Aqueous polymer dispersions

Abstract

A process for the manufacture of an aqueous polymer dispersion comprising the steps of i)providing a mixture of a first and second polymer each having a viscosity greater than 30 Pa·s at 100swhen measured at 100° C., the mixture comprising a) from 1 to 60 parts by weight of a first polymer immiscible in aqueous medium and optionally comprising reactive moieties and b) from 40 to 99 parts by weight of a second polymer comprising dispersing 10 groups, the polymer being miscible in the aqueous medium and optionally further comprising moieties reactive with the moieties on the first polymer ii) causing the polymers to melt at a chosen temperature under conditions of high shear in an extruder to form an intimate mixture of the polymers iii)optionally causing the reactive moieties of the first and second polymer to 1 react with each other under conditions of high shear in an extruder, to form a reacted mixture iv) quench cooling the molten mixture of step ii) or step iii) outside the extruder to form a solid product v) optionally breaking up the solid product into smaller pieces 20 vi) contacting the solid product with the aqueous medium wherein the aqueous medium dissolves the second polymer but not the first polymer to form a dispersion comprising microparticles of the first polymer in an aqueous solution of the second polymer.