EP0354365B1 - Process for electrolytically colouring anodised aluminium surfaces with metal salts - Google Patents

Process for electrolytically colouring anodised aluminium surfaces with metal salts Download PDF

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Publication number
EP0354365B1
EP0354365B1 EP89112556A EP89112556A EP0354365B1 EP 0354365 B1 EP0354365 B1 EP 0354365B1 EP 89112556 A EP89112556 A EP 89112556A EP 89112556 A EP89112556 A EP 89112556A EP 0354365 B1 EP0354365 B1 EP 0354365B1
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Prior art keywords
tin
acid
salts
metal salts
electrolyte
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German (de)
French (fr)
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EP0354365A1 (en
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Dieter Dr. Brodalla
Jürgen Lindener
Loert Dr. De Riese-Meyer
Willi Dr. Wüst
Christine Schröder
Willi Dr. Buchmeier
Jürgen Föll
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Henkel AG and Co KGaA
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Henkel AG and Co KGaA
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/18—After-treatment, e.g. pore-sealing
    • C25D11/20—Electrolytic after-treatment
    • C25D11/22—Electrolytic after-treatment for colouring layers

Definitions

  • the present invention relates to a process for the electrolytic metal salt coloring of anodized surfaces of aluminum and aluminum alloys, a defined oxide layer being produced by means of direct current in an acidic solution and then colored by means of alternating current using an acidic electrolyte containing tin (II) salts.
  • aluminum is known to be coated with a natural oxide layer, the layer thickness of which is generally less than 0.1 ⁇ m (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 The 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 also used in some processes.
  • the oxide layer consists of a relatively compact, depending on the anodizing conditions up to 0.15 ⁇ m thick barrier layer directly on the metallic aluminum, on which there is a porous, X-ray amorphous cover layer.
  • the anodization is usually carried out in 10 to 20% sulfuric acid at a voltage of 10 to 20 V and the resulting current density 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 different organic and inorganic dyes.
  • the colored Al oxide surfaces are compacted by boiling in water for a long time or by treatment with superheated steam. This changes the Oxide layer on the surface in a hydrate phase (AlOOH), whereby the pores are closed due to volume increase. Due to its high mechanical strength, the "compressed" Al oxide layer offers a good protective effect for the enclosed dyes and the underlying metal.
  • the adsorptive coloring is based on the incorporation of organic dyes into the pores of the anodizing layer.
  • Methods for inorganic adsorptive staining are also known. They can be divided into single-bath and multi-bath processes. In the single-bath process, the Al part to be colored is immersed in a heavy metal salt solution, the corresponding colored oxide or hydroxide hydrate being deposited in the pores by hydrolysis.
  • the component to be colored is immersed in solutions of the reactants, which then individually penetrate into the pores of the oxide layer and form the color pigment here.
  • solutions of the reactants which then individually penetrate into the pores of the oxide layer and form the color pigment here.
  • a further disadvantage of the adsorptive processes is that the pigments only penetrate into the outermost layer area, so that the color can quickly fade due to abrasion under mechanical stress.
  • Electrolytic coloring processes have been known since the mid-1930s, in which anodized aluminum can be colored in heavy metal salt solutions by treatment with alternating current.
  • 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. You work 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.
  • the heavy metal pigment is deposited into the pores of the anodic oxide layer in the half period of the alternating current, in which aluminum is the cathode, 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 in tin electrolytes 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 already oxidized to tin (IV) compounds through the action of atmospheric oxygen. This is very undesirable when coloring in tin electrolytes of anodized aluminum, because 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.
  • DE-OS 28 50 136 proposes adding iron (II) salts from the group of sulfuric acid, sulfonic acids and amidosulfonic acids as stabilizers for the tin (II) compounds to the electrolyte containing tin (II) salts.
  • Sulfamic acid (amidosulfonic acid) or its salts are also frequently used alone or in combination with other stabilizers (JP-OSen 75 26066, 76 122637, 77 151643, 59 190 389, 54 162637; 79 039254; GB-PS 14 82 390) .
  • polyfunctional phenols such as the diphenols hydroquinone, pyrocatechol and resorcinol (JP-OSen 58 113391, 57 200221; FR-PS 23 84 037) and the triphenols phloroglucin (JP-OS 58 113391), pyrogallol (SA Pozzoli, F. Tegiacchi; Corrosive corrosion protection Alum., Event Eur. Foed. Korros., Vortr. 88th 1976 , 139-45; JP-OSen 58 113391; 57 200221) or gallic acid (JP-OS 53 13583) have already been described in this connection.
  • SA Pozzoli F. Tegiacchi
  • Corrosive corrosion protection Alum. Event Eur. Foed. Korros., Vortr. 88th 1976 , 139-45; JP-OSen 58 113391; 57 200221
  • gallic acid JP-OS 53 13583
  • DE-PS 36 11 055 describes an acidic Sn (II) -containing electrolyte with the addition of at least one soluble diphenylamine or substituted diphenylamine derivative, which stabilizes the Sn (II) and gives faultless colorations.
  • reducing agents such as thioethers or alcohols (DE-OS 29 21 241), glucose (HU-PS 34779), thiourea (JP-OS57 207197), formic acid (JP-OS 78 19150), formaldehyde (JP-OSes) are sometimes used 75 26066, 60 56095; FR-PS 23 84 037), thiosulfates (JP-OSen 75 26066, 60 56095), hydrazine (HU-PS 34779; JP-OS 54 162637) and boric acid (JP-OSen 59 190390, 58 213898) ) used alone or in combination with the aforementioned stabilizers.
  • thioethers or alcohols DE-OS 29 21 241
  • glucose HU-PS 34779
  • thiourea JP-OS57 207197
  • formic acid JP-OS 78 19150
  • formaldehyde JP-OSes
  • JP-OSes
  • complexing agents such as ascorbic, citric, oxalic, lactic, malonic, maleic and tartaric acid are also used (JP-OSen 75 26066, 77 151643, 59 190389, 60 52597 57 207197 54 162637, 54 097545, 53 022834 79, 039254 74 028576, 59 190390 58 213898, 56 023299; HU-PS 34779; FR-PS 23 84 037).
  • Another important 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 colored in one process and medium shades are to be achieved. 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 thanks to good spreadability, since more parts can be colored in one operation.
  • 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 staining 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-OS 26 09 146 describes a process for coloring in tin electrolytes, in which the scattering ability is set by the special circuit and voltage arrangement.
  • DE-OS 20 25 284 describes that the use of tin (II) ions alone increases the scatterability, especially if tartaric acid or ammonium tartrate is added to improve the conductivity.
  • the tin (II) coloring has a tertiary current distribution (the current distribution is mainly determined by surface resistances and not by the conductivity of the electrolyte).
  • DE-PS 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 and aromatic carboxylic and sulfonic acids (sulfophthalic acid or sulfosalicylic acid).
  • good spreadability 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; the pH value cannot be decisive for a particular improvement in the spreadability. It is not described whether the added organic acids have an effect on the spreadability. The spreadability achieved is also not quantitatively recorded.
  • DE-PS 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.
  • 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.
  • 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.
  • the present invention has for its object to provide an improved process for the electrolytic metal salt coloring of anodized surfaces of aluminum and aluminum alloys, wherein firstly a defined oxide layer is generated by means of direct current in acidic solution and then this is achieved by means of alternating current or alternating current superimposed on it using tin ( II) salts containing acidic electrolytes.
  • the object of the present invention was to largely protect the tin (II) salts contained in the electrolyte from oxidation to tin (IV) compounds by adding suitable compounds which do not have the abovementioned disadvantages.
  • Another object of the present invention was, in combination with new compounds which stabilize the tin (II) salts, to additionally improve the scatterability in the electrolytic metal salt coloring.
  • the added compounds should serve to replenish the used bath solutions required concentrated Sn (II) sulfate solutions (up to 200 g Sn 2+ / 1) to improve their storage stability.
  • the variation in the chain lengths is to be understood to mean that the compounds to be used according to the invention are sufficiently water-soluble.
  • the compounds stabilizing tin (II) salts used according to the invention have no waste water problems with regard to highly toxic waste water.
  • electrolytes which preferably contain 0.1 to 2 g / l of the compounds of the formulas (I) to (IV) which stabilize the tin (II) salts.
  • Another preferred embodiment of the present invention is that as a stabilizing Substance in the above concentrations 2-tert-butyl-1,4-dihydroxybenzene (tert-butylhydroquinone), methylhydroquinone, trimethylhydroquinone, 4-hydroxy-2,7-naphthalene-disulfonic acid and / or p-hydroxyanisole is used.
  • tert-butylhydroquinone 2-tert-butyl-1,4-dihydroxybenzene
  • methylhydroquinone methylhydroquinone
  • trimethylhydroquinone 4-hydroxy-2,7-naphthalene-disulfonic acid and / or p-hydroxyanisole
  • 1 to 50 g / l, preferably 5 to 25 g / l, p-toluenesulfonic acid and / or 2-naphthalenesulfonic acid can be added to the electrolyte to improve the scatterability.
  • the dyeing is usually carried out with the aid of a tin (II) sulfate solution which contains about 3 to 20 g, preferably 7 to 16 g, of tin per liter. It is colored at a pH of 0.35 to 0.5, corresponding to 16 to 22 g of sulfuric acid per liter, at a temperature of about 14 to 30 ° C.
  • the alternating voltage or alternating current superimposed on direct current (50 Hz) is preferably set at 10 to 25 V, preferably 15 to 18 V with an optimum of approximately 17 V ⁇ 3 V.
  • direct current superimposed on alternating current is equivalent to an alternating current superimposed on direct current.
  • the value of the terminal voltage is given in each case.
  • the coloring starts with a resulting current density of mostly about 1 A / dm2, which then drops to a constant value of 0.2 to 0.5 A / dm2.
  • metal concentration in the dyebath and dipping times different tones are obtained, which can vary between champagne-colored and various bronze tones to black.
  • the method of the present invention is characterized in that the electrolyte additionally contains 0.1 to 10 g / l iron, preferably in the form of iron (II) sulfate.
  • the method of the present invention is characterized in that the electrolyte contains further heavy metal salts in addition to tin, for example nickel, cobalt, copper and / or zinc (see Wernick et al, loc. Cit.).
  • the sum of the heavy metal ions - including tin - is preferably in the range from 3 to 20 g / l, in particular in the range from 7 to 16 g / l.
  • such an electrolyte contains 4 g / l Sn (II) ions and 6 g / l Ni (II) ions, both in the form of sulfate salts.
  • Such an electrolyte shows the same coloring properties as an electrolyte which contains only 10 g / l Sn (II) or only 20 g / l nickel.
  • One advantage is the lower wastewater pollution from heavy metal salts.
  • Fig. 1 gives a basic possibility of building a dye bath to assess the spreadability again, with the aluminum sheet serving as the working electrode. The other geometric factors can be seen in the figure.
  • aqueous electrolyte was prepared, each containing 10 g / l H2SO4 and SnSO4 and corresponding amounts of a stabilizer. 1 l solutions were stirred vigorously at room temperature with a magnetic stirrer and gassed with 12 l / h pure oxygen through a glass frit. The content of Sn (II) ions was continuously recorded iodometrically.
  • Table 2 show the results of the Sn (II) concentration change in dye baths under electrical stress.
  • An aqueous electrolyte was prepared which contained 10 g / l Sn (II) ions, 20 g / l H2SO4 and corresponding amounts of a stabilizer.
  • the permanent electrolysis was carried out with stainless steel electrodes.
  • the flowing amount of electricity was registered with an Ah counter.
  • the characteristic behavior of the oxide layer to be colored was simulated by corresponding sine distortion of the alternating current at high capacitive loads.
  • the amount of Sn (II) ions oxidized by electrode reactions was determined by continuous iodometric titration of the electrolyte and by gravimetric determination of the reductively deposited Sn and the difference between the sum of these two values and the starting amount of dissolved Sn (II).
  • the Ah value was chosen as a measure of the stabilizing effect, at which a reduction in the Sn (II) concentration by oxidative reaction at the electrodes by 5 g / l can no longer be prevented.
  • Test sheets of the dimensions 50 mm x 500 mm x 1 mm as shown in Fig. 1 from the DIN material Al 99.5 (material no. 3.0255) were conventionally pretreated (degreased, pickled, pickled, rinsed) and according to the GS process (200 g / l H2SO4, 10 g / l Al, air flow 8 m3 / m2 h, 1.5 A / dm2, 18 ° C) anodized for 50 min. The result was a layer build-up of approximately 20 ⁇ m.
  • the sheets pretreated in this way were colored electrolytically as described in the following examples.
  • the test panels were colored in a special test chamber for 135 s.
  • the dyeing voltage was varied between 15 and 21 V.
  • the dye bath contained 10 g / l Sn2+ and 20 g / l H2SO4 as a bath additive as well as different amounts of p-toluenesulfonic acid (3.1-3.3) or 2-naphthalenesulfonic acid (3.4) (10 g / l).
  • 10 g / l phenolsulfonic acid and in comparative example 3 10 g / l sulfophthalic acid were used accordingly.
  • the aim of the experiments should be to clarify the improvement in the depth scatter of the aluminum sheets colored in this way when p-toluenesulfonic acid and 2-naphthalenesulfonic acid are added to the dyebath.
  • the results of the deep scatter measurements with the addition of 0, 10 and 20 g / l p-toluenesulfonic acid and 2-naphthalenesulfonic acid at coloring tensions of 15, 18 and 21 V are shown in Tab. 3.
  • the tin distribution on the test sheet is measured at 10 different locations in the longitudinal direction.
  • the measurement is carried out with a scattered light reflectometer against the white standard TiO2 (99%).
  • Example 3 Analogously to Example 3, the dyebath according to Examples 3.2 and 3.3 contained 4 g / l Sn2+ and 6 g / l Ni2+ instead of 10 g / l Sn2+. The same results were obtained when measuring the litter.

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Description

Die vorliegende Erfindung betrifft ein Verfahren zur elektrolytischen Metallsalzeinfärbung anodisierter Oberflächen von Aluminium und Aluminiumlegierungen, wobei man mittels Gleichstrom in saurer Lösung eine definierte Oxidschicht erzeugt und diese anschließend mittels Wechselstrom unter Verwendung eines Zinn(II)-Salze enthaltenden sauren Elektrolyten einfärbt.The present invention relates to a process for the electrolytic metal salt coloring of anodized surfaces of aluminum and aluminum alloys, a defined oxide layer being produced by means of direct current in an acidic solution and then colored by means of alternating current using an acidic electrolyte containing tin (II) salts.

Aluminium überzieht sich bekanntlich wegen seines unedlen Charakters mit einer natürlichen Oxidschicht, deren Schichtdicke im allgemeinen kleiner als 0,1 µm ist (Wernick, Pinner, Zurbrügg, Weiner; "Die Oberflächenbehandlung von Aluminium", 2. Auflage, Eugen Leuze Verlag, Saulgau/Württ., 1977).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 (Wernick, Pinner, Zurbrügg, Weiner; "The surface treatment of aluminum", 2nd edition, Eugen Leuze Verlag, Saulgau / Württ., 1977).

Auf chemischem Wege (z.B. mit Chromsäure) ist es möglich, dickere modifizierbare Oxidschichten zu erzielen. Diese Schichten sind 0,2 bis 2,0 µm dick und bilden einen hervorragenden Korrosionsschutz. Diese Oxidschichten sind weiterhin vorzügliche Grundlagen für Lacke, Firnisse usw., lassen sich aber nur schwer einfärben.By chemical means (e.g. with chromic acid) it is possible to achieve thicker, modifiable oxide layers. These layers are 0.2 to 2.0 µm thick and provide excellent protection against corrosion. These oxide layers are still excellent bases for paints, varnishes, etc., but are difficult to color.

Erheblich dickere Oxidschichten lassen sich erhalten, wenn man Aluminium elektrolytisch oxidiert. Dieser Vorgang wird als Anodisieren, im älteren Sprachgebrauch auch als Eloxieren bezeichnet. Als Elektrolyt dient hierbei vorzugsweise Schwefelsäure, Chromsäure oder Phosphorsäure. Auch organische Säuren wie z.B. Oxal-, Malein-, Phthal-, Salicyl-, Sulfosalicyl-, Sulfophthal-, Wein- oder Citronensäure werden bei einigen Verfahren angewendet.Significantly thicker oxide layers can be obtained by electrolytically oxidizing aluminum. This The 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 also used in some processes.

Am häufigsten wird jedoch Schwefelsäure verwendet. Je nach Anodisierbedingungen kann man nach diesem Verfahren Schichtdicken von bis zu 150 µm erzielen. Für Außenanwendungen wie z.B. Fassadenverkleidungen oder Fensterrahmen genügen jedoch Schichtdicken von 20 bis 25 µm.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 such as Facade cladding or window frames, however, suffice for layer thicknesses of 20 to 25 µm.

Die Oxidschicht besteht aus einer relativ kompakten, je nach Anodisierbedingungen bis zu 0,15 µm starken Sperrschicht direkt auf dem metallischen Aluminium, auf der sich eine poröse, röntgenamorphe Deckschicht befindet.The oxide layer consists of a relatively compact, depending on the anodizing conditions up to 0.15 µm thick barrier layer directly on the metallic aluminum, on which there is a porous, X-ray amorphous cover layer.

Die Anodisierung erfolgt in der Regel in 10 bis 20 %iger Schwefelsäure bei einer Spannung von 10 bis 20 V und der daraus resultierenden Stromdichte sowie einer Temperatur von 18 bis 22 °C innerhalb von 15 bis 60 min, je nach gewünschter Schichtdicke und Verwendungszweck.The anodization is usually carried out in 10 to 20% sulfuric acid at a voltage of 10 to 20 V and the resulting current density and a temperature of 18 to 22 ° C within 15 to 60 minutes, depending on the desired layer thickness and intended use.

Die so hergestellten Oxidschichten besitzen ein hohes Aufnahmevermögen für eine Vielzahl verschiedenartiger organischer und anorganischer Farbstoffe.The oxide layers produced in this way have a high absorption capacity for a large number of different organic and inorganic dyes.

Nach der Einfärbung werden die gefärbten Al-Oxidoberflächen durch längeres Kochen in Wasser oder Behandeln mit Heißdampf verdichtet. Hierbei wandelt sich die Oxidschicht an der Oberfläche in eine Hydrat-Phase (AlOOH) um, wodurch infolge von Volumenvergrößerung die Poren verschlossen werden. Die so "verdichtete" Al-Oxidschicht bietet infolge ihrer hohen mechanischen Festigkeit eine gute Schutzwirkung für die eingeschlossenen Farbstoffe und das darunterliegende Metall.After coloring, the colored Al oxide surfaces are compacted by boiling in water for a long time or by treatment with superheated steam. This changes the Oxide layer on the surface in a hydrate phase (AlOOH), whereby the pores are closed due to volume increase. Due to its high mechanical strength, the "compressed" Al oxide layer offers a good protective effect for the enclosed dyes and the underlying metal.

Weiterhin gibt es Verfahren, bei denen man durch Behandlung mit z.B. NiF₂-haltigen Lösungen eine sogenannte Kaltverdichtung erzielen kann.There are also methods in which treatment with e.g. NiF₂-containing solutions can achieve a so-called cold compression.

Bei der Farbanodisierung (Integralverfahren) erfolgt die Färbung direkt bei der Anodisierung. Hierzu werden jedoch spezielle Legierungen benötigt, wobei bestimmte Legierungsbestandteile als Pigmente in der gebildeten Oxidschicht zurückbleiben und den Farbeffekt hervorrufen. Anodisiert wird hier meistens in einer organischen Säure bei hohen Spannungen von mehr als 70 V. Die Farbtöne sind jedoch auf braun, bronze, grau und schwarz beschränkt. Das Verfahren liefert zwar äußerst licht- und wetterbeständige Färbungen, jedoch wird es in neuerer Zeit immer weniger angewendet, da es aufgrund des hohen Strombedarfs und der hohen Baderwärmung nicht ohne aufwendige Kühleinrichtungen kostengünstig betrieben werden kann.In the case of color anodizing (integral process), the coloring takes place directly during anodizing. However, special alloys are required for this, certain alloy components remaining as pigments in the oxide layer formed and causing the color effect. Anodizing is usually carried out in an organic acid at high voltages of more than 70 V. However, the colors are limited to brown, bronze, gray and black. Although the process provides extremely light and weather-resistant dyeings, it has been used less and less recently because it cannot be operated cost-effectively without complex cooling devices due to the high power requirements and the high temperature of the bath.

Die adsorptive Färbung beruht auf der Einlagerung von organischen Farbstoffen in die Poren der Anodisierschicht.The adsorptive coloring is based on the incorporation of organic dyes into the pores of the anodizing layer.

An Farbtönen sind im Prinzip alle Bunttöne sowie schwarz möglich, wobei der Metallcharakter des Untergrundes weitgehend erhalten bleibt. Nachteilig an diesem Verfahren ist jedoch die geringe Lichtbeständigkeit vieler organischer Farbstoffe, so daß nur eine kleine Anzahl von ihnen für die Außenanwendung bauaufsichtlich zugelassen sind.In principle, all hues as well as black are possible in terms of color tones, whereby the metal character of the substrate is largely retained. However, the disadvantage of this process is the low lightfastness many organic dyes, so that only a small number of them are approved for use by the building authorities.

Verfahren zur anorganischen Adsorptivfärbung sind ebenfalls bekannt. Sie lassen sich unterteilen in einbadige und mehrbadige Verfahren. Bei den einbadigen Verfahren wird das zu färbende Al-Teil in eine Schwermetallsalzlösung getaucht, wobei sich in den Poren durch Hydrolyse das entsprechende gefärbte Oxid oder Hydroxid-Hydrat abscheidet.Methods for inorganic adsorptive staining are also known. They can be divided into single-bath and multi-bath processes. In the single-bath process, the Al part to be colored is immersed in a heavy metal salt solution, the corresponding colored oxide or hydroxide hydrate being deposited in the pores by hydrolysis.

Bei den mehrbadigen Verfahren wird das zu färbende Bauteil in Lösungen der Reaktionspartner eingetaucht, die dann einzeln in die Poren der Oxidschicht eindringen und hier das Farbpigment bilden. Derartige Verfahren haben jedoch keine größere Verbreitung gefunden.In the multi-bath process, the component to be colored is immersed in solutions of the reactants, which then individually penetrate into the pores of the oxide layer and form the color pigment here. However, such methods have not been widely used.

Nachteilig bei den adsorptiven Verfahren ist weiterhin, daß die Pigmente nur in den äußersten Schichtbereich eindringen, so daß bei mechanischer Beanspruchung schnell ein Verblassen der Farbe durch Abrieb eintreten kann.A further disadvantage of the adsorptive processes is that the pigments only penetrate into the outermost layer area, so that the color can quickly fade due to abrasion under mechanical stress.

Bereits seit Mitte der dreißiger Jahre sind elektrolytische Färbeverfahren bekannt, bei denen anodisiertes Aluminium in Schwermetallsalzlösungen durch Behandlung mit Wechselstrom gefärbt werden kann. Hierbei kommen vor allem die Elemente der ersten Übergangsreihe wie Cr, Mn, Fe, Co, Ni, Cu sowie insbesondere Sn zur Anwendung. Die Schwermetallsalze werden zumeist als Sulfate eingesetzt, wobei mit Schwefelsäure ein pH-Wert von 0,1 bis 2,0 eingestellt wird. Man arbeitet bei einer Spannung von etwa 10 bis 25 V und der daraus resultierenden Stromdichte. Die Gegenelektrode kann entweder aus Graphit bzw. Edelstahl bestehen oder aus dem gleichen Material, welches im Elektrolyten gelöst ist.Electrolytic coloring processes have been known since the mid-1930s, in which anodized aluminum can be colored in heavy metal salt solutions by treatment with alternating current. 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. You work 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.

Bei diesem Verfahren wird das Schwermetallpigment in der Halbperiode des Wechselstroms, in der Aluminium die Kathode ist, in die Poren der anodischen Oxidschicht hinein abgeschieden, während in der zweiten Halbperiode die Aluminiumoxidschicht durch anodische Oxidation weiter gestärkt wird. Das Schwermetall lagert sich auf dem Grund der Poren ab und bewirkt so die Färbung der Oxidschicht.In this method, the heavy metal pigment is deposited into the pores of the anodic oxide layer in the half period of the alternating current, in which aluminum is the cathode, 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.

Mit verschiedenen Metallen können sehr unterschiedliche Färbungen erzeugt werden, wie z.B. mit Silber: braun-schwarz, mit Kobalt: schwarz, mit Nickel: braun, mit Kupfer: rot, mit Tellur: dunkelgold, mit Selen: rot, mit Mangan: goldgelb, mit Zink: braun, mit Cadmium: dunkelbraun, mit Zinn: champagnerfarben, bronze bis schwarz.Very different colorations can be created with different metals, e.g. with silver: brown-black, with cobalt: black, with nickel: brown, with copper: red, with tellurium: dark gold, with selenium: red, with manganese: golden yellow, with zinc: brown, with cadmium: dark brown, with tin: champagne-colored, bronze to black.

Hauptsächlich werden jedoch Nickel- und in letzter Zeit insbesondere Zinnsalze angewendet, wobei je nach Arbeitsweise Farbtöne erhalten werden, die von goldgelb über hellbraun und bronze bis zu dunkelbraun und schwarz variierbar sind.Mainly, however, nickel and, in particular, tin salts have recently been used, and depending on the working method, color tones are obtained which can be varied from golden yellow to light brown and bronze to dark brown and black.

Ein Problem bei der Färbung in Zinnelektrolyten ist jedoch die leichte Oxidierbarkeit des Zinns, welche bei der Anwendung schnell und unter Umständen sogar schon bei der Lagerung der Sn-Lösungen zu Ausfällungen von basischen Zinn(IV)-Oxidhydraten (Zinnsäure) führt. Wäßrige Zinn(II)-Sulfatlösungen werden bekanntermaßen schon durch die Einwirkung von Luftsauerstoff zu Zinn(IV)-Verbindungen aufoxidiert. Dies ist bei der Färbung in Zinnelektrolyten von anodisiertem Aluminium sehr unerwünscht, da es einerseits den Prozeßablauf stört (häufiges Erneuern bzw. Nachdosieren der durch Niederschlagsbildung unbrauchbaren Lösungen) und andererseits zu erheblichen Mehrkosten durch die nicht zur Färbung ausnutzbaren Zinn(IV)-Verbindungen führt. Es sind daher eine Reihe von Verfahren entwickelt worden, die sich insbesondere durch die Art der Stabilisierung der meist schwefelsauren Zinn(II)-Sulfatlösungen für die elektrolytische Aluminiumfärbung unterscheiden.A problem with the coloring in 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 already oxidized to tin (IV) compounds through the action of atmospheric oxygen. This is very undesirable when coloring in tin electrolytes of anodized aluminum, because 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.

Die DE-OS 28 50 136 schlägt beispielsweise vor, dem Zinn(II)-Salze enthaltenden Elektrolyt Eisen(II)-Salze aus der Gruppe der Schwefelsäure, der Sulfonsäuren und der Amidosulfonsäuren als Stabilisatoren für die Zinn(II)-Verbindungen zuzusetzen.DE-OS 28 50 136, for example, proposes adding iron (II) salts from the group of sulfuric acid, sulfonic acids and amidosulfonic acids as stabilizers for the tin (II) compounds to the electrolyte containing tin (II) salts.

Mit Abstand am häufigsten werden phenolartige Verbindungen wie Phenolsulfonsäure, Kresolsulfonsäure oder Sulfosalicylsäure eingesetzt (S.A. Pozzoli, F. Tegiacchi; Korros. Korrosionsschutz Alum., Veranst. Eur. Foed. Korros., Vortr. 88th 1976, 139-45; JP-OSen 78 13583, 78 18483, 77 135841, 76 147436, 74 31614, 73 101331, 71 20568, 75 26066, 76 122637, 54 097545, 56 081598; GB-PS 14 82 390).By far the most common are phenol-like compounds such as phenolsulfonic acid, cresolsulfonic acid or sulfosalicylic acid (SA Pozzoli, F. Tegiacchi; Korros. Korrosionschutz Alum., Organ. Eur. Foed. Korros., Vortr. 88th 1976 , 139-45; JP-OSen 78 13583, 78 18483, 77 135841, 76 147436, 74 31614, 73 101331, 71 20568, 75 26066, 76 122637, 54 097545, 56 081598; GB-PS 14 82 390).

Ebenfalls häufig kommen Sulfaminsäure (Amidosulfonsäure) bzw. deren Salze allein oder in Kombination mit anderen Stabilisatoren zum Einsatz (JP-OSen 75 26066, 76 122637, 77 151643, 59 190 389, 54 162637; 79 039254; GB-PS 14 82 390).Sulfamic acid (amidosulfonic acid) or its salts are also frequently used alone or in combination with other stabilizers (JP-OSen 75 26066, 76 122637, 77 151643, 59 190 389, 54 162637; 79 039254; GB-PS 14 82 390) .

Auch mehrfunktionelle Phenole wie z.B. die Diphenole Hydrochinon, Brenzcatechin und Resorcin (JP-OSen 58 113391, 57 200221; FR-PS 23 84 037) sowie die Triphenole Phloroglucin (JP-OS 58 113391), Pyrogallol (S.A. Pozzoli, F. Tegiacchi; Korros. Korrosionsschutz Alum., Veranst. Eur. Foed. Korros., Vortr. 88th 1976, 139-45; JP-OSen 58 113391; 57 200221) bzw. Gallussäure (JP-OS 53 13583) sind in diesem Zusammenhang bereits beschrieben.Also polyfunctional phenols such as the diphenols hydroquinone, pyrocatechol and resorcinol (JP-OSen 58 113391, 57 200221; FR-PS 23 84 037) and the triphenols phloroglucin (JP-OS 58 113391), pyrogallol (SA Pozzoli, F. Tegiacchi; Corrosive corrosion protection Alum., Event Eur. Foed. Korros., Vortr. 88th 1976 , 139-45; JP-OSen 58 113391; 57 200221) or gallic acid (JP-OS 53 13583) have already been described in this connection.

In der DE-PS 36 11 055 wird ein saurer Sn(II)-haltiger Elektrolyt mit einem Zusatz von mindestens einem löslichen Diphenylamin oder substituiertem Di-phenylaminderivat beschrieben, der das Sn(II) stabilisiert und fehlerfreie Färbungen ergibt.DE-PS 36 11 055 describes an acidic Sn (II) -containing electrolyte with the addition of at least one soluble diphenylamine or substituted diphenylamine derivative, which stabilizes the Sn (II) and gives faultless colorations.

Diese Verbindungen haben jedoch den Nachteil, daß sie größtenteils toxikologisch bedenklich sind und das Abwasser der Anodisierbetriebe zusätzlich belasten. Insbesondere gelten die als Stabilisatoren eingesetzten Phenole als besonders umweltbelastend.However, these compounds have the disadvantage that they are largely toxicologically unsafe and additionally pollute the waste water of the anodizing plants. In particular, the phenols used as stabilizers are particularly harmful to the environment.

Des weiteren werden zuweilen Reduktionsmittel wie Thioether bzw.- alkohole (DE-OS 29 21 241), Glucose (HU-PS 34779), Thioharnstoff (JP-OS57 207197), Ameisensäure (JP-OS 78 19150), Formaldehyd (JP-OSen 75 26066, 60 56095; FR-PS 23 84 037), Thiosulfate (JP-OSen 75 26066, 60 56095), Hydrazin (HU-PS 34779; JP-OS 54 162637) sowie Borsäure (JP-OSen 59 190390, 58 213898) allein oder in Kombination mit vorgenannten Stabilisatoren angewendet.Furthermore, reducing agents such as thioethers or alcohols (DE-OS 29 21 241), glucose (HU-PS 34779), thiourea (JP-OS57 207197), formic acid (JP-OS 78 19150), formaldehyde (JP-OSes) are sometimes used 75 26066, 60 56095; FR-PS 23 84 037), thiosulfates (JP-OSen 75 26066, 60 56095), hydrazine (HU-PS 34779; JP-OS 54 162637) and boric acid (JP-OSen 59 190390, 58 213898) ) used alone or in combination with the aforementioned stabilizers.

In einigen Verfahren wird auch mit Komplexbildnern wie Ascorbin-, Citronen-, Oxal-, Milch-, Malon-, Malein- sowie Weinsäure gearbeitet (JP-OSen 75 26066, 77 151643, 59 190389, 60 52597 57 207197 54 162637, 54 097545, 53 022834 79, 039254 74 028576, 59 190390 58 213898, 56 023299; HU-PS 34779; FR-PS 23 84 037).In some processes, complexing agents such as ascorbic, citric, oxalic, lactic, malonic, maleic and tartaric acid are also used (JP-OSen 75 26066, 77 151643, 59 190389, 60 52597 57 207197 54 162637, 54 097545, 53 022834 79, 039254 74 028576, 59 190390 58 213898, 56 023299; HU-PS 34779; FR-PS 23 84 037).

Komplexbildner wie z. B. Weinsäure zeigen zwar einen hervorragenden Stabilisierungseffekt, was die Vehinderung von Ausfällungen aus den Färbebädern betrifft, jedoch können sie im allgemeinen die Zinn(II)-haltigen Färbebäder nicht vor Oxidation zu Zinn(IV)-Verbindungen schützen. Diese werden dann nur komplex gebunden in Lösung gehalten und können somit auch zur Färbung keinen Beitrag mehr leisten. Weiterhin können sich in stark Komplexbildner-haltigen Färbebädern Zinn(IV)-Komplexe so stark anreichern, daß beim anschließenden Verdichten diese Komplexe in den Poren der Oxidschicht hydrolisiert werden, wobei dann unlösliche Zinn(IV)-Verbindungen gebildet werden, die zu unerwünschten weißen Belägen auf den gefärbten Oberflächen führen können.Complexing agents such. B. Tartaric acid has an excellent stabilizing effect as regards the prevention of precipitates from the dye baths, but in general they cannot protect the tin baths containing tin (II) from oxidation to tin (IV) compounds. These are then only held in solution in complex form and can therefore no longer contribute to the coloring. Furthermore, tin (IV) complexes can accumulate so strongly in dye baths containing complexing agents that during the subsequent densification these complexes are hydrolyzed in the pores of the oxide layer, insoluble tin (IV) compounds then being formed, which lead to undesirable white deposits can lead to the colored surfaces.

Ein weiteres wichtiges Problem bei der elektrolytischen Färbung stellt die sogenannte Streufähigkeit (Tiefenstreuung) dar, worunter man die Produkteigenschaft versteht, anodisierte Aluminiumteile, die sich in unterschiedlichem Abstand zur Gegenelektrode befinden, mit einem einheitlichen Farbton zu färben. Eine gute Streufähigkeit ist insbesondere dann wichtig, wenn die verwendeten Aluminiumteile eine komplizierte Form haben (Einfärbung der Vertiefungen), wenn die Aluminiumteile sehr groß sind und wenn aus wirtschaftlichen Gründen viele Aluminiumteile in einem Färbevorgang gleichzeitig gefärbt werden und mittlere Farbtöne erzielt werden sollen. In der Anwendung ist daher eine hohe Streufähigkeit sehr erwünscht, da Fehlproduktionen vermieden werden und die optische Qualität der gefärbten Aluminiumteile allgemein besser ist. Das Verfahren wird durch eine gute Streufähigkeit wirtschaftlicher, da mehr Teile in einem Arbeitsgang gefärbt werden können.Another important 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 colored in one process and medium shades are to be achieved. 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 thanks to good spreadability, since more parts can be colored in one operation.

Der Begriff Streufähigkeit ist nicht mit dem Begriff der Gleichmäßigkeit identisch und muß von diesem streng unterschieden werden.The concept of spreadability is not identical to the concept of uniformity and must be strictly distinguished from it.

Die Gleichmäßigkeit betrifft eine Einfärbung mit möglichst geringen lokalen Störungen im Farbton (fleckige Einfärbung). Eine schlechte Gleichmäßigkeit ist meist durch Verunreinigungen wie Nitrat oder durch Verfahrensfehler in der Anodisation begründet. Ein guter Färbeelektrolyt darf in keinem Fall die Gleichmäßigkeit der Einfärbung beeinträchtigen.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 staining electrolyte must under no circumstances impair the uniformity of the coloring.

Ein Färbeverfahren kann eine gute Gleichmäßigkeit erzielen und trotzdem eine schlechtes Streuvermögen haben; die Umkehrung ist auch möglich. Die Gleichmäßigkeit wird im allgemeinen nur von der chemischen Zusammensetzung des Elektrolyten beeinflußt, während die Streufähigkeit auch von elektrischen und geometrischen Parametern, wie beispielsweise der Form des Werkstücks oder dessen Positionierung und Größe, abhängt.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.

Die DE-OS 26 09 146 beschreibt ein Verfahren zur Färbung in Zinnelektrolyten, bei dem die Streufähigkeit durch die besondere Schaltungs- und Spannungsanordnung eingestellt wird.DE-OS 26 09 146 describes a process for coloring in tin electrolytes, in which the scattering ability is set by the special circuit and voltage arrangement.

DE-OS 20 25 284 beschreibt, daß allein die Verwendung von Zinn(II)-Ionen die Streufähigkeit heraufsetzt, insbesondere dann, wenn man Weinsäure oder Ammoniumtartrat zur Verbesserung der Leitfähigkeit zusetzt.DE-OS 20 25 284 describes that the use of tin (II) ions alone increases the scatterability, especially if tartaric acid or ammonium tartrate is added to improve the conductivity.

Die Praxis hat jedoch gezeigt, daß die alleinige Verwendung von Zinn(II)-Ionen nicht in der Lage ist, die Probleme der Einfärbung bezüglich der Streufähigkeit zu lösen. Die Verwendung von Weinsäure zur Verbesserung der Streufähigkeit ist nur von geringer Wirksamkeit, da Weinsäure lediglich die Leitfähigkeit etwas erhöht.However, practice has shown that the use of tin (II) ions alone is not able to solve the problems of coloring with regard to the scatterability. The use of tartaric acid to improve the spreadability is of little effectiveness since tartaric acid only increases the conductivity somewhat.

Eine geringfügige Erhöhung der Leitfähigkeit bringt jedoch keinen wirtschaftlichen Nutzen, da bei der Zinn(II)-Färbung eine tertiäre Stromverteilung herrscht, (die Stromverteilung ist hauptsächlich durch Oberflächenwiderstände bestimmt und nicht durch die Leitfähigkeit des Elektrolyten).However, a slight increase in conductivity has no economic benefit, since the tin (II) coloring has a tertiary current distribution (the current distribution is mainly determined by surface resistances and not by the conductivity of the electrolyte).

Die DE-PS 24 28 635 beschreibt die Verwendung einer Kombination von Zinn(II)- und Zinksalzen unter Zugabe von Schwefelsäure und zusätzlich Borsäure sowie aromatischen Carbon- und Sulfonsäuren (Sulfophthalsäure oder Sulfosalicylsäure). Insbesondere soll eine gute Streufähigkeit dann erzielt werden, wenn der pH-Wert zwischen 1 und 1,5 liegt. Die Einstellung des pH-Wertes auf 1 bis 1,5 ist dabei eine Grundvoraussetzung für eine gute elektrolytische Einfärbung; für eine besondere Verbesserung der Streufähigkeit kann der pH-Wert nicht entscheidend sein. Ob die zugesetzten organischen Säuren einen Einfluß auf die Streufähigkeit haben, ist nicht beschrieben. Auch ist die erzielte Streufähigkeit nicht quantitativ erfaßt.DE-PS 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 and aromatic carboxylic and sulfonic acids (sulfophthalic acid or sulfosalicylic acid). In particular, good spreadability 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; the pH value cannot be decisive for a particular improvement in the spreadability. It is not described whether the added organic acids have an effect on the spreadability. The spreadability achieved is also not quantitatively recorded.

Die DE-PS 32 46 704 beschreibt ein Verfahren zur elektrolytischen Färbung, in dem ein gutes Streuvermögen durch den Einsatz einer speziellen Geometrie im Färbebad gewährleistet wird. Außerdem sollen Kresol- und Phenolsulfonsäure, organische Substanzen wie Dextrin und/oder Thioharnstoff und/oder Gelatine eine gleichmäßige Einfärbung gewährleisten.DE-PS 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.

Nachteil dieses Verfahrens ist der hohe Investitionsaufwand, welcher für die Erstellung der mechanischen Einrichtungen benötigt wird.The disadvantage of this method is the high investment that is required for the creation of the mechanical devices.

Der Zusatz von Abscheidungsinhibitoren wie Dextrin, Thioharnstoff und Gelatine hat nur geringen Einfluß auf die Streufähigkeit, da sich der Abscheidungsprozeß beim elektrolytischen Färben von dem der galvanischen Verzinnung wesentlich unterscheidet. Eine Möglichkeit, die Verbesserungen in der Streufähigkeit zu messen, wird auch hier nicht angegeben.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.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, ein verbessertes Verfahren zur elektrolytischen Metallsalzeinfärbung anodisierter Oberflächen von Aluminium und Aluminiumlegierungen zur Verfügung zu stellen, wobei man zunächst mittels Gleichstrom in saurer Lösung eine definierte Oxidschicht erzeugt und diese anschließend mittels Wechselstrom oder gleichstromüberlagertem Wechselstrom unter Verwendung eines Zinn(II)-Salze enthaltenden sauren Elektrolyten einfärbt. Insbesondere bestand die Aufgabe der vorliegenden Erfindung darin, die in dem Elektrolyten enthaltenen Zinn(II)-Salze durch Zusatz geeigneter, die obengenannten Nachteile nicht besitzende Verbindungen weitgehend vor einer Oxidation zu Zinn(IV)-Verbindungen zu schützen.The present invention has for its object to provide an improved process for the electrolytic metal salt coloring of anodized surfaces of aluminum and aluminum alloys, wherein firstly a defined oxide layer is generated by means of direct current in acidic solution and then this is achieved by means of alternating current or alternating current superimposed on it using tin ( II) salts containing acidic electrolytes. In particular, the object of the present invention was to largely protect the tin (II) salts contained in the electrolyte from oxidation to tin (IV) compounds by adding suitable compounds which do not have the abovementioned disadvantages.

Eine weitere Aufgabe der vorliegenden Erfindung bestand darin, in Kombination mit neuen, die Zinn(II)-Salze stabilisierenden Verbindungen zusätzlich die Streufähigkeit bei der elektrolytischen Metallsalzeinfärbung zu verbessern.Another object of the present invention was, in combination with new compounds which stabilize the tin (II) salts, to additionally improve the scatterability in the electrolytic metal salt coloring.

Zusätzlich sollten die zugesetzten Verbindungen dazu dienen, die zur Nachdosierung der verbrauchten Badlösungen benötigten konzentrierten Sn(II)-sulfatlösungen (bis zu 200 g Sn ²⁺/1) in ihrer Lagerstabilität zu verbessern.In addition, the added compounds should serve to replenish the used bath solutions required concentrated Sn (II) sulfate solutions (up to 200 g Sn ²⁺ / 1) to improve their storage stability.

Die Aufgabe der vorliegenden Erfindung, ein verbessertes Verfahren zur elektrolytischen Metallsalzeinfärbung anodisierter Oberflächen von Aluminium und Aluminiumlegierungen zur Verfügung zu stellen, wobei man zunächst mittels Gleichstrom in saurer Lösung eine definierte Oxidschicht erzeugt und diese anschließend mittels Wechselstrom oder gleichstromüberlagertem Wechselstrom unter Verwendung eines Zinn(II)-Salze enthaltenden sauren Elektrolyten einfärbt, wird dadurch gelöst, daß der Elektrolyt 0,01 g/l bis zur Löslichkeitsgrenze eine oder mehrere, die Zinn(II)-Salze stabilisierende wasserlösliche Verbindungen der allgemeinen Formeln (I) bis (IV)

Figure imgb0001

enthält, wobei

R₁
für Wasserstoff, Alkyl, Aryl, Alkylaryl, Alkylarylsulfonsäure, Alkylsulfonsäure sowie deren Alkalimetallsalze mit jeweils 1 bis 22 C-Atomen,
R₂
für Wasserstoff, Alkyl, Aryl, Alkylaryl, Alkylarylsulfonsäure, Alkylsulfonsäure und deren Alkalimetallsalze mit jeweils 1 bis 22 C-Atomen,
R₃
für einen oder mehrere Wasserstoff- und/oder Alkyl-, Aryl-, Alkylarylreste mit 1 bis 22 C-Atomen und
R₄ und R₅
für einen oder mehrere Wasserstoff-, Alkyl-, Aryl- und/oder Alkylarylreste, Sulfonsäure, Alkylsulfonsäure, Alkylarylsulfonsäure sowie deren Alkalimetallsalze mit 1 bis 22 C-Atomen
stehen,
wobei wenigstens einer der Reste R₁, R₂ und R₃ für einen Rest ungleich Wasserstoff steht.The object of the present invention to provide an improved process for the electrolytic metal salt coloring of anodized surfaces of aluminum and aluminum alloys, wherein firstly a defined oxide layer is generated by means of direct current in acidic solution and this is then produced by means of alternating current or alternating current superimposed on it using tin (II). -Colours containing acidic electrolytes is dissolved in that the electrolyte 0.01 g / l up to the solubility limit one or more water-soluble compounds of the general formulas (I) to (IV) stabilizing the tin (II) salts
Figure imgb0001
contains, where
R₁
for hydrogen, alkyl, aryl, alkylaryl, alkylarylsulfonic acid, alkylsulfonic acid and their alkali metal salts, each having 1 to 22 carbon atoms,
R₂
for hydrogen, alkyl, aryl, alkylaryl, alkylarylsulfonic acid, alkylsulfonic acid and their alkali metal salts each having 1 to 22 carbon atoms,
R₃
for one or more hydrogen and / or alkyl, aryl, alkylaryl radicals having 1 to 22 carbon atoms and
R₄ and R₅
for one or more hydrogen, alkyl, aryl and / or alkylaryl radicals, sulfonic acid, alkylsulfonic acid, alkylarylsulfonic acid and their alkali metal salts with 1 to 22 carbon atoms
stand,
where at least one of the radicals R₁, R₂ and R₃ represents a radical not equal to hydrogen.

Die Variation in den Kettenlängen ist dahingehend zu verstehen, daß die erfindungsgemäß einzusetzenden Verbindungen eine ausreichende Wasserlöslichkeit besitzen.The variation in the chain lengths is to be understood to mean that the compounds to be used according to the invention are sufficiently water-soluble.

Gegenüber bekannten Stabilisatoren für Zinn(II)-Verbindungen, wie beispielsweise Pyrogallol, weisen die erfindungsgemäß verwendeten, Zinn(II)-Salze stabilisierenden Verbindungen keine Abwasserprobleme im Hinblick auf stark toxische Abwässer auf.Compared with known stabilizers for tin (II) compounds, such as, for example, pyrogallol, the compounds stabilizing tin (II) salts used according to the invention have no waste water problems with regard to highly toxic waste water.

Gemäß einer bevorzugten Ausführungsform der vorliegenden Erfindung werden Elektrolyte verwendet, die vorzugsweise 0,1 bis 2 g/l der die Zinn(II)-Salze stabiliserenden Verbindungen nach den Formeln (I) bis (IV) enthalten.According to a preferred embodiment of the present invention, electrolytes are used which preferably contain 0.1 to 2 g / l of the compounds of the formulas (I) to (IV) which stabilize the tin (II) salts.

Eine weitere bevorzugte Ausführungsform der vorliegenden Erfindung besteht darin, daß als stabilisierende Substanz in den o.g. Konzentrationen 2-tert.-Butyl-1,4-dihydroxybenzol (tert.-Butylhydrochinon), Methylhydrochinon, Trimethylhydrochinon, 4-Hydroxy-2,7-naphthalin-disulfonsäure und/oder p-Hydroxyanisol eingesetzt wird.Another preferred embodiment of the present invention is that as a stabilizing Substance in the above concentrations 2-tert-butyl-1,4-dihydroxybenzene (tert-butylhydroquinone), methylhydroquinone, trimethylhydroquinone, 4-hydroxy-2,7-naphthalene-disulfonic acid and / or p-hydroxyanisole is used.

Gemäß einer Ausführungsform der vorliegenden Erfindung können dem Elektrolyten zur Verbesserung der Streufähigkeit 1 bis 50 g/l, vorzugsweise 5 bis 25 g/l, p-Toluolsulfonsäure und/oder 2-Naphthalinsulfonsäure zugesetzt werden.According to one embodiment of the present invention, 1 to 50 g / l, preferably 5 to 25 g / l, p-toluenesulfonic acid and / or 2-naphthalenesulfonic acid can be added to the electrolyte to improve the scatterability.

Obwohl die Verwendung von Eisen(II)-Salzen aus der Gruppe der Sulfonsäuren in Zinn(II)-Salze enthaltenden sauren Elektrolyten prinzipiell bekannt ist (DE-OS 28 50 136), war es überraschend, daß beispielsweise p-Toluolsulfonsäure allein kaum als stabilisierende Verbindung für Zinn(II)-Salze wirkt, daß aber andererseits durch die Verwendung von p-Toluolsulfonsäure die Streufähigkeit bei der elektrolytischen Einfärbung von anodisierten Aluminiumoberflächen verbessert wird.Although the use of iron (II) salts from the group of sulfonic acids in acidic electrolytes containing tin (II) salts is known in principle (DE-OS 28 50 136), it was surprising that, for example, p-toluenesulfonic acid alone was hardly a stabilizing agent Compound for tin (II) salts works, but on the other hand, the use of p-toluenesulfonic acid improves the scatterability in the electrolytic coloring of anodized aluminum surfaces.

Üblicherweise erfolgt die Färbung mit Hilfe einer Zinn(II)-Sulfatlösung, die etwa 3 bis 20 g, vorzugsweise 7 bis 16 g Zinn pro Liter enthält. Es wird bei einem pH-Wert von 0,35 bis 0,5, entsprechend 16 bis 22 g Schwefelsäure pro Liter, bei einer Temperatur von etwa 14 bis 30 °C eingefärbt. Die Wechselspannung oder gleichstromüberlagerte Wechselspannung (50 Hz) wird vorzugsweise bei 10 bis 25 V, vorzugsweise 15 bis 18 V mit einem Optimum von etwa 17 V ± 3 V eingestellt. Im Sinne der vorliegenden Erfindung ist der Begriff "gleichstromüberlagerter Wechselstrom" einem wechselstromüberlagerten Gleichstrom gleichzusetzen. Angegeben ist jeweils der Wert der Klemmenspannung. Die Färbung beginnt bei einer hieraus resultierenden Stromdichte von meist etwa 1 A/dm², die dann jedoch auf einen konstanten Wert von 0,2 bis 0,5 A/dm² abfällt. Je nach Spannung, Metallkonzentration im Färbebad und Tauchzeiten werden unterschiedliche Töne erhalten, die zwischen champagnerfarben über verschiedene Bronzetöne bis schwarz variieren können.The dyeing is usually carried out with the aid of a tin (II) sulfate solution which contains about 3 to 20 g, preferably 7 to 16 g, of tin per liter. It is colored at a pH of 0.35 to 0.5, corresponding to 16 to 22 g of sulfuric acid per liter, at a temperature of about 14 to 30 ° C. The alternating voltage or alternating current superimposed on direct current (50 Hz) is preferably set at 10 to 25 V, preferably 15 to 18 V with an optimum of approximately 17 V ± 3 V. For the purposes of the present invention, the term “direct current superimposed on alternating current” is equivalent to an alternating current superimposed on direct current. The value of the terminal voltage is given in each case. The coloring starts with a resulting current density of mostly about 1 A / dm², which then drops to a constant value of 0.2 to 0.5 A / dm². Depending on the tension, metal concentration in the dyebath and dipping times, different tones are obtained, which can vary between champagne-colored and various bronze tones to black.

In einer weiteren Ausführungsform ist das Verfahren der vorliegenden Erfindung dadurch gekennzeichnet, daß der Elektrolyt zusätzlich 0,1 bis 10 g/l Eisen, vorzugsweise in der Form von Eisen-(II)-Sulfat, enthält.In a further embodiment, the method of the present invention is characterized in that the electrolyte additionally contains 0.1 to 10 g / l iron, preferably in the form of iron (II) sulfate.

Gemäß einer weiteren Ausführungsform ist das Verfahren der vorliegenden Erfindung dadurch gekennzeichnet, daß der Elektrolyt weitere Schwermetallsalze neben Zinn enthält, beispielsweise Nickel, Cobalt, Kupfer und/oder Zink (siehe Wernick et al, loc. cit.).According to a further embodiment, the method of the present invention is characterized in that the electrolyte contains further heavy metal salts in addition to tin, for example nickel, cobalt, copper and / or zinc (see Wernick et al, loc. Cit.).

Im Hinblick auf die einzusetzenden Mengen an Schwermetall-Ionen gilt: Vorzugsweise liegt die Summe der Schwermetall-Ionen - einschließlich Zinn - im Bereich von 3 bis 20 g/l, insbesondere im Bereich von 7 bis 16 g/l. Beispielsweise enthält ein derartiger Elektrolyt 4 g/l Sn(II)-Ionen und 6 g/l Ni(II)-Ionen, beides in Form von Sulfat-Salzen.With regard to the amounts of heavy metal ions to be used, the following applies: the sum of the heavy metal ions - including tin - is preferably in the range from 3 to 20 g / l, in particular in the range from 7 to 16 g / l. For example, such an electrolyte contains 4 g / l Sn (II) ions and 6 g / l Ni (II) ions, both in the form of sulfate salts.

Ein solcher Elektrolyt zeigt die gleichen Färbeeigenschaften wie ein Elektrolyt der nur 10 g/l Sn(II) oder nur 20 g/l Nickel enthält. Ein Vorteil besteht in der geringeren Abwasserbelastung durch Schwermetallsalze.Such an electrolyte shows the same coloring properties as an electrolyte which contains only 10 g / l Sn (II) or only 20 g / l nickel. One advantage is the lower wastewater pollution from heavy metal salts.

Fig. 1 gibt eine prinzipielle Möglichkeit des Aufbaus eines Färbebades zur Beurteilung der Streufähigkeit wieder, wobei das Aluminiumblech als Arbeitselektrode dient. Die übrigen geometrischen Faktoren sind der Figur zu entnehmen.Fig. 1 gives a basic possibility of building a dye bath to assess the spreadability again, with the aluminum sheet serving as the working electrode. The other geometric factors can be seen in the figure.

Das erfindungsgemäße Verfahren soll anhand der folgenden Beispiele näher erläutert werden:The process according to the invention will be explained in more detail with the aid of the following examples:

BeispieleExamples Beispiel 1example 1 Schnelltest zur Beurteilung der Lagerstabilität von FärbebädernRapid test to assess the storage stability of dye baths

Die Beispiele in Tabelle 1 geben die Ergebnisse zur Lagerstabilität von Färbebädern wieder.The examples in Table 1 show the results on the storage stability of dye baths.

Es wurde jeweils ein wäßriger Elektrolyt hergestellt, der jeweils 10 g/l H₂SO₄ und SnSO₄ sowie entsprechende Mengen eines- Stabilisators enthielt. 1-l-Lösungen wurden bei Raumtemperatur mit einem Magnetrührer kräftig gerührt und über eine Glasfritte mit 12 l/h reinem Sauerstoff begast. Der Gehalt an Sn(II)-Ionen wurde dabei ständig jodometrisch erfaßt.

Figure imgb0002
Figure imgb0003
 An aqueous electrolyte was prepared, each containing 10 g / l H₂SO₄ and SnSO₄ and corresponding amounts of a stabilizer. 1 l solutions were stirred vigorously at room temperature with a magnetic stirrer and gassed with 12 l / h pure oxygen through a glass frit. The content of Sn (II) ions was continuously recorded iodometrically.
Figure imgb0002
Figure imgb0003

Beispiel 2Example 2 Test zur Beurteilung der Stabilisierungswirkung von Additiven in Färbebädern unter elektrischer BelastungTest to assess the stabilizing effect of additives in dye baths under electrical stress

Die Beispiele in Tabelle 2 geben die Ergebnisse der Sn(II)-Konzentrationsänderung in Färbebädern unter elektrischer Belastung wieder. Es wurde jeweils ein wäßriger Elektrolyt hergestellt, der 10 g/l Sn(II)Ionen, 20 g/l H₂SO₄ und entsprechende Mengen eines Stabilisators enthielt. Die Dauerelektrolyse erfolgte mit Edelstahlelektroden. Die fließende Strommenge wurde mit einem Ah-Zähler registriert. Das charakteristische Verhalten der zu färbenden Oxidschicht wurde durch entsprechende Sinusverzerrung des Wechselstromes bei hoher kapazitiver Belastung simuliert. Die Menge an durch Elektrodenreaktionen oxidierten Sn(II)-Ionen wurde durch laufende jodometrische Titration des Elektrolyten sowie durch gravimetrische Bestimmung des reduktiv abgeschiedenen Sn und der Differenz aus der Summe dieser beiden Werte zur Ausgangsmenge an gelöstem Sn(II) ermittelt. Als Maß für die stabilisierende Wirkung wurde der Ah-Wert gewählt, bei dem eine Absenkung der Sn(II)-Konzentration durch oxidative Reaktion an den Elektroden um 5 g/l nicht mehr verhindert werden kann.

Figure imgb0004
The examples in Table 2 show the results of the Sn (II) concentration change in dye baths under electrical stress. An aqueous electrolyte was prepared which contained 10 g / l Sn (II) ions, 20 g / l H₂SO₄ and corresponding amounts of a stabilizer. The permanent electrolysis was carried out with stainless steel electrodes. The flowing amount of electricity was registered with an Ah counter. The characteristic behavior of the oxide layer to be colored was simulated by corresponding sine distortion of the alternating current at high capacitive loads. The amount of Sn (II) ions oxidized by electrode reactions was determined by continuous iodometric titration of the electrolyte and by gravimetric determination of the reductively deposited Sn and the difference between the sum of these two values and the starting amount of dissolved Sn (II). The Ah value was chosen as a measure of the stabilizing effect, at which a reduction in the Sn (II) concentration by oxidative reaction at the electrodes by 5 g / l can no longer be prevented.
Figure imgb0004

Beispiel 3Example 3 Elektrolytische EinfärbungElectrolytic coloring

Es wurden Probebleche der Dimension 50 mm x 500 mm x 1 mm wie in Fig. 1 dargestellt aus dem DIN-Werkstoff Al 99.5 (Werkstoff-Nr. 3.0255) konventionell vorbehandelt (entfettet, gebeizt, dekapiert, gespült) und nach dem GS-Verfahren (200 g/l H₂SO₄, 10 g/l Al, Luftdurchsatz 8 m³/m² h, 1.5 A/dm², 18 °C) 50 min anodisiert. Es ergab sich hierbei ein Schichtaufbau von etwa 20 µm. Die so vorbehandelten Bleche wurden wie in den folgenden Beispielen näher beschrieben, elektrolytisch eingefärbt.Test sheets of the dimensions 50 mm x 500 mm x 1 mm as shown in Fig. 1 from the DIN material Al 99.5 (material no. 3.0255) were conventionally pretreated (degreased, pickled, pickled, rinsed) and according to the GS process (200 g / l H₂SO₄, 10 g / l Al, air flow 8 m³ / m² h, 1.5 A / dm², 18 ° C) anodized for 50 min. The result was a layer build-up of approximately 20 µm. The sheets pretreated in this way were colored electrolytically as described in the following examples.

Beispiel 3.1 bis 3.4 und Vergleichsbeispiele 2 und 3Examples 3.1 to 3.4 and Comparative Examples 2 and 3

Die Versuchsbleche wurden, wie in Fig. 1 dargestellt, in einer speziellen Testkammer 135 s lang gefärbt. Die Färbespannung wurde hierbei zwischen 15 und 21 V variiert. Das Färbebad enthielt neben 10 g/l Sn²⁺ und 20 g/l H₂SO₄ als Badadditiv noch unterschiedliche Mengen p-Toluolsulfonsäure (3.1-3.3) oder 2-Naphthalinsulfonsäure (3.4) (10 g/l). In Vergleichsbeispiel 2 wurden 10 g/l Phenolsulfonsäure und in Vergleichsbeispiel 3 10 g/l Sulfophthalsäure entsprechend eingesetzt. Ziel der Versuche sollte es sein, die Verbesserung der Tiefenstreuung der so eingefärbten Al-Bleche bei Zusatz von p-Toluolsulfonsäure und 2-Naphthalinsulfonsäure zum Färbebad zu verdeutlichen. Die Ergebnisse der Tiefenstreumessungen unter Zusatz von 0, 10 und 20 g/l p-Toluolsulfonsäure und 2-Naphthalinsulfonsäure bei Färbespannungen von 15, 18 und 21 V sind in Tab. 3 dargestellt.As shown in FIG. 1, the test panels were colored in a special test chamber for 135 s. The dyeing voltage was varied between 15 and 21 V. The dye bath contained 10 g / l Sn²⁺ and 20 g / l H₂SO₄ as a bath additive as well as different amounts of p-toluenesulfonic acid (3.1-3.3) or 2-naphthalenesulfonic acid (3.4) (10 g / l). In comparative example 2, 10 g / l phenolsulfonic acid and in comparative example 3 10 g / l sulfophthalic acid were used accordingly. The aim of the experiments should be to clarify the improvement in the depth scatter of the aluminum sheets colored in this way when p-toluenesulfonic acid and 2-naphthalenesulfonic acid are added to the dyebath. The results of the deep scatter measurements with the addition of 0, 10 and 20 g / l p-toluenesulfonic acid and 2-naphthalenesulfonic acid at coloring tensions of 15, 18 and 21 V are shown in Tab. 3.

Ermittlung der StreufähigkeitDetermination of the spreadability

Zunächst wird die Zinnverteilung auf dem Testblech an 10 verschiedenen Stellen in Längsrichtung gemessen.First, the tin distribution on the test sheet is measured at 10 different locations in the longitudinal direction.

Begonnen wird 1 cm vom Rand in Schritten von 5 cm.Start from 1 cm from the edge in 5 cm increments.

Die Messung erfolgt mit einem Streulichtreflektometer gegen den Weißstandard TiO₂ (99 %).The measurement is carried out with a scattered light reflectometer against the white standard TiO₂ (99%).

Der Zinngehalt berechnet sich daraus wie folgt:

Figure imgb0005

R = Reflektivität in %
The tin content is calculated as follows:
Figure imgb0005
R = reflectivity in%

Der mittlere Sn-Gehalt ist dann:

Figure imgb0006
The mean Sn content is then:
Figure imgb0006

Die Streufähigkeit ergibt sich dann daraus wie folgt:

Figure imgb0007
Tabelle 3 Ergebnis der Tiefenstreumessungen (%) bei Variation der Färbespannung und der zugesetzten Menge an streufähigkeitbeeinflussender Substanz. Beispiel 3.1 3.2 3.3 3.4 Vgl.2 Vgl.3 Gehalt Streuverbesserer (g/l) Färbespannung (V) 0 10 20 10 10 10 15 44% 52% 76% 51% 49% 46% 18 56% 74% 90% 71% 60% 59% 21 76% 88% 93% 86% 80% 79% The spreadability then results from this as follows:
Figure imgb0007
 Table 3 Result of the depth scatter measurements (%) with variation of the coloring tension and the added amount of substance influencing the scattering ability. example 3.1 3.2 3.3 3.4 See 2 See 3 Spreading improver content (g / l) Dyeing voltage (V) 0 10th 20th 10th 10th 10th 15 44% 52% 76% 51% 49% 46% 18th 56% 74% 90% 71% 60% 59% 21 76% 88% 93% 86% 80% 79%

Beispiel 4Example 4

Dieses Beispiel verdeutlicht die Verbesserung der Tiefenstreuung bei gleichzeitigem Zusatz von p-Toluolsulfonsäure und tert.-Butylhydrochinon. Die Bleche wurden wie in Beispiel 3 beschrieben, vorbehandelt und anschließend elektrolytisch eingefärbt. Die Ergebnisse dieser Testreihe sind in Tab. 4 dargestellt. Tabelle 4 Ergebnis der Tiefenstreumessungen (%) bei Zusatz von tert.-Butylhydrochinon + p-Toluolsulfonsäure zum Färbebad Färbespannung (V) Badadditiv tert.-Butylhydrochinon (2 g/l) tert.-Butylhydrochinon (2 g/l) + p-Toluolsulfonsäure (20 g/l) 15 43% 82% 18 59% 96% This example illustrates the improvement in depth scattering with the simultaneous addition of p-toluenesulfonic acid and tert-butylhydroquinone. The sheets were pretreated as described in Example 3 and then colored electrolytically. The results of this series of tests are shown in Table 4. Table 4 Result of the depth scatter measurements (%) when adding tert-butylhydroquinone + p-toluenesulfonic acid to the dyebath Dyeing voltage (V) Bath additive tert-butyl hydroquinone (2 g / l) tert-butyl hydroquinone (2 g / l) + p-toluenesulfonic acid (20 g / l) 15 43% 82% 18th 59% 96%

Beispiel 5Example 5

Analog Beispiel 3 enthielt das Färbebad entsprechend den Beispielen 3.2 und 3.3 anstelle von 10 g/l Sn²⁺ hierbei 4 g/l Sn²⁺ und 6 g/l Ni²⁺. Es resultierten die gleichen Ergebnisse bei der Teifenstreumessung.Analogously to Example 3, the dyebath according to Examples 3.2 and 3.3 contained 4 g / l Sn²⁺ and 6 g / l Ni²⁺ instead of 10 g / l Sn²⁺. The same results were obtained when measuring the litter.

Mit nur 10 g/l Schwefelsäure werden etwas dunklere Färbungen erzielt als mit 20 g/l Schwefelsäure.With only 10 g / l sulfuric acid, somewhat darker colorations are achieved than with 20 g / l sulfuric acid.

Claims (9)

  1. A process for electrolytically colouring anodized surfaces of aluminium and aluminium alloys with metal salts, in which a defined oxide layer is first produced with direct current in acidic solution and is then coloured with alternating current or alternating current superimposed on direct current using an acidic electrolyte containing tin(II) salts, characterized in that the electrolyte contains from 0.01 g/l to the solubility limit of one or more water-soluble compounds stabilizing tin(II) salts and corresponding to general formulae (I) to (IV)
    Figure imgb0009
     in which
    R₁   represents hydrogen, alkyl, aryl, alkylaryl, alkylarylsulfonic acid, alkylsulfonic acid and alkali metal salts thereof containing 1 to 22 C atoms,
    R₂   represents hydrogen, alkyl, aryl, alkylaryl, alkylarylsulfonic acid, alkylsulfonic acid and alkali metal salts thereof containing 1 to 22 C atoms,
    R₃   represents one or more hydrogen and/or alkyl, aryl, alkylaryl radicals containing 1 to 22 C atoms and
    R₄ and R₅   represent one or more hydrogen, alkyl, aryl and/or alkylaryl radicals, sulfonic acid, alkylsulfonic acid, alkylarylsulfonic acid and alkali metal salts thereof containing 1 to 22 C atoms,
    at least one of the substituents R₁, R₂ and R₃ not being hydrogen.
  2. A process as claimed in claim 1, characterized in that the electrolyte contains 0.1 to 2 g/l of the compounds stabilizing the tin(II) salts.
  3. A process as claimed in claims 1 and 2, characterized in that the stabilizing compounds are selected from 2-tert.butyl-1,4-dihydroxybenzene, methyl hydroquinone, trimethyl hydroquinone, 4-hydroxy-2,7-naphthalene disulfonic acid and/or p-hydroxyanisole.
  4. A process as claimed in claims 1 to 3, characterized in that the electrolyte contains 1 to 50 g/l and preferably 5 to 25 g/l p-toluene sulfonic acid and/or naphthalenesulfonic acid.
  5. A process as claimed in claims 1 to 4, characterized in that the electrolyte contains 3 to 20 g/l and preferably 7 to 16 g/l tin in the form of tin(II) sulfate and electrolytic colouring is carried out at a pH value of 0.1 to 2, preferably at a pH value of 0.35 to 0.5, at a temperature of 14 to 30°C, at an a.c. voltage with a frequency of 50 Hz, at a terminal voltage of 10 to 25 V and preferably 15 to 18 V and at the resulting current density.
  6. A process as claimed in claim 5, characterized in that the electrolyte contains 0.1 to 10 g/l iron, preferably in the form of iron(II) sulfate.
  7. A process as claimed in claim 6, characterized in that the electrolyte contains other colouring heavy metal salts of nickel, cobalt, copper and/or zinc.
  8. A process as claimed in claim 7, characterized in that the total quantity of tin and other colouring heavy metal salt in the electrolyte is from 3 to 20 g/l and preferably from 7 to 16 g/l.
  9. A process as claimed in claim 8, characterized in that the electrolyte contains 4 g/l tin in the form of water-soluble tin(II) salt and 6 g/l nickel in the form of water-soluble nickel salt.
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JPS55131195A (en) * 1979-03-30 1980-10-11 Sumitomo Light Metal Ind Ltd Electrolytic coloring method for aluminum
DE2921241A1 (en) * 1979-04-19 1980-10-23 Alusuisse ACID TIN-II CONTAINING ELECTROLYT
JPS5620568A (en) * 1979-07-30 1981-02-26 Mitsui Petrochem Ind Ltd Production of di 2-tert-butylperoxy-2-propyl benzene
IT1142650B (en) * 1981-12-31 1986-10-08 Grace Italiana Spa ALUMINUM ELECTRO-COLORING PLANT AND PROCESS
JPS59190389A (en) * 1983-04-13 1984-10-29 Tateyama Alum Kogyo Kk Method for coloring aluminum or aluminum alloy
DE3611055C1 (en) * 1986-04-02 1987-06-19 Alusuisse Acid tin(II)-containing electrolyte

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AU608992B2 (en) 1991-04-18
AR241811A1 (en) 1992-12-30
HU205973B (en) 1992-07-28
DK355689A (en) 1990-01-20
FI89812B (en) 1993-08-13
FI893466A0 (en) 1989-07-18
DE58904127D1 (en) 1993-05-27
JP2916168B2 (en) 1999-07-05
NO177233B (en) 1995-05-02
NO177233C (en) 1995-08-09
YU142989A (en) 1991-04-30
DK355689D0 (en) 1989-07-18
NO892946L (en) 1990-01-22
HUT50888A (en) 1990-03-28
ATE88510T1 (en) 1993-05-15
US5064512A (en) 1991-11-12
DE3824403A1 (en) 1990-01-25
CN1039452A (en) 1990-02-07
DD284061A5 (en) 1990-10-31
EP0354365A1 (en) 1990-02-14
CN1041446C (en) 1998-12-30
KR900001887A (en) 1990-02-27
FI89812C (en) 1993-11-25
NO892946D0 (en) 1989-07-18
ES2041899T3 (en) 1993-12-01
PL162190B1 (en) 1993-09-30
CA1339115C (en) 1997-07-29
JPH0273994A (en) 1990-03-13
FI893466A (en) 1990-01-20
SU1722235A3 (en) 1992-03-23
YU46733B (en) 1994-04-05
KR960011248B1 (en) 1996-08-21
TR23878A (en) 1990-10-16
BR8903541A (en) 1990-03-13
MX173050B (en) 1994-01-31
PT91208A (en) 1990-02-08
ZA895472B (en) 1990-03-28
NZ229976A (en) 1991-04-26
PT91208B (en) 1995-03-01
AU3824289A (en) 1990-01-25

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