Aqueous coating composition and method of preparing thereof

An aqueous coating composition comprising,

• (A) an emulsion polymer comprising, based on the weight of the emulsion polymer,
• from 0.48% to 1.20% by weight of structural units of a dihydrogen phosphate ester of an alcohol in which the alcohol contains or is substituted with a polymerizable vinyl or olefinic group, a salt thereof, or mixtures thereof,
• from 0.5% to 3% by weight of structural units of diacetone (meth)acrylamide,
• from 10% to 80% by weight of structural units of a vinyl aromatic monomer,
• structural units of a C1-C24-alkyl ester of (meth)acrylic acids, and
• optionally, structural units of an α, β-ethylenically unsaturated carboxylic acid, a salt thereof, or mixtures thereof;
• (B) a dicarboxylic acid, a salt thereof, or mixtures thereof;
• wherein the dicarboxylic acid has the structure of formula (I):
• HOOC—R—COOH (I)
• where R is alkylene, alkenylene, alkynylene, cycloalkylene, cycloalkenylene, cycloalkynylene, arylene, or heterocyclic arylene;
• containing 6 to 18 carbon atoms;
• wherein the dicarboxylic acid, the salt thereof, or mixtures thereof are present in an amount to provide —OOC—R—COO— segments at a concentration of from 0.28% to 1.0% by weight, based on the weight of the aqueous coating composition;
• and
• (C) from 0.05% to 5% by weight of a flash rust inhibitor, based on the weight of the aqueous coating composition,
• wherein the emulsion polymer is a multistage emulsion polymer comprising from 50% to 80% by weight of a polymer A and from 20% to 50% by weight of a polymer B, based on the weight of the multistage emulsion polymer,
• wherein the polymer A comprises, based on the weight of the polymer A, from 0.3% to 2.4% by weight of structural units of the phosphorous acid monomer, the salt thereof, or mixtures thereof;
• from 0.5% to 6% by weight of structural units of the diacetone (meth)acrylamide;
• and from 10% to 75% by weight of structural units of the vinyl aromatic monomer;
• wherein the polymer B comprises, based on the weight of the polymer B, from zero to 2.5% by weight of structural units of the phosphorous acid monomer, the salt thereof, or mixtures thereof;
• from zero to 2.5% by weight of structural units of the diacetone (meth)acrylamide;
• and from 10% to 100% by weight of structural units of the vinyl aromatic monomer;
• wherein at least one of the polymer A and polymer B further comprises structural units of the C1-C24-alkyl ester of (meth)acrylic acid.