EP0268058B1 - Process for the electrochemical graining of aluminum or its alloys for supports for printing plates - Google Patents

Description

The invention relates to a process for the production of plate, foil or strip-shaped aluminum or its alloys as a carrier material for printing plates, in which firstly mechanically and subsequently electrochemically in a nitrate-containing electrolyte is roughened with direct current.

Printing plates, with this term are meant offset printing plates in the context of the present invention, generally consist of a support and at least one radiation (light)-sensitive reproduction layer arranged on it, this layer either from the consumer (in the case of non-precoated plates) or from industrial manufacturer (for pre-coated boards) is applied to the substrate.

Aluminum or one of its alloys has established itself as a layer material in the printing plate field. In principle, these substrates can also be used without a modifying pretreatment, but they are generally modified in or on the surface, for example by mechanical, chemical and / or electrochemical roughening (sometimes called grain or etching in the relevant literature), a chemical one or electrochemical oxidation and / or treatment with hydrophilizing agents.

In the modern, continuously operating high-speed systems of the manufacturers of printing plate supports and / or precoated printing plates, a combination of the above-mentioned modification types is often used, in particular a combination of electrochemical roughening and anodic oxidation, optionally with a subsequent hydrophilization step.

The roughening is carried out, for example, in aqueous acids such as aqueous HCl or HNO₃ solutions or in aqueous salt solutions such as aqueous NaCl or Al (NO₃) ₃ solutions using alternating current. The roughness depths that can be achieved in this way (given, for example, as the mean roughness depths R _z ) of the roughened surface are in the range from about 1 to 15 μm, in particular in the range from 2 to 8 μm. The roughness depth is determined in accordance with DIN 4768 (as of October 1970). The roughness depth R _z is then the arithmetic mean of the individual roughness depths of five adjacent individual measurement sections.

The roughening is carried out, inter alia, in order to improve the adhesion of the reproduction layer on the substrate and the water flow of the printing plate resulting from the printing plate by irradiation (exposure) and development. By irradiation and development (or decoating in the case of reproductive layers working electrophotographically), the image points which carry color during later printing and the non-image points which carry water (generally the exposed carrier surface), which creates the actual printing form. Very different parameters have an influence on the later topography of the roughened aluminum surface. For example, the following references provide information:

In the article "The Alternating Current Etching of Aluminum Lithographic Sheet" by AJ Dowell in Transactions of the Institute of Metal Finishing, 1979, Vol. 57, pp. 138 to 144, basic explanations are given on the roughening of aluminum in aqueous hydrochloric acid solutions, the following process parameters varied and the corresponding effects were examined. The electrolyte composition is changed with repeated use of the electrolyte, for example with regard to the H⁺ (H₃O⁺) ion concentration (measurable via the pH) and the Al³⁺ ion concentration, with effects on the surface topography being observed. The temperature variation between 16 ° C and 90 ° C shows a changing influence only from about 50 ° C, which is expressed, for example, by the sharp decline in the formation of layers on the surface. The roughening time change between 2 and 25 min also leads to an increasing metal dissolution with increasing exposure time. The variation of the current density between 2 and 8 A / dm² results in higher roughness values with increasing current density. If the acid concentration is in the range 0.17 to 3.3% of HCl, then only insignificant changes in the hole structure occur between 0.5 and 2% of HCl, below 0.5% of HCl there is only a local attack on the surface and at the high values an irregular dissolution of aluminum takes place.

The use of hydrochloric acid or nitric acid as an electrolyte for roughening aluminum substrates can therefore be assumed to be known. A uniform grain size can be obtained which is suitable for lithographic plates and is within a useful roughness range. In pure nitric acid electrolytes, the setting of a flat and uniform surface topography is difficult, and it is necessary to maintain the operating conditions within very narrow limits.

• die DE-A 22 50 275 (= GB-A 1 400 918) nennt als Elektrolyten bei der Wechselstrom-Aufrauhung von Aluminium für Druckplattenträger wäßrige Lösungen eines Gehalts von 1,0 bis 1,5 Gew.-% an HNO₃ oder von 0,4 bis 0,6 Gew.-% an HCl und gegebenenfalls 0,4 bis 0,6 Gew.-% an H₃PO₄,
• die DE-A 28 10 308 (= US-A 4 072 589) nennt als Elektrolyten bei der Wechselstrom-Aufrauhung von Aluminium wäßrige Lösungen eines Gehalts von 0,2 bis 1,0 Gew.-% an HCl und O,8 bis 6,O Gew.-% an HNO₃.

The influence of the composition of the electrolyte on the roughening quality is also described, for example, in the following publications:

• DE-A 22 50 275 (= GB-A 1 400 918) names as electrolytes in the AC roughening of aluminum for printing plate supports aqueous solutions with a content of 1.0 to 1.5% by weight of HNO₃ or 0, 4 to 0.6% by weight of HCl and optionally 0.4 to 0.6% by weight of H₃PO₄,
• DE-A 28 10 308 (= US-A 4 072 589) mentions aqueous solutions with a content of 0.2 to 1.0% by weight of HCl and O.8 to 6 as electrolytes in the AC roughening of aluminum , O wt .-% of HNO₃.

• die DE-A 28 16 307 (= US-A 4 172 772) den Zusatz von Monocarboxysäuren, wie Essigsäure zu Salzsäureelektrolyten,
• die US-A 3 963 594 von Gluconsäure,
• die EP-A 0 036 672 von Citronen- und Malonsäure und
• die US-A 4 052 275 von Weinsäure.

Additions to the HCl electrolyte have the task of preventing an adverse local attack in the form of deep holes. So describes

• DE-A 28 16 307 (= US-A 4 172 772) the addition of monocarboxy acids, such as acetic acid to hydrochloric acid electrolytes,
• US Pat. No. 3,963,594 to gluconic acid,
• EP-A 0 036 672 of citric and malonic acid and
• U.S. 4,052,275 to tartaric acid.

All these organic electrolyte components have the disadvantage that they are electrochemically unstable and decompose at high current loads (voltage).

Inhibiting additives, as described in US Pat. No. 3,887,447 with phosphoric and chromic acid, in DE-A 25 35 142 (= US Pat. No. 3,980,539) with boric acid, have the disadvantage that the protective action frequently breaks down locally and there can be individual, particularly pronounced scars.

JP application 91 334/78 describes AC roughening in a combination of hydrochloric acid and an alkali halide to produce a lithographic base material.

DE-A 16 21 115 (= US-A 3 632 486 and US-A 3 766 043) describes direct current roughening in dilute hydrofluoric acid, the strip being switched as a cathode.

DE-C 120 061 describes a treatment for producing a water-attracting layer by using electricity, which can also take place in hydrofluoric acid.

• der Einsatz von Wechselstrom, bei dem die Anodenspannung und der anodische coulombische Eingang größer als die Kathodenspannung und der kathodische coulombische Eingang sind, gemäß der DE-A 26 50 762 (= US-A 4 087 341), wobei im allgemeinen die anodische Halbperiodenzeit des Wechselstroms geringer als die kathodische Halbperiodenzeit eingestellt wird; auf diese Methode wird beispielsweise auch in der DE-A 29 12 060 (= US-A 4 301 229), der DE-A 30 12 135 (= GB-A 2 047 274) oder der DE-A 30 30 815 (= US-A 4 272 342) hingewiesen,
• der Einsatz von Wechselstrom, bei dem die Anodenspannung deutlich gegenüber der Kathodenspannung erhöht wird, gemäß der DE-A 14 46 026 (= US-A 3 193 485),
• die Unterbrechung des Stromflusses während 10 bis 120 sec und ein Stromfluß während 30 bis 300 sec, wobei Wechselstrom und als Elektrolyt eine wäßrige 0,75 bis 2 n HCl-Lösung mit NaCl- oder MgCl₂-Zusatz eingesetzt werden, gemäß der GB-A 879 768. Ein ähnliches Verfahren mit einer Unterbrechung des Stromflusses in der Anoden-  oder Kathodenphase nennt auch die DE-A 30 20 420 (= US-A 4 294 672).

Another known possibility of improving the uniformity of the electrochemical roughening is to modify the current form used, these include, for example

• the use of alternating current, in which the anode voltage and the anodic coulombic input are greater than the cathode voltage and the cathodic coulombic input, according to DE-A 26 50 762 (= US-A 4 087 341), the anodic half-period of the AC is set less than the cathodic half-period; this method is also used, for example, in DE-A 29 12 060 (= US-A 4 301 229), DE-A 30 12 135 (= GB-A 2 047 274) or DE-A 30 30 815 (= US-A 4,272,342),
• the use of alternating current, in which the anode voltage is significantly increased compared to the cathode voltage, according to DE-A 14 46 026 (= US-A 3 193 485),
• the interruption of the current flow for 10 to 120 sec and a current flow for 30 to 300 sec, alternating current and an aqueous 0.75 to 2 N HCl solution with NaCl or MgCl₂ addition being used as electrolyte, according to GB-A 879 768. A similar procedure with an interruption of the current flow in the anode or cathode phase, the DE-A 30 20 420 (= US-A 4 294 672).

The methods mentioned can lead to relatively uniformly roughened aluminum surfaces, but they sometimes require a relatively large amount of equipment and can only be used within very narrow parameter limits.

Another method known from the patent literature is the combination of two roughening methods.

So describe US-A 3 929 591, GB-A 1 582 620, JP-A 123 204/78, DE-A 30 31 764 (= GB-A 2 058 136), DE-A 30 36 174 (= GB -A 2 060 923), EP-A 0 131 926, DE-A 30 12 135 (= GB-A 2 047 274) and JP-B 16 918/82 in different versions the combination of a pre-structuring which takes place mechanically in the first step , which is followed by an electrochemical roughening with optionally modified alternating current in electrolytes containing hydrochloric acid or nitric acid, after a chemical cleaning (pickling), if appropriate, a further cleaning step then being able to take place.

All of the above-mentioned applications use the advantage of double roughening, which is in particular a power saving, but use alternating current in the second stage.

From EP-A 0 131 926 a process for the production of plate, foil or band-shaped aluminum or its alloys as a carrier material for printing plates is known, in which first mechanical roughening and then electrochemical roughening in a 0.1 to 10 wt % Electrolyte containing nitric acid is carried out, the electrochemical roughening being carried out with direct current. After mechanical roughening, an alkaline etching is carried out with a sodium or potassium hydroxide solution. Furthermore, an alkaline treatment with an aqueous sodium hydroxide solution is carried out after the electrochemical roughening. It is then anodized in sulfuric acid, phosphoric acid or a mixture thereof until an oxide layer of 0.1 to 10 g / m² is formed.

US-A-2,344,510 describes the use of a direct current roughening in an electrolyte containing hydrochloric acid, which follows a mechanical roughening as the second roughening.

The object of the present invention is to provide a method for the electrochemical roughening of aluminum for printing plate supports with direct current, which provides a uniform, scar-free and area-wide roughening structure without having to maintain a large outlay on equipment and / or particularly narrow parameter limits and in terms of energy is saved.

The finished printing plates should have a high print run and low wiping water consumption.

This object is achieved in that solutions of alkali metal, alkaline earth metal, ammonium or aluminum nitrate and / or mixtures thereof and / or mixtures with nitric acid are used as the nitrate-containing electrolyte and that the concentration of the nitrate compound is from 1.0 g / l to is set to the saturation limit.

In an embodiment of the method, the concentration of the nitrate compound is adjusted from greater than 100 g / l to the saturation limit.

It is preferred to roughen with a direct current of 1 to 300 A / dm² and a charge of 1 to 400 C / dm², in particular with a direct current of 10 to 100 A / dm² and a charge of 10 to 200 C / dm². Electrochemical roughening is carried out for a time of 1 to 300 s, in particular 2 to 60 s. In the process, in addition to mechanical and / or electrochemical roughening, an alkaline cleaning step and anodization are carried out in such a way that the cleaning is carried out by acids or alkalis or by hydroxyl ions generated in the electrolytic bath during electrochemical roughening.

With the process, surfaces of the printing plate supports that are excellently suitable for lithographic applications are obtained, which, in addition to the energy saving due to the special shape and arrangement of the micropores, bring with them the advantages of a reduction in water consumption and increased circulation stability. These advantages can be achieved neither by using alternating current in systems containing hydrochloric or nitric acid, nor by using direct current in hydrochloric acid described in US Pat. No. 2,344,510 (see comparative examples V1 to V5).

Alternating current in nitric acid electrolytes leads to largely deposit-free surfaces, while the process according to the invention with direct current in the weakly corrosive, nitrate-containing electrolyte during the electrochemical step creates a protective whitish deposit in the pores, which can favorably influence the roughening process. Obviously, the action of more corrosive chloride ions when using DC leads to other carrier structures that are not so suitable for modern lithographic printing plates.

Electrochemical roughening with direct current takes place at a temperature of 20 to 80 ° C.

In an embodiment of the method, the mechanical roughening is carried out with a wet abrasive as a wet brush, but other mechanical methods, such as dry brushing, sandblasting, spherical grain, embossing and similar methods can also be used for the mechanical pre-structuring.

After the roughening steps, the sheet is preferably cleaned by an etching step with metal removal. This etching step (pickling) can be carried out either with acids or alkalis or by means of aggressive agents generated electrochemically in the bath, for example by generating cathodic hydroxyl ions.

In a preferred embodiment, a nitrate electrolyte is used, the concentration of the nitrate compound being between 1.0 g / l and the saturation limit, particularly preferably between 5.0 g / l and 100.0 g / l. Aluminum nitrate and / or nitric acid and / or sodium nitrate is used as the preferred compound containing nitrate ions. Combinations of other compounds containing nitrate ions are of course also within the scope of the invention.

It has proven to be particularly advantageous if aluminum salts are added to the electrolyte, preferably in an amount of 20 to 150 g / l.

As a direct current, a current density of 1 to 300 A / dm², preferably 10 to 100 A / dm², is used for the plate, which is preferably connected as an anode, so that a charge of 1 to 400 C / dm², preferably 10 to 200 C / dm², flows.

The current density used is less critical than the total amount of charge.

The result of a surface produced by the method according to the invention is a very uniform support surface with excellent lithographic properties that can be varied over a wide roughness depth range (R _z = 2 to 7 μm).

The process according to the invention is carried out either discontinuously or preferably continuously with strips made of aluminum or its alloys. In general, the process parameters in continuous processes during electrochemical roughening lie in the following ranges: the temperature of the electrolyte between 20 and 80 ° C, the current density between 1 and 300 A / dm², the residence time of a material point to be roughened in the electrolyte between 1 and 300 s, preferably between 2 and 60 s, and the electrolyte flow rate at the surface of the material to be roughened between 5 and 1000 cm / s. In discontinuous processes, the required current densities tend to be in the lower part and the dwell times are in the upper part of the ranges specified, the flow of the electrolyte can also be dispensed with.

In addition to pure direct current, pulsed, corrugated and differently shaped direct currents can also be used as long as the plate does not change polarity during the entire roughening process.

• "Reinaluminium" (DIN-Werkstoff Nr. 3.0255), d. h. bestehend aus mehr als 99,5 % Al und den folgenden zulässigen Beimengungen von (maximale Summe von 0,5 %) 0,3 % Si, 0,4 % Fe, 0,03 % Ti, 0,02 % Cu, 0,07 % Zn und 0,03 % Sonstigem, oder
• "Al-Legierung 3003" (vergleichbar mit DIN-Werkstoff Nr. 3.0515), d. h. bestehend aus mehr als 98,5 % Al, den Legierungsbestandteilen 0 bis 0,3 % Mg und 0,8 bis 1,5 % Mn und den folgenden zulässigen Beimengungen von 0,5 % Si, 0,5 % Fe, 0,2 % Ti, 0,2 % Zn, 0,1 % Cu und 0,15 % Sonstigem.

In the process according to the invention, the following can be used as materials to be roughened, for example, which are either in the form of a plate, film or tape:

• "Pure aluminum" (DIN material no. 3.0255), ie consisting of more than 99.5% Al and the following admissible admixtures of (maximum sum of 0.5%) 0.3% Si, 0.4% Fe, 0 , 03% Ti, 0.02% Cu, 0.07% Zn and 0.03% other, or
• "Al alloy 3003" (comparable to DIN material no. 3.0515), ie consisting of more than 98.5% Al, the alloy components 0 to 0.3% Mg and 0.8 to 1.5% Mn and the following admissible admixtures of 0.5% Si, 0.5% Fe, 0.2% Ti, 0.2% Zn, 0.1% Cu and 0.15% other.

However, the method according to the invention can also be applied to other aluminum alloys.

• Das Gleichstrom-Schwefelsäure-Verfahren, bei dem in einem wäßrigen Elektrolyten aus üblicherweise ca. 230 g H₂SO₄ pro 1 Liter Lösung bei 10 bis 22 °C und einer Stromdichte von 0,5 bis 2,5 A/dm² während 10 bis 60 min anodisch oxidiert wird. Die Schwefelsäurekonzentration in der wäßrigen Elektrolytlösung kann dabei auch bis auf 8 bis 10 Gew.-% H₂SO₄ (ca. 100 g/l H₂SO₄) verringert oder auch auf 30 Gew.-% (365 g/l H₂SO₄) und mehr erhöht werden.
• Die "Hartanodisierung" wird mit einem wäßrigen H₂SO₄ enthaltenden Elektrolyten einer Konzentration von 166 g/l H₂SO₄ (oder ca. 230 g/l H₂SO₄) bei einer Betriebstemperatur von 0 bis 5 °C, bei einer Stromdichte von 2 bis 3 A/dm², einer steigenden Spannung von etwa 25 bis 30 V zu Beginn und etwa 40 bis 100 V gegen Ende der Behandlung und während 30 bis 200 min durchgeführt.

According to the electrochemical roughening step which characterizes the invention, after a possible further cleaning step with metal removal, as described above, an anodic oxidation of the aluminum can follow in a further process step to be used, for example in order to improve the abrasion and adhesion properties of the surface of the carrier material. The usual electrolytes, such as H₂SO₄, H₃PO₄, H₂C₂O₄, amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof can be used for anodic oxidation will. Reference is made, for example, to the following standard methods for the use of aqueous electrolytes containing H₂SO₄ for the anodic oxidation of aluminum (see, for example, BM Schenk, material aluminum and its anodic oxidation, Francke Verlag, Bern 1948, page 760; Praktische Galvanotechnik, Eugen G Leuze Verlag, Saulgau 1970, pages 395 ff. And pages 518/519; W. Hübner and CT Speiser, The Practice of Anodic Oxidation of Aluminum, Aluminum Verlag, Düsseldorf 1977, 3rd edition, pages 137 ff.):

• The direct current sulfuric acid process in which in an aqueous electrolyte from approximately 230 g H₂SO₄ per 1 liter of solution at 10 to 22 ° C and a current density of 0.5 to 2.5 A / dm² for anodic for 10 to 60 min is oxidized. The sulfuric acid concentration in the aqueous electrolyte solution can also be reduced to 8 to 10% by weight of H₂SO₄ (approx. 100 g / l H₂SO₄) or increased to 30% by weight (365 g / l H₂SO₄) and more.
• The "hard anodizing" is carried out with an aqueous electrolyte containing H₂SO₄ at a concentration of 166 g / l H₂SO₄ (or approx. 230 g / l H₂SO₄) at an operating temperature of 0 to 5 ° C, at a current density of 2 to 3 A / dm², an increasing voltage of about 25 to 30 V at the beginning and about 40 to 100 V towards the end of the treatment and for 30 to 200 min.

In addition to the processes for anodic oxidation of printing plate support materials already mentioned in the previous paragraph, the following processes can also be used, for example: B. can the anodic oxidation of aluminum in an aqueous H₂SO₄ containing electrolyte, the Al³⁺ ion content is set to values of more than 12 g / l (according to DE-A 28 11 396 = US-A 4 211 619) in an aqueous electrolyte containing H₂SO₄ and H₃PO₄ (according to DE-A 27 07 810 = US-A 4 049 504) or in an aqueous electrolyte containing H₂SO₄, H₃PO₄ and Al³⁺ ions (according to DE-A 28 36 803 = US-A 4,229,226).

Direct current is preferably used for the anodic oxidation, but alternating current or a combination of these types of current (eg direct current with superimposed alternating current) can also be used. The layer weights of aluminum oxide range from 1 to 10 g / m², corresponding to a layer thickness of approximately 0.3 to 3.0 µm. After the stage of electrochemical roughening and before an anodic oxidation, a modification can also be applied which causes surface abrasion from the roughened surface, as described, for example, in DE-A 30 09 103. Such a modifying intermediate treatment can u. a. allow the build-up of abrasion-resistant oxide layers and a lower tendency to tone when printing later.

The stage of anodic oxidation of the aluminum printing plate support material can also be one or multiple post-treatment levels can be recreated. Aftertreatment is understood in particular to mean a hydrophilizing chemical or electrochemical treatment of the aluminum oxide layer, for example an immersion treatment of the material in an aqueous polyvinylphosphonic acid solution according to DE-C 16 21 478 (= GB-A 1 230 447), an immersion treatment in an aqueous alkali silicate Solution according to DE-B 14 71 707 (= US-A 3 181 461) or an electrochemical treatment (anodization) in an aqueous alkali silicate solution according to DE-A 25 32 769 (= US-A 3 902 976). These post-treatment stages serve in particular to additionally increase the hydrophilicity of the aluminum oxide layer, which is already sufficient for many areas of application, the remaining known properties of this layer being at least retained.

In principle, all layers are suitable as light-sensitive reproduction layers which, after exposure, optionally with subsequent development and / or fixation, provide an image-like area from which printing can take place and / or which represent a relief image of an original. They are applied either by the manufacturer of presensitized printing plates or by so-called dry resists or directly by the consumer to one of the usual carrier materials.

The light-sensitive reproduction layers include such as z. B. in "Light-Sensitive Systems" by Jaromir Kosar, John Wiley & Sons Verlag, New York 1965, are described: The layers containing unsaturated compounds, in which these compounds are isomerized, rearranged, cyclized or crosslinked during exposure (Kosar, Chapter 4); the layers containing photopolymerizable compounds, in which monomers or prepolymers optionally polymerize during exposure by means of an initiator (Kosar, Chapter 5); and the layers containing o-diazo-quinones such as naphthoquinonediazides, p-diazo-quinones or diazonium salt condensates (Kosar, Chapter 7).

The suitable layers also include the electrophotographic layers, ie those which contain an inorganic or organic photoconductor. In addition to the light-sensitive substances, these layers can of course also contain other constituents, such as, for example, resins, dyes, pigments, wetting agents, sensitizers, adhesion promoters, indicators, plasticizers or other customary auxiliaries. In particular, the following light-sensitive compositions or compounds can be used in the coating of the carrier materials:
positive-working, o-quinonediazide, preferably o-naphthoquinonediazide compounds, which are described, for example, in DE-C 854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273 and 1 124 817;
negative working condensation products from aromatic diazonium salts and compounds with active carbonyl groups, preferably condensation products from diphenylamine diazonium salts and formaldehyde, which are described, for example, in DE-C 596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123, US Pat. Nos. 2,679,498 and 3,050,502 and GB-A 712 606;
Negative working, mixed condensation products of aromatic diazonium compounds, for example according to DE-A 20 24 244, which each have at least one unit of the general types A (-D) _n and B connected by a double-bonded intermediate member derived from a condensable carbonyl compound. These symbols are defined as follows: A is the remainder of a compound containing at least two aromatic carbocyclic and / or heterocyclic nuclei, which is capable of condensing with an active carbonyl compound in an acidic medium at at least one position. D is a diazonium salt group attached to an aromatic carbon atom of A; n is an integer from 1 to 10 and B is the remainder of a diazonium group-free compound capable of condensing with an active carbonyl compound in an acidic medium at at least one position on the molecule;
positive-working layers according to DE-A 26 10 842, which contain a compound which cleaves off on irradiation, a compound which has at least one COC group which can be cleaved off by acid (for example an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally a binder;
Negative working layers of photopolymerizable monomers, photoinitiators, binders and optionally other additives. The monomers used here are, for example, acrylic and methacrylic acid esters or reaction products of diisocyanates with partial esters of polyhydric alcohols, as described, for example, in US Pat. Nos. 2,760,863 and 3,060,023 and DE-A 20 64 079 and 23 61 041. Suitable photoinitiators include benzoin, benzoin ethers, multinuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives or synergistic mixtures of various ketones. A variety of soluble organic polymers can be used as binders, e.g. B. polyamides, polyesters, alkyd resins, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene oxide, gelatin or cellulose ether;
Negative working layers according to DE-A 30 36 077, which contain a diazonium salt polycondensation product or an organic azido compound as the photosensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as the binder.

It is also possible to apply photo-semiconducting layers, such as are described, for example, in DE-C 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047, to the support materials, thereby producing highly light-sensitive, electrophotographic layers.

The materials for printing plate supports roughened by the process according to the invention have a very uniform topography, which has a positive influence on the support stability and the water flow during printing of printing forms made from these supports. Compared to the use of other processes, "scars" (compared to the roughening of the surroundings: distinctive depressions) occur less frequently, and these can even be completely suppressed; the method according to the invention is particularly successful in producing flat, scar-free supports. Comparative examples V1 to V5, in direct comparison with examples 1 to 4, show the effect of direct current in electrolytes containing nitrate ions as a means of achieving uniform surfaces which have significant advantages in printing in terms of reducing the wiping water requirement and increasing the circulation . These surface properties can be realized without any great expenditure on equipment.

example 1

6,6 Gew.-Teile

Kresol-Formaldehyd-Novolak (mit dem Erweichungsbereich 105° - 120°C nach DIN 53 181),

1,1 Gew.-Teile

des 4-(2-Phenyl-prop-2-yl)-phenylesters der Naphthochinon-(1,2)-diazid-(2)-sulfonsäure-(4),

0,6 Gew.-Teile

2,2ʹ-Bis- naphthochinon-(1,2)-diazid-(2)-sulfonyloxy-(5) -dinaphthyl-(1,1ʹ)-methan,

0,24 Gew.-Teile

Naphthochinon-(1,2)-diazid-(2)-sulfochlorid-(4),

0,08 Gew.-Teile

Kristallviolett,

91,36 Gew.-Teile

Gemisch aus 4 Vol.-Teilen Ethylenglykolmonomethylether, 5 Vol.-Teilen Tetrahydrofuran und 1 Vol.-Teil Essigsäurebutylester

druckt eine so erhaltene Druckform bei einem Wischwasserverbrauch von 23 Skalenteilen eine Auflage von 175.000.An aluminum sheet is pre-structured wet with cutting abrasives using rotating brushes to a roughness depth R _z of 4.3 µm, then pickled in a 3% sodium hydroxide solution for 30 s, in the next step with a direct current of 20 A / dm² for 10 s anodically roughened at 40 ° C in an electrolyte of 20 g / l HNO₃ and 50 g / l Al (NO₃) ₃ · 9 H₂O and then cleaned for 1 min in a bath of 2.5% NaOH at 60 ° C. After anodizing to 3 g / m² oxide and coating with a solution

6.6 parts by weight

Cresol-formaldehyde novolak (with a softening range of 105 ° - 120 ° C according to DIN 53 181),

1.1 parts by weight

the 4- (2-phenyl-prop-2-yl) phenyl ester of naphthoquinone (1,2) diazide (2) sulfonic acid (4),

0.6 parts by weight

2,2ʹ-bis-naphthoquinone- (1,2) -diazide- (2) -sulfonyloxy- (5) -dinaphthyl- (1,1ʹ) -methane,

0.24 parts by weight

Naphthoquinone- (1,2) -diazide- (2) -sulfochloride- (4),

0.08 parts by weight

Crystal violet,

91.36 parts by weight

Mixture of 4 parts by volume of ethylene glycol monomethyl ether, 5 parts by volume of tetrahydrofuran and 1 part by volume of butyl acetate

prints a print form thus obtained with a wash water consumption of 23 scale parts and a print run of 175,000.

Example 2

A plate produced and coated as in Example 1, but anodically roughened in the electrochemical step with 60 A / dm 2 for 3 s in the same electrolyte prints 165,000 copies with the same coating. The water consumption is 25 divisions.

Example 3

A prepared and coated as in Example 1, but in 10% aluminum nitrate solution at 20 A / dm² for 5 s anodically roughened plate, which was cleaned in 2.5% NaOH at 60 ° C for 60 s, prints 150,000 copies under the same conditions with a water consumption of 30 scale divisions.

Example 4

A plate produced and coated as in Example 1, but anodically roughened in 7% sodium nitrate solution at 30 A / dm² for 5 s, prints 155,000 copies under the same conditions with a water consumption of 32 scale parts.

Comparative Example V1

A plate produced and coated as in Example 1, but anodically roughened with an alternating current of 20 A / dm 2 for 10 s, has a print run of 110,000 prints and a water consumption of 45 scale divisions.

Comparative example V2

A plate produced and coated analogously to Example 1, but anodically roughened with an alternating current of 20 A / dm 2 for 20 s has a circulation of 120,000 and a water consumption of 40 scale parts.

Comparative Example V3

A plate produced and coated as in Example 1, but anodically roughened with direct current of 20 A / dm 2 for 10 s in 20 g / l HCl, prints 110,000 copies and has a water consumption of 42 divisions.

Comparative Example V4

A plate produced and coated in the same way as in Example 1, with DC current of 20 A / dm 2 for 10 s but anodically roughened in 10 g / l HCl, prints 115,000 and has a wiping water consumption of 41 scale parts.

Comparative Example V5

A plate manufactured and coated as in Comparative Example V4, but anodically roughened in 12 g / l HCl and 50 g AlCl₃ · 6 H₂O has a circulation of 115,000 and a water consumption of 39 scale parts.

In all examples, the printing was carried out under the same conditions using the same printing press (Roland Favorit). The application quantity of the wiping water is determined by a display device in a dampening unit from Dahlgren. These are relative comparative measurements. The lower the scale divisions, the lower the water consumption.

Claims (10)

1. Process for manufacturing plates, foils or webs of aluminium or aluminium alloys, for use as support materials for printing plates, the process comprising first mechanically and then electrochemically graining in a nitrate-containing electrolyte by means of a direct current, characterised in that, as the nitrate-containing electrolyte, solutions of alkali metal nitrate, alkaline earth metal nitrate, ammonium nitrate or aluminium nitrate and/or mixtures thereof and/or mixtures with nitric acid are used and that the concentration of the nitrate compound is adjusted to a value from 1.0 g/l up to the saturation limit.
2. A process as claimed in claim 1, characterised in that the concentration of the nitrate compound is adjusted to a value from higher than 100 g/l up to the saturation limit.
3. A process as claimed in claims 1 and 2, characterised in that graining is effected by means of a direct current from 1 to 300 A/dm² and a quantity of charge from 1 to 400 C/dm².
4. A process as claimed in claim 3, characterised in that graining is effected by means of a direct current from 10 to 100 A/dm² and a quantity of charge from 10 to 200 C/dm².
5. A process as claimed in any one or more of claims 1 to 4, characterised in that electrochemical graining is carried out for a duration from 1 to 300 s.
6. A process as claimed in claim 5, characterised in that electrochemical graining is carried out for a duration from 2 to 60 s.
7. A process as claimed in any one or more of claims 1 to 6, in which an alkaline cleaning step and an anodising treatment are carried out in addition to mechanical and/or electrochemical graining, characterised in that cleaning is effected by means of acids or alkali metal hydroxide solutions or by hydroxyl ions produced in the electrolytic bath in the electrochemical graining process.
8. A process as claimed in claim 7, characterised in that electrochemical graining is carried out at a temperature from 20 to 80 °C.
9. A process as claimed in claim 7, characterised in that mechanical graining is carried out by slurry brushing.
10. A process as claimed in any one or more of claims 1 to 8, characterised in that electrochemical graining is carried out in an agitated electrolyte at a rate of flow ranging between 5 and 1000 cm/s.