At Hume, we market two, three and five layer co –extruders. Typical applications include Industry packaging (e.g. shrink film, stretch film, bag film or container liners), Consumer packaging (e.g. packaging film for frozen products, shrink film for transport..
packaging, food wrap film, packaging bags, or form, fill and seal packaging film), Laminating film (e.g. laminating of aluminium or paper used for packaging for example milk or coffee), Barrier film (e.g. film made of raw materials such as polyamides and EVOH acting as an aroma or oxygen barrier used for packaging food, e. g. cold meats and cheese), films for the packaging of medical products, Agricultural film (e.g. greenhouse film, crop forcing film, silage film, silage stretch film).
The majority of polymer films are manufactured by film blower extruders (blown film extrusion). Film blowing process: A single screw extruder is used to melt the polymer and force it into a tubular die. Air is blown into the centre of the extrude tube and causes it to expand in the radial direction. Adjustments to wall thickness and diameter are made in this continuous bubble or tube.
Extension of the melt in both the radial and down-stream direction stops at the freeze line (frost line) due to crystallization of the melt. The nip rolls collect the film, as well as sealing the top of the bubble to maintain the air pressure inside. This is used extensively with polyethylene and polypropylene.