Process for preparing a coating with improved resistance to yellowing and the resulting coating

A process for preparing a coated substrate having a high glass and improved resistance to yellowing which comprises coating a substrate with a one-component coating composition comprising

• a) a blocked polyisocyanate which is the reaction product of a polyisocyanate with an oxime or lactam blocking agent for isocyanate groups and
• b) a polyhydroxy polyacrylate and/or a polyhydroxy polyester,
• provided that component a) and/or component b) contains the group, --CO--(R)N--N(R)--CO--, wherein R represents hydrogen, in an amount of 0.01 to 5% by weight, based on the solids content of components a) and b),
• by applying said one-component coating composition wet-on-wet to a coating composition containing acid groups and/or melamine resins which has previously been applied to the substrate.

A coated substrate having a high glass and improved resistance to yellowing which is prepared by a process which comprises coating a substrate with a one-component coating composition comprising

• a) a blocked polyisocyanate which is the reaction product of a polyisocyanate with an oxime or lactam blocking agent for isocyanate groups and
• b) a compound containing at least two isocyanate-reactive groups,
• provided that component a) and/or component b) contains the group, --CO--(R)N--N(R)--CO--, wherein R represents hydrogen or an optionally substituted hydrocarbon radical, in an amount of 0.01 to 5% by weight, based on the solids content of components a) and b),
• by applying said one-component coating composition wet-on-wet to a coating composition containing acid groups and/or melamine resins which has previously been applied to the substrate or by adding a melamine resin to the one-component coating composition prior to applying it to the substrate, which may optionally have been precoated.

A coated substrate having a high glass and improved resistance to yellowing which is prepared by a process which comprises coating a substrate with a one-component coating composition comprising

• a) a blocked polyisocyanate which is the reaction product of a polyisocyanate with an oxime or lactam blocking agent for isocyanate groups and
• b) a polyhydroxy polyacrylate and/or a polyhydroxy polyester,
• provided that component a) and/or component b) contains the group, --CO--(R)N--N(R)--CO--, wherein R represents hydrogen, in an amount of 0.01 to 5% by weight, based on the solids content of components a) and b),
• by applying said one-component coating composition wet-on-wet to a coating composition containing acid groups and/or melamine resins which has previously been applied to the substrate.