IR-sensitive lithographic printing plate precursors provide a stable print-out image using a unique IR radiation-sensitive composition in an infrared radiation-sensitive image-recording layer. This IR radiation-sensitive composition includes: (1) a free radical initiator composition that comprises an electron-donating agent; (2) a free radically polymerizable composition; and (3) a color-changing compound that is represented by the Structure (I) having a conjugated carbon chain between the aromatic terminal groups. The compound also has a SO.sub.2R.sup.3 group wherein R.sup.3 represents alkyl, aryl or heteroaryl groups. After IR imaging, these precursors exhibit desirable printout images both fresh and after dark storage. The precursors can be developed off-press or on-press.

A lithographic printing plate precursor is disclosed including a support and a coating comprising (i) a photopolymerisable layer including a polymerisable compound, a photoinitiator and an asymmetrically substituted infrared absorbing compound.

A positive-working lithographic printing plate precursor including a support and an image-recording layer formed on the support and consisting of a positive-working photosensitive resin composition, in which the positive-working photosensitive resin composition contains a compound having at least one electron-withdrawing group and at least one phenolic hydroxyl group in one molecule, an alkali-soluble resin, and an infrared absorber, and the electron-withdrawing group excludes a sulfonyl group; and a method of preparing a lithographic printing plate using the positive-working lithographic printing plate precursor.

There is provided an on-press development type lithographic printing plate precursor including a support, and an image-recording layer provided on the support, in which the image-recording layer contains (1) or (2). (1) a borate compound represented by Formula (1) and an electron-accepting polymerization initiator (2) a borate compound represented by Formula (1a) in Formula (1) and Formula (1a), R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each independently represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted alkynyl group, and R.sup.1, R.sup.2, R.sup.3, and R.sup.4 may each independently have a ring structure. Provided that at least one of R.sup.1, R.sup.2, R.sup.3, or R.sup.4 is different from the other. M.sup.+ represents a cation. Ma.sup.+ represents an iodonium cation.

##STR00001##

There are provided an on-press development type lithographic printing plate precursor including a support, and an image-recording layer on the support, in which the image-recording layer contains two or more electron-donating polymerization initiators and an electron-accepting polymerization initiator, and the two or more electron-donating polymerization initiators are borate compounds, and at least one of the two or more electron-donating polymerization initiators is a borate compound represented by Formula (1), in which, R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each independently represent a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted alkynyl group, and R.sup.1, R.sup.2, R.sup.3, and R.sup.4 may each independently have a ring structure, provided that at least one of R.sup.1, R.sup.2, R.sup.3, or R.sup.4 is different from the other, and M.sup.+ represents a cation.

##STR00001##