Surface tension of plastic film

The surface tension of a plastic film depends on the free energy of the surface of the plastic film, which in turn depends on the molecular structure of the film material itself. Most plastic films such as polyolefin films (LDPE, HDPE, LLDPE, PP) are non-polar polymers with low surface free energy and low surface wet tension, typically around 30 dynes/cm.

In theory, if the surface tension of the object is less than 33 dynes/cm, ordinary inks or adhesives cannot adhere firmly, so the surface must be treated. Polyester (PET, PBT, PEN, PETG) is a polar polymer with a high surface free energy and a surface wet tension of 40 dynes/cm or more. However, for high-speed color printing or to increase the bonding between the vacuum-aluminized layer and the surface of the BOPET film, it is also necessary to surface-treat the BOPET film to further increase the surface wet tension.

https://www.xmlfilm.com