Anm in situ Technique for Monitoring Curing Process of UV-Curable Adhesives Using Relative Conductivity

We investigated the cure kinetics of the cationic UV-curable adhesives containing cycloaliphatic
epoxide, oxetane and £-caprolactone poiyol using a specially designed sensor consisted of two ITO (Indium Tin Oxide)-coated glasses and a spacer sandwiched between them. This instrument is based on the determination of a function of electrical conductivity as well as the capacitance of a resin sample. The measurement results revealed that as the concentration of photoinitiator was increased and the sample thickness was decreased, the relative conductivity rapidly decreased, which means that the formulation with higher concentration of photoinitiator and thin sample thickness gave shorter gelation time, higher cross-link density, and faster cure rate. The instrument consisted of a control unit and a specially designed sensor has been proven to be sensitive and reliable, and subsequently provided new possibilities to monitor the curing behaviors of the photo-curable resins besides the UVcurable adhesives.