A more firm way of soft packing
When we go to the supermarket, we often see a lot of food bags, such as potato chips, and candy bags. These bags are very light and feel a layer of material. In fact, they are not, a lot of thin layers of film are squeezed into, and then print people's favorite patterns. The process is not as simple as we think.
The co extruded flexible packaging material is made up of multilayer plastic sheets or thin films. It is made of two or more plastic resins by one-step process. The substrate of CO extrusion film is never easy to separate. Each resin is melted in a separate extruder, and the melt passes through the co extrusion die and keeps them in a uniform layer without mixing. In the design of CO extrusion process, in order to prevent the mixing between layers and layers, the rheology of the polymer should be carefully considered, especially the flow pattern and the process of the melt viscosity through co extrusion die and the single layer material.
Because many materials are extruded together, if the viscosity between the two polymers is not enough, the overall adhesion effect of the final product will be affected. That is, layers and layers may be separated under stress. In this case, it is necessary to add third materials, that is, the adhesive layer. In essence, it is a thermoplastic adhesive. By adhering tightly to the two materials, the adhesive layer keeps the integrity of the multilayer material. The adhesive layer must also be melted in a special extruder as a separate layer to the mold. Therefore, many co extrusion materials are three layers of structure, two are plastic, and third are adhesive layer as the two kinds of materials. The co extrusion film with more than four layers of structure is also very common. For example, if EVOH is included as an impervious layer, it must be sandwiched between two kinds of polymers to prevent tidal gas penetration, which should be added to the adhesive layer and should be at least five layers. Although the resin melts from a single extruder can supply double or more layers of the coextruded membrane structure, each new type of resin in the structure must have a special extruder.
Co extruded films or sheets are widely used in the packaging industry. Such as an elastic outer packing film with different adhesive properties on the inner and outer surfaces; a light brown polyethylene in an inner layer and a snack food bag made of a white polyethylene coextrusion film with a beautiful appearance inside and outside the outer layer. Www.kslfilm.com
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