Process and apparatus for preparing polymer dispersions

A process for preparing polymer dispersions of at least one of the polymerizable monomers from the groups consisting of alkyl (meth)acrylates, vinyl esters of carboxylic acids having 1-20 carbon atoms, vinylaromatic compounds, nitrites, vinyl halides, vinyl ethers, hydrocarbons having 2-8 carbon atoms, and hydroxyl-containing monomers in emulsion polymerization technology at a polymerization temperature of at least 40° C., in the presence of a free-radical polymerization initiator, which comprises preparing the polymer, which forms to at least 85% by weight from one or more of these monomers. In a first stage, water, as reaction-inert solvent, dispersing assistants where appropriate, seed where appropriate, and a first portion of monomer(s), where appropriate, are introduced. In a second stage, the initiator is added, and in a third stage, the remainder or full amount of monomer(s) are added directly or in emulsion form in the presence of further water and, where appropriate, further dispersing assistant or other auxiliaries. It is possible for the first and second stages or second and third stages in each case also to be run in one stage while second and third stages can be run through in a gradient procedure, and in all or some stages the reaction mixture present as a dispersion is moved by an external circuit ( 10 ) which leads from and back to the polymerization vessel ( 2 ) and which comprises one or more extremely low-shear-conveying cylinder or tubular diaphragm pumps ( 7 ) and at least one heat exchanger ( 8 ), the polymerization temperature being between 40° C. and 120° C.