AU2537600A - Improved sealing method for anodized metal surfaces - Google Patents

Description

H 3817 -1 15.12.1998 "Improved post-sealing process for anodised metal surfaces" This invention relates to the production of corrosion-inhibiting and/or decorative coatings on metals by anodic oxidation. It concerns an improved process for post sealing porous, electrochemically-produced anodised coatings in order further to 5 improve the properties thereof, in particular to reduce dirt adherence. Electrochemical anodic oxidation of metals in 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 Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. 9 (1987), pp. 174-176. 10 According to this article, titanium, magnesium and aluminum and alloys thereof are anodisable, anodisation of aluminum and alloys thereof being of the greatest industrial significance. The electrolytically-produced anodised coatings protect the aluminum surfaces from the action of weathering and other corrosive media. Anodised coatings are also applied in order to create a harder surface, thus increasing the wear 15 resistance of aluminum. Particular decorative effects may be achieved by means of the intrinsic color of the anodised coatings or by absorptive or electrolytic coloring. Aluminum is anodised in an acidic electrolyte, sulfuric acid being most commonly used. Further suitable electrolytes are phosphoric acid, oxalic acid and chromic acid. The properties of the anodised coatings may be greatly varied by selection of the 20 electrolyte, the temperature thereof and by the current density and duration of anodisation. Anodisation is conventionally performed using direct current or using direct current having a superimposed alternating current. Freshly anodised coatings may subsequently be colored by immersion in solutions of a suitable dye or by an alternating current treatment in an electrolyte containing a 25 metal salt, preferably containing tin. As an alternative to subsequent coloring, colored anodised coatings may be obtained by so-called color anodisation processes, in which anodisation is performed in solutions of organic acids, such as in particular sulfophthalic acid or sulfanilic acid, each optionally blended with sulfuric acid.

-2 These anodically-produced protective coatings, 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 frequently described as "oxide coatings". The above investigation has, 5 however, demonstrated that these coatings are vitreous and contain tetrahedrally coordinated aluminum. Octahedrally-coordinated aluminum, as in aluminum oxides, was not found. This patent application thus uses the more general term "anodised coatings" instead of the misleading term "oxide coatings". However, such coatings do not yet fulfil all requirements with regard to corrosion 10 protection, as they still have a porous structure. It is consequently necessary to post seal the anodised coatings. This post-sealing is frequently performed using hot or boiling water, alternatively using steam, and is described as "sealing". This treatment seals the pores, so considerably increasing corrosion protection. There are numerous literature references relating to this post-sealing process. The following may be 15 mentioned by way of example: 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. However, not only are the pores sealed during post-sealing of the anodised coatings, 20 but a velvety deposit of a greater or lesser thickness, the so-called sealing deposit, is formed over the entire surface. This deposit, which consists of hydrated aluminum oxide, is visually unattractive, reduces adhesion when bonding such aluminum components and promotes subsequent soiling and corrosion. Since the subsequent manual removal of this sealing deposit by mechanical or chemical methods is costly, 25 attempts have been made to prevent the formation of this sealing deposit by means of chemical additives in the sealing bath. According to DE C-26 50 989, additions of cyclic polycarboxylic acids having 4 to 6 carboxyl groups per molecule, in particular cyclohexane hexacarboxylic acid, are suitable for this purpose. According to DE-A-38 20 650, certain phosphonic acids, for example 1-phosphonopropane-1,2,3 30 tricarboxylic acid, may also be used. The use of other phosphonic acids is known -3 from EP-A-122 129. DE-C-22 11 553 describes a process for post-sealing anodic oxide coatings on aluminum and aluminum alloys in aqueous solutions containing phosphonic acids or the salts thereof and calcium ions, wherein the molar ratio of calcium ions:phosphonic 5 acid 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. Phosphonic acids which may, for example, be considered are: 1-hydroxypropane-, 1-hydroxybutane-, 1 hydroxypentane-, 1 -hydroxyhexane- 1, 1-diphosphonic acid, together with 1 -hydroxy- 1 phenylmethane-1,1-diphosphonic acid and preferably 1-hydroxyethane- 1,1 10 diphosphonic acid, 1-aminoethane-, 1 -amino- 1-phenylmethane-, dimethyl aminoethane-, dimethylaminobutane-, diethylaminomethane-, propyl- and butylaminomethane-1,1-diphosphonic acid, aminotrimethylene phosphonic acid, ethylene diamine-tetramethylene phosphonic acid, diethylene triamine-pentamethylene phosphonic acid, aminotri-(2-propylene-2-phosphonic acid), phosphonosuccinic acid, 15 1-phosphono-1-methylsuccinic acid and 2-phosphonobutane-1,2,4-tricarboxylic acid. On the basis of the practical examples of the said patent, this process is a conventional hot post-sealing process using post-sealing times of between 60 and 70 minutes at anodised coating thicknesses of between about 18 and about 22 pm. Post sealing time is thus about 3 minutes per pm of coating thickness. 20 When using water which contains no additives other than the stated sealing deposit inhibitors, elevated temperatures (at least 90*C) and relatively long treatment times of the order of about 1 hour for an anodised coating of about 20 pm are necessary for effective post-sealing. This corresponds to a post-sealing time of about 3 minutes 25 per micrometer of anodised coating thickness. The post-sealing process is thus highly energy intensive and, due to its duration, may act as a bottleneck in the production process. Attempts have thus already been made to find additives for the post-sealing bath which promote the post-sealing process, so that it may proceed at lower temperatures (so-called cold post-sealing or cold sealing) and/or using shorter 30 treatment times. The following have, for example, been proposed as additives which facilitate post-sealing at temperatures of below 90*C: nickel salts, in particular -4 fluorides, which are sometimes used in practice (EP 171 799), nitrosylpentacyano ferrate, complex fluorides of titanium and zirconium, together with chromates or chromic acid, optionally in conjunction with further additives. As an alternative to actual post-sealing, hydrophobisation of the oxide coating by means of long-chain 5 carboxylic acids or waxes has been recommended, as has treatment with acrylamides, which should apparently be polymerised in the pore voids. Further details in this connection may be found in the above-stated reference by S. Wernick et al.. With the exception of post-sealing using nickel compounds, it has not proved possible to implement these proposals in practice. 10 An accelerated, hot post-sealing process is known from US-A-5 411 607 in which the anodised metal components are immersed in an aqueous solution containing lithium. The lithium concentration is preferably in the range from 0.01 to 50 g/l and in particular in the range from 0.01 to 5 g/l. It is moreover suggested that the post sealing solution should additionally contain a sealing deposit inhibitor. This is 15 preferably present in a concentration of between 0.1 and 10 g/l and is preferably an aromatic disulfonate. According to US-A-5 478 415, which has the same priority as the above-mentioned US-A-5 411 607, accelerated hot post-sealing may proceed using an aqueous solution which contains at least 0.01 g/l of lithium ions and 0.1 to 10 g/l of a sealing deposit inhibitor. Here too, the sealing deposit inhibitor is preferably an 20 aromatic disulfonate. DE-A-195 38 777 discloses an accelerated hot post-sealing process in which the anodised metal components are contacted with an anodising solution which contains a total of 0.1 to 5 g/l of one or more alkali metal and/or alkaline earth metal ions and a total of 0.0005 to 0.2 g/l of a sealing deposit inhibitor in the form of phosphonic acids or cyclic polycarboxylic acids. 25 The teaching of the latter three cited documents allows hot post-sealing times to be substantially shortened. DE-A-196 21 819 provides similar teaching. It relates to a process for post-sealing anodised metal surfaces, characterised in that the anodised metal is contacted with an aqueous solution for a period of between 0.5 and 2 minutes per micrometer of anodised coating thickness, which solution is at a temperature of 30 between 75*C and its boiling point and has a pH in the range from 5.5 to 8.5 and -5 which contains: (a) a total of 0.0001 to 0.01 g/l of one or more alkali metal and/or alkaline earth metal ions; and 5 (b) a total of 0.0005 to 0.5 g/l of one or more organic acids selected from cyclic polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids; the solution containing a larger quantity of the metal ions (a) than is required for complete neutralisation of the acids (b). DE-A-196 21 818 teaches a process for post-sealing anodised metal surfaces, 10 characterised in that the anodised metal is contacted with an aqueous solution for a period of between 0.5 and 2 minutes per micrometer of anodised coating thickness, which solution is at a temperature of between 75*C and its boiling point and has a pH in the range from 5.5 to 8.5 and which contains: (a) a total of 0.0004 to 0.05 g/l, preferably 0.005 to 0.02 g/l, of one or more 15 cationic, anionic or non-ionic surfactants; and (b) a total of 0.0005 to 0.5 g/l of one or more organic acids selected from cyclic polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids. Despite the prior art, there is a need for post-sealing processes which either reduce 20 the cost of post-sealing or improve the properties of the post-sealed anodised coatings. Properties of the post-sealed anodised coatings which are in particular need of improvement are soiling behavior and dirt adherence. Superficially soiled anodised metal surfaces are, on the one hand, aesthetically displeasing, which is regarded as problematic, particularly in architectural applications. On the other hand, layers of 25 dirt accelerate corrosion. There is therefore a particular need for anodised metal surfaces to which dirt does not readily adhere. In this way, dirt, on the one hand, becomes fixed less rapidly and on the other hand is extensively washed off again by precipitation. The present invention relates in the first instance to a process for post-treatment of -6 anodised metal surfaces, wherein the metal surfaces are contacted, for the purpose of post-sealing or after post-sealing, with an aqueous solution which exhibits a pH in the range from 1 to 14 and contains from 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or 5 copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids. The above-mentioned monomeric and/or polymeric acids having fluoroalkyl groups may constitute the only active substances dissolved in the aqueous solution, except for additives for adjusting the pH. Substances which may be used, if necessary, to adjust 10 the pH are in particular ammonia or acetic acid. In principle, it is irrelevant whether the monomeric and/or polymeric acids are used as such or in the form of salts. As a result of the adjustment of the pH to within the stated range, the equilibrium between free acid and acid anions is thus established in accordance with the acidity constant of the respective acid. 15 In one embodiment of the process according to the present invention, the above mentioned fluorine-containing acids are introduced during post-sealing of the anodised coatings. This embodiment of the present invention is accordingly characterised in that the anodised metal surfaces are post-sealed by contacting the metal surfaces with an aqueous solution for a period of between 0.5 and 4 minutes per micrometer of 20 anodised coating thickness, which solution has a pH in the range from 5.5 to 8.5 and which contains 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids. The above-mentioned acids having fluoroalkyl groups may also be used in conjunction 25 with other components, which are known to have a favourable effect on the post sealing of anodised coatings and which may, for example, contribute to reducing the sealing deposits, lowering the sealing temperature and shortening the post-sealing time. Examples of such groups of substances and individual substances were given in the description of the prior art. Accordingly, preferred embodiments of the present -7 invention may involve the aqueous solution used for post-sealing additionally containing one or more of the following components: (a) a total of 0.0005 to 0.5 g/l of one or more organic acids without fluoroalkyl groups, selected from cyclic polycarboxylic acids having 3 to 6 carboxyl 5 groups and/or phosphonic acids; (b) a total of 0.0004 to 0.05 g/l of one or more cationic, anionic or nonionic surfactants; (c) a total of 0.0001 to 0.01 g/l of lithium and/or magnesium ions; (d) 1.2 to 2.0 g/l of nickel ions and 0.5 to 0.8 g/l of fluoride ions. 10 In a further embodiment of the process according to the present invention, the anodised coatings are post-sealed by one of the processes known from the prior art, which were described by way of example in the introduction. Following this post sealing, optionally after intermediate rinsing with water, the anodised and post-sealed metal surfaces are contacted with the above-mentioned fluorine-containing acids. 15 Accordingly, an alternative embodiment of the present invention involves the anodised metal surfaces being post-sealed by contacting the metal surfaces with an aqueous solution for a period of between 0.5 and 4 minutes per micrometer of anodised coating thickness, which solution has a pH in the range from 5.5 to 8.5 and which contains one or more of the following components: 20 (a) a total of 0.0005 to 0.5 g/l of one or more organic acids without fluoroalkyl groups, selected from cyclic polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids; (b) a total of 0.0004 to 0.05 g/l of one or more cationic, anionic or nonionic surfactants; 25 (c) a total of 0.0001 to 0.01 g/l of lithium and/or magnesium ions; (d) 1.2 to 2.0 g/1 of nickel ions and 0.5 to 0.8 g/1 of fluoride ions; and thereafter by contacting them with an aqueous solution for a period ranging from 5 seconds to 15 minutes, which solution has a pH in the range from 1 to 14 and which contains 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 30 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids.

-8 In these two embodiments, the organic acids (a) are preferably selected from saturated, unsaturated or aromatic carbocyclic six-membered ring carboxylic acids having 3 to 6 carboxyl groups. Preferred examples of such acids are trimesic acid, trimellitic acid, pyromellitic acid, mellitic acid and the particularly preferred 5 cyclohexane-hexacarboxylic acid. The total quantity of carboxylic acids is preferably in the range from 0.001 to 0.05 g/l. The preferably used cyclohexane hexacarboxylic acid exists in the form of various stereoisomers. As is known from DE-A-26 50 989, preferred cyclohexane hexacarboxylic acids are those which bear 5 carboxyl groups in cis position and 1 in 10 trans position or 4 carboxyl groups in cis position and 2 in trans position. In a second specific embodiment, the organic acids (a) are 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 15 acid, 1-hydroxyethane-1,1-diphosphonic acid, 1-aminoethane-1,1-diphosphonic acid, 1-amino-1 -phenylmethane- 1,1 -diphosphonic acid, dimethyl-aminoethane-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), 20 hexamethylene diaminotetra-(methylene phosphonic acid), n-propyliminobis (methylene-phosphonic acid), aminotri-(2-propylene-2-phosphonic acid), phosphono succinic acid, 1-phosphono-1-methyl-succinic acid and 1-phosphonobutane-1,2,4 tricarboxylic acid. Of this selection, 1-phosphonopropane-1,2,3-tricarboxylic acid, 1, 1-diphosphonopropane-2,3-dicarboxylic acid, aminotri(methylenephosphonic acid) 25 are particularly preferred. The phosphonic acids (b) are preferably used in a quantity of 0.003 to 0.05 g/l. Polyphosphino-carboxylic acids which may be considered as copolymers of acrylic acid and hypophosphites are also suitable. One example of such a compound is Belclene* 500 from FMC Corporation, Great Britain. Various groups of surfactants may be used as a further optional component in the -9 process according to the present invention. Cationic surfactants (b) may, for example, be selected from quaternary ammonium salts, in which at least one alkyl or arylalkyl residue comprises at least 8 carbon atoms. An example of such a surfactant is C 2

.

4 alkyl-dimethylbenzylammonium chloride. Pyridinium salts, such as dodecylpyridinium 5 chloride, may also be used as additional cationic surfactants. Examples of anionic surfactants (b) which may be used are alkyl or alkylaryl sulfates and sulfonates. Linear alkyl sulfates, such as lauryl sulfate, are preferred for environmental reasons. The anionic surfactants may be used as alkali metal or ammonium salts, lithium salts being particularly preferred. 10 However, nonionic surfactants are preferably used as surfactants (b). These may be selected, for example, from alkoxylates, such as ethoxylates and/or propoxylates of fatty alcohols or fatty amines. By fatty alcohols and fatty amines are meant compounds having an alkyl residue of at least 8 carbon atoms. Such substances may exist as pure substances having a defined alkyl residue or consist of mixed products, 15 as may be obtained from natural fats and oils. It is also possible for the end groups of the alkoxylate to be blocked, i.e. etherification may be repeated at the terminal OH group. Examples of such nonionic surfactants are octanol x 4 EO (EO = ethylene oxide) and octanol x 4.5 EO-butyl ether. If fatty amine oxylates are used as nonionic surfactants instead of fatty alcohol ethoxylates, improved post-sealing results tend to 20 be obtained. Therefore, the nonionic surfactants (b) are preferably selected from fatty amine ethyoxylates having 10 to 18 carbon atoms in the alkyl residue and 3 to 15 ethylene oxide units per molecule. Specific examples are coconut oil amine x 5 EO and coconut oil amine x 12 EO. A further preferred embodiment involves the aqueous solution additionally containing 25 a total of 0.0001 to 0.01 g/l of lithium and/or magnesium ions. The use of components (a), (b) and/or (c) makes it possible to select post-sealing times which lie in the lower half of the stated range and may amount to between about 0.5 and about 2 minutes per yAm of anodised coating thickness. Irrespective of the embodiment of the present invention selected, the post-sealing bath - 10 may contain 1.2 to 2.0 g/l of nickel ions and 0.5 to 0.8 g/l of fluoride ions. This component allows post-sealing to be carried out as so-called cold post-sealing, i.e. at temperatures ranging between about 15 and about 70*C. Without the addition of nickel fluoride or other additives, which allow the post-sealing temperature to be 5 lowered so that it falls within this so-called "cold post-sealing range", post-sealing may be performed in the so-called intermediate temperature range, i.e. from about 70 to about 90*C, or in the so-called hot temperature range, i.e. between 90*C and the boiling point of the post-sealing bath. These temperature ranges apply to the post sealing process, irrespective of which of the two above-described embodiments of the 10 process according to the present invention is used. If the process is performed in accordance with the latter embodiment, in which the treatment with fluorine-containing acids is performed after post-sealing itself, the aqueous solution of fluorine-containing acids may be at a temperature ranging between about 15*C and the boiling point of the solution. The period of time over 15 which the post-sealed metal surfaces are contacted with the aqueous solution of the fluorine-containing carboxylic acids may be shorter, the higher the temperature of this aqueous solution. The acids, to be used according to the present invention, with fluoroalkyl groups having 2 to 22 carbon atoms is preferably selected from fluorocarboxylic acids, 20 fluoroalkylphosphinic acids, fluoroalkylphosphonic acids, fluoroalkylphosphonic acid esters, which still have free acid functions, and fluoroalkylsulfonic acids. Acids of this type having fluoroalkyl groups are particularly preferred, these fluoroalkyl groups being perfluoroalkyl groups. However, this does not mean that the entire acid molecule has to be perfluorinated. Rather, it may additionally bear unfluorinated 25 methylene or methyl groups. Indeed, this statement is intended to mean that, whenever a fluorine atom is bonded to a carbon atom, the other valencies of this carbon atom, which are not saturated by bonding to adjacent carbon atoms or heteroatoms of the acids, are saturated by bonding to fluorine atoms. In other words, acids are preferred whose carbon atoms do not bear both hydrogen atoms and fluorine 30 atoms. It is particularly preferred to use acids in which the carbon atoms adjoining - 11 the acid function constitute normal methylene groups, while more remote carbon atoms constitute either perfluoro-methylene or perfluoromethyl groups. If fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid are used, the distribution of the fluorine atoms and hydrogen atoms bonded to the individual carbon 5 atoms is irrelevant. In each of the above-described embodiments, the process according to the present invention may be used for the post-treatment of anodised metal surfaces, the thickness of the anodised coating lying within the range of normal anodised coating thicknesses (about 15 to about 25 pm, in particular about 18 to about 22 pm) or within the thin 10 layer anodisation range (about 1 to about 15 pm). The post-sealing bath using fluorine-containing organic acids suitable for the post sealing process according to the present invention may, in principle, be produced in situ by dissolving the constituents in (preferably completely deionised) water in the appropriate concentration range. Preferably, however, an aqueous concentrate already 15 containing all the necessary constituents of the post-sealing bath in the correct quantity ratio is used to prepare the post-sealing baths, from which concentrate the ready-to-use solution is obtained by dilution with water, for example by a factor of between about 10 and about 1000. It may be necessary in so doing to adjust the pH to the range according to the present invention using ammonia or using acetic acid. 20 The present invention accordingly also relates to an aqueous concentrate for the preparation of the aqueous solution for use in the post-sealing process according to the present invention, wherein the concentrate yields the ready-to-use aqueous solution by dilution with water by a factor of between about 10 and about 1000. The process according to the present invention yields post-sealed anodised coatings, 25 the quality features of which correspond to those laid down by industrial regulations (for example those laid down by Qualanod). However, these post-sealed anodised coatings additionally exhibit a further characteristic, which is less marked in the anodised coatings produced according to the prior art. Dirt particles adhere less well to the surface, such that the latter is less rapidly soiled under similar conditions and - 12 the dirt is relatively easy to remove. When used for external architectural purposes, this means that soiling of the anodised metal surfaces post-treated according to the present invention is easily washed off by precipitation. Accordingly, the present invention relates, in a further instance, to the use of acids 5 with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids to reduce dirt adherence to anodised metal surfaces. This use involves the above-mentioned acids having fluoroalkyl groups, to which the above more detailed explanations relate, being used in the context of one of the post-treatment processes 10 described in more detail above. To reduce dirt adherence to anodised metal surfaces, the fluoroalkyl group-containing acids specified in more detail above are accordingly used in the above-described post-treatment processes. The features of this use are summarised again in claims 9 to 12. It is irrelevant to the post-sealing process according to the present invention or the use 15 according to the present invention whether or not the metal surfaces were colored during anodisation or after anodisation and prior to post-sealing. The post-sealing process according to the present invention and the use according to the present invention may accordingly be applied both to colored and uncolored anodised coatings. Any coloring may be carried out electrochemically (for example 20 conventional coloring using tin salts), by self-coloring or using organic dip dyes. Examples (A) Fluorinated acids in post-sealing bath AlMg 1 grade aluminum sheets were prepared using a treatment sequence conventional in the prior art: 25 degreasing: P3-almeco* 18, 5 %, 5 mins, 70"C rinsing: process water - 13 pickling: P3-almeco* 57, 3 %, 1 min, 50*C rinsing: process water deoxidising: Novox* 4902, 2 %, 1 min, room temperature rinsing: completely deionised water 5 anodising: sulfuric acid, 18%, 40 mins, 18*C, 1.5 A/dm 2 , 16 V rinsing: completely deionised water The anodised aluminum sheets having an anodised coating thickness in the range from about 18 to about 20 tm were then post-sealed using post-sealing solutions according to the following Tables for 60 minutes at a temperature between 95 and 100*C. In 10 all cases, the appearance of the surface was assessed as good. The following quality parameters were measured: (1) Acid corrosion loss in mg/dm 2 , determined to ISO 3210. To this end, 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 15 g of chromium(VI) oxide per liter. On completion of the test period, the specimen is rinsed with deionised water and dried for 15 minutes at 60*C in a drying cabinet. The specimen is then re-weighed. The difference in weight between the first and second weighings is calculated and divided by the size of the surface in din 2 . Weight loss is expressed as AG in mg/dn 2 (1 dm 2 20 100 cm 2 ) and should not exceed 30 mg/dm2. (2) Admittance Y 2 0 was determined to German standard DIN 50949 using an Anotest Y D 8.1 meter supplied by Fischer. The measuring system consists of two electrodes, one of which is conductively connected to the base material of the specimen. The second electrode is immersed in an electrolyte cell, 25 which may be placed upon the coating to be tested. This cell takes the form of a rubber ring having an internal diameter of 13 mm and a thickness of about 5 mm, the annular surface of which is self-adhesive. The measurement area is 1.33 cm 2 . A potassium sulfate solution (35 g/1) in completely deionised water is used as the electrolyte. The admittance value read from the meter is 30 converted in accordance with the instructions of DIN 50949 to a measurement - 14 temperature of 25*C and a coating thickness of 20 tm. The resultant values, which should preferably be within the range between about 10 and about 20 tS, are shown in the Table. (3) Dye droplet test to ISO 2143. This is used to test to what extent a dye solution 5 is absorbed on the anodised surface. For the test, first of all a droplet of an acid solution (hexafluorosilicic acid or a solution of potassium fluoride in sulfuric acid) at about 23*C is placed onto the clean, dry, horizontal test surface and left to work for exactly one minute. Then, the acid droplet is washed off and the test area is allowed to dry. Then, a droplet of a dye 10 solution (Aluminum blue 2 LW or Sanodal red B3 LW) having a pH ranging between about 5 and about 6 and a temperature of about 23*C is placed on the same point on the test sheet and left to work for one minute. The droplet of dye solution is then rinsed off and the test surface is wiped with a moist cloth and then dried. The intensity of the colored spot remaining on the test surface 15 is assessed visually by comparison with a reference scale indicated in the test instructions. The intensity of coloring is expressed by a scale of 0 to 5, 0 representing no coloring (corresponding to a non-absorptive surface) and 5 representing strong coloring (corresponding to a fully absorptive anodised coating). The lower the number, the better post-sealed the anodised coating. 20 (4) Soiling behavior. A 5% dispersion of ground coal fly ash (grain size about 10 tm) in completely deionised water was used for testing soiling. A color meter (Croma-Meter CR-300, Minolta) and a gloss meter (mikro-TRI-gloss, Gardner) were used for the purpose of evaluation. Implementation and evaluation were as follows: 25 Implementation (a) Measurement of L*a*b* value of coated, as yet unsoiled test sheet using color meter, together with 60* gloss, (b) steeping of test sheet in completely deionised water for 15 mins, (c) thorough stirring of test dirt, distribution of 2 ml thereof with disposable 30 pipette on almost vertically disposed test sheet, (d) complete drying of test sheet in drying cabinet at 40*C (about 20 mins), (e) rinsing in a vessel using completely deionised water (by movement to and - 15 fro 10 x respectively), (f) re-drying of test sheet at 40 0 C, (g) measurement of L*a*b* value of soiled test sheet with color meter, together with 600 gloss. 5 Evaluation Measurement of L*a*b* using Minolta color meter: calculation of A value in %: AL* = (L*soile/L*unsoile) x 100% 60* gloss measurement with Gardner micro-TRI-gloss device 10 calculation of A value in %: AGE = (GEsoie/GEumoue) x 100% Repetition of 3(b) to (g) until AL* and AGE are constant or markedly greater than those of an uncoated test sheet (blank sheet). Post-sealing and quality parameters are listed in Table 1. 15 Table 1: Post-sealing and quality parameters (a) Component ("Comp 1") according to the present invention: perfluorinated monoalkyl phosphate (RfCH 2

CH

2 0)P(O)(ONH 4

)

2 Rf = F(CF 2 - CF 2

)

3

-

8 (Zonyl@FSP, DuPont); optional additive: cyclohexane hexacarboxylic acid according to DE-A-26 50 20 989 ("CHHS") pH 5.5 - 6.0 - 16 Ex. No. Comp 1 CHHS AG Y20 Dye droplet test mg/i mg/i mg/dm2 /S 1 1750 0 4 12 0 2 700 0 5 12 1 3 175 0 3 12 0 5 4 70 0 4 12 2 5 35 0 3 11 2 6 7 6.6 18 16 2 (b) Component ("Comp 1") according to the present invention: perfluorinated dialkyl phosphate (RfCH 2

CH

2

O)

2

P(O)(ONH

4 ), Rf = F(CF 2 - CF 2

)

3

-

8 10 (Zonyl@FSE, DuPont); optional additive: cyclohexane hexacarboxylic acid according to DE-A-26 50 989 ("CHHS") pH 5.5 - 6.0 Ex. No. Comp 1 CHHS AG Y20 Dye droplet test mg/i mg/i mg/dm2 is 15 7 1260 0 4 16 0 8 700 0 5 12 2 9 12.6 6.6 17 13 1 (c) Component ("Comp 1") according to the present invention: perfluorinated mono/dialkyl phosphate (RfCH 2

CH

2 0)P(O)(OH) 2 + (RfCH 2

CH

2 0) 2 P(O)(OH) 20 Rf = F(CF 2 - CF 2

)

3

-

8 (Zonyl@UR, DuPont); optional additive: cyclohexane hexacarboxylic acid according to DE-A-26 50 989 ("CHHS") - 17 pH 5.5 - 6.0 Ex. No. Comp 1 CHHS AG Y 2 0 Dye droplet test mg/l mg/i mg/dm2 /S 10 2400 0 3 17 0 11 960 0 3 15 1 5 12 480 0 10 18 2 13 240 0 2 11 1 As described above, to test soiling behavior, test sheets were soiled once per test cycle, allowed to dry and the dirt was rinsed off. After each test cycle, the change in color and gloss value was measured in relation to the unsoiled sheet. Table 2 10 contains data relating to relative color value and relative gloss per soiling cycle, wherein the use according to the present invention of perfluorinated monoalkyl phosphate is compared with the use of the standard post-sealing bath additive cyclohexane-hexacarboxylic acid serving as a comparison. Table 2 shows that color and gloss values vary only slightly from cycle to cycle when subjected to the 15 treatment according to the present invention, while the comparison sheets display a marked deterioration, which indicates adherent dirt.

- 18 Table 2: Soiling behavior. Invention: post-sealing with the addition of 35 mg/i of perfluorinated monoalkyl phosphate (Zonyl@FSP); comparison: post-sealing with the addition of 13.2 mg/i cyclohexane hexacarboxylic acid ("CHHS") Test cycle %AL %AGE Zonyl FSP CHHS Zonyl FSP CHHS 5 0 100 100 100 100 1 99.5 84.5 96.4 37.4 2 98.4 63.3 96.3 9.9 3 98.4 51.2 94.7 1.8 4 97.6 46.7 95.1 1.2 10 5 97.4 43.9 92.2 1.0 6 96.5 42.3 91.0 1.0 7 96.7 41.9 88.1 1.0 8 97.8 87.4 9 98.4 86.9 15 (B) Post-treatment using fluorinated acids after post-sealing Aluminum sheets were prepared as described under (A). They were then post-sealed by a process according to the prior art in an aqueous solution of 13.2 mg/l cyclohexane-hexacarboxylic acid at a temperature of 95*C and having a pH in the range from 5.5 to 6 for 30 or 60 minutes. They were then immersed, when still 20 moist, in a solution which contained 7 g/l Zonyl*FSP (c.f. Table 1), was at room temperature and exhibited a pH of 7. The sheets were subsequently dried using compressed air. The surface quality thereof was tested in accordance with Qualanod, as described above under (A). The results are given in Table 3.

- 19 Table 3: Treatment parameters and surface qualities relating to post-sealing and subsequent treatment with perfluorinated monoalkyl phosphate Zonyl@FSP Ex. No. Post-sealing Treatment AG in Y 2 0 in Dye droplet time using time using mg/dm 2 ItS test CHHS in Zonyl@FSP in minutes minutes 14 60 5 14 11 1 5 15 60 1 16 10 1 16 30 5 19 16 1 17 30 1 22 16 2 Comp.1 60 none 18 15 1 Comp.2 30 none 25 25 2 - 3 10 In another series of tests, sheets which had been post-sealed and post-treated using perfluorinated monoalkyl phosphate as described under (B) were examined with regard to the effect of the variables concentration of active substance, temperature and treatment time on the surface coverage of test sheets with perfluorinated monoalkyl phosphate. The sheets had been post-sealed for 60 minutes. The post-sealed test sheets 15 were left in the Zonyl*FSP solution, respectively for one minute, 5 minutes and 15 minutes. Surface coverage was measured using the count rate (in kilopulses per second) determined by X-ray fluorescence measurement of phosphorus. The results are contained in Tables 5 to 7.

- 20 Table 5: X-ray fluorescence pulse rates for different concentrations of Zonyl*FSP; pH = 7, room temperature 15 minutes 5 minutes 1 minute 2 % 0.448 0.4668 0.527 1 % 0.2257 0.2369 0.216 5 0.50 % 0.1703 0.1573 0.153 0.10 % 0.1386 0.1071 0.097 Table 6: X-ray fluorescence pulse rate exhibited by Zonyl*FSP solution at different temperatures; concentration 0.7 wt. %, pH = 7 15 minutes 5 minutes 1 minute 20 0 C 0.1712 0.1573 0.153 10 40 0 C 0.4618 0.3803 0.215 60 0 C 0.9507 0.3635 0.307 Table 7: X-ray fluorescence pulse rates exhibited by Zonyl@FSP solution at different pH values, adjusted using acetic acid or ammonia; concentration 0.7 wt.%, room temperature 15 minutes 5 minutes 1 minute 15 pH 5 1.0981 0.7926 0.56 pH 7 0.1712 0.1573 0.153 pH 9 0.1432 0.1405 0.138

Claims (12)

1. A process for post-treating anodised metal surfaces, characterised in that the metal surfaces are contacted, for the purpose of post-sealing or after post sealing, with an aqueous solution which exhibits a pH in the range from 1 to 5 14 and contains from 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids.

2. A process according to claim 1 wherein the anodised metal surfaces are post 10 sealed by contacting the metal surfaces with an aqueous solution for a period of between 0.5 and 4 minutes per micrometer of anodised coating thickness, which solution has a pH in the range from 5.5 to 8.5 and which contains 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or 15 methacrylic acid or respectively the salts of these acids.

3. A process according to claim 2 wherein the aqueous solution additionally contains one or more of the following components: (a) a total of 0.0005 to 0.5 g/l of one or more organic acids without fluoroalkyl groups, selected from cyclic polycarboxylic acids having 20 3 to 6 carboxyl groups and/or phosphonic acids; (b) a total of 0.0004 to 0.05 g/l of one or more cationic, anionic or nonionic surfactants; (c) a total of 0.0001 to 0.01 g/l of lithium and/or magnesium ions; (d) 1.2 to 2.0 g/l of nickel ions and 0.5 to 0.8 g/l of fluoride ions. - 22

4. A process according to claim 1 wherein the anodised metal surfaces are post sealed by contacting the metal surfaces with an aqueous solution for a period of between 0.5 and 4 minutes per micrometer of anodised coating thickness, which solution has a pH in the range from 5.5 to 8.5 and which contains one 5 or more of the following components: (a) a total of 0.0005 to 0.5 g/l of one or more organic acids without fluoroalkyl groups, selected from cyclic polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids; (b) a total of 0.0004 to 0.05 g/l of one or more cationic, anionic or non 10 ionic surfactants; (c) a total of 0.0001 to 0.01 g/l of lithium and/or magnesium ions; (d) 1.2 to 2.0 g/l of nickel ions and 0.5 to 0.8 g/l of fluoride ions; and thereafter by contacting them with an aqueous solution for a period ranging from 5 seconds to 15 minutes, which solution has a pH in the range 15 from 1 to 14 and which contains 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids.

5. A process according to one or more of claims 1 to 4 wherein the acids having 20 fluoroalkyl groups with 2 to 22 carbon atoms are preferably selected from fluorocarboxylic acids, fluoroalkylphosphinic acids, fluoroalkylphosphonic acids, fluoroalkyl-phosphonic acid esters and fluoroalkylsulfonic acids.

6. A process according to one or more of claims 1 to 5 wherein the fluoroalkyl groups are perfluoroalkyl groups. - 23

7. An aqueous concentrate which, when it has been diluted with water by a factor of between 10 and 1000 and if necessary has had its pH adjusted, yields an aqueous solution which may be used in the process according to one or both of claims 2 and 3. 5

8. Use of acids having fluoroalkyl groups with 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids to reduce dirt adherence to anodised metal surfaces.

9. Use according to claim 8 wherein the metal surfaces are contacted with an 10 aqueous solution for a period of between 0.5 and 4 minutes per micrometer of anodised coating thickness, which solution is at a temperature of between 15*C and its boiling point and has a pH in the range from 5.5 to 8.5 and which contains 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of 15 acrylic acid and/or methacrylic acid or respectively the salts of these acids.

10. Use according to claim 9 wherein the aqueous solution may additionally contain one or more of the following components: (a) a total of 0.0005 to 0.5 g/l of one or more organic acids without fluoroalkyl groups, selected from cyclic polycarboxylic acids having 20 3 to 6 carboxyl groups and/or phosphonic acids; (b) a total of 0.0004 to 0.05 g/l of one or more cationic, anionic or nonionic surfactants; (c) a total of 0.0001 to 0.01 g/l of lithium and/or magnesium ions; (d) 1.2 to 2.0 g/l of nickel ions and 0.5 to 0.8 g/l of fluoride ions. - 24

11. Use according to claim 8 wherein the anodised metal surfaces are post-sealed by contacting the metal surfaces with an aqueous solution for a period of between 0.5 and 4 minutes per micrometer of anodised coating thickness, which solution has a pH in the range from 5.5 to 8.5 and which contains one 5 or more of the following components: (a) a total of 0.0005 to 0.5 g/l of one or more organic acids without fluoroalkyl groups, selected from cyclic polycarboxylic acids having 3 to 6 carboxyl groups and/or phosphonic acids; (b) a total of 0.0004 to 0.05 g/l of one or more cationic, anionic or 10 nonionic surfactants; (c) a total of 0.0001 to 0.01 g/l of lithium and/or magnesium ions; (d) 1.2 to 2.0 g/l of nickel ions and 0.5 to 0.8 g/l of fluoride ions, and thereafter by contacting them with an aqueous solution for a period ranging from 5 seconds to 15 minutes, which solution has a pH in the range 15 from 1 to 14 and which contains 0.01 to 10 g/l of one or more acids with fluoroalkyl groups having 2 to 22 carbon atoms and/or fluorinated polymers or copolymers of acrylic acid and/or methacrylic acid or respectively the salts of these acids.

12. Use according to one or more of claims 8 to 11 wherein the acids having 20 fluoroalkyl groups with 2 to 22 carbon atoms are preferably selected from fluorocarboxylic acids, fluoroalkylphosphinic acids, fluoroalkylphosphonic acids, fluoroalkyl-phosphonic acid esters and fluoroalkylsulfonic acids.