EP0161608A1 - 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

Abstract

The process for the production of plate, film or tape-shaped materials based on chemically, mechanically and / or electrochemically roughened and anodized aluminum or one of its alloys, the aluminum oxide layers of which are post-treated with an aqueous solution containing phosphorus oxo anions, is designed in this way that the aftertreatment of the aluminum oxide layer is carried out by immersion in an aqueous solution containing hexametaphosphate anions. In a preferred embodiment, this solution is adjusted to a pH of 1 to 5 with an acid. These materials with reduced adsorption behavior are preferably used as a carrier material for offset printing plates.

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 pre-coated 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 by photomechanical means. 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 easily removed 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 der DE-C 16 71 614 (= US-A 3 511 661) wird an sich eine anodische Oxidation von Druckplattenträgermaterialien aus Aluminium in einer wäßrigen H₃P0₄-Lösung beschrieben, in einem Vergleichsbeispiel (Beispiel 12) aber auch eine zweistufige Variante durchgeführt, bei der zunächst in einer wäßrigen H₂S0₄-Lösung anodisch oxidiert und anschließend das Material durch Eintauchen in eine wäßrige H₃P0₄- oder Na₂HPO₄-Lösung nachbehandelt wird; zusätzlich muß dann noch eine Hydroxyethylcellulose-Schicht vor dem Beschichten mit dem strahlungsempfindlichen Gemisch aufgebracht werden.

In practice, the carrier materials, in particular anodically oxidized carrier materials based on aluminum, are used for 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 subjected to, for example, the following methods:

• DE-C 16 71 614 (= 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 first anodized in an aqueous H ₂ S0 ₄ solution and then the material is aftertreated by immersion in an aqueous H ₃ P0 ₄ or Na ₂ HPO ₄ solution; in addition, a hydroxyethyl cellulose layer must then be applied before coating with the radiation-sensitive mixture.

From DE-A 22 51 710 (= GB-A 1 410 768) the non-electrolytic aftertreatment of an aluminum plate in an aqueous H ₂ S0 ₄ solution oxidized printing plate support material in an aqueous H ₃ P0 ₄ solution is also known. 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 25 40 561 (= US Pat. No. 4,116,695), treatment with steam or hot water and after a customary anodic oxidation of the aluminum (e.g. in an aqueous H ₂ S0 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 ₃ 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 H ₂ S0 ₄ solution and b) in an aqueous solution with a content on anions containing phosphorus (phosphorus oxo, phosphorofluoro and / or phosphorus oxofluoro anions) 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 HP0 ₃ ), diphosphoric acid (H ₄ P ₂ 0 ₇ ), sodium pyrophosphate (Na ₄ P ₂ 0 ₇ ), triphosphoric acid (H ₅ P ₃ O ₁₀ ), sodium triphosphate (Na ₅ P ₃ O ₁₀ ), Polyphosphoric acid (H _{n + w} P _n O _{3n + 1} ), hexasodium tetrapolyphosphate (Na ₆ P ₄ O ₁₃ ), hexasodium metaphosphate [Na ₆ (P0 ₃ ) ₆ 1, disodium monofluorophosphate (Na ₂ P0 ₃ 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, high-performance systems, it is also desirable to obtain a method for post-treatment of the oxide layers which 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.

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 plate, film or strip-shaped 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 a phosphorus oxo anion tend aqueous solution are treated. The process according to the invention is then characterized in that the aftertreatment of the aluminum oxide layers is carried out by immersion in an aqueous solution containing hexametaphosphate anions.

The hexametaphosphate anions are derived from the polymetaphosphoric acid H _n P _n O _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 0 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 non-electrolytically as immersion treatment, either discontinuously or preferably continuously in modern belt systems. The treatment times are expediently in the range of 0.5 to 120 seconds and the treatment temperature at 15 to 80 ^* C, especially at 20 to 75 ° C. The procedure used changes the previously created surface topography (such as roughness and oxide pores) practically not or only insignificantly, so that this is the case 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, if necessary after pre-cleaning, is first mechanically (e.g. by brushing and / or with abrasive treatment), chemically (e.g. by etching agent) and / or electrochemically (e.g. B. roughened by AC treatment in aqueous acid or salt solutions). Electrochemical roughening is preferably carried out in the process according to the invention, but these aluminum support materials can also be roughened mechanically before the electrochemical stage (for example by brushing with wire or nylon brushes and / or with an abrasive treatment). 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, particularly in the case of continuous process management, in the electrochemical roughening stage are in the following areas: the temperature of the aqueous electrolyte, which generally contains 0.3 to 5.0% by weight of acid (s) (even higher in the case of salts), between 20 and 60 ° C., the current density between 3 and 200 A / dm ² , the residence time a material point to be roughened in the electrolyte between 3 and 100 seconds and the electrolyte flow rate at 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 of the roughened surface is in the range from 1 to 15 _/ um, in particular from 1.5 to 8.0 _/ um. 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 AlC1 _{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.

Pre-cleaning includes, for example, treatment with aqueous NaOH solution with or without degreasing agent 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 _Z S0 ₄ , H ₃ P0 ₄ , H ₂ C ₂ 0 ₄ , amidosulfonic acid, sulfosuccinic acid, sulfosa can be used for anodic oxidation licylic acid or mixtures thereof are used; 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 H ₂ S0 ₄ and A, 3 + is particularly preferred ^- ion-containing solution 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, 1 154 123, 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 20 65 732, 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 26 10 842, der DE-C 27 18 254 oder der DE-A 29 28 636, die eine bei Bestrahlung Säure abspaltende Verbindung, eine monomere oder polymere Verbindung, die mindestens eine durch Säure abspaltbare C-0-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 20 64 079 und 23 61 041 beschrieben wird;
• negativ-arbeitende Schichten gemäß der DE-A 30 36 077, 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 condensates tion products from diphenylamine diazonium salts and formaldehyde, for example in DE-C 596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123, US-A 2 679 498 and 3 050 502 and the GB -A 712 606;
• Reproductive layers containing negative-working, mixed condensation products of aromatic diazonium compounds, for example according to DE-C 20 65 732, 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 26 10 842, DE-C 27 18 254 or DE-A 29 28 636, which contain a compound which cleaves off under irradiation, a monomeric or polymeric compound which has at least one C-cleavable by acid -0-C group (z. B. 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; as monomers are, for example, acrylic and methacrylic acid esters or conversion tion 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;
• Negative-working layers according to DE-A 30 36 077, which contain a diazonium salt polycondensation product or an organic azido compound as a photosensitive compound and a high molecular weight polymer with pendant alkenylsulfonyl or cycloalkenylsulfonylurethane groups as a binder.

It is also possible to use photo-semiconducting layers such as e.g. in DE-C 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 are described, are applied to the carrier materials produced according to the invention, thereby producing highly light-sensitive, electrophotographic printing plates.

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, the base carrier materials of which have been post-treated by the two-stage process according to the invention, are distinguished from those plates in which the same base material is used other aqueous solutions containing phosphorus oxo anions were aftertreated, in particular by a lower tendency to form color fog (see subsequent comparative experiments). This special effect of the hexametaphosphate anions in a pure immersion treatment was not foreseeable, 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 relate to 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 Solution containing A1 ^{3 +} ions anodized with direct current. The oxide layer, which has a layer weight of approximately 2.5 g / m ² , is converted into a layer at a temperature of 45 to 50 ° C. for 15 seconds

An aqueous solution containing hexasodium hexametaphosphate (Na ₆ P ₆ 0 ₁₈ ) of pH 7 was immersed. 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 of Example 1 is followed, but the Na ₆ P ₆ 0 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 of Example 2 is followed, but the Na ₆ P ₆ 0 ₁₈ solution additionally contains 10 g / 1 of citric acid and thus a pH of 2.5.

Example 5 and Comparative Example 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, as shown in 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. A process for the production of plate, film or tape-shaped materials based on chemically, mechanically and / or electrochemically roughened and anodized aluminum or one of its alloys, the aluminum oxide layers of which are post-treated with an aqueous solution containing phosphorus oxo anions, characterized that the aftertreatment of the aluminum oxide layer is carried out by immersion in an aqueous solution containing hexametaphosphate anions. 2. The method according to claim 1, characterized in that the aqueous solution contains a water-soluble salt of hexametaphosphoric acid. 3. The method according to claim 1 or 2, characterized in that the aqueous solution contains hexasodium hexametaphosphate. 4. The method according to any one of claims 1 to 3, characterized in that the aqueous solution is adjusted to a pH of 1 to 5 with an acid. 5. The method according to claim 4, characterized in that a hydroxycarboxylic acid is used as acid. 6. The method according to claim 5, characterized in that citric acid is used as acid. 7. The method according to any one of claims 1 to 6, characterized in that the aqueous solution contains 3 to 150 g / l of hexametaphosphate anions. 8. The method according to any one of claims 1 to 7, characterized in that the materials are roughened electrochemically in an aqueous electrolyte solution based on HCl and / or HN0 ₃ . 9. The method according to any one of claims 1 to 8, characterized in that the materials are anodized in an aqueous electrolyte solution based on H ₂ S0 ₄ . 10. Use of the materials produced according to one of claims 1 to 8 as a carrier material for offset printing plates carrying radiation-sensitive reproduction layers.