PETpla.net Insider 01+02 / 2016

CAPPING / CLOSURES 26 PET planet insider Vol. 17 No. 01+02/16 www.petpla.net Different applications, neck finishes for various, part 5 Closure for PET bottles PETplanet insider is publishing extracts from successive chapters of Ottmar Brandau’s “Bottles, Preforms and Closures”, which was published by hbmedia. A newly revised version is reissued under the Elsevier imprint. 4.3.1.4 Double seal This seal is a combination of the plug seal and the second outside seal and shares their attributes. By having two equally engaging sealing lips, it can overcome preform damage to either the inside or outside wall of the bottle neck. Because two lips have to be engaged, the application torque of the capper is higher and so are mould costs (Fig. 4.11) . • Medium removal torque • Resistant to smaller inside and out- side preform damages • Good resistance to mechanical influ- ences • Very good for CSD applications • Seal performance depends on applica- tion torque • High production costs • Higher application torque • Difficult to sterilise 4.3.1.5 Triple seal Here three sealing lips engage with the bottle neck using the inside, top, and outside. This method is most resistant to any preform damage but requires the highest application torque. Unscrewing this type of cap also requires extra torque (Fig. 4.12) . • Medium removal torque • Resistant to smaller inside and out- side preform damages • Good resistance to mechanical influ- ences • Very good for CSD applications • Easy to sterilise • Higher application torque 4.3.2 Two-piece closures Although most end users would prefer one-piece caps, liners may be required for a variety of reasons. As discussed in Chapter 5.4, liners are always used with polypropylene (PP) closures. Other liner uses may enhance the functionality or shelf life of the package. The liner material must be soft enough to squeeze between the harder cap and bottle materials. Ethyl- ene vinyl acetate (EVA) is commonly used but other materials may be chosen for specific applications. Caps made for use with liners feature a pro- trusion in the outer rim that holds the liner in place. The main seal is formed not at the top of the neck but rather on the outside seal area. This design better withstands top loads. Liners are made thick enough to overcome neck and bottle tolerances and minor surface damage. Liners can be inserted into the caps in three ways:  Liner material is punched to the correct size and inserted into the cap, often in the same special-pur- pose machine. This is a relatively expensive operation because some CAPS & CLOSURES