The present invention provides an initiator system including an infrared-absorbing
compound that exhibits an electronic transition band in the near-infrared region,
an initiator, and a metallocene compound. Upon exposure to infrared radiation,
the initiator system is capable of producing radicals sufficient to initiate a
photopolymerization reaction. Suitable infrared-absorbing compounds include indocyanine
dyes, for example. Trihalomethyl triazine compounds and onium compounds are suitable
initiators. Suitable metallocene compounds include ferrocenes and titanocenes.
The present invention also provides an infrared-sensitive composition including
an ethylenically unsaturated polymerizable component, an infrared-absorbing compound
that exhibits an electronic transition band in the near-infrared region, an initiator,
and a metallocene compound. The infrared-sensitive composition provides improved
photospeed and sensitivity in some embodiments. A printing plate precursor including
an infrared-sensitive coating is also provided. The printing plate precursor exhibits
enhanced shelf life in some embodiments. A method of making a printing plate precursor
and a method for making a printable lithographic printing plate are further provided
by the invention.