Waterborne coating composition and a paint system thereof having improved chip resistance

A substrate including a waterborne paint film having improved chip resistance wherein the waterborne paint film is produced by a waterborne coating composition comprising:

• (a) an aqueous polyurethane dispersion substantially free from co-solvents, said aqueous polyurethane dispersion having a glass transition temperature from 0° C. or less and having carboxyl groups;
• and
• (b) a water-soluble cross-linker reactive with said carboxyl groups;
• wherein said aqueous polyurethane dispersion and said water-soluble cross-linker form a binder component of said waterborne coating composition, said binder composition comprising from 60 to 90% by weight of said polyurethane dispersion and from 10 to 40% by weight of said water-soluble cross-linker.

A layered paint system comprising:

• a vehicle;
• a waterborne primer layer for application across said vehicle, said waterborne primer layer comprising;
• (a) an aqueous polyurethane dispersion substantially free from co-solvents, said aqueous polyurethane dispersion having a glass transition temperature from 0° C. or less and having carboxyl groups;
• and
• (b) a water-soluble cross-linker reactive with said carboxyl groups;
• wherein said aqueous polyurethane dispersion and said water-soluble cross-linker form a binder component of said waterborne primer layer, said binder composition comprising from 60 to 90% by weight of said aqueous polyurethane dispersion and from 10 to 40% by weight of said water-soluble cross-linker.

An acrylic-free, waterborne coating composition for producing a waterborne paint film having improved chip resistance on a substrate, said waterborne coating composition comprising:

• (a) an aqueous polyurethane dispersion substantially free from co-solvents and having at least one carboxyl group, said aqueous polyurethane dispersion having a glass transition temperature from 0° C. or less;
• and
• (b) a water-soluble cross-linker reactive with said carboxyl groups;
• wherein said aqueous polyurethane dispersion and said water-soluble cross-linker form a binder component of said waterborne coating composition, said binder component comprising from 60 to 90% by weight of said aqueous polyurethane dispersion based on 100% by weight of said binder component and from 10 to 40% by weight of said water-soluble cross-linker based on 100% by weight of said binder component;
• and
• wherein said water coating composition produces the waterborne paint film to have a paint film loss of from 0.05 to 0.8 percent according to a Gravel Chip Test.

An acrylic-free, waterborne coating composition for producing a waterborne paint film having improved chip resistance on a substrate, said waterborne coating composition comprising:

• (a) an aqueous polyurethane dispersion substantially free from co-solvents and having at least one carboxyl group, said aqueous polyurethane dispersion having a glass transition temperature from 0° C. or less;
• and
• (b) a water-soluble cross-linker reactive with said carboxyl groups;
• wherein said aqueous polyurethane dispersion and said water-soluble cross-linker form a binder component of said waterborne coating composition, said binder component comprising from 60 to 90% by weight of said aqueous polyurethane dispersion based on 100% by weight of said binder component and from 10 to 40% by weight of said water-soluble cross-linker based on 100% by weight of said binder component;
• and
• wherein said water coating composition has a film build of from 0.5 to 5.0 mils of the waterborne paint film and a paint film loss of from 0.05 to 0.8 percent according to a Gravel Chip Test.