A study of the conditions and variables that affect the printing of shrink films on waterbased flexography
Printing shrink labels with waterbased flexographic inks require a great deal of attention from the press operator. Lack of heat from the dryers can cause drying related problems, while an increase in the dryer temperature can shrink the material. Some press manufacturers recommend presses that are equipped with powerful dryers and expensive chill roll systems. Manufacturers also suggest the use of a corona treatment unit to improve ink adhesion. Newcomers, that do not wish to invest in new presses and equipment of this kind, struggle with finding a proper combination of press speed and dryer settings that may offer acceptable print results. The main objective of this research project was to establish an optimal press speed for a conventional flexographic printing technique that could output acceptable printing products for heat sensitive materials. To accomplish the research objective, a series of shrink film samples were evaluated from two main flexographic print runs. One run was performed using a corona treatment unit and another one without corona treatment. These print runs were executed using waterbased inks on a shrinkable film. Each run was divided into six press speed segments. For each segment, the press was set at a different speed. Following the print operation, a series of tests were conducted to determine the press speed boundaries that were best suited for printing without affecting the performance of the shrink film or inks. Samples were evaluated by employing an adhesion test, re-wetting test, shrinkage test, a blocking test and an offsetting test. Tests performed during the course of this research project established that shrink labels could be printed on a conventional waterbased flexographic press as long as the press uses corona treatment and that the maximum press speed does not exceed 150 feet per minute. Printing shrink films without corona treatment should not be performed since ink adhesion fails at all press speeds and blocking and offsetting issues are visible when press speed reaches 150 feet per minute.