PROCESS FOR WET ON WET APPLICATION OF A MULTILAYER COATING
A wet on wet process for multilayer coating of a substrate includes applying on the substrate to be coated a surfacer layer of an organic solvent-based surfacer coating composition comprising at least one polyaspartic acid ester, at least one polyisocyanate cross-linking agent with free isocyanate groups, at least one pigment and/or extender and at least one organic solvent. The surfacer layer on coated substrate is flashed off and a top coat layer is applied on the surfacer layer.
1 . Wet on wet process for multilayer coating of a substrate, the process comprising the steps of:
(i) applying on the substrate to be coated a surfacer layer of an organic solvent-based surfacer coating composition comprising:
A) at least one polyaspartic acid ester;
B) at least one polyisocyanate cross-linking agent with free isocyanate groups;
C) at least one pigment and/or extender; and
D) at least one organic solvent;
(ii) flashing off the surfacer layer; and
(iii) applying a top coat layer on the surfacer layer.
2 . The wet on wet process of claim 1 , wherein the surfacer coating composition further comprises E) at least one additional binder component.
3 . The wet on wet process of claim 2 , wherein the binder component is selected from the group consisting of hydroxy-functional binders, amino-functional binders, aminoalcohol-functional binders, aldimines and/or ketimines.
4 . The wet on wet process of claim 1 , wherein the surfacer coating composition comprises B) at least one aromatically bound polyisocyanate cross-linking agent with free isocyanate groups.
5 . The wet on wet process according to claim 1 , wherein flashing off the surfacer layer is performed for 15 minutes or less.
6 . The wet on wet process according to claim 1 , wherein the top coat layer comprises a base coat layer and a clear coat layer.
7 . The wet on wet process according to claim 1 , wherein the top coat layer is a pigmented single stage top coat layer.
8 . The wet on wet process of claim 6 , wherein the clear coat layer comprises at least one polyaspartic acid ester and at least one polyisocyanate cross-linking agent with free isocyanate groups
9 . The wet on wet process of claim 8 , wherein the base coat layer comprises at least one polyisocyanate cross-linking agent with free isocyanate groups.
10 . The wet on wet process of claim 6 , wherein the base coat is a water-based base coat.
11 . The wet on wet process according to claim 1 , wherein the polyaspartic acid ester is a compound of Formula (I):
wherein X represents an n-valent organic group, obtained by removal of the amino groups from a primary polyamine or polyetheramine; R 1 and R 2 are the same or different organic groups which are inert towards isocyanate groups, R 3 , R 4 and R 5 are the same or different and represent hydrogen or organic groups which are inert towards isocyanate groups, and n represents an integer with a value of at least 2, or
a chain-extended aspartate prepolymer which
(i) is free of isocyanate groups,
(ii) is a reaction product of
(ii-a) a mixture comprising at least one di-aspartic acid ester and at least one amino-functional mono-aspartic acid ester, wherein the molar ratio between the at least one di-aspartic acid ester and the at least one amino-functional mono-aspartic acid ester is from about 99.5:0.5 to about 50:50, and
(ii-b) at least one polyisocyanate.
12 . The wet on wet process according to claim 1 , wherein the organic solvent-based surfacer coating composition is applied using at least one of a manual pressure feed spray gun, a suction feed spray gun, airless and airmix techniques, pressure pot techniques and non-manual automated techniques.
13 . The wet on wet process according to claim 1 , wherein the substrate is a metal substrate.
14 . The wet on wet process according to claim 13 , wherein the metal substrate comprises vehicle bodies or vehicle body parts.
15 . The wet on wet process according to claim 13 , further comprising a step of pretreating the substrate to be coated with an acidic aqueous composition comprising at least one of phosphate ions, a water-soluble titanium compound and a water-soluble zirconium compound and water.
16 . The wet on wet process according to claim 15 , further comprising a step of subjecting the pre-treated substrate to a flash-off phase.
17 . The wet on wet process of claim 15 , wherein the acidic aqueous composition comprises about 1 to about 25% by weight, relative to the total amount of the acidic aqueous composition, of phosphate ions.
18 . The wet on wet process of claim of claim 15 , wherein the acidic aqueous composition comprises about 0.3 to about 3% by weight, relative to the total amount of the acidic aqueous composition, of the water-soluble titanium compound and the water-soluble zirconium compound, calculated as elemental titanium and zirconium.
19 . The wet on wet process according to claim 15 , wherein the water-soluble titanium compound and the water-soluble zirconium compound is selected from a group consisting of titanium containing complex fluoro acids, zirconium containing complex fluoro acids, fluoro complexes of titanium, fluoro complexes of zirconium, and a combination thereof.
20 . The wet on wet process according to claim 15 , wherein the acidic aqueous composition is applied by wiping.