LED Curing Versus Conventional UV Curing Systems: Property Comparisons of Acrylates and Epoxies

The development of high power short wavelength light emitting diodes (LED) in the late 90s created the potential of a solid state ultraviolet/visible curing source. The benefits of LEDs are low heat, portability and low power consumption. These advantages are particularly attractive for the curing of various adhesives, inks, and coatings in applications where dimensional stability of the substrates is required. The properties of urethane acrylate adhesives are compared when cured with an LED light vs. a multiple wavelength mercury arc lamps. The UV sources at higher intensity settings may cause full cure in less than a second. Some surface tack may be present, but it is due to surface oxygen inhibition and not the UV source. Curing studies with epoxies, on the other hand, illustrate that curing with LED systems is limited by the absorption of common cationic photoinitiator systems. Current high power LEDs are commercially available at wavelengths of 400 nm or higher. In order to match the spectral emission of the LED light, epoxies may have to be modified. An example of a modified epoxy that can be cured with a longer wavelength LED is demonstrated.