PETpla.net Insider 01+02 / 2018

CAPS & CLOSURES 22 PET planet Insider Vol. 19 No. 01+02/18 www.petpla.net Collaborative action to clarify cap ovality issues Round table for oval caps The lightweighting of plastic caps for PET bottles necessarily involves compromises for both application and functional perfor- mance of the closure. One consequence of lower rigidity is the increased risk of deformation of the caps during transport and storage, compounded by the effect of higher capacity bulk storage bins. This deformation is characterised by an ovali- sation of the cap body which may cause blockage of the cap infeed to the capper and resulting line jams. The Cetie PET Finishes working group thus identified the need to set up a specific group dedicated to cap ovality, and this new working group recently held its first meeting in Cetie offices in Paris. As the contribution to ovalisation depends on conditions encountered by the caps after leaving the cap pro- duction site, the manufacturer is not in a position to guarantee a given low ovality for caps as received. Gener- ally, cap suppliers’ ovality specifica- tions will thus be wider than those given by the capping machine supplier for trouble free operation. In addition, although the principle is understood, there is no single recognised definition of cap ovality as a quantity and how it should be measured. Moreover, as avoiding jams is a prime concern for bottlers, optical inspection equipment is increasingly favoured on incoming caps streams to reject, in particular, those whose ovalisation is detected as potentially line-blocking. Line jams may be par- ticularly penalising for aseptic filling if sterility is broken and involves a 3-hour plus production stop. However, in the absence of a clear understand- ing of the extent to which the capper can accept a degree of ovality, appro- priately setting the criteria for rejection remains a recurrent difficulty, as this will depend for example on the cap design. Inspection thus may result in high cap reject rates if restrictive ovality reject criteria are favoured. Cases are reported where unaccept- ably high reject rates for lightweight caps have led the bottler to revert to heavier caps even for lines otherwise designed for lightweight versions. Although blockage on the cap infeed is the principal issue, there is apparently little known on the extent to which ovalised caps may also affect cap application and subsequent func- tional performance. It is generally con- sidered that once inserted in the cap- ping chuck the cap will be forced to recover its initial roundness, and after capping the correct shape maintained by the finish. However, there might be cases where for example the correct positioning on the finish of the sealing feature or the tamper-evident band be affected by residual ovalising forces. The issue is thus complex and no single actor in the value chain – cap supplier, capping equipment supplier, optical inspection equipment supplier or filler/brand-owner currently has the means to ensure that the adoption of lightweighted caps might not be jeopardised by problems attributed to cap ovality. This is typically an area where it is beneficial for the actors concerned to participate in a collec- tive action to exchange industrial experience and develop appropriate guidance for the industry based on objective shared knowledge. Cap ovality working group Cetie is an inter-professional association dedicated to producing technical reference documentation - best practice, recommendations and specifications - for the bottling industries. It provides facilities to enable such collaborative initiatives for the development of authoritative reference documents by the technical experts from its member companies, within working groups either dedicated to general themes or to specific sub- jects. The Cetie PET Finishes working group thus identified the need to set up a specific group dedicated to cap ovality, and this new working group CAPS & CLOSURES