Why do more people choose co-extruded film?
The co-extruded flexible package is composed of a multi-layer plastic sheet or film, which is produced by a one-step process using two or more plastic resins by a flat extrusion or inflation process. The substrate of the coextruded film is never easy to separate. Each of the resins was separately melted in a separate extruder, and then the melt was passed through a co-extrusion die and held in uniform layers without mixing. In the design of the co-extrusion process, in order to prevent the layer-to-layer mixing, the rheology of the polymer should be carefully considered, especially the flow pattern and the melt viscosity after the co-extrusion die are the same as the single-layer material. .
Because many materials are pressed together, if the viscosity of the two polymers is insufficient, it will affect the overall adhesion of the final product. That is, the layers and layers may be separated under stress. In this case, it is necessary to add a third material, an adhesive layer, which is essentially a thermoplastic adhesive. The adhesive layer maintains the integrity of the multilayer material by tightly bonding the two materials. The adhesive layer must also be melted in a dedicated extruder and fed into the mold as a separately added layer. Therefore, many coextruded materials are three-layer structures, two are plastics, and the third is an adhesive layer as the first two material bonding materials. Coextruded films that are structurally more than four layers are also common. For example, if EVOH is included as a barrier layer, it must be sandwiched between two polymers to prevent moisture penetration, so that the adhesion layer should be at least a five-layer structure. Although the resin melt from a single extruder can be supplied to two or more layers of a coextruded film structure, each new resin in the structure must have a dedicated extruder. I hope this article will help you understand why more and more flexible packaging bags use co-extruded membranes