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Comparison of 5 and 3 layers The barrier layer in a 5 layer structure is usually in the core, isolating it from atmospheric moisture. Because the barrier layer is in the core, other materials can be used to significantly enhance barrier properties. Nylon can be used in the core layer, so that a 5-layer structure having a PE surface layer can cope with more materials like a PE film, improving process capability. Moreover, the processor can use the colorant in the outer layer without affecting the tie layer or the barrier layer.
3-layer films, especially those using nylon, have a tendency to curl because of the different physical properties in asymmetric structures. For a 5-layer structure, it is more common to use a symmetrical or near symmetrical structure to reduce curl. The curl in the 3-layer structure can only be controlled by using a nylon copolymer. In a five-layer structure, processors can use nylon 6 to obtain a nylon layer that is approximately half the thickness of a three-layer film. This saves raw material costs while providing the same barrier properties and improved processability.
Comparison of Layers 7 and 5 For high barrier films, EVOH is often used as a barrier to replace nylon. Although EVOH has excellent oxygen barrier properties when dry, it rapidly deteriorates when wet. Therefore, it is common to compress EVOH into two layers of PE in a 5-layer structure to prevent moisture. In a 7-layer EVOH structure, EVOH can be compressed into two adjacent PE layers and then protected with the outer PE. This greatly improves the overall oxygen barrier properties and makes the 7-layer structure less susceptible to moisture.
Shredding or tearing may also be a problem for a 5-layer structure. The development of the seven-layer structure will cause the harder barrier layer to be torn into the same two layers by the connecting thin layer. This maintains the barrier properties while allowing the package to be more resistant to breakage or tearing. Moreover, the 7-layer structure allows the processor to tear the outer layer to reduce raw material costs. The more expensive polymers can be used as the surface layer, while the less expensive polymers can replace most of the previous surface layers.
Comparison of 9 and 7 layers In general, the barrier portion of the high barrier film occupies 5 layers within the structure. Because of advances in polymer and processing technology, the percentage of overall thickness in this part of the overall structure is continuously decreasing, but the same barrier properties are maintained.
However, it is still necessary to maintain the overall film thickness. From the 7th floor to the 9th floor, the processor can obtain the best mechanical, appearance and cost performance. For high barrier films, the additional versatility offered by a 7 or 9 extrusion line can be very substantial. The cost of purchasing a 7- or 9-layer extrusion line compared to a 5-layer line can have a payback period of less than one year.
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