Pulsed irradiation for high-throughput curing applications

A xenon flash lamp was used to create intense pulsed light (IPL) irradiation to cure acrylate coatings at very high rates and ambient temperature; we investigate whether the achievable conversion can be increased compared to conventional irradiation and as the dose rate is increased with IPL parameters - pulse intensity, pulse duration, and pulse repeat period - and with the photoinitiator (PI) concentration and the curing temperature. Conversion of acrylate double bonds was measured using Fourier transform infrared (FTIR) spectroscopy. In all cases, cure conversion increases with the number of pulses until it plateaus at the maximum achievable value, when the reduced mobility of reactive species prevents further reaction. Changing the pulse intensity, the pulse duration, and the pulse period - and even changing the photoinitiator loading - do not appreciably affect the achievable conversion at ambient temperature. Increasing the temperature can result in somewhat higher achievable conversion, but with the loss of advantages of ambient temperature cure. Consistent with the expectation that the cure rate should depend strongly on intensity, a single measured pulse with high dose rate can achieve millisecond-timescale cure of acrylate coatings, providing adequate curing dose while avoiding damage to the substrate from excessive exposure. In multiple pulse patterns, the achievable cure can be attained more quickly with higher dose rate; as opposed to a single pulse irradiation, the introduction of dark periods can reduce the total irradiation dose needed to attain the achievable cure conversion.