EP0675976B1 - Method for the electrolytic inking of aluminium surfaces using a.c. - Google Patents

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

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 reddish tones Gold tones in the range from champagne to gold to bronze tones.

Aluminum is known to be coated with a natural oxide layer due to its base character, the layer thickness of which is generally less than 0.1 µm (Wernick, 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 usually carried out in 10 to 20% by weight sulfuric acid with a current density of 1.5 A / dm ² and a temperature of 18 to 22 ° C. within 15 to 60 minutes, depending on the desired layer thickness and intended use.

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

Electrolytic coloring processes, in which anodized aluminum can be colored in heavy metal salt solutions by treatment with alternating current, have been known since the mid-1930s. The elements of the first transition series such as Cr, Mn, Fe, Co, Ni, Cu and especially Sn are used here. 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 when current is applied. This is very undesirable when coloring in tin electrolytes of anodized aluminum, since on the one hand it interferes with the process flow (frequent renewal or replenishment of the solutions which are unusable due to the formation of precipitation) and on the other hand leads to considerable additional costs due to the tin (IV) compounds which cannot be used for coloring. A number of processes have therefore been developed which differ in particular in 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 SA Pozzoli, F. Tegiacchi; Korros. Korrosionschutz Alum., Event. Eur. Foed. Korros., 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), and the triphenols phloroglucin (JP-A-58 113391 ) 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 57 200221) have already been described in this connection.

Another important general problem in electrolytic coloring is the so-called scattering ability (depth scattering), which is the product property of coloring anodized aluminum parts that are at different distances from the counterelectrode with a uniform color. Good spreadability 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 to be colored at the same time and medium shades are to be achieved. In application, therefore, a high spreadability is very desirable, since incorrect production is 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 concept of spreadability is not identical to the concept of uniformity and must be strictly distinguished from it. 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 the shape of the workpiece or its positioning and size.

DE-A-24 28 635 describes the use of a combination of tin (II) and zinc salts with the addition of sulfuric acid and additionally boric acid as well as aromatic carboxylic and sulfonic acids (sulfophthalic acid or sulfosalicylic acid) in the electrolytic graying 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. The disadvantage of this method is the high investment that is required for the creation of 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 spreading capacity is also not given here.

From the applicant's European patent application EP-A-354 365 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) are used together with the scatter improvers p-toluenesulfonic acid and / or naphthalenesulfonic acid.

However, the production of certain reddish hues 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-38 24 402, AC coloring with dye baths containing silver ions for producing reddish-brown decorative colors is known. These colors are obtained through the use of p-toluenesulfonic acid in the dye baths. Although this compound is known from tin-II dyeing as a scatter improver, it is used for dyeing with silver ions to produce light-resistant gold tones without a visible green tinge. Dye baths containing silver ions usually do not require any litter improvers since the litter properties of these baths are sufficient.

From DE-C-741 743 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 colors that are produced using this process show efflorescence on the surface after a short period of time when exposed to intense light, are therefore not lightfast and therefore not suitable for architectural applications useful (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 electrolytically colored with copper electrolytes, these were excluded from Qualanod's "Specifications for the Quality Sign of Anodic Oxidation Coatings on Wrought Aluminum for Architectural 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 20 568 an electrolyte solution is known which contains tin (II) sulfate, cresol sulfonic acids or phenol sulfonic acids, sulfuric acid and alternatively a sulfate of nickel, cobalt, cadmium, 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 coloring electrolyte in order to ensure a uniform coloring of the aluminum oxide layer with shorter coloring 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 leave reddish hues 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 optionally copper ions. The process is characterized in that after the electrolytic dyeing step, aftertreatment is carried out with an aqueous solution or suspension which contains at least one thiocarboxamide. This post-treatment 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 is achieved with brightening of the color.

From JP-A-53 116 348 and JP-A-54 116 349 methods for AC coloring of anodized aluminum surfaces are known, whereby reddish to black shades are 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 at an AC voltage of 2 to 18 V. Subsequently there is a second AC treatment in an electrolyte containing nickel, cobalt or tin ions. The same corrosion inhibitor as described above is also used here. This bath also 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 common 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 architecture and for decorative applications.

FR-A-2 085 799 also describes corresponding dyebaths which contain 2 different metal ions selected from tin (II), copper (II) and silver ions.

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 extremely uniform distribution of the color depth over the entire surface, even with workpieces of complex shape.

Furthermore, it is a further object of the present invention to provide corresponding colored aluminum surfaces which, moreover, correspond to special corrosion protection requirements.

• (a) Benzolsulfonaten der allgemeinen Formel (I),
  
  wobei

  R

  für einen oder mehrere stellungsisomere Reste und jeweils für Wasserstoff, Hydroxyl, Carboxyl oder Aldehyd steht, mit der Maßgabe, daß nicht mehr als ein Carboxylrest (COOX) mit dem Benzolring verknüpft ist und

  X

  für Wasserstoff oder ein Alkalimetallkation, ausgewählt aus Natrium oder Kalium, steht und

• (b) Naphthalindisulfonaten der allgemeinen Formel (II),
  
  wobei

  R'

  für einen oder mehrere stellungsisomere Reste und jeweils für Wasserstoff, Hydroxyl, Carboxyl oder Aldehyd steht, mit der Maßgabe, daß in 1-Stellung des Naphthalinrings keine Hydroxygruppe anwesend ist und

  X

  die oben genannte Bedeutung hat,

  und wobei die Färbebäder A im wesentlichen frei sind von Zinn (II)-und/oder Silberionen.

Colored aluminum surfaces with reddish gold tones with good depth dispersion are made available by means of a process for the electrolytic alternating current coloring of anodized aluminum surfaces in acidic, copper (II) ion-containing dye baths A, using an electrolyte additive A '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 (COOX) is linked to the benzene ring and

  X

  represents 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,

  and wherein the dye baths A are essentially free of tin (II) and / or silver ions.

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 markedly 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 scatter improvers for coloring with tin (II) ion-containing dye baths is known, it was found that for electrolytic alternating current coloring of anodized aluminum surfaces in copper (II) ion-containing dye baths, only selected scatter improvers can be used, while other scatter improvers to very light layers or even for discoloration, 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 hexacarboxylic 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 / l, in particular 1 to 2 g / l, 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 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 to introduce copper (II) ionene 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 litter improvers in copper baths containing copper (II) ions, it was found that only selected litter 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, with 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 of the present invention in that the electrolyte additive A 'is used in an amount of 2 to 30 g / l, in particular 5 to 20 g / l, based on the dyebath A.

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 (11) 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 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.

For the purposes 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 usually about 1 A / dm ² , which then, however, generally drops to a constant value of 0.2 to 0.5 A / dm ² . Depending on the tension, the metal concentration in the dye bath and the immersion times, different colors are obtained.

According to the present invention, all of the above-mentioned objects are achieved in a process according to claim 1, wherein in a further process step with aluminum dye baths B containing tin (II) ions and / or silver ions, aluminum surfaces are electrolytically colored by means of alternating current.

Here, in a manner known per se, acidic dyebaths B containing tin (II) ions are used which contain stabilizing agents for tin (II) ions (antioxidants) and scattering improvers in the form of an electrolyte additive B '.

wobei

R¹ und R²

jeweils für Wasserstoff, Alkyl, Aryl, Alkylaryl, Alkyl-arylsulfonsäure, Alkylsulfonsäure sowie deren Alkalimetallsalze mit jeweils 1 bis 22 C-Atomen stehen,

R³

für einen oder mehrere Wasserstoff- und/oder Alkyl-, Aryl-, Alkylarylreste mit 1 bis 22 C-Atomen steht,

R⁴

für einen oder mehrere Sulfonsäurereste (SO₃X),

R⁵

für einen oder mehrere Wasserstoff- und/oder Alkyl-, Aryl-, Alkylarylreste mit 1 bis 22 C-Atomen stehen, und

X

die obige Bedeutung aufweist,

wobei wenigstens einer der Reste R¹, R² und R³ ein Rest ungleich Wasserstoff ist, und
Streuverbesserer der allgemeinen Formel (VIII) und/oder (IX),

wobei

R⁶

für einen oder mehrere stellungsisomere Reste und jeweils für Wasserstoff, Hydroxyl, Carboxyl, Aldehyd und C_1-6-Alkyl,

R⁷

für einen oder mehrere Carboxylatreste (COO) oder Sulfonsäurereste (SO₃X) und

X

für Wasserstoff oder ein Alkalimetallkation, ausgewählt aus Natrium und/oder Kalium, steht,

Das Färbebad B ist im wesentlichen frei von Kupfer (II)-Ionen. Die zeitliche Reihenfolge der Anwendung der beiden Farbebäder A und B ist vertauschbar.The electrolyte additive B for an acidic, tin (II) -containing dye bath for AC coloring of anodized aluminum surfaces contains stabilizing agents for tin (II) ions of the general formulas (III) to (VII),

in which

R ¹ and R ²

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 radicals having 1 to 22 carbon atoms,

R ⁴

for one or more sulfonic acid residues (SO ₃ X),

R ⁵

represent one or more hydrogen and / or alkyl, aryl, alkylaryl radicals having 1 to 22 carbon atoms, and

X

has the above meaning

wherein at least one of the radicals R ¹ , R ² and R ^{3 is} a radical other than hydrogen, and
Spreading improvers of the general formula (VIII) and / or (IX),

in which

R ⁶

for one or more positionally isomeric radicals and in each case for hydrogen, hydroxyl, carboxyl, aldehyde and C _1-6 alkyl,

R ⁷

for one or more carboxylate residues (COO) or sulfonic acid residues (SO ₃ X) and

X

represents hydrogen or an alkali metal cation selected from sodium and / or potassium,

The dye bath B is essentially free of copper (II) ions. The order in which the two dye baths A and B are used is interchangeable.

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 B 'according to the invention alone and in connection with the copper bath (II) -ion-containing dye bath A is the use of oxidation-stable, water-soluble scattering improvers in tin baths (II) ion-containing dye baths. 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 help of the present invention it is possible, by using different dyebaths A and B, which contain copper (II) ions on the one hand and tin (II) ions and / or silver ions on the other, to achieve intense color depths with great uniformity obtained if the copper (II) ion-containing dye bath A is equipped with special scatter improvers and also contains the tin (II) ion-containing dye bath stabilizing agent 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 / l, in particular 7 to 16 g / l, of tin (II) ions. The tin (II) ions are preferably introduced into the dye baths B 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-dihydroxy-benzene (tert-butyl hydroquinone), methyl hydroquinone, trimethyl hydroquinone, 4-hydroxy-2,7-naphthalenedisulfonic acid, naphthalene-1,5-disulfonic acid and / or p -Hydroxyanisole used. In a preferred embodiment of the present invention, the dyebath B contains at least one of the compounds of the general formulas (III) to (VII) in an amount of 0.01 to 2 g / l as a stabilizing agent for stannous 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, 1-naphthol-2,3-sulfonic acid, naphthalenesulfonic acid, p-toluenesulfonic acid and / or benzene hexacarboxylic 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 B also contains scatter improvers in an amount of 0.1 to 30 g / l.

Another preferred embodiment of the present invention is that the essentially copper-free dye bath B contains silver ions. While it has been necessary in the prior art to introduce organic agents into the dyebath in order to avoid green tints of the silver staining, it is possible with the aid of the present invention to produce reddish gold tones using dyebaths containing silver ions without the use of organic additives get along. As is known, the use of scatter improvers for dyeing with silver ions is not necessary, since this already gives a sufficiently good scatterability. However, if tin (II) ions are present in dye bath B at the same time, the use of the above-mentioned scatter improvers is generally necessary 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 / l, preferably 0.3 to 1.2 g / l, 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 B are generally not required, it is possible to use additives known from the prior art here as well. However, in contrast to the prior art, these additives are not absolutely necessary to achieve the reddish gold tones. For example, however, the dyebath B 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 / l, preferably 5 to 25 g / l, of electrolyte solution.

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

The dyeing is usually carried out using a tin (II) and / or dye bath B containing 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 to 30 ° C. The alternating voltage or alternating current superimposed on the direct current (50 to 60 Hz) is preferably set 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).

If, for the purposes of the present invention, the copper bath containing dye (11) 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 shifted in time becomes. It is necessary that the dyebath B 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 A contains no significant amounts of tin (II) ions and / or silver ions.

In a first embodiment of the present invention, the process is therefore characterized in that the anodized aluminum surfaces are first treated with the dyebaths A containing copper (II) ions and then with the dyebath B 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 B containing tin (II) ions and / or silver ions and then with the dye baths A containing copper (II) ions colors. In extensive experiments it was found that the order of the two dyeing steps is apparently not important for the result of the uniformity in the sense of good depth dispersion 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 are far superior to the prior art methods in terms of corrosion resistance that use the same metal cations in the dye baths at the same time.

The following examples illustrate preferred embodiments of the present invention.

Examples Test methods Assessment of the Scatterability in Dye Baths Containing Copper (II) Ions A

Test sheets measuring 50 mm x 460 mm x 1 mm made of DIN material Al 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 / l of Cu ions (CuSO ₄ x 5H ₂ O) and 8 g / l of sulfuric acid, the dyebath 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 coloring that is too light can usually be improved by extending the dyeing time in the direction of a darker dyeing, the scatterability of a bath is an inherent property of the dye bath chosen 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 from dye baths A and the comparative examples was to be expected. In fact, the overall corrosion properties are about the same. Table 1 Ex. Spreading improver Conc.g / l visual assessment. scattering comment 1 5-sulfosalicylic acid 5 Well 89.8 brighter 2nd 5-sulfosalicylic acid 10th Well 88.0 brighter 3rd 5-sulfosalicylic acid 20th satisfying 94.7 brighter 4th 2-Naphthol-3,6-disulfonic acid sodium salt 5 satisfying 85.6 brighter 5 2-Naphthol-3,6-disulfonic acid sodium salt 10th satisfying 94.7 brighter 6 2-sulfobenzoic acid 5 satisfying 79.4 - 7 2-sulfobenzoic acid 20th Well 87.0 - 8th 2-sulfobenzoic acid 2nd Well 94.6 - + 5-sulfosalicylic acid 10th See 1 without - satisfying 74.4 - See 2 Benzene hexacarboxylic acid 5 insufficient - * discolored See 3 Citric acid 5 insufficient - * discolored See 4 1-Naphthol-2,3-disulfonic acid sodium salt 5 satisfying 69.9 - See 5 Naphthalene trisulfonic acid sodium salt 5 satisfying 75.3 - See 6 2-Sulfoterephthalic acid mono Na salt 5 insufficient - * discolored See 7 Sulfosuccinic acid 5 insufficient - * discolored * The scatter was not determined for very uneven sheet ends.

Electrolytic coloring

Test sheets made of the DIN material Al 99.5 (No. 3.0255) were conventionally pretreated (degreased, pickled, decapitated) and according to the GS process (200 g / l sulfuric acid, 10 g / l Al (III), air throughput, 1, 5 A / dm ² , 18 ° C) anodized for 60 minutes. The result was a layer build-up of approximately 20 µm. The sheets thus pretreated were electrolytically colored with alternating current (50 Hz) as described in the following examples. The following dye baths were used:

Dye bath I

• 10.0 g / l Sn
• 20.0 g / l sulfuric acid (96% by weight)
• 0.2 g / l methylhydroquinone
• 2.5 g / l 5-sulfosalicylic acid
• 10.0 g / l 4-sulfophthalic acid

Dye bath II

• 8.0 g / l CuSO ₄ x 5H ₂ 0
• 8.0 g / l sulfuric acid (96% by weight)
• 2.0 g / l 2-sulfobenzoic acid
• 10.0 g / l 5-sulfosalicylic acid

Dye bath III (comparison)

• 6.0 g / l Sn
• 4.0 g / l CuSO ₄ x 5H ₂ O
• 10.0 g / l sulfuric acid (96% by weight)
• 0.2 g / l methylhydroquinone
• 5.0 g / l 5-sulfosalicylic acid
• 10.0 g / l 4-sulfophthalic acid

Dye bath IV

• 0.5 g / l Ag ₂ SO ₄
• 8.0 g / l sulfuric acid (96% by weight)

Dye bath V

• 0.1 g / l Ag ₂ SO ₄
• 8.0 g / l sulfuric acid (96% by weight)

Dye bath VI (comparison)

• 0.5 g / l Ag ₂ SO ₄
• 8.0 g / l CuSO ₄ x 5 H ₂ O
• 8.0 g / l sulfuric acid (96% by weight)
• 2.0 g / l sulfobenzoic acid
• 10.0 g / l 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 Al 99.5 (No. 3.0255) were pretreated conventionally (degreased, pickled, decapitated) and according to the GS process (200 g / l sulfuric acid, 10 g / l Al (III), air throughput 1 , 5 A / dm ² , 10 ° C) anodized for 60 minutes. The result was a layer build-up of approximately 20 µm. The sheets pretreated in this way were colored as described in Table 2. Between the first and second staining 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 1st color bath 2nd dye bath 9 I. II 10th I. II 11 I. II 12th I. II 13 I. II 14 I. II 15 II I. 16 II I. 17th II IV 18th II IV 19th II IV 20th 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 according to DIN 50 021. 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 has been significantly improved in Examples 9 to 16 according to the invention. 1. Dye bath dyeing conditions 2. Dye bath dyeing conditions Corrosion (h) colour Ex. Duration (min) Voltage (V) Duration (min) Voltage (V) 9 0.5 11 5.0 17.5 > 1000 bright 10th 3.0 15 3.0 17.5 1000 dark 11 5.0 15 1.0 17.5 1000 dark 12th 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 10th 17.5 1.0 11.0 > 1000 medium 16 2nd 20th 0.5 11.0 > 1000 medium 17th 0.5 17.5 1.0 12.0 > 1000 18th 1.0 17.5 1.0 10.0 > 1000 19th 1.5 17.5 1.0 10.0 > 1000 20th 1.0 12th 0.5 17.5 > 1000 21 1.5 12th 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 3rd 15 - - 600 medium See 9 5 15 - - 500 dark See 10 4th 15 - - 350 - See 11 3rd 12th - - 450 -

Claims (22)

1. A process for the electrolytic alternating-current colouring of anodized aluminium surfaces in acidi colouring baths containing copper(II) ions, tin(II) ions and/or silver ions, characterized in that two separat acidic colouring baths A and B are used in a time-stag gered sequence,

   - colouring bath A containing copper(II) ions and an electrolyte additive A' selected from

   (a) benzene sulfonates corresponding to general formula (I):

   

   in which

   R   stands for one or more position-isomeric radicals and represents hydrogen, hydroxyl, carboxyl or aldehyde, with the proviso that not more than one carboxylic group (COOX) is attached to the benzene ring, and

   X   represents hydrogen or an alkali metal cation selected from sodium or potassium, and

   (b) naphthalene disulfonates corresponding to general formula (II) :

   

   in which

   R'   stands for one or more position-isomeric radicals and represents hydrogen, hydroxyl, carboxyl or aldehyde, with the proviso that no hydroxy group is present in the 1-position of the naphthalene ring, and

   X   is as defined above,

   and being substantially free from tin(II) ions and/or silver ions,

   - colouring bath B containing tin(II) ions and/or silver ions and an electrolyte additive B' containing stabilizers for tin(II) ions, where present, corresponding to general formulae (III) to (VII):

   

   

   in which

   R¹ and R²   represent hydrogen, alkyl, aryl, alkylaryl, alkylaryl sulfonic acid, alkyl sulfonic acid and alkali metal salts thereof containing 1 to 22 carbon atoms,

   R³   represents one or more hydrogen and/or alkyl, aryl, alkylaryl radicals containing 1 to 22 carbon atoms,

   R⁴   represents one or more sulfonic acid groups (SO₃X),

   R⁵   represents one or more hydrogen and/or alkyl, aryl and alkylaryl radicals containing 1 to 22 carbon atoms and

   X   is as defined above,

   at least one of the substituents R¹, R² and R³ not being hydrogen, and
   throw improvers corresponding to general formulae (VIII) and/or (IX):

   

   in which

   R⁶   stands for one or more position-isomeric radicals and represents hydrogen, hydroxyl, carboxyl, aldehyde and C_1-6 alkyl,

   R⁷   represents one or more carboxyl groups (COO) or sulfonic acid groups (SO₃) and

   X   is hydrogen or an alkali metal cation selected from sodium and/or potassium,

   and being substantially free from copper(II) ions

   - and the sequence in which the two colouring baths are used being interchangeable.
2. A process as claimed in claim 1, characterized in that colouring baths A containing 1 to 3 g/l and, more particularly, 1 to 2 g/l of copper(II) ions are used.
3. A process as claimed in one or more of claims 1 and 2, characterized in that copper(II) ions are introduced into colouring bath A in the form of copper(II) sulfate.
4. A process as claimed in one or more of claims 1 to 3, 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. A process as claimed in claim 4, characterized in that the sodium salts of the acids are used.
6. A process as claimed in one or more of claims 1 to 5, characterized in that the electrolyte additive A' is used in a quantity of 2 to 30 g/l and, more particularly, 5 to 20 g/l, based on colouring bath A.
7. A process as claimed in one or more of claims 1 to 6, characterized in that an electrolyte solution containing sulfuric acid, more particularly in a quantity of 2 to 25 g/l, is used in colouring bath A.
8. A process as claimed in one or more of claims 1 to 7, characterized in that colouring bath A is operated at a pH value of 0.5 to 2, at a temperature of 10 to 30°C, at an a.c. voltage frequency of 50 to 60 Hz and at a terminal voltage of 10 to 25 V.
9. A process as claimed in claim 1, characterized in that colouring baths B containing 3 to 20 g/l and, more particularly, 7 to 16 g/l of tin(II) ions are used.
10. A process as claimed in claim 1 or 9, characterized in that the tin(II) ions are introduced into the colouring baths B in the form of tin(II) sulfate.
11. A process as claimed in one or more of claims 1 and 9 to 10, characterized in that the stabilizer for tin(II) ions corresponding to general formulae (III) to (VII) in the electrolyte additive B' is selected from tert.butyl hydroquinone, methyl hydroquinone, trimethyl hydroquinone, 4-hydroxy-2,7-naphthalene disulfonic acid and/or naphthalene-1,5-disulfonic acid and/or p-hydroxyanisole.
12. A process as claimed in one or more of claims 1 and 9 to 11, characterized in that the stabilizers for tin(II) compounds corresponding to general formulae (III) to (VII) are used in a quantity of 0.01 to 2 g/l, based on colouring bath B.
13. A process as claimed in one or more of claims 1 and 9 to 12, characterized in that the throw improvers corresponding to general formulae (VIII) and/or (IX) in the electrolyte additive B' are selected from 5-sulfosalicylic acid, 4-sulfophthalic acid, 2-sulfobenzoic acid, benzoic acid, sulfoterephthalic acid, naphthalene trisulfonic acid, 1-naphthol-2,3-sulfonic acid, naphthalene sulfonic acid, p-toluene sulfonic acid and/or benzene hexacarboxylic acid.
14. A process as claimed in claim 13, characterized in that the sodium salts of the acids are used.
15. A process as claimed in one or more of claims 1 and 9 to 14, characterized in that the throw improvers corresponding to general formulae (VIII) and/or (IX) are used in a quantity of 0.1 to 30 g/l, based on colouring bath B.
16. A process as claimed in claim 1, characterized in that colouring baths B containing 0.1 to 10 g/l and, more particularly, 0.3 to 1.2 g/l silver ions are used.
17. A process as claimed in claim 16, characterized in that the silver ions are introduced in the form of water-soluble salts, more particularly nitrates, acetates and/or sulfates.
18. A process as claimed in claim 16 or 17, characterized in that colouring bath B contains p-toluene sulfonic acid and/or water-soluble alkali metal, ammonium and/or alkaline earth metal salts thereof, more particularly in a quantity of 3 to 100 g/l and preferably in a quantity of 5 to 25 g/l electrolyte solution B'.
19. A process as claimed in one or more of claims 1 and 9 to 18, characterized in that an electrolyte solution containing sulfuric acid, more particularly in a quantity of 2.5 to 100 g/l and preferably in a quantity of 5 to 30 g/l, is used in colouring bath B.
20. A process as claimed in one or more of claims 1 and 9 to 19, characterized in that colouring bath B is operated at a pH value of 0.1 to 2, at a temperature of 10 to 30°C, at an a.c. voltage frequency of 50 to 60 Hz and at a terminal voltage of 4 to 25 V and, more particularly, 8 to 18 V.
21. A process as claimed in one or more of claims 1 to 20, characterized in that the anodized aluminium surfaces are coloured first with the colouring baths containing copper(II) ions and then with the colouring baths containing tin(II) ions and/or silver ions.
22. A process as claimed in one or more of claims 1 to 20, characterized in that the anodized aluminium surfaces are coloured first with the colouring baths containing tin(II) ions and/or silver ions and then with the colouring baths containing copper(II) ions.