EP0154201B1 - Process for the aftertreatment of aluminium oxide layers with aqueous solutions containing alkali-metal silicate, and their use in the production of supports for off-set 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 alkali metal silicate.

Backing 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 aid 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.

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 which have become relatively more soluble after the irradiation (exposure) must be easy to remove from the support without residue by development in order to produce the hydrophilic non-image areas.

The carrier exposed in the non-image areas must have a high affinity for water, i. H. 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 often 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:

In DE-C 907147 (= US-A 2 714 066), DE-B 14 71 707 (= US-A 3 181 461 and US-A 3 280 734) or DE-A 25 32 769 (= US -A 3 902 976) describes processes for the hydrophilization of printing plate support materials based on optionally anodically oxidized aluminum, in which these materials are treated with aqueous sodium silicate solution without or with the use of electric current.

From DE-C 11 34 093 (= US-A 3 276 868) and DE-C 16 21 478 (= US-A 4 153 461) it is known to use polyvinylphosphonic acid or copolymers based on vinylphosphonic acid, acrylic acid and vinyl acetate for the hydrophilization of printing plate support materials based on optionally anodized aluminum.

• die härtende Nachbehandlung von durch Tauchbehandlung in wäßrigen Alkalisilikatlösungen hergestellten Silikatschichten auf Druckplattenträgern aus Aluminium mit einer wäßrigen Ca(N0₃)₂-Lösung oder allgemein einer Erdalkalisalz-Lösung nach den US-A 2 882 153 und US-A 2 882 154 (= GB-A-764 442) wobei in der Regel Erdalkalisalzkonzentrationen von mehr als 3 Gew.-% angewandt werden ; die Trägermaterialien werden nur chemisch oder mechanisch aufgerauht und nicht anodisch oxidiert,
• ein Verfahren gemäß der DE-A 22 23 850 (= US-A 3 824 159) zur Beschichtung von Aluminiumformstücken, -blechen, -gußstücken oder -folien (u. a. auch für Offsetdruckplatten, aber speziell für Kondensatoren), bei dem eine anodische Oxidation in einem wäßrigen Elektrolyten aus einem Alkalisilikat und einem organischen Komplexbildner durchgeführt wird ; zu den Komplexbildnern zählen neben Aminen, Aminosäuren, Sulfonsäuren, Phenolen und Glykolen auch Salze organischer Carbonsäuren wie Maleinsäure, Fumarsäure, Citronensäure oder Weinsäure, oder das Verfahren zur Herstellung von kornartigen oder gemaserten Oberflächen auf Aluminium nach der DE-B 26 51 346 (GB-A 1 523 030), das direkt auf Aluminium mit Wechselstrom in einem Elektrolyten durchgeführt wird, der in wäßriger Lösung 0,01 bis 0,5 Mol/1 eines Alkalimetall- oder Erdalkalimetallhydroxids oder -salzes (z. B. einem Silikat) und gegebenenfalls 0,01 bis 0,5 Mol/I eines Sperrschichtbildners enthält, zu den Sperrschichtbildnern sollen u. a. Citronensäure, Weinsäure, Bernsteinsäure, Milchsäure, Äpfelsäure oder deren Salze gehören.

Although these post-treatment processes often lead to sufficient results, they cannot meet all, often very complex, requirements for a printing plate support material, as are currently placed on high-performance printing plates in practice. For example, after treatment with alkali metal silicates, which lead to good developability and hydrophilicity, a certain deterioration in the storage life of reproductive layers applied thereon may occur. In the treatment of carriers with water-soluble organic polymers, their good solubility, particularly in aqueous alkaline developers, as are used predominantly for the development of positive-working reproduction layers, leads to a weakening of the hydrophilizing effect. The alkali resistance, which is required in particular when using high-performance developers in the field of positive-working reproduction layers, is not sufficient. Occasionally, depending on the chemical composition of the reproductive layers, fogging occurs in the non-image areas, which is likely to be caused by adsorptive effects. Modifications of the silicating processes have also been described in the prior art, for example:

• the curing aftertreatment of silicate layers produced by immersion treatment in aqueous alkali silicate solutions on aluminum printing plate supports with an aqueous Ca (N0 ₃ ) ₂ solution or generally an alkaline earth metal salt solution according to US Pat. Nos. 2,882,153 and 2,882,154 (= GB -A-764 442) wherein alkaline earth metal salt concentrations of more than 3% by weight are generally used; the carrier materials are only chemically or mechanically roughened and not anodically oxidized,
• a method according to DE-A 22 23 850 (= US-A 3 824 159) for coating aluminum moldings, sheets, castings or foils (including for offset printing plates, but especially for capacitors), in which anodic oxidation in an aqueous electrolyte of an alkali silicate and an organic complexing agent is carried out; to the com In addition to amines, amino acids, sulfonic acids, phenols and glycols, plexing agents also include salts of organic carboxylic acids such as maleic acid, fumaric acid, citric acid or tartaric acid, or the process for producing grain-like or grained surfaces on aluminum according to DE-B 26 51 346 (GB-A 1 523 030), which is carried out directly on aluminum with an alternating current in an electrolyte which, in aqueous solution, contains 0.01 to 0.5 mol / 1 of an alkali metal or alkaline earth metal hydroxide or salt (e.g. a silicate) and optionally 0, Contains 01 to 0.5 mol / l of a barrier layer, the barrier layer should include citric acid, tartaric acid, succinic acid, lactic acid, malic acid or their salts.

However, these known modifications of silicatization, anodic oxidation processes or surface structuring with electrolytes with a content of organic acids or their salts - if they can be transferred to printing plate supports made of aluminum at all or are sensible for them - do not yet lead to a surface which is suitable for high-performance printing plates is, d. H. the silicate layers have not yet been improved in terms of application technology in such a way that they fully meet the requirements described above.

EP-A 0 095 581 describes an aftertreatment process for aluminum oxide layers, aftertreatment being carried out with an alkali silicate solution which additionally contains at least one aliphatic hydroxymono-, di- or tricarboxylic acid, an aliphatic dicarboxylic acid or a water-soluble salt of these acids.

In the older, non-prepublished DE-A 32 32 485 a process for the aftertreatment of roughened and anodized aluminum supports for printing plates is described, which is carried out in two stages a) with an aqueous alkali metal silicate solution and b) with an aqueous alkaline earth metal salt solution.

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 Silikalisierungsverfahren improved in effect.

The invention is based on the known process for the production of plate, foil or tape-shaped materials based on electrochemically in an aqueous solution containing nitric acid or mechanically and electrochemically roughened and anodically oxidized aluminum or one of its alloys containing nitric acid. the aluminum oxide layers are aftertreated with an aqueous solution containing alkali metal silicate. The invention is then characterized in that the aftertreatment is carried out with an aqueous solution containing alkali metal silicate and alkaline earth metal cations.

In general, water-soluble alkaline earth metal salts, preferably calcium or strontium salts, are used as the compounds which provide alkaline earth metal ions, which also includes hydroxides in addition to the acid-derived compounds, in particular nitrates. In preferred embodiments, the aqueous solution contains 0.5 to 30% by weight, in particular 1 to 15% by weight, of alkali metal silicate (such as sodium metasilicate or the sodium and tetrasilicates contained in the water glass) and 0.001 to 0.5% by weight, in particular 0.005 to 0.3% by weight, of alkaline earth metal ions (such as Ca ²⁺ or Sr ²⁺ ). In addition, this aqueous solution can also contain at least one complexing agent for alkaline earth metal ions such as hydroxycarboxylic acids, aminocarboxylic acids, nitrogen or hydroxy compounds containing hydroxyl or carboxyl groups (for example levulinic acid, ethylenediaminetetraacetic acid or salts thereof).

The aftertreatment can be carried out as an immersion treatment or also electrochemically, the latter procedure often bringing about a further increase in the alkali resistance and / or improvement in the adsorption behavior of the material. The electrochemical process variant is carried out in particular with direct or alternating current, trapezoidal, rectangular or triangular current or overlapping forms of these types of current; the current density is generally 0.1 to 10 A / dm ² and / or the voltage is 1 to 100 V, the rest of the parameters depend on z. B. from electrode spacing or the electrolyte composition. The aftertreatment of the materials can be carried out discontinuously or continuously in 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. It is assumed that a firmly adhering cover layer forms in the pores of the aluminum oxide layer, which protects the oxide from attacks. 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. These aluminum carrier materials can also be roughened mechanically (for example by brushing with wire or nylon brushes and / or with abrasive treatments), if necessary after pre-cleaning, before the electrochemical stage will. 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 continuous process control, in the electrochemical roughening stage are in the following ranges: the temperature of the aqueous electrolyte, in particular 0.3 to 3.0% by weight of nitric acid (HNO ₃ ), between 20 and 60 ° C. the current density between 3 and 200 Aldm ² , the residence time of a material point to be roughened in the electrolyte between 3 and 100 sec 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 80 Hz is 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 _{z of} the roughened surface is in the range from 1 to 15 μm, in particular from 1.5 to 8.0 μm. In addition to HN0 ₃ , aluminum ions in the form of aluminum salts, in particular Al (NO ₃ ) ₃ , can also be added to the aqueous electrolyte; the addition of certain other acids and salts such as boric acid or borates or of corrosion inhibitors such as amines is also known.

As can be seen from the comparative experiments shown below, the aftertreatment according to the invention is surprisingly effective only after roughening in aqueous electrolytes based on HNO ₃ , but not, for example, after roughening in an electrolyte based on HCl.

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 have only a rinsing and / or cleaning effect and for example to remove deposits formed during roughening (“Schmant •) or simply serve to remove 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. 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 image-like area 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 Verbindund 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--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 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 will :

• 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, 1 154 123, U.S. 2,679,498 and 3,050,502 and GB 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 and 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 on irradiation, a monomeric or polymeric compound which has at least one C-cleavable by acid --OC group (e.g. an orthocarboxylic acid ester group or a carboxylic acid amidacetal 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 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 can also be photoconductive layers such as z. B. in DE-C 11 17 391, 15 22 497, 15 72 312, 23 22 046 and 23 22 047 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, the base support materials of which have been post-treated by the process according to the invention, are distinguished from those in which the same base material has been post-treated with aqueous solutions containing only alkali metal silicates, by improved hydrophilicity of the non-image areas, a lower tendency to form color fog and improved alkali resistance. These observations also apply to a two-stage post-treatment with alkaline earth metal ions in the second stage.

• Bei der Untersuchung, ob die Oberfläche eine Farbstoffadsorption 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 adsorbiert. Die Werte 0 bis 5 bedeuten keine (0), eine sehr schwache (1) bis starke (5) Farbstoffadsorption, es werden nur halbe Stufen angegeben.

In the above description and the examples below,% 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, 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 adsorbed 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.

The alkali resistance of the surface is determined by immersing a piece of plate not provided with a radiation-sensitive layer in an aqueous dilute NaOH solution for a certain period of time (for example 30 minutes) and then visually assessing the oxide layer. The values a to e mean no (a) to strong (e) oxide layer attack, only whole steps are given.

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-phenylprop-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 support material. Practical printing plates and printing forms can be created from it.

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 untreated oxide layer is rated 3 in dye adsorption and a in alkali resistance.

Comparative Example V2

The procedure of V 1 is followed, but roughened in an aqueous solution containing 0.9% of HCl; dye adsorption is rated 5 and alkali resistance a.

Comparative Example V 3

The procedure of V 1 is followed, but test pieces of the strip are after-treated in an aqueous solution containing 4% of Na ₂ SiO ₃ for 30 seconds at 40 ° C. by dipping; the post-treated oxide layer is rated 3.5 in dye adsorption and a in alkali resistance.

Comparative Example V4

The procedure according to V 2 is followed, but test pieces of the strip are after-treated in an aqueous solution containing 4% of Na ₂ Si0 ₃ for 30 seconds at 40 ° C. by dipping; the post-treated oxide layer is rated 3 in dye adsorption and a in alkali resistance.

Comparative example V5

The procedure is V 1, but test pieces of the strip are after-treated electrochemically (40 V DC) for 30 seconds at 25 ° C. in an aqueous solution containing 4% of Na ₂ SiO ₃ ; the post-treated oxide layer is rated 1 in dye adsorption and a in alkali resistance.

Comparative Example V 6

The procedure is V 2, but test pieces of the strip are aftertreated electrochemically (40 V DC) for 30 seconds at 25 ° C. in an aqueous solution containing 4% of Na ₂ Si0 ₃ ; the post-treated oxide layer is rated 1.5 in dye adsorption and a in alkali resistance.

Comparative Example V 7

The procedure is according to V 1, but test pieces of the tape are in an aqueous solution containing 4% of Na _z Si0 ₃ for 30 seconds at 40 ° C. in the first stage and in a 0.1% Sr ^{2 +} ion [in the form after-treatment of Sr (NO ₃ ) ₂ ] in aqueous solution in the second stage for 10 seconds at 25 ° C. by immersion; the two-stage post-treated oxide layer is rated 2.5 in dye adsorption and a in alkali resistance.

example 1

The procedure according to V 7 is followed, but in one stage in an aqueous solution containing 4% of Na ₂ SiO ₃ and 0.1% of Sr ^{2 +} ions [in the form of Sr (NO ₃ ) ₂ ] for 30 seconds at 40 ° C treated by diving; the oxide layer aftertreated according to the invention is rated 1 in dye adsorption and a in alkali resistance.

Example 2

The procedure according to V 7 is followed, but in one stage in an aqueous solution containing 4% of Na ₂ Si0 ₃ , 0.1% of Sr ^{2 +} ions [in the form of Sr (OH) ₂ ] and additionally 0.1% of levulinic acid Solution after-treated for 30 seconds at 40 ° C. by immersion; the oxide layer aftertreated according to the invention is rated 1 in dye adsorption and a in alkali resistance.

Example 3

The procedure of Example 1 is followed, but after-treated electrochemically (25 V DC) for 30 seconds at 25 ° C .; the oxide layer aftertreated according to the invention is rated 0.5 in dye adsorption and a in alkali resistance.

Comparative Example V 8

The procedure of Example 1 is followed, but the electrochemical roughening step is carried out in aqueous HCl solution; the post-treated oxide layer is rated 4 in dye adsorption and a in alkali resistance.

Claims (11)

1. Process for manufacturing materials in the form of sheets, foils or webs, based on aluminum or an alloy thereof, which has been grained electrochemically in an aqueous solution containing nitric acid or mechanicaiiy and electrochemically in a solution containing nitric acid and anodically oxidized and the aluminum oxide layers of which are post-treated with an aqueous solution containing alkali metal silicate, wherein post-treatment is performed in an aqueous solution containing alkali metal silicate and alkaline earth metal ions.

2. A process as claimed in Claim 1, wherein water-soluble alkaline earth metal salts are employed as compounds which yield alkaline earth metal ions.

3. A process as claimed in Claim 2, wherein calcium or strontium salts, in particular nitrates or hydroxides, are employed as alkaline earth metal salts.

4. A process as claimed in any of Claims 1 to 3, wherein the aqueous solution used for post-treatment contains 0.5 to 30 % by weight of alkali metal silicate and 0.001 to 0.5 % by weight of alkaline earth metal ions.

5. A process as claimed in any of Claims 1 to 4, wherein the aqueous solution used for post-treatment contains 1 to 15 % by weight of alkali metal silicate and 0.005 to 0.3 % by weight of alkaline earth metal ions.

6. A process as claimed in any of Claims 1 to 5, wherein the aqueous solution used for post-treatment additionally contains at least one complex- forming substance for alkaline earth metal ions.

7. A process as claimed in any of Claims 1 to 6, wherein post-treatment is an electrochemical or immersion treatment performed for a period of 0.5 to 120 seconds and at a temperature of 15 to 80 °C.

8. A process as claimed in Claim 7, wherein post-treatment is performed electrochemically at a current density of 0.1 to 10 Aldm² and/or a voltage of 1 to 100 V.

9. A process as claimed in any of Claims 1 to 8, wherein the materials are electrochemically roughened in an aqueous solution containing 0.3 to 3.0 % by weight of nitric acid.

10. A process as claimed in any of Claims 1 to 9, wherein anodic oxidation of the materials is performed in one or two steps, in aqueous solutions containing H_zS0₄ and/or H₃P0₄.

11. Use of the process as claimed in any of Claims 1 to 10 for manufacturing a support material for offset printing plates.