PETpla.net Insider 10 / 2015

CAPPING CLOSURES 26 PET planet insider Vol. 16 No. 10/15 www.petpla.net Different applications, neck finishes for varios, part 4 Closure for PET bottles PETplanet Insider is publishing extracts from successive chapters of Ottmar Brandau’s “Bottle, Preform and Closures”, which was published by hbmedia. A newly revised version is reissued under the Elsevier imprint. 4.3 Closure types 4.3.1 One-piece Closures A one-piece closure consists of only one piece rather than a closure and a liner. Sealing lips of various shapes and numbers are moulded into the cap, forming a connection between cap and neck that prevents the liquid from spilling out. These caps usually require an injection-moulded neck rather than an extrusion blow- moulded one as only tight tolerances can guarantee a proper fit. Over the years designers have invented a variety of solutions of which we will show the most promi- nent ones. Some of these were appli- cation driven; others had more to do with patent protection. There can be several challenges to a proper seal. Most importantly besides correct tolerances are dam- ages to the bottle neck. These occur frequently when injection-moulded preforms fall onto conveyors and storage containers. Most vulnerable are the outside and top surface of the neck, but even the inside surface can be scratched. Some seals therefore use more than one sealing lip, so if one fails there is another to prevent leakage (Fig. 4.8) 4.3.1.1 Standard Plug Seal This is the most common seal and an all-around good performer. A plug- shaped cap protrusion reaches into the neck and is dimensioned to form an interference fit, i.e., the plug out- side diameter is larger than the neck inside diameter. It cannot be used for carbonated contents because the inside pres- sure would lift the plug off the neck wall and escape. Because it has little in terms of undercuts, sterilisation is relatively easy. Damages to the inside wall of the neck have to be fairly low before they affect the seal, but when they do failure must be expected. 4.3.1.2 Outside Seal (1) This cap is somewhat the opposite of the standard plug seal. Instead of the inside, it seals on the top and top rim of the neck. A tiny wedge at the top cap surface prevents the seal- ing lip from slipping out. Because preforms are easier damaged on the outside and top, this seal’s weakness would be failure due to missing seal- ing area on the neck. Because of its rather large under- cut, this closure is hard to sterilise. It works well with CSD because the pressure has no lever on the cap. It is Fig. 4.8