METHOD FOR SPECIFICALLY ADJUSTING THE ELECTRICAL CONDUCTIVITY OF CONVERSION COATINGS
20180334748 ยท 2018-11-22
Inventors
- Olaf Dahlenburg (Neu-Isenburg, DE)
- Frank Hollmann (Leutkirch, DE)
- Michael Droege (Frankfurt am Main, DE)
- Thomas Kolberg (Heppenheim, DE)
- Lisa Schmeier (Freigericht-Bernbach, DE)
Cpc classification
International classification
Abstract
Provided herein is a method for specifically adjusting the electrical conductivity of a conversion coating, wherein a metallic surface or a conversion-coated metallic surface is treated with an aqueous composition which comprises at least one kind of metal ions selected from the group consisting of the ions of molybdenum, copper, silver, gold, palladium, tin, and antimony and/or at least one electrically conductive polymer selected from the group consisting of the polymer classes of the polyamines, polyanilines, polyimines, polythiophenes, and polypryrols.
Claims
1. A method for specifically adjusting the electrical conductivity of a conversion coating, the method comprising treating at least one of a metallic surface and a conversion-coated metallic surface with an aqueous composition which comprises at least one kind of metal ion selected from the group consisting of ions of molybdenum, copper, silver, gold, palladium, tin, and antimony and at least one electrically conductive polymer selected from the group consisting of polymer classes of polyamines, polyanilines, polyimines, polythiophenes, and polypryrols.
2. The method according to claim 1, further comprising: first treating the metallic surface with a substantially nickel-free zinc phosphate solution to form a substantially nickel-free phosphate coating on the metallic surface and second treating the coated metallic surface with the aqueous composition as an after-rinse solution.
3. The method according to claim 1, further comprising: first treating the metallic surface with a conversion and passivating solution which contains between 10 and 500 mg/l of Zr in complexed form, so as to form a corresponding thin-film coating on the metallic surface and second treating the coated metallic surface with the aqueous composition as an after-rinse solution.
4. The method according to claim 1, wherein the aqueous composition comprises a conversion and passivating solution which contains between 10 and 500 mg/l of Zr in complexed form.
5. The method according to claim 17, wherein the organosilane can be hydrolyzed to at least one of an aminopropylsilanol, 2-aminoethyl-3-aminopropylsilanol and bis(trimethoxysilylpropyl)amine.
6. The method according to claim 1, wherein the aqueous composition comprises molybdenum ions.
7. The method according to claim 6, wherein the aqueous composition further comprises zirconium ions.
8. The method according to claim 7, wherein the aqueous composition further comprises between 20 and 225 mg/l of the molybdenum ions and between 50 and 200 mg/l of the zirconium ions.
9. The method according to claim 1, wherein the aqueous composition comprises at least one of a polyamine and polyimine.
10. The method according to claim 1, wherein the aqueous composition is an after-rinse solution and has a pH between 3.5 and 5.
11. The method according to claim 1, wherein the aqueous composition comprises copper ions.
12. The method according to claim 11, wherein the aqueous composition comprises between 150 and 225 mg/l of the copper ions.
13. An aqueous composition for specifically adjusting the electrical conductivity of a conversion coating, the aqueous composition comprising at least one kind of metal ion selected from the group consisting of ions of molybdenum, copper, silver, gold, palladium, tin, and antimony and at least one electrically conductive polymer selected from the group consisting of polymer classes of polyamines, polyanilines, polyimines, polythiophenes, and polypryrols.
14. A concentrate from which an aqueous composition as defined in claim 13 is obtainable by dilution with a suitable solvent by a factor of between 1 and 100 and addition of a pH-modifying substance.
15. A conversion-coated metallic surface which is obtainable by a method according to claim 1.
16. The method according to claim 3, wherein the metallic surface comprises at least one of organosilance, hydrolysis product thereof, condensation product thereof in a concentration range between 5 and 200 mg/l.
17. The method according to claim 4, wherein the aqueous composition further comprises at least one of an organosilane, a hydrolysis product thereof, and a condensation product thereof with a concentration range between 5 and 200 mg/l.
18. The method according to claim 2, further comprising drying the coated metallic surface before the second treating.
19. The method according to claim 3, further comprising drying the coated metallic surface before the second treating.
Description
COMPARATIVE EXAMPLE 1
[0097] A test plate made of electrolytically galvanized steel (ZE) was coated using a phosphating solution containing 1 g/l of nickel. No after-rinsing was performed. The current density i was then measured in A/cm.sup.2 over the voltage E in V applied against a silver/silver chloride (Ag/AgCl) electrode (see
[0098] In all of the examples and comparative examples, the measured current density i is dependent on the electrical conductivity of the conversion coating. The relationship is as follows: the higher the measured current density i, the higher the electrical conductivity of the conversion coating as well. With conversion coatings, it is not possible to carry out direct measurement of the electrical conductivity in ?S/cm, of the kind which is possible in liquid media.
[0099] In the present case, therefore, the current density i measured for a nickel-containing conversion coating serves always as a reference point for statements made about the electrical conductivity of a given conversion coating.
[0100] The indication 1E in
COMPARATIVE EXAMPLE 2
[0101] A test plate as per comparative example 1 was coated using a nickel-free phosphating solution, without after-rinsing, and then the current density i was measured over the voltage E as per comparative example 1 (see
[0102] As can be seen from
COMPARATIVE EXAMPLE 3
[0103] A test plate as per comparative example 1 was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution containing about 120 mg/l of ZrF.sub.6.sup.2? (calculated as Zr), with a pH of about 4. The current density i over the voltage E was measured as per comparative example 1 (see
[0104] As can be seen from
EXAMPLE 1
[0105] A test plate as per comparative example 1 was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution containing about 220 mg/l of copper ions, with a pH of about 4. The current density i over the voltage E was measured as per comparative example 1 (see
[0106] As can be seen from
EXAMPLE 2
[0107] A test plate as per comparative example 1 was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution which contained about 1 g/l (calculated on the basis of the pure polymer) on electrically conductive polyamine (Lupamin? 9030, manufacturer BASF) and had a pH of about 4. The current density i over the voltage E was measured as per comparative example 1 (see
[0108] As can be seen from
COMPARATIVE EXAMPLE 3
[0109] A test plate made of hot-dip-galvanized steel (EA) was coated using a phosphating solution containing 1 g/l of nickel. The test plate thus coated was subsequently treated with an after-rinse solution containing about 120 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) with a pH of about 4, after which the current density i in A/cm.sup.2 was measured over the voltage E in V applied against a silver/silver chloride (Ag/AgCl) electrode (see
COMPARATIVE EXAMPLE 4
[0110] A test plate as per comparative example 3 was coated using a nickel-free phosphating solution without after-rinsing, and then the current density i over the voltage E was measured as per comparative example 3 (see
[0111] As can be seen from
EXAMPLE 3
[0112] A test plate as per comparative example 3 was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution containing about 120 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) and 220 mg/l of molybdenum ions, with a pH of about 4. The current density i over the voltage E was measured as per comparative example 1 (see
[0113] As can be seen from
COMPARATIVE EXAMPLE 5
[0114] Hot-dip-galvanized (HDG) or electrolytically galvanized (EG) steel test plates were sprayed at 60? C. for 180 s with an aqueous cleaning solution which contained a surfactant and had a pH of 10.8. The cleaning solution was subsequently rinsed off from the test plates by spraying them with mains water for 30 s first and then with deionized water for 20 s. The cleaned test plates were thereafter immersed for 175 s into a conversion/passivating solution which contained 40 mg/l of Si, 140 mg/l of Zr, 2 mg/l of Cu, and 30 mg/l of free fluoride and had a pH of 4.8 and a temperature of 30? C. The aqueous conversion/passivating solution was subsequently rinsed off from the test plates by immersing them in deionized water for 50 s and subsequently spraying them with deionized water for 30 s. The test plates thus pretreated were then cathodically dip-coated either with a first specific CEC material (CEC 1) or with a second specific CEC material (CEC 2).
EXAMPLE 4
[0115] Hot-dip-galvanized (HDG) or electrolytically galvanized (EG) steel test plates were treated as per comparative example 5, with the difference that the aqueous conversion/passivating solution was subsequently rinsed off from the test plates by immersing them for 50 s into an aqueous solution containing 100 mg/l of Mo (calculated as metal), which was added in the form of ammonium heptamolybdate, (after-rinse solution) and subsequently spraying them with deionized water for 30 s.
EXAMPLE 5
[0116] Hot-dip-galvanized (HDG) or electrolytically galvanized (EG) steel test plates were treated as per comparative example 5, with the difference that the aqueous conversion/passivating solution was subsequently rinsed off from the test plates by immersing them for 50 s into an aqueous solution containing 200 mg/l of Mo (calculated as metal), which was added in the form of ammonium heptamolybdate, (after-rinse solution) and subsequently spraying them with deionized water for 30 s.
EXAMPLE 6
[0117] Hot-dip-galvanized (HDG) or electrolytically galvanized (EG) steel test plates were treated as per comparative example 5, with the difference that the aqueous conversion/passivating solution additionally contained 100 mg/l of Mo (calculated as metal), which was added in the form of ammonium heptamolybdate.
[0118] The test plates as per comparative example 5 (CE5) and examples 4 to 6 (E4 to E6) were subsequently subjected to a paint adhesion test from the automobile manufacturer PSA (heat-humidity test).
[0119] The cross-cut and coating loss results obtained can be seen in tab. 1. In the case of the cross-cut results, 1 stands for the best and 6 for the worst score. For the coating loss results, 100% denotes complete loss of coating.
[0120] The test plates as per comparative example 5 (CE5) and examples 4 to 6 (E4 to E6) were also investigated by the method known as that of cathodic polarization.
[0121] This method describes an accelerated electrochemical test which is performed on coated steel panels having being subjected to defined damage. According to the principle of an electrostatic holding test, testing takes place to determine how effectively the coating on the metal test plate withstands the process of corrosive undermining.
[0122] The scratched test plate (scratching tool for 0.5 mm scratch width, e.g. Clemen testing tip (R=1 mm); stencil for scratching) is installed in the measuring cell (galvanostat as current source (20 mA in the regulating range); thermostat with connections for temperature regulation 40? C. +/?0.5? C., glass electrolysis cell with heating jacket, complete with reference electrode; counter electrode, gasket and ovals). It must be ensured here that the two electrode rods lie parallel to the scratch.
[0123] After the lid has been locked in, the cell is filled with about 400 mL of 0.1 M Na sulfate solution. The clips are then connected as follows: green-blue clip to working electrode (metal plate), orange-red clip to counter electrode (electrode with parallel rods), white clip to reference electrode (in Haber-Luggin capillary).
[0124] The cathodic polarization is then started via the control software (control instrument with software) and a current of 20 mA is set on the test plate over a period of 24 hours. During this time, the measuring cell is conditioned at 40? C.+/?0.5 degree using the thermostat. In the 24-hour exposure time, hydrogen is evolved at the cathode (test plate) and oxygen at the counter electrode.
[0125] Following measurement, the metal plate is immediately uninstalled, in order to avoid secondary corrosion, and is rinsed off with DI water and dried in the air. Using a blunt knife, the coating film detached is removed. Other detached regions of coating can be removed using a strong textile adhesive tape (e.g., Tesaband 4657 gray). Thereafter the exposed area is evaluated (ruler, magnifying glass if needed).
[0126] For this purpose, the width of the detached area is determined with an accuracy of 0.5 mm, with a spacing of 5 mm in each case. The averaged delamination width is calculated according to the following equations:
d.sub.1=(a.sub.1+a.sub.2+a.sub.3+ . . . )/n Equation 1
d=(d.sub.1?w)/2 Equation 2
[0127] d.sub.1: average delamination width in mm
[0128] a.sub.1, a.sub.2, a.sub.3: individual delamination widths in mm
[0129] n: number of individual widths
[0130] w: width of scratch mark in mm
[0131] d: average width of delamination, width of undermining in mm
[0132] The result is reported in mm and is rounded to one decimal place. The standard deviation of the measurements is below 20%. The delamination values obtained in this way are likewise shown in tab. 1.
[0133] Test plates as per comparative examples 1 to 3 (CE1 to CE3) and also examples 1 and 2 (E1 and E2) were CEC-coated and then subjected to a DIN EN ISO 2409 cross-cut test. Testing took place in each case on 3 plates before and after exposure for 240 hours to condensation water (DIN EN ISO 6270-2 CH). The corresponding results are found in tab. 2. A cross-cut result of 0 here is the best, a result of 5 the worst score.
TABLE-US-00007 TABLE 1 (Comp.) Test CEC Cross-cut Coating loss Delamination ex. plate coating (1-6) (%) (mm) CE5 HDG CEC 1 6 50 11.9 6 50 CEC 2 2 0 8.9 2 0 EG CEC 1 6 50 8.5 6 50 CEC 2 2 0 6.3 2 0 E4 HDG CEC 1 3 1 2.9 2 1 CEC 2 2 0 2.8 2 0 EG CEC 1 2 1 1.9 4 1 CEC 2 2 0 2.4 1 0 E5 HDG CEC 1 5 1 3.3 5 1 CEC 2 3 0 2.6 2 0 EG CEC 1 2 1 2.1 2 1 CEC 2 2 0 1.7 2 0 E6 HDG CEC 1 2 1 2.8 2 0 CEC 2 2 0 2.2 2 0 EG CEC 1 1 1 1.4 2 0 CEC 2 2 0 1.6 1 0
TABLE-US-00008 TABLE 2 (Comparative) Cross-cut (0-5) Example before exposure after exposure CE1 0/0/0 1/1/0 CE2 1/0/0 3/1/0 CE3 0/0/1 1/5/4 E1 1/0/0 0/0/1 E2 1/1/1 1/1/1
[0134] As can be seen from tab. 1, the use of Mo, both in the conversion/passivating solution and in the after-rinse solution, especially in conjunction with the CEC 1 coating, leads to the advantage of improved coating adhesion (lower cross-cut and coating loss scores for E4 to E6 in comparison to CE5). Tab. 1 further reveals that Mo, both in the conversion/passivating solution and in the after-rinse solution, leads to significantly reduced delamination (E4 to E6 in comparison to CE5).
[0135] This positive effect is attributable to the fact that the use of Mo leads to increased conductivity of the surface and therefore very largely prevents attack on the conversion coat during the current-flow-dependent cathodic electrocoating.
[0136] Tab. 2 reveals the poor results of CE2 and especially CE3 in each case after exposure, whereas E1 (copper ions) and E2 (electroconductive polyamine) yield results which are good and are comparable to CE1 (nickel-containing phosphating).
EXAMPLE 7
[0137] A test plate as per comparative example 1 was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution which contained about 1 g/l (calculated on the basis of the pure polymer) of electrically conductive polyimine having a number-average molecular weight of 5000 g/mol (Lupasol? G 100, manufacturer BASF) and had a pH of about 4.
EXAMPLE 8
[0138] A test plate as per comparative example 1 was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution containing 130 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) and 20 mg/l of molybdenum ions and, additionally, 1.2 g/l (calculated on the basis of the pure polymer) of polyacrylic acid having a number-average molecular weight of 60 000 g/mol and had a pH of about 4.
COMPARATIVE EXAMPLE 6
[0139] Corresponds to comparative example 1, with the difference that a test plate made of hot-dip-galvanized steel (EA) is used.
COMPARATIVE EXAMPLE 7
[0140] Corresponds to comparative example 2, with the difference that a test plate made of hot-dip-galvanized steel (EA) is used.
EXAMPLE 9
[0141] A test plate made of hot-dip-galvanized steel (EA) was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution which contained about 1 g/l (calculated on the basis of the pure polymer) of electrically conductive polyimine having a number-average molecular weight of 5000 g/mol (Lupasol? G 100, manufacturer BASF) and had a pH of about 4.
EXAMPLE 10
[0142] A test plate made of hot-dip-galvanized steel (EA) was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution containing 130 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) and 20 mg/l of molybdenum ions and, additionally, 1.2 g/l (calculated on the basis of the pure polymer) of polyacrylic acid having a number-average molecular weight of 60 000 g/mol and had a pH of about 4.
COMPARATIVE EXAMPLE 8
[0143] Corresponds to comparative example 1, with the difference that a test plate made of steel is used.
COMPARATIVE EXAMPLE 9
[0144] Corresponds to comparative example 2, with the difference that a test plate made of steel is used.
EXAMPLE 11
[0145] A test plate made of steel was coated using a nickel-free phosphating solution. The test plate thus coated was subsequently treated with an after-rinse solution containing 230 mg/l of copper ions, with a pH of about 4.
COMPARATIVE EXAMPLE 10
[0146] Corresponds to comparative example 1, with the difference that the phosphating solution contains 1 g/l of BF.sub.4.sup.? and 0.2 g/l of SiF.sub.6.sup.2? and, after the phosphating, treatment takes place with an with an after-rinse solution containing about 120 mg/l of ZrF.sub.6.sup.2? (calculated as Zr), with a pH of about 4.
COMPARATIVE EXAMPLE 11
[0147] Corresponds to comparative example 2, with the difference that the phosphating solution contains 1 g/l of BF.sub.4.sup.? and 0.2 g/l of SiF.sub.6.sup.2?.
EXAMPLE 12
[0148] A test plate made of electrolytically galvanized steel (ZE) was coated using a nickel-free phosphating solution which contained 1 g/l of BF.sub.4.sup.? and 0.2 g/l of SiF.sub.6.sup.2?. The test plate thus coated was subsequently treated with an after-rinse solution containing 160 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) and 240 mg/l of molybdenum ions, with a pH of about 4.
COMPARATIVE EXAMPLE 12
[0149] 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 of BF.sub.4.sup.? and 0.2 g/l of SiF.sub.6.sup.2?, and, after the phosphating, treatment takes place with an with an after-rinse solution containing about 120 mg/l of ZrF.sub.6.sup.2? (calculated as Zr), with a pH of about 4.
COMPARATIVE EXAMPLE 13
[0150] 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 of BF.sub.4.sup.? and 0.2 g/l of SiF.sub.6.sup.2?.
EXAMPLE 13
[0151] A test plate hot-dip-galvanized steel (EA) was coated using a nickel-free phosphating solution which contained 1 g/l of BF.sub.4.sup.? and 0.2 g/l of SiF.sub.6.sup.2?. The test plate thus coated was subsequently treated with an after-rinse solution containing 160 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) and 240 mg/l of molybdenum ions, with a pH of about 4.
COMPARATIVE EXAMPLE 14
[0152] Corresponds to comparative example 1, with the difference that the phosphating solution contains 1 g/l of SiF.sub.6.sup.2? and, after the phosphating, treatment takes place with an with an after-rinse solution containing about 120 mg/l of ZrF.sub.6.sup.2? (calculated as Zr), with a pH of about 4.
COMPARATIVE EXAMPLE 15
[0153] Corresponds to comparative example 2, with the difference that the phosphating solution contains 1 g/l of SiF.sub.6.sup.2?.
EXAMPLE 14
[0154] A test plate made of electrolytically galvanized steel (ZE) was coated using a nickel-free phosphating solution which contained 1 g/l of SiF.sub.6.sup.2?. The test plate thus coated was subsequently treated with an after-rinse solution containing 160 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) and 240 mg/l of molybdenum ions, with a pH of about 4.
COMPARATIVE EXAMPLE 16
[0155] 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 of SiF.sub.6.sup.2?, and, after the phosphating, treatment takes place with an with an after-rinse solution containing about 120 mg/l of ZrF.sub.6.sup.2? (calculated as Zr), with a pH of about 4.
COMPARATIVE EXAMPLE 17
[0156] 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 of Si F.sub.6.sup.2?.
EXAMPLE 15
[0157] A test plate made of hot-dip-galvanized steel (EA) was coated using a nickel-free phosphating solution which contained 1 g/l of SiF.sub.6.sup.2?. The test plate thus coated was subsequently treated with an after-rinse solution containing 160 mg/l of ZrF.sub.6.sup.2? (calculated as Zr) and 240 mg/l of molybdenum ions, with a pH of about 4.
[0158] Test plates as per comparative examples 1, 2, 6 and 7 (CE1, CE2, CE6, and CE7) and also examples 7 to 10 (E7 to E10) were CEC-coated. This was done using four programs which differed in terms of (a) the ramp time, in other words the time to attainment of maximum voltage, (b) the maximum voltage and/or (c) the time of exposure to maximum voltage:
TABLE-US-00009 Program 1: (a) 30 sec (b) 240 V (c) 150 sec Program 2: (a) 30 sec (b) 220 V (c) 150 sec Program 3: (a) 3 sec (b) 240 V (c) 150 sec Program 4: (a) 3 sec (b) 220 V (c) 150 sec
[0159] The film thickness of the deposited CEC coating, measured in each case by means of a Fischer DUALSCOPE , can be seen in tab. 3.
[0160] Test plates as per comparative examples 8 to 17 (CE8 to CE17) and also examples 11 to 15 (E11 to E15) were subjected to analysis by X-ray fluorescence (XFA). Tab. 4 shows the amounts of copper and, respectively, zirconium and molybdenum (calculated as metal in each case) determined in each case in the surface. The stated test plates were subsequently CEC-coated. This was done using the following programs, which according to (comparative) example differed in terms of (a) the ramp time, in other words the time to attainment of maximum voltage, (b) the maximum voltage and/or (c) the time of exposure to maximum voltage:
TABLE-US-00010 CE8, CE9, E11: (a) 30 sec (b) 250 V (c) 240 sec CE10, CE11, CE14, (a) 30 sec (b) 260 V (c) 300 sec CE15, E12, E14: CE12; CE13, CE16; (a) 30 sec (b) 260 V (c) 280 sec CE17, E13, E15:
[0161] The film thickness of the deposited CEC coating, measured in each case by means of a Fischer DUALSCOPE?, can be seen in tab. 4.
TABLE-US-00011 TABLE 3 Program 1: Program 2: Program 3: Program 4: Film Film Film Film (Comparative) thickness thickness thickness thickness example (?m) (?m) (?m) (?m) CE1 19.4 17.7 21.4 18.4 CE2 16 15 17.4 15.9 E7 20.4 17.8 22.6 19.1 E8 19 17.4 19.8 18 CE6 21.5 19.5 21.2 19.2 CE7 19.1 17 18.6 17.1 E9 22.8 20 23.5 20.5 E10 20.3 18.7 21.6 18.8
TABLE-US-00012 TABLE 4 (Comparative) Cu content Mo content Zr content CEC thickness example (mg/m.sup.2) (mg/m.sup.2) (mg/m.sup.2) (?m) CE8 0 19.5 CE9 0 19.9 E11 20 22.9 CE10 0 5 19.7 CE11 0 0 18 E12 8 6 19.6 CE12 0 7 21.6 CE13 0 0 20 E13 5 6 21.7 CE14 0 5 19.7 CE15 0 0 18 E14 9 8 19.1 CE16 0 6 22.1 CE17 0 0 20 E15 10 10 21.7
[0162] Tab. 3 shows in each case a significant decrease in the film thickness of the CEC coating in the case of nickel-free as compared to nickel-containing phosphating (CE2 vs. CE1; CE7 vs. CE6). By using the after-rinse solutions of the invention, however, the film thickness obtained in the case of nickel-free phosphating can be increased again (E7 and E8 vs. CE2; E9 and E10 vs. CE6)in the case of E7 and E9, it can be increased, indeed, beyond the level of the nickel-containing phosphating.
[0163] From tab. 4 it is evident that the use of a copper-containing after-rinse solution of the invention (in the case of previous nickel-free phosphating) leads to incorporation of copper into the test plate surface. As a consequence the CEC deposition is improved, even relative to the nickel-containing system (E11 vs. CE8). The copper content of the surface increases its conductivity. This results in more effective CEC deposition, a phenomenon manifested, under otherwise identical conditions, in the higher film thickness of the CEC coating. Through the use of zirconium-containing and molybdenum-containing after-rinse solutions of the invention (after nickel-free phosphating), accordingly, molybdenum is incorporated into the surface of the test plates, a feature which brings the CEC deposition back again (almost) to the level of the nickel-containing phosphating (E12 vs. CE10; E13 vs 0E12; E14 vs. CE14; E15 vs. CE16).