Nanoparticle deposition from liquid flame spray onto moving roll-to-roll paperboard material

Nanostructured coatings have been prepared on a flexible, moving paperboard using deposition of ca. 40-nm-sized titanium dioxide nanoparticles generated by a liquid flame spray process, directly above the paperboard, to achieve improved functional properties for the material. Properties such as surface wettability can be extensively improved by a thin layer of nanoparticles on the substrate. Owing to the vulnerability to heat, the substrate needs to be moved rapidly through the flame. This, on the other hand, generates a setting for a roll-to-roll coating process, which favors upscaling of the method. In this article, we characterize the flame process for nanoparticle coating and quantify the operational window for this method. The amount of deposited material as a function of substrate speed through the flame is discussed. Although the thermophoretic flux of nanoparticles is estimated to be very high from the hot flame onto the cold substrate, other factors were observed to limit the deposited amount of particles. Total mass yields of 5%-20% of the injected precursor material into the titanium dioxide nanocoating on the paperboard were achieved. With these yields, a highly hydrophobic surface was obtained by a mass loading of 10-50 mg/m(2) of titanium dioxide on the paperboard.