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
  • B41C1/1025—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 using materials comprising a polymeric matrix containing a polymeric particulate material, e.g. hydrophobic heat coalescing particles
• • 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
  • B41C2201/14—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
  • B41C2210/04—Negative working, i.e. the non-exposed (non-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 heat-sensitive, negative working 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 image-wise exposure and processing of an imaging material called plate precursor.
• plate precursor an imaging material
• heat-sensitive printing plate precursors have become very popular in the late 1990s.
• 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, insolubilization by crosslinking of a polymer, heat-induced solubilization, or by particle coagulation of a thermoplastic polymer latex.
• a (physico-)chemical process such as ablation, polymerization, insolubilization by crosslinking of a polymer, heat-induced solubilization, or by particle coagulation of a thermoplastic polymer latex.
• the most popular thermal plates form an image by a heat-induced solubility difference in an alkaline developer between exposed and non-exposed areas of the coating.
• the coating typically comprises an oleophilic binder, e.g. a phenolic resin, of which the rate of dissolution in the developer is either reduced (negative working) or increased (positive working) by the image-wise exposure.
• the solubility differential leads to the removal of the non-image (non-printing) areas of the coating, thereby revealing the hydrophilic support, while the image (printing) areas of the coating remain on the support.
• Typical examples of such plates are described in e.g.
• Negative working plate precursors which do not require a pre-heat step may contain an image-recording layer that works by heat-induced particle coalescence of a thermoplastic polymer latex, as described in e.g. EP-As 770 494, 770 495, 770 496 and 770 497.
• EP-As 770 494, 770 495, 770 496 and 770 497 disclose a method for making a lithographic printing plate comprising the steps of (1) image-wise exposing an imaging element comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder and a compound capable of converting light into heat, (2) and developing the image-wise exposed element by applying fountain and/or ink.
• EP-A 800928 discloses a heat-sensitive imaging element comprising on a hydrophilic support an image-forming layer comprising an infrared absorbing compound and hydrophobic thermoplastic particles dispersed in an alkali soluble or swellable resin which contains phenolic hydroxy groups.
• EP-A 1243413 discloses a method for making a negative-working heat-sensitive lithographic printing plate precursor comprising the steps of (i) applying on a lithographic base having a hydrophilic surface an aqueous dispersion comprising hydrophobic thermoplastic particles and particles of a polymer B which have a softening point lower than the glass transition temperature of said hydrophobic thermoplastic particles and (ii) heating the image-recording layer at a temperature which is higher than the softening point of polymer B and lower than the glass temperature of the hydrophobic thermoplastic particles.
• Such image recording layers have also been combined with additional layers as described in EP-A 881096 wherein a heat-sensitive imaging element for making a lithographic printing plate is disclosed which comprises on a lithographic base provided with a hydrophilic surface
• a negative-working lithographic printing plate precursor comprising on a support having a hydrophilic surface or which is provided with a hydrophilic layer, a coating comprising:
• a printing plate precursor comprising the specific combination of a phenolic resin (present in a first layer) and a polymer comprising at least one sulphonamide group (present in a layer below said first layer), provides a printing plate with a high run-length that gives prints with an excellent image quality and no toning.
• thermoplastic polymer particles present in the first layer of the lithographic printing plate precursor of the present invention are selected from polyethylene, poly(vinyl)chloride, polymethyl(meth)acrylate , polyethyl (meth)acrylate, poyvinylidene chloride, poly(meth)acrylonitrile, polyvinylcarbazole, polystyrene or copolymers thereof.
• the thermoplastic polymer particles are represented by poly(meth)acrylonitrile or derivatives thereof, or mixtures of polystyrene and poly(meth)acrylonitrile or derivatives thereof.
• the thermoplastic polymer particles represented by poly(meth)acrylonitrile or derivatives thereof, or mixtures of polystyrene and poly(meth)acrylonitrile or derivatives thereof comprise at least 5 wt% of nitrogen containing units, more preferably at least 30 wt% of nitrogen containing units.
• the latter mixture may comprise at least 50 wt% of polystyrene, and more preferably at least 65 wt% of polystyrene.
• the thermoplastic polymer particles comprise styrene and acrylonitrile units in a weight ratio between 1:1 and 5:1 (styrene:acrylonitrile), e.g. in a 2:1 ratio.
• the weight average molecular weight of the thermoplastic polymer particles may range from 5,000 to 1,000,000 g/mol.
• the hydrophobic particles preferably have a number average particle diameter below 200 nm, more preferably between 2 nm and 150 nm, most preferably between 10 and 100 nm.
• the amount of hydrophobic thermoplastic polymer particles contained in the first layer is preferably between 20% by weight of the total weight of the first layer and 95% by weight and more preferably between 25% by weight and 90% by weight and most preferably between 30% by weight and 88% by weight.
• thermoplastic polymer particles are present as a dispersion in an aqueous coating liquid of the top layer and may be prepared by the methods disclosed in US 3,476,937. Another method especially suitable for preparing an aqueous dispersion of the thermoplastic polymer particles comprises:
• the first layer further comprises a first hydrophobic binder which is preferably soluble or swellable in an aqueous alkaline solution but preferably not soluble or swellable in water (i.e. at about a neutral pH).
• the first hydrophobic binder is present as particles in the aqueous dispersion.
• a dispersion of the first hydrophobic binder may be obtained when the pH of the dispersion is not sufficiently high to cause dissolution of the binder.
• the weight ratio of the thermoplastic polymer particles and the first hydrophobic binder in the aqueous dispersion of the first layer is preferably larger than 0.8, more preferably larger than 1.0 and most preferably larger than 1.4.
• the thickness of the first layer is preferably at least 0.3 micron thick, more preferably at least 0.5 micron thick.
• the first hydrophobic binder is represented by a phenolic resin such as for example novolac, resoles and polyvinyl phenols. Typical examples of such polymers are described in DE 400 742 8, DE 402 730 1 and DE 444 582 0.
• the first hydrophobic binder is a phenolic resin which is chemically modified;
• the phenolic resin which is chemically modified is preferably a phenolic resin comprising a phenolic monomeric unit which comprises a phenyl-group and a hydroxy-group and 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.
• alkali-soluble phenolic resins which are chemically modified with an organic substituent, are described in EP 934 822, EP 1 072 432, US 5 641 608, EP 0 982 123, WO 99/01795, EP 02 102 446, filed on 15/10/2002, EP-A 02 102 444, filed on 15/10/2002, EP 02 102 445, filed on 15/10/2002, EP 02 102 443, filed on 15/10/2002, EP 03 102 522, filed on 13/08/2003.
• modified resins described in EP 02 102 446, filed on 15/10/2002 are preferred, specially those resins wherein the phenyl-group of the phenolic monomeric unit or the hydroxy-group of the phenolic monomeric unit is substituted with a group having the structure of formula (I) defined below.
• a substituted hydroxy-group is meant that the substituent is covalently bonded to the oxygen atom of the hydroxy-group replacing the hydrogen atom.
• Q has the structure of formula (I).
• the first hydrophobic binder preferably has a softening temperature below 100°C, more preferably below 75°C and most preferably below 50°C.
• the glass transition temperature of the hydrophobic thermoplastic particles is preferably higher than the softening temperature of the first hydrophobic binder which allows the heating of the composition up to a temperature above the softening temperature of the first hydrophobic binder without substantially triggering the image mechanism of heat-induced fusion or coalescence of the hydrophobic thermoplastic particles.
• the heating to a temperature above the softening temperature of the first hydrophobic binder and preferably below the glass transition temperature of the thermoplastic hydrophobic particles, may - depending on the time and temperature of the heating step - result in a slight, a partial or complete fusing of the particles of the first hydrophobic binder which may lead to the formation of a film matrix wherein the thermoplastic hydrophobic particles are dispersed.
• the heating may be performed during the drying of the coated layer, or otherwise the drying may be carried out at a lower temperature, e.g. room temperature, and then the heating may be performed as a separate step after the drying.
• a difference in the capacity of being penetrated and/or solubilised by the aqueous alkaline solution is generated upon image-wise exposure with heat and/or infrared light.
• This difference is obtained by a thermally induced coagulation of the hydrophobic polymer particles. Coagulation may result from heat-induced coalescence, softening or melting of the thermoplastic polymer particles.
• the decreased capacity of the first layer of being penetrated and/or solubilised by the aqueous alkaline solution created upon laser exposure results in a clean out of the non-imaged parts without solubilising and/or damaging the imaged parts. Furthermore, the imaged parts act as a shield for the alkali soluble layer underneath and prevents its solubilization at this areas.
• the development with the aqueous alkaline solution is preferably done within an interval of 5 to 120 seconds.
• the coagulation temperature of the hydrophobic thermoplastic particles should be sufficiently below the decomposition temperature of the polymer particles and is preferably higher than 50 °C, more preferably higher than 100°C.
• the second layer located between the first layer and the hydrophilic support of the printing plate precursor of the present invention comprises a polymer comprising at least one sulphonamide group.
• a polymer comprising at least one sulphonamide group' is also referred to as "a sulphonamide polymer”.
• the sulphonamide group is preferably represented by -NR-SO 2 -, -SO 2 -NR-, R-SO 2 -NR'- or RR'N-SO 2 - wherein R and R' each independently represent hydrogen or an organic substituent.
• the sulphonamide polymer is preferably alkali soluble.
• the second layer may further comprise additional hydrophobic binders such as a phenolic resin (e.g.
• novolac, resoles or polyvinyl phenols a chemically modified phenolic resin or a polymer containing a carboxy group, a nitrile group or a maleimide group.
• the thickness of the second layer is preferably at least 0.2 micrometer thick, more preferably at least 0.5 micrometer thick.
• suitable sulphonamide polymers are those described in EP-A 0 933 682, EP 0 894 622 (page 3 line 16 to page 6 line 30), EP-A 0 982 123 (page 3 line 56 to page 51 line 5), EP-A 1 072 432 (page 4 line 21 to page 10 line 29) and WO 99/63407 (page 4 line 13 to page 9 line 37).
• the isocyclic or heterocyclic radicals R 11 may contain a plurality (in general two to three) fused or unfused rings.
• R 11 represents a monocylic or bicyclic radical.
• the heteroatoms present in the heterocyclic radicals are preferably oxygen, sulfur and/or nitrogen atoms.
• Heterocyclic radicals containing one ring, such as a five-membered ring or a six-membered ring, are preferred examples. This ring may contain one or two nitrogen atoms and optionally also an oxygen atom; examples of such heterocyclic radicals are morpholin-2- and -3-yl, pyridin-2-, -3- and -4-yl and pyrimidin-2-and -4-yl.
• R 12 represents hydrogen or an optionally substituted alkyl or aryl group.
• the substituents optionally present in the alkyl and aryl groups of R 7 to R 10 and R 12 may be represented by a halogen such as a chlorine or bromine atom, or a hydroxyl group.
• the substituents optionally present in the iso-or heterocyclic radical R 11 may be represented by a halogen atom, a hydroxyl, amino, alkylamino, dialkylamino, alkoxy or alkyl group.
• a preferred example of a polymer comprising N-(4-sulfamoylphenyl)maleimide units according to formula IIa or formula IIb are homopolymers or copolymers wherein R 7 , R 8 , R 9 and R 10 each independently represent hydrogen or an optionally substituted alkyl group; the substituents optionally present in the alkyl groups of R 7 to R 10 may be represented by a halogen such as a chlorine or bromine atom or a hydroxyl group.
• R 11 represents hydrogen, an alkyl, alkanoyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group;
• a polymer which comprises at least one sulphonamide group and which is preferably alkali soluble is a homopolymer or copolymer comprising a structural unit represented by the following general formula (III): wherein Ar represents an optionally substituted aromatic hydrocarbon ring; preferred examples of an optionally substituted aromatic hydrocarbon ring are a benzene ring, a naphthalene ring or an anthracene ring.
• the divalent linking group may contain up to 20 carbon atoms and may contain at least one atom selected from C, H, N, O and S.
• Preferred divalent linking groups are a linear alkylene group having 1 to 18 carbon atoms, a linear, branched, or cyclic group having 3 to 18 carbon atoms, an alkynylene group having 2 to 18 carbon atoms and an arylene group having 6 to 20 atoms, -O-, -S-, -CO-, -CO-O-, -O-CO-, -CS-, -NR h R i -, -CO-NR h -, -NR h -CO-, -NR h -CO-O-, -O-CO-NR h -, -NR h -CO-NR i -, -NR h -CS-NR i -, a phenylene group, a naphtalene group, an anthracene group, a heterocyclic group, or combinations thereof, wherein R h and R i are each independently represented by hydrogen or an optionally substituted alkyl,
• Preferred substituents on the latter groups are an alkoxy group having up to 12 carbon atoms, a halogen or a hydroxyl group.
• X is a methylene group, an ethylene group, a propylene group, a butylene group, an isopropylene group, cyclohexylene group, a phenylene group, a tolylene group or a biphenylene group;
• Z is a bi-, tri- or quadrivalent linking group
• Z is a terminal group
• it is preferably hydrogen or an optionally substituted linear, branched, or cyclic alkylene or alkyl group having 1 to 18 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a s-butyl group, a pentyl group, a hexyl group, a cyclopentyl group, a cyclohexyl group, an octyl group, an arylene or aryl group having 6 to 20 carbon atoms; a linear, branched, or cyclic alkenylene or alkenyl group having 2 to 18 carbon atoms, a linear, branched, or cycl
• Examples of preferred substituent groups optionally present on Z are an alkoxy group having up to 12 carbon atoms, a halogen atom or a hydroxyl group.
• Z is a bi, tri- or quadrivalent linking group, it is preferably represented by an above mentioned terminal group of which hydrogen atoms in numbers corresponding to the valence are eliminated therefrom.
• the structural unit represented by the general formula (III) has preferably the following groups:
• a polymer which comprises at least one sulphonamide group and which is preferably alkali soluble is a homopolymer or copolymer comprising a structural unit represented by the following general formula (IV): wherein: R 16 represents hydrogen or a hydrocarbon group having up to 12 carbon atoms; preferably R 16 represents hydrogen or a methyl group; X 1 represents a single bond or a divalent linking group.
• the divalent linking group may have up to 20 carbon atoms and may contain at least one atom selected from C, H, N, O and S.
• Preferred divalent linking groups are a linear alkylene group having 1 to 18 carbon atoms, a linear, branched, or cyclic group having 3 to 18 carbon atoms, an alkynylene group having 2 to 18 carbon atoms and an arylene group having 6 to 20 atoms, -O-, -S-, -CO-, -CO-O-, -O-CO-, -CS-, -N h R i R -, -CO-NR h -, -NR h -CO-, -NR h -CO-O-, -O-CO-NR h -, -NR h -CO-NR i -, -NR h -CS-NR i -, a phenylene group, a naphtalene group, an anthracene group, a heterocyclic group, or combinations thereof, wherein R h and R i each independently represent hydrogen or an optionally substituted alkyl, al
• Preferred substituents on the latter groups are an alkoxy group having up to 12 carbon atoms, a halogen or a hydroxyl group.
• X 1 is a methylene group, an ethylene group, a propylene group, a butylene group, an isopropylene group, cyclohexylene group, a phenylene group, a tolylene group or a biphenylene group;
• Z 1 is a bi-, tri- or quadrivalent linking group
• Z 1 is a terminal group
• it is preferably represented by hydrogen or an optionally substituted linear, branched, or cyclic alkylene or alkyl group having 1 to 18 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a t-butyl group, a s-butyl group, a pentyl group, a hexyl group, a cyclopentyl group, a cyclohexyl group, an octyl group, an arylene or aryl group having 6 to 20 carbon atoms; a linear, branched, or cyclic alkenylene or alkenyl group having 2 to 18 carbon atoms, a linear,
• Z is a bi, tri- or quadrivalent linking group, it is preferably represented by an above mentioned terminal group of which hydrogen atoms in numbers corresponding to the valence are eliminated therefrom.
• Examples of preferred substituent groups optionally present on Z 1 are an alkoxy group having up to 12 carbon atoms, a halogen atom or a hydroxyl group.
• the structural unit represented by the general formula (IV) has preferably the following groups:
• 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.
• the support is a metal support such as aluminum or stainless steel.
• the support can also be a laminate comprising an aluminum foil and a plastic layer, e.g. polyester film.
• a particularly preferred lithographic support is an electrochemically grained and anodized aluminum support.
• the aluminium is preferably grained by electrochemical graining, and anodized by means of anodizing techniques employing phosphoric acid or a sulphuric acid/phosphoric acid mixture. Methods of both graining and anodization of aluminum are very well known in the art.
• both the adhesion of the printing image and the wetting characteristics of the non-image areas are improved.
• different type of grains can be obtained.
• the aluminium support By anodising the aluminium support, its abrasion resistance and hydrophilic nature are improved.
• the microstructure as well as the thickness of the Al 2 O 3 layer are determined by the anodising step, the anodic weight (g/m 2 Al 2 O 3 formed on the aluminium surface) varies between 1 and 8 g/m 2 .
• the grained and anodized aluminum support may be post-treated to improve the hydrophilic properties of its surface.
• the aluminum oxide surface 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 an organic acid and/or salt thereof, e.g. carboxylic acids, hydrocarboxylic acids, sulphonic acids or phosphonic acids, or their salts, e.g. succinates, phosphates, phosphonates, sulphates, and sulphonates.
• a citric acid or citrate solution is preferred. 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. Still further, 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. More detailed descriptions of these treatments are given in GB 1084070, DE 4423140, DE 4417907, EP 659909, EP 537633, DE 4001466, EP A 292801, EP A 291760 and US 4458005.
• the support can also be a flexible support, which is provided with a hydrophilic layer, hereinafter called 'base layer'.
• the flexible support is e.g. paper, plastic film, thin aluminum or a laminate thereof.
• Preferred examples of plastic film are polyethylene terephthalate film, polyethylene naphthalate film, cellulose acetate film, polystyrene film, polycarbonate film, etc.
• the plastic film support may be opaque or transparent.
• the base layer is preferably a cross-linked hydrophilic layer obtained from a hydrophilic binder cross-linked with a hardening agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolyzed tetra-alkylorthosilicate.
• a hardening agent such as formaldehyde, glyoxal, polyisocyanate or a hydrolyzed tetra-alkylorthosilicate.
• the thickness of the hydrophilic base layer may vary in the range of 0.2 to 25 ⁇ m and is preferably 1 to 10 ⁇ m.
• the hydrophilic binder for use in the base layer is e.g.
• hydrophilic (co)polymer such as homopolymers and copolymers of vinyl alcohol, acrylamide, methylol acrylamide, methylol methacrylamide, acrylate acid, methacrylate acid, hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride/vinylmethylether copolymers.
• the hydrophilicity of the (co)polymer or (co)polymer mixture used is preferably the same as or higher than the hydrophilicity of polyvinyl acetate hydrolyzed to at least an extent of 60% by weight, preferably 80% by weight.
• the amount of hardening agent, in particular tetraalkyl orthosilicate, is preferably at least 0.2 parts per part by weight of hydrophilic binder, more preferably between 0.5 and 5 parts by weight, most preferably between 1 parts and 3 parts by weight.
• the base layer may also comprise Al 2 O 3 and an optional binder.
• Deposition methods for the Al 2 O 3 onto the flexible support may be (i) physical vapor deposition including reactive sputtering, RF-sputtering, pulsed laser PVD and evaporation of aluminium, (ii) chemical vapor deposition under both vacuum and non-vacuum condition, (iii) chemical solution deposition including spray coating, dipcoating, spincoating, chemical bath deposition, selective ion layer adsorption and reaction, liquid phase deposition and electroless deposition.
• the Al 2 O 3 powder can be prepared using different techniques including flame pyrolisis, ball milling, precipitation, hydrothermal synthesis, aerosol synthesis, emulsion synthesis, sol-gel synthesis (solvent based), solution-gel synthesis (water based) and gasphase synthesis.
• the particle size of the Al 2 O 3 powders can vary between 2 nm and 30 ⁇ m; more preferably between 100 nm and 2 ⁇ m.
• the hydrophilic base layer may also contain substances that increase the mechanical strength and the porosity of the layer.
• colloidal silica may be used.
• the colloidal silica employed may be in the form of any commercially available water dispersion of colloidal silica for example having an average particle size up to 40 nm, e.g. 20 nm.
• inert particles of larger size than the colloidal silica may be added e.g. silica prepared according to Stöber as described in J. Colloid and Interface Sci., Vol. 26, 1968, pages 62 to 69 or alumina particles or particles having an average diameter of at least 100 nm which are particles of titanium dioxide or other heavy metal oxides.
• hydrophilic base layers for use in accordance with the present invention are disclosed in EP 601240, GB 1419512, FR 2300354, US 3971660, and US 4284705.
• the coating preferably also contains a compound which absorbs infrared light and converts the absorbed energy into heat.
• concentration of the IR absorbing compound in the coating is typically between 0.25 and 10.0 wt.%, more preferably between 0.5 and 7.5 wt.%.
• the infrared absorbing compound can be present in the first layer and/or the second layer and/or an optionally other layer.
• Preferred IR absorbing compounds are dyes such as cyanine and merocyanine dyes or pigments such as carbon black. Examples of suitable IR absorbers are described in e.g. EP 823327, 978376, 1029667, 1053868, 1093934; WO 97/39894 and 00/29214.
• a preferred compound is the following cyanine dye:
• the protective layer generally comprises at least one water-soluble polymeric 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 0.05 to 3.0 ⁇ m, particularly preferably from 0.10 to 1.0 ⁇ m.
• the coating may further contain additional ingredients.
• colorants can be added such as dyes or pigments which provide a visible colour 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.
• Polymers particles such as matting agents and spacers are also well known components of lithographic coatings which can be used in the plate precursor of the present invention.
• the printing plate precursor of the present invention 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 of the present invention is preferably not sensitive 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 material can be handled without the need for a safe light environment.
• the printing plate precursor of the present invention 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, such as a semiconductor laser diode, a Nd:YAG or a Nd:YLF laser.
• the required laser power depends on the sensitivity of the image-recording layer, 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: 10-25 ⁇ 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 1500 m/sec and may require a laser power of several Watts.
• the Agfa Galileo T (trademark of Agfa Gevaert N.V.) is a typical example of a plate-setter using the ITD-technology.
• XTD plate-setters for thermal plates having a typical laser power from about 20 mW to about 500 mW operate at a lower scan speed, e.g. from 0.1 to 20 m/sec.
• the Creo Trendsetter plate-setter family (trademark of Creo) and the Agfa Excalibur plate-setter family (trademark of Agfa Gevaert N.V.) both make use of the XTD-technology.
• the known plate-setters can be used as an off-press exposure apparatus, which offers the benefit of reduced press downtime.
• 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 non-exposed areas of the first layer and the corresponding parts of the underlying layer are removed by supplying an aqueous alkaline developer, which may be combined with mechanical rubbing, e.g. by a rotating brush.
• the development step may be followed by a drying step, a rinsing step and/or a gumming step.
• the plate precursor can, if required, then be post-treated with a suitable correcting agent or preservative as known in the art.
• the layer can be briefly heated at a temperature which is higher than the glass transition temperature of the thermoplastic particles, e.g. between 100°C and 230°C for a period of 40 minutes to 5 minutes ("baking").
• the exposed and developed plates can be baked at a temperature of 230°C for 5 minutes, at a temperature of 150°C for 10 minutes or at a temperature of 120°C for 30 minutes.
• this baking step the resistance of the printing plate to washout agents, correction agents and UV-curable printing inks increases.
• Such a thermal post-treatment is described, inter alia, in DE 14 47 963 and GB 1 154 749.
• the printing plate thus obtained can be used for conventional, so-called wet offset printing, in which ink and an aqueous dampening liquid are supplied to the plate.
• Another suitable printing method uses so-called single-fluid ink without a dampening liquid.
• Single-fluid inks which are suitable for use in the method of the present invention 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.
• the printing plate precursors are obtained by coating two layers on a substrate as follows: firstly, a coating solution is applied onto the lithographic base and dried, and subsequently, another coating solution is applied on top of this dried layer.
• the solvent used to apply the coatings is a mixture of 50% methylethyl ketone (MEK) / 50% Dowanol PM (1-methoxy-2-propanol from Dow Chemical Company).
• SP-01 was prepared using 3 monomers, i.e. 4-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl)-N-(4,6-dimethyl-2-pyrimidinyl)-benzenesulfonamide (monomer 1), benzyl maleimide (monomer 2) and (4-hydroxy-3,5-dimethylbenzyl)methacrylamide (monomer 3).
• a 50% solution of 2,2-di(tert.butylperoxy)butane in isododecane/methyl-ethyl ketone was used as initiator. This initiator was obtained under the trade name Trigonox D-C50 from Akzo Nobel, Amersfoort, The Netherlands.
• monomer 1 CASRN 233761-16-5
• a jacketed 10 liter reactor equipped with a condenser cooled with cold water and nitrogen inlet was filled with the 651,55 g of butyrolactone.
• the reactor was stirred at 100 rpm using a rotor blade stirrer.
• the monomers were added, i.e. 465,86 g of monomer 1, 224,07 g of monomer 2 and 294,07 g of monomer 3.
• the residual monomer still present in the bottles is disssolved/dispersed in 300 g butyrolactone and added to the reactor.
• the stirring speed is then raised to 130 rpm.
• the reactor was purged with nitrogen.
• the reactor was heated to 140 °C during 2,5 hours and stabilized at 140 °C during 30 minutes. Afterwards the monomers are dissolved and a dark brown solution is obtained. Subsequently 36,86 g of the 50 weight % initiator solution was added during 2 hours. Whereas the reaction is exothermic, the reactor is cooled in order to stay at 140 °C. After adding of the initiator the rotation speed is raised to 150 rpm. The reaction mixture is stirred for an additional 19 hours. Afterwards, the reactor content was cooled to 110 °C and the polymer solution was diluted using 2010 g of Dowanol PM (1-methoxy-2-propanol). The reaction mixture was allowed to cool further during the addition of the cold methoxypropanol in a period of 5 minutes. Subsequently the reactor was cooled further to room temperature and the resulting 25 weight % polymer solution was collected in a drum.
• a 0.20 mm thick aluminum foil was degreased by immersing the foil in an aqueous solution containing 5 g/l of sodium hydroxide at 50°C and rinsed with demineralized water.
• the foil was then electrochemically grained using an alternating current in an aqueous solution containing 4 g/l of hydrochloric acid, 4 g/l of hydroboric acid and 5 g/l of aluminum ions at a temperature of 35°C and a current density of 1200 A/m 2 to form a surface topography with an average center-line roughness Ra of 0.5 ⁇ m, measured with a TALYSURF 10 apparatus from TAYLOR HOBSON Ltd.
• the aluminum foil was then etched with an aqueous solution containing 300 g/l of sulfuric acid at 60°C for 180 seconds and rinsed with demineralized water at 25°C for 30 seconds.
• the foil was subsequently subjected to anodic oxidation in an aqueous solution containing 200 g/l of sulfuric acid at a temperature of 45°C, a voltage of about 10 V and a current density of 150 A/m 2 for about 300 seconds to form an anodic oxidation film of 3.00 g/m 2 of Al 2 O 3 , then washed with demineralized water, posttreated with a solution containing polyvinylphosphonic acid (2.2 g/m 2 ).
• the printing plate precursor was produced by first coating the coating defined in Table 1 onto the above-described lithographic base. The coating was applied at a wet coating thickness of 20 ⁇ m and then dried at 130°C for two minutes. The dry coating weight was 0.3 g/m 2 . Composition of the first coating (g/m 2 ). INGREDIENTS Parts g/m 2 Alnovol SP452 0.270 Tri- methoxybenzoic acid 0.030
• a second coating as defined in Table 2 was coated at a wet coating thickness of 30 ⁇ m and dried at 60°C for two minutes.
• the dry coating weight was 0.7 g/m 2 .
• Composition of the second coating INGREDIENTS Parts g/m 2 Polyacrylic acid 0.090 Polystyrene latex 0.0450 IR dye 0.060
• the printing plate precursor was then imaged on a CREO TRENDSETTER 3244 T, a plate-setter available from CREO, Burnaby, Canada, at 2450 dpi with a 200 lpi screen at an energy density of 220 mJ/m 2 .
• the plates were developed in an AUTOLITH T processor, available from AGFA-GEVAERT NV, operating at 25°C, in TD 5000 as developing solution (trademark form Agfa Gevaert N.V.).
• the plates obtained after processing were used as a printing master and mounted on a Heidelberg GTO46 printing press available from Heidelberger Druckmaschinen AG, Heidelberg, Germany.
• K + E Novavit 800 Skinnex was used as ink, and 4% of Combifix XL / 10% of isopropanol as fountain solution; both commercially available from BASF Drucksysteme GmbH.
• the image quality was determined by measuring the maximum highlight rendering (i.e. % dot area) of a 200 lpi screen on the print after 1000 prints. The maximum highlight rendering was 5% @200 lpi indicating a low image quality.
• a 0.30 mm thick aluminum foil AA1050 commercially available from ALCAN, was degreased by immersing the foil in an aqueous solution containing 34 g/l of sodium hydroxide at 70°C for 6 seconds and rinsed with demineralized water for 2 seconds.
• the foil was then electrochemically grained using an alternating electric current in an aqueous solution containing 12 g/l of hydrochloric acid and 9 g/l of aluminum sulphate at a temperature of 37°C and a current density of 105 A/dm 2 .
• the aluminum foil was then rinsed with demineralized water and desmutted in an aqueous solution containing 145 g/l of sulfuric acid at 80°C for 8 seconds.
• the grained aluminum foil was subsequently subjected to DC anodic oxidation in an aqueous solution containing 145 g/l of sulfuric acid at a temperature of 57°C, at a current density of 30 A/dm 2 to form an anodic oxidation film of 4.09 g/m 2 of Al 2 O 3 , measured by gravimetric experiments.
• the foil has a surface topography with an average center-line roughness Ra of 0.25 ⁇ m, measured with a TALYSURF 10 apparatus from TAYLOR HOBSON Ltd.
• the printing plate precursors were produced by first coating the coating defined in Table 3 onto the above-described lithographic base. The coating was applied at a wet coating thickness of 30 ⁇ m and then dried at 130°C for two minutes. The dry coating weight was 0.25 g/m 2 . Composition of the first coating (g/m 2 ). INGREDIENTS Parts (g) Alnovol SPN452 0.185 Trimethoxy benzoic acid 0.035 PVCB 0.030
• a second coating as defined in Table 4 was coated at a wet coating thickness of 30 ⁇ m and dried at 60°C for two minutes.
• the dry coating weight was 0.7 g/m 2 .
• Composition of the second coating (g/m 2 ) INGREDIENTS G Comparative Example 2
• Comparative Example 3 Comparative Example 4
• Polyacrylic acid / / 0.105 Polyacrylonitrile / polystyrene latex 0.381 0.634 0.490 Alnovol SPN452 0.253 / / 50094 IR-1 0.066 0.066 0.105
• the printing plate precursors were exposed with a CREO TRENDSETTER 3244 T (plate-setter trademark of CREO, Burnaby, Canada) operating at 2450 dpi at an energy density of 220 mJ/cm 2 using a 200 lpi screen.
• CREO TRENDSETTER 3244 T plate-setter trademark of CREO, Burnaby, Canada
• the plates were developed using an AUTOLITH T processor, available from AGFA-GEVAERT NV, operating at 25°C, in TD 5000 as developing solution (trademark form Agfa Gevaert N.V.).
• the printing plate precursors were produced by first coating the coating defined in Table 6 onto the above described lithographic base. The coating was applied at a wet coating thickness of 30 ⁇ m and then dried at 130°C for two minutes. The dry coating weight was 0.25 g/m 2 for Comparative Examples 5 and 6 and for Invention Example 8; the dry coating weight was 0.5 g/m 2 for Comparative Example 7 and for Invention Example 9. Composition of the first coating (g/m 2 ). INGREDIENTS G Comp. Example 5 Comp. Example 6 Comp. Example 7 Invention Example 8 Invention Example 9 Alnovol SPN452 0.220 0.250 0.44 / / Tri-methoxy benzoic acid 0.03 / 0.06 / / SP-01 / / / 0.25 0.50
• a second coating as defined in Table 7 was coated at a wet coating thickness of 30 ⁇ m and dried at 60°C for two minutes.
• the dry coating weight was 0.7 g/m 2 .
• Composition of the second coating (g/m 2 ) INGREDIENTS g Examples 5-9 Polyacrylonitrile /styrene latex 0.381 Alnovol SPN452 0.253 S0094 IR-1 0.066
• the printing plate precursors were exposed and developed as described in the Comparative Examples 2-4.
• the printing plate precursors were produced by first coating the coating defined in Table 9 onto the above described lithographic base.
• the coating solution (comprising a mixture of isopropanol/water for Invention Examples 11 and 13 and for Invention Examples 10 and 12 only water) was applied at a wet coating thickness of 30 ⁇ m and then dried at 130°C for two minutes.
• the dry coating weight was 0.5 g/m 2 for invention Examples 10 and 11 and 0.1 g/m 2 for invention Examples 12 and 13.
• Composition of the first coating (g/m 2 ).
• a second coating as defined in Table 10 was coated at a wet coating thickness of 30 ⁇ m and dried at 60°C for two minutes. The dry coating weight was 0.7 g/m 2 . Composition of second coating (g/m 2 ).
• INGREDIENTS g Invention Examples 10-11 Invention Example 12-13 Polyacrylonitrile styrene latex 0.420 0.525 Alnovol SPN452 0.210 0.070 S0094 IR-1 0.070 0.035
• the printing plate precursors were exposed and developed as described in the Comparative Examples 2-7 and Invention Examples 8 and 9.
• the printing plate precursor of Invention Example 13 was mounted on a Sakmai Oliver 52 press using K + E Novavit 800 Skinnex available from BASF Drucksysteme GmbH as ink and Emerald premium 4% as fountain. After 100,000 prints the 1% highlight of a 200 lpi screen was still rendered on the print indicating an excellent run lenght resistance.

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• 2004
  • 2004-06-11 EP EP04102654A patent/EP1604818B1/de not_active Expired - Lifetime
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