Kinetic and mechanical properties of dual curable adhesives for display bonding process

UV–thermal dual curable adhesives were prepared using an acrylic resin with 2,2′-azobis(4-methoxy-2.4-dimethyl valeronitrile), which exhibits ten hour half-life decomposition temperature of 30 °C, in order to address issues related to monomers that cannot be cured in a shaded area during the display bonding process. We investigated the dual curing behavior of the resin with variations in the UV dose and in the thermal radical initiator content, and we also assessed the influence of the dual curing on the mechanical properties. The curing behavior was assessed through the use of photo-DSC and FT-IR conversion. In addition, the degree of crosslinking was investigated via gel fraction, and the thermal properties were measured via DSC and TGA. Peel strength, probe tack and pull-off tests were performed to evaluate the bonding performance of the dual curable adhesives. The adequate level of thermal radical initiator (TRI) content to obtain a high conversion and degree of crosslinking was approximately 0.1 phr. These were the optimum values to adjust the balance between the unstable state and the insufficient contents, and the thermal curing behavior was promoted with an increase in the UV dose and in the thermal initiator content. The gel fraction and the FT-IR ATR results clearly indicate that an enhanced network structure was formed under low UV and high thermal radical initiator content conditions. Therefore, in a low UV dose condition, the mechanical properties improved, even with a low molecular weight due to a high network formation.