WO2017202891A1 - Process for corrosion-protecting phosphatization of a metallic surface with reduced pickling erosion - Google Patents

Abstract

The present invention relates to a process for corrosion-protecting phosphatization of a metallic surface in which the surface is successively contacted with the following aqueous compositions: i) an alkaline or acidic cleaner composition, ii) a first washing composition, iii) optionally a second washing composition, iv) an acidic phosphatization composition, v) optionally a third washing composition and vi) a composition containing a (meth)acrylate- and/or epoxide-based KTL, wherein an activating agent is added to the cleaner composition i) and/or wherein between the contacting with the first washing composition ii) or optionally the second washing composition iii) and the phosphatization composition (iv) the metallic surface is contacted with an aqueous activating composition vii), wherein at least one of the compositions i) to v) contains at least one compound of formula (I) R¹O-(CH₂)_x-Z-(CH₂)_y-OR² and wherein R¹ and R² are each independently of one another H or an HO-(CH₂)_w group where w ≥ 2, x and y are each independently of one another 1 to 4, and Z is an S atom or a C-C triple bond, and to an aqueous composition for reducing pickling erosion in corrosion-protecting phosphatization of metallic surfaces.

Description

 Process for corrosion-protecting phosphating of a metallic surface with reduced pickling removal

The invention relates to a process for the corrosion-protective phosphating of a metallic surface and to an aqueous composition for the reduction of pickling in the corrosion-protective phosphating of metallic surfaces.

In the corrosion-protective phosphating of metal strips and metallic components - such as those used in vehicle construction - aqueous cleaning and phosphating solutions are used, which have a pH in the clearly acidic or alkaline range or in the clearly acidic range.

During cleaning, the acidic or alkaline pH initially serves to remove oxide films and impurities from the metallic surface. During the subsequent acid phosphating, the oxidative proton attack on the metallic surface itself causes the metal cations necessary for the formation of the phosphate coating to be dissolved out of it (so-called anodic metal dissolution).

In other words, there is a pickling of the metallic surface. Such can take place not only in the phosphating but also in the cleaning, namely, when the metallic surface itself is attacked after the removal of oxide films and impurities.

This raises the problem that the metallic surface receives an uneven morphology due to excessive pickling removal, which translates to the deposited coatings, in particular phosphate coatings insofar that they also have a certain unevenness. This in turn leads to a reduction in the adhesion of subsequent coatings, in particular cathodic electrodeposition paints, and, associated therewith, the corrosion protection. The object of the invention was therefore to provide a method for corrosion-protective phosphating a metallic surfaces with reduced pickling and a composition for reducing the pickling in the corrosion-protective phosphating metallic surfaces available.

This object is achieved by a method according to claim 1, a composition according to claim 20, a concentrate according to claim 21 and a use according to claim 22. Advantageous embodiments are each described in the dependent claims. In the method of anti-corrosive phosphating of a metallic surface according to the invention, the surface is contacted successively with the following aqueous compositions: i) an alkaline or acidic cleaner composition,

 ii) a first rinse composition,

 iii) optionally a second rinse composition,

 iv) an acid phosphating composition,

 v) optionally a third rinse composition and

 vi) a composition comprising a (meth) acrylate and / or epoxide-based KTL, wherein the activating composition i) an activating agent is added and / or wherein the metallic surface between the contacting with the first rinsing composition ii) or optionally the second rinsing composition iii) and the phosphating composition iv) is brought into contact with an aqueous activating composition vii), wherein at least one of the compositions i) to v) comprises at least one compound of the formula I

R ^{1 is} O- (CH ₂ ) x Z- (CH ₂ ) y-OR ² (I), and wherein R ¹ and R ^{2 are} each independently H or an HO- (CH ₂ ) _w group with w> 2, x and y are each independently 1 to 4, and Z is an S atom or a CC triple bond ,

definitions:

In the present case, an "aqueous composition" is to be understood to mean one which contains water, for the most part, ie more than 50% by weight, as the solvent / dispersant, Preferably, the aqueous composition is a solution, more preferably about A solution containing only water as a solvent, The fact that the metallic surface is sequentially contacted with the aqueous compositions i) to vi) does not preclude contacting them with one or more further compositions before and / or after this sequence It is also not excluded that the metallic surface is brought into contact with one or more further compositions between the contacting with the different compositions i) to vi).

The at least one compound of formula I acts as a physical corrosion inhibitor which is adsorbed by van der Waals forces on the metallic surface, forming a monomolecular, homogeneous, densely packed layer thereon. By means of said layer, the metallic surface is physically shielded from a proton or hydroxide ion attack and thus the pickling of the surface is prevented or at least reduced.

According to a first preferred embodiment, the detergent composition i) contains at least one compound of the formula I. The concentration of the at least one compound of the formula I in the detergent composition i) is preferably in the range from 6 to 625 mg / l, particularly preferably in the range from 31 to 313 mg / L (calculated as 2-butyne-1,4-diol). According to a second preferred embodiment, the first rinsing composition ii), the second rinsing composition iii) and / or the third rinsing composition v) comprises at least one compound of the formula I.

The use of the at least one compound of formula I in one or more of the rinse compositions has the advantage of reducing the formation of flash rust on steel and / or galvanized steel.

The concentration of the at least one compound of the formula I is in the first rinsing composition ii), in the second rinsing composition iii) and in the third rinsing composition v) preferably in the range from 1 to 100 mg / l, particularly preferably in the range from 6 to 60 mg / L (calculated as 2-butyne-1,4-diol).

According to a third preferred embodiment, the phosphating composition iv) comprises at least one compound of the formula I.

The concentration of the at least one compound of the formula I in the phosphating composition iv) is in the range from 1 to 100 mg / l, preferably in the range from 1 to 10 mg / l (calculated as 2-butyne-1,4-diol).

In the method according to the invention, the metallic surface must be activated for the phosphating. This can be done by adding to the detergent composition i) an activating agent and / or bringing the metallic surface into contact with the first rinsing composition ii) or optionally the second rinsing composition iii) and the phosphating composition iv) with an aqueous activating composition vii) ,

The activation serves to deposit a multiplicity of the finest phosphate particles as seed crystals on the metallic surface. These help in the process step of phosphating, ie in contact with the phosphating iv) - preferably without intermediate rinsing - form a particular crystalline phosphate layer with the highest possible number of densely arranged fine phosphate crystals or a largely closed phosphate layer. According to a first preferred embodiment, the cleaning composition is added to an activating agent, in particular titanium phosphate or zinc phosphate, ie purification and activation are carried out in one step. According to a second, further preferred embodiment, the metallic surface is contacted with the first rinsing composition ii) or optionally the second rinsing composition iii) and the phosphating composition iv) with an aqueous rinse

Activation composition vii). Particularly suitable as activating compositions are acidic or alkaline compositions based on titanium phosphate or zinc phosphate.

Optionally, the metallic surface is brought into contact with the first rinsing composition ii) or optionally the second rinsing composition iii) and the phosphating composition iv) with an aqueous pickling composition viii) and then with a fourth rinsing composition ix). However, contacting with the pickling composition viii) is in any case preceded by contacting with the activating composition vii).

However, it is also possible to contact the metallic surface before contacting it with the detergent composition i) with an aqueous pickling composition viii) and then a fourth rinsing composition ix).

The pickling composition viii) 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, more preferably it contains at least one mineral acid selected from the group consisting of sulfuric acid, hydrochloric acid, hydrofluoric acid and nitric acid, most preferably it contains sulfuric acid. According to a further embodiment, the pickling composition viii) contains at least one compound of the formula I.

The concentration of the at least one compound of the formula I in the mordant composition viii) 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).

The use of the at least one compound of the formula I in the pickling composition has the advantage of particularly effectively reducing pickling.

Alternatively or additionally, however, the fourth rinsing composition ix) may also contain at least one compound of the formula I.

Preferably, the detergent composition is i) alkaline, more preferably has a pH of 9.5 or greater.

The first rinsing composition ii), the second rinsing composition iii) and the third rinsing composition v) preferably have a pH in the range from 2 to 10, more preferably in the range from 3 to 10.

The first rinse composition is preferably weakly acidic, slightly alkaline or neutral. Particularly preferably, it has a pH in the range from 6 to 9.

The second rinse composition is preferably weakly weakly alkaline or neutral. Most preferably, it has a pH in the range of 7 to 9.

The third rinse composition preferably has a pH in the range of 4 to 9, more preferably it is slightly acidic, slightly alkaline or neutral. Most preferably, it has a pH in the range of 6 to 8. The phosphating composition iv) may be zinc phosphate (so-called zinc phosphating) or an alkali metal phosphate (so-called Iron phosphating). It preferably contains zinc phosphate and optionally manganese phosphate and / or nickel ions.

Most preferably, the phosphating composition iv) contains zinc phosphate and manganese phosphate and is substantially nickel-free, i. it contains less than 0.3 g / l of nickel ions.

It very particularly preferably contains 0.3 to 3.0 g / l of zinc ions, 0.3 to 2.0 g / l of manganese ions and 8 to 25 g / l of phosphate ions (calculated as P2O ₅ ).

When the phosphating composition iv) is a substantially nickel-free phosphating composition containing zinc phosphate and manganese phosphate, it is advantageous to subsequently contact the metallic surface with a third rinse composition v) containing molybdenum ions and / or zirconium ions.

In this way, paint adhesion and corrosion protection results can be achieved, which are comparable to those of a nickel-containing reference system. The molybdenum ions are preferably added as molybdate, more preferably as ammonium heptamolybdate and particularly preferably as ammonium heptamolybdate x 7 H ₂ O of the third rinsing composition v). The molybdenum ions can also be added as sodium molybdate.

However, molybdenum ions can also be added, for example, in the form of at least one salt containing molybdenum cations, such as molybdenum chloride, to the third rinse composition v) and then oxidized to molybdate by a suitable oxidizing agent. In such a case, the third rinse composition v) itself contains a corresponding oxidizing agent.

More preferably, the third rinse composition contains v) molybdenum ions and / or zirconium ions, most preferably molybdenum ions in combination with zirconium ions, wherein the content of molybdenum ions and zirconium ions is in the range of 10 to 500 mg / l each (calculated as metal).

The content of molybdenum ions is preferably in the range from 20 to 225 mg / l, particularly preferably from 50 to 225 mg / l and very particularly preferably from 100 to 225 mg / l and the content of zirconium ions in the range from 50 to 300 mg / l, more preferably from 50 to 150 mg / l.

Preferably, the at least one compound of the formula I is a mixture of a compound of the formula 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 an HO- CH ₂ ) _w - group with w> 2.

In this case, based on wt .-% mixing ratio of the compound of formula I in which R ¹ and R ^{2 are} both H, and the compound of formula I in which R ¹ and R ^{2 are} each independently a HO- (CH _{2 W} group with w> 2 are in the range of 0.5: 1 to 2: 1, preferably in the range of 0.75: 1 to 1, 75: 1 and particularly preferably in the range of 1: 1 to 1, 5: 1 (calculated as 2-butyne-1,4-diol and 2-butyne-1,4-diol bis (2-hydroxyethyl ether)).

Preferably, in the at least one compound of formula IR ¹ and R ^{2 are} both H or an HO- (CH ₂ ) 2 group, the sum of x and y is 2 to 5 and Z is a CC triple bond.

More preferably, the at least one compound of the formula I is 2-butyne-1,4-diol and / or 2-butyne-1,4-diol bis (2-hydroxyethyl ether).

The at least one compound of the formula I is particularly preferably a mixture of 2-butyne-1,4-diol and 2-butyne-1,4-diol bis (2-hydroxyethyl ether), the mixing ratio based on wt Range of 0.5: 1 to 2: 1, preferably in the range of 0.75: 1 to 1, 75: 1 and particularly preferably in the range 1: 1 to 1, 5: 1.

The metallic surface treated with the method according to the invention is preferably the surface of a metal strip or a metallic component, for example a body.

The metallic surface may include bare steel, electrolytically galvanized and / or hot-dip galvanized steel, aluminum and / or an aluminum alloy. According to a preferred embodiment, in addition to bare steel and / or galvanized steel, the metallic surface also contains aluminum or an aluminum alloy (so-called multimetal capability).

The process according to the invention has proved to be advantageous in the case of acrylate- and / or epoxide-based cathodic electrocoating paint (EPC) in terms of improved paint adhesion and improved corrosion protection.

Subsequently, a topcoat is optionally applied to the KTL-coated metallic surface.

The present invention also relates to an aqueous composition for reducing pickling in the corrosion-protective phosphating of metallic surfaces, which contains at least one compound of the formula I as described above.

In addition, it relates to a concentrate from which the aqueous composition according to the invention can be obtained by dilution with a suitable solvent and / or dispersion medium, preferably with water, and optionally adjusting the pH.

The dilution factor is preferably in the range from 1:10 to 1: 10,000, particularly preferably in the range from 1:50 to 1: 200.

Finally, the present invention also relates to the use of the metallic surface treated by the method according to the invention.

Claims

claims 1 . Process for the corrosion-protective phosphating of a metallic surface, characterized in that the surface is brought into contact successively with the following aqueous compositions: i) an alkaline or acidic cleaner composition,  ii) a first rinse composition,  iii) optionally a second rinse composition,  iv) an acid phosphating composition,  v) optionally a third rinse composition and  vi) a composition comprising a (meth) acrylate and / or epoxide-based KTL, wherein the activating composition i) an activating agent is added and / or wherein the metallic surface between the contacting with the first rinsing composition ii) or optionally the second rinsing composition iii) and the phosphating composition iv) is brought into contact with an aqueous activating composition vii), wherein at least one of the compositions i) to v) comprises at least one compound of the formula I R ^{1 is} O- (CH ₂ ) x Z- (CH ₂ ) y-OR ² (I), and wherein R ¹ and R ^{2 are} each independently H or an HO- (CH ₂ ) _w - group with w> 2 , x and y are each independently 1 to 4, and Z is an S atom or a CC triple bond. 2. The method according to claim 1, characterized in that the cleaning composition contains i) at least one compound of formula I. 3. The method according to claim 2, characterized in that the concentration of the at least one compound of formula I in the range of 6 to 625 mg / l, preferably in the range of 31 to 313 mg / l (calculated as 2-butyne-1,4 -diol) is located. 4. The method according to any one of the preceding claims, characterized in that the first rinsing composition ii), the second rinsing composition iii) and / or the third rinsing composition v) contains at least one compound of formula I. 5. The method according to claim 4, characterized in that the concentration of the at least one compound of formula I in the range of 1 to 100 mg / l, preferably in the range of 6 to 60 mg / l (calculated as 2-Butin- 1, 4 -diol) is located 6. The method according to any one of the preceding claims, characterized in that the phosphating composition iv) contains at least one compound of formula I. 7. The method according to claim 6, characterized in that the concentration of the at least one compound of formula I in the range of 1 to 100 mg / l, preferably in the range of 1 to 10 mg / l (calculated as 2-Butin- 1, 4 -diol) is located. 8. The method according to any one of the preceding claims, characterized in that the activating agent contained in the detergent composition i) or in the activation composition vii) is titanium phosphate or zinc phosphate. 9. The method according to any one of the preceding claims, characterized in that the cleaner composition i) is alkaline, preferably has a pH of 9.5 or more. 10.Verfahren according to any one of the preceding claims, characterized in that the first rinsing composition ii) has a pH in the Range from 6 to 9, the second rinse composition iii) has a pH in the range of 7 to 9, and the third rinse composition v) has a pH in the range of 4 to 9. 1 1. Method according to one of the preceding claims, characterized in that the phosphating composition iv) 0.3 to 3.0 g / l Zinc ions, 0.3 to 2.0 g / l of manganese ions and 8 to 25 g / l of phosphate ions (calculated as P2O ₅ ) contains and is substantially nickel-free. 12. The method according to any one of the preceding claims, characterized in that the metallic surface is brought into contact with a third rinsing composition v) containing molybdenum ions and / or zirconium ions, wherein the content of molybdenum ions in the range of 20 to 225 mg / l (calculated as metal) and the content of zirconium ions in the range of 50 to 300 mg / l (calculated as metal). 13. The method according to claim 12, characterized in that the third rinsing composition contains v) molybdenum ions in combination with zirconium ions. 14. The method according to any one of the preceding claims, characterized in that the at least one compound of formula I is a mixture of a compound of formula I, wherein R ¹ and R ^{2 are} both H, and a compound of formula I, wherein R ¹ and R ^{2 are} each independently an HO (CH ₂ ) _W group with w> 2. 15. The method according to claim 14, characterized in that the wt .-% relative mixing ratio of the compound of formula I in which R ¹ and R ^{2 are} both H, and the compound of formula I, wherein R ¹ and R ² each independently is an HO- (CH ₂ ) _W group with w> 2, in the range of 0.5: 1 to 2: 1, preferably in the range of 0.75: 1 to 1.75: 1, and more preferably in the range of 1: 1 to 1, 5: 1 (calculated as 2-butyn-1, 4-diol and 2-butyne-1,4-diol bis (2-hydroxyethyl ether)). 16. The method according to any one of the preceding claims, characterized in that in the at least one compound of the formula IR ¹ and R ^{2 are} both H or a HO- (CH ₂ ) ₂ group, the sum of x and y is 2 to 5 , and Z is a CC double bond. 17. The method according to claim 16, characterized in that the at least one compound of formula I is 2-butyne-1, 4-diol and / or 2-butyne-1, 4-diol bis (2-hydroxyethyl ether). 18. The method according to claim 17, characterized in that the at least one compound of formula I is a mixture of 2-butyne-1, 4-diol and 2-butyne-1, 4-diol-bis (2-hydroxyethyl ether). 19. The method according to any one of the preceding claims, characterized in that the metallic surface in addition to bare steel and / or galvanized steel also contains aluminum or an aluminum alloy. 20. Aqueous composition for reducing pickling in the corrosion-protective treatment of metallic surfaces, characterized in that it contains at least one compound of the formula I according to claim 1 or one of claims 14 to 18. 21. Concentrate from which a composition according to claim 20 can be obtained by dilution with a suitable solvent and / or dispersion medium and optionally adjusting the pH. 22. Use of the treated with a method according to any one of claims 1 to 19 metallic surface.