EP0034324B1 - Process for the preservation of flatbed printing formes in their developed state for printing - Google Patents

Abstract

This invention relates to an improved process for preserving a planographic printing form which is ready for printing. In the process, the planographic printing form is treated with an aqueous solution of a water-soluble, film-forming high-molecular weight organic compound and a hydrophilizing acid and is then dried. The hydrophilizing acid used is an organic phosphonic acid, in particular polyvinyl phosphonic acid, preferably in a concentration from 0.05 to 10 percent by weight. As the water-soluble, high-molecular weight organic compound gum arabic, dextrin or polyvinyl alcohol is appropriately used.

Description

The invention relates to a method for preserving ready-to-print planographic printing forms in order to protect the plates during storage from being used for printing against the ingress of air and dirt and at the same time to permanently hydrophilize their non-printing surface areas.

It is known that ready-to-print planographic printing plates have to be subjected to such a protective treatment before each prolonged storage. Aqueous gum arabic solution is very widely used as the treatment solution. It is also known to use dextrin solutions.

DE-A 26 59 754 describes the use of aqueous polyvinyl alcohol solutions for the same purpose.

DE-A 25 04 594 also discloses the combination of carboxyl-containing acrylamide polymers with acids, in particular phosphoric acid, as hydrophilizing agents and for the preservation of printing forms.

The known preservatives normally have an effect which is sufficient for many carrier materials. However, it was found that this protective film applied afterwards was not always sufficient to prevent sound from occurring during the printing process. As a rule, special care must be taken in printing forms with anodically oxidized aluminum as the carrier material in order to prevent oleophilic contamination of the carrier surface exposed by development, e.g. B. by dust or dirt particles or by fingerprints, before preservation, since such contaminants are usually only difficult to remove without attacking the print layer or the carrier surface. Such contamination can easily occur not only in the time between development and preservation, but also during development or during the manufacture of the printing plate by self-coating.

FR-A 2 350 209 also mentions dextrins as a water-soluble film-forming component in preservative treatment solutions for printing forms, but apart from that they contain not only water as a solvent, but also also a petroleum fraction, glycerin and a surfactant.

DE-B 11 21 632 names aqueous solutions of vinyl or polyvinylphosphonic acid, which may additionally contain, for example, dextrins or vegetable gums, but these are used as dampening agents or cleaning agents. Dampening solutions (fountain solution) are used in addition to the ink during the actual printing process to print from offset printing forms. In concentrated form, these dampening solutions are also intended to clean the metallic non-image areas on greasy or oily areas. In this application, however, in contrast to the method according to the invention, the printing forms should not be protected against air ingress and dirt during prolonged storage and before printing, and at the same time should be permanently hydrophilized in the non-image areas.

The older, non-prepublished EP-A 0 012 956 describes a cleaning process for photosensitive layers which have been baked after development (ie heated to a temperature of above 180 ° C.) and contain positive-working, o-quinonediazides, and which are used for removal during baking precipitation created in the non-image areas. For this purpose, an aqueous solution is used which has a content of 0.01 to 50% by weight of polyvinylphosphonic acid and, if additional preservation is desired, additionally has gum arabic or polyvinyl alcohol. Planographic printing forms treated in this way are expressly excluded in the process according to the invention (“disclaimer”).

The object of the invention is to provide a preservation method which allows the image background of planographic printing plates not only to be protected against later contamination, but also to be freed from existing smaller oleophilic contaminants.

The invention relates to a process for preserving ready-to-print planographic printing plates with a carrier material based on aluminum, in which the planographic printing plate is treated with an aqueous solution of a water-soluble film-forming high-molecular organic compound and a hydrophilizing acid and is dried after this treatment.

The process according to the invention is characterized in that an organic phosphonic acid is used as the hydrophilizing acid, with the exception of the planographic printing plates characterized above according to EP-A 0 012 956.

The invention ensures that a clean, toneless background is obtained when printing, even if this background already contained oleophilic contaminants on the plate before preservation.

Suitable organic phosphonic acids are aromatic, heterocyclic, aliphatic and cycloaliphatic low and high molecular weight phosphonic acids and their derivatives.

Examples are vinylphosphonic acid, polyvinylphosphonic acid, 2-phosphono-ethane-1-sulfonic acid, 3,3-diphosphono-pimelic acid, vinylphosphonic acid monomethyl ester, 4-chlorophenylphosphonic acid, 4-chloro-3-nitro-phenylphosphonic acid, β-styrylphosphonic acid and water-soluble copolymers of vinylphosphonic acid with acrylic acid and / or vinyl acetate. Polyvinylphosphonic acid is particularly preferred.

The concentration of the phosphonic acid in the preservation solution is generally 0.05 to 10, preferably 0.1-5% by weight, based on the total content of the solution.

As water-soluble film-forming high-molecular organic compounds, all such substances are generally suitable, which are usually used as components of preservation solutions for planographic printing forms. Suitable examples are gum arabic, dextrins and polyvinyl alcohol. The concentration of the high molecular weight compounds is generally between 4 and 40, preferably between 5 and 35% by weight.

The preservation solution can be applied to the plate surface by hand rubbing or tamponing, by dipping in a bath, or in a processing device by rolling, spraying, or the like. The plate surface is then dried.

Aluminum is used as the carrier material for the printing forms to be treated. In particular, the known and preferably used carrier materials with a refined surface come into consideration, for. B. mechanically, chemically or electrochemically roughened and optionally treated with alkali silicates, polymeric acids or other known agents aluminum. In particular, the solution is suitable for the treatment of printing plates with supports made of anodically oxidized aluminum, the oxide layer also being treated with the above-mentioned agents, e.g. B. silicates, can be pretreated.

The printing image parts of the printing form can be produced in any known manner. As a rule, this is done by exposing a light-sensitive layer and developing with a developer solution. Imaging can also be done electrophotographically by charging, exposing, concreting and fixing a photoconductor layer. In any case, the nature of the carrier surface exposed during development and to be hydrophilized is of greater importance for the effectiveness of the treatment solution than the nature and the manner in which the printing layer is produced. Preference is given to the photosensitive layers generally used for planographic printing, based on positive or negative working diazo compounds, of azido compounds, light-crosslinkable polymers or photopolymerizable systems, and the photoconductor layers based on organic photoconductors and binders.

Suitable positive-working light-sensitive layers can contain, as light-sensitive components, o-quinonediazides or combinations of photolytic acid generators and acid-cleavable acetal or orthocarboxylic acid compounds. Such layers preferably contain water-insoluble binders soluble in aqueous alkali, e.g. B. phenolic resins. Suitable layers are described in DE-C 938 233, 195 166 and 26 10 842 and DE-A 23 31 377, 27 42 631, 28 28 037, 27 18 254 and 29 28 636. However, the baked-in layers containing o-quinonediazides described in EP-A 0 012 956 are excluded.

As negative working layers, those based on diazonium salt condensation products, p-quinonediazides or photopolymerizable mixtures are preferably used. Suitable materials of this type are described in the following publications: DE-C 1 104 824.1 134 093.1 214 086, 20 27 467, DE-A 20 24 244, 20 34 655, 27 39 774 and 28 22 887.

Organic photoconductors are preferably used as photoconductors, for example those as described in DE-C 11 20 875 or DE-B 25 26 720. Suitable binders in the photoconductor layer are preferably those which are insoluble in water and soluble in aqueous alkaline solutions. Copolymers containing carboxyl groups are particularly preferred. The production of suitable electrophotographic materials and their processing into printing forms is described in the publications mentioned above.

The following examples illustrate preferred embodiments of the method according to the invention. Unless otherwise stated, percentages and ratios are to be understood in weight units. Parts by weight (Gt) and parts by volume (Vt) are in the ratio of g to ccm.

example 1

beschichtet und getrocknet. Das erhaltene lichtempfindliche Material wurde unter einem 21-stufigen Stufenkeil mit Dichteinkrementen von 0,15 so belichtet, daß die Stufe 9 voll gedeckt war. Es wurde mit einer 5 %igen wäßrigen Natriummetasilikatlösung entwickelt.An electrochemically roughened and anodized aluminum foil was coated with a solution of

coated and dried. The light-sensitive material obtained was exposed under a 21-step wedge with density increments of 0.15 so that step 9 was fully covered. It was developed with a 5% aqueous sodium metasilicate solution.

• 16 Gt Polyvinylalkohol mit einer Viskosität von 4 mPa - s in 4 %iger wäßriger Lösung bei 20 °C und einem Restacetylgehalt von 10,7 %,
• 14 Gt gelbes Kartoffeldextrin, vollständig wasserlöslich, Ostwald-Viskosität = 2,80 bei 20 °C in 4 %iger wäßriger Lösung ; pH-Wert 2,8 und
• 9 Gt Polyvinylphosphonsäure in 261 Gt Wasser

überwischt und nach dieser Behandlung getrocknet. Die hierbei aufgetragene Schicht hatte ein Gewicht von ungefähr 1 g/m². In der Druckmaschine wurden tonfreie Drucke erhalten, auch wenn zuvor oleophile Verunreinigungen auf die trockene Platte gelangt waren.This plate was then covered with a solution of the following composition

• 16 pbw of polyvinyl alcohol with a viscosity of 4 mPa.s in a 4% strength aqueous solution at 20 ° C. and a residual acetyl content of 10.7%,
• 14 pbw of yellow potato dextrin, completely water-soluble, Ostwald viscosity = 2.80 at 20 ° C in 4% aqueous solution; pH 2.8 and
• 9 pbw of polyvinylphosphonic acid in 261 pbw of water

wiped and dried after this treatment. The layer applied here had a weight of approximately 1 g / m ² . Toneless prints were obtained in the printing press, even if oleophilic contaminants had previously got onto the dry plate.

Example 2

• 0,7 Gt eines Polykondensationsprodukts, hergestellt aus 1 Mol 3-Methoxy-diphenylamin-4-diazo- niumsulfat und 1 Mol 4,4'-Bis-methoxymethyldiphenylether in 85 %iger Phosphorsäure, isoliert als Mesitylensulfonat,
• 3,4 Gt 85 %iger Phosphorsäure und
• 3,0 Gt des Reaktionsproduktes aus einem Epoxidharz vom Schmelzpunkt 70 °C und dem EpoxidÄquivalentgewicht 459 mit Salzsäure in Ethylenglykol (vgl. DE-A 20 34 654) in
  
  beschichtet und getrocknet. Das lichtempfindliche Material wurde bildmäßig belichtet und mit einer Lösung von
  
  entwickelt. Die fertige Platte wurde dann mit einer Lösung von
  
  überwischt und nach dieser Behandlung getrocknet. Es wurden tonfreie Drucke erhalten, auch wenn die Platte mit feuchten unsauberen Händen gehandhabt worden war.

An aluminum foil roughened by brushing with an abrasive suspension was immersed in a 60 ° C. bath of 0.3% polyvinylphosphonic acid in water for one minute and dried. She was then provided with a solution by

• 0.7 pbw of a polycondensation product, prepared from 1 mol of 3-methoxy-diphenylamine-4-diazonium sulfate and 1 mol of 4,4'-bis-methoxymethyldiphenyl ether in 85% phosphoric acid, isolated as mesitylene sulfonate,
• 3.4 pbw of 85% phosphoric acid and
• 3.0 pbw of the reaction product from an epoxy resin with a melting point of 70 ° C. and the epoxy equivalent weight 459 with hydrochloric acid in ethylene glycol (cf. DE-A 20 34 654) in
  
  coated and dried. The light-sensitive material was exposed imagewise and with a solution of
  
  developed. The finished plate was then covered with a solution of
  
  wiped and dried after this treatment. Tint-free prints were obtained even if the plate was handled with damp, unclean hands.

A similar result was obtained when electrochemically roughened, anodically oxidized aluminum was used as the carrier material and the procedure was otherwise the same.

Example 3

aufgebracht und zu einer gleichmäßigen Photoleiterschicht mit einem Gewicht von 5 g/m² getrocknet.A solution of. Was placed on a 300 J.Lm thick substrate made of electrolytically roughened and anodized aluminum

applied and dried to a uniform photoconductor layer with a weight of 5 g / m ² .

The plate was charged with a corona to approximately - 450 V and exposed in a repro camera with 8 autophot lamps of 500 W each for 25 seconds.

entwickelt, und das Tonerbild wurde durch kurzes Erwärmen auf etwa 170-180 °C fixiert. An den Nichtbildstellen wurde die Photoleiterschicht durch Behandeln mit einer Lösung aus

und Abspülen mit Wasser entfernt.The resulting charge image was made with a toner powder

was developed, and the toner image was fixed to about 170-180 ° C by brief heating. At the non-image areas, the photoconductor layer was removed by treatment with a solution

and rinsed with water removed.

gleichmäßig beschichtet und nach dieser Behandlung getrocknet.The plate was scraped off and then preserved with a solution of

evenly coated and dried after this treatment.

With the printing form treated in this way, tone-free prints were obtained, even if the background had been contaminated by fingerprints or otherwise before or after preservation.

Similar results were obtained when 5 pbw of 3,3-diphosphonopimelic acid were used in the preservation solution instead of 0.5 pbw of polyvinylphosphonic acid.

Example 4

An electrolytically roughened and anodized aluminum foil was coated with the following solution and dried:

entwickelt. Auf die fertige Druckplatte wurde die in Beispiel 1 angegebene Konservierungslösung aufgetragen und nach dieser Behandlung getrocknet. Es wurden ähnlich gute Ergebnisse erhalten.The photopolymerizable layer was exposed imagewise and with a solution of

developed. The preservation solution specified in Example 1 was applied to the finished printing plate and dried after this treatment. Similar good results were obtained.

Claims (4)

1. A process for preserving planographic printing formes which are ready for printing, by treating the planographic printing forme with an aqueous solution of a water-soluble, film-forming, high-molecular weight organic compound and a hydrophilizing acid and drying it, characterized in that an organic phosphonic acid is used as the hydrophilizing acid.

2. A process as claimed in claim 1, wherein the organic phosphonic acid comprises polyvinyl phosphonic acid.

3. A process as claimed in claim 1, wherein the organic phosphonic acid is employed in a concentration ranging from 0.05 to 10 percent by weight.

4. A process as claimed in claim 1, wherein the watersoluble, high-molecular weight organic compound comprises gum arabic, dextrin or polyvinyl alcohol.