An on-press development type lithographic printing plate precursor includes a support, and an image-recording layer on the support, in which the image-recording layer contains an infrared absorber, a polymerization initiator, a polymerizable compound, and at least one compound selected from the group consisting of a compound represented by Formula (1) and a compound represented by Formula (2) (in Formulae (1) and (2), Ra.sub.1 and Ra.sub.2 represent an alkyl group, Rb.sub.1 and Rb.sub.3 represent an alkyl group, Rb.sub.2 and Rb.sub.4 represent an alkyl group, and EWG's each independently represent a hydrogen atom or an electron-withdrawing group, provided that at least one of the four EWG's in Formula (1) represents an electron-withdrawing group).

A positive-working lithographic printing plate precursor includes a coating optimized for producing a minimum extent of ablation when exposed to heat and/or light. The coating includes an infrared absorbing agent which contains a structural element according to Formula I:

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wherein A represents SR.sup.1 wherein R.sup.1 represents an optionally substituted alkyl, aralkyl, alkaryl, cycloalkyl, alkenyl, alkynyl, aryl, or heteroaryl group, and/or combinations thereof; and Q=CHRCHR, CRCR or CHRCHRCHR and R, R and R independently represent hydrogen, an alkyl, cycloalkyl, aralkyl, alkaryl, aryl or heteroaryl group, or R and R or R and R form together a cyclic structure.

A negative type photosensitive resin composition includes a polymer compound which contains a linking group represented by Formula A-1 in a main chain and an ethylenically unsaturated group; and a polymerization initiator. In Formula A-1, R.sup.1 and R.sup.2 each independently represent a hydrogen atom or a monovalent organic group, and X.sup.1 represents a linking group represented by any of Formulae A-2 to A-6.

A negative type planographic printing plate precursor includes an image recording layer containing the negative type photosensitive resin composition.

A method of preparing a planographic printing plate includes, in order, an exposure step of image-exposing the negative type planographic printing plate precursor; and a development step of performing development by removing a non-exposed portion of the exposed negative type planographic printing plate precursor using a developer.

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A method of making a lithographic printing plate includes the steps of a) image-wise exposing a lithographic printing plate precursor including a hydrophilic support and a coating containing a colorant precursor to form a lithographic image consisting of printing areas and non-printing areas, b) developing the plate precursor to remove the coating in the non-printing areas from the support, and c) drying the plate precursor, and d) subjecting the plate precursor to heat or radiation to induce a colour change of the coating in the printing areas, wherein before step b) the coating in the non-printing areas and the support are characterised by a CIE 1976 colour difference E.sub.1 which is 5.0 or less, and after step d) the CIE 1976 colour difference E.sub.2 between the coating in the printing areas and the non-printing areas is more than 6.8.

An on-press development type lithographic printing plate precursor, including an image-recording layer on a support, in which the image-recording layer contains an infrared absorber A, a borate compound B, an iodonium compound C, and a color forming substance precursor D, and a surface free energy of an outermost layer on an image-recording layer side is 115 mJ/m.sup.2 or less, and a method of preparing a lithographic printing plate, a lithographic printing method, and a laminate using the on-press development type lithographic printing plate precursor.

An actinic ray-sensitive or radiation-sensitive resin composition includes a resin (A) containing a repeating unit represented by General Formula (4) and a crosslinking agent (C) containing a polar group, in which the crosslinking agent (C) is a compound represented by General Formula (1) or a compound in which two to five structures represented by General Formula (1) are connected via a linking group or a single bond represented by L.sub.1 in General Formula (3). ##STR00001##

An on-press development type 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, a polymerizable compound, and a color-developing substance precursor, and in a case where the image-recording layer is exposed to an infrared laser having a wavelength of 830 nm at an energy density of 110 mJ/cm.sup.2, a loss of ethylenically unsaturated bonds in an exposed area in the image-recording layer is 10% to 40% of ethylenically unsaturated bonds in a non-exposed area in the image-recording layer, and a method for preparing a lithographic printing plate or a lithographic printing method using the on-press development type lithographic printing plate precursor.

An on-machine development type planographic printing plate precursor has a support and an image-recording layer on the support. The image-recording layer contains an initiator, an infrared absorber capable of donating electrons to the initiator, and a color-developing substance precursor. The image-recording layer can form an image by exposure to infrared laser, and in a case where the image-recording layer is exposed to an infrared laser with a wavelength of 830 nm at an energy density of 110 mJ/cm.sup.2, a brightness change L of the image-recording layer before and after the exposure is 3.0 or more. A method for preparing a planographic printing plate and a planographic printing method employ the on-machine development type planographic printing plate precursor.

An on-press development type lithographic printing plate precursor has a support, an image-recording layer, and an outermost layer in this order. The image-recording layer contains an infrared absorber, an electron-accepting polymerization initiator, and a polymerizable compound. LUMO of the electron-accepting polymerization initiator-LUMO of the infrared absorber is 0.45 eV or more, and the outermost layer contains a discoloring compound. A method of preparing a lithographic printing plate and a lithographic printing method employ the on-press development type lithographic printing plate precursor.

The invention is directed to a lithographic printing plate precursor including, in the following order: a support; an image-recording layer containing a radical polymerizable compound and a radical polymerization initiator; and a protective layer containing a star polymer, and the star polymer is preferably a polymer in which from 3 to 10 polymer chains are branched from a central skeleton.