WO2003052171A2

WO2003052171A2 - Sealing of anodized metallic surfaces in order to improve the weathering behaviour thereof

Info

Publication number: WO2003052171A2
Application number: PCT/EP2002/013838
Authority: WO
Inventors: Josef Kresse; Gabriele Hecht
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 2001-12-15
Filing date: 2002-12-06
Publication date: 2003-06-26
Also published as: DE10161847A1; AU2002364389A8; WO2003052171A3; AU2002364389A1

Abstract

The invention relates to an aqueous solution for sealing anodized metallic surfaces having a pH value of between 5.5 and 8.5, and containing a) a total of between 0.4 and 50 mg/l of at least one cationic, anionic or non-ionic surfactant, and b) between 0.5 and 500 mg/l of a copolymer of 1) acrylic acid or methacrylic acid or the esters thereof with alcohols having between 1 and 3 C atoms, and 2) hypophosphite salts. The solution is characterised in that it also contains a total of between 0.1 and 100 mg/l of at least one of the following substances: c1) polymers or copolymers based on maleic acid or maleic anhydride, c2) phosphinocarboxylic acid copolymers, and c3) non-polymer organic phosphonic acids. The sealing caused by said solution improves the weathering behaviour of the anodized metallic surfaces.

Description

"Compaction of anodized metal surfaces to improve the weather behavior"

The invention is in the field of producing anti-corrosion and / or decorative coatings on metals by anodic oxidation. It relates to an improved method for compacting the electrochemically produced porous anodizing layers in order to further improve their properties, in particular their weather behavior.

The electrochemical anodic oxidation of metals in suitable electrolytes is a widespread process for the formation of corrosion-protective and / or decorative coatings on suitable metals. These methods are briefly characterized, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. 9 (1987), pp. 174-176. Accordingly, titanium, magnesium and aluminum and their alloys can be anodized, the anodization of aluminum and its alloys having the greatest technical importance. The electrolytically produced anodizing layers protect the aluminum surfaces from the effects of the weather and other corrosive media. 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 varied within wide limits by the choice of the electrolyte, its temperature, the current density and the anodizing time. The anodization is usually carried out with direct current or with an alternating current superimposed direct current.

These anodically produced protective layers are often referred to as “oxide layers”. However, it is known that these layers are glass-like and tetrahedral contains 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 requirements with regard to corrosion protection, since they still have a porous structure. For this reason, it is necessary to compact the anodizing layers. This compression is often carried out with hot or boiling water, alternatively with steam, and is referred to as "sealing". As a result, the pores are closed and the corrosion protection is considerably increased. There is extensive literature on this compression process, which is cited, for example, in WO 97/14828.

When the anodizing layers are compacted, not only are the pores closed, but a more or less strong velvety coating, the so-called sealing coating, is formed on the entire surface. This covering made of hydrated aluminum oxide is optically disturbing, reduces the adhesive strength when gluing such aluminum parts and promotes later contamination and corrosion. Since the subsequent removal of this sealing covering by hand by mechanical or chemical means is complex, attempts are made to prevent the formation of this sealing covering by chemical additives to the sealing bath. Examples of such additives can be found in WO 97/14828.

When using water which contains no other additives besides the mentioned sealing agents, high temperatures (at least 95 ° C.) and relatively long treatment times of the order of about 1 hour with an anodizing layer of about are generally required for effective compaction 20 μm required. This corresponds to a compression time of approximately 3 minutes per micrometer of anodizing layer thickness. For this reason, additives for the compression bath which support the compression process, so that it is used at lower temperatures, have already been sought (so-called cold compression or cold sealing) and / or with shorter treatment times. Some measures for this are cited in WO 97/14828.

The cited document relates to a process for compacting anodized metal surfaces, in which the anodized metal is brought into contact with an aqueous solution having a temperature between 75 ° C. and the boiling point and a temperature for a period of between 0.5 and 2 minutes per micrometer of anodizing layer thickness pH in the range from 5.5 to 8.5 and which 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 contains one or more organic acids selected from cyclic polycarboxylic acids with 3 to 6 carboxyl groups and / or phosphonic acids and / or polyphosphinocarboxylic acids. In the special embodiment of DE-A-196 21 813, the solution contains a larger amount of the metal ions of group a) than is necessary for the complete neutralization of the acids of group b).

However, the previously known compression methods do not lead to satisfactory weather behavior in the long term. This means how the anodized and compacted metal surface behaves in the long term when exposed to sunlight and weather. Under the influence of these factors, iridescent and then dull-looking coatings are formed on anodized metal surfaces, in particular on aluminum surfaces in the architectural field. This disrupts the aesthetic impression of the metal surfaces. Either you accept this annoying impression of "being old" or you try to remove the weather coverings by complex cleaning measures. There is therefore a need for an improved compression method for anodized metal surfaces, which improves the weather behavior of the compressed metal surfaces.

In a first embodiment, the present invention relates to an aqueous solution for compacting anodized metal surfaces, which has a pH in the range from 5.5 to 8.5 and which a) a total of 0.4 to 50 mg / 1 of one or more cationic, anionic or nonionic surfactants and b) 0.5 to 500 mg / 1 of a copolymer of 1) acrylic acid or methacrylic acid or their esters with alcohols with 1 to 3 C- Contains atoms and 2) hypophosphite salts, characterized in that they additionally contain a total of 0.1 to 100 mg / l, preferably 0.5 to 20 mg / l, in particular 1 to 10 mg / l, of one or more of the following substances: d) polymers or copolymers based on maleic acid or

Maleic anhydride c2) phosphinocarboxylic acid copolymers c3) non-polymeric organic phosphonic acids.

The substances of groups d), c2) and c3) have in common that they are suitable for the formation of chelate complexes. So far they have been used to prevent the deposition of hardness in water.

The pH of the aqueous solution is preferably in the range from 5.5 to 7, in particular in the range from 5.5 to 6.5. If necessary, the pH can be adjusted with ammonia or with acetic acid. With ammonium acetate as a buffer, it can be kept in the required range.

The aqueous solution preferably contains 1 to 25 mg / l of the surfactants a). It is preferred that the surfactants of group a) are nonionic surfactants, which are preferably selected from fatty alcohol or fatty amine ethoxylates with 8 to 18 carbon atoms in the alkyl radical and with 2 to 15 ethylene oxide units. Fatty alcohol ethoxylates are preferred, especially those with 2 to 8 ethylene oxide units in the molecule.

The copolymers of group b) are preferably present in a concentration between 3 and 50 mg / l. Copolymers of acrylic acid and sodium hypophosphite are preferably used. Such products are known under the CAS numbers 71050-62-9 and 82851-89-6. In addition to components a) and b), the aqueous solution according to the invention contains at least one of components d), c2) and / or c3). This third component has the effect that the aqueous solution, when compacting anodized metal surfaces, leads to significantly better weather behavior than components a) and b) alone. According to d), this third component can be polymers or copolymers based on maleic acid or maleic anhydride. In the latter case, the maleic anhydride can be at least partially hydrolyzed to maleic acid. For example, a maleic anhydride-ethyl acrylate-vinyl acetate copolymer can be used, which has the CAS no. 113221- 69-5. A hydrolyzed polymaleic anhydride with CAS No. 26099-09-2 is also suitable.

Phosphinocarboxylic acid copolymers which do not fall under the definition of group b) are suitable as component c2). For example, an acrylic acid-2-acrylamido-2-methylpropanesulfonic acid-sodium salt-phosphinic acid-sodium salt copolymer with the CAS no. 110224-99-2.

Group c3) comprises non-polymeric organic phosphonic acids which are known as complexing agents. These are preferably molecules with either several phosphonic acid groups in the molecule, in particular in the geminal position, or molecules which also carry carboxylic acid groups in addition to phosphonic acid groups. Examples include: 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- Hydroxy1-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, butylaminoethanl, 1 -diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminotetra (methylenephosphonic acid), diethylenetriaminopenta (methylenephosphonic acid), hexamethylenediamino-tetra (methylenephosphonic acid), n-propylene acid , Aminotri (2-propylene 2-phosphonic acid), phosphonosuccinic acid, 1-phosphono-1methyl succinic acid, 1-phosphonobutane-1, 2,4-tricarboxylic acid.

In addition, the aqueous solution can contain 0.0001 to 5 g / l of lithium and / or magnesium ions, in particular lithium ions. These ions are preferably used as acetate salts. For example, the aqueous solution can additionally contain 10 to 100 mg / l lithium ions.

The compression bath according to the invention can in principle be produced on site by dissolving the constituents in - preferably fully demineralized - water in the required concentration range. Preferably, however, an aqueous concentrate is used to prepare the compression baths, which already contains all the necessary components of the compression bath in the correct proportions and from which the ready-to-use solution is obtained by dilution with water, for example by a factor of between about 100 and about 1000. If necessary, the pH must be adjusted to the range according to the invention with ammonia or with acetic acid. The invention accordingly also comprises an aqueous concentrate for the preparation of the aqueous solution, the concentrate yielding the ready-to-use aqueous solution by dilution with water by a factor between about 100 and about 1000.

In a further aspect, the present invention relates to a method for compacting anodized metal surfaces, characterized in that after the anodizing, the metal surfaces are coated with a solution according to one or more of claims 1 to 4 for a period of time in the range from 1 to 4 minutes per μm anodizing layer thickness brings into contact, which has a temperature in the range of 90 ° C to the boiling point, preferably in the range of 95 to 100 ° C. The anodized metal surfaces can be brought into contact with the treatment solution by spraying the solution onto the metal surface or preferably by immersing the metal parts in the aqueous solution. At the technically usual anodizing layer thickness and one average treatment time of 3 minutes per micrometer anodizing layer thickness, the contact times are preferably in the range of 50 to 70 minutes.

The compression method according to the invention is preferably used for anodized aluminum or anodized aluminum alloys. However, it can also be applied to the anodizing layers of other anodizable metals such as titanium and magnesium or their alloys. It can be used both for uncolored anodizing layers and for those which are produced using conventional processes such as integral coloring, adsorptive coloring using organic dyes, reactive coloring using inorganic color pigments, electrochemical coloring using metal salts, in particular tin salts, or a Interference staining were colored.

The process according to the invention improves the weather behavior compared to compaction with an aqueous solution which does not contain any of the components c) under otherwise identical process conditions. This means that the anodized metal surfaces treated in this way have a reduced formation of deposits when weathered outdoors. This keeps the aluminum surfaces aesthetically pleasing and clean for a long time. The effort for cleaning can be significantly reduced. Accordingly, in a last aspect, the invention encompasses the use of the aqueous solution described to improve the weathering behavior of anodized metal surfaces compared to treatment with aqueous solutions which do not have the composition according to the invention comprising at least 3 components a), b) and c).

Examples

Aluminum sheets of the type AlMg 1 were conventionally anodized with direct current in sulfuric acid (1 hour, layer thickness 20 μm). The sheets were then placed in one of the compression solutions for 60 minutes dipped below table. The dive time was 60 minutes. The sheets were then dried and tested in a QUV rapid weathering test under the influence of UV radiation and water of condensation. The color change ΔE was checked after 49 days of testing and optically assessed. The greater the value of ΔE, the greater the color change and the worse the weather behavior to be expected outdoors. The color change _E was determined by measuring the L * a * b * values at the start of the test and after 49 days of the test. ΔE is calculated as follows:

ΔE = [(L * _end - L * _start ) ² + (a * _end - a * A _n f _an g) ² + (b * end ^- b * start) ² ] '

The QUV rapid weathering test consists of 2 cycles that are repeated for the duration of the test.

1st UV cycle: 4 h, 60 ° C with UVB light

2nd condensation cycle: 8 h, 40 ° C

The QUV test is based on ISO 4892, ASTM G53, D4329, D4587, D4799, SAE J2020.

Test solutions and test results (concentration data as active substance concentrations in mg / l)

Comparative solution: 1 mg / l surfactant (octanol ethoxylated with 4 mol ethylene oxide, likewise in the examples according to the invention) + 12 mg / l cyclohexane hexacarboxylic acid. ΔE = 7.5

Examples 1 to 9: Solutions according to the invention. In addition to the substances listed in the table, all solutions contained 6 mg / l of surfactant a) and 30 mg / l of lithium ions, which were used as acetate. The pH of all solutions was 6.0.

Claims

claims

1. Aqueous solution for compacting anodized metal surfaces, which has a pH in the range from 5.5 to 8.5 and which a) a total of 0.4 to 50 mg / l of one or more cationic, anionic or nonionic surfactants and b) 0.5 to 500 mg / l of a copolymer of 1) acrylic acid or methacrylic acid or its ester with alcohols with 1 to 3 carbon atoms and 2) hypophosphite salts, characterized in that it additionally contains a total of 0.1 to 100 mg / l contains one or more of the following substances: d) polymers or copolymers based on maleic acid or

2. Aqueous solution according to claim 1, characterized in that the surfactants of group a) are nonionic surfactants, which are preferably selected from fatty alcohol or fatty amine ethoxylates with 8 to 18 carbon atoms in the alkyl radical and with 2 to 15 ethylene oxide units.

3. Aqueous solution according to one or both of claims 1 and 2, characterized in that it contains phosphonic acids of group c3) which 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-hydroxy1-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, butylaminoethanl, 1 - diphosphonic acid, aminotri (methylenephosphonic acid), ethylene diaminotetra (methylenephosphonic acid), diethylenetriamineopenta (methylenephosphonic acid), hexamethylenediaminotetra (methylenephosphonic acid), n- Propyliminobis (methylenephosphonic acid), aminotri (2-propylene-2-phosphonic acid), phosphonosuccinic acid, 1-phosphono-1-methylsuccinic acid, 1-phosphonobutane-1, 2,4-tricarboxylic acid.

4. Aqueous solution according to one or more of claims 1 to 3, characterized in that it additionally contains 0.0001 to 5 g / l lithium and / or magnesium ions.

5. Aqueous concentrate, which after dilution with water by a factor between 100 and 1000 and, if necessary, adjusting the pH, gives an aqueous solution according to one or more of claims 1 to 4.

6. A method for compacting anodized metal surfaces, characterized in that the metal surfaces are brought into contact with a solution according to one or more of claims 1 to 4 after anodizing for a period of time in the range from 1 to 4 minutes per μm anodizing layer thickness, which temperature in the range from 90 ° C to the boiling point, preferably in the range from 95 to 100 ° C.

7. Use of a solution according to one or more of claims 1 to 4 to improve the weathering behavior of anodized metal surfaces.