Dark Reaction
A dark reaction is any chemical reaction that occurs in the absence of a source of UV energy. An example would be if a UV-curable formulation in a drum is either improperly stored or stored beyond its recommended storage time and a noticeable increase in viscosity has occurred. The increase in viscosity is a good indication that there has been some dark reaction in the drum. Another example is the continued cure of a cationically polymerizable coating that occurs after the exposure step and the source is removed. In this case, the dark reaction is an expected part of the polymerization process.