Patent ID: 6329020
Filing Date: 2001-12-11
Classification: B05D,C08F

Abstract:
A method for the preparation of a multilayer coating for motor vehicles, which comprises a saturated base coat prepared from an aqueous dispersion of a particulate polymer phase applied to a substrate, said polymer phase containing particles having a diameter of from 10 nm to 500 nm, the polymer having a number average molecular weight of from 10,000 to 500,000 and an acid number of from 12 to 40, wherein said aqueous dispersion is obtained by polymerization, without addition of an emulsifier and in the presence of a water insoluble polymerization initiator, of:(a) from 0.65 to 9 parts by wt. of at least one unsaturated monomer that does not contain any carboxyl moiety and, other than the unsaturated bond, does not contain any other moiety that is reactive under the polymerization conditions and under the conditions of any subsequent curing, together with from 10 to 65% by weight, based on the total monomers, of one or more hydroxyl moiety containing monomers that are copolymerizable with said unsaturated monomer, said hydroxyl moiety containing monomer having the following formula:R""--CH.dbd.CR'--X--R""'wherein R'=--H or --C.sub.n H.sub.2n+1 ;n=1 to 6;R""=R' or --COOC.sub.n H.sub.2n+1 ; R""'=a linear or branched C.sub.1-6 alkyl group with 1 to 3 OH groups; and X=--COO--, --CONH--, --CH.sub.2 O or --O--,and from 0 to 7 wt %, based on the total monomers, of a monomer which is ethylenically polyunsaturated, in the presence of(b) 1 part by of an aqueous dispersion of a urea containing polyurethane, based on the polyurethane portion, which is produced by chain extension of a prepolymer containing an NCO moiety, said prepolymer being based on a polyester containing from 1 to 10% NCO moieties with at least two urethane moieties per molecule, and containing at least partially neutralized carboxyl moieties corresponding to an acid number of from 20 to 50 and having a number average molecular weight of from 600 to 6,000, with a polyamine having having reactive aminogroups selected from the group consisting of primary and secondary aminogroups in an aqueous medium without any added emulsifier, drying the base coated substrate, and applying to the base coat a transparent second coat, said second coat being water-dilutable, or being dissolved in an organic solvent, and baking the coated substrate at a maximum temperature of 140.degree. C.