A powder coating composition comprises at least one thermosetting resin such as epoxy resins, carboxy- or hydroxy-functional polyesters; hydroxy-, carboxyl- or glycidyl-functional acrylic resins; andor hydroxy- or carboxyl-functional fluoropolymers, fluorochloropolymers or fluoroacrylic polymers blended with a at least one poly and at least one curing agent for the thermosetting resin. A set of cases can be divided into bins. The thickness of each layer is nearly identical and the overall thickness of the light-sensitive film being at least equal to 35 nm. The load seal ring exerts reaction forces on the pair of lip portions and outwardly in the axial direction.