High-speed FFS film: which specs make the difference?

High-speed FFS: the specifications that determine your line speed

FFS (form, fill and seal) lines now operate at speeds that were unthinkable ten years ago. Sixty-five metres per minute is no longer the exception. One hundred metres is achievable for some applications. But every increase in line speed places relentless strain on your film. What was tolerable at forty metres per minute breaks at sixty-five. Here are the specifications that really matter.

Tensile strength and elongation

On a high-speed FFS line, the film is continuously subjected to stress: unwinding from the roll, forming around the product, sealing, cutting. Tensile strength in the machine direction determines whether your film survives the unwinding process. Elongation at break determines whether micro-imperfections escalate into a line stoppage. For high-speed FFS, we typically look for: higher tensile strength in the machine direction (MD), controlled elongation, and uniform thickness distribution.

Sealing behaviour

Not every film seals at the same speed. Sealing temperature, sealing window and hot-tack are the three parameters that can make or break your cycle time. A sealing window that is too narrow forces your operator to make constant adjustments. Insufficient hot-tack causes the film to split open immediately after sealing, particularly with products whose weight exerts force on the seam as they fall. Always ask your film manufacturer for the sealing window in degrees Celsius, not just the ‘recommended sealing temperature’.

Slip and blocking

Too much slip and your film will slide uncontrollably over the mould shoulder. Too little slip and the roll will stick, resulting in unwinding errors. Blocking (film sticking to itself on the roll) is often only noticed after a few weeks’ storage. For high speeds, we always require a controlled coefficient of friction (COF) between 0.15 and 0.25, depending on the product and machine.

Thickness distribution and gauge variation

A film with a nominal thickness of fifty microns that in practice varies between forty-five and fifty-five microns will cause problems on a high-speed line. Variation means variable stretch, variable sealing and, ultimately, a variable risk of breakage. Reputable manufacturers continuously measure gauge variation and ensure it remains within an agreed tolerance.

Practical checklist before testing

Before testing a new film on your FFS line, request the following data:

• Tensile strength MD and TD (in MPa)
• Elongation at break MD and TD (in per cent)
• Seal temperature and seal window (in degrees Celsius)
• Hot-tack curve
• Static and dynamic COF
• Thickness distribution with tolerance
• Recycled content and origin

If you do not receive this data, you are buying on blind trust.

Is your FFS line not running at the speed promised by the manufacturer? Often, the problem lies with the film, not the machine. Discuss your packaging requirements.