Enhancing Adhesion for Graphic Overlays: The Essential Guide to Surface Pre-treatment of PET Films

PET film surface treatment for graphic overlays & membrane panels

Why is Surface Pre-treatment Necessary for PET Films?

PET (Polyethylene Terephthalate) films are widely used in the printing and packaging industries due to their outstanding physical and chemical properties. The high symmetry in the molecular structure of PET endows it with a certain ability for crystalline orientation. However, this also results in a non-polar characteristic on its surface, making it challenging for conventional coatings to adhere properly. If coatings or printing are applied directly onto PET films, issues like peeling or detachment may occur. To improve this condition and enhance the material’s adhesiveness, surface pre-treatment becomes a crucial step.

Surface Pre-treatment Processes for PET Films

  • Corona Treatment:
    • This process reorganizes the molecular structure on the substrate’s surface under a high-voltage electric field, creating more polar sites, and thus enhancing the adhesiveness of coatings or inks. To ensure the longevity of the treatment effects and prevent the surface activity from diminishing over time, PET films usually undergo a secondary corona treatment before any coating or printing is done. Despite its effectiveness in improving adhesiveness, this method comes with high equipment costs and complex operations, potentially making it less suitable for small and medium-sized enterprises with limited budgets.
  • Flame Treatment:
    • This method improves the PET film’s surface adhesiveness by rapidly covering it at high temperatures, instantaneously reaching up to 1000°C. This induces oxidative reactions of the surface macromolecules, generating polar groups, and thus enhancing adhesiveness. However, this method demands precise control over the treatment conditions, such as the temperature of flame treatment and the distance between the flame and the PET surface, to prevent damage from under-burning or over-burning.
  • PET Promoter/Primer:
    • Applying a PET promoter or primer for surface treatment is an economical and effective method. The material can be directly sprayed or coated onto the PET surface, forming a thin layer of 10-15 micrometers. After drying, it is ready for roll-up, and secondary printing or coating of other materials can be done within a year. Additionally, the PET promoter or primer can serve as a main agent, compatible with color pastes, gold and silver powders, conductive materials, magnetic materials, etc., for widespread applications in film printing, silk screen printing of keyboard materials, conductive and magnetic coating carriers, model pre-coating, and more.

The primary goal of surface treatment is to enhance the film surface’s adhesiveness, improving its affinity for inks and coatings. This can be achieved by changing the film surface’s chemical properties or physical structure. Surface treatment can create a micro-rough structure on the film, increasing its surface area, and thus enhancing the adhesiveness of coatings or inks. Additionally, this treatment improves the film’s surface energy, making it more receptive to being wetted by coatings or inks, ensuring an even distribution of the coating and a good adhesion effect.

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