in a method for producing a coated thermoplastic material , thermoplastic material is fed into a twin - screw extruder to produce a homogenous melt as the thermoplastic material is advanced . while the melt is in plastic state an adhesion promoter for a coating material to be applied later or a small amount of a coating material to be applied later as adhesion promoter is added to the melt which is then transferred to an injection mold and allowed to cure to form a thermoplastic body . the thermoplastic body is then coated with the coating material .