Aqueous copolymer dispersions and their use in coating compositions

An aqueous copolymer dispersion obtained by a free radical-initiated multi-stage emulsion polymerization process comprising:

• (a) polymerizing in a reaction zone in a first polymerization stage a first monomer composition comprising at least 88 weight percent of at least one vinyl ester of a C1 to C18 carboxylic acid and up to 12 weight percent ethylene to produce a first stage polymer having a glass transition temperature Tg of greater than 20° ° C.;
• and
• (b) polymerizing in the reaction zone, in a second polymerization stage and in the presence of the first stage polymer, a second, different monomer composition comprising at least one vinyl ester of a C1 to C18 carboxylic acid and at least one C2 to C8 alkyl ester of acrylic or methacrylic acid in an amount up to 30 weight percent of the total monomers in the second monomer composition to produce a second stage polymer having a glass transition temperature Tg of less than or equal to 20° ° C.,
• wherein the first monomer composition is substantially free of C2 to C8 alkyl esters of acrylic or methacrylic acid;
• wherein the second monomer composition is metered into the reaction zone during at least part of the second polymerization stage, and
• wherein each of the polymerization stages (a) and (b) is conducted in the presence of a stabilizing system which comprises at least 0.1 weight percent of at least one protective colloid, at least 0.05 weight percent of at least one ionic surfactant and less than 2 weight percent of nonionic surfactant, all percentages in the stabilizing system being based on the total weight of monomers in the first and second monomer compositions.