EP1543959B1 - Précurseur de plaque d'impression lithographique sensible à la chaleur - Google Patents

Précurseur de plaque d'impression lithographique sensible à la chaleur Download PDF

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Publication number
EP1543959B1
EP1543959B1 EP20040101643 EP04101643A EP1543959B1 EP 1543959 B1 EP1543959 B1 EP 1543959B1 EP 20040101643 EP20040101643 EP 20040101643 EP 04101643 A EP04101643 A EP 04101643A EP 1543959 B1 EP1543959 B1 EP 1543959B1
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EP
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Prior art keywords
printing plate
coating
group
plate precursor
lithographic printing
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EP20040101643
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German (de)
English (en)
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EP1543959A3 (fr
EP1543959A2 (fr
Inventor
Marc Van Damme
Huub Van Aert
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Agfa NV
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Agfa Graphics NV
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C1/00—Forme preparation
    • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
    • B41C1/1008—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C1/00—Forme preparation
    • B41C1/10—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme
    • B41C1/1008—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme 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
    • B41C1/1016—Forme preparation for lithographic printing; Master sheets for transferring a lithographic image to the forme 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 characterised by structural details, e.g. protective layers, backcoat layers or several imaging layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
    • B41C2201/02—Cover layers; Protective layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
    • B41C2201/04—Intermediate layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2201/00—Location, type or constituents of the non-imaging layers in lithographic printing formes
    • B41C2201/14—Location, type or constituents of the non-imaging layers in lithographic printing formes characterised by macromolecular organic compounds, e.g. binder, adhesives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/02—Positive working, i.e. the exposed (imaged) areas are removed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/06—Developable by an alkaline solution
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/22—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by organic non-macromolecular additives, e.g. dyes, UV-absorbers, plasticisers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/24—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by a macromolecular compound or binder obtained by reactions involving carbon-to-carbon unsaturated bonds, e.g. acrylics, vinyl polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41C—PROCESSES FOR THE MANUFACTURE OR REPRODUCTION OF PRINTING SURFACES
    • B41C2210/00—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation
    • B41C2210/26—Preparation or type or constituents of the imaging layers, in relation to lithographic printing forme preparation characterised by a macromolecular compound or binder obtained by reactions not involving carbon-to-carbon unsaturated bonds
    • B41C2210/262—Phenolic condensation polymers, e.g. novolacs, resols

Definitions

  • the present invention relates to a positive-working heat-sensitive lithographic printing plate precursor.
  • Lithographic printing presses use a so-called printing master such as a printing plate which is mounted on a cylinder of the printing press.
  • the master carries a lithographic image on its surface and a print is obtained by applying ink to said image and then transferring the ink from the master onto a receiver material, which is typically paper.
  • ink as well as an aqueous fountain solution (also called dampening liquid) are supplied to the lithographic image which consists of oleophilic (or hydrophobic, i.e. ink-accepting, water-repelling) areas as well as hydrophilic (or oleophobic, i.e. water-accepting, ink-repelling) areas.
  • driographic printing the lithographic image consists of ink-accepting and ink-abhesive (ink-repelling) areas and during driographic printing, only ink is supplied to the master.
  • Printing masters are generally obtained by the so-called computer-to-film method wherein various pre-press steps such as typeface selection, scanning, color separation, screening, trapping, layout and imposition are accomplished digitally and each color selection is transferred to graphic arts film using an image-setter.
  • the film can be used as a mask for the exposure of an imaging material called plate precursor and after plate processing, a printing plate is obtained which can be used as a master.
  • a typical printing plate precursor for computer-to-film methods comprise a hydrophilic support and an image-recording layer of a photosensitive polymer which include UV-sensitive diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely used.
  • a photosensitive polymer which include UV-sensitive diazo compounds, dichromate-sensitized hydrophilic colloids and a large variety of synthetic photopolymers. Particularly diazo-sensitized systems are widely used.
  • the exposed image areas become insoluble and the unexposed areas remain soluble in an aqueous alkaline developer.
  • the plate is then processed with the developer to remove the diazonium salt or diazo resin in the unexposed areas.
  • the exposed areas define the image areas (printing areas) of the printing master, and such printing plate precursors are therefore called 'negative-working'.
  • positive-working materials wherein the exposed areas define the non-printing areas, are known, e.g. plates having a novolac/naphtoquinone-diazide coating which dissolves in the developer only at exposed areas.
  • thermoplastic polymer latex In addition to the above photosensitive materials, also heat-sensitive printing plate precursors have become very popular. Such thermal materials offer the advantage of daylight-stability and are especially used in the so-called computer-to-plate method wherein the plate precursor is directly exposed, i.e. without the use of a film mask. The material is exposed to heat or to infrared light and the generated heat triggers a (physico-)chemical process, such as ablation, polymerization, insolubilisation by cross-linking of a polymer, heat-induced solubilisation, decomposition, or particle coagulation of a thermoplastic polymer latex.
  • a (physico-)chemical process such as ablation, polymerization, insolubilisation by cross-linking of a polymer, heat-induced solubilisation, decomposition, or particle coagulation of a thermoplastic polymer latex.
  • the known heat-sensitive printing plate precursors typically comprise a hydrophilic support and a coating containing an oleophilic polymer, which is alkali-soluble in exposed areas (positive working material) or in the non-exposed areas (negative working material) and an IR-absorbing compound.
  • an oleophilic polymer is typically a phenolic resin.
  • WO 97/39894 describes a positive-working heat-sensitive printing plate precursor which is sensitive to IR light but not to UV light comprising a support and an IR-sensitive coating comprising an oleophilic polymer that is soluble in an aqueous alkaline developer and a dissolution inhibitor which reduces the solubility of the polymer in the developer.
  • EP-A 0 864 420 describes a positive-working heat-sensitive printing plate precursor comprising a support, a first layer containing an oleophilic polymer that is soluble in an aqueous alkaline developer and an IR-sensitive top layer of which the penetrability by or solubility in the aqueous alkaline developer is changed upon exposure to IR light.
  • EP-A 0 934 822 describes a photosensitive composition for a lithographic printing plate wherein the composition contains an alkali-soluble resin having phenolic hydroxyl groups and of which at least some of the phenolic hydroxyl groups are esterified by a sulphonic acid or a carboxylic acid compound.
  • EP-A 1 072 432 describes an image forming material which comprises a recording layer which is formed of a composition whose solubility in water or in an alkali aqueous solution is altered by the effects of light or heat.
  • This recording layer comprises a polymer of vinyl phenol or a phenolic polymer, wherein hydroxy groups and alkoxy groups are directly linked to the aromatic hydrocarbon ring.
  • the alkoxy group is composed of 20 or less carbon atoms.
  • thermo-resist composition which undergo a thermally-induced chemical transformation effective either to ablate the composition or to increase or decrease its solubility in a particular developer.
  • the thermo-resist composition comprises phenolic polymers in which free hydroxyl groups are protected. Upon heating in the presence of an acid these protecting groups split off resulting in a solubility change of the composition.
  • the hydroxyl protecting groups may be ethers, such as alkyl-, benzyl-, cycloalkyl- or trialkylsilyl-ethers, and oxycarbonyl groups.
  • EP-A 0 982 123 describes a photosensitive resin composition or recording material wherein the binder is a phenolic polymer, substituted with a specific functional group on the aromatic hydrocarbon ring such as a halogen atom, an alkyl group having 12 or less carbon atoms, an alkoxy group, an alkylthio group, a cyano group, a nitro group or a trifluoromethyl group, or wherein the hydrogen atom of the hydroxy group of the phenolic polymer is substituted with a specific functional group such as an amide, a thioamide or a sulphonamide group.
  • a specific functional group on the aromatic hydrocarbon ring such as a halogen atom, an alkyl group having 12 or less carbon atoms, an alkoxy group, an alkylthio group, a cyano group, a nitro group or a trifluoromethyl group, or wherein the hydrogen atom of the hydroxy group of the phenolic polymer is substituted
  • the coating of the recording material has such a high density that improves the intra-film transistivity of heat obtained by the light-to-heat conversion at the time of laser exposure.
  • the high density of the coating makes the image recording material less susceptible to external influences such as humidity and temperature. Consequently, the storage stability of the image recording material can also be enhanced.
  • US 4 939 229 describes a method for the preparation of branched novolacs, useful for photoresist compositions, by reacting a tris- or tetrakis(dialkylaminoalkyl)phenol with a phenolic compound in the presence of an acid catalyst. Due to the reaction with these intermediate dialkylaminoalkyl-phenol compounds, a reproducible method for the synthesis of branched novolacs is obtained.
  • WO99/01795 describes a method for preparing a positive working resist pattern on a substrate wherein the coating composition comprises a polymeric substance having functional groups such that the functionalised polymeric substance has the property that it is developer insoluble prior to delivery of radiation and developer soluble thereafter.
  • Suitable functional groups are known to favor hydrogen bonding and may comprise amino, amido, chloro, fluoro, carbonyl, sulphinyl and sulphonyl groups and these groups are bonded to the polymeric substance by an esterification reaction with the phenolic hydroxy group to form a resin ester.
  • WO 2004035310 WO 2004035686 , WO 2004035645 , WO 2004035687 and EP 1506858 (all not pre-published) describe positive-working heat-sensitive lithographic printing plate precursors wherein the coating comprises phenolic resins which are modified by various substituents that improve the chemical resistance of the coating, i.e. which render the coating less vulnerable to attack by the organic chemicals that are typically present in fountain solutions, plate cleaners, blanket wash liquids, etc.
  • substitution typically produces a reduction of the sensitivity of the plate because also the resistance of the coating towards the developer is increased : in positive-working lithographic printing plate precursors the exposure energy required for rendering the exposed areas of the coating soluble in the developer determines the sensitivity of the precursor.
  • a high developer resistance of the unexposed areas is advantageous because it results in a high developer dissolution contrast, also called development latitude : advantageously, the exposed areas of the coating are completely dissolved in the developer before the non-exposed areas are affected by the developer.
  • US 2003/165774 discloses to a radiation sensitive coating composition for printing plates which contain two superposing layers, the first layer containing soluble alkali phenolic resin such as novolak as the binding polymer and one or more IR dyes.
  • the second layer, coated on the first one contains a different polymer for the purposes of protecting and insolubilise the phenolic resin of the first layer. After IR exposure, the energy absorbed by the IR dye is transferred as heat and destroys the phenolic resin protection, allowing dissolution thereof in an alkali solution.
  • EP-A 625 728 discloses a radiation sensitive composition for preparing a positive or negative working lithographic printing plate comprising a resole resin, a novolac resin, a latent Bronsted acid and an IR absorber.
  • the solubility of the composition in aqueous alkaline developing solution is both reduced in exposed areas and increased in unexposed areas.
  • US 6,436,596 discloses a quality control method for a planographic printing plate having dispersed on a substrate a photosensitive layer formed by a resin soluble in an aqueous alkali solution and a compound that absorbs light to generate heat.
  • EP-A 1 366 926 discloses a photosensitive composition including (A) a vinyl polymer containing a copolymerization component having a carboxyl group, and (B) a polymer compound including a phenolic hydroxyl group, and (C) an IR absorber.
  • EP-A 914 941 discloses a method for making a positive working lithographic printing plate having a heat mode imaging element comprising a first layer including a polymer soluble in an aqueous alkaline solution and a top layer which is unpenetrable by an alkaline developer.
  • US 2002/9671 discloses a positive-working IR-sensitive mixture which contains a binder which is insoluble in water but soluble or at least swellable in an aqueous alkali, and carbon black particles dispersed in such a binder, the dispersed canbon black particles forming the radiation-sensitive component essential for the imagewise differentiation.
  • the positive-working heat-sensitive lithographic printing plate precursors according to claims 1-3 of the present invention comprises a hydrophilic support and an oleophilic coating provided thereon, said coating comprising an infrared light-to-heat converter, a binder which is soluble in an aqueous alkaline developer and a polymeric development accelerator.
  • the polymeric development accelerator is a polymer that improves the dissolution contrast during processing between exposed and non-exposed areas, without substantially affecting the developer resistance of the non-exposed areas, i.e. resulting in an improved sensitivity. "Without substantially affecting the developer resistance” means that the addition of the polymeric development accelerator changes the value of the Developer Resistance, as defined in the Examples section below, by at most 7 %, more preferably at most 5 %, most preferably at most 2 %.
  • the sensitivity is improved while maintaining the Under-Exposure Latitude UEL, as defined in the Examples section below, at a high value of at least 20%, more preferably at least 30 %, even more preferably at least 40 % and most preferably at least 50 %.
  • the alkali-soluble binder is a chemically modified phenolic resin that provides an improved chemical resistance.
  • the addition of the polymeric development accelerator surprisingly is capable of improving the sensitivity, i.e. decreasing the developer resistance of the exposed areas, while preserving the developer resistance of the unexposed areas at a high level.
  • the lithographic printing plate precursor of the present invention comprises a hydrophilic support and an oleophilic coating provided thereon; the coating comprises an infrared light-to-heat converter such as an infrared dye or pigment, an alkali-soluble binder and a polymeric development accelerator, hereafter also referred to as "PDA".
  • an infrared light-to-heat converter such as an infrared dye or pigment, an alkali-soluble binder and a polymeric development accelerator, hereafter also referred to as "PDA”.
  • the PDA used in the plate precursor of the present invention is a phenolic novolac which comprises at least one of the following recurring phenolic monomeric units meta-cresol or monohydroxy benzene, also called phenol, and wherein the phenolic monomeric units are condensed with formaldehyde.
  • the amount of meta-cresol in the phenolic formaldehyde resin is preferably at least 70 mol%, more preferably at least 90 mol%, and most preferably essentially 100 mol%.
  • the amount of phenol in the phenolic formaldehyde resin is at least 40 mol%, more preferably at least 55 mol%, and most preferably at least 70 mol%.
  • the PDA is a phenolic resin which comprises at least 5 mol% of a recurring monomeric unit having at least one phenolic hydroxyl group and at least one alkali solubilising group, more preferably at least 10 mol% of this recurring monomeric unit, most preferably at least 20 mol% of this recurring monomeric unit.
  • An alkali solubilising group is a group which increases the solubility of the PDA in an aqueous alkaline solution; the alkaline solution has preferably a pH of at least 10.
  • the alkali solubilising group is preferably selected from a hydroxyl group, a carboxylic acid group, a sulphonic acid group, a sulphuric acid group, a phosphonic acid group, a phosphoric acid group or a thiol group; a phenolic hydroxyl group is more preferred.
  • the recurring monomeric unit having at least one phenolic hydroxyl group and at least one alkali solubilising groups has at least two phenolic hydroxyl groups and such a recurring monomeric unit is preferably selected from resorcinol, pyrocatechol, hydroquinone, hydroxy hydroquinone, pyrogallol, phloroglucinol or dihydroxy benzoic acid; resorcinol is more preferred.
  • the recurring monomeric unit having at least one phenolic hydroxyl group and at least one alkali solubilising groups is preferably condensed with formaldehyde or aceton, more preferably with formaldehyde.
  • the average molecular weight M n of the polymeric development accelerator is preferably in the range of 300 to 50000 or for M w in the range of 400 to 100000, more preferably in the range of 500 to 5000 for M n or in the range of 800 to 20000 for M w , most preferably in the range of 500 to 2500 for M n or in the range of 800 to 12000 for M w .
  • polymers which can be used as a polymer development accelerator are listed below.
  • the average molecular weight M n or M w (in g/mol) as indicated in this list, is given by the supplier or is determined by means of Size Exclusion Chromatography, using as eluent tetrahydrofuran or a solution of 0.21 w/w % LiCl in dimethyl acetamide and using polystyrene as calibration standard.
  • the amount of the PDA in the coating may depend on the dissolution kinetic of the alkali-soluble binder because binders, which have a lower dissolution rate, preferably need a higher amount of the PDA.
  • the ratio of the amount of the PDA to the amount of the alkali-soluble binder varies from 0.01 to 1 (parts in weight), more preferably 0.05 to 0.8 (parts in weight), most preferably from 0.1 to 0.5 (parts in weight).
  • the support of the lithographic printing plate precursor has a hydrophilic surface or is provided with a hydrophilic layer.
  • the support may be a sheet-like material such as a plate or it may be a cylindrical element such as a sleeve which can be slid around a print cylinder of a printing press.
  • a preferred support is a metal support such as aluminum or stainless steel.
  • the metal can also be laminated to a plastic layer, e.g. polyester film.
  • a particularly preferred lithographic support is an electrochemically grained and anodized aluminum support. Graining and anodization of aluminum is well known in the art.
  • the anodized aluminum support may be treated to improve the hydrophilic properties of its surface.
  • the aluminum support may be silicated by treating its surface with a sodium silicate solution at elevated temperature, e.g. 95°C.
  • a phosphate treatment may be applied which involves treating the aluminum oxide surface with a phosphate solution that may further contain an inorganic fluoride.
  • the aluminum oxide surface may be rinsed with a citric acid or citrate solution. This treatment may be carried out at room temperature or may be carried out at a slightly elevated temperature of about 30 to 50°C.
  • a further interesting treatment involves rinsing the aluminum oxide surface with a bicarbonate solution.
  • the aluminum oxide surface may be treated with polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid, polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinyl alcohol, and acetals of polyvinyl alcohols formed by reaction with a sulfonated aliphatic aldehyde It is further evident that one or more of these post treatments may be carried out alone or in combination.
  • the coating which is provided on the support, may consist of one or more layer(s).
  • additional layers besides the layer(s) which comprise the alkali-soluble binder or the layer(s) which comprise the infrared light-to-heat converter are e.g. a "subbing" layer which improves the adhesion of the coating to the support and a covering layer which protects the coating against contamination or mechanical damage.
  • the alkali-soluble binder can be present in one or more layer(s) of the coating.
  • the amount of the binder is advantageously from 40 to 99.8% by weight, preferably from 70 to 99.4% by weight, particularly preferably from 80 to 99% by weight, based in each case on the total weight of the non-volatile components of the coating.
  • the alkali-soluble binder is preferably an organic polymer which has acidic groups with a pKa of less than 13 to ensure that the layer is soluble or at least swellable in aqueous alkaline developers.
  • the binder is a polymer or polycondensate, for example a polyester, polyamide, polyurethane or polyurea.
  • Polycondensates and polymers having free phenolic hydroxyl groups as obtained, for example, by reacting phenol, resorcinol, a cresol, a xylenol or a trimethylphenol with aldehydes, especially formaldehyde, or ketones are also particularly suitable.
  • Condensates of sulfamoyl- or carbamoyl-substituted aromatics and aldehydes or ketones are also suitable.
  • Polymers of bismethylol-substituted ureas, vinyl ethers, vinyl alcohols, vinyl acetals or vinylamides and polymers of phenylacrylates and copolymers of hydroxylphenylmaleimides are likewise suitable.
  • polymers having units of vinylaromatics, N-aryl(meth)acrylamides or aryl (meth)acrylates may be mentioned, it being possible for each of these units also to have one or more carboxyl groups, phenolic hydroxyl groups, sulfamoyl groups or carbamoyl groups.
  • Specific examples include polymers having units of 2-hydroxyphenyl (meth)acrylate, of N-(4-hydroxyphenyl)(meth)acrylamide, of N-(4-sulfamoylphenyl)-(meth)acrylamide, of N-(4-hydroxy-3,5-dimethylbenzyl)-(meth)acrylamide, or 4-hydroxystyrene or of hydroxyphenylmaleimide.
  • the polymers may additionally contain units of other monomers which have no acidic units.
  • Such units include vinylaromatics, methyl (meth)acrylate, phenyl(meth)acrylate, benzyl (meth)acrylate, methacrylamide or acrylonitrile.
  • the polycondensate is a phenolic resin, such as a novolac, a resole or a polyvinylphenol.
  • the novolac is preferably a cresol/formaldehyde or a cresol/xylenol/formaldehyde novolac, the amount of novolac advantageously being at least 50% by weight, preferably at least 80% by weight, based in each case on the total weight of all binders.
  • the alkali-soluble binder is a phenolic resin wherein the phenyl group or the hydroxy group of the phenolic monomeric unit are chemically modified with an organic substituent.
  • the phenolic resins which are chemically modified with an organic substituent may exhibit an increased chemical resistance against printing chemicals such as fountain solutions or press chemicals such as plate cleaners.
  • the addition of a PDA exhibits an improved sensitivity without substantially affecting the developer resistance.
  • Examples of preferred chemically modified phenolic resins are described in EP-A 0 934 822 , EP-A 0 996 869 , EP-A 1 072 432 , US 5,641,608 , EP-A 0 982 123 , WO99/01795 , EP-A 933682 , EP-A 894622 and WO 99/63407 and in the not pre-published WO 2004035686 , WO 2004035645 , WO 2004035687 and EP 1506858 .
  • the dissolution behavior of the coating in the developer can be fine-tuned by optional solubility regulating components.
  • the coating may also contain developer resistance means, also called development inhibitors, i.e. one or more ingredients which are capable of delaying the dissolution of the unexposed areas during processing.
  • developer resistance means also called development inhibitors, i.e. one or more ingredients which are capable of delaying the dissolution of the unexposed areas during processing.
  • the dissolution inhibiting effect is preferably reversed by heating, so that the dissolution of the exposed areas is not substantially delayed and a large dissolution differential between exposed and unexposed areas can thereby be obtained.
  • developer resistance means can be added to a layer comprising the alkali-soluble binder or to another layer of the coating.
  • Inhibitors of this type typically comprise at least one hydrogen bridge forming group such as nitrogen atoms, onium groups, carbonyl (-CO-), sulfinyl (-SO-) or sulfonyl (-SO 2 -) groups and a large hydrophobic moiety such as one or more aromatic nuclei.
  • Suitable inhibitors improve the developer resistance because they delay the penetration of the aqueous alkaline developer into the coating.
  • Such compounds can be present in the layer(s) comprising the alkali-soluble binder, as described in e.g. EP-A 950 518 , and/or in a development barrier layer on top of said layer, as described in e.g. EP-A 864 420 , EP-A 950 517 , WO 99/21725 and WO 01/45958 .
  • the solubility of the barrier layer in the developer or the penetrability of the barrier layer by the developer can be increased by exposure to heat or infrared light.
  • inhibitors which delay the penetration of the aqueous alkaline developer into the coating include the following :
  • the above mentioned inhibitor of type (b) and (c) tends to position itself, due to its bifunctional structure, at the interface between the coating and air and thereby forms a separate top layer even when applied as an ingredient of the coating solution of the layer comprising the alkali-soluble binder.
  • the surfactants also act as a spreading agent which improves the coating quality.
  • the separate top layer thus formed seems to be capable of acting as the above mentioned barrier layer which delays the penetration of the developer into the coating.
  • the inhibitor of type (a) to (c) can be applied in a separate solution, coated on top of the layer(s) comprising the alkali-soluble binder.
  • a solvent in the second coating solution that is not capable of dissolving the ingredients present in the first layer so that a highly concentrated water-repellent or hydrophobic phase is obtained at the top of the coating which is capable of acting as the above mentioned development barrier layer.
  • the infrared light absorbing dye or pigment may be present in the same layer(s) as the alkali-soluble binder, in the optional barrier layer discussed above and/or in an optional other layer.
  • the IR absorber is concentrated in or near the barrier layer, e.g. in an intermediate layer between the alkali-soluble binder and the barrier layer.
  • said intermediate layer comprises the IR absorbing compound in an amount higher than the amount of IR absorbing compound in the alkali-soluble binder or in the barrier layer.
  • Preferred IR absorbing dyes are cyanine dyes, merocyanine dyes, indoaniline dyes, oxonol dyes, pyrilium dyes and squarilium dyes.
  • IR dyes examples include e.g. EP-As 823327 , 978376 , 1029667 , 1053868 , 1093934 ; WO 97/39894 and 00/29214 .
  • a preferred compound is the following cyanine dye : The preferred amount of this dye is less than 40 mg/m 2 .
  • the protective layer generally comprises at least one water-soluble binder, such as polyvinyl alcohol, polyvinylpyrrolidone, partially hydrolyzed polyvinyl acetates, gelatin, carbohydrates or hydroxyethylcellulose, and can be produced in any known manner such as from an aqueous solution or dispersion which may, if required, contain small amounts, i.e. less than 5% by weight, based on the total weight of the coating solvents for the protective layer, of organic solvents.
  • the thickness of the protective layer can suitably be any amount, advantageously up to 5.0 ⁇ m, preferably from 0.1 to 3.0 ⁇ m, particularly preferably from 0.15 to 1.0 ⁇ m.
  • the coating and more specifically the layer(s) comprising the alkali-soluble binder may further contain additional ingredients.
  • Colorants can be added such as dyes or pigments which provide a visible color to the coating and which remain in the coating at unexposed areas so that a visible image is produced after exposure and processing.
  • contrast dyes are the amino-substituted tri- or diarylmethane dyes, e.g. crystal violet, methyl violet, victoria pure blue, flexoblau 630, basonylblau 640, auramine and malachite green.
  • the dyes which are discussed in depth in the detailed description of EP-A 400 706 are suitable contrast dyes.
  • Surfactants especially perfluoro surfactants, silicon or titanium dioxide particles, polymers particles such as matting agents and spacers are also well-known components of lithographic coatings.
  • any known method can be used.
  • the above ingredients can be dissolved in a solvent mixture which does not react irreversibly with the ingredients and which is preferably tailored to the intended coating method, the layer thickness, the composition of the layer and the drying conditions.
  • Suitable solvents include ketones, such as methyl ethyl ketone (butanone), as well as chlorinated hydrocarbons, such as trichloroethylene or 1,1,1-trichloroethane, alcohols, such as methanol, ethanol or propanol, ethers, such as tetrahydrofuran, glycol-monoalkyl ethers, such as ethylene glycol monoalkyl ether, e.g.
  • 2-methoxy-1-propanol or propylene glycol monoalkyl ether and esters, such as butyl acetate or propylene glycol monoalkyl ether acetate. It is also possible to use a mixture which, for special purposes, may additionally contain solvents such as acetonitrile, dioxane, dimethylacetamide, dimethylsulfoxide or water.
  • Any coating method can be used for applying one or more coating solutions to the hydrophilic surface of the support.
  • a multi-layer coating can be applied by coating/drying each layer consecutively or by the simultaneous coating of several coating solutions at once.
  • the volatile solvents are removed from the coating until the coating is self-supporting and dry to the touch.
  • the residual solvent content may be regarded as an additional composition variable by means of which the composition may be optimised.
  • Drying is typically carried out by blowing hot air onto the coating, typically at a temperature of at least 70°C, suitably 80-150°C and especially 90-140°C. Also infrared lamps can be used.
  • the drying time may typically be 15-600 seconds.
  • a heat treatment and subsequent cooling may provide additional benefits, as described in WO99/21715 , EP-A 1 074 386 , EP-A 1 074 889 , WO00/29214 , and unpublished Eur. patent application nos. 02 102 413 , 02 102 414 , 02 102 415 , filed on 04.10.2002.
  • the plate precursor can be image-wise exposed directly with heat, e.g. by means of a thermal head, or indirectly by infrared light, preferably near infrared light.
  • the infrared light is preferably converted into heat by an IR light absorbing compound as discussed above.
  • the heat-sensitive lithographic printing plate precursor is preferably not sensitive to visible light, i.e. no substantial effect on the dissolution rate of the coating in the developer is induced by exposure to visible light.
  • the coating is not sensitive to ambient daylight, i.e. visible (400-750 nm) and near UV light (300-400 nm) at an intensity and exposure time corresponding to normal working conditions so that the plate precursor can be handled without the need for a safe light environment.
  • the coating does not comprise photosensitive ingredients, such as (quinone)diazide or diazo(nium) compounds, photoacids, photoinitiators, sensitizers etc., which absorb the near UV and/or visible light that is present in sun light or office lighting and thereby change the solubility of the coating in exposed areas.
  • photosensitive ingredients such as (quinone)diazide or diazo(nium) compounds, photoacids, photoinitiators, sensitizers etc., which absorb the near UV and/or visible light that is present in sun light or office lighting and thereby change the solubility of the coating in exposed areas.
  • the printing plate precursor can be exposed to infrared light by means of e.g. LEDs or a laser.
  • the light used for the exposure is a laser emitting near infrared light having a wavelength in the range from about 750 to about 1500 nm, more preferably 750 to 1100 nm, such as a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser.
  • the required laser power depends on the sensitivity of the plate precursor, the pixel dwell time of the laser beam, which is determined by the spot diameter (typical value of modern plate-setters at 1/e 2 of maximum intensity : 5-25 ⁇ m), the scan speed and the resolution of the exposure apparatus (i.e. the number of addressable pixels per unit of linear distance, often expressed in dots per inch or dpi; typical value : 1000-4000 dpi).
  • ITD plate-setters for thermal plates are typically characterized by a very high scan speed up to 500 m/s and may require a laser power of several Watts.
  • An XTD platesetter equipped with one or more laserdiodes emitting in the wavelength range between 750 and 850 nm is an especially preferred embodiment for the method of the present invention.
  • the known plate-setters can be used as an off-press exposure apparatus, which offers the benefit of reduced press down-time.
  • XTD plate-setter configurations can also be used for on-press exposure, offering the benefit of immediate registration in a multi-color press. More technical details of on-press exposure apparatuses are described in e.g. US 5,174,205 and US 5,163,368 .
  • the formation of the lithographic image by the plate precursor is due to a heat-induced solubility differential of the coating during processing in the developer.
  • the solubility differentiation between image (printing, oleophilic) and non-image (non-printing, hydrophilic) areas of the lithographic image is believed to be a kinetic rather than a thermodynamic effect, i.e. the non-image areas are characterized by a faster dissolution in the developer than the image-areas.
  • the underlying hydrophilic surface of the support is revealed at the non-image areas.
  • the non-image areas of the coating dissolve completely in the developer before the image areas are attacked so that the latter are characterized by sharp edges and high ink-acceptance.
  • the time difference between completion of the dissolution of the non-image areas and the onset of the dissolution of the image areas is preferably longer than 10 seconds, more preferably longer than 20 seconds and most preferably longer than 60 seconds, thereby offering a wide development latitude.
  • the non-image areas of the coating are removed by immersion in a conventional aqueous alkaline developer, which may be combined with mechanical rubbing, e.g. by a rotating brush. During development, any water-soluble protective layer present is also removed.
  • Silicate-based developers which have a ratio of silicon dioxide to alkali metal oxide of at least 1 are preferred to ensure that the alumina layer (if present) of the substrate is not damaged.
  • Preferred alkali metal oxides include Na 2 O and K 2 O, and mixtures thereof.
  • the developer may optionally contain further components, such as buffer substances, complexing agents, antifoams, organic solvents in small amounts, corrosion inhibitors, dyes, surfactants and/or hydrotropic agents as well known in the art.
  • the developer may further contain compounds which increase the developer resistance of the non-image areas, e.g. a polyalcohol such as sorbitol, preferably in a concentration of at least 40 g/l, and/or a poly(alkylene oxide) containing compound such as e.g. Supronic B25, commercially available from RODIA, preferably in a concentration of at most 0.15 g/l.
  • the development is preferably carried out at temperatures of from 20 to 40 °C in automated processing units as customary in the art.
  • alkali metal silicate solutions having alkali metal contents of from 0.6 to 2.0 mol/l can suitably be used. These solutions may have the same silica/alkali metal oxide ratio as the developer (generally, however, it is lower) and likewise optionally contain further additives.
  • the required amounts of regenerated material must be tailored to the developing apparatuses used, daily plate throughputs, image areas, etc. and are in general from 1 to 50 ml per square meter of plate precursor.
  • the addition can be regulated, for example, by measuring the conductivity as described in EP-A 0 556 690 .
  • the processing of the plate precursor may also comprise a rinsing step, a drying step and/or a gumming step.
  • the plate precursor can, if required, be post-treated with a suitable correcting agent or preservative as known in the art.
  • the layer can be briefly heated to elevated temperatures ("baking").
  • the printing plate thus obtained can be used for conventional, so-called wet offset printing, in which ink and an aqueous dampening liquid is supplied to the plate.
  • Another suitable printing method uses so-called single-fluid ink without a dampening liquid.
  • Suitable single-fluid inks have been described in US 4,045,232 ; US 4,981,517 and US 6,140,392 .
  • the single-fluid ink comprises an ink phase, also called the hydrophobic or oleophilic phase, and a polyol phase as described in WO 00/32705 .
  • a suitable method for determining the energy density value for the practical exposure of a positive-working thermal plate will be explained hereafter.
  • a halftone image is exposed on the plate at various energy density values and the actual dot area obtained on the plate, after processing according to the conditions (time, temperature, developer) used, is then measured by means of a reflection densitometer and compared with the target dot area that was set in the software (RIP) of the imagesetter.
  • RIP software
  • FIG. 1 A typical example of such a method is shown in Figure 1 wherein the dot area obtained on the plate, exposed with a 50% 200 lpi screen (about 80 lines/cm), is plotted versus the energy density of the exposure.
  • the dot area values were obtained by means of a CC Dot 3 densitometer, commercially available from Centurfax Ltd.
  • Figure 1 shows that at low energy densities, the dot area on the plate is larger than the target value of 50% : it is believed that, due to the underexposure, the coating just around the edge of the dot does not dissolve sufficiently rapidly in the developer. At too high energy density values, the overexposure of the coating around the dot leads to dissolution of the edges of the dot, resulting in a dot area value that is lower than 50%. These effects are especially significant when the laser spot has a pronounced gaussian intensity profile and less with a steep intensity profile.
  • the REED value is defined as the minimum energy density at which the dot area on the plate, occupied by a screened image corresponding to a 50% halftone in the image data, coincides with the 50% target value. It is clear to the skilled person that a lower REED value indicates a higher sensitivity of the plate.
  • CP clearing point
  • Exposure of a positive-working thermal plate at an energy density which is insufficient to raise the temperature of the coating up to the threshold value of the imaging mechanism has no significant effect on the dissolution kinetics of the exposed area.
  • the coating normally remains on the support, i.e. the optical density of the coating essentially equals D u , the optical density of the unexposed plate.
  • the temperature in the coating approaches and eventually exceeds the threshold temperature and, as a result, the density of the coating that remains on the plate after processing decreases.
  • the minimum energy density that is required to produce a reduction of the optical density of the exposed and processed plate coating by a factor of 95%, i.e. to produce an optical density of 0.05*D u , is defined herein as the 'clearing point' .
  • CP can be measured by exposing a solid wedge on the plate, i.e. a series of areas consisting entirely of 0% dots (full exposure at all imagesetter pixels) which are exposed on the plate at various energy density values.
  • a solid wedge i.e. a series of areas consisting entirely of 0% dots (full exposure at all imagesetter pixels) which are exposed on the plate at various energy density values.
  • the method is explained with reference to Figure 2 wherein these energy density values form a series of discrete values resulting in a step-wedge, but it should be clear to the skilled reader that the energy density values may also vary continuously so as to obtain a continuous wedge.
  • a preferred continuous wedge varies by not more than 10 mJ/cm 2 per cm wedge length. The minimum and maximum energy density for exposing the wedge should be adjusted to the particular type of plate that is being tested.
  • the step-wedge used for the present Examples ranged from 30 to 300 mJ/cm 2 with intervals of 20 mJ/cm 2 .
  • the wedge was generated by the software that controls the imagesetter, although similar results can be obtained by other means, e.g. by placing a wedge filter in the light path of the imagesetter, preferably in contact with the plate.
  • CP was determined by plotting the discrete values of optical density of the exposed and processed plate vs. the energy density as shown in Figure 2 and establishing by interpolation at which energy density the optical density of the coating is reduced by 95%.
  • a high UEL value is preferred because fluctuation of processing conditions, batch-to-batch speed variations of the plate precursor, etc., have no significant influence when UEL is high, i.e. when REED is large compared to CP.
  • UEL is low, shifts of the CP and REED values may result in an incomplete clean-out of the exposed areas, resulting in toning (ink-acceptance at the non-image areas).
  • DR Developer Resistance
  • D o is the optical density of the unexposed and undeveloped plate coating
  • D 2 is the optical density of the coating of the unexposed plate after being put through the processor twice. A smaller value of DR indicates a higher developer resistance.
  • Optical density values for measuring CP and DR were obtained by means of a GretagMacbeth D19C 47B/P densitometer, commercially available from Gretag - Macbeth AG.
  • Such reflection densitometers are typically equipped with several filters (e.g. cyan, magenta, yellow) : the optical density was measured with the filter that corresponds to the color of the coating, e.g. a cyan filter is preferably used for measuring the optical density of a blue colored coating. All optical density values were measured with reference to the uncoated support of the plate.
  • the printing plate precursors were produced by coating the solution defined in Table 1 onto an electrochemically roughened and anodically oxidised aluminum sheet (anodic weight of 3 g/m 2 ), the surface of which has been rendered hydrophilic by treatment with an aqueous solution of polyvinyl phosphonic acid, at a wet coating thickness of 26 ⁇ m and then dried.
  • Table 1 composition of the coating solution INGREDIENTS Parts (grams) Tetrahydrofuran 210.16 20 wt.% solution of POLYMER-01 (1) in Dowanol PM (2) 158.03 Dowanol PM (2) 330.04 Methyl ethyl ketone 267.99 S0094 (3) 1.52 1 wt.% solution of TegoGlide 410 (4) in Dowanol PM 21.72 PDA-01 (solid) 10.54
  • the printing plate precursors were then exposed with a CREO TRENDSETTER 3244 T, a plate-setter available from CREO, Burnaby, Canada, at 2450 dpi with a 50% screen (200 lpi) and with a solid area (100%) at different energy densities ranging from 60 mJ/cm 2 up to 280 mJ/cm 2 .
  • the plates were developed in an AUTOLITH T processor, operating at 25°C, in a developing solution composed of a mixture of 870 g demineralised water, 108 g sodium metasilicate.5aqua, 0.135 g Supronic B25, commercially available from RODIA, and 41.7 ml of a 70 wt.% aqueous solution of sorbitol.
  • the Invention Examples 1 and 2 demonstrate that a positive-working printing plate precursor which comprises a PDA, exhibits a higher sensitivity, i.e. a lower value for REED and CP, in comparison with the Comparative Example 1, having no PDA, or with the Comparative Examples 2 and 3, having a low molecular weight developer accelerator. Also, the UEL exhibits an increased value for the Invention Examples 1 and 2 in comparison with the Comparative Examples 1 to 3.
  • the resistance against the developer (DR) is much higher for the Invention Examples 1 and 2 in comparison with the Comparative Examples 2 and 3: due to the presence of low molecular weight development accelerators, the values for DR are increased to 8 % resp. 19 %.
  • the Comparative Example 1 shows no difference in optical density, and this high DR is substantially not affected by adding the PDA of the Invention Examples 1 and 2, showing a difference in optical density of only 2 %.
  • the Invention Example 3 demonstrates that a positive-working printing plate precursor which comprises a PDA exhibits a higher sensitivity, i.e. a lower value for REED and CP, in comparison with the Comparative Examples 4 and 5, which comprise an ortho-cresol novolac or a para-cresol novolac. Also, the UEL exhibits an increased value for the Invention Example 3 in comparison with the Comparative Examples 3 and 4. Invention Example 3 shows a difference in optical density of 1 %, and, due to the absence of a low molecular weight developer accelerator, this high DR is substantially the same than the DR of the Comparative Examples 4 and 5, showing a difference in optical density of 2 %.
  • This example is carried out in the same way as Invention Example 1, with the exception that the printing plate precursor is produced by coating the solution defined in Table 9 on the support. After coating and drying the printing plate precursor was stored for 3 days at 50°C.
  • the developing solution of Invention Example 1 is replaced by the developing solution TD6000, commercially available from AGFA.
  • Table 9 composition of the coating solution INGREDIENTS Parts (grams) Tetrahydrofuran 207.80 20 wt.% solution of POLYMER-01 (1) in Dowanol PM (2) 205.84 Dowanol PM (2) 286.00 Methyl ethyl ketone 263.80 S0094 (3) 1.302 1 wt.% solution of TegoGlide 410 (4) in Dowanol PM 21.55 PDA-09 (solid) 13.71 (1), (2), (3) and (4) as defined in Table 1.
  • Table 10 results of REED, CP, UEL and DR Invention Example 4 REED (mJ/m 2 ) 113 CP (mJ/m 2 ) 60 UEL (%) 47 DR (%) 7
  • Invention Example 4 demonstrates that, after aging for 3 days at 50°C, a positive-working printing plate precursor which comprises a PDA exhibits a high sensitivity, i.e. a low value for REED and CP, a high UEL-value and a low DR-value.
  • This example is carried out in the same way as Invention Example 1, with the exception that the printing plate precursor is produced by coating the solution defined in Table 11 on the support at a wet coating thickness of 20 ⁇ m and then dried for one minute at 130°C.
  • the developing solution of Invention Example 1 is replaced by the developing solution TD6000, commercially available from AGFA.
  • Table 11 composition of the coating solution INGREDIENTS Parts (grams) ALNOVOL SPN452 (1) 5.76 Dowanol PM (2) 14.36 Methyl ethyl ketone 23.38 S0094 (3) 0.137 1 wt.% solution of Basonyl Blue 640 (5) in Dowanol PM 3.45 1 wt.% solution of TegoGlide 410 (4) in Dowanol PM 1.37 1 wt.% solution of TegoWet 265 (6) in Dowanol PM 0.56 PDA-09 (solid) 0.73 (1) ALNOVOL SPN452 is a is a solution of a novolac resin, 40 % by weight in Dowanol PM (2), obtained from CLARIANT GmbH.
  • Basonyl Blue 640 is a quaternized triarylmethane dye, commercially available from BASF.
  • TEGOWET 265 is a polysiloxane copolymer, commercially available from Tego Chemie Service GmbH.
  • Table 12 results of the measurements Invention Example 5 Comparative Example 6 Comparative Example 7 REED (mJ/m 2 ) 124 122 113 CP (mJ/m 2 ) ⁇ 60 83 ⁇ 60 UEL (%) >64 39 >53 DR(%) 0 1 9
  • the Invention Example 5 demonstrates that a positive-working printing plate precursor which comprises a PDA, exhibits for about the same REED an improved CP and an improved UEL in comparison with the Comparative Example 6 which comprises a low molecular weight developer accelerator instead of a PDA. Due to an increased amount of the low molecular weight developer accelerator, the Comparative Example 7 exhibits, in comparison with the Invention Example 5, about the same REED and CP, but the high DR-value indicates a reduced resistance against the developer.

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Claims (16)

  1. Un précurseur de plaque d'impression lithographique thermosensible à effet positif, comprenant un support ayant une surface hydrophile ou un support revêtu d'une couche hydrophile et un revêtement oléophile appliqué sur ledit support, ledit revêtement contenant une substance transformant de la lumière infrarouge en chaleur et un liant soluble en milieu alcalin, caractérisé en ce que le revêtement contient en outre un accélérateur de développement polymère,
    ladite addition de l'accélérateur de développement polymère permettant d'améliorer la dissolution des zones exposées du revêtement dans la solution révélatrice pendant le développement et d'augmenter ainsi la sensibilité,
    ladite addition de l'accélérateur de développement polymère provoquant une modification de 7% au plus de la résistance au révélateur des zones non exposées du revêtement, la mesure de la résistance au révélateur étant effectuée selon la procédure décrite dans la description de la présente invention,
    le rapport pondéral dudit accélérateur de développement polymère dans le revêtement étant compris entre 0,01 et 1 par rapport à la quantité du liant soluble en milieu alcalin, et
    ledit accélérateur de développement polymère étant une résine à base de formaldéhyde phénolique, contenant au moins 70 moles % de méta-crésol comme unité monomère structurale.
  2. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 1, caractérisé en ce que l'accélérateur de développement polymère n'est pas un formaldéhyde phénolique contenant au moins 70 moles % de méta-crésol comme unité monomère structurale, mais une résine à base de formaldéhyde phénolique contenant au moins 40 moles % de monohydroxybenzène comme unité monomère structurale.
  3. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 1, caractérisé en ce que l'accélérateur de développement polymère n'est pas un formaldéhyde phénolique contenant au moins 70 moles % de méta-crésol comme unité monomère structurale, mais une résine phénolique contenant au moins 5 moles % d'une unité monomère structurale contenant au moins un groupe hydroxyle phénolique et au moins un groupe solubilisant en milieu alcalin.
  4. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 3, caractérisé en ce que le groupe solubilisant en milieu alcalin est un groupe hydroxyle, un groupe acide carboxylique, un groupe acide sulfonique, un groupe acide sulfurique, un groupe acide phosphorique, un groupe acide phosphonique ou un groupe thiol.
  5. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 4, caractérisé en ce que l'unité monomère structurale contient au moins 2 groupes hydroxyle phénolique.
  6. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 4, caractérisé en ce que l'unité monomère structurale est de la résorcine, de la pyrocatéchine, de l'hydroquinone, de l'hydroxyhydroquinone, du pyrogallol, de la phloroglucine ou de l'acide dihydroxybenzoïque.
  7. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon l'une quelconque des revendications précédentes, caractérisé en ce que le liant soluble en milieu alcalin est une résine phénolique.
  8. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 7, caractérisé en ce que la résine phénolique est une résine novolaque, une résine résol ou un polymère de polyvinylphénol.
  9. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 7 ou 8, caractérisé en ce que le groupe phényle ou le groupe hydroxyle de l'unité monomère phénolique de la résine phénolique est chimiquement modifié par un substituant organique.
  10. Précurseur de plaque d'impression lithographique thermosensible à effet positif selon la revendication 9, caractérisé en ce que le groupe phényle de l'unité monomère phénolique de la résine phénolique est substitué par un groupe répondant à la structure -N=N-Q dans laquelle le groupe -N=N- est lié à un atome de carbone du groupe phényle par une liaison covalente et Q est un groupe aromatique, ledit groupe de la structure -N=N-Q ayant la structure chimique répondant à la formule I :
    Figure imgb0006
     où :
    n représente 0, 1, 2 ou 3,
    R1 représente un atome d'hydrogène, un groupe alkyle éventuellement substitué, un groupe alkényle éventuellement substitué, un groupe alkynyle éventuellement substitué, un groupe cycloalkyle éventuellement substitué, un groupe hétérocyclique éventuellement substitué, un groupe aryle éventuellement substitué, un groupe hétéroaryle éventuellement substitué, un groupe aralkyle éventuellement substitué ou un groupe hétéroaralkyle éventuellement substitué, -SO2-NH-R2, -NH-SO2-R4, -CO-NR2-R3, -NR2-CO-R4, -O-CO-R4, -CO-O-R2, -CO-R2, -SO3-R2, -SO2-R2, -SO-R4, -P(=O)(-O-R2)(-O-R3), -NR2-R3, -O-R2, -S-R2, -CN, -NO2, un atome d'halogène, un groupe -N-phtalimidyle, un groupe -M-N-phtalimidyle ou un groupe -M-R2, où M représente un groupe de liaison divalent contenant 1 à 8 atomes de carbone,
    R2, R3, R5 et R6 représentent, indépendamment l'un de l'autre, un atome d'hydrogène, un groupe alkyle éventuellement substitué, un groupe alkényle éventuellement substitué, un groupe alkynyle éventuellement substitué, un groupe cycloalkyle éventuellement substitué, un groupe hétérocyclique éventuellement substitué, un groupe aryle éventuellement substitué, un groupe hétéroaryle éventuellement substitué, un groupe aralkyle éventuellement substitué ou un groupe hétéroaralkyle éventuellement substitué, R4 représente un groupe alkyle éventuellement substitué, un groupe alkényle éventuellement substitué, un groupe alkynyle éventuellement substitué, un groupe cycloalkyle éventuellement substitué, un groupe hétérocyclique éventuellement substitué, un groupe aryle éventuellement substitué, un groupe hétéroaryle éventuellement substitué, un groupe aralkyle éventuellement substitué ou un groupe hétéroaralkyle éventuellement substitué,
    ou dans laquelle au moins deux desdits groupes R1 à R4 représentent conjointement les atomes nécessaires pour former une structure cyclique,
    ou dans laquelle R5 et R6 représentent conjointement les atomes nécessaires pour former une structure cyclique.
  11. Précurseur de plaque d'impression lithographique selon l'une quelconque des revendications précédentes, caractérisé en ce que le revêtement contient en outre un inhibiteur de dissolution.
  12. Précurseur de plaque d'impression lithographique selon la revendication 11, caractérisé en ce que l'inhibiteur de dissolution est un polymère hydrophobe.
  13. Précurseur de plaque d'impression lithographique selon la revendication 11, caractérisé en ce que l'inhibiteur de dissolution est
    - un polymère comprenant des unités de siloxane et/ou des unités de perfluoroalkyle ou
    - un copolymère séquencé ou greffé composé d'un bloc d'oxyde de polyalkylène et d'un bloc comprenant des unités de siloxane et/ou des unités de perfluoroalkyle.
  14. Précurseur de plaque d'impression lithographique selon la revendication 11, caractérisé en ce que l'inhibiteur de dissolution est un composé organique contenant un groupe aromatique et au moins un site de liaison hydrogène.
  15. Un procédé pour la confection d'un précurseur de plaque d'impression lithographique thermosensible, comprenant les étapes ci-après :
    - la mise à disposition d'un support ayant une surface hydrophile ou d'un support revêtu d'une couche hydrophile et
    - l'application d'un revêtement oléophile selon l'une quelconque des revendications 1 à 10 sur la surface hydrophile du support.
  16. Un procédé pour la confection d'une plaque d'impression lithographique à effet positif, comprenant les étapes ci-après :
    - la mise à disposition d'un précurseur de plaque d'impression lithographique thermosensible selon l'une quelconque des revendications 1 à 14,
    - l'exposition sous forme d'image du revêtement à de la lumière infrarouge ou à de chaleur et
    - le développement du revêtement exposé ou chauffé sous forme d'image dans un révélateur alcalin aqueux afin de dissoudre les zones exposées ou chauffées du revêtement dans le révélateur alcalin aqueux.
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EP1543959A2 (fr) 2005-06-22

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