite sheets have a good thermal tolerance because of high amount of stable inorganic pigments. Additional benefit of the substrate is its good printability. In case of the pigment-NFC substrates, the solvent of the ink can penetrate to the structure and there is no significant spreading of the ink. Two pigment types were used to address the effect of raw materials on substrate smoothness and porosity. Precipitated calcium carbonate (PCC) gives smoother surface than kaolin pigment. However, the structure formed using PCC is more porous leading to a weaker conductivity of printed structures. The effect of different pigment particle sizes on substrate properties will be discussed in a more detail. We will also demonstrate the feasibility of the pigment-NFC substrate for printed electronic structures (RFID tags). Characteristics of the printed structures will be presented and compared to the ones printed on reference plastic substrates. The combination of a good dimensional stability with a low surface roughness, a high thermal tolerance, low material costs and good printability makes these biodegradable substrates potential for printed electronics applications. In particular, they could replace oil-based plastics in some applications.