Reactive Inkjet Formulations - Curing By Electron Beam

Abstract

Ultraviolet light (UV) reactive inkjet printing has become well known as a reliable printing method for graphic display printed products. Single pass UV-curing inkjet printing systems are now becoming technically feasible, where sheets or a web are printed when passing under a static array of printheads. An area of interest for UV inkjet is indirect contact food packaging, but UV inkjet inks are less than ideal.The energy of a typical UV photon is below the chemical bond energy of acrylate monomers; this means that the curing reaction cannot be initiated without the presence of a photoinitiator. As the energy of electron beam (EB) electrons easily exceeds the bond energy of acrylate monomers, they will initiate cure without added photoinitiator. Problems of migration, taint, and odour associated with uncured photoinitiator and photoinitiator fragments are then eliminated.EB curing of reactive inks is well known for offset and flexography indirect food packaging printing, as there is potential for low migration. There is therefore a strong driver to extend this curing process to ink jet systems.In this paper the concept of combining EB as the cure method and inkjet as the printing method is discussed, with the objective of printing indirect contact food packaging. The paper focuses on aspects of the formulation of photoinitiator free reactive inkjet inks, including monomer selection and type and the effect this has on migration levels when cured by an electron beam process.