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New Methods to determine the come-off time of paper labels
G. Wenk, I. Weber, R. Pahl

In the beverage industry labels are removed from returnable bottles in bottle cleaning machines. For a successful cleaning process the labels come-off time is crucial. If the labels detach too late in this process, they can block rinsing nozzles and affect the cleaning effectiveness of the machine.The term "come-off time" is defined by DIN?16524-6 as the time a tested label needs, to fully separate from a Petri dish when immersed in a caustic bath. However, the method according to DIN?165246 does not account for any double bonding of neck-ring labels, used on so called long-neck or ale bottles. Furthermore, many procedure steps of DIN?16524-6 are executed manually by the examiner, are not defined precisely or are impractical. Tests performed at the VLB Berlin showed that results between different examiners can differ significantly. In this paper the results of the IGF research project 15343?N are presented. Within this project the come-off behaviour of different paper labels was tested against various influencing factors. It was found that the amount of labelling glue is of particular importance in combination with metallised paper labels. Deriving from that knowledge, an existing model for the come-off behaviour was extended, allowing to develop a Modified Method and an Extended Method to overcome existing limitations and inaccuracies of DIN?16524-6.In Germany and many other countries beer and non-alcoholic beverages are filled in returnable glass bottles. After consumption of the beverage the empty bottles are returned to the beverage manufacturer, where they have to be cleaned in bottle cleaning machines, before they are refilled, labelled and packed again, ready for resale. To fully remove paper labels by means of a bottle cleaning machine, the come-off time of a paper label is crucial. If the come-off time is too short, labels might already detach while pre-soaked in one or more baths at increasing temperatures. Since these first baths of bottle cleaning machines are usually not equipped with a label discharge system, the labels would accumulate in the pre-soaking station. The ideal point for detaching paper labels is after the bottles immerse in the main caustic bath, where, after a residence time, the caustic is jetted over the bottles to remove remaining parts of labels, which have been soaked off but still remain in the bottle cells. Once flushed out of the cells, the labels are removed by the label discharge.

Descriptors: paper labels, metallised paper labels, come-off time, bottle cleaning machine

BrewingScience - Monatsschrift fr Brauwissenschaft, 63 (September/October 2010), pp. 112-121