Corona treatment systems
Most plastics have a non-polar, electrically well insulating and water-repellent surface. It is poorly wettable for printing inks, solvents, aqueous polymer dispersions, adhesives or adhesion promoters. This is especially true for polyethylene, polypropylene and polyester films. The printing of such plastics (films or 3D objects) or their further processing by laminating or coating is therefore not possible. The inks would not adhere, delamination would occur in the production of composite films.
Corona treatment is the most commonly used form of surface treatment. The aim of this method is to increase the polarisation of the surface, which significantly improves wettability and chemical affinity.
The effect achieved by the corona treatment is an increase in surface tension to values between 38 to 60 mN/m. Since the surface tension is caused by dispersive and polar interaction components the introduction of polar functional groups in particular increased the polar component of the surface tension.
To avoid errors, is is important that the surface tension of the film is higher than that of the coating material. In addition, the ratio between polar and dispersive interaction of the film should be as similar as possible to the surface tension of the coating material. Only then can an optimal wetting, and thus adhesion be achieved.