Continuous process for the agglomeration of PTFE powders in a liquid medium

摘要

A process for the continuous agglomeration of granular tetrafluoroethylene polymer powders which cannot be processed from the melt to give molding powders having a high bulk density, an improved powder flow and particle stability and a narrow particle size distribution is described. In this process, the powder to be agglomerated is first introduced uniformly into a pretreatment stage and is dispersed and pre-agglomerated in this stage in the liquid agglomeration medium, composed of water and an organic liquid capable of wetting polytetrafluoroethylene, is then agglomerated to the desired average particle diameter in an agglomeration stage and is finally treated further in an after-treatment stage in order to develop the final shape of the particles. Finally, the powder is separated from the liquid medium and is dried. This makes it possible to obtain, in an economical manner and with excellent processing properties, high-grade agglomerated molding powders of such tetrafluoroethylene polymers, in particular of such polymers which have been modifed with small quantities of perfluoro-(alkyl-vinyl) ethers.