Top Tips for Checking the Treat Side of Substrates
A practical guide to identifying the treated (functional) side of packaging films using dyne pens and chemical tests across polyester, polyolefins, and various coated substrates.
Overview
When film rolls lack identification labels, determining the functional (treated) side is essential for production. Dyne solution pens provide a quick and effective method for identifying treated surfaces across various film types.
Testing Procedure
- Clean the film surface thoroughly and remove at least one outer wrap from the roll
- Fold the sample to expose both sides
- Apply dyne pen solution across the web on both sides
- Evaluate the results
- Maintain separate pen sets for different substrate types
Film-Specific Testing Methods
Polyester: Polyester has a natural dyne level of 44, so use a 58 dyne solution pen. The solution beads up on untreated PET but wets out (remains flat) on treated surfaces.
Polypropylene & Polyethylene: A 44-48 dyne pen works effectively. Dyne solution beads on untreated sides and wets out on treated surfaces.
Silicon Oxide (SiOx) or Aluminum Oxide (AlOx) Coated Films: Dyne solution beads on uncoated PET but wets out on coated surfaces. Water provides an alternative test method. Additionally, coated films typically curl away from the coated side.
PVdC Coated Films: Use potassium hydroxide solution; the film turns black when PVdC is present.
PVC Coated Films: Using the same chemical solution, the film turns brown/red when PVC is present.
PVOH Coated Films: Apply potassium iodide and iodine solution; PVOH coating changes to dark brown.