Aqueous dip-coating composition for electroconductive substrates, comprising dissolved bismuth

Abstract

The present invention relates to an aqueous coating composition (A) having a pH in a range from 4.0 to 6.5 and comprising at least one cathodically depositable binder (A1), a total amount of at least 130 ppm of Bi, based on the total weight of (A), including at least 30 ppm of Bi in a form (A3) in solution in (A) and optionally at least 100 ppm of Bi in a form (A4) not in solution in (A), and at least one at least bidentate complexing agent (A5) suitable for complexing Bi, (A5) being a compound of the general formula (1) or an anion of this compound, for at least partly coating an electrically conductive substrate with an electrocoat material, to a method for producing (A), to the use of (A) for at least partly coating an electrically conductive substrate with an electrocoat material, to a corresponding coating method, to an at least partly coated substrate obtainable by this method, and to a method for setting and/or maintaining the concentration of component (A3) and/or optionally (A4) in the coating composition (A) during the coating method.

Claims

1. An aqueous coating composition (A) for at least partly coating an electrically conductive substrate with an electrocoat material, comprising: (A1) at least one cathodically depositable binder; (A2) optionally at least one crosslinking agent; bismuth; and (A5) at least one at least bidentate complexing agent of formula (1) or an anion of said compound which is suitable for complexing bismuth; the coating composition (A) having a pH in a range from 4.0 to 6.5, wherein the coating composition (A) comprises a total amount of at least 130 ppm of bismuth, based on the total weight of the coating composition (A), including: (A3) at least 30 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is in solution in the coating composition (A), and (A4) optionally at least 100 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is not in solution in the coating composition (A), ##STR00004## wherein R.sup.1 is a C.sub.1-6 aliphatic radical substituted by at least one OH group, m is 0 or 1, R.sup.a and R.sup.b in each case independently of one another are selected from the group consisting of H and C.sub.1-6 aliphatic radicals, optionally substituted by at least one OH group, and mixtures thereof, R.sup.2, R.sup.3, R.sup.4, and R.sup.5 in each case independently of one another are H or are a C.sub.1-6 aliphatic radical optionally substituted by at least one OH group, n is 1 or 2, o is 1 or 2, p is 0, 1, 2, or 3, and R.sup.6 is C(O)OH, S(O).sub.2OH, P(O)(OH).sub.2, NR.sup.7R.sup.8, or a C.sub.1-6 aliphatic radical which is substituted by at least one OH group, where R.sup.7 and R.sup.8 in each case independently of one another are selected from the group consisting of H and C.sub.1-6 aliphatic radicals which are optionally substituted by at least one OH group and mixtures thereof; with the proviso that at least one of the radicals R.sup.7 and R.sup.8 is a C.sub.1-6 aliphatic radical which is substituted by at least one OH group.

2. The coating composition (A) as claimed in claim 1, wherein at least 100 ppm of bismuth, based on the total weight of the coating composition (A), are present as component (A3) in a form in which it is in solution in the coating composition (A).

3. The coating composition (A) as claimed in claim 1, wherein the radical R.sup.6 is C(O)OH or is NR.sup.7R.sup.8 or is a C.sub.1-6 aliphatic radical which is substituted by at least one OH group.

4. The coating composition (A) as claimed in claim 1, wherein: R.sup.1 is a C.sub.1-4 aliphatic radical substituted by at least one OH group, m is 0 or 1, R.sup.a and R.sup.b in each case independently of one another are selected from the group consisting of H and C.sub.1-4 aliphatic radicals, optionally substituted by at least one OH group, and mixtures thereof, R.sup.2, R.sup.3, R.sup.4, and R.sup.5 in each case independently of one another are H or are a C.sub.1-4 aliphatic radical optionally substituted by at least one OH group, n is 1 or 2, o is 1 or 2, p is 0, 1, or 2, and R.sup.6 is C(O)OH, NR.sup.7R.sup.8, or a C.sub.1-4 aliphatic radical which is substituted by at least one OH group, where R.sup.7 and R.sup.8 in each case independently of one another are selected from the group consisting of H and C.sub.1-6 aliphatic radicals which are optionally substituted by at least one OH group, and mixtures thereof; with the proviso that at least one of the radicals R.sup.7 and R.sup.8 is a C.sub.1-6 aliphatic radical which is substituted by at least one OH group.

5. The coating composition (A) as claimed in claim 1, wherein component (A5) is selected from the group consisting of N,N,N,N-tetrakis-2-hydroxypropylethylenediamine, N,N-bis(2-hydroxyethyl)glycine, N-(tri(hydroxy-methyl)methyl)glycine, N-hydroxyethylaminoacetic acid, triethanolamine, triisopropanolamine, and N,N,NN-tetrakis-2-hydroxyethylethylenediamine, and mixtures thereof.

6. The coating composition (A) as claimed in claim 1, wherein the at least one complexing agent (A5) is present in the aqueous coating composition (A) in a fraction of at least 5 mol %, based on the total amount of bismuth present in the coating composition (A).

7. The coating composition (A) as claimed in claim 1, wherein components (A3) and (A5) are present in the form of a complex and/or salt of components (A3) and (A5) in the coating composition (A).

8. The coating composition (A) as claimed in claim 1, wherein the coating composition (A) comprises: (A4) at least 100 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is not in solution in the coating composition (A).

9. The coating composition (A) as claimed in claim 1, wherein the coating composition (A) comprises a total amount of at least 300 ppm of bismuth, based on the total weight of the coating composition (A), including (A3) at least 100 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is in solution in the coating composition (A), and (A4) at least 200 ppm of bismuth, based on the total weight of the coating composition (A), in a form in which it is not in solution in the coating composition (A).

10. The coating composition (A) as claimed in claim 1, wherein the total amount of bismuth present in the coating composition (A) is in a range from at least 500 ppm to 20 000 ppm.

11. The coating composition (A) as claimed in claim 1, wherein the coating composition (A) is obtainable by at least partly converting at least one water-insoluble bismuth compound, by partial reaction of this compound with at least one at least bidentate complexing agent (A5) suitable for complexing bismuth, into at least one water-soluble bismuth compound (A3) in water, optionally in the presence of at least one of components (A1) and/or (A2), to give a mixture comprising at least components (A3) and (A5), and optionally (A1) and/or (A2) and/or (A4), of the coating composition (A), and optionally mixing the resulting mixture at least with component (A1) and optionally component (A2), to give the coating composition (A).

12. The coating composition (A) as claimed in claim 1, wherein the binder (A1) is a polymeric resin which has at least partly protonated tertiary amino groups.

13. The coating composition (A) as claimed in claim 12, wherein the tertiary amino groups each independently of one another have at least two C.sub.1-3 alkyl groups each at least singly substituted by a hydroxyl group.

14. A method for producing the aqueous coating composition (A) as claimed in claim 1, wherein the method comprises at least step (0): (0) at least partly converting at least one water-insoluble bismuth compound, by at least partial reaction of this compound with at least one complexing agent (A5), into at least one water-soluble bismuth compound (A3) in water, to give a mixture comprising at least components (A3) and (A5) and also, optionally, (A4) of the coating composition (A).

15. A method for producing an electrically conductive substrate comprising coating at least part of an electrically conductive substrate with a coating composition according to claim 1.

16. A method for at least partly coating an electrically conductive substrate with an electrocoat material, comprising at least a step (1): (1) contacting the electrically conductive substrate, connected as cathode, with the aqueous coating composition (A) as claimed in claim 1, step (1) being carried out in at least two successive stages (1a) and (1b): (1a) at an applied voltage in a range from 1 to 50 V, which is applied over a duration of at least 5 seconds, and (1b) at an applied voltage in a range from 50 to 400 V, with the proviso that the voltage applied in stage (1b) is greater by at least 10 V than the voltage applied in stage (1a).

17. The method as claimed in claim 16, wherein the voltage applied in stage (1a) is such that the deposition current density is at least 1 A/m.sup.2.

18. The method as claimed in claim 16, wherein the voltage applied in stage (1a) is applied over a duration in a range from at least 5 to 300 seconds.

19. The method as claimed in claim 16, wherein the voltage applied in stage (1b) in the range from 50 to 400 V takes place in a time interval of 0 to 300 seconds after implementation of stage (1a) and is maintained for a period in the range from 10 to 300 seconds at a value within the stated voltage range of 50 to 400 V.

20. An electrically conductive substrate coated at least partly with the aqueous coating composition (A) as claimed in claim 1.

21. An article or component produced from at least one substrate as claimed in claim 20.

22. A method for setting and/or maintaining the concentration of component (A3) and/or optionally (A4) in the coating composition (A) during implementation of the method according to claim 16, wherein at preselected intervals of time, a determination is made of the fraction of component (A3) and/or optionally (A4) in the coating composition (A) in ppm, based on the total weight of the coating composition (A), and the fraction of component (A5) in the coating composition (A) is increased no later than when the fraction of component (A3) in ppm is lower than a preselected setpoint value for this component in the coating composition (A), or the fraction of component (A4) optionally present in the coating composition (A) is increased no later than when the fraction of component (A4) in ppm is lower than a preselected setpoint value for this component in the coating composition (A).

Description

INVENTIVE AND COMPARATIVE EXAMPLES

(1) 1. Production of Inventive Aqueous Coating Compositions and of a Comparative Coating Composition V1

(2) The CathoGuard 520 and CathoGuard 800 pigment pastes from BASF that are used for producing the exemplary inventive coating compositions below contain bismuth subnitrate. The skilled person knows of the production of such pigment pastes from, for example, DE 10 2008 016 220 A1 (page 7, table 1, variant B).

(3) Coating Composition Z1

(4) 9 g of the commercially available product Quadrol (N,N,N,N-tetrakis-2-hydroxypropylethylenediamine) are introduced into 2402.5 g of deionized water to produce a mixture M1. The mixture M1 is subsequently admixed, furthermore, with 295 g of a pigment paste (commercially available product CathoGuard 520 from BASF with a solids content of 65.0 wt %) with stirring at room temperature (18-23 C.), to give the mixture M2. The mixture M2 is stirred over a time of 26 hours at room temperature (18-23 C.). This resulting mixture is subsequently admixed with 2215 g of an aqueous dispersion of a binder and of a crosslinking agent (commercially available product CathoGuard 520 from BASF with a solids content of 37.5 wt %). Following this addition, the resulting mixture is admixed with an amount of acetic acid so as to bring about a pH of 5.7. The molar ratio of bismuth (calculated as metal) to Quadrol in the coating composition is 1:0.5.

(5) Coating Composition Z2

(6) Coating composition Z2 is produced in analogy to the method described in connection with coating composition Z1, with the difference that instead of Quadrol (N,N,N,N-tetrakis-2-hydroxypropylethylenediamine, 5.02 g of the commercially available product bicine (N,N-bis(2-hydroxyethyl)glycine) are used. The molar ratio of bismuth (calculated as metal) to bicine in the coating composition is 1:0.5.

(7) Coating Composition Z3

(8) Coating composition Z3 is produced in analogy to the method described in connection with coating composition Z1, with the difference that instead of Quadrol (N,N,N,N-tetrakis-2-hydroxypropylethylenediamine), 7.27 g of THEED (N,N,N,N-tetrakis-2-hydroxyethylethylenediamine) are used. Furthermore, before addition of the aqueous dispersion of the binder and crosslinking agent, the mixture M2 is stirred for a time of 23 hours at room temperature (18-23 C.). The molar ratio of bismuth (calculated as metal) to THEED in the coating composition is 1:0.5.

(9) Coating Composition Z4

(10) Coating composition Z4 is produced by adding a further 15.06 g of bicine (N,N-bis((2-hydroxyethyl)glycine) to coating composition Z2. Moreover, thereafter, a pH of 5.55 is set by addition of acetic acid. The molar ratio of bismuth (calculated as metal) to bicine in the coating composition is 1:2.

(11) Table 1a provides an overview of the resulting inventive coating compositions Z1 to Z4.

(12) TABLE-US-00001 TABLE 1a Inventive examples Z1-Z4 Z1 Z2 Z3 Z4 CathoGuard 520/wt % 48.82 48.86 48.83 48.71 THEED/wt % 0.15 Quadrol/wt % 0.18 Bicine/wt % 0.10 0.41 Deionized water/wt % 45.01 45.04 45.02 44.91 Pigment paste CathoGuard 5.99 6.00 6.00 5.98 520 containing bismuth subnitrate/wt % pH 5.70 5.70 5.70 5.55 Conductivity/S/cm

(13) The respective pH values in table 1a are determined in each case at a temperature in the range from 18 to 23 C., where ascertained. Where the pH of the respective coating composition is adjusted subsequently by addition of an acid, the amounts of acid used are not given in the table above.

(14) Coating Composition Z5

(15) 60.24 g of bicine (N,N-bis(2-hydroxyethyl)glycine) are introduced into 2564 g of deionized water to produce a mixture M1. The mixture M1 is subsequently admixed, furthermore, with 306 g of a pigment paste (commercially available product CathoGuard 800 from BASF with a solids content of 65 wt %) with stirring at room temperature (18-23 C.), to give the mixture M2. The mixture M2 is then stirred over a time of 22 hours at room temperature (18-23 C.). This resulting mixture is subsequently admixed with 2130 g of an aqueous dispersion of a binder and of a crosslinking agent (commercially available product CathoGuard 800 from BASF with a solids content of 37.5 wt %). The molar ratio of bismuth (calculated as metal) to Bicine in the coating composition is 1:6.

(16) Coating Composition Z6

(17) 87.26 g of THEED are introduced into 2564 g of deionized water to prepare a mixture M1, and the pH of the mixture M1 is adjusted to 5.7 by addition of acetic acid. Added subsequently to the mixture M1, moreover, are 306 g of a pigment paste (commercially available product CathoGuard 520 from BASF with a solids content of 65 wt %) with stirring at room temperature (18-23 C.), to give the mixture M2. The mixture M2 is stirred over a time of 22 hours at room temperature (18-23 C.). This resulting mixture is thereafter admixed with 2130 g of an aqueous dispersion of a binder and of a crosslinking agent (commercially available product CathoGuard 520 from BASF with a solids content of 37.5 wt %). The molar ratio of bismuth (calculated as metal) to THEED in the coating composition is 1:6.

(18) Coating Composition Z7

(19) Coating composition Z7 is produced in analogy to the method described in connection with coating composition Z5, with the difference that instead of bicine, 53.99 g of Quadrol are used and, following addition of the pigment paste, the pH of the mixture M2 is adjusted to 5.68 by addition of lactic acid. Moreover, following addition of the aqueous dispersion of the binder and of the crosslinking agent, the pH is again adjusted using lactic acid to 5.7. The molar ratio of bismuth (calculated as metal) to Quadrol in the coating composition is 1:3.

(20) Table 1b provides an overview of the resulting inventive coating compositions Z5 to Z7.

(21) TABLE-US-00002 TABLE 1b Inventive examples Z5-7 Z5 Z6 Z7 CathoGuard 800/wt % 42.09 42.14 CathoGuard 520/wt % 41.87 Bicine/wt % 1.19 THEED/wt % 1.72 Quadrol/wt % 1.07 Deionized water/wt. % 50.67 50.40 50.73 Pigment paste CathoGuard 6.05 6.05 800 containing bismuth subnitrate/wt % Pigment paste CathoGuard 6.02 520 containing bismuth subnitrate/wt % pH 5.61 5.77 5.70 Conductivity/S/cm 2070 5210 3340

(22) The respective pH values and conductivities in table 1b are determined in each case at a temperature in the range from 18 to 23 C. Where the pH of the respective coating composition is adjusted subsequently by addition of an acid, the amounts of acid used are not given in the table above.

(23) Coating Composition Z8

(24) A mixture of bicine (N,N-bis((2-hydroxyethyl)glycine) (32.6 g) and deionized water (910 g) and bismuth subnitrate (57.4 g) is prepared and is stirred for a time of 24 hours at a temperature in a range from 18 to 23 C. The undissolved fraction is then separated off using a fluted filter. The filtrate is made up to 1000 g with deionized water and the bismuth content is determined by X-ray fluorescence analysis. It amounts to 5 g/kg. The filtrate thus admixed with deionized water is used as Bi1.

(25) An aqueous dispersion of a binder and crosslinking agent (commercially available product CathoGuard 520 from BASF, with a solids content of 37.5 wt %), a pigment paste P1, and fractions of deionized water are combined and mixed with stirring at room temperature (18-23 C.). A total of 2130 g of CathoGuard 520, 306 g of pigment paste P1, and 1564 g of deionized water are used here. Subsequently Bi1 (1000 g) is added to prepare the coating composition Z8, and the resulting mixture is stirred for a time of 24 hours.

(26) The pigment paste P1 which is used is prepared in accordance with the method described in DE 10 2008 016 220 A1, page 7, table 1, variant B, but in the present case no bismuth subnitrate is used for preparing the pigment paste P1. The pigment paste P1 therefore contains no bismuth subnitrate.

(27) Coating Composition Z9

(28) A mixture of bicine (N,N-bis((2-hydroxyethyl)glycine) (40.32 g) and deionized water (508.2 g) and bismuth subnitrate (9.0 g) is prepared and is stirred for a time of 24 hours at a temperature in a range from 18 to 23 C. The undissolved fraction is then separated off using a fluted filter. The filtrate is made up to 1000 g with deionized water and the bismuth content is determined by X-ray fluorescence analysis. It amounts to 5.82 g/kg. The filtrate thus admixed with deionized water is used as Bi2.

(29) An aqueous dispersion of a binder and crosslinking agent (commercially available product CathoGuard 800 from BASF, with a solids content of 37.5 wt %), a pigment paste P1, and fractions of deionized water are combined and mixed with stirring at room temperature (18-23 C.). Pigment paste P1 corresponds to the pigment paste used in preparing Z8. A total of 1830 g of CathoGuard 800, 223 g of pigment paste P1, and 1079 g of deionized water are used here. Subsequently Bi2 (998 g) is added to prepare the coating composition Z9, and the resulting mixture is stirred for a time of 24 hours.

(30) Coating Composition Z10

(31) A mixture of Bicin (N,N-bis((2-hydroxyethyl)glycine) (96.60 g) and deionized water (846.0 g) and bismuth subnitrate (57.4 g) is prepared and is stirred for a time of 24 hours at a temperature in a range from 18 to 23 C. The undissolved fraction is then separated off using a fluted filter. The filtrate is made up to 1000 g with deionized water and the bismuth content is determined by X-ray fluorescence analysis. It amounts to 13.50 g/L. The filtrate thus admixed with deionized water is used as Bi3.

(32) An aqueous dispersion of a binder and crosslinking agent (commercially available product CathoGuard 800 from BASF, with a solids content of 37.5 wt %), a pigment paste P1, and fractions of deionized water are combined and mixed with stirring at room temperature (18-23 C.). Pigment paste P1 corresponds to the pigment paste used in preparing Z8 and Z9. A total of 2215 g of CathoGuard 800, 270 g of pigment paste P1, and 2330 g of deionized water are used here. Subsequently Bi3 (185 g) is added to prepare the coating composition Z10, and the resulting mixture is stirred for a time of 24 hours.

(33) Comparative Coating Composition V1

(34) An aqueous dispersion of a binder and of a crosslinking agent (commercially available product CathoGuard 520 from BASF with a solids content of 37.5 wt %), a pigment paste (commercially available product CathoGuard 520 from BASF with a solids content of 65.0 wt %), and fractions of deionized water are combined to form a comparative coating composition (V1) and mixed with stirring at room temperature (18-23 C.). A total of 2275 g of CathoGuard 520, 295 g of CathoGuard 520 pigment paste, and 2430 g of deionized water are used. The pigment paste used to prepare V1, CathoGuard 520 from BASF, contains bismuth subnitrate.

(35) Comparative Coating Composition V2

(36) Coating composition V2 is prepared in analogy to the method described in connection with coating composition Z1, with the difference that instead of Quadrol 23.11 g of taurine are used and, following addition of the pigment paste, the pH of the mixture M2 is adjusted to 5.70 by addition of acetic acid. The molar ratio of bismuth (calculated as metal) to taurine in the coating composition is 1:3.

(37) Comparative Coating Composition V3

(38) Coating composition V3 is prepared in analogy to the method described in connection with coating composition Z1, with the difference that instead of Quadrol 13.86 g of L-asparagine are used and, following addition of the pigment paste, the pH of the mixture M2 is adjusted to 5.70 by addition of acetic acid. The molar ratio of bismuth (calculated as metal) to L-asparagine in the coating composition is 1:1.5.

(39) Table 1c provides an overview of the resulting inventive coating compositions Z8 to Z10 and also of V1 to V3.

(40) TABLE-US-00003 TABLE 1c Examples Z8-Z10 Z8 Z9 Z10 V1 V2 V3 CathoGuard 44.59 45.50 48.68 48.77 520/wt % CathoGuard 44.31 44.30 800/wt % Bi1/wt % 19.31 Bi2/wt % 24.16 Bi3/wt % 3.70 Taurine/wt % 0.47 L-Asparagine/ 0.28 wt % Deionized 30.19 26.13 46.60 48.60 44.87 44.97 water/wt % Pigment paste 5.91 5.40 5.40 P1/wt % Pigment paste 5.90 5.98 5.98 CathoGuard 520/wt % pH 6.0 5.70 5.70 5.30 5.70 5.70 Conductivity/ 2500 2000 2300 2190 S/cm

(41) The respective pH values and conductivities (where determined) in table 1c are ascertained in each case at a temperature in the range from 18 to 23 C. If the pH of the coating composition in question is adjusted subsequently by addition of an acid, the amounts of acid used are not given in the table above.

(42) After they been produced, each of the coating compositions Z1-Z10 and V1-V3 thus produced is introduced into a dip-coating bath. The coating compositions Z1 to Z5 and also Z8 to Z10 are ultrafiltered at a temperature in the range from 18-23 C. over a time of 60 minutes, and then a determination of the bismuth content, calculated as metal, in mg/L in the ultrafiltrate is made by means of atomic emission spectroscopy (ICP-OES) in accordance with the method described above. The corresponding values are reproduced in table id.

(43) TABLE-US-00004 TABLE 1d Coating Bismuth content of composition ultrafiltrate/mg/L V1 6.4 Z1 310 Z2 44 Z3 100 Z4 190 Z5 1100 Z8 300 Z9 790 Z10 140
2. Production of Coated Electrically Conductive Substrates by Means of One of the Inventive Aqueous Coating Compositions 21-210 or of the Comparative Coating Compositions V1-V3

(44) The aqueous coating compositions Z1-Z10 and V1-V3 are each applied as dip coatings to different substrates. Each of the compositions Z1-Z10 and V1-V3, is applied to the various substrates immediately after its production as described above.

(45) Three kinds of metal test panels are used, these being T1 (hot dip galvanized steel (HDG)) and T2 (aluminum (ALU)) and also T3 (cold-rolled steel (CRS)) as examples of electrically conductive substrates. Each of the two sides of the respective panels used has an area of 10.5 cm.Math.19 cm, giving an overall area of around 400 cm.sup.2.

(46) They are first of all cleaned in each case by immersion of the panels into a bath containing an aqueous solution comprising the commercially available products Ridoline 1565-1 (3.0 wt %) and Ridosol 1400-1 (0.3 wt %) from Henkel, and also water (96.7 wt %), for a time of 1.5 to 3 minutes at a temperature of 62 C. This is followed by mechanical cleaning (using fine brushes), after which the panels are again immersed into the bath for a time of 1.5 minutes.

(47) The substrates cleaned in this way are subsequently rinsed with water (for a time of 1 minute) and with deionized water (for a time of 1 minute).

(48) Immediately thereafter, one of the inventively employed aqueous coating compositions Z1 to Z10 is applied to each panel T1, T2, and T3, respectively, with the respective panel being immersed in each case into a corresponding dip-coating bath comprising one of the compositions Z1 to Z10. The dip-coating bath here has a respective temperature of 32 C.

(49) Coating in the dip-coating bath is carried out by means of a two-stage deposition step and coating step, which provides two stages (1a) and (1b), where first of all, galvanostatically, current strengths in the range from 0.02 to 0.32 A are applied for a time of 120 seconds (corresponding to stage (1a)), to give a preliminary deposition of bismuth. In certain cases, moreover, the deposition time at a defined current strength is varied. The results of this preliminary bismuth deposition as per stage (1a) of the step are shown below in tables 2a to 2g. The bismuth content here in each case is determined according to the above-described X-ray fluorescence analysis (XFA).

(50) Tables 2a to 2m:

(51) TABLE-US-00005 TABLE 2a bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z1, at different current strengths, in each case over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.16 23 11 17 0.18 25 16 16 0.20 26 17 15 0.22 29 15 13 0.24 22 25 22

(52) TABLE-US-00006 TABLE 2b bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z2, at different current strengths, in each case over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.16 50 36 48 0.18 50 36 46 0.20 47 32 48 0.22 44 39 42 0.24 55 * 56 *not determined

(53) TABLE-US-00007 TABLE 2c bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z3, at different current strengths, in each case over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.16 43 27 25 0.18 49 28 27 0.20 48 30 25 0.22 38 25 24 0.24 39 37 36

(54) TABLE-US-00008 TABLE 2d bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z4, at different current strengths, in each case over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.16 132 84 99 0.18 * * 116 0.20 135 93 104 0.22 * * 103 0.24 122 * 98 0.26 121 82 96 0.28 97 80 84 0.30 99 78 81 0.32 * * 86 *not determined

(55) TABLE-US-00009 TABLE 2e bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z5, at different current strengths, in each case over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.05 491 60 47 0.08 482 138 122 0.11 473 216 203 0.14 478 299 303 0.17 480 344 343 0.20 531 376 336 0.23 443 368 330 0.26 412 409 325 0.29 352 347 293

(56) TABLE-US-00010 TABLE 2f bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1 and T3 after implementation of stage (1a), starting from the coating composition Z6, at different current strengths, in each case over a time of 120 seconds Current T1, bismuth T3, bismuth strength content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] 0.05 101 39 0.08 152 72 0.11 214 100 0.14 238 128 0.17 272 150 0.20 281 181 0.23 * 157 0.26 * 185 0.29 * 177 *not determined

(57) TABLE-US-00011 TABLE 2g bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z7, at different current strengths, in each case over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.05 228 32 34 0.08 207 72 80 0.11 193 106 104 0.14 246 134 120 0.17 239 160 124 0.20 248 156 121 0.23 216 147 101 0.26 203 138 85 0.29 * * 73 *not determined

(58) TABLE-US-00012 TABLE 2h bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z8, at a current strength of 0.13 A, over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.13 267 159 148

(59) TABLE-US-00013 TABLE 2i bismuth layer add-on (in mg of bismuth per m.sup.2of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z9, at a current strength of 0.15 A/s, over different times Time T1, bismuth T2, bismuth T3, bismuth period content in content in content in [s] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 30 147.9 * 64.9 60 209.3 * 149.8 90 252.5 * 222.4 120 334.2 290.6 301.3 *not determined

(60) TABLE-US-00014 TABLE 2j-1 bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z10, at different current strengths, over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0 27.6 * * 0.05 63.8 38.7 31.2 0.08 * * 58.6 0.11 * * 61.5 0.14 60.9 53.7 62.8 0.17 * * 69.6 0.20 * * 62.7 0.23 62.6 59.3 60.0 *not determined

(61) TABLE-US-00015 TABLE 2j-2 bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition Z10, at a current strength of 0.15 A/s, over different times Time T3, bismuth period content in [s] [mg/m.sup.2] 90 54.1 120 61.7 150 72.2

(62) TABLE-US-00016 TABLE 2k bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the comparative coating composition V1, at a voltage of 4 V, over a time of 120 seconds T1, bismuth T2, bismuth T3, bismuth Voltage content in content in content in [V] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 4 0 0 5

(63) TABLE-US-00017 TABLE 2l bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition V2, at different current strengths, over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.10 16 6 12 0.12 16 6 11 0.14 16 7 11 0.16 15 9 11 0.18 15 9 11 0.20 14 8 11 0.22 13 8 10 0.24 12 8 10 *not determined

(64) TABLE-US-00018 TABLE 2m bismuth layer add-on (in mg of bismuth per m.sup.2 of surface area) of the coating applied to the substrates T1, T2, and T3 after implementation of stage (1a), starting from the coating composition V3, at different current strengths, over a time of 120 seconds Current T1, bismuth T2, bismuth T3, bismuth strength content in content in content in in [A] [mg/m.sup.2] [mg/m.sup.2] [mg/m.sup.2] 0.10 16 6 12 0.12 17 8 12 0.14 17 9 12 0.16 15 9 12 0.18 14 10 11 0.20 14 8 10 0.22 18 9 10 0.24 * 18 19 *not determined

(65) Subsequently, for some of the substrates obtained after stage (1a), stage (1b) of step (1) of the method of the invention is carried out, with application either of a voltage of 4 V, potentiostatically, or of current strengths in the range from 0.12 to 0.22 A, galvanostatically, each being raised over the course of stage (1b) continuously and linearly to a voltage in the region of 220-260 V, in each case over a time of 10 seconds, by means of a voltage ramp. This respectively voltage is then held for a time in the range from 60 to 120 seconds (hold time), to coat the respective substrate in a dry film thickness of 20 m with the respective coating composition.

(66) In detail, for coating of the substrates T2 or T3 with one of the compositions V1, Z3, Z6, Z1, Z12, or Z13, the following parameters are selected:

(67) V1:

(68) Stage (1a): 4 V over 120 seconds (potentiostatically)

(69) Stage (1b): voltage ramp: linear increase in voltage to 260 V over a time of 10 seconds and hold time of 60 seconds at this voltage

(70) Z2:

(71) Stage (1a): 0.22 A over 120 seconds (galvanostatically)

(72) Stage (1b): voltage ramp: linear increase in voltage to 240 V over a time of 10 seconds and hold time of 120 seconds at this voltage

(73) Z4:

(74) Stage (1a): 0.12 A over 120 seconds (galvanostatically)

(75) Stage (1b): voltage ramp: linear increase in voltage to 240 V over a time of 10 seconds and hold time of 90 seconds at this voltage

(76) Z5:

(77) Stage (1a): 0.15 A over 120 seconds (galvanostatically)

(78) Stage (1b): voltage ramp: linear increase in voltage to 250 V over a time of 10 seconds and hold time of 120 seconds at this voltage

(79) Moreover, step (1) here is carried out with a dip-coating bath temperature of 34 C.

(80) Z8:

(81) Stage (1a): 0.13 A over 120 seconds (galvanostatically)

(82) Stage (1b): voltage ramp: linear increase in voltage to 220 V over a time of 10 seconds and hold time of 90 seconds at this voltage

(83) The baking step that follows is accomplished by baking the resulting coatings in each case at 175 C. (oven temperature) for a time of 25 minutes. The dry film thicknesses of the aqueous coating compositions of the invention baked onto the respective substrates are in each case 20 m.

(84) 3. Investigation of the Anticorrosion Effect of the Coated Substrates

(85) The substrates T2 or T3 (T228 and T328), coated with the coating composition 28, and the substrates T2 or T3 (T2V1 and T3V1), coated with the comparative composition V1, are investigated.

(86) All of the tests below were carried out in accordance with the aforementioned methods of determination and/or with the corresponding standard. Each value in table 3a or 3b is the average value (with standard deviation) from a double or triple determination.

(87) TABLE-US-00019 TABLE 3a Inv. Inv. Inv. Inv. Comp. Ex. Ex. Ex. Ex. ex. Substrate T3 T3 T3 T3 T3 (CRS) (CRS) (CRS) (CRS) (CRS) Coating composition Z2 Z4 Z5 Z8 V1 Undermining [mm] 2.9 1.2 0.5 0.7 4.1 according to DIN EN ISO 4628-8 after 504 h of salt spray mist testing to DIN EN ISO 9227 NSS Undermining [mm] to 10.6 7.1 1.9 3.8 12.8 DIN EN ISO 4628-8 after 10 cycles of the VDA alternating climate test to VDA 621-415

(88) TABLE-US-00020 TABLE 3b Inv. Inv. Inv. Inv. Comp. Ex. Ex. Ex. Ex. ex. Substrate T2 T2 T2 T2 T2 (ALU) (ALU) (ALU) (ALU) (ALU) Coating composition Z2 Z4 Z5 Z8 V1 Maximum thread length 9.6 7.4 8.9 8.9 12.4 [mm] as per DIN EN 3365 after 1008 h Average thread length 4.5 2.7 4.1 2.8 7.5 [mm] as per PAPP WT 3102 (Daimler) after filiform corrosion as per DIN EN 3365 after 1008 h

(89) As can be seen from tables 3a and 3b, the substrates coated by the method of the invention with an aqueous coating composition of the invention consistently exhibit an improved anticorrosion effect in comparison to the substrate coated with the comparative coating composition.