Blown Film Extrusion

The process involves extruding a tube of molten polymer (typically polyethylene) through a die and inflating it to several times its initial diameter to form a thin film tubular bubble. This bubble is cooled as it is drawn upwards and eventually freezes, before collapsing to be wound and either slit for processing as a flat film or kept in tubular form for making plastic bags. Solidification occurs at the frost line and the position of this frost line is controlled by several parameters, such as airflow, speed and difference to the surrounding temperature.