FR2487381A1 - Aq. acid soln. for surface treating aluminium - contains titanium and/or zirconium cpd. and polyelectrolyte dispersant - Google Patents

Abstract

The aq. acid soln. has a pH of less than 6 and contains one or more acids, bases or salts contg. titanium and/or zirconium (pref. in amt. to give a total cation concn. of 0.00004-0.02 g.atom/l), less than 500 (esp. 30-100) ppm. water-soluble polyelectrolyte dispersant of mol. wt. less than 100000 (pref. 500-10000) in amt. 1-100 g/g.atom of Zr and/or Ti, and pref. complexing agents for Al and the Ti and/or Zr cpds. and a pH controller. Pref. Ti and/or Zr cpds. are e.g. H2TiF6, Na2TiF6, K2TiF6, etc. Suitable complexing agents for these cpds. are e.g. hydrofluoric acid, fluorides, condensed phosphoric acids, etc. Suitable complexing agents for Al are hydrofluoric, (hepta)gluconic and EDTA acids and salts. The polyelectrolyte is e.g. (co)polymers of acrylic acid, polyamines, polyimines, polyvinyls, polymethacrylates and maleic anhydride copolymers, etc. The soln. produces, in a single active treatment stage, a protective layer on aluminium (alloys) which improves adhesion of organic finishes and improves corrosion resistance. The soln. is at least as effective as conventional phosphating-chromating solns. but avoids the problems due to presence of hexavalent chromium ions.

Description

Aqueous acid solution, its use for
surface treatment of base metals
aluminum, and concentrated to prepare it.

 The invention relates to an acidic aqueous solution for the treatment in a single active step of aluminum or aluminum alloy surfaces making it possible to generate on said surfaces a protective layer which improves on the one hand the cohesion between the metal and any organic coating applied subsequently, and on the other hand the resistance of said surfaces to corrosion.

 In industry today, to improve the corrosion resistance of aluminum or aluminum alloy surfaces and the adhesion of organic coatings applied subsequently, chromation or phospho-chromation processes are used which have well-known drawbacks, in particular due to the toxicity of the products containing hexavalent chromium used, and problems of environmental pollution due to the discharge of rinsing water and sludge resulting from these processes.

 It has certainly already been proposed methods for treating aluminum surfaces using solutions which do not contain hexavalent chromium compounds. However, it should be noted that in general, these processes are complex; they provide for the application of the anti-corrosion coating in two stages, using two different treatment solutions, more or less complex, with intermediate washing stages. water for example. So far, none of these processes, perhaps because of their complexity, has given rise to industrial developments.

 The object of the invention is therefore, above all, to develop a solution for the treatment of surfaces of aluminum or aluminum alloys, not having the drawbacks of solutions which contain hexavalent chromium and capable of generating, in a single active treatment step, on said surfaces, a protective layer which improves the cohesion between the metal and any organic coating applied subsequently, while giving these surfaces marked resistance to corrosion.

 To do this, in accordance with the invention, use is made of an aqueous acid solution of pH less than 6, characterized in that it comprises, in addition to an effective amount of at least one compound chosen from the group consisting of acids , the bases and the salts comprising titanium or zirconium or these two elements simultaneously, as well as optionally at least one complexing agent for these compounds and at least one complexing agent for aluminum in an amount of less than 500 ppm, preferably included between 10 and 250 ppm and better still between 30 and 100 ppm of at least one water-soluble dispersing polyelectrolyte having a molecular weight of less than 100,000, preferably from 500 to 10,000, in a proportion of 1 to 100 g per gram atom of zirconium, titanium or all of these two elements.

More particularly, this aqueous acid solution of pH less than 6 is characterized in that it essentially comprises
a) at least one compound chosen from acids, bases and salts comprising titanium and zirconium or these two elements simultaneously in a proportion such that the total concentration of corresponding cations is between 4.10-5 and 2.10-2 atom- gram per liter
b) insofar as insoluble titanium or zirconium compounds are used or are liable to form, at least one complexing agent for these compounds in a proportion which makes it possible to completely dissolve them;
c) at least one agent complexing aluminum ions capable of appearing in the solution during the treatment
d) from 10 to 500 ppm, preferably from 10 to 250 ppm and better still between 30 and 100 ppm of at least one water-soluble dispersing polyelectrolyte having a molecular weight of less than 100,000, preferably from 500 to 10,000, in a proportion of 1 to 100 g per gram atom of zirconium, titanium or all of these two elements; and
e) possibly a pH regulating agent capable of fixing the pH to a value less than 6.

Among the acids, bases and salts of titanium and zirconium which can be used to prepare the aqueous acid solution according to the invention, there may be mentioned very particularly
With regard to titanium: H2TiF6, Na2TiF6, K2TiF6, (NH4) 2TiF6, TiOS04, Ti (S04) 2, Ti (OH) 4; and
Regarding zirconium: H2ZrF6, Na2ZrF6,
K2ZrF6, (NH4) 2ZrF6, Zr0S04, Zr (S04) 2, Zr (OH) 4, zirconium acetate, zirconium and ammonium carbonate.

 The titanium and / or zirconium are preferably provided in the form of soluble compounds, for example in the form of fluotitanic or fluozirconic acid or in the form of ammonium fluotitanates or fluozirconates or of an alkali metal such as lithium, sodium or potassium.

 Particularly advantageous results are obtained when the total concentration of titanium and / or zirconium in the solution at the time of use is of the order of 4.10 3 gram-atom per liter; this concentration is therefore preferred according to the invention.

 When the titanium and / or zirconium compounds used in the preparation of the solution according to the invention are insoluble in water or when such compounds are formed in the solution, the protective layer obtained is of poor quality , or even clearly bad. Consequently, the precipitation of insoluble compounds in the treatment solution should be avoided. To do this, complexing agents are used, that is to say compounds capable of complexing the titanium and / or zirconium ions in order to completely dissolve them. Among the compounds which can play this role, mention may be made of l hydrofluoric acid, fluorides, condensed phosphoric acids and condensed phosphates, hydrogen peroxide, gluconic, citric, lactic acids and their salts, ethylenediaminetetracic acid (EDTA) and its salts.

 The quantity of complexing agent having the role of solubilizing the insoluble titanium and / or zirconium salts introduced into the solution or liable to form therein must be such that perfect solubilization is obtained.

 During the treatment of an aluminum surface or an aluminum alloy with an aqueous acid solution, aluminum ions may appear and accumulate in the solution. To remedy this denial inconvenience, at least one agent complexing aluminum ions is preventively added to the solution, thus preventing the precipitation of aluminum compounds within the solution. Such an agent can be chosen in particular from hydrofluoric, gluconic, heptagluconic, ethylenediaminetetracetic acids and the salts of these acids.

Hydrofluoric acid and ammonium and alkali metal fluorides are preferred.

 The concentration of "free fluoride" ions thus added depends on the ratio of aluminum surface or aluminum alloy treated / volume of the bath. However, it is accepted that a concentration of "free fluoride" ions between 0.2 g / l and 1 g / l is necessary to ensure good stability of the bath with respect to the possible accumulation of aluminum ions . Insofar as one would also like to complex titanium and / or zirconium ions by means of "free fluoride" ions, it goes without saying that the proportion of these ions should be increased accordingly.

 The polyelectrolytes suitable according to the invention can belong to very different categories.

In particular, it has been found that good results can be obtained with polyelectrolytes of functional nature, whether cationic, nonionic or anionic.

These polyelectrolytes are generally chosen from polymers and copolymers derived from acrylic acid, polyamines, polyimines, polyvinyls, polymethacrylates and copolymers of maleic anhydride
Very good results are obtained with products of the acrylic acid polymer type such as those marketed for example under the brands CYANAxMER.
P 35 (polyacrylamide from the company American Cyanamid, from
Medium PM 8000), CYANAMER P 35 X (another polyacrylamide from the company American Cyanamid), GOODRITE K 732 (polyacrylic acid from the company Goodrich, of medium PM 5000) and GOODRITE K 739 (other polyacrylic acid from the company Goodrich).

 The solution according to the invention must in any event have a pH of less than 6 and preferably between 3.5 and 5. To adjust the pH to the desired value, recourse may be had, depending on the composition of the solution, to an acid or a base. Any acid or base not liable to interfere with the coating operation may be suitable for this purpose. However, use is preferably made of the use of nitric acid when the solution comprising the components a), b) and c) and the water has a too high pH, in particular greater than 6, or on the contrary to l ammonia when the pg of this solution is too acidic, especially when it is less than 3.5.

 The invention further provides a method for improving corrosion resistance and receptivity to organic primers of an aluminum or aluminum alloy surface, characterized in that it comprises the treatment of a such surface by the aqueous acid solution according to the invention.

More particularly, this process consists in subjecting said surface to successive treatments which consist in 10) degreasing with an alkaline detergent; 20) rinse with water 30) treat with the aqueous acid solution according to the invention
tion, 40) rinse with water 5) rinse with demineralized water.

The aqueous acid solution according to the invention can be applied to the surface to be treated by any conventional process such as in particular spraying, immersion and coating. However, the application of the spray solution has been found to be particularly suitable. In this case, one can for example operate by respecting the following sequences
10) degreasing the surface to be treated with a mildly alkaline detergent for 10 to 20 seconds, at a temperature of 30 to 550C
20) rinsing with tap water
30) spray treatment with the solution according to the invention for 5 to 30 seconds, at a temperature of 3 to 550C
40) rinsing with tap water; and
50) rinsing with demineralized water.

 As alkaline detergent, it is possible to use a product based on sodium hydroxide and surfactants suitable for the treatment of aluminum, for example the product marketed by the applicant under the brand name RIDOLINE 72.

 Although the surfaces treated by the general method described above, and even more so according to the particular method described above, already exhibit good corrosion resistance and good receptivity towards organic primers, their performance can be further improved. by subjecting them to a post-rinsing treatment applied for example after step No. 4 above with an aqueous acid solution containing the same active compounds, in the same proportions as the treatment solution according to the invention, but however at a concentration less, for example of the order of 10 times more diluted.

 The post-treatment solution may either correspond, as regards its composition of active compounds, to the solution used under 30) above, or else to any other solution according to the invention. This post-treatment step can be followed by rinsing with demineralized water.

 The invention further relates to an aqueous concentrate which, by dilution with water and optionally the addition of a pH regulating agent, leads to the solution according to the invention.

 It further relates, in the context of their application to the implementation of the invention, the various constituents of the above-mentioned concentrate taken alone or in partial mixtures, in the proportions imposed for the preparation of said concentrate.

 To remedy the exhaustion of the bath in its active constituents, it is added, when necessary, a quantity of concentrate sufficient to restore the desired proportions of active constituents.

 The following nonlimiting examples serve to illustrate the invention.

In these examples, the procedure is as follows:
Aluminum plates of AM1 grade are used (sold by the company Péchiney-Ugine-Kuhlmann and comprising more than 95% of aluminum, 1.2% of manganese and small amounts of silicon, iron and copper) and 20 x 10 cm format.

 The plates are cleaned by spraying under a pressure of 1 bar of a slightly alkaline detergent, for example that identified above, for 40 seconds, at 550C. They are then rinsed under running water for 10 seconds, then treated with the studied conversion solution. To do this, the solution concerned is sprayed, under 1 bar, on the plate to be treated for 20 seconds, at a temperature which depends on its particular composition.

 Then, the plate is rinsed with running water for 10 seconds, then with deionized water for 10 seconds and finally dried in an oven at 800C for 5 minutes.

The different treated plates are painted, under the same conditions, under a thickness of 20 p, with two types of paints, namely on the one hand
a paint based on polyesters, for example the beige paint marketed by the company ASTRAL under the reference 574, and on the other hand
- an acrylic paint, for example the blue paint sold by the company ASTRAL under the reference 365.

On each of the treated plates, then painted, three different tests are carried out, namely
- a physical adhesion test such as one of those known under the names of: grid test, conical mandrel and Erichsen;
- the accelerated corrosion test with copper-acetic acid or "cass-test", carried out according to standard ASTM B368 (on a plate with a cross wound); and
- the "salt spray" test carried out according to standard ASTM B117 (also on a plate with a cross wound).

Comparative example 1.

A conventional commercially available aqueous phosphating solution is used as the aluminum treatment solution. This solution has the following composition - monosodium phosphate: 8.1 g / l - sodium molybdate: 0.2 g / l - oxalic acid: 0.4 g / l - sodium bifluoride: 0.4 g / l - agent nonionic surfactant: 0.6 q / l
(CMULSOL NP 10, marketed by the
Rhone-Poulenc company) - anionic surfactant: 0.3 g / l
The nH of this solution is adjusted to 5.5 by sodium hydroxide and its temperature of use is between 45 and 50 C.

Comparative example 2.

 The standard treatment solution for aluminum used is a commercially available aqueous phospho-chromating solution which represents one of the solutions currently known as being the most effective.

This solution has the following composition - phosphoric acid at 75: 12.77 g / l - chromic acid: 3.5 g / l - hydrofluoric acid at 70%: 1.8 g / l - hydrogen peroxide at 30%: 0, 32 g / l
The temperature of this solution is 300C
Example 1.

 An aqueous acid solution according to the invention intended to produce, on the surface of the aluminum, an organic film containing titanium is used as the treatment solution for aluminum.

This solution has the following composition - fluotitanic acid at 60%: 2.0 g / l - ammonia at 260 Be: 8.1 g / l - GOODRITE K 732: 0.09g / l
The pH of this solution is 4.2 and its operating temperature is between 45 and 50 ° C.

Example 2.

 As the treatment solution for the aluminum, an aqueous acid solution according to the invention intended for producing, on the surface of the aluminum, an organic film containing zirconium is used.

This solution has the following composition - ammonium hexafluozirconate: 1.0 g / l - cyanamer P 35: 0.2 g / l - hydrofluoric acid at 70 X: 0.3 g / l
The pH of this solution is adjusted to 5 with ammonia and its temperature of use is between 45 and 50 ° C.

 The results obtained in the various examples above for a series of 5 plates for each paint color and each example are collated in the following Tables I and II TABLE I: Results of the tests carried out on the aluminum plates coated with beige paint based on polyesters.

salt spray "cass-test" tests
grip 72 h 1030 h
physical comparative example 1 7 1 1 comparative example 2 9 10 10 example 1 8 6 8 example 2 9 10 10
TABLE II: Results of tests carried out on aluminum plates coated with blue acrylic paint.

salt spray "cass-test" tests
grip 72 h 1000 h
physical comparative example 1 8 1 1 comparative example 2 9 10 9 example 1 9 10 6 example 2 10 10 10
The scores expressed in these tables are arbitrary scores set between 0 and 10 taking into account the results obtained for the following parameters - appearance of the coating at the level of the wound and in
full plate - tearing at the level of the wound - breakdown.

 The comparative examination of these tables shows that the solution according to the invention has an equivalent or even better efficiency than the phospho-chromating solution of comparative example 2 known as being one of the most effective currently on the market, without presenting the drawbacks linked in particular to the presence of hexavalent chromium.

 As goes without saying, and as it already follows from the above, the invention is in no way limited to those of its embodiments and of application which have been more especially envisaged; on the contrary, it embraces all its variants.

Claims (19)

 REV NDICA'rIONS  1. An aqueous acid solution of pH less than 6 for the treatment of an aluminum or aluminum alloy surface in order to improve its resistance to corrosion and its receptivity to organic primers, characterized in that it comprises, in addition to an effective amount of at least one compound chosen from the group consisting of acids, bases and salts comprising titanium or zirconium or these two elements simultaneously, as well as possibly at least one complexing agent for these compounds and at least one aluminum complexing agent, an amount of less than 500 ppm, preferably between 10 and 250 ppm, and better still between 30 and 100 ppm of at least one water-soluble dispersing polyelectrolyte, having a molecular weight less than 100,000, preferably from 500 to 10,000, in a proportion of 1 to 100 g per gram atom of zirconium, titanium or all of these two elements.  2. An aqueous acid solution according to claim 1, characterized in that it essentially comprises  a) at least one compound chosen from acids, bases and salts comprising titanium or zirconium or these two elements simultaneously in a proportion such that the total concentration of corresponding cations is between 4.10-5 and 2.10.2 gram-atom per liter;  b) insofar as insoluble titanium or zirconium compounds are used or are likely to form, at least one complexing agent for these compounds in a proportion making it possible to completely dissolve them;  c) at least one agent complexing aluminum ions capable of appearing in the solution during the treatment;  d) from 10 to 500 ppm, preferably from 10 to 250 ppm, and better still between 30 and 100 ppm of at least one dispersing polyelectrolyte, soluble in water, having a molecular weight of less than 100,000, preferably of 500 to 10,000, in a proportion of 1 to 100 g per gram atom of zirconium, titanium or of all of these two elements; and  e) possibly a pH regulating agent capable of fixing the pH to a value less than 6,  3. An aqueous acid solution according to claim 1 or 2, characterized in that its pH is between 3.5 and 5.  4. An aqueous acid solution according to one of claims 1 to 3, characterized in that the compound or compounds according to a) is or are chosen from the group consisting of H2TiF6, Na2TiF6, K2TiF6, (NH4) 2TiF6, TiOSO, Ti (SO) Tî (OH) 4, TiC14, H2ZrF6, Na2ZrF6 'K2ZrF6, (NH4) ZrF ZrOSO4, Zr (S04) 2, Zr (OH) 4, zirconium acetate and zirconium and ammonium carbonate.  5. An aqueous acid solution according to claim 4, characterized in that the compound or compounds according to a) is or are chosen from the group consisting of fluotitanic acid and fluozirconic acid or their ammonium salts or of alkali metals.  6. An aqueous acid solution according to one of claims 1 to 5, characterized in that the total concentration of titanium and zirconium is of the order of 4.10 3 atom-grams per liter.  7. An aqueous acid solution according to any one of claims 1 to 6, characterized in that the agent (s) complexing agent (s) of the titanium and zirconium ions is or are chosen from the group consisting of l hydrofluoric acid, fluorides, condensed phosphoric acids and their salts, hydrogen peroxide, gluconic, citric, lactic and ethylenediaminetetraacetic acids and their salts.  8. An aqueous acid solution according to one of claims 1 to 7, characterized in that the agent (s) complexing (s) of the aluminum ions is or are chosen (s) from the group consisting of hydrofluoric acids, gluconic, heptagluconic, ethylenediaminetetracetic and their salts.  9. An aqueous acid solution according to claim 8, characterized in that the agent (s) complexing (s) of aluminum ions is or are chosen) from the group consisting of hydrofluoric acid, ammonium fluoride and alkali metal fluorides.  10. Acid aqueous solution according to claim 9, characterized in that the concentration of added "free fluoride" ions is between 0.2 and 1.0 g / l,  11. An aqueous acid solution according to one of claims 1 to 10, characterized in that the water-soluble dispersing polyelectrolyte is a polymer of acrylic acid or its derivatives.  12.- Solution according to one of claims 1 to 11, characterized in that the pH regulating agent is nitric acid or ammonia, depending on the proper pH of the solution.  13.- A method for improving the corrosion resistance and the receptivity to organic primers of an aluminum or aluminum alloy surface, characterized in that it comprises the treatment of such a surface with the acid solution aqueous according to one of claims 1 to 12.  14.- Method according to claim 13, characterized in that it consists in subjecting said surface to successive treatments which consist in 10) degreasing with an alkaline detergent 2 ") rinsing with water 30) treating with the aqueous acid solution according to one of claims 1 to 12 40) rinse with water 50) rinse with demineralized water.  15.- Method according to claim 13 or 14, characterized in that the treatment with the aqueous acid solution is carried out by spraying, immersion or coating, preferably by spraying.  16.- Method according to one of claims 13 to 15, characterized in that it further comprises a post-rinse step by means of the aqueous acid solution used for the treatment, or of another solution according to one of claims 1 to 12, slightly diluted.  17. An aqueous concentrate which can be used to constitute an aqueous acid solution according to one of claims 1 to 12 by adding water and optionally a pH regulating agent.  18.- Application to the constitution of the concentrate according to claim 17 of the constituents thereof taken alone or in partial mixtures, in the proportions imposed for its preparation.  19.- Use of the aqueous acid solution according to one of claims 1 to 12 for the treatment of aluminum surfaces or aluminum alloys.