Coextruded - Why?
Vol. 14 #2, June 1987
Coextruded products are universally accepted for many applications. For example, recently the TV publicized Kraft’s salad dressing bottles. Mobil’s white inside trash bag. Fritolay’s potato chip bag. American-National’s ham can. Signode’s stretch film. But, we are constantly asked, "Why coextruded?" A simple answer is, "Everything can be better—coextruded." Economics, proper ties and market requirements cover most of the reasons.
Economics
1. Reprocessed and cheaper resin and fillers in the middle layer will reduce resin costs.
2. Pigmenting (coloring) only the out side layer (no color pigments in other layers) will reduce pigment usage.
3. Combining non-compatible resins with an adhesive (tie) layer are often cheaper coextruded than laminated.
Properties
1. Better strength, barrier and other properties can be obtained. For example:
grocery check out counter sacks using layers of L-LDPE and HDPE are stronger than blended or straight resins.
2. Barrier layer can be incorporated into the inside layer; while relying on the other layers for heat sealing, strength, rigidity and other properties.
Market Considerations
1. Shiny surface can be obtained with a high clarity film grade resin on the outside layer.
2. Different colors on the inside and outside layers.
3. Different tachifier (on cling) on the inside and outside for stretch film.
Production equipment requires more extruders and multi-layer dies, which in creases capital costs. Expensive coextruded products usually are assisted with a micro processor, which also raises capital costs. Labor skill levels are higher and increase operating costs. However, in many applications, these capital and operating costs are overcome by production, end use economics or market requirements.
- Jerry. Kretzschmar
See also
Coextruded multilayer distribution
Coextruded sheets
Coextrusion: opportunities and challenges
Correcting flow instability in coextrusion
Interfacial instabilities during coextrusion of LDPEs
Sheet/film coextrusion grows
"Wave" pattern instability in multilayer coextrusion