EP0857227B1 - Short duration hot seal for anodised metal surfaces - Google Patents

Description

The invention is in the field of producing anti-corrosion and / or decorative coatings on metals by anodic oxidation. It affects one improved process for compacting the electrochemically produced porous Anodizing layers to further improve their properties.

The electrochemical anodic oxidation of metals in suitable electrolytes is a widely used process for the formation of anti-corrosion and / or decorative coatings on suitable metals. These procedures are for example in "Ullmann's Encyclopedia of Industrial Chemistry", 5th Edition, Vol. 9 (1987), pp. 174 - 176 briefly characterized. Accordingly, titanium, magnesium and Aluminum and their alloys can be anodized, the anodization of Aluminum and its alloys have the greatest technical importance. The Electrolytically produced anodizing layers protect the aluminum surfaces the influences of weather and other corrosive media. Furthermore Anodizing layers applied to obtain a harder surface and thus to achieve increased wear resistance of the aluminum. Through the own color of the anodizing layers or by absorptive or electrolytic coloring achieve special decorative effects. The aluminum is anodized in an acidic electrolyte, with sulfuric acid being the most common. Other suitable electrolytes are phosphoric acid, oxalic acid and chromic acid. The Properties of the anodizing layers can be determined by the choice of the electrolyte, its temperature as well as the current density and the anodizing time within wide limits vary. The anodization is usually carried out with direct current or with a AC-superimposed DC.

The fresh anodizing layers can be immersed in a suitable solution Dye or by an AC treatment in a metal salt containing are preferably subsequently colored in a tin-containing electrolyte. As an alternative to the subsequent coloring, colored anodizing layers can be used obtained by so-called color anodization processes, for which the Anodization in solutions of organic acids, such as sulfophthalic acid in particular or sulfanilic acid, optionally in a mixture with sulfuric acid, used.

These anodically produced protective layers, the structure of which has been scientifically investigated (R. Kniep, P. Lamparter and S. Steeb: "Structure of Anodic Oxide Coatings on Aluminum" Angew. Chem. Adv. Mater 101 (7), pp. 975 - 977 (1989)), are often referred to as "oxide layers". However, the above study has shown that these layers are glass-like and contain tetrahedrally coordinated aluminum. Octahedral coordinated aluminum as in the aluminum oxides was not found. Therefore, in this patent application the more general term "anodizing layers" is used instead of the misleading term "oxide layers".

However, these layers do not yet meet all the requirements with regard to the Corrosion protection because they still have a porous structure. This is why it is necessary to compact the anodizing layers. This densification is common with hot or boiling water, alternatively with steam, and referred to as "sealing". This closes the pores and thus the Corrosion protection increased significantly. There is one about this compression process extensive literature. Examples include: S. Wernick, R. Pinner and P. G. Sheasby: "The Surface Treatment and Finishing of Aluminum and its Alloys" (Vol. 2, 5th Edition, Chapter 11: "Sealing Anodic Oxide Coatings"), ASM International (Metals Park, Ohio, USA) and Finishing Publications LTD (Teddington, Middlesex, England) 1987.

When compacting the anodizing layers, however, not only the pores become closed, but it forms a more or less on the entire surface strong velvety covering, the so-called sealing covering. This one from hydrated Alumina existing covering is optically disturbing, reduces the adhesive strength the gluing of such aluminum parts and promotes later pollution and Corrosion. Since the subsequent removal of this sealing covering by hand mechanically or chemically complex is attempted through chemical additives to the sealing bath to the formation of this sealing covering prevent. According to DE-C-26 50 989, additives are cyclic for this Polycarboxylic acids with 4 to 6 carboxyl groups in the molecule, especially those Cyclohexane hexacarboxylic acid. According to DE-A-38 20 650, certain can also be Phosphonic acids, for example 1-phosphonopropane-1,2,3-tricarboxylic acid use. From EP-A-122 129 is the use of further Phosphonic acids known. DE-C-22 11 553 describes a method for Compacting anodic oxide layers on aluminum and aluminum alloys in aqueous ones containing phosphonic acids or their salts and calcium ions Solutions, the molar ratio of calcium ions to phosphonic acid is set at least 2: 1. A higher ratio of calcium ions is preferred to phosphonic acids from about 5: 1 to about 500: 1. As Phosphonic acids are suitable, for example: 1-hydroxypropane, 1-hydroxybutane, 1-hydroxypentane, 1-hydroxyhexane-1,1-diphosphonic acid and 1-hydroxy-1-phenylmethane-1,1-diphosphonic acid and preferably 1-hydroxyethane-1,1-diphosphonic acid, 1-aminoethane, 1-amino-1-phenylmethane, Dimethylaminoethane, dimethylaminobutane, diethylaminomethane, propyl and Butylaminomethane-1,1-diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, Diethylenetriaminepentamethylenephosphonic acid, Aminotri- (2-propylene-2-phosphonic acid), phosphonosuccinic acid, 1-phosphono-1-methyl succinic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid. According to the Embodiments of this patent are conventional Hot compression process with compression times between 60 and 70 minutes Anodizing layer thicknesses between about 18 and about 22 microns. The compression time is about 3 minutes per µm layer thickness.

When using water that, in addition to the mentioned sealant preventers Contains no other additives are for effective compaction previously high temperatures (at least 90 ° C) and relatively long treatment times in of the order of about 1 hour with an anodizing layer of about 20 µm required. This corresponds to a compression time of about 3 minutes each Micrometer anodizing layer thickness. The compression process is very much so energy consuming and because of its duration can be a bottleneck for the production speed represent. Therefore, additives became a compression bath wanted to support the compression process, so that this at deeper Temperatures (so-called cold compression or cold sealing) and / or at shorter ones Treatment times expire. As additives that compress in the temperature range allow below 90 ° C, for example, have been proposed: nickel salts, in particular fluorides, some of which are used in practice (EP-A-171 799), Nitrosylpentacyanoferrate, complex fluorides of titanium and zirconium as well Chromates or chromic acid, optionally in conjunction with other additives. As an alternative to an actual compression, the hydrophobization of the Oxide layer using long-chain carboxylic acids or waxes recommended as well as the Treatment with acrylamides to be polymerized in the pore space. Closer Information on this can be found in the above-mentioned literature reference by S. Wernick et al. be removed. With the exception of consolidation, these suggestions could do not enforce with nickel compounds in practice.

Processes for cold compression using are technically introduced Nickel fluoride. Because of the toxic properties of nickel salts, this will result however, complex measures for wastewater treatment are required.

There is therefore still a need for alternative compression methods for anodized surfaces that make it possible to shorten the compaction times Increase production speed and / or that for compaction to reduce the amount of energy required without doing it ecologically and health-wise to use questionable heavy metals such as nickel.

From US-A-5 411 607 a short-term hot compression process is known, in which the anodized metal parts are immersed in a lithium-containing aqueous solution. The lithium concentration is preferably in the range from 0.01 to 50 g / l and especially in the range of 0.01 to 5 g / l. It is also proposed that the Compression solution also contains a sealant inhibitor. This is preferably present and in a concentration between 0.1 and 10 g / l preferably an aromatic disulfonate. According to US-A-5 478 415, which to the same priority as the above cited US-A-5 411 607 may be one Brief hot compression with an aqueous solution, which is at least 0.01 g / l Contains lithium ions and from 0.1 to 10 g / l of a sealing deposit inhibitor. Here too the sealant inhibitor is preferably an aromatic disulfonate.

The teaching of the latter two documents enables a clear one Reduction of hot compression times. From economic and environmental technology However, for reasons it would be desirable to use a compression method clearly to have reduced use of chemicals available. The invention turns the Task to provide such a procedure.

a) insgesamt 0,0001 bis 5 g/l eines oder mehrerer Alkalimetall- und/oder Erdalkalimetallionen und

b) insgesamt 0,0005 bis 0,5 g/l einer oder mehrerer organischer Säuren, ausgewählt aus cyclischen Polycarbonsäuren mit 3 bis 6 Carboxylgruppen und/oder Phosphonsäuren und/oder Polyphosphinocarbonsäuren,

enthält, wobei die Lösung eine größere Menge der Metallionen der Gruppe a) enthält, als zur vollständigen Neutralisation der Säuren der Gruppe b) erforderlich ist.The invention relates to a method for compacting anodized metal surfaces, characterized in that the anodized metal is brought into contact with an aqueous solution having a temperature between 75 ° C. and the boiling point and for a period of between 0.5 and 2 minutes per micrometer of anodizing layer thickness has a pH in the range from 5.5 to 8.5 and the

a) a total of 0.0001 to 5 g / l of one or more alkali metal and / or alkaline earth metal ions and

b) a total of 0.0005 to 0.5 g / l of one or more organic acids, selected from cyclic polycarboxylic acids with 3 to 6 carboxyl groups and / or phosphonic acids and / or polyphosphinocarboxylic acids,

contains, the solution containing a larger amount of the metal ions of group a) than is necessary for complete neutralization of the acids of group b).

The contact of the treatment solutions with the anodized metals can by spraying the solutions onto the metal surfaces or preferably by immersing the metal parts in the solutions. With the technically usual Anodizing layer thickness of about 20 microns are the required treatment times only in the range of 20 to 40 minutes. According to the invention, it is therefore preferred that the anodized metal for a period between 1 and 2 minutes per Micrometer anodizing layer thickness with the aqueous solution defined above in Touches. The temperature of the treatment solution is preferably in the Range between 90 ° C and the boiling point and especially in the range from 94 to 98 ° C, for example at 96 ° C.

The pH of the aqueous solution is preferably in the range 5.5 to 7, especially in the range 5.5 to 6.5. The adjustment of the pH value can if necessary with ammonia or acetic acid. With ammonium acetate as a buffer it can be kept in the required area.

Lithium and magnesium are particularly suitable as metal ions of group a). The metals can be in the form of their concentration range water-soluble salts are used, for example as acetate, lactate, sulfate, Oxalate and / or nitrate. Acetates are particularly suitable.

In a special embodiment, the organic acids of group b) selected from saturated or unsaturated or aromatic carbocyclic Six-ring carboxylic acids with 3 to 6 carboxyl groups. Preferred examples such acids are trimesic acid, trimellitic acid, pyromellitic acid, mellitic acid and the particularly preferred cyclohexane hexacarboxylic acid. The total amount such carboxylic acids are preferably in the range from 0.0005 to 0.2 g / l, in particular from 0.001 to 0.1 g / l, and particularly preferably in the range of 0.001 up to 0.05 g / l.

The preferred cyclohexane hexacarboxylic acid exists in the form different stereoisomers. As known from DE-A-26 50 989 those cyclohexane hexacarboxylic acids preferred, the 5 cis and 1 trans or which carry 4 cis and 2 trans carboxyl groups.

When using the above-mentioned six-ring carboxylic acids as acids Group b) preferably contains 0.1 to 5 g / l of the aqueous treatment solution in particular 0.2 to 2.5 g / l of metal ions of group a).

In a second special embodiment, the organic acids are of the group b) selected from the phosphonic acids: 1-phosphonopropane-1,2,3-tricarboxylic acid, 1,1-diphosphonopropane-2,3-dicarboxylic acid, 1-hydroxypropane-1,1-diphosphonic acid, 1-hydroxybutane-1,1-diphosphonic acid, 1-hydroxy-1-phenylmethane-1,1-diphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, 1-amino-1-phenylmethane-1,1-diphosphonic acid, Dimethylaminoethane-1,1-diphosphonic acid, propylaminoethane-1,1-diphosphonic acid, Butylaminoethane-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminotetra (methylenephosphonic acid), Diethylenetriamineopenta (methylenephosphonic acid), Hexamethylene diaminotetra (methylenephosphonic acid), n-propyliminobis (methylenephosphonic acid), Aminotri (2-propylene-2-phosphonic acid), Phosphonosuccinic acid, 1-phosphono-1-methylsuccinic acid and 1-phosphonobutane-1,2,4-tricarboxylic acid. From this selection are the 1-phosphonopropane-1,2,3-tricarboxylic acid, 1,1-diphosphonopropane-2,3-dicarboxylic acid and the aminotri (methylenephosphonic acid) is particularly preferred. Furthermore are Polyphosphinocarboxylic acids as organic acids of group b) in particular preferably suitable as copolymers of acrylic acid and hypophosphites can be understood. An example of this is Belclene ® 500 from FMC Corporation, UK.

The above-mentioned phosphonic acids and polyphosphinocarboxylic acids are preferred as acids of group b) in an amount of 0.003 to 0.1 and used in particular in an amount of 0.003 to 0.05 g / l. Using such acids as group b) acids contain the aqueous treatment solution preferably 0.0001 to 0.01 g / l and in particular a maximum of 0.005 g / l Group a) metal ions.

In addition, it is of course possible according to the invention, also mixtures the aforementioned six-ring carboxylic acids, phosphonic acids and Use polyphosphinocarboxylic acids as group b) acids.

The aqueous compression solution additionally contains approximately as an optional component 0.001 to 0.05 g / l surfactants, selected from the group of the cationic, non-ionic or anionic surfactants. Coming as cationic surfactants for example, quaternary ammonium salts. Preferably be however anionic surfactants such as alkyl or alkylaryl sulfates or -sulfonates used. For environmental reasons, linear alkyl sulfates such as for example lauryl sulfate, is preferred. The anionic surfactants are called Alkali metal salts are used, with lithium salts being particularly preferred. As nonionic surfactants can use fatty amine or fatty alcohol ethoxylates become. Fatty alcohol ethoxylates with 4-8 ethylene oxide units are preferred. The concentration of the surfactants is preferably in the range from 0.002 to 0.02 g / l.

Particularly good compaction results are obtained when the Metal surfaces immediately after the short-term hot compaction described above for a period between 30 and 120 seconds in fully desalinated Water is immersed, the temperature above 90 ° C, preferably above 96 ° C.

The compression bath suitable for the compression process according to the invention can in principle by dissolving the components in - preferably fully desalinated - Water in the required concentration range can be produced on site. However, one is preferably used to prepare the compression baths aqueous concentrate that already contains all the necessary components of the Compression bath in the right proportions and from which one can Dilute with water by a factor between 10 and 1000 receives the ready-to-use solution. If necessary, the pH value adjusted to the range according to the invention with ammonia or with acetic acid become. The invention accordingly also includes an aqueous concentrate for preparation the aqueous solution for use in the short-term hot compression process according to the invention, taking the concentrate by diluting it with water a factor between 10 and 1000 the ready-to-use aqueous Solution results.

According to the accelerated and energy-saving method according to the invention compacted anodizing layers can be produced in their Layer properties are not inferior to those conventionally produced. As Technically, test parameters for the layer quality are in particular the removal of acid in Chromic acid, the apparent conductance and the color drop test are important. This Quality indicators of the layers are checked according to standard test procedures that are given in the example section.

The compression method according to the invention is preferably for anodized Aluminum or anodized aluminum alloys used. However, it can also on the anodizing layers of other anodizable metals, such as, for example Use titanium and magnesium or their alloys. It is for both undyed anodizing layers can be used as well for those after conventional methods such as integral staining, one Adsorptive staining using organic dyes, a reactive one Coloring with the formation of inorganic color pigments, an electrochemical Coloring using metal salts, especially tin salts, or interference staining. With adsorptively colored anodizing layers The inventive method has the further advantage that the shorter compaction time is possible with conventional hot compaction Bleeding of the dye can be reduced.

Examples

Al 99.5 aluminum sheets were conventionally anodized (Direct current / sulfuric acid, one hour, layer thickness 20 µm) and if necessary colored electrochemically or with organic dipping colors. Then the Sheets for times between 30 and 60 minutes in the invention Compaction solutions or comparative solutions dipped according to the tables. The Solutions had a temperature of 96 ° C. Following the treatment according to Tables were the plates immersed in boiling demineralized water for one minute and then dried. After that, the quality of compaction with checked the usual quality tests described below. Their Results are also shown in the tables. They show that with the The inventive method after only 30 minutes of compression results can be obtained, which experience has shown with a conventional Hot compression bath only after an hour. In contrast, they are Compaction results after half an hour of treatment with comparison solutions insufficient quality.

The apparent conductance Y ₂₀ was determined in accordance with the German standard DIN 50949 using an Anotest YD 8.1 measuring device from Fischer. The measuring system consists of two electrodes, one of which is conductively connected to the base material of the sample. The second electrode is immersed in an electrolyte cell that can be placed on the layer to be examined. This cell is designed as a rubber ring with an inner diameter of 13 mm and a thickness of approximately 5 mm, the ring surface of which is self-adhesive. The measuring area is 1.33 cm ² . A potassium sulfate solution (35 g / l) in deionized water is used as the electrolyte. The apparent conductance readable on the measuring device is converted according to the specifications of DIN 50949 to a measuring temperature of 25 ° C and to a layer thickness of 20 µm. The values obtained, which should preferably be in the range between approximately 10 and approximately 20 μS, are entered in the tables.

As a parameter that indicates open-pore and therefore poorly compressed layers, was the residual reflection after staining with dye based on the German Measured according to standard DIN 50946. The measuring surface was measured using a self-adhesive measuring cell of the Anotest device described above narrowed down. The test area is covered with an acid solution (25 ml / l sulfuric acid, 10 g / l KF) wetted. After exactly one minute, the acid solution is washed off and the Test area dried. Then the test area with dye solution (5 g / l Sanodal blue), which is left to act for a minute. After rinsing under the measuring cell is removed from flowing water. The stained test area is marked by Rub off using a mild powder detergent from loosely adhering Dye exempted. After drying the surface becomes a relative Reflection measurement made by the measuring head of a light reflection measuring device (Micro Color from Dr. Lange) once on an undyed part of the Surface and second is placed on the stained measuring surface. The Residual reflection in% is obtained by taking the quotient from the measured value of the colored area divided by the measured value of the uncolored area with a hundred multiplied. Residual reflection values between 95 and 100% are good evidence Compaction quality, while values below 95% are considered unacceptable. The The higher the values of the residual reflection, the higher the compression quality. The found values are entered in the tables.

In addition, the acid removal was measured based on ISO 3210. For this purpose, the test plate is weighed to the nearest 0.1 mg and then immersed for 15 minutes at 38 ° C in an acid solution containing 35 ml of 85% phosphoric acid and 20 g of chromium (VI) oxide per liter. At the end of the test period, the sample is rinsed with deionized water and dried in a drying cabinet at 60 ° C. for 15 minutes. The sample is then weighed again. The weight difference between the first and the second measurement is calculated and divided by the size of the surface in dm ² . Weight loss is expressed as Δ G in mg / dm ² (1 dm ² = 100 cm ² ) and should not exceed 30 mg / dm ² .

Vergl. 1:

25 g/l Polyphosphinocarbonsäure-Lösung (45 gew.-%ig in Wasser)
   (Acrylsäure-Natriumhypophosphit-Copolymer, "Belclene ® 500", FMC Corporation, Großbritannien)
5 g/l Lithiumlaurylsulfat
   ("Texapon ® LLS", Henkel KGaA, Deutschland)

Beisp. 1:

wie Vergl. 1, zusätzlich:
1 g/l Lithiumacetat

Beisp. 2:

wie Vergl. 1, zusätzlich:
1 g/l Magnesiumacetat

Vergl. 2:

25 g/l Belclene ® 500

Beisp. 3:

wie Vergl. 2, zusätzlich:
0,5 g/l Magnesiumacetat

Beisp. 4:

wie Vergl. 2, zusätzlich:
0,2 g/l Magnesiumacetat

Vergl. 3:

25 g/l Beldene ® 500
2,5 g/l Lithiumlaurylsulfat

Beisp. 5:

wie Vergl. 3, zusätzlich:
1 g/l Magnesiumacetat

Beisp. 6:

wie Vergl. 3, zusätzlich:
0,5 g/l Magnesiumacetat

Beisp. 7:

wie Vergl. 3, zusätzlich:
25 g/l Magnesiumacetat

The following concentrates for comparison solutions and inventive treatment solutions were prepared by dissolving the active ingredients in deionized water:

Cf. 1:

25 g / l polyphosphinocarboxylic acid solution (45% by weight in water)
(Acrylic acid-sodium hypophosphite copolymer, "Belclene® 500", FMC Corporation, Great Britain)
5 g / l lithium lauryl sulfate
("Texapon ® LLS", Henkel KGaA, Germany)

Ex. 1:

like cf. 1, additionally:
1 g / l lithium acetate

Ex. 2:

like cf. 1, additionally:
1 g / l magnesium acetate

Cf. 2:

25 g / l Belclene ® 500

Ex. 3:

like cf. 2, in addition:
0.5 g / l magnesium acetate

Ex. 4:

like cf. 2, in addition:
0.2 g / l magnesium acetate

Cf. 3:

25 g / l Beldene ® 500
2.5 g / l lithium lauryl sulfate

Ex. 5:

like cf. 3, in addition:
1 g / l magnesium acetate

Ex. 6:

like cf. 3, in addition:
0.5 g / l magnesium acetate

Ex. 7:

like cf. 3, in addition:
25 g / l magnesium acetate

For the tests, 2 g of concentrate was made up to 1 liter with deionized water. The test sheets were immersed for 30 minutes each in the treatment solutions according to the invention according to Examples 1 to 7 and the comparison solutions according to Comparative Examples 1 to 3. Test results Solution Apparent conductance Y ₂₀ (µS) Residual reflection (%) Acid removal (mg / dm ² ) Cf. 1 22 98 23.9 Ex. 1 21 100 13.1 Ex. 2 22 100 14.5 Cf. 2nd 27 98 24.1 Ex. 3 21 100 13.4 Ex. 4 18th 100 11.8 Cf. 3rd 19th 98 23.5 Ex. 5 19th 100 13.2 Ex. 6 17th 100 12.5 Ex. 7 18th 100 13.0

Vergl. 4:

13 ppm Cyclohexanhexacarbonsäure

Vergl. 5:

wie Vergl. 4

Beisp. 8:

wie Vergl. 4, zusätzlich
340 ppm Li (als 5 g/l Li-Acetat Dihydrat)

Beisp. 9:

wie Beisp. 8

Beisp. 10:

wie Vergl. 4, zusätzlich
850 ppm Mg (als 5 g/l Mg-Acetat Tetrahydrat)

Beisp. 11:

wie Beisp. 10

Prüfergebnisse und Behandlungszeiten Lösung gemäß Zeit (Min.) Scheinleitwert Y₂₀ (µS) Restreflexion (%) Säureabtrag (mg/dm²) Vergl. 4 30 28 93 18 Vergl. 5 60 14 97 12 Beisp. 8 30 20 97,5 11 Beisp. 9 40 14 97,5 11 Beisp. 10 30 16 97,5 11 Beisp. 11 40 12 99 10 For the comparative examples 4 and 5 below and examples 8 to 11 according to the invention, the treatment solutions were each prepared directly, ie without diluting the corresponding concentrates, by dissolving the specified active compounds in deionized water. The duration of the treatment of the test sheets (immersion) was varied here; the respective times are shown in Table 2.

Cf. 4:

13 ppm cyclohexane hexacarboxylic acid

Cf. 5:

like cf. 4th

Ex. 8:

like cf. 4, in addition
340 ppm Li (as 5 g / l Li acetate dihydrate)

Ex. 9:

like Ex. 8

Ex. 10:

like cf. 4, in addition
850 ppm Mg (as 5 g / l Mg acetate tetrahydrate)

Ex. 11:

like Ex. 10

Test results and treatment times Solution according to Time (min.) Apparent conductance Y ₂₀ (µS) Residual reflection (%) Acid removal (mg / dm ² ) Cf. 4th 30th 28 93 18th Cf. 5 60 14 97 12th Ex. 8 30th 20th 97.5 11 Ex. 9 40 14 97.5 11 Ex. 10 30th 16 97.5 11 Ex. 11 40 12th 99 10th

The layers of Comparison 1 had fingerprints. The rest For example, the appearance of the layers was good.

Claims (14)

1. A process for sealing anodized metal surfaces, wherein the anodized metal is brought into contact, for between 0.5 and 2 minutes per micrometre of anodic coating thickness, with an aqueous solution which has a temperature between 75 °C and its boiling point and a pH in the range of from 5.5 to 8.5 and which contains:

   (a) 0.0001 to 5 g/l total of one or more alkali metal and/or alkaline earth metal ions; and

   (b) 0.0005 to 0.5 g/l total of one or more organic acids selected from cyclic polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids and/or polyphosphinocarboxylic acids,

   the solution containing a larger quantity of the metal ions (a) than is required for the complete neutralization of the acids (b).
2. A process as claimed in claim 1 wherein the aqueous solution has a temperature in the range of from 94 to 98°C.
3. A process as claimed in one or both of claims 1 and 2, wherein the aqueous solution has a pH in the range of from 5.5 to 7.
4. A process as claimed in one or more of claims 1 to 3 wherein the metal ions (a) are selected from Li and Mg.
5. A process as claimed in one or more of claims 1 to 4 wherein the organic acids (b) are selected from saturated or unsaturated or aromatic carbocyclic six-ring carboxylic acids having 3 to 6 carboxyl groups.
6. A process as claimed in claim 5 wherein the carboxylic acids are selected from trimesic acid, trimellitic acid, pyromellitic acid, mellitic acid and cyclohexane hexacarboxylic acid.
7. A process as claimed in one or both of claims 5 and 6 wherein the aqueous solution contains the carboxylic acids in a total quantity of 0.001 to 0.05 g/l.
8. A process as claimed in one or more of claims 5 to 7 wherein the aqueous solution contains 0.2 to 2.5 g/l total of metal ions (a).
9. A process as claimed in one or more of claims 1 to 4 wherein the organic acids (b) are selected from: 1-phosphonopropane-1,2,3-tricarboxylic acid, 1,1 diphosphonopropane-2, 3-dicarboxylic acid, 1-hydroxypropane- 1,1-diphosphonic acid, 1-hydroxybutane-1,1-diphosphonic acid, 1-hydroxy-1-phenylmethane-1,1-diphosphonic acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, 1-amino-1-phenylmethane-1,1-diphosphonic acid, dimethylaminoethane-1,1-diphosphonic acid, propylaminoethane-1,1-diphosphonic acid, butylaminoethane-1,1-diphosphonic acid, aminotri(methylene phosphonic acid), ethylene diaminotetra(methylene phosphonic acid), diethylene triaminopenta(methylene phosphonic acid), hexamethylene diaminotetra(methylene phosphonic acid), n-propyliminobis(methylenephosphonic acid), aminotri(2-propylene-2-phosphonicacid), phosphonosuccinic acid, 1-phosphono-1-methylsuccinic acid, 1-phosphonobutane-1,2,4-tricarboxylic acid and polyphosphinocarboxylic acids.
10. A process as claimed in claim 9 wherein the aqueous solution contains the acids (b) in a quantity of 0.003 to 0.05 g/l.
11. A process as claimed in one or both of claims 9 and 10 wherein the aqueous solution contains up to 0.005 g/l total of metal ions (a).
12. A process as claimed in one or more of claims 1 to 11 wherein the aqueous solution additionally contains 0.001 to 0.05 g/l of nonionic or anionic surfactants.
13. A process for sealing anodized metal surfaces wherein, after the treatment according to one or more of claims 1 to 12, the metal surfaces are dipped for between 30 and 120 seconds in fully demineralized water which has a temperature above 90 °C.
14. An aqueous concentrate for preparing the aqueous solution for use in the process according to one or more of claims 1 to 13, which produces the ready-to-use aqueous solution by means of dilution with water by a factor between 10 and 1000.