DE60119278T2 - Cleaning method for reuse of a print carrier by laser ablation - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The The present invention relates to a process for removing color-enhancing Areas of a print master for the master substrate to reuse and can be recoated.

GENERAL STATE OF THE ART

at Printing presses use a so-called pressure master like a on a drum of the printing press clamped pressure plate. The master surface carries on color-enhancing areas built image and a deduction is obtained by first Ink applied to the image and then the color of the master a receiving material, usually paper, is transmitted. In conventional lithographic printing is both ink and fountain solution water-based on the lithographic image, made of oleophilic (or hydrophobic, i.e., ink-receptive, water-repellent) Areas and hydrophilic (or oleophobic, i.e. hydrophilic, ink-repelling) Areas constructed, appropriate. In so-called driographic The lithographic image consists of ink-receptive and ink-repellent prints (i.e., color repellent) Areas and will be during of driographic printing, just apply printing ink to the master.

print Master are usually after the so-called computer-to-film process get where different pre-presses like the font type, Scanning, production of color separations, rastering, trapping, layout and imposition digitally and each color separation via an imagesetter on a graphic Film is exposed. After development, the film can be used as a mask for the Exposure of an image-forming material as a printing plate precursor designated, used and after the development of the plate becomes obtained a printing plate, which is used as a master.

In In recent years, the so-called computer-to-plate (CTP) process has to a considerable extent gained in importance. In this process, also as direct refers to digital plate imaging (direct-to-plate method), is waived on the production of a film and that because the digital document about a so-called platesetter transferred directly to a printing plate precursor becomes. One particular type of CTP process will have one a plate drum of a printing press mounted printing plate precursor over a exposed in the press exposed. This method may be referred to as a "computer-to-press" method and printing presses with built-in platesetter become sometimes called digital presses. An overview of digital presses found in "Proceedings of the Imaging Science & Technology's 1997 International Conference on Digital Printing Technologies (Non-Impact Printing 13) ". Computer-to-press procedure are described in e.g. EP-A 640 478, EP-A 770 495, EP-A 770 496, WO 94/1280, EP-A 580 394 and EP-A 774 364.

It There are two types of such on-press imaging methods. At a first type, a printing plate precursor is clamped in a printing press, exposed imagewise, optionally developed, then used as a pressure master and after all removed from the press and eliminated, creating a new plate material for each image need becomes. An example for this technology is the Quickmaster DI 46-4 (trademark of Heidelberger Druckmaschinen, Germany). Disadvantage of this procedure is that for every printing cycle requires a new record, which is an increase the cost of the printing process.

In a second type of on-press imaging systems, the same lithographic substrate is used for multiple print runs (hereafter referred to as print cycles). At each print cycle, one or more heat-sensitive or radiation-sensitive layers are applied to the lithographic substrate to produce a printing plate precursor and a print master is obtained after imagewise exposure and eventual development. Upon completion of the print cycle, the ink-attracting areas of the print master are removed from the lithographic substrate during a cleaning step, yielding a recyclable substrate that can be used in a next cycle of coating, exposure, and printing without having to clamp a new plate onto the cylinder , Examples of such systems with on-press coating and on-press imaging are described in eg US 4,718,340 . US 5,188,033 . US 5,713,287 EP-A 786 337 and EP-A 802 457. The substrate can be reused in a number of printing cycles. This number is due to the delicate balance between the efficiency of the cleaning step and the maintenance of the lithographic quality of the substrate, ie an aggressive cleaning step ensures efficient removal of all traces of the lithographic coating, but at the same time carries the risk of attacking the lithograph cal surface of the substrate. A mild cleaning step, on the other hand, reduces the risk of aggressive exposure to the lithographic coating, but incomplete removal of the lithographic coating will result in the appearance of ghost images (with the image of a previous print job still visible in the following print job). In practice, the same substrate can not be used indefinitely and must be replaced after a certain number of printing cycles.

Out US 4,718,340 For example, a method is known in which the lithographic coating is removed from the substrate by laser ablation. However, the very high temperature encountered during ablation in the lithographic coating results in damage to the lithographic surface of typical substrates such as a roughened and anodized aluminum support.

SHORT PRESENTATION THE PRESENT INVENTION

task The present invention is to provide a method for proper cleaning the substrate of a printing master without compromising the quality of the substrate, leaving it without occurrence of ghosting in a next printing cycle can be used again. This task is solved by the method described in claim 1. Although the procedure is also possible Use in other printing techniques such as high pressure, particularly suitable But it is for cleaning a lithographic printing master. In a preferred embodiment becomes the cleaning method for reuse as defined in claim 1 of the substrate in a method as defined in claim 2 with on-press coating and on-press exposure applied. This method allows convenient removal of ink-attracting Areas from the substrate of the printing master (without occurrence of ghosting in the following printing cycle) without affecting the lithographic quality of the substrate, eliminating the same substrate in a large number of printing cycles with coating, exposure, printing and cleaning can be used, this number is preferably more than 5 Printing cycles, more preferably more than 10 printing cycles and all more preferably more than 30 pressure cycles.

Further preferred embodiments The present invention is described in the subclaims. Further advantages and embodiments The present invention will become apparent from the following description seen.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

substratum

The in the inventive method used substrate is made of a support and a cast thereon Built up primer layer.

Of the carrier can be a sheet-like material such as a plate or a cylindrical Element like a sleeve-shaped plate which is pushed onto the plate cylinder of a printing press. The carrier can also be the plate cylinder itself. The carrier can also a train with enough high flexibility to be wound on a spool can. Of the carrier can be made of a plastic, a metal like aluminum or a Be made of a composite material or a laminate thereof, e.g. a laminate of plastic and metal. Preferred examples for plastic are a polyethylene terephthalate (PET) film, a polyethylene naphthalate film, a cellulose acetate film, a polystyrene film, a polycarbonate film etc. The plastic carrier can be opaque or translucent be.

A particularly preferred support is an electrochemically roughened and anodized aluminum support. The primer layer described below ensures proper protection of the roughened alumina surface during the laser ablation step. The anodized aluminum support may be subjected to processing to improve the hydrophilic properties of the support surface. For example, the aluminum support can be silicated by processing the support surface with a sodium silicate solution at elevated temperature, eg 95 ° C. Alternatively, a phosphate processing may be performed wherein the alumina surface is processed with an optional further inorganic fluoride-containing phosphate solution. Further, the alumina surface may be rinsed with a citric acid or citrate solution. This treatment can be carried out at room temperature or at a slightly elevated temperature between about 30 ° C and 50 ° C. Another interesting method is to rinse the alumina surface with a bicarbonate solution. Further, the alumina 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 Polyvi nylalkoholen, which are formed by reaction with a sulfonated aliphatic aldehyde processed. Further, it is obvious that one or more of these post treatments may be performed separately or in combination. More detailed descriptions of these treatments can be found in GB-A 1 084 070, DE-A 4 423 140, DE-A 4 417 907, EP-A 659 909, EP-A 537 633, DE-A 4 001 466, EP-A 292,801, EP-A 291,760 and US-P 4,458,005.

If a plastic film is used as the carrier, it is advantageous to apply an adhesion-promoting layer, also referred to as an adhesive layer, between the carrier and the primer layer. Particularly suitable adhesive layers for use in the present invention comprise a hydrophilic binder and colloidal silica as described in EP-A 619 524, EP-A 620 502 and EP-A 619 525. The amount of silica in the adhesive layer is preferably between 200 mg / m ² and 750 mg / m ² . Further, the ratio of silica to hydrophilic binder is preferably not more than 1 and the specific surface area of the colloidal silica is preferably at least 300 m ² / g, more preferably at least 500 m ² / g. The adhesive layer may further contain other adhesion promoting substances, such as organic sulfonic acids, titanates, silanes, and zirconium compounds, eg, ammonium zirconyl carbonate, zirconium oxide, zirconium propionate, and other zirconium-based compounds described in The Use of Zirconium in Surface Coatings, Application Information, Sheet 117 (ex.), PJ Moles, Magnesium Electron, Inc., Flemington, NJ, USA.

The primer layer contains a hydrophilic binder crosslinked with a crosslinking agent, such as formaldehyde, glyoxal, polyisocyanate or a hydrolyzed tetraalkylorthosilicate, as described in EP-A 601 240, GB 1 419 512 . FR 2 300 354 . US 3,971,660 and US 4,284,705 , Further preferred crosslinking agents are carbonates such as zinc carbonate or zirconium compounds, eg, ammonium zirconyl carbonate, zirconium oxide, zirconium propionate, and other zirconium-based compounds described in "The Use of Zirconium in Surface Coatings," Application Information, Sheet 117 (l.), PJ Moles, Magnesium Elektron, Inc., Flemington, NJ, USA. The amount of crosslinking agent, in particular tetraalkyl orthosilicate, is preferably at least 0.2 parts by weight per part by weight of hydrophilic binder, more preferably between 0.5 parts by weight and 5 parts by weight per part by weight of hydrophilic binder, most preferably between 1 part by weight and 3 parts by weight per part by weight of hydrophilic binder. The thickness of the hydrophilic primer layer is preferably between 0.1 and 20 microns, more preferably between 1 and 10 microns.

The hydrophilic binder for use in the primer layer e.g. a hydrophilic (co) polymer such as homopolymers and copolymers of vinyl alcohol, acrylamide, methylolacrylamide, methylolmethacrylamide, Acrylic acid, methacrylic acid, Hydroxyethyl acrylate, hydroxyethyl methacrylate or maleic anhydride vinylmethyl ether copolymers. The hydrophilicity of the used (co) polymer or (co) polymer mixture is preferably higher or equal to the hydrophilicity of at least 60% by weight, preferably at least 80% by weight hydrolyzed polyvinyl acetate. polyvinyl alcohol (PVOH) is particularly preferred.

The primer layer also contains a metal oxide, preferably particles of an oxide of Ti, Zr, Hf or mixtures thereof. TiO ₂ is very particularly preferred, in particular TiO ₂ having a particle size between 0.1 and 1 μm. A hydroxide of the metal is also suitable. The amount of metal oxide in the primer layer is preferably between 60 and 90%, more preferably between 70 and 85%, based on the total weight of the layer. Preferably, the primer layer is capable of reflecting any unabsorbed exposure radiation back into the imaging layer (s).

Imaging material

To the inventive method coating the above-described substrate with a coating, in the case of imagewise exposure and possible development of ink-attracting areas. The coating may be one or more imaging layers be constructed. Preferably, only a single layer is formed the substrate attached. The image-forming material thus obtained can sensitive to light or sensitive to heat be the latter choice because of the daylight resistance is preferred. The image-recording layer of the material is preferably non-ablative. The term "non-ablative" is understood to mean that the image recording layer while the exposure step is not substantially removed. The imaging material is preferably processless, i. becomes a lithographic image Obtained immediately after exposure without wet development or through Supply of fountain solution and / or ink, i. by starting the printing cycle to be developed.

The material can be positive working, ie the exposed areas of the coating form the non-printing areas of the master, or negative working, ie the exposed areas of the coating form the printing areas of the master. In the following, two embodiments of a most preferred negative working material having a single imaging layer will now be discussed.

In a first most preferred embodiment, the working mechanism of the image-forming layer is based on the thermally-induced coalescence of hydrophobic thermoplastic polymeric particles, preferably dispersed in a hydrophilic binder, as described, for example, in US Pat EP 770 494 . EP 770 495 . EP 770 497 . EP 773,112 . EP 774 364 and EP 849,090 , The coalesced polymeric particles form a hydrophobic printing area that can not be readily removed by fountain solution and / or ink, while the unexposed layer forms a non-printing area that is rapidly removed by fountain solution and / or ink. The thermal coalescing can be initiated by direct application of heat, for example by means of a thermal head, or by light absorption of one or more compounds which are capable of converting light, particularly preferably infrared light emitted eg by a solid-state laser, into heat. Particularly useful light-to-heat converting compounds include, for example, dyes, pigments, carbon black, metal carbides, borides, metal nitrides, carbonitrides, bronze-structured oxides, and conductive polymeric dispersions such as polypyrrole, polyaniline, or polythiophene-based conductive polymer dispersions. Infrared absorbing dyes and carbon black are most preferred.

The hydrophobic thermoplastic polymer particles are preferred a coagulation temperature over 35 ° C and especially preferred over 50 ° C on. Coagulation may occur as a result of softening or melting of the thermoplastic polymer particles under the action of heat. The coagulation temperature subject to the thermoplastic hydrophobic polymeric particles Although no specific upper limit, but should be enough under the decomposition temperature of the polymeric particles. The coagulation temperature is preferably at least 10 ° C below the temperature at the decomposition of the polymeric particles entry. As specific examples of hydrophobic polymer particles are e.g. Polyethylene, polyvinyl chloride, polymethyl (meth) acrylate, Polyethyl (meth) acrylate, polyvinylidene chloride, polyacrylonitrile, polyvinylcarbazole, To call polystyrene or copolymers thereof. Very particularly preferred becomes polystyrene. The weight average molecular weight of the polymers can vary between 5,000 and 1,000,000 g / mole. The particle size of the hydrophobic Particles can be between 0.01 μm and 50 μm, more preferably between 0.05 microns and 10 microns, and most preferably between 0.05 μm and 2 μm lie. The amount of hydrophobic thermoplastic polymeric particles in the image-forming layer is preferably between 20 wt .-% and 65 wt.%, more preferably between 25 wt.% and 55 wt.% and most preferably between 30% and 45% by weight.

suitable hydrophilic binders are for example synthetic homo- or Copolymers such as a polyvinyl alcohol, a poly (meth) acrylic acid, a Poly (meth) acrylamide, a polyhydroxyethyl (meth) acrylate, a polyvinyl methyl ether or natural Binders such as gelatin, a polysaccharide such as e.g. Dextran, Pullulan, Cellulose, gum arabic and alginic acid.

In the second most preferred embodiment contains the image-forming Layer an aryldiazosulfonate homopolymer or copolymer, which before the exposure hydrophilic and by fountain solution and / or ink is removable and by the exposure hydrophobic and less removable is done. For the exposure come the same means as above related discussed with the thermal coalescence of polymeric particles in Question. Alternatively, the aryldiazosulfonate polymer may also be by exposure to UV light, e.g. with a UV laser or a UV lamp, be converted from hydrophilic to hydrophobic (switched).

in der R⁰, R¹ und R² unabhängig voneinander jeweils ein Wasserstoffatom, eine Alkylgruppe, eine Nitrilgruppe oder ein Halogenatom, z.B. Cl, bedeuten, L eine zweiwertige Verbindungsgruppe bedeutet, n 0 oder 1 bedeutet, A eine Arylgruppe bedeutet und M ein Kation bedeutet. L bedeutet vorzugsweise eine zweiwertige Verbindungsgruppe aus der Gruppe bestehend aus -(X)_t-CONR³-, -(X)_t-COO-, -X- und -(X)_t-CO-, wobei t 0 oder 1 bedeutet, R³ ein Wasserstoffatom, eine Alkylgruppe oder eine Arylgruppe bedeutet und X eine Alkylengruppe, eine Arylengruppe, eine Alkylenoxygruppe, eine Arylenoxygruppe, eine Alkylenthiogruppe, eine Arylenthiogruppe, eine Alkylenaminogruppe, eine Arylenaminogruppe, Sauerstoff, Schwefel oder eine Aminogruppe bedeutet. A bedeutet vorzugsweise eine nicht-substituierte Arylgruppe, z.B. eine nicht-substituierte Phenylgruppe, oder eine Arylgruppe, z.B. eine Phenylgruppe, die mit einer oder mehreren Alkylgruppen, Arylgruppen, Alkoxygruppen, Aryloxygruppen oder Aminogruppen substituiert ist. M bedeutet vorzugsweise ein Kation wie NH₄ ⁺ oder ein Metallion wie ein Kation von Al, Cu, Zn, einem Erdalkalimetall oder einem Alkalimetall.Preferred examples of such aryldiazosulfonate polymers are the compounds obtained by homo- or copolymerization of aryldiazosulfonate monomers with other aryldiazosulfonate monomers and / or with vinyl monomers such as (meth) acrylic acid or esters thereof, (meth) acrylamide, acrylonitrile, vinyl acetate, vinyl chloride, vinylidene chloride, styrene, α Methylstyrene, etc. can be prepared. Suitable aryldiazosulfonate polymers for use in the present invention correspond to the formula:

in which R ⁰ , R ¹ and R ² independently of one another each represent a hydrogen atom, an alkyl group, a nitrile group or a halogen atom, eg Cl, L is a divalent linking group, n is 0 or 1, A is an aryl group and M is a cation means. L is preferably a divalent linking group selected from the group consisting of - (X) _t -CONR ³ -, - (X) _t -COO-, -X- and - (X) _t -CO-, where t is 0 or 1, R ^{3 represents} a hydrogen atom, an alkyl group or an aryl group, and X represents an alkylene group, an arylene group, an alkyleneoxy group, an aryleneoxy group, an alkylene thio group, an arylene thio group, an alkyleneamino group, an arylene amino group, oxygen, sulfur or an amino group. A is preferably an unsubstituted aryl group, for example an unsubstituted phenyl group, or an aryl group, for example a phenyl group, which is substituted by one or more alkyl groups, aryl groups, alkoxy groups, aryloxy groups or amino groups. M is preferably a cation such as NH ₄ ⁺ or a metal ion such as a cation of Al, Cu, Zn, an alkaline earth metal or an alkali metal.

suitable Aryldiazosulfonatmonomere for the preparation of the above polymers described in EP-A 339 393, EP-A 507 008 and EP-A 771 645.

As mentioned above, For example, the image forming material may be further than the image recording layer (s) one or more, applied to the lithographic substrate Auxiliary layer (s) included. The light absorbing compound can in another layer, that of the other ingredients mentioned above such as the hydrophobic thermoplastic polymer particles and the Aryldiazosulfonatpolymer containing layer close be. Or the imaging material may be a protective topcoat, by the developing fluid, the fountain solution and / or the ink is removable and protection against handling and mechanical damage. A contains a suitable protective topcoat Polyvinyl alcohol.

coating step

The coating of the substrate with the image recording layer (s) and auxiliary layer (s) may be accomplished by thermally induced or friction induced transfer of a donor material as described in U.S. Pat EP 1 048 458 or by powder coating, as described, for example, in EP-A 974 455 and EP-A No. 99203682 filed on 03.11.99, or by application of a liquid solution by any known coating method, such as, for example, by spin coating, dip coating, knife coating, curtain coating, Air brush coating, gravure roll coating, reverse roll coating, extrusion coating, cascade coating and curtain coating. An overview of these coating techniques can be found in Modern Coating and Drying Technology, Edward Cohen and Edgar B. Gutoff Editors, VCH Publishers, Inc., New York, NY, 1992. The casting solution can also be prepared by printing techniques such as inkjet, gravure, flexo or offset printing, applied to the substrate. The ink-jet printing as described in EP-A No. 00202700 filed on Jul. 31, 2000 is particularly preferred.

To In another, very particularly preferred embodiment, a casting solution by means of one with a spray nozzle stocked Head on the press ("on press ") on the Substrate sprayed. Preferred values for the spray parameters are in the two filed on September 15, 1999 Patent Applications EP-A No. 99203064 and EP-A No. 99203065. In a preferred Configuration moves the spray head in the direction of the printing cylinder axis along the lithographic base while the cylinder is in Angular direction turns. The printing press cylinder is preferably the plate cylinder on which the pressure master is clamped during the printing cycle is.

The Coating by spraying or spin coating is preferred for applying an image-recording layer as described above thermoplastic polymeric particles or an aryldiazosulfonate polymer contains.

exposure step

The image forming material used in the present invention may be heated or exposed. The heating or exposure is preferably carried out on the press, that is, while the material is clamped on a printing press cylinder, preferably the plate cylinder equipped with the printing master during the printing cycle. The heating or exposure can be done for example with a thermal head, digitally modulated lamps, LED diodes or a laser head. One or more lasers are preferred, such as a He / Ne laser, an Ar laser or a violet laser diode. Most preferably, the light used for the exposure is not visible light, so that daylight resistant materials can be used, eg UV light (UV laser light) or near infrared light with a wavelength between about 700 and about 1500 nm emitting laser, eg Semiconductor laser diode, a Nd: YAG laser or a Nd: YLF laser. The laser power required depends on the sensitivity of the imaging layer, the pixel dwell time of the laser beam as determined by the beamwidth (a typical value at 1 / e ^{2 of} the maximum intensity is between 10 and 25 microns for modern platesetters), the scan speed, and the resolution of the Recorder (ie the number of addressable pixels per unit length, often expressed as dots per cm or dots per inch (dpi) - typical values are between 1,000 and 4,000 dpi). More detailed technical information on on-press platesetter are eg in US 5,174,205 and US 5,163,368 described.

any development step

Preferably the imaging material does not require a separate development step, i.e. the print can be started immediately after exposure. When Alternatively, the imaging material may be e.g. by supply of Printing ink and / or fountain to be developed. In this embodiment The stages of development and printing form a single concurrent one Process, i. after exposure, the printing process by feeding started from printing ink and / or fountain solution to the material, wherein the imaging layer after the first pair of revolutions of the impression cylinder (usually less than 20, more preferably less than 10 turns) completely is developed and then over receive high quality printed copies throughout the printing cycle become. Both of the above-described preferred embodiments of imaging materials, i.e. based on a thermal coalescence of thermoplastic polymeric particles or aryldiazosulfonate polymers are particular suitable for Such a process with a "hidden" development the press. The unexposed areas of the imaging layer be while the first passes the printing press dissolved in the ink and / or the dampening water. Preferably the removed ingredients are transferred to the printing paper.

Of the On-press development of the imaging material may be an eventual Step forward by first passing the imaging layer through Supply of water or an aqueous liquid moistened or swell.

cleaning step

According to the method of the invention, the ink-attracting areas of the printing master are removed by laser ablation. During the cleaning step, the laser light is absorbed by the layers or layers present on the substrate, whereby the absorbed light is converted into heat and the temperature in the layer (s) rises sufficiently to be ablated by, for example, chemical decomposition Evolve evaporation of the layer (s). It may be necessary to use a vacuum device which removes any waste generated during the ablation step or any fumes formed during the ablation step. Such devices are described in eg US 5,934,197 . US 5 574 493 and EP-A 988 969.

Preferably, the image-recording layer (s) and auxiliary layer (s) are added to dyes or pigments which have a high absorbance at the emission wavelength of the laser used in the ablation step. Preferred lasers are an infrared laser, for example a CO ₂ laser, an Nd: YAG laser or one or more high-power laser diodes. To avoid excessive heating of the substrate, it is preferable to use a pulsed laser operating, for example, at a pulse rate between 1 and 10 Hz. According to a preferred embodiment, the same laser device is used for both the imagewise exposure of the imaging material and for the cleaning of the printing master after the print job has been completed. In this embodiment, it is preferable to use different power settings, filters, modulators, or other known means to switch the light intensity of the laser from a low value during the exposure step to a high value during the ablation stage.

Of the Cleaning step is preferably carried out on the press, i. while that Material on a printing press cylinder, preferably on the during the Printing cycle with the printing master equipped plate cylinder, clamped is.

To the laser ablation step, the cleaned substrate in a next Cycle of coating, exposure and printing are used. As mentioned above is the number of consecutive cycles in which the same Substrate is used limited. Once due to inexpedient cleaning Ghosting or due to wear of the hydrophilic layer one To observe deterioration of the lithographic quality of the substrate so the substrate can be replaced by fresh material. In the embodiment, In which a flexible substrate is used, a fresh substrate can be used by unwinding such a material from a roll. Such a role can be arranged in the printing press, even in the printing cylinder itself, e.g. by a supply cassette with a Unwinding and take-up reel used within the plate cylinder As described in EP-A 640 478. Furthermore, the plate supply using a fresh with pre-cut bow Substrate loaded supply cassette to be automated. Of course, too manually loading a fresh substrate within the scope of the present invention.

EXAMPLES

Example 1 (comparative Example)

Production of the lithographic substrate

A 0.30 mm thick aluminum foil is 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 film is then electrochemically roughened with alternating current at a temperature of 35 ° C. and a current density of 1200 A / m ² in an aqueous solution containing 4 g / l hydrochloric acid, 4 g / l boric acid and 5 g / l aluminum ions. to obtain a surface topography with an arithmetic mean roughness Ra of 0.5 μm.

After rinsing with demineralized water, the aluminum foil is etched with an aqueous solution containing 300 g / l sulfuric acid at 60 ° C. for 180 s and then rinsed with demineralized water at 25 ° C. for 30 s. Subsequently, the film is anodized at a temperature of 45 ° C, a voltage of about 10 V and a current density of 150 A / m ² for about 300 s in an aqueous solution containing 200 g / l of sulfuric acid to give an anodic, 3 g / Obtained m ² Al ₂ O ₃ containing oxidation film, then washed with demineralized water, then first with a solution containing polyvinylphosphonic acid and then with a solution containing aluminum trichloride, then rinsed with demineralized water for 120 s at 20 ° C and dried.

manufacturing of the imaging material

A 2.61 wt .-% aqueous solution is made by offsetting a polystyrene latex, a heat absorbing Attachment and a hydrophilic binder set. This solution will applied to the above-described substrate. After drying has the image-recording layer has a thickness of 0.83 μm and contains 75% by weight of the polystyrene latex, 10% by weight of the infrared absorbing light Dye IR-1 (see formula below) and 15% by weight of polyacrylic acid (Glascol E15, trademark of N.V. Allied Colloids Belgium) as hydrophilic Binder.

IR-1

IR-1

The above solution is sprayed onto the lithographic base. This is the lithographic Pad stretched on a drum at a line speed from 164 m / min. is turned. The spray solution for the imaging element is by means of a at a speed of 1.5 m / min. in the direction of the cylinder axis moving spray nozzle applied. The spray nozzle is fixed at a distance of 40 mm to the substrate. The flow rate the spray solution is to 7 ml / min. set. While the spraying process an air pressure of 90 psi is generated in the spray head. The obtained Layer is at an air temperature of 70 ° C during the spraying process and subsequently dried for another 30 s.

The nozzle is a compressed air spray nozzle SUV76, trademark of Spraying Systems Belgium, Brussels.

exposure of the imaging material

The imaging element described above is thermally exposed in a Creo 3244 ^™ Outer Drum Plateetter at 2,400 dpi, a drum speed of 150 ppm and a power of 15.5 watts. The imaged plates are used using K + E 800 Skinnex ink and Rotamatic fountain solution in a print run of 5,000 copies on a GTO46 printing press. The print quality is evaluated.

cleaning step

To finished printing cycle, the plate is laser ablated with a at 1,064 nm emitting Nd: YAG laser at a power of 4 W, a pulse rate of 2 Hz, a line speed of 1 cm / s and a distance of 15 cm between the plate and the laser head. The ink will not be removed before the cleaning step. After that will be the same substrate again for a next, as described above Cycle of coating, exposure and printing used.

Example 2

The the same steps as in Example 1 are repeated, but with the difference being that instead of the roughened and anodized aluminum support a lithographic according to the invention Substrate is used.

manufacturing of the lithographic substrate

To 446 g of an aqueous dispersion containing 25 wt .-% TiO ₂ with an average particle size between 0.3 and 0.5 microns and 2.5 wt .-% polyvinyl alcohol (from Wacker Chemie GmbH, Germany, under the goods character POLYVIOL WX sold hydrolyzed polyvinyl acetate), 218 g of an aqueous dispersion of 22 wt .-% hydrolyzed tetramethoxysilane. To this mixture is added 10 g of a 4.1% by weight solution of AKYPO OP80 ^™ . Akypo OP80 is a commercially available surfactant from Chemy. 2 g of a 5% strength by weight solution of the fluorosurfactant N-polyoxyethylene ethyl perfluorooctane acid amide are also added. The volume is then brought to 1000 ml with distilled water and the pH is adjusted to 4.0 with NaOH.

The above casting solution is applied to a heat-set, biaxially stretched polyethylene terephthalate film having a thickness of 175 μm, to give a coating having a total dry thickness of 6.83 g / m ² . The casting solution is applied in a wet film thickness of 50 microns and the film dried with air at 50 ° C and a moisture content of 4 g / m ² .

Example 3

In this example, the primer layer of Example 2 is applied to the lithographic substrate of Example 1. Here, a roughened and anodized aluminum support is coated with a TiO ₂ / PVOH layer.

Example 4

In this example, the procedure is analogous to Example 3, but with the difference that the primer layer is applied in a total dry thickness of 2 g / m ² .

Example 5

In This example is analogous to Example 2, but with the Difference that the heat sensitive Image forming element is produced as follows:

manufacturing of the imaging material

To 312 g of an aqueous dispersion containing 25 wt .-% TiO ₂ having an average particle size between 0.3 and 0.5 microns and 2.5 wt .-% polyvinyl alcohol (from Wacker Chemie GmbH, Germany, under the trademark POLYVIOL WX sold hydrolyzed polyvinyl acetate), 152 g of an aqueous dispersion of 22 wt .-% hydrolyzed tetramethoxysilane. To this mixture is added 10 g of a 4.1% by weight solution of AKYPO OP80 ^™ . Akypo OP80 is a commercially available surfactant from Chemy. Subsequently, 330.6 g of a 12.05 wt .-% polystyrene-containing emulsion is added. This emulsion is non-ionically stabilized. There is also added a solution containing 2 g of an IR-absorbing dye (the formula below) in 18 g of ethanol. Finally, the volume is brought to 1000 ml with distilled water and the pH is adjusted to 4.0 with NaOH.

This solution is applied in a total thickness of 0.5 g / m ² to the lithographic substrate described in Example 2. The resulting layer is dried at an air temperature of 70 ° C during the spraying process and then for a further 10 minutes. The spray nozzle is a compressed air spray nozzle type SUV76, trademark of Spraying Systems Belgium, Brussels.

IR-2

IR-2

Results

To the second, above-described cycle of coating, exposure and printing are evaluated by visual inspection the cleaning quality, coating quality and print quality. In this evaluation, a quotation between 0 and 5 is given, where 0 is a very good quality and 5 corresponds to a very poor quality. The evaluation the cleaning quality done by examination the cleanliness of the substrate obtained after the first cycle. The coating quality is through examination the smoothness of evaluated in the second cycle applied layer. The print quality is through exam the stain behavior and the presence of ghosting during the evaluated second cycle.

From the above results, it can be seen that by coating the support with a crosslinked hydrophilic layer containing a metal oxide such as TiO ₂ , a substantial improvement in cleaning quality and print quality is achieved.

Claims (10)

A method for removing ink-attracting areas from a print master by laser ablation, characterized in that the print master comprises a substrate composed of a support and a primer layer, the primer layer containing a crosslinked hydrophilic binder and a metal oxide. A lithographic printing process in which Using a reusable substrate printed as follows becomes: (a) providing a substrate consisting of a support and a primer layer containing a crosslinked hydrophilic binder and contains a metal oxide, is constructed, (b) applying one or more layers the primer layer for forming an image forming material, (C) Production of a printing master with ink-attracting areas imagewise heating or Exposure of the imaging material and eventual development the imaging material, (d) printing, (e) Distance the ink-attracting areas of the print master by laser ablation and (f) repetition of steps (a) to (d). Method according to claim 2, characterized in that the imaging material is a hydrophobic thermoplastic containing polymeric particles or a Aryldiazosulfonat polymer Contains image recording layer. Method according to claim 2 or 3, characterized that while Step (e) Ablation waste and / or flue gases by means of a vacuum device be removed. Method according to one of the preceding claims, characterized characterized in that the laser is an infrared laser. Method according to one of the preceding claims, characterized characterized in that the laser is a pulse laser. Method according to one of the preceding claims, characterized in that the metal is Ti, Zr, Hf or a mixture thereof is. Method according to one of the preceding claims, characterized characterized in that the primer layer further comprises a hydroxide of the Contains metal. Method according to one of the preceding claims, characterized characterized in that the carrier a plastic carrier, an aluminum carrier or a laminate of a plastic carrier and an aluminum carrier. Method according to claim 9, characterized in that that the aluminum carrier a roughened and anodized aluminum support.