Among the application materials of plastic packaging bags, there are often three-layer, five-layer, seven-layer, and nine-layer composite films. What is the difference between different layers of composite film?
5 layer and 3 layer comparison
The barrier layer in the 5-layer composite film is usually in the core, which insulates it from the moisture in the atmosphere. Because the barrier layer is in the core, other materials can be used to greatly enhance the barrier performance. Nylon can be used in the core layer, so that the 5-layer structure with a PE surface layer can cope with more materials like PE film and improve the process capability. Moreover, the processor can use pigments in the outer layer without affecting the bonding layer or barrier layer.
Three-layer composite films, especially those using nylon, have a tendency to curl because of the different physical properties in the asymmetric structure. For 5-layer structures, it is more common to use symmetrical or nearly symmetrical structures to reduce curling. Curl in a 3-layer structure can only be controlled by using nylon copolymers. In a five-layer structure, the processor can use nylon 6, and it is possible to obtain a nylon layer that is almost half the thickness of the three-layer film. This saves raw material costs while providing the same barrier properties and improved processing performance.
7th floor and 5th floor comparison
For high-barrier films, EVOH is often used as a barrier layer to replace nylon. Although EVOH has excellent oxygen barrier properties when dry, it deteriorates rapidly when wet. Therefore, it is common to compress EVOH into a 5-layer structure between two PE layers to prevent moisture. In the 7-layer EVOH composite film structure, EVOH can be compressed into two adjacent PE layers, and then protected by the outer layer of PE. This greatly improves the overall oxygen barrier and makes the 7-layer structure less susceptible to moisture.
Shattering or tearing can also be a problem for 5-layer structures. Moving to a 7-layer structure will cause the harder barrier layer to be torn apart by the connecting thin layer into the same two layers. This maintains the barrier properties while making the package more resistant to shattering or tearing. Moreover, the 7-layer structure allows the processor to tear the outer layer to reduce the cost of raw materials. More expensive polymers can be used as the thin surface layer, and cheaper polymers can replace most of the previous surface layers.
9th floor compared with 7th floor
Generally, the barrier part of the high barrier composite film occupies 5 layers in the structure. Because of advances in polymers and processing technology, the percentage of the overall thickness of this part in the entire structure is constantly decreasing, but the same barrier properties are maintained.
However, it is still necessary to maintain the film thickness of the overall composite film. The development from 7-layer to 9-layer enables the processor to obtain the best mechanical, appearance and cost performance. For high-barrier films, the additional versatility provided by the 7-layer or 9-layer extrusion line may be very impressive. The increased cost of purchasing a 7-layer or 9-layer extrusion line compared with a 5-layer production line can have a payback period of less than one year.