IR-sensitive lithographic printing plate precursors provide a stable print-out image using a unique IR-sensitive image-recording layer. The IR radiation-sensitive layer includes: (1) a free radical initiator composition with an electron-donating agent and one or more iodonium cations; (2) a free radically polymerizable composition; and (3) a color-changing compound of Structure (I) having an indene ring in the conjugated chain between the aromatic terminal groups. The IR radiation-sensitive composition and layer also contains one or more borate ions such that the molar ratio of one or more borate ions to the one or more iodonium ions is at least 0.5:1. After IR imaging, these precursors exhibit desirable printout images both fresh and after dark storage. The precursors can be developed on-press.

The invention pertains to a printing form precursor, and particularly a printing form precursor that can form printing forms, or printing plates, having improved properties. The printing form precursor includes a photopolymerizable composition containing an additive having a structure of Formula (I). The presence of the additive results in ease of processing and/or better cleanout and reduction in webmarkings on solid areas of the printing form.

A lithographic printing plate precursor is disclosed including a support and a coating comprising (i) a photopolymerisable layer including a polymerisable compound and a photoinitiator, and a toplayer provided above the photopolymerisable layer; characterized in that the toplayer has a thickness comprised between 0.1 g/m.sup.2 and 1.75 g/m.sup.2 and includes an infrared absorbing compound which includes a thermocleavable group which transforms into a group which is a stronger electrondonor upon exposure to heat and/or IR radiation, and is capable of forming a printout image upon exposure to heat and/or IR radiation.

Provided are: a lithographic printing plate precursor having a support and an image-recording layer on the support, in which the image-recording layer contains an onium polymerization initiator, a borate compound, an infrared absorber, a chromogenic agent, and a compound A which is an onium salt formed of a cation having a shape index lower than a shape index of a cationic moiety of the onium polymerization initiator; a method of preparing a lithographic printing plate using the lithographic printing plate precursor; and a lithographic printing method.

IR-sensitive lithographic printing plate precursors provide a stable print-out image using a unique IR radiation-sensitive composition. This IR radiation-sensitive composition includes: a) free radically polymerizable component; an b) IR radiation absorber; c) an initiator composition; a d) borate compound; and a e) compound capable of forming a colored boronic complex during or after exposure of the infrared radiation-sensitive image-recording layer to infrared radiation. The resulting print-out image exhibits an excellent color contrast between the exposed and non-exposed regions. After IR imaging, these precursors can be developed off-press or on-press.

Provided is a lithographic printing plate precursor having a support and an image-recording layer on the support, in which the image-recording layer contains an infrared absorber, a polymerization initiator, and a polymer A, a weight-average molecular weight of the polymer A is more than 15,000 and 150,000 or less, and an ethylenically unsaturated bond valence of the polymer A is 3.0 mmol/g or more.

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.2—R.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 including a polymerisable compound, an optionally substituted trihaloalkyl sulfone initiator, a leuco dye and a specific infrared absorbing compound including a six membered ring in the central position.

A lithographic printing plate precursor including an image recording layer on a hydrophilic support, in which the image recording layer includes a polymerization initiator, an infrared absorbent, a polymerizable compound, and an acid color former, and the infrared absorbent includes a compound represented by Formula 1, as well as a method of preparing a lithographic printing plate by use of the lithographic printing plate precursor. In Formula 1, at least one of Ar.sub.1 or Ar.sub.2 has a group represented by —X, where X represents a halogen atom, —C(═O)—X.sub.2—R.sub.11, —C(═O)—NR.sub.12R.sub.13, —O—C(═O)—R.sub.14, —CN, —SO.sub.2N.sub.15R.sub.16, or a perfluoroalkyl group, X.sub.2 represents a single bond or an oxygen atom, R.sub.11 and R.sub.14 each independently represents an alkyl group or an aryl group, and R.sub.12, R.sub.13, R.sub.15 and R.sub.16 each independently represents a hydrogen atom, an alkyl group, or an aryl group: ##STR00001##

Provided is a lithographic printing plate precursor having an aluminum support, an image-recording layer, and a water-soluble overcoat layer in this order, in which the image-recording layer contains an infrared-absorbing polymethine colorant having HOMO of −5.2 eV or less, a polymerization initiator, a polymerizable compound, and a polymer, and the polymer has a constitutional unit formed of an aromatic vinyl compound and a constitutional unit formed of an acrylonitrile compound. Also provided are a method for preparing a lithographic printing plate using the lithographic printing plate precursor.