On-press developable thermosensitive lithographic plates utilizing an onium or borate salt initiator

A method of lithographically printing images on a receiving medium, comprising in order:

• (a) providing on a lithographic press a lithographic printing member comprising (i) a substrate;
• and (ii) a thermosensitive layer comprising a free radical polymerizable ethylenically unsaturated monomer having at least one terminal ethylenic group, an infrared absorbing dye, and a free-radical initiator selected from the group consisting of onium salt and borate salt;
• wherein said substrate is a sheet material mounted on a plate cylinder or is the surface of a plate cylinder of the lithographic press;
• and said thermosensitive layer is capable of hardening upon exposure to an infrared laser radiation, is soluble or dispersible in and on-press developable with ink (for waterless plate) or ink and/or fountain solution (for wet plate), and exhibits an affinity or aversion substantially opposite to the affinity or aversion of said substrate to at least one printing liquid selected from the group consisting of ink and an abhesive fluid for ink;
• (b) imagewise exposing the plate with the infrared laser radiation according to digital imaging information to cause hardening of the thermosensitive layer in the exposed areas;
• and
• (c) operating said press to contact said exposed plate with ink and/or fountain solution to remove the thermosensitive layer in the non-hardened areas, and to lithographically print images from said plate to the receiving medium.

A method of lithographically printing images on a receiving medium, comprising in order:

• (a) providing a lithographic plate comprising (i) a hydrophilic substrate;
• and (ii) an oleophilic thermosensitive layer comprising a free radical polymerizable ethylenically unsaturated monomer having at least one terminal ethylenic group, an infrared absorbing dye, and a free-radical initiator selected from the group consisting of onium salt and borate salt;
• wherein said thermosensitive layer is capable of hardening upon exposure to an infrared laser radiation, and is soluble or dispersible in ink and on-press developable with ink and fountain solution;
• (b) imagewise exposing the plate with the infrared laser radiation according to digital imaging information to cause hardening of the thermosensitive layer in the exposed areas;
• and
• (c) contacting said exposed plate with ink and fountain solution on a lithographic press to remove the thermosensitive layer in the non-hardened areas, and to lithographically print images from said plate to the receiving medium.