Production of aqueous polymer compositions

Process for the production of an organic solvent-free aqueous crosslinkable polymer composition useful for coating, which process is organic solvent-free and comprises:

• a) preparing an aqueous solution of an acid-functional oligomer built from olefinically unsaturated monomers, said oligomer having a number average molecular weight Mn within the range of from 500 to 50,000 and a glass transition temperature (Tg) below 50.degree. C., said oligomer being formed using an organic solvent-free aqueous emulsion or aqueous solution polymerisation process, and said acid functionality by itself or by neutralization thereof rendering the oligomer water-soluble, and said oligomer also having crosslinker functional groups for imparting crosslinkability when the aqueous polymer composition is subsequently dried,
• b) conducting an aqueous emulsion polymerization process to form an aqueous emulsion of a hydrophobic polymer from at least one olefinically unsaturated monomer in the presence of the aqueous solution of the oligomer, said hydrophobic polymer having a Tg which is at least 25.degree. C. higher than the Tg of said oligomer, and said hydrophobic polymer optionally having crosslinker functional groups for imparting crosslinkability when the aqueous polymer composition is subsequently dried, and
• c) combining the aqueous emulsion from b) with a crosslinking agent by addition of the crosslinking agent after the polymerisation in step b) and/or performing the polymerisation in the presence of the crosslinking agent, said crosslinking agent being reactable with the crosslinker functional groups of the oligomer and (if present) of the hydrophobic polymer on subsequent drying to effect crosslinking, wherein said crosslinking agent is not an agent which effects crosslinking by the formation of ionic bonds,
• and wherein further, said polymer composition on drying has a Koenig hardness of at least 40 sec and said polymer composition has a minimum film forming temperature of .ltoreq.55.degree. C.