CN101652251A - Method for making a lithographic printing plate precursor - Google Patents

Abstract

A method for making a lithographic printing plate precursor is disclosed comprising the steps of : - providing a grained and anodized aluminum support; - treating the support with an aqueous solutioncomprising a compound containing a silicate anion and one or more cations; - treating the support with an aqueous solution comprising a compound containing an organic acid group and/or an ester or a salt thereof; applying a coating on to said treated support comprising an image-recording layer including hydrophobic thermoplastic polymer particles having a particle size ranging between 20 nm and 55nm.

Description

Method for making lithographic printing plate precursors

technical field

[0001] The present invention relates to methods of making thermal and/or photosensitive printing plate precursors.

Background technique

[0002] Lithographic printing presses use a so-called printing master, such as a printing plate mounted on a cylinder of the printing press. The master bears a lithographic image on its surface to which a print is made by applying ink to the image and subsequently transferring the ink from the master to a printing substrate, usually paper. In conventional so-called "wet" lithography, ink and an aqueous dampening solution (also called dampening liquid) are provided to a surface composed of oleophilic (or hydrophobic, ie accepts ink but repels water) areas and hydrophilic (or hydrophobic) areas. A lithographic image composed of areas that accept water but repel ink. In so-called driographic printing, the lithographic image consists of ink-receptive and ink-abhesive (ink-repelling) areas and during driographic printing only ink is supplied to the master.

[0003] Printing masters are generally obtained by image-wise exposure and processing of an imaged material called a plate precursor. In the late 1990s, besides the known photosensitive printing plates suitable for UV contact exposure through film masks (so-called pre-photographic printing plates), heat-sensitive printing plate precursors became very popular. Such thermal materials offer the advantage of sunlight stability and are particularly useful in so-called computer-to-plate processes, where the printing plate precursor is exposed directly, i.e. without the use of a film mask . Exposing a material to heat or exposure to infrared light and the resulting heat triggers (physico)chemical processes such as ablation, polymerization, insolubility through polymer crosslinking, heat-induced solubilization or coagulation of particles by thermoplastic polymer latex (coagulation).

[0004] The most common heat-sensitive printing plates form an image by a heat-induced solubility difference in an alkaline developer between exposed and unexposed areas of the coating. The coating typically comprises an oleophilic binder, such as a phenolic resin, whose dissolution rate in the developer is either reduced (negative working) or increased (positive working) by imagewise exposure. During processing, the solubility difference leads to the removal of the non-image (non-printed) areas of the coating, thereby exposing the hydrophilic support, while the image (printed) areas of the coating remain on the support. Typical examples of such printing plates are described, for example, in EP-A 625728, 823327, 825927, 864420, 894622 and 901902. Negative-working embodiments of such heat-sensitive materials often require a preheating step between exposure and development, as described in, for example, EP-A 625,728.

[0005] Negative-working printing plate precursors that do not require a preheating step may comprise thermally initiated thermal activation by thermoplastic polymer particles (latex) as described in e.g. The particle coalescence (coalescence) to plate (work) the image recording layer. These patents disclose a method of making a lithographic printing plate comprising the steps of: (1) imagewise exposing an imaged element comprising particles of a hydrophobic thermoplastic polymer dispersed in a hydrophilic base and a compound capable of converting light into heat, (2) and developing the imagewise exposed element by applying fountain solution and/or ink.

[0006] Some of these thermal methods enable platemaking without wet processing and are based, for example, on the ablation of one or more layers in the coating. In exposed areas, the underlying surface is exposed, which has a different affinity for ink or fountain solution than the unexposed coating surface.

[0007] Other thermal methods that enable printing platemaking without wet processing are for example methods based on thermally induced hydrophilic/lipophilic conversion of one or more layers in the coating to produce Different from the affinity for ink or fountain solution at the unexposed coating surface.

EP-A 1 614 538 describes negative-working lithographic printing plate precursors comprising a support having a hydrophilic surface or having a hydrophilic layer and a coating provided thereon, the coating comprising an image-recording layer , the image-recording layer comprises hydrophobic thermoplastic polymer particles and a hydrophilic base material, characterized in that the average particle size of the hydrophobic thermoplastic polymer particles is 45 nm to 63 nm, and the amount of the hydrophobic thermoplastic polymer particles in the image-recording layer is at least 70 wt %, relative to the image recording layer.

[0009] EP-A 1 614 539 and EP-A 1 614 540 describe a method of manufacturing a lithographic printing plate comprising the steps of: (1) imaging exposing the imaging element disclosed in EP-A 1 614 538 and (2 ) to develop the imagewise exposed element by application of an aqueous alkaline solution.

[0010] WO2006/037716 describes a method of preparing a negative-working lithographic printing plate comprising the steps of: (1) imagewise exposing comprising hydrophobic thermoplastic polymer particles dispersed in a hydrophilic binder and capable of converting light into heat and (2) developing the imagewise exposed element by applying a gum solution; characterized in that the average particle size of the thermoplastic polymer particles is from 40 nm to 63 nm and wherein the amount of hydrophobic thermoplastic polymer particles is greater than 70 wt % and less than 85 wt % %, relative to the image recording layer.

[0011] Unpublished European patent application EP-A 06 114 473 (filing date 24-05-2006) discloses a printing plate precursor comprising thermoplastic polymer particles having an average particle size of less than 40 nm and an infrared light absorbing dye, later or in an amount greater than 0.80 mg/m ² of the total surface of the hydrophobic particle without regard to optional counterions.

[0012] Unpublished EP-A 06 122 415 (filing date 17-10-2006) discloses a thermal negative-working lithographic printing plate precursor comprising an image-recording layer on a support, said image-recording layer comprising Hydrophobic thermoplastic polymer particles, infrared light-absorbing dyes and compounds including aromatic moieties and at least one acidic group or salts thereof, and have a maximum red-shifted light absorption peak at a wavelength of 300nm-450nm. Unpublished EP-A 06 122 423 (filing date 17-10-2006) discloses a thermal negative-working lithographic printing plate precursor comprising an image-recording layer on a support comprising a hydrophobic thermoplastic polymer Object particles, infrared light-absorbing dyes, and dyes with a specified structure and a maximum red-shifted light absorption peak at 451nm-750nm.

EP 1 247 644 discloses a lithographic printing plate comprising a support which has been subjected to a hydrophilic surface treatment by immersing it in an aqueous solution comprising one or more hydrophilic compounds which selected from compounds having sulfonic acid groups, polyvinylphosphonic acid, sugar compounds or silicate compounds. Alternatively, a solution comprising an alkali metal silicate, potassium zirconium fluoride or a mixture of phosphate and inorganic fluorine compound may be used.

[0014] EP 1 142 707 discloses a method by which the density of the micropores present at the anodized layer of a grained and anodized aluminum support is controlled by a special treatment, such as in an aqueous acid or alkaline solution Treatment of the support (pore widening treatment), which may be followed by treatment with hydrophilic compounds such as polyvinylphosphonic acid, compounds containing sulfonic acid groups and sugar compounds. After the pore widening process, a pore sealing process can be performed.

[0015] JP 2005/063518 discloses a method of manufacturing a photosensitive lithographic printing plate comprising the steps of treating a grained and anodized aluminum support with sodium silicate and polyvinylphosphonic acid, followed by Dry carrier.

[0016] A major problem associated with negative-working printing plates made according to the mechanism of thermally induced latex-coalescence is their low sensitivity. It has been disclosed in the prior art that the sensitivity of such printing plates can be improved by applying a coating comprising hydrophobic thermoplastic particles with a small particle size. However, the shelf life obtained with printing plate precursors comprising such small hydrophobic thermoplastic particles is greatly reduced.

Contents of the invention

[0017] It is an object of the present invention to provide a method for the manufacture of negative-working heat-sensitive lithographic printing plate precursors with improved shelf life.

[0018] This object is achieved by claim 1, namely, a method of manufacturing a lithographic printing plate precursor comprising the steps of:

- Provide grained and anodized aluminum carrier;

- treating the support with an aqueous solution comprising a compound comprising a silicate anion and one or more cations;

- treating the support with an aqueous solution comprising a compound containing organic acid groups and/or an ester or salt thereof;

- applying a coating to said treated support comprising an image-recording layer comprising hydrophobic thermoplastic polymer particles having a particle size of 20 nm to 55 nm.

[0019] According to the present invention, it was surprisingly found that the shelf-life of the printing plate is significantly improved compared to such a printing plate comprising a carrier after-treatment according to the prior art, which includes graining and anodizing An aluminum support which is first treated with an aqueous solution comprising a compound comprising a silicate anion and one or more cations, and subsequently treated with an aqueous solution comprising a compound comprising an organic acid group and/or an ester or salt thereof.

[0020] Other features, elements, steps, characteristics and advantages of the invention will become more apparent from the following detailed description of the preferred embodiments of the invention.

Detailed ways

[0021] The support of the lithographic printing plate precursor was a grained and anodized aluminum support. The support may be a sheet of material such as a printing plate or it may be a cylindrical element such as a sleeve which slides around a printing cylinder of a printing press. The aluminum support typically has a thickness of about 0.1-0.6 mm. However, this thickness may suitably vary depending on the size of the printing plate used and/or the size of the plate-setters to which the printing plate precursors are exposed.

[0022] The aluminum is preferably grained by electrochemical granulation, anodized by anodization techniques using sulfuric acid or sulfuric acid/phosphoric acid mixtures. Both graining and anodizing of aluminum are very well known in the art.

[0023] By graining (or roughening) the aluminum support, both the adhesion of the printed image and the wetting characteristics of the non-image areas are improved. By varying the type and/or concentration of electrolyte and the applied voltage during the granulation step, different types of granules can be obtained. Surface roughness is often expressed as the arithmetic mean mean line roughness Ra (ISO 4287/1 or DIN 4762) and can vary between 0.05 and 1.5 μm. The aluminum substrate of the invention preferably has a Ra value below 0.45 μm, more preferably below 0.40 μm, still more preferably below 0.30 μm and most preferably below 0.25 μm. The lower limit of the Ra value is preferably about 0.1 μm. Further details on preferred Ra values for the surface of grained and anodized aluminum supports are described in EP 1 356 926.

[0024] By anodizing the aluminum carrier, its wear resistance and hydrophilicity are improved. The microstructure and thickness of the Al ₂ O ₃ layer were determined by anodization steps, the anode weight (g/m ² , Al ₂ O ₃ formed on the aluminum surface) varied between 1 and 8 g/m ² . In the present invention, the anode weight is preferably > 3 g/m ² , more preferably > 3.2 g/m ² ; still more preferably > 3.5 g/m ² ; most preferably > 4.0 g/m ² .

[0025] An optimal ratio between the pore size of the surface of the aluminum support and the average particle size of the hydrophobic thermoplastic particles (provided thereon) can increase the printing life of the printing plate and can improve the toning properties of the print. This ratio of the average pore size of the surface of the aluminum support to the average particle size of the thermoplastic particles (present in the image-recording layer of the coating) is preferably from 0.05:1 to 1.0:1, more preferably from 0.10:1 to 0.80:1 , and most preferably 0.15:1 to 0.65:1.

[0026] According to the present invention, the support is first treated with an aqueous solution comprising a compound (Compound A) comprising a silicate anion and one or more cations. A silicate anion is preferably an anion in which one or more central silicon atoms are surrounded by electronegative ligands such as fluorine or oxygen atoms. The silicate anions are preferably selected from phosphosilicates, orthosilicates, metasilicates, hydrosilicates, polysilicates or pyrosilicates salts (pyrosilicates). The one or more cations render the compound electrically neutral and are preferably selected from alkali metals, Mg, Be, Zn, Fe, Ca, Al, Mn or Zr, and/or mixtures thereof. In particular, alkali metals such as sodium, potassium and lithium are preferred. In particular, preferred compounds herein are alkali metal orthosilicates, such as sodium or potassium orthosilicate, and alkali metal metasilicates, such as sodium or potassium metasilicate.

[0027] The aqueous solution containing Compound A may contain a suitable amount of a hydroxide such as sodium hydroxide, potassium and/or lithium to increase the pH. The solution may further comprise an alkaline earth metal salt or a Group IV (IVB) metal salt. Alkaline earth metal salts are, for example, water-soluble salts such as nitrates (strontium nitrate, magnesium and barium), sulfates, hydrochlorides, phosphates, acetates, oxalates and borates. Group IV (IVB) metal salts are, for example, titanium tetrachloride, titanium trichloride, titanium potassium fluoride, titanium potassium oxalate, titanium sulfate, titanium tetrachloride, chlorine Zirconia (zirconium chloride), zirconium dioxide, zirconium oxychloride (zirconium oxychloride) and zirconium tetrachloride and so on. These alkaline earth metal salts and Group IV (IVB) metal salts may be used alone or in combination of two or more thereof.

[0028] The aqueous solution comprising compound A preferably has a concentration of 5-100 g/l, more preferably a concentration of 10-50 g/l and has a pH value of preferably 10-13 at 25°C. The treatment is preferably carried out, for example, by immersing the support in said aqueous solution for preferably 0.5-40 seconds, and more preferably 1-20 seconds, at a preferred temperature of 20-100° C. and more preferably 25-50° C. Second.

[0029] After treating the support with an aqueous solution comprising Compound A, the support is further treated with an aqueous solution comprising a compound containing an organic acid group and/or an ester or salt thereof (Compound B). Suitable examples thereof include compounds comprising carboxylic acid groups and/or phosphonic acid groups, or salts thereof. Suitable examples of compounds comprising carboxylic acid groups such as hydroxycarboxylic acid groups are gluconic acid, citric acid or tartaric acid. A suitable example of a compound having a phosphonic acid group is represented by the following formula I or a salt thereof:

and where:

R ^and R are ^{independently} hydrogen, optionally substituted linear, branched, cyclic or heterocycloalkyl having up to 8 carbon atoms, halogen, hydroxyl, optionally substituted aryl or heteroaryl base;

^R is optionally substituted linear, branched, cyclic or heterocycloalkyl, halogen, hydroxy, optionally substituted aryl or heteroaryl, carboxyl, phosphonic acid having up to 8 carbon atoms group, phosphoric acid group, sulfuric acid group or sulfonic acid group.

Optional substituents present on straight chain, branched chain, ring or heterocycloalkyl or on aryl or heteroaryl are halogen such as chlorine or bromine atom, hydroxyl, amino, (two) alkane Amino groups, alkoxy groups, carboxyl groups, sulfonic acid groups, sulfuric acid groups, phosphoric acid groups and phosphonic acid groups. An aryl or heteroaryl group may further include an alkyl group as an optional substituent.

In a more preferred embodiment, the compound with phosphonic acid group is represented by formula II or its salt:

and where:

R and R are ^{independently} hydrogen, optionally substituted linear, branched, cyclic or heterocycloalkyl having up to 8 carbon atoms, halogen, hydroxyl, optionally substituted aryl ^or heteroaryl base.

On linear, branched or cyclic or heterocycloalkyl or on aryl or heteroaryl, the optional substituents present are halogen such as chlorine or bromine atom, hydroxyl, amino, (two) alkane Amino groups, alkoxy groups, carboxyl groups, sulfonic acid groups, sulfuric acid groups, phosphoric acid groups and phosphonic acid groups. An aryl or heteroaryl group may further include an alkyl group as an optional substituent.

In the most preferred embodiment, the compound with phosphonic acid group is represented by formula III or its salt:

and where:

^R6 is independently hydrogen, optionally substituted straight chain, branched chain, cyclic or heterocycloalkyl or optionally substituted aryl or heteroaryl.

On linear, branched or cyclic or heterocycloalkyl or on aryl or heteroaryl the optional substituents present are halogen such as chlorine or bromine atom, hydroxyl, amino, (two) alkane Amino groups, alkoxy groups, carboxyl groups, sulfonic acid groups, sulfuric acid groups, phosphoric acid groups and phosphonic acid groups. An aryl or heteroaryl group may further include an alkyl group as an optional substituent.

[0035] Specific compounds particularly suitable for use in the present invention are the following compounds com-1 and com-2.

[0036] Preferably, compound B is a polymer comprising repeating structural units containing organic acid groups and/or an ester or salt thereof. Suitable examples thereof include polyvinylphosphonic acid, polyvinylmethylphosphonic acid, phosphonate esters of polyvinyl alcohol, polyacrylic acid, polymethacrylic acid and copolymers of acrylic acid and vinylphosphonic acid. Solutions containing polyvinylphosphonic acid or poly(meth)acrylic acid are highly preferred.

[0037] The treatment with an aqueous solution comprising compound B is preferably carried out by, for example, impregnating the support in said aqueous solution, preferably at a concentration of 0.5-100 g/l, more preferably at a concentration of 1-50 g /l; the immersion temperature is preferably 20-120°C, more preferably 50-100°C; the immersion time is preferably 1-120s, more preferably 2-60s.

In a highly preferred embodiment, the support is first treated with a solution comprising an alkali metal orthosilicate or an alkali metal metasilicate, followed by treatment with a solution comprising polyvinylphosphonic acid or poly(formic acid). base) solution processing of acrylic acid.

[0039] In particular, the solution used for anodic post-treatment may also contain materials such as chelating agents, tannins, sulfuric acid, fluorides and other additives, which are known to improve the lithographic properties of the substrate.

[0040] For the application of the post anodic solution, besides the highly preferred dip-coated support, various other coating techniques such as spray coating, slot coating, reverse roll coating or electrochemical coating. Among these coating techniques, spray coating is preferred. Single pass methods are also preferred as they help to avoid contamination which might otherwise occur due to recirculation of the solution.

[0041] The lithographic printing plate precursors of the present invention comprise a heat sensitive coating on a hydrophilic support. The heat-sensitive coating comprises particles of a hydrophobic thermoplastic polymer, preferably dispersed in a hydrophilic matrix. The coating may comprise one or more layers and the layer comprising the hydrophobic thermoplastic polymer particles is referred to herein as the image-recording layer.

[0042] Due to the heat developed during the exposing step, the thermoplastic polymer particles may fuse or coagulate in order to form a developer-resistant phase, which corresponds to the printed areas of the printing plate. Coagulation may result from heat-induced coalescence, softening or melting of thermoplastic polymer particles. The thermoplastic polymer particles preferably have an average particle size below 200nm, preferably 10nm to 75nm, more preferably 15nm to 65nm and most preferably 20nm to 55nm. The thermoplastic polymer particles preferably have an average particle size of less than 45 nm, more preferably less than 38 nm, and most preferably less than 36 nm. Particle size is defined as particle diameter, measured by photon correlation spectroscopy (also known as quasi-elastic or dynamic light scattering). The amount of hydrophobic thermoplastic polymer particles present in the image-recording layer of the coating is preferably at least 60 wt%, more preferably at least 70 wt%, and most preferably at least 80 wt%. Alternatively, the amount of hydrophobic thermoplastic polymer particles in the image-recording layer of the coating is 65 wt% to 85 wt%, more preferably, 75 wt% to 85 wt%. The weight percent of thermoplastic polymer particles is determined relative to the weight of all components in the image-recording layer.

The thermoplastic polymer particles are preferably hydrophobic polymers selected from the group consisting of polyethylene, polyvinyl chloride, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polyvinylidene chloride ), poly(meth)acrylonitrile, polyvinylcarbazole, polystyrene or copolymers thereof. According to a preferred embodiment, the thermoplastic polymer particles comprise polystyrene or derivatives thereof, mixtures of polystyrene and poly(meth)acrylonitrile or derivatives thereof, or polystyrene and poly(meth)acrylonitrile Copolymers of acrylonitrile or derivatives thereof. The latter copolymer may comprise at least 50 wt% polystyrene, more preferably at least 65 wt% polystyrene. In order to obtain sufficient resistance to organic chemicals such as hydrocarbons used in plate cleaning agents, the thermoplastic polymer particles preferably comprise at least 5% by weight of nitrogen-containing units, as described in EP 1 219 416, more preferably At least 30% by weight of nitrogen-containing units, such as (meth)acrylonitrile. According to a most preferred embodiment, the thermoplastic polymer particles consist essentially of styrene and acrylonitrile units in a weight ratio of 1:1 to 5:1 (styrene:acrylonitrile), for example in a ratio of 2:1.

[0044] The thermoplastic polymer particles may have a weight average molecular weight of 5,000 to 1,000,000 g/mol.

[0045] The thermoplastic polymer particles present in the coating can be applied to a lithographic base in the form of a dispersion in an aqueous coating liquid and can be obtained through the disclosure in US 3,476,937 or EP 1 217 010 method to prepare. Another method particularly suitable for preparing aqueous dispersions of thermoplastic polymer particles includes:

- dissolving thermoplastic polymers in organic water-insoluble solvents,

- dispersing the solution thus obtained in water or an aqueous medium, and

- The organic solvent is removed by evaporation.

[0046] The coating also preferably includes a hydrophilic binder, which is preferably soluble in the aqueous developer. Examples of suitable hydrophilic binders are homopolymers and copolymers of vinyl alcohol, acrylamide, methylolacrylamide, methylolmethacrylamide, acrylic acid, methacrylic acid, hydroxyethyl acrylate, methylol hydroxyethyl acrylate and maleic anhydride/vinyl methyl ether copolymer.

[0047] The coating preferably also includes one or more compounds that absorb infrared light and convert the absorbed energy into heat. The amount of infrared absorber in the coating is preferably 0.25-25.0 wt%, more preferably 0.5-20.0 wt%. Infrared absorbing compounds may be present in the image-recording layer and/or in the optional other layers. Preferred IR absorbing compounds are dyes such as cyanine, merocyanine, indoaniline, oxonol, pyrilium and squarilium dyes or pigments such as carbon black. Examples of suitable infrared absorbers are described, for example, in the following documents: EP 823 327, EP 978 376, EP 1029 667, EP 1 053 868, EP 1 093 934; WO 97/39894 and WO 00/29214. Infrared absorbing dyes, which become strongly colored upon exposure by infrared radiation or heating and thereby form visible images, are also of interest and are described extensively in EP 1 614541 and PCT2006/063327. Another preferred IR compound is the following cyanine dye IR-1:

[0048] In addition to the image-recording layer, the coating may comprise one or more additional layers. In addition to an optional light-absorbing layer comprising one or more compounds capable of converting infrared light into heat, the coating may also include protective layers, such as overcoats, which are removed during processing. This layer protects the coating surface, in particular from mechanical damage, and generally comprises at least one water-soluble binder, such as polyvinyl alcohol, polyvinylpyrrolidone, partially hydrolyzed polyvinyl acetate, gelatin, carbohydrates or hydroxyethyl base cellulose. The protective layer may be produced in any known manner, such as from an aqueous solution or dispersion, and may contain small amounts, ie less than 5 wt%, of organic solvents. The thickness of the protective layer is advantageously at most 5.0 μm, preferably 0.1-3.0 μm, particularly preferably 0.15-1.0 μm. The coating layer may further include, for example, an adhesion-improving layer between the image-recording layer and the support.

[0049] Optionally, the coating may further comprise additional ingredients such as surfactants, especially perfluorosurfactants, colorants, silica or titanium particles or polymer particles such as matting agents and spacers. In particular, it is beneficial to add colorants such as dyes or pigments, which provide visible color to the coating and remain in the exposed areas of the coating after processing steps. Thus, the image areas that were not removed during the processing step form a visible image on the printing plate and inspection of the printing plate that has been developed at this step becomes possible. Typical examples of such contrast dyes are amino-substituted tri- or diarylmethane dyes such as crystal violet, methyl violet, victoria pure blue, fiexoblau 630, basonylblau 640, gold Amine (auramine) and malachite green (malachitegreen). Furthermore, the dyes discussed in depth in the detailed description of EP 400 706 are suitable contrast dyes. Dyes in combination with specific additives, which only slightly color the coating but which become strongly colored after exposure, are also of interest.

[0050] Preferably, the image-recording layer comprises an organic compound, characterized in that said organic compound comprises at least one phosphonic acid group or at least one phosphoric acid group or a salt thereof, as in unpublished European patent application 05109781 (filing date 2005 -10-20). In a particularly preferred embodiment, the image-recording layer includes an organic compound as represented by Formula III above. These compounds may be present in the image-recording layer in an amount of: 0.05-15 wt%, preferably 0.5-10 wt%, more preferably 1-5 wt%, relative to the total weight of the ingredients of the image-recording layer.

[0051] The coating, more preferably the image-recording layer, may further comprise a light stabilizer or antioxidant. The light stabilizer or antioxidant is preferably selected from sterically hindered phenols, hindered amine light stabilizers (HALS) and their N-oxyl (oxyl) groups, tocopherol, hydroxylamine derivatives such as hydroxamic acid and Substituted hydroxylamines, hydrazides, thioethers, trivalent organophosphorous compounds such as phosphites and reductones. In a particularly preferred embodiment, the photostabilizer is a reductone. Most preferably, the photostabilizer is an ascorbic acid or isoascorbic acid derivative according to formula IV:

Formula IV

wherein R ^{and R} are independently a hydrogen atom, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aralkyl, optionally substituted Alkaryl, optionally substituted heterocyclyl or optionally substituted heteroaryl. ^R1 and ^R2 may be the necessary atoms to form a carbocyclic or heterocyclic ring.

[0052] In the most preferred embodiment, ^{both R1} and ^R2 are C-1 to C-5 alkyl. Alkyl refers to all possible variations for each number of carbon atoms in the alkyl group, i.e. for 3 carbon atoms: n-propyl and isopropyl; for 4 carbon atoms: n-pentyl , 1,1-dimethylpropyl, 2,2-dimethylpropyl and 2-methylbutyl; and so on.

[0053] The stabilizer according to formula IV is preferably added in the following amounts: 1-100 mg/m ² , more preferably 2-50 mg/m ² , most preferably 5-25 mg/m ² .

Typical examples of light stabilizers according to formula IV are as follows:

[0055] Any coating method may be used to apply two or more coating solutions to the hydrophilic surface of the support. Multi-layer coatings can be applied by coating/drying layers successively or by coating several coating solutions simultaneously at once. In the drying step, volatile solvents are removed from the coating until the coating is self-supporting and dry to the touch. However, it is not necessary (and not necessarily even possible) to remove all of the solvent in the drying step. In fact, the residual solvent content can be seen as an additional composition variable by which the composition can be optimized. Drying is generally carried out by blowing hot air onto the coating, generally at a temperature of at least 70°C, suitably 80-150°C and especially 90-140°C. In addition infrared lamps can be used. Drying times may generally range from 15-600 seconds.

[0056] Between coating and drying, or after the drying step, heat treatment and subsequent cooling can provide additional benefits, such as WO99/21715, EP-A 1074386, EP-A1074889, WO00/29214, and WO/04030923, Described in WO/04030924, WO/04030925.

[0057] The printing plate precursors of the invention may be image-wise exposed to heat directly, eg by means of a thermal head, or indirectly by means of infrared light, eg by means of LEDs or infrared lasers. The infrared light is preferably converted into heat by means of an IR light absorbing compound as described above. Preferably, a laser emitting near-infrared light with a wavelength of about 700 to about 1500 nm is used, for example, a semiconductor laser diode, Nd:YAG or Nd:YLF laser. Most preferably, lasers emitting between 780-830nm are used. The required laser power depends on the sensitivity of the image-recording layer, the pixel exposure time of the laser beam (this is typical for modern plate-setters at a maximum intensity of 1/e2 through the spot diameter: 10 -25μm), the scanning speed and the resolution of the exposure device (that is, the number of accessible pixels per unit linear distance, often expressed in dots per inch or dpi; typical value: 1000-4000dpi).

[0058] Two types of laser-exposure devices are commonly used: internal (ITD) and external drum (XTD) platesetters. ITD plate-setters for thermal printing plates are generally characterized by very high scanning speeds, up to 500 m/s, and can require several watts of laser power. XTD plate-setters for thermal printing plates with typical laser powers of about 200 mW to about 1 W operate at lower scan speeds, eg, 0.1-10 m/s. An XTD plate setter equipped with one or more laser diodes emitting in the wavelength range 750-850 nm is a particularly preferred embodiment of the method according to the invention.

[0059] Known plate setters can be used as off-press exposure devices, which offer the benefit of reduced press downtime. The XTD plate setter configuration can also be used for in-press exposure, which offers the benefit of immediate registration in multicolor presses. Further technical details of in-line-press exposure devices are described for example in US 5,174,205 and US 5,163,368.

[0060] After exposure, the precursor can be developed by means of a suitable processing liquid, such as an aqueous alkaline solution, thereby removing the non-image areas of the coating; the developing step can be combined with mechanical rubbing, for example by using a rotating brush. During development, any water-soluble protective layer present is also removed.

[0061] Preferred aqueous alkaline developers are silicate-type developers having a silica to alkali metal oxide ratio of at least 1 and a pH > 11. Preferred alkali metal oxides include _Na2O and _K2O , and mixtures thereof. A particularly preferred developer solution of the silicate type is a developer solution comprising sodium or potassium metasilicate, ie a silicate in which the ratio of silicon dioxide to alkali metal oxide is one. The developer may optionally contain other components such as buffer substances, complexing agents, defoamers, small amounts of organic solvents, preservatives, dyes, surfactants and/or hydrotropic agents, as known in the art known. Preferred surfactants include nonionic surfactants such as Genapol C 200 (trademark of Clariant GmbH) and amphoteric surfactants such as librateric AA30 (trademark of Libra Chemicals Limited).

[0062] Development is preferably performed at a temperature of 20-40°C in automated processing equipment as commonly used in the art. In an embodiment in which a silicate-type developer is used, for regeneration, an alkali metal silicate solution having an alkali metal content of 0.6 to 2.0 mol/L may be suitably used. These solutions may have the same silica/alkali metal oxide ratio as the developer (however, generally lower) and optionally contain other additives as well. The required amount of recycled material must be suitable for the developing device used, the daily processing capacity of the printing plate, the image area, etc., and is usually 1-50 mL/square meter of the printing plate precursor. For example, the addition of extenders can be adjusted by measuring the conductivity of the developer, as described in EP 0 556 690.

[0063] It is also possible to develop the printing plate using fresh water or an aqueous solution, for example, a gum solution. A gum solution is generally an aqueous liquid that includes one or more surface protective compounds capable of protecting the lithographic image of the printing plate from contamination or damage. Suitable examples of such compounds are film-forming hydrophilic polymers or surfactants. The gum solution preferably has a pH of 4-10, more preferably 5-8. Preferred gum solutions are described in EP 1342568.

[0064] Alternatively, the printing plate precursor may be placed directly on press after exposure and developed on-press by providing ink and/or fountain solution to the precursor.

[0065] More details on the development step can be found, for example, in EP 1614538, EP 1614539, EP 1614540 and WO/2004071767.

[0066] The development step may be followed by a washing step and/or a gumming step. The gumming step involves post-treatment of the lithographic printing plate using a gum solution as described above.

[0067] The printing plate precursors may be post-treated with suitable correctors or preservatives as known in the art. To increase the resistance of the finished printing plate and thus extend its run length, the layer can be heated to high temperatures (so called "baking"). During the baking step, the printing plate may be heated at a temperature above the glass transition temperature of the thermoplastic particles, for example at 100°C to 230°C for 40 minutes to 5 minutes. The preferred baking temperature is higher than 60°C. For example, an exposed and developed plate can be baked at 230°C for 5 minutes, at 150°C for 10 minutes or at 120°C for 30 minutes. Baking can be carried out in conventional hot-air ovens or by irradiation with lamps emitting in the infrared or ultraviolet spectrum. Due to this baking step, the resistance of the printing plate to plate cleaners, correctors and UV-curable printing inks increases. Such thermal aftertreatments are described, for example, in DE 1447963 and GB 1 154 749.

[0068] The printing plate thus obtained can be used in conventional so-called wet offset printing, in which ink and an aqueous dampening liquid are supplied to the printing plate. Another suitable printing method uses so-called single-fluid inks without dampening liquid. Suitable single fluid inks have been described in US 4,045,232; US 4,981,517 and US 6,140,392. In the most preferred embodiment, the single fluid ink comprises an ink phase, also known as a hydrophobic or lipophilic phase, and a polyol phase, as described in WO 00/32705.

Example

Example 1

1. Prepare the reference substrate AS-01.

A 0.3 mm thick aluminum foil was degreased by spraying with an aqueous solution containing 34 g/l NaOH at 70° C. for 6 seconds and rinsing with demineralized water for 3.6 seconds. The foil was then electrochemically grained within 8 seconds, using an alternating current, in an aqueous solution containing 15 g/l HCl, 15 g/l SO ₄ ^2- ions and 5 g/l Al ³⁺ ions at a temperature of 37 °C and about 100 A /dm ² (charge density of about 800C/dm ² ). The aluminum foil was then stripped of the black film by etching with an aqueous solution containing 145 g/l of sulfuric acid at 80° C. for 5 seconds and rinsing with demineralized water for 4 seconds. The foil was subsequently anodized in 10 seconds in an aqueous solution of sulfuric acid containing 145 g/l at a temperature of 57 °C and a current density of 33 A/dm ² (charge density of 330 C/dm ² ) and washed with demineralized water for 7 seconds and dried at 120°C for 7 seconds. A reference substrate AS-01 was obtained.

2. Prepare post-anodized (PAT) substrates AS-02 to AS-07.

Subsequently, the untreated substrate AS-01 was dipped in Na-silicate (silicate) solution (see below) at a temperature of 30 °C for a dipping time of 10 seconds, yielding substrates AS-02 to AS-04 ( Table 1). Substrates AS-05 to AS-07 were obtained by further treating the silicate-treated substrates with a PVPA solution (see below) with an immersion temperature of 70° C. and a immersion time of 5 seconds (Table 1 ).

After each immersion step, the post-anodized samples were rinsed with demineralized water for 5 seconds and dried according to the conditions described in Table 1.

The support thus obtained had a surface roughness Ra of 0.35-0.4 μm (measured using an interferometer NT1100) and an anode weight of 4.0 g/m ² .

Na-silicate solution:

A solution of sodium orthosilicate (Natriumsilikat 5/2, commercially available from Roland N.V) in demineralized water at a concentration of 25 g/l was used. This solution is referred to herein as "Na-silicate solution".

PVPA solution:

A solution of PVPS 100 (polyvinylphosphonic acid, trademark of Clariant GmbH) in demineralized water at a concentration of 20 g/l was used. This solution is referred to herein as "PVPA solution".

Table 1: Substrates AS-02 to AS-07

Al substrate PATSol.1 Drying temperature ℃ Drying time seconds PATSol.2 Drying temperature ℃ Drying time seconds AS-02 Na-silicate room temperature to dry - - - AS-03 Na-silicate 120 180 - - - AS-04 Na-silicate 160 180 - - - AS-05 Na-silicate not dry not dry PVPA room temperature to dry AS-06 Na-silicate not dry not dry PVPA 120 180 AS-07 Na-Silicic Acid not dry not dry PVPA 160 180

Al substrate PATSol.1 Drying temperature ℃ Drying time seconds PATSol.2 Drying temperature ℃ Drying time seconds Salt

3. Preparation of latex LX-01.

Polymer emulsions are prepared by semi-continuous emulsion polymerization, where all monomers (styrene and acrylonitrile) are added to the reactor. The total amount of surfactant (3%, relative to the amount of monomer) was present in the reactor before starting the monomer addition. In a 2-liter double-jacketed reactor, 10.8 grams of sodium lauryl sulfate (SDS Ultra Pure, by Alkemi BV, Lokeren, Belgium) and 1243.9 grams of demineralized water were added. The reactor was flushed with nitrogen and heated up to 80°C. When the reactor contents reached a temperature of 80°C, 12 grams of a 5% aqueous sodium persulfate solution were added. Subsequently, the reactor was heated at 80° C. for 15 minutes. Then, the monomer mixture (238.5 grams of styrene and 121.5 grams of acrylonitrile) was dosed over 180 minutes. Simultaneously, during the monomer addition, additional persulfate aqueous solution (24 g of 5% _{Na2S2O8 in} water) _was added. After the monomer addition was complete, the reactor was heated at 80°C for 30 minutes. To reduce the amount of residual monomer, a redox-initiating system (1.55 g of sodium formaldehyde sulfoxylate dihydrate (SFS) dissolved in 120 g of water and 2.57 g of 70 wt% t-butylhydrogen dihydrate diluted with 22.5 g of water) was added peroxide (TBHP)). Aqueous solutions of SFS and TBHP were added separately over 80 minutes. The reaction was then heated for another 10 minutes and then cooled to room temperature. 100 ppm of Proxyl ultra (5-bromo-5-nitro-1,3-dioaxane) was added as an antimicrobial agent and the latex was filtered using coarse filter paper.

This gave a latex dispersion with a solids content of 20.84% and a pH of 3.46. The average particle size was 36 nm (measured using a Brookhaven BI-90 analyzer, commercially available from Brookhaven Instrument Company, Holtsville, NY, USA.).

4. Preparation of printing plate precursors PPP-02 to PPP-07.

The coating solutions for the printing plate precursors PPP-02 to PPP-07 were prepared as follows: the latex dispersion LX-01 was added to demineralized water and the obtained dispersion was stirred for 10 minutes. Subsequently, the IR-dye is added and after stirring the solution for 60 minutes, the polyacrylic acid solution is added. After stirring for 10 minutes, the DEQUEST 2010 solution was added and then after stirring for a further 10 minutes, the surfactant solution was added. The coating dispersion was stirred for an additional 30 minutes and the pH was adjusted to 3.6. Table 2 lists the dry coating weights of the different components of the coatings.

The coating solution obtained was then coated on the Al-substrates AS-02 to AS-07 with a wet thickness of 30 μm using a coating knife. After drying at 60°C, this gave the printing plate precursors PPP-02 to PPP-07.

Table 2: Dry coating weights.

Element g/ ^m2 Latex LX-01(1) 0.540 IR-Dye IR-2(2) 0.108 Polyacrylic acid(3) 0.081 DEQUEST 2010(4) 0.025 Surfactants (5) 0.005 Total (g/m ² ) 0.759

(1) Latex LX-01, as synthesized in the above 3rd point;

(2) IR dye aqueous solution, which contains 1wt% of IR-2:

(3) An aqueous solution comprising 5 wt% polyacrylic acid (PAA) (Aquatreat AR7H, commercially available from National Starch & Chemical Company);

(4) An aqueous solution comprising 10 wt% of hydroxyethyl-diphosphonate (HEDP, commercially available from Monsanto Solutia Europe);

(5) An aqueous surfactant solution containing 5 wt% of a fluorosurfactant Zonyl FS0100 (trademark of Dupont).

5. Exposure and printing of printing plate precursors PPP-02 to PPP-07.

In each of the printing plate precursors PPP-02 to PPP-07, one printing plate was exposed immediately ("fresh" printing plate precursor), and the other printing plate was stored at 80% relative humidity and 35°C before exposure7 Days, these are "aged" printing plate precursors.

All "fresh" and "aged" printing plate precursors were exposed to a Creo TrendSetter 324440W fast head IR-laser platesetter using exposure series 210-180-150-120-90mJ/ ^cm2 @150rpm using addressing at 2400dpi ability (addressability) and 200lpi screen (screen). These exposed printing plates were set directly on a Heidelberg GTO46 press (available from Heidelberger Druckmaschinen AG) without any processing or pretreatment. Printing was performed using a compressive blanket and using 3% Agfa Prima FS101 (trademark of Agfa) + 10% isopropanol (as fountain solution) and K+E 800 black ink (trademark of K&E).

Use the following start-up procedure: first 5 revolutions with meshed dampening roll, then 5 revolutions with meshed dampening and ink rollers, then start printing. 1000 prints on 80 g offset paper.

6. Print the result.

6.1 Sensitivity.

Plate sensitivity is defined as the lowest fluence at which 2% of the dots are fully visible on print 1.000 with the aid of a 5X magnifier. Plate sensitivities obtained for all aged and fresh plates were ≤ 150 mJ/m ² .

6.2 Shelf Life Results.

The shelf life of printing plates is measured from the clean-out results obtained on aged printing plates. A printing plate has an excellent shelf life if its scavenging properties are maintained or only slightly decreased after the aging cycle.

The clearance results obtained for the fresh comparative and inventive printing plates PP-02 to PP-07 were 5 for all printing plates. The clearance results measured for the aged samples are given in Table 3.

Table 3: Cleaning results of aged printing plates.

printed version Al substrate Clear ^* PP-02 (comparative example) AS-02 0 PP-03 (comparative example) AS-03 0 PP-04 (comparative example) AS-04 0 PP-05 (Example of the present invention) AS-05 4/5 PP-06 (Example of the present invention) AS-06 4 PP-07 (Example of the present invention) AS-07 4

^* Clearance is measured on sheet using the following criteria:

0 = completely black image at print ≤ 25 and print 250;

1 = heavily pigmented image at print ≤ 25 but completely black image at print 250;

2 = Severely colored images at print ≤ 25 and print 250;

3 = Moderately colored image at print ≤ 25 and print 250;

4 = slight coloring at 250 printing;

5 = perfectly clean background at print ≤ 25 and print 250.

And values below 4 are not suitable for high-quality printing.

The results in Table 3 show that with a single-step anodic post-treatment (Na-silicate treatment only), no proper cleaning of the printing plate was obtained after storage under warm and humid conditions, indicating a poor shelf life of the printing plate (compared to printing version PP-02 to PP-04). When Na-silicate anodic post-treatment followed by PVPA anodic post-treatment, the removal performance after storage in warm and humid conditions dropped only slightly to 4/5, indicating an excellent shelf life (inventive printing plate PP-05 to PP-07).

Example 2

1. Prepare post-anodized (PAT) substrates AS-08 to AS-16.

Untreated substrate AS-01 (see Example 1) was immersed in Na-metasilicate solution (see below), PVPA solution, PAA solution (see below) and/or mixed solution (see below) according to Conditions described in Table 4. The temperature of each of these solutions was 70°C.

After the respective dipping steps, the post-anodized substrates AS-08 to AS-16 were rinsed with demineralized water for 5 seconds and dried at room temperature.

The composition of the PVPA solution is described in Example 1.

Na-Metasilicate solution:

Sodium metasilicate pentahydrate (commercially available from Van Baerle & Co. Chemische Fabrik) was dissolved in demineralized water at a concentration of 25 g/l. This solution is referred to herein as "Na-metasilicate solution".

PAA solution:

A solution of Aqualic AS58 (polyacrylic acid, trademark of Nippon Shokubai (Japan)) in demineralized water at a concentration of 20 g/l was used. This solution is referred to herein as "PPA solution".

Mixed Na-Metasilicate/PAA solution:

Solutions of a mixture of sodium metasilicate and polyacrylic acid were used in concentrations of 25 g/l and 20 g/l, respectively.

Mixed Na-Metasilicate/PVPA solution:

Solutions of mixtures of sodium metasilicate and polyvinylphosphonic acid were used in concentrations of 25 g/l and 20 g/l, respectively.

Table 4: Aluminum substrates AS-08 to AS-16.

Al substrate PAT solution 1 Immersion time/second PAT solution 2 Immersion time/second AS-08 comparative example PAA 5 - - AS-09 comparative example PVPA 5 - - AS-10 comparative example Na-Metasilicate 10 - - AS-11 comparative example Na-Metasilicate+PAA 10 - - AS-12 comparative example Na-Metasilicate+PVPA 10 - - AS-13 comparative example PAA 5 Na-Metasilicate 10 AS-14 comparative example PVPA 5 Na-Metasilicate 10 AS-15 Invention Na-Metasilicate 10 PAA 5 AS-16 Invention Na-Metasilicate 10 PVPA 5

2. Preparation of latex LX-02.

In an 8-liter double-jacketed reactor, 40.0 g of sodium dodecyl sulfate (SDSUltra Pure, available from Alkemi BV, Lokeren, Belgium) and 5495.3 g of demineralized water were added. The reactor was flushed with nitrogen and heated to 75°C. When the reactor contents reached a temperature of 75°C, a mixture of 15.9 grams of styrene and 8.1 grams of acrylonitrile (ie 1.5% of the total monomer content) was added to prepare a latex seed. After mixing for 10 minutes, in order to disperse the added monomer evenly, a portion of the initiator solution (50% of the total amount of initiator), ie, 105.6 grams of 5% sodium persulfate in water, was added. The reactor was then heated to 80° C. over a period of 30 minutes and then a monomer mixture of 1044.1 grams of styrene and 531.9 grams of acrylonitrile was dosed over a period of 180 minutes. At the same time, 105.6 g of a 5% sodium persulfate solution were dosed, also within 180 minutes. When the monomer addition was complete, the reactor was heated at 80°C for 30 minutes. To reduce the amount of residual monomers, a redox-initiating system was added: 6.99 g of sodium formaldehyde sulfoxylate dihydrate (SFS) dissolved in 534 g of water and 11.43 g of 70 wt% t-butyl hydroperoxide diluted with 100 g of water base (TBHP) solution. Aqueous solutions of SFS and TBHP were added separately over 80 minutes. The reaction was then heated for another 10 minutes and then cooled to room temperature. 100 ppm of 5-bromo-5-nitro-1,3-dioxane was added as an antimicrobial agent and the latex was filtered using coarse filter paper. This yielded a latex dispersion LX-02 with a solids content of 20.74 wt% and a pH of 2.99. The average particle size was 41 nm (measured using a Brookhaven BI-90 analyzer, commercially available from Brookhaven Instrument Company, Holtsville, NY (USA)).

3. Preparation of printing plate precursors PPP-08 to PPP-16.

The coating solutions of the printing plate precursors PPP-08 to PPP-016 were prepared as follows: the latex dispersion LX-02 was added to demineralized water and the obtained dispersion was stirred for 10 minutes. Subsequently, the IR-dye was added, and after stirring the solution for 60 minutes, the polyacrylic acid solution was added. After 10 minutes of stirring, the DEQUEST 2010 solution was added and then after another 10 minutes of stirring, the surfactant solution was added. The coating dispersion was stirred for an additional 30 minutes and the pH was adjusted to 3.6. Table 5 lists the dry coat weights for the different coating compositions.

The obtained coating solutions were then coated onto Al substrates AS-08 to AS-16, using a coating knife, at a wet thickness of 30 μm. After drying at 60°C, this yielded the printing plate precursors PPP-08 to PPP-16.

Table 5: Dry coating weights.

Element g/ ^m2 Latex LX-02(1) 0.406 IR-dye IR-3(2) 0.075 Polyacrylic acid(3) 0.056 DEQUEST 2010(4) 0.016 Ascorox(5) 0.013 Surfactant(6) 0.005 Total (g/m ² ) 0.571

(1) Latex LX-02 synthesized in the above 2nd point;

(2) IR dye aqueous solution, containing 1wt% of IR-3:

(3) an aqueous solution of polyacrylic acid (PAA, Aqualic AS58, a trademark of Nippon Shokubai (Japan)) containing 5 wt%;

(4) an aqueous solution containing 10 wt% of 1-hydroxyethylidene-1,1-diphosphoric acid (HEDP, commercially available from Monsanto Solutia Europe);

(5) Antioxidant ST-01 (see the description above);

(6) An aqueous surfactant solution containing 5 wt % of a fluorosurfactant Zonyl FSO100 (trademark of Dupont).

4. Exposure and printing of printing plate precursors PPP-08 to PPP-16.

In each of the printing plate precursors PPP-08 to PPP-16, one printing plate was exposed immediately ("fresh" printing plate precursor), and the other printing plate was stored at 80% relative humidity and 35°C before exposure7 Days; these are "aged" printing plate precursors.

All "fresh" and "aged" printing plate precursors were exposed to a Creo TrendSetter 324440W fast head IR-laser platesetter using exposure series 210-180-150-120-90mJ/ ^cm2 @150rpm using addressing at 2400dpi ability (addressability) and 200lpi screen (screen). These exposed printing plate precursors were set directly on a Heidelberg GTO46 press equipped with a Kompac III dampening system (trademark of VARN) without any treatment or pretreatment. Printing was performed using a compressive blanket and using 4% Emerald Premium 3520 (trade mark of Anchor) as fountain solution and K+E 800 black ink (trade mark of K&E).

Use the following start-up procedure: first 5 revolutions with meshed dampening roll, then 5 revolutions with meshed dampening and ink rollers, then start printing. 1000 prints on 80 g offset paper.

5. Print the result.

5.1 Sensitivity.

Plate sensitivity is defined as the lowest fluence at which 2% of the dots are fully visible on print 1.000 with the aid of a 5X magnifier. The plate sensitivity obtained for all fresh printing plates was ≦120 mJ/m ² . For the comparative printing plates PP-10, PP-13 and PP-14 it was difficult to determine the sensitivity because of the poor cleaning performance.

5.2 Shelf Life Results.

The shelf life of the printing plates was measured from the cleaning results obtained on aged printing plates. A printing plate has an excellent shelf life if its scavenging properties are maintained or only slightly decreased after the aging cycle.

Fresh contrast and cleanout results provided by printing plates PP-08 to PP-16 according to the invention were equal to 5 for all printing plates, with the exception of comparative printing plates PP-10, PP-13 and PP-14, which Has bad cleaning properties. The cleaning results obtained for the aged comparative and printing plates of the invention are given in Table 6.

Table 6: Cleaning results of aged printing plates.

printed version Printed Clear ^* PP-08 (comparative example) 3 PP-09 (comparative example) 2 PP-10 (comparative example) 1 PP-11 (comparative example) 3 PP-12 (comparative example) 2 PP-13 (comparative example) 0 PP-14 (comparative example) 0 PP-15 (the embodiment of the present invention) 4 PP-16 (the embodiment of the present invention) 4

^* Use the following clearance criteria:

0 = completely black image at print ≤ 25 and print 250;

1 = heavily pigmented image at print ≤ 25 but completely black image at print 250;

2 = Severely colored images at print ≤ 25 and print 250;

3 = Moderately colored image at print ≤ 25 and print 250;

4 = slight coloring at 250 printing;

5 = perfectly clean background at 250 prints.

And values below 4 are not suitable for high-quality printing.

The results in Table 6 show that:

- Comparative printing plates PP-08 to PP-12 gave poor cleaning results after storage in warm and humid conditions, these printing plates including support, which had a single-step anodic post-treatment (Na-metasilicate solution, PVPA solution, mixed Na-metasilicate/PAA solution or mixed Na-metasilicate/PVPA solution).

- Comparative printing plates PP-13 to PP-14 gave unacceptable scavenging results after storage in warm and humid conditions, these printing plates consisted of a support which was first treated with a PVPA solution or PAA solution and subsequently with a metasilicate Solution processing.

- After storage under warm and humid conditions, the printing plates PP-15 to PP-16 according to the invention give excellent cleaning properties, these printing plates comprise a support which is firstly treated with a Na-metasilicate solution and subsequently with a PVPA solution Or PAA solution treatment.

Claims (10)

1. A method of manufacturing a lithographic printing plate precursor, comprising the steps of: (i) providing a grained and anodized aluminum support; (ii) treating the support with an aqueous solution comprising a compound comprising a silicate anion and one or more cations; (iii) treating the support with an aqueous solution comprising a compound containing an organic acid group and/or an ester or salt thereof; (iv) applying a coating to said treated support comprising an image-recording layer comprising hydrophobic thermoplastic polymer particles having an average particle size of 20 nm to 55 nm. 2. The method according to claim 1, wherein the amount of hydrophobic thermoplastic polymer particles present in the image layer is at least 70% relative to the total weight of the ingredients. 3. The method according to any one of the preceding claims, wherein the silicate anion is selected from the group consisting of phosphosilicates, orthosilicates, metasilicates, hydrosilicates, polysilicates or pyrosilicates. 4. A method according to claim 3, wherein the silicate anion is orthosilicate or metasilicate. 5. The method according to any one of the preceding claims, wherein the organic acid groups are selected from carboxylic acid groups and/or phosphonic acid groups. 6. The method according to any one of claims 1-5, wherein the compound of step (iii) is a polymer comprising repeating structural units, which contain organic acid groups. 7. The method according to claim 6, wherein the polymer is polyvinylphosphonic acid or poly(meth)acrylic acid. 8. The method according to any one of the preceding claims, wherein the support has an Ra value below 0.45 μm and an anodic weight > 3.2 g/ ^m2 . 9. A method of manufacturing a lithographic printing plate, comprising the steps of: (i) providing a printing plate precursor according to the method of claims 1-8; (ii) exposing said printing plate precursor to light and/or heat; (iii) optionally developing said exposed precursor with a processing liquid. 10. A printing method comprising the steps of: (i) providing a printed version according to the method of claim 9; (ii) Setting the obtained printing plate on a printing press and providing ink and/or fountain solution.