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
  • 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
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/36—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties
  • B41M5/368—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used using a polymeric layer, which may be particulate and which is deformed or structurally changed with modification of its' properties, e.g. of its' optical hydrophobic-hydrophilic, solubility or permeability properties involving the creation of a soluble/insoluble or hydrophilic/hydrophobic permeability pattern; Peel development
• • 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
  • B41C2210/14—Multiple imaging layers
• • 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 invention relates to lithographic printing.
• this invention relates to multilayer imageable elements useful as lithographic printing plate precursors that have good solvent resistance, and to methods of providing lithographic printing plates therefrom.
• ink receptive regions are generated on a hydrophilic surface.
• the hydrophilic regions retain the water and repel the ink, and the ink receptive regions accept the ink and repel the water.
• the ink is transferred to the surface of a material upon which the image is to be reproduced.
• the ink is first transferred to an intermediate blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
• Imageable elements useful as lithographic printing plate precursors typically comprise an imageable layer applied over the hydrophilic surface of a substrate.
• the imageable layer includes one or more radiation-sensitive components, which may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material.
• the exposed regions or the non- exposed regions of the imageable layer are removed by a suitable developer, revealing the underlying hydrophilic surface of the substrate. If the exposed regions are removed, the precursor is positive working. Conversely, if the non-exposed regions are removed, the precursor is negative working.
• the regions of the imageable layer i.e., the image areas
• the regions of the hydrophilic surface revealed by the developing process accept water and aqueous solutions, typically a fountain solution, and repel ink.
• a lithographic printing plate comes in contact with fountain solution
• the printing plate is often subjected to aggressive blanket washes, such as a "UV wash" to remove ultraviolet curable inks.
• aggressive blanket washes such as a "UV wash” to remove ultraviolet curable inks.
• many of these systems have limited resistance to either fountain solution and/or aggressive blanket washes.
• imaged positive-working imageable elements are developed to remove exposed regions of all layers to reveal the hydrophilic substrate.
• considerable residue can build up in the developer due to insufficient solubility of removed polymeric binders, particularly polymeric binders from the top layer.
• Build up of sludge or residue causes a number of maintenance problems besides lowering the useful life of the developer.
• imageable elements that can be developed to provide lithographic printing plates without a significant buildup of significant residue or sludge in the developer from insolubility of the polymeric binders used in the various element layers, and particularly in the top layer.
• the present invention provides a positive- working imageable element comprising a photothermal conversion material, a substrate, and an underlayer over the substrate that is removable by an alkaline developer, and an ink receptive top layer over the underlayer, in which: before thermal imaging, the top layer is dissolvable in an alkaline developer much more slowly than the underlayer, after thermal imaging to form exposed and non-exposed regions in the element, the exposed regions are more removable by the alkaline developer than the non-exposed regions, and the top layer comprises a polymeric material comprising recurring units comprising an anhydride, the polymeric material being present in an amount of at least 60 weight % based on topcoat layer dry weight.
• This invention also provides a method for forming a lithographic printing plate comprising:
• the invention also provides a lithographic printing plate obtained by the noted method.
• the imageable elements and the imaged elements prepared therefrom exhibit excellent resistance to the chemicals and solvents used in the preparation and use of lithographic printing plates.
• the imageable elements of this invention contain polymeric binders in the outer layer that are very soluble in the developers used for processing. Thus, minimal residue or sludge builds up in the developers.
• polymeric material co-polymer, added polymer, substituted styrene, substituted maleic anhydride, carboxylic acid containing monomer, maleic anhydride polymer, photothermal conversion material, surfactant, and similar terms also include mixtures of such materials.
• the modifiers "a”, “an”, and “the” are not intended to be limited to the. singular tense. Unless otherwise specified, all percentages are percentages by weight and all temperatures are in degrees Centigrade (degrees Celsius).
• Thermal imaging refers to imaging with a hot body, such as a thermal head, or with infrared radiation.
• the invention is an imageable element comprising a substrate (defined below), an underlayer, and a top layer.
• the element also comprises a photothermal conversion material in various locations as described in more detail below.
• the top layer dissolves in an alkaline developer much more slowly than the underlayer.
• the time it takes to dissolve the top layer in the alkaline developer is at least 5 times (preferably at least 10 times) the time required for the underlayer to dissolve in the alkaline developer.
• the exposed regions in the element are more removable by the alkaline developer than the non-exposed regions.
• the underlayer is also removable by the alkaline developer.
• the top layer comprises a polymeric material in an amount of at least 60 weight %, based on the total top layer dry weight.
• the polymeric material is present in an amount of at least 75 weight %, more preferable in an amount of at least 90 weight %, and most preferably in an amount of at least 95 weight %, based on the total top coat dry layer.
• This polymeric material comprises recurring units comprising an anhydride, as described in more detail below.
• this polymeric binder containing anhydride groups is the only type of polymeric material used as a binder in the top layer but mixtures of this type of polymeric material can be used in this manner.
• the top layer may also comprise other ingredients, such as, photothermal conversion materials, dyes or colorants, and surfactants that are conventional ingredients of imageable elements.
• a surfactant such as a fluorinated surfactant or a polyethoxylated dimethylpolysiloxane co-polymer, or a mixture of surfactants may be present to help disperse the other ingredients in a coating solvent and/or to act as a coating aid.
• a dye or colorant may be present to aid in the visual inspection of the imaged or developed element.
• Printout dyes distinguish the exposed regions from the non-exposed regions during processing. Contrast dyes distinguish the non-exposed regions from the exposed regions in the developed imageable element for example, the resulting lithographic printing plate.
• the top layer typically consists essentially of the polymeric material and, optionally, one or more photothermal conversion materials, one or more dyes or colorants, and one or more surfactants.
• the top layer typically consists essentially of the polymeric material and, optionally, one or more dyes or colorants or one or more surfactants, or one or more colorants and one or more surfactants.
• the top layer comprises a polymeric material that is a polymer having recurring groups that include an anhydride group.
• anhydride we mean both substituted and unsubstituted anhydride groups.
• the anhydride group is part of the hydrophobic b ackbone of the polymer.
• the polymeric material can be a homopolymer, it is generally a copolymer that is derived from one or more anhydride-containing monomers and one or more of styrene or styrene derivatives. Thus, mixtures of both types of monomers can be used to prepare the polymeric material.
• the polymer having anhydride groups generally has a weight average molecular weight of at least 1,000 and generally from about 1,500 to about 8,000.
• the recurring units comprising an anhydride group generally comprise at least 15 mol % and preferably from about 40 to about 60 mol % of the total recurring units in the polymer chain.
• recurring units from styrene or a styrene derivative generally comprise at least 15 mol % and up to 85 mol % of the total recurring units in the polymer chain.
• Recurring units of additional monomers such as acrylate and methacrylate monomers, such as methyl acrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, and butyl methacrylate; acrylonitrile; methacrylonitrile; methacrylamides, such as methacrylamide and N, N-dimethyl methacrylamide; and acrylamides, such as acrylamide and N,N-dimethyl acrylamide, may also be present to provide less than 20 mol % of the recurring units.
• such additional recurring units are not present and the co-polymer consists essentially of recurring units having an anhydride group and recurring units derived from styrene or substituted styrene.
• R 2 can be hydrogen, halogen, hydroxyl, cyano, sulfonamide, substituted or unsubstituted alkyl groups having 1 to 6 carbon atoms, substituted or unsubstituted alkoxyl groups having 1 to 6 carbon atoms, substituted or unsubstituted acyl groups having 1 to 7 carbon atoms, substituted or unsubstituted acyloxy groups having 1 to 7 carbon atoms, or substituted or unsubstituted carboalkoxy groups having 1 to 7 carbon atoms.
• Halogen includes fluoro (F), chloro (Cl), and bromo (Br).
• An example of a sulfonamide group is -SO 2 NH 2 .
• Alkyl groups of one to six carbon atoms include but are not limited to, methyl, chloromethyl, methoxymethyl, ethyl, n-propyl, is ⁇ -propyl, n- butyl, sec-butyl, is ⁇ -butyl, *-butyl, n-pentyl, ⁇ -pentyl, weo-pentyl, n-hexyl, iso-hexyl, 1,1 -dimethyl -butyl, 2,2-dimethyl-butyl, cyclopropyl, cyclobutyl, cyclopentyl, methylcyclopentyl, and cyclohexyl.
• Alkoxy groups of 1 to 6 carbon atoms are -OR 3 groups in which R 3 is a substituted or unsubstituted alkyl group of 1 to 6 carbon atoms, such as are listed above. Examples include but are not limited to methoxy, ethoxy, n- propoxy, /so-propoxy, n-butoxy, and f-butoxy.
• Acyl groups of 1 to 7 carbon atoms are -C(O)R 3 groups in which R 3 is a substituted or unsubstituted alkyl group of 1 to 6 carbon atoms, such as are listed above. Examples include but are not limited to CH 3 CO- (acetyl), CH 3 CH 2 CO-, CH 3 (CH 2 ) 2 CO-, CH 3 (CHa) 3 CO-, (CH 3 ) 3 CCO-, and
• (CHa) 3 CCH 2 CO- Acyloxy groups of 1 to 7 carbon atoms are -OC(O)R 3 groups in which R 3 is a substituted or unsubstituted alkyl group of 1 to 6 carbon atoms, such as are listed above. Examples include but are not limited to H 3 CC(O)O- (acetyloxy), CH 3 CH 2 C(O)O-, CH 3 (CHz) 2 C(O)O-, CH 3 (CHa) 3 C(O)O-, (CH 3 ) 3 CC(O)O-, and (CHs) 3 CCHaC(O)O-.
• Carboalkoxy groups of 1 to 7 carbon atoms are -CO 2 R 3 groups in which R 3 is an alkyl group of 1 to 6 carbon atoms, such as are listed above. Examples include but are not limited to -COaCH 3 , (carbomethoxy), -CO 2 CH 2 CH 3 (carboethoxy), -CO 2 (CHa) 2 CH 3 , -CO 2 (CH 2 ) 3 CH 3 , -CO 2 C(CHs) 3 (carbo-f-butoxy), -CO 2 CH 2 C(CH 3 ) 3 , -CO 2 (CH 2 ⁇ CH 3 , and -CO 2 (CH 2 ) 5 CH 3 .
• R 2 is hydrogen or a substituted or unsubstituted methyl.
• a most preferred monomer represented by the noted formula is styrene but other useful styrene derivatives such as 4-methylstyrene, ⁇ -methylstyrene, and ⁇ - methylstyrene are demonstrated in the Examples below.
• R 2 is shown in the noted formula as a single substituent on the phenyl group, it is contemplated that up to 4 of the same or different R 2 groups can be attached to the phenyl group in the monomers. Thus, a mixture of the same or different R 2 groups can be present.
• the polymers containing anhydride groups may be prepared by free radical polymerization. In a typical preparation, one or more monomers are polymerized to produce the polymer. Free radical polymerization is well known to those skilled in the art and is described, for example, in Chapters 20 and 21, of Macromolecules. Vol. 2, 2nd Ed., H.G. Elias, Plenum, New York, 1984.
• Useful free radical initiators are peroxides such as benzoyl peroxide, hydroperoxides such as cumyl hydroperoxide and azo compounds such as 2,2'-azobis(isobutyronitrile) (AIBN). Chain transfer agents, such as dodecyl mercaptan, may be used to control the molecular weight of the compound.
• Suitable solvents for free radical polymerization include liquids that are inert to the reactants and which will not otherwise adversely affect the reaction, for example, water; esters such as ethyl acetate and butyl acetate; ketones such as methyl ethyl ketone, methyl isobutyl ketone, methyl propyl ketone, and acetone; alcohols such as methanol, ethanol, ⁇ -propyl alcohol, n-propanol, 1-methoxyethanol (Methyl CELLOSOLVE ® ), n- butanol; ethers such as dioxane and tetrahydrofuran; amides, such as, N 5 N- dimethylformamide and N,N-dimethylacetamide, and mixtures thereof.
• Added Polymer such as, N 5 N- dimethylformamide and N,N-dimethylacetamide, and mixtures thereof.
• the added polymer comprises about 0.1 wt% to about 20 wt%, preferably about 1 wt% to about 20 wt% of the top layer, based on total top layer dry weight.
• the added polymer is typically a phenolic resin, such as a novolac resin, a resole resin, or a polyvinyl phenol.
• the preferred added polymers are novolac resins.
• Novolac resins are commercially available and are well known to those skilled in the art. They are typically prepared by the condensation reaction of a phenol, such as phenol, m-cresol, ⁇ -cresol,p-cresol, etc, with an aldehyde, such as formaldehyde, paraformaldehyde, acetaldehyde, etc. or ketone, such as acetone, in the presence of an acid catalyst.
• the weight average molecular weight is typically about 1,000 to 15,000.
• Typical novolac resins include, for example, phenol-formaldehyde resins, cresol- fbrmaldehyde resins, phenol-cresol-formaldehyde resins, /?- ⁇ -butylphenol-formaldehyde resins, and pyrogallol-acetone resins.
• Solvent soluble novolac resins having a weight average molecular weight of at least 10,000; solvent soluble r ⁇ -cresol/p-cresol novolac resins that. comprises at least 10 mol% p-cresol and have a weight average molecular weight of at least 8,000; and mixtures thereof may be particularly useful.
• the underlayer is between the top layer and the substrate. It is over the substrate and, typically, directly on the substrate.
• the underlayer comprises a polymeric material that is removable by the developer, and preferably soluble in the developer.
• the polymeric material is preferably insoluble in the solvent used to coat the top layer so that the top layer can be coated over the underlayer without dissolving the underlayer.
• Other ingredients, additional polymers, photothermal conversion materials, and surfactants, may also be present in the underlayer.
• Useful polymeric materials include carboxy functional acrylics, vinyl acetate/crotonate/vinyl neodecanoate copolymers phenolic resins, maleated wood rosin, and combinations thereof.
• Particularly useful polymeric materials are polyvinylacetals and copolymers that comprise N-substituted maleimides, especially N-phenylmaleimide; methacrylamides, especially methacrylamide; and acrylic and/or methacrylic acid, especially methacrylic acid.
• the preferred polymeric materials of this type are copolymers of N-phenylmaleimide, methacrylamide, and methacrylic acid, more preferably those that contain about 25 to about 75 mol%, preferably about 35 to about 60 mol% of N-phenylmaleimide; about 10 to about 50 mol%, preferably about 15 to about 40 mol% of methacrylamide; and about 5 to about 30 mol%, preferably about 10 to about 30 mol%, of methacrylic acid.
• Other hydrophilic monomers, such as hydroxyethyl methacrylate may be used in place of some or all of the methacrylamide.
• Other alkaline soluble monomers, such as acrylic acid may be used in place of some or all of the methacrylic acid.
• the underlayer may also comprise one or more other polymeric materials, provided addition of these polymeric materials does not adversely affect the chemical resistance and solubility properties of the underlayer.
• Preferred other polymeric materials, when present, are novolac resins, which may be added to improve the run length of the printing member by a post-development bake process.
• Imageable elements that are to be imaged with infrared radiation typically comprise an infrared absorber, known as a photothermal conversion material.
• Photothermal conversion materials absorb radiation and convert it to heat.
• the photothermal conversion material may be present in the underlayer and/or a separate absorber layer between the top layer and the underlayer.
• a photothermal conversion material is not necessary for imaging with a hot body, imageable elements that contain a photothermal conversion material may also be imaged with a hot body, such as a thermal head or an array of thermal heads.
• the photothermal conversion material is in the underlayer and more preferably, it is only in the underlayer.
• the photothermal conversion material may be any material that can absorb radiation and convert it to heat. Suitable materials include dyes and pigments. Typical pigments include, for example, carbon black, Heliogen Green, Nigrosine Base, iron (III) oxide, manganese oxide, Prussian Blue, and Paris Blue.
• the size of the pigment particles should not be more than the thickness of the layer that contains the pigment. Preferably, the size of the particles will be half the thickness of the layer or less.
• the photothermal conversion material may be a dye with the appropriate absorption spectrum and solubility.
• Dyes especially dyes with a high extinction coefficient in the range of 700 nm to 1200 nm, are preferred.
• suitable dyes include dyes of the following classes: methine, polymethine, aryhnethine, cyanine, hemicyanine, streptocyanine, squarylium, pyrylium, oxonol, naphthoquinone, anthraquinone, porphyrin, azo, croconium, triarylamine, thiazolium, indolium, oxazolium, indocyanine, indotricarbocyanine, oxatricarbocyanine, phthalocyanine, thiocyanine, thiatricarbocyanine, merocyanine, cryptocyanine, naphthalocyanine, polyaniline, polypyrrole, polythiophene, chalc
• Absorbing dyes are disclosed in numerous publications, for example, Nagasaka, EP 0,823,327; DeBoer, U.S. Patent 4,973,572; Jandrue, U.S. Patent 5,244,771; Patel, U.S. Patent 5,208,135; and Chapman, U.S. Patent 5,401,618.
• useful absorbing dyes include: ADS-830A and ADS-1064 (American Dye Source, Montreal, Canada), EC2117 (FEW, Wolfen, Germany), Cyasorb ER.99 and Cyasorb IR 165 (Glendale Protective Technology), Epolite IV-62B and Epolite III-178 (Epoline), SpectraIR 830A and SpectraIR 840A (Spectra Colors), as well as IR Dyes A, B, and C, whose structures are shown as follows.
• Water-soluble photothermal conversion materials include, for example, cyanine dyes that have one or more sulfate and/or sulfonate groups.
• Other infrared absorbing cyanine anions that contain two to four sulfonate groups are disclosed, for example, in West, U.S. Patent 5,107,063; Pearce, U.S. Patent 5,972,838; Chapman, U.S. Patent 6,187,502; Fabricius, U.S. Patent 5,330,884; and Japanese Kokai 63-033477.
• the preparation of cyanine dyes with polysulfonate anions is disclosed, for example, in U.S.
• Patent Application Publication 2005/0113546 (Tao et al.), the disclosure of which is incorporated herein by reference.
• the preparation of N-alkyl sulfate cyanine compounds is disclosed, for example, in U.S. Patent 7,018,775 (Tao), the disclosure of which is incorporated herein by reference.
• the amount of photothermal conversion present in the element is generally sufficient to provide an optical density of at least 0.05, and preferably, an optical density of from about 0.5 to at least about 2 to 3 at the imaging wavelength.
• the amount of compound required to produce a particular optical density at a particular wavelength can be determined using Beer's law. Although the amount present will depend on the compound or compounds chosen, when the photothermal conversion material is only present in the underlayer, it typically comprises about 0.2 wt% to about 8 wt%, more typically about 0.5 wt% to about 4 wt% of the underlayer.
• the photothermal conversion material may be present in a separate absorber layer. When an absorber layer is present, it is between the top layer and the underlayer.
• the absorber layer preferably consists essentially of the photothermal conversion material and, optionally, a surfactant. It may be possible to use less of the photothermal conversion material if it is present in a separate absorber layer.
• the absorber layer preferably has a thickness sufficient to absorb at least 90%, preferably at least 99%, of the imaging radiation. Typically, the absorber layer has a coating weight of about 0.02 g/m 2 to about 2 g/m 2 , preferably about 0.05 g/m 2 to about 1.5 g/m 2 . Elements that comprise an absorber layer are disclosed in Shimazu, U.S. Patent 6,593,055, the disclosure of which is incorporated herein by reference.
• the element may comprise a barrier layer between the underlayer and the top layer.
• the barrier layer comprises a polymeric material that is soluble in the developer. If this polymeric material is different from the polymeric material in the underlayer, it is preferably soluble in at least one organic solvent in which the polymeric material in the underlayer is insoluble.
• a preferred polymeric material for the barrier layer is polyvinyl alcohol.
• the substrate comprises a support, which may be any material conventionally used to prepare imageable elements useful as lithographic printing plates.
• the support is preferably strong, stable, and flexible. It should resist dimensional change under conditions of use so that color records will register in a full-color image.
• it can be any self-supporting material, including, for example, polymeric films such as polyethylene terephthalate film, ceramics, metals, or stiff papers, or a lamination of any of these materials.
• Metal supports include aluminum, zinc, titanium, and alloys thereof. *"
• polymeric films contain a sub-coating on one or both surfaces improve adhesion to subsequent layers. The nature of this layer or layers depends upon the substrate and the composition of subsequent layer or layers.
• subbing layer materials are adhesion-promoting materials, such as alkoxysilanes, aminopropyltriethoxysilane, glycidoxypropyltriethoxysilane and epoxy functional polymers, as well as conventional subbing materials used on polyester bases in photographic films.
• the substrate comprises a sheet of aluminum or an aluminum alloy
• it should be of sufficient thickness to sustain the wear from printing and thin enough to wrap around a cylinder in a printing press, typically about 100 ⁇ m to about 600 ⁇ m. It is typically cleaned, roughened, and anodized by various methods known in the art. Initially, a degreasing treatment with a surfactant, an organic solvent, or an alkaline water solution is typically administered to the remove oil and grease from the surface of the sheet.
• the surface may be roughened by well known techniques, such as mechanical roughening, for example ball polishing, brush polishing, blast polishing and buff polishing, chemical roughening in which the surface is roughened by selectively dissolving the surface, or electrochemical roughening, or a combination of such chemical, mechanical, and/or electrochemical treatments (multi-graining).
• Etching of the substrate is performed using hot acidic (such as sulfuric or phosphoric) solutions or alkaline solutions (such as sodium hydroxide or trisodium phosphate mixed with sodium hydroxide).
• Anodic oxidation may be carried out to form a hydrophilic layer of aluminum oxide of the surface, typically a layer of aluminum oxide of at least 0.3 g/m 2 in weight.
• Anodic oxidation is performed by passing a current using the support as an anode in an electrolytic solution comprising an electrolyte, such as, for example, sulfuric acid, phosphoric acid, chromic acid, boric acid, citric acid, oxalic acid, or a mixture thereof.
• an electrolyte such as, for example, sulfuric acid, phosphoric acid, chromic acid, boric acid, citric acid, oxalic acid, or a mixture thereof.
• the cleaned, roughened, and anodized support may be hydrophilized with an alkali metal silicate, such as aqueous potassium silicate, lithium silicate, or, typically, sodium silicate. Hydrophilization is described, for example, in
• the support is either immersed in or electrolyzed in an aqueous solution of the alkali metal silicate.
• the substrate comprises an interlayer between the aluminum support and the overlying layer or layers.
• the interlayer may be formed by treatment of the aluminum support with, for example, silicate, dextrine, hexafluorosilicic acid, phosphate/fluoride, polyvinyl phosphonic acid (PVPA), vinyl phosphonic acid co- polymers, or a water-soluble diazo resin.
• Co-polymers that comprise (1) phosphonic acid groups and/or phosphate groups, and (2) acid groups and/or groups that comprise alkylene glycol or polyalkylene glycol side chains, which are useful as interlayer materials are also disclosed in U.S. Patent Application Publication 2006/000401 (Hayashi et al.), the disclosure of which is incorporated herein by reference.
• Co-polymers that comprise (1) acid groups and/or phosphonic acid groups, and (2) silyl groups substituted with three alkoxy and/or phenoxy groups, useful as interlayer material are disclosed in U.S. Patent 7,049,048 (Hunter et al.), the disclosure of which is incorporated herein by reference.
• the back side of the support i.e., the side opposite the top layer and the underlayer
• solvent and “coating solvent” include mixtures of solvents. These terms are used although some or all of the materials may be suspended or dispersed in the solvent rather than in solution. Selection of coating solvents depends on the nature of the components present in the various layers.
• the imageable element may be prepared by sequentially applying the underlayer over the hydrophilic surface of the substrate; applying the absorber layer or the barrier layer if present, over the underlayer; and then applying the top layer using conventional techniques.
• the underlayer may be applied by any conventional method, such as coating or lamination. Typically the ingredients are dispersed or dissolved in a suitable coating solvent, and the resulting mixture coated by conventional methods, such as spin coating, bar coating, gravure coating, die coating, or roller coating.
• the underlayer may be applied, for example, from mixtures of methyl ethyl ketone, l-methoxypropan-2-ol, ⁇ - butyrolactone, and water; from mixtures of diethyl ketone, water, methyl lactate, and ⁇ - butyrolactone; and from mixtures of diethyl ketone, water, and methyl lactate.
• Preparation of imageable elements that comprise a barrier layer is disclosed in Patel, U.S.
• Patent 6,723,490 the disclosure of which is incorporated herein by reference.
• Preparation of imageable elements that comprise an absorber layer is disclosed in Shimazu, U.S. Patent 6,593,055. the disclosure of which is incorporated herein by reference.
• the top layer is coated on the underlayer.
• the top layer should be coated from a solvent in which the underlayer layer is essentially insoluble.
• the coating solvent for the top layer should be a solvent in which the components of the top layer are sufficiently soluble that the top layer can be formed and in which any underlying layers are essentially insoluble.
• the solvents used to coat the underlying layers are more polar than the solvent used to coat the top layer.
• the top layer may be applied, for example, from diethyl ketone and/or methyl isobutyl ketone, or from mixtures of diethyl ketone and/or methyl isobutyl ketone with l-methoxy-2-propyl acetate.
• An intermediate drying step i.e., drying the underlayer to remove coating solvent before coating the top layer over it, may also be used to prevent mixing of the layers.
• the underlayer, the top layer, or both layers may be applied by conventional extrusion coating methods from a melt mixture of layer components.
• a melt mixture typically contains no volatile organic solvents.
• the imageable elements may be thermally imaged with a laser or an array of lasers emitting modulated near infrared or infrared radiation in a wavelength region that is absorbed by the imageable element.
• Infrared radiation especially infrared radiation in the range of about 700 nm to about 1200 nm, is typically used for imaging. Imaging is conveniently carried out with a laser emitting at about 830 nm, about 1056 ran, or about 1064 nm.
• Suitable commercially available imaging devices include image setters such as the CREO ® Trendsetter (Eastman Kodak Company, Burnaby, British Columbia, Canada), the Screen PlateRite model 4300, model 8600, and model 8800 (Screen, Rolling Meadows, Chicago, Illinois, USA), and the Gerber Crescent 42T (Gerber Systems, South Windsor, CT, USA).
• the imageable element may be thermally imaged using a hot body, such as a conventional apparatus containing a thermal printing head.
• a suitable apparatus includes at least one thermal head but would usually include a thermal head array, such as a TDK Model No.
• LV5416 used in thermal fax machines and sublimation printers, the GS618-400 thermal plotter (Oyo Instruments, Houston, TX, USA), or the Model VP-3500 thermal printer (Seikosha America, Mahwah, NJ, USA).
• Imaging produces an imaged element, which comprises a latent image of imaged (exposed) regions and complementary non-imaged (non-exposed) regions.
• Development of the imaged element to form a printing plate, or printing form converts the latent image to an image by removing the imaged regions, revealing the hydrophilic surface of the underlying substrate.
• the developer may be any liquid or solution that can penetrate and remove the exposed regions of the top layer, the underlying regions of, if present, the absorber layer or barrier layer, and the underlying regions of the underlayer without substantially affecting the complimentary non-exposed regions.
• Development is carried out for a long enough time to remove the exposed regions of the top layer, the underlying regions of, if present, the absorber layer or barrier layer, and the underlying regions of the underlayer in the developer, but not long enough to remove the non-exposed regions of the top layer.
• the exposed regions are described as being “soluble” or “removable” in the developer because they are removed, and dissolved and/or dispersed, more rapidly in the developer than the non-exposed regions.
• the underlayer is dissolved in the developer
• the absorber layer is either dissolved or dispersed in the developer
• the top layer is dispersed in the developer.
• Useful developers are aqueous solutions having a pH of about 7 or above.
• Common components of developers are surfactants; chelating agents, such as salts of ethylenediamine tetraacetic acid; organic solvents such as benzyl alcohol and phenoxyethanol; and alkaline components such as inorganic metasilicates, organic metasilicates, hydroxides or bicarbonates.
• Typical aqueous alkaline developers are those that have a pH between about 8 and about 13.5, typically at least about 11, preferably at least about 12.
• the developer may comprise a surfactant or a mixture of surfactants.
• Preferred surfactants include: alkali metal salts of alkyl naphthalene sulfonates; alkali metal salts of the sulfate monoesters of aliphatic alcohols, typically having six to nine carbon atoms; and alkali metal sulfonates, typically having six to nine carbon atoms.
• a preferred alkali metal is sodium.
• the surfactant or mixture of surfactants typically comprises about 0.5 wt % to about 15 wt % based on the weight of the developer, preferably about 3 wt % to about 8 wt %, based on the weight of the developer.
• a developer may comprise a buffer system to keep the pH relatively constant, typically between about 5.0 and about 12.0, preferably between about 6.0 and about 11.0, more preferably between about 8.0 and about 10.0. Numerous buffer systems are known to those skilled in the art.
• buffer systems include, for example: combinations of water-soluble amines, such as mono-ethanol amine, diethanol amine, tri-ethanol amine, or trw-propyl amine, with a sulfonic acid, such as benzene sulfonic acid or 4-toluene sulfonic acid; mixtures of the terra sodium salt of ethylene diamine tetracetic acid (EDTA) and EDTA; mixtures of phosphate salts, such as mixtures of mono-alkali phosphate salts with tri-alkali phosphate salts; and mixtures of alkali borates and boric acid.
• Water typically comprises the balance of the developer.
• Some developers contain one or more organic solvents.
• Such developers comprise an organic solvent or a mixture of organic solvents.
• the developer is a single phase. Consequently, the organic solvent must be miscible with water, or at least soluble in the developer to the extent it is added to the developer, so that phase separation does not occur.
• the following solvents and mixtures of these solvents are suitable for use in the developer: the reaction products of phenol with ethylene oxide and propylene oxide, such as ethylene glycol phenyl ether (phenoxyethanol); benzyl alcohol; esters of ethylene glycol and of propylene glycol with acids having six or fewer carbon atoms, and ethers of ethylene glycol, diethylene glycol, and of propylene glycol with alkyl groups having six or fewer carbon atoms, such as 2-ethylethanol and 2-butoxyethanol.
• a single organic solvent or a mixture of organic solvents can be used.
• the organic solvent is typically present in the developer at a concentration of between about 0.5 wt% to about 15 wt%, based on the weight of the developer, preferably between about 3 wt% and about 5 wt%, based on the weight of the developer.
• Such organic solvent-containing developers generally have a pH of from about 6.5 to about 11 and preferably from about 6.5 to about 8.5.
• solvent-based developers include ND-I Developer, 956 Developer and 955 Developer (Eastman Kodak Company). Developers consisting of 1 part ND-I Developer and 3 to 5 parts of water are also useful.
• Another useful solvent-based developer is identified below as Developer A and is a mixture of 726.39 parts water, 6.64 parts monoethanolamine, 34.44 parts diethanolamine, 177.17 parts PELEX ® NB-L (sodium alkyl naphthalene sulfonate anionic surfactant, Kao Corp., Chuo-ku, Tokyo, Japan), and 55.36 parts benzyl alcohol.
• Other useful developers are aqueous alkaline developers, such as 3000 Developer and 9000 Developer (Eastman Kodak Company).
• the developer is typically applied to the precursor by spraying the element with sufficient force to remove the exposed regions.
• development may be carried out in a processor equipped with an immersion-type developing bath, a section for rinsing with water, a gumming section, a drying section, and a conductivity- measuring unit, or the imaged precursor may be brushed with the developer. In each instance, a printing plate is produced.
• Development may conveniently be carried out in a commercially available spray-on processor, such as an 85 NS (Kodak Polychrome Graphics) or in a commercially available immersion-type processor such as the PK910 Mark II Processor (Kodak Polychrome Graphics).
• a gumming solution comprises one or more water-soluble polymers, for example cellulose, polyvinylalcohol, polymethacrylic acid, polymethacrylamide, polyvinylmethylether, polyhydroxyethylmethacrylate, gelatin, and polysaccharide such as dextran, pullulan, gum arabic, and algmic acid.
• a preferred material is gum arabic.
• a developed and gummed plate may also be baked to increase the run length of the plate. Baking can be carried out, for example at about 220 0 C to about 240 0 C for about 7 minutes to 10 minutes, or at a temperature of 120 0 C for 30 minutes.
• the imageable elements of the invention have excellent resistance to press room chemicals and solvents encountered in printing. They can be thermally imaged and developed to form lithographic printing plates. Once the imageable element has been imaged and developed to form a lithographic printing plate, printing can then be carried out by applying a fountain solution and lithographic ink to the image on its surface.
• the fountain solution is taken up by the surface of the hydrophilic substrate revealed by the imaging and development process, and the ink is taken up by the regions of the layers not removed by the development process.
• the ink is then transferred to a suitable receiving material (such as cloth, paper, metal, glass or plastic) either directly or indirectly using an offset printing blanket to provide a desired impression of the image thereon.
• IR Dye C Infrared absorbing dye (Honeywell, Morristown, NJ) (see structure above)
• Polymer B A copolymer of N-phenylmaleimide 40 mol%, methacrylamide 35 mol% and methacrylic acid 25 mol% (Clariant, Germany) Polymer 1 Poly(styrene-maleic anhydride), Mw 224,000 (Aldrich Chemical Co.)
• Polymer 2 Poly(styrene-maleic anhydride) cumene terminated, Mw 1,600 (Aldrich Chemical Co.) Polymer 3 Poly(styrene-maleic anhydride) cumene terminated, Mw 1,700 (Aldrich Chemical Co.) Polymer 4 Poly(styrene-maleic anhydride) cumene terminated, Mw 1,900 (Aldrich Chemical Co.) Polymer 5 Poly(4-acetoxystyrene-maleic anhydride) (synthesis below)
• RX-04 A styrene/maleic anhydride copolymer as supplied by Gifu Shellac (Japan).
• SWORD 1 * ExcelTM Thermally sensitive, positive working, multi-layer, printing plate precursor (Eastman Kodak Company)
• Developer A2 comprised water 6 parts, and 1 part of following components, by weight:
• Polymer H was an N-phenylmaleimide/ methacrylamide/ methacrylic acid copolymer that was prepared as follows:
• Synthesis of Polymer 5 A 500 ml reaction vessel was fitted with a heating mantle, stirrer, thermometer, condenser, and nitrogen atmosphere. A mixture of maleic anhydride (15.07 g), 4-acetoxystyrene (24.93 g), and 96 g of dry dioxolane was added to the vessel and heated to 6O 0 C under a nitrogen atmosphere. Nitrogen was bubbled through the mixture for 1 h. Then the nitrogen inlet was removed from the mixture, and 1.0Ig of AIBN were added. The reaction mixture was heated under nitrogen for 8 hours at 60 0 C.
• the reaction mixture was cooled to room temperature, and the resulting copolymer was isolated by pouring the reaction mixture into 2 liters of diethylether/hexane (50/50 by volume). The copolymer was filtered off, washed several times with diethylether/hexane and dried for 48 hours at 50 0 C. Yield: 37 g of Polymer 5.
• Polymer 6 (1.72 g, 4% yield) derived from 50 mol % styrene and 50 mol % 2,3-dimethylmaleic anhydride was synthesized as follows:
• Polymer 7 (7.97 g, 20% yield) derived from 50 mol % styrene and 50 mol % citraconic anhydride was synthesized as follows: 1. Equipped a four neck round bottom flask (1000 ml) with a condenser, a nitrogen supply, a thermometer, a stirrer, and a heating mantle.
• Polymer 8 (34.68 g, 87% yield) derived from 45 mol % Styrene, 5 mol % 4-methylstyrene, and 50 mol % maleic anhydride was synthesized as follows:
• Polymer 9 (38.47 g, 96% yield) derived from 45 mol % styrene, 5 mol % ⁇ -methylstyrene and 50 mol % maleic anhydride was synthesized as follows:
• Polymer 10 (31.43 g, 79% yield) derived from 45 mol% styrene, 5 mol% ⁇ -methylstyrene and 50 mol% maleic anhydride was synthesized as follows:
• Polymer 11 (38.47 g, 96% yield) derived from 40 mol% styrene, 10 mol% ⁇ -methylstyrene and 50 mol% maleic anhydride was synthesized as follows: 1. Equipped a four neck round bottom flask (1000 ml) with a condenser, a nitrogen supply, a thermometer, a stirrer, and a heating mantle.
• Polymer 12 (29.86 g, 75% yield) derived from 66.67 mol% styrene and
• Imageable elements were prepared by the following procedure.
• Underlaver A coating solution containing 6.5 wt% of a mixture of 84.5 wt% of Polymer A 9 15 wt% of IR Dye A, and 0.5 wt% of Byk ® 307 in a mixture of 2- butanone/l-methoxy-2-propanol/ ⁇ -butyrolactone/water (65:15:10:10 by weight) was coated onto Substrate A using a 0.03 in wire wound bar, and the resulting element dried at 135°C for 35 seconds.
• the coating weight of the underlayer was 1.5 g/m 2 .
• Top layer A coating solution containing 7.1 wt% of a mixture of 99.1 wt% of co-polymer, 0.4 wt% of ethyl violet, and 0.5 wt% of Byk ® 307 in diethylketone/1- methoxy-2-propanol acetate (92:8, v:v) was coated onto the underlayer using a 0.006 in wire wound bar, and the resulting imageable element dried at 135°C for 35 seconds.
• the coating weight of the top layer was 0.7 g/m 2 .
• Developer Drop Test A large drop of Developer Al was placed on the surface of the top layer at 30 second intervals at 22°C up to 5 minutes. The time of the first visible signs of developer attack and the time to completely remove the top layer were recorded.
• the imageable element was thermally imaged on a CREO ® Trendsetter 3244 at 8 watts using plot 0 and plot 12 internal test patterns.
• the imaging energies were 136, 115, 100, 88, and 19 mJ/cm 2 .
• the resulting imaged imageable element developed at 30 0 C in a PK91 OH processor (Eastman Kodak Company) using Developer A and an immersion time of 12 sec.
• the resulting lithographic printing plates were evaluated for cleanout (lowest imaging energy at which the imaged regions are completely removed by the developer), and best resolution (imaging energy at which printing plate performs best).
• Baking Test A 2x10 inch strip of the imageable element was placed in a Mathis
• Comparative Example 1 is a SWORD ® ExcelTM thermally sensitive, positive working, multi-layer, printing plate precursor. The results are shown in Tables 1 and 2.
• Example 5 Imageable elements from Example 2 were placed in a humidity chamber at 40 0 C and 80% relative humidity for 1, 3, 7 and 10 days. The aged imageable elements and an imageable element that had not been aged were evaluated as described above, except that imaging energies of 126, 119, 112, 105, 100, 95, 90, 86, 82 and 19 mJ/cm 2 were used in the imaging and processing tests. The results are given in Table 4. Table 4
• Imageable elements prepared using styrene/maleic anhydride Polymer 2 and Polymer 5 in the top layer were evaluated as described in the General Procedures, except that 956 Developer was used in the developer drop test. The results are given in Table 5.
• Example 7 required more mechanical agitation in order to completely process the imaged imageable element. This was achieved by increasing the pressure of the plush rollers in the processor.
• the top layer containing Polymer 5 was able to resist deletion up to 3 min. This indicated that some degree of cross-linking had occurred in the coating. Cross-linked coatings provide better run-length on press.
• An imageable element was prepared by coating two organic layers onto Substrate A.
• the first coating (basecoat) was applied to Substrate A with a 0.012 inch wire-wound bar.
• the coating was applied as a 7.0% solution from a mixture of methylethylketone/l-methoxy ⁇ -propanol/butyrolactone/water (50:30:10:10 by weight) to produce a dry coat weight of 1.5 g/m 2 . It was dried at a temperature of 125°C for 35 seconds.
• the first coating had the following formula:
• the second organic coating (top layer) was applied on top of the basecoat with a 0.006 inch wire-wound bar.
• the coating was applied as a 6.0% solution from a mixture of diethylketone/l-methoxy-2-propanol acetate (92:8 w/w) to produce a dry coat weight of 0.6 g/m 2 . It was dried at a temperature of 125 0 C for 35 seconds.
• the second coating contained 100 parts by weight of RX-04.
• the imageable element was subject to the following tests, i) Developer drop test, basecoat only sample: Drops of 'Developer A2' were placed onto a sample, onto which only basecoat had been coated. The drops were applied at 2-second intervals up to 20 seconds and then rinsed immediately with water. The time taken for the developer to completely remove the basecoat was recorded. ii) Developer drop test, topcoated sample: Drops of 'Developer A2' were placed onto a sample of the imageable element.
• Imaging and processing tests The imageable elements were imagewise exposed with 830 nm radiation on a Creo ® 3244 Trendsetter. The 'Plot 0' internal test pattern was applied at 8 watts with exposure energies of 162, 144, 129, 117, 108, 99, 92, 86, 81 and 78 mJ/cm 2 .
• the imaged elements were developed in a Kodak Polychrome Graphics PK910II processor using Developer A2 at 30 0 C with an immersion time of 12 seconds.
• the resulting printing plates were evaluated for cleanout (lowest energy where exposed areas are completely removed by developer), and best resolution (imaging energy at which plate performs best).
• a sample of the imaging element was imaged at 144 m J/cm with a file that contained suitable image for printing tests. The sample was processed as above and mounted on a Komori Sprint II 28 inch lithographic printing press. 1200 impressions were printed.
• an underlayer formulation was applied to Substrate A using a 0.012 inch wire- wound bar to produce a dry film weight of about 1.5 g/m 2 .
• the formulation was applied as a 7.0% solution from a mixture of methylethylketone/l-methoxy-2-propanol/butyrolactone/water (50:30:10:10 by weight) and dried at a temperature of about 135°C for 35 seconds.
• the formulation contained the following components:
• topcoat formulations were prepared and used at a concentration of 6.0% w/w by dissolving the components (parts by weight) in a mixture of diethylketone/lmethoxy-2-propanol acetate (92:8 w/w).
• topcoat formulations were applied to the dried underlayer using a 0.006 in wire wound bar and dried at about 135°C for 35 seconds.
• the dry coating weight was approximately 0.6 g/m 2 .
• the imageable elements were exposed with 808 nm radiation on a Screen PTR4300 platesetter.
• the Comparative Example 2 internal test pattern was used to plot a power series at a drum speed of 1000 rpm. A total of nine plot patterns were exposed at powers of 50% to 90% with increments of 5%.
• Exposed elements were then developed in a Kodak Polychrome Graphics PK910II processor using Developer A2 at 3O 0 C with an immersion time of 12 seconds.
• the resulting printing plates were evaluated for cleanout (lowest energy where exposed areas are completely removed by developer), and the best resolution (imaging energy at which plate performs best).

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