Patterned perforation of polyester films by excimer laser ablation

The effects of 248 nm KrF excimer laser irradiation on combinations of different thickness polyethylene terephtalate (PET) films and different stainless steel mask mesh opening sizes were considered as a possible method to achieve different size perforation patterns on different thickness PET films. The findings of this work will provide an effective and controllable perforation technology. Therefore, ablation behavior of PET films was investigated for different laser energy fluence and number of laser pulses. The morphology of irradiated samples was observed by optical microscopy, and atomic forced microscopy was employed to study the topography and microstructures after laser ablation. An attempt has been made to correlate these findings with the orientation, strength, and mechanical properties of the polymer. The experimental results reveal that the percentage of perforation and the average perforated area increase with increasing number of pulses for all film thicknesses. The affected area, defined as the perforated area plus the heat affected zone (a black-char-region around the perforated area), decreases with increasing number of pulses at higher fluence values as the polymer chains tend to curl and shrink by absorbing energy. High laser fluence seems to lead to surface depressions due to thermal shock and surface stress waves along the process directions confirmed by tensile testing, x-ray analyses, and atomic force microscopy.