EP0161608B1 - Process for the aftertreatment of layers from aluminium oxide with aqueous solutions containing phosphoroxo anions, and their use in the production of supports for offset printing plates - Google Patents

Description

The invention relates to an aftertreatment process for roughened and anodically oxidized aluminum, in particular of support materials for offset printing plates with aqueous solutions containing phosphorus oxo anions.

Carrier materials for offset printing plates are provided either by the consumer directly or by the manufacturer of precoated printing plates on one or both sides with a radiation (light) sensitive layer (reproduction layer), with the help of which a printing image of a template is generated photomechanically. After this printing form has been produced from the printing plate, the layer support carries the image points which will guide the color during later printing and at the same time forms the hydrophilic background for the lithographic printing process at the non-image points (non-image points) during later printing.

• - Die nach der Bestrahlung (Belichtung) relativ löslicher gewordenen Teile der strahlungsempfindlichen Schicht müssen durch eine Entwicklung leicht zur Erzeugung der hydrophilen Nichtbildstellen rückstandsfrei vom Träger zu entfernen sein.
• - Der in den Nichtbildstellen freigelegte Träger muß eine große Affinität zu Wasser besitzen, d. h. stark hydrophil sein, um beim lithographischen Druckvorgang schnell und dauerhaft Wasser aufzunehmen und gegenüber der fetten Druckfarbe ausreichend abstoßend zu wirken.
• - Die Haftung der strahlungsempfindlichen Schicht vor bzw. der druckenden Teile der Schicht nach der Bestrahlung muß in einem ausreichenden Maß gegeben sein.

The following requirements must therefore be placed on a layer support for reproduction layers for the production of offset printing plates:

• - The parts of the radiation-sensitive layer that have become relatively more soluble after the irradiation (exposure) must be easy to remove from the support without residue by development to produce the hydrophilic non-image areas.
• - The carrier exposed in the non-image areas must have a great affinity for water, ie be highly hydrophilic, in order to absorb water quickly and permanently during the lithographic printing process and to be sufficiently repellent to the bold printing ink.
• - The adhesion of the radiation-sensitive layer before or the printing parts of the layer after the irradiation must be sufficient.

Aluminum is used in particular as the base material for such substrates. It is roughened according to known methods by dry brushing, wet brushing, sandblasting, chemical and / or electrochemical treatment. In order to increase the abrasion resistance, the roughened substrate can also be subjected to an anodization step to build up a thin oxide layer.

In practice, the carrier materials, in particular anodically oxidized carrier materials based on aluminum, are subjected to a further treatment step to improve the layer adhesion, to increase the hydrophilicity and / or to facilitate the developability of the radiation-sensitive layers before the application of a radiation-sensitive layer for example the following methods.

DE-C 1 671 614 (= US-A 3 511 661) describes an anodic oxidation of printing plate support materials made of aluminum in an aqueous H ₃ PO ₄ solution, but in a comparative example (example 12) also a two-stage variant carried out, in which firstly anodized in an aqueous H ₂ SO ₄ solution and then the material is aftertreated by immersion in an aqueous H ₃ P0 ₄ or Na ₂ HP0 ₄ solution; in addition, a hydroxyethyl cellulose layer must then be applied before coating with the radiation-sensitive mixture.

DE-A 2 251 710 (= GB-A 1 410 768) also discloses the non-electrolytic aftertreatment of an aluminum plate in an aqueous H ₂ S0 ₄ solution which has been anodically oxidized in an aqueous H ₃ P0 ₄ solution. The US-A 3 808 000 describes similarly.

As an intermediate stage in the process for producing a printing plate support material according to DE-C 2 540 561 (= US Pat. No. 4,116,695), prior to treatment with steam or hot water and after a customary anodic oxidation of the aluminum (e.g. in an aqueous H ₂ SO ₄ solution) is also carried out by immersion in an aqueous solution containing either an acid (e.g. meta, pyro or polyphosphoric acid) or a base (e.g. Na ₃ P0 ₄ or K _a P0 ₄ ) contains.

In the two-stage process for the anodic oxidation of printing plate support materials made of aluminum according to EP-A 0 086 957 (= ZA-A 83/0947), a) in an aqueous HZS04 solution and b) in an aqueous solution containing phosphorus Anions (phosphorus oxo, phosphorofluoro and / or phosphorus oxofluoro anions) are treated electrochemically. Specifically, the following compounds are mentioned for stage b): phosphoric acid (H ₃ P0 ₄ ), sodium dihydrogen phosphate (NaH ₂ P0 ₄ ), disodium hydrogen phosphate (Na ₂ HP0 ₄ ), trisodium phosphate (Na ₃ P0 ₄ ), phosphorous acid (H ₃ P0 ₃ ), disodium phosphite (Na ₂ HPO ₃ ), diphosphoric acid (H ₄ P ₂ 0 ₇ ), sodium pyrophosphate (Na ₄ P ₂ 0 ₇ ), triphosphoric acid (H5P ₃ 0 ₁₀ ), sodium triphosphate (Na ₅ P ₃ O ₁₀ ), Polyphosphoric acid (H _{n + 2} P _n 0 _{3n + 1} ), hexasodium tetrapolyphosphate (Na ₆ P ₄ 0 ₁₃ ), hexasodium metaphosphate [Na ₆ (P0 ₃ ) ₆₁ , disodium monofluorophosphate (Na ₂ PO ₂ F) and potassium hexafluorophosphate (KPF ₆ ).

Although these post-treatment processes can often lead to sufficient results, these do not always meet the constantly increasing requirements for a practical support material suitable for the application of a wide variety of radiation-sensitive reproduction layers, and in particular also a less complex production process for this support material. This applies not only to the alkali resistance, which is particularly required when using high-performance developers in the field of positive-working radiation-sensitive reproduction layers, but also to the adsorption behavior of the oxide layers. The latter property is important because it occurs that - depending on the chemical composition of the reproduction layers - fogging (e.g. coloring) occurs in the non-image areas, which is likely to be caused by adsorptive effects. For the practice of producing these carrier materials in high-speed In addition, it is desirable for high-performance systems to obtain a method for post-treatment of the oxide layers that is as prone to failure as possible and requires little energy; ie, for example, that immersion treatment with comparable surface properties of the treated oxide layer is more preferable to electrochemical treatment.

DE-A 2 609 577 describes a process for producing sealed anodic oxide thin layers on aluminum and aluminum alloys prior to their coating, the oxide layer being treated in an aqueous solution which contains phosphorus compounds at at least 80.degree. The main phosphorus compounds used are orthophosphoric acid, phosphorous acid and salts of the acids mentioned, and phosphorus compounds of tungsten or molybdic acid. The purpose of the treatment is to prevent hairline cracks in these oxide layers, for example to improve the application of paint.

The object of the present invention is to propose a method for the aftertreatment of flat aluminum, which can be carried out in addition to anodic oxidation of the aluminum and leads to a surface on the aluminum oxide thus produced, which in particular meets the practical requirements of a high-performance printing plate described at the outset and already known dipping methods improved in effect.

The invention is based on the known process for the production of sheet, film or strip materials based on chemically, mechanically and / or electrochemically roughened and anodically oxidized aluminum or one of its alloys, the aluminum oxide layers of which contain an aqueous solution containing phosphorus oxo anions be treated. The process according to the invention is then characterized in that the aftertreatment of the aluminum oxide layer is not carried out electrolytically by immersion treatment in an aqueous solution containing hexametaphosphate anions.

The hexametaphosphate anions are derived from the polymetaphosphoric acid H _n P _n 0 _3n , in which n = 6 (hexametaphosphoric acid). They are generally produced by dissolving a water-soluble salt of this acid, in particular an alkali metal salt such as Na ₆ P ₆ O ₁₈ , in water. In a preferred embodiment of the process, this salt solution is brought to a pH of 1 to 5, in particular 1.5 to 4, with an acid (for example tartaric acid, citric acid or phosphoric acid), in particular a water-soluble organic acid (preferably a hydroxycarboxylic acid) such as citric acid , 5, set. The aqueous solution generally contains 1 to 300 g / l of hexametaphosphate anions, preferably 3 to 150 g / l and in particular 5 to 100 g / l.

The aftertreatment is carried out discontinuously or preferably continuously in the modern belt systems. The treatment times are expediently in the range from 0.5 to 120 seconds and the treatment temperatures are from 15 to 80 ° C., in particular from 20 to 75 ° C. The procedure used changes the previously generated surface topography (such as roughness and oxide pores) practically not or only insignificantly, so that the method according to the invention is particularly suitable for the treatment of materials in which the retention of this topography plays a major role, for example for printing plate support materials.

Suitable base materials for the material to be treated according to the invention include those made of aluminum or one of its alloys, which have, for example, a content of more than 98.5% by weight of Al and proportions of Si, Fe, Ti, Cu and Zn. In particular for the production of printing plate support materials, the flat aluminum is first mechanically, if necessary after pre-cleaning, (for example by brushing and / or with an abrasive treatment); roughened chemically (e.g. by etching agents) and / or electrochemically (e.g. by alternating current treatment in aqueous acid or salt solutions). The electrochemical roughening is preferably carried out in the process according to the invention, but these aluminum carrier materials can also be roughened mechanically (for example by brushing with wire or nylon brushes and / or with an abrasive treatment) even before the electrochemical stage. All process steps can be carried out discontinuously with plates or foils, but they are preferably carried out continuously with tapes.

In general, the process parameters, in particular in the case of a continuous process, in the electrochemical roughening stage lie in the following ranges: the temperature of the aqueous electrolyte generally containing 0.3 to 5.0% by weight of acid (s) (also higher in the case of salts) 20 and 60 ° C, the current density between 3 and 200 A / dm ² , the residence time of a material point to be roughened in the electrolyte between 3 and 100 seconds and the electrolyte flow rate on the surface of the material to be roughened between 5 and 100 cm / sec; in the batchwise process, the required current densities tend to be in the lower part and the dwell times are in the upper part of the ranges specified, and the flow of the electrolyte can also be dispensed with. Normally, alternating current of a frequency of 50 to 60 Hz is usually used as the type of current, but modified types of current such as alternating current with different amplitudes of the current strength for the anode and cathode current, lower frequencies, current interruptions or superimposition of two currents of different frequency and waveform are also possible. The average roughness depth R _{2 of} the roughened surface is in the range from 1 to 15 μm, in particular from 1.5 to 8.0 μm. If the aqueous electrolyte contains acid (s), in particular HCl and / or HN0 ₃ , aluminum ions in the form of aluminum salts, in particular Al (N0 ₃ ) ₃ and / or AICI _{3 can also be} added to it; the addition of certain other acids and salts such as boric acid or borates or of corrosion inhibitors such as amines is also known.

The pre-cleaning includes, for example, treatment with aqueous NaOH solution with or without Degreasing agents and / or complexing agents, trichlorethylene, acetone, methanol or other commercially available aluminum stains. The roughening or, in the case of several roughening stages, also between the individual stages, an abrasive treatment can additionally be carried out, in particular a maximum of 2 g / m ^{2 being} removed (up to 5 g / m ² between the stages); In general, aqueous solutions of alkali metal hydroxide or aqueous solutions of alkaline salts or aqueous acid solutions based on HN0 ₃ , H ₂ SO ₄ or H ₃ PO ₄ are used as abrasive solutions. In addition to an abrasive treatment stage between the roughening stage and a subsequent anodizing stage, such non-electrochemical treatments are also known which essentially only have a rinsing and / or cleaning effect and, for example, for removing deposits formed during roughening ("Schmant") or simply for Serve removal of electrolyte residues; For example, dilute aqueous alkali hydroxide solutions or water are used for these purposes.

After the electrochemical roughening process, anodic oxidation of the aluminum follows in a further process step, for example to improve the abrasion and adhesion properties of the surface of the carrier material. The usual electrolytes such as H ₂ S0 ₄ , H ₃ P0 ₄ , H ₂ C ₂ 0 ₄ , amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof can be used for anodic oxidation; in particular, H ₂ S0 ₄ and H ₃ P0 _{4 are used} alone, in a mixture and / or in a multi-stage anodizing process; an aqueous solution containing H ₂ S0 ₄ and A1 ^{3 +} ions is particularly preferably used. The oxide layer weights are generally in particular between 1 and 8 g / m ² (corresponding to about 0.3 to 2.5 μm layer thickness).

The materials produced according to the invention are preferably used as supports for offset printing plates, i. H. a radiation-sensitive coating is applied to one or both sides of the carrier material either by the manufacturer of presensitized printing plates or directly by the consumer. In principle, all layers are suitable as radiation (light) sensitive layers which, after irradiation (exposure), optionally with subsequent development and / or fixation, provide an imagewise surface from which printing can take place.

• positiv-arbeitende, o-Chinondiazide, insbesondere o-Naphthochinondiazide wie Naphthochinon-(1,2)-diazid-(2)-sulfonsäureester oder -amide, die nieder- oder höhermolekular sein können, als lichtempfindliche Verbindung enthaltende Reproduktionsschichten, die beispielsweise in den DE-C 854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273, 1 124 817 und 2 331 377 und den EP-A 0 021 428 und 0 055 814 beschrieben werden;
• negativ-arbeitende Reproduktionsschichten mit Kondensationsprodukten aus aromatischen Diazoniumsalzen und Verbindungen mit aktiven Carbonylgruppen, bevorzugt Kondensationsprodukte aus Diphenylamindiazoniumsalzen und Formaldehyd, die beispielsweise in den DE-C 596 731, 1 138 399, 1 138 400, 1 138 401,1 142 871,1 1 154123, den US-A 2 679 498 und 3 050 502 und der GB-A 712 606 beschrieben werden;
• negativ-arbeitende, Mischkondensationsprodukte aromatischer Diazoniumverbindungen enthaltende Reproduktionsschichten, beispielsweise nach der DE-C 2 065 732, die Produkte mit mindestens je einer Einheit aus a) einer kondensationsfähigen aromatischen Diazoniumsalzverbindung und b) einer kondensationsfähigen Verbindung wie einem Phenolether oder einem aromatischen Thioether, verbunden durch ein zweibindiges, von einer kondensationsfähigen Carbonylverbindung abgeleitetes Zwischenglied wie einer Methylengruppe aufweisen;
• positiv-arbeitende Schichten nach der DE-A 2 610 842, der DE-C 2 718 254 oder der DE-A 2 928 636, die eine bei Bestrahlung Säure abspaltende Verbindung, eine monomere oder polymere Verbindung, die mindestens eine durch Säure abspaltbare C-O-C-Gruppe aufweist (z. B. eine Orthocarbonsäureestergruppe oder eine Carbonsäureamidacetalgruppe) und gegebenenfalls ein Bindemittel enthalten;
• negativ-arbeitende Schichten aus photopolymerisierbaren Monomeren, Photoinitiatoren, Bindemitteln und gegebenenfalls weiteren Zusätzen; als Monomere werden dabei beispielsweise Acryl- und Methacrylsäureester oder Umsetzungsprodukte von Diisocyanaten mit Partialestern mehrwertiger Alkohole eingesetzt, wie es beispielsweise in den US-A 2 760 863 und 3 060 023 und den DE-A 2 064 079 und 2 361 041 beschrieben wird;
• negativ-arbeitende Schichten gemäß der DE-A 3 036 077, die als lichtempfindliche Verbindung ein Diazoniumsalz-Polykondensationsprodukt oder eine organische Azidoverbindung und als Bindemittel ein hochmolekulares Polymeres mit seitenständigen Alkenylsulfonyl- oder Cycloalkenylsulfonylurethan-Gruppen enthalten.

In addition to the layers containing silver halides used in many fields, various others are also known, such as e.g. As described in "Light-Sensitive Systems" by Jaromir Kosar, John Wiley & Sons Verlag, New York 1965: the colloid layers containing chromates and dichromates (Kosar, Chapter 2); 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 other components such. B. contain resins, dyes or plasticizers. In particular, the following light-sensitive compositions or compounds can be used in the coating of the carrier materials produced by the process according to the invention:

• positive-working, o-quinonediazides, in particular o-naphthoquinonediazides such as naphthoquinone- (1,2) -diazid- (2) -sulfonic acid esters or amides, which can be of low or higher molecular weight, as a photosensitive compound-containing reproduction layers, for example in the DE-C 854 890, 865 109, 879 203, 894 959, 938 233, 1 109 521, 1 144 705, 1 118 606, 1 120 273, 1 124 817 and 2 331 377 and EP-A 0 021 428 and 0 055 814;
• negative-working reproduction layers with 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 1 154123, US-A 2,679,498 and 3,050,502 and GB-A 712,606;
• Reproductive layers containing negative-working, mixed condensation products of aromatic diazonium compounds, for example according to DE-C 2 065 732, the products with at least one unit each of a) a condensable aromatic diazonium salt compound and b) a condensable compound such as a phenol ether or an aromatic thioether, connected by have a double bonded intermediate derived from a condensable carbonyl compound such as a methylene group;
• positive-working layers according to DE-A 2 610 842, DE-C 2 718 254 or DE-A 2 928 636 which contain a compound which cleaves off on irradiation, a monomeric or polymeric compound which has at least one COC which can be cleaved off by acid Group (e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally contain a binder;
• negatively working layers made of photopolymerizable monomers, photoinitiators, binders and optionally other additives; the monomers used 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 2,064,079 and 2,361,041;
• Negative-working layers according to DE-A 3 036 077, which as a light-sensitive compound Contain diazonium salt polycondensation product or an organic azido compound and as a binder a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups.

It can also be photoconductive layers such as z. B. in DE-C 1 117 391, 1 522 497, 1 572 312, 2 322 046 and 2 322 047 are described, applied to the carrier materials produced according to the invention, whereby highly light-sensitive, electrophotographic printing plates are formed.

The coated offset printing plates obtained from the carrier materials produced according to the invention are converted into the desired printing form in a known manner by imagewise exposure or irradiation and washing out of the non-image areas with a developer, preferably an aqueous developer solution.

Surprisingly, offset printing plates, whose base support materials have been post-treated by the two-stage process according to the invention, are distinguished in particular by a lower tendency to form color fog compared to those plates in which the same base material has been post-treated with other aqueous solutions containing phosphorus oxo anions (see the following comparative experiments). This special effect of the hexametaphosphate anions in a pure immersion treatment was not predictable, since the whole group of anions shows a similar effect in the electrochemical treatment.

• Bei der Untersuchung, ob die Oberfläche eine Farbstoffadsorption (Schleierbildung) zeigt, wird ein mit der strahlungsempfindlichen Schicht versehenes Plattenstück belichtet, entwickelt und dann eine Hälfte mit einem Korrekturmittel behandelt. Je größer die Differenz in beispielsweise den Farbwerten zwischen der unkorrigierten und der korrigierten Hälfte ist, desto mehr Farbe ist an der unkorrigierten Trägermaterialoberfläche absorbiert. Die Werte 0 bis 5 bedeuten keine (0), eine sehr schwache (1) bis starke (5) Farbstoffadsorption, es werden nur halbe Stufen angegeben; gelegentlich auch über 5 liegende Werte weisen zusätzlich auf einen Oxidschichtabtrag hin.

In the above description and the following examples,% data always mean% by weight, unless stated otherwise. Parts by weight are in parts by volume in the ratio of g to cm ^3. The following methods for determining parameters were used in the examples:

• When examining whether the surface shows dye adsorption (fogging), a plate piece provided with the radiation-sensitive layer is exposed, developed and then half is treated with a correction agent. The greater the difference in, for example, the color values between the uncorrected and the corrected half, the more color is absorbed on the uncorrected substrate surface. The values 0 to 5 mean no (0), very weak (1) to strong (5) dye adsorption, only half steps are given; Occasionally, values above 5 also indicate an oxide layer removal.

Either a negative working layer containing a reaction product of polyvinylbutyral with propenylsulfonyl isocyanate, a polycondensation product of 1 mol of 3-methoxy-diphenylamine-4-diazonium sulfate and 1 mol of 4,4'-bismethoxymethyl-diphenyl ether is precipitated as mesitylene sulfonate, H, as the radiation-sensitive layer ₃ P0 ₄ , Viktoriareinblau FGA and phenylazodiphenylamine or a positive working with a content of a cresol-formaldehyde novolak, 4- (2-phenyl-prop-2-yl) -phenyl ester of the naphthoquinone- (1,2) -diazid- (2) -sulfonic acid- (4), polyvinyl butyral, naphthoquinone- (1,2) -diazide- (2) -sulfonic acid chloride- (4) and crystal violet applied to the carrier material. Practical printing plates and printing forms can be created from it.

Example 1 and Comparative Example V1

An aluminum strip is electrochemically roughened in an aqueous solution containing 1.4% of HN0 ₃ and 6% of Al (N0 ₃ ) ₃ using alternating current (115 A / dm ² at 35 ° C.) and in an aqueous H ₂ S0 ₄ and Al ^{3 + -} ion containing solution anodized with direct current. The oxide layer, which has a layer weight of approximately 2.5 g / m ² , is immersed for 15 seconds at a temperature of 45 to 50 ° C. in an aqueous solution of pH 7 containing hexasodium hexametaphosphate (Na ₆ P ₆ 0 ₁₈ ). The changes in the dye adsorption obtained with increasing proportions of this salt are shown in the table. The comparative example is carried out without an aftertreatment.

Example 2 and Comparative Example V2

The procedure of Example 1 is followed, but roughened in an aqueous solution containing 0.9% of HCl.

Example 3 and Comparative Example V 3

The procedure is as in Example 1, but the Na ₆ P ₆ O ₁₈ solution additionally contains 10 g / 1 of citric acid and thus a pH of 2.5.

Example 4 and Comparative Example V 4

The procedure is as in Example 2, but the Na ₆ P ₆ O ₁₈ solution additionally contains 10 g / l of citric acid and thus a pH of 2.5.

Comparative Examples V 5 to V 20

The procedure is as in Example 1 (V5 to V12) or Example 2 (V13 to V20), but with other compounds which likewise give phosphorus oxo anions according to the table, or no aftertreatment is carried out. It is shown that with both common types of electrochemical roughening with hexasodium hexametaphosphate there is a more pronounced reduction in dye adsorption than with other salts or acids which provide phosphorus oxo anions. The effect is affected by a change in pH, e.g. B. with the addition of citric acid, significantly increased again; it also occurs with the addition of other, not too strong acids, in the pH range from 1 to 5 in a similar order of magnitude.

Claims (10)

1. Process for manufacturing materials in the form of sheets, foils or webs, based on chemically, mechanically and/or electrochemically roughened and anodically oxidized aluminum or an alloy thereof, the aluminum oxide layers of which are post-treated with an aqueous solution containing phosphoroxo anions, wherein post-treatment of the aluminum layers is performed non-electrolytically by immersion into an aqueous solution with a content of hexametaphosphate anions.

2. Process as claimed in Claim 1, wherein the aqueous solution contains a water-soluble salt of hexametaphosphoric acid.

3. Process as claimed in Claim 1 or 2, wherein the aqueous solution contains hexasodiumhexametaphosphate.

4. Process as claimed in any of Claims 1 to 3, wherein the aqueous solution is adjusted to a pH between 1 and 5 by means of an acid.

5. Process as claimed in Claim 4, wherein the acid used is a hydroxycarboxylic acid.

6. Process as claimed in Claim 5, wherein the acid used is citric acid.

7. Process as claimed in any of Claims 1 to 6, wherein 3 g/I to 150 g/I of hexametaphosphate anions are contained in the aqueous solution.

8. Process as claimed in any of Claims 1 to 7, wherein the materials are electrochemically roughened in an aqueous electrolyte solution based on HCI and/or HN0₃.

9. Process as claimed in any of Claims 1 to 8, wherein the materials are anodically oxidized in an aqueous solution based on H₂SO₄.

10. Use of the process as claimed in any of Claims 1 to 9, for manufacturing support materials for offset printing plates carrying radiation-sensitive reproduction layers.