Are you painting the front or the back of the emblem? If you paint the back, then mount it, the paint doesn't flake off because it's pretty well protected. Also, make sure you sand by hand. Any type of machine to sand, will melt the plastic (Dremel)
Once you get the color you want on there, go over it a few times with primer. This "fills" the color in, and protects the paint from the glue/tape.
