Multi-layer coatings and methods of preparing the same

1 . A multi-layer coating system comprising:

1) a first basecoat layer formed from a first coating composition comprising:

a) at least two different free polyisocyanates comprising:

i) a free aliphatic polyisocyanate having a weight average molecular weight of less than 600 g/mol, present in an amount of 3.5 to 8 weight %, based on the total resin solids of the first coating composition; and

ii) a uretdione dimer different from the free aliphatic polyisocyanate i), present in an amount greater than 9.5 weight %, based on the total resin solids of all the free polyisocyanate in the first coating composition;

b) at least two different types of polymeric core-shell particles comprising:

i) hydroxyl functional polymeric core-shell particles, wherein a polymeric core and a polymeric shell of the hydroxyl functional core-shell particles each independently comprise an addition polymer derived from ethylenically unsaturated monomers, wherein the hydroxyl functional polymeric core-shell particles are present in the first coating composition in an amount of 20 to 60 percent by weight, based on the total weight of resin solids of the first coating composition; and

ii) carboxylic acid functional polymeric core-shell particles, wherein a polymeric core of the carboxylic acid functional core-shell particles comprises an addition polymer derived from ethylenically unsaturated monomers including a monomer having at least two ethylenically unsaturated groups and a polymeric shell of the carboxylic acid functional core-shell particles comprises urethane linkages and carboxylic acid functional groups, wherein the carboxylic acid functional polymeric core-shell particles are present in the first coating composition in an amount of 0.1 to 20 percent by weight, based on the total weight of resin solids of the first coating composition; and

c) a crosslinking agent different from the free polyisocyanates a);

2) a second basecoat layer positioned over at least a portion of the first basecoat layer, the second basecoat layer formed from a second coating composition comprising:

a) second carboxylic acid functional polymeric core-shell particles, wherein a polymeric core of the second carboxylic acid functional core-shell particles comprises an addition polymer derived from ethylenically unsaturated monomers and a polymeric shell of the second carboxylic acid functional core-shell particles comprises urethane linkages and carboxylic acid functional groups, wherein the second carboxylic acid functional polymeric core-shell particles are present in the second coating composition in an amount of greater than 20 and up to 60 percent by weight, based on the total weight of resin solids of the second coating composition; and

b) a second crosslinking agent; and

3) a topcoat layer positioned over at least a portion of the second basecoat layer, the topcoat layer formed from a topcoat coating composition comprising a second free polyisocyanate and a film-forming resin reactive with the second free polyisocyanate.

2 . The multi-layer coating system of claim 1 , wherein the polymeric shell of the hydroxyl functional polymeric core-shell particles in the first coating composition comprises from 5 to 30 weight % of the core-shell particles, based on the total solids weight of the core-shell particles.

3 . The multi-layer coating system of claim 1 , wherein the polymeric shell of the hydroxyl functional polymeric core-shell particles in the first coating composition is obtained from components that comprise greater than 10 weight % of a hydroxyl functional ethylenically unsaturated monomer, based on the total weight of the components that form the polymeric shell.

4 . The multi-layer coating system of claim 1 , wherein the crosslinking agent c) in the first coating composition comprises an aminoplast resin.

5 . The multi-layer coating system of claim 1 , wherein the second crosslinking agent b) in the second coating composition comprises an aminoplast resin.

6 . The multi-layer coating system of claim 1 , wherein the second coating composition comprises greater than 25 weight % and up to 50 weight % of the second carboxylic acid functional polymeric core-shell particles, based on a total resin solids of the second coating composition.

7 . The multi-layer coating system of claim 1 , wherein the second coating composition further comprises second hydroxyl functional polymeric core-shell particles that are the same as or different from the hydroxyl functional polymeric core-shell particles in the first coating composition, wherein a polymeric core and a polymeric shell of the second hydroxyl functional polymeric core-shell particles of the second coating composition each independently comprise an addition polymer derived from ethylenically unsaturated monomers.

8 . The multi-layer coating system of claim 1 , wherein the second coating composition further comprises a third free polyisocyanate different from the second crosslinking agent.

9 . The multi-layer coating system of claim 1 , wherein the first coating composition and the second coating composition each independently comprise at least one colorant.

10 . The multi-layer coating system of claim 1 , wherein a weight ratio of the core to the shell of the hydroxyl functional polymeric core-shell particles in the first coating composition is from 95:5 to 70:30.

11 . The multi-layer coating system of claim 1 , further comprising a primer coating layer, wherein the first coating layer is positioned over at least a portion of the primer coating layer.

12 . The multi-layer coating system of claim 1 , wherein the free aliphatic polyisocyanate comprises an isocyanurate, a trimer and/or a biuret.

13 . A substrate at least partially coated with the multi-layer coating system of claim 1 .

14 . The substrate of claim 13 , wherein the substrate comprises at least a portion of an automobile.

15 . A process of coating a substrate with a multi-layer coating comprising:

(1) depositing a first coating composition onto at least a portion of the substrate, wherein the first coating composition comprises:

a) at least two different free polyisocyanates comprising:

i) a free aliphatic polyisocyanate having a weight average molecular weight of less than 600 g/mol, present in an amount of 3.5 to 8 weight %, based on the total resin solids of the first coating composition; and

ii) a uretdione dimer different from the free aliphatic polyisocyanate i), present in an amount greater than 9.5 weight %, based on the total resin solids of all the free polyisocyanate in the first coating composition;

b) at least two different types of polymeric core-shell particles comprising:

i) hydroxyl functional polymeric core-shell particles, wherein a polymeric core and a polymeric shell of the hydroxyl functional core-shell particles each independently comprise an addition polymer derived from ethylenically unsaturated monomers, wherein the hydroxyl functional polymeric core-shell particles are present in the first coating composition in an amount of 20 to 60 percent by weight, based on the total weight of resin solids of the first coating composition; and

ii) carboxylic acid functional polymeric core-shell particles, wherein a polymeric core of the carboxylic acid functional core-shell particles comprises an addition polymer derived from ethylenically unsaturated monomers including a monomer having at least two ethylenically unsaturated groups and a polymeric shell of the carboxylic acid functional core-shell particles comprises urethane linkages and carboxylic acid functional groups, wherein the carboxylic acid functional polymeric core-shell particles are present in the first coating composition in an amount of 0.1 to 20 percent by weight, based on the total weight of resin solids of the first coating composition; and

c) a crosslinking agent different from the free polyisocyanates a);

(2) depositing a second coating composition directly onto at least a portion of the first coating composition (A) after the first coating composition is dehydrated or (B) before the first coating composition is dehydrated, wherein the second coating composition comprises:

a) second carboxylic acid functional polymeric core-shell particles, wherein a polymeric core of the second carboxylic acid functional core-shell particles comprises an addition polymer derived from ethylenically unsaturated monomers and a polymeric shell of the second carboxylic acid functional core-shell particles comprises urethane linkages and carboxylic acid functional groups, wherein the second carboxylic acid functional polymeric core-shell particles are present in the second coating composition in an amount of greater than 20 and up to 60 percent by weight, based on the total weight of resin solids of the second coating composition; and

b) a second crosslinking agent;

(3) dehydrating: (a) the second coating composition after (2) (A); or (b) simultaneously the first coating composition and the second coating composition after (2) (B); and

(4) depositing a topcoat coating composition over at least a portion of the dehydrated second coating composition, the topcoat coating composition comprising a second free polyisocyanate and at least one film-forming resin reactive with the second free polyisocyanate.

16 . The process of claim 15 , wherein the first coating composition is dehydrated before application of the second coating composition.

17 . The process of claim 15 , wherein both the first and second coating compositions are simultaneously dehydrated.

18 . The process of claim 15 , wherein the first coating composition and second coating composition are dehydrated at a temperature ranging from ambient temperature to 90° C.

19 . The process of claim 15 , further comprising curing the first and second coating compositions at a temperature of 120° C. or less.

20 . The process of claim 15 , further comprising curing the first and second coating compositions and the topcoat coating composition simultaneously at a temperature of 120° C. or less.