Film blowing

Film blowing is, along with flat extrusion, one of the main methods for producing polymer films. The structures produced are generally between 10 and 200 µm thick. Sheath blow molding is preferred to flat extrusion when packaging is required to have good mechanical performance. In fact, the sheath blowing process inevitably induces a slight bi-stretch, which is particularly desirable for the manufacture of films used in spotting. This process also enables the production of very large films that can be used for the production of agricultural tarpaulins. The sheath blow-molding process also offers the advantage of enabling a high-capacity industrial line to be set up on a small surface area, compared with that required for a flat extrusion line. Recent technological developments have made it possible to produce complex films from a wide range of polymeric materials. Modern blow-molding lines can produce multilayer structures. Generally speaking, films are made up of five layers obtained from three materials:

• an inexpensive resin used as a mechanical structure;

• a resin binder ;

• an expensive resin with barrier properties, for example.

Recent technological innovations include optimized cooling, continuous thickness control and increased productivity.