Carrier gas UV laser ablation sensitizers for photopolymerized thin films

Designed carrier gas UV laser ablation sensitizers were synthesized and proved to greatly enhance the UV laser ablation of photopolymerized thin films. Polymers containing dense ester groups are reported to have better laser ablation performance because of the tendency of the ester groups to decompose into gaseous products (“carrier gases”) during the ablation process. In order to introduce this mechanism to cationic UV curable coatings for better laser ablation, a series of “carrier gas” sensitizers were synthesized by reacting hydroxyl containing reactive diluents such as oxetane and polyester polyols with monomethyl oxalyl chloride or dimethyl oxalate; the oxalyl group is considered a “carrier gas” generating moiety. Furthermore, a UV absorbing chromophore, naphthalene, is either chemically bound to the oxalyl containing molecules or blended with the synthesized oxalyl containing compounds to produce a synergistic effect. The “carrier gas” sensitizers were added into a typical cationic UV curable formulation to form sensitized coatings, which were then characterized by thermogravimetric analysis, real time FTIR and ablated by a 355 nm laser. The ablation vias were examined using optical profilometry and SEM. Compared to the control, the sensitized coatings were found to have similar thermal decomposition temperatures and higher functional group conversion during photopolymerization. All of the sensitized coatings containing the “carrier gas” sensitizers exhibited better UV laser ablation performance than the control. The combination of naphthalene derivatives and the oxalyl group gave a better ablation result, suggesting a synergistic effect. The chemical combination of the naphthalene and oxalyl group exhibited better ablation sensitization than their blends, suggesting a more efficient intramolecular laser energy utilization process.