With electrostatic painting, the paint molecules are positively charged because they leave the spray nozzle in an electric field that directs them to the negative charge of the metal surface. The attraction between positive and negative molecules is 75 times stronger than gravity, the pull is so strong that even the lightly sprayed paint over or away from the metal surface will try to change direction to land on the metal.
The paint molecules are attracted by the highest load, the sprayed drops will automatically go into the area without paint to create a uniform surface.