In extrusion engineering, the term co-extrusion stands for the merging of two or more plastic melts polymers of the same or different types before they leave the profile die. Coex film combines the positive properties of different film and/or foil materials with each other.
In this way, for example, by using coex film, the barrier or welding (hot seal) properties can be tailored to a product.
Production
Coex film is produced using the blow method. Granulate is liquefied in an extruder. An air bubble, similar to a soap bubble, is then produced around which the liquefied plastic solidifies again. The air flow rate, quantity of granulate and drawing off speed determine the film thickness. Coex is the abbreviation for co-extrusion.
Co-extrusion means that during production in an extruder, several materials are liquefied and are later solidified in layers on top of each other. In this way a film can be produced from several granulates with unrelated materials.
Use
A typical example of the use of coex film is as film for potting compost – black on one side and white on the other. But coex film is now also used for drinks packaging, plastic bottles, for example for ketchup, or bags for fruit and vegetables. In the automotive industry, the coex technique is used to produce plastic fuel tanks (KKB), in that an inner, diffusion-tight layer is combined with an external layer capable of withstanding mechanical loads. Several functional layers can be combined depending on the manufacturer and intended use. Up to 6 layers (multi-layers) are possible with current state of the art equipment
Advantages
Properties previously reserved for individual materials or do not arise until several materials are laminated can be freely combined with coex film. In the meantime, renewable resources are also increasingly being included in the material mix.
An example of co-extrusion can also be found in the home: Toothpaste with colourful stripes. Both pastes are extruded together through a nozzle.