The present invention provides an on-press development type lithographic printing plate precursor including, in the following order, a support, an image-recording layer, and a protective layer, in which the image-recording layer contains a) a polymerizable compound, b) an infrared absorber, c) a polymerization initiator, and d) a color forming substance precursor, and the protective layer contains an ultraviolet absorber, and a method of preparing a printing plate.

Negative-working, radiation-sensitive printing plates include or consist of a hydrophilic first layer or substrate and, thereover, an oleophilic imaging layer that includes an iodonium borate free-radical initiators in accordance herewith have the structure

##STR00001##

where X and Y are alkoxy, p and q range independently from 0 to 5, and p+q5; or p and q may range independently from 0 to 4, with p+q4.

A color developing composition which develops colors in a high density and does not significantly discolor when aged, a lithographic printing plate precursor which has excellent plate-inspecting properties by means of color development and is capable of maintaining strong color development even when aged after color development, a plate making method for a lithographic printing plate in which the lithographic printing plate precursor is used, and a new compound that can be preferably used as a color developer. The color developing composition of the present invention includes a compound represented by Formula 1. The compound in the present invention is represented by Formula 1. In Formula 1, R.sup.1 represents a group in which an R.sup.1O bond is cleaved by heat or exposure to infrared rays. ##STR00001##

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 includes a halogenated polymer and a nitrite and/or nitrate salt.

Provided are a planographic printing plate precursor for furnishing a planographic printing plate in which edge stain does not occur, adhesion to interleaving paper is prevented, and the water width with respect to edge stain at the time of printing is wide; a method of producing the same, and a printing method using the same. The planographic printing plate precursor including: a support; an image recording layer formed on the support; and a water-soluble compound having a molecular weight in a range of 60 to 300 and a solubility of 10 g/L or greater in water at 20 C., in which a content of the compound per unit area in a region on the image recording layer side from an end portion of the planographic printing plate precursor to a portion inside the end portion by 5 mm is greater than a content of the compound per unit area in a second region other than the first region by an amount of 50 mg/m.sup.2 or greater.

A stack including: a lithographic printing plate precursor including an image-recording layer which contains an infrared absorber, a polymerizable compound, and a polymerization initiator; and an interleaving paper stacked on the lithographic printing plate precursor, in which air permeation resistance of the interleaving paper is 55 seconds or more, or a stack including: a lithographic printing plate precursor including an image-recording layer which contains an infrared absorber, a polymerizable compound, and a polymerization initiator; and an interleaving paper stacked on the lithographic printing plate precursor, in which the interleaving paper is overlapped with the lithographic printing plate precursor to be in contact with a surface of the lithographic printing plate precursor on an image-recording layer side, and a color difference ?E of the image-recording layer before and after storage in a dark room in an environment of 25? C. and 55% RH for 3 days is less than 3.0.

The present invention provides a printing plate precursor including a layer which includes a polymer and is provided on a printing surface side of an aluminum support, and a layer which includes particles and is provided on a side opposite to the printing surface side, in which a modulus of elasticity of the particles is 0.1 GPa or more, and in a case where a Bekk smoothness of an outermost layer surface on the side opposite to the printing surface side is denoted by b second, a specific expression (1) is satisfied; a printing plate precursor laminate; a method for making a printing plate; and a printing method.

A planographic printing plate precursor having an image recording layer on a support, and an overcoat layer in this order, in which the overcoat layer includes particles, the overcoat layer is an outermost layer, and an occupation area ratio of the particles in a surface of the overcoat layer is 30% by area or more; and a method of producing a planographic printing plate obtained by using the planographic printing plate precursor.

A photosensitive resin printing original plate is disclosed in which a side surface light-blocking layer does not peel off from a metal support during handling of the printing original plate, and which enables efficient production of the side surface light-blocking layer. A water-developable photosensitive resin printing original plate, includes at least: a support; and a photosensitive resin layer arranged on the support, in which a peripheral side surface of the water-developable photosensitive resin printing original plate is covered with a light-blocking layer; the light-blocking layer contains carbon black and a vinyl polymer at a mass ratio of 80/20 to 30/70; and the vinyl polymer is an alcohol-soluble vinyl polymer containing 25 to 65 mol % of a hydroxyl group with respect to a constituent monomer unit in a molecule (in the case of being chemically modified, a constituent monomer unit after the modification).

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 a polymerizable compound, a polymerization initiator, and an infrared absorber, and a color forming substance precursor, and a color forming substance generated from the color forming substance precursor has a maximal absorption wavelength in a wavelength range of 380 nm or more and less than 580 nm, at which an absorbance difference with respect to the color forming substance precursor is 0.1 or more, and a maximal absorption wavelength in a wavelength range of 580 nm or more and 750 nm or less, at which an absorbance difference with respect to the color forming substance precursor is 0.07 or more, and a method of preparing lithographic printing plate or a lithographic printing method, using the on-press development type lithographic printing plate precursor.