EP0351680A1 - Use of p-toluene sulfonic acid in the electrolytic colouring of anodically obtained aluminium surfaces - Google Patents

Abstract

Undesirable greenish tinges that normally result when coloring anodized aluminum by AC electrolysis in solutions of silver salts can be avoided by adding to the electrolytes an appropriate amount of p-toluenesulfonic acid and/or its salts. The coloring solution may also contain (i) sulfuric acid, (ii) alkali metal, ammonium and/or alkaline earth metal salts of sulfuric acid and/or (iii) alkali metal, ammonium and/or alkaline earth metal acetates.

Description

The invention relates to the electrolytic coloring of anodically produced surfaces of aluminum and / or aluminum alloys in aqueous electrolytes containing silver salt by means of alternating current and using p-toluenesulfonic acid.

From S. Wernick, R. Pinner, P. Sheasby, "The Surface Treatment and Finishing of Aluminum and its Alloys", 5th edition (1987), p. 611, Finishing Publications Ltd., Paddington-Middlesex, Great Britain the electrolytic coloring in electrolytes containing silver salt is known. However, only greenish-gold colorations are usually achieved here, which find little acceptance particularly when used in the architectural field.

Chemical Abstracts 105 (10), Unit 87 431z, discloses the electrolytic coloring of aluminum using an electrolyte containing silver nitrate and sulfuric acid. The coloring process was used for the surface treatment of lamps and aluminum workpieces. It is described that the problems that usually arise from dyeing with organic dyes are solved.

Chemical Abstracts 93 (20), Section 194 174y, describes the coloring of anodically produced aluminum with molybdate solutions. Studies have been done to blue and obtain green colored, anodized aluminum surfaces in a multi-stage process. Various solutions containing (NH₄) ₆Mo₄O₂₄ x 4 H₂O, SnSO₄, C₇H₆O₄S and H₂SO₄ were used alone or in combination with silver nitrate solutions. This is a multi-stage process, the electrolyte solutions containing combinations of the salts mentioned.

JP-A 55-131195 describes the electrolytic coloring of aluminum with a number of metal salts. In the electrolytic dye bath after the anodic oxidation by AC electrolysis in a bath containing a hydroxyalkanolsulfonic acid of the general formula HO-R-SO₃H, said electrolytic dyeing is carried out.

Surprisingly, it was found that with the addition of p-toluenesulfonic acid to electrolyte baths containing silver salts, a warm, brilliant and, above all, light-resistant gold tone can be achieved without a visible green tint when coloring anodically produced surfaces of aluminum and / or aluminum alloys by means of alternating current. With longer coloring, a reddish-brown, very decorative hue is created.

The invention thus relates to the use of p-toluenesulfonic acid and / or its water-soluble alkali metal, ammonium and / or alkaline earth metal salts for the electrolytic coloring of anodically produced surfaces of aluminum and / or aluminum alloys in aqueous electrolyte solutions containing silver salts, by means of alternating current or alternating current superimposed on direct current.

Compared to the adsorptive gold coloring using iron (III) oxalate and also the electrolytic coloring using potassium permanganate, the electrolytic coloring according to the invention also has the decorative effect has the advantage that it can be easily and permanently over-dyed with organic dyes and so, for example, with dyes such as Sanodalblau ^R from Sandoz AG, Basel, Switzerland, a lightfast green can also be achieved as a combination dyeing.

Other sulfonic acids do not show the desired effect of the reddish-yellow color in gold tints. Rather, these result in less preferred greenish gold tones in the decorative area, as the comparative examples 4 to 7 below show.

The subsequent use of the term "p-toluenesulfonic acid" also includes their water-soluble alkali metal salts and / or their water-soluble alkaline earth metal salts. Usually p-toluenesulfonic acid is used in the form of the monohydrate because of its better solubility in water.

According to one embodiment of the present invention, p-toluenesulfonic acid is used in an amount of 3 to 100 g / l electrolytic solution, while a preferred embodiment of the present invention consists in using 5 to 25 g / l p-toluenesulfonic acid.

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. The use of silver sulfate is preferred.

Another embodiment of the present invention is that the electrolyte solution, if desired, 2.5 to 100 g / l sulfuric acid and / or its alkali metal, ammo contains nium and / or alkaline earth metal salts. A particular embodiment of the present invention is that an electrolyte solution is used which contains 2.5 to 25 g / l sulfuric acid. The alkali metal, ammonium and / or alkaline earth metal salts which can be used instead of or together with this are those of sodium, potassium, ammonium, magnesium or mixtures thereof, preferably in the form of the sulfates and / or the acetates.

The use of magnesium sulfate together with or instead of the sulfuric acid is particularly preferred.

To achieve the best possible coloring, a terminal voltage of 4 to 20 V is set according to the invention. A preferred embodiment of the present invention is to set the terminal voltage in the range from 8 to 16 V. Alternating current or alternating current superimposed with direct current is used. Here, the "alternating current superimposed with direct current" is equivalent to "direct current superimposed with alternating current". The voltage applied to the bath is defined as the terminal voltage.

The generation of gold tones is preferred within the scope of the invention. These preferably result in a voltage range of 8 to 16 V, the treatment times should be shorter the higher the voltage is selected. In this sense, the treatment times are usually in the range of 0.5 to 3 minutes.

In general, more intense colorations result, the longer the treatment time (coloring time), the higher the voltage and the higher the silver concentrations in the electrolyte.

In this sense, brown tones result in dyeing times of more than 3 min and higher voltage values, i.e. especially more than 10 V.

At higher silver concentrations, i.e. from 2 to 10 g / l, deep black colorations result.

Voltage values of more than 16 V should generally be avoided with dyeing times of more than 3 minutes, since otherwise the oxide layer may flake off.

Electrolyte solutions which contain further cations can also be used within the scope of the invention. Preferred as such are: Cu (II), Ni (II) and Co (II). This results in a wide range of other warm colors.

The lightfastness of the surfaces achieved after compression is extremely good. After Wernick, Pinner, Zurbrügg, Weiner "The surface treatment of aluminum", 2nd edition, Leuze Verlag, Saulgau / Württ. (1977) p. 364 f, light fastness in the range around the value 8 is found in standardized processes.

Examples Pretreatment:

For the following examples and comparative examples, test sheets (dimension 50 mm x 40 mm x 1 mm) made of the material AlMg 1 (DIN material no. 3.3315) were used.

Before the anodizing, the sheets were degreased, pickled and pickled using conventional methods. The degreasing was carried out with an alkaline cleaner containing borates, carbonates, phosphates and nonionic surfactants (P3-almeco ^R 18, Henkel KGaA, Düsseldorf), bath concentration 5% by weight at 70 ° C. in the course of 15 minutes.

For the pickling, a mixture (3: 1) of sodium hydroxide and a pickling agent containing alkali, alcohols and salts of inorganic acids (P3-almeco ^R 46, Henkel KGaA, Duesseldorf) was used. Bath concentration: 8% by weight, temperature: 65 ° C, immersion time: 12 min.

The pickling was carried out using an acidic pickling agent containing salts of inorganic acids and inorganic acids (P3-almeco ^R 90, Henkel KGaA, Düsseldorf), in a concentration of 15% by weight, at a temperature of 20 ° C. in the course of 3 minutes .

After each of the above process steps, the sheets were rinsed thoroughly with deionized water.

The subsequent anodization was carried out using the direct current sulfuric acid method; Bath composition: 180 g / l sulfuric acid, 10 g / l aluminum, air injection: 8 m³ / m²h, temperature: 20 ° C, DC voltage 15 V, current density 1.4 A / dm², anodizing time: 2700 to 3600 sec, depending on the requirements for the production of a constant oxide layer of 20 µm.

After thorough rinsing again with deionized water, the dyeing treatment according to the invention was carried out as described in the examples and comparative examples.

The sheets were then rinsed again and subjected to a compression process. At a temperature of about 98 ° C in the course of 60 min. (corresponding to 3 min./µm) the compression. As an additive, a sealing coating inhibitor based on polycarboxylic acids and ammonium acetate was used as a buffer substance (P3-almeco ^R seal SL, Henkel KGaA, Düsseldorf).

example 1

Using an electrolyte containing 1 g / l of silver sulfate and 20 g / l of sulfuric acid, a reddish-gold-yellow surface color of the above-mentioned aluminum bleach was achieved in the course of 1 min at a terminal voltage of 16 V with the addition of 20 g / l of p-toluenesulfonic acid.

Comparative Example 1

Using the same electrolyte as in Example 1, but without using p-toluenesulfonic acid, an olive greenish-yellow tone of the aluminum sheet was achieved under the same electrolysis conditions.

Example 2

Using an electrolyte containing 1 g / l of silver sulfate and 20 g / l of sulfuric acid, a reddish-brown surface color was achieved at a terminal voltage of 14 V over the course of 8 minutes using 20 g / l of p-toluenesulfonic acid.

Comparative Example 2

Using an electrolyte according to Example 2, but without using p-toluenesulfonic acid, an olive-brown surface coloring of the above-mentioned aluminum sheets was achieved under the same electrolysis conditions.

Example 3

Using an electrolyte containing 1 g / l silver nitrate and 20 g / l sulfuric acid, a bronze-brown surface coloring of the above-mentioned aluminum sheets was achieved in the course of 4 min at a terminal voltage of 12 V using 15 g / l p-toluenesulfonic acid.

Comparative Example 3

Using an electrolyte according to Example 3, a light olive-brown color was achieved under the same electrolysis conditions without using p-toluenesulfonic acid.

Example 4

Subsequent over-staining before the sealing treatment of the gold-colored sheets obtained above with Sanodalblau ^R from Sandoz AG, Basel, Switzerland, in a concentration of 5 g / l, pH 5.5, gave a green color over the course of 20 min at 60 ° C. was extremely lightfast.

Example 5

Using an electrolyte containing 1 g / l of silver sulfate and 5 g / l of sulfuric acid, was added in the course of 1 min a terminal voltage of 16 V with the addition of 20 g of p-toluenesulfonic acid achieved a reddish-gold surface coloring of the above-mentioned aluminum sheets.

Comparative Example 4

Using an electrolyte containing 1 g / l silver sulfate and 5 g / l sulfuric acid, a greenish-yellow-gold surface coloring of the above-mentioned aluminum sheets was achieved in the course of 1 min at a terminal voltage of 16 V with the addition of 20 g / l methanesulfonic acid.

Comparative Example 5

Using an electrolyte containing 1 g / l of silver sulfate and 5 g / l of sulfuric acid, a greenish-yellow-gold surface color of the above was obtained in the course of 1 min at a terminal voltage of 16 V with the addition of 20 g / l of naphthalene-2-sulfonic acid Aluminum sheets achieved.

Comparative Example 6

Using an electrolyte containing 1 g / l silver sulfate and 5 g / l sulfuric acid, a greenish-yellow-gold surface coloring of the above-mentioned aluminum sheets was achieved in the course of 1 min at a terminal voltage of 16 V with the addition of 20 g / l benzenesulfonic acid.

Comparative Example 7

Using an electrolyte containing 1 g / l of silver sulfate and 5 g / l of sulfuric acid, the reaction was carried out over a period of 1 min at a terminal voltage of 16 V with addition of 20 g / l of butane sulfonic acid achieved a greenish-yellow-gold surface coloring of the above-mentioned aluminum sheets.

Example 6

Using an electrolyte containing 0.5 g / l of silver sulfate and 20 g / l of sulfuric acid, a reddish-yellow-gold surface color of the above was obtained in the course of 1 min with the addition of 20 g / l of p-toluenesulfonic acid at a terminal voltage of 16 V. Aluminum sheets achieved.

Example 7

Using an electrolyte containing 0.5 g / l of silver sulfate and 15 g / l of magnesium sulfate (in the form of MgSO₄. 7H₂O) one was in the course of 2 min at a terminal voltage of 14 V with the addition of 20 g / l of p-toluenesulfonic acid reddish-yellow-gold surface coloring of the above aluminum sheets achieved.

Claims (11)

1. Use of p-toluenesulfonic acid and / or its water-soluble alkali metal, ammonium and / or alkaline earth metal salts for the electrolytic coloring of anodized surfaces of aluminum and / or aluminum alloys in silver salt-containing, aqueous electrolyte solutions, by means of alternating current or alternating current superimposed on direct current. 2. Use of p-toluenesulfonic acid and / or its water-soluble alkali metal, ammonium and / or alkaline earth metal salts according to claim 1 in an amount of 3 to 100 g / l electrolyte solution. 3. Use of p-toluenesulfonic acid and / or its water-soluble alkali metal, ammonium and / or alkaline earth metal salts according to claim 1 in an amount of 5 to 25 g / l electrolyte solution. 4. Use according to claims 1 to 3, in an electrolyte solution containing 0.1 to 10 g / l silver in the form of water-soluble salts, preferably in the form of the nitrates, acetates and / or sulfates. 5. Use according to claims 1 to 3, in an electrolyte solution containing 0.3 to 1.2 g / l of silver in the form of water-soluble salts, preferably in the form of the nitrates, acetates and / or sulfates. 6. Use according to claims 1 to 5, in an electrolytic solution containing 2.5 to 100 g / l sulfuric acid and / or their alkali metal, ammonium and / or alkaline earth metal salts. 7. Use according to claim 1 to 5, in an electrolytic solution containing 2.5 to 25 g / l sulfuric acid and / or its alkali metal, ammonium and / or alkaline earth metal salts. 8. Use according to claims 1 to 7, characterized in that the sulfates of sodium, potassium, magnesium, ammonium and / or their acetates and mixtures thereof are used as the alkali metal, ammonium and / or alkaline earth metal salt. 9. Use according to claims 1 to 8, characterized in that the electrolyte solution contains further transition metal cations, preferably Cu (II), Ni (II) and Co (II). 10. Use according to claims 1 to 9, at a terminal voltage of 4 to 20 V. 11. Use according to claims 1 to 9, at a terminal voltage of 8 to 16 V.