A spray painter propels a cloud of atomised paint at a surface to be painted. Because the paint particles are spread out, the paint creates a uniform covering, getting on everything in front of it fairly evenly, but normal spray painting is not perfect. The cloud may be denser in the middle, creating an uneven paint job. There is also the problem of overspray - clouds of paint particles that get in the air, posing a health problem and getting on things that they aren't meant to. An electrostatic spray painter helps to reduce both of these problems
Charging the Paint
There are several different ways that the paint can be electrostatically charged. In some systems, a negative electric charge is applied to the paint while it is actually in the reservoir. In other systems, the charge is applied while the paint is in the barrel of the spray painter gun. Compressed gas propels the paint through the gun, where it rubs against the side, gaining a static electric charge. In some systems, the paint is propelled straight through an electric field, which charges it. Whatever the system, by the time the paint is in the air is on its way to the target, it has a negative electric charge.
The particles of paint all have the same electric charge, which makes them repel each other. The nearer the particles are too each other, the more they repel. This helps to even out the paint particles to get a consistent cloud of paint which will coat the target evenly. The cloud of paint is usually sprayed at something metal, such as a car door or bike frame. The metal object is grounded - electrically connected to the ground. Because the paint particles have a charge, they are attracted to the grounded door, which lets them even out their charge. This reduces the overspray. The particles are electromagnetically attracted to their target, so they are less likely to fly off into the air.