Mono and Bis Substituted Polymeric Aminobenzoates as Amine Synergists for UV Curing

Type II photoinitiator systems are used extensively in litho and flexo printing of packaging inks. These systems require a hydrogen donor to generate the curing system. Without them the radical generation necessary to bring about polymerisation is very slow and ineffective for curing inks at speed. Simple aliphatic amines are very efficient hydrogen donors. However, they have several drawbacks. Typically these are odour and volatility. This can lead to loss of gloss finish due to migration and surface 'bloom'. Dimethylaminobenzoate esters based on aromatic tertiary amines were developed to counter these drawbacks and have been shown to provide excellent reactivity, Insolubility in water made them particularly suitable for thin film litho printing where an oil-water balance is used to form the image. Aminobenzoates such as Ethyl 4- imethylaminobenzoate, (EDB/ EPD) and 2 Ethylhexyl 4- dimethylaminobenzoate, (EHA) have been adopted in many type II systems. Here they perform a role of producing an active free radical from the excited state of the . During the UV curing process, the alkyl amino radical becomes part of the growing polymer chain by reacting with the unsaturated functional groups on monomers and polymers. Despite the general acceptance and widespread use of aminobenzoates in the UV curing industry it has been found that the ethyl ester in particular has the potential to migrate and the remaining unreacted amine is easily extracted from the cured film.