The requirements of many products, particularly in packaging applications, are so stringent that they cannot be met by a single plastics. In order to meet the requirements, often two or more materials have to be combined. There are a number of techniques to combine different materials; some of the more important ones are: co extrusion, coating, and lamination. Co extrusion was covered in session 1; we will now discuss coating and lamination in more detail.
Extrusion Coating
In extrusion coating, a molten layer of plastics film is combined with a moving solid web or substrate. The substrate can be paper, paperboard, foil, plastics film, or fabrics; the substrate can also be a multi-layer product.
Extrusion Lamination
Extrusion lamination involves two or more substrates, for instance paper and aluminium foil, combined by using a plastics film as the adhesive between the two substrates. The extruded sheet or film can be laminated with a film on one side or both sides. The laminate can be paper, foil, mesh, or a number of other materials. With lamination, many different structures of sheet or film products can be made. The laminate is unrolled from a payoff and combined with the film and immediately led into a set of nip rolls. After lamination, the film is handled as a regular film.
