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; after the trimming of the edge, the two webs obtained rolled up in two reels.
By annealing the product obtained on the biorientation equipment, it is possible to obtain heat set film such us: BOPP, BOPA, BOPET and special products.
POF the annealing can be placed in line or off line. Partial annealing can also be integrated in the orientation.