EP0575244B1 - 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 treatment aluminum-based substrates for anodizing.

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 application, in particular for the manufacture of frames.

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

At the end of this treatment, said parts and profiles are protected by an artificially formed Al ₂ O ₃ oxide layer; according to 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 micrometers.

• 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 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 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 profiles,
• a uniform, mat 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 sections are pickled to a thickness of approximately 30 microns, which corresponds to a weight loss of approximately 90 g / m ² .

To carry out the satin finishing step, we have already had use of alkaline baths containing a strong base, NaOH or KOH; this gives the substrate the mat appearance research. The shine of the substrate which reflects the state of "dullness" obtained and which is measured according to the ISO standard 7668, at 60 ° C., is between 35 and 70 after the step of satin finish and is between 5 and 13 after oxidation anodic; plus the figure obtained when measuring the the lower the gloss, the more matt the surface high.

In order to standardize the matt aspect of aluminum, it has been proposed to use for architectural application so-called permanent satin baths (without no emptying of the tanks) which balance at strong 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 in it for a period of approximately 15 to about 25 minutes depending on the desired mattness.

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

To increase the mattness 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 NaOH + Al + H ₂ O → NaAlO ₂ + 3/2 H ₂ makes the environment very reducing and causes the generation of ammonia from nitrates, resulting in air pollution and corrosion of facilities. This technique has therefore been generally abandoned.

Environmental protection requires, on the worldwide, as well as aqueous effluent discharges that solids are more and more weak; so we try to recycle used products and regenerate them as well than recovering non-regenerable waste.

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

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 AlO ₂ ^- + 2H ₂ O → Al (OH) ₃ + OH ^- the regenerated soda being recycled into the satin-finishing bath.

However, it is then necessary to work with dilute 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 (patent application European No. 0 104 821) to carry out the satin finishing step by using a bath consisting of an aqueous solution diluted hexafluorophosphoric acid which may contain nitric acid.

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

The invention therefore aims to provide a method and a bath of the kind in question which do not exhibit the disadvantages inherent in the prior art and thanks to which it is possible to impart excellent mattness treated substrates.

And the Applicant Company has had the merit of find that, unexpectedly and surprisingly, it became possible to obtain substrates with a 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 from then on that a bath is used for the satin-finishing step acid 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.

• jusqu'à 25% en poids d'acide chlorhydrique ou nitrique et
• de 1 à 25% en poids d'un acide minéral fluoré ou d'un de ses sels choisi de préférence dans le groupe constitué par HF, H₂SiF₆, HPF₆, HBF₄, K₂ZrF₆, K₂TiF₆, NH₄F, NH₄HF₂.

It is known, however, from document US-A-4 502 925, the use, in a treatment process, with a view to its anodization, of aluminum foil, which must be provided with a surface suitable for use of said sheet as part of a lithographic plate, of an acidic aqueous bath comprising

• up to 25% by weight of hydrochloric or nitric acid and
• from 1 to 25% by weight of a fluorinated mineral acid or a salt thereof preferably chosen from the group consisting of HF, H ₂ SiF ₆ , HPF ₆ , HBF ₄ , K ₂ ZrF ₆ , K ₂ TiF ₆ , NH ₄ F, NH ₄ HF ₂ .

It follows that the subject of the invention is the use, for the satin-finishing step, in a treatment process for the anodizing of parts and profiles of aluminum or one of its alloys used in application architectural, in particular for the manufacture of frames, of an acid bath comprising at least one of the compounds of the group comprising the fluometallic acids H ₂ TiF ₆ , H ₂ ZrF ₆ and H ₂ SiF _{6 as} well as their alkali salts or d ammonium at a concentration of at least 1 g / l and at least one of the acids of the group comprising nitric acid, sulfuric acid and phosphoric acid at a concentration of between 0.5 and 100 ml per liter of bath, expressed as concentrated commercial acid and advantageously non-ionic, anionic, cationic surfactants and third-party solvents.

According to an advantageous embodiment, 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 '' not more than 40 g / m ² of aluminum.

The bath according to the invention for the treatment, with a view to their anodization, of parts and profiles of aluminum or one of its alloys used in architectural application, in particular for the manufacture of frames, is characterized by the fact that it comprises at least one of the compounds from the group comprising the fluometallic acids H ₂ TiF ₆ , H ₂ ZrF ₆ and H ₂ SiF _{6 as} well as their alkali or ammonium salts at a concentration of at least 1 g / l and at least one of the acids from the group consisting of sulfuric and phosphoric acids at a concentration of between 0.5 and 100 ml per liter of bath, expressed as concentrated commercial acid and advantageously nonionic surfactants , anionic, cationic and third-party solvents.

The concentrate according to the invention which is capable of providing by dilution with water the bath according to the invention defined above, is characterized in that it contains at least one of the compounds of the group comprising fluometallic acids H ₂ TiF ₆ , H ₂ ZrF ₆ and H ₂ SiF _{6 as} well as their alkali or ammonium salts at a concentration of commercial product of between 50 and 99.5% and at least one acid from the group consisting of sulfuric and phosphoric acids at a concentration of commercial product of 0.5 to 50%.

Sulfuric and phosphoric acids have the advantage of being present on the anodic oxidation lines in the acid degreasing (H ₃ PO ₄ ), bleaching (HNO ₃ ) and anodic oxidation (H ₂ SO ₄ ) baths. ; 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.

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

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 / m ² of the substrate.

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

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

Third party solvents can for example be glycols.

The temperature of the satin-finishing bath is understood 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 / m ² , 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 in accordance with the invention, a complementary light alkaline pickling carried out according to a process in itself known and such that it leads to pickling of at most 40 g / m ² 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, possibly 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 marketed by the Applicant Company under the PROGAL G 313 TA brand.

The alkaline pickling bath thus formed is put 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. using the following nonlimiting examples and in which are described advantageous embodiments of the invention.

EXAMPLE 1

Aluminum profiles, reference 6063 according to ISO standard 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, Stage 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). Bath No. Chemical composition of pickling baths Fluorinated product Complementary acid b1 H ₂ TiF ₆ at 60%: 40 g / l H ₂ SO ₄ at 98% = 3 ml b2 H ₂ ZrF ₆ at 45%: 68 g / l " b3 H ₂ SiF ₆ at 34%: 63 g / l " b4 50% HF: 35.5 g / l " b5 HPF ₆ at 60%: 36 g / l " b6 HBF ₄ 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 / m ² .

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

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 / m ² .

• 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 b7 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 / m ² , comparable to the cumulative of acid and alkaline pickling. 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 / m ² of aluminum.

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

We know, and this point is confirmed by experiments using baths b7 and b8, it suffices to increase the pickling rate in the satin-finishing bath alkaline to reduce shine.

It follows from Table II that with an overall pickling rate of between 40 and 50 g / m ² obtained by using a bath in accordance with the invention followed by a conventional alkaline satin-finishing bath, the gloss measured according to the ISO 7668 standard (at 60 °) on the profiles after bleaching is lower than that obtained in the experiment using the b8 bath (prior art) for conventional pickling rates of the order of 80-90 g / m ² . 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 bath based on HBF ₄ (b6) which also gives a better shine-must be discarded since it requires a time of action incompatible with industrial use, this time being greater than 1 hour 10 minutes then that all of the experiments carried out with the 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 HPF ₆ (b5) give poor results.

EXAMPLE 2

6063 series 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. Bath No. Chemical composition of pickling baths Fluorinated product Complementary acid b1 H ₂ TiF ₆ at 60% = 25 ml / l 98% H ₂ SO ₄ = 5.4 g / l b9 " 35% HCl = 11.5 g / l b10 " HNO ₃ at 60% = 11.5 g / l b11 " H ₃ PO ₄ at 75% = 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 / m ² . These baths are used respectively to carry out experiments 1 and 9 to 14, the results of which are collated in Table IV. Exp. No. Acid pickling rate Alkaline satin finish Overall stripping rate Shine after step 8 Observation 1 24 g / m ² 16 g / m ² 40 g / m ² 18 9 27 g / m ² 23 g / m ² 50 g / m ² 24 Sharp appearance of the aluminum surface 10 17 g / m ² 27 g / m ² 44 g / m ² 12 11 22 g / m ² 26 g / m ² 48 g / m ² 26 12 30 g / m ² 27 g / m ² 57 g / m ² 47 13 25 g / m ² 26 g / m ² 51 g / m ² 58 14 25 g / m ² 25 g / m ² 50 g / m ² 51

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

Organic acids do not provide conditions described above, a noticeable improvement 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 K ₂ TiF _{6 as} well as the temperature and by examining the influence of these variations on the pickling speed of aluminum parts.

The time required to obtain a pickling rate of approximately 24 g / m ^{2 was determined} for each of the K ₂ TiF ₆ concentrations and for each of the temperatures chosen, the 98% sulfuric acid concentration being 3 ml / l .

The results are collated in Table V. K ₂ TiF ₆ Temperature Time required to have a pickling rate of approximately 24 g / m ² 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 concentration of K ₂ TiF ₆ and the temperature. A good compromise for industrial use of the process according to the invention is a concentration of K ₂ TiF ₆ of between 22 and 57 ml / l and a temperature of between 20 and 40 ° C.

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

EXAMPLE 4

We treat aluminum profiles by proceeding as in Example 1, except for steps 5, 6, 7 and 8 which are omitted.

The acid pickling bath (step 3) used is constituted by the bath bl described in Example 1. Sa working temperature is 30 ° C and soaking time is 15 minutes.

The mattness of the profiles, measured after step 4 according to ISO 7668 (60 °) is 22; this dullness is comparable to that obtained in the experiments carried out with baths b1 to b3 of Example 1 and clearly 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 clearly improved compared to the dullness measured in the same conditions according to experiment 8 of example 1 and which industrially located at 12-15.

Claims (4)

1. Use, for the chemical etching step, in a process of treatment for anodisation of elements and profiles made of aluminum or of one of its alloys for architectural uses, particularly for the manufacture of door or window frames, of an acid bath comprising at least one of the compounds of the group comprising the fluometallic acids H₂TiF₆, H₂ZrF₆, H₂SiF₆ and their alkaline or ammonium salts at a concentration of at least 1 g/l and at least one of the acids selected from the group consisting of nitric acid, sulfuric acid and phosphoric acid at a concentration comprised between 0.5 and 100 ml per litre of bath, expressed in commercial concentrated acid, and advantageously nonionic, anionic or cationic surfactive agents and co-solvents.
2. Chemical etching bath for treating, for the purpose of their anodisation, of elements and profiles made of aluminum or of one of its alloys for architectural uses, particularly for the manufacture of door or window frames, characterized by the fact that it comprises at least one of the compounds of the group comprising the fluometallic acids H₂TiF₆, H₂ZrF₆, H₂SiF₆ and their alkaline or ammonium salts at a concentration of at least 1 g/l and at least one of the acids selected from the group consisting of nitric acid, sulfuric acid and phosphoric acid at a concentration comprised between 0.5 and 100 ml per litre of bath, expressed in commercial concentrated acid, and advantageously nonionic, anionic or cationic surfactive agents and co-solvents.
3. Concentrate capable to provide by dilution with water the bath according to claim 2, characterized by the fact that it contains at least one of the compounds of the group comprising the fluometallic acids H₂TiF₆, H₂ZrF₆, H₂SiF₆ and their alkaline or ammonium salts at a concentration, expressed with respect to the commercial product, comprised between from 50 and 99.5% and at least one acid of the group consisting of sulphuric and phosphoric acids at a concentration, expressed with respect to the commercial product, of from 0.5 to 50%.
4. Concentrate capable to provide by dilution with water and with one of the sulphuric and phosphoric acids, the bath according to claim 2, characterized by the fact that it contains at least one of the compounds selected from the group comprising the fluometallic acids H₂TiF₆, H₂ZrF₆, H₂SiF₆ and their alkaline or ammonium salts at a concentration, expressed with respect to the commercial product, comprised between 50 and 99.5%.