Extrusion coating is one of the processes used to produce a large range of thin multilayer structures.
Extrusion coating or co-extrusion operations use high melt temperatures to lower the melt viscosity. This improves coating thickness uniformity and adhesion. The process simultaneously producing a foam sheet while adding a film layer to top, bottom or both top and bottom of the sheet through a multi-layered extrusion die to create a single sheet in a single operation.
This provides a base layer of foam with cap layers of material having different properties from the foam. These properties may be designed for protection, printability or aesthetics.
Co-extrusion processing plays an important role in manufacturing paper and plastic products. By laminating polyethylene onto paper through the co-extrusion process, water resistant paper products such as milk cartons can be obtained.
Low density polyethylene (LDPE) is especially suitable for use in the extrusion coating process. The polyethylene coating provides increased tear resistance, scuff resistance, a heat sealable surface, resistance against chemicals, grease resistance, and a good barrier against water and various gases.
A major application is in the coating of board for milk and fruit juice cartons, as an LDPE/board/LDPE or LDPE/ board/adhesive/aluminum foil/LDPE laminate (the latter for aseptic packaging). Other applications include specialized laminates for liquid and food packaging, and industrial and building uses.
Co-extrusions of laminates
