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How to choose the best treatment method for adhesion to film: corona, ozone, or flame
High dyne does not guarantee a bond. You need a strong boundary layer plus an oxidized surface. Corona, ozone, and flame do different jobs.
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Adhesion is interfacial force, chemical or mechanical. Untreated polyethylene sits slightly under 31 dynes and will not hold ink. Low-molecular-weight fractions on the surface are waxes and oils — a weak boundary layer. Failure on untreated film is often cohesive in that layer, not “the ink let go.” A strong boundary layer is anchored and has internal strength. That, plus oxidation, is the job of treatment. High dyne alone does not guarantee it.
Joint-strength data on LDPE (same adhesive, different treatment): untreated 31 dynes / 3.45 MPa; degreased 33 dynes / 8.28 MPa; treated in air 42 dynes / 18.6 MPa; treated in argon 33 dynes / 19.3 MPa; treated in fluorine 20 dynes / 19.7 MPa. The fluorine sample is the lowest dyne and among the strongest bonds. Polarized-light work shows a higher-melting, higher-molecular-weight skin only nanometers thick. Crosslinking the low-molecular-weight fraction is the mechanism.
Starting surface tensions: PP 29–31 dynes/cm, PE 30–31, PVC 38–39, PET 41–44, nylon 38–46. Raise the solid at least 10 dynes/cm above the liquid you are putting on it.
What's in this guide
- Corona
- Ozone (extrusion coating)
- Flame
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