PETpla.net Insider 06 / 2015

CAPPING CLOSURES 30 PET planet insider Vol. 16 No. 06/15 www.petpla.net Introduction, closure history and closure function, part 1 Closures for PET bottles PETplanet Insider is publishing extracts from successive chapters of Ottmar Brandau’s “Bottle, Preforms, Closures”, which was published by hbmedia. A newly revised version is reissued under the Elsevier imprint. Introduction Closures usually are the least expensive part of a container. On the other hand, they are the primary inter- face between the product and the cus- tomer. Today’s closures have to offer high-performance functions such as resistance to gas pressures up to 12 bar and temperatures up to 65°C. This is necessary if we consider that these containers have to be transported and stored in countries where tempera- tures reach 55°C with even higher temperatures in truck trailers. Also, a modern closure has to provide easy processability at capping speeds of up to 70.000bph without breaking the tamper evidence. It has to be opened easily by elderly people and children, showing clear tamper evidence, and it has to reseal the con- tainer perfectly after first use. Closures also carry decorations like four colour printing on the outside and promotional engravings or printings showing an instant win on the inside. Considering that such closures are sold between 0.5 and 0.9 US cents per piece, it is clear that the production has to be more than only efficient. A high- performance injection moulding (IM) or compression moulding (CM) machine can provide more than 1000 closures per minute. Offset printing machines can print up to 4000 closures in 1 minute with decorations in four colours. The investment for such a closure production line today is well over 1 million USD. If we consider that 67% of the closure cost is for raw materi- als and the second factor with 7% is energy, we can understand why there are only a few companies worldwide that can exist in this highly competitive market of plastic closures (Fig. 4.1). 4.1.1 Closure History The first mass-produced closure able to keep up with CSDs was a metal closure with a crown-shaped flange, lined with natural cork. This goes back to 1892 when William Painter invented the crown cork. It took almost 80 years until a young man named Albert Obrist from Switzerland introduced a one- component high-density polyethylene (HDPE) closure for returnable glass bottles in Switzerland. The advantage of prethreaded plastic closures was obvious, but it took 15 years for other companies to introduce plastic clo- sures that were able to compete with the solution of Obrist. These closures were based on the design of aluminum closures mostly with shell and liner and in some cases also with an inserted tamper evident band. The two different backgrounds of the developing compa- nies were the reason for the develop- ment of injection moulded closures from Obrist and the compression- molded closures from HC Industries together with Alcoa. Still today there is only a handful of companies able to produce plastic closures for soft drinks with constant quality and high performance. This