1-Hydroxycyclohexyl phenyl ketone (184) is a new type of high-efficiency photoinitiator introduced by Ciba-Geigy Company in Switzerland in the 1980s. It is a highly efficient and yellowing-resistant free radical (I) type solid Chemicalbook bulk photoinitiator, which has the advantages of long storage time, high initiation efficiency, and wide ultraviolet absorption range. Oligomers are commonly used for UV curing of unsaturated prepolymers (such as acrylates), and are especially suitable for coatings and inks that require a high degree of yellowing.