MXPA98009947A

MXPA98009947A - Post-sealed thermal, accelerated, of anodized metal surfaces using solutions with content of agents tensioacti

Info

Publication number: MXPA98009947A
Application number: MXPA/A/1998/009947A
Authority: MX
Inventors: Korner Tosten; Kresse Josef
Original assignee: Henkel Kgaa 40589 Duesseldorf De
Priority date: 1996-05-31
Filing date: 1998-11-27
Publication date: 1999-04-27

Abstract

The present invention consists of a process for the post-sealing of anodized metal surfaces, characterized in that the anodized metal is brought into contact with an aqueous solution, for a period between 0.5 and 2 minutes per micrometer of the anodized coating, whose solution it is at a temperature between 75 ° C and its boiling point, and has a pH from 5.5 to 8.5 and which contains: (a) a total of 0.0004 to 0.05 g / l of one or more cationic, anionic or surface active agents. non-ionic, and (b) a total of 0.0005 to 0.5 g / l of one or more organic acids that are selected from: polycarboxylic acids having from 3 to 6 carboxyl groups and / or phosphonic acids. Nonionic surfactants are preferred as surfactants and polyphosphinocarboxylic acids are preferred as the acids. The alkali metal and / or alkaline earth metal cations, preferably Di and / or Mg ions, are optionally present in amounts of 0.0001 to 5 g.

Description

POST THERMAL, ACCELERATED, OF ANODIZED METAL SURFACES USING SOLUTIONS CONTAINING AGENTS TENSOAC IVOS This invention relates to the production of corrosion inhibiting and / or decorative coatings on metals by anodic oxidation. It refers to an improved process for post-sealing porous anodized coatings, produced electrochemically to further improve the properties thereof. Electrochemical anodic oxidation of metals into suitable electrolytes is a widely used process for the formation of corrosion inhibiting and / or decorative finishes on metals suitable for this purpose.These processes are briefly described in Ullman's Encyclopedia of Industrial Chemistry, 5th edition, volume 9 (1987), pp. 175-176. According to this reference, titanium, magnesium and aluminum and their alloys are anodisable, with the anodization of aluminum and alloys thereof of great industrial interest. The electrolytically produced anodized coatings protect aluminum surfaces from weathering and other corrosive media. Anodized coatings are also applied to create a harder surface, thereby increasing the wear resistance of aluminum. The "specific decorative effects can be achieved by means of intrinsic color of the anodized coatings or by absorbent or electrolytic coloring." Aluminum is anodized in an acid electrolyte, the most commonly used being sulfuric acid Other suitable electrolytes are phosphoric acid, oxalic acid and chronic acid The properties of anodized coatings can vary widely due to the selection of the electrolyte, the temperature of the electrolyte and the current density and duration of the anodization.The anodization is traditionally carried out using direct current or using direct current having an Super-imposed alternating current The freshly anodized coatings can subsequently be colored by immersion in solutions of a suitable dye or by an alternating current treatment in an electrolyte containing metal salt, preferably containing tin. Subsequent sentence, anodized coatings with color can be obtained by the processes called anodization with color, in which the anodization is carried out in solutions of organic acids, such as in particular sulphophthalic acid or sulphanilic acid, each optionally mixed with sulfuric acid. These protective coatings produced anodically, 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 described as "oxide coatings". Internal research however has shown that these coatings are vitreous and contain aluminum with tetrahedral coordination. Aluminum coordinated octahedrally, as in aluminum oxides, was not found. In this case, the more general term "anodized coatings" is used instead of the misused term "rust coatings". However, these coatings still do not meet all the requirements with respect to corrosion protection, as they still have a porous structure. Consequently, a subsequent sealing of the anodized coatings is necessary. This subsequent sealing is often done using hot or boiling water, otherwise steam is used, and is described as "sealing". This treatment seals the pores, thus considerably increasing the "protection against corrosion" There are numerous references in the literature related to this subsequent sealing process, the following can be mentioned by way of example: S. ernik, R. Pinner and P.G. Sheasby: "The Surface Treatment and Finishing of Aluminum, and its Alloys" (volume 2, 5th edition, chapter 11: "Sealing Anodic Oxide Coatings"), SDM International (Metals Park, Ohio, USA) and Finisshing Publications Ltd. (Teddington , Middlesex, England) 1987. However, not only are the pores sealed during the subsequent sealing of the anodized coating, but a velvety deposit of greater or lesser thickness, the so-called "sealing deposit", is formed over the entire surface. This deposit, which consists of hydrous aluminum oxide, is visually unattractive, reduces adhesion when these aluminum components are joined and favors subsequent fouling and corrosion. Since the subsequent annual removal of this sealing deposit by expensive mechanical or chemical methods is costly, attempts have been made to prevent the formation of this seal deposit by means of chemical additives in the sealing bath. According to DEC 2650989, additions of cyclic polycarboxylic acids having from 4 to 6 carboxyl groups, per molecule in particular the cyclohexanecarboxylic acid are suitable for this purpose. According to DE-A-38 20 650, it is also possible to use certain phosphonic acids, for example, 1-phosphonopropan-1,2,3-tricarboxylic acid. The use of other phosphonic acids is known from EP-A-122 129. DE-C 22 11 553 describes a process for the subsequent sealing of anodic oxide coatings on aluminum and aluminum alloys in aqueous solutions containing phosphonic acids or salts thereof and calcium ions, wherein the molar ratio of the calcium ions: phosphonic acids is adjusted to at least 2: 1. A higher ratio of calcium ions: phosphonic acids of about 5: 1 to about 500: 1 is preferably used. The phosphonic acids that can, for example, be considered are: 1-hydroxy-propan-, 1-hydroxy-butan-, 1-hydroxypentan-, 1-hydroxyhexan-1, 1-diphosphonic acid together with 1-hydroxy acid. l-Phenylmethane-1,1-diphosphonic acid and preferably 1-hydroxyethane-1, 1-diphosphonic acid, 1-amino-ethano-, 1-amino-1-phenylmethane, dimethylamino-ethano-, dimethylamino-butan-, diethylamino methan-, propyl- and butyl-aminomethan-1, 1-diphosphonic acid, amino-trimethylene-phosphonic acid, ethylene-diamine-tetramethylene-phosphonic acid, diethylene-triamine-pentamethylene-phosphonic acid, aminotri (2-propylene-phosphonic acid) , phosphonosuccinic acid, 1-phosphono-1-methylsuccinic acid and 2-phosphonobutan-1,2,4-tricarboxylic acid. On the basis of the practical examples of the aforementioned patent, this process is a conventional thermal post-sealing process using post-sealing times of between 60 and 70 minutes in anodized coating thicknesses of between about 18 and about 22 [mu] m. The post-sealing time is, in this way, approximately 3 minutes per? M thickness of the coating. When water is used that does not contain additives other than the established sealant inhibitors, the elevated temperatures (at least 90 ° C) and relatively long treatment times of the order of about 1 hour for an anodized coating of about 20 μm to Now they have been necessary. This corresponds to a post-sealing time of approximately 3 minutes per thickness of anodized coating. The subsequent sealing process in this way is highly energy intensive and, due to its duration, can act as a bottleneck in the production process. In this way, attempts have already been made to find additives for the bath of the subsequent seal that favor the post-sealing process, so that it can be carried out at lower temperatures (the so-called cold stamping or cold stamping) and / or the use of shorter treatment times. The following, for example, has been proposed as additives that facilitate post-sealing at temperatures below 90 ° C: nickel salts, in particular fluorides, which are sometimes used in practice (EP 171 799); nitrosyl pentacyanoferrate; complex fluorides of titanium and zirconium together with chromates or chromic acid, optionally together with other additives. As an alternative to real post-sealing, the hydrophobicization of the oxide coating by means of long-chain carboxylic acids or waxes has been recommended, as is the treatment with acrylamides, which apparently would be polymerized in the pore spaces. Other details in this sense can be found in the aforementioned reference of S. Wernick et al. With the exception of post-sealing using nickel compounds, it has not been possible to implement these proposals in practice. Processes for cold stamping using nickel fluoride have been implemented in the industry. However, due to the toxic properties of the nickel salts, this represents costly wastewater treatment measures. In this way, there is still a need for alternative post-sealing processes for anodized surfaces that make it possible to increase the production speed in shorter post-sealing times and / or to reduce the energy consumption necessary for post-sealing without using heavy metals such as nickel , which are questionable about environmental and health aspects. From US-A-5 411 607 an accelerated thermal post-sealing process is known in which the anodized metal components are immersed in an aqueous solution containing lithium. The lithium concentration is preferably 0.01 to 50 g / 1, in particular 0.01 to 5 g / 1. It is further suggested that the sealing solution should also contain a seal deposit inhibitor. This preferably will be present in a concentration of between 0.1 and 10 g / 1 and, preferably it is an aromatic disulfonate. According to US-A 5 478 415, which has the same priority as the aforementioned US-A-5 411 607, the accelerated thermal post-sealing can proceed using an aqueous solution containing at least 0.01 g / 1 of lithium ions and 0.1 to 10 g / 1 of an inhibitor of the sealing deposits. In this case also, the inhibitor of the seal deposits preferably is an aromatic disulfonate. The application of German Patent 195 38 777.5 describes an accelerated thermal post-sealing process in which the components of the anodized metal are brought into contact with an anodizing solution containing a total of 0.1 to 5 g / 1 of 1 or more metal ions alkaline and / or alkaline earth metals and a total of 0.0005 to 0.2 g / 1 of a seal deposition inhibitor in the form of phosphonic acids or cyclic polycarboxylic acids. The teachings of the last three documents mentioned allow thermal post-sealing times reduced substantially. However, it would be desirable on economic and environmental aspects to have available post-sealing processes that consume distinctly smaller amounts of chemical substances. An objective of the present invention is to provide this process. The present invention provides a process for the post-sealing of anodized metal surfaces, characterized in that the anodized metal is contacted with an aqueous solution for a period of between 0.5 and 2 minutes per thickness of anodized coating, whose solution is found a temperature between 75 ° C and its boiling point, and has a pH of 5.5 to 8.5 and which contains: (a) a total of 0.0004 to 0.05 g / 1, preferably 0.005 to 0.02 g / 1 of one or more cationic, anionic or non-ionic surfactants; and (b) a total of 0.0005 to 0.05 g / 1, of one or more organic acids that are selected from: cyclic polycarboxylic acids having from 3 to 6 carboxyl groups and / or phosphonic acids. The treatment solutions can be contacted with the anodized metals by spraying the solutions onto the metal surfaces or, preferably, by immersing the anodized metals in the solutions. In conventional industrial anodized coating thicknesses of approximately 20%, the necessary treatment times are still only 20 to 40 minutes, the temperature of the treatment solution is preferably from 94 to 98 ° C, preferably approximately 96 ° C .

The pH of the aqueous solution is preferably from 5.5 to 7, in particular from 5.5 to 6.5. The pH, if necessary, can be adjusted using ammonia or acetic acid. The pH can be maintained within the necessary range using a buffer solution of ammonium acetate. The cationic surfactants (a) can be selected, for example, from quaternary ammonium salts in which at least one alkyl or aralkyl moiety has at least 8 carbon atoms. An example of this substance is alkyl-C12-14-dimethibenzylammonium chloride. Pyridinium salts, such as dodecylpyridinium chloride, can also be used as cationic surfactants. Examples of the anionic surfactants (a) that can be used are alkyl or aralkyl sulfates and sulfonates. In this case, linear alkyl sulphates, such as lauryl sulfate, are preferred for environmental reasons. The anionic surfactants are used as alkali metal or ammonium salts, with lithium salts being particularly preferred. However, preferably nonionic surfactants are used as the surfactants (a). These can be selected for example from the "alkoxylates such as ethoxylates and / or propoxylates of fatty alcohols or fatty amines. For purposes of the present, fatty amines alcohols are compounds having a Alkyl portion containing at least 8 carbon atoms These substances can be pure substances having a defined alkyl moiety or consisting of mixtures of products, such as those obtained from natural fats and oils.These alkoxylates can also be terminated at one end, ie, etherified again in the terminal OH group. examples of nonionic surfactants are octanol x 4E0 (EO = ethylene oxide) and octanol x 4.5 EO-butyl ether. the best results postsellado tend to be obtained if ethoxylates of fatty amines are used instead of ethoxylates of fatty alcohols such as nonionic surfactants. (a) in this manner, preferably are selected from the ethoxylates of fatty amines having 10 to 18 carbon atoms in the alkyl portion and from 3 to 15 ethylene oxide units per molecule. Specific examples are fatty amine from coconut oil x 5 EO and fatty amine from coconut oil x 12 EO. In a specific embodiment, organic acids (b) are selected from saturated, unsaturated or carbocyclic aromatic carboxylic acids with 6-membered rings having from 3 to 6 carboxyl groups. Preferred examples of these acids are trimesic acid, trimellitic acid, pyromellitic acid, mellitic acid and particularly preferably cyclohexane-hexacarboxylic acid. The total amount of the carboxylic acids is preferably from 0.001 to 0.05 g / 1. The preferred cyclohexane hexacarboxylic acid exists as different steroids. As is known from DE-A 26 50 989, preferred cyclohexane-hexacarboxylic acids are those having 5 carboxyl groups in cis position and one in trans position or 4 carboxyl groups in cis position and 2 in trans position. In another specific embodiment, the organic acids (b) are selected from phosphonic acids: 1-fosfonopropan-l, 2, 3-tricarboxylic acid, 1,1-difosfonopropan-2, 3-dicarboxylic acid 1-hydroxypropane-1 , 1-diphosphonic, 1-hydroxy-butan-1, 1-diphosphonic acid, 1-hydroxy-1-phenylmethane-1, 1-diphosphonic acid, 1-hydroxy-1-diphosphonic acid, 1-diphosphonic acid amino-ethane-l, 1-diphosphonic acid, 1-amino-l-fenilmetan-l, 1-diphosphonic dimetilaminoetan-1, 1-diphosphonic acid, propilaminoetan-1, 1-diphosphonic butilaminoetan-1 acid, 1- diphosphonic, amino tri (methylene phosphonic acid), ethylenediamine tetra (methylene phosphonic acid), diethylenetriamine penta (methylene phosphonic acid), hexamethylene diamine tetra (methylene phosphonic acid), n-propyliminobis (methylene phosphonic acid), amino tri- (2-propylene-2-phosphonic acid), phosphonosuccinic acid, 1-phosphono-1-methylsuccinic acid and 1-phosphonobutan-1,2,4-tricarboxylic acid. Of this selection, 1-phosphonopropan-1,2,3-tricarboxylic acid, 1,1-diphosphonopropane-2,3-dicarboxylic acid and amino tri (methylene phosphonic acid) are particularly preferred. The phosphonic acids (b) are preferably used in an amount of 0.003 to 0.05 g / 1. Polyphosphinocarboxylic acids which can be considered as copolymers of acrylic acid and hypophosphites are also suitable. An example of this compound is "Belclene® 500" from FMC Corporation, Great Britain. However, it may be advantageous for the effectiveness of the post-sealing if the aqueous post-sealing solution additionally contains a total of 0.001 to 5 g / 1 of one or more alkali metal and / or alkaline earth metal ions. These alkali metal or alkaline earth metal ions can be present as counterions for the acids (b). However, preferably the aqueous solution contains a greater amount of alkali metal ions and / or alkaline earth metal ions than those required for complete neutralization of the acids (b). It is particularly preferred if these additional alkali metal and / or alkaline earth metal ions, which exceed the amount necessary to complete the neutralization of the acids (b), are selected from lithium and magnesium. To reduce the use of chemicals to a minimum, the content of the aqueous solution of these alkali metal and / or alkaline earth metal ions is generally limited to a maximum of 0.005 g / 1. Larger contents, for example, up to 5 g / 1, however, do not deteriorate the post-sealing results. These alkali metal and / or alkaline earth metal ions, in particular lithium and magnesium, can be used in the form of the salts thereof which are soluble in water in the established concentration range. Anionic tensides (a), for example, can be used as counterions. Also suitable are, for example, acetates, lactates, sulfates, oxalates and / or nitrates. Acetates are particularly suitable. Particularly good post-sealing results are obtained if, immediately after the accelerated thermal post-sealing described above, the metal surfaces are immersed in fully de-ionized water for a period of between 30 and 120 seconds, the water being at a temperature above 90 ° C, preferably above 96 ° C. The post-sealing bath suitable for the post-sealing process according to the present invention can, in principle, be produced in situ by dissolving the constituents in water (preferably completely de-ionized) in the suitable concentration range. However, preferably, an aqueous concentrate is used which already contains all the necessary constituents of the post-sealing bath in the correct ratio of quantities, from which the solution ready for use is obtained by dilution with water, for example, in a factor of between about 100 and about 1000. In doing so, it may be necessary to adjust the pH to the range according to the present invention using ammonia or acetic acid. Accordingly, the present invention also relates to an aqueous concentrate for the preparation of the aqueous solution for use in the accelerated, thermal post-sealing process of the present, producing the concentrate of the aqueous solution ready for use by dilution with water in a factor of between about 100 and about 1000. It is possible using the accelerated and energy saving process, in accordance with the present invention to produce anodized, post-sealed coatings, which, with respect to the coating properties thereof, are not less than Traditionally produced coatings. The significant test parameters for the industry for coating quality are, in particular, the loss of acid corrosion in chromic acid, the admittance and testing of the dye drops. These parameters of coating quality are tested using the standard test methods indicated in the examples. The post-sealing process in accordance with the present invention is preferably used for anodized aluminum or anodized aluminum alloys. However, it can also be used in anodized coatings of other anodizable metals, such as titanium and magnesium or alloys of these metals. It is possible to use it for colorless anodized coatings and for color coatings using conventional methods, such as self-coloring, absorbent coloration using organic dyes, reactive staining to form inorganic coloring pigments, electrochemical staining using metal salts, in particular tin salts, or coloration by interference. In the case of anodized coatings colored by absorption, the process according to the invention has the additional advantage that, due to the reduced duration of the post-sealing, it is possible to reduce the run-off of the colorant which is possible in conventional thermal post-sealing.

Examples Al 99.5 grade aluminum sheets were anodized as usual (direct current / sulfuric acid, 1 hour, coating thickness 20?) And optionally electrochemically colored or using organic dyes by immersion. The sheets were then immersed for 30 minutes in post-sealing solutions according to the present invention or comparative solutions according to the table. For this purpose, 2 g of concentrate were in each case prepared for one liter using completely deionized water. The solutions were at a temperature of 96 ° C. After treatment according to the table, the sheets were immersed for 1 minute in boiling fully deionized water and then dried. The quality of the post-sealing was then verified by the conventional quality tests described below. The results of these tests are also shown in the table. These demonstrate that, using the process according to the present invention: Table: test results Table: test results (Continued) Post-sealing results are obtained after only 30 minutes, which experience has shown to be obtained only after one hour using a conventional thermal post-sealing bath. On the contrary, the post-sealing results after half an hour of treatment using the comparative solutions show inadequate quality. Admittance Y20 was determined in accordance with the German standard DIN 50 949 using an Anotest DY 8.1 meter supplied by Fisher. The measurement system consists of two electrodes, one of which is conductively connected to the base material of the sample. The second electrode is immersed in a cell, which can be placed on the coating to be tested. This cell takes the form of a rubber ring that has an internal diameter of 13 mm and a thickness of 5 mm, the annular surface of which is self-adhesive. The area of measurement is 1.33 cm. A solution of potassium sulfate (35 g / 1) in completely deionized water is used as the electrolyte. The value of the admittance read from the meter is converted, in accordance with the instructions of DIN 50 949, into a measurement temperature of 25 ° C and an S coating thickness of 20 ?. The resulting values, which preferably should be between approximately 10 and approximately 20%, are shown in the table. The residual reflection after coloring with the dye according to the German standard DIN 50 946 is measured as a parameter that shows coatings with open pores and thus poorly post-sealed. The area of the measurement was delimited using a self-adhesive measuring cell from the previously described Anotest device. The test area is moistened using an acid solution (25 ml / l sulfuric acid, 10 g / 1 KF). After exactly 1 minute, the acid solution is washed and the test area is dried. The test area is then moistened with the coLorante solution (5 g / 1 of Sanodal blue) which is allowed to act on the surface for 1 minute. After rinsing under running water, the measuring cell is removed. Any colorant barely adhered to the colored test surface is removed by rubbing with a mild powder cleaner. Once the surface has been dried, the measurement of the relative reflection is made by placing the measuring head of the light reflection meter (Micro Color Provided by the company Dr. Lange) once on an uncolored area of the surface and on second place on the colored measuring surface. The residual reflection in% is obtained by multiplying the quotient of the value measured by the colored surface divided by the measured value of the non-colored surface by 100. The residual values of the reflection between 95 and 100% indicate good post-sealing quality, while values lower than 95% are considered unacceptable. The higher the residual reflection value, the higher the quality of the post-sealing. The found values are shown in the table. The loss of acid corrosion is also measured in accordance with ISO 3210. For this purpose, the test sheet is weighed to an accuracy of 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 for 15 minutes at 60 ° C in a drying cabinet. The sample is weighed again. The difference in weight between the first and the second weight is calculated and divided by the size of the surface in di. Weight loss is expressed as? G in MG / dm2 (1 dm2 = 100cm2) and should not exceed 30 mg / dm2. The following concentrates for the comparison solutions and the treatment solutions according to the present invention were prepared by dissolving the active ingredients in completely deionized water: comparison 1.25 g / 1 of a polyphosphino carboxylic acid solution (45% by weight in water) (acrylic acid / sodium hypophosphite copolymer, "Belclene® 500", FMC Corporation, Great Britain Example 1: as the comparison 1, more: 10 g / 1 coconut amine x 5 EO Example 2: as comparison 1, plus: 10 g / 1 coconut amine x 12 EO Example 3: "as comparison 1, plus: 5 g / 1 of coconut amine x 5-EO Example 4: as comparison 1, plus: 10 g / 1 of coconut amine x 5 EO 2 g / 1 of magnesium acetate Example 5: as comparison 1, plus: 10 g / 1 coconut amine x 5 EO 0.5 g / 1 magnesium acetate Example 6: as comparison 1, plus: 10 g / 1 coconut amine x 12 EO 2 g / 1 lithium acetate Example 7: as comparison 1, plus: 2 g / 1 coconut amine x 5 EO Example 8: as comparison 1, plus: 15 g / 1 coconut amine x 5 EO Example 9: as comparison 1, plus: 5 g / 1 octanol x 4 EO Example 10: as comparison 1, plus: 5 g / 1 of Li lauryl sulfate Example 11: as comparison 1, plus: 5g / l of lauryl-dimethyl-benzylammonium chloride For the tests, 2g of the concentrate were constituted up to one liter with completely deionized water.

Claims

CLAIMS A process for the post-sealing of anodized metal surfaces, is characterized in that the anodized metal is put in contact with an aqueous solution for a period of between 0.5 and 2 minutes per thickness of anodized coating, whose solution is at a temperature between 75 ° C and its boiling point, and has a pH value in the range of 5.5 to 6.5 and which contains: (a) a total of 0.0004 to 0.05 g / 1, of one or more cationic, anionic or surface active agents nonionics selected from quaternary ammonium salts, in which at least one alkyl or arylalkyl moiety contains at least 8 carbon atoms, pyridinium salts, alkyl or alkylaryl sulfates and sulfonates, and fatty alcohol alkoxylates or fatty amines having a - alkyl with at least 8 carbon atoms; and (b) a total of 0.0005 to 0.05 g / 1, of one more organic acids selected from cyclic polycarboxylic acids having from 3 to 6 carboxyl groups and / or phosphonic acids. The process as mentioned in claim 1 is characterized in that the aqueous solution is at a temperature in the range of 94 to 98 ° C. The process as mentioned in one or more claims 1 and 2, is characterized in that the aqueous solution has a pH value in the range of 5.5 to 7. The process as mentioned in one or more claims 1 and 3, is characterized in that The surfactants of group (a) are nonionic surfactants. The process is mentioned in claim 4, characterized in that the nonionic surfactants are selected from ethoxylated fatty amines having from 10 to 18 carbon atoms in the alkyl portion and from 3 to 15 units of ethylene oxide per molecule. The process as mentioned in one or more of claims 1 to 5, is characterized in that group b) organic acids are selected from carboxylic acids unsaturated or aromatic 6-membered carbocyclic rings having from 3 to 6 carboxyl groups. The process as mentioned in claim 6 is characterized in that the carboxylic acids are selected from trimesic acid, trimellitic acid, pyromellitic acid, mellitic acid and cyclohexane hexacarboxylic acid. The process as mentioned in one or both of claims 6 and 7 is characterized in that the aqueous solution contains the carboxylic acids in a total amount of 0.001 to 0.05 g / 1. The process as mentioned in one or more of claims 1 to 5, characterized in that the organic acids of group b) are selected from: 1-phosphonopropan-1,2,3-tricarboxylic acid, 1,1-diphosphonopropan- 2, 3-dicarboxylic acid, 1-hydroxypropan-1,1-diphosphonic acid, 1-hydroxy-butan-1,1-diphosphonic acid, 1-hydroxy-1-phenylmethane-1, 1-diphosphonic acid, 1-hydroxy acid ethan-1, diphosphonic acid, 1-amino-ethan-1, 1-diphosphonic acid, 1-amino-1-phenylmethane-1, 1-diphosphonic acid, dimethylaminoethane-1, 1-diphosphonic acid, propylaminoethane-1 acid, 1-diphosphonic acid, butylaminoethane-1, 1-diphosphonic acid, amino tri (methylene phosphonic acid), ethylenediamine tetra (methylenphosphonic acid), diethylenetriamine penta (methylene phosphonic acid), hexamethylene diamine tetra (methylene phosphonic acid), n-propyliminobis (methylene phosphonic acid) , amino tri- (2-propylene-2-phosphonic acid), phosphonosuccinic acid, 1-phosphono-l-methyl-succinic acid and 1-phosphonobu acid tan-l, 2,4-tricarboxylic and polyphosphinocarboxylic acids. The process as mentioned in claim 9 is characterized in that the organic acid of group b) is selected from the polyphosphinocarboxylic acids. The process as mentioned in one or both of claims 9 and 10, is characterized in that the aqueous solution contains the acids of group b) in an amount of 0.003 to 0.05 g / 1. The process as mentioned in one or more of claims 1 to 11, characterized in that the aqueous solution also contains a total of 0.0001 to 5 g / 1 of one or more alkali metal and / or alkaline earth metal ions. He processed as mentioned in claim 12, characterized in that the aqueous solution contains a quantity of alkali metal and / or alkaline earth metal ions greater than that necessary to complete the neutralization of the acids of group b). The process as mentioned in claim 13, characterized in that the aqueous solution contains a total of 0.005 g / 1 of alkali metal and / or alkaline earth metal ions. The process as mentioned in one or more of claims 12 to 14 is characterized in that the alkali metal and / or alkaline earth metal ions are selected from Li and Mg.A process for post-sealing anodized metal surfaces is characterized in that after the treatment according to one or more of claims 1 to 15, the metal surfaces are immersed for a period of between 30 and 120 seconds in fully deionized water, which It is at a temperature of more than 90 ° C. An aqueous concentrate for the preparation of the aqueous solution which is used in the process as mentioned in one or more of claims 1 to 15, which produces the ready-to-use aqueous solution by dilution with water by a factor between 100 and 1000 .