Choosing film for a VFFS machine comes down to 6 specifications, and the one most often left off an enquiry — seal initiation temperature — is the one that stops the line.
Most film problems on a vertical form-fill-seal line are not film faults. They are mismatches: a reel specified against the product, ordered from someone who never asked what machine it was going on. Six things decide whether a film runs well, and a converter selling pouches alone rarely asks about any of them.
The six
- Web width. Set by the forming collar and the bag width, not chosen. Too narrow and the seal has nothing to work with; too wide and the film folds badly and wastes material every bag. Give us the collar size or the finished bag dimensions and we slit to it.
- Seal initiation temperature. The temperature at which the sealant starts to bond. It has to suit your jaw temperature and dwell time at the speed you actually run. Too high and seals are weak at speed; too low and the film sticks to the jaws and strings. This is the single most useful number to give a film supplier and the one most often omitted.
- Coefficient of friction. How the film slides over the former and against itself. Too high and it drags and mistracks; too low and the reel telescopes and the bag will not stay where it is put. A film that runs beautifully on one machine can be wrong on another purely on COF.
- Stiffness. The film has to hold its shape over the forming tube without buckling. Stiffer film forms cleaner bags; too stiff and it cracks at the fold. Stiffness comes from the structure and the thickness together, which is why thinning a film to save money changes how it runs.
- Thickness tolerance. Not the nominal thickness — the variation around it. A film varying widely across the web seals inconsistently, and inconsistent seals on a fast line are leakers found by a customer rather than by you.
- Core size and reel diameter. Mundane and a genuine cause of a stopped line. The core has to fit your unwind shaft and the reel has to fit the machine. Send both.
Why this is hard to buy
A converter who sells pouches does not own a filling machine and has no reason to know how yours behaves. A machinery supplier who sells lines does not make film. The specification sits in the gap between them, and the buyer ends up carrying it.
ALLWINS sells both — packaging machinery is a separate division of the group — which is the only reason we can specify a film against a machine rather than against a product description. It is also why we ask for the machine model in the first email rather than the fifth.
A practical starting point
If you have film that runs well, send a sample and the specification sheet. Matching a known-good film is faster and more reliable than deriving one, and we can measure what the sheet leaves out.
If you are starting from nothing, send the machine model, the bag dimensions, the product and the speed you want to run. The structures available are in films and rolls, and back seal pouches is the format most VFFS lines produce.
The standards behind this are public: see FDA 21 CFR 177, for the food-contact grades these films come in.
Film for a VFFS machine in short
- Six specifications decide whether a reel runs: web width, seal initiation temperature, coefficient of friction, stiffness, thickness tolerance and core size.
- Seal initiation temperature is the one most often left off an enquiry and the one that most often stops a line.
- Coefficient of friction is why a film that runs on one machine mistracks on another.
- If you have film that runs well, send a sample — matching a known-good film beats deriving one.
Key Information
Choosing film for a VFFS (vertical form-fill-seal) machine comes down to six specifications, and the one most often left off an enquiry — seal initiation temperature — is the one that stops the line.
- Six specifications define a VFFS film: structure, thickness, reel width, core diameter, seal initiation temperature and coefficient of friction.
- Seal initiation temperature is the point at which the sealant layer begins to bond; a film that seals too high slows the machine, one that seals too low blocks on the reel.
- Reel width has to match the forming collar, not the bag width.
- Coefficient of friction determines whether the film feeds or slips; it is specified, not assumed.
- Most VFFS film failures are specification mismatches rather than film defects.
Why does my VFFS film seal on one machine but not another?
Because seal initiation temperature is matched to the jaw temperature and dwell time of a particular machine. The same reel on a faster line has less dwell, so a film that sealed at 140 °C may need a lower-initiation sealant.
What reel width should I order for a 150 mm bag?
The reel width is set by the forming collar and the seal allowances, not by the bag width, so it is always wider than the finished bag. Send the collar size and the machine model and the width follows from them.
Can one film run on both a VFFS and a pre-made pouch line?
Rarely without compromise. A pre-made pouch is made up first and filled later, so it is built for a different seal geometry and a different handling path.
