Aqueous copolymer dispersion and coating composition

1. An aqueous copolymer dispersion comprising:

an emulsion copolymer, wherein the emulsion copolymer comprises, as a copolymerized unit, based on the dry weight of the copolymer, at least 90 wt % an ethylenically unsaturated nonionic monomer, and up to 10 wt % an ethylenically unsaturated stabilizer monomer, and wherein the emulsion copolymer is not a multi-stage emulsion copolymer comprising at least two stages; and

two hydrophobic aromatic ketones, wherein the aromatic ketones are, based on the dry weight of the copolymer, from 0.6 to 3 wt % benzophenone and from 0.5 to 3 wt % of a benzophenone derivative; and

wherein the dispersion comprises 0 or less than 0.1 wt % hydrophilic aromatic ketone.

2. The aqueous copolymer dispersion of claim 1 , wherein the derivative is selected from methyl-2-benzoylbenzoate, 4-hydroxy benzophenone, 4-amino benzophenone, 4-hydrocarboxyl benzophenone, 4-carboxymethyl benzophenone and 3-nitro benzophenone.

3. The aqueous copolymer dispersion of claim 2 , wherein the derivative is methyl-2-benzoylbenzoate.

4. The aqueous copolymer dispersion of claim 3 , wherein the amount of methyl-2-benzoylbenzoate in the dispersion ranges from 1 to 3 wt %.

5. The aqueous copolymer dispersion of claim 3 , wherein the dispersion comprises from 0.6 to 2 wt % benzophenone and from 1 to 3 wt % methyl-2-benzoylbenzoate.

6. The aqueous copolymer dispersion of claim 1 , wherein the emulsion copolymer further comprises, as a copolymerized unit, based on the dry weight of the copolymer, up to 5 wt % of allyl methacrylate, diallyl phthalate, 1,4-butylene glycol dimethacrylate, 1,2-ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate or divinyl benzene.

7. An aqueous coating composition comprising:

an emulsion copolymer, two hydrophobic aromatic ketones, and a coating adjuvant,

wherein the aromatic ketones are, based on the dry weight of the copolymer, from 0.6 to 3 wt % benzophenone and from 0.5 to 3 wt % of a benzophenone derivative;

wherein the emulsion copolymer comprises, as a copolymerized unit, based on the dry weight of the copolymer, at least 90 wt % an ethylenically unsaturated nonionic monomer, and up to 10 wt % an ethylenically unsaturated stabilizer monomer, and wherein the emulsion copolymer is not a multi-stage emulsion copolymer comprising at least two stages; and

wherein the coating composition comprises 0 or less than 0.1 wt % hydrophilic aromatic ketone.

8. The aqueous coating composition of claim 7 , wherein the derivative is selected from methyl-2-benzoylbenzoate, 4-hydroxy benzophenone, 4-amino benzophenone, 4-hydrocarboxyl benzophenone, 4-carboxymethyl benzophenone and 3-nitro benzophenone.

9. The aqueous coating composition of claim 8 , wherein the derivative is methyl-2-benzoylbenzoate.

10. An aqueous copolymer dispersion comprising:

an emulsion copolymer; and

two hydrophobic aromatic ketones, wherein the aromatic ketones are, based on the dry weight of the copolymer, from 0.6 to 3 wt % benzophenone and from 0.5 to 3 wt % of a benzophenone derivative, wherein the dispersion comprises 0 or less than 0.1 wt % hydrophilic aromatic ketone, and

wherein a coating film made from the aqueous copolymer dispersion exhibits a CIE delta b of less than or equal to 0.10 after:

exposure for 7 days to 23° C. and 50% relative humidity;

exposure for 3 days to 40° C.;

exposure for 4 hours to UV light having an irradiance of 0.77 W/m 2 /nm in a QUV Weathering Tester, Model QUV, with UVA-340 nm lamps;

application of Premix GB (China national standard coal ash slurry in water) to the coating and exposure for 2 hours to 23° C. and 50% relative humidity followed by a rinse with deionized water; and

repeat of the coal slurry application and rinse four times.

11. The aqueous copolymer dispersion of claim 10 , wherein the derivative is selected from methyl-2-benzoylbenzoate, 4-hydroxy benzophenone, 4-amino benzophenone, 4-hydrocarboxyl benzophenone, 4-carboxymethyl benzophenone and 3-nitro benzophenone.

12. The aqueous copolymer dispersion of claim 11 , wherein the derivative is methyl-2-benzoylbenzoate.

13. The aqueous copolymer dispersion of claim 12 , wherein the amount of methyl-2-benzoylbenzoate in the dispersion ranges from 1 to 3 wt %.

14. The aqueous copolymer dispersion of claim 12 , wherein the dispersion comprises from 0.6 to 2 wt % benzophenone and from 1 to 3 wt % methyl-2-benzoylbenzoate.

15. The aqueous copolymer dispersion of claim 10 , wherein the emulsion copolymer further comprises, as copolymerized unit, based on the dry weight of the copolymer, up to 5 wt % of allyl methacrylate, diallyl phthalate, 1,4-butylene glycol dimethacrylate, 1,2-ethylene glycol dimethacrylate, 1,6-hexanediol diacrylate or divinyl benzene.