For the semi-rigid sheet structures and flexible film structures discussed so far, the resins used are both different and partly identical. Semi-rigid sheets mostly use high modulus resins such as HIPS, HDPE and PP as the thickest structural layer: soft films use more low modulus resins as the thicker structural layer, such as LDPE and LLDPE, and both use PP. and PVDC. Nylon is used more often in flexible films. Not to mention the gas barrier properties of nylon, it also has valuable puncture, tear and abrasion resistance as well as its thermoformability where required.
An example of an important film that is often co-extruded is a packaging film for smoked beef or pork sausages. The composition of these films varies considerably. The common design of the packaging is that half of it is thermoformable and the other half is printed non-formable. The non-formed part is usually a laminate, consisting of a layer of PET printed on the reverse side, plus a sealing layer. The moulded part can be co-extruded and is usually 50-75µm (2-3 mils) thick. The formed half usually has a nylon outer surface to make the film abrasion resistant and to make it thermoformable, in addition to EVOH as a barrier layer and ionic cross-linked polymers as a heat sealing layer. The film structure also contains a suitable adhesive layer and LDPE or LLDPE to obtain the desired properties and to reduce the cost of raw materials. In this way, there is a great similarity between this multilayer structure and the structure of the sheet. From the point of view of the temperature compatibility of the structure, the nylon used must have a low melt temperature; therefore nylon 6 or a nylon copolymer is usually chosen.
A diagram of a single-layer cast film line configuration. For co-extrusion, the important additions are the feed head or multi-collector die head and more extruders. The same principles apply to the design of the feed head or die head for co-extrusion with a flat die head for the production of semi-rigid structures as described in the previous section.
Nanjing Sumino Precision Machinery Co., Ltd. has professional cast film production lines. Our main cast film manufacturing lines are: TPU hot melt film production line, CPP/CPE cast film production line, EVA solar encapsulation film production line, PE hygiene breathable film production line, PVDF cast film production line, PP three-dimensional film production line, medical blood purification film production line, multi-layer co-extrusion barrier film production line, LLDPE winding film production line, etc.
