EP3449040B1 - Composition for reducing the removal of material by pickling in the pickling of metal surfaces that contain galvanized and/or ungalvanized steel - Google Patents

Description

The invention relates to an aqueous composition for reducing the pickling removal when pickling metallic surfaces containing bright and / or galvanized steel and a method for pickling a corresponding metallic surface with reduced pickling removal.

Atmospheric corrosion or during heat treatment (e.g. heat development during forming or welding) of iron and steel create scale and rust layers on the metal surface. Pickling refers to the dissolution of these oxide layers in mineral acid solutions in order to achieve a clean metallic surface for further processing.

This essentially serves to remove oxide films from rust - FeO, Fe ₂ O ₃ , Fe ₃ O ₄ and iron oxide hydrates - or zinc oxide from the surface, which in turn increases the adhesive strength and uniformity of subsequent coatings, in particular a conversion coating, on the surface.

Here, however, there is the problem that excessive pickling attack not only removes the oxide film from the surface, but also attacks the metallic surface itself, so that iron (II), iron (III) ions or zinc ions in due to proton-induced oxidation Go solution (anodic metal dissolution). In other words: pickling of the metallic surface occurs.

For example, when pickling a steel surface using a solution containing sulfuric acid, the following reactions occur:

FeO + H ₂ SO ₄ → FeSO ₄ + H ₂ O (1)

Fe ₃ O ₄ + 4 H ₂ SO ₄ → Fe ₂ (SO ₄ ) ₃ + FeSO ₄ + 4 H ₂ O (2)

Fe ₂ O ₃ + 3 H ₂ SO ₄ → Fe ₂ (SO ₄ ) ₃ + 3 H ₂ O (3)

Fe + H ₂ SO ₄ → FeSO ₄ + 2 H · (briefly on the metal surface) (4)

Fe + H ₂ SO ₄ → FeSO ₄ + H ₂ ↑ (5)

The atomic hydrogen (H ·) which develops in accordance with equation (4) is preferably absorbed on iron, penetrates into the crystal lattice and combines there to form hydrogen molecules (H ₂ ). The pressures generated by the hydrogen gas deteriorate the mechanical properties of the metal. One also speaks of "hydrogen embrittlement". This embrittlement is irreversible and can lead to cracks or pickling bubbles. The decisive factor for the extent of embrittlement is the amount of hydrogen developed during pickling removal.

Due to excessive pickling removal and, above all, the cracks and pickling bubbles formed due to the pickling hydrogen embrittlement, the metallic surface receives an uneven morphology, which is transferred to subsequent coatings to the extent that they also have a certain unevenness. This in turn leads to a reduction in the adhesive strength of the coatings and in the corrosion protection they produce.

Various compounds are known from the prior art, for example alkali metal alkoxylates or thiodiglycolate alkoxylates, which act as pickling inhibitors, i.e. reduce the pickling removal.

With regard to the quality of subsequent conversion treatments, it has been shown that the use of pickling inhibitors is desirable which have an inhibition value (= reduction in pickling removal based on a corresponding pickling without pickling inhibitor) of over 95 percent, and the aforementioned pickling inhibitors from the prior art Technology do not have such high values.

Only N, N'-diethylthiourea and mixtures of N, N'-di (o-tolyl) thiourea, N, N'-dibutylthiourea and hexamethylenetetraamine give satisfactory results due to an inhibition value of 96 percent each.

However, the use of N, N'-diethylthiourea is increasingly undesirable since this is very questionable from a toxicological and environmental point of view.

The use of a mixture of N, N'-di (o-tolyl) thiourea, N, N'-dibutylthiourea and hexamethylenetetraamine is based on the REACH regulation (European regulation "R egistration, E valuation, A uthorisation and Restriction of Ch emicals"), however, no longer possible.

Each of the pamphlets FR 1 475 895 A , US 2009/032057 A1 , FR 2 158 664 A5 , US 3,310,497 A. , DE 25 07 059 A1 , DE 10 2015 005521 A1 each discloses an aqueous composition for reducing the pickling removal when pickling steel surfaces and / or galvanized steel surfaces containing an acid, such as sulfuric acid, hydrochloric acid or phosphoric acid, and 2-butyne-1,4-diol as a corrosion inhibitor.

The object of the invention was therefore to provide a composition for reducing the removal of pickling when pickling metallic surfaces containing bright and / or galvanized steel, and a method for pickling a corresponding metallic surface with reduced pickling removal, which completely with a subsequent pickling Conversion treatment is compatible and less toxicologically harmful and less harmful to the environment.

Preferably also in the event of a carry-over, i.e. incomplete removal of the composition does not adversely affect the formation of the conversion coating and a water-wettable surface is available.

Furthermore, the reduced pickling removal should preferably increase the service life of a corresponding pickling bath.

This object is achieved by a composition according to claim 1, a concentrate according to claim 7, a method according to claim 8 and a use according to claim 15. Advantageous embodiments are described in the dependent claims.

The aqueous composition according to the invention for reducing the removal of pickling when pickling metallic surfaces containing bright and / or galvanized steel contains a mixture of a compound of the formula I.

R ¹ O- (CH ₂ ) _x -C≡C- (CH ₂ ) _y -OR ² (I),

in which R ¹ and R ^{2 are} both H, and a compound of the formula I in which R ¹ and R ^{2 are} each, independently of one another, an HO (CH ₂ ) _w group with w ≥ 2, with each of the two compounds of the formula I x and y are each independently 1 to 4.

Definitions:

In the present case, an "aqueous composition" is to be understood to mean one which for the most part, i.e. contains more than 50% by weight of water as a solvent / dispersant. The aqueous composition is preferably a solution, more preferably a solution which contains only water as a solvent.

In the present case, the “galvanized steel” can be either electrolytically galvanized or hot-dip galvanized steel.

Compounds of the formula I act as physical corrosion inhibitors which are adsorbed on the metallic surface by Van der Waals forces, as a result of which a monomolecular, homogeneous, densely packed layer is formed thereon. Said layer physically shields the metallic surface from a proton attack at least partially and thus prevents or at least reduces the pickling removal of the surface.

It was surprisingly found that by using certain mixtures of different compounds of the formula I, a clear synergy effect can be achieved with regard to a reduction in the pickling removal.

The aqueous composition according to the invention is essentially free of N, N'-diethylthiourea, N, N'-di (o-tolyl) thiourea, N, N'-dibutylthiourea and hexamethylenetetraamine.

"Essentially free" means that the aforementioned compounds have not been added to the composition at will, so that they are at most impurities in the starting materials used. The total content of these compounds in the composition according to the invention is preferably below 5 mg / l, more preferably below 1 mg / l.

The mixing ratio, based on% by weight, of the compound of the formula I in which R ¹ and R ^{2 are} both H and the compound of the formula I in which R ¹ and R ^{2 are} each independently an HO- (CH ₂ ) _w Group with w ≥ 2 is preferably in the range from 0.5: 1 to 2: 1, particularly preferably in the range from 0.75: 1 to 1.75: 1 and very particularly preferably in the range from 1: 1 to 1.5: 1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol-bis (2-hydroxyethyl ether)).

The sum of x and y in each of the two compounds of the formula I is preferably 2 to 5.

More preferably, the aqueous composition contains a mixture of 2-butyne-1,4-diol and 2-butyne-1,4-diol-bis (2-hydroxyethyl ether).

The mixing ratio based on% by weight is again preferably in the range from 0.5: 1 to 2: 1, particularly preferably in the range from 0.75: 1 to 1.75: 1 and very particularly preferably in the range 1: 1 up to 1.5: 1.

According to a preferred embodiment, the composition additionally contains at least one compound of the formula II

R ¹ O- (CH ₂ ) _x -S- (CH ₂ ) _y -OR ² (II),

wherein R ¹ and R ^{2 are} each independently H or a HO- (CH ₂ ) _w group with w ≥ 2, and x and y are each independently 1 to 4.

The at least one compound of the formula II is preferably HO-CH ₂ -S-CH ₂ .

The aqueous composition according to the invention can be obtained from the concentrate according to the invention by dilution with a suitable solvent and / or dispersion medium, preferably with water, and if necessary adjusting the pH.

When adding the concentrate to the pickling solution in step ii) (see below), the dilution factor is preferably in the range from 1:23 to 1: 225.

In contrast, the dilution factor when adding the concentrate to the rinsing solution in step iii) (see below) is preferably in the range from 1: 225 to 1: 2250.

1. i) gegebenenfalls gereinigt und/oder gespült,
2. ii) mit einer wässrigen Beizzusammensetzung in Kontakt gebracht und
3. iii) mit einer wässrigen Spülzusammensetzung in Kontakt gebracht,

wobei die Beizzusammensetzung in Schritt ii) und/oder die Spülzusammensetzung in Schritt iii) mindestens eine erfindungsgemäße Zusammensetzung wie vorstehend beschrieben ist.In the method according to the invention for pickling a metallic surface containing bright and / or galvanized steel, the surface is processed in successive process steps

1. i) optionally cleaned and / or rinsed,
2. ii) contacted with an aqueous pickling composition and
3. iii) contacted with an aqueous rinse composition,

wherein the pickling composition in step ii) and / or the rinsing composition in step iii) is at least one composition according to the invention as described above.

In the optional cleaning in step i), an alkaline cleaning solution is preferably used, particularly preferably with a pH of 9.5 or more.

The pickling composition ii) preferably contains at least one compound selected from the group consisting of phosphonates, condensed phosphates and citrate and / or at least one mineral acid selected from the group consisting of sulfuric acid, hydrochloric acid, hydrofluoric acid and nitric acid, particularly preferably it contains at least one mineral acid selected from the group consisting of sulfuric acid, hydrochloric acid, hydrofluoric acid and nitric acid, very particularly preferably contains sulfuric acid.

The pH of the rinsing composition in step iii) is preferably strongly acidic, neutral or slightly alkaline, particularly preferably it is in the range from 2 to 8.

According to a first preferred embodiment, the pickling composition in step ii) is a composition according to the invention as described above.

The total concentration of the mixture of the two compounds of the formula I in the pickling composition is preferably in the range from 31 to 620 mg / l, particularly preferably in the range from 31 to 310 mg / l (calculated as 2-butyne-1,4-diol) .

The use of the mixture of the two compounds of the formula I in the pickling composition has the advantage of reducing the pickling removal particularly effectively.

According to a second preferred embodiment, the rinsing composition in step iii) is a composition according to the invention as described above.

The total concentration of the mixture of the two compounds of the formula I in the rinsing composition is preferably in the range from 3 to 62 mg / l, particularly preferably in the range from 3 to 31 mg / l (calculated as 2-butyne-1,4-diol) . Even during the rinsing of the previously pickled metallic surface, mineral acid is still present from the liquid film adhering to the surface, so that the pickling attack continues, albeit in a weakened form. As a result, flash rust is formed. The use of the mixture of the two compounds of formula I in the rinsing composition has the advantage of reducing this rust formation.

According to a third preferred embodiment, the pickling composition in step ii) and the rinsing composition in step iii) are each a composition according to the invention as described above. The mixture of the two compounds of the formula I in the pickling composition and that in the rinsing composition can be the same or a different mixture.

The total concentration of the mixture of the two compounds of the formula I in the pickling composition is again preferably in the range from 31 to 620 mg / l, particularly preferably in the range from 31 to 310 mg / l (calculated as 2-butyne-1,4-diol ) and in the rinsing composition preferably in the range from 3 to 62 mg / l, particularly preferably in the range from 3 to 31 mg / l (calculated as 2-butyne-1,4-diol).

The metallic surface containing bright and / or galvanized steel pickled with the method according to the invention is preferably the surface of a metallic component / workpiece, for example a steel tube, of wires or screws (piece goods).

The metallic surface pickled with the method according to the invention is therefore used in the area of parts treatment.

The pickled and rinsed metallic surface is preferably first conversion-treated. For the conversion treatment there is preferably one acidic aqueous composition for use, which contains zinc phosphate, manganese phosphate and optionally nickel ions (so-called zinc phosphating).

However, a thin film coating can also be carried out by means of an acidic aqueous composition which contains a titanium, zirconium and / or hafnium compound and optionally copper ions and / or a compound which releases copper ions, optionally a polymer and / or copolymer and optionally a Organoalkoxysilan and / or a hydrolysis and / or a condensation product thereof.

The optionally rinsed metallic surface is then painted. A base lacquer, which is preferably a KTL (cathodic electro-dipping lacquer), particularly preferably a (meth) acrylate or epoxy-based KTL, is preferably applied first, and then a top lacquer is applied.

In the area of cold forming, on the other hand, a lubricant containing salts, polymers and / or soaps is applied to the pickled and rinsed metallic surface.

The present invention is intended to be illustrated by the following exemplary embodiments, which are not to be understood as restrictive.

Embodiments

Aqueous pickling solutions A to F were prepared, each containing 20% by weight H ₂ SO ₄ , 50 g / L Fe ²⁺ and optionally one or two pickling inhibitors.

Their composition can be seen in Table 1 below: <b> Table 1 </b> Pickling solution Pickling inhibitor (s) Pickling inhibitor content A --- --- B N, N'-diethylthiourea 150 mg / l C. N, N'-di (o-tolyl) thiourea + N, N'-dibutylthiourea + hexamethylenetetraam in total 100 mg / l D But-2-in-1,4-diol 100 mg / l E 2-butyne-1,4-diol-bis (2-hydroxyethyl ether) 50 mg / l F But-2-in-1,4-diol + 2-butyne-1,4-diol-bis (2-hydroxyethyl ether) 50 mg / l or 25 mg / l

Test sheets made of CRS (cold-rolled steel) were weighed before treatment with one of the pickling solutions.

Three sheets were then immersed for 5 minutes in a bath with one of the pickling solutions B to F (with pickling inhibitor (s)) and one sheet for the same time in a bath with pickling solution A (without pickling inhibitor). The baths had a temperature of 60 ° C. The plates were rotated at a speed of 400 rpm.

Then all the sheets were rinsed with demineralized water, dried and weighed. The weight loss due to the treatment with pickling solution represents the pickling removal.

The mean value of the pickling removal was formed for each of the three sheets which had been treated with one of the pickling solutions B to F, and this was related to the pickling removal for the one sheet treated with pickling solution A in each case. The The result in percent was subtracted from 100 percent and the respective inhibitory value of the pickling inhibitor (s) was determined (see table 2 below). Table 2 Pickling solution Inhibitory value A 0% B 96% C. 96% D 85% E 92% F 97%

The pickling inhibitors of pickling solutions B and C to be avoided from a toxicological and environmental point of view each had an excellent inhibitory value of 96%. The inhibitory values of the individual inhibitors but-2-in-1,4-diol (pickling solution D) and 2-butyne-1,4-diol-bis (2-hydroxyethyl ether) (pickling solution E) remained clear at 85% and 92%, respectively back there. However, the inhibitory value of the mixture according to the invention of the two last-mentioned pickling inhibitors (pickling solution F) was surprisingly high at 97% and even exceeded that of the aforementioned pickling inhibitors.

The sheets were then zinc-phosphated. The pickling solutions B and F were added to the phosphating bath in increasing amounts. On the one hand, the look of the sheets was evaluated. On the other hand, the layer weights in g / m ² calculated from P ₂ O _{5 were} determined by means of XRF.

The results are for the pickling solutions B of the prior art - containing different amounts of N, N'-diethylthiourea - in Table 3 and for the pickling solutions F according to the invention - containing different amounts of the mixture of but-2-in-1,4-diol and 2-butyne-1,4-diol-bis (2-hydroxyethyl ether) - shown in Table 4 . <b> Table 3 </b> Pickling inhibitor content Sheet appearance (school grades from 1 = very good to 6 = unsatisfactory) Layer weight in g / m ² (calculated as P ₂ O ₅ ) --- 1 2,864 10 mg / l 5 2,272 25 mg / l 6+ 0.320 100 mg / l 6 0.144 200 mg / l 6 0.192 Pickling inhibitor content Sheet appearance (school grades from 1 = very good to 6 = unsatisfactory) Layer weight in g / m ² (calculated as P ₂ O ₅ ) --- 1 3,264 25 or 12.5 mg / l 2nd 3,264 50 or 25 mg / l 2- 3,264 100 or 50 mg / l 4-5 3,008

It can be clearly seen from Table 3 that steel with increasing N, N'-diethylthiourea content leads to a dramatic decrease in the layer thickness and thus to an increasingly inadequate formation of the phosphate layer.

As can be seen from Table 4 , only a significantly higher content of but-2-yne-1,4-diol and 2-butyne-1,4-diol-bis (2-hydroxyethyl ether) has a significantly negative influence on the stratification.

Accordingly, the mixture according to the invention not only reduces the pickling removal, but also does not lead to any disturbances in the layer formation in a subsequent phosphating step, for example due to the carryover of the pickling solution.

Claims (15)

1. An aqueous composition for reducing the corrosive removal of material in the pickling of metallic surfaces comprising bare and/or galvanized steel, wherein the composition comprises a mixture of a compound of the formula I
   
           R¹O-(CH₂)_x-C≡C-(CH₂)_y-OR²     (I),
   
   in which R¹ and R² are both H and a compound of the formula I in which R¹ and R² are each, independently of one another, an HO-(CH₂)_w- group with w ≥ 2, where x and y are each, independently of one another, from 1 to 4 in each of the two compounds of the formula I.
2. The composition according to claim 1, wherein the mixing ratio in % by weight of the compound of the formula I in which R¹ and R² are both H and the compound of the formula I in which R¹ and R² are each, independently of one another, an HO-(CH₂)_w-group with w ≥ 2 is in the range from 0.5:1 to 2:1, preferably in the range from 0.75:1 to 1.75:1 and particularly preferably in the range from 1:1 to 1.5:1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether).
3. The composition according to claim 1 or 2, wherein the sum of x and y is from 2 to 5 in each of the two compounds of the formula I.
4. The composition according to claim 3, wherein it comprises a mixture of 2-butyne-1,4-diol and 2-butyne-1,4-diol bis(2-hydroxyethyl) ether.
5. The composition according to any of the preceding claims, wherein it additionally comprises at least one compound of the formula II
   
           R¹O-(CH₂)_x-S-(CH₂)_y-OR²     (II),
   
   where R¹ and R² are each, independently of one another, H or an HO-(CH₂)_w- group with w ≥ 2 and x and y are each, independently of one another, from 1 to 4.
6. The composition according to claim 5, wherein the at least one compound of the formula II is HO-CH₂-S-CH₂-OH.
7. A concentrate from which a composition according to any of the preceding claims is obtainable by dilution with a suitable solvent and/or dispersion medium and optionally adjustment of the pH.
8. A process for pickling a metallic surface comprising bare and/or galvanized steel, wherein the surface is, in successive process steps

   i) optionally cleaned and/or rinsed,

   ii) brought into contact with an aqueous pickling composition and

   iii) brought into contact with an aqueous rinsing composition,

   where the pickling composition in step ii) and/or the rinsing composition in step iii) is a composition according to any of claims 1 to 6.
9. The process according to claim 8, wherein the pickling composition in step ii) is a composition according to any of claims 1 to 4.
10. The process according to claim 9, wherein the total concentration of the two compounds of the formula I is in the range from 31 to 620 mg/l, preferably in the range from 31 to 310 mg/l (calculated as 2-butyne-1,4-diol) .
11. The process according to any of claims 8 to 10, wherein the pickling composition in step ii) comprises sulfuric acid.
12. The process according to any of claims 8 to 11, wherein the rinsing composition in step iii) is a composition according to any of claims 1 to 6.
13. The process according to claim 12, wherein the total concentration of the two compounds of the formula I is in the range from 3 to 62 mg/l, preferably in the range from 3 to 31 mg/l (calculated as 2-butyne-1,4-diol) .
14. The process according to any of claims 8 to 13, wherein the pH of the rinsing composition in step iii) is in the range from 2 to 8.
15. The use of the metallic surface pickled by means of a process according to any of claims 8 to 14 in the field of treatment of parts.