The art of lithographic printing is based on the immiscibility of oil and water, wherein water or fountain solution is preferentially retained by either the imaged area or the non-imaged area, and the oily substance or ink does not adhere to the water, but instead only to those areas where no water or fountain solution is present. Commonly the ink is transferred to an intermediate material called a blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
A widely used type of lithographic printing plate has a light (UV) sensitive coating applied to an aluminum base support. The coating may respond to the light by having the portion that is exposed becoming soluble and removed by a subsequent development process. Such a plate is said to be a positive working plate. Conversely, when the area that is exposed becomes hardened or polymerized the plate is referred to as a negative working plate. In both instances the image areas are ink-receptive or oleophilic. The background or hydrophilic area is typically aluminum, which has been grained and anodized to provide a hydrophilic surface.
Direct digital imaging of offset printing plates (computer to plate CTP) is a technology that has assumed importance to the printing industry. In the use of this plate material, graphic information made by computer typesetting and desktop publishing is directly printed onto a plate by using a laser without an intermediate transfer material (film). The CTP process enables the rationalization and shortening of the platemaking process as well as a reduction in material costs. Advances in solid-state laser technology have made high powered diode lasers emitting energy at about 830 nm attractive light sources for carrying out this direct process. At least two printing technologies have been introduced that can be imaged with laser. Plates that can be imaged in this way are commercially sold by all of the major printing plate manufacturers. These materials require a development step to produce the final image.
A further printing technology is described for example in EP-A-0 573 091, U.S. Pat. Nos. 5,353,705 and 5,379,698. This technology does not require a development step, but instead relies on ablation to physically remove the imaged areas from the plate. Ablation requires high laser energy and power, resulting in low throughput and problems with debris after imaging.
Direct digital imaging without the use of a development step has been disclosed in U.S. Pat. No. 5,569,573 as a thermosensitive lithographic printing original plate comprising a substrate, a hydrophilic layer containing a hydrophilic binder polymer, and a microcapsuled oleophilic material which forms an image area by heating; the hydrophilic binder polymer having a three-dimensional cross-link and a functional group which chemically combines with the oleophilic material in the microcapsule when the microcapsule is decomposed, and the microcapsuled oleophilic material having a functional group which chemically combines with the hydrophilic binder polymer when the microcapsule is decomposed. Development is not required in the platemaking process so that there are no problems with waste treatment and the like.
Sulfamides have found utility in photosensitive media primarily as peripheral addenda, rather than as active ingredients in the photosensitive process. For example, U.S. Pat. No. 5,360,700 teaches the use of sulfamides as antifungal agents in silver halide solutions. This patent asserts that for the improved liquid preservability, it is preferable to add an antifungal agent to the stabilizing solution which is used instead of water washing. The antifungal agents which can be preferably used are salicylic acid, sorbic acid, dehydroacetic acid, hydroxybenzoic acid compounds, alkylphenol compounds, thiazole compounds, pyridine compounds, guanidine compounds, carbamate compounds, morpholine compounds, quaternary phosphonium compounds, ammonium compounds, urea compounds, isoxazole compounds, propanolamine compounds, sulfamide derivatives and amino acid compounds. Some of the preferred thiazole compounds include 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-one. The sulfamide derivatives include fluorinated sulfamide, 4-chloro-3,5-dinitrobenzenesulfamide, sulfanylamide, acetosulfamine, sulfapyridine, sulfaguanidine, sulfathiazole, sulfadiazine, sulfamerazine, sulfamethazine, sulfaisoxazole, homosulfamine, sulfisomidine, sulfaguanidine, sulfamethizole, sulfapyradine, phthalisosulfathiazole and succinylsulfathiazole.
Silver sulfadiazine has been used in a wide array of applications in the pharmaceutical environment, mostly for its antimicrobial properties. It is stable, insoluble in water, alcohol and ether and does not appear to stain or darken like other silver salts, such as silver nitrate. The applicants are, however, unaware of the use of silver salts of sulfadiazine and sulfamerazine for purposes other than direct or indirect antimicrobial activity or other medical purposes.
Polymers and metal salts or metal compounds have been combined for many various reasons, usually with the metal salts or metal compounds as fillers or compositing agents.
U.S. Pat. No. 5,948,599 describes a method of forming an image in a printing plate comprising the steps: (a) providing a radiation sensitive printing plate comprising a substrate coated with: (i) a coating comprising (1) a disperse water-insoluble heat-softenable phase A, and (2) a continuous binder phase B that is soluble or swellable in an aqueous medium; at least one of disperse phase A or continuous phase B having a reactive grouping, or precursor therefore, such that insolubilization of said coating occurs at elevated temperature and/or on exposure to actinic radiation, and (ii) a substance capable of strongly absorbing radiation and transferring the energy thus obtained as heat to the disperse phase so that at least partial coalescence of the coating occurs;
(b) image-wise exposing the radiation sensitive plate to a beam of high intensity radiation, by directing the radiation at sequential areas of the coating and modulating the radiation so that the particles in the coating are selectively at least partially coalesced; developing the image-wise exposed plate with aqueous medium to selectively remove the areas containing the non-coalesced particles and leave an image on the substrate resulting from the at least partially coalesced particles; and
(c) heating the developed plate and/or subjecting it to actinic radiation to effect rapid reaction of said reactive grouping and insolubilization of said image.
U.S. Pat. No. 5,840,469 discloses a thermographic element comprising a support having coated thereon a thermographic emulsion comprising: (a) a light insensitive silver salt (for example, silver salt of a carboxylic acid having 4 to 30 carbon atoms, silver benzoates, silver salts of compounds having mercapto or thione groups such as silver 3-mercapto-4-phenyl-1,2,4-triazolate, silver salts of thioglycolic acid and dicarboxylic acids, silver salts of benzotriazoles or imadazoles, and the like); a gallic acid reducing agent; and an infrared absorbing compound. Polymeric binders are also useful in forming the layer (as shown in column 5, lines 2–16). The system provides a change in optical density because of the thermally induced reduction of silver ion to form silver metal when the system is exposed to infrared radiation.
U.S. Pat. No. 6,352,819 describes high contrast thermographic and photothermographic materials comprising a barrier layer to prevent migration of diffusible by-products resulting from high temperature development. The barrier layer comprises a film-forming polymer(s) that reacts with or acts as a physical barrier to diffusible by-products resulting from development.
Lithographic printing plates based on free-radical initiated polymerization/curing mechanisms are known to be susceptible to quenching by oxygen. A method useful for preventing oxygen quenching of radiation-generated free radicals is to overcoat the photosensitive coating of a printing plate with a water-soluble polymeric resin. See for example U.S. Pat. No. 5,786,127, U.S. Pat. No. 5,340,681, U.S. Pat. No. 5,286,594, U.S. Pat. No. 5,273,862, U.S. Pat. No. 4,927,737, U.S. Pat. No. 6,051,366, EP 1,000,387 and EP 0 917 544.
U.S. Pat. No. 5,677,108, U.S. Pat. No. 5,677,110 and U.S. Pat. No. 5,997,993 disclose an on-press developable lithographic printing plate precursor comprising a lithographic hydrophilic printing plate substrate, a photohardenable photoresist, and a layer of polymeric protective overcoat. The overcoat functions as an oxygen barrier, as well as imparting the plate with a non-tacky surface and an enhanced resistance to the adverse influence of ambient humidity. The overcoat contains a polyphosphate salt and may further contain a fountain soluble or dispersible crystalline compound to facilitate on-press removability.
Heat-sensitive lithographic printing plates not requiring a wet development step after exposure have been desired by the industry for a long time. One approach to no-process lithographic printing plates relies on ablation to physically remove the imaging layer from the printing plate precursor. Unfortunately, ablative printing plates can only be exposed on imaging devices that are fitted with a vacuum device to collect the by-products of the ablative imaging step (particulate and gaseous debris). Recently the use of a laser transparent, water-soluble top coating over an ablatable imaging layer such that when ablatively removed with a laser, the ablative debris is contained by the top coating, has been proposed. See for example WO99/41077 and U.S. Pat. No. 6,468,717.
A water-soluble overcoat may also be provided to protect the hydrophilic layer during storage and handling and to improve lithographic latitude. See for example U.S. Pat. No. 5,997,993, U.S. Pat. No. 6,171,748, U.S. Pat. No. 6,468,717, U.S. Pat. No. 6,503,684 and U.S. Pat. No. 6,513,433.
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