PETpla.net Insider 04/ 2013

BOTTLE MAKING 31 PET planet insider Vol. 14 No. 04/13 www.petpla.net at any point on the shoulder or the lat- eral surface nor must the bottom zone be compressed or crimped under load. Particularly if low-cost bottles with very thin walls are used, it must be ensured that enough material is provided in the base zone to prevent such bottom failures. Internal pressure For the determination of the required internal pressure perfor- mance, the contents are the principal determining factor. Will the bottle be used for still liquids or is it intended for carbonated products? In the latter case, the amount of dissolved CO 2 must also be taken into account. Also to be considered are the temperature and humidity environment in which the filled bottles will be positioned to sterilize the headspace and the cap. The contents will generate a vacuum when they cool down. This vacuum condition must not result in the bottle collapsing inward. For this purpose special hot-fill panels can be incor- porated in the bottle design, which counteract the tendency of the bottle to collapse. Handling stability The handling or gripping stability is a rather subjective parameter. The customer should have an opportu- nity to handle similar products so that he can decide which level of grip he desires. Premium products will certainly require a higher handling stability than low-cost products. For certain lightweight containers, e.g., for edible oils, the handling stability can be improved by horizontal ribs. Depending on the design, however, this may result in a “concertina” effect, which would compromise the top-load properties. Also the presence of cer- tain design elements, such as logos, recessed handles, etc., can have a positive as well as negative effect on the handling stability. Stress cracking Especially if exposed to alka- line solutions, PET tends to stress crack when a certain level of stress is Please order your copy at the PETplanet insider book shop: https://www.petpla.net/books Bottles, Preforms and Closures A Design Guide for PET Packaging Second Edition by Ottmar Brandau 115,00 € 180 pages © Copyright Elsevier 2012 applied. Such stress cracking mostly occurs near the moulding gate. In the case of bottles for carbonated drinks in particular, this may have a significant impact on the quality of the bottle base. Such alkaline solutions promoting stress cracking not only are encountered in the rinsing processes for returnable bottles but are also components of many of the lubricants used for conveyor belts. Although modern belt lubricants are acid based, the stress cracking test has proved to be a good method of evaluating the quality of a container. The stress cracking behaviour of the bottle may also depend on the selected preform and has an influence on the geometric design of the base as well as on the parameters of the stretch blow mould- ing process. Barrier Depending on the contents, the bottles may need certain barrier prop- erties to ensure the required shelf life for the contents. For example, bottles used for CSDs, sparkling mineral water, or beer may require a barrier against the loss of CO 2 . On the other hand, fruit juices, mixed milk drinks containing fruit juice, or beers must be protected against the ingress of O 2 to prevent premature deterioration as a result of oxidation. Sometimes a barrier against water vapour may also be required, for example, in the case of bottles used for edible oils. The barrier problem is more pronounced with smaller bottles because here the surface/volume ratio of the container is rather high, which is a drawback of smaller containers. Although larger bottles for mineral waters and CSDs will have a sufficient barrier as a result of the biaxial stretching of the PET material, single-serve bottles, which are increasingly replacing beverage cans, will require additional barrier enhancements such as multi-layer constructions or coatings. Ultraviolet (UV) radiation is det- rimental to dairy products and beer. As a rule, such products will require collared bottles or the use of preforms made from specially formulated resins with UV blockers. Yet, apart from the bottle size, the required barrier prop- erties do not have an influence on the bottle design. They can, however, have an influence on the selection of the preform (colour, multilayer) (see Chapter 2). Problems of delamination in multilayer bottles, which occurred a year or two ago with certain bottle designs, have now largely been eliminated through modifications in preform production and by running preforms on the low temperature side of the process window. *This article was published in Bottles, Preforms and Closures, Ottmar Brandau, Chapter 1.2., Copyright Elsevier 2012