Coating additive

A coating formulation comprising a coating additive copolymer comprising, as copolymerized units, by dry weight based on total dry weight of the copolymer,

• from 20% to 60%, at least one acetoacetoxy or acetoacetamide functional ethylenically unsaturated monomer, and
• from 40% to 80% at least one water soluble ethylenically unsaturated monomer having the following structure:
• D-(CH2CH2O)h—(CH2CH(CH3)O)k-E
• wherein h is an integer of from 0 to 150;
• and k is an integer of from 0 to 30;
• wherein D is an ethylenically unsaturated group comprising methacrylate (CH2═C(CH3)CO2—), methacrylamide (CH2═C(CH3)CONH—), acrylate (CH2=CHCO2—), acrylamide (CH2=CHCONH—), vinyl ether (CH2═CH—O—), or allyl ether (CH2═CHCH2—O—);
• and
• wherein E is a capping group, and is selected from H, alkyl having 1 to 4 carbon atoms, and anionic salt groups comprising a lithium, sodium, potassium, or ammonium salt of phosphonate, phosphate, sulfate, or sulfonate;
• sodium vinylsulfonate;
• or sodium p-styrenesulfonate;
• wherein the coating formulation comprises, as copolymerized units, from 0.1% to 2% by dry weight based on total dry weight of the coating formulation, of the acetoacetoxy or acetoacetamide functional ethylenically unsaturated monomer.