JP2011207138A - Image erasing method for thermal lithographic printing plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image erasing method for a thermal lithographic printing plate, which has an image forming layer containing thermoplastic particles and/or thermal-melting substances on a support, and forms an image on the image forming layer by a thermosensitive method, and to provide an image erasing method which prevents the generation of stain and re-imaging when the number of printing sheets is increased, and is especially excellent in the erasure of the imaging portion stuck with ink.SOLUTION: The image erasing method for a thermal lithographic printing plate is performed by coating an aqueous solution which contains at least one type of amine structure and has a pH of 12 or greater on the unnecessary portion in the thermal lithographic printing plate which has an image forming layer containing thermoplastic particles and/or thermal-melting substances on a support, and forms an image on the image forming layer by the thermosensitive method.

Description

  The present invention relates to an image erasing method of a heat-sensitive lithographic printing plate using an image-forming layer that undergoes phase conversion by heat, and relates to a heat-sensitive lithographic printing plate that does not require layer removal processing such as a conventional ablation method or an on-machine development method. The present invention relates to an image erasing method.

  In recent years, a computer-to-plate (CTP) system for producing a lithographic printing plate by digital recording based on image information has been widely used for the purpose of filmless in order to obtain a lithographic printing plate quickly. As a lithographic printing plate material using the CTP method, a photopolymer that forms an image by an ink jet method or an electrophotographic method on a support having a hydrophilic surface, has photosensitivity, and is developed after image exposure. There are several types such as type and silver salt photograph type. However, the resolution is still not sufficient with the ink jet method and the electrophotographic method, and the photopolymer type and the silver salt photographic type are disadvantageous in terms of environmental suitability because it takes time to produce a printing plate because of development processing. is there. Therefore, there is a demand for a lithographic printing plate that can support the CTP method and does not require development processing.

  As a printing plate called a processless lithographic printing plate capable of forming an image without using a processing solution such as a developing solution, a lithographic printing plate produced by various CTP methods using laser, ink jet, or thermal head recording is used. Technology has been proposed. For example, plate making with a dry electrophotographic laser printer as described in JP-A-6-138719, JP-A-6-250424, etc., heat melting as described in JP-A-9-58144 Known is a plate making using an on-demand ink jet printer using mold ink, or a plate making with a thermal printer using a thermal transfer ink ribbon described in JP-A-63-166590.

  Further, for example, in Japanese Patent Application Laid-Open No. 58-199153, Japanese Patent Application Laid-Open No. 59-174395, Japanese Patent Application Laid-Open No. 63-116891, Japanese Patent Application Laid-Open No. 11-286184, etc., there is no thermal transfer ribbon or the like. As a processless lithographic printing plate capable of performing heat drawing with a heat-sensitive lithographic printing plate, a heat-sensitive lithographic printing plate having a heat-sensitive recording layer containing a thermoplastic resin and / or a heat-meltable substance is described. On the other hand, as a processless lithographic printing plate capable of obtaining an oleophilic image part by heating and drawing with an infrared laser or the like, for example, Japanese Patent Application Laid-Open No. 2000-190649, Japanese Patent Application Laid-Open No. 2000-301847, etc. A heat-sensitive lithographic printing plate having an image-forming layer containing conductive particles or a thermoplastic resin is described. These heat-sensitive lithographic printing plates are more preferable than the above-described processless lithographic printing plates in that no consumption materials such as toner and IJ ink are required.

  By the way, also in these heat-sensitive lithographic printing plates, for example, as in the conventional PS plate, an unnecessary image that is inevitably generated or an image portion that needs to be corrected may be generated. It is necessary to erase the above. As for erasing unnecessary image areas in the PS plate, there is known a method in which the unnecessary image areas are eluted with an erasing liquid containing an organic solvent or corrected with an erasing liquid that is etched with an acid or the like. JP-A-51-33442, JP-A-55-121447, JP-A-60-17748, and the like. However, when the erasing liquid for PS plate is applied to the processless lithographic printing plate as described above, the hydrophilicity originally possessed by the processless lithographic printing plate is impaired by elution with an organic solvent, etching with an acid or the like. In some cases, sufficient hydrophilicity cannot be imparted, and the erased portion is stained.

  In JP 2005-154682 A (Patent Document 1) and JP 2005-187707 A (Patent Document 2), recurrence color prevention is performed by erasing handwriting written with writing ink using a decolorable dye. Although an erasing solution having a pH of 10 to 12 containing polyethyleneimine and / or a polyethyleneimine derivative as an agent is described, this is for visually erasing written handwriting, and an unnecessary image in a lithographic printing plate It was not intended to erase the part on the printing plate.

  JP-A-2006-133363 (Patent Document 3) and JP-A-2006-231666 (Patent Document 4) correct an unnecessary image portion of a processless lithographic printing plate containing hydrophilic particles and a photothermal conversion agent. As a method, an erasing solution containing an ink solvent and having a pH of 1 to 4 is described. However, a processless lithographic printing plate which does not require on-press development, for example, JP 2009-255298 A (Patent Document 5) In the case of heat-sensitive lithographic printing plates that do not require the development processing shown in (2), there may be cases where sufficient hydrophilicity cannot be imparted, or the areas where the erasing solution is applied may be visualized and soiled instead of being erased. It was.

  JP 2007-196557 A (Patent Document 6) contains at least polyvinyl alcohol and colloidal silica having a silanol group in order to erase unnecessary image areas and stains of a lithographic printing plate material excellent in on-press development property. However, when this method is applied to a processless lithographic printing plate that does not require on-press development, sufficient erasability may not be obtained. In particular, when an unnecessary image is found after the start of printing and the image to which ink is attached is erased, smearing occurs, or when a large number of sheets are printed, the image is reimaged and sufficient erasability cannot be obtained. There was a problem and improvement was desired.

JP 2005-154682 A Japanese Patent Laid-Open No. 2005-187707 JP 2007-196557 A JP 2006-133363 A JP 2009-255498 A JP 2006-231666 A

  An object of the present invention is to provide an image erasing method of a heat-sensitive lithographic printing plate having an image forming layer containing thermoplastic particles and / or a heat-meltable substance on a support and having a phase change by heat, An object of the present invention is to provide an image erasing method that is excellent in erasing an image portion to which ink has adhered, without causing smearing or re-imaging when the number of printed sheets increases.

  The above object of the present invention is to provide at least one unnecessary image portion of a heat-sensitive lithographic printing plate having an image forming layer containing thermoplastic particles and / or a heat-meltable substance on a support and having a phase change by heat. It was achieved by an image erasing method characterized by applying an aqueous solution containing a water-soluble polymer having a kind of amine structure and having a pH of 12 or more.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an image erasing method for a heat-sensitive lithographic printing plate having an image forming layer containing thermoplastic particles and / or a heat-meltable substance on a support and having a phase change by heat. As a result, it is possible to provide an image erasing method that is excellent in erasing an image portion to which ink has adhered, without causing smearing or re-imaging.

  Hereinafter, the present invention will be described in detail. The aqueous solution used in the image erasing method of the present invention is an aqueous solution containing at least one water-soluble polymer having an amine structure and having a pH of 12 or more. The water-soluble polymer having an amine structure used in the present invention is a water-soluble polymer having a primary to tertiary amino group in the structural unit, such as polyallylamine, allylamine-diallylamine copolymer, allylamine-dimethylallylamine. Examples thereof include a copolymer and polyethyleneimine.

  The water-soluble polymer having an amine structure used in the present invention has a number average molecular weight of 100,000 or less, preferably 10,000 or less. Use of a polymer having a number average molecular weight exceeding 100,000 is not preferable because the ink may be reattached to a portion where the image portion has been erased.

  In the aqueous solution used in the image erasing method of the present invention, it is preferable to use a water-soluble polymer having at least one amine structure in a range of 0.1 to 10 g per liter, more preferably per liter. It is used in the range of 0.5 to 5 g. When the addition amount is less than the preferred range, there may be a case where a sufficient effect cannot be obtained when erasing the image with the ink attached. When the added amount exceeds the preferable range, the image is transferred to a portion other than the erased image via a roller of the printing press. Ink may re-adhere to the erased area.

  The pH of the aqueous solution used in the image erasing method of the present invention is adjusted to 12 or more and 14 or less, more preferably 12.5 or more and 13.5 or less. As the pH adjuster, for example, potassium hydroxide, sodium hydroxide, lithium hydroxide, trisodium phosphate, or amine compounds such as monoethanolamine, diethanolamine, and triethanolamine can be used as the alkaline substance. As an acidic substance, as an inorganic acid, carbonic acid, phosphoric acid, sulfurous acid and a salt thereof are good, and nitric acid and sulfuric acid can be used for adjusting pH. Examples of the organic acid include citric acid, malonic acid, succinic acid, acetic acid, p-toluenesulfonic acid, tartaric acid, malic acid, lactic acid, and salts thereof. Examples of the salt include sodium salts, potassium salts, and ammonium salts of the above acids. These acids and salts may be used alone or in combination of two or more.

  The object of the present invention is achieved by applying an aqueous solution containing at least one water-soluble polymer having an amine structure and having a pH of 12 or more to an unnecessary image portion of a heat-sensitive lithographic printing plate. In addition to the above compounds, known buffers, complexing agents, surfactants, and the like can be contained according to the purpose. For example, an inorganic acid such as phosphoric acid or sulfuric acid, an organic acid such as succinic acid or propionic acid can be used as a buffering agent, and iminodiacetic acid, ethylenediaminetetraacetic acid or the like can be mixed as a complexing agent. . Surfactants include, for example, natural surfactants such as saponins, glycerin-based and glycidol-based nonionic surfactants, higher alkylamines, quaternary ammonium salts, pyridine and other heterocyclic rings, and cationic interfaces such as sulfoniums. Activators, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, sulfate ester group, amphoteric surfactants such as amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohol, fluorine containing fluorine System anions and amphoteric surfactants can be used.

  The aqueous solution used in the image erasing method of the present invention may contain inorganic fine particles such as colloidal silica, alumina sol, and titania sol, and preferably colloidal silica can be used. As a result, the hydrophilicity of the erased portion is improved, and the ink can be more effectively prevented from adhering to the erased portion. In addition, an aqueous solution containing at least one amine structure and having a pH of 12 or more, which is used in the image erasing method of the present invention, is applied to the image area, and then the aqueous solution containing the inorganic fine particles is overlapped. Application can also be preferably performed for efficient erasing.

  In the aqueous solution used in the image erasing method of the present invention, a phthalein indicator such as α-naphtholphthalein, p-cresolphthalein, o-cresolphthalein, phenolphthalein is used for the purpose of improving the visibility of the applied part. , Thymolphthalein, xylenolphthalein, dibromophenol tetrabromophenylsulfonephthalein, nitrophenolsulfonephthalein, and the like can be used. By using these, it is possible to prevent application to places other than the desired location, and to erase the image more efficiently.

  Moreover, when using the said phthalein type | system | group indicator, discoloration of an indicator can be prevented by using together with preservatives, such as ascorbic acids, besides alkali sulfites, such as sodium sulfite and potassium sulfite.

  The image erasing method of the present invention can be applied to a heat-sensitive lithographic printing plate in which an image is formed on an image-forming layer containing thermoplastic particles and / or a heat-meltable material on a support by a heat-sensitive method. Hereinafter, the configuration of a heat-sensitive lithographic printing plate to which the image erasing method of the present invention can be preferably applied will be described.

  The thermoplastic particles contained in the image forming layer refer to an aqueous dispersion of particles made of a solid organic polymer compound made of a chain polymer and exhibiting plasticity upon heating, and made of an organic polymer compound. Specifically, synthetic rubber latex including modified products such as styrene butadiene copolymer, acrylonitrile butadiene copolymer, methyl methacrylate butadiene copolymer, styrene acrylonitrile butadiene copolymer, and styrene methyl methacrylate butadiene copolymer. An aqueous dispersion comprising: styrene maleic anhydride copolymer, methyl vinyl ether maleic anhydride copolymer, polyacrylic acid copolymer, polystyrene, styrene / acrylic acid ester copolymer, polyacrylic acid ester An aqueous dispersion of particles made of polymethacrylic acid ester, acrylic acid ester / acrylic acid ester copolymer, low melting point polyamide resin or the like can also be used. In the present invention, the image forming layer can contain thermoplastic particles by coating and drying the image forming layer coating liquid containing the aqueous dispersion. These thermoplastic particles can be used alone or in combination of two or more. In view of the affinity with the vehicle (binder component) of the printing ink, synthetic rubber latex is preferred as such thermoplastic particles, and thermoplastic particles comprising a styrene-butadiene copolymer and a modified product thereof are particularly desirable. The blending amount of the thermoplastic particles is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass with respect to the total solid content of the image forming layer. Moreover, in order to make the melting and fusing effect due to heat easy to develop, it is preferable to use the thermoplastic particles having a glass transition temperature of 50 to 150 ° C, more preferably 55 to 120 ° C. If the glass transition temperature is less than 50 ° C., a phase change occurs in a liquid state during the production process, and oleophilicity appears in the non-image area, which may cause printing stains. When the temperature exceeds 150 ° C., the polymer is hardly melted by heat, and it may be difficult to form a strong image with a relatively small output laser or a small thermal printer.

  As the heat-meltable substance contained in the image forming layer, an organic compound having a melting point of 50 to 150 ° C. can be suitably used. In particular, by including the above-described thermoplastic particles and a heat-meltable substance in the image forming layer, it is possible to obtain a heat-sensitive lithographic printing plate excellent in ink acceptability in the image area. If the melting point of the hot-melt material is less than 50 ° C, it may melt during the manufacturing process and cause background stains on the printed matter. On the other hand, if it exceeds 150 ° C, it is difficult to melt by applying heat from a thermal head etc. May be poorly expressed. Specific examples of such hot-melt materials include 1-phenoxy-2-naphthoxy (1) -ethane, 1-phenoxy-4-naphthoxy (2) -butane, and 1- (2-isopropylphenoxy) -2. -Naphthoxy (2) -ethane, 1- (4-methylphenoxy) -3-naphthoxy (2) -propane, 1- (2-methylphenoxy) -2-naphthoxy (2) -ethane, 1- (3-methyl Phenoxy) -2-naphthoxy (2) -ethane, 1-phenoxy-2-naphthoxy (2) -ethane, 1-phenoxy-6-naphthoxy (2) -hexane, 1- (2-phenylphenoxy) -2-phenoxy Ethane, 1- (4-phenylphenoxy) -2- (2-methylphenoxy) -ethane, 1,4-diphenoxybutane, 1,4-bis (4-methylphenoxy) butane 1,2-di (3,4-dimethylphenoxy) ethane, 1- (4-phenylphenoxy) -3-phenoxypropane, 1-phenoxy-2- (4-t-butylphenoxy) ethane, 1,2 -Diphenoxyethane, 1- (4-methylphenoxy) -2-phenoxyethane, 1- (2,3-dimethylphenoxy) -2-phenoxyethane, 1- (3,4-dimethylphenoxy) -2-phenoxyethane 1- (4-ethylphenoxy) -2-phenoxyethane, 1- (4-isopropylphenoxy) -2-phenoxyethane, 1,2-bis (2-methylphenoxy) ethane, 1- (4-methylphenoxy) -2- (2-methylphenoxy) ethane, 1- (4-t-butylphenoxy) -2- (2-methylphenoxy) ethane, 1,2-bis ( -Methylphenoxy) ethane, 1- (4-methylphenoxy) -2- (3-methylphenoxy) ethane, 1- (4-ethylphenoxy) -2- (3-methylphenoxy) ethane, 1,2-bis ( 4-methylphenoxy) ethane, 1- (2,3-dimethylphenoxy) -2- (4-methylphenoxy) ethane, 1- (2,5-dimethylphenoxy) -2- (4-methylphenoxy) ethane, phenoxy Acetic acid-β-naphthol ester, 2-naphthoxyacetic acid-p-cresol ester, 2-naphthoxyacetic acid-m-cresol ester and the like, and waxes such as carnauba wax, microcrystalline wax, paraffin wax, polyethylene wax, Lauric acid, stearic acid, oleic acid, palmitic acid, behenic acid, mon Fatty acids such as phosphate, and their esters, also amides can be used.

  These hot-melt materials are generally solid materials at room temperature, but are preferably used after being subjected to a fine dispersion treatment in order to increase the heat reactivity. The fine dispersion treatment method is a wet dispersion method generally used at the time of producing a coating material, and a bead mill such as a roll mill, a colloid mill, a ball mill, an attritor, and a sand mill can be used. In the bead mill, ceramic beads such as zirconia, titania and alumina, metal beads such as chrome and steel, and glass beads can be used. The dispersed particle diameter is preferably from 0.1 to 1.2 μm in median diameter, particularly preferably from 0.3 to 0.8 μm. The median diameter is the particle diameter (cumulative average diameter) at which the cumulative curve becomes 50% when the total curve of one population of particles is 100%, and the particle size distribution is evaluated. As one of the parameters to be measured, it can be measured using, for example, a laser diffraction / scattering particle size distribution measuring apparatus LA920 (manufactured by Horiba, Ltd.).

  The preferred blending amount of the heat-meltable substance is 5 to 95% by mass based on the total solid content of the image forming layer when used alone, and relative to the total solid content of the image forming layer when used in combination with thermoplastic particles. 50 to 95% by mass. These hot melt materials may be used alone or in combination of two or more hot melt materials.

  The image forming layer of the heat-sensitive lithographic printing plate to which the image erasing method of the present invention can be applied preferably contains a water-soluble polymer compound. Examples of such water-soluble polymer compounds include polyvinyl alcohol, carboxy-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, silanol-modified polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, starch and derivatives thereof, gelatin, casein, and sodium alginate. , Polyvinylpyrrolidone, styrene / maleic acid copolymer salt, styrene / acrylic acid copolymer salt, and the like. These water-soluble polymer compounds may be used alone or in combination of two or more, and gelatin and polyvinyl alcohol rich in film formation and modified products thereof are particularly preferably selected for maintaining hydrophilicity in the non-image area. The blending amount of the water-soluble polymer compound is preferably 0.5 to 30% by mass, more preferably 3 to 25% by mass, based on the total solid content of the image forming layer.

  In order to improve the water resistance and mechanical strength of the non-image area, the image forming layer preferably contains a curing agent (waterproofing agent) depending on the type of the water-soluble polymer compound. As the curing agent, melamine resin, epoxy resin, polyisocyanate compound, aldehyde compound, silane compound, chromium alum, divinyl sulfone, and the like that can impart water resistance by promoting the crosslinking of the resin can be used, but it is particularly preferable. As the hardener, divinyl sulfone is preferably used in the case of gelatin, and glyoxal is preferably used in the case of polyvinyl alcohol. The compounding amount of the curing agent is preferably 1 to 30% by mass, more preferably 2 to 15% by mass, based on the solid content of the water-soluble polymer compound.

  The image forming layer of the heat-sensitive lithographic printing plate that can be applied to the image erasing method of the present invention further contains a photothermal conversion substance in addition to the above-mentioned thermoplastic particles, heat-meltable substance, water-soluble polymer compound and the like. As a result, not only the thermal head but also writing with active light such as an infrared laser becomes possible. From this viewpoint, the image forming layer of the heat-sensitive lithographic printing plate that can be applied to the printing method of the present invention preferably contains a photothermal conversion substance. As a photothermal conversion substance that can be used for the heat-sensitive lithographic printing plate, a material that efficiently absorbs light and converts it into heat is preferable. Depending on the light source used, for example, a semiconductor laser that emits near infrared light is used as a light source. When used, a near-infrared light absorber having an absorption band in the near infrared is preferable. For example, carbon black, cyanine dyes, polymethine dyes, azurenium dyes, squalium dyes, thiopyrylium dyes, naphthoquinone dyes Organic compounds such as dyes and anthraquinone dyes, phthalocyanine, azo and thioamide organometallic complexes, iron powder, graphite powder, iron oxide powder, lead oxide, silver oxide, chromium oxide, iron sulfide, chromium sulfide, etc. Metal compounds etc. are mentioned.

  The heat-sensitive lithographic printing plate that can be applied to the image erasing method of the present invention includes phenol derivatives and aromatic carboxylic acid derivatives used for general heat-sensitive recording paper and pressure-sensitive recording paper to ensure image visibility. And a color developer (electron-donating dye precursor).

  Specific examples of the developer that can be used in the image forming layer of the heat-sensitive lithographic printing plate that can be applied to the image erasing method of the present invention include 4-cumylphenol, hydroquinone monobenzyl ether, 4,4′- Isopropylidene diphenol, 1,1-bis (4-hydroxyphenyl) cyclohexane, 4,4'-dihydroxydiphenyl-2,2-butane, 4,4'-dihydroxydiphenylmethane, 2,2-bis (4-hydroxyphenyl) ) -4-methylpentane, 2,2-bis (4-hydroxyphenyl) heptane, bis (4-hydroxyphenylthioethoxy) methane, 1,5-di (4-hydroxyphenylthio) -3-oxapentane, 1 , 1-bis (4-hydroxyphenyl) -1-phenylethane, 1,4-bis [α-methyl-α- (4′-hy Droxyphenyl) ethyl] benzene, 1,3-bis [α-methyl-α- (4′-hydroxyphenyl) ethyl] benzene, 4,4′-dihydroxydiphenyl sulfide, di (4-hydroxy-3-methylphenyl) ) Sulphine, 4-hydroxy-4'-methyldiphenylsulfone, 4-hydroxy-4'-isopropoxydiphenylsulfone, 2,4'-dihydroxydiphenylsulfone, 4,4'-dihydroxydiphenylsulfone, bis (3-allyl- 4-hydroxyphenyl) sulfone, 4-hydroxyphenyl-4'-benzyloxyphenylsulfone, 4-hydroxy-3 ', 4'-tetramethylenebiphenylsulfone, 3,4-dihydroxyphenyl-p-tolylsulfone, 4,4 '-Dihydroxybenzophenone, 4-hydride Phenolic compounds such as benzyl roxybenzoate, N, N'-di-m-chlorophenylthiourea, N- (phenoxyethyl) -4-hydroxyphenylsulfonamide, 4- [3- (p-tolylsulfonyl) propyloxy Aromatic carboxylic acids such as zinc salicylate, 4- [2- (p-methoxyphenoxy) ethyloxy] zinc salicylate, 5- [p- (2-p-methoxyphenoxyethoxy) cumyl] zinc salicylate, zinc p-chlorobenzoate Examples of the acid salt include organic acid substances such as zinc salts of acids and antipyrine complexes of zinc thiocyanate.

  Specific examples of color formers (electron-donating dye precursors) that can be used in the image forming layer of heat-sensitive lithographic printing plates that can be applied to the image erasing method of the present invention include (1) triarylmethane compounds 3,3'-bis (p-dimethylaminophenyl) -6-dimethylaminophthalide (crystal violet lactone), 3,3'-bis (p-dimethylaminophenyl) phthalide, 3- (p-dimethylamino) Phenyl) -3- (1,2-dimethylindol-3-yl) phthalide, 3- (p-dimethylaminophenyl) -3- (2-methylindol-3-yl) phthalide, 3- (p-dimethylamino) Phenyl) -3- (2-phenylindol-3-yl) phthalide, 3,3-bis (1,2-dimethylindol-3-yl) -5-dimethylaminophenyl Lido, 3,3-bis (1,2-dimethylindol-3-yl) -6-dimethylaminophthalide, 3,3-bis (9-ethylcarbazol-3-yl) -5-dimethylaminophthalide, 3,3-bis (2-phenylindol-3-yl) -5-dimethylaminophthalide, 3-p-dimethylaminophenyl-3- (1-methylpyrrol-2-yl) -6-dimethylaminophthalide, etc .: (2) 4,4'-bis-dimethylaminobenzhydrin benzyl ether, N-halophenyl leucooramine, N-2,4,5-trichlorophenyl leucooramine, etc. as diphenylmethane compounds: (3) xanthene Rhodamine B-anilinolactam, rhodamine Bp-nitroanilinolactam, rhodamine Bp-chloro Nilinolactam, 3-diethylamino-7-dibenzylaminofluorane, 3-diethylamino-7-octylaminofluorane, 3-diethylamino-7-phenylfluorane, 3-diethylamino-7- (3,4-dichloroanilino) fluorane, 3-diethylamino-7- (2-chloroanilino) fluorane, 3-diethylamino-6-methyl-7-anilinofluorane, 3-dibutylamino-6-methyl-7-anilinofluorane, 3-piperidino-6 Methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-anilinofluorane, 3-ethyl-tolylamino-6-methyl-7-phenethylfluorane, 3-diethylamino-7- ( 4-nitroanilino) fluorane and the like: (4) As thiazine compounds, Nzoyl leucomethylene blue, p-nitrobenzoyl leucomethylene blue and the like: (5) As spiro compounds, 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'-dichloro-spiro-dinaphthopyran, 3- Examples include benzyl spiro-dinaphthopyran, 3-methylnaphtho- (3-methoxy-benzo) -spiropyran, 3-propyl-spiro-dibenzopyran and the like. Two or more of these may be used in combination.

  Conventionally, in thermosensitive recording paper etc., by adsorbing the above-mentioned thermoplastic particles and heat-melting substances with inorganic pigments with high oil absorption such as silicon oxide, zinc oxide, titanium oxide, aluminum hydroxide, calcium carbonate, etc. It is formulated so as to prevent the sticking phenomenon with the thermal head to improve the sticking phenomenon and not to hinder the image drawing. However, when the image forming layer of the heat-sensitive lithographic printing plate to which the image erasing method of the present invention can be applied contains the above inorganic pigment, the printing durability may be lowered. Therefore, the image forming layer contains an inorganic pigment. It is preferable not to contain substantially. Here, “substantially” means that the amount of the inorganic pigment is less than 10% by mass relative to the total solid content of the image forming layer, and more preferably less than 5% by mass.

  The image forming layer of the heat-sensitive lithographic printing plate to which the image erasing method of the present invention can be applied has a dry film thickness of 0 from the viewpoints of printing durability of image areas, water resistance of non-image areas, and mechanical strength. It is preferably 5 to 20 μm, more preferably 1 to 10 μm. Further, the image forming layer is preferably provided as the outermost layer in order to obtain ink acceptability of an image portion sufficient for use as a lithographic printing plate.

  As the support used in the heat-sensitive lithographic printing plate to which the image erasing method of the present invention can be applied, a water-resistant support such as a plastic film or resin-coated paper is preferably used. Specifically, polyolefin films such as polyethylene and polypropylene, polyethersulfone, polyester, poly (meth) acrylate, polycarbonate, polyamide, and polyvinyl chloride, and plastic-coated paper with a laminated or coated plastic on the surface, melamine Paper that has been water-resistant by a wet paper strength agent such as formaldehyde resin, urea formaldehyde resin, or epoxidized polyamide resin can be used.

  The thickness of the support is preferably from 100 to 300 μm from the viewpoint of the recording suitability of the thermal plate making apparatus and the suitability of the lithographic printing press.

  The surface of such a support may be subjected to treatments such as plasma treatment, corona discharge treatment, deep ultraviolet irradiation treatment, and subbing treatment in order to enhance adhesion with the image forming layer. The subbing layer provided on the water-resistant support by the subbing treatment is composed of an acetal resin such as polyvinyl butyral, a polyester resin having a hydroxyl group at the molecular chain end, a (meth) acrylic acid / (meth) acrylic ester copolymer And a resin selected from vinylidene chloride / vinyl chloride copolymer and the like. The thickness of the undercoat layer is preferably 0.1 to 10 μm as a dry film thickness. In addition, a hydrophilic layer containing a hydrophilic material can be provided in order to increase the hydrophilicity of the non-image area where the printing ink is not deposited during printing. The hydrophilic layer may be a single layer or may be formed from a plurality of layers, but the hydrophilic material includes metal oxide fine particles such as colloidal silica, alumina sol, titania sol, and other metal oxide sols. The hydrophilic layer described in JP-A-2006-347047 can also be preferably used. The hydrophilic layer preferably has a dry film thickness of 0.2 to 20 μm.

  The heat-sensitive lithographic printing plate to which the image erasing method of the present invention can be applied is prepared by applying a coating solution prepared by mixing each material of the image forming layer and dissolving or dispersing it in an appropriate solvent on a support by a known coating method. It can be manufactured by coating and drying. A preferred solvent is water. However, in order to prevent the image forming layer from being thermally denatured by heat during drying, the drying treatment is preferably performed in an atmosphere of 50 ° C. or lower for about 30 seconds to 10 minutes.

  The heat-sensitive lithographic printing plate to which the image erasing method of the present invention can be applied may be provided with an undercoat layer to improve the adhesion between the image forming layer and the support as described above. If necessary, a plurality of functions for improving conductivity and antistatic property, a curling prevention layer for preventing curling as a printing plate, a curling promoting layer for imparting desired curling, and the like can be provided.

  Next, a plate making method by a heat sensitive method of a heat sensitive planographic printing plate that can be applied to the image erasing method of the present invention described above will be described. Since the heat-sensitive lithographic printing plate has a heat-sensitive image forming layer, the image portion is irradiated with light containing, for example, infrared light of 760 nm to 1200 nm by blending a photothermal conversion substance in the image forming layer. It is preferable to form an image portion by a solid laser or a semiconductor laser that emits infrared rays. In particular, laser exposure enables desired image-like recording directly from digital information of a computer. It is also possible to draw an image forming layer with a thermal head or a heat block by a thermal method to form an image portion. According to the thermal head, a desired image-like recording can be performed directly from digital information of a computer. .

When a thermal head is used, a line printer using a thick film or thin film line head, a serial printer using a thin film serial head, or the like can be used. The recording energy density is preferably 10 to 100 mJ / mm ² , and the head image recording density is preferably 300 dpi or more in order to obtain a relatively high quality output image.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. Unless otherwise indicated,% represents mass%.

In carrying out the image erasing method of the present invention, the following thermosensitive lithographic printing plate was prepared.
<Thermal lithographic printing plate>
1,2-bis (3-methylphenoxy) ethane (KS-232 manufactured by Sanko Co., Ltd.) is used as a heat-melting substance, and zirconia beads are used in a small dynomill (bead mill) for fine dispersion treatment at a solid concentration of 30%. It was. The dispersion particle diameter (median diameter) of the dispersion was 0.52 μm as measured using LA920 manufactured by Horiba, Ltd. Next, an image forming layer coating solution shown below was prepared.
(Image forming layer coating solution)
・ Water-soluble polymer compound; gelatin (12% aqueous solution)
(IKP Co., Ltd. IK3000) 80.0 parts by mass Thermoplastic resin; carboxy-modified styrene-butadiene copolymer (solid content 45%)
(Lacstar 7132-C, manufactured by Dainippon Ink & Chemicals, Inc.) 30.0 parts by mass-Hot melt material dispersion (30% dispersion) 15.0 parts by mass-Developer; 4-hydroxy-4- 1. Isopropoxydiphenyl sulfone (Nippon Soda Co., Ltd. D-8) 4.5 mass parts Color former; 3-Dibutylamino-6-methyl-7-anilinofluorane (Yamamoto Kasei Co., Ltd. ODB2) 7 parts by mass ・ Waterproofing agent; 1.2 parts by mass of divinylsulfone ・ 16.8 parts by mass of water

A double-sided polyethylene-coated paper (RC paper) having a thickness of 180 μm was subjected to corona discharge processing, and then an image-forming layer coating solution having the above formulation was applied to provide an image-forming layer having a dry film thickness of 5 μm. The direct thermal printer (Toshiba Tec Corporation Barcode Printer B-433 Line Thermal Head 300 dpi) test printing mode (printing speed 2 inches / second, applied energy 18. Images were recorded at 6 mJ / mm ² ).

Next, the following erase solutions (Comparative Examples 1 to 4, Examples 1 to 9) were prepared.
Comparative Example 1 PS plate eraser Xylene 3.8 parts by weight Diethylene glycol monomethyl ether 17.4 parts by weight Cyclohexanone 36.7 parts by weight Dioxane 9.8 parts by weight Water 10.8 parts by weight Acid Rhodamine B 0.002 parts by weight Poly Oxyethylene polyoxypropylene ether 9.8 parts by mass Hydroxypropyl methylcellulose 6.0 parts by mass α-cyclodextrin 5.0 parts by mass The mixture of the above composition was stirred to prepare an erasing solution of Comparative Example 1.

Comparative Example 2; Erase solution described in JP-A-2005-154682, Example 2 (page 7) Potassium sulfite 0.2 parts by mass Polyethyleneimine (Epomin SP-012 (manufactured by Nippon Shokubai Co., Ltd.)) 2.0 mass Part Triethanolamine 1.0 part by weight Sodium carbonate 0.7 part by weight Ben ヅ isothiazolone aqueous solution (manufactured by Perpachem Asia Ltd., Topside 600)
0.15 parts by mass Water 95.95 parts by mass The mixture was stirred with the above composition to obtain an erasing solution of Comparative Example 2. The pH of the obtained erasing solution was 11.5.

Comparative Example 3; Erase solution described in JP-A-2005-154682, Example 9 (page 7) Potassium sulfite 0.2 parts by mass Polyethyleneimine (Epomin PP-061 (manufactured by Nippon Shokubai Co., Ltd.)) 2.0 mass Part Triethanolamine 1.0 part by weight Sodium carbonate 0.7 part by weight Ben ヅ isothiazolone aqueous solution (manufactured by Perpachem Asia Ltd., Topside 600)
0.15 parts by mass Water 95.95 parts by mass The mixture was stirred with the above composition to obtain an erasing solution of Comparative Example 3. The pH of the obtained erasing solution was 11.3.

  About the comparative example 4 and Examples 1-9 eraser, it added and prepared the water-soluble polymer which has various amine structures shown in Table 1, and addition amount to water. The pH was adjusted using sodium hydroxide and sulfuric acid.

  The obtained erasing liquid is applied to the image part (image line having a width of 100 μm and a length of 10 mm) of the above-described heat-sensitive lithographic printing plate, and an ink is printed using an offset printing machine (3200CD manufactured by Ryobi Imaging Co., Ltd.). After using DIC New Champion F-Gloss Black (N) and Mitsubishi Paper Co., Ltd. SLM-OD 10% diluted solution as the dampening solution, the plate surface is etched with dampening cotton with dampening cotton and then the plate surface is etched. Offset printing was performed and the erasability was compared.

  As for erasability, the printed matter on the 3,000th sheet is visually marked with no stain / re-image, ◎, almost without stain / re-image, and slightly stained / re-imaged. An object was marked with △, and an object with clearly stained / reimaged was marked with ×. In addition, for the erasability of the image part to which the ink adhered after printing, the printing machine was stopped after printing 100 sheets, and the printing was resumed after applying and erasing the erasing liquid on the image part of the plate surface, The presence or absence of smearing / re-imaging in the image erasing part after printing 3,000 sheets was evaluated visually. The evaluation criteria are: ◎ no dirt / re-imaged, ◎ little dirt / re-imaged, △ slightly smeared / re-imaged tendency, △ clearly dirty / re-imaged. The thing where conversion was recognized was set as x. The results are shown in Table 2.

  As is clear from the above results, the image erasing method of the present invention has an image forming layer containing thermoplastic particles and / or a heat-meltable substance on a support, and the image forming layer is subjected to image formation by a heat sensitive method. An image erasing method for a heat-sensitive lithographic printing plate that forms an image can be provided, and when the number of printed sheets increases, it does not cause stains or re-images. An image erasing method excellent in erasing can be provided.

Claims (1)

An image erasing method for a heat-sensitive lithographic printing plate comprising thermoplastic particles and / or a heat-meltable substance on a support and having an image-forming layer that undergoes phase conversion by heat, wherein the water-soluble composition has at least one amine structure. An image erasing method for a heat-sensitive lithographic printing plate, comprising applying an aqueous solution containing a functional polymer and having a pH of 12 or more.