A closure device (10) for a container (12) includes a filling device (14) that can be attached to an opening (16) of the container (12) A closure structure such as a membrane (18), a system (34), or a duckbill closure (54, 84) is attached to the filling device (14) in such a way that the opening (16) of the container (12) is sealed when the filling device (14) is attached to the opening (16). The closure structure is coated at least partially with polytetrafluoroethylene (22, 38, 60, 94) on one side (20, 40, 58, 90) that is accessible from outside the container (12) in the assembled state of the filling device (14) on the container (12).