EP0008440B1 - Process for the anodic oxidation of aluminium and its application as printing-plate substrate material - Google Patents

Description

The invention relates to a method for the anodic oxidation of aluminum, the use of the material produced thereafter as a printing plate carrier material and a method for producing a printing plate carrier material.

In the processing of aluminum or its alloys, for example in the form of strips, foils or plates, there has been a trend in recent decades towards the continuous improvement of the aluminum surface in order to prepare it for a wide variety of applications. The most diverse properties that are to be achieved with regard to the surface include, for example: corrosion resistance, appearance, density, hardness, wear resistance, absorption capacity and adhesion for paint or synthetic resin coatings, dyeability, gloss, etc. The development of bright rolled aluminum proceeded starting with chemical, mechanical and electrochemical surface treatment processes, whereby combinations of the different processes are also used in practice.

In particular when processing such strip, foil or plate-shaped material made of aluminum or its alloys, which is to be used as a carrier material for (planographic) printing plates, the combination of a mostly mechanical or electrochemical roughening stage has become the preliminary conclusion of technical development a subsequent treatment step by anodic oxidation of the roughened aluminum surface. However, depending on the desired print run of the treated printing plate, anodic oxidations can also be carried out on aluminum materials which are not subjected to a separate roughening treatment, they then only have to have a surface on which a sufficiently adhesive aluminum oxide layer can be produced by the anodic oxidation, which in turn should offer good adhesion for a light-sensitive layer to be applied.

Anodic layers on (planographic) printing plates are particularly suitable for better guidance of the fountain solution (= increased hydrophilicity) and for increasing the resistance to abrasion and thus, for example, to prevent the loss of printing parts on the surface during the printing process and also have, for example, a increased adhesive strength compared to the photosensitive layer.

Due to their natural porosity, conventional anodic layers also have disadvantages. Depending on the anodizing conditions, these are an increased susceptibility to alkali, which can be found, for example, in the usual media used for the development of the light-sensitive layers or in the fountain solution, and a more or less irreversible adsorption of substances from the applied coating. This adsorption can then lead to the so-called "fog", i. H. a discoloration of the oxide layer, which becomes visible in the then image-free parts of the printing plate after the development of the exposed photosensitive layer. This "fog" is particularly evident in the frequently required chemical correction, especially with positive plates, e.g. B. to remove film edges of the printed image, the substances causing the veil are also dissolved out of the depth of the oxide layer. The corrected areas appear as bright areas on a tinted background. In the worst case, the sensitivity to alkali and the correction spots mentioned lead to difficulties in printing, which can be caused by the tendency of the printing plates to toning in their non-image areas and by a reduced circulation of the printing plates.

• Das Gleichstrom-Schwefelsäure-Verfahren, bei dem in einem wäßrigen Elektrolyten aus üblicherweise ca. 230 g H₂S0₄ pro 1 Itr. 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.-% H₂S0₄ (ca. 100 g H₂S0_4/Itr.) verringert oder auch auf 30 Gew.-% (365 g H₂S0_4/ttr.) und mehr erhöht werden. Durch die bei der anodischen Oxidation aus AI-Atomen entstehenden AI^3+-lonen befindet sich im wäßrigen, H₂S0₄ enthaltenden Elektrolyten auch immer ein bestimmter Anteil an A1^3+-lonen, der jedoch möglichst konstant gehalten wird, um reproduzierbare Ergebnisse hinsichtlich der Schichteigenschaften zu erzielen. Diese Konstanthaltung der A1^3+-lonenkonzentration wird durch eine kontinuierliche Elektrolytregeneration erreicht, wobei der AI^3+-lonengehalt im Bereich von etwa 8 bis 12 g A1³⁺/ltr. gehalten wird. Die Erschöpfung eines für das genannte Verfahren geeigneten wäßrigen, H₂S0₄ enthaltenden Elektrolyten tritt spätestens bei etwa 15 bis 18 g Al³⁺/Itr. ein, wobei Werte von mehr als 12 g A1³⁺/ltr. bereits in der Praxis möglichst vermieden werden.

The following standard methods for the anodic oxidation of aluminum in aqueous electrolytes containing H ₂ SO ₄ are known from the prior art (see, for example, BM Schenk, material aluminum and its anodic oxidation, Francke Verlag - Bern, 1948, page 760; practical electroplating technology , 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 .), H ₂ S0 _{4 has} proven to be the most useful electrolyte acid for most applications:

• The direct current sulfuric acid process, in which in an aqueous electrolyte usually from about 230 g H ₂ S0 ₄ per 1 liter. Solution is anodized at 10 ° to 22 ° C and a current density of 0.5 to 2.5 A / dm ² for 10 to 60 min. The sulfuric acid concentration in the aqueous electrolyte solution can also be reduced to 8 to 10% by weight of H ₂ S0 ₄ (approx. 100 g of H ₂ S0 _{4 /} liter) or to 30% by weight (365 g of H ₂ S0 _{4 /} ttr.) And more can be increased. As a result of the Al ^{3 +} ions formed in the anodic oxidation from Al atoms, there is always a certain proportion of A1 ^{3 +} ions in the aqueous electrolyte containing H ₂ S0 ₄ , but this is kept as constant as possible to ensure reproducible results to achieve the layer properties. This constant maintenance of the A1 ^{3 +} ion concentration is achieved by continuous electrolyte regeneration, the AI ^{3 +} ion content being in the range from approximately 8 to 12 g of A1 ³⁺ / ltr. is held. The exhaustion of an aqueous electrolyte containing H ₂ SO ₄ suitable for the process mentioned occurs at the latest at about 15 to 18 g of Al ³⁺ / it. a, where values of more than 12 g A1 ³⁺ / ltr. should be avoided as far as possible in practice.

The »hard anodization« is carried out with an aqueous electrolyte containing H ₂ SO _{4 with} a concentration of 166 g H ₂ S0 _{4 /} ltr. (or about 230 g H ₂ S0 _{4 /} ltr.) at an operating temperature of 0 ° to 5 ° C, at a current density of 2 to 3 A / dm ² , an increasing voltage of about 25 to 30 V at the beginning and about 40 to 100 V towards the end of the treatment and carried out for 30 to 200 min.

Although these processes provide oxide layers on aluminum which can be used for many fields of application, they have some disadvantages, for example, when used for the production of support materials for printing plates. These include, on the one hand, the increased susceptibility of the layers produced afterwards to alkali and the "fog" and, on the other hand, the energy to be achieved, in particular in the case of "hard anodizing", in order to achieve and keep the low electrolyte temperatures constant and the relatively long residence times of aluminum for the economically advantageous continuous anodizing of aluminum in the electrolyte.

To improve the properties of oxide layers, in particular for printing plate support materials, other known anodizing processes with additions of various organic compounds or chromic acid are also unsuitable, namely they lead to more or less colored oxides. Phosphoric acid as the sole electrolyte or in mixtures has so far had little or no significance for anodizing processes that can be used on a large industrial scale. With this acid, layer growth only leads to relatively thin layers. However, these thin layers are not so dense that they can be used, for example, as forming layers for capacitors with z. B. from borates or citric acid layers could compete (see M. Schenk, material aluminum and its anodic oxidation, Francke Verlag Bern, 1948, page 324). The strong redissolving power of phosphoric acid for aluminum oxide offers not only a possible explanation for this behavior (M. Schenk, page 385), but also that thicker and also abrasion-resistant oxide layers cannot be produced under economically justifiable conditions or only under difficult conditions. The large-pore structure of the oxide layers produced in phosphoric acid (M. Schenk, page 585) and the lower abrasion resistance of these layers are probably also to be attributed to this redissolving power.

Modified electrolytes based on phosphoric acid are therefore described in particular in the processes for the anodic oxidation of aluminum known from the prior art. The process for the anodic treatment of objects made of aluminum according to DE-C-821 898 is carried out with an anodic gloss step in a bath of 70% H ₂ SO ₄ , 20% H ₃ PO ₄ and 10% water at a current density of 15 to 30A / dm ² , a temperature between 70 and 90 ° C and carried out for 3 to 5 minutes and results in shiny and reflective surfaces.

From DE-C-825 937 a method for anodizing aluminum objects is known, in which a bath of 40 to 60% H ₂ SO ₄ , 5 to 35% H ₃ PO ₄ , 5 to 25% sulfonic acids of benzene and the rest of the water is used at a temperature of 65 to 100 ° C.

DE-C-957616 describes a process for the galvanic production of uniformly granular, shiny surfaces on aluminum, in which the electrolyte comprises 40 to 70% by volume H ₂ SO ₄ , 0 to 20% by volume H ₃ PO ₄ , Contains 2 to 5 vol .-% HNO ₃ , 0.5 to 2 vol .-% HF and a wetting agent. The electrolyte temperature is approximately 60 to 100 ° C. over a period of 3 to 10 minutes, and the current density ranges from approximately 30 to 40 A / dm ² at the beginning and 10 to 15 A / dm ² towards the end of the treatment.

In the anodizing step in the process for producing a lithographic printing plate according to DE-C-1 671 614 (= US-A-3511 661), which leads to an anodized aluminum support, a 42-50 -, 68- or 85% H ₃ P0 _{4 brought} into effect. The current densities used are 1.615, 2.153, 2.583 or 2.691 A / dm ² , the thickness of the aluminum oxide layer is at least 50 · 10- ⁹ m, and the cells of the aluminum oxide layer are 15 to 75. 10- ⁹ m wide.

The process for producing offset printing plates made of aluminum according to DE-A-1 956795 (= GB-A-1 240 577) has, inter alia, an anodizing stage in which the previously etched printing plate is in a bath with 7.5 vol. % H ₂ SO ₄ and 5 vol.% H ₃ P0 _{4 is} anodized at a temperature of 23.9 ° C for 10 min and with a current density of 1.08 A / dm ² .

From DE-A-2 251 710 (= GB-PS 1 410 768) a process for the production of printing plate supports is known, in which an aluminum support anodically oxidized in an H ₂ SO ₄ containing electrolyte with an aqueous H ₃ PO ₄ - Solution is not post-treated electrolytically. In one example, a mixed electrolyte of 15% H ₂ S0 ₄ and 5% H ₃ P0 _{4 is used} for anodic oxidation for 8 min at 20 ° C and a current density of 2.5 A / dm ² .

DE-A-314 295 (= US Pat. No. 3,808,000) describes a process for treating a printing plate surface made of aluminum, in which the surface anodically oxidized in H ₂ S0 _{4 is} non-electrolytically aftertreated in an aqueous H ₃ P0 ₄ solution becomes.

In the process for the anodic pretreatment of elongated aluminum material according to DE-B-2 522 926, an aqueous solution containing 10 to 25% H ₂ SO ₄ and 20 to 50% H ₃ P0 _{4 is used} at temperatures above 80 ° C . The pretreatment is completed in about 5 to 6 seconds at a current density of 100 A / dm ² . The bath is used to dissolve aluminum oxide at high current densities and within a short time.

The process for producing colored, anodized aluminum according to DE-A-2 548 177 has an anodizing stage in which the aluminum is anodized in an H ₃ PO ₄ and a small amount of another acid such as e.g. B. H ₂ S0 ₄ containing bath is treated. As a concrete example, a bath of H ₃ PO ₄ (80 g / liter) and H ₂ SO ₄ (10 g / liter) is listed, in which the aluminum is treated for 2 minutes. Before this treatment, however, the surface is already anodized in H ₂ S0 ₄ (165 g / l) for 30 min at 20 ° C. and a current density of 1.5 A / dm ² .

From DE-A-2 707 810 (= US-A-4 049 504) a process for the production of offset printing plates is known, in which metal plates (in particular aluminum) are anodized in an aqueous solution of H ₂ SO ₄ and H ₃ PO ₄ be oxidized. The current densities are 1 to 16 A / dm ² , the temperatures of the electrolyte solution are 25 ° C to 50 ° C, the anodizing time is 15 seconds to 3 minutes. For 1 to 3 parts by weight of HzS0 _{4 there} should be 3 to 1 part by weight of H ₃ P0 ₄ in the acid mixture, the acid concentration should be between 5 and 40% by weight.

DE-A-2 729 391 describes a process for producing a support plate for lithography, in which a porous oxidized layer is produced in an electrolyte which is a mixture of H ₃ PO ₃ (phosphorous acid) and H ₂ SO ₄ contains, the current density should be about 0.1 to 2 A / dm ² .

The process for anodizing aluminum according to FR-A-1 285 053 is used as a preliminary step before the application of a chrome or nickel layer and in an electrolyte containing 5 to 45% by volume of H ₃ PO ₄ , 1 to 30 Vol .-% H ₂ S0 ₄ and 25 to 94 vol .-% water at a temperature of 27 ° C to 60 ° C, a duration of 1 to 30 min and a current density of 1.3 to 13 A / dm ² performed .

The anodic oxidation leading to bright, well reflecting surfaces on aluminum according to US Pat. No. 2,703,781 is made in an electrolyte from 15 to 40% by weight H ₃ PO ₄ , 2 to 10% by weight H ₂ SO ₄ and 50 to 83 wt .-% water at a current density of about 0.5 to 3 A / dm ² , a duration of 0.5 min to 50 min and a temperature of 15 ° C to 32 ° C.

From US-A-3 940 321 a process for the treatment of aluminum is known, in which the aluminum is first anodized in H ₂ S0 ₄ and then in H ₃ P0 ₄ .

EP-A-4569 (= DE-A-2 811 396), which has not been previously published, describes a process for the anodic oxidation of strip-shaped, sheet-like or plate-shaped material made of aluminum or its alloys in an aqueous, H ₂ SO ₄ and Al ³ Electrons containing ⁺ ions are proposed, in which the electrolyte has a concentration of H ₂ S0 ₄ of 25 to 100 g / ltr. and on Al ³⁺ ions from 10 to 25 g / ltr. at a current density of 4 to 25 A / dm ² and at a temperature of 25 ° C to 65 ° C.

However, these methods known from the prior art for the anodic oxidation of aluminum or its alloys and / or the materials produced thereafter, in particular printing plate support materials, have some disadvantages: The problem of the aluminum oxide layers produced in H ₃ PO ₄ as the sole electrolyte acid was mentioned already mentioned at the beginning, but the layers produced in mixed electrolytes from H ₂ S0 ₄ and H ₃ P0 ₄ are not usable in all areas of application. With a high electrolyte concentration in the anodizing bath of, for example, more than 50%, the polishing and leveling effect outweighs the layer growth, so that the surface structure necessary to achieve good anchoring of a layer to be applied (e.g. a light-sensitive layer) cannot be achieved; The same applies if high temperatures of, for example, more than 65 ° C. to 70 ° C. are used during the anodizing process. Low current densities of less than approximately 2 A / dm2 or high current densities of more than approximately 30 A / dm ² in conjunction with anodizing times of more than approximately 1.5 to 2 minutes also lead to layers that are either too slow for large-scale use or grow with too large porosity or where the layer build-up is too small or no, because the back-dissolving power of the electrolyte predominates. In the non-electrolytic or anodic aftertreatment of aluminum oxide layers produced in H ₂ SO ₄ in solutions containing H ₃ P0 ₄ , parts of the previously built-up oxide layer are dissolved again, so that there may be faults, particularly with regard to the abrasion resistance, adsorption capacity and structure of the surface, which then occur For example, in the case of printing plate carrier materials, this can lead to the increased susceptibility to alkali and "fog" mentioned at the beginning.

The object of the invention is therefore to propose a process for the production of anodically oxidized aluminum which uses the advantages of the electrolyte types H ₂ S0 ₄ and H ₃ P0 ₄ without taking on the disadvantages described, ie with the abrasion-resistant, alkali-resistant, little porous aluminum oxide layers of sufficient strength can be produced on aluminum strips, foils or plates with economically justifiable energy costs.

The invention is based on the known process for the anodic oxidation of strip, foil or plate-shaped material made of aluminum or its alloys in an aqueous electrolyte containing sulfuric acid and phosphoric acid, if appropriate after prior mechanical, chemical or electrochemical roughening. The process according to the invention is characterized in that the material in an electrolyte has a concentration of sulfuric acid of 25 to 150 g / l, phosphoric acid of 10 to 50 g / l. and anodized on aluminum ions of 5 to 25 g / l, at a current density of 4 to 25 A / dm ² and at a temperature of 25 ° to 65 ° C. In a preferred embodiment, this method is used with the Features specified for the production of a tape, film or plate-shaped printing plate carrier material. In the further explanations, the term printing plate is generally understood to mean a printing plate for planographic printing, which mainly consists of a flat support made of one or more materials and one or more light-sensitive layers which are also mounted thereon.

The process is carried out in particular in an electrolyte with a concentration of sulfuric acid of 25 to 75 g / l, of phosphoric acid of 25 to 40 g / l. and on aluminum ions of 10, preferably 12 to 20 g / Itr., at a current density of 6 to 15 A / dm2 and at a temperature of 35 ° C to 55 ° C.

• - »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 0,03% sonstigem, oder
• - »AI-Legierung 3003« (vergleichbar mit DIN-Werkstoff Nr. 3.0515), d. h. bestehend aus ≧98,5% Al, den Legierungsbestandteilen 0 bis 0,3% Mg und 0,8 bis 1,5% Mn und den folgenden zulässigen Beimengungen von 0,5% Si, 0,5% Fe, 0,2% Ti, 0,2% Zn, 0,1% Cu und 0,15% sonstigem

Aluminum or one of its alloys is used as the metal base for the strip, foil or plate-shaped material. Among them are preferred (also used in the following examples):

• - »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 0.03% other, or
• - »AI alloy 3003« (comparable to DIN material no. 3.0515), ie consisting of ≧ 98.5% Al, the alloy components 0 to 0.3% Mg and 0.8 to 1.5% Mn and the following admissible admixtures of 0.5% Si, 0.5% Fe, 0.2% Ti, 0.2% Zn, 0.1% Cu and 0.15% other

to understand.

The electrolyte is made of conc. H ₂ S0 ₄ , conc. H ₃ P0 ₄ , water and an added aluminum salt, especially aluminum sulfate, prepared so that it, to 1 liter. Based on electrolyte, 25 to 150 g of H ₂ SO ₄ , preferably 25 to 75 g of H ₂ SO ₄ , 10 to 50 g of H ₃ PO ₄ , preferably 25 to 40 g of H ₃ PO ₄ , and 5 to 25 g of A1 in solution ^{3 + -} ions, preferably 10, in particular 12 to 20 g of Al ^{3 + -} ions contains. The concentration ranges of the electrolyte components are checked at regular intervals, since they are of crucial importance for an optimal course of the process, and the electrolyte is then regenerated discontinuously or preferably continuously. Detailed information on the production, monitoring and regeneration of electrolytes in the anodic oxidation of aluminum can be found in W. Huebner, CT Speiser, The Practice of Anodic Oxidation of Aluminum, Aluminum Verlag - Düsseldorf, 1977, 3rd edition, pages 141 to 148 and pages 154 to 157, can be found there, there are also basic information on the procedure for the anodic oxidation of aluminum (page 149 and page 150).

The process according to the invention can be carried out batchwise or in particular continuously. A device such as that described in DE-B-2234424 (= US-A-3871 982) is suitable for carrying out the continuous procedure. This device has a treatment tub filled with the electrolyte, an inlet and an outlet for the band to be treated in the two end walls of the tub below the liquid level of the electrolyte, at least one electrode arranged above the metal band and devices for generating a rapid electrolyte flow between the transport path of the tape and the electrode surface. The electrolyte flow is generated by a bell-like chamber arranged along each end wall of the trough, which overflows the electrolyte with a liquid drain into a reserve container located below the trough, a gas space above the liquid level that is sealed off from the outside air, and a gas chamber that begins in this gas space. contains gas line connected to a suction pump. In addition, this device also has a pump for conveying the electrolyte from the reserve container into the tub.

Treatment devices of a different design are also suitable for the method according to the invention, as long as they ensure the conditions listed below with regard to treatment duration, electrolyte movement, material and heat exchange.

The method according to the invention is expediently carried out in such a way that the duration of the treatment of the anodic oxidation - ie the stay of a surface point in the area of influence of the electrode (s) - ranges from 5 to 60 seconds, preferably from 10 to 35 seconds. Layer weights of aluminum oxide in the range from 1 to 10 g / m ² (corresponding to a layer thickness of approximately 0.3 to 3.0 μm), preferably approximately 2 to 4 g / m ² , can then be obtained.

Good electrolyte circulation is required in the practice of the invention. This can be generated either by stirring or by pumping around the electrolyte. In the case of continuous operation (see, for example, DE-B-2234424), care must be taken to ensure that the electrolyte is guided as parallel as possible to the strip to be treated at high speed under turbulent flow while ensuring good material and heat exchange. The flow rate of the electrolyte relative to the strip is then expediently more than 0.3 m / sec. Direct current is preferably used for the anodic oxidation, but alternating current or a combination of these types of current (eg direct current with superimposed alternating current or the like) can also be used.

The method according to the invention for the anodic oxidation of aluminum can also be used, in particular in the embodiment of the method according to the invention for producing a Printing plate carrier material - one or more pretreatment stages, in particular a roughening stage, are preceded. Pretreatment is understood to mean either a mechanical surface treatment by grinding, polishing, brushing or blasting, a chemical surface treatment for degreasing, pickling or matting or an electrochemical surface treatment by the action of the electric current (mostly from alternating current) in an acid such as HCI or HN0 ₃ . Under these pretreatment stages, the mechanical and electrochemical treatment of the surfaces of the aluminum in particular lead to roughened surfaces. The average roughness depth Rz is in the range from about 1 to 15 μm, in particular in the range from 4 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 distances. The individual roughness depth is defined as the distance between two parallels to the middle line, which touch the roughness profile at the highest or lowest point within the individual measuring section. 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 of the shape of the geometrically ideal profile, which divides the roughness profile so that the sums of the material-filled areas above it and the material-free areas below it are equal.

The method according to the invention for the anodic oxidation of aluminum can also - like this also in particular in the embodiment of the method according to the invention for producing a printing plate support material - be followed by one or more post-treatment stages. Aftertreatment means in particular a chemical or electrochemical treatment of the aluminum oxide layer, for example an immersion treatment of the material in an aqueous polyvinylphosphonic acid solution according to DE-C-1 621 478 (= GB-A-1230447), an immersion treatment in an aqueous alkali silicate Solution according to DE-B-1 471 707 (= US-A-3181 461) or an electrochemical treatment (anodization) in an aqueous alkali silicate solution according to DE-A-2 532 769 (= US-A-3 902 976 ). These post-treatment mares serve in particular to further increase the hydrophilicity of the aluminum oxide layer, which is already sufficient for many areas of application, the other known properties of this layer being at least retained.

• Als lichtempfindliche Schichten sind grundsätzlich alle Schichten geeignet, die nach dem Belichten, gegebenenfalls mit einer nachfolgenden Entwicklung und/oder Fixierung eine bildmäßige Fläche liefern, von der gedruckt werden kann.

A field of application for a material anodically oxidized by the process according to the invention and optionally also pretreated and / or post-treated is in particular its use as a carrier material in the production of printing plates bearing a photosensitive layer. Here, either at the manufacturer of presensitized printing plates or when coating a carrier material at the consumer, the carrier material is coated with one of the following light-sensitive materials:

• 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.

In addition to the layers containing silver halides used in many fields, various others are also known, such as e.g. B. 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). Suitable layers also include the electrophotographic layers, i.e. H. those containing 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.

• 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, 1 114 705, 1 118 606, 1 120 273 und 1 124 817 beschrieben werden.

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, 1 114 705, 1 118 606, 1 120 273 and 1 124 817.

Negative-working condensation products from aromatic diazonium salts and compounds with active carbonyl groups, preferably condensation products from diphenylamine diazonium salts and formaldehyde, which are described, for example, in DE-C-596 731, 1 138 399, 1 138 400, 1 138 401, 1 142 871, 1 154 123, US-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-2 024 244, which each have at least one unit of the general types A (-D) "and B connected by a double bond derived from a condensable carbonyl compound Have intermediate link. 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 acidic medium at at least one position on the molecule.

Positive-working layers according to DE-A-2 610 842, which contain a compound which cleaves off on irradiation, a compound which has at least one COC group which can be cleaved by acid (for example an orthocarboxylic acid ester group or a carboxylic acid amide acetal group) and optionally a binder .

Negative working layers made of photopolymerizable monomers, photoinitiators, binders and optionally other additives. The monomers used here are, for example, acrylic and methacrylic acid esters or reaction products of diisocyanates with partial esters of polyhydric alcohols, as described, for example, in US Pat. Nos. 2,760,863 and 3,060,023 and DE-A-2,064,079 and 2,361,041 . As photoinitiators are u. a. Benzoin, benzoin ethers, mercury 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.

• - Bestimmung des Flächengewichtes von Aluminiumoxidschichten durch chemisches Ablösen (nach DIN 50 944 in der Ausgabe vom März 1969): Die Aluminiumoxidschicht wird durch eine Lösung aus 37 ml H₃P0₄ (Dichte von 1,71 g/ml bei 20° C entsprechend 85% H₃PO₄), 20 g CrO₃ und 963 ml H₂0 dest. bei 90 bis 95° C während 5 min vom Grundmetall abgelöst und der dabei entstehende Gewichtsverlust durch Wiegen der Probe vor und nach dem Ablösen bestimmt. Aus dem Gewichtsverlust und dem Gewicht der mit der Schicht bedeckten Oberfläche wird das Flächengewicht der Schicht berechnet und in g/m² angegeben.
• - Prüfung der Güte der Verdichtung anodisch erzeugter Oxidschichten im Anfärbeversuch (angelehnt an DIN 50 946 in der Ausgabe vom Juni 1968): Diese qualitative Meßmethode läßt insbesondere in Kombination mit einer nachfolgenden quantitativen Farbortbestimmung Aussagen darüber zu, ob und in welchem Ausmaß die anodisch oxidierte Oberfläche eines Aluminiummaterials zur »Schleierbildung« neigt. Zur Messung wird ein flächiger Materialabschnitt von 5 cm - 12 cm hälftig während 20 min in eine Lösung von 0,5 g/Itr. an Aluminium-Blau (^@Solway Blue BN 150 der ICI) in H₂0 dest. bei 40° bis 45° C eingetaucht, mit H₂0 dest. abgespült und getrocknet. Der Grad der Anfärbung ist ein Maß für die Güte der Verdichtung. Je weniger Farbstoff aufgenommen worden ist, desto besser ist die Verdichtung, d. h., je weniger neigt die untersuchte Oberfläche zur »Schleierbildung«.
• - Farbortbestimmung (nach DIN 5033, Blatt 1 vom Juli 1962, Blatt 3 vom April 1954, Blatt 6 vom September 1964 und Blatt 7 vom Oktober 1966): Dabei werden die Farbmaßzahlen für den ungefärbten und den angefärbten Teil der Probe (angefärbt mit Aluminium-Blau) bestimmt. Als Normlichtart wird die Normlichtart C (spektrale Strahlungsverteilung einer gasgefüllten Wolfram-Glühlampe der Verteilungstemperatur von 2854 K) verwendet und die drei Farbwerte der zu messenden Farbvalenz bestimmt. Als Ergebnis können die trichromatischen Farbmaßzahlen des Normvalenz-Systems angegeben werden, in der Praxis genügt (zumindest im vorliegenden Fall) häufig bereits die Angabe eines Normfarbwertes oder Normfarbwertanteils. Bei der Farbortbestimmung der Probe ist dann die Differenz zwischen den Normfarbwertanteilen x, des ungefärbten Teils der Probe und x_II des angefärbten Teils der Probe ein Maß für die Verdichtung der Oberfläche, d. h., je größer der Differenzwert, desto weniger dicht ist die Oberfläche und desto eher tritt die »Schleierbildung« auf.
• - Prüfung der Alkaliresistenz der Oberfläche (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 um so 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 H₂0 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 Schwarzfärbung der Untersuchungsstelle zu erkennen ist.

In summary, an anodized oxidized strip, foil or plate-shaped material made of aluminum or its alloys can be produced in a surprising manner by the process according to the invention, which has an abrasion-resistant, alkali-resistant and less porous surface in sufficient strength for many fields of application. In particular, a printing plate carrier material produced according to this method and provided with a light-sensitive layer shows no or at least reduced "fog". This goal could be achieved in the process according to the invention by the combination of process features which were often judged to be more detrimental to the achievement of this goal in the art, namely the use of a low total acid concentration, a targeted distribution of the sulfur and phosphoric acid fractions, a high AI ^{3+ -} ion concentration, a relatively high electrolyte temperature, a high current density and a high flow rate of the electrolyte. It is possible that some of the features of the method have already become known in certain sub-areas, but this does not apply to the combination of all features. Despite the relatively high electrolyte temperature, the back-dissolving capacity of the electrolyte is of the order of magnitude that can be observed at lower electrolyte temperatures. Likewise, the "burns" of aluminum oxide that are often feared due to the higher current density surprisingly fail to materialize. Percentages in the following examples are based on weight, parts by weight to parts by volume are in the same ratio as kg to Itr. The following standard methods are used to assess the aluminum materials anodized by the method according to the invention:

• - Determination of the weight per unit area of aluminum oxide layers by chemical detachment (according to DIN 50 944 in the March 1969 edition): The aluminum oxide layer is replaced by a solution of 37 ml H ₃ P0 ₄ (density of 1.71 g / ml at 20 ° C corresponding to 85 % H ₃ PO ₄ ), 20 g CrO ₃ and 963 ml H ₂ 0 dist. detached from base metal at 90 to 95 ° C for 5 min and the resulting weight loss determined by weighing the sample before and after detachment. The weight per unit area of the layer is calculated from the weight loss and the weight of the surface covered with the layer and is given in g / m ² .
• - Testing the quality of the compaction of anodically produced oxide layers in a coloring test (based on DIN 50 946 in the June 1968 edition): This qualitative measuring method, in combination with a subsequent quantitative determination of the color location, allows statements to be made as to whether and to what extent the anodized surface of an aluminum material tends to "fog". To measure a flat section of material from 5 cm - 12 cm in half for 20 min in a solution of 0.5 g / Itr. on aluminum blue ( ^@ Solway Blue BN 150 from ICI) in H ₂ 0 dest. immersed at 40 ° to 45 ° C, with H ₂ 0 dist. rinsed and dried. The degree of staining is a measure of the quality of the compression. The less dye is absorbed, the better the compaction, ie the less the surface examined tends to "fog".
• - Color locating (according to DIN 5033, sheet 1 from July 1962, sheet 3 from April 1954, sheet 6 from September 1964 and sheet 7 from October 1966): The color measures for the undyed and the stained part of the sample (stained with aluminum Blue). The standard illuminant C is used (spectral radiation distribution of a gas-filled tungsten light bulb with a distribution temperature of 2854 K) and the three color values of the color valence to be measured are determined. As a result, the trichromatic color measures of the norm valence system can be given, in practice it is sufficient (at least in the present Case) often already the specification of a standard color value or standard color value portion. When determining the color location of the sample, the difference between the standard color value components x, the undyed part of the sample and x _{II of} the colored part of the sample is a measure of the compaction of the surface, ie the larger the difference value, the less dense the surface and the more the "veil formation" occurs more.
• - Testing the alkali resistance of the surface (according to US-A-3 940 321, columns 3 and 4, lines 29 to 68 and lines 1 to 8): The measure of the alkali resistance of an aluminum oxide layer is the dissolution rate of the layer in seconds in an alkaline zincate solution . 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. A drop of a solution of 500 ml of distilled H ₂ O, 480 g of KOH and 80 g of zinc oxide is placed on the surface to be examined and the period of time until the appearance of metallic zinc is determined, which can be recognized by the blackening of the examination site.

example 1

Bare aluminum strip with a thickness of 0.3 mm is degreased with an alkaline pickling solution (an aqueous solution of 20 g NaOH per liter solution) at an elevated temperature of about 50 to 70 ° C. The electrochemical roughening of the aluminum surface takes place in an apparatus created according to the teaching of DE-B-2234424 with alternating current and in an electrolyte containing HN0 ₃ . A similar device is used for the subsequent anodic oxidation with direct current, but the current is supplied via a contact roller.

The anodizing electrolyte contains 50 g H ₂ SO ₄ / Itr., 25 g H ₃ PO ₄ / Itr. and 10 g Al ³⁺ / Itr., the Al ³⁺ ion concentration by dissolving 123.5 g Al ₂ (SO ₄ ) ₃ .18 H ₂ 0 per Itr. is produced. At a bath temperature of 35 ° C. and a current density of 8 A / dm ² (direct current), approximately 3.1 g / m ^{2 of} aluminum oxide can be obtained in an anodizing time of approximately 25 seconds. The flow in the above-mentioned apparatus is turbulent for achieving a good material and heat exchange, the flow rate of the electrolyte is more than 0.3 m / sec.

A solution with the following components is used to produce a presensitized printing plate from this material:

The weight of the photosensitive layer applied to the anodized support is approximately 3 g / m ² .

To produce a printing form, exposure is carried out in a known manner and developed with an aqueous alkaline solution. With a printing form prepared in this way, around 150,000 prints of good quality can be produced using the offset process.

To measure the "fog" sensitivity of the printing plate, it is stained before the photosensitive layer is applied.

When determining the color location, a measure of the color acceptance of the surface is a color value difference x _I -x _II of 1 · 10 ³ .

The zincate test gives a measurement time of about 38 seconds. The "fog" of the printing plate support is low and the alkali resistance good.

Example 2

Rolled aluminum strip with a thickness of 0.3 mm is alkali pickled and electrochemically roughened as described in Example 1. The subsequent anodic oxidation is performed in a prepared in accordance with the teaching of DE-AS 2,234,424 apparatus with an electrolyte containing 60 g of H ₂ S0 _{4 /} ltr., 40 g H ₃ PO ₄ / Itr. and 20 g Al ³⁺ / Itr. contains. At a bath temperature of 35 ° C and a current density of 8 A / dm ² , about 2.8 g / m ^{2 of} aluminum oxide can be built up in 25 seconds. The dyeing test gives a difference in color value x _I -x _II of 4.4 · 10 ³ , the zincate test a measuring time of 36 seconds

After applying a light-sensitive layer as described in Example 1, about 160,000 prints of good quality can be obtained in the offset process.

If the anodization of the roughened surface is carried out in the above-mentioned acid mixture at 55 ° C. and a current density of 12 A / dm ² , approximately 3.4 g / m2 of aluminum oxide are obtained. The difference in color values x _I -x _II increases slightly to 9.4 · 10 ³ , the measured value in the zincate test drops to 31 seconds. In the offset process, the output exceeds 150,000 prints in good quality. The "fog" of both oxide layers is low, their alkali resistance good.

Example 3

Roll-bright aluminum strip with a thickness of 0.3 mm is alkali-pickled and electrochemically roughened according to the instructions in Example 1. The anodic oxidation takes place in a device created according to the teaching of DE-B-2 234 424 with an electrolyte containing 50 g of H ₂ SO ₄ / Itr. And 25 g of H ₃ PO ₄ / Itr. and 12 g AI ³⁺ / Itr. contains, at a temperature of 55 ° C and a current density of 12 A / dm ² . Immediately afterwards, the aluminum oxide surface thus obtained is washed with an aqueous solution of 2 g / l according to the teaching of DE-A-2 532 769. Na-metasilicate anodized at 25 ° C and a current density of 0.9 A / dm ^{2 for} 60 seconds.

3.0 g / m ^{2 of} aluminum oxide are obtained with a color value fraction difference x _I -x _IIn of 4.0 · 10 ³ and a measuring time in the zincate test of 98 sec. This in “color fog” behavior and alkali resistance to the Print layer produced significantly according to Example 2 at 55 ° C., after applying a light-sensitive layer according to Example 1, performs a minimum of 150,000 good prints in the offset process. The gaining of advantages for lithographic surfaces through the use of already known aftertreatment processes also for aluminum oxide layers produced according to the invention becomes clear here.

Example 4

An aluminum strip material pickled and roughened as described in Example 1 is in a device according to DE-AS 2234424 in an aqueous solution with 150g H2S04 / ltr., 50 g H ₃ PO ₄ / Itr., 5 g Al ³⁺ / Itr. (added as 61.75 g / ltr. Al ₂ (SO ₄ ) ₃ .18 H ₂ 0) anodized. At a temperature of 40 ° C and a current density of 11 A / dm ² , about 2.5 g / m ^{2 of} aluminum oxide can be built up in 25 seconds.

After application of a light-sensitive layer and further processing in each case as described in Example 1, 80,000 good prints can be produced from the printing form thus obtained.

The dyeing test gives a difference in color values x _I -x _II of 12 · 10 ³ . The alkali resistance in the zincate test is 31 sec.

As the total acid concentration increases, the color fog sensitivity of the oxide obtained increases, its alkali resistance and the print run to be achieved decrease; however, printing plate substrates with properties sufficient for many cases can still be obtained.

Example 5

A by the procedure of Example 1 and stained alkaline electrochemically roughened aluminum strip material of the starch is 0.3 mm anodized in a solution containing 50 g of H ₂ S0 _{4 /} ltr., 25 g H ₃ PO ₄ / Itr. and 13 g Al ³⁺ / Itr. contains. Deviating from the apparatus used in Example 1 according to the teaching of DE-B-2234424, the process is carried out in a device with less electrolyte movement and thus poorer material and heat exchange, for example a device as in DE-B-1 621 115, column 3 , Lines 1 to 10 described.

At 40 ° C and 6 A / dm ² , about 2.7 g / m ^{2 of} aluminum oxide can be generated in 30 seconds. The color value fraction difference x _I -x _II of 23.9 · 10 ³ and the alkali resistance in the zincate test of 41 sec determined in the dyeing test show an increase or decrease compared to the oxide layers obtained under more favorable conditions according to DE-B-2234424, but are even better than with comparative oxide layers, which are produced in sulfuric acid as the sole electrolyte acid. After coating with a light-sensitive mixture according to Example 1, more than 150,000 good prints can be produced using the offset process.

If the anodization is carried out at 55 ° C. and 12 A / dm ² , about 3.4 g / m ^{2 of} oxide are formed in 30 seconds. Due to the somewhat more unfavorable conditions of origin (increased temperature, low material and heat exchange), this oxide shows a color value difference x _I -x _II of 32 · 10 ³ in the dyeing test and a somewhat lower alkali resistance tested in the zincate test (36 sec).

After coating with a light-sensitive layer, as described in Example 1, nevertheless produce more than 150,000 good prints from this print medium.

This example shows the wide range in the applicability of the anodizing electrolytes according to the invention, which bring about significant improvements in the properties of the oxide layer even under difficult anodizing conditions.

Example 6

Rolled aluminum strip with a thickness of 0.3 mm is degreased with an alkaline solution, electrochemically roughened and anodized according to the instructions in Example 1. The electrolyte in the anodic oxidation contains 25 g H ₂ SO ₄ / Itr., 25 g H ₃ PO ₄ / Itr. and 5 g Al ³ + / Itr. At 55 ° C bath temperature and 8 A / dm ² current density, approx. 1.95 g / m ² oxide can be built up in 25 seconds. The untreated material has an alkali resistance in the zincate test of 63 sec.

The surface is prepared for the subsequent sensitization by immersing the aluminum support in a 0.1% aqueous solution of polyvinylphosphonic acid (molecular weight about 100,000) at 60 ° C. for 4 minutes.

The photosensitive coating is carried out with 1.4 parts by weight of mixed condensate of 1 mol of 3-methoxydiphenylamine-4-diazonium sulfate and 1 mol of 4,4'-bis-methoxymethyl diphenyl ether, prepared in 85% aqueous phosphoric acid and as Mesitylene sulfonate precipitated, 0.2 part by weight of p-toluenesulfonic acid monohydrate, 3 parts by weight of polyvinyl butyral (containing 6S to 71% polyvinyl butyral, 1% polyvinyl acetate and 24 to 27% polyvinyl alcohol units, the viscosity of a 5% solution in butanol at 20 ° C is 20-30 mPa · s), 80 parts by volume of ethylene glycol monomethyl ether and 20 parts by volume of butyl acetate. The diazo mixed condensate layer exposed under a negative is mixed with a mixture of 50 parts by weight of water, 15 parts by weight of isopropanol, 20 parts by weight of n-propanol, 12.5 parts by weight of n-propyl acetate, 1.5 Parts by weight of polyacrylic acid and 1.5 parts by weight of acetic acid developed.

Very good prints can be produced from the printing form thus obtained. The non-image areas are free of fog. Oxide layers produced according to the invention thus allow the use of methods and chemicals which are usually used to improve the operation of negative layers without restriction.

Example 7

A roughened aluminum strip prepared according to the instructions in Example 1 is made in an electrolyte from 50 g H ₂ SO ₄ / Itr., 25 g H ₃ PO ₄ / Itr. and 12 g Al ³⁺ / Itr. anodized. At a bath temperature of 55 ° C and a current density of 12 A / dm ² , 3.1 g / m ^{2 of} aluminum oxide can be built up in 30 seconds. In the dyeing test, there is a difference in color values x _I -x _II of 9.5 · 10 ³ and a zincate test time of about 34 seconds.

In addition to a positive working solution, as described in Example 1, a negative working photopolymer solution of the following proportions can also be used for the light-sensitive coating:

The aluminum support provided with this photopolymer layer in an amount of 5 g / m ^{2 also} receives a cover layer of approx. 1 g / m2, which is produced from the following solution:

After exposure and development, in accordance with the manner given in DE-C-1 193 366, a printing form with high printing performance that is free of fog at the image-free locations is obtained.

An alkaline cleaned and electrochemically roughened aluminum strip according to the instructions of Example 1 is in an aqueous electrolyte with 100 g H ₃ PO ₄ / Itr. anodically oxidized as the sole electrolyte acid. At 40 ° C bath temperature and a current density of 4 A / dm ² in a device according to DE-B-2234424 with contact roller in about 25 seconds 0.85 g / m ^{2 of} aluminum oxide can be built up.

The resistance to alkali, measured in the zincate test, is moderate (16 sec), the tendency to »color fog«, judged in the dye test, is very low (difference in color value x _I -x _II of about 1 - 10 ³ ).

The oxide layer, which can still be built up without burns, shows a real alkali resistance and thus clearly the disadvantages of using phosphoric acid as the sole anodizing electrolyte, but also indicates the advantage of the very low sensitivity to color fog.

If, under otherwise identical conditions (100 g / Itr. H ₃ PO ₄ , 40 ° C, 25 sec residence time, 4 A / dm ² ), about 20 g Al ³⁺ / Itr. than 246.8 g / Itr. Al ₂ (SO ₄ ) ₃ .18 H ₂ 0, there is already a certain positive effect with regard to a slightly increased oxide weight of 0.95 g / m ² , an alkali resistance improved to 22 sec in the zincate test, with only a slight increased "color haze" sensitivity (difference in color values x _I --x _II = 4 · 10 ³ ), however, the thickness of the oxide layer is not yet sufficient for an economical procedure.

Comparative Example V2

An aluminum strip with a thickness of 0.3 mm is alkali pickled, electrochemically roughened and anodized according to the information in Example 1. The anodic oxidation is carried out with an electrolyte of 150 g H ₂ SO ₄ / Itr. and 5 g Al ³⁺ / Itr. carried out. At 40 ° C bath temperature and a current density of 12 A / dm ² , about 2.8 g / m ^{2 of} aluminum oxide can be applied in 30 seconds. The dyeing test gives a difference in color value x _I -x _II of 27-10 ³ . In the zincate test, the oxide layer is already penetrated after 22 seconds.

After coating with a light-sensitive mixture as described in Example 1, a printing plate is obtained which, after being copied, shows a strong "fog". Around 140,000 good prints can be produced using the offset process.

If the temperature is increased to 55 ° C. and the current density to 16 A / dm ² during the anodic oxidation, approximately 3.4 g / m ² oxide can be produced. The dyeing test experienced an increase in the difference in color value x _I -x _II to 42-10 ³ , while the resistance in the zincate test decreased to 16 seconds. In contrast, example 2 shows the progress which can be achieved according to the invention in the coloring test (ie reduced fog formation) and alkali resistance at a likewise increased temperature and current density.

The base coated with a light-sensitive mixture according to Example 1 shows a very strong "fog" after the copy. The print run using the offset process only achieves about 95,000 prints in good quality.

Comparative Example V 3

Rolled aluminum strip is pretreated and anodized according to the instructions in Example 1. The anodic oxidation takes place in an electrolyte containing 75 g H ₂ SO ₄ / it. and 20 g A1 ³⁺ / ltr. contains (according to the teaching of DE-A-2 811 396).

At 40 ° C bath temperature and a current density of 9 A / dm ² , approximately 2.5 g / m ^{2 of} aluminum oxide can be applied. The dyeing test gives a difference in color value x _I -x _II of 16-10 ³ , in the zincate test 32 seconds are achieved.

After coating with the photosensitive mixture described in Example 1, about 150,000 prints of good quality can be produced after copying and development.

The progress that results from the use of the method according to the invention compared to this already greatly improved method is clear when comparing the material produced with the same acid concentration in Example 1.

Comparative Example V 4

According to the information in Example 1, aluminum strip sections which have been pretreated with alkaline and electrochemically roughened are mixed in H ₂ S0 ₄ or H ₂ S0 _{4 /} H ₃ P0 ₄ mixtures of various concentrations with and without addition of aluminum ions (introduced as Al ₂ (SO ₄ ) ₃ .18 H ₂ 0) anodized for 30 seconds at 30 ° C. with a current density of 8 A / dm ² . The composition of the anodizing electrolyte, conductivity and the oxide layer thicknesses produced and their coloring behavior are listed in the Table included. It turns out that the addition of aluminum ions generally favors the oxide thickness growth and contributes greatly to the reduction of the colorability, expressed by the difference in color value xi-xii. This result is particularly significant at the lower total acid concentrations preferred according to the invention. The aluminum ion additive reduces the specific conductivity at higher total acid concentrations, however, at the lower acid concentrations preferred according to the invention, the conditions are unexpectedly mostly reversed and this additive improves the specific conductivity and thus also the economy of the process.

Claims (6)

1. Process for anodically oxidizing materials in the form of strips, foils, or sheets comprised of aluminum or aluminum alloys in an aqueous electrolyte containing sulfuric acid and phosphoric acid, if appropriate, after a foregoing mechanical, chemical or electrochemical roughening, characterized in that the material is anodically oxidized in an electrolyte having a concentration of sulfuric acid ranging from 25 to 150 g per liter, of phosphoric acid ranging from 10 to 50 g per liter, and of aluminum ions ranging from 5 to 25 g per liter, at a current density ranging from 4 to 25 A/dm², and a temperature ranging from 25 to 65° C.

2. Process according to claim 1 characterized in that the material is anodically oxidized in an electrolyte having a concentration of sulfuric acid ranging from 25 to 75 g per liter, of phosphoric acid ranging from 25 to 40 g per liter, and of aluminum ions ranging from 10 g, preferably from 12, to 20 g per liter, at a current density ranging from 6 to 15 a/dm², and a temperature ranging from 35 to 55° C.

3. Process for the preparation of a support material for printing plates in the form of a strip, a foil or a sheet, by anodically oxidizing aluminum or aluminum alloys in an aqueous electrolyte containing sulfuric acid and phosphoric acid, if appropriate, after a foregoing mechanical, chemical or electrochemical roughening, characterized in that the support material is anodically oxidized in an electrolyte having a concentration of sulfuric acid ranging from 25 to 150 g per liter, of phosphoric acid ranging from 10 to 50 g per liter, and of aluminum ions ranging from 5 to 25 g per liter, at a current density ranging from 4 to 25 A/dm², and a temperature ranging from 25 to 65° C.

4. Process according to claim 3 characterized in that the support material is anodically oxidized in an electrolyte having a concentration of sulfuric acid ranging from 25 to 75 g per liter, of phosphoric acid ranging from 25 to 40 g per liter, and of aluminum ions ranging from 10 g, preferably from 12, to 20 g per liter, at a current density ranging from 6 to 15 A/dm², and a temperature ranging from 35 to 55° C.

5. Use of the material which has been anodically oxidized according to the process of claim 1 or claim 2 as a support material in the preparation of printing plates carrying a light-sensitive layer.

6. Use according to claim 5, in which the light-sensitive layers which may be dyed, contain diazo compounds, diazoquinones, diazo mixed condensates or photopolymerizable compounds.