DYNAMIC MECHANICAL ANALYSIS OF UV-CURABLE COATINGS WHILE CURING

摘要

A method has been developed for following the dynamic mechanical properties of a UV-curable coating while the sample is curing. The resulting data and plots can be used to measure the material's cure speed. The precision is sufficiently high to allow small differences in cure speed between different formulations to be reliably estimated. The sample is contained in parallel plate stress rheometer in which the usual metal bottom plate has been replaced by a UV-transparent quartz plate, allowing UV light to illuminate the sample from below. A nitrogen atmosphere is established before every run. The instrument is set up to measure G′, G″, and phase angle vs. time at a frequency of 10 Hz, taking 72 data points per second. Two seconds after a run starts, the software puts out a signal for input to a relay that opens the UV shutter Two arbitrary criteria for cure times are: 1) The time for G′ to reach 2X10~4 Pa; 2) The time for the phase angle to decrease to 45° Typical cure times for fiber optic coatings range from 0.2 to 0.6 seconds.