Polyolefins like polyethylene and polypropylene have naturally low surface energy, generally measured in dyne levels well below what most inks, adhesives, and coatings need to wet out and bond properly. Corona treatment solves this by passing the film between an electrode and a grounded roller across a small air gap, where a high-voltage electrical discharge ionizes the air, creating a corona of charged particles that bombards the film surface. This bombardment oxidizes the surface and creates polar functional groups, raising the film's surface energy, often referred to in the industry by its dyne level, from somewhere in the low 30s up into the high 30s or low 40s dynes per centimeter.
The treatment is applied in-line as the film travels through the extrusion or converting process, immediately before winding, and it's typically tested with dyne pens or dyne test solutions that change wetting behavior at known surface energy thresholds, giving a quick pass or fail check on the treatment level. Corona treatment does fade over time, generally dropping somewhat within days to weeks after treatment, which is why treated film is often specified with a target dyne level and a recommended print or laminate window after production.
Without adequate corona treatment, ink will bead up, smear, or scratch off a printed film, and laminating adhesives or extrusion coatings may fail to bond properly, so corona treatment is a standard, expected step for nearly any polyolefin film destined for printing, lamination, or coating.
Glossary
Corona Treatment
An in-line surface treatment that uses electrical discharge to raise a film's surface energy, improving how well ink, adhesive, or coating sticks to it.
Example
A film going straight to a flexographic printer needs to arrive with a verified dyne level, often 38 to 40 dynes per centimeter, which is achieved through corona treatment during the extrusion or converting process.
Nuance
Customers sometimes treat corona treatment as a one-time, permanent fix, but treated surface energy decays over time and with exposure to heat, humidity, or handling. A film treated weeks before printing or laminating may need to be retreated, or the printer may need to plan for a tighter turnaround window to avoid adhesion problems.