What Is a Blown Film Machine? Mono, AB, ABA and Co-Ex

Film is the first link in bag production. Its quality directly affects seal performance, bag strength and how efficiently your bag machines run. Most bag film is made on a blown film machine. This guide explains how blown film extrusion works, how mono, AB, ABA and multi-layer co-extruded structures differ, and how to plan a blown film line together with your bag making machines.

How a blown film machine works

1. Feeding and extrusion: Resin pellets (HDPE, LDPE, LLDPE plus additives) enter the extruder, where the screw and heater zones melt and homogenise them.
2. Die: The melt exits a circular die as a tube.
3. Blowing: Air is blown into the tube to form a bubble. The ratio of bubble to die diameter, the blow-up ratio, sets film width and mechanical properties.
4. Cooling: An air ring cools the bubble from outside; cooling efficiency affects both output and clarity.
5. Collapsing and haul-off: The bubble is flattened between nip rollers at the top of the tower. Haul-off speed sets film thickness.
6. Gusseting, slitting and winding: Gussets are formed if needed, edges are trimmed and the film is wound into rolls.

Thickness is set by the balance between extruder output and haul-off speed. Bag films typically start around 8 microns and can exceed 100 microns for heavy-duty sacks.

Mono, AB, ABA and co-ex: the key differences

Mono-layer blown film

One extruder and a single-layer die. Simple design, low investment and maintenance costs. Widely used for t-shirt bags, standard garbage bags and general-purpose film. Because the whole film is one blend, any recycled content also shows on the surface.

AB (two-layer) blown film

Two extruders form two different layers. For example, the inner layer can carry a recycled or lower-cost blend while the outer layer uses a print-friendly or glossier resin, cutting cost while protecting surface quality.

ABA (three layers, two extruders)

Typically two extruders create a three-layer structure: identical outer skins (A) around a different core (B). The core can hold an economical recycled or filled blend while the skins stay clean and sealable. It is a very popular cost-versus-quality solution for bag producers.

Multi-layer co-extrusion (ABC and beyond)

Three or more extruders, each layer with its own job: strength, barrier, sealant, print surface. Used for food packaging, technical films and demanding applications, with higher investment and process know-how requirements.

Which structure is right for you?

• Standard t-shirt and garbage bags on a tight budget: Mono-layer is usually enough.
• Lower cost with recycled content and a clean surface: AB or ABA stands out.
• Printed, glossy, high-quality carrier and boutique bags: ABA lets you optimise the skins for print and appearance.
• Food, barrier and technical packaging: Multi-layer co-ex is required.

Key parameters to evaluate

• Screw diameter and L/D ratio: Define output and melt homogeneity.
• Die diameter and film width range: Match them to your bag widths.
• Rotating die or oscillating haul-off: Spreads gauge variations so they do not stack up on the roll, improving winding quality.
• Air ring efficiency: Directly affects output and film optics.
• Winder type: Single or twin-station winders reduce roll change downtime.
• Energy consumption: Heater and motor efficiency make up a large part of operating cost.

Planning blown film and bag machines together

Film line capacity should be balanced against the total demand of the bag machines it feeds; typically one blown film line supplies several converting machines. Film width and gusset size must fit the working range of machines such as t-shirt bag machines or perforated roll bag machines. Edge trim and rejected rolls can be fed back into production with a plastic recycling machine.

Conclusion

A blown film machine is a strategic investment for bag producers who want control over material cost. Choose between mono, AB, ABA or multi-layer structures based on your product mix, recycling strategy and quality targets. Explore Mestaş Makina's blown film machines, and read how to start a plastic bag factory for full-line planning. For a technical discussion, call or WhatsApp +90 537 718 18 34.