Automatic Blown Film Dies for Mono- and Coextrusion Technical and Economical Advantages, 1990 Polymers, Laminations & Coatings Conference Proceedings

In the infancy of blown film extrusion, the prime objective was to increase the output rates of the extrusion equipment and to distribute system conditioned thickness irregularities so no hoops would be visible on the roll. These problems were resolved satisfactorily by the introduction of internal bubble cooling and oscillating haul-off systems and rotating dies, resp.

Over the last decade, the demands on blown film extrusion systems have become increasingly exacting. This develop-ment is attributable to the arrival of a great number of new resins, the coextrusion process and, last but not least, to the demand for wider extrusion systems allowing multiple-up slitting and, in some cases, providing slit-seal facility.

After the development of the oscillating haul-off and internal bubble cooling, automatic blown film dies for mono and coextrusion processes represent another milestone in the history of blown film equipment.

Through active levelling of gauge tolerances, irrespective of their nature and where they occur, tolerances can today be reduced to a level which would have been unthinkable only a short time ago and cannot possibly be achieved using conventional methods.

The consistently high film quality, in turn, contributes to reduced scrap at all processing stages, from extrusion to the final product. The raw material savings thus created as well as a reduction of the average film thickness which may be possible depending on the type of product involved, result in return on investment in only 1 or 2 years, even not taking into account the additional profit realized through higher film quality.

Irrespective of how long it actually takes until return on investment is achieved, it can be forecast that, true to the motto “the better is the enemy of the good”, quality standards in the area of blown film extrusion will be continu-ously going upwards.

Those who are not prepared to accept this challenge are bound to fail on account of lacking competitiveness.