Abstract: Improved photopolymerization initiator systems are comprised of a spectral sensitizer that sensitizes in the ultraviolet or visible regions of the spectrum and an N-aryl, O-aryl or S-aryl polycarboxylic acid co-initiator. The improved initiator systems are incorporated in photo-polymerizable compositions containing one or more addition-polymerizable ethylenically-unsaturated compounds to form compositions suitable for the preparation of radiation-sensitive layers in lithographic printing plates adapted to be imagewise-exposed with ultraviolet- or visible-light-emitting lasers such as argon-ion lasers and frequency doubled Nd:YAG lasers. Such plates are able to effectively meet the dual requirements of very high photospeed and very good shelf-life required in computer-to-plate systems.

Abstract: An alkaline developing composition for processing a lithographic printing plate includes an alkali metal silicate and at least 6 weight % of a thickener such as glycerine. The lithographic printing plate can be either positive- or negative-working, and includes negative-working thermal plates.

Abstract: Lithographic plate compositions and a method for their production have been discovered that are especially useful in conjunction with digitally controlled lasers to directly construct printable images on lithographic plates. The plates comprise a substrate and an ablatable polymeric coating on the substrate where the ablatable, imageable coating is prepared by in situ or solution polymerization of conjugated monomers deposited on the plate by vapor deposition or in solution. Examples of such monomers are thiophene, pyrrole and aniline.

Abstract: Improved aluminum substrates suitable for use in the production of lithographic printing plates. A surfactant surface treatment for such aluminum substrates improves the quality of radiation sensitive coatings subsequently applied to the substrate. The surfactant may be in a layer comprising a mixture of a hydrophilizing composition and a surfactant on the aluminum alloy surface; or a hydrophilizing layer comprising a hydrophilizing composition may be on the aluminum alloy surface and a surfactant layer comprising a surfactant on the hydrophilizing layer.

Abstract: An alkaline developing composition for processing a lithographic printing plate includes an alkali metal silicate present in an amount to provide at least about 42 g SiO.sub.2 per 1000 g of composition, and a weight ratio of SiO.sub.2 to M.sub.2 O of from about 0.55 to about 0.925 wherein M is said the metal. The lithographic printing plate can be either positive- or negative-working, and includes negative-working thermal plates.

Abstract: A photosensitive composition can be used to prepare negative-working photosensitive elements such as lithographic printing plates. The composition includes a first photocrosslinkable aromatic resin having photocrosslinkable groups and a number average molecular weight of at least about 1500. Also included is a polymerizable monomer, a photocrosslinkable polyester and a photoinitiator. The photosensitive resins are present at a total weight ratio to the monomer of at least 1.5:1.

Abstract: Binders useful in photosensitive compositions contain units A, B, C and D, wherein A is present in an amount of 0.5 to 15 wt. % and is of the formula ##STR1## B is present in an amount of 10 to 35 wt. % and is of the formula ##STR2## C is present in an amount of 10 to 50 wt. % and is of the formula ##STR3## wherein R.sup.1 is methyl, ethyl, propyl, and D is present in an amount of 25 to 70 wt. % and is of the formula ##STR4## wherein n is an integer of from 1 to 3 and R.sup.2, R.sup.3 are hydrogen or methyl and R.sup.4 is alkyl, aralkyl or aryl.

Abstract: A radiation sensitive composition containing an adduct of a diazonium resin having pendant diazonium groups, with a sulfonated acrylic copolymer having pendant sulfonate groups. The sulfonated acrylic copolymer contains an acrylic moiety and a sulfonated styryl or acrylic moiety. The copolymer may optionally contain styryl moieties. The composition is useful as a radiation sensitive layer in imaging elements for graphic arts applications and is particularly useful in preparing durable, long-wear, printing plates.

Abstract: A photosensitive composition can be used to prepare negative-working photosensitive elements such as lithographic printing plates. The composition includes a first photocrosslinkable aromatic resin having photocrosslinkable groups and a number average molecular weight of at least about 1500. Also included is a polymerizable monomer, a photocrosslinkable polyester, a photocrosslinkable copolymer of styrene and maleic anhydride, and a photoinitiator. The photocrosslinkable resins are present at a total weight ratio to the polymerizable monomer of at least 1.5:1.

Abstract: An alkaline developing composition for processing a lithographic printing plate includes an alkali metal silicate, at least 6 weight % of a thickener such as glycerine, and a nonionic fluorosurfactant or a phosphate ester hydrotrope. Lithographic printing plates that can be developed using this composition are either positive- or negative-working, and include both positive- and negative-working thermal plates.