There are two types of film extrusion: cast film and blown film. The film extrusion process is a continuous operation of melting and conveying a polymer in a heated screw-and-barrel assembly. The homogenous melt is forced to flow through a screen pack, then through either a round or flat die, from which it exits to meet the desired width and thickness.
Polyolefins are the most widely-used plastics for film extrusion. Polyolefins that can be extruded as monolayer and multi-layer film include low density polyethylene (LDPE); linear low density polyethylene (LLDPE); high density polyethylene (HDPE); ethylene copolymers, such as ethylene vinyl acetate (EVA) and ethylene methyl acrylate (EMA); polypropylene and propylene copolymers and thermoplastic olefins (TPOs).
Benefits and Applications
In general, the advantages gained with polyolefin films are ease of processing, light weight, good toughness and tear resistance, flexibility (even at low temperatures), outstanding chemical resistance and relatively low cost compared with other plastics.
Major customer application areas for polyolefin films are:
- Packaging for food, textiles, consumer products, industrial products, medical products, merchandise, including:
- Agriculture
- Construction
- Consumer products, including diaper backing, garment bags, household wrap and trash bags
- Materials handling, including stretch wrap and shrink wrap
Properties
The basic properties of polyolefins can be changed using a broad range of chemical modifiers. In addition, polyolefin-based films can be coextruded with various other polymers, including ethylene vinyl alcohol (EVOH), nylon, polyester barrier resins and adhesive tielayers, to produce multilayer films with special, high-performance properties.