EP0575244A1 - Process for treating aluminium-based substrates before their anodisation, bath used in this process and concentrate for preparing this bath - Google Patents

Abstract

Process for treating aluminium-based substrates with a view to their anodic oxidation, characterised in that it contains a surface treatment or satining (enamelling, surfacing, glazing) stage using an acid bath comprising at least one fluorinated derivative of titanium and/or of zirconium and/or of silicon and at least one acid of the group comprising nitric, sulphuric and phosphoric acids.

Description

The subject of the invention is a method of treating aluminum-based substrates with a view to their anodization.

It also relates to a bath used in this process as well as a concentrate for the preparation of the bath.

Substrates, i.e. parts and profiles based on aluminum, in other words aluminum or one of its alloys, are used in industry and in particular in architectural applications, in particular for manufacturing doorframes.

To protect them during their use, the above-mentioned parts and profiles can be painted or be subjected to an electrolytic anodizing treatment of aluminum in an acid medium.

After this treatment, said parts and profiles are protected by an artificially formed Al₂O d'oxide layer; depending on the desired degree of protection which is a function of the use of the parts inside or outside, the alumina layer can be more or less thick; its thickness is generally between 2 and 30 microns.

• une étape de dégraissage généralement en milieu alcalin pour éliminer les souillures organiques, étant toutefois noté que des dégraissages faisant intervenir l'acide phosphorique sont parfois utilisés,
• une étape de rinçage à l'eau courante froide,
• une étape de traitement chimique de surface ou satinage pour gommer les défauts de surface des pièces et pour conférer à l'aluminium un aspect généralement non brillant,
• une ou plusieurs étapes de rinçage en eau froide,
• une étape de blanchiment acide généralement à l'aide d'acide nitrique,
• une ou plusieurs étapes de rinçage en eau froide,
• l'oxydation anodique proprement dite, souvent réalisée dans le cas des applications architecturales à l'aide d'une solution à base d'acide sulfurique,
• une ou plusieurs étapes de rinçage d'abord en eau courante puis en eau déminéralisée,
• une étape dite de colmatage servant à fermer les pores créés par l'oxydation anodique.

Anodic oxidation or anodization constitutes one of the stages of a sequence generally comprising:

• a degreasing step generally in an alkaline medium in order to remove organic stains, it being noted however that degreasing involving phosphoric acid is sometimes used,
• a rinsing step with cold running water,
• a step of chemical surface treatment or satin-finishing to erase the surface defects of the parts and to give the aluminum a generally non-shiny appearance,
• one or more rinsing steps in cold water,
• an acid bleaching step generally using nitric acid,
• one or more rinsing steps in cold water,
• the anodic oxidation proper, often carried out in the case of architectural applications using a solution based on sulfuric acid,
• one or more rinsing steps first in running water then in demineralized water,
• a so-called clogging step used to close the pores created by anodic oxidation.

• la suppression des traits de filage liés au passage des profilés dans des filières plus ou moins âgées,
• la suppression des zones de ségrégation cristalline, notamment dans le cas de profilés creux,
• un aspect uniforme mat et reproductible en fin de traitement.

The characteristics of the protection conferred on aluminum substrates depend essentially on the anodic oxidation and the following stages; on the other hand, the appearance of the substrate depends on the steps preceding the anodic oxidation, these steps aiming to achieve:

• the elimination of the spinning lines linked to the passage of the profiles in more or less old dies,
• the elimination of crystalline segregation zones, in particular in the case of hollow sections,
• a uniform matte and reproducible appearance at the end of treatment.

To do this, the steps preceding the anodic oxidation include the so-called satin-finishing step producing a pickling which consists in removing the surface layer from the substrates; in practice, the treated parts or profiles are pickled to a thickness of approximately 30 microns, which corresponds to a weight loss of approximately 90 g / m².

To carry out the satin-finishing step, alkaline baths containing a strong base, NaOH or KOH have already been used; the desired mat appearance is thus given to the substrate. The gloss of the substrate which reflects the state of "dullness" obtained and which is measured according to ISO standard 7668, at 60 ° C., is between 35 and 70 after the satin-finishing step and is between 5 and 13 after 1 'oxidation anodic; the lower the figure obtained when measuring the gloss, the higher the dullness of the surface.

In order to standardize the matt appearance of aluminum, it has been proposed to use for architectural application so-called permanent satin-finishing baths (without any emptying of the tanks) which are balanced at high free soda contents ( between 80 and 120 g / l) and aluminum (between 120 and 180 g / l). These baths are at a temperature between 50 and 70 ° C; the substrates are immersed therein for a period of about 15 to about 25 minutes depending on the desired mattness.

To keep the concentrated aluminum salts in solution, complexing agents such as gluconate are added to the above baths.

rend le milieu très réducteur et entraîne la génération d'ammoniac à partir des nitrates, d'où une pollution aérienne ainsi qu'une corrosion des installations. Cette technique a donc été généralement abandonnée.To increase the dullness of the treated parts without increasing the pickling thickness, it has been proposed to add nitrogenous derivatives such as, for example, nitrates to the satin-finishing bath; however, it turns out that the evolution of hydrogen generated by the aluminum attack reaction $$\text{NaOH + Al + H₂O → NaAlO₂ + 3/2 H₂}$$

makes the medium very reducing and leads to the generation of ammonia from nitrates, resulting in air pollution and corrosion of the installations. This technique has therefore been generally abandoned.

Environmental protection means that, on a global level, discharges of both aqueous and solid effluents are increasingly low; we therefore try to recycle used products and regenerate them as well as recover non-regenerable waste.

With regard to solid discharges, landfill becomes more and more difficult due to the filling of the latter and it therefore appears necessary to minimize, in the context of the surface preparation of aluminum before anodic oxidation , the chemical attacks related to satin-finishing in order to subsequently minimize aluminum hydroxide sludge from neutralization of bath effluents.

la soude régénérée étant recyclée dans le bain de satinage.To reduce the amounts of sludge, it has been proposed to use baths without adding organic complexing agents; the advantage of these baths is to facilitate the precipitation of aluminum hydroxide and therefore the regeneration of soda according to the equation $$\text{AlO₂⁻ + 2H₂O → Al (OH) ₃ + OH⁻}$$

the regenerated soda being recycled into the satin-finishing bath.

However, it is then necessary to work with diluted satin-finishing baths (approximately 10 g / l of free sodium hydroxide and 12 g / l of dissolved aluminum), the precipitation reaction can be carried out in an annex installation; however, the risk of precipitation of Al (HO) ₃ in the working tank remains great, with the consequence of stopping production and cleaning the tank.

It has also been proposed (European patent application No. 0 104 821) to carry out the satin-finishing step by using a bath consisting of a dilute aqueous solution of hexafluorophosphoric acid which may contain nitric acid.

However, the dullness of the substrates thus treated is poor.

The invention therefore aims to provide a method and a bath of the kind in question which do not have the drawbacks inherent in the prior art and by which it is possible to impart excellent dullness to the treated substrates.

And the Applicant Company had the merit of finding that, unexpectedly and surprisingly, it became possible to obtain substrates having an excellent mattness and appearance without risk of exploitation and while reducing the amount of alkaline releases ( soda and aluminate) as well as the pickling thickness that an acid bath comprising at least one fluorinated derivative of titanium and / or zirconium and / or silicon is used for the satin-finishing step, as well as at least one acid from the group comprising nitric acids, sulfuric and phosphoric.

It follows that the method according to the invention for treating aluminum-based substrates with a view to their anodization is characterized by the fact that it comprises a surface treatment or satin-finishing step using an acid bath comprising at least one fluorinated derivative of titanium and / or zirconium and / or silicon as well as at least one acid from the group comprising nitric, sulfuric and phosphoric acids.

According to an advantageous embodiment of the above process, the satin-finishing step using the acid bath is followed by a complementary light satin-finishing step using an alkaline bath, the conditions of this satin-finishing being such that it leads to pickling of up to 40 g / m² of aluminum.

The bath according to the invention for the treatment of aluminum-based substrates with a view to their anodization is characterized in that it comprises at least one fluorinated derivative of titanium and / or zirconium and / or silicon as well as '' at least one acid from the group comprising nitric, sulfuric and phosphoric acids.

The concentrate according to the invention which is capable of providing by dilution with water the bath according to the invention can contain the fluorinated derivative of titanium and / or zirconium and / or silicon in a concentration of commercial product of 50 to 99.5% and the acid of the group comprising nitric, sulfuric and phosphoric acids at a concentration of commercial product of 0.5 to 50%.

Nitric, sulfuric and phosphoric acids have the advantage of being present on the anodic oxidation lines in acid degreasing (H₃PO₄), bleaching (HNO₃) and anodic oxidation baths. (H₂SO₄); they can also be regenerated from these baths by already known methods (ion exchange resins for example); they can also be used directly in the acid pickling bath if their pollution rate allows, which is the case in the context of the present invention.

Taking into account this possibility of recycling nitric, sulfuric or phosphoric acids, a concentrate according to the invention suitable for supplying the bath according to the invention after dilution with water and recycled acid can comprise, in addition to water, a fluorinated derivative of titanium and / or zirconium and / or silicon at a concentration of commercial product of between 50 and 99.5%.

Such a concentrate can be diluted in water to a concentration of between 1 per thousand and 10% to constitute the ready-to-use bath.

According to one embodiment of the satin-finishing bath in accordance with the invention used in the process in accordance with the invention, the fluorinated derivative of titanium, zirconium or silicon is chosen from the group comprising the fluometallic acids H₂TiF₆, H₂ZrF₆, H₂SiF₆, as well as their alkali or ammonium salts.

According to another advantageous embodiment, the pickling bath according to the invention comprises the fluorinated derivative of titanium and / or zirconium and / or silicon at a concentration of at least 1 g / l, and nitric acid and / or sulfuric and / or phosphoric at a concentration between 0.5 and 100 ml per liter of bath, expressed as concentrated commercial acid.

The above concentrations as well as the duration and the temperature of the satin-finishing step are adjusted so as to obtain a pickling rate of at least 5 g / m² of the substrate.

To optimize the degreasing step or possibly eliminate it, you can add to the satin-finishing bath or to the concentrate of nonionic, anionic or cationic surfactants and "third solvents".

The surfactants in question can be chosen from the group comprising alkylphenols, alcohols and polyalkoxylated amines, alkyl-, alkylaryl- and arylsulfates, sulfonates, phosphates and quaternary ammoniums.

The third solvents can for example be glycols.

The temperature of the satin-finishing bath is between 15 ° C and 80 ° C and, preferably, between 20 and 60 ° C.

The time during which the action of the bath is maintained, time which depends on the concentration and the temperature and which must be sufficient to result in a pickling of at least 5 g / m², is between 1 minute and 1 hour. For productivity reasons, the processing time in industry will preferably not exceed about thirty minutes.

It is advantageous to provide, following the acid pickling according to the invention, a complementary light alkaline pickling carried out according to a process known per se and such that it leads to pickling of at most 40 g / m² d 'aluminum; one can, for example, use a bath having a temperature between 40 and 70 ° C and containing, on the one hand, between 10 and 180 g / l of aluminum (i.e. between 30 and 550 g / l of sodium aluminate), on the other hand, between 10 and 150 g / l of free sodium hydroxide and, on the other hand, optionally additives intended to keep the aluminum in solution in the case of high contents, such as example of organic complexing agents such as gluconate and sorbitol.

Such an additive which is based on gluconate can be that sold by the Applicant Company under the brand PROGAL G 313 TA.

The alkaline pickling bath thus formed is used for a period of 2 to 20 minutes on the parts coming out of the acid pickling bath.

The invention can be understood even better with the aid of the nonlimiting examples below and in which advantageous embodiments of the invention are described.

EXAMPLE 1

Etape 1 :

Dégraissage sodique aqueux dans une solution aqueuse à 100 g/l d'IPRO 77 AP commercialisé par la Société Demanderesse,

Etape 2 :

Rinçage froid à l'eau courante,

Etape 3 :

Décapage (satinage) acide (voir les 8 expériences comparatives dont les caractéristiques résultent du Tableau I),

Etape 4 :

Rinçage froid à l'eau courante,

Etape 5 :

Décapage (satinage) alcalin avec un bain ayant les caractéristiques indiquées plus loin,

Etape 6 :

Rinçage froid à l'eau courante,

Etape 7 :

Blanchiment nitrique dans un bain à 180 g/l d'acide nitrique concentré dans l'eau,

Etape 8 :

Rinçage froid à l'eau courante,

Etape 9 :

Oxydation anodique sulfurique dans un bain à 180 g/l d'acide sulfurique concentré (température 18°C),

Etape 10:

Rinçage froid à l'eau courante,

Etape 11:

Rinçage dans de l'eau déminéralisée,

Etape 12:

Colmatage à l'eau déminéralisée chaude (98°C).

TABLEAU I Bain N° Composition chimique des bains de décapage Produit fluoré Acide complémentaire b1 H₂TiF₆ à 60% : 40 g/l H₂SO₄ à 98% = 3 ml b2 H₂ZrF₆ à 45% : 68 g/l " b3 H₂SiF₆ à 34% : 63 g/l " b4 HF   à 50% : 35,5 g/l " b5 HPF₆  à 60% : 36 g/l " b6 HBF₄  à 50% : 26 g/l " b7 et b8 Eau pure - Aluminum profiles, reference 6063 according to ISO 209, are treated as follows:

Step 1 :

Aqueous sodium degreasing in an aqueous solution at 100 g / l of IPRO 77 AP marketed by the Applicant Company,

2nd step :

Cold rinse with running water,

Step 3:

Pickling (satin) acid (see the 8 comparative experiments whose characteristics result from Table I),

Step 4:

Cold rinse with running water,

Step 5:

Alkaline pickling (satin finishing) with a bath having the characteristics indicated below,

Step 6:

Cold rinse with running water,

Step 7:

Nitric bleaching in a 180 g / l bath of concentrated nitric acid in water,

Step 8:

Cold rinse with running water,

Step 9:

Anodic sulfuric oxidation in a bath with 180 g / l of concentrated sulfuric acid (temperature 18 ° C),

Step 10:

Cold rinse with running water,

Step 11:

Rinsing in demineralized water,

Step 12:

Clogging with hot demineralized water (98 ° C).

TABLE I Bath No. Chemical composition of pickling baths Fluorinated product Complementary acid b1 H₂TiF₆ at 60%: 40 g / l 98% H₂SO₄ = 3 ml b2 45% H₂ZrF₆: 68 g / l " b3 H₂SiFi at 34%: 63 g / l " b4 50% HF: 35.5 g / l " b5 HPF₆ at 60%: 36 g / l " b6 HBF₄ at 50%: 26 g / l " b7 and b8 Pure water -

The temperature of the acid pickling bath is 30 ° C.

The treatment time is chosen to have a pickling of approximately 25 g / m².

We therefore carried out 8 comparative experiments using successively baths b1 and b8.

soude libre

environ 100 g/l

aluminium

environ 140 g/l

température

60°C.

Step 5 uses a permanent satin-finishing bath, the characteristics of which are:

free soda

about 100 g / l

aluminum

about 140 g / l

temperature

60 ° C.

The treatment time in this bath and when the acid pickling baths are those called b1 to b6, is that necessary to have a pickling rate of approximately 25 g / m².

• . ainsi dans l'expérience mettant en oeuvre le bain b7, on maintient l'action du bain alcalin de l'étape 5 pendant un temps suffisant pour obtenir un décapage d'environ 50 g/m², comparable au cumul des décapages acide et alcalin des expériences 1 à 6, et
• . dans l'expérience mettant en oeuvre le bain b8, on procède selon la pratique actuelle sur les lignes d'oxydation anodique de l'aluminium, à savoir un satinage alcalin classique d'environ 18 à 20 minutes qui se traduit par un décapage d'environ 80 à 90 g/m² d'aluminium.

This time is not respected for the control experiments using baths b1 and b8:

• . thus in the experiment using bath b7, the action of the alkaline bath of step 5 is maintained for a time sufficient to obtain a pickling of approximately 50 g / m², comparable to the cumulative acid pickling. and alkaline from experiments 1 to 6, and
• . in the experiment using bath b8, the procedure is carried out according to current practice on the anodic oxidation lines of aluminum, namely a conventional alkaline satin-finish of approximately 18 to 20 minutes which results in a pickling of about 80 to 90 g / m² of aluminum.

The results recorded are collated in Table II. TABLE II Exp. No. Acid pickling rate Alkaline satin finish Overall pickling rate Shine after step 8 Observation 1 24 g / m² 16 g / m² 40 g / m² 18 Correct appearance of aluminum 2 30 g / m² 17 g / m² 47 g / m² 28 Formation of a blackish deposit after presatinage which is eliminated in the alkaline stage 3 19 g / m² 23 g / m² 42 g / m² 36 Correct appearance of aluminum 4 26 g / m² 20 g / m² 46 g / m² 68 Correct appearance of aluminum 5 22 g / m² 21 g / m² 43 g / m² 56 Formation of a blackish deposit after presatinage which is eliminated in the alkaline stage 6 20 g / m² 21 g / m² 41 g / m² 30 Correct appearance of aluminum 7 - 51 g / m² 59 g / m² 53 Reference to comparable stripping rate 8 - 86 g / m² 86 g / m² 40 Current practical reference

It is known, and this point is confirmed by the experiments using the baths b7 and b8, that it suffices to increase the rate of pickling in the alkaline satin-finishing bath to reduce the gloss.

It results from Table II that with an overall pickling rate of between 40 and 50 g / m² obtained by using a bath in accordance with the invention followed by a conventional alkaline satin-finishing bath, the gloss measured according to the standard ISO 7668 (at 60 °) on the profiles after bleaching is lower than that obtained in the experiment using the b8 bath (prior art) for rates conventional pickling in the range of 80-90 g / m². The appearance of the parts obtained with the process according to the invention is comparable, or even better than that of the parts obtained with the alkaline process alone, and this for an overall pickling rate less than half. The experiment involving the HBF₄-based bath (b6), which also gives better shine, should be discarded because it requires an action time incompatible with industrial use, this time being greater than 1 hour 10 minutes while the all the experiments carried out with baths b1 to b5 were carried out with the parts being soaked for not more than 40 minutes in the acid pickling bath.

Baths based on HF (b4) and HPF₆ (b5) give poor results.

EXAMPLE 2

Series 6063 aluminum profiles are treated as shown in Example 1.

For step 3, the baths b1 and b9 to b14 defined in Table III are used. TABLE III Bath No. Chemical composition of pickling baths Fluorinated product Complementary acid b1 H₂TiF₆ at 60% = 25 ml / l 98% H₂SO₄ = 5.4 g / l b9 " 35% HCl = 11.5 g / l b10 " 60% HNO₃ = 11.5 g / l b11 " 75% H₃PO₄ = 7.2 g / l b12 " oxalic acid = 7.1 g / l b13 " sulfamic acid = 10.7 g / l b14 " citric acid = 10.5 g / l

Baths b1 and b9 to b14 are used at 30 ° C and for the time necessary to cause the treated parts to lose weight in the order of 25 g / m². These baths are used respectively to carry out the Experiments 1 and 9 to 14, the results of which are collated in Table IV. TABLE IV Exp. No. Acid pickling rate Alkaline satin finish Overall pickling rate Shine after step 8 Observation 1 24 g / m² 16 g / m² 40 g / m² 18 9 27 g / m² 23 g / m² 50 g / m² 24 Sharp appearance of the aluminum surface 10 17 g / m² 27 g / m² 44 g / m² 12 11 22 g / m² 26 g / m² 48 g / m² 26 12 30 g / m² 27 g / m² 57 g / m² 47 13 25 g / m² 26 g / m² 51 g / m² 58 14 25 g / m² 25 g / m² 50 g / m² 51

The greatest efficiency is obtained with baths based on sulfuric, nitric and phosphoric acids. Hydrochloric acid induces appearance defects.

Organic acids do not bring, under the conditions described above, a significant improvement in dullness.

EXAMPLE 3

Series 6063 aluminum profiles are treated by proceeding as in Example 1, but by varying in step 3 the concentration of potassium fluorotitanate K₂TiF₆ as well as the temperature and by examining the influence of these variations on the speed of pickling of aluminum parts.

The time required to obtain a pickling rate of approximately 24 g / m² was determined for each of the K₂TiF₆ concentrations and for each of the temperatures selected, the 98% sulfuric acid concentration being 3 ml / l.

The results are collated in Table V. TABLE V K₂TiF₆ Temperature Time required to have a pickling rate of approximately 24 g / m² 0.9 g / l 30 ° C 400 minutes 60 ° C 66 minutes 80 ° C 26 minutes 22 g / l 20 ° C 29 minutes 30 ° C 15 minutes 40 ° C 8 minutes 60 ° C 3 minutes 80 ° C 1 minute 57 g / l 20 ° C 18 minutes 30 ° C 6 minutes 60 ° C 1 minute 88 g / l 20 ° C 6 minutes 30 ° C 1 minute

On examination of Table V, it appears that the speed of pickling of aluminum depends on both the K₂TiF₆ concentration and the temperature. A good compromise for industrial use of the process according to the invention is a K₂TiF₆ concentration of between 22 and 57 ml / l and a temperature of between 20 and 40 ° C.

The processing time is then between six minutes and about thirty minutes, time easily manageable on a production line.

EXAMPLE 4

Aluminum profiles are treated in the same way as in Example 1, with the exception of steps 5, 6, 7 and 8 which are omitted.

The acid pickling bath (step 3) used consists of the bath bl described in example 1. Its working temperature is 30 ° C. and the soaking time is 15 minutes.

The mattness of the profiles, measured after step 4 according to ISO standard 7668 (at 60 °) is 22; this mattness is comparable to that obtained in the experiments carried out with baths b1 to b3 of Example 1 and significantly improved compared to that obtained in the experiments carried out with the control baths b7 and b8 of Example 1.

In addition, the dullness, measured according to the same method at the end of step 12, is 5, that is to say markedly improved compared to the dullness measured under the same conditions according to experiment 8 of Example 1 and which is industrially 12-15.

Claims (9)

Process for treating aluminum-based substrates with a view to their anodization, characterized in that it comprises a surface treatment or satin-finishing step using an acid bath comprising at least one fluorinated derivative of titanium and / or zirconium and / or silicon as well as at least one acid from the group comprising nitric, sulfuric and phosphoric acids. Satin bath for the treatment of aluminum-based substrates for their anodization, characterized in that it comprises at least one fluorinated derivative of titanium and / or zirconium and / or silicon as well as at least one acid from the group comprising nitric, sulfuric and phosphoric acids. Concentrate suitable for supplying by dilution with water the bath according to claim 2, characterized in that it contains a fluorinated derivative of titanium and / or zirconium and / or silicon in a concentration of commercial product of 50 to 99.5% and an acid from the group comprising nitric, sulfuric and phosphoric acids at a concentration of commercial product of 0.5 to 50%. Concentrate suitable for supplying, by dilution with water and one of the nitric, sulfuric and phosphoric acids, the bath according to claim 2, characterized in that it contains a fluorinated derivative of titanium and / or zirconium and / or silicon at a concentration of commercial product of between 50 and 99.5%. Process according to Claim 1, characterized in that the temperature of the satin-finishing bath is between 15 and 80 ° C, preferably between 20 and 60 ° C and that the period during which the action of the bath is maintained is between 1 minute and 1 hour, preferably less than about thirty minutes. Method according to one of claims 1 or 5, characterized in that the satin-finishing step using the acid bath is followed by a satin-finishing step light alkaline supplement using a poorly concentrated alkaline bath. Satin bath according to claim 2 and intended to be used in the process according to one of claims 1, 5 or 6, characterized in that the fluorinated derivative of titanium, zirconium or silicon is chosen from the group comprising fluometallic acids H₂TiF₆, H₂ZrF₆, H₂SiF₆, as well as their alkali or ammonium salts. Bath according to claim 7, characterized in that it comprises the fluorinated derivative of titanium and / or zirconium and / or silicon at a concentration of at least 1 g / l, and nitric and / or sulfuric acid and / or phosphoric at a concentration of between 0.5 and 100 ml per liter of bath, expressed as concentrated commercial acid. Bath according to one of claims 2, 7 or 8, characterized in that it comprises nonionic, anionic, cationic surfactants and third solvents.