Expansible press plunger, an attachment unit for attaching a container element to a container body and a method for sealing a packaging container

An expansible press plunger comprising:

• a plunger having a plunger body aligned with a plunger axis extending in an axial direction perpendicular to a radial direction;
• an expansion tool side wall having an inner surface and an outer surface, the expansion tool side wall defining a cavity within which the plunger body translates along the plunger axis, wherein the outer surface includes a sealing extension protruding from the outer surface and a deformation extension protruding from the outer surface, the side wall being transformable between an unexpanded state and a radially expanded state, wherein the side wall comprises a first inclined plane surface being inclined away from the plunger axis and wherein the plunger body comprises a second inclined plane surface the second inclined plane surface of the plunger body contacting and applying pressure to the corresponding first inclined plane surface of the side wall when the side wall is in the radially expanded state, wherein the side wall is transformable between the unexpanded state and the radially expanded state by movement of the plunger body along the plunger axis downward inside of the side wall wherein the side wall is made of a material which can be repeatedly flexed and/or stretched.