Checking the corona treatment of films

Surface treatments to improve adhesion properties play an important role in many areas of polymer technology. Flame treatments or corona treatments are used to increase the surface energy of injection-molded parts or films and thus influence properties such as printability or static charge. Checking the quality of such treatments using simple test methods such as test inks is not always reliable.
This is where X-ray photoelectron spectroscopy (XPS / ESCA) can provide important information about the surface condition of the polymer. In addition to providing information about the quality of the treatment carried out, the measurement also allows any contamination on the surface to be detected.

X-ray photoelectron spectrum of a PET film (right) after corona treatment. By determining the ratios of the characteristic oxygen and carbon lines of the PET on the surface, the quality of the corona treatment and its ageing can be investigated.

A PET film shows poor processing properties after corona treatment (static charge, poor printability). It is suspected that the corona treatment may have penetrated to the unprinted outer side. X-ray photoelectron spectroscopy is used to determine the percentage ratio of oxygen and carbon in atomic % based on the intensity of the O1s and C1s signal lines on the unprinted side. These values are compared with those of an untreated film. In this way, corona treatment of the examined side of the film could be ruled out.