A lithographic printing plate precursor including an image recording layer containing an infrared absorber represented by Formula I, on a support, and a method of producing a lithographic printing plate and a lithographic printing method using the lithographic printing plate precursor.

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The imaging sensitivity of negative-working lithographic printing plate precursors is improved by removing ozone from the ambient air surrounding the precursors that can be stored near an imaging means such as a platesetter prior to use. Ozone can be removed using a suitable filter containing activated charcoal or other ozone decomposing means, through which ambient air is filtered before and during the imaging process.

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.

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.

A negative-working infrared radiation-sensitive lithographic printing plate precursor can be imaged and developed on-press to provide a lithographic printing plate. Such precursor has an initiator composition that contains compound A of Structure (I) and one or more compounds collectively as compound B of Structure (II) or Structure (III):

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wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently alkyl groups each having 3 to 6 carbon atoms; at least one of R.sub.3 and R.sub.4 is different from R.sub.1 or R.sub.2; the difference of total number of carbon atoms in R.sub.1 and R.sub.2 and the total number of carbon atoms in R.sub.3 and R.sub.4 is 0, 1, or 2; the difference of total number of carbon atoms in R.sub.1 and R.sub.2 and the total number of carbon atoms in R.sub.5 and R.sub.6 is 0, 1, or 2; and X.sub.1, X.sub.2 and X.sub.3 are the same or different anions.

Provided is a method of producing a planographic printing plate, including: subjecting a planographic printing plate precursor, which has a support and a positive-working image recording layer, to image-wise exposure; and developing it using an alkaline aqueous solution which contains a specific compound and has a pH of from 8.5 to 10.8, in this order. The recording layer has: a lower layer containing a water-insoluble and alkali-soluble resin and an infrared ray absorbing agent; and an upper layer containing a water-insoluble and alkali-soluble polyurethane resin and a polyorganosiloxane. The specific compound is a nonionic or anionic surfactant, or at least one compound represented by Formula (1) or (2), wherein R.sup.11, R.sup.12, and R.sup.13 each represent an alkyl group; R.sup.14 represents an alkylene group; and R.sup.15 represents a single bond or a divalent linking group containing a hetero atom; and R.sup.21, R.sup.22, and R.sup.23 each represent an alkyl group. ##STR00001##

Provided is a method of producing a planographic printing plate, including: subjecting a planographic printing plate precursor, which has a support and a positive-working image recording layer, to image-wise exposure; and developing it using an alkaline aqueous solution which contains a specific compound and has a pH of from 8.5 to 10.8, in this order. The recording layer has: a lower layer containing a water-insoluble and alkali-soluble resin and an infrared ray absorbing agent; and an upper layer containing a water-insoluble and alkali-soluble polyurethane resin and a polyorganosiloxane. The specific compound is a nonionic or anionic surfactant, or at least one compound represented by Formula (1) or (2), wherein R.sup.11, R.sup.12, and R.sup.13 each represent an alkyl group; R.sup.14 represents an alkylene group; and R.sup.15 represents a single bond or a divalent linking group containing a hetero atom; and R.sup.21, R.sup.22, and R.sup.23 each represent an alkyl group. ##STR00001##

An infrared-sensitive color developing composition develops colors in a high density with an infrared exposure and does not significantly discolor when aged. A lithographic printing plate precursor which has extremely excellent plate-inspecting properties and favorable storage stability and is capable of maintaining favorable color-developing properties is provided, as is a plate making method for a lithographic printing plate in which the lithographic printing plate precursor is used. A new compound that can be preferably used as an infrared-sensitive color developer is also provided. An infrared-sensitive color developing composition of the invention includes a compound represented by Formula (1) (Component A). In addition, the compound in the present invention is represented by Formula (1). ##STR00001##

Disclosed is a waterless planographic printing plate precursor including at least a substrate, a heat sensitive layer and an ink repellent layer in this order, wherein the substrate has a white color layer or a white color surface, and wherein the heat sensitive layer includes at least (a) an infrared-absorbing dye having a maximum absorption wavelength of 700 to 1,000 nm, (b) a dye that changes color by proton acceptance, and (c) a proton-donating compound. The present invention provides a waterless planographic printing plate precursor capable of obtaining high contrast between the image area and the non-image area by exposure without the need for a special layer.

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 an infrared absorber, a polymerization initiator, a polymerizable compound, and one or more compounds selected from the group consisting of a compound represented by Formula (1) and a compound represented by Formula (2) (in Formula (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 EDG's each independently represent a hydrogen atom or an electron-donating group, provided that at least one of the four EDG's in Formula (1) represents an electron-donating group).