Adhesive and coating systems that use ultraviolet (UV) or visible light to begin the curing are intrinsically very attractive systems to the manufacturing engineer, allowing assembly of components and then “curing on command” by exposing to the radiation. The adhesives can be cured using free radicals for acrylic adhesives or cations for cationic monomers.
Two types of acrylic monomers are used in these systems: acrylates and methacrylates. A wide range of mono-functional (one reactive group per molecule) and multi-functional (more than one reactive group per molecule) monomers are available, giving wide flexibility in formulating these systems. In recent years, visible light photoinitiators have become widely available, and systems using LED light are now possible instead of high-intensity UV systems. The major issue with this type of curing is surface inhibition by atmospheric oxygen, often necessitating nitrogen blanketing, particularly for coating applications.