What is the cause of the tacky surface of a cured acrylate-based light-curable adhesive?
In most cases the adhesive is cured. The tacky surface that is observed is due to the inhibition of the polymerization reaction by oxygen at the surface. In the bulk of the material, once the finite level of oxygen is depleted (by exposure to light), the polymerization will initiate. At the adhesive’s surface, however, oxygen is continuously replenished by oxygen molecules in the atmosphere, which results in continuous inhibition of the polymerization. The end result is a tacky surface, composed of a combination of lower molecular weight polymers and uncured material. When bonding two surfaces together, oxygen inhibition is generally not observed. In most cases, oxygen inhibition is seen when package geometry allows a portion of the adhesive to be directly exposed to the atmosphere during cure. Oxygen inhibition can be overcome by curing the material under nitrogen.
