What are the differences between three-layer, five-layer, seven-layer and nine-layer coextrusion films

Flexible packaging materials, often have three, five, seven, nine layers of film. What is the difference between different layers of films? This paper focuses on the analysis, for your reference.

Comparison of 5 layers and 3 layers

The barrier layer in the five layer structure is usually in the core, which insulates it from the water 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 PE surface layer can deal with more materials similar to PE film and improve the process ability. Moreover, the processor can use the pigment in the outer layer without affecting the bonding layer or barrier layer.

Three layer films, especially those using nylon, tend to curl because of the different physical properties in asymmetric structures. For 5-layer structure, it is more common to use symmetric or near symmetric structure to reduce curl. The crimp in the 3-layer structure can only be controlled by using nylon copolymer. In a 5-layer structure, only when the processor can use nylon 6 can it be possible to obtain a nylon layer about half the thickness of three layers. This saves raw material costs while providing the same barrier properties and improved processability.

Comparison between the 7th floor and the 5th floor

For high barrier films, EVOH is often used as a barrier layer to replace nylon. Although EVOH has excellent oxygen barrier properties when it is dry, it will deteriorate rapidly when it is wet. Therefore, it is common to compress EVOH into two PE layers in 5-layer structure to prevent moisture. In the 7-layer EVOH structure, EVOH can be compressed into two adjacent PE layers, and then protected by the outer PE layer. This greatly improves the overall oxygen resistance and makes the 7-layer structure less susceptible to moisture.

Fragmentation or tearing can also be a problem for a five story structure. The development of 7-layer structure will make the harder barrier layer split into two identical layers by connecting thin layers. This maintains the barrier property while making the package more resistant to breakage or tearing. Moreover, the 7-layer structure enables the processor to tear the outer layer to reduce the cost of raw materials. More expensive polymers can be used as surface layers, while cheaper polymers can replace most of the previous layers.

Comparison between the 9th floor and the 7th floor

Generally, the barrier part of the high barrier film occupies five layers in the structure. Because of the progress in polymer and processing technology, the percentage of the overall thickness of this part in the whole structure is constantly decreasing, but the same barrier performance is maintained.

However, it is still necessary to maintain the overall film thickness. From 7 layers to 9 layers, the processors can get the best mechanical, appearance and cost performance. For high barrier films, the additional versatility provided by a 7-layer or 9-layer extrusion line can be considerable. The increased cost of purchasing a 7-layer or 9-layer extrusion line can have a payback period of less than one year compared with a 5-layer production line.

Post time: Mar-05-2021