Those plastics are tough to glue because as they cool after coming out of the mold the have a glaze rise to the surface. The roughing it up was the key to getting it to stick. I use to do plastics printing and to get the ink to stick we had to flame treat them just before printing to burn it off the surface and then use a NASTY ink with a lot of chemicals in it to basically chemically melt its way onto the surface.