The orientation line works by the so-called “double-bubble process”, i.e. the polymers are extruded through a circular die and immediately water-quenched to form a thick primary tube which is then re-heated up to a suitable temperature and blown to form the main bubble of thin film.
The non-contact simultaneous orientation is achieve thanks to the air inflated during the start up phase. This air allows the transversal orientation while the machine direction orientation is taken simultaneously thanks to the speed different between the stretching nip roll and the tower nip roll.
The bubble is cooled by air and then flattened. The film pass though an annealing ovens to reduce the retraction of the film.