Two more layers, what's the difference? The core difference and performance gap between 9-layer and 7-layer co extruded films

The "number of layers" of co extruded film is not simply a numerical difference, but an intuitive reflection of material combination, functional integration, and performance performance. The 9-layer co extruded film has an additional 2-layer structure compared to the 7-layer structure, which brings about an essential upgrade in material design flexibility, functional segmentation ability, and application scenarios. The following analysis will be conducted from the core differences and illustrated with examples:

1、 Substantive difference: comprehensive differences from materials to performance
1. Material combination flexibility: 9 layers are better at "functional segmentation"
The core advantage of co extruded film is the multifunctional integration achieved through the composite of different materials. The more layers, the finer the types of materials and functional zones that can be included.

7-layer co extruded film: The material combination is limited by the number of extruders, and usually can only achieve "basic functional integration", such as the simple division of "outer layer (wear-resistant)+support layer (strength)+barrier layer (moisture-proof/oxygen)+heat sealing layer (sealing)", which is difficult to simultaneously meet multiple subdivision requirements (such as anti-static, puncture resistance, high transparency, etc.).
9-layer co extruded film: The additional 2 layers can be used as a "functional optimization layer", such as adding a "transition layer" between the barrier layer and the support layer (to improve material compatibility), or adding a "smooth layer" on the outside of the heat sealing layer (to reduce friction and prevent adhesion), making material combinations more flexible.
2. Core performance: 9 layers have significant advantages in "extreme scenarios"
Increasing the number of layers can enhance key performance by optimizing the structure, especially in high demand scenarios where the gap is significant

barrier
The effect can be enhanced by "multi-layer barrier stacking" on the 9th layer. For example, for oxygen barrier, 7 layers may only have 1 layer of EVOH (barrier material), while 9 layers can be designed as a composite barrier structure of "EVOH+PA+EVOH", which can reduce oxygen permeability by more than 50% (from 10cc/(m ² · 24h) to below 5cc).
weather resistance
In high temperature, low temperature, or acid-base environments, a 9-layer "buffer layer" design is more optimal. For example, in cold chain packaging, a "low-temperature resistant toughening layer" (such as POE) can be added to the 9th layer to maintain flexibility at -30 ℃, while the 7th layer may become brittle due to the lack of this layer.
Puncture resistance and strength
In industrial packaging, 9 layers can be alternately stacked with "PA (polyamide)+PE (polyethylene)" (such as 3 layers of PA+4 layers of PE+2 layers of functional layers), which increases the puncture resistance by more than 30% compared to 7 layers (2 layers of PA+5 layers of PE), making it more suitable for packaging sharp metal parts.
3. Application scenarios: The 9th layer focuses on "high demand areas", while the 7th layer focuses on "cost-effective scenarios"
The difference in layers directly determines the "threshold" for applicable scenarios:

7-layer co extruded film: suitable for scenarios with moderate performance requirements, such as ordinary snack packaging (requiring basic moisture resistance), daily necessities film bags (requiring tear resistance), agricultural cover films (requiring UV resistance), etc. Typical examples include potato chip packaging bags (structure: PE/PA/PE, 7-layer simplified version).
9-layer co extruded film: focusing on high demand scenarios, such as:
High temperature steamed food packaging (must withstand high temperatures of 121 ℃ without leakage): an additional two-layer optimized combination of heat sealing layer and barrier layer to avoid delamination after steaming;
Precision electronic packaging (requiring high barrier moisture resistance+anti-static): By adding an "anti-static layer (such as conductive PE)" and a "high barrier EVOH layer", the humidity transmittance can be controlled below 0.1g/(m ² · 24h) to protect the chip from moisture;
Medical dialysis bag (with chemical corrosion resistance and high cleanliness): It uses a 9-layer structure to isolate different liquid contact layers and prevent material dissolution.
4. Cost and cost-effectiveness: 9-layer "high performance and high cost", 7-layer "enough is enough"
9-layer co extruded film: requires 9 extruders (7 for 7 layers), increasing equipment investment by about 30%; The material combination is more complex (possibly incorporating expensive materials such as EVOH and PA), and the cost per square meter is 20% -50% higher than that of a 7-story building, but it can meet the packaging needs of high value-added products (such as medical and high-end food).
7-layer co extruded film: With lower equipment and material costs, it is suitable for mass production and scenarios where performance requirements are not extreme, and has a higher cost-effectiveness.
2、 Example: Performance gap in the same scenario
Taking "Fresh Meat Vacuum Packaging" as an Example:

7-layer co extruded film: The barrier layer is only 1 layer of EVOH, with an oxygen permeability of about 8cc/(m ² · 24h). The meat preservation period is about 7-10 days, and it is prone to bag breakage due to insufficient puncture resistance when stored at low temperatures (0-4 ℃).
9-layer co extruded film: Adding an additional 2 layers of "POE toughening layer" and "extra EVOH barrier layer" reduces oxygen permeability to below 3cc/(m ² · 24h), extends shelf life to 15-20 days, and increases puncture resistance by 40%. The bag is not easily broken at low temperatures.
In short, the difference between 9-layer and 7-layer co extruded films is essentially the difference between "functional refinement" and "performance ceiling" - having two more layers means more precise material design, stronger scene adaptation capabilities, and "admission qualifications" for high demand fields.