# US 2015/0177618 A1 · Method for on-press developable lithographic plate utilizing light-blocking material > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2015/0177618 A1 - Document ID: US20150177618A1 - Status: Published application - Kind: A1 - Application number: 14/136,282 - Filed: 2013-12-20 - Published: 2015-06-25 - Earliest claimed: 2013-12-20 - Inventors: Gary Ganghui Teng - Web page: https://patentgrep.com/patent/US20150177618A1 ## CPC - G03F 7/38: Treatment before imagewise removal, e.g. prebaking {(G03F7/265 takes precedence)} - B41C 1/1008: {by removal or destruction of lithographic material on the lithographic support, e.g. by laser or spark ablation; by the use of materials rendered soluble or insoluble by heat exposure, e.g. by heat produced from a light to heat transforming system; by on-the-press exposure or on-the-press development, e.g. by the fountain of photolithographic materials} - G03F 7/11: having cover layers or intermediate layers, e.g. subbing layers {(G03F7/091 - G03F7/093, B41N3/03 take precedence)} - B41C 2210/04: Negative working, i.e. the non-exposed (non-imaged) areas are removed - B41C 2210/08: Developable by water or the fountain solution - G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G) - B41C: PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES (photomechanical processes for producing printing surfaces G03F; photoelectrical processes for producing printing surfaces G03G) ## Abstract A method for applying a light-blocking material onto an imagewise exposed lithographic printing plate is disclosed. The exposed plate comprises on a substrate a photosensitive layer having hardened areas and non-hardened areas (for negative plate) or solubilized areas and non-solubilized areas (for positive plate). The non-hardened or solubilized areas of said photosensitive layer are removable with ink and/or fountain solution on a lithographic press. The light-blocking material is applied to the plate preferably from a solution or dispersion containing such material. The application of the light-blocking material prevents at least a portion of the room light in a certain wavelength (such as ultraviolet) range from reaching the photosensitive layer, thus allowing improved room light stability of the exposed plate. ## Claims ### Claim 1 A method of lithographically printing images on a receiving medium, comprising in order: (a) providing a lithographic plate comprising on a substrate a photosensitive layer soluble or dispersible in ink and/or fountain solution and capable of hardening upon exposure to a laser having a wavelength selected from 200 to 1200 nm; (b) imagewise exposing said plate with said laser to cause hardening of said photosensitive layer in the exposed areas, so as to form hardened areas in the exposed areas and non-hardened areas in the non-exposed areas; (c) applying a light-blocking material onto said plate on at least the photosensitive layer coated side, wherein said light-blocking material as applied to said plate prevents at least a portion of light within the wavelength range of from 200 to 780 nm from reaching said photosensitive layer; (d) developing said plate with ink and/or fountain solution on a lithographic press to remove the non-hardened areas of said photosensitive layer; and (e) lithographically printing images from said plate to the receiving medium. ### Claim 2 (depends on 1) The method of claim 1 wherein said light-blocking material as applied to said plate prevents at least 50% of light in the wavelength range of from 300 to 450 nm from reaching said photosensitive layer. ### Claim 3 (depends on 1) The method of claim 1 wherein said light-blocking material as applied to said plate prevents at least 90% of light in the wavelength range of from 300 to 450 nm from reaching said photosensitive layer. ### Claim 4 (depends on 1) The method of claim 1 wherein said light-blocking material as applied to said plate prevents at least 99% of light in the wavelength range of from 300 to 450 nm from reaching said photosensitive layer. ### Claim 5 (depends on 1) The method of claim 1 wherein said light-blocking material as applied to said plate prevents at least 90% of light in the wavelength range of from 300 to 450 nm from reaching said photosensitive layer and is transparent in the wavelength range of from 500 to 780 nm. ### Claim 6 (depends on 1) The method of claim 1 wherein said light-blocking material is applied from a solution or dispersion to said plate; and said plate is dried to remove any excess water and/or organic solvent until the plate surface no longer looks wet, after application of said solution or dispersion and before said on-press development. ### Claim 7 (depends on 1) The method of claim 1 wherein said light-blocking material, by itself or together with other materials applied with said light-blocking material, forms a thin layer on said plate, with or without part of said light-blocking material diffusing into the photosensitive layer, and/or overcoat for plate with overcoat. ### Claim 8 (depends on 1) The method of claim 1 wherein said light-blocking material is applied from an aqueous solution or dispersion comprising an ultraviolet light absorbing dye and/or pigment and a water soluble polymer. ### Claim 9 (depends on 1) The method of claim 1 wherein said light-blocking material is a dye having an absorption maximum within the wavelength range of from 300 to 450 nm. ### Claim 10 (depends on 1) The method of claim 1 wherein said light-blocking material is a pigment having an absorption and/or scattering maximum within the wavelength range of from 300 to 450 nm. ### Claim 11 (depends on 1) The method of claim 1 wherein said light-blocking material is a dye, a pigment, or a combination of at least one dye and/or at least one pigment, capable of blocking light in the wavelength range of from 300 to 450 nm, and is transparent to most wavelength range of visible light. ### Claim 12 (depends on 1) The method of claim 1 wherein said plate further includes a water soluble or dispersible overcoat on said photosensitive layer. ### Claim 13 (depends on 1) The method of claim 1 wherein said laser is an infrared laser having a wavelength selected from 750 to 1200 nm. ### Claim 14 (depends on 1) The method of claim 1 wherein said laser is a violet or ultraviolet laser having a wavelength selected from 200 to 430 nm. ### Claim 15 A method of lithographically printing images on a receiving medium, comprising in order: (a) providing a lithographic plate comprising on a substrate a photosensitive layer capable of hardening upon exposure to a laser having a wavelength selected from 200 to 1200 nm; (b) imagewise exposing said plate with said laser to cause hardening of said photosensitive layer in the exposed areas, so as to form hardened areas in the exposed areas and non-hardened areas in the non-exposed areas; (c) applying a light-blocking solution or dispersion onto said plate on the photosensitive layer coated side, wherein said solution or dispersion comprises a light-blocking material having an absorption maximum within the wavelength range of from 200 to 450 nm; (f) developing said plate with ink and/or fountain solution on a lithographic press to remove the non-hardened areas of said photosensitive layer; and (d) lithographically printing images from said plate to the receiving medium. ### Claim 16 (depends on 15) The method of claim 15 wherein said solution or dispersion forms a thin layer on the plate on the photosensitive layer coated side. ### Claim 17 (depends on 15) The method of claim 15 wherein said plate is dried to remove any excess water and/or organic solvent on said plate until the plate surface no longer looks wet, after application of said solution or dispersion and before said on-press development. ### Claim 18 (depends on 15) The method of claim 15 wherein said light-blocking solution or dispersion forms a thin layer on said plate on the photosensitive layer coated side and said thin layer prevents at least 90% of light with wavelengths of from 250 to 500 nm from reaching said photosensitive layer and is transparent in the wavelength range of from 550 to 780 nm. ### Claim 19 (depends on 15) The method of claim 15 wherein said light-blocking solution or dispersion forms a thin layer on said plate on the photosensitive layer coated side and said thin layer prevents at least 90% of light with wavelengths of from 300 to 450 nm from reaching said photosensitive layer and is transparent in the wavelength range of from 550 to 700 nm. ### Claim 20 (depends on 15) The method of claim 15 wherein said light-blocking solution or dispersion is an aqueous solution or dispersion comprising an ultraviolet light absorbing dye and/or pigment and a water soluble polymer.