| 主权项 |
1. A process for multilayer coating of a metal substrate, the process comprising the steps of:
pretreating the metal substrate to be coated with an acidic aqueous composition comprising:
a) phosphate ions comprising ammonium hydrogen phosphate, b) a water-soluble titanium compound selected from the group consisting of: a hexafluoro titanium acid or a hexafluoro titanate, and optionally c) a zirconium compound selected from the group consisting of: a hexafluoro zirconium acid or a hexafluoro zirconate, wherein the acidic aqueous composition comprises about 1 to about 16% by weight, relative to the total amount of the acidic aqueous composition, of phosphate ions and about 0.5 to about 1% by weight, relative to the total amount of the acidic aqueous composition, of the water-soluble titanium and, if present, zirconium compound, calculated as elemental titanium and zirconium, and wherein the acidic aqueous composition has a pH value of about 1 to about 4; andwater in an amount of about 30% to about 99% by weight, relative to the total amount of the acid aqueous composition; subjecting the metal substrate to a flash-off phase to form a metal oxide conversion layer on the metal substrate, said flash-off phase being performed for a time period of about 1 minute to about 2 minutes at a temperature of about 20 to about 23 degrees Celsius; applying a surfacer layer of an organic-solvent based surfacer coating composition comprising:
a polyaspartic acid ester of formula I: wherein X represents an n-valent organic group, obtained by removal of the amino groups from a primary polyamine or polyetheramine; R1 and R2 are the same or different organic groups which are inert towards isocyanate groups, R3, R4 and R5 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, wherein the organic-solvent based surfacer coating composition comprises about 5 to about 60% by weight, relative to the total amount of the organic-solvent based surfacer coating composition, of the polyaspartic acid ester;a polyisocyanate cross-linking agent with free isocyanate groups, wherein the cross-linking agent consists of aliphatically and/or cycloaliphatically bound isocyanate groups with an average NCO functionality of about 2 to about 6;at least one epoxy-functional silane compound chosen from (3-glycidoxypropyl)trimethoxysilane, (3-glycidoxypropyl)triethoxysilane, (3-glycidoxypropyl)triisopropoxysilane, beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and beta-(3,4-epoxycyclohexyl) ethyltriethoxysilaneat least one aldimine and/or ketimime;pigments and/or extenders, wherein the organic-solvent based surfacer coating composition has a pigment volume concentration (PVK) of about 20% to about 65%; andan organic solvent, wherein the surfacer layer is applied such that it has a resulting dry film thickness of about 25 to about 400 μm; curing the surfacer layer; applying a top coat layer overlying the cured surfacer layer; and curing the top coat layer. |
