Plasma-assisted Ball Milling for Surface Activation and Dispersion Enhancement of ATO Nanoparticles for Near-Infrared-Reflective Automotive Window Films

To reduce cooling energy consumption in mobility applications, window films that simultaneously provide high visible-light transmittance and effective near-infrared shielding are required. In this study, we aimed to improve the dispersion stability of antimony tin oxide(ATO) nanoparticles, a near-infrared-reflective material, with target performances of over 60% visible-light trnasmittance and over 40% near-infrared reflectance. Although the primary particle size of ATO is approximately 40 nm, its high surface energy promotes severe agglomeration, which can increase film haze and cause optical non-uniformity. To address this issue, a plasma-assisted ball milling process was applied. ATO particles and zirconia beads were placed ina chamber and subjected to plasma treatment. The treated particles were subsequently dispersed by stirring using methyl ethyl ketone(MEK) as the solvent and BYK-180 as the dispersant. Paritlce size was analyzed by dynamic light scattering. Under the same stirring conditions, the average particle size was approximately 200 nm without plasma treatment, whereas it decreased to approximately 120 nm after plasma treatment at 500 W for 5 min. This reduction is attributed to the removal of surface contaminants, improved wettability induced by plasma treatment, and the disruption of agglomerates by ball milling. These results demonstrate that plasma-assisted ball milling is an effective process for enhancing the dispersion of ATO nanoparticles and has potential for application in the fabrication of transparent near-infrared-reflective window films.