Humidity and Its Affect on LCAs
In the uncured state, humidity under most normal conditions of 0-70% Relative Humidity (RH) has no impact on a light-curable adhesives. It does not affect the curing time, chemical properties, or adhesion to the substrate. At 70% RH or higher, we would want to watch for condensation on the surface of the substrate that is being bonded or coated, as this would effectively act as a barrier between the adhesive and the substrate, and may reduce the bond strength localized around those droplets.
In the cured state, high levels of humidity for extended periods of time at high temperature may affect some acrylated urethanes by causing hydrolysis in certain formulations, which may decrease the bond strength and cohesive strength of the light-curable material. Applications that require exposure to these conditions should be tested thoroughly to determine suitability for the application. An indication of this effect can be seen by looking on the data sheet to determine the % water absorption, but this is only an indicator, and testing in the actual application should be done. Limiting the exposure to the adhesive bond line through proper design can reduce the impact of humidity on the adhesive.