Multi-layer co-extruded composite film structure: Regardless of the number of layers, it is generally divided into base layer, functional layer and bonding layer according to the function of each layer of the film.

Base layer: 

Generally, it is the inner and outer layers of the composite film, and it must have good physical and mechanical properties, molding and processing properties, and heat sealing layer.It must also have good heat sealing and thermal welding properties, and its cost is relatively low. It has good support and retention for the functional layer, and accounts for the highest proportion in the composite film, which determines the overall rigidity of the composite film. The base material is mainly PE, PP, EVA, PET, and PS.

Functional layer: 

The co-extruded functional layer of the packaging film is mostly a barrier layer, which is usually the middle of the multi-layer composite film. The main barrier resins used are EVOH, PVDC, PVA, PA, PET, etc. Among them, the most commonly used high barrier materials are EVOH and PVDC. The common PA and PET have similar barrier properties and are medium barrier materials.

Adhesive layer:

Because some base resins have poor affinity with the functional layer resins, some adhesive layers need to be placed between the two layers to act as glue in order to form an "integrated" composite film. The adhesive layer uses adhesive resins, commonly used are maleic anhydride grafted polyolefins, EVA.

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