Aqueous polymer dispersion and aqueous coating composition comprising the same

1. An aqueous dispersion of a multistage polymer, wherein the multistage polymer comprises:

(A) a first polymer comprising as polymerized units, based on the weight of the first polymer,

(a1) from 2.1% to 10% by weight of diacetone (meth)acrylamide, a hydroxy-functional (meth)acrylic acid alkyl ester, or mixtures thereof,

(a2) from 2.8% to 10% by weight of a phosphorous-containing acid monomer,

(a3) from 75% to 92% by weight of a hydrophilic (meth)acrylic acid alkyl ester, and

(a4) from 0 to 3.8% by weight of an α, β-ethylenically unsaturated carboxylic acid;

wherein the first polymer has a number average molecular weight of from 3,000 to 20,000; and

(B) a second polymer comprising as polymerized units, based on the weight of the second polymer,

(b1) from 50% to 100% by weight of a hydrophobic (meth)acrylic acid alkyl ester,

(b2) from 0 to 10% by weight of a carbonyl-containing functional monomer, and

(b3) from 0 to 50% by weight of a hydrophilic monomer;

wherein the second polymer has a glass transition temperature at least 40° C. lower than that of the first polymer, and the weight ratio of the first polymer to the second polymer is from 25:75 to 50:50.

2. The aqueous dispersion of claim 1 , wherein the second polymer comprises as polymerized units, based on the weight of the second polymer, from 0.8% to 10% by weight of the carbonyl-containing functional monomer.

3. The aqueous dispersion of claim 1 , further comprising from 0.5% to 10% by weight of a polyfunctional carboxylic hydrazide containing at least two hydrazide groups per molecule, based on the total weight of the first and second polymers.

4. The aqueous dispersion of claim 3 , wherein the polyfunctional carboxylic hydrazide is selected from adipic dihydrazide, tartaric acid dihydrazide, oxalic dihydrazide, isophthalic dihydrazide, polyacrylic polyhydrazide, or mixtures thereof.

5. The aqueous dispersion of claim 1 wherein the hydroxy-functional (meth)acrylic acid alkyl ester is selected from 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, or mixtures thereof.

6. The aqueous dispersion of claim 1 wherein the phosphorous-containing acid monomer (a2) is selected from phosphoethyl (meth)acrylate, phosphopropyl (meth)acrylate, phosphobutyl (meth)acrylate, or mixtures thereof.

7. The aqueous dispersion of claim 1 wherein the hydrophilic (meth)acrylic acid alkyl ester (a3) is selected from methyl (meth)acrylate, ethyl (meth)acrylate, or mixtures thereof.

8. The aqueous dispersion of claim 1 wherein the hydrophobic (meth)acrylic acid alkyl ester (b1) is selected from butyl (meth)acrylate, iso-butyl (meth)acrylate, 2-ethylhexyl acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, or mixtures thereof.

9. The aqueous dispersion of claim 1 , wherein the weight ratio of the first polymer to the second polymer is from 30:70 to 40:60.

10. The aqueous dispersion of claim 1 , wherein the first polymer has a glass transition temperature of from 60° C. to 110° C., and the second polymer has a glass transition temperature of −50° C. or higher.

11. The aqueous dispersion of claim 1 , wherein the first polymer comprises as polymerized units, based on the weight of the first polymer,

(a1) from 3% to 6% by weight of diacetone (meth)acrylamide, the hydroxy-functional (meth)acrylic acid alkyl ester, or mixtures thereof;

(a2) from 2.8% to 6% by weight of the phosphorous-containing acid monomer;

(a3) from 80% to 90% by weight of the hydrophilic (meth)acrylic acid alkyl ester; and

(a4) from 0 to 3.5% by weight of the α, β-ethylenically unsaturated carboxylic acid; and

the second polymer comprises as polymerized units, based on the weight of the second polymer,

(b1) from 60% to 80% by weight of the hydrophobic (meth)acrylic acid alkyl ester,

(b2) from 2.5% to 8% by weight of the carbonyl-containing functional monomer, and

(b3) from 5% to 40% by weight of the hydrophilic monomer.

12. An aqueous coating composition comprising the aqueous dispersion of claim 1 .

13. A process of preparing a coating, comprising:

forming the aqueous coating composition of claim 12 ,

applying the aqueous coating composition to a substrate, and

drying, or allowing to dry, the applied aqueous coating composition to form the coating.

14. The coating composition of claim 12 when applied to a substrate at a thickness of 145 to 155 microns has a wet edge time of 11 minutes or more and/or a repair time of 16 minutes or more at 21-25° C. and 45-55% relative humidity.

15. The coating composition of claim 12 when applied to a substrate and dried at a dry film thickness of 50 to 60 microns has a 24-hour water resistance level of at least 3.

16. A process of preparing an aqueous dispersion of a multistage polymer by a multistage free-radical polymerization, comprising:

(i) preparing a first polymer in an aqueous medium by a free-radical polymerization in the presence of a chain transfer agent and neutralizing the obtained first polymer to a pH value of at least 6, wherein the first polymer comprises as polymerized units, based on the weight of the first polymer,

(a1) from 2.1% to 10% by weight of diacetone (meth)acrylamide, a hydroxy-functional (meth)acrylic acid alkyl ester, or mixtures thereof,

(a2) from 2.8% to 10% by weight of a phosphorous-containing acid monomer,

(a3) from 75% to 92% by weight of a hydrophilic (meth)acrylic acid alkyl ester, and

(a4) from 0 to 3.8% by weight of an α, β-ethylenically unsaturated carboxylic acid; and

(ii) preparing a second polymer in the presence of the first polymer obtained from step (i) by a free-radical polymerization, wherein the second polymer comprises as polymerized units, based on the weight of the second polymer,

(b1) from 50% to 100% by weight of a hydrophobic (meth)acrylic acid alkyl ester,

(b2) from 0 to 10% by weight of a carbonyl-containing functional monomer, and

(b3) from 0 to 50% by weight of a hydrophilic monomer;

wherein the second polymer has a glass transition temperature at least 40° C. lower than that of the first polymer, and the weight ratio of the first polymer to the second polymer is from 25:75 to 50:50 and wherein the number average molecular weight of the first polymer is from 3000 to 20,000.