EP0675976A1

EP0675976A1 - Method for the electrolytic inking of aluminium surfaces using a.c.

Info

Publication number: EP0675976A1
Application number: EP94903803A
Authority: EP
Inventors: Peter Kuhm; Christine Schroeder; Volker Sander; Juergen Lindener; Riese-Meyer Loert De
Original assignee: Henkel AG and Co KGaA
Current assignee: Henkel AG and Co KGaA
Priority date: 1992-12-24
Filing date: 1993-12-16
Publication date: 1995-10-11
Anticipated expiration: 2013-12-16
Also published as: JPH08504889A; EP0675976B1; DE4244021A1; WO1994015002A1; ATE142716T1; DE59303783D1; ES2091131T3; US5587063A

Abstract

PCT No. PCT/EP93/03574 Sec. 371 Date Jul. 28, 1995 Sec. 102(e) Date Jul. 28, 1995 PCT Filed Dec. 16, 1993 PCT Pub. No. WO94/15002 PCT Pub. Date Jul. 7, 1994Anodized aluminum surfaces are electrolytically colored using alternating current in a process in which two different coloring baths are sequentially employed. One bath contains copper(II) ions and an additive which improves throwing power thereby providing uniform distribution of the depth of color. The other bath contains tin(II) ions, silver ions, or both tin(II) and silver ions. If tin(II) ions are included, additives which stabilize tin(II) ions and improve throwing power are also included. Either bath may be used first. The use of two separate coloring baths provides colored aluminum surfaces which have excellent resistance to corrosion. Workpieces with reddish-gold hues and darker tones can be produced.

Description

Process for electrolytic alternating current coloring of aluminum surfaces

The invention describes a new process for the electrolytic alternating current coloring of anodized aluminum surfaces in acidic copper (II) ion-containing dye baths, optionally in conjunction with other acidic dye baths containing Sn (II) ions and / or silver ions, in particular for the production of red stichi ¬ against gold tones in the range from champagne to gold to bronze tones.

Because of its base character, aluminum is known to be coated with a natural oxide layer, the layer thickness of which is generally less than 0.1 μm (Wemick, Pinner, Zurbrügg, Weiner; "The surface treatment of aluminum", 2nd edition, Eugen Leuze Verlag, Saulgau / Württ., 1977).

Significantly thicker oxide layers can be obtained by electrolytically oxidizing aluminum. This process is known as anodizing, in older parlance also anodizing. Sulfuric acid, chromic acid or phosphoric acid is preferably used as the electrolyte. Organic acids, such as oxalic, maleic, Phthalic, salicylic, sulfosalicylic, sulfophthalic, tartaric or citric acid are used in some processes.

However, sulfuric acid is most commonly used. Depending on the anodizing conditions, this process can achieve layer thicknesses of up to 150 μm. For outdoor applications, e.g. Facade cladding or window frames, however, layer thicknesses of 20 to 25 μm are sufficient.

The anodization is generally carried out in 10 to 20% by weight sulfuric acid with a current density of 1.5 A / mm 2 and a temperature of 18 to 22 ° C. within 15 to 60 minutes, depending on the desired layer thickness and purpose.

The oxide layers produced in this way have a high absorption capacity for a large number of organic and inorganic substances or dyes.

Electrolytic dyeing processes in which anodized aluminum can be dyed in heavy metal salt solutions by treatment with alternating current have been known since the mid-1930s. The elements of the first transition row, such as Cr, Mn, Fe, Co, Ni, Cu and in particular Sn, are used above all. The heavy metal salts are mostly used as sulfates, with a pH of 0.1 to 2.0 being set with sulfuric acid. One works at a voltage of about 10 to 25 V and the resulting current density. The counter electrode can either consist of graphite or stainless steel or of the same material that is dissolved in the electrolyte.

In this process, the heavy metal pigment is in the half period of the alternating current, in which aluminum is the cathode, in the Pores of the anodic oxide layer are deposited, while in the second half period the aluminum oxide layer is further strengthened by anodic oxidation. The heavy metal is deposited on the bottom of the pores, causing the oxide layer to color.

A problem with the coloring with tin electrolytes, however, is the easy oxidizability of the tin, which leads to precipitations of basic tin (IV) oxide hydrates (tin acid) when used and, if necessary, even when the Sn solutions are stored. Aqueous tin (II) sulfate solutions are known to be oxidized to tin (IV) compounds by the action of atmospheric oxygen or by reaction at the electrodes under current load. This is very undesirable when coloring in tin electrolytes of anodized aluminum, since on the one hand it interferes with the process (frequent renewal or replenishment of the solutions which are unusable due to the formation of precipitation) and on the other hand at considerable additional costs due to the tin (IV) compounds which cannot be used for coloring leads. A number of processes have therefore been developed which differ in particular by the type of stabilization of the mostly sulfuric acid tin (II) sulfate solutions for the electrolytic aluminum coloring.

By far the most common are phenol-like compounds such as phenolsulfonic acid, cresolsulfonic acid or sulfosalicylic acid (see, for example, in Pozzoli, F. Tegiacchi; Corros. Corrosion Protection Alu., Event Eur. Foed. Corros., Vortr. 88th 1976. 139-45 ). Also polyfunctional phenols, for example the diphenols hydroquinone, pyrocatechol and resorcinol (see in Japanese laid-open publications JP-A-58 113391, 57 200221 and in FR-A-23 84 037), as well as the triphenols phloroglucin (JP-A-58113391) and Pyrogallol (SA Pozzoli, F. Tegiacchi; Corros. Corrosion Protection Alum., event Eur. Foed. Korros., Vortr. 88th 1976. 139-45 or in Japanese laid-open publications JP-A-58 113391 and 57200221) have already been described in this connection.

Another important general problem in electrolytic coloring is the so-called scattering ability (deep scattering), which is understood to mean the product property of coloring anodized aluminum parts which are at different distances from the counterelectrode with a uniform color. Good scatterability is particularly important if the aluminum parts used have a complicated shape (coloring of the depressions), if the aluminum parts are very large and if, for economic reasons, many aluminum parts are colored simultaneously in one dyeing process and medium shades are achieved should be. In application, therefore, a high spreadability is very desirable, since incorrect productions are avoided and the optical quality of the colored aluminum parts is generally better. The process is more economical due to its good spreadability, since more parts can be colored in one operation.

The term spreadability is not identical to the term uniformity and must be strictly differentiated from this. The uniformity concerns a coloring with the least possible local disturbances in the color (spotty coloring). Poor uniformity is mostly due to impurities such as nitrate or process errors in the anodization. A good coloring electrolyte must under no circumstances impair the uniformity of the coloring.

A dyeing process can achieve good uniformity and still have poor spreading power; the reverse is also possible. The uniformity is generally only influenced by the chemical composition of the electrolyte, while the Scatterability also depends on electrical and geometric parameters, such as, for example, the shape of the workpiece or its positioning and size.

DE-A-24 28635 describes the use of a combination of tin (II) and zinc salts with the addition of sulfuric acid and additionally boric acid and aromatic carboxylic and sulfonic acids (sulfophthalic acid or sulfosalicylic acid) in the electrolytic gray coloring of anodized aluminum objects .

In particular, excellent scattering of the coloring effect should be achieved when the pH is between 1 and 1.5. Setting the pH to 1 to 1.5 is a basic requirement for good electrolytic coloring. It is not described whether the added organic acids have an effect on the spreadability. The spreadability achieved is also not quantified.

DE-A-32 46 704 describes a process for electrolytic coloring in which good scattering capacity is ensured by using a special geometry in the dye bath. In addition, cresol and phenol sulfonic acid, organic substances such as dextrin and / or thiourea and / or gelatin are intended to ensure uniform coloring. Night l of this method is the high investment that is required to create the mechanical devices. The addition of deposition inhibitors such as dextrin, thiourea and gelatin has only a minor influence on the scatterability, since the deposition process in electrolytic dyeing differs significantly from that in galvanic tinning. A possibility of measuring the improvements in the spreadability is also not given here. From the European patent application EP-A-354 365 of the applicant, a method for electrolytic metal salt coloring of anodized aluminum surfaces is also known, in which antioxidants of a general formula (see in the patent claims) together with the scatter improvers p-toluenesulfonic acid and / or Naphthalenesulfonic acid can be used.

However, the production of certain reddish tones is not possible with the use of dye baths containing Zn (II) alone, so that other heavy metal ions have been used for dyeing for a long time. For example, from DE-A-3824402, AC coloring with dye baths containing silver ions for the production of reddish-brown decorative color tones is known. These colors are obtained through the use of p-toluenesulfonic acid in the dye baths. Although this compound is known from the dyeing with tin (II) ions as a scattering enhancer, it is used in the dyeing with silver ions to produce light-resistant gold tones without a visible green cast. Dye baths containing silver ions usually do not require any litter improvers since the litter properties of these baths are sufficient.

From DE-C-741743 the electrolytic alternating current coloring with copper-containing electrolytes is known. Although anodized aluminum plates colored by electrolytic alternating current coloring with copper-containing electrolytes have been used for house facades, particularly in Japan, since the early 1960s, the color tones to be obtained are difficult to produce reproducibly (Wernick et al., Loc. Cit.). Dark shades of color produced by this process show efflorescence on the surface after a short time with intensive exposure, are accordingly not lightfast and are therefore not suitable for architectural applications can be used (EP Short et al., Paper 830389 SAE Conference, February 1983, Detroit, USA, and Wernick et al., loc. cit.). Because of the poor corrosion resistance of aluminum surfaces colored with alternating current with copper electrolytes, these were excluded from the Qualanod quality specification "Specifications for the Quality Sign of Anodic Oxidation Coatings on Wrought Aluminum for Arehiteetural Purposes", Zurich 1983. The disadvantages of the known copper stains compared to nickel and cobalt-based stains in the salt spray test are also from Short et al., Loc. cit.

Red-tinged gold and bronze tones have been particularly in demand recently for architectural applications. From JP-B-71 020568 an electrolytic solution is known which contains tin (II) sulfate, cresolsulfonic acids or phenolsulfonic acids, sulfuric acid and alternatively a sulfate of nickel, cobalt, cadium, zinc, potassium, chromium, iron, zirconium, manganese, Contains magnesium, lead or copper in a dye bath.

From GB-A-1 482 390 an electrolyte is also known which contains tin and copper. However, the surfaces obtained in this way are relatively poorly corrosion-resistant.

In DE-B-24 50 175, amino alcohols, especially alkanolamines, are added to the silver dyeing electrolyte in order to ensure a uniform coloring of the aluminum oxide layer with shorter dyeing times.

A detailed state of the art exists for dyeing processes which work in one step with an electrolyte containing both silver and copper ions and which leave reddish tones on anodized aluminum surfaces. JP-A-54 031 describes this 045 a weakly alkaline electrolyte, which in addition to silver and copper salts contains amines, ammonia or their salts in addition to organic acids. The amines serve as ligands to form complexes of the two heavy metals.

JP-A-56 116 899 reports a process for coloring anodized aluminum surfaces with an electrolyte containing silver and, if appropriate, copper ions. The process is characterized in that after the electrolytic dyeing step, an aqueous solution or suspension which contains at least one thiocarboxamide is used. This aftertreatment is intended to prevent discoloration of the substrates when exposed to light.

DE-C-21 44 969 describes a process for the electrochemical alternating-current coloring of anodized aluminum in acidic solution by means of an electrolyte which, in addition to silver ions, also contains copper ions. A special feature of this process is the coloring of the aluminum oxide layer with a shade that is darker than desired. As a further process step, DC electrolysis is therefore carried out (the object to be colored is switched as an anode) until the desired color tone has been achieved with lightening of the color.

Methods for alternating current coloring of anodized aluminum surfaces are known from JP-A-53 116 348 and JP-A-54 116 349, reddish to black shades being obtained. Here it is described to first dye in a sulfuric or phosphoric acid electrolyte which further contains an ion of a metal nobler than hydrogen (silver, copper) and a magnesium salt, boric acid or an aluminum salt as a corrosion inhibitor. It is colored with an alternating current voltage of 2 to 18 V. Subsequently a second alternating current treatment takes place in an electrolyte which contains nickel, cobalt or tin ions. The same corrosion inhibitor as described above is also used here. In addition, this bath contains oxalic acid, citric acid, tartaric acid, ammonia and / or amines.

However, the process described here suffers considerable losses of tin due to oxidation to tin (IV) compounds. In addition, thin white deposits can remain on the colored workpieces, which reduce the quality of the coloring. Furthermore, the depth of color on the colored surfaces is uneven in the sense of poorer scattering. In the case of conventional workpieces, the color depth in some places is less than half the value in the most colored area. Accordingly, these workpieces are unsuitable for use in the architectural field and for decorative applications.

The main object of the present invention is now to provide a method for the electrolytic alternating current coloring of anodized aluminum surfaces, in which in particular reddish gold tones can be obtained. Another main object of the present invention is to provide colored aluminum surfaces which have an extraordinarily uniform distribution of the color depth over the entire surface, even in the case of workpieces of complex shape.

In addition, a further object of the present invention is to provide corresponding colored aluminum surfaces which, moreover, correspond to special corrosion protection requirements. In a first embodiment of the present invention, colored aluminum surfaces with reddish gold tones with good depth dispersion are made available to solve the main tasks by means of a process for the electrolytic alternating coloring of anodized aluminum surfaces in acidic, copper (II) ion-containing dye baths characterized in that an electrolyte additive A is selected which is selected from (a) benzenesulfonates of the general formula (I),

in which

R represents one or more positionally isomeric radicals and each represents hydrogen, hydroxyl, carboxyl or aldehyde, with the proviso that no more than one carboxyl radical (C00X) is linked to the benzene ring and X is hydrogen or an alkali metal cation selected from

Sodium or potassium, and (b) naphthalene disulfonates of the general formula (II),

in which

R 'represents one or more positionally isomeric radicals and each represents hydrogen, hydroxyl, carboxyl or aldehyde, with the proviso that no hydroxyl group is present in the 1-position of the naphthalene ring and X has the meaning given above.

With the aforementioned method, it is possible to color anodized aluminum surfaces with copper ions and to achieve an extremely uniform distribution of the color depth (depth scatter). As expected, the corrosion resistance of the layers obtained in this way could not be appreciably improved compared to the referenced prior art, which deals solely with coloring using copper (II) ions.

While from the prior art, for example from EP-A-354 365 and DE-A-40 34 304, a large number of scattering improvers for the coloring with tin (II) ion-containing dye baths is known, according to the present invention found that only selected scatter improvers can be used for the electrolytic alternating current coloring of anodized aluminum surfaces in copper baths containing copper (II) ions, while other scatter improvers to very light layers or even for decolorization, ie Non-staining, led.

It has surprisingly been found that the litter improvers particularly preferred in connection with tin-containing dye baths, such as benzene hexaearbonic acid or 4-sulfophthalic acid, cannot be used without disadvantage in dye baths containing copper (II) ions.

To produce reproducible surface layers, it is of course necessary to keep the concentration of copper (II) ions in the dye bath as constant as possible. Accordingly, a particularly preferred embodiment of the present invention is that the dyebath contains 1 to 3 g / 1, in particular 1 to 2 g / 1, of copper (II) ions. Within this range is one extraordinarily attractive color intensity adjustable. An increase in the copper content beyond the limit values mentioned firstly results in economic disadvantages. On the other hand, the colorations become uneven and difficult to reproduce. If the quantities mentioned fall short, it is necessary to extend the dyeing times accordingly in order to achieve the deepest possible color depth, which in turn represents an economic disadvantage.

Although the type of introduction of the copper (II) ions into the dye baths to be used is of minor importance, it is preferred, however, to introduce copper (II) ions in the form of copper (II) sulfate into the dye baths . This type of introduction is particularly advantageous when the electrolyte consists of sulfuric acid, so that in this case no further, possibly disruptive anions are introduced into the dye baths.

In the course of the extensive studies on the effect of the scattering improvers in copper baths containing copper (II) ions, it was found that only selected scattering improvers give particularly good results. Accordingly, in a particularly preferred embodiment of the present invention, the electrolyte additive A is selected from 2-sulfobenzoic acid, sulfosalicylic acid, 2-naphthol-3,6-disulfonic acid and mixtures thereof. In this sense, the corresponding sodium and / or potassium salts are, of course, also to be used, the sodium salts being preferred. With the help of these connections, a particularly uniform color depth was obtained even with complicatedly shaped geometric workpieces.

The amount of the electrolyte additive A to be used essentially corresponds to the amount which is already known from the tin coloring. Accordingly, there is a preferred embodiment form of the present invention in that the electrolyte additive A is used in an amount of 2 to 30 g / 1, in particular 5 to 20 g / 1, based on the dyebath.

As mentioned above, a number of measures are known to the person skilled in the art to prepare acidic electrolytes. In this sense, it is particularly preferred to use an electrolyte which contains sulfuric acid, in particular in an amount of 2 to 25 g / l.

The dyeing is usually carried out using an acidic copper (I Kupfer) sulfate solution at a pH of 0.5 to 2, corresponding to 16 to 22 g of sulfuric acid per liter, at a temperature of 10 to 30 ° C. The alternating voltage or alternating current superimposed on the direct current (50 to 60 Hz) is preferably set at a terminal voltage of 10 to 25 V, preferably at 15 to 18 V, with an optimum of approximately 17 V + 1 V.

In the sense of the present invention, the term alternating current coloring means either the coloring with pure alternating current or the coloring with "direct current superimposed alternating current" or "alternating current superimposed direct current". The coloring begins at a current density resulting from the voltage of mostly about 1 A / dm ^, which then, however, generally drops to a constant value of 0.2 to 0.5 A / dm ^. Depending on the tension, the metal concentration in the dyebath and the dipping times, different colors are obtained.

A further embodiment of the present invention for solving all of the abovementioned objects consists in a process in which, in a further process step, aluminum surfaces are electrolytically colored by means of alternating current using acidic dye baths containing tin (II) ions and / or silver ions. Here, for example, acidic, tin (II) ion-containing dye baths are used, which contain stabilizing agents for tin (II) ions (antioxidants) and scatter improvers in the form of an electrolyte additive B.

The electrolyte additive B for an acidic, tin (II) -containing dye bath for AC coloring of anodized aluminum surfaces is characterized in that it contains stabilizing agents for tin (II) ions of the general formulas (III) to (VII),

in which

Rl and R ² each represent hydrogen, alkyl, aryl, alkylaryl, alkyl arylsulfonic acid, alkyl sulfonic acid and their alkali metal salts each having 1 to 22 carbon atoms, R ^{3 represents} one or more hydrogen and / or alkyl, aryl,

Alkylaryl radicals having 1 to 22 carbon atoms, R ⁴ for one or more sulfonic acid (SO3X), R5 fo _r one or more hydrogen and / or alkyl, aryl,

Are alkylaryl radicals having 1 to 22 carbon atoms, and X has the meaning given above, wherein at least one of the radicals R ¹ , 2 and R ^{3 is} a radical different

Is hydrogen, and

Spreading improvers of the general formula (VIII) and / or (IX),

(VIII) (IX)

in which

R6 for one or more positionally isomeric residues and in each case for

Hydrogen, hydroxyl, carboxyl, aldehyde and Cι_6-alkyl, R7 for one or more carboxylate residues (C00) or sulfonic acid residues (SO3X) and X for hydrogen or an alkali metal cation, selected from

Sodium and / or potassium.

Dye baths that contain only silver ions generally do not require any scatter enhancers or stabilizers for silver ions.

An essential advantage of the electrolyte additive according to the invention B alone and in connection with the copper bath containing copper (II) ions is the use of oxidation-stable, water-soluble scattering improvers in tin baths containing tin (II) ions. According to the invention, it is therefore particularly important to equip the litter improver with functional groups that are stable to oxidation, such as carboxyl, hydroxyl and / or sulfonic acid groups. The functional groups mentioned also ensure the required water solubility.

With the aid of the present invention, it is possible to obtain intense color depths with great uniformity by using various dyebaths which contain copper (II) ions on the one hand and tin (II) ions and / or silver ions on the other , if the copper (II) ion-containing dye bath is equipped with special scatter enhancers and, moreover, the tin (II) ion-containing dye bath also contains stabilizing agents for tin (II) ions and scatter improvers.

For the purposes of the present invention, it is therefore preferred to carry out the coloring with the aid of a solution containing tin (II) ions, which preferably contains 3 to 30 g / 1, in particular 7 to 16 g / 1, tin (II) ions contains. The tin (II) ions are preferably introduced into the dye baths in the form of tin (II) sulfate.

For the purposes of the present invention, stabilizers for tin (II) ions of the general formulas (III) to (VII) in the abovementioned. Concentrations in particular 2-tert-butyl-1,4-dihydroxybenzene (tert-butylhydroquinone), methylhydroquinone, trimethylhydroquinone, 4-hydroxy-2,7-naphtha1in-disulfonic acid, naphtha1in-1,5-disulfonic acid and / or p-hydroxyanisole used. In a preferred embodiment of the present invention, the coloring bath contains at least one of the compounds of one of the general formulas (III) to (VII) in an amount of 0.01 to 2 g / l as a stabilizing agent for tin ( II) ions.

In the context of the present invention, in particular 5-sulfosalicylic acid, 4-sulfophthalic acid, 2-sulfobenzoic acid, benzoic acid are used as scattering improvers of the general formulas (VIII) and / or (IX) Sulfoterephthalic acid, naphthalenetrisulfonic acid, l-naphthol-2,3-sulfonic acid, naphthalenesulfonic acid, p-toluenesulfonic acid and / or benzenehexaearbonic acid are used. The combination of 5-sulfosalicylic acid and 4-sulfophthalic acid has proven to be particularly effective in the sense of a synergistic effect. The sodium salts of the acids mentioned are preferably used. In a preferred embodiment of the present invention, the dye bath also contains scatter improvers in an amount of 0.1 to 30 g / l.

A further preferred embodiment of the present invention consists in that the essentially copper-free dye bath contains silver ions. While it was necessary in the prior art to introduce organic agents into the dyebath in order to avoid green tints of the silver dyeing, it is possible with the aid of the present invention to produce reddish shades of gold using dyebaths containing silver ions which do not use get along with organic additives. As is known, the use of scatter improvers for dyeing with silver ions is not necessary, since a sufficiently good scatterability is already obtained. However, if tin (II) ions are present in the dye bath at the same time, it is generally necessary to use the abovementioned scatter improvers in order to obtain a uniform surface.

According to a further embodiment of the present invention, the electrolyte solution contains 0.1 to 10 g / 1, preferably 0.3 to 1.2 g / 1, silver in the form of water-soluble salts, for example in the form of the nitrates, acetates and / or sulfates, where the use of silver sulfate is particularly preferred.

Although the use of organic additives in the sense of the present invention in the dyeing with silver ions Dye baths are generally not required, it is also possible to use additives known from the prior art here. In order to achieve the reddish gold tones, however - in contrast to the prior art - these additives are not absolutely necessary. For example, however, the dyebath can contain p-toluenesulfonic acid and / or its water-soluble alkali metal, ammonium and / or alkaline earth metal salts, in particular in an amount of 3 to 100 g / 1, preferably 5 to 25 g / 1, of electrolyte solution.

Although a number of other acidic electrolytes are also known to the person skilled in the art in the present field, it is particularly preferred in the sense of the present invention to use a sulfuric acid electrolyte which contains sulfuric acid in particular in an amount of 2.5 to 100 g / l and preferably in an amount of 5 to 30 g / 1.

The dyeing is usually carried out with the aid of a tin bath containing tin (II) ions and / or silver ions at a pH of 0.1 to 2.0, corresponding to 16 to 22 g of sulfuric acid per liter, at a temperature of about 10 up to 30 ^° C. The alternating voltage or alternating current superimposed on direct current (50 to 60 Hz) is preferably at 4 to 25 V, in particular at 8 to 18 V and particularly preferably at 15 to 18 V, with an optimum of approximately 17 V + 1 V, (terminal voltage) set.

If, for the purposes of the present invention, the copper bath containing dye (IΙ) ions is separated from the dye bath containing tin (II) ions and / or silver ions, it can be seen from this that the sequence of the two process steps is staggered in time is achieved. It is necessary here that the dye bath containing tin (II) ions and / or silver ions does not contain any significant amounts of copper (II) ions and conversely, the copper (II) ion-containing dye bath contains no significant amounts of tin (II) ions and / or silver ions.

In a first embodiment of the present invention, the method is therefore characterized in that the anodized aluminum surfaces are first treated with the copper baths containing copper (II) ions and then with the dye bath containing tin (II) ions and / or silver ions colors.

In a further embodiment of the present invention, the process is therefore characterized in that the anodized aluminum surfaces are first treated with the dye bath containing tin (II) ions and / or silver ions and then with the copper (II) ion-containing dye baths colors. In extensive experiments it was found that the order of the two coloring steps is obviously not important for the result of the uniformity in the sense of a good depth spread and intensity of the color depth.

It has been found that with the aid of the method according to the invention, particularly intense, visually appealing, reddish gold tones in the range from champagne to bronze or brown tones can be obtained on anodized aluminum surfaces which, in terms of corrosion resistance, far exceed the prior art methods are superior, who use the same metal cations at the same time in the dye baths.

The following examples illustrate preferred embodiments of the present invention. Examples

Test methods

Assessment of the scatterability in dyebaths containing copper (II) ions

Test sheets measuring 50 mm x 460 mm x 1 mm made of the DIN material AI 99.5 were conventionally pretreated and then electrolytically colored in a dye bath with a suitable geometry (electrode at a distance of 1 to 5 cm from the counter electrodes). In addition to 2 g / 1 Cu-Iohen (D1SO4 x 5H2O) and 8 g / 1 sulfuric acid, the dye bath also contained different amounts of test substances (see examples and comparative examples). The standard dyeing was 17.5 V (AC 50 Hz) for 90 seconds.

The coloring result was recorded numerically as follows: First, the copper distribution on the test sheet was determined at 10 different locations in the longitudinal direction (i.e. every 5 cm) by measurement with a scattered light reflectometer against the white standard titanium dioxide (= 99%). The "mean coloration" results from the individual measured values. The scatterability is determined from this as a measure of the correspondence of each measuring point with the mean value and is given as a percentage value. The scatterability of 100% means that the test sheet is colored uniformly over the entire length. The closer the values come to 0%, the more differently the sheet ends are colored.

Table 1 below shows the examples and comparative examples examined. The color intensity of the sheets was compared with that of Comparative Example 1. The remark "lighter" means a lower color intensity compared to that Comparative Example 1. By contrast, the remark "decolorized" means that the layer has become decolorized. While too bright a color can generally be improved by extending the dyeing time in the direction of a darker color, the scatterability of a bath is an inherent property of the chosen dye bath and cannot be changed by varying the voltage or the duration of the test. The corrosion properties of the sheets obtained are not determined since no significant difference between the examples of the invention and the comparative examples was to be expected. In fact, the overall corrosion properties are approximately the same.

Table 1

Ex. Scatter Improver Conc. Visual Scattering Comment g / 1 Assessment.

1 5-sulfosalicylic acid 5 a good 89.8 lighter

2 5-sulfosalicylic acid 10 good 88.0 brighter

3 5-sulfosalicylic acid 20 satisfactory 94.7 lighter

4 2-Naphthol-3,6-di- 5 satisfactory 85.6 pale sulfonic acid sodium salt

5 2-Naphthol-3,6-di- 10 satisfactory 94.7 pale sodium sulfonic acid salt

6 2-sulfobenzoic acid 5 satisfactory 79.4

7 2-sulfobenzoic acid 20 good 87.0

8 2-sulfobenzoic acid 2 good 94.6

+ 5-sulfosalicylic acid 10

See, .1 without - satisfactory 74.4

See, .2 Benzo1hexaearbonic acid 5 insufficient - * decolorized

See .3 citric acid 5 insufficient - * decolorized

See .4 l-Naphthol-2,3-di- 5 satisfactory 69.9 sulfonic acid sodium salt

See .5 naphthalene trisulfone- 5 satisfactory 75.3 acid-sodium salt

See, .6 2-Sulfoterephthal- 5 insufficient _ * decolorizes acid mono-Na-sa1z

See .7 Su1fobersuccinic acid 5 insufficient _ * decolorized

* The scatter was not determined for very uneven sheet ends. Electrolytic coloring

Test sheets made of the DIN material AI 99.5 (No. 3.0255) were conventionally pretreated (degreased, pickled, decapitated) and according to the GS process (200 g / 1 sulfuric acid, 10 g / 1 AI (III), air throughput, 1.5 A / dm ² , 18 ° C) anodized for 60 minutes. This resulted in a layer structure of approximately 20 μm. The sheets pretreated in this way were, as described in the following examples, electrolytically colored with alternating current (50 Hz). The following dye baths were used:

Dye bath I

10.0 g / 1 Sn

20.0 g / 1 sulfuric acid (96% by weight)

0.2 g / 1 methylhydroquinone

2.5 g / 1 5-sulfosalicylic acid

10.0 g / 1 4-sulfophthalic acid

Dye bath II

8.0 g / 1 CUSO4 x 5H20 8.0 g / 1 sulfuric acid (96% by weight) 2.0 g / 1 2-sulfobenzoic acid 10.0 g / 1 5-sulfosalicylic acid

Dye bath III (comparison)

6.0 g / 1 Sn

4.0 g / 1 CUSO4 x 5H2O 10.0 g / 1 sulfuric acid (96% by weight) 0.2 g / 1 methylhydroquinone 5.0 g / 1 5-sulfosalicylic acid 10.0 g / 14-sulfophthalic acid

Dye bath IV

0.5 g / 1 Ag ₂ S04

8.0 g / 1 sulfuric acid (96% by weight)

Dye bath V

0.1 g / 1 Ag ₂ S0 ₄

8.0 g / 1 sulfuric acid (96% by weight)

Dye bath VI (comparison)

0.5 g / 1 Ag2Sθ4 8.0 g / 1 CUSO4 x 5 H ₂ 0 8.0 g / 1 sulfuric acid (96% by weight) 2.0 g / 1 sulfobenzoic acid 10.0 g / 1 5-sulfosalicylic acid

In the experiments for electrochemical coloring using alternating current described in detail below, the aforementioned dye baths were combined in different orders. Test sheets made of the DIN material AI 99.5 (No. 3.0255) were conventionally pretreated (degreased, pickled, and decapitated) and by the GS method (200 g / 1 sulfuric acid, 10 g / 1 AI (III), Air throughput 1.5 A / dm ² , 10 ° C) anodized for 60 minutes. This resulted in a layer structure of approximately 20 μm. The sheets pretreated in this way were colored as described in Table 2. Between the first and second dyeing steps, the sample sheet was briefly rinsed with water. However, this process step is not mandatory in the technical implementation of the dyeing process necessary and only served here to carry out further tests with the same baths under the same conditions.

Table 2 below shows the chronological order of the dye baths used.

Table 2

Example 1. Dye bath 2. Dye bath

9 II

10 1, II

11 II

12 II

13 II

14 II

15 I

16 I

17 IV

18 IV

19 IV

20 IV II

21 IV II

22 V II

23 II V

See 8 III -

See 9 III -

See 10 VI -

See 11 VI -

It can be seen from Table 3 below that, with the aid of the examples of the invention, each is exceptionally good Corrosion protection values could be obtained. The corrosion behavior of the treated sheets was examined in a salt spray test in accordance with DIN 50021. In the examples according to the invention, the test was usually stopped after 1000 h since no corrosion was discernible. In a xenon test, it was found that in the examples and comparative examples there was no difference in the light resistance with the coloring. In addition, the intensity of the coloring was assessed visually in some examples. The depth spread was rated good to sufficient in all cases without significant differences. In contrast to comparative examples 9 and 10, it was found that the corrosion behavior in examples 9 to 16 according to the invention has been significantly improved.

Table 3

1st dye bath 2nd dye bath

Staining conditions Staining conditions Corrosion paint

At «» p. Duration of tension Duration of tension (h)

(min) (V) (min) (V)

9 0.5 11 5.0 17.5> 1000 bright

10 3.0 15 3.0 17.5 1000 dark

11 5.0 15 1.0 17.5 1000 dark

12 0.5 11 1.0 17.5> 1000 bright

13 0.5 11 0.5 17.5> 1000 bright

14 0.5 15 1.0 12.0 1000 bright

15 10 17.5 1.0 11.0> 1000 medium

16 2 20 0.5 11.0> 1000 medium

17 0.5 17.5 1.0 12.0> 1000

18 1.0 17.5 1.0 10.0> 1000

19 1.5 17.5 1.0 10.0> 1000

20 1.0 12 0.5 17.5> 1000

21 1.5 12 2.0 11.0> 1000

22 1.0 15 2.0 11.0> 1000

23 0.5 17.5 1.0 12.0> 1000

See .8 3 15 - - 600 medium

See .9 5 15 - - 500 dark

See 10 4 15 - - 350 -

See 11 3 12 - - 450 -

Claims

Patent claims

1. A process for the electrolytic alternating current coloring of anodized aluminum surfaces in acidic, copper (II) ion-containing dye baths, characterized in that an electrolyte additive A is used which is selected from (a) benzenesulfonates of the general formula (I),

in which

2. The method according to claim 1, characterized in that dye baths are used which contain 1 to 3 g / 1, in particular 1 to 2 g / 1 copper (II) ions.

3. The method according to one or more of claims 1 and 2, da¬ characterized in that copper (II) ions in the form of copper (II) sulfate is introduced into the dyebath.

4. The method according to one or more of claims 1 to 3, da¬ characterized in that the electrolyte additive A is selected from 2-sulfobenzoic acid, sulfosalicylic acid, 2-naphthol-3,6-disulfonic acid and mixtures thereof.

5. The method according to claim 4, characterized in that one uses the sodium salts of the acids.

6. The method according to one or more of claims 1 to 5, characterized in that the electrolyte additive A is used in an amount of 2 to 30 g / 1, in particular 5 to 20 g / 1, based on the dyebath.

7. The method according to one or more of claims 1 to 6, characterized in that an electrolytic solution is used which contains sulfuric acid, in particular in an amount of 2 to 25 g / l.

8. The method according to one or more of claims 1 to 7, da¬ characterized in that at a pH of 0.5 to 2, a temperature of 10 to 30 ° C, an AC voltage frequency of 50 to 60 Hz and a terminal voltage of 10 to 25 V electrolytically colored.

9. The method according to one or more of claims 1 to 8, characterized in that in an additional acid dyebath containing tin (II) ions and / or silver ions, anodized aluminum surfaces are colored electrolytically by means of alternating current, wherein an electrolyte additive B is used, the stabilizing agent for tin (II) ions, if present, of the general formulas (III) to (VII),

(VI) (VII)

in which

Rl and R2 each represent hydrogen, alkyl, aryl, alkylaryl, alkyl arylsulfonic acid, alkylsulfonic acid and their alkali metal salts each having 1 to 22 carbon atoms, R ^{3 represents} one or more hydrogen and / or alkyl, aryl,

Alkylaryl residues with 1 to 22 carbon atoms, R ⁴ for one or more sulfonic acid residues (SO3X) and R5 for one or more hydrogen and / or alkyl, aryl and

Alkylaryl having from 1 to 22 carbon atoms, and X has the above meaning, wherein at least one of the radicals Rl, R2 or ^R3 represents a radical identical un¬ is hydrogen, and throw improvers corresponding to general formulas (VIII) and / or (IX) ,

(VIII) (IX)

in which

R ⁶ for one or more positionally isomeric radicals and in each case for

Hydrogen, hydroxyl, carboxyl, aldehyde and Cι_6-alkyl, R7 for one or more carboxyl residues (C00) or sulfonic acid residues (SO3) and X for hydrogen or an alkali metal cation, selected from

Sodium and / or potassium.

10. The method according to claim 9, characterized in that one uses a dyebath containing 3 to 20 g / 1, in particular 7 to 16 g / 1, tin (II) ions.

11. The method according to claim 9 or 10, characterized in that the tin (II) ions are introduced in the form of tin (II) sulfate in the Färbe¬ baths.

12. The method according to one or more of claims 9 to 11, characterized in that the stabilizing agent for tin (II) - Ion of the general formulas (III) to (VII) is selected from tert-butylhydroquinone, methylhydroquinone, trimethylhydroquinone, 4-hydroxy-2,7-naphthalenedisulfonic acid and / or naphthalene-1,5-disulfonic acid and / or p- Hydroxyanisole.

13. The method according to one or more of claims 9 to 12, characterized in that the stabilizing agents for tin (IΙ) compounds of the general formulas (III) to (VII) in an amount of 0.01 to 2 g / 1, based on the dye bath.

14. The method according to one or more of claims 9 to 13, characterized in that the scatter improvers of the general formulas (VIII) and / or (IX) are selected from 5-sulfosalicylic acid, 4-sulfophthalic acid, 2-sulfobenzoic acid, Benzoic acid, sulfoterephthalic acid, naphthalenetrisulfonic acid, l-naphthol-2,3-sulfonic acid, naphthalenesulfonic acid, p-toluenesulfonic acid and / or benzene hexacarboxylic acid.

15. The method according to claim 14, characterized in that one uses the sodium salts of the acids.

16. The method according to one or more of claims 9 to 15, characterized in that the spreading improvers of the general formulas (VIII) and / or (IX) in an amount of 0.1 to 30 g / 1, based on the Dye bath, begins.

17. The method according to claim 9, characterized in that one uses a dyebath containing 0.1 to 10 g / 1, in particular 0.3 to 1.2 g / 1 silver ions.

18. The method according to claim 17, characterized in that introducing the silver ions in the form of water-soluble salts, in particular Ni trates, acetates and / or sulfates.

19. The method according to claim 17 or 18, characterized in that the dyebath p-toluenesulfonic acid and / or its water-soluble alkali metal, ammonium and / or alkaline earth metal salts, in particular in an amount of 3 to 100 g / 1, preferably 5 to 25 g / 1 electrolyte solution.

20. The method according to one or more of claims 9 to 19, characterized in that an electrolytic solution is used, the sulfuric acid, in particular in an amount of 2.5 to 100 g / 1 sulfuric acid and preferably in an amount of 5 to 30 g / 1.

21. The method according to one or more of claims 9 to 20, characterized in that at a pH of 0.1 to 2, a temperature of 10 to 30 ° C, an AC voltage frequency of 50 to 60 Hz and a terminal voltage of 4 to 25 V, in particular 8 to 18 V electrolytic colors.

22. The method according to one or more of claims 1 to 21, characterized in that the anodized aluminum surfaces first with the copper (II) ion-containing dye baths and then with the dye baths containing tin (II) ions and / or colors silver ions.

23. The method according to one or more of claims 1 to 21, characterized in that the anodized aluminum surfaces first with the dye baths containing tin (II) ions and / or Silver ions and then dye with the copper (II) ion-containing dye baths.