Co-Extrusion

The process of extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before chilling.

Co-extrusion is a process that allows the combination of different materials and colors in a single sheet.
This is done to achieve special properties which are specific to a certain polymer, or for aesthetic effects with color, or for economic reasons where an inexpensive material "sub-strata" is combined with a more expensive material "cap".

The process of extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before chilling. Each material is fed to the die from a separate extruder, but the orifices may be arranged so that each extruder supplies two or more plies of the same material. The advantage of CO-extrusion is that each ply of the laminate imparts a desired characteristic property, such as stiffness, heat-sealability, impermeability or resistance to some environment, all of which properties would be impossible to attain with any single material.

Applications
Within the building and construction industries, sheet extrusion is used for a variety of applications. One of the main uses of extruded PS sheet is for thermal insulation materials for walls, roofs, and under floors.
In the automotive industry, sheet is currently used to produce interior trim, panels, and dashboards. Foamed polyolefin sheet, both cross-linked and non-cross-linked, is also used in automotive applications.
There are a number of other applications where thermoformed sheet plays a significant role. These include the manufacturing of luggage, refrigerator liners, and shower units.

Advantages
"Co-extrusion is another tool in the well-outfitted converter's tool chest," according to Bruce Foster, technical sales manager of Mica Corp.
"It provides better quality monolayer extrusion coatings over a wider variety of widths and line speeds; the potential to save on the amount of premium resins by filling with lower cost materials; and the possibility to make multi-layer, multi-functional structures in a single pass."