Abstract
A new substrate containing cellulose nanofibrils and inorganic pigment particles has been developed for printed electronics applications. The studied composite structure contains 80% fillers and is mechanically stable and flexible. Before drying, the solids content can be as low as 20% due to the high water binding capacity of the cellulose nanofibrils. We have studied several drying methods and their effects on the substrate properties. The aim is to achieve a tight, smooth surface keeping the drying efficiency simultaneously at a high level. The methods studied include: (1) drying on a hot metal surface; (2) air impingement drying; and (3) hot pressing. Somewhat surprisingly, drying rates measured for the pigment-cellulose nanofibril substrates were quite similar to those for the reference board sheets. Very high dewatering rates were observed for the hot pressing at high moisture contents. The drying method had significant effects on the final substrate properties, especially on short-range surface smoothness. The best smoothness was obtained with a combination of impingement and contact drying. The mechanical properties of the sheets were also affected by the drying method and associated temperature.
Highlights
The growth of the printed electronics market is based on new low-cost materials and products.Recently, novel bio-degradable cellulose nanocomposite substrate materials have been introduced that compete well in price and material properties against oil-based plastic substrates [1,2]
In laboratory-scale experiments, it was shown that the pigment-cellulose nanofibril (PCN) substrate can be dried using conventional drying methods, such as contact drying and air impingement drying methods
Despite the very large bound water content of the cellulose nanofibrils (CNF) gel, the estimated drying rates for the PCN substrate are comparable with the drying rates of typical board with the same external drying conditions
Summary
The growth of the printed electronics market is based on new low-cost materials and products. We study several available drying methods and their combinations that are in use in paper and board technology In these industries, water from the web after the forming section is removed in the press section and the subsequent drying section. An evaporation rate of 100 kg/m2/h is a common level for this type of dryer [10] Another very effective method for removing moisture and improving mechanical properties is press drying. Drying rates of 100–200 kg/m2/h are possible, depending on the process parameters [12] This investigation was concentrated on determining the final PCN substrate properties and the drying rates for contact drying, impingement drying and press drying at moderate temperatures. We found a relatively large variation in the measured surface and mechanical properties depending on the drying method
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