PETpla.net Insider 04/ 2013

CAPPING / CLOSURES 36 PET planet insider Vol. 14 No. 04/13 www.petpla.net 38mm neck finishes and correspond- ing closure designs in the market are certainly economical (i.e. light-weight) solutions. However, the combination of these necks and closures does not create a very stable packaging, especially against high temperatures, but even at room temperature also. This can be visualised when pinching a bottle with a 38mm ACF neck finish which results in severe ovalisation (c.f. Fig. 1). Fig 1: Bottle with a 38mm neck finish (inner bore diameter of 33.4mm), pinched at the middle part, resulting in severe ovalisation of the neck. The ratio of wall thickness (WT) to inner bore diameter (IBD) is being used as a measure of the stability of the neck. If we compare the situation of the 38mm neck finish to a 26mm neck finish customised by Corvaglia for flat water applications, we arrive at a much more favourable ratio for the flat water neck finish than for the sensitive beverage neck finish. The difference, as depicted in Fig. 2 is roughly 40%. In other words, the most expensive and sensitive drinks today are shipped in the cheapest packag- ing available. Additionally, for packages as unstable as the 38mm ACF example, a safe packaging is only created by the mutual stabilization of closure and neck in a tightly screwed state. Once partly unscrewed, this stability is lost and the product safety of a sensitive drink can no longer be guaranteed. Another interesting point to note is the fact that these ‘weak’ necks are better stabilised by one-piece than by two-piece closures. The reason for this is that the liner in two-piece clo- sures only acts from above the neck, providing no horizontal guidance, whereas common one-piece closures do provide this guidance. Now, what happens if the tight combination between closure and neck is loosened? For the sealing parts of the closure we are talking about rather small HDPE components, where relatively small temperature variations resulting in small dimen- sional changes can have a relatively large effect on the sealing behaviour in such a delicate stabilising combina- tion. Sidel (2) recently proposed a qualification test for packages filled under aseptic conditions. When it comes to product and PET packaging, the company’s Product Package Inter- action laboratory assesses whether the products are packaged aseptically in order to ensure that the properties of the product and its packaging are not altered in any way. In this respect, they are tested over time through physical and chemical testing as well as by sensory analysis. For the recent qualification test proposed by Sidel, half of the samples under evaluation are partly unscrewed leading to a breach of the package’s stabilisation. The test contains temperature cycles that are run to simulate filling and real-life conditions of the pack- age. The combination of a ‘weak’ package like the 38mm ACF neck, breaching the stabilising effect of a tightly screwed closure and running temperature cycles with it poses a huge challenge to design a closure maintaining under all conditions the sealing performance of packages for sensitive drinks. For these kinds of packages the stability can only be guaranteed when neck and closure are tightly screwed together, partial unscrewing leads to a breach of stability. Currently, Corva- glia has taken on this challenge. In cooperation with the Zurich University of Applied Sciences (ZHAW) Insti- tute of food and beverage innovation (ILGI) the company is in the process of improving current closure designs in order to guarantee product safety of sensitive beverages even under the worst conditions. www.corvaglia.ch Fig 2: Above: 38mm neck finish for aseptic cold fill applications as used for sensi- tive drinks (SD). The wall thickness (WT) is 1.3mm, the inner bore diameter (IBD) is 33.4mm resulting in a ratio of 3.9%. Below: Corvaglia Short Neck (CSN) 26 mm neck finish for flat water applications. The wall thickness (WT) is 1.2mm, the inner bore diameter (IBD) is 21.8mm resulting in a ratio of 5.5%. References: 1. H.-D. Belitz, W. Grosch, P. Schieberle: Lehrbuch der Lebens- mittelchemie. 5th Edition, Springer, 2001, ISBN 3-540-41096-1, p. 509. 2. Presentation by A. Maurey, Food Scientist, Sidel, held at CE.T.I.E. PET working group meet- ing on April 24th 2012 in Paris (France).