Surface chemistry of polycarbonate film and adhesion of ultraviolet‐cured inks

One of the primary uses of polycarbonate film is in screen‐printing applications, with ultraviolet (UV)‐cured inks becoming increasingly popular due to environmental concerns. During multicolor printing operations, regions of the polycarbonate film surface are unavoidably exposed to UV irradiation during the cure of adjacent regions. Subtle changes in the polycarbonate surface chemistry affect subsequent printing on the UV‐exposed surface, primarily manifest as a decrease in the ink adhesion level. In this study, static secondary‐ion‐mass spectroscopy (SIMS), x‐ray photoelectron spectroscopy (XPS), and contact angle measurements were used to show that the surface becomes oxidized and water wettable. The degree of photo‐oxidation, nature of the photoproducts, and ink adhesion characteristics were measured as a function of the UV wavelength window. Filtering out the short wavelengths (λ≪300 nm) from a medium pressure Hg lamp resulted in significantly less photo‐oxidation compared to identical exposures from the unfiltered UV. The ink/polymer interfaces were also examined by transmission electron microscopy (cross section) and by peeling followed by XPS and static SIMS analysis. Based on these results, mechanisms for ink/polycarbonate interface adhesion are proposed.