PETpla.net Insider 01+02 / 2012

PREFORM PRODUCTION 12 PET planet insider Vol. 13 No. 01+02/12 www.petpla.net Sipa’s latest processes for producing and handling lightweighting bottles Lighter PET bottle necks Sipa says that lightweighting PET bottles requires an holistic approach, which considers every aspect of design, develop- ment and engineering, preform injection moulding, bottle blow moulding, handling, filling and sealing. As well as lightening the container body, Sipa has been paying attention to reduc- ing weight in PET bottle necks – which is where the bottle wall is at its thickest. Taking blow moulding to the extremes of its capability has already yielded results in producing very light containers, the thickness and weight of the neck is deter- mined by the preform injection moulding process. Design and development In designing a lightweight neck, Sipa identifies a number of key issues. All areas relating to function and neck seal have to be maintained unchanged, so that the same closure can be used. Sipa has analysed the way the design performs all along the line, in order to minimise the need to change the configuration of the existing production operation – the blower, filling line, and so on. It has endeavoured to ensure that only the neck-ring needs to be changed, thus enabling the existing injection mould to be retained. It analyses how the neck performs during fill- ing, in order to ascertain how much the wall thickness in the neck can be reduced. Where necessary, air vents and exhaust are optimised and treatments on the mould surface are considered. If it is possible, Sipa conducts industrial tests at the cus- tomer’s site, with the use of a single neck-ring installed on the existing mould. Injection moulding Moulding a lightweight neck can be challenging. The small quantity of PET resin used could cause the material to cool too quickly inside the injection mould, which may lead to a ‘short shot’; this occurs when too-cool resin is unable to fill the cavity all the way to the top of the neck. All factors are considered during development including resin viscosity, which may affect the pro- cess and its thermal profile inside the hot runner. Several tests are undertaken in order to ensure per- fect neck injection: inclduing dimen- sional checks to verify the correct formation of the thread; pressure resitance and proper opening of the thread; chemical and/or biological contamination; and other physical and mechanical tests. The preference, when converting the injection mould to a lightweight neck, is to change only the lip – for example, when cutting weight from 3.9 to 3.2g. Reverse engineering limits the risk of creating defects in the final product and helps to ensure the correct mechanical matching and durability of the mould’s compo- nents. Sipa’s tool shops across the world are equipped to carry out the procedures. Light weighting SPECIAL