Patent EA-005016-B1 (EA)
Title: Chemical imaging sciences of a lithographic printing plate
Inventor: HARRISON BRUCE R
IPC: G03F7/26
Filed: 2001-05-08
Abstract: 1. A process for imaging a printing plate having a coating comprising diazo compounds, characterized by the step of applying imagewise an insolubilizing chemical to the coating. 2. The process of claim 1, characterized by one or more of the following features: (a) wherein the insolubilizing chemical is in the form of an aqueous solution having a pH greater than 7.5, preferably between 7.5 and 13.5; (b) wherein the coating is aqueous borne, and (c) wherein the insolubilizing chemical causes the diazo functional groups in the coating to chemically react, and, if desired, comprising the further steps of: (a) heating the plate, and (b) applying a developer solution to the plate, and if desired exposing the developed plate with an UV light. 3. The process of claim 1 or 2, characterized in that the imagewise application of the insolubilizing chemical is performed using an ink jet printhead. 4. The process of claim 3, characterized by one or more of the following features: (a) wherein individual drops of the solution applied by the ink jet printhead have a volume in the range of 1 to 100 picoliters, (b) wherein individual drops applied to the plate by the ink jet printhead create image dots having approximate diameter in the range of 10 to 100 microns, and (c) wherein individual drops applied to the plate by the ink jet printhead result in individual image dots in the coating having areas in the range of 80 to 8000 microns squared. 5. A printing plate, characterized by comprising: (a) a substrate having a coated surface comprising diazo compounds and characterized by an effective pH, and (b) on part of the coated surface, a latent image defined by a region of higher effective pH, or different water concentration. 6. The printing plate of claim 5, characterized in that the substrate comprises an aluminum substrate. 7. The printing plate of claim 5 or 6, characterized by, on part of the substrate, a coating insoluble in a developer, wherein said insolubility has been imparted by reaction with hydroxyl ions. 8. The printing plate of claim 5 or 6, characterized in that on a part of the coated substrate, there is defined a latent image characterized by a region of different effective water concentration, and wherein the diazo resins in the latent image preferably are insoluble in a developer. 9. The printing plate of claim 5 or 6, characterized in that a part of said coating defines an image by insolubility of said part in a developer, and wherein said insoluble part contains a higher concentration of alkaline materials than the soluble part of said coating, wherein the substrate preferably comprises and aluminum plate, and the coating preferably has a thickness of 1 to 3 microns. 10. The printing plate of claim 5 or 6, characterized in that the substrate has a surface covered at least in part with a coating which coating is at least in part photosensitive, wherein a part of said coating defines an image by insolubility of said image in a developer, and wherein said insoluble image contains a higher concentration of alkaline materials than the soluble portion of said coating, wherein the substrate preferably comprises and aluminum plate, and the coating preferably has a thickness of 1 to 3 microns. 11. A computer to plate system, characterized by comprising: (a) a printhead containing a plurality of ink jet nozzles such that the printhead is capable of jetting imagewise a basic solution, (b) a printing plate having a coated surface containing diazo compounds capable of being imaged by the printhead, and (c ) a developer capable of dissolving the non-imaged coating. 12. A computer to plate system, characterized by comprising: (a) an ink jet printer with a printhead capable of imaging printing plates, (b) an ink capable of insolubilizing a coating containing diazo compounds, and (c) a printing plate having a coating comprising diazo compounds. 13. A computer to plate system according to claim 11 or 12, characterized by one or more of the following features: (a) wherein said coating is aqueous-borne, (b) wherein said coating further contains latex, (c) wherein said printhead is a piezoelectric drop on demand printhead, and (d) wherein said printhead under normal operating conditions generates drops with diameters in the range from 10 to 50 microns. 14. A microdrop sprayable image forming composition for differentially patterning a light sensitive coating of a persensitized printing plate to a developing solution, characterized by comprising: (a) from 5 to 70 percent by weight of a humidifying co-solvent, (b) from 0.001 to 10 percent by weight of a surfactant, (c) a pH elevating agent in an amount sufficient to impart a pH to the composition of from 7.5 to 13.5; and (d) a balance of water; which composition is capable of forming a latent image to the printing plate when the composition is applied in an imagewise pattern onto the light sensitive coating such that portions of the coating applied with the composition have a different solubility in the developing solution than portions of the coating which are not applied with the composition. 15. The composition of claim 14, characterized in that the pH elevating agent is selected from sodium carbonate, sodium bicarbonate, lithium carbonate, sodium hydroxide, potassium hydroxide, sodium tetraboratedecahydrate, sodium phyrophosphatedecahydrate, sodium phosphate, sodium metasilicate, triethonol amine, and combinations thereof. 16. A method for imaging a light sensitive coating on a printing plate, characterized by comprising the steps of: (a) providing a printing plate comprising a support and a light sensitive coating on the support; (b) forming a latent image on the printing plate by imagewise applying a pattern of an image forming composition to the light sensitive coating such that portions of the coating applied with the composition have a different solubility in a developing solution than portions of the coating which are not applied with the composition; and (c) either only removing the portions of the coating applied with the composition or only removing the portions of the coating not applied with the composition with a developing solution. 17. The method of claim 16, characterized in that the image forming composition comprises: (a) from 5 to 70 percent by weight of a humidifying co-solvent, (b) from 0.001 to 10 percent by weight of a surfactant, (c) a pH elevating agent in an amount sufficient to impart a pH to the composition of from 7.5 to 13.5; and (d) a balance of water. 18. The method of claim 17, characterized in that the pH elevating agent is selected from sodium carbonate, sodium bicarbonate, lithium carbonate, sodium hydroxide, potassium hydroxide, sodium tetraboratedecahydrate, sodium phyrophosphatedecahydrate, sodium phosphate, sodium metasilicate, triethonol amine, and combinations thereof.