DE60009255T2 - Flat printing process with a reusable carrier surface - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The The present invention relates to a method for cleaning and reuse the lithographic substrate of a printing master.

GENERAL STATE OF THE ART

at conventional lithographic printing, ink and fountain solution on the color-attracting (oleophilic) and water-attracting (hydrophilic) areas having surface attached to a printing master. The colored image pattern is then from the surface of the master on a blanket cylinder with a compressible Surface transferred. from Blanket cylinder, the image is printed on paper. The master is usually a printing plate that forms an image on a dimensionally stable substrate like wearing an aluminum bow. The imaged aluminum plate is made by means of a mechanical locking mechanism, a register-containing positioning of the plate on the surface of Ensures plate cylinder, attached to the plate cylinder of a printing press. After finished Print cycle, the mechanical locking system is unlocked and can remove the printing plate containing the printing plate and be eliminated, whereupon another pressure plate clamped and can be locked. Now a new print cycle can be started become.

The Production of printing masters is usually carried out according to the so-called Computer-to-film process, where each color separation by means of an imagesetter is imprinted on a graphic film. After development can the movie as a mask for the exposure of an image-forming material, as a printing plate precursor referred to, used and after development of the printing plate is obtained as a master usable printing plate. These steps usually done in appropriate exposure and development facilities and the printing plates are then fed to the printing press and a in the cylinder itself built-in locking mechanism of press operators clamped on the printing cylinder. Although the attachment of the printing cylinder usually a manual process, but robotic devices are already being designed been used with which the printing plates are positioned and fastened can.

In In recent years, the so-called computer-to-plate process has come to a large extent Dimensions Gained 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 data over a so-called platesetter transferred directly to a printing plate precursor become. On-press imaging is a direct-to-plate process (also referred to as direct-to-press method), in which the Picture on the clamped on the plate cylinder of a printing press Plate is exposed. Main advantage of the latter method in comparison for off-press plate making, the improved register is between Printing stations of a multi-color printing machine.

There are two types of such on-press imaging methods. In a first type, a printing plate precursor is mounted in a printing press, imagewise exposed, optionally developed, then used as a printing master, and finally removed from the press and removed, thereby requiring a new plate material for each image. An example of this technology is the well-known GTO-DI model manufactured by Heidelberg, manufactured by Heidelberg Druckmaschinen AG (Germany) and sold individually in US 5,339,737 is described. Disadvantage of this method is that a new plate is required for each printing cycle, which entails an increase in the cost of the printing process.

at a second type of on-press imaging systems will be the same lithographic substrate for several print runs (hereinafter referred to as print cycles) used. Each printing cycle becomes a heat-sensitive or radiation-sensitive one Layer applied to the lithographic substrate to a printing plate precursor and will after imagewise exposure and possibly Development to get a print master. After completion of the printing cycle become the ink-attracting areas of the print master during a Purification step away from the lithographic substrate, whereby a recyclable substrate is obtained in a next cycle of coating, exposure and printing can be used without that a new plate is aufzuspannen on the cylinder. Examples for such Systems with on-press coating and on-press imaging are described in e.g. B.

US 5,188,033 . US 5,713,287 . EP-A 786,337 and EP-A 802 457 , From the latter patent application, a device is known, comprising a pressure element, a means for the uniform coating, an agent for the scanning exposure of the uniformly coated coating according to an image pattern and a means for developing the uniformly coated coating, whereby an image is obtained on the printing element, the image being composed of ink-attracting areas on an ink-repellent background or ink-repellent areas on an ink-attracting background. In a preferred embodiment, the coating contains hydrophobic thermoplastic polymeric particles in a hydrophilic binder.

at the known on-press coating process is a successful one Cleaning of the lithographic substrate is therefore often not achievable because no suitable compromise between on the one hand the chemical Reactivity the cleaning fluid across from the ink-withdrawing areas to be removed and the other required inertia the cleaning fluid across from the brittle one lithographic surface can be found. A typical lithographic surface is both mechanically and chemically very vulnerable. A lithographic surface exists usually from a microporous structure, through which a good differentiation between the spreading properties of the printing ink and the fountain solution is secured. Anodised aluminum plates contain a lithographic surface with one or more metal oxides, on which absorptive phenomena take place can. These metal oxides are particularly susceptible to chemical conversion in forms that no longer have lithographic effectiveness.

Of Further, the above-mentioned microporosity of a lithographic surface is also very vulnerable for mechanical Damage. The presence of solid particles in cleaning fluids, often to achieve a convenient mechanical cleaning the lithographic surface is required, inevitably results in a disorder of Microstructure of the surface. By doing that, ink and applied image-forming layer penetrate the microporous structure, a thorough cleaning is necessary the occurrence of ghosting in the subsequent printing cycles, which an incomplete Removal of the previous image is to be avoided.

The known cleaning fluids contain about it addition usually solvents, the harmful for hoses, pumps and seals are and / or require a very thorough rinse with water, otherwise they would interfere with the coating step in the next printing cycle.

Out U.S. 4,880,555 and 5,203,926 For example, disc cleaning agents are known which are used to correct for artifacts (soiling, fingerprints, scratches) in the non-image areas of a lithographic printing master. However, such cleaning liquids are not able to erase the image areas. In JP-A 61 219044 there is described a wiping liquid containing more than 50% by weight of benzyl alcohol and a small amount of hydrofluoric acid.

SHORT PRESENTATION THE PRESENT INVENTION

task The present invention is a lithographic printing process to provide a cleaning step in which the color attracting areas of a printing master in a more convenient manner can be removed and the substrate is then reused in a next printing cycle can. In particular, a cleaning step is claimed, the due to a low risk of damage to the lithographic surface the substrate is characterized. Another task of the present The invention is to provide a printing method in which a cleaning fluid used is the hardware of the printing press or cleaning device not damaged, especially a liquid, the inert opposite Rubber is, and not a long rinse step after cleaning required.

Be solved the above objects by the method defined in claim 1. The cleaning liquid defined in claim 1 ensures a convenient removal the ink-attracting areas of the printing master defined in claim 1. After several (> 10) Printing cycles with coating, exposure, printing and cleaning are no ghosting to watch. The cleaning fluid does not affect rubber tubes and rubber seals and in the possible rinsing rich small amounts Water.

Further Objects of the present invention will become apparent from the following Description visible.

preferred embodiments the method according to the invention are described in the subclaims.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The in the process according to the invention used cleaning fluid contains an alcohol. Suitable examples of the alcohol are methoxypropanol, Propoxyethanol, 2-butoxyethanol, propanol, 2- (propoxy) -ethanol, Phenoxyethanol, benzyl alcohol, butoxypropanol, ethoxypropanol, 1-isobutoxy-2-propanol, 1-isomethoxy-2-propanol, 1-propoxy-2-propanol, diacetone alcohol, tetrahydrofurfuryl alcohol, Catechol, trimethylolpropane, ethanediol, propanediol and butanediol. Very particular preference is given to 2-butoxyethanol and benzyl alcohol. The alcohol can be a liquid Alcohol that acts as a substantially pure liquid on the print master can be attached. Particularly preferred is the cleaning liquid an aqueous one Solution, which contains an alcohol in an amount between 1% by weight and 20% by weight, particularly preferably between 2% by weight and 10% by weight and very particularly preferably contains between 2 wt .-% and 5 wt .-%.

In a preferred embodiment contains the cleaning fluid also an alkanolamine in a maximum ratio of 20 wt .-%. suitable examples for the alkanolamine are diethanolamine, diethylethanolamine, diisopropanolamine, Monoethanolamine, monoisopropanolamine, triethanolamine, triisopropanolamine, Aminoethoxyethanol, aminoethylaminoethanol, monopropanolamine, methylaminoethanol, Hydroxylamine, N-butylethanolamine, N-ethyldiethanolamine, diglycolamine and dimethylglyoxime. Very particular preference is given to monoethanolamine.

The cleaning fluid contains preferably also a surfactant in an amount of between 0.001% by weight and 5% by weight.

The above cleaning fluids are very suitable for removing the ink-attracting areas of a print master by coating a hydrophilic substrate with a hydrophobic thermoplastic polymer particles and a hydrophilic binder containing casting solution is obtained. The thus obtained Imaging material is negative working, d. H. at exposure hydrophobic areas are formed. These areas form the printing Areas of the master. It is assumed that the applied Heat one Coagulation of the hydrophobic polymer particles triggers, wherein a hydrophobic phase is formed while the hydrophobic polymer Particles unchanged in the non-heated Remain areas. Coagulation can be as a result of softening or melting enter the thermoplastic polymer particles under the action of heat.

The Cleaning fluids according to the invention are able to both the remaining on the printing areas Printing ink as the hydrophobic phase itself, the printing areas their color-attracting properties lends to remove. In a preferred embodiment includes the method according to the invention two cleaning steps: first is an alcohol removing the ink and then a the hydrophobic areas removing alkanolamine on the master appropriate. Furthermore Alcohol and the alkanolamine can still other solvents like an amide, z. Dimethylformamide or 2-N-methylpyrrolidone, be placed on the master, either in admixture with the alcohol or alkanolamine or in a separate purification step.

The used according to the invention Contains imaging material preferably hydrophobic thermoplastic polymer particles having a mean particle size between 40 nm and 2,000 nm, more preferably between 40 nm and 200 nm, to increase the sensitivity and the throughput and foaming to prevent. Furthermore, the polymeric particles preferably have a coagulation temperature of more than 50 ° C and more preferably more than 70 ° C. The coagulation temperature Although the polymeric particles is not subject to any specific upper Limit, but should be enough lower than the decomposition temperature of the polymeric particles. Prefers is a coagulation temperature that is at least 10 ° C below the Decomposition temperature of the polymeric particles is.

preferred examples for thermoplastic hydrophobic polymer particles for use in of the present invention have a Tg of more than 80 ° C. The Weight average molecular weight of the polymers can be between 5,000 and 5,000,000 g / mol vary. Preference is given to polymeric particles from the group consisting of polyvinyl chloride, polyvinylidene chloride, Polyesters, polyurethanes, polyacrylonitrile, polyvinylcarbazole, etc. and copolymers or mixtures thereof. Very particularly preferred Examples are polystyrene and polymethyl methacrylate or copolymers the same.

• – wird das hydrophobe thermoplastische Polymer in einem organischen wasserunmischbaren Lösungsmittel gelöst,
• – wird die so erhaltene Lösung in Wasser oder einem wässrigen Medium dispergiert, und
• – wird das organische Lösungsmittel abgedampft.

The polymeric particles are included as a dispersion in the casting solution and may be prepared according to the methods described in U.S. Pat U.S. Patent 3,476,937 be prepared described methods. In another, particularly suitable for the preparation of an aqueous dispersion of the thermoplastic polymer particles process

• The hydrophobic thermoplastic polymer is dissolved in an organic water-immiscible solvent,
• The solution thus obtained is dispersed in water or an aqueous medium, and
• - The organic solvent is evaporated.

suitable hydrophilic binders for use in the present invention are preferably water-soluble (Co) polymers, for example synthetic homopolymers or copolymers such as 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. Dextran, pullulan, Cellulose, gum arabic, alginic acid, Inulin or chemically modified inulin.

The Casting solution preferably contains anionic, cationic, nonionic or amphoteric surfactants. Perfluoro surfactants are favored. Particular preference is given to nonionic perfluoro surfactants. The surfactants can be used individually or preferably used in combination.

The application ratio of the coating is preferably between 0.3 and 20 g / m ² , more preferably between 0.5 and 5 g / m ² . The amount of hydrophobic thermoplastic polymer particles in the coating is preferably between 50 and 90% by weight, and more preferably between 60 and 80% by weight, based on the total weight of the layer.

The used according to the invention Substrate may be a plastic carrier or a ceramic carrier, however, it is preferably a metal support such as an aluminum support. The Substrate has a hydrophilic surface and is characterized preferably by a roughness value of at least 0.2 μm, particularly preferred at least 0.3 μm, z. B. an electrochemically and / or mechanically grained and anodised aluminum carrier. The substrate may be a sheet-like material, such as a plate, however, the casting solution may as well directly on the then serving as a substrate plate cylinder a Rotary printing press are attached. The lithographic substrate also has a seamless sleeve-shaped pressure plate be, the z. B. is obtained by a plate by means of a laser is soldered into a cylindrical shape. These sleeve-shaped pressure plate can then be pushed around the printing drum, rather than conventional Pressure plate to be clamped in the printing press. More details about sleeve-shaped printing plates can be found in "Graphical Nieuws ", 15, 1995, Pages 4 to 6.

Exposure of the image forming material obtained by applying the above-mentioned coating solution to the lithographic substrate can be effected by direct thermal recording by means of e.g. As a thermal head or by irradiation with high-energy light. In the latter embodiment, the heat-sensitive material preferably contains a compound capable of converting light into heat, preferably a compound having a sufficient absorption in the wavelength range of the light source used for the imagewise exposure. Particularly useful compounds are, for example, dyes, and in particular, infrared-absorbing dyes as described in U.S. Pat EP-A 908 307 and pigments and in particular infrared absorbing pigments such as carbon black, metal carbides, borides, metal nitrides, metal carbonitrides, bronze structure oxides and bronze family related oxides, but without the A component, e.g. B. WO _2.9 . It is also possible to use conductive polymer dispersions, such as conductive polypyrrole or polyaniline-based polymer dispersions. The lithographic performance, and especially the print run stability, depends inter alia on the thermal sensitivity of the imaging material. In this regard, it has been found that very good and favorable results can be achieved with gas black.

The in the process according to the invention applied pictorial exposure is preferably an imagewise scanning exposure using a laser or an LED diode laser. Prefers is the use of one in the infrared or near infrared range, i.e. in the wavelength range between 700 and 1,500 nm, emitting laser. Especially preferred become emitting diodes in the near infrared range.

The printing cycle according to the invention will be further described below with reference to a preferred embodiment. First, a grained and anodized aluminum plate is clamped onto the plate cylinder of a rotary printing press. Subsequently, the above-described casting solution is sprayed on the hydrophilic lithographic surface of the plate to obtain a continuous image-forming layer. Preferred values for the spray parameters are in EP-A 1 084 830 and EP-A 1 084 862 described. The imaging layer is then exposed imagewise, with the exposed areas converted to hydrophobic ink attracting areas and the unexposed areas remaining hydrophilic. The hydrophobic Areas form the printing areas of the master. Subsequently, the print begins by application of printing ink and a fountain solution to the print master. For expedient detachment and removal of the unexposed areas of the coating is preferably during some revolutions of the press ( 10 ) only fountain solution is applied to the plate, after which the supply of the ink starts. After the printing cycle, the lithographic substrate is made recyclable by treatment with a cleaning liquid as described above. Finally, the substrate can be rinsed and dried, after which a new printing cycle can be started by spraying the casting solution onto the recycled substrate.

The Cleaning stage can be carried out in a cleaning unit similar to the one known Blanket cleaning system similar is to be made. According to this embodiment a cloth is preferably wetted with the cleaning liquid and 1 to 50 turns, more preferably 2 to 10 turns long at a contact pressure between 0.1 and 5 Pa and a rotational speed between 2 to 50 m / min. brought into contact with the printing plate. Subsequently become the surface the pressure plate and the cleaning cloth separated and becomes the cloth adjusted until again a dry and clean part of the cloth to disposal stands.

The cleaning fluid can also by spraying, layer by layer application or spin-on of the cleaning fluid be mounted on the lithographic substrate or cloth. The removal of the ink-attracting areas can also be done with a absorbent medium other than a cloth. The cleaning can also by combining the treatment with the cleaning liquid according to the invention with other mechanical wipers such as a rotary brush, through Injecting water or a volatile medium such as air or by means of a solvent or dry ice tablets. The cleaning process may also include a Vakuumabsaugschritt.

The cleaning step is preferably followed by a rinsing step in which water is sprayed onto the substrate. The plate can then be dried with a cloth, z. Using the same blanket cleaning system as described above. The cleaning step preferably comprises only a slight moistening of the lithographic surface, ie no more than 50 ml / m ^{2 of} water are applied to the plate. The rinsing step may be repeated several times, preferably 2 to 5 times.

Preferably find all the steps of the method according to the invention on the press instead of. The lithographic substrate may also be placed on a drum in a suitable coating device clamped (off-press coating) and subsequently for the purpose of its imagewise exposure be mounted in a plate-setter (off-press exposure). After that The printing master thus obtained can be applied to a cylinder of the printing press be clamped and the pressure by supplying ink and fountain solution started. After the printing cycle, the plate can be cleaned as described above, either on the press or in a proper cleaning device, and can the recycled Substrate in a next Pressure cycle can be used again.

EXAMPLES

The explain the following examples the present invention without being limited thereto. All Parts and percentages are in weight, if nothing else is noted.

example 1

manufacturing the lithographic base

A 0.30 mm thick aluminum foil is made by dipping the foil in an aqueous, 5 g / l of sodium hydroxide solution degreased at 50 ° C and demineralized Water rinsed. The film is then heated at a temperature of 35 ° C and a current density of 1,200 A / m2 in an aqueous Solution, the 4 g / l hydrochloric acid, 4 g / l of hydrobromic acid and 5 g / l of aluminum ions, electrochemically grained with alternating current to obtain a surface topography having an arithmetic mean roughness Ra of 0.5 μm.

To flush with demineralized water, the aluminum foil with a aqueous, 300 g / l sulfuric acid containing solution 180 s at 60 ° C etched and subsequently 30 s at 25 ° C rinsed with demineralised water.

Subsequently, the film is at a temperature of 45 ° C, a voltage of 10 V and a current density of 150 A / m ^{2 for} 300 s in an aqueous solution containing 200 g / l sulfuric acid to obtain an anodic oxidation foil containing 3.0 g / m ² Al ₂ O ₃ , then washed with demineralised water, then first post-processed with a solution containing polyvinylphosphonic acid and then with a solution containing aluminum trichloride, then rinsed with demineralized water at 20 ° C. for 120 s and dried.

Applying the casting solution

A 2.61% by weight aqueous solution is prepared by adding a polystyrene latex, Dye I and a hydrophilic binder. After spraying and drying, the layer thus obtained contains 75% by weight of the polystyrene latex, 10% by weight of the dye I and 15% by weight of Glascol E 15 ^TM . Glascol E 15 is a polyacrylic acid available from NV Allied Colloids Belgium.

Dye I has the following structure

Preparation of the imaging material

The abovementioned aluminum substrate is heated to a line speed of 164 m / min. rotating drum clamped. The above solution is sprayed onto the substrate by means of a SUJ1 compressed air spray nozzle from Spraying Systems Belgium (Brussels). The spray nozzle is fixed at a distance of 80 mm to the substrate and the flow rate of the spray solution is adjusted to 7 ml / min. set. During spraying, the spray nozzle moves at a speed of 1.5 m / min. and an air pressure of 7.58 × 10 ⁵ Pa is generated in the spray head. The applied layer is dried by means of hot air (70 ° C).

printing step

The Imaging material is processed at a resolution of 2,400 dpi, a rotational speed 150ppm and 15.5 watts in a Creo 324 4 external drum imagesetter imaged. The imaged plates are made using K + E 800 Skinnex as printing ink and Rotamatic fountain solution for one print run of 5,000 copies in one print cycle on a GTO 46 press used. The print quality is excellent.

Recyclable Make of the lithographic substrate

The plate is mounted on a drum of a cleaning unit comparable to a typical blanket cleaning system. A cloth is filled with an aqueous, 2.5% 2-butoxyethanol Cleaning liquid moistened. For cleaning, the cloth is held in contact with the printing plate for 5 drum rotations at a pressure of 9 × 10 ⁴ Pa. The cloth rotates at a speed of 20 m / min, based on the plate. Subsequently, 30 ml / m ^{2 of} water are sprayed onto the printing plate as a rinsing liquid, after which the moistened plate is brought into contact with a dry and clean part of the cloth (the settings are the same as in the cleaning step, contact time: 1 turn). The rinse step is repeated 4 times.

Example 2

In Example 2 is repeated as in Example 1, but with the difference that the cleaning fluid 2.5% 2-butoxyethanol and 3% ethanolamine.

Example 3

In Example 3 is repeated as in Example 1, but with the difference that two purification steps are performed. In a first Step becomes a watery, 2.5% 2-butoxyethanol-containing solution and in a second step a watery, 3% ethanolamine containing solution used. A single rinse step enough.

Results

Of the mentioned above Cycle of spray coating, Imaging, pressure, cleaning, rinsing and drying will be 10 times for each of the three above-defined cleaning liquids repeated. To every cycle, the cleanliness of the plate, the coating quality and the print quality (Staining, occurrence of ghosting) visually evaluated. With each of the above-described cleaning liquids for all these Criteria obtained excellent results.

The chemical reactivity the above cleaning fluids across from Gum of the frequently in Blanket cleaning systems used EPDM type (a terpolymer from ethylene, propylene and a non-conjugated diene) is tested. After 24 hours Dipping the rubber in the cleaning fluid will cause the (as a result Swelling caused) weight gain of the rubber measured. In the The cleaning fluids used in Examples 1, 2 and 3 cause a weight gain of at most 0.12%, which is considered acceptable is looked at.

Claims (12)

A marked by the following steps lithographic direct-to-plate printing process with one again utilizable substrate with a hydrophilic surface (A) Preparation of a negative-working image-forming material Application of a hydrophobic thermoplastic particles and a hydrophilic Binding containing casting solution the hydrophilic surface, (B) Production of a printing master with ink-attracting areas pictorial exposure the image-forming material, (c) application of printing ink and Dampening water on the pressure master, (d) removal of all color attracting Areas of the print master by application of an aqueous solution that is between 1 and 20 Wt .-% of an alcohol. Method according to claim 1, characterized in that that the watery solution further contains an alkanolamine. Method according to claim 2, characterized in that that the watery solution the alkanolamine in a maximum amount of 20% by weight. Method according to claim 2 or 3, comprising two purification steps includes, initially the alcohol and then the alkanolamine is applied to the print master. Method according to one of the preceding claims, which further comprising a step (e), in which the substrate with Water rinsed becomes. A method according to claim 5, characterized in that during step (e) water in an amount of not more than 50 ml / m ^{2 is} sprayed onto the substrate. Method according to one of the preceding claims, characterized characterized in that the pressure master during step (d) by means of mechanical Means such as a cloth or a rotary brush or by spraying Water or a volatile Medium is wiped. Method according to one of the preceding claims, characterized characterized in that the alcohol is benzyl alcohol or 2-butoxyethanol is. Method according to one of the preceding claims, characterized characterized in that the alkanolamine is ethanolamine. Method according to one of the preceding claims, characterized in that the substrate is a plate cylinder of a rotary printing press or a clamped on a plate cylinder of a rotary printing press Plate or sleeve-shaped plate is. Method according to one of the preceding claims, characterized characterized in that the casting solution or the cleaning fluid sprayed onto the substrate become. Use of between 1 and 20 wt .-% of a Alcohol and preferably also containing an alkanolamine aqueous solution to remove all inking areas of a lithographic printing master.