7-Layer EVOH Barrier Blown Film Machine

Both produce 7-layer film, but they differ in how the layers are generated. A 5-extruder machine uses die-head flow splitting: Extruders A, B and C each feed two symmetric layers simultaneously, while Extruder D feeds the EVOH core. This means the outer and inner PE layers are identical in formula, as are the two TIE layers and the two PA layers.

A 7-extruder machine has one independent extruder per layer — no flow splitting. This allows every layer to carry a different material formula. For example, the outer PE layer can include white masterbatch and slip additives for printing, while the inner PE layer carries anti-fog or anti-block additives for seal performance — without any compromise between the two.

For most food vacuum packaging applications, the 5-extruder symmetric configuration is sufficient. The 7-extruder configuration is specified when outer and inner surface functional requirements are genuinely different.

The die head on a co-extrusion blown film machine contains multiple spiral mandrel flow channels. In a symmetric structure, the die head splits a single extruder's melt stream into two separate channels — one feeding the outer layer and one feeding the corresponding inner layer. Because both layers receive the same melt from the same extruder, they are identical in material composition.

This is the same principle used in 3-layer ABA machines, where 2 extruders produce 3 layers: Extruder A is split by the die head to feed both outer layers, while Extruder B feeds the core. The 7-layer symmetric machine extends this logic — 5 extruders produce 7 layers through 3 split channels and 2 dedicated channels (TIE outer/inner share one extruder each, PA outer/inner share one extruder, and EVOH has its own dedicated extruder).

The structural layers (L1, L3, L5, L7 in a symmetric structure) process LDPE, LLDPE and mLLDPE. The TIE layers process maleic anhydride-grafted adhesive resins. The PA layers process Nylon PA6 or PA6,66. The EVOH core processes EVOH grades with 32–44 mol% ethylene content — lower ethylene content delivers higher barrier performance but requires higher processing temperatures and is more sensitive to moisture.

EVOH and PA are both hygroscopic and must be pre-dried before processing. EVOH in particular has a narrow processing window — temperature control to ±1°C is critical to prevent degradation. LayerQuestar specifies OMRON PID controllers on all zones for this reason.

As a theoretical reference, a PE/TIE/PA/EVOH/PA/TIE/PE structure with approximately 10% EVOH layer thickness can achieve an OTR below 1.5 cc/m²·day at 23°C, 0% RH. A 5-layer PE/TIE/EVOH/TIE/PE structure typically achieves 1–3 cc/m²·day under the same conditions.

Actual barrier performance depends on EVOH grade (ethylene content), EVOH layer thickness as a percentage of total film gauge, blow-up ratio (BUR), processing temperature and humidity conditions during and after production. EVOH barrier performance degrades significantly at high relative humidity — the PA layers in a 7-layer structure help protect the EVOH core from moisture absorption.

Contact LayerQuestar with your specific application requirements for a structure recommendation and barrier performance guidance.

A 7-layer line has a higher capital cost than a 5-layer line, primarily due to the additional extruders, the more complex 7-channel die head, and the larger machine footprint. For specific pricing, contact LayerQuestar directly — configuration, film width and extruder count all affect the final figure.

On the running cost side, the dominant variable is resin cost — particularly EVOH and PA, which are significantly more expensive than PE. A 7-layer structure uses more PA than a 5-layer structure, which increases material cost per kilogram of film. However, the improved barrier performance of a 7-layer structure often allows thinner total film gauge to achieve the same shelf life target, partially offsetting the higher resin cost.

EVOH is more demanding to process than standard PE resins. The main challenges are:

• Moisture sensitivity: EVOH must be pre-dried before processing. Moisture causes bubble instability and reduces barrier performance.
• Narrow processing window: EVOH degrades if held at processing temperature for too long or if temperature exceeds the recommended range. Precise PID temperature control is essential.
• Shutdown purging: EVOH left in the die head during shutdown will degrade. A proper purge sequence using PE is required before every shutdown.
• Incompatibility with PE: EVOH does not bond to PE without a TIE layer. Skipping or under-specifying the TIE layer results in delamination.

LayerQuestar provides operator training as part of commissioning to cover all EVOH handling and processing protocols.

The blown film line produces rolls of flat or gusseted barrier film. Depending on your end product, typical downstream equipment includes:

• Slitter-rewinder — to cut master rolls to finished width
• Pouch-making machine — for vacuum pouches and stand-up barrier bags
• Thermoforming line — for tray-lidding and vacuum skin packaging
• FFS (form-fill-seal) machine — for high-speed automated packaging lines
• Corona treater — if the film will be printed or laminated

Contact LayerQuestar to discuss turnkey line configurations that combine the blown film line with downstream converting equipment.

Installation and commissioning time for a 7-layer line is longer than for a 3- or 5-layer machine, due to the greater number of extruders, the complexity of the die-head alignment, and the EVOH processing qualification requirements. Typical commissioning duration is [NEEDS CLIENT VERIFICATION — confirm standard commissioning timeline for 7-layer lines].

LayerQuestar provides on-site commissioning engineers as standard. The commissioning scope includes mechanical installation verification, electrical and control system check, initial film run with all 7 layers, and operator training on EVOH handling protocols.

Yes — the machine can run with the EVOH extruder purged and the channel bypassed or substituted with a compatible resin, effectively producing a 5- or 6-layer structure on a 7-layer platform. This flexibility allows the line to serve multiple product families from a single machine.

However, the 7-layer line is optimised and priced for barrier film production. If your primary application does not require EVOH or PA, a 5-layer or 3-layer line will deliver better value. Contact LayerQuestar to discuss the right configuration for your specific product mix. [NEEDS CLIENT VERIFICATION — confirm partial-layer operating mode support]