Production of polymer dispersions, used as e.g. surface coatings and paints, comprises mixing a polymer, a surfactant and water in a twin-screw extruder

摘要

Production of polymer dispersions comprises mixing polymer, surfactant and water in twin-screw extruder comprising feed zone, melting zone, two mixing zones and discharge zone. A ring of molten polymer is formed between melting zone and first mixing zone, and seals in the contents of the feed zone. The discharge zone has a pressure-retaining device. The final solids content of dispersion is adjusted by adding water to last mixing zone Production of polymer dispersions with a solids content of 5-95 wt.% comprises mixing at least one polymer, at least one surfactant and water in a twin-screw extruder operating at a screw speed of at least 600 rpm, where: (a) the extruder comprises a feed zone into which the polymer is introduced; a melting zone in which the polymer is melted; a first mixing zone into which part of the water is fed to form a polymer-water mixture; a last mixing zone into which the rest of the water is fed and mixed with the polymer-water mixture; and a discharge zone; (b) the surfactant is introduced into the feed zone, the melting zone, the first mixing zone and/or the last mixing zone; (c) the design of the screws is such that a ring of molten polymer is formed between the melting zone and the first mixing zone and seals in the contents of the feed zone; (d) the discharge zone has a pressure-retaining device; and (e) the final solids content of the dispersion is adjusted by adding the appropriate amount of water to the last mixing zone.