Softer packaging is more secure

[China Packaging Network News] When visiting the supermarket, we often see a lot of food packaging bags, such as potato chips bags, candy bags, these bags to pick up a particularly light, the feeling is made of a layer of material, in fact, not many, many are Several layers of film are extruded, and then printed on people's favorite patterns. The process is not as simple as we thought.

The coextruded flexible packaging material is composed of multiple layers of plastic sheets or films and is made by a one-step method using a flat extrusion or inflation process using two or more plastic resins. The substrate of the coextruded film is never easy to separate. Each resin was separately melted in a separate extruder and then the melt was passed through a co-extrusion die and kept in uniform layers without mixing. When designing a co-extrusion process, in order to prevent the mixing between the layers, the rheology of the polymer should be carefully considered, especially the flow pattern and the melt viscosity after the co-extrusion of the mold and the single-layer material are the same. .

Because many materials are co-extruded together, if the adhesion between the two polymers is not sufficient, the overall adhesive effect of the final product will be affected. That is, layers and layers may be separated under stress. In this case, a third material, the adhesive layer, is added, which is essentially a thermoplastic adhesive. By tightly bonding the two materials, the adhesive layer maintains the integrity of the multilayer material. 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 more than four layers in structure are also common. For example, if EVOH is contained as an impermeable layer, it must be sandwiched between two polymers to prevent moisture penetration, so that the adhesive layer should be at least a five-layer structure. Although the resin melt from a single extruder can supply two or more layers of a coextruded film structure, each new type of resin in the structure must have a dedicated extruder.

Coextruded films or sheets are widely used in the packaging industry. For example, there is a pallet elastic packaging film with different adhesion properties on the inner and outer surfaces; a snack food made of a co-extruded film of brown polyethylene with light-irradiation in the inner layer and white polyethylene on the inner and outer layers. Bags and so on.