Initiator system for radiation curable compositions, radiation curable compositions containing such an initiator system, a process for curing said compositions and products covered therewith

Claim 1

An initiator system for radiation curable compositions said initiator system comprising: (a) a photoinitiator, with the exception of a compound of the formula: ##STR8## where R 1 =H or a substituted or unsubstituted alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a cycloalkyl or cycloalkenyl group having 5 to 8 carbon atoms, a substituted or unsubstituted aryl group having 6 to 20 carbon atoms, a furfuryl group or the group ##STR9## where Y represents a methyl group and Z an alkyl group having 2 to 4 carbon atoms or Y and Z together form a 1,3- or 1,4- alkylene group having 3 or 4 carbon atoms, which is substituted or not with an alkoxy group having 1 to 4 carbon atoms; R 2 = a substituted or unsubstituted alkyl group or alkenyl group having 4 to 20 carbon atoms, a cycloalkyl group or cycloalkenyl group having 5 to 8 carbon atoms, an alkaryl group having 4 to 16 carbon atoms in the alkyl group or a furfuryl group; R 3 and R 4 may be the same or different and represent a hydrogen, a chlorine or a bromine atom or a phenyl group, a substituted or unsubstituted alkyl group or alkoxy group having 1 to 4 carbon atoms, or a dialkyl amino group of which the alkyl groups have 1 to 4 carbon atoms and may be substituted or not with a hydroxyl group; (b) a synergistic amount of a Na, K and/or Li-salt of an organic acid having at least 4 carbon atoms which is compatible with the curable compositions, and (c) a solvent for component b in such an amount that the solution of salt b in the curable compositions is just about saturated or nearly saturated.