| 摘要 |
In a further improvement to the process of principal application P 3021369.5, granular, free-flowing crude tetrafluoroethylene polymer powders which cannot be processed from the melt, comprising from 0.004 to 0.075 mol% of polymerised units of a perfluoroalkyl vinyl ether of the formula CF2=CF-O-Rf, in which Rf is a perfluoroethyl, perfluoro-n-propyl or perfluoro-n-butyl radical, and polymerised tetrafluoroethylene units, can be obtained by maintaining a stirrer speed corresponding to a specific power consumption of from 0.5 to 1.5 watts/l of aqueous medium, measured in the aqueous medium before commencement of the polymerisation, in a critical phase of the polymerisation process, commencing on formation of from 1.5 to 3% by weight and extending as far as the formation of from 8 to 12% by weight of polymer solids in the suspension polymerisation with stirring. These measures allow the bulk density of such crude polymer powders to be increased to 880 g/l, the flowability achieves values of 2.5 s/50 g, and the particle stability achieves values of 2.5 s/50 g. A further improvement on conversion into ram extrudates is thus achieved.
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