DE1446461B2 - Sealing bath for anodically oxidized aluminum surfaces, use of the same and method for sealing anodically oxidized aluminum surfaces - Google Patents

Description

The present invention relates to methods and means for sealing on the surfaces of Artificially produced oxide coatings on aluminum objects. In particular, the invention relates to that Sealing of such oxide coatings using an aqueous solution of sulfosalicylic acid and at least one electrolyte consisting of metal sulfate and / or sulfuric acid generated became.

In general, anodic oxide coatings are made by adding an aluminum article or -shaped body entered in a suitable electrolyte and an electric current through the Electrolyte is allowed to flow, with the aluminum part serving as an anode. With the here occurring Decomposition of the electrolyte releases oxygen, which chemically interacts with the aluminum and its alloy constituents and a hard oxide layer on the surface of the aluminum article or molded body forms. This process has become known as "anodic oxidation". The oxide layer is usually subjected to a treatment known as sealing is to prevent loss of color when staining with dyes and to make them more stable in general and to make them more resistant to corrosion.

This sealing can be achieved in a number of different ways. A form of sealing the Coatings, especially when they are colored with an organic dye, consist of being anodic to bring oxidized aluminum objects or shaped bodies into solutions that contain substantial quantities hydrolyzable metal salts, especially nickel acetate and / or cobalt acetate. These salts serve to "fix" or pickle the dye and must therefore be used in appropriate quantities will. In certain cases, this process creates an unsightly residue known as "Dirt" is known and can be observed on the finished objects or after light rubbing occurs. This residue affects the appearance of the part and must be replaced by suitable Medium, e.g. B. polishing, which is troublesome and expensive, and the price of the finished item elevated.

It is known from US Pat. No. 2,888,388 that the formation of "dirt" is anodic 5 to prevent oxidized and subsequently colored aluminum surfaces during sealing by the fact that the sealing solution contains substantial amounts of a metal acetate, a lignin sulfonate and a Buffers such as boric acid may be incorporated. With this one

ίο procedures should remove the dyes used afterwards are fixed, so that there can be no analogy to the sealing bath according to the invention. In addition, the known sealing bath has certain disadvantages. First is the cost of the Treatment bath by the prices for its ingredients and the relatively large quantities that of which are used, quite high. Second, the treatment bath tends to be unstable and to bring about undesirable side effects after a relatively short period of use, with the oxide layers treated with it receive an unsightly brownish shade. From these The lifespan of such a treatment bath is relatively short.

During a series of tests on anodically oxidized and at the same time colored coatings, which are described in US Pat. No. 3,031,387, it was found that the sealing baths known to date are unsatisfactory for these coatings because, in addition to the other disadvantages mentioned above, they have an unsightly effect Generate dirt, as shown by the test results reported below.
Three baths A, B and C were prepared in accordance with the information in US Pat. These known baths were compared with three baths D, E and F according to the present invention. Furthermore, two baths G and H were investigated, which are outside the scope of the invention and serve to demonstrate the range of effects.

Sealing conditions 20 minutes, 94.4 to 96.7 ° C

composition nickel g / l pH Dirt and paint compared to unsealed 6061 Pieces of alloy bath Lignin- acetate boron value light dirt and sulfonate 5.0 acid 5052 brown discoloration 6351 A. 2.4 5.0 5.8 yellow discoloration Dirt and brown light dirt 5.0 Discoloration B. 1.8 5.0 5.8 yellow discoloration Dirt and brown brown dirt 5.0 Discoloration C. 0.6 5.0 5.8 Dirt and yellow no dirt or heavy dirt 0.5 Discoloration Discoloration D. 2.4 0 5.0 no dirt or no dirt or no dirt or 0.5 Discoloration Discoloration Discoloration E. 1.8 0 5.0 no dirt or no dirt or no dirt or 0.5 Discoloration Discoloration Discoloration F. 0.6 0 5.0 no dirt or very light brown no dirt or 1.0 Discoloration Discoloration Discoloration G 0.6 0 5.0 light yellow ver light brown ver. light dirt 1.5 coloring coloring H 0.6 0 5.0 yellow discoloration no discoloration or dirt dirt not sealed

In general, the coatings described in U.S. Patent 3,031,387 can be used in one Electrolyte that contains at least one metal sulfate and / or sulfuric acid in addition to sulfosalicylic acid will. Such an electrolyte consists essentially of an aqueous solution of about 5 to 50 percent by weight sulfosalicylic acid and at least one metal sulfate and / or sulfuric acid in an amount corresponding to no more than 15 percent by weight of sulfuric acid. Preferably contains the Electrolyte sulfuric acid. A suitable metal sulfate is iron (III) sulfate. Even small amounts of metal sulphate and / or sulfuric acid, d. H. Metal sulfate and / or sulfuric acid quantities that are at least 0.1 percent by weight of sulfuric acid, exercise a favorable influence on the according to the invention Electrolytes off. The preferred ranges are 7 to 15 weight percent sulfosalicylic acid and one Amount of metal sulfate and / or sulfuric acid, which corresponds to 0.1 to 4 percent by weight sulfuric acid.

It has been found that fully colored oxidized aluminum surfaces such as those produced after aforementioned processes have been produced at much lower cost and without the formation of "dirt" or discoloration of the finished product can be effectively sealed by the finished product is immersed in a sealing bath that is relatively small and accurate Contains defined amounts of a metal ion-donating compound and an organic sulfonate.

The subject of the invention is thus a sealing bath for anodically oxidized and at the same time colored aluminum surfaces, which contains nickel acetate and lignosulfonate and thereby characterized in that it consists essentially of a 0.02 to 0.8 g / L nickel acetate and 0.1 to 3.0 g / L one An aqueous solution containing lignosulfonate and has a pH between 4 and 6.

Appropriately, the sealing bath according to the invention consists essentially of a 0.3 to 0.6 g / l, preferably 0.5 g / l nickel acetate and 0.5 to 2.0 g / l of a lignin sulfonate, preferably 1.0 g / l Sodium lignosulfonate, containing aqueous solution and has a pH of about 5.

In a sealing bath according to the invention, nickel acetate and the lignosulfonate are thus in Total amounts less than 3.8 g / l and in a ratio of nickel acetate to lignin sulfonate of contain approximately 1: 1 to 1: 5.

In practice, the components of the sealing bath according to the invention are used as a dry mixture, which consists of nickel acetate and a lignosulfonate in a ratio of about 1: 1 to 1: 5, stored and shipped. For use, this mixture can be dissolved in water in such amounts that a solution is obtained which contains less than 3.8 g of the mixture per liter of water.

The sealing bath according to the invention is preferably used for sealing anodically oxidized and at the same time colored aluminum surfaces are used, which were generated in an electrolyte, which consists essentially of an aqueous solution of sulfosalicylic acid and at least one metal sulfate and / or sulfuric acid.

The sealing bath according to the invention is expediently used at a temperature of 85 to ^100.degree. C., preferably at a temperature of about 99.degree.

The invention finally relates to a method for sealing anodically oxidized and thereby simultaneously colored aluminum surfaces, which is characterized in that the to be sealed The object was immersed in a sealing bath of the type described for about 10 to 30 minutes will.

In the following examples, commercially available aluminum alloys were used, as described in are given in the following table. Of course, other alloys can also be used.

alloy VoSi VoFe VoCu From % Mg VoZn "/» Ti VoCr 5052 0.10
0.68
0.32
0.94 0.20
0.32
0.26
0.17 0.009
0.24
0.01
0.00 0.02
0.03
0.01
0.56 2.44
0.93
0.50
0.57 0.05
0.05
0.00
0.03 0.003
0.01
0.01
0.03 0.20
0.23
0.00
0.01 6061-T6 ..
6063-T5 ..
6351-T5 ..

In the table, the rest of the substances are in each case aluminum. Alloys 5052 and 6061-T6 were made in the form of plates with a thickness of 1 mm, the alloys 6063-T5 and 6351-T5 in Form of compacts used. The individual alloys were electrolytically anodized as follows.

1. 5 minutes cleaning at a temperature of 71 ° C in an alkaline detergent bath with inhibitor and a detergent concentration of 65 g / l. A suitable alkaline The detergent bath consists, for example, of an aqueous solution of 40 g / l sodium carbonate, 20 g / l sodium phosphate and 5 g / l sodium metasilicate.

2. Rinse in cold water.

3. 5 minutes at a temperature of etching at 71 ⁰ C in a 5gewichtsprozentigen caustic soda solution.

4. Rinse in cold water.

5. Immerse in 30 weight percent room temperature nitric acid for 2 minutes.

6. Rinse in cold water.

7. Electrolytic anodizing with a current density of 0.025 A / cm ² and a temperature of 25 ± 1 ° C in a bath with the following composition:

anodized:

5-sulfosalicylic acid 95.9 g / l

Sulfuric acid 6.7 g / l

Alloys 6061 and 6351 were anodized at a current density of 0.025 A / cm ² until the voltage between anode and cathode reached 65V. Beyond this point the anodic oxidation continued at 65 volts. The total duration of the anodic oxidation was 40 minutes. With the alloys 5052 and 6063 the anodic oxidation was carried out at a current density of

I 446

0.025 A / cm ² continued until the anode-cathode voltage reached 60V. Beyond this point the anodic oxidation continued at 60 volts. The total anodic oxidation time was 45 minutes.

8. Careful rinsing in cold water.

9. The anodized plates 5052 and 6061-T6 were then put into coupons from 7.62 x 10.16 cm cut. The anodically oxidized pressed pieces made from 6063-T5 and 6351-T5 were cut into test pieces 10.16 cm in length.

10. Sealing in one sealing bath each of the specified compositions A to E.

11. After the test pieces have been discharged from the sealing tank, spray them off with warm water Water and air dry.

The sealing baths used in process step 10 had the following compositions A to E and were used under the specified conditions.

Nickel acetate 0.5 g / l

Sodium lignosulfonate 1.0 g / l

Rest water

Temperature 99 ° C

pH 4.9

Time 20 minutes

The specified sealing bath was also used at temperatures of 95 ° C for 15 minutes and with a pH of 5.0 is used.

For all of the alloys listed in the table, the surfaces of the specimens were anodized perfectly sealed, as evidenced by its resistance to staining upon exposure of dyes or inks. It could be on the surfaces of the finished item neither a “dirt” formation nor a brownish discoloration can be found. The bathroom was used continuously for 2 days to seal anodically oxidized aluminum objects and remained fully effective during this time. The costs of the said sealing bath are much lower than the cost of the usual, well-known sealing baths described at the beginning, the nickel acetate, Cobalt acetate, calcium lignosulfonate and boric acid.

B.

Nickel acetate 0.5 g / l

Ammonium lignosulfonate 1.0 g / l

Rest water

This bath was found to be as fully effective as that of the first example.

Nickel acetate 0.2 g / l

Sodium lignosulfonate 1.0 g / l

Rest water

This bath also gave satisfactory results with the alloys listed in the table.

D (comparative example)

Sodium lignosulfonate 5 g / l

Rest water

This bath gave poor results.

E (comparative example)

Nickel acetate 1.0 g / l

Sodium lignosulfonate 5.0 g / l

Rest water

This bath gave poor results.

These and other experiments have shown that the nickel acetate content of the bath is preferred can be between 0.3 to 0.6 g / l, but that it must not exceed 0.8 g / l, otherwise it will lead to a "Dirt" formation can occur. On the other hand, the nickel acetate content should never be less than 0.02 g / l fall, otherwise the sealing bath loses its effectiveness. The lignin sulfonate content of the bath can preferably be between 0.5 and 2.0 g / l. However, it should never exceed 3.0 g / l, otherwise the finished item may be discolored brown. Finally, the lignosulphonate content of the bath should be never fall below 0.1 g / l in order to be able to effectively prevent the formation of "dirt".

In order to deal with the specified small amounts of nickel acetate and lignosulfonate In order to obtain results, it is essential, as already mentioned, that the pH of the Solution is maintained between 4 and 6, preferably at or close to 5. An additional buffer, like boric acid but is not required.

In the description and in the claims, the term "aluminum" denotes aluminum high purity, technically pure aluminum and aluminum-based alloys that are at least Contains weight percent aluminum.

Claims (8)

Patent claims: 1. Sealing bath for anodically oxidized and at the same time colored aluminum surfaces, which Contains nickel acetate and lignosulfonate, characterized in that the bath essentially of a 0.02 to 0.8 g / l nickel acetate and 0.1 to 3.0 g / l of a lignin sulfonate containing aqueous solution and has a pH between 4 and 6. 2. Sealing bath according to claim 1, characterized in that the bath is substantially from an aqueous containing 0.3 to 0.6 g / l nickel acetate and 0.5 to 2.0 g / l of a lignin sulfonate Solution exists and has a pH of about 5. 3. Sealing bath according to claim 1, characterized in that the bath is substantially from an aqueous containing about 0.5 g / l nickel acetate and about 1.0 g / l sodium lignosulfonate Solution exists and has a pH of about 5. 4. Sealing bath according to claim 1, characterized in that the bath is substantially an aqueous solution of nickel acetate and a lignosulfonate in a ratio in the range is from about 1: 1 to 1: 5. 5. Use of the sealing bath according to claims 1 to 4 for anodically oxidized
and at the same time colored aluminum surfaces which were produced in an electrolyte which essentially consists of an aqueous solution of sulfosalicylic acid and at least one metal sulfate and / or sulfuric acid. 6. Method of sealing anodic oxy- 1 441 dated and at the same time colored aluminum surfaces, characterized in that the The object is immersed in a bath according to claims 1 to 5 for about 10 to 30 minutes. 7. The method according to claim 6, characterized in that the object is immersed in a bath which consists essentially of a 0.3 to 0.6 g / l nickel acetate and 0.5 to 2.0 g / l sodium lignosulfonate containing aqueous solution and that to a pH of about 5 and on a temperature between about 85 and 100 ⁰ C is maintained. 8. The method according to claim 6, characterized in that the object. is immersed for about 20 minutes in a bath consisting essentially of an aqueous solution containing about 0.5 g / l nickel acetate and about 1.0 g / l sodium lignosulfonate and which has a pH of about 5 and a temperature of about 99 ⁰ C is kept. 009 537/306