DK150715B - PROCEDURE FOR SEALING ANODICALLY GENERATED OXIDE LAYERS ON ALUMINUM OR ALUMINUM ALLOYS - Google Patents

Description

150715 f

The invention relates to a method for sealing anodically generated oxide layers on aluminum or aluminum alloys in aqueous solutions containing phosphonic acids or their salts and calcium ions having a pH of 5 to 6.5 at temperatures between 90 ° C and the boiling point.

5

The process prevents the formation of disruptive aluminum hydroxide coatings (sealing coatings) on the surfaces and avoids difficulties due to the water hardness salts.

For the purpose of corrosion protection, anodic oxide layers are often applied to aluminum surfaces. These oxide layers protect the aluminum surfaces from the effects of weather and other corrosive media.

Furthermore, the anodic oxide layers are also applied to obtain a harder surface and thus achieve a greater wear resistance of the aluminum. Due to the intrinsic color or partial lightness of the oxide layers, particularly decorative effects can be obtained.

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A number of methods are known for applying anodic oxide layers to aluminum. Eg. For example, DC oxide layers are produced in solutions of sulfuric acid (DC-sulfuric acid method). However, often solutions of organic acids, especially sulfophthalic acid or sulphanilic acid, or these in admixture with sulfuric acid are also used. The latter methods are especially known as autocolor methods.

However, these anodically applied oxide layers do not meet all the requirements for corrosion protection as they have a porous structure. For this reason, it is necessary afterwards to seal the oxide layers. This sealing is often done with hot or boiling water and is termed “sealing.” This closes the pores, thus greatly increasing the corrosion protection.

However, when sealing anodically applied oxide layers, not only are the pores closed, but also a more or less thick velvety coating is formed on the entire surface, the so-called sealing coating. This consists of hydrated alumina and is non-gripping, so that the decorative effect of the layer thereby being damaged. Furthermore, it decreases the adhesiveness of adhering such aluminum parts and later promotes soiling and corrosion due to the enlarged effective surface. For this reason, it has so far been necessary to remove the coating mechanically by hand or by chemical means.

25 It is already known to remove this coating again from sealed and sealing coating surfaces using a mineral acid · finishing. Thus, in this process, an additional treatment step is necessary and, in addition, it requires a very careful post-treatment with the mineral acid to exclude damage to the layer. It is also a matter of the prior art to prevent sealing coatings from performing a sealing with solutions containing nickel acetate and lignin sulfate. One disadvantage of this way of working is that the resulting oxide layers yellowish under the influence of light. Methods have also been described in which to prevent sealing coatings, a hot water seal occurs during the addition of certain polyacrylates or certain dextrins. These methods have proved excellent. However, in many cases, especially when not working carefully, drying residue may remain. These are undesirable. However, they can easily be removed by a rinsing.

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From DE-Specification No. 1175524 a method is known for € 11 treatment of the surface of aluminum by anodic generation of oxide layers with a subsequent seal in an aqueous solution at a temperature between 90 ° C and the boiling point and having a pH of 5 5-6 The solution may contain phosphonic acids or their salts, including calcium. The solutions contain organic compounds with at least three electronegative groups in the molecule, including at least one free or one with an inorganic or organic base saturated acid group. The acid groups may also be phosphonic acid groups. As an example, polyfluoroalkylphosphonic acid is mentioned. Instead of the acids, the water-soluble salts, among which, e.g. a. Mention calcium salts. This method is to provide coatings which are precisely to be avoided by the method of the present invention and to obtain a seal. Furthermore, the problem of preventing sealing coatings is not affected.

The object of the present invention is to provide a method which avoids the aforementioned disadvantages and which therefore makes it possible to prevent the formation of sealing coatings and which avoids difficulties due to the hardness of the water, so that non-sealing agents can also be used. desalinated or uncured water. Precipitations of the hardness of the water are avoided far, or with water of great hardness only fluffy, heavy precipitates are formed, which do not settle on the sealed parts, but on the bottom and can easily be rinsed out of the baths. The appearance of the surface is not affected by the method according to the invention, but the effects obtained by the pretreatment and anodization are retained.

The process according to the invention is characterized in that the sealing is carried out with solutions containing one or more phosphonic acids or their water-soluble salts which form complexes with divalent metals in an amount of 0.001 to 0.05 g / l and calcium ions, molar ratios of calcium ions up phosphonic acids are at least 2: 1 which phosphonic acids have the general formulas 35 R

H 2 ^ 3 P "c" p® 3 H 2 (r = Phenyl residue or alkyl residue having 1 to 5 I C atoms)

Preferably hydroxyethanediphosphonic acid, 4 150715

^> N - C <^ "II

R 2 is a hydrogen atom or alkyl radical of 1 to 4 C atoms R 3 is a hydrogen atom or alkyl radical of 1 to 4 C atoms or phenyl radical, R 4 'CXY \

^; N - CXY - PO3H2 III

wherein X and Y are a hydrogen atom or an alkyl radical of 1 to 4 C atoms in R 2 is a -PO 1 group or a group of the formula CXY P0, Ho X 32 - CH 2 - N or cxy - po3h2 cxy - po3h2 -ch2- / xcxyp3h2

XCXY - CH2 - N

CXYP03H2 or R5

I J

H 2 O 3 P - C - COOH

H2 - C - COOH IV

wherein R 9 is a hydrogen atom, a methyl group or a-CH 2 -CH 2 -COOH group 5

As hydroxyalkanediphosphonic acid of formula I, e.g. 1-hydroxypropane, 1-hydroxybutane, 1-hydroxypentane, 1-hydroxyhexane-1,1-diphosphonic acid and 1-hydroxy-1-phenylmethane-1,1-diphosphonic acid and preferably 1-hydroxyethane-1,1-diphosphonic acid are used. . As phosphonic acid 5 of the general formula II, e.g. These are: 1-aminoethane, 1-amino-1-phenylmethane, dimethylaminoethane, dimethylaminobutane, diethylaminomethane, propyl and butylaminomethane-1,1-diphosphonic acid. Examples of phosphonic acids of general formula III are amino trimethylenephosphonic acid, ethylenediaminetetramethylene phosphonic acid, diethylene = 10 triamine pentamethylene phosphonic acid, aminotri- (2-propylene-2-phosphone = acid). Phosphonic acids of general formula IY may be used phosphonic succinic acid, 1-phosphonic l-methyl succinic acid and 2-phosphonic butane 1,2,4-tricarboxylic acid.

Instead of the listed phosphonic acids, their water-soluble salts can also be used, such as sodium, potassium, ammonium or alkanolamine salts. The phosphonic acids or water-soluble salts are preferably used in an amount of 0.001 to 0.05 g / l. They can be used individually or in admixture. Particularly good has been found a mixture of 20 1-hydroxyethane-1,1-diphosphonic acid and aminotrimethylene phosphonic acid in the 4: 1 to 1: 4 weight ratio.

The solutions containing the phosphonic acids or their salts are adjusted, if necessary, to a pH of 5 to 6.5. This setting can be done with ammonia or acetic acid.

To prepare the solutions, normal water that is neither fully desalinated nor cured can be used. When fully desalted or distilled or very soft water is used to prepare the solutions, an addition of calcium ions is required. Preferably water-soluble calcium salts such as CaCl 2 or Ca (NO 2) may be used. The molar ratio of calcium ions: phosphonic acids must be at least 2: 1.

In general, it is advantageous to use a higher ratio of calcium ions to phosphonic acids of approx. 5: 1 to approx. 500: 1.

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A preferred embodiment of the process consists in further adding to the sealing solutions a dextrin in an amount of 0.1 to 5 g / l, preferably 0.1 to 2 g / l. In particular, dextrins having a viscosity of 50 to 400 cP are used in 50% solution at 4n 20 ° C. Viscosity is measured with a Brookfield rotational viscometer.

In the following examples, the aluminum alloys are designated according to DIN 1725. The quality of the oxide layer was determined by the so-called apparent conductivity value according to DIN 50.949 and by the loss factor d according to DIN draft 50.920.

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Example 1 Aluminum profiles (AlMg 2), which were conventionally degreased alkaline and stained and then oxidized anodically by the steady-stream sulfuric acid method (layer thickness 22 µm), were sealed with a solution of 0.003 g / l -hydroxyethane-1,1-diphosphonic acid and 0.5 g / l dextrin (viscosity 100 cP, measured in 50% solution at 20 ° C) in water with 15 ° dH adjusted with ammonia to a pH of 5.8, at 100 ° C for 70 minutes. The profiles showed no sealing coating, the layer thickness was unchanged, and the apparent conductivity (y = 8.5) and the loss factor (d = 0.4l) showed a good seal. Even after prolonged use, there were no solid deposits of water hardeners in the sealing solution. A fluffy, heavy precipitate formed which did not settle on the profiles and which could easily be removed from the bath by spraying.

The same result was obtained when instead of 1-hydroxyethane-1,1-diphosphonic acid, the di, tri and tetrasodium or potassium or ammonium salts or a triethanolamine salt were used. The adjustment of the pH was carried out with acetic acid, in the case of the alkaline salts.

Example 2 Ordinarily, degreased aluminum sheet (AlSii), which had been oxidized anodically by the DC-sulfuric acid-oxalic acid method (layer thickness 21 µm), was sealed with a solution of 0.007 g / l of 1-hydroxy = ethane-1. 1-diphosphonic acid in deionized water with the addition of 10 mg / l calcium ions and the adjustment of the pH of 5.6 with 35 ammonia at 100 ° C for 60 minutes.

The gaze showed no sealing coating, and apparent conductivity (y = 12) and loss factor (d = 0.49) showed good sealing. The same results could be obtained with di-, tri- and tetra-alkali metal or airuno-sodium salts.

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Example 5 As usual, alkaline degreased and hoisted aluminum profiles (AlMgSiO, 5) which had been anodically oxidized by an autocolor method 5 (layer thickness 18 µm) were sealed for 60 minutes at 100 ° C in a solution of 0.005 g / l. 1-hydroxyethane-1,1-diphosphonic acid, 0.005 g / l aminotrimethylene phosphonic acid and lg / l dextrin (viscosity 200 cP, measured in 50% solution at 20 ° C) in water of 35 ° dH, adjusted with ammonia to a pH value of 5.9. The profiles showed no sealing coating and a good seal was demonstrated by an apparent conductivity (y = 10.5) and loss factor (d = 0.47). The hardness of the water was not bothered to notice during the process, as precipitates of hardness dariners formed only in the form of fluffy, easily settable precipitates which did not settle on the sealed parts but on the bottom of the bath.

Virtually the same results were obtained when the alkaline metal or anmonium salts were used instead of the aforementioned phosphonic acids, the alkaline reacting salts being adjusted by acetic acid to a pH between 5.8 and 6.0.

Example 4

Aluminum profiles (AlMgSi0.5), which were conventionally degreased alkaline and stained, were oxidized anodically by the direct-sulfuric acid-25, x method (layer thickness 20-22 µm). The profiles were sealed in a solution containing 0.01 g / L of 1-hydroxyethane-1,1-diphosphonic acid and 2 g / L of dextrin (viscosity 150 cP, measured in 50% solution at 20 ° C) in water of 20 ° dH, adjusted with ammonia to a pH value ρβά 5.8 at 98 to 100 ° C for 60 minutes. The profiles showed no sealing 30 ,.

coating, and the apparent conduction value (y = 9.0) and loss factor (d = 0.40) showed a good seal. No disturbance occurred as a result of the hardness of the water.

Example 5 In the same way as described in Example 4, aluminum profiles were sealed in solutions containing, instead of l-hydroxyethane-1,1-diphosphonic acid, one of the following phosphonic acids in the same amount: 40

Claims (3)

A process for sealing anodically produced oxide layers on aluminum and aluminum alloys in aqueous solutions containing phosphonic acids or their salts and calcium ions having a pH of 5 to 6.5 at temperatures between 90 ° C and the boiling point, characterized by performing the seal with solutions containing one or more phosphonic acids or their water-soluble salts forming divalent metal complexes in an amount of 0.001 to 0.05 g / l and calcium ions, the molar ratio of calcium ions to phosphonic acids being at least 2; 1 which phosphonic acids have the general formulas R (R = phenyl residue or ^ 2 ^ 3 C 1-4 alkyl residue having 1 to 5 J QH C atoms) preferably hydroxyethanedipho sphonic acid f 150715% r3 / PO3h2 ^ - - N - C <f II ^ -po3h2 where and R is the hyiarogenate or alkyl residue having 1 to 4 C atoms R3 is a hydrogenaton ions or alkyl residue having 1 to 4 C atoms or phenyl residue, R4 - CXY ^ - CXY - PO3H2 1τ1 H2 PO3 - CXY ^ wherein X and Y are a hydrogen atom or, an alkyl radical of 1 to 4 C atoms R4 is a -PO3H2 group or a group of the formula ✓cxY - po3h £ - CH2 - or CXY - PO3H2 CXY - PO3H2 - CH2 - CXYP03H2 CXY - CH2 - ^ "CXYP03H2 25 or * 5 H203P - C - COOH IV IL, - C - COOH 30 ^ wherein R3 is a hydrogen atom, a methyl group or a -CH2-CH2-C00H-Grupp