Electrostatic, rotating bell (ESRB) application is one of the most important coating application techniques for industries with demanding specifications for optical attractiveness of coatings, such as automotive. The ESRB process involves production of droplets using a high-speed rotating bell, which are subsequently transported to the substrate being coated via shaping air [1-3]. An electrical potential is applied between the bell and the substrate which further helps droplet atomization and transport. This research investigates the effects of inertia, centrifugal force, drag force, and electrostatic force on the atomization mechanism and particle size distribution using an automotive OEM base coat formulation. Coating flow rate (CFR), shaping air flow rate (SAFR), bell speed (BS), and electrostatic potential (EP) were used as primary parameters to create various atomization conditions and particle size distributions. The atomization mechanism, ligament formation, and particle size distribution were measured using high-speed laser shadowography and image processing. The effects of governing forces and particle size generated on efficiency of droplet transfer to the substrate and optical appearance of the coatings were studied to generate operating windows for optimum process efficiency and appearance. 陰影法激光粒徑分析儀