CONCENTRATED DISPERSIONS OF FLUORINATED POLYMERS AND PROCESSES FOR THEIR PREPARATION

摘要

: Aqueous, colloidal dispersions of fluorinated polymers can be concentrated, after adding a stabilizing emulsifier, to high solids contents by ultrafiltration over customary semi-permeable membranes if pulps which keep the dispersion free from contact with components which cause frictional forces are used for conveying the dispersio A considerable proportion of the stabilizing emulsifier added and high proportions of the fluorine-containing emulsifier originally contained in the fluorinated polymer dispersion from the emulsion polymerization can be removed via the aqueous permeate. The fluorine-containing emulsifier can be recovered by a downstream basic anion exchanger and the stabilizing emulsifier contained in the filtrate flowing out of the anion exchanger can be concentrated in this filtrate by reverse osmosis and optionally recycled into the ultrafiltration process. Fluorinated polymer dispersions which, in addition to having a high solids content, are distinguished by particularly low contents of fluorinecontaining emulsifier and of stabilizing emulsifier can be obtained. The process can be applied to all known aqueous, colloidal dispersions of fluorinated homopolymers and copolymers.