Raise dyne level on PE, BOPP, and PET film with corona treatment before flexo printing. YAOSHG covers watt density, placement, and QA for durable adhesion.
Surface Energy and Ink Wet-Out on Film
Flexographic inks wet out only when film surface energy exceeds the ink surface tension. Untreated PE and some BOPP grades arrive below 38 dynes, which leads to fisheyes, pinholes, and rub-off in downstream bag making. Corona treatment raises polarity by micro-oxidation of the surface without measurable thickness change. Treat immediately before the first print deck because dyne level decays with time, dust, and silicone contamination from slip additives. YAOSHG integrates inline treaters on CI film presses such as the Apex 6-color CI film press with watt density control tied to line speed.
Watt Density and Treater Gap Settings
Watt density, expressed as watts per square meter per minute of exposure, is the primary process variable—not raw electrode power alone. Increase density when raising line speed or when switching to low-slip film that quenches treatment effect. Electrode gap and roll covering condition equally influence uniformity; a worn silicone sleeve creates streaks that print through as banded adhesion failure. Target 40–46 dynes for solvent flexo on PE shopping bag film, then validate with dyne pens or test inks rather than assuming nameplate settings. Sleeve-change CI lines in the King sleeve CI series benefit from automatic gap tracking when web width changes between jobs.
Placement Relative to the First Print Deck
Mount the corona treater after unwind splicing and web cleaning, but before the first anilox. Treating after printing destroys the image; treating too far upstream allows decay and handling scuff. Keep the treater-to-print distance under three meters on high-slip films and under one meter on critical label work. Ground the treater frame and isolate ozone exhaust per local safety codes. On gearless film platforms like the 8-color gearless full servo film press, synchronize treater output with speed ramp during startup so the first meters of a roll are not under-treated.
Material-Specific Treatment Notes
PE and LLDPE respond well to standard corona but lose dyne level fastest; schedule retreat if rolls sit more than eight hours. BOPP with high slip requires higher watt density and may need flame or plasma on metallized surfaces where corona is less effective. PET for label facestock often arrives pretreated—verify incoming dyne before adding unnecessary treatment that can migrate additives. When printing compostable films, confirm that treatment does not exceed supplier limits for heat-sensitive biopolymers. Pair treatment setup with BOPP flexo printing guidance and PE film printing tips for complete material readiness.
Quality Assurance and Troubleshooting Adhesion
Establish incoming and post-treat dyne checks at shift start and after every splice. Run a standardized tape pull or rub test on the first color before full production. If adhesion fails mid-run, inspect for treater arcing, electrode contamination, or web wander that changes gap. Back-treat on the rewind side is rarely needed for surface print but may apply on some lamination structures. Document treater power, speed, and dyne results per roll for traceability when customers report field failure. Link persistent rub-off issues to ink picking troubleshooting when ink splits between film and plate instead of failing at the surface.
Need help selecting a flexo press?
Send your material, web width, color count, target speed and sample packaging format. YAOSHG engineers will recommend a suitable machine series.