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 positive type planographic printing plate precursor including: a support; and an image recording layer provided on the support, in which the image recording layer contains: a phenol compound containing a phenolic hydroxyl group and a substituent A represented by CH.sub.2OR in a molecule thereof, and having a molecular weight of from 200 to 2,000; a polymer having at least one selected from the group consisting of a urea bond and a urethane bond in a main chain thereof; and an infrared absorbent.

Provided are: a positive type photosensitive resin composition including a polyester containing a sulfonamide group in a main chain thereof, and an infrared absorbent; a positive type planographic printing plate precursor obtained by using the positive type photosensitive resin composition; and a method of producing a planographic printing plate.

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.

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:

##STR00001##

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 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 ink-based digital printing system for variable data lithographic printing includes an imaging member having a surface configured to absorb dampening fluid. A dampening fluid patterning system jets dampening fluid onto the imaging member surface according to image data to form a dampening fluid pattern. The system includes a transfer member that receives the jetted dampening fluid pattern from the imaging member at a dampening fluid loading nip for subsequent inking of the dampening fluid pattern to form an ink pattern. The ink pattern is transferred to a substrate from the transfer member at an ink pattern transfer nip.

Provided are a photosensitive resin composition which enables production of a lithographic printing plate precursor having a non-image portion which has good solubility in an alkali aqueous solution and which enables production of a lithographic printing plate having excellent chemical resistance and excellent printing durability, a lithographic printing plate precursor obtained by using the photosensitive resin composition, a method for producing a lithographic printing plate, and a new polymer compound. The photosensitive resin composition of the present invention contains: a polymer compound which has an amine bond or a quaternary ammonium salt bond, and at least one bond selected from the group consisting of a urea bond, a urethane bond, and a carbonate bond in the main chain and has a sulfonamide group or a phenolic hydroxyl group in the main chain and/or the side chain; and an infrared absorbing material.

An ink-based digital printing system for variable data lithographic printing includes an imaging member having a surface configured to absorb dampening fluid. A dampening fluid patterning system jets dampening fluid onto the imaging member surface according to image data to form a dampening fluid pattern. The system includes a transfer member that receives the jetted dampening fluid pattern from the imaging member at a dampening fluid loading nip for subsequent inking of the dampening fluid pattern to form an ink pattern. The ink pattern is transferred to a substrate from the transfer member at an ink pattern transfer nip.

A positive-working lithographic printing plate includes a support having a hydrophilic surface or a hydrophilic layer, and a heat- and/or light-sensitive coating provided including at least two different (ethylene vinyl) acetal copolymer including a plurality of ethylenic moieties A having a structure according to the following formula:

##STR00001##

wherein R.sup.2 and R.sup.3 independently represent hydrogen, a halogen or an optionally substituted linear, branched, or cyclic alk(en)yl group, or an optionally substituted aromatic or heteroaromatic group.