Method for producing a multicoat paint system

Abstract

The present invention relates to a method for producing a multicoat paint system on a metallic substrate, in which a basecoat or a plurality of directly successive basecoats are produced directly on a metallic substrate coated with a cured electrocoat, a clearcoat is produced directly on the one basecoat or the uppermost of the plurality of basecoats, and then the one or more basecoats and the clearcoat are jointly cured, and wherein at least one basecoat material used for production of the basecoats comprises at least one aqueous dispersion comprising at least one copolymer (CP), said copolymer (CP) being preparable by initially charging an aqueous dispersion of at least one polyurethane, and then polymerizing a mixture of olefinically unsaturated monomers in the presence of the polyurethane from (i), in which a water-soluble initiator is used, the olefinically unsaturated monomers are metered in such that a concentration of 6.0% by weight, based on the total amount of olefinically unsaturated monomers used for polymerization, in the reaction solution is not exceeded over the entire reaction time, and the mixture of the olefinically unsaturated monomers comprises at least one polyolefinically unsaturated monomer, and comprises at least one linear hydroxy-functional reaction product (R) having an acid number less than 20 mg KOH/g, the preparation of which involves using at least one compound (v) containing two functional groups (v.1) and an aliphatic or araliphatic hydrocarbyl radical (v.2) which is arranged between the functional groups and has 12 to 70 carbon atoms.

Claims

1. A method for producing a multicoat paint system (M) on a metallic substrate (S), said method comprising: (1) producing a cured electrocoat (E.1) on the metallic substrate (S) by electrophoretic application of an electrocoat (e.1) to the substrate (S) and subsequent curing of the electrocoat (e.1), (2) producing (2.1) a basecoat (B.2.1) or (2.2) a plurality of directly successive basecoats (B.2.2.x) directly on the cured electrocoat (E.1) by (2.1) applying an aqueous basecoat material (b.2.1) directly to the electrocoat (E.1) or (2.2) applying a plurality of basecoat materials (b.2.2.x) in direct succession to the electrocoat (E.1), (3) producing a clearcoat (K) directly on (3.1) the basecoat (B.2.1) or (3.2) an uppermost basecoat (B.2.2.x) by applying a clearcoat material (k) directly to (3.1) the basecoat (B.2.1) or (3.2) the uppermost basecoat (B.2.2.x), (4) jointly curing (4.1) the basecoat (B.2.1) and the clearcoat (K) or (4.2) the basecoats (B.2.2.x) and the clearcoat (K), wherein the basecoat material (b.2.1) or at least one of the basecoat materials (b.2.2.x) comprises at least one aqueous dispersion comprising at least one copolymer (CP), said copolymer (CP) being preparable by (i) initially charging an aqueous dispersion of at least one polyurethane, and then (ii) polymerizing a mixture of olefinically unsaturated monomers in the presence of the polyurethane from (i), in which (a) a water-soluble initiator is used, (b) the olefinically unsaturated monomers are metered so that a concentration of 6.0% by weight, based on the total amount of olefinically unsaturated monomers used for polymerization, in the reaction solution is not exceeded over the entire reaction time, and (c) the mixture of the olefinically unsaturated monomers comprises at least one polyolefinically unsaturated monomer, and comprises at least one linear hydroxy-functional reaction product (R) having an acid number less than 20 mg KOH/g, the preparation of which involves using at least one compound (v) containing two functional groups (v0.1) and an aliphatic or araliphatic hydrocarbyl radical (v.2) which is arranged between the functional groups and has 12 to 70 carbon atoms; wherein the at least one reaction product (R) is selected from the group consisting of reaction products preparable by reaction of dimer fatty acids with at least one aliphatic dihydroxy-functional compound of the general structural formula (I): ##STR00006## where R is a C.sub.3 to C.sub.6 alkylene radical and n is correspondingly selected such that the compound of the formula (I) has a number-average molecular weight of 120 to 6000 g/mol, the dimer fatty acids and the compounds of the formula (U are used in a molar ratio of 0.7/2.3 to 1.6/1.7, and the resulting reaction product has a number-average molecular weight of 600 to 40000 g/mol and an acid number of less than 10 mg KOH/g, reaction products preparable by reaction of dimer fatty acids with at least one dihydroxy-functional compound of the general structural formula (II): ##STR00007## where R is a divalent organic radical comprising 2 to 10 carbon atoms, R.sup.1 and R.sup.2 are each independently straight-chain or branched alkylene radicals having 2 to 10 carbon atoms, X and Y are each independently O, S or NR.sup.3 in which R.sup.3 is hydrogen or an alkyl radical having 1 to 6 carbon atoms, and m and n are correspondingly selected such that the compound of the formula (II) has a number-average molecular weight of 450 to 2200 g/mol, where components (a) and (b) are used in a molar ratio of 0.7/2.3 to 1.6/1.7 and the resulting reaction product has a number-average molecular weight of 1200 to 5000 g/mol and an acid number of less than 10 mg KOH/g, and reaction products preparable by reaction of dimer fatty acids with dimer diols, where the dimer fatty acids and dimer diols are used in a molar ratio of 0.7/2.3 to 1.6/1.7 and the resulting reaction product has a number-average molecular weight of 1200 to 5000 g/mol and an acid number of less than 10 mg KOH/g.

2. The method as claimed in claim 1, wherein the mixture of olefinically unsaturated monomers used in (ii) comprises 0.1 to 6.0 mol % of polyolefinically unsaturated monomers.

3. The method as claimed in claim 1, wherein the mixture of olefinically unsaturated monomers used in (ii) comprises allyl methacrylate, and no further polyolefinically unsaturated monomers are present.

4. The method as claimed in claim 1, wherein the olefinically unsaturated monomers in (ii) (b) are metered in such that a concentration of 4.0% by weight, based on the total amount of olefinically unsaturated monomers used for polymerization, in the reaction solution is not exceeded over the entire reaction time.

5. The method as claimed in claim 1, wherein the functional groups (v.1) of the at least one compound (v) are selected from the group consisting of hydroxcyl groups and carboxyl groups.

6. The method as claimed in claim 1, wherein dimeric fatty acids and/or dimer diols are used as compound (v) in the preparation of the reaction product (R).

7. The method as claimed in claim 1, wherein the reaction product (R) is preparable by reaction of at least one dimer fatty acid with at least one aliphatic, araliphatic or aromatic dihydroxy-functional compound having a number-average molecular weight of 120 to 6000 g/mol.

8. The method as claimed in claim 7, wherein the aliphatic, araliphatic and/or aromatic dihydroxy-functional compound(s) used are at least one selected from the group consisting of polyether diols, polyester diols and dimer diols.

9. The method as claimed in claim 1, wherein the basecoat material (b.2.1) or at least one, or all, of the basecoat materials (b.2.2.x) comprise(s) at least one hydroxyl-functional polymer other than (CP) and (R) as a binder, selected from the group consisting of polyurethanes, polyesters, polyacrylates and copolymers of these polymers and a melamine resin as a crosslinking agent.

10. The method as claimed in claim 1, wherein the basecoat material (b.2.1) or at least one, or all, of the basecoat materials (b.2.2.x), comprise(s) at least one color pigment and/or effect pigment.

11. The method as claimed in claim 1, wherein the basecoat material (b.2.1) or at least one of the basecoat materials (b.2.2.x) comprises a lamellar aluminum pigment or other metal effect pigment.

12. The method as claimed in claim 1, wherein the basecoat material (b.2.1) or at least one, or all, of the basecoat materials (b.2.2.x), is/are one-component coating compositions.

13. The method as claimed in claim 1, wherein the joint curing (4) is performed at temperatures of 100 to 250? C. for a period of 5 to 60 min.

14. The method as claimed in claim 1, wherein (2.2) two basecoats (B.2.2.a) and (B2.2.z) are produced, for which the aqueous basecoat materials (b.2.2.a) and (b.2.2.z) used are identical and comprise effect pigments.

15. The method as claimed in claim 14, wherein the basecoat material (b.2.2.a) is applied by electrostatic spray application, and the basecoat material (b.2.2.z) by pneumatic application.

16. The method as claimed in claim 1, wherein (2.2) at least two basecoats are produced, the first basecoat (B.2.2.a) directly atop the electrocoat (E.1) comprising white pigments and black pigments, and the further basecoats (B.2.2.x) comprising effect pigments.

17. A multicoat paint system (M) which has been produced by the method as claimed in claim 1.

18. The method as claimed in claim 9, wherein all of the basecoat materials (b.2.2.x), comprise(s) at least one hydroxyl-functional polymer other than (CP) and (R) as a binder, selected from the group consisting of polyurethanes, polyesters, polyacrylates and copolymers of these polymers and a melamine resin as a crosslinking agent.

19. The method as claimed in claim 10, wherein all of the basecoat materials (b.2.2.x), comprise(s) at least one color pigment and/or effect pigment.

Description

EXAMPLES

(1) Specification of Particular Components Used and Test Methods

(2) Dimer Fatty Acid:

(3) The dimer fatty acid used contains less than 1.5% by weight of trimeric molecules, 98% by weight of dimeric molecules and less than 0.3% by weight of fatty acid (monomer). It is prepared on the basis of linolenic acid, linoleic acid and oleic acid (Pripol? 1012-LQ-(GD), from Croda).

(4) Polyester (P1):

(5) Prepared as per example D, column 16 lines 37 to 59 of DE 4009858 A. The corresponding solution of the polyester has a solids content of 60% by weight, using butyl glycol rather than butanol as the solvent, meaning that the solvents present are principally butyl glycol and water.

(6) Graft Copolymer (GCP1):

(7) Polyurethane-based graft copolymer prepared according to DE 19948004-A1 (page 27example 2), solids content adjusted to 32.5% by weight with water.

(8) Determination of Number-Average Molecular Weight:

(9) The number-average molecular weight was determined by means of vapor pressure osmosis. Measurement was effected using a vapor pressure osmometer (model 10.00 from Knauer) on concentration series of the component under investigation in toluene at 50? C., with benzophenone as calibration substance for determination of the experimental calibration constant of the instrument employed (in accordance with E. Schr?der, G. M?ller, K.-F. Arndt, Leitfaden der Polymercharakterisierung, Akademie-Verlag, Berlin, pp. 47-54, 1982, in which benzil was used as calibration substance).

(10) Preparation of a Reaction Product (R) for Use in Accordance with the Invention

(11) In a 4 l stainless steel reactor equipped with anchor stirrer, thermometer, condenser, thermometer for overhead temperature measurement and water separator, 2000.0 g of linear diolic PolyTHF1000 (2 mol), 579.3 g of dimer fatty acid (1 mol) and 51 g of cyclohexane were heated to 100? C. in the presence of 2.1 g of di-n-butyltin oxide (Axion? CS 2455, from Chemtura). Heating was continued gently until the onset of the condensation. With a maximum overhead temperature of 85? C., heating was then continued in steps up to 220? C. The progress of the reaction was monitored via the determination of the acid number. When an acid number of ?3 mg KOH/g was reached, cyclohexane still present was removed by vacuum distillation. A viscous resin was obtained.

(12) Amount of condensate (water): 34.9 g

(13) Acid number: 2.7 mg KOH/g

(14) Solids content (60 min at 130? C.): 100.0%

(15) Molecular weight (vapor pressure osmosis):

(16) Mn: 2200 g/mol

(17) Viscosity: 5549 mPas,

(18) (measured at 23? C. using a rotational viscometer from Brookfield, model CAP 2000+, spindle 3, shear rate: 1333 s.sup.?1)

(19) Preparation of a Copolymer (CP) to be Used in Accordance with the Invention

(20) The copolymer (CP) or an aqueous dispersion comprising said polymer was prepared as shown below.

(21) a) A dispersion of an alpha-methylstyryl-containing polyurethane was prepared on the basis of the patent DE 19948004 B4, page 27, example 1, Herstellung eines erfindungsgem??en Polyurethans (B) [Preparation of a polyurethane (B) of the invention], except with additional use of trimethylolpropane and with a solids content of the resulting dispersion of only 29% rather than 35.1% by weight. Based on the adduct (B2) mentioned in the patent DE 19948004 B4, preparation example 1, an adduct was prepared with monoethanolamine rather than with diethanolamine:

(22) For this purpose, a reaction vessel equipped with stirrer, internal thermometer, reflux condenser and electrical heater was first initially charged, under nitrogen, with 200.0 parts by weight of methyl ethyl ketone, 800.0 parts by weight of N-methylpyrrolidone and 221.3 parts by weight of monoethanolamine (from BASF SE) at 20? C. To this mixture were added dropwise, over the course of one and a half hours, 778.7 parts by weight of 1-(1-isocyanato-1-methylethyl)-3-(1-methylethenyl)benzene (TMI? (META) Unsaturated Aliphatic Isocyanate, from Cytec) having an isocyanate content of 20.4% by weight of isocyanate, such that the reaction temperature did not exceed 40? C. The resulting reaction mixture was stirred until no free isocyanate groups were detectable any longer. Thereafter, the reaction mixture was stabilized with 200 ppm of hydroquinone.

(23) The theoretical solids content of the solution of the described adduct thus-prepared was 50% by weight.

(24) Then, in a further reaction vessel equipped with stirrer, internal thermometer, reflux condenser and electrical heater, 431.7 parts by weight of a linear polyester polyol and 69.7 parts by weight of dimethylolpropionic acid (from GEO Specialty Chemicals) were dissolved in 355.8 parts by weight of methyl ethyl ketone and 61.6 parts by weight of N-methylpyrrolidone under nitrogen. The linear polyester polyol had been prepared beforehand from dimerized fatty acid (Pripol? 1012, from Uniqema), isophthalic acid (from BP Chemicals) and hexane-1,6-diol (from BASF SE) (weight ratio of the starting materials: dimeric fatty acid to isophthalic acid to hexane-1,6-diol=54.00:30.02:15.98) and had a hydroxyl number of 73 mg KOH/g solids and a number-average molar mass of 1379 g/mol. Added to the resulting solution at 45? C. were 288.6 parts by weight of isophorone diisocyanate (Basonat? I, from BASF SE) having an isocyanate content of 37.75% by weight. After the exothermic reaction had abated, the reaction mixture was heated gradually to 80? C. while stirring. Stirring was continued at this temperature until the isocyanate content of the solution was constant at 3.2% by weight. Thereafter, the reaction mixture was cooled to 65? C., and 85.2 parts by weight of the above-described adduct were added together with 21.8 parts by weight of trimethylolpropane (from BASF SE). The resulting reaction mixture was stirred at 65? C. until the isocyanate content of the solution had fallen to 1.0% by weight. Now 22.2% by weight of the diethanolamine (from BASF SE) were added and the content of isocyanate groups was monitored until no free isocyanate groups were detectable any longer. The resulting dissolved polyurethane was admixed with 139.7 parts by weight of methoxypropanol and 43.3 parts by weight of triethylamine (from BASF SE). 30 minutes after the addition of amine, the temperature of the solution was lowered to 60? C., after which 1981 parts by weight of deionized water were added while stirring over the course of 30 minutes. The methyl ethyl ketone was distilled out of the resulting dispersion at 60? C. under reduced pressure. Thereafter, any losses of solvent and water were compensated for.

(25) The dispersion of an alpha-methylstyryl-containing polyurethane thus obtained had a solids content of 29.0% by weight, the acid number was 34.0 mg KOH/g solids, and the pH was 7.0 (measured at 23? C.)

(26) b) To prepare the aqueous primary dispersion of the copolymer (CP) of the invention, under a nitrogen atmosphere, 1961.2 parts by weight of the alpha-methylstyryl-containing polyurethane dispersion according to a) were diluted with 40.0 parts by weight of methoxypropanol (0.07% based on polyurethane) and 686.5 parts by weight of deionized water, and heated to 80? C. After the reactor contents had been heated to 80? C., 0.6 part by weight of ammonium peroxodisulfate, dissolved in 35.7 parts by weight of deionized water, were introduced into the reactor under standard pressure. Subsequently, with continued stirring, a mixture of 301.6 parts by weight of methyl methacrylate, 261.6 parts by weight of n-butyl acrylate, 5.6 parts by weight of allyl methacrylate (0.87 mol % based on total vinyl monomer) and 134.9 parts by weight of N-methylpyrrolidone was added homogeneously over the course of five hours. With commencement of the addition of the monomer mixture, a solution of 1.1 parts by weight of ammonium peroxodisulfate in 71.3 parts by weight of deionized water was likewise added within five hours.

(27) During the free-radical polymerization, every 30 minutes, the content of free monomers was determined by means of gas chromatography (GC) (GC: once with 50 m silica capillary column with polyethylene glycol phase and once with 50 m silica capillary column with polydimethylsiloxane phase, carrier gas: helium, split injector 150? C., oven temperature 40-220? C., flame ionization detector, detector temperature 275? C., internal standard: isobutyl acrylate), and the highest total monomer content based on dispersion of 0.5% by weight was found after 30 min (3.1% by weight based on the total amount of olefinically unsaturated monomers used for polymerization). After the simultaneous end of the metered addition of monomer and initiator, the resulting reaction mixture was stirred at 80? C. for a further hour and then cooled to room temperature.

(28) The resulting primary dispersion of the copolymer had a very good storage stability. The solids content thereof was 32.5% by weight, the acid number was 18.8 mg KOH/g solids, and the pH thereof was 7.0. The particle size (z average) by means of photon correlation spectroscopy was 96 nm. By means of gas chromatography (GC: once with 50 m silica capillary column with polyethylene glycol phase and once with 50 m silica capillary column with polydimethylsiloxane phase, carrier gas: helium, split injector 250? C., oven temperature 40-220? C., flame ionization detector, detector temperature 275? C., internal standard: n-propyl glycol), a content of 2.7% by weight of methoxypropanol and 5.7% by weight of N-methylpyrrolidone was found.

(29) After the extraction of the freeze-dried polymer by means of tetrahydrofuran, the gel content was found gravimetrically to be 80.3% by weight. For this purpose, the dispersion was freeze-dried and the mass of the freeze-dried polymer was determined, and then the polymer was extracted in an excess of tetrahydrofuran (ratio of tetrahydrofuran to freeze-dried copolymer=300:1) at 25? C. for 24 hours. The insoluble content (gel content) was isolated, dried at 50? C. in an air circulation oven for 4 hours, and then re-weighed.

(30) Production of a Non-Inventive Waterborne Basecoat Material 1 that can be Applied Directly to the Cathodic Electrocoat as a Color-Imparting Coat

(31) The components listed under aqueous phase in table A were stirred together in the order stated to form an aqueous mixture. In the next step an organic mixture was prepared from the components listed under organic phase. The organic mixture was added to the aqueous mixture. The combined mixture was then stirred for 10 minutes and adjusted, using deionized water and dimethylethanolamine, to a pH of 8 and to a spray viscosity of 58 mPas under a shearing load of 1000 s.sup.?1 as measured with a rotary viscometer (Rheomat RM 180 instrument from Mettler-Toledo) at 23? C.

(32) TABLE-US-00001 TABLE A Waterborne basecoat material 1 Component Parts by weight Aqueous phase 3% NaMg sheet silicate solution 27 Deionized water 15.9 Butyl glycol 3.5 Polyurethane-modified polyacrylate; prepared 2.4 as per page 7 line 55 to page 8 line 23 of DE 4437535 A1 50% by weight solution of Rheovis? PU 1250 0.2 (BASF), rheological agent Polyester 1 (P1) 2.5 TMDD (BASF) 1.2 Melamine-formaldehyde resin (Luwipal 052 4.7 from BASF SE) 10% dimethylethanolamine in water 0.5 Graft copolymer (CP) 19.6 Isopropanol 1.4 Byk-347? from Altana 0.5 Pluriol? P 900 from BASF SE 0.3 Tinuvin? 384-2 from BASF SE 0.6 Tinuvin 123 from BASF SE 0.3 Carbon black paste 4.3 Blue paste 11.4 Mica dispersion 2.8 Organic phase Aluminum pigment, available from Altana- 0.3 Eckart Butyl glycol 0.3 Graft copolymer (CP) 0.3

(33) Production of the Blue Paste:

(34) The blue paste was produced from 69.8 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 12.5 parts by weight of Paliogen? Blue L 6482, 1.5 parts by weight of dimethylethanolamine (10% in demineralized water), 1.2 parts by weight of a commercial polyether (Pluriol? P900 from BASF SE) and 15 parts by weight of deionized water.

(35) Production of the Carbon Black Paste:

(36) The carbon black paste was produced from 25 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 10 parts by weight of carbon black, 0.1 part by weight of methyl isobutyl ketone, 1.36 parts by weight of dimethylethanolamine (10% in demineralized water), 2 parts by weight of a commercial polyether (Pluriol? P900 from BASF SE) and 61.45 parts by weight of deionized water.

(37) Production of the Mica Dispersion:

(38) The mica dispersion was produced by mixing, using a stirrer unit, of 1.5 parts by weight of graft copolymer (CP) and 1.3 parts by weight of the commercial mica Mearlin Ext. Fine Violet 539V from Merck.

(39) Production of a Non-Inventive Waterborne Basecoat Material 2 that can be Applied Directly to the Cathodic Electrocoat as a Color-Imparting Coat

(40) The waterborne basecoat material 2 was produced analogously to table A, except using the graft copolymer (GCP1) rather than the graft copolymer (CP). Also, in the production of the mica dispersion used, the graft copolymer (GCP1) rather than the graft copolymer (CP) was used.

(41) Production of a Non-Inventive Waterborne Basecoat Material 3 that can be Applied Directly to the Cathodic Electrocoat as a Color-Imparting Coat

(42) The waterborne basecoat material 3 was produced analogously to table A, except using the graft copolymer (GCP1) rather than the graft copolymer (CP), and using the reaction product (R) rather than the polyester P1. Also, in the production of the mica dispersion used, the graft copolymer (GCP1) rather than the graft copolymer (CP) was used.

(43) Production of an Inventive Waterborne Basecoat Material I1 that can be Applied Directly to the Cathodic Electrocoat as a Color-Imparting Coat

(44) The waterborne basecoat material I1 was produced analogously to table A, except using the reaction product (R) rather than the polyester P1.

(45) TABLE-US-00002 TABLE B Comparison of waterborne basecoat materials 1-3 and I1 Binder 1 Binder 2 Waterborne basecoat Graft copolymer Polyester (P1) material 1 (CP) Waterborne basecoat Graft copolymer Polyester (P1) material 2 (GCP1) Waterborne basecoat Graft copolymer Reaction product material 3 (GCP1) (R) Waterborne basecoat Graft copolymer Reaction product material I1 (CP) (R)

(46) Comparison Between Waterborne Basecoat Materials 1-3 and Waterborne Basecoat Material I1

(47) To determine the pinhole limit and the pinhole count, the multicoat paint systems were produced by the following general method:

(48) A cathodically electrocoated steel sheet of dimensions 30?50 cm was provided with an adhesive strip on one longitudinal edge, in order to be able to determine the coat thickness differences after the coating. The waterborne basecoat material was applied electrostatically in wedge format. The resulting waterborne basecoat film was flashed off at room temperature for one minute and then dried in an air circulation oven at 70? C. for 10 minutes. A customary two-component clearcoat material was applied to the dried waterborne basecoat film. The resulting clearcoat film was flashed off at room temperature for 20 minutes. Subsequently, the waterborne basecoat film and the clearcoat film were cured in an air circulation oven at 140? C. for 20 minutes. After the visual assessment of the pinholes in the resulting multicoat paint system in wedge format, the coat thickness of the pinhole limit was determined. The results can be found in table 1.

(49) TABLE-US-00003 TABLE 1 Pinhole limit and pinhole count for waterborne basecoat materials 1-3 and waterborne basecoat material I1 Pinhole limit Pinhole WBM (micrometers) count 1 23 14 2 15 84 3 25 9 I1 38 1

(50) The results confirm that the use of the inventive combination of binders distinctly increases the pinhole limit compared to waterborne basecoat materials 1-3, while at the same time reducing the pinhole count.

(51) Preparation of a Non-Inventive Waterborne Basecoat Material 4 that can be Applied Directly to the Cathodic Electrocoat as a Non-Color-Imparting Coat

(52) The components listed under aqueous phase in table B were stirred together in the order stated to form an aqueous mixture. In the next step an organic mixture was prepared from the components listed under organic phase. The organic mixture was added to the aqueous mixture. The combined mixture was then stirred for 10 minutes and adjusted, using deionized water and dimethylethanolamine, to a pH of 8 and to a spray viscosity of 58 mPas under a shearing load of 1000 s.sup.?1 as measured with a rotary viscometer (Rheomat RM 180 instrument from Mettler-Toledo) at 23? C.

(53) TABLE-US-00004 TABLE C Waterborne basecoat material 4 Component Aqueous phase Parts by weight 3% NaMg sheet silicate solution 18.5 Deionized water 5.6 Butyl glycol 4.48 Polyurethane-modified polyacrylate; prepared as per page 7 line 55 to page 8 line 23 of DE 4437535 A1 50% by weight solution of Rheovis? PU 1250 (BASF), rheological agent Polyester (P1) 1.68 TMDD (BASF) 1.12 Melamine-formaldehyde resin (Cymel 203 from 5.6 Cytec) 10% dimethylethanolamine in water 0.56 Graft copolymer (CP) 28.16 Triisobutyl phosphate 1.7 2-Ethylhexanol 0.9 1-Propoxy-2-propanol 1.5 Isopar L from Exxon Mobile 0.9 Solvent naphtha 160/180 from Shell 0.6 Pluriol? P 900 from BASF SE 0.6 White paste 26.5 Carbon black paste 1.6

(54) Production of the White Paste:

(55) The white paste was produced from 43 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 50 parts by weight of titanium rutile 2310, 3 parts by weight of 1-propoxy-2-propanol and 4 parts by weight of deionized water.

(56) Production of the Carbon Black Paste:

(57) The carbon black paste was produced from 25 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 10 parts by weight of carbon black, 0.1 part by weight of methyl isobutyl ketone, 1.36 parts by weight of dimethylethanolamine (10% in demineralized water), 2 parts by weight of a commercial polyether (Pluriol? P900 from BASF SE) and 61.45 parts by weight of deionized water.

(58) Production of a Non-Inventive Waterborne Basecoat Material 5 that can be Applied Directly to the Cathodic Electrocoat as a Color-Imparting Coat

(59) Waterborne basecoat material 5 was produced analogously to table C, except using the graft copolymer (GCP1) rather than the graft copolymer (CP).

(60) Production of a Non-Inventive Waterborne Basecoat Material 6 that can be Applied Directly to the Cathodic Electrocoat as a Color-Imparting Coat

(61) Waterborne basecoat material 6 was produced analogously to table C, except using the graft copolymer (GCP1) rather than the graft copolymer (CP), and using the reaction product (R) rather than the polyester P1.

(62) Production of an Inventive Waterborne Basecoat Material I2 that can be Applied Directly to the Cathodic Electrocoat as a Color-Imparting Coat

(63) Waterborne basecoat material I2 was produced analogously to table C, except using the reaction product (R) rather than the polyester (P1).

(64) TABLE-US-00005 TABLE D Binder composition of waterborne basecoat materials 4-6 and I2 Binder 1 Binder 2 Waterborne basecoat Graft copolymer Polyester (P1) material 4 (CP) Waterborne basecoat Graft copolymer Polyester (P1) material 5 (GCP1) Waterborne basecoat Graft copolymer Reaction product material 6 (GCP1) (R) Waterborne basecoat Graft copolymer Reaction product material I2 (CP) (R)

(65) Production of a Waterborne Basecoat Material 7 that can be Applied Directly to Waterborne Basecoat Materials 4-6 and I2 as a Color-Imparting Coat

(66) TABLE-US-00006 TABLE E Waterborne basecoat material 7 Component Parts by weight Aqueous phase 3% NaMg sheet silicate solution 20.35 Deionized water 17.27 Butyl glycol 2.439 Polyurethane-modified polyacrylate; prepared 2.829 as per page 7 line 55 to page 8 line 23 of DE 4437535 A1 50% by weight solution of Rheovis? PU 1250 0.234 (BASF), rheological agent 3% by weight aqueous Rheovis? AS S130 4.976 solution; rheological agent, available from BASF, in water TMDD (BASF) 1.317 Melamine-formaldehyde resin (Cymel? 1133 3.512 from Cytec) 10% dimethylethanolamine in water 1.356 Polyurethane dispersion - prepared according 24.976 to WO 92/15405 (page 14 line 13 to page 15 line 28) Isopropanol 1.659 BYK-347? from Altana 0.537 Pluriol? P 900 from BASF SE 0.39 2-Ethylhexanol 1.854 Triisobutyl phosphate 1.151 Nacure? 2500 from King Industries 0.39 Tinuvin? 384-2 from BASF SE 0.605 Tinuvin 123 from BASF SE 0.39 Blue paste 0.605 Organic phase Aluminum pigment 1, available from Altana- 4.585 Eckart Aluminum pigment 2, available from Altana- 0.907 Eckart Butyl glycol 3.834 Polyester; prepared as per example D, column 3.834 16 lines 37-59 of DE-A-4009858

(67) Production of the Blue Paste:

(68) The blue paste was produced from 69.8 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 12.5 parts by weight of Paliogen? Blue L 6482, 1.5 parts by weight of dimethylethanolamine (10% in demineralized water), 1.2 parts by weight of a commercial polyether (Pluriol? P900 from BASF SE) and 15 parts by weight of deionized water.

(69) Comparison between Waterborne Basecoat Materials 4-6 and Waterborne Basecoat Material I2

(70) To determine the pinhole limit and the pinhole count, the multicoat paint systems were produced by the following general method:

(71) A cathodically electrocoated steel sheet of dimensions 30?50 cm was provided with an adhesive strip on one longitudinal edge, in order to be able to determine the coat thickness differences after the coating. Waterborne basecoat materials 4-6 and I2 were applied electrostatically in wedge format. Subsequently, this construction was flashed off at room temperature for 4 minutes.

(72) After this time, waterborne basecoat material 7 was applied in a coat thickness of 12-14 ?m, flashed off at room temperature for 4 minutes and then dried in an air circulation oven at 70? C. for 10 minutes. A customary two-component clearcoat material was applied to the dried waterborne basecoat film. The resulting clearcoat film was flashed off at room temperature for 20 minutes. Subsequently, the waterborne basecoat film and the clearcoat film were cured in an air circulation oven at 140? C. for 20 minutes. After the visual assessment of the pinholes in the resulting multicoat paint system in wedge format, the coat thickness of the pinhole limit was determined. The results (reporting only the coat thicknesses of waterborne basecoats 4-6 and I2 from which pinholes can be detected) can be found in table 2.

(73) TABLE-US-00007 TABLE 2 Pinhole limit and pinhole count for waterborne basecoat materials 4-6 and waterborne basecoat material I2 Pinhole limit Pinhole WBM (micrometers) count 4 22 31 5 17 165 6 23 9 I2 >35 none

(74) The results show that the use of the inventive combination of binders distinctly increases the pinhole limit compared to waterborne basecoat materials 4-6, while at the same time reducing the pinhole count, and preventing the occurrence of pinholes up to the maximum coat thickness of the wedge obtained.

(75) Production of a Waterborne Basecoat Material 8 that can be Applied Directly Beneath Waterborne Basecoat Materials 9-11 and I3 as a Non-Color-Imparting Coat

(76) TABLE-US-00008 TABLE F Waterborne basecoat material 8 Component Aqueous phase Parts by weight 3% NaMg sheet silicate solution 14 Deionized water 16 Butyl glycol 1.4 Polyester (P1) 2.3 3% by weight aqueous Rheovis? AS S130 6 solution; rheological agent, available from BASF, in water TMDD (BASF) 1.6 Melamine-formaldehyde resin (Cymel? 1133 5.9 from Cytec) 10% dimethylethanolamine in water 0.4 Polyurethane dispersion - prepared according 20 to WO 92/15405 (page 14 line 13 to page 15 line 28) 2-Ethylhexanol 3.5 Triisobutyl phosphate 2.5 Nacure? 2500 from King Industries 0.6 White paste 24 Carbon black paste 1.8

(77) Production of the Carbon Black Paste:

(78) The carbon black paste was produced from 25 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 10 parts by weight of carbon black, 0.1 part by weight of methyl isobutyl ketone, 1.36 parts by weight of dimethylethanolamine (10% in demineralized water), 2 parts by weight of a commercial polyether (Pluriol? P900 from BASF SE) and 61.45 parts by weight of deionized water.

(79) Production of the White Paste:

(80) The white paste was produced from 43 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 50 parts by weight of titanium rutile 2310, 3 parts by weight of 1-propoxy-2-propanol and 4 parts by weight of deionized water.

(81) Production of a Non-Inventive Waterborne Basecoat Material 9 that can be Applied Directly to Waterborne Basecoat Material 8 as a Color-Imparting Coat

(82) TABLE-US-00009 TABLE G Waterborne basecoat material 9 Component Parts by weight Aqueous phase 3% NaMg sheet silicate solution 24.4 Deionized water 15 Butyl glycol 1.7 Polyurethane-modified polyacrylate; prepared 3.7 as per page 7 line 55 to page 8 line 23 of DE 4437535 A1 Polyester (P1) 5 50% by weight solution of Rheovis? PU 1250 0.2 (BASF), rheological agent 3% by weight aqueous Rheovis? AS S130 3.6 solution; rheological agent, available from BASF, in water TMDD (BASF) 2 Melamine-formaldehyde resin (Luwipal 052? 6.9 from BASF SE) 10% dimethylethanolamine in water 0.4 Graft copolymer (CP) 13.4 Tinuvin? 384-2 from BASF SE 1 Tinuvin 123 from BASF SE 0.5 Blue paste 0.7 Organic phase Aluminum pigment 1, available from Altana- 5.6 Eckart Aluminum pigment 2, available from Altana- 1.2 Eckart Butyl glycol 8 Graft copolymer (CP) 6.7

(83) Production of the Blue Paste:

(84) The blue paste was produced from 69.8 parts by weight of an acrylated polyurethane dispersion produced as per international patent application WO 91/15528, binder dispersion A, 12.5 parts by weight of Paliogen? Blue L 6482, 1.5 parts by weight of dimethylethanolamine (10% in demineralized water), 1.2 parts by weight of a commercial polyether (Pluriol? P900 from BASF SE) and 15 parts by weight of deionized water.

(85) Production of a Non-Inventive Waterborne Basecoat Material 10 that can be Applied Directly to Waterborne Basecoat Material 8 as a Color-Imparting Coat

(86) Waterborne basecoat material 10 was produced analogously to table G, except using the graft copolymer (GCP1) rather than the graft copolymer (CP).

(87) Production of a Non-Inventive Waterborne Basecoat Material 11 that can be Applied Directly to Waterborne Basecoat Material 8 as a Color-Imparting Coat

(88) Waterborne basecoat material 11 was produced analogously to table G, except using the graft copolymer (GCP1) rather than the graft copolymer (CP), and using the reaction product (R) rather than the polyester P1.

(89) Production of an Inventive Waterborne Basecoat Material I3 that can be Applied Directly to Waterborne Basecoat Material 8 as a Color-Imparting Coat

(90) Waterborne basecoat material I3 was produced analogously to table G, except using the reaction product (R) rather than the polyester P1.

(91) TABLE-US-00010 TABLE H Binder composition of waterborne basecoat materials 9-11 and I3 Binder 1 Binder 2 Waterborne basecoat Graft copolymer Polyester (P1) material 9 (CP) Waterborne basecoat Graft copolymer Polyester (P1) material 10 (GCP1) Waterborne basecoat Graft copolymer Reaction product material 11 (GCP1) (R) Waterborne basecoat Graft copolymer Reaction product material I3 (CP) (R)

(92) Comparison Between Waterborne Basecoat Materials 9-11 and Waterborne Basecoat Material 13

(93) To determine the pinhole limit and the pinhole count, the multicoat paint systems were produced by the following general method:

(94) A cathodically electrocoated steel sheet of dimensions 30?50 cm was provided with an adhesive strip on one longitudinal edge, in order to be able to determine the coat thickness differences after the coating. Waterborne basecoat material 8 was applied in a coat thickness of 16-18 ?m. Subsequently, this construction was flashed off at room temperature for 4 minutes.

(95) Waterborne basecoat materials 9-11 and I3 were each applied electrostatically in wedge format, flashed off at room temperature for 4 minutes and then dried in an air circulation oven at 70? C. for 10 minutes. A customary two-component clearcoat material was applied to the dried waterborne basecoat film. The resulting clearcoat film was flashed off at room temperature for 20 minutes. Subsequently, the waterborne basecoat film and the clearcoat film were cured in an air circulation oven at 140? C. for 20 minutes. After the visual assessment of the pinholes in the resulting multicoat paint system in wedge format, the coat thickness of the pinhole limit was determined. The results (reporting only the coat thicknesses of waterborne basecoats 9-11 and 13 from which pinholes can be detected) can be found in table 3.

(96) TABLE-US-00011 TABLE 3 Pinhole limit and pinhole count for waterborne basecoat materials 9-11 and waterborne basecoat material I3 Pinhole limit Pinhole WBM (micrometers) count 9 16 5 10 11 41 11 19 9 I3 >24 none

(97) The results show that the use of the inventive combination of binders distinctly increases the pinhole limit compared to waterborne basecoat materials 9-11, while at the same time reducing the pinhole count, and preventing the occurrence of pinholes up to the maximum coat thickness of the wedge obtained.

BRIEF DESCRIPTION OF THE FIGURES

(98) FIG. 1:

(99) Schematic formation of a multicoat paint system (M) of the invention, arranged on a metallic substrate (S), and comprising a cured electrocoat (E.1) and a basecoat (B.2.1) and a clearcoat (K), which have been cured jointly.

(100) FIG. 2:

(101) Schematic formation of a multicoat paint system (M) of the invention, arranged on a metallic substrate (S), and comprising a cured electrocoat (E.1), two basecoats

(102) (B.2.2.x), namely a first basecoat (B.2.2.a) and an uppermost basecoat (B.2.2.z) arranged above it, and a clearcoat (K), which have been cured jointly.

(103) FIG. 3:

(104) Schematic formation of a multicoat paint system (M) of the invention, arranged on a metallic substrate (S), and comprising a cured electrocoat (E.1), three basecoats (B.2.2.x), namely a first basecoat (B.2.2.a), a basecoat (B.2.2.b) arranged above it and an uppermost basecoat (B.2.2.z), and a clearcoat (K), which have been cured jointly.