EP0086957B1 - Method of producing support materials for offset printing plates - Google Patents

Abstract

The process for manufacturing support materials for offset-printing plates is carried out in two stages. These materials are in the form of plates, foils, or strips, composed of aluminum, or an alloy thereof, which have been roughened by chemical, mechanical and/or electrochemical treatment. These two stages comprise an anodic oxidation in (a) an aqueous electrolyte based on sulfuric acid, and in (b) an aqueous electrolyte with a content of anions which contain phosphorus. An electrolyte with a content, in solution, of phosphoroxo anions, phosphorofluoro anions, and/or phosphoroxofluoro anions is employed in stage (b), and the treatment is carried out at a voltage between about 10 and 100 V, at a temperature of from about 10 DEG to 80 DEG C., and for a duration of from abut 1 to 60 seconds. The electrolyte is, in particular, an oxygen acid of phosphorus, or a salt with the above-mentioned anions. Following stage (b), it is also possible to carry out an additional treatment to impart hydrophilic properties to the support material.

Description

The invention relates to a two-stage anodic oxidation process for aluminum, which is used as a carrier material for offset printing plates.

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 light-sensitive layer (copying layer), with the aid of which a printing image is generated photomechanically. After the printing image has been produced, the support carries the printing image areas and at the same time forms the hydrophilic background for the lithographic printing process in the non-image areas (non-image areas).

• - Die nach der Belichtung relativ löslicher gewordenen Teile der lichtempfindlichen 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 lichtempfindlichen Schicht vor bzw. der druckenden Teile der Schicht nach der Belichtung muß in einem ausreichenden Maß gegeben sein.
• - Das Trägermaterial soll eine gute mechanische Beständigkeit z. B. gegen Abrieb und eine gute chemische Resistenz, insbesondere gegenüber alkalischen Medien besitzen.

The following requirements must therefore be placed on a layer support for light-sensitive material for the production of lithographic plates:

• - The parts of the photosensitive layer which have become relatively more soluble after 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 high 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 light-sensitive layer before or the printing parts of the layer after exposure must be sufficient.
• - The carrier material should have good mechanical resistance, for. B. against abrasion and good chemical resistance, especially against alkaline media.

Aluminum, which is roughened on the surface by known methods by dry brushing, wet brushing, sandblasting, chemical and / or electrochemical treatment, is used particularly frequently as the base material for such layer supports. To increase the abrasion resistance, electrochemically roughened substrates in particular are subjected to an anodization step to build up a thin oxide layer. These anodic oxidation processes are usually carried out in electrolytes such as H _z S0 ₄ , H ₃ P0 ₄ , H ₂ C ₂ O ₄ , H ₃ BO ₃ , amidosulfonic acid, sulfosuccinic acid, sulfosalicylic acid or mixtures thereof. The oxide layers built up in these electrolytes or electrolyte mixtures differ in structure, layer thickness and resistance to chemicals. In the production of offset printing plates, in particular aqueous H ₂ SO ₄ or H ₃ PO ₄ solution are used.

• - Das Gleichstrom-Schwefelsäure-Verfahren, bei dem in einem wäßrigen Elektrolyten aus üblicherweise ca. 230 g H₂S0₄ pro 1 I 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.-% HzS04 (ca. 100 g H₂SO₄/l) verringert oder auch auf 30 Gew.-% (365 g H₂SO₄/l) und mehr erhöht werden.
• - Die « Hartanodisierung wird mit einem wäßrigen, H₂SO₄ enthaltenden Elektrolyten einer Konzentration von 166 g H₂SO₄/l (oder ca. 230 g H₂SO₄/l) 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.

Reference is made, for example, to the following standard methods for the use of aqueous electrolytes containing H ₂ S0 ₄ for the anodic oxidation of aluminum (see, for example, BM Schenk, material aluminum and its anodic oxidation, Francke Verlag - Bern, 1948, page 760; Practical electroplating, Eugen G. Leuze Verlag - Saulgau, 1970, page 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 usually about 230 g H ₂ S0 ₄ per 1 I solution at 10 ° to 22 ° C and a current density of 0.5 to 2.5 A / dm ² is anodized for 10 to 60 min. The sulfuric acid concentration in the aqueous electrolyte solution can also be reduced to 8 to 10% by weight HzSO4 (approx. 100 g H ₂ SO ₄ / l) or to 30% by weight (365 g H ₂ SO ₄ / l) and be increased more.
• - The «hard anodization is carried out with an aqueous electrolyte containing H ₂ SO _{4 with} a concentration of 166 g H ₂ SO ₄ / l (or approx. 230 g H ₂ SO ₄ / l) at an operating temperature of 0 ° to 5 ° C, at a current density of 2 to 3 A / dm ² , a rising 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.

Aluminum oxide layers produced in this way are amorphous and, in the case of offset printing plates, usually have a layer weight of approximately 1 to 8 g / m ² , corresponding to a layer thickness of approximately 0.3 to 2.5 μm. The oxide layers are characterized by a fine channel-like structure; they have good mechanical resistance, which in particular protects the filigree structure of an electrochemically roughened aluminum against abrasion. A disadvantage of using an anodically oxidized carrier material for offset printing plates is the relatively low resistance of the oxide layers produced in H ₂ SO ₄ electrolytes to alkaline solutions, such as are increasingly being used, for example, in the processing of presensitized offset printing plates, preferably in contemporary developer solutions for exposed negative- or especially positive-working light-sensitive layers.

• In der DE-C-16 71614 (= US-A-3511 661) wird ein Verfahren zur Herstellung einer lithographischen Druckplatte beschrieben, bei dem der Aluminiumträger bei einer Temperatur von mindestens 17 °C in einer 42, 50, 68 oder 85 %igen wäßrigen H₃P0₄-Lösung anodisch oxidiert wird, bis die Aluminiumoxidschicht eine Dicke von mindestens 50 nm hat.

The anodic oxidation of aluminum in aqueous electrolytes containing phosphoric acid or phosphates is also known:

• DE-C-16 71614 (= US-A-3511 661) describes a process for producing a lithographic printing plate in which the aluminum support is at 42, 50, 68 or 85% strength at a temperature of at least 17 ° C. aqueous H ₃ P0 ₄ solution is anodically oxidized until the aluminum oxide layer has a thickness of at least 50 nm.

From DE-A-18 09 248 (= US-A-3 594 289) a method is known in which a printing plate Germ material from aluminum in an 50% aqueous H ₃ P0 ₄ solution at an current density of 0.5 to 2.0 A / dm ² and a temperature of 15 to 40 ° C is anodized.

The process for the anodic oxidation of aluminum supports, in particular for printing plates, according to DE-A-23 28 311 (US-A-3 836 437) is carried out in a 5 to 50% strength aqueous Na ₃ PO ₄ solution at a temperature of 20 up to 40 ° C, a current density of 0.8 to 3.0 A / dm ² and for a period of 3 to 10 min. The aluminum oxide layer produced in this way should have a weight of 10 to 200 mg / m ² .

The aqueous bath for the electrolytic treatment of aluminum, which is then to be provided with a water-soluble or water-dispersible coating substance, according to DE-B-23 49113 (= US Pat. No. 3,960,676) contains 5 to 45% of silicates, 1 to 2 , 5% of permanganates or from 1% to saturation of borates, phosphates, chromates, molybdate or vanadates.

DE-A-25 07 386 (= GB-A-1 495 861) describes the anodic oxidation of printing plate support materials made of aluminum, which are used at 10 to 40 ° C. using alternating current in a 1 to 20% aqueous H ₃ P0 ₄ - or polyphosphoric acid solution is carried out at a current density of 1 to 5 A / dm ² .

From DE-A-27 29 391 (= GB-A-1 587 260) a carrier material for printing plates is known which carries an oxide layer which consists of anodic oxidation of aluminum in an aqueous solution of H ₃ PO ₃ or a mixture H ₂ SO ₄ / H ₃ PO _{3 is} generated; Then this relatively porous oxide layer is overlaid with a second oxide film of the “barrier layer” type, which can be formed, for example, in aqueous solutions containing boric acid, tartaric acid or borates by anodic oxidation. Both the first stage (example 3, 5 min) and the second stage (example 3, 2 min) are carried out very slowly, as well as the second at a relatively high temperature (80 °).

An oxide layer produced in these electrolytes is often more resistant to alkaline media than an oxide layer produced in an electrolyte based on H ₂ SO ₄ solution; it also has some other advantages, such as a lighter surface, better water flow or low adsorption of dyes (“fog” in the non-image areas), but it also has significant disadvantages. In a modern belt system for the production of printing plate carriers, with practical tensions and dwell times, for example, only oxide layer weights of up to about 1.5 g / m ² can be produced, a layer thickness that naturally offers less protection against mechanical abrasion than a thicker one in an H ₂ S0 ₄ electrolyte produced oxide layer. Due to the larger pore volume and diameter of an oxide layer built up in H ₃ P0 ₄ , the mechanical stability of the oxide itself is also lower, which results in a further loss in terms of abrasion resistance.

Methods have also become known which attempt to combine the advantages of both electrolytes by using electrolyte mixtures of H ₂ SO ₄ and H ₃ P0 ₄ or by a two-stage treatment.

The process for the production of printing plate support materials made of aluminum according to DE-OS-22 51 710 (= GB-PS-1 410 768) is carried out in such a way that the aluminum is first anodically oxidized in an electrolyte containing H ₂ SO ₄ and this oxide layer subsequently in a 5 to 50% by volume aqueous H ₃ PO ₄ solution is aftertreated without the action of electric current. The actual oxide layer should have a weight per unit area of 1 to 6 g / m ² , this weight decreasing significantly when immersed in the aqueous H ₃ P0 ₄ solution, for example by about 2 to per minute immersion time in an aqueous H ₃ P0 ₄ solution 3 g / m2. Electrochemical treatment in the H ₃ PO ₄ solution should also be possible (example 11) or the use of a mixed electrolyte composed of H ₃ PO ₄ / H ₂ SO ₄ (example 12), in which case an oxide layer is also removed.

Similar processes, in which, however, the treatment with the aqueous H _a P0 ₄ solution takes place exclusively without the influence of electric current, are also known from DE-A-2314 295 (= US-A-3 808 000) or DE-A -24 04 657 (= GB-A-1 441 476). A two-stage electrochemical treatment in an electrolyte based on N ₂ SO ₄ and then in an electrolyte based on H _a P0 ₄ is also described in DE-A-25 48177 or US-A-3 940 321.

A mixed electrolyte of H ₂ S0 ₄ and H ₃ P0 ₄ for the production of printing plate support materials is described in DE-A-27 07 810 (= US-A-4 049 504) and DE-OS-28 36 803 (= US-A-4 229 266), the latter also specifying a specific content of aluminum ions.

In EP-A-0 007 233 and 0 007 234, support materials for printing plates made of aluminum are anodized so that they act as central conductors first through a bath with aqueous H ₃ P0 ₄ and an anode and then into a bath with aqueous H _z S0 ₄ and run a cathode. The two electrodes can also be connected to an AC voltage source. It is also stated, but not further specified, that the treatment with H ₃ PO _{4 can be} a pure immersion treatment or that neutral or alkaline solutions would also be possible instead of the acids.

The processes with mixed electrolytes lead to the fact that - with increasing H ₃ P0 ₄ content - the properties of the oxide layer are shifted towards anodic oxidation in pure aqueous H ₃ P0 ₄ solutions, but they never reach them. On the other hand, the positive properties of anodic oxidation in pure aqueous N ₂ SO ₄ solutions (oxide layer thickness, abrasion resistance) also decrease. In terms of production technology, bathroom monitoring (for a solution with multiple components) is also very complex and difficult to control. The two-stage anodic Oxidation or treatment leads to the oxide layer built up in the H _Z S0 ₄ electrolyte being dissolved back to an excessive extent in the H ₃ PO ₄ solution under the previously known conditions.

• - die Tauchbehandlung in wäßrigen Lösungen von TiF₄, ZrF₄, HfF₄ oder entsprechenden komplexen Säuren oder Salzen aus der DE-B-13 00 415 (= US-A-3 440 050),
• - die Tauchbehandlung in wäßrigen Lösungen von Silikaten, Bichromaten, Oxalaten oder Farbstoffen aus der DE-B-14 71 701 (= US-A.3 181 461 und 3 280 734),
• - die Tauchbehandlung in einer wäßrigen Polyvinylphosphonsäurelösungaus der DE-C-16 21478 US-A-4 153 461),
• - die elektrolytische Behandlung in einer wäßrigen Natriumsilikat-Lösung aus der DE-A-25 32 769 (= US-A-3 902 976),
• - das teilweise Ablösen der Oxidschicht mit wäßrigen Säuren oder Basen (u. a. mit einer wäßrigen Na₃P0₄-Lösung) ohne Einwirkung von elektrischem Strom oder unter kathodischen Elektrolysebedingungen in einem ersten Schritt, und das Behandeln mit heißem Wasser oder Wasserdampf in einem zweiten Schritt aus der DE-A-25 40 561 (= GB-A-1 517 746), das Wasser kann auch gelöste Salze in einer Menge bis zu 20 Gew.-% enthalten (u. a. Phosphate oder Borate), und sein pH-Wert soll im Bereich von 2 bis 11 liegen ; die Behandlungstemperatur liegt bei 70 bis 130 °C, oder
• - eine Wärmebehandlung bei 100 bis 300 °C während etwa 1 min in trockener Luft oder unter Verwendung von Wasserdampf aus der DE-A-27 16 604.

The following post-treatment steps for aluminum anodized in an aqueous H ₂ S0 ₄ solution are also known in the field of printing plate support materials:

• the immersion treatment in aqueous solutions of TiF ₄ , ZrF ₄ , HfF ₄ or corresponding complex acids or salts from DE-B-13 00 415 (= US-A-3 440 050),
• immersion treatment in aqueous solutions of silicates, bichromates, oxalates or dyes from DE-B-14 71 701 (= US Pat. Nos. 3,181,461 and 3,280,734),
• - immersion treatment in an aqueous polyvinylphosphonic acid solution from DE-C-16 21478 US-A-4 153 461),
• the electrolytic treatment in an aqueous sodium silicate solution from DE-A-25 32 769 (= US-A-3 902 976),
• - The partial detachment of the oxide layer with aqueous acids or bases (including with an aqueous Na ₃ P0 ₄ solution) without exposure to electric current or under cathodic electrolysis conditions in a first step, and treatment with hot water or steam in a second step DE-A-25 40 561 (= GB-A-1 517 746), the water can also contain dissolved salts in an amount of up to 20% by weight (including phosphates or borates), and its pH should be in the Range from 2 to 11; the treatment temperature is 70 to 130 ° C, or
• - A heat treatment at 100 to 300 ° C for about 1 min in dry air or using steam from DE-A-27 16 604.

Of these aftertreatment methods, only the silication and boehmite formation (reaction with H ₂ O at a higher temperature) lead to a certain improvement in the alkali resistance of the oxide layers. Silicating can, however, lead to a deterioration in the shelf life of presensitized (already coated) printing plates; and boehmite formation is difficult to carry out in modern, high-speed belt systems, since it requires a relatively long treatment time (of more than 1 min, for example of 5 min), and boehmite formation can also lead to a deterioration in the layer adhesion.

• - in der EP-A-0 008 212 eine Elektrolyse in einem Borationen enthaltenden Bad vor der anodischen Oxidation in einem zweiten Bad (z. B. einer wäßrigen H_zS0₄-Lösung), der pH-Wert des ersten Bades sollte bei 9 bis 11 liegen und die Behandlungstemperatur bei 50 bis 80 °C ; die Stärke der ersten Schicht soll bei mindestens 2 µm liegen, die der zweiten bei höheren Werten (z. B. bei etwa 20 gm),
• - in der DE-B-2651 346 (= GB-A-1 523 030) eine Elektrolyse in einer wäßrigen Lösung aus einem Salz (wie einem Borat oder Phosphat) und gegebenenfalls einer Säure oder einem Salz als Sperrschicht-Bildner (z. B. Borsäure oder Ammoniumborat).

It is also occasionally described, for example, to carry out certain surface modifications before the anodic oxidation in H ₂ SO ₄ solutions

• - in EP-A-0 008 212 an electrolysis in a bath containing borate ions before the anodic oxidation in a second bath (e.g. an aqueous H _z SO ₄ solution), the pH of the first bath should be 9 to 11 and the treatment temperature at 50 to 80 ° C; the thickness of the first layer should be at least 2 µm, that of the second at higher values (e.g. around 20 gm),
• - in DE-B-2651 346 (= GB-A-1 523 030) electrolysis in an aqueous solution of a salt (such as a borate or phosphate) and optionally an acid or a salt as a barrier layer former (e.g. Boric acid or ammonium borate).

However, both publications only refer to aluminum, which is to be used for window frames, panels (paneling) and fastenings for building structures or decorative aluminum moldings for vehicles or household items. In addition, the formation of thinner layers would lead to them being too easily dissolved again during the second treatment.

In DE-B-2431 793 (GB-A-1 412929) an aluminum surface is treated with hot water or steam (to form a boehmite layer) and then an electrolysis in an aqueous solution of a salt of the silica, phosphorus , Molybdenum, vanadium, permanganic, tin or tungstic acid performed. This treatment is said to lead to a greater layer thickness, improved toughness, a finer structure and thus greater corrosion resistance (e.g. against acids or alkali). A similar process is also described in DE-B-24 32 364 (= US-A-3 945 899), where the surface of the aluminum can be present not only as a boehmite layer but also as a chemical conversion layer as a result of a chromate or phosphate treatment . The electrolysis time in the examples is in the range from 2 to 10 min. However, both treatment steps are too lengthy for modern belt systems, and in addition the non-electrolytically produced aluminum layers are less suitable for the practical requirements placed on high-performance printing plates (e.g. with regard to abrasion resistance and the interactions with the light-sensitive layer).

According to US Pat. No. 3,940,321, which, as already mentioned, describes a two-stage electrochemical treatment of aluminum supports, in which work is carried out first with a sulfuric acid and then with a phosphoric acid electrolyte, the duration of the electrolysis, in particular with the phosphoric acid electrolyte, to reach a maximum layer thickness at room temperature and a voltage of 12 V up to 20 min. The oxide layers produced in phosphoric acid are relatively stable in alkalis, but only relatively short electrolysis times can be verified in modern conveyor systems. Therefore these oxide layers will not reach maximum layer thicknesses. It is therefore necessary to make these relatively thin oxide layers particularly resistant to alkalis.

The object of the present invention is therefore to propose a method for increasing the alkali resistance of carrier materials for offset printing plates on the basis of roughened and anodically oxidized aluminum, which is relatively quick and without great effort in modern belt systems can be carried out in which the proportion of the oxide redissolution is low or a redissolution does not occur. At the same time, the known positive individual properties of oxide layers produced in aqueous sulfuric acid or aqueous phosphoric acid should also be retained in their current combination.

The invention relates to a process for the production of plate, film or tape-shaped support materials for offset printing plates made of chemically, mechanically and / or electrochemically roughened aluminum or one of its alloys by a two-stage anodic oxidation in a) an aqueous electrolyte based on sulfuric acid and then b) an aqueous electrolyte containing anions containing phosphorus, at a voltage between 10 and 100 V and at a temperature of 10 to 80 ° C. The process according to the invention is then characterized in that compounds containing Al ^{3 +} ions are added in stage a) and stage b) in an aqueous electrolyte containing a phosphoric acid, including the known phosphoric acid and / or a salt, with a Alkali, alkaline earth or ammonium cation and a Phosphoroxo, Phosphorfluoro- and / or Phosphoroxofluoro anion for a period of 1 to 60 seconds.

In a preferred embodiment of the process according to the invention, stage b) is carried out for a period of 5 to 60 seconds, at a voltage between 20 and 80 V and at a temperature of 15 to 60 ° C.

• Phosphorsäure H₃PO₄
• Natriumdihydrogenphosphat NaH₂P0₄
• Dinatriumhydrogenphosphat Na₂HP0₄
• Trinatriumphosphat Na₃P0₄
• Phosphorige Säure H₃P0₃
• Dinatriumphosphit Na₂HPO₃
• Diphosphorsäure (Pyrophosphorsäure) H₄P₂O₇
• Natriumpyrophosphat Na₄P₂O₇
• Triphosphorsäure H₅P₃O₁₀
• Natriumtriphosphat Na₅P₃O₁₀
• Polyphosphorsäure H_n+2P_nO_3n+1
• Hexanatriumtetrapolyphosphat Na₆P₄O₁₃
• Hexanatriummetaphosphat Na_e(P0₃)₆
• Dinatriummonofluorphosphat Na₂P0₃F
• Kaliumhexafluorphosphat KPF₆

The aqueous electrolyte with the stated content of certain phosphorus-containing anions preferably contains either a phosphoric acid or a salt with the corresponding anion, in particular a salt with an alkali metal, alkaline earth metal or ammonium cation and a phosphorus oxo, phosphorofluoro or phosphorus oxofluoro anion . The concentration of the aqueous electrolyte can be varied within wide limits; it is preferably between 5 and 500 g / l when using a phosphoroxo compound, in particular between 10 and 200 g / l and when using a phosphorus fluoro- or phosphoroxofluoro compound between 1 and 50 g / l, in particular between 5 and 25 g / l. Examples of suitable compounds containing phosphorus in the electrolyte are:

• Phosphoric acid H ₃ PO 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 (pyrophosphoric acid) H ₄ P ₂ O ₇
• Sodium pyrophosphate Na ₄ P ₂ O ₇
• Triphosphoric acid H ₅ P ₃ O ₁₀
• Sodium triphosphate Na ₅ P ₃ O ₁₀
• Polyphosphoric acid H _{n + 2} P _n O _{3n + 1}
• Hexasodium tetrapolyphosphate Na ₆ P ₄ O ₁₃
• Hexasodium metaphosphate Na _e (P0 ₃ ) ₆
• Disodium monofluorophosphate Na ₂ P0 ₃ F
• Potassium hexafluorophosphate KPF ₆

When using phosphoroxo anions, the alkali resistance of the layers produced by the process according to the invention generally remains - relatively independent of the electrolyte concentration - in a comparable range, ie in a range of approximately ± 50%, provided that the zincate test times are used as a basis; a certain exception is Na ₃ PO ₄ , which - with increasing electrolyte concentration - also results in increases in alkali resistance of up to about 100%. The current profile can be characterized approximately in such a way that, after a very short initial current density of approximately 3 to 10 A / dm ^2, this drops to values of less than 1 A / dm ² after approximately 2 to 5 seconds, and already after approximately 10 to 20 seconds to drop towards 0.

With the use of higher voltages, the alkali resistance of the layers generally also increases; An exception to this is the execution of the process in an electrolyte containing KPF ₆ , since a maximum of about 40 V occurs in the alkali resistance. With the exposure times of a maximum of 60 seconds used in the process according to the invention, only a very slight redissolving of the oxide layer occurs, for example, from about 2.8 g / m ² to about 2.5 to 2.7 g / m when using acids in stage b) m ² , ie up to about 0.3 g / m ² . If, on the other hand, salts, in particular neutral salts, are used in room b), there is practically no change in the oxide layer weight. When using higher temperatures in the process according to the invention, the redissolution of the oxide layer can occasionally be accelerated, so that in these cases work should be carried out in the middle or lower temperature range.

• - « Reinaluminium » (DIN-Werkstoff Nr. 3.0255), d. h. bestehend aus ≥ 99,5 % AI 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,t 3 % Sonstigem, oder
• - « A₁-Legierung 3003 » (vergleichbar mit DIN-Werkstoff Nr. 3.0515), d. h. bestehend aus ≥ 98,5 % Al, den Legierungsbestandteilen 0 bis 0,3 % Mg und 0,08 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.

Suitable substrates for the production of the carrier materials are those made of aluminum or one of its alloys. These include, for example:

• - "Pure aluminum" (DIN material no. 3.0255), ie consisting of ≥ 99.5% AI 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, t 3% other, or
• - "A ₁ alloy 3003" (comparable to DIN material no. 3.0515), ie consisting of ≥ 98.5% Al, the alloy components 0 to 0.3% Mg and 0.08 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.

These aluminum carrier materials are still mechanical (e.g. by brushing and / or with abrasive treatments), chemical (e.g. by etching agents) or electrochemical (e.g. by AC treatment in aqueous HCI, HN0 ₃ - or in salt solutions ) roughened. Aluminum printing plates with electrochemical roughening are used in particular in the process according to the invention.

In general, the process parameters in the roughening stage are in the following ranges: the temperature of the electrolyte between 20 and 60 ° C, the active substance (acid, salt) concentration between 5 and 100 g / I, the current density between 15 and 130 A / dm ² , the residence time between 10 and 100 sec and the electrolyte flow rate on the surface of the workpiece to be treated between 5 and 100 cm / sec; AC is usually used as the type of current, but modified types of current such as AC with different amplitudes of the current strength are also possible for the anode and cathode currents. The average roughness depth R _{z of} the roughened surface is in the range from about 1 to 15 μm, in particular in the range from 3 to 8 μm.

The roughness depth is determined in accordance with DIN 4768 in the version from October 1970, the roughness depth R _z is then the arithmetic mean of the individual roughness depths of five adjacent individual measuring sections. The individual roughness depth is defined as the distance between two parallels to the middle line that touch the roughness profile at the highest or lowest point within the individual measurement sections. The individual measuring section is the fifth part of the length of the part of the roughness profile which is used directly for evaluation and is projected perpendicularly onto the middle line. The middle line is the line parallel to the general direction of the roughness profile from the shape of the geometrically ideal profile, which divides the roughness profile so that the sum of the material-filled areas above it and the material-free areas below it are equal.

After the roughening process, a first anodic oxidation of the aluminum then follows in a further process step [step a)]. This is carried out in an electrolyte based on H ₂ S0 ₄ , as shown at the beginning when the prior art was assessed. In addition to sulfuric acid in the main, a suitable electrolyte according to the invention additionally contains Al ^{3 +} ions, which are introduced, for example, in the form of Al ₂ (SO ₄ ) ₃ . As described in DE-A-28 11 396 = US-A-4 211619, the Al ³⁺ content can also be adjusted to values of more than 12 g / l. Direct current is preferably used for anodic oxidation in this stage, but also in stage b) explained above, but alternating current or a combination of these types of current (e.g. direct current with superimposed alternating current) can also be used. The layer weights of the aluminum oxide layer produced in stage a) can range from approximately 1 to 8 g / m ² , corresponding to a layer thickness of approximately 0.3 to 2.5 m, and are preferably approximately 1.4 to 3 .0 g / m ² , corresponding to about 0.4 to 1.0 m. This oxide layer is then treated further in step b) after rinsing with water.

These roughened and two-stage anodically oxidized carrier materials are used in the production of offset printing plates having a light-sensitive layer, although they can also be additionally hydrophilized beforehand, for example, as explained in the description of the prior art.

In principle, all layers are suitable as light-sensitive layers which, after exposure, optionally with subsequent development and / or fixation, provide an imagewise surface from which printing can take place. They are applied either to the manufacturer of presensitized printing plates or directly by the consumer to the carrier material produced according to the invention.

• Positiv arbeitende o-Chinondiazid-, bevorzugt o-Naphthochinondiazid-Verbindungen, 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 und 1 124817 beschrieben werden.

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-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 124817.

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 154123, US-A-2 679 498 and 3 050 502 and GB-A-712 606.

Negative 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 compound free of diazonium groups and capable of condensing with an active carbonyl compound in an acid medium at at least one position on the molecule.

Positive-working layers according to DE-A-2610 842, which contain a compound which cleaves off on irradiation, a compound which has at least one C-0-C group which can be cleaved off by acid (e.g. an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally contain 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 part 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 . As photoinitiators are u. a. Benzoin, benzoin ethers, multinuclear quinones, acridine derivatives, phenazine derivatives, quinoxaline derivatives, quinazoline derivatives or synergistic mixtures of different 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 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 2322047 are described, applied to the carrier materials produced according to the invention, whereby highly light-sensitive, electrophotographic printing plates are formed.

• - Das Schichtgewicht des im H₂SO₄-haltigen Elektrolyten aufgebauten Aluminiumoxids wird nicht oder nur in geringem Maße beeinträchtigt, wodurch die mechanische Festigkeit (gute Abriebfestigkeit) erhalten bleibt.
• - Die Oberfläche ist heller als bei einer alleinigen Anodisierung in H₂SO₄-haltigen Elektrolyten, was zu einem verbesserten Kontrast zwischen Bild- und Nichtbildstellen der Druckform führt.
• - Die Alkaliresistenz ist der in einem H₃P0₄-haltigen Elektrolyten aufgebauten Oxidschicht qualitativ zumindest gleichwertig und wegen der größeren Schichtdicke quantitativ sogar überlegen.
• - Die Adsorption des Oxids für beispielsweise Farbstoffe aus der lichtempfindlichen Schicht wird deutlich reduziert oder sogar unterdrückt, wodurch eine « Farbschleier »-Bildung nach dem Entwicklungsvorgang verhindert werden kann.
• - Die Wasserführung des Oxids beim Drucken ist gegenüber einem nur in Stufe a) erzeugten Oxid verbessert ; die Auflagenleistung ist mit der herkömmlicher Druckplatten, d. h. einstufig in H₂S0₄- haltigen Elektrolyten anodisch oxidiert, vergleichbar.

The coated offset printing plates obtained from the carrier materials produced by the process 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, for example an aqueous alkaline developer solution. Surprisingly, offset printing plates, the support materials of which have been treated by the process according to the invention, are distinguished from those in which the same support material has been treated without the use of step b) by a considerably improved alkali resistance. In addition, the carrier materials produced according to the invention or the offset printing plates or printing plates produced from them have the following characteristics:

• - The layer weight of the aluminum oxide built up in the H ₂ SO ₄ -containing electrolyte is not or only slightly impaired, as a result of which the mechanical strength (good abrasion resistance) is retained.
• - The surface is lighter than when anodizing alone in H ₂ SO ₄ -containing electrolytes, which leads to an improved contrast between image and non-image areas of the printing form.
• - The alkali resistance is qualitatively at least equivalent to the oxide layer built up in an H ₃ P0 ₄ -containing electrolyte and even quantitatively superior due to the greater layer thickness.
• - The adsorption of the oxide for, for example, dyes from the light-sensitive layer is significantly reduced or even suppressed, as a result of which “color fog” can be prevented after the development process.
• - The water flow of the oxide during printing is improved compared to an oxide produced only in step a); the print run performance is comparable to that of conventional printing plates, ie anodically oxidized in one step in H ₂ S0 ₄ - containing electrolytes.

• Zinkattest (nach US-A-3 940 321, Spalten 3 und 4, Zeilen 29 bis 68 und Zeilen 1 bis 8) :
  • Als Maß für die Alkaliresistenz einer Aluminiumoxidschicht gilt die Auflösegeschwindigkeit der Schicht in sec in einer alkalischen Zinkatlösung. Die Schicht ist umso alkalibeständiger je länger sie zur Auflösung braucht. Die Schichtdicken sollten in etwa vergleichbar sein, da sie natürlich auch einen Parameter für die Auflösegeschwindigkeit darstellen. Man bringt einen Tropfen einer Lösung aus 500 ml H_zO dest., 480 g KOH und 80 g Zinkoxid auf die zu untersuchende Oberfläche und bestimmt die Zeitspanne bis zum Auftreten von metallischem Zink, was an einer Dunkelfärbung der Untersuchungsstelle zu erkennen ist.

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 . In addition, the following methods for testing the alkali resistance of the surface were used in the examples, the results of which were summarized in tables:

• Zinc certificate (according to US-A-3 940 321, columns 3 and 4, lines 29 to 68 and lines 1 to 8):
  • The rate at which the layer dissolves in an alkaline zincate solution is used as a measure of the alkali resistance of an aluminum oxide layer. The layer is more alkali-resistant the longer it takes to dissolve it. The layer thicknesses should be roughly comparable, since of course they also represent a parameter for the dissolution rate. One drop of a solution of 500 ml of H _z O dest., 480 g KOH and 80 g of zinc oxide on the surface to be examined, and determines the time to onset of metallic zinc, that of darkening of the examination is recognizable.

Gravimetric removal

The sample of a defined size, which is protected by a layer of lacquer on the back, is moved in a bath containing an aqueous solution of 6 g / l of NaOH. The weight loss suffered in this bath is determined gravimetrically. Times of 1, 2, 4 or 8 minutes are selected as the treatment time in the alkaline bath.

Comparative Example V1

A bright rolled aluminum sheet with a thickness of 0.3 mm was degreased with an aqueous alkaline pickling solution at a temperature of about 50 to 70 ° C. The electrochemical roughening of the aluminum surface was carried out using alternating current in an electrolyte containing HN0 ₃ , a surface roughness having an R _Z value of about 6 μm being obtained. The subsequent anodic oxidation was carried out in one process in accordance with the process described in DE-OS 28 11396 aqueous electrolytes containing H _z S0 ₄ and Al ₂ (SO ₄ ) ₃ , which resulted in a layer weight of 2.8 g / m ² .

example 1

An aluminum strip prepared according to the information in Comparative Example -V ₁ was anodically treated at room temperature at a direct voltage of 40 V in an aqueous solution containing 100 g / IH ₃ PO ₄ for 30 seconds. A steel electrode was used as the cathode in all examples. The oxide weight determination of the oxide, which is now lighter in comparison to comparative example V1, gave a value of 2.6 g / m ² . For further results and process variations, see Table 1.

Example 2

An aluminum strip prepared as described in Comparative Example V1 was anodically treated at room temperature at a direct voltage of 40 V in an aqueous solution containing 100 g / l Na ₃ PO ₄ for 30 seconds. The appearance of the surface corresponded to that of Example 1. The oxide weight determination gave a value of 2.8 g / m ² . For further results and process variations, see Table 1.

• 0,70 Gew.-Teile des Polykondensationsproduktes aus 1 Mol 3-Methoxy-diphenylamin-4-diazo- niumsulfat und 1 Mol 4,4'-Bis-methoxymethyl-diphenylether, ausgefällt als Mesitylensulfonat,
• 3,40 Gew.-Teile 85%ige Phosphorsäure,
• 3,00 Gew.-Teile eines modifizierten Epoxidharzes, erhalten durch Umsetzen von 50 Gew.-Teilen eines Epoxidharzes mit einem Molgewicht unterhalb 1 000 und 12,8 Gew.-Teilen Benzoesäure in Ethylenglykolmonomethylether in Gegenwart von Benzyltrimethylammoniumhydroxid,
• 0,44 Gew.-Teile feingemahlenes Heliogenblau G (C. I. 74100)
• 62,00 Vol.-Teile Ethylenglykolmonomethylether,
• 30,60 Vol.-Teile Tetrahydrofuran und
• 8,00 Vol.-Teile Butylacetat.

To produce an offset printing plate, this support was coated with the following negative-working photosensitive solution:

• 0.70 parts by weight of the polycondensation product from 1 mol of 3-methoxy-diphenylamine-4-diazo-niumsulfate and 1 mol of 4,4'-bis-methoxymethyl-diphenyl ether, precipitated as mesitylene sulfonate,
• 3.40 parts by weight of 85% phosphoric acid,
• 3.00 parts by weight of a modified epoxy resin obtained by reacting 50 parts by weight of an epoxy resin with a molecular weight below 1,000 and 12.8 parts by weight of benzoic acid in ethylene glycol monomethyl ether in the presence of benzyltrimethylammonium hydroxide,
• 0.44 part by weight of finely ground heliogen blue G (CI 74100)
• 62.00 parts by volume of ethylene glycol monomethyl ether,
• 30.60 parts by volume of tetrahydrofuran and
• 8.00 parts by volume of butyl acetate.

• 2,80 Gew.-Teilen Na₂SO₄ . 10H₂0,
• 2,80 Gew.-Teilen M_gSO₄ · 7H₂0,
• 0,90 Gew.-Teilen 85 %ige Phosphorsäure,
• 0,08 Gew.-Teilen Phosphorige Säure,
• 1,60 Gew.-Teilen nichtionischem Netzmittel,
• 10,00 Gew.-Teilen Benzylalkohol,
• 20,00 Gew.-Teilen n-Propanol und
• 60,00 Gew.-Teilen Wasser

entwickelt.After exposure through a negative mask, a solution of

• 2.80 parts by weight of Na ₂ SO ₄ . 10H ₂ 0,
• 2.80 parts by weight M _g SO ₄ · 7H ₂ 0,
• 0.90 parts by weight of 85% phosphoric acid,
• 0.08 part by weight of phosphorous acid,
• 1.60 parts by weight of nonionic wetting agent,
• 10.00 parts by weight of benzyl alcohol,
• 20.00 parts by weight of n-propanol and
• 60.00 parts by weight of water

developed.

The printing plate thus produced was quick to develop and free of fog. The bright appearance of the carrier surface resulted in a very good contrast between image and non-image areas. The circulation was 200,000.

Example 3

• 6,00 Gew.-Teile Kresol-Formaldehyd-Novolak (mit dem Erweichungsbereich 105 bis 120 °C nach DIN 53181)
• 1,10 Gew.- Teile des 4-(2-Phenyl-prop-2-yl)-phenylesters der Naphthochinon-(1,2)-diazid-(2)-sulfonsäure-(4),
• 0,81 Gew.-Teile Polyvinylbutyral,
• 0,75 Gew.-Teile Naphthochinon-(1,2)-diazid-(2)-sulfochlorid-(4),
• 0,08 Gew.-Teile Kristallviolett,
• 91,36 Gew.-Teile Lösemittelgemisch aus 4 Vol.-Teilen Ethylenglykolmonomethylether, 5 Vol.-Teilen Tetrahydrofuran und 1 Vol.-Teil Butylacetat.

An aluminum strip prepared and anodically aftertreated in accordance with Example 2 was coated with the following positive-working light-sensitive solution to produce an offset printing plate:

• 6.00 parts by weight cresol-formaldehyde novolak (with a softening range of 105 to 120 ° C according to DIN 53181)
• 1.10 parts by weight of the 4- (2-phenyl-prop-2-yl) phenyl ester of naphthoquinone (1,2) diazide (2) sulfonic acid (4),
• 0.81 part by weight of polyvinyl butyral,
• 0.75 part by weight of naphthoquinone- (1,2) -diazide- (2) -sulfochloride- (4),
• 0.08 part by weight of crystal violet,
• 91.36 parts by weight of solvent 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.

• 5,30 Gew.-Teile Natriummetasilikat - 9 H₂0
• 3,40 Gew.-Teile Trinatriumphosphat - 12 H₂O
• 0,30 Gew.-Teile Natriumdihydrogenphosphat (wasserfrei)
• 91,00 Gew.-Teile Wasser.

The coated tape was dried in the drying tunnel at temperatures up to 1200C. The printing plate thus produced was exposed under a positive template and developed with a developer of the following composition:

• 5.30 parts by weight of sodium metasilicate - 9 H ₂ 0
• 3.40 parts by weight of trisodium phosphate - 12 H ₂ O
• 0.30 parts by weight of sodium dihydrogen phosphate (anhydrous)
• 91.00 parts by weight of water.

The printing form obtained was perfect in terms of copying and printing technology and had a very good contrast after exposure, the print run was 150,000.

Examples 4 to 17

An aluminum sheet pickled, electrochemically roughened and anodized according to the information given in comparative example V1 was after-treated anodically with direct voltage at room temperature with the aqueous electrolyte solutions listed in Table 1. The treatment parameters also given in Table 1 were used for this.
(See table 1 page 10 f.)

Examples 18 to 38

An aluminum sheet prepared according to the specifications of Comparative Example V1 was anodized with the aqueous electrolyte solutions listed in Table 2 at room temperature for 30 seconds. The voltages and concentrations used for this are also shown in this table.

Example 39

• 10,00 Gew.-Teile 2,5-Bis(4'-diethylaminophenyl)-1,3,4-oxadiazol
• 10,00 Gew.-Teile eines Mischpolymerisates aus Styrol und Maleinsäureanhydrid mit einem Erweichungspunkt von 210 °C
• 0,02 Gew.-Teile Rhodamin FB (C. I. 45 170)
• 300,00 Gew.-Teile Ethylenglykolmonomethylether

A support which was anodically aftertreated in accordance with Example 26 with a voltage of 60 V for 30 seconds was coated with the following solution to produce an electrophotographically operated offset printing plate:

• 10.00 parts by weight of 2,5-bis (4'-diethylaminophenyl) -1,3,4-oxadiazole
• 10.00 parts by weight of a copolymer of styrene and maleic anhydride with a softening point of 210 ° C.
• 0.02 part by weight of Rhodamine FB (CI 45 170)
• 300.00 parts by weight of ethylene glycol monomethyl ether

• 35 Gew.-Teilen Natriummetasilikat . 9 H₂0,
• 140 Gew.-Teilen Glyzerin,
• 550 Gew.-Teilen Ethylenglykol und
• 140 Gew.-Teilen Ethanol

getaucht. Die Platte wurde dann mit einem kräftigen Wasserstrahl abgespült, wobei die nicht mit Toner bedeckten Stellen der Photoleiterschicht entfernt wurden, die Platte war dann druckfertig.The layer was negatively charged to about 400 V in the dark using a corona. The charged plate was exposed imagewise in a repro camera and then developed with an electrophotographic suspension developer which had a dispersion of 3.0 parts by weight of magnesium sulfate in a solution of 7.5 parts by weight of pentaerythritol resin ester in 1200 parts by volume of an isoparaffin mixture with a boiling range of 185 to 210 ° C. After removing the excess developer liquid, the developer was fixed and the plate was poured into a solution for 60 seconds

• 35 parts by weight of sodium metasilicate. 9 H ₂ 0,
• 140 parts by weight of glycerin,
• 550 parts by weight of ethylene glycol and
• 140 parts by weight of ethanol

submerged. The plate was then rinsed off with a powerful jet of water, removing the areas of the photoconductor layer not covered with toner, and the plate was then ready for printing.

Example 40

An aluminum strip prepared as described in Example 2 was immersed in a further treatment step (additional hydrophilization) in a 0.2% aqueous solution of polyvinylphosphonic acid at 50 ° C. for 20 seconds. After drying, the support material additionally hydrophilized in this way was further processed as described in Example 2, the ink-repelling effect of the non-image areas being able to be improved. An even more favorable hydrophilization was achieved with the complex-type reaction products described in DE-OS 31 26 636 from a) such polymers as polyvinylphosphonic acid and b) a salt of an at least divalent metal cation.

Claims (5)

1. A process for manufacturing support materials for offset printing plates, these materials being in . the form of plates, sheets or webs, from aluminum or an alloy thereof, which has been grained by chemical, mechanical and/or electrochemical treatment, this process employing a two-stage anodic oxidation in a) an aqueous electrolyte based on sulphuric acid, and, thereafter, in b) an aqueous electrolyte with a content of anions which contains phosphorus, at a voltage between 10 and 100 V and a temperature of 10 to 80 °C, wherein in stage a) A1³⁺ ion-containing compounds are added, and stage b) is carried out in an aqueous electrolyte with a content of an acid with phosphoroxo anions, including phosphoric acid which is known per se, and/or of a salt with an alkali metal cation, alkaline earth metal cation or ammonium cation and a phosphoroxo anion, phosphorofluoro anion or phosphoroxofluoro anion, for a duration of 1 to 60 seconds.

2. The process as claimed in claim 1, wherein b) is carried out at a voltage between 20 and 80 V, at a temperature of 15 to 60 °C, and for a duration of 5 to 60 seconds.

3. The process as claimed in claim 1 or 2, wherein the aqueous electrolyte, in b), contains 5 to 500 g/liter of a phosphoroxo compound.

4. The process as claimed in claim 1 or 2, wherein the aqueous electrolyte, in b), contains 1 to 50 g/liter of a phosphorofluoro compound, or of a phosphoroxofluoro compound.

5. The process as claimed in one of claims 1 to 4, wherein, after the stage b), a treatment to impart hydrophilic properties is additionally carried out.