EP3280830B1 - Method for specifically adjusting the electrical conductivity of conversion coatings - Google Patents

Description

The present invention relates to a method for the targeted adjustment of the electrical conductivity of a conversion coating on a metallic surface by means of an aqueous composition as well as a corresponding aqueous composition and a corresponding conversion coating.

Conversion coatings on metallic surfaces are known from the prior art. WO 2005/061761 A1 relates to a process for the two-stage anti-corrosion treatment of metal surfaces, such as vehicle bodies or household appliances. Such coatings serve to protect the metallic surfaces from corrosion and also act as an adhesion promoter for subsequent paint coats US-A-2008/230395 discloses a method in which a conversion solution containing Zr ions and a condensate of a silane is used.

The subsequent paint layers are mainly cathodically deposited electrodeposition paints (KTL). Since a current must flow between the metallic surface and the treatment bath when KTL is deposited, it is important to set a defined electrical conductivity of the conversion coating in order to ensure efficient and homogeneous deposition.

Conversion coatings are therefore usually applied using a phosphating solution containing nickel. The nickel ions built into the conversion coating or the elementally deposited nickel ensure a suitable conductivity of the coating during the subsequent electrodeposition coating.

However, because of their high toxicity and environmental pollution, nickel ions are no longer desirable as a component of treatment solutions and should therefore be avoided if possible or at least reduced in their content.

The use of nickel-free or low-nickel phosphating solutions is known. However, a targeted adjustment of the electrical conductivity of corresponding phosphate coatings is still associated with serious problems.

Other nickel-free or low-nickel systems are thin-film coatings, which are, for example, thin coatings of zirconium oxide and optionally at least one organosiloxane and / or of at least one organic polymer.

Here too, however, the targeted setting of the electrical conductivity for the purpose of subsequent electrocoating is still unsatisfactory. In many cases, more or less pronounced inhomogeneities in the deposited KTL cannot be avoided (so-called mapping).

In the case of the low-nickel or nickel-free systems mentioned, unfavorable KTL deposition conditions can also lead to poor corrosion and paint adhesion values due to a not optimally adjusted electrical conductivity of the conversion coating.

The object of the present invention was therefore to provide a method with which the electrical conductivity of a conversion coating on a metallic surface can be set in a targeted manner, and in which in particular the disadvantages known from the prior art are avoided.

This object is achieved by the method according to the invention and the conversion coating according to the invention.

In the method according to the invention for the targeted adjustment of the electrical conductivity of a conversion coating, a metallic surface is first treated with a conversion / passivation solution containing 10 to 500 mg / l Zr in complexed form, calculated as metal, and at least one organosilane and / or at least one Hydrolysis product thereof and / or at least one condensation product thereof in a concentration range of 5 to 200 mg / l, calculated as Si, contains, whereby a corresponding thin film coating is formed on the metallic surface, and the metallic surface coated in this way is after optional drying with an aqueous Composition treated as a rinsing solution, which comprises 20 to 225 mg / l of molybdenum ions.

By an "aqueous composition" is meant a composition which for the most part, ie more than 50% by weight, contains water as a solvent. In addition to dissolved constituents, it can also comprise dispersed, ie emulsified and / or suspended constituents.

The metallic surface is preferably steel, hot-dip galvanizing, electrolytic galvanizing, aluminum or their alloys such as Zn / Fe or Zn / Mg.

Aqueous compositions can contain a type of metal ions selected from the group consisting of the ions of the following metals in the following preferred, particularly preferred and very particularly preferred concentration ranges (all calculated as the corresponding metal): Mon 1 to 1000 mg / l 10 to 500 mg / l 20 to 225 mg / l Cu 1 to 1000 mg / l 3 to 500 mg / l 5 to 225 mg / l Ag 1 to 500 mg / l 5 to 300 mg / l 20 to 150 mg / l Au 1 to 500 mg / l 10 to 300 mg / l 20 to 200 mg / l Pd 1 to 200 mg / l 5 to 100 mg / l 5 to 100 mg / l Sn 1 to 500 mg / l 2 to 200 mg / l 3 to 100 mg / l Sb 1 to 500 mg / l 2 to 200 mg / l 3 to 100 mg / l

The metal ions contained in the aqueous composition either separate in the form of a salt, which contains the corresponding metal cation (e.g. molybdenum or tin) preferably in at least two oxidation states - in particular in the form of an oxide hydroxide, a hydroxide, a spinel or a defect spinel - or elemental on the surface to be treated (e.g. copper, silver, gold or palladium).

According to the invention, an aqueous composition is used as the rinsing solution and the metal ions are molybdenum ions. These are preferably added to the aqueous composition as molybdate, more preferably as ammonium heptamolybdate and particularly preferably as ammonium heptamolybdate × 7H _{2 O.}

Molybdenum ions can, however, also be added to the aqueous composition in the form of at least one salt containing molybdenum cations, such as molybdenum chloride, and then oxidized to molybdate by a suitable oxidizing agent, for example by the accelerators described below.

The aqueous composition further preferably contains molybdenum ions in combination with copper ions, tin ions or zirconium ions.

It particularly preferably contains molybdenum ions in combination with zirconium ions and optionally a polymer or copolymer, in particular selected from the group consisting of the polymer classes of polyamines, polyanilines, polyimines, polythiophenes and polypryrenes and their mixtures and copolymers and polyacrylic acid, the zirconium ion content being im Range from 10 to 500 mg / l (calculated as metal).

The content of molybdenum ions is in the range from 20 to 225 mg / l, preferably from 50 to 225 mg / l and particularly preferably from 100 to 225 mg / l, and the content of zirconium ions is preferably in the range from 30 to 300 mg / l, especially preferably from 50 to 200 mg / l.

According to a further preferred embodiment, the composition contains copper ions. The post-rinse solution then preferably contains this in a concentration of 5 to 225 mg / l, more preferably 150 to 225 mg / l.

According to a further embodiment, the aqueous composition according to the invention contains at least one electrically conductive polymer selected from the group consisting of the polymer classes of polyamines, polyanilines, polyimines, polythiophenes and polypryrenes. A polyamine and / or polyimine, particularly preferably a polyamine, is preferably used.

The polyamine is preferably a polyethylene amine, and the polyimine is a polyethyleneimine.

The at least one electrically conductive polymer is preferably in a concentration in the range from 0.1 to 5.0 g / l, more preferably from 0.2 to 3.0 g / l and particularly preferably in the range from 0.5 to 1 , 5 g / l (calculated as pure polymer).

Cationic polymers such as polyamines or polyethyleneimines are preferably used as electrically conductive polymers.

Preferably only treatment solutions are used in the method according to the invention and also aqueous compositions according to the invention which are less than 1.5 g / l, more preferably less than 1 g / l, more preferably less than 0.5 g / l, particularly preferably less than 0.1 g / l and very particularly preferably contain less than 0.01 g / l nickel ions.

If a treatment solution or aqueous composition according to the invention contains less than 0.01 g / l nickel ions, it should be considered to be at least essentially free of nickel.

The conversion coatings that are treated with the post-rinse solution are thin-film coatings. The thin-film coatings are thin coatings of zirconium oxide and at least one organosiloxane. Such conversion coatings are applied by means of a corresponding conversion / passivation solution.

On the one hand, phosphating solutions and conversion / passivation solutions are described below.

i) phosphating solution

The phosphating solution can be an aqueous zinc phosphate solution or an aqueous alkali metal phosphate solution.

If it is a zinc phosphate solution, it preferably comprises the following components in the following preferred and particularly preferred concentration ranges: Zn 0.3 to 3.0 g / l 0.5 to 2.0 g / l Mn 0.3 to 2.0 g / l 0.5 to 1.5 g / l Phosphate (calculated as P ₂ O ₅ ) 8 to 25 g / l 10 to 18 g / l free fluoride 30 to 250 mg / l 50 to 180 mg / l Complex fluoride (calculated e.g. as SiF ₆ ^2- and / or BF ₄ ^- ) up to 5 g / l 0.5 to 3 g / l

With regard to the manganese ions, however, a concentration in the range from 0.3 to 2.5 g / l, and with regard to the free fluoride, a concentration in the range from 10 to 250 mg / l has already proven to be advantageous.

The complex fluoride is preferably tetrafluoroborate (BF ₄ ^- ) and / or hexafluorosilicate (SiF ₆ ^2- ).

According to a particularly preferred embodiment, the complex fluoride is a combination of tetrafluoroborate (BF ₄ ^- ) and hexafluorosilicate (SiF ₆ ^2- ), the concentration of tetrafluoroborate (BF ₄ ^- ) in the range up to 3 g / l, preferably of 0.2 to 2 g / l, and the concentration of hexafluorosilicate (SiF ₆ ^2- ) in the range up to 3 g / l, preferably from 0.2 to 2 g / l.

According to a further particularly preferred embodiment, the complex fluoride is hexafluorosilicate (SiF ₆ ^2- ) with a concentration in the range from 0.2 to 3 g / l, preferably from 0.5 to 2 g / l.

According to a further particularly preferred embodiment, the complex fluoride is tetrafluoroborate (BF ₄ ^- ) with a concentration in the range from 0.2 to 3 g / l, preferably from 0.5 to 2 g / l.

In addition, the phosphating solution preferably contains at least one accelerator selected from the group consisting of the following compounds in the following preferred and particularly preferred concentration ranges: Nitroguanidine 0.2 to 3.0 g / l 0.2 to 1.55 g / l H ₂ O ₂ 10 to 100 mg / l 15 to 50 mg / l Nitroguanidine / H ₂ O ₂ 0.2 to 2.0 g / L / 10 to 50 mg / L 0.2 to 1.5 g / l / 15 to 30 mg / l nitrite 30 to 300 mg / l 90 to 150 mg / l

With regard to nitroguanidine, however, a concentration in the range from 0.1 to 3.0 g / l, and with regard to H ₂ O _2, a concentration in the range from 5 to 200 mg / l has already proven advantageous.

Furthermore, it can be characterized by the following preferred and particularly preferred parameter ranges: FS 0.3 to 2.0 0.7 to 1.6 FS (dil.) 0.5 to 8 1 to 6 GSF 12 to 28 22 to 26 GS 12 to 45 18 to 35 S value 0.01 to 0.2 0.03 to 0.15 Temperature ° C 30 to 50 ° C 35 to 45 ° C

With regard to the FS parameter, however, a value in the range from 0.2 to 2.5, and with regard to the temperature in the range from 30 to 55 ° C., has already proven advantageous.

"FS" stands for free acid, "FS (dil.)" For free acid (diluted), "GSF" for total acid according to Fischer, "GS" for total acid and "S value" for acid value.

These parameters are determined as follows:

Free acid (FS):

To determine the free acid, 10 ml of the phosphating solution are pipetted into a suitable vessel, for example a 300 ml Erlenmeyer flask. Contains the phosphating solution complex fluoride, 2-3 g of potassium chloride are added to the sample. It is then titrated with 0.1 M NaOH using a pH meter and an electrode to a pH of 3.6. The amount of 0.1 M NaOH consumed in ml per 10 ml of the phosphating solution gives the value of the free acid (FS) in points.

Free acid (diluted) (FS (dil.)):

To determine the free acid (diluted), 10 ml of the phosphating solution are pipetted into a suitable vessel, for example a 300 ml Erlenmeyer flask. 150 ml of deionized water are then added. Using a pH meter and electrode, titrate with 0.1 M NaOH to pH 4.7. The amount of 0.1 M NaOH consumed in ml per 10 ml of the diluted phosphating solution gives the value of the free acid (diluted) (FS (dil.)) In points. The complex fluoride content can be determined from the difference to the free acid (FA). If this difference is multiplied by the factor 0.36, the result is the content of complex fluoride as SiF ₆ ^2- in g / l.

Total acid according to Fischer (GSF):

Following the determination of the free acid (diluted), the diluted phosphating solution is titrated after adding potassium oxalate solution using a pH meter and an electrode with 0.1 M NaOH up to a pH value of 8.9. The consumption of 0.1 M NaOH in ml per 10 ml of the dilute phosphating solution gives the total acid according to Fischer (GSF) in points. If this value is multiplied by 0.71, the total content of phosphate ions is calculated as P ₂ O ₅ (see W. Rausch: "The phosphating of metals". Eugen G. Leuze-Verlag 2005, 3rd edition, pp. 332 ff ).

Total acid (GS) :

The total acid (GS) is the sum of the divalent cations it contains as well as free and bound phosphoric acids (the latter are phosphates). It is determined by the consumption of 0.1 M NaOH using a pH meter and an electrode. For this purpose, 10 ml of the phosphating solution are pipetted into a suitable vessel, for example a 300 ml Erlenmeyer flask, and diluted with 25 ml of deionized water. Then with 0.1 M NaOH up to a pH value of 9 titrated. The consumption in ml per 10 ml of the diluted phosphating solution corresponds to the number of points for the total acid (GS).

Acid value (S value):

The so-called acid value (S value) stands for the ratio FS: GSF and results from dividing the value of the free acid (FS) by the value of the total acid according to Fischer (GSF).

ii) conversion Z-passivation solution

The conversion / passivation solution is aqueous and always comprises 10 to 500 mg / l, preferably 30 to 300 mg / l and particularly preferably 50 to 200 mg / l Ti, Zr and / or Hf in complexed form (calculated as metal). These are preferably fluorocomplexes. In addition, the conversion / passivation solution always comprises 10 to 500 mg / l, preferably 15 to 100 mg / l and particularly preferably 15 to 50 mg / l of free fluoride.

It contains 10 to 500 mg / l, more preferably 30 to 300 mg / l and particularly preferably 50 to 200 mg / l Zr in complexed form (calculated as metal).

It additionally contains at least one organosilane and / or at least one hydrolysis product thereof and / or at least one condensation product thereof in a concentration range from 5 to 200 mg / l, more preferably from 10 to 100 mg / l and particularly preferably from 20 to 80 mg / l (calculated as Si).

The at least one organosilane preferably has at least one amino group. It is particularly preferably one which can be hydrolyzed to an aminopropylsilanol and / or to 2-aminoethyl-3-aminopropylsilanol and / or a bis (trimethoxysilylpropyl) amine.

The conversion / passivation solution can also contain the following components in the following concentration ranges and preferred concentration ranges: Zn 0 to 5 g / l 0.05 to 2 g / l Mn 0 to 1 g / l 0.05 to 1 g / l nitrate 0 to 10 g / l 0.01 to 5 g / l

iii) post-rinse solution

A rinsing solution for treating an already conversion-coated metallic surface is also described.

The rinsing solution contains molybdenum ions. These are preferably added to the rinsing solution as molybdate, more preferably as ammonium heptamolybdate and particularly preferably as ammonium heptamolybdate × 7 H _{2 O.}

Molybdenum ions can, however, also be added to the rinsing solution in the form of at least one salt containing molybdenum cations such as molybdenum chloride and then oxidized to molybdate by a suitable oxidizing agent, for example by the accelerators described above.

The final rinse solution also preferably contains molybdenum ions in combination with copper ions, tin ions or zirconium ions.

It particularly preferably contains molybdenum ions in combination with zirconium ions and optionally a polymer or copolymer, in particular selected from the group consisting of the polymer classes of polyamines, polyanilines, polyimines, polythiophenes and polypryrenes and their mixtures and copolymers and polyacrylic acid, the content of molybdenum ions and zirconium ions each in the range from 10 to 500 mg / l (calculated as metal).

The content of molybdenum ions is 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 30 to 300 mg / l, particularly preferably from 50 to 200 mg / l.

According to a further preferred embodiment, the post-rinse solution contains copper ions. The post-rinse solution then preferably contains this in a concentration of 5 to 225 mg / l, more preferably 150 to 225 mg / l.

According to a further embodiment, the rinsing solution contains at least one electrically conductive polymer selected from the group consisting of the polymer classes of polyamines, polyanilines, polyimines, polythiophenes and polypryrenes. A polyamine and / or polyimine, particularly preferably a polyamine, is preferably used.

The polyamine is preferably a polyethylene amine, and the polyimine is a polyethyleneimine.

The at least one electrically conductive polymer is preferably in a concentration in the range from 0.1 to 5.0 g / l, more preferably from 0.2 to 3.0 g / l and particularly preferably in the range from 0.5 to 1 , 5 g / l (calculated as pure polymer).

Cationic polymers such as polyamines or polyethyleneimines are preferably used as electrically conductive polymers.

The post-rinse solution preferably additionally comprises 10 to 500 mg / l, more preferably 30 to 300 mg / l and particularly preferably 50 to 200 mg / l Ti, Zr and / or Hf in complexed form (calculated as metal). These are preferably fluorocomplexes. In addition, the post-rinse solution preferably comprises 10 to 500 mg / l, more preferably 15 to 100 mg / l and particularly preferably 15 to 50 mg / l of free fluoride.

A post-rinse solution comprising Ti, Zr and / or Hf in complexed form preferably additionally contains at least one organosilane and / or at least one hydrolysis product thereof and / or at least one condensation product thereof in a concentration range from 5 to 200 mg / l, more preferably from 10 to 100 mg / l and particularly preferably from 20 to 80 mg / l (calculated as Si).

The at least one organosilane preferably has at least one amino group. It is particularly preferably one which can be hydrolyzed to an aminopropylsilanol and / or to 2-aminoethyl-3-aminopropylsilanol and / or a bis (trimethoxysilylpropyl) amine.

The pH of the post-rinse solution is preferably in the acidic range, more preferably in the range from 3 to 5, particularly preferably in the range from 3.5 to 5.

According to a preferred embodiment of the method according to the invention, a metallic surface is first treated with a conversion / passivation solution which contains 10 to 500 mg / l Zr in complexed form (calculated as metal) and optionally at least one organosilane and / or at least one hydrolysis product thereof and / or contains at least one condensation product thereof in a concentration range from 5 to 200 mg / l (calculated as Si), and thus a corresponding thin-film coating is formed on the metallic surface.

After optional drying, the metallic surface coated in this way is treated with a rinsing solution according to the invention and in this way a thin-film coating with a defined electrical conductivity is obtained.

Then - again after optional drying - an electrodeposition paint is cathodically deposited on the metallic surface coated in this way.

The method according to the invention allows the electrical conductivity of a conversion coating to be set in a targeted manner. The conductivity can be either be larger, the same size or smaller than that of a corresponding nickel-containing conversion coating.

The electrical conductivity of a conversion coating set using the method according to the invention can be influenced by varying the concentration of a given metal ion or electrically conductive polymer.

The present invention also relates to a concentrate which, by diluting with water by a factor of between 1 and 100, preferably between 5 and 50, and, if necessary, adding a pH-modifying substance, produces an aqueous composition according to the invention.

Finally, the present invention also relates to a conversion-coated metallic surface which can be obtained by the method according to the invention. In the following, the present invention is to be explained by non-restrictive exemplary embodiments and comparative examples; only Examples 4 and 5 are according to the invention.

Comparative example 1

A test plate made of electrolytically galvanized steel (ZE) was coated with a phosphating solution containing 1 g / l nickel. No rinsing was carried out. The current density i in A / cm ^{2 was then} measured via the voltage E in V applied vs. a silver / silver chloride (Ag / AgCl) electrode (see Fig. 1 : ZE_Variation11_2: curve 3). The measurement was carried out using so-called linear sweep voltammetry (potential range: -1.1 to -0.2 V _ref ; scan rate: 1 mV / s).

In all examples and comparative examples, the measured current density i is dependent on the electrical conductivity of the conversion coating. The following applies: the higher the measured current density i, the higher the electrical conductivity of the conversion coating. A direct measurement of the electrical conductivity in µS / cm, as it is possible in liquid media, cannot be carried out with conversion coatings.

In the present case, therefore, the current density i measured for a nickel-containing conversion coating is always used as a reference point for statements about the electrical conductivity of a given conversion coating.

The specification "1E" in the Figures 1 to 4 always stands for "10". For example, "1E-4" means "10 ^-4 " accordingly.

Comparative example 2

A test plate according to Comparative Example 1 was coated with a nickel-free phosphating solution without rinsing, and the current density i was then measured using the voltage E according to Comparative Example 1 (see FIG Fig. 1 . ZE_Variation1_1: curve 1; ZE_Variation1_3: curve 2).

How Fig. 1 it can be seen that the rest potential of the nickel-free system (comparative example 2) is shifted to the left compared to that of the nickel-containing system (comparative example 1). The electrical conductivity is also lower: the "arms" of curve 1 and curve 2 are each below curve 3, ie towards lower current densities.

Comparative example 3

A test plate according to Comparative Example 1 was made using a nickel-free

Coated phosphating solution. The test plate coated in this way was then treated with a post-rinse solution containing approx. 120 mg / l ZrF ₆ ^2- (calculated as Zr) and having a pH of approx. The current density i over the voltage E was measured according to comparative example 1 (see Fig. 2 . ZE_Variation6_1: curve 1; ZE_Variation6_2: curve 2). It is compared with Comparative Example 1 ( Fig. 2 : ZE_Variation11_2: curve 3).

How Fig. 2 it can be seen that the rest potential of the nickel-free system when using a post-rinse solution containing ZrF ₆ ^2- S (comparative example 3) is shifted to the left compared to that of the nickel-containing system (comparative example 1). The electrical conductivity is also lower in the nickel-free system mentioned (cf. the comments on Comparative Example 2).

example 1

A test plate according to Comparative Example 1 was coated using a nickel-free phosphating solution. The test plate coated in this way was then treated with a rinsing solution containing approx. 220 mg / l copper ions and having a pH of approx. The current density i over the voltage E was measured according to comparative example 1 (see Fig. 3 . ZE_Variation2_1: curve 1; ZE_Variation2_2: curve 2). Comparison is again made with comparative example 1 ( Fig. 3 : ZE_Variation11_2: curve 3).

How Fig. 3 It can be seen that the resting potential of the nickel-free system when using a post-rinse solution containing copper ions (Example 1) corresponds to that of the nickel-containing system (Comparative Example 1). The conductivity of this nickel-free system is slightly higher than that of the nickel-containing system.

Example 2

A test plate according to Comparative Example 1 was coated using a nickel-free phosphating solution. The test plate coated in this way was then treated with a rinsing solution which contained approx. 1 g / l (calculated on the pure polymer) of electrically conductive polyamine (Lupamin® 9030, manufacturer BASF) and had a pH of approx. The current density i over the voltage E was measured according to comparative example 1 (see Fig. 4 . ZE_Variation3_1: curve 1; ZE_Variation3_2: curve 2). It is compared with Comparative Example 1 ( Fig. 4 : ZE_Variation11_2: curve 3).

How Fig. 4 As can be seen, the rest potential of the nickel-free system when using a post-rinse solution containing an electrically conductive polymer (Example 2) corresponds to that of the nickel-containing system (Comparative Example 1). The electrical conductivity of the nickel-free system is somewhat reduced compared to the nickel-containing system.

Comparative example 3

A test plate made of hot-dip galvanized steel (EA) was coated with a phosphating solution containing 1 g / l nickel. The test plate coated in this way was then treated with a post-rinse solution containing approx. 120 mg / l ZrF ₆ ^2- (calculated as Zr) with a pH of approx. 4 and then the current density i in A / cm ² over the vs. one Silver / silver chloride (Ag / AgCl) electrode applied voltage E measured in V (see Fig. 5 : EA 173: curve 1). The measurement was carried out using so-called linear sweep voltammetry.

Comparative example 4

A test plate according to Comparative Example 3 was coated with a nickel-free phosphating solution without rinsing, and the current density i was then measured using the voltage E according to Comparative Example 3 (see FIG Fig. 5 . EA 167: curve 3; EA 167 2: curve 2).

How Fig. 5 it can be seen that the rest potential of the nickel-free system (comparative example 4) is shifted to the right compared to that of the nickel-containing system (comparative example 3). The electrical conductivity is significantly lower in the nickel-containing system, which is due to the passivation using the post-rinse solution containing ZrF ₆ ^2- .

Example 3

A test plate according to Comparative Example 3 was coated using a nickel-free phosphating solution. The test plate coated in this way was then treated with a post-rinse solution containing approx. 120 mg / l ZrF ₆ ^2- (calculated as Zr) and 220 mg / l molybdenum ions with a pH of approx. The current density i over the voltage E was measured according to comparative example 1 (see Fig. 6 . EA 178: curve 3; EA 178 2: curve 2). A comparison is made with comparative example 3 ( Fig. 6 : EA 173: curve 1).

How Fig. 6 As can be seen, the resting potential of the nickel-free system when using a post-rinse solution containing ZrF ₆ ² and molybdenum ions (example 3) corresponds to that of the nickel-containing system (comparative example 3). The addition of molybdenum ions (Example 3) to the post-rinse solution containing ZrF ₆ ^2- (Comparative Example 3) made it possible to significantly increase the conductivity on the substrate surface.

Comparative example 5

Hot-dip galvanized (HDG) or electrolytically galvanized (EG) test plates made of steel were sprayed with an aqueous cleaning solution which contained a surfactant and had a pH of 10.8 for 180 s at 60 ° C. The cleaning solution was then rinsed off the test plates by spraying them first with city water for 30 s and then with deionized water for 20 s. The cleaned test plates were then immersed for 175 s in a conversion / passivation solution which contained 40 mg / l Si, 140 mg / l Zr, 2 mg / l Cu and 30 mg / l free fluoride and had a pH of 4, 8 and a temperature of 30 ° C. The aqueous conversion / passivation solution was then rinsed off the test plates by immersing them in deionized water for 50 s and then spraying them with deionized water for 30 s. The test plates pretreated in this way were then either cathodically dip coated with a first special KTL lacquer (KTL 1) or with a second special KTL lacquer (KTL 2).

Example 4

Hot-dip galvanized (HDG) or electrolytically galvanized (EG) test plates made of steel were treated according to Comparative Example 5 with the difference that the aqueous conversion / passivation solution was then rinsed off the test plates by immersing them in an aqueous solution with 100 mg / l for 50 s Mo (calculated as metal), which was added in the form of ammonium heptamolybdate, (rinsing solution) was immersed and then sprayed with deionized water for 30 s.

Example 5

Hot-dip galvanized (HDG) or electrolytically galvanized (EG) test plates made of steel were treated according to Comparative Example 5 with the difference that the aqueous conversion / passivation solution was then rinsed off the test plates by placing them in an aqueous solution with 200 mg / l for 50 s Mo (calculated as metal), which was added in the form of ammonium heptamolybdate, (rinsing solution) was immersed and then sprayed with deionized water for 30 s.

Example 6

Hot-dip galvanized (HDG) or electrolytically galvanized (EG) test plates made of steel were treated according to Comparative Example 5 with the difference that the aqueous conversion / passivation solution additionally contained 100 mg / l Mo (calculated as metal), which was added in the form of ammonium heptamolybdate.

The test plates according to Comparative Example 5 (CE5) and Examples 4 to 6 (B4 to B6) were then subjected to a paint adhesion test by the automobile manufacturer PSA (Cataplasma test).

The cross-cut and paint loss results obtained are shown in Table 1 . For the cross-sectional results, 1 is the best and 6 is the worst. In the paint loss results, 100% means complete paint loss.

The test plates according to Comparative Example 5 (CE5) and Examples 4 to 6 (B4 to B6) were also examined using the so-called cathodic polarization method.

This method describes a short-term electrochemical test that is carried out on coated steel sheets that have been damaged in a defined manner. According to the principle of an electrostatic holding test, it is tested how well the coating of the test sheet resists the process of corrosive infiltration.

The scribed test sheet (scribe for 0.5 mm scribe width, e.g. Clemen test tip (R = 1 mm); template for scribing) is installed in the measuring cell (galvanostat as power source (20 mA in the control range); thermostat with connections for temperature control 40 ° C +/- 0.5 ° C; glass electrolysis cell with temperature control jacket, complete with reference electrode; counter electrode, sealing ring and olive). Make sure that the two electrode rods are parallel to the scratch.

After the lid has clicked into place, the cell is filled with approx. 400 mL 0.1 M Na sulfate solution. Then the clamps are connected as follows: green-blue clamp to working electrode (sheet metal), orange-red clamp to counter electrode (electrode with parallel bars), white clamp to reference electrode (in Haber-Luggin capillary).

The cathodic polarization is then started via the control software (control unit with software) and a current of 20 mA is set on the test panel over a period of 24 hours. During this time, the measuring cell is tempered to 40 ° C +/- 0.5 degrees with the aid of the thermostat. During the 24-hour exposure period, hydrogen develops on the cathode (test sheet) and oxygen on the counter electrode.

After the measurement, the sheet metal is removed immediately to avoid secondary corrosion, rinsed with deionized water and dried in the air. With the help of a blunt knife, the peeled paint layer is removed. Further peeled paint areas can be removed with a strong textile adhesive tape (e.g. Tesa tape 4657 gray). The exposed area is then evaluated using a ruler and, if necessary, a magnifying glass).

$$\mathrm{d}=\left({\mathrm{d}}_1-\mathrm{w}\right)/2$$

• d₁: Mittelwert der Enthaftungsbreite in mm
• a₁, a₂, a₃: Einzelwerte der Enthaftungsbreite in mm
• n: Anzahl der Einzelwerte
• w: Breite des Anritzes in mm
• d: mittlere Breite der Enthaftung, Unterwanderungsbreite in mm

For this purpose, the width of the detached surface is determined with an accuracy of 0.5 mm at a distance of 5 mm. The mean width of the delamination is calculated according to the following equations: $${\mathrm{d}}_1=\left(a_1+a_2+a_3+...\right)/\mathrm{n}$$

$$\mathrm{d}=\left({\mathrm{d}}_1-\mathrm{w}\right)/2$$

• d ₁ : Average value of the delamination width in mm
• a ₁ , a ₂ , a ₃ : Individual values of the delamination width in mm
• n: number of individual values
• w: width of the scratch in mm
• d: mean width of the delamination, infiltration width in mm

The result is given in mm and rounded to one decimal place. The standard deviation of the measurements is below 20%. The so determined Delamination values are also shown in Table 1 .

Test plates according to Comparative Examples 1 to 3 (CE1 to CE3) and Examples 1 and 2 (B1 and B2) were KTL-coated and then subjected to a cross-cut test according to DIN EN ISO 2409. 3 panels each were tested before and after exposure to condensation water for 240 hours (DIN EN ISO 6270-2 CH). The corresponding results can be found in Table 2. A cross-section result of 0 is the best, and a cross-section of 5 is the worst. <b> Table 1: </b> (Cf.-) Ex. Test plate KTL paint Cross cut (1-6) Paint loss (%) Delamination (mm) VB5 HDG KTL 1 6th 50 11.9 6th 50 KTL 2 2 0 8.9 2 0 EG KTL 1 6th 50 8.5 6th 50 KTL 2 2 0 6.3 2 0 B4 HDG KTL 1 3 1 2.9 2 1 KTL 2 2 0 2.8 2 0 EG KTL 1 2 1 1.9 4th 1 KTL 2 2 0 2.4 1 0 B5 HDG KTL 1 5 1 3.3 5 1 KTL 2 3 0 2.6 2 0 EG KTL 1 2 1 2.1 2 1 KTL 2 2 0 1.7 2 0 B6 HDG KTL 1 2 1 2.8 2 0 KTL 2 2 0 2.2 2 0 EG KTL 1 1 1 1.4 2 0 KTL 2 2 0 1.6 1 0 (Comparative) example Cross cut (0-5) from stress after exposure VB1 0/0/0 1/1/0 VB2 1/0/0 3/1/0 VB3 0/0/1 1/5/4 B1 1/0/0 0/0/1 B2 1/1/1 1/1/1

As can be seen in Tab. 1 , the use of Mo both in the conversion / passivation solution and in the rinsing solution, especially in connection with the KTL 1 lacquer, has the advantage of improved lacquer adhesion (lower cross-cut and lacquer loss values for B4 to B6 compared to VB5). In addition, Tab. 1 shows that Mo leads to a significantly reduced delamination both in the conversion / passivation solution and in the post-rinse solution (B4 to B6 compared to VB5).

This positive effect is due to the fact that the use of Mo leads to an increased conductivity of the surface and thus largely prevents an attack on the conversion layer during the current flow-dependent cathodic dip painting.

Tab. 2 shows the poor results of VB2 and especially VB3 after exposure, while B1 (copper ions) and B2 (electrically conductive polyamine) deliver good - VB1 (nickel-containing phosphating) - comparable results.

Example 7

A test plate according to Comparative Example 1 was coated using a nickel-free phosphating solution. The test plate coated in this way was then treated with a rinsing solution which contained approx. 1 g / l (calculated on the pure polymer) of electrically conductive polyimine with a number average molecular weight of 5000 g / mol (Lupasol® G 100, manufacturer BASF) and a pH -Value of approx. 4.

Example 8

A test plate according to Comparative Example 1 was coated using a nickel-free phosphating solution. The test plate coated in this way was then treated with a post-rinse solution containing 130 mg / l ZrF ₆ ^2- (calculated as Zr) and 20 mg / l molybdenum ions, which additionally contained 1.2 g / l (calculated on the pure polymer) polyacrylic acid with a number average Molecular weight of 60,000 g / mol and a pH of about 4.

Comparative example 6

Corresponds to comparative example 1 with the difference that a test plate made of hot-dip galvanized steel (EA) is used.

Comparative example 7

Corresponds to comparative example 2 with the difference that a test plate made of hot-dip galvanized steel (EA) is used.

Example 9

A test plate made of hot-dip galvanized steel (EA) was coated with a nickel-free phosphating solution. The test plate coated in this way was then treated with a rinsing solution which contained approx. 1 g / l (calculated on the pure polymer) of electrically conductive polyimine with a number average molecular weight of 5000 g / mol (Lupasol® G 100, manufacturer BASF) and a pH -Value of approx. 4.

Example 10

A test plate made of hot-dip galvanized steel (EA) was coated with a nickel-free phosphating solution. The test plate coated in this way was then treated with a post-rinse solution containing 130 mg / l ZrF ₆ ^2- (calculated as Zr) and 20 mg / l molybdenum ions, which additionally contained 1.2 g / l (calculated on the pure polymer) polyacrylic acid with a number average Molecular weight of 60,000 g / mol and a pH of about 4.

Comparative example 8

Corresponds to Comparative Example 1 with the difference that a test plate made of steel is used.

Comparative example 9

Corresponds to Comparative Example 2 with the difference that a test plate made of steel is used.

Example 11

A steel test plate was coated with a nickel-free phosphating solution. The test plate coated in this way was then treated with a rinsing solution containing 230 mg / l copper ions and having a pH of approx.

Comparative example 10

Corresponds to comparative example 1 with the difference that the phosphating _{solution contains 1 g / l BF 4} ^- and 0.2 g / l SiF ₆ ^2- and after phosphating with an approx. 120 mg / l ZrF ₆ ^2- (calculated as Zr) containing rinsing solution with a pH of approx. 4 is treated.

Comparative Example 11

Corresponds to comparative example 2 with the difference that the phosphating solution contains _{1 g / l BF 4} ^- and 0.2 g / l SiF ₆ ^2-.

Example 12

A test plate made of electrolytically galvanized steel (ZE) was coated with a nickel-free phosphating solution which contained 1 g / l BF ₄ ^- and 0.2 g / l SiF ₆ ^2- . The test plate coated in this way was then treated with a post-rinse solution containing 160 mg / l ZrF ₆ ^2- (calculated as Zr) and 240 mg / l molybdenum ions with a pH of approx.

Comparative example 12

Corresponds to comparative example 1 with the difference that a test plate made of hot-dip galvanized steel (EA) is used, the phosphating _{solution contains 1 g / l BF 4} ^- and 0.2 g / l SiF ₆ ^2- and after phosphating with a with an approx. 120 mg / l ZrF ₆ ^2- (calculated as Zr) containing rinsing solution with a pH value of approx. 4 is treated.

Comparative example 13

Corresponds to comparative example 2 with the difference that a test plate made of hot-dip galvanized steel (EA) is used and the phosphating solution is 1 g / l BF ₄ ^- and Contains 0.2 g / l SiF ₆ ^2- .

Example 13

A test plate made of hot-dip galvanized steel (EA) was coated with a nickel-free phosphating _{solution which contained 1 g / l BF 4} ^- and 0.2 g / l SiF ₆ ^2- . The test plate coated in this way was then treated with a post-rinse solution containing 160 mg / l ZrF ₆ ^2- (calculated as Zr) and 240 mg / l molybdenum ions with a pH of approx.

Comparative example 14

Corresponds to comparative example 1 with the difference that the phosphating solution _{contains 1 g / l SiF 6} ^2- and after phosphating with a post-rinse solution containing approx. 120 mg / l ZrF ₆ ^2- (calculated as Zr) with a pH of about 4 is treated.

Comparative example 15

Corresponds to comparative example 2 with the difference that the phosphating solution contains _{1 g / l SiF 6} ^2-.

Example 14

A test plate made of electrolytically galvanized steel (ZE) was coated with a nickel-free phosphating solution which contained 1 g / l SiF ₆ ^2- . The test plate coated in this way was then treated with a post-rinse solution containing 160 mg / l ZrF ₆ ^2- (calculated as Zr) and 240 mg / l molybdenum ions with a pH of approx.

Comparative example 16

Corresponds to comparative example 1 with the difference that a test plate made of hot-dip galvanized steel (EA) is used, the phosphating solution _{contains 1 g / l SiF 6} ^2- and after phosphating with an approx. 120 mg / l ZrF ₆ ^2- (calculated is treated as a post-rinse solution containing Zr) with a pH of approx. 4.

Comparative example 17

Corresponds to comparative example 2 with the difference that a test plate made of hot-dip galvanized steel (EA) is used and the phosphating solution contains _{1 g / l SiF 6} ^2-.

Example 15

A test plate made of hot-dip galvanized steel (EA) was coated with a nickel-free phosphating solution which contained 1 g / l SiF ₆ ^2- . The test plate coated in this way was then treated with a post-rinse solution containing 160 mg / l ZrF ₆ ^2- (calculated as Zr) and 240 mg / l molybdenum ions with a pH of approx.

Test plates according to Comparative Examples 1, 2, 6 and 7 (CE1, CE2, CE6 and CE7) and Examples 7 to 10 (B7 to B10) were KTL-coated. Four programs were used, which differed in terms of (a) the ramp duration - i.e. the time until the maximum voltage is reached -, (b) the maximum voltage and / or (c) the duration of the application of the maximum voltage: Program 1: (a) 30 sec. (b) 240V (c) 150 sec. Program 2: (a) 30 sec. (b) 220V (c) 150 sec. Program 3: (a) 3 sec. (b) 240V (c) 150 sec. Program 4: (a) 3 sec. (b) 220V (c) 150 sec.

The layer thickness of the deposited KTL lacquer, measured in each case by means of a Fischer DUALSCOPE®, is shown in Tab. 3 .

Test plates according to Comparative Examples 8 to 17 (VB8 to VB17) and Examples 11 to 15 (B11 to B15) were subjected to an X-ray fluorescence analysis (XRF). Tab. 4 shows the specific content of copper or zirconium and molybdenum (each calculated as metal) in the surface. The test panels mentioned were then KTL-coated. The following programs were used, which, depending on the (comparative) example, differ with regard to (a) the ramp duration - i.e. the time until the maximum voltage is reached -, (b) the maximum voltage and / or (c) the duration of the application of the maximum voltage: VB8, VB9, B11: (a) 30 sec. (b) 250V (c) 240 sec. VB10, VB11, VB14, VB15, B12, B14: (a) 30 sec. (b) 260V (c) 300 sec. VB12; VB13, VB16; VB17, B13, B15: (a) 30 sec. (b) 260V (c) 280 sec.

The layer thickness of the 2nd layer measured by means of a Fischer DUALSCOPE® The KTL lacquer deposited is shown in Tab. 4 . <b> Table 3: </b> (Comparative) example Program 1: Layer thickness (µm) Program 2: Layer thickness (µm) Program 3: Layer thickness (µm) Program 4: Layer thickness (µm) VB1 19.4 17.7 21.4 18.4 VB2 16 15th 17.4 15.9 B7 20.4 17.8 22.6 19.1 B8 19th 17.4 19.8 18th VB6 21.5 19.5 21.2 19.2 VB7 19.1 17th 18.6 17.1 B9 22.8 20th 23.5 20.5 B10 20.3 18.7 21.6 18.8 (Comparative) example Cu content (mg / m ² ) Mo content (mg / m ² ) Zr content (mg / m ² ) KTL thickness (µm) VB8 0 --- --- 19.5 VB9 0 --- --- 19.9 B11 20th --- --- 22.9 VB10 --- 0 5 19.7 VB11 --- 0 0 18th B12 --- 8th 6th 19.6 VB12 --- 0 7th 21.6 VB13 --- 0 0 20th B13 --- 5 6th 21.7 VB14 --- 0 5 19.7 VB15 --- 0 0 18th B14 --- 9 8th 19.1 VB16 --- 0 6th 22.1 VB17 --- 0 0 20th B15 --- 10 10 21.7

Tab. 3 shows a clear decrease in the layer thickness of the KTL lacquer with the nickel-free compared to the nickel-containing phosphating (VB2 vs. VB1; VB7 vs. VB6). By using the rinsing solutions according to the invention, however, the layer thickness obtained with nickel-free phosphating can be increased again (B7 and B8 vs. VB2; B9 and B10 vs. VB6) - in the case of B7 and B9 even beyond the level of nickel-containing phosphating.

Table 4 shows that the use of a copper-containing rinsing solution according to the invention (with prior nickel-free phosphating) leads to the incorporation of copper into the test plate surface. As a result, there is an improved KTL deposition - even compared to the nickel-containing system (B11 vs. VB8). The copper content of the surface increases its conductivity. This leads to a more effective KTL deposition, which is expressed in the higher layer thickness of the KTL lacquer under otherwise identical conditions. The use of zirconium and molybdenum-containing rinsing solutions according to the invention (after nickel-free phosphating) leads to the incorporation of molybdenum into the surface of the test plates, which brings the KTL deposition back (approximately) to the level of the nickel-containing phosphating (B12 vs. VB10; B13 vs VB12 .; B14 vs. VB14; B15 vs. VB16).

Claims (8)

1. A method for specifically adjusting the electrical conductivity of a conversion coating, wherein a metallic surface is first treated with a conversion/passivating solution which comprises 10 to 500 mg/l of Zr in complexed form, calculated as metal, and comprises at least one organosilane and/or at least one hydrolysis product thereof and/or at least one condensation product thereof in a concentration range of 5 to 200 mg/l, calculated as Si, so as to form a corresponding thin-film coating on the metallic surface, and wherein the metallic surface thus coated, after optional drying, is treated with an aqueous composition as an after-rinse solution which comprises 20 to 225 mg/l of molybdenum ions.
2. The method according to claim 1, wherein the organosilane is one which can be hydrolyzed to an aminopropylsilanol and/or to 2-aminoethyl-3-aminopropylsilanol and/or is a bis(trimethoxysilylpropyl)amine.
3. The method according to claim 1 or 2, wherein the aqueous composition comprises zirconium ions.
4. The method according to claim 3, wherein the aqueous composition comprises 50 to 200 mg/l of zirconium ions.
5. The method according to any of the preceding claims, wherein the aqueous composition comprises a polyamine and/or polyimine.
6. The method according to any of the preceding claims, wherein the aqueous composition comprises copper ions.
7. The method according to claim 6, wherein the aqueous composition comprises 150 to 225 mg/l of copper ions.
8. A conversion-coated metallic surface which is obtainable by a method according to any of claims 1 to 7.

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