Polymer powders redispersible in water for dry construction material formulations

A process for producing protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in the form of water-redispersible powders,

• by producing aqueous dispersions of protective-colloid-stabilized polymers based on ethylenically unsaturated monomers by polymerization of one or more ethylenically unsaturated monomers in an aqueous medium and drying said dispersions in the presence of one or more drying aids, wherein
• the drying aids include a) one or more inorganic salts selected from the group of alkali metal sulfates and alkali metal sulfites and b) optionally one or more water-soluble organic polymers and
• the inorganic salts a) are present in the aqueous dispersions of the protective-colloid-stabilized polymers based on ethylenically unsaturated monomers in dissolved form after all drying aids have been added,
• wherein the inorganic salts a) are employed as drying aids to an extent of ≥25% by weight based on the total weight of the drying aids, and
• wherein the proportion of any water-soluble organic polymers b) employed as drying aids is ≤40% by weight based on the total weight of protective colloids and any water-soluble organic polymers b) employed as drying aids,
• with the proviso that the protective colloids are added before or during the polymerization, and
• that any water-soluble organic polymers b) employed as drying aids are added to the aqueous dispersions of the protective-colloid-stabilized polymers after production of said aqueous dispersions by polymerization, and
• that the protective colloids stabilize the polymerization batch during the polymerization in an aqueous medium and also the polymer particles formed in the course of the polymerization and that the protective colloids are incorporated into the polymer particles formed in the course of the polymerization, and
• that any water-soluble organic polymers b) employed as drying aids, as a result of their addition after the polymerization, encase the polymer particles formed in the course of the polymerization.